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Derailed Proteostasis as a Determinant of Cardiac Aging
Accepted Manuscript Derailed proteostasis as a determinant of cardiac aging Marit Wiersma, MSc, Robert H. Henning, MD, PhD, Bianca J.J.M. Brundel, PhD PII:
S0828-282X(16)00228-2
DOI:
10.1016/j.cjca.2016.03.005
Reference:
CJCA 2071
To appear in:
Canadian Journal of Cardiology
Received Date: 14 December 2015 Revised Date:
21 February 2016
Accepted Date: 7 March 2016
Please cite this article as: Wiersma M, Henning RH, Brundel BJJM, Derailed proteostasis as a determinant of cardiac aging, Canadian Journal of Cardiology (2016), doi: 10.1016/j.cjca.2016.03.005. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Derailed proteostasis as a determinant of cardiac aging
Marit Wiersma, MSc1,2, Robert H. Henning, MD, PhD1, Bianca J.J.M. Brundel, PhD1,2#
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Department of Clinical Pharmacy and Pharmacology, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands
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Correspondence: Dr. Bianca Brundel Department of Physiology De Boelelaan 1118 1081HV Amsterdam The Netherlands Phone: +31-06-27339900 [email protected]
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Department of Physiology, Institute for Cardiovascular Research, VU University Medical Center, Amsterdam, The Netherlands
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ACCEPTED MANUSCRIPT Abstract
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Age comprises the single most important risk factor for cardiac disease development. The incidence and prevalence of cardiac diseases, which represent the main cause of death worldwide, will rise even more due to the aging population. A hallmark of aging is that it is accompanied by a gradual derailment of proteostasis, e.g. the homeostasis of protein synthesis, folding, assembly, trafficking, function and degradation. Loss of proteostasis is highly relevant to cardiomyocytes, as they are post-mitotic cells and therefore not constantly replenished by proliferation. The derailment of proteostasis during aging is thus an important factor that preconditions for the development of age-related cardiac diseases, such as atrial fibrillation. In turn, frailty of proteostasis in aging cardiomyocytes is exemplified by its accelerated derailment in multiple cardiac diseases. Here, we review 2 major components of the proteostasis network, the stress-responsive and protein degradation pathways, in healthy and aged cardiomyocytes. Furthermore, we discuss the relation between derailment of proteostasis and age-related cardiac diseases, including atrial fibrillation. Finally, we introduce novel therapeutic targets which may possibly attenuate cardiac aging and thus limit cardiac disease progression. Online summary
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Age comprises the single most important risk factor for cardiac disease development. A hallmark of aging is the gradual derailment of proteostasis, e.g. the homeostasis of protein synthesis, folding and degradation. The derailment of proteostasis during aging preconditions for cardiac disease development. We review 2 major components of the proteostasis network, the stress-responsive and protein degradation pathways, in healthy and aged cardiomyocytes and introduce novel therapeutic targets which may attenuate cardiac aging and disease progression.
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ACCEPTED MANUSCRIPT Introduction: a healthy proteostasis is the keystone of a healthy heart
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Cardiovascular diseases (CVDs) are the main cause of death worldwide and in the EU CVDs account for 47% of all disease-related deaths yearly. Its incidence is agerelated, with 3 per 1000 and 74 per 1000 persons affected in the age groups of 35-44 and 85-94 years, respectively. CVDs are present in 33% of the adult population in the USA; over 50% of this CVD population is older than 60 years of age. Moreover, CVDs account for a high socioeconomic burden; its medical costs outnumber those of any other disease, as CVDs are the most common cause for hospitalizations especially in the elderly. As the population is aging, projections foresee a steep increase in the incidence, prevalence and medical costs of CVDs (from $565 billion in 2015 to $1 trillion in 2030).1,2 In view of global aging, it is ever more important to develop adequate strategies to counteract aging-related effects to arrest this trend.
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Recent findings indicate that a healthy protein homeostasis (proteostasis) plays a key role in safeguarding the proper functioning of the heart by maintaining proper cell function through adequate synthesis, folding, assembly, trafficking, function and degradation of proteins.3,4 A proper proteostasis is especially warranted in postmitotic cells, such as cardiomyocytes, which have limited regenerative capacity. Accordingly, an optimal function of proteostasis is required to maintain a healthy heart.
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Proteostasis is maintained by a regulated network of molecular chaperones, stressresponsive pathways and protein degradation pathways. In healthy conditions, this network shows a basal activation that is induced upon cellular stress, including CVD. To respond to cellular stress, cells may deploy three main stress-responsive pathways: the heat shock response (HSR), the mitochondrial unfolded protein response (UPRmito) and the endoplasmic reticulum (ER) unfolded protein response (UPRER) as well as two main degradation pathways: the ubiquitin-proteasome system and macroautophagy (hereafter ‘autophagy’). As the name implies, each of the stress-responsive pathways is activated upon stress in a specific cellular compartment (Figure 1). Nevertheless, these pathways may also be activated and act in parallel upon severe cellular stress.3,4 The HSR is activated upon cytosolic and/or nuclear stress and leads to the dissociation of heat shock factor 1 (HSF1) from the inhibitory molecular chaperones heat shock protein (HSP)70 and HSP90, whereafter HSF1 homotrimerizes. Trimerized HSF1 translocates to the nucleus and binds to the promotor of hsp genes (Figure 1A, grey lines).3,4 In addition, mitochondrial stress activates the UPRmito, which is regulated by activation of the transcription factor associated with stress 1 (ATFS1). Mitochondrial stress blocks the import of ATFS1 in the mitochondrion, which results in ATFS1 being translocated to the nucleus instead. At the nucleus, ATFS1 binds to the promotor region of genes coding for mitochondrial chaperones and components of mitochondrial import, fission and respiratory chain complexes (Figure 1A, blue lines).5 Furthermore, ER stress activates the UPRER, which itself 3
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activates three stress-responsive sensors in parallel, namely inositol-requiring enzyme 1 (IRE1), activating transcription factor 6 (ATF6) and protein kinase-like endoplasmic reticulum kinase (PERK). These three transmembrane proteins are kept inactive by the binding of HSPA5 (also known as BiP or GRP75) to their luminal domain. However, ER stress results in the dissociation of HSPA5, thus activating the sensors. Both IRE1 and PERK homodimerize and autophosphorylate upon activation. Subsequently, IRE1 splices X-box binding protein 1 (XBP1) mRNA and the product, XPB1s, is a transcription factor which translocates to the nucleus and activates transcription of UPRER molecular chaperones and folding catalysts. Activated PERK phosphorylates eukaryotic initiation factor 2 alpha (eIF2α), which inhibits protein translation and synthesis, except for activating transcription factor 4 (ATF4). Subsequently, ATF4 induces expression of growth arrest and DNA damageinducible protein 34 (GADD34) and C/EBP homologous protein (CHOP), which, respectively, attenuate PERK activation and activate the apoptotic pathway. The third sensor activated by ER stress, ATF6, is transported to and subsequently cleaved in the Golgi apparatus. The N-terminal fragment translocates to the nucleus, where it induces expression of other molecular chaperones involved in the UPRER (Figure 1A, green lines).3,4
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Aberrant proteins, which the proteostasis network is not able to properly refold, are degraded by one of the two main degradation pathways, the ubiquitin-proteasome system (UPS) or autophagy.3,4 The UPS is specialized in the degradation of single, short-lived or misfolded proteins. Promoted by molecular chaperones, these proteins are polyubiquitinated and transferred to the cytosolic proteasomes to be unfolded and degraded after deubiquitination (Figure 1B).3,4 The second degradation pathway, autophagy, is a bulk degradation system in which large cytosolic proteins, protein aggregates and organelles are sequestered into a double-membrane structure, called an autophagosome. This autophagosome fuses with a lysosome, after which lysosomal hydrolases degrade the contents into recyclable ATP, amino acids and fatty acids (Figure 1C).
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When these stress-response pathways and/or protein degradation pathways are dysregulated, proteostasis becomes derailed, which is observed in multiple cardiac diseases. For example, heart failure features the activation of the UPRER and UPRmito and the reduced activity of the HSR, UPS and autophagy.6-8 Similarly, cardiomyopathies are associated with increased UPRER activation and reduced UPS and autophagic activity.6,9 Furthermore, metabolic syndrome-related cardiac disease shows reduced autophagy and mitochondrial function.10 In contrast, activation of degradation pathways is increased, and the HSR gets exhausted in (longstanding) persistent atrial fibrillation.11,12 The common denominator of derailed proteostasis in various – mostly age-related – cardiac diseases suggests that proper proteostasis maintenance is an important aspect of healthy cardiac aging. Proteostasis declines during aging
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ACCEPTED MANUSCRIPT Experimental findings reveal that during aging, the gradual failure of stressresponsive and degradation pathways impair the proteostasis network resulting in the accumulation of cellular damage over time (Figure 2A).13 The importance of the factor time in bringing about the failure of proteostasis explains why the incidence of diseases, such as neurodegenerative and cardiovascular diseases, increases with age.
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Increased proteotoxicity during aging
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The relation between aging and proteostasis has been extensively studied in several model systems, particularly in Caenorhabditis elegans and Drosophila melanogaster. During aging in C. elegans, various proteins tend to aggregate and become proteotoxic, including proteins engaged in protein homeostasis and quality control, such as the proteasome, ribosomes and molecular chaperones, including HSP70 and HSP90.14 Furthermore, aging affects the proteome of C. elegans by an upregulation of proteins involved in the UPS, oxidative stress defense and DNA replication and repair and downregulation of ER, mitochondrial and ribosomal proteins.15 The decline in ribosomal proteins corresponds with age-related diminishing of protein synthesis rate.16 Aged D. melanogaster show increased carbonylated and ubiquitinated proteins and a decline in proteasome function.17 Similar changes have been documented in mammals, as aged mice show differential expression of mitochondrial proteins, proteins involved in defense against oxidative stress and chaperones or proteins involved in the stress-response.18 In addition, aging of ex vivo human dermal fibroblasts also display reduced expression of chaperone, proteosomal, ribosomal and mitochondrial proteins.19 Together, the findings from experimental studies indicate aging to prompt proteotoxicity, likely because of a hampered functioning of the proteostasis network.
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Derailment of proteostasis network during aging
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During aging, the function of the stress-responsive and protein degradation pathways of the proteostasis network declines. Aging thus attenuates the HSR20, UPRER21 and UPRmito20 upon cellular stress. The expression of multiple mitochondrial proteins, including chaperones and components of the electron transport chain, is reduced during aging and mitochondrial function and morphology are changed. 20 In case of the UPRER, aging attenuates HSPA5 induction and eIF2α phosphorylation, while GADD34 and CHOP expression are enhanced.21 Similar to the stress-responsive pathways, aging impairs both protein degradation pathways, the UPS and autophagy, by affecting expression and/or activation.22,23 Experimental findings reveal aging to be accompanied by expression of the low-activity 20S proteasomes, in contrast to the high-activity 26S proteasomes, which are mostly found in young animals.23 This divergence could possibly be explained by the dependency of the 26S proteasome assembly on ATP, the latter being decreased during aging.23 Furthermore, aging attenuates the proper mounting of an autophagy response, which could have rescued, or delayed the effects of the age-related dysfunctionality of the 5
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UPS. Loss of autophagy also generally leads to increased ROS levels as the degradation of damaged, old or otherwise dysfunctional mitochondria is impaired. These dysfunctional mitochondria generate high levels of ROS, in turn promoting proteotoxic stress and accelerating detrimental effects on the cell.22 In addition, aging modulates mTOR activity, and depending on the species, gender and organ studied, mTOR activity is either up- or downregulated.24 As mTOR is an important negative regulator of autophagy, aberrant activity may attenuate autophagy during aging. Thus, aging affects the proper function of all stress-responsive and protein degradation pathways at various levels, thereby progressively disturbing the proteostasis network. Proteostasis and longevity
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While aging induces a gradual dysfunction of stress-responsive and protein degradation pathways, these pathways seem fortified in long-lived species.25 Thus, a higher expression of several chaperones, including HSP60 in mitochondria, HSPA5 and GRP94 in ER and HSP70 in cytosol, correlates with enhanced lifespan.25 Furthermore, long-lived species show enhanced autophagic and proteosomal function compared to short-lived species. Moreover, long-lived species appear to excessively enhance their proteotoxic defense in comparison to short-lived species, by inducing high levels of HSP and substantial activation of autophagic and proteosomal clearance.25 These observations suggest that long-lived species deploy their intrinsic defense mechanisms to the maximum to protect from age-related derailment of proteostasis.
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Similar to long-lived species, boosting components of the proteostatic network prolong life of short-lived species. This is exemplified by the notion that both C. elegans26 and D. melanogaster27 have a longer lifespan when HSPs are overexpressed. Conversely, HSF1 knockdown reduces lifespan and features proteins that more promptly aggregate.15 Moreover, overexpression of mitochondrial chaperones HSPA928 or HSP2227 increases lifespan and mitochondrial function in aged C. elegans or D. melanogaster, respectively. Furthermore, enhancing UPRER function to counteract the age-related decline in UPRER activity by overexpression of XBP1s, also resulted in an increased life span in C. elegans.29 Similar to the stressresponsive pathways, enhancement of protein degradation pathways also promotes longevity, as shown by overexpression of proteasome subunits30 and induction of autophagy.22,31 Moreover, inhibition of mTOR increases lifespan in mice and C. elegans, possibly conveyed via induction of autophagy.32 Thus, experimental evidence reveals that aging diminishes the function of both the stress-responsive and the degradation pathways of the proteostasis network. This may result in progressive derailment of proteostasis, accumulation of cellular damage and, ultimately, agerelated diseases, such as CVD. Importantly, experimental evidence suggests that boosting components of these pathways rescues the proteostasis network from aging effects and promotes longevity.
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ACCEPTED MANUSCRIPT Cardiac proteostasis in the elderly
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Age-related changes in the proteostasis network are also present in cardiomyocytes. The expression of heat shock proteins is reduced in aged cardiomyocytes33, which may be due to an upregulation of Rho expression33, as activation of Rho prevents the mounting of HSR by attenuation of HSF1-binding to the promotor region of hsp genes.34 Cardiac mitochondrial function also decreases during aging, due to a variety of mitochondrial changes, including loss of cristae, destruction of inner membranes, swelling, decreased expression of mitochondrial proteins and loss of ATP production.33 In turn, mitochondrial changes impair maintenance of a proper proton gradient and functional respiratory chain, which contributes to increased ROS production. Subsequently, increased amount of ROS in aged cardiomyocytes leads to excess protein damage and a less effective stress response. Importantly, ROS stimulates the lysosomal formation of lipofuscin aggregates35, consisting of aggregated liposomal proteins and lipids, that effectively impair autophagy by preventing fusion of lysosomes to autophagosomes. Consequently, aging-related impairment of autophagy promotes accumulation of dysfunctional mitochondria, representing the major part of the extralysosomal waste in aged cardiomyocytes.36 Dysfunctional mitochondria are known to produce increased amount of ROS, thereby triggering a vicious circle of high ROS production and the subsequent low stress response. In addition, accumulation of dysfunctional mitochondria and aberrant proteins results in functional loss in cardiomyocytes.35 Moreover, impaired autophagy affects the UPS, as damaged or aged proteasomes are degraded by autophagy.35 In accord with the prominent role of autophagy, ATG5 knockout mice display both increased polyubiquitination and attenuated mitochondrial function.36
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The impaired stress-responsive and protein degradation pathways render aged cardiomyocytes susceptible to cellular damage. As cardiomyocytes are post-mitotic cells, and are therefore not constantly replaced by proliferation, the whole heart is highly susceptible to protein damage. During normal aging, the structure and function of the heart changes (Figure 2B), resulting in a decline of diastolic function in rest and systolic function during exercise, impairment of Ca2+ homeostasis, cardiac hypertrophy and fibrosis.37 Cardiac hypertrophy originates from changes in ion channels and Ca2+ homeostasis, and fibrosis during aging, which puts additional strain on the remaining cardiomyocytes to match cardiac demands. Interestingly, stimulation of autophagy in the aged heart decreases hypertrophy, improves contractile function, reduces protein damage and restores Ca2+ homeostasis.38 Conversely, impairment of autophagy predisposes the heart to early dilated cardiomyopathy development.36 Although cardiac aging is related to reduced activation of autophagy, most CVDs, including heart failure, myocardial infarction and atrial fibrillation, are related to excessive activation of autophagy (Table 1). Interestingly, reduced activity of autophagy is observed in CVDs caused by overexpression of (mutant) proteins, including dilated and desmin-related cardiomyopathy. These studies showed that (mutant) protein expression results in 7
ACCEPTED MANUSCRIPT protein aggregates which are toxic for the cardiomyocytes. Protein aggregates are cleared by autophagy but chronic overexpression results in exhaustion of the autophagy machinery, ultimately resulting in accumulation of protein aggregates and loss of cardiomyocyte function. These observations indicate that in case of proteotoxicity, activators of autophagy may be beneficial, whereas other CVDs likely benefit from inhibitors of autophagy.
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Accumulating evidence reveals cardiac diseases to accelerate aging-induced derailment of proteostasis37 and atrial fibrillation (AF) is an excellent example of the adverse effects of cardiac aging on disease development. AF is the most common age-related clinical tachyarrhythmia, characterized by electrical and structural remodeling and atrial contractile dysfunction.39 Derailment of proteostasis is associated with the AF-related structural remodeling and, thereby, may create a substrate for both initiation and progression of AF.40 The HSR gets exhausted in patients with (long-standing) persistent AF, and induction of HSP expression was found to protect against AF progression.11,12 Furthermore, AF is associated with aberrant phosphatase and kinase activities. As several components of the proteostasis network, including components of the UPRER (IRE1, PERK), are regulated by these posttranslational modifications, the aberrant function could influence them.41 In addition, changes in phosphorylation-increased deacetylation of structural proteins by histone deacetylase 6 (HDAC6) contributes to reduced contractile function, structural remodeling and AF progression.42 Together, these findings suggest that proteostasis derailment is an important feature in the initiation and progression of AF, which may explain its prevalence increasing with age. Therapeutic targets to attenuate cardiac aging and disease
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Fortifying proteostasis may prevent the detrimental changes associated with aging and cardiac diseases, in line with observations of extended lifespan in model systems that overexpress components of the proteostasis network. Thus, (pharmacological) boosting of the proteostasis network may represent an appealing strategy to prevent and/or treat cardiac diseases, including AF, cardiomyopathies and heart failure. Lifestyle interventions
Sustained caloric restriction (without restriction of vitamins and micronutrients) is found to increase lifespan in various experimental model systems from yeast to mice43 and decreases the risk of cardiac diseases, by improving contractile function and precluding cardiac hypertrophy and cardiomyopathy in rodents and monkeys.38 Autophagy induction is commonly believed to constitute an important effector of caloric restriction.44 However, sustained caloric restriction is not feasible for most humans38. Except caloric restriction, exercise also reduces the risk of CVDs and has been proposed to slow cardiac aging. Exercise reduces cardiac fibrosis and hypertrophy and improves diastolic function, contractile function and Ca2+ homeostasis.45 Moreover, exercise has a positive effect on HSP expression, mitochondrial function and, indirectly, proteasome function.45 Interestingly, exercise 8
ACCEPTED MANUSCRIPT induces autophagy in mice cardiac muscle.46 In addition, voluntary exercise in a desmin-related cardiomyopathy mouse model showed reduced protein aggregation and reduced disease progression.47 This indicates that regular exercise may be able to improve cardiac outcome in aging and cardiac disease progression. Pharmacological interventions
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Boosting the HSR
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Pharmacological induction of HSP expression has beneficial effects in several cardiac diseases.11,12,48 Geranylgeranylacetone (GGA) is an HSP inducer, used in Japan as anti-ulcer drug since 1984 without reported serious side effects49, and is therefore currently the most promising compound to boost the HSR. GGA treatment in experimental models of cardiac disease attenuated structural damage and improved function of the heart.11,12,48 In vitro, GGA protected against contractile dysfunction and cardiomyocyte damage by attenuation of sarcomere damage.11,12 In vivo, GGA protected against desmin-related cardiomyopathy by attenuation of fibrosis, which may be due to increased aggregate clearance by GGA-induced augmented HSPB1 expression.48 In addition, in vivo GGA treatment reduced inducibility of AF in heart failure50 and atrial ischemia.51 Another HSP inducer, BGP15, was found to protect against contractile dysfunction in a D. melanogaster model for AF and no serious side-effects were reported in a phase II clinical study for insulin resistance.52 Importantly, recent research found BGP-15 to protect from heart failure and AF in in vivo mice models.53 Thus, both GGA and BGP-15 show promising cardioprotective effects probably by boosting the HSR (Table 2). As GGA is already on the market for decades, its features a favorable safety profile, while this is currently still unknown for BGP15. Autophagy induction to counteract aging and proteotoxicity
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As autophagy shows reduced activation during aging and overexpression of (mutant) proteins, induction of autophagy may represent an interesting strategy to attenuate CVD onset and progression. Interestingly, rapamycin treatment induces similar effects as caloric restriction in mice.37 Rapamycin is an inhibitor of the nutrientsensing mTOR, and its administration thus resulting in the activation of autophagy.37,38 The inhibition of mTOR activity increases lifespan in vivo54, even in old mice55, as rapamycin treatment resulted in induced voluntary exercise, reduced cardiac inflammation and hypertrophy, enhanced ejection fraction, and also in increased mitochondrial function.56 Moreover, rapamycin treatment protected in vitro against Hutchinson-Gilford, an accelerated aging disorder.57 In addition to clinical studies in which rapamycin is used to treat cancer58 and auto-immune disease59 (Table 2), experimental evidence suggests rapamycin mitigates progression of heart failure.60 Moreover, rapamycin-treatment attenuated contractile dysfunction and cardiac hypertrophy in aged mice with reversal of diastolic dysfunction and agerelated cardiac proteomic changes.38 In addition, rapamycin treatment prevented diabetic cardiomyopathy in mice.61 Although rapamycin is an FDA approved drug, 9
ACCEPTED MANUSCRIPT caution is needed as rapamycin may exert serious side effects, including suppression of the immune system62, dermatological changes62, lung toxicity63 and increased risk of diabetes development.64 Due to these adverse effects, multiple derivatives of rapamycin have been developed. Unfortunately, these derivatives do not only inhibit mTOR activity, but also increase Akt activity, which can drive cancer development.62 Inhibition of autophagy to counteract CVDs
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Various CVDs show excessive activation of autophagy (Table 1). Therefore, inhibition of autophagy may represent an interesting target for treatment of CVDs, which are not caused by the overexpression of a (mutant) protein. However, inhibitors of autophagy, such as bafilomycin, cause cellular toxicity.65 Thus, direct inhibition of autophagy may currently not be feasible. However, indirect inhibition of autophagy, by targeting upstream activation pathways may be applicable. One of the pathways implicated in cardiac disease and autophagy activation is the UPRER.
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Inhibition of UPRER
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As the ER is the cellular compartment where most proteins (at least one-third) are synthesized and folded,4 this compartment is highly susceptible for proteotoxic stress. Reinforcing the UPRER with 4-phenylbutyric acid (4PBA) in experimental models protects from progression of multiple diseases, including obesity, diabetes, cancer, cystic fibrosis and neurodegenerative disorders.66 Importantly, 4PBA is already an FDA approved drug to treat urea cycle disorder67, with no reported serious side effects.68 Interestingly, 4PBA has several modes of action; it is an ammonia scavenger, a weak histone deacetylase inhibitor and a chemical chaperone.66 At the moment, 4PBA is in clinical trials for several disorders related to proteotoxicity, including amyotrophic lateral sclerosis (NCT00107770) and Huntington's disease (NCT00212316) (Table 2). Results of these studies may inform us about possible effectiveness of 4PBA in respect to cardiac diseases.
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In summary, loss of proteostasis during aging compromises the proper functioning of cardiomyocytes, promoting development of cardiac diseases, including AF. In addition, existing cardiac disease further compromises proteostasis, thereby accelerating the progression of contractile dysfunction and disease. Targeting of key components of proteostasis may thus represent an interesting therapeutic approach to attenuate aging and cardiac disease onset in the elderly. Several compounds fortifying proteostasis are already marketed, such as GGA and 4PBA, and their clinical potential may be readily explored. Compounds targeting autophagy may be of high potential depending on outcomes of current research. However, regular exercise and caloric restriction throughout life may represent the easiest and cheapest intervention to boost cardiac proteostasis and thus slow cardiac aging, reduce the incidence of cardiac diseases and improve clinical outcome. Acknowledgements
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ACCEPTED MANUSCRIPT We gratefully acknowledge the Dutch Heart Foundation (2013T096 and 2013T144) and LSH-Impulse grant (40-43100-98-008) for research support. Disclosures
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ACCEPTED MANUSCRIPT References 1. Mozaffarian D, Benjamin EJ, Go AS, et al. Heart disease and stroke statistics--2015 update: A report from the american heart association. Circulation. 2015;131(4):e29-322.
2. Farmakis D, Stafylas P, Giamouzis G, Maniadakis N, Parissis J. The medical and
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socioeconomic burden of heart failure: A comparative delineation with cancer. Int J Cardiol. 2015;203:279-281.
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3. Labbadia J, Morimoto RI. The biology of proteostasis in aging and disease. Annu Rev Biochem. 2015;84:435-464.
M AN U
4. Diaz-Villanueva JF, Diaz-Molina R, Garcia-Gonzalez V. Protein folding and mechanisms of proteostasis. Int J Mol Sci. 2015;16(8):17193-17230.
5. Jovaisaite V, Mouchiroud L, Auwerx J. The mitochondrial unfolded protein response, a
2014;217(Pt 1):137-143.
TE D
conserved stress response pathway with implications in health and disease. J Exp Biol.
6. Su H, Wang X. The ubiquitin-proteasome system in cardiac proteinopathy: A quality
EP
control perspective. Cardiovasc Res. 2010;85(2):253-262.
7. Cui J, Sinoway LI. Cardiovascular responses to heat stress in chronic heart failure. Curr
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Heart Fail Rep. 2014;11(2):139-145.
8. Dai DF, Hsieh EJ, Liu Y, et al. Mitochondrial proteome remodelling in pressure overloadinduced heart failure: The role of mitochondrial oxidative stress. Cardiovasc Res. 2012;93(1):79-88.
9. Ortega A, Rosello-Lleti E, Tarazon E, et al. Endoplasmic reticulum stress induces different molecular structural alterations in human dilated and ischemic cardiomyopathy. PLoS One. 2014;9(9):e107635.
12
ACCEPTED MANUSCRIPT 10. Sciarretta S, Boppana VS, Umapathi M, Frati G, Sadoshima J. Boosting autophagy in the diabetic heart: A translational perspective. Cardiovasc Diagn Ther. 2015;5(5):394-402.
11. Brundel BJ, Henning RH, Ke L, van Gelder IC, Crijns HJ, Kampinga HH. Heat shock
human atrial fibrillation. J Mol Cell Cardiol. 2006;41(3):555-562.
RI PT
protein upregulation protects against pacing-induced myolysis in HL-1 atrial myocytes and in
12. Brundel BJ, Shiroshita-Takeshita A, Qi X, et al. Induction of heat shock response protects
SC
the heart against atrial fibrillation. Circ Res. 2006;99(12):1394-1402.
13. Lopez-Otin C, Blasco MA, Partridge L, Serrano M, Kroemer G. The hallmarks of aging.
M AN U
Cell. 2013;153(6):1194-1217.
14. David DC, Ollikainen N, Trinidad JC, Cary MP, Burlingame AL, Kenyon C. Widespread protein aggregation as an inherent part of aging in C. elegans. PLoS Biol.
TE D
2010;8(8):e1000450.
15. Walther DM, Kasturi P, Zheng M, et al. Widespread proteome remodeling and aggregation in aging C. elegans. Cell. 2015;161(4):919-932.
EP
16. Kirstein-Miles J, Scior A, Deuerling E, Morimoto RI. The nascent polypeptide-associated
AC C
complex is a key regulator of proteostasis. EMBO J. 2013;32(10):1451-1468.
17. Tsakiri EN, Sykiotis GP, Papassideri IS, Gorgoulis VG, Bohmann D, Trougakos IP. Differential regulation of proteasome functionality in reproductive vs. somatic tissues of drosophila during aging or oxidative stress. FASEB J. 2013;27(6):2407-2420.
18. Chakravarti B, Seshi B, Ratanaprayul W, et al. Proteome profiling of aging in mouse models: Differential expression of proteins involved in metabolism, transport, and stress response in kidney. Proteomics. 2009;9(3):580-597.
13
ACCEPTED MANUSCRIPT 19. Waldera-Lupa DM, Kalfalah F, Florea AM, et al. Proteome-wide analysis reveals an ageassociated cellular phenotype of in situ aged human fibroblasts. Aging (Albany NY). 2014;6(10):856-878.
20. Liang V, Ullrich M, Lam H, et al. Altered proteostasis in aging and heat shock response in
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C. elegans revealed by analysis of the global and de novo synthesized proteome. Cell Mol Life Sci. 2014;71(17):3339-3361.
21. Naidoo N, Ferber M, Master M, Zhu Y, Pack AI. Aging impairs the unfolded protein
SC
response to sleep deprivation and leads to proapoptotic signaling. J Neurosci.
M AN U
2008;28(26):6539-6548.
22. Simonsen A, Cumming RC, Brech A, Isakson P, Schubert DR, Finley KD. Promoting basal levels of autophagy in the nervous system enhances longevity and oxidant resistance in adult drosophila. Autophagy. 2008;4(2):176-184.
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23. Vernace VA, Arnaud L, Schmidt-Glenewinkel T, Figueiredo-Pereira ME. Aging perturbs 26S proteasome assembly in drosophila melanogaster. FASEB J. 2007;21(11):2672-2682.
24. Baar EL, Carbajal KA, Ong IM, Lamming DW. Sex- and tissue-specific changes in mTOR
EP
signaling with age in C57BL/6J mice. Aging Cell. 2015.
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25. Pride H, Yu Z, Sunchu B, et al. Long-lived species have improved proteostasis compared to phylogenetically-related shorter-lived species. Biochem Biophys Res Commun. 2015;457(4):669-675.
26. Morley JF, Morimoto RI. Regulation of longevity in caenorhabditis elegans by heat shock factor and molecular chaperones. Mol Biol Cell. 2004;15(2):657-664.
14
ACCEPTED MANUSCRIPT 27. Morrow G, Samson M, Michaud S, Tanguay RM. Overexpression of the small mitochondrial Hsp22 extends drosophila life span and increases resistance to oxidative stress. FASEB J. 2004;18(3):598-599.
28. Yokoyama K, Fukumoto K, Murakami T, et al. Extended longevity of caenorhabditis
(mortalin)/mthsp70/Grp75. FEBS Lett. 2002;516(1-3):53-57.
RI PT
elegans by knocking in extra copies of hsp70F, a homolog of mot-2
29. Taylor RC, Dillin A. XBP-1 is a cell-nonautonomous regulator of stress resistance and
SC
longevity. Cell. 2013;153(7):1435-1447.
M AN U
30. Chondrogianni N, Georgila K, Kourtis N, Tavernarakis N, Gonos ES. 20S proteasome activation promotes life span extension and resistance to proteotoxicity in caenorhabditis elegans. FASEB J. 2015;29(2):611-622.
31. Harrison DE, Strong R, Sharp ZD, et al. Rapamycin fed late in life extends lifespan in
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genetically heterogeneous mice. Nature. 2009;460(7253):392-395.
32. Wu JJ, Liu J, Chen EB, et al. Increased mammalian lifespan and a segmental and tissuespecific slowing of aging after genetic reduction of mTOR expression. Cell Rep.
EP
2013;4(5):913-920.
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33. Bodyak N, Kang PM, Hiromura M, et al. Gene expression profiling of the aging mouse cardiac myocytes. Nucleic Acids Res. 2002;30(17):3788-3794.
34. Meijering RA, Wiersma M, van Marion DM, et al. RhoA activation sensitizes cells to proteotoxic stimuli by abrogating the HSF1-dependent heat shock response. PLoS One. 2015;10(7):e0133553.
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ACCEPTED MANUSCRIPT 35. Terman A, Kurz T, Navratil M, Arriaga EA, Brunk UT. Mitochondrial turnover and aging of long-lived postmitotic cells: The mitochondrial-lysosomal axis theory of aging. Antioxid Redox Signal. 2010;12(4):503-535.
age-related cardiomyopathy. Autophagy. 2010;6(5):600-606.
RI PT
36. Taneike M, Yamaguchi O, Nakai A, et al. Inhibition of autophagy in the heart induces
37. Chiao YA, Rabinovitch PS. The aging heart. Cold Spring Harb Perspect Med.
SC
2015;5(9):a025148.
38. Quarles EK, Dai DF, Tocchi A, Basisty N, Gitari L, Rabinovitch PS. Quality control
M AN U
systems in cardiac aging. Ageing Res Rev. 2015;23(Pt A):101-115.
39. Schotten U, Verheule S, Kirchhof P, Goette A. Pathophysiological mechanisms of atrial fibrillation: A translational appraisal. Physiol Rev. 2011;91(1):265-325.
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40. Ausma J, Wijffels M, Thone F, Wouters L, Allessie M, Borgers M. Structural changes of atrial myocardium due to sustained atrial fibrillation in the goat. Circulation. 1997;96(9):31573163.
EP
41. Verfaillie T, Salazar M, Velasco G, Agostinis P. Linking ER stress to autophagy: Potential
AC C
implications for cancer therapy. Int J Cell Biol. 2010;2010:930509.
42. Zhang D, Wu CT, Qi X, et al. Activation of histone deacetylase-6 induces contractile dysfunction through derailment of alpha-tubulin proteostasis in experimental and human atrial fibrillation. Circulation. 2014;129(3):346-358.
43. Speakman JR, Mitchell SE. Caloric restriction. Mol Aspects Med. 2011;32(3):159-221.
44. Han X, Turdi S, Hu N, Guo R, Zhang Y, Ren J. Influence of long-term caloric restriction on myocardial and cardiomyocyte contractile function and autophagy in mice. J Nutr Biochem. 2012;23(12):1592-1599.
16
ACCEPTED MANUSCRIPT 45. Ferreira R, Moreira-Goncalves D, Azevedo AL, Duarte JA, Amado F, Vitorino R. Unraveling the exercise-related proteome signature in heart. Basic Res Cardiol. 2015;110(1):454-014-0454-5. Epub 2014 Dec 5.
46. He C, Bassik MC, Moresi V, et al. Exercise-induced BCL2-regulated autophagy is
RI PT
required for muscle glucose homeostasis. Nature. 2012;481(7382):511-515.
47. Maloyan A, Gulick J, Glabe CG, Kayed R, Robbins J. Exercise reverses preamyloid
Proc Natl Acad Sci U S A. 2007;104(14):5995-6000.
SC
oligomer and prolongs survival in alphaB-crystallin-based desmin-related cardiomyopathy.
M AN U
48. Sanbe A, Daicho T, Mizutani R, et al. Protective effect of geranylgeranylacetone via enhancement of HSPB8 induction in desmin-related cardiomyopathy. PLoS One. 2009;4(4):e5351.
49. Fujimura N, Jitsuiki D, Maruhashi T, et al. Geranylgeranylacetone, heat shock protein
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90/AMP-activated protein kinase/endothelial nitric oxide synthase/nitric oxide pathway, and endothelial function in humans. Arterioscler Thromb Vasc Biol. 2012;32(1):153-160.
50. Chang SL, Chen YC, Hsu CP, et al. Heat shock protein inducer modifies arrhythmogenic
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substrate and inhibits atrial fibrillation in the failing heart. Int J Cardiol. 2013;168(4):4019-
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4026.
51. Sakabe M, Shiroshita-Takeshita A, Maguy A, et al. Effects of a heat shock protein inducer on the atrial fibrillation substrate caused by acute atrial ischaemia. Cardiovasc Res. 2008;78(1):63-70.
52. Literati-Nagy B, Kulcsar E, Literati-Nagy Z, et al. Improvement of insulin sensitivity by a novel drug, BGP-15, in insulin-resistant patients: A proof of concept randomized double-blind clinical trial. Horm Metab Res. 2009;41(5):374-380.
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ACCEPTED MANUSCRIPT 53. Sapra G, Tham YK, Cemerlang N, et al. The small-molecule BGP-15 protects against heart failure and atrial fibrillation in mice. Nat Commun. 2014;5:5705.
54. Bjedov I, Toivonen JM, Kerr F, et al. Mechanisms of life span extension by rapamycin in
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the fruit fly drosophila melanogaster. Cell Metab. 2010;11(1):35-46.
55. Harrison DE, Strong R, Sharp ZD, et al. Rapamycin fed late in life extends lifespan in genetically heterogeneous mice. Nature. 2009;460(7253):392-395.
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56. Flynn JM, O'Leary MN, Zambataro CA, et al. Late-life rapamycin treatment reverses age-
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related heart dysfunction. Aging Cell. 2013;12(5):851-862.
57. Cao K, Graziotto JJ, Blair CD, et al. Rapamycin reverses cellular phenotypes and enhances mutant protein clearance in hutchinson-gilford progeria syndrome cells. Sci Transl Med. 2011;3(89):89ra58.
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58. Alemi AS, Rosbe KW, Chan DK, Meyer AK. Airway response to sirolimus therapy for the treatment of complex pediatric lymphatic malformations. Int J Pediatr Otorhinolaryngol. 2015.
59. Bride KL, Vincent T, Smith-Whitley K, et al. Sirolimus is effective in relapsed/refractory
EP
autoimmune cytopenias: Results of a prospective multi-institutional trial. Blood. 2015.
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60. Bishu K, Ogut O, Kushwaha S, et al. Anti-remodeling effects of rapamycin in experimental heart failure: Dose response and interaction with angiotensin receptor blockade. PLoS One. 2013;8(12):e81325.
61. Das A, Durrant D, Koka S, Salloum FN, Xi L, Kukreja RC. Mammalian target of rapamycin (mTOR) inhibition with rapamycin improves cardiac function in type 2 diabetic mice: Potential role of attenuated oxidative stress and altered contractile protein expression. J Biol Chem. 2014;289(7):4145-4160.
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ACCEPTED MANUSCRIPT 62. Lamming DW, Ye L, Sabatini DM, Baur JA. Rapalogs and mTOR inhibitors as anti-aging therapeutics. J Clin Invest. 2013;123(3):980-989.
63. Chhajed PN, Dickenmann M, Bubendorf L, Mayr M, Steiger J, Tamm M. Patterns of
RI PT
pulmonary complications associated with sirolimus. Respiration. 2006;73(3):367-374.
64. Johnston O, Rose CL, Webster AC, Gill JS. Sirolimus is associated with new-onset diabetes in kidney transplant recipients. J Am Soc Nephrol. 2008;19(7):1411-1418.
SC
65. Drose S, Altendorf K. Bafilomycins and concanamycins as inhibitors of V-ATPases and
M AN U
P-ATPases. J Exp Biol. 1997;200(Pt 1):1-8.
66. Kolb PS, Ayaub EA, Zhou W, Yum V, Dickhout JG, Ask K. The therapeutic effects of 4phenylbutyric acid in maintaining proteostasis. Int J Biochem Cell Biol. 2015;61:45-52.
67. Berry SA, Lichter-Konecki U, Diaz GA, et al. Glycerol phenylbutyrate treatment in
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children with urea cycle disorders: Pooled analysis of short and long-term ammonia control and outcomes. Mol Genet Metab. 2014;112(1):17-24.
68. Carducci MA, Gilbert J, Bowling MK, et al. A phase I clinical and pharmacological
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evaluation of sodium phenylbutyrate on an 120-h infusion schedule. Clin Cancer Res.
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2001;7(10):3047-3055.
69. Bishu K, Ogut O, Kushwaha S, et al. Anti-remodeling effects of rapamycin in experimental heart failure: Dose response and interaction with angiotensin receptor blockade. PLoS One. 2013;8(12):e81325.
70. Yang L, Gao JY, Ma J, et al. Cardiac-specific overexpression of metallothionein attenuates myocardial remodeling and contractile dysfunction in l-NAME-induced experimental hypertension: Role of autophagy regulation. Toxicol Lett. 2015;237(2):121-132.
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ACCEPTED MANUSCRIPT 71. Chen MC, Chang JP, Wang YH, Liu WH, Ho WC, Chang HW. Autophagy as a mechanism for myolysis of cardiomyocytes in mitral regurgitation. Eur J Clin Invest. 2011;41(3):299-307.
72. Munasinghe PE, Riu F, Dixit P, et al. Type-2 diabetes increases autophagy in the human
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heart through promotion of beclin-1 mediated pathway. Int J Cardiol. 2016;202:13-20.
73. Kanamori H, Takemura G, Goto K, et al. Autophagic adaptations in diabetic
cardiomyopathy differ between type 1 and type 2 diabetes. Autophagy. 2015;11(7):1146-
SC
1160.
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74. Ma MQ, Thapalia BA, Lin XH. A 6 hour therapeutic window, optimal for interventions targeting AMPK synergism and apoptosis antagonism, for cardioprotection against myocardial ischemic injury: An experimental study on rats. Am J Cardiovasc Dis. 2015;5(1):63-71.
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75. Huang Z, Han Z, Ye B, et al. Berberine alleviates cardiac ischemia/reperfusion injury by inhibiting excessive autophagy in cardiomyocytes. Eur J Pharmacol. 2015;762:1-10.
76. Wu X, He L, Chen F, et al. Impaired autophagy contributes to adverse cardiac
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remodeling in acute myocardial infarction. PLoS One. 2014;9(11):e112891.
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77. Maloyan A, Sayegh J, Osinska H, Chua BH, Robbins J. Manipulation of death pathways in desmin-related cardiomyopathy. Circ Res. 2010;106(9):1524-1532.
78. Yuan Y, Zhao J, Yan S, et al. Autophagy: A potential novel mechanistic contributor to atrial fibrillation. Int J Cardiol. 2014;172(2):492-494.
79. Garcia L, Verdejo HE, Kuzmicic J, et al. Impaired cardiac autophagy in patients developing postoperative atrial fibrillation. J Thorac Cardiovasc Surg. 2012;143(2):451-459.
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ACCEPTED MANUSCRIPT 80. Choi JC, Muchir A, Wu W, et al. Temsirolimus activates autophagy and ameliorates cardiomyopathy caused by lamin A/C gene mutation. Sci Transl Med. 2012;4(144):144ra102.
81. Kassiotis C, Ballal K, Wellnitz K, et al. Markers of autophagy are downregulated in failing
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human heart after mechanical unloading. Circulation. 2009;120(11 Suppl):S191-7.
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Table 1. Autophagy in several cardiac disease models cardiac disease model autophagy Heart failure Mouse69 70 Hypertension Mouse Pig70 70 Rat Mitral regurgitation Human71 72 Diabetic cardiomyopathy Human Mouse73 74 Myocardial infarct Rat Mouse75 Mouse76 77 Desmin-related cardiomyopathy Mouse Atrial fibrillation Dog78 78 Human Human71 79 Postoperative atrial fibrillation Human Dilated cardiomyopathy Mouse80 81 Human
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ACCEPTED MANUSCRIPT Table 2. Drugs with potential benefit in preventing age-related cardiac diseases and proteostatic loss, which are currently in clinical trials for human application.
GGA (teprenone)
HSP induction
IV
BGP-15 Rapamycin (sirolimus, temsirolimus, everolimus)
HSP induction Autophagy inducer
4PBA (buphenyl)
ER stress inhibitor
II II II I/II I I II II III I/II II II/III IV II/III I II I/II I II II I/II II/III
indication
Identifier (clinicaltrials.gov) Gastric ulcers NCT01190657 Gastritis NCT01547559 Gastric lesion NCT01397448 Diabetes Mellitus NCT01069965 Tuberous Sclerosis NCT01526356 Kidney transplantation NCT01014234 Autoimmune blood diseases NCT00392951 Leukemia NCT00780104 Sarcoma NCT00450320 Systemic lupus erythematosus NCT00779194 Breast cancer NCT01698918 Liver transplantation NCT01150097 Cystic Fibrosis NCT00590538 Pulmonary Tuberculosis NCT01580007 Maple Syrup Urine Disease NCT01529060 Diabetes NCT00533559 Urea Cycle Disorders NCT00947544 Lymphoma NCT00002909 HIV NCT01702974 Amyotrophic lateral sclerosis NCT00107770 Parkinson’s Disease NCT02046434 Brain Tumor NCT00006450 Huntington’s disease NCT00212316 Spinal muscular atrophy NCT00528268 Proteinuric nephropathies NCT02343094
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ACCEPTED MANUSCRIPT Figure legends
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Figure 1 The stress-responsive and protein degradation pathways of the proteostasis network. A Cellular stress induces ER stress (green lines), which drives the dissociation of HSPA5 from IRE1, PERK and ATF6. IRE1 splices XBP1 mRNA, resulting in an active XBP1 transcription factor. PERK phosphorylates eIF2α, resulting in a general protein translation block, and activates the transcription of genes related to ER stress, including transcription factor ATF4. ATF6 is translocated to the Golgi apparatus, where it is cleaved. XBP1, ATF4 and spliced ATF6 all translocate to the nucleus and bind to the promotor of genes of molecular chaperones involved in resolving ER stress. Cytosolic stress (grey lines) promotes the dissociation of HSP70 and HSP90 from HSF1, thereby activating the latter. Active HSF1 homotrimerizes and translocates to the nucleus as a transcription factor to promote expression of HSPs, which help to restore proteostasis. Mitochondrial stress (blue lines) inhibits the import of ATFS1 into the mitochondria, where it is degraded by mitochondrial proteases under normal conditions. The cytosolic accumulation of ATFS1 leads to the translocation of this transcription factor to the nucleus, where it binds to the promotor of genes involved in resolving mitochondrial stress. B The ubiquitin-proteasome system degrades single proteins. Folded proteins (green) can become misfolded (red) under stress conditions. Chaperones (HSPs) are induced to refold the protein. When refolding cannot be achieved, HSPs promote polyubiquitination of the misfolded protein and direct the complex to the proteasome. There, deubiquitinating (DUB) enzymes remove the polyubiquitin chain from the proteins, after which the protein is unfolded and degraded. C The autophagiclysosomal pathway degrades large proteins, aggregates and/or organelles. These are sequestered in double-layered membranes, called autophagosomes, which fuses with lysosomes, after which lysosomal hydrolases degrade the contents in to recyclable ATP, amino acids and fatty acids.
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Figure 2 Aging reduces proteostatic function and increases risk for cardiac diseases. A During aging the function of the pathways of the proteostasis network declines. Consequently, protein aggregation and risk for cardiac disease development increases. B Cardiac aging is associated with electrical and structural changes in the heart and a decline in the function of proteostatic pathways. This decline results in increased cellular stress. Due to a diminished stress response of the proteostatic pathway, cellular stress is detrimental for aged hearts and lead to development of cardiac diseases.
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S0828-282X(16)00228-2
DOI:
10.1016/j.cjca.2016.03.005
Reference:
CJCA 2071
To appear in:
Canadian Journal of Cardiology
Received Date: 14 December 2015 Revised Date:
21 February 2016
Accepted Date: 7 March 2016
Please cite this article as: Wiersma M, Henning RH, Brundel BJJM, Derailed proteostasis as a determinant of cardiac aging, Canadian Journal of Cardiology (2016), doi: 10.1016/j.cjca.2016.03.005. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Derailed proteostasis as a determinant of cardiac aging
Marit Wiersma, MSc1,2, Robert H. Henning, MD, PhD1, Bianca J.J.M. Brundel, PhD1,2#
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Department of Clinical Pharmacy and Pharmacology, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands
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Correspondence: Dr. Bianca Brundel Department of Physiology De Boelelaan 1118 1081HV Amsterdam The Netherlands Phone: +31-06-27339900 [email protected]
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Department of Physiology, Institute for Cardiovascular Research, VU University Medical Center, Amsterdam, The Netherlands
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ACCEPTED MANUSCRIPT Abstract
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Age comprises the single most important risk factor for cardiac disease development. The incidence and prevalence of cardiac diseases, which represent the main cause of death worldwide, will rise even more due to the aging population. A hallmark of aging is that it is accompanied by a gradual derailment of proteostasis, e.g. the homeostasis of protein synthesis, folding, assembly, trafficking, function and degradation. Loss of proteostasis is highly relevant to cardiomyocytes, as they are post-mitotic cells and therefore not constantly replenished by proliferation. The derailment of proteostasis during aging is thus an important factor that preconditions for the development of age-related cardiac diseases, such as atrial fibrillation. In turn, frailty of proteostasis in aging cardiomyocytes is exemplified by its accelerated derailment in multiple cardiac diseases. Here, we review 2 major components of the proteostasis network, the stress-responsive and protein degradation pathways, in healthy and aged cardiomyocytes. Furthermore, we discuss the relation between derailment of proteostasis and age-related cardiac diseases, including atrial fibrillation. Finally, we introduce novel therapeutic targets which may possibly attenuate cardiac aging and thus limit cardiac disease progression. Online summary
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Age comprises the single most important risk factor for cardiac disease development. A hallmark of aging is the gradual derailment of proteostasis, e.g. the homeostasis of protein synthesis, folding and degradation. The derailment of proteostasis during aging preconditions for cardiac disease development. We review 2 major components of the proteostasis network, the stress-responsive and protein degradation pathways, in healthy and aged cardiomyocytes and introduce novel therapeutic targets which may attenuate cardiac aging and disease progression.
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ACCEPTED MANUSCRIPT Introduction: a healthy proteostasis is the keystone of a healthy heart
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Cardiovascular diseases (CVDs) are the main cause of death worldwide and in the EU CVDs account for 47% of all disease-related deaths yearly. Its incidence is agerelated, with 3 per 1000 and 74 per 1000 persons affected in the age groups of 35-44 and 85-94 years, respectively. CVDs are present in 33% of the adult population in the USA; over 50% of this CVD population is older than 60 years of age. Moreover, CVDs account for a high socioeconomic burden; its medical costs outnumber those of any other disease, as CVDs are the most common cause for hospitalizations especially in the elderly. As the population is aging, projections foresee a steep increase in the incidence, prevalence and medical costs of CVDs (from $565 billion in 2015 to $1 trillion in 2030).1,2 In view of global aging, it is ever more important to develop adequate strategies to counteract aging-related effects to arrest this trend.
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Recent findings indicate that a healthy protein homeostasis (proteostasis) plays a key role in safeguarding the proper functioning of the heart by maintaining proper cell function through adequate synthesis, folding, assembly, trafficking, function and degradation of proteins.3,4 A proper proteostasis is especially warranted in postmitotic cells, such as cardiomyocytes, which have limited regenerative capacity. Accordingly, an optimal function of proteostasis is required to maintain a healthy heart.
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Proteostasis is maintained by a regulated network of molecular chaperones, stressresponsive pathways and protein degradation pathways. In healthy conditions, this network shows a basal activation that is induced upon cellular stress, including CVD. To respond to cellular stress, cells may deploy three main stress-responsive pathways: the heat shock response (HSR), the mitochondrial unfolded protein response (UPRmito) and the endoplasmic reticulum (ER) unfolded protein response (UPRER) as well as two main degradation pathways: the ubiquitin-proteasome system and macroautophagy (hereafter ‘autophagy’). As the name implies, each of the stress-responsive pathways is activated upon stress in a specific cellular compartment (Figure 1). Nevertheless, these pathways may also be activated and act in parallel upon severe cellular stress.3,4 The HSR is activated upon cytosolic and/or nuclear stress and leads to the dissociation of heat shock factor 1 (HSF1) from the inhibitory molecular chaperones heat shock protein (HSP)70 and HSP90, whereafter HSF1 homotrimerizes. Trimerized HSF1 translocates to the nucleus and binds to the promotor of hsp genes (Figure 1A, grey lines).3,4 In addition, mitochondrial stress activates the UPRmito, which is regulated by activation of the transcription factor associated with stress 1 (ATFS1). Mitochondrial stress blocks the import of ATFS1 in the mitochondrion, which results in ATFS1 being translocated to the nucleus instead. At the nucleus, ATFS1 binds to the promotor region of genes coding for mitochondrial chaperones and components of mitochondrial import, fission and respiratory chain complexes (Figure 1A, blue lines).5 Furthermore, ER stress activates the UPRER, which itself 3
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activates three stress-responsive sensors in parallel, namely inositol-requiring enzyme 1 (IRE1), activating transcription factor 6 (ATF6) and protein kinase-like endoplasmic reticulum kinase (PERK). These three transmembrane proteins are kept inactive by the binding of HSPA5 (also known as BiP or GRP75) to their luminal domain. However, ER stress results in the dissociation of HSPA5, thus activating the sensors. Both IRE1 and PERK homodimerize and autophosphorylate upon activation. Subsequently, IRE1 splices X-box binding protein 1 (XBP1) mRNA and the product, XPB1s, is a transcription factor which translocates to the nucleus and activates transcription of UPRER molecular chaperones and folding catalysts. Activated PERK phosphorylates eukaryotic initiation factor 2 alpha (eIF2α), which inhibits protein translation and synthesis, except for activating transcription factor 4 (ATF4). Subsequently, ATF4 induces expression of growth arrest and DNA damageinducible protein 34 (GADD34) and C/EBP homologous protein (CHOP), which, respectively, attenuate PERK activation and activate the apoptotic pathway. The third sensor activated by ER stress, ATF6, is transported to and subsequently cleaved in the Golgi apparatus. The N-terminal fragment translocates to the nucleus, where it induces expression of other molecular chaperones involved in the UPRER (Figure 1A, green lines).3,4
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Aberrant proteins, which the proteostasis network is not able to properly refold, are degraded by one of the two main degradation pathways, the ubiquitin-proteasome system (UPS) or autophagy.3,4 The UPS is specialized in the degradation of single, short-lived or misfolded proteins. Promoted by molecular chaperones, these proteins are polyubiquitinated and transferred to the cytosolic proteasomes to be unfolded and degraded after deubiquitination (Figure 1B).3,4 The second degradation pathway, autophagy, is a bulk degradation system in which large cytosolic proteins, protein aggregates and organelles are sequestered into a double-membrane structure, called an autophagosome. This autophagosome fuses with a lysosome, after which lysosomal hydrolases degrade the contents into recyclable ATP, amino acids and fatty acids (Figure 1C).
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When these stress-response pathways and/or protein degradation pathways are dysregulated, proteostasis becomes derailed, which is observed in multiple cardiac diseases. For example, heart failure features the activation of the UPRER and UPRmito and the reduced activity of the HSR, UPS and autophagy.6-8 Similarly, cardiomyopathies are associated with increased UPRER activation and reduced UPS and autophagic activity.6,9 Furthermore, metabolic syndrome-related cardiac disease shows reduced autophagy and mitochondrial function.10 In contrast, activation of degradation pathways is increased, and the HSR gets exhausted in (longstanding) persistent atrial fibrillation.11,12 The common denominator of derailed proteostasis in various – mostly age-related – cardiac diseases suggests that proper proteostasis maintenance is an important aspect of healthy cardiac aging. Proteostasis declines during aging
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ACCEPTED MANUSCRIPT Experimental findings reveal that during aging, the gradual failure of stressresponsive and degradation pathways impair the proteostasis network resulting in the accumulation of cellular damage over time (Figure 2A).13 The importance of the factor time in bringing about the failure of proteostasis explains why the incidence of diseases, such as neurodegenerative and cardiovascular diseases, increases with age.
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Increased proteotoxicity during aging
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The relation between aging and proteostasis has been extensively studied in several model systems, particularly in Caenorhabditis elegans and Drosophila melanogaster. During aging in C. elegans, various proteins tend to aggregate and become proteotoxic, including proteins engaged in protein homeostasis and quality control, such as the proteasome, ribosomes and molecular chaperones, including HSP70 and HSP90.14 Furthermore, aging affects the proteome of C. elegans by an upregulation of proteins involved in the UPS, oxidative stress defense and DNA replication and repair and downregulation of ER, mitochondrial and ribosomal proteins.15 The decline in ribosomal proteins corresponds with age-related diminishing of protein synthesis rate.16 Aged D. melanogaster show increased carbonylated and ubiquitinated proteins and a decline in proteasome function.17 Similar changes have been documented in mammals, as aged mice show differential expression of mitochondrial proteins, proteins involved in defense against oxidative stress and chaperones or proteins involved in the stress-response.18 In addition, aging of ex vivo human dermal fibroblasts also display reduced expression of chaperone, proteosomal, ribosomal and mitochondrial proteins.19 Together, the findings from experimental studies indicate aging to prompt proteotoxicity, likely because of a hampered functioning of the proteostasis network.
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Derailment of proteostasis network during aging
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During aging, the function of the stress-responsive and protein degradation pathways of the proteostasis network declines. Aging thus attenuates the HSR20, UPRER21 and UPRmito20 upon cellular stress. The expression of multiple mitochondrial proteins, including chaperones and components of the electron transport chain, is reduced during aging and mitochondrial function and morphology are changed. 20 In case of the UPRER, aging attenuates HSPA5 induction and eIF2α phosphorylation, while GADD34 and CHOP expression are enhanced.21 Similar to the stress-responsive pathways, aging impairs both protein degradation pathways, the UPS and autophagy, by affecting expression and/or activation.22,23 Experimental findings reveal aging to be accompanied by expression of the low-activity 20S proteasomes, in contrast to the high-activity 26S proteasomes, which are mostly found in young animals.23 This divergence could possibly be explained by the dependency of the 26S proteasome assembly on ATP, the latter being decreased during aging.23 Furthermore, aging attenuates the proper mounting of an autophagy response, which could have rescued, or delayed the effects of the age-related dysfunctionality of the 5
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UPS. Loss of autophagy also generally leads to increased ROS levels as the degradation of damaged, old or otherwise dysfunctional mitochondria is impaired. These dysfunctional mitochondria generate high levels of ROS, in turn promoting proteotoxic stress and accelerating detrimental effects on the cell.22 In addition, aging modulates mTOR activity, and depending on the species, gender and organ studied, mTOR activity is either up- or downregulated.24 As mTOR is an important negative regulator of autophagy, aberrant activity may attenuate autophagy during aging. Thus, aging affects the proper function of all stress-responsive and protein degradation pathways at various levels, thereby progressively disturbing the proteostasis network. Proteostasis and longevity
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While aging induces a gradual dysfunction of stress-responsive and protein degradation pathways, these pathways seem fortified in long-lived species.25 Thus, a higher expression of several chaperones, including HSP60 in mitochondria, HSPA5 and GRP94 in ER and HSP70 in cytosol, correlates with enhanced lifespan.25 Furthermore, long-lived species show enhanced autophagic and proteosomal function compared to short-lived species. Moreover, long-lived species appear to excessively enhance their proteotoxic defense in comparison to short-lived species, by inducing high levels of HSP and substantial activation of autophagic and proteosomal clearance.25 These observations suggest that long-lived species deploy their intrinsic defense mechanisms to the maximum to protect from age-related derailment of proteostasis.
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Similar to long-lived species, boosting components of the proteostatic network prolong life of short-lived species. This is exemplified by the notion that both C. elegans26 and D. melanogaster27 have a longer lifespan when HSPs are overexpressed. Conversely, HSF1 knockdown reduces lifespan and features proteins that more promptly aggregate.15 Moreover, overexpression of mitochondrial chaperones HSPA928 or HSP2227 increases lifespan and mitochondrial function in aged C. elegans or D. melanogaster, respectively. Furthermore, enhancing UPRER function to counteract the age-related decline in UPRER activity by overexpression of XBP1s, also resulted in an increased life span in C. elegans.29 Similar to the stressresponsive pathways, enhancement of protein degradation pathways also promotes longevity, as shown by overexpression of proteasome subunits30 and induction of autophagy.22,31 Moreover, inhibition of mTOR increases lifespan in mice and C. elegans, possibly conveyed via induction of autophagy.32 Thus, experimental evidence reveals that aging diminishes the function of both the stress-responsive and the degradation pathways of the proteostasis network. This may result in progressive derailment of proteostasis, accumulation of cellular damage and, ultimately, agerelated diseases, such as CVD. Importantly, experimental evidence suggests that boosting components of these pathways rescues the proteostasis network from aging effects and promotes longevity.
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ACCEPTED MANUSCRIPT Cardiac proteostasis in the elderly
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Age-related changes in the proteostasis network are also present in cardiomyocytes. The expression of heat shock proteins is reduced in aged cardiomyocytes33, which may be due to an upregulation of Rho expression33, as activation of Rho prevents the mounting of HSR by attenuation of HSF1-binding to the promotor region of hsp genes.34 Cardiac mitochondrial function also decreases during aging, due to a variety of mitochondrial changes, including loss of cristae, destruction of inner membranes, swelling, decreased expression of mitochondrial proteins and loss of ATP production.33 In turn, mitochondrial changes impair maintenance of a proper proton gradient and functional respiratory chain, which contributes to increased ROS production. Subsequently, increased amount of ROS in aged cardiomyocytes leads to excess protein damage and a less effective stress response. Importantly, ROS stimulates the lysosomal formation of lipofuscin aggregates35, consisting of aggregated liposomal proteins and lipids, that effectively impair autophagy by preventing fusion of lysosomes to autophagosomes. Consequently, aging-related impairment of autophagy promotes accumulation of dysfunctional mitochondria, representing the major part of the extralysosomal waste in aged cardiomyocytes.36 Dysfunctional mitochondria are known to produce increased amount of ROS, thereby triggering a vicious circle of high ROS production and the subsequent low stress response. In addition, accumulation of dysfunctional mitochondria and aberrant proteins results in functional loss in cardiomyocytes.35 Moreover, impaired autophagy affects the UPS, as damaged or aged proteasomes are degraded by autophagy.35 In accord with the prominent role of autophagy, ATG5 knockout mice display both increased polyubiquitination and attenuated mitochondrial function.36
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The impaired stress-responsive and protein degradation pathways render aged cardiomyocytes susceptible to cellular damage. As cardiomyocytes are post-mitotic cells, and are therefore not constantly replaced by proliferation, the whole heart is highly susceptible to protein damage. During normal aging, the structure and function of the heart changes (Figure 2B), resulting in a decline of diastolic function in rest and systolic function during exercise, impairment of Ca2+ homeostasis, cardiac hypertrophy and fibrosis.37 Cardiac hypertrophy originates from changes in ion channels and Ca2+ homeostasis, and fibrosis during aging, which puts additional strain on the remaining cardiomyocytes to match cardiac demands. Interestingly, stimulation of autophagy in the aged heart decreases hypertrophy, improves contractile function, reduces protein damage and restores Ca2+ homeostasis.38 Conversely, impairment of autophagy predisposes the heart to early dilated cardiomyopathy development.36 Although cardiac aging is related to reduced activation of autophagy, most CVDs, including heart failure, myocardial infarction and atrial fibrillation, are related to excessive activation of autophagy (Table 1). Interestingly, reduced activity of autophagy is observed in CVDs caused by overexpression of (mutant) proteins, including dilated and desmin-related cardiomyopathy. These studies showed that (mutant) protein expression results in 7
ACCEPTED MANUSCRIPT protein aggregates which are toxic for the cardiomyocytes. Protein aggregates are cleared by autophagy but chronic overexpression results in exhaustion of the autophagy machinery, ultimately resulting in accumulation of protein aggregates and loss of cardiomyocyte function. These observations indicate that in case of proteotoxicity, activators of autophagy may be beneficial, whereas other CVDs likely benefit from inhibitors of autophagy.
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Accumulating evidence reveals cardiac diseases to accelerate aging-induced derailment of proteostasis37 and atrial fibrillation (AF) is an excellent example of the adverse effects of cardiac aging on disease development. AF is the most common age-related clinical tachyarrhythmia, characterized by electrical and structural remodeling and atrial contractile dysfunction.39 Derailment of proteostasis is associated with the AF-related structural remodeling and, thereby, may create a substrate for both initiation and progression of AF.40 The HSR gets exhausted in patients with (long-standing) persistent AF, and induction of HSP expression was found to protect against AF progression.11,12 Furthermore, AF is associated with aberrant phosphatase and kinase activities. As several components of the proteostasis network, including components of the UPRER (IRE1, PERK), are regulated by these posttranslational modifications, the aberrant function could influence them.41 In addition, changes in phosphorylation-increased deacetylation of structural proteins by histone deacetylase 6 (HDAC6) contributes to reduced contractile function, structural remodeling and AF progression.42 Together, these findings suggest that proteostasis derailment is an important feature in the initiation and progression of AF, which may explain its prevalence increasing with age. Therapeutic targets to attenuate cardiac aging and disease
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Fortifying proteostasis may prevent the detrimental changes associated with aging and cardiac diseases, in line with observations of extended lifespan in model systems that overexpress components of the proteostasis network. Thus, (pharmacological) boosting of the proteostasis network may represent an appealing strategy to prevent and/or treat cardiac diseases, including AF, cardiomyopathies and heart failure. Lifestyle interventions
Sustained caloric restriction (without restriction of vitamins and micronutrients) is found to increase lifespan in various experimental model systems from yeast to mice43 and decreases the risk of cardiac diseases, by improving contractile function and precluding cardiac hypertrophy and cardiomyopathy in rodents and monkeys.38 Autophagy induction is commonly believed to constitute an important effector of caloric restriction.44 However, sustained caloric restriction is not feasible for most humans38. Except caloric restriction, exercise also reduces the risk of CVDs and has been proposed to slow cardiac aging. Exercise reduces cardiac fibrosis and hypertrophy and improves diastolic function, contractile function and Ca2+ homeostasis.45 Moreover, exercise has a positive effect on HSP expression, mitochondrial function and, indirectly, proteasome function.45 Interestingly, exercise 8
ACCEPTED MANUSCRIPT induces autophagy in mice cardiac muscle.46 In addition, voluntary exercise in a desmin-related cardiomyopathy mouse model showed reduced protein aggregation and reduced disease progression.47 This indicates that regular exercise may be able to improve cardiac outcome in aging and cardiac disease progression. Pharmacological interventions
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Boosting the HSR
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Pharmacological induction of HSP expression has beneficial effects in several cardiac diseases.11,12,48 Geranylgeranylacetone (GGA) is an HSP inducer, used in Japan as anti-ulcer drug since 1984 without reported serious side effects49, and is therefore currently the most promising compound to boost the HSR. GGA treatment in experimental models of cardiac disease attenuated structural damage and improved function of the heart.11,12,48 In vitro, GGA protected against contractile dysfunction and cardiomyocyte damage by attenuation of sarcomere damage.11,12 In vivo, GGA protected against desmin-related cardiomyopathy by attenuation of fibrosis, which may be due to increased aggregate clearance by GGA-induced augmented HSPB1 expression.48 In addition, in vivo GGA treatment reduced inducibility of AF in heart failure50 and atrial ischemia.51 Another HSP inducer, BGP15, was found to protect against contractile dysfunction in a D. melanogaster model for AF and no serious side-effects were reported in a phase II clinical study for insulin resistance.52 Importantly, recent research found BGP-15 to protect from heart failure and AF in in vivo mice models.53 Thus, both GGA and BGP-15 show promising cardioprotective effects probably by boosting the HSR (Table 2). As GGA is already on the market for decades, its features a favorable safety profile, while this is currently still unknown for BGP15. Autophagy induction to counteract aging and proteotoxicity
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As autophagy shows reduced activation during aging and overexpression of (mutant) proteins, induction of autophagy may represent an interesting strategy to attenuate CVD onset and progression. Interestingly, rapamycin treatment induces similar effects as caloric restriction in mice.37 Rapamycin is an inhibitor of the nutrientsensing mTOR, and its administration thus resulting in the activation of autophagy.37,38 The inhibition of mTOR activity increases lifespan in vivo54, even in old mice55, as rapamycin treatment resulted in induced voluntary exercise, reduced cardiac inflammation and hypertrophy, enhanced ejection fraction, and also in increased mitochondrial function.56 Moreover, rapamycin treatment protected in vitro against Hutchinson-Gilford, an accelerated aging disorder.57 In addition to clinical studies in which rapamycin is used to treat cancer58 and auto-immune disease59 (Table 2), experimental evidence suggests rapamycin mitigates progression of heart failure.60 Moreover, rapamycin-treatment attenuated contractile dysfunction and cardiac hypertrophy in aged mice with reversal of diastolic dysfunction and agerelated cardiac proteomic changes.38 In addition, rapamycin treatment prevented diabetic cardiomyopathy in mice.61 Although rapamycin is an FDA approved drug, 9
ACCEPTED MANUSCRIPT caution is needed as rapamycin may exert serious side effects, including suppression of the immune system62, dermatological changes62, lung toxicity63 and increased risk of diabetes development.64 Due to these adverse effects, multiple derivatives of rapamycin have been developed. Unfortunately, these derivatives do not only inhibit mTOR activity, but also increase Akt activity, which can drive cancer development.62 Inhibition of autophagy to counteract CVDs
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Various CVDs show excessive activation of autophagy (Table 1). Therefore, inhibition of autophagy may represent an interesting target for treatment of CVDs, which are not caused by the overexpression of a (mutant) protein. However, inhibitors of autophagy, such as bafilomycin, cause cellular toxicity.65 Thus, direct inhibition of autophagy may currently not be feasible. However, indirect inhibition of autophagy, by targeting upstream activation pathways may be applicable. One of the pathways implicated in cardiac disease and autophagy activation is the UPRER.
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As the ER is the cellular compartment where most proteins (at least one-third) are synthesized and folded,4 this compartment is highly susceptible for proteotoxic stress. Reinforcing the UPRER with 4-phenylbutyric acid (4PBA) in experimental models protects from progression of multiple diseases, including obesity, diabetes, cancer, cystic fibrosis and neurodegenerative disorders.66 Importantly, 4PBA is already an FDA approved drug to treat urea cycle disorder67, with no reported serious side effects.68 Interestingly, 4PBA has several modes of action; it is an ammonia scavenger, a weak histone deacetylase inhibitor and a chemical chaperone.66 At the moment, 4PBA is in clinical trials for several disorders related to proteotoxicity, including amyotrophic lateral sclerosis (NCT00107770) and Huntington's disease (NCT00212316) (Table 2). Results of these studies may inform us about possible effectiveness of 4PBA in respect to cardiac diseases.
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In summary, loss of proteostasis during aging compromises the proper functioning of cardiomyocytes, promoting development of cardiac diseases, including AF. In addition, existing cardiac disease further compromises proteostasis, thereby accelerating the progression of contractile dysfunction and disease. Targeting of key components of proteostasis may thus represent an interesting therapeutic approach to attenuate aging and cardiac disease onset in the elderly. Several compounds fortifying proteostasis are already marketed, such as GGA and 4PBA, and their clinical potential may be readily explored. Compounds targeting autophagy may be of high potential depending on outcomes of current research. However, regular exercise and caloric restriction throughout life may represent the easiest and cheapest intervention to boost cardiac proteostasis and thus slow cardiac aging, reduce the incidence of cardiac diseases and improve clinical outcome. Acknowledgements
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ACCEPTED MANUSCRIPT We gratefully acknowledge the Dutch Heart Foundation (2013T096 and 2013T144) and LSH-Impulse grant (40-43100-98-008) for research support. Disclosures
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ACCEPTED MANUSCRIPT References 1. Mozaffarian D, Benjamin EJ, Go AS, et al. Heart disease and stroke statistics--2015 update: A report from the american heart association. Circulation. 2015;131(4):e29-322.
2. Farmakis D, Stafylas P, Giamouzis G, Maniadakis N, Parissis J. The medical and
RI PT
socioeconomic burden of heart failure: A comparative delineation with cancer. Int J Cardiol. 2015;203:279-281.
SC
3. Labbadia J, Morimoto RI. The biology of proteostasis in aging and disease. Annu Rev Biochem. 2015;84:435-464.
M AN U
4. Diaz-Villanueva JF, Diaz-Molina R, Garcia-Gonzalez V. Protein folding and mechanisms of proteostasis. Int J Mol Sci. 2015;16(8):17193-17230.
5. Jovaisaite V, Mouchiroud L, Auwerx J. The mitochondrial unfolded protein response, a
2014;217(Pt 1):137-143.
TE D
conserved stress response pathway with implications in health and disease. J Exp Biol.
6. Su H, Wang X. The ubiquitin-proteasome system in cardiac proteinopathy: A quality
EP
control perspective. Cardiovasc Res. 2010;85(2):253-262.
7. Cui J, Sinoway LI. Cardiovascular responses to heat stress in chronic heart failure. Curr
AC C
Heart Fail Rep. 2014;11(2):139-145.
8. Dai DF, Hsieh EJ, Liu Y, et al. Mitochondrial proteome remodelling in pressure overloadinduced heart failure: The role of mitochondrial oxidative stress. Cardiovasc Res. 2012;93(1):79-88.
9. Ortega A, Rosello-Lleti E, Tarazon E, et al. Endoplasmic reticulum stress induces different molecular structural alterations in human dilated and ischemic cardiomyopathy. PLoS One. 2014;9(9):e107635.
12
ACCEPTED MANUSCRIPT 10. Sciarretta S, Boppana VS, Umapathi M, Frati G, Sadoshima J. Boosting autophagy in the diabetic heart: A translational perspective. Cardiovasc Diagn Ther. 2015;5(5):394-402.
11. Brundel BJ, Henning RH, Ke L, van Gelder IC, Crijns HJ, Kampinga HH. Heat shock
human atrial fibrillation. J Mol Cell Cardiol. 2006;41(3):555-562.
RI PT
protein upregulation protects against pacing-induced myolysis in HL-1 atrial myocytes and in
12. Brundel BJ, Shiroshita-Takeshita A, Qi X, et al. Induction of heat shock response protects
SC
the heart against atrial fibrillation. Circ Res. 2006;99(12):1394-1402.
13. Lopez-Otin C, Blasco MA, Partridge L, Serrano M, Kroemer G. The hallmarks of aging.
M AN U
Cell. 2013;153(6):1194-1217.
14. David DC, Ollikainen N, Trinidad JC, Cary MP, Burlingame AL, Kenyon C. Widespread protein aggregation as an inherent part of aging in C. elegans. PLoS Biol.
TE D
2010;8(8):e1000450.
15. Walther DM, Kasturi P, Zheng M, et al. Widespread proteome remodeling and aggregation in aging C. elegans. Cell. 2015;161(4):919-932.
EP
16. Kirstein-Miles J, Scior A, Deuerling E, Morimoto RI. The nascent polypeptide-associated
AC C
complex is a key regulator of proteostasis. EMBO J. 2013;32(10):1451-1468.
17. Tsakiri EN, Sykiotis GP, Papassideri IS, Gorgoulis VG, Bohmann D, Trougakos IP. Differential regulation of proteasome functionality in reproductive vs. somatic tissues of drosophila during aging or oxidative stress. FASEB J. 2013;27(6):2407-2420.
18. Chakravarti B, Seshi B, Ratanaprayul W, et al. Proteome profiling of aging in mouse models: Differential expression of proteins involved in metabolism, transport, and stress response in kidney. Proteomics. 2009;9(3):580-597.
13
ACCEPTED MANUSCRIPT 19. Waldera-Lupa DM, Kalfalah F, Florea AM, et al. Proteome-wide analysis reveals an ageassociated cellular phenotype of in situ aged human fibroblasts. Aging (Albany NY). 2014;6(10):856-878.
20. Liang V, Ullrich M, Lam H, et al. Altered proteostasis in aging and heat shock response in
RI PT
C. elegans revealed by analysis of the global and de novo synthesized proteome. Cell Mol Life Sci. 2014;71(17):3339-3361.
21. Naidoo N, Ferber M, Master M, Zhu Y, Pack AI. Aging impairs the unfolded protein
SC
response to sleep deprivation and leads to proapoptotic signaling. J Neurosci.
M AN U
2008;28(26):6539-6548.
22. Simonsen A, Cumming RC, Brech A, Isakson P, Schubert DR, Finley KD. Promoting basal levels of autophagy in the nervous system enhances longevity and oxidant resistance in adult drosophila. Autophagy. 2008;4(2):176-184.
TE D
23. Vernace VA, Arnaud L, Schmidt-Glenewinkel T, Figueiredo-Pereira ME. Aging perturbs 26S proteasome assembly in drosophila melanogaster. FASEB J. 2007;21(11):2672-2682.
24. Baar EL, Carbajal KA, Ong IM, Lamming DW. Sex- and tissue-specific changes in mTOR
EP
signaling with age in C57BL/6J mice. Aging Cell. 2015.
AC C
25. Pride H, Yu Z, Sunchu B, et al. Long-lived species have improved proteostasis compared to phylogenetically-related shorter-lived species. Biochem Biophys Res Commun. 2015;457(4):669-675.
26. Morley JF, Morimoto RI. Regulation of longevity in caenorhabditis elegans by heat shock factor and molecular chaperones. Mol Biol Cell. 2004;15(2):657-664.
14
ACCEPTED MANUSCRIPT 27. Morrow G, Samson M, Michaud S, Tanguay RM. Overexpression of the small mitochondrial Hsp22 extends drosophila life span and increases resistance to oxidative stress. FASEB J. 2004;18(3):598-599.
28. Yokoyama K, Fukumoto K, Murakami T, et al. Extended longevity of caenorhabditis
(mortalin)/mthsp70/Grp75. FEBS Lett. 2002;516(1-3):53-57.
RI PT
elegans by knocking in extra copies of hsp70F, a homolog of mot-2
29. Taylor RC, Dillin A. XBP-1 is a cell-nonautonomous regulator of stress resistance and
SC
longevity. Cell. 2013;153(7):1435-1447.
M AN U
30. Chondrogianni N, Georgila K, Kourtis N, Tavernarakis N, Gonos ES. 20S proteasome activation promotes life span extension and resistance to proteotoxicity in caenorhabditis elegans. FASEB J. 2015;29(2):611-622.
31. Harrison DE, Strong R, Sharp ZD, et al. Rapamycin fed late in life extends lifespan in
TE D
genetically heterogeneous mice. Nature. 2009;460(7253):392-395.
32. Wu JJ, Liu J, Chen EB, et al. Increased mammalian lifespan and a segmental and tissuespecific slowing of aging after genetic reduction of mTOR expression. Cell Rep.
EP
2013;4(5):913-920.
AC C
33. Bodyak N, Kang PM, Hiromura M, et al. Gene expression profiling of the aging mouse cardiac myocytes. Nucleic Acids Res. 2002;30(17):3788-3794.
34. Meijering RA, Wiersma M, van Marion DM, et al. RhoA activation sensitizes cells to proteotoxic stimuli by abrogating the HSF1-dependent heat shock response. PLoS One. 2015;10(7):e0133553.
15
ACCEPTED MANUSCRIPT 35. Terman A, Kurz T, Navratil M, Arriaga EA, Brunk UT. Mitochondrial turnover and aging of long-lived postmitotic cells: The mitochondrial-lysosomal axis theory of aging. Antioxid Redox Signal. 2010;12(4):503-535.
age-related cardiomyopathy. Autophagy. 2010;6(5):600-606.
RI PT
36. Taneike M, Yamaguchi O, Nakai A, et al. Inhibition of autophagy in the heart induces
37. Chiao YA, Rabinovitch PS. The aging heart. Cold Spring Harb Perspect Med.
SC
2015;5(9):a025148.
38. Quarles EK, Dai DF, Tocchi A, Basisty N, Gitari L, Rabinovitch PS. Quality control
M AN U
systems in cardiac aging. Ageing Res Rev. 2015;23(Pt A):101-115.
39. Schotten U, Verheule S, Kirchhof P, Goette A. Pathophysiological mechanisms of atrial fibrillation: A translational appraisal. Physiol Rev. 2011;91(1):265-325.
TE D
40. Ausma J, Wijffels M, Thone F, Wouters L, Allessie M, Borgers M. Structural changes of atrial myocardium due to sustained atrial fibrillation in the goat. Circulation. 1997;96(9):31573163.
EP
41. Verfaillie T, Salazar M, Velasco G, Agostinis P. Linking ER stress to autophagy: Potential
AC C
implications for cancer therapy. Int J Cell Biol. 2010;2010:930509.
42. Zhang D, Wu CT, Qi X, et al. Activation of histone deacetylase-6 induces contractile dysfunction through derailment of alpha-tubulin proteostasis in experimental and human atrial fibrillation. Circulation. 2014;129(3):346-358.
43. Speakman JR, Mitchell SE. Caloric restriction. Mol Aspects Med. 2011;32(3):159-221.
44. Han X, Turdi S, Hu N, Guo R, Zhang Y, Ren J. Influence of long-term caloric restriction on myocardial and cardiomyocyte contractile function and autophagy in mice. J Nutr Biochem. 2012;23(12):1592-1599.
16
ACCEPTED MANUSCRIPT 45. Ferreira R, Moreira-Goncalves D, Azevedo AL, Duarte JA, Amado F, Vitorino R. Unraveling the exercise-related proteome signature in heart. Basic Res Cardiol. 2015;110(1):454-014-0454-5. Epub 2014 Dec 5.
46. He C, Bassik MC, Moresi V, et al. Exercise-induced BCL2-regulated autophagy is
RI PT
required for muscle glucose homeostasis. Nature. 2012;481(7382):511-515.
47. Maloyan A, Gulick J, Glabe CG, Kayed R, Robbins J. Exercise reverses preamyloid
Proc Natl Acad Sci U S A. 2007;104(14):5995-6000.
SC
oligomer and prolongs survival in alphaB-crystallin-based desmin-related cardiomyopathy.
M AN U
48. Sanbe A, Daicho T, Mizutani R, et al. Protective effect of geranylgeranylacetone via enhancement of HSPB8 induction in desmin-related cardiomyopathy. PLoS One. 2009;4(4):e5351.
49. Fujimura N, Jitsuiki D, Maruhashi T, et al. Geranylgeranylacetone, heat shock protein
TE D
90/AMP-activated protein kinase/endothelial nitric oxide synthase/nitric oxide pathway, and endothelial function in humans. Arterioscler Thromb Vasc Biol. 2012;32(1):153-160.
50. Chang SL, Chen YC, Hsu CP, et al. Heat shock protein inducer modifies arrhythmogenic
EP
substrate and inhibits atrial fibrillation in the failing heart. Int J Cardiol. 2013;168(4):4019-
AC C
4026.
51. Sakabe M, Shiroshita-Takeshita A, Maguy A, et al. Effects of a heat shock protein inducer on the atrial fibrillation substrate caused by acute atrial ischaemia. Cardiovasc Res. 2008;78(1):63-70.
52. Literati-Nagy B, Kulcsar E, Literati-Nagy Z, et al. Improvement of insulin sensitivity by a novel drug, BGP-15, in insulin-resistant patients: A proof of concept randomized double-blind clinical trial. Horm Metab Res. 2009;41(5):374-380.
17
ACCEPTED MANUSCRIPT 53. Sapra G, Tham YK, Cemerlang N, et al. The small-molecule BGP-15 protects against heart failure and atrial fibrillation in mice. Nat Commun. 2014;5:5705.
54. Bjedov I, Toivonen JM, Kerr F, et al. Mechanisms of life span extension by rapamycin in
RI PT
the fruit fly drosophila melanogaster. Cell Metab. 2010;11(1):35-46.
55. Harrison DE, Strong R, Sharp ZD, et al. Rapamycin fed late in life extends lifespan in genetically heterogeneous mice. Nature. 2009;460(7253):392-395.
SC
56. Flynn JM, O'Leary MN, Zambataro CA, et al. Late-life rapamycin treatment reverses age-
M AN U
related heart dysfunction. Aging Cell. 2013;12(5):851-862.
57. Cao K, Graziotto JJ, Blair CD, et al. Rapamycin reverses cellular phenotypes and enhances mutant protein clearance in hutchinson-gilford progeria syndrome cells. Sci Transl Med. 2011;3(89):89ra58.
TE D
58. Alemi AS, Rosbe KW, Chan DK, Meyer AK. Airway response to sirolimus therapy for the treatment of complex pediatric lymphatic malformations. Int J Pediatr Otorhinolaryngol. 2015.
59. Bride KL, Vincent T, Smith-Whitley K, et al. Sirolimus is effective in relapsed/refractory
EP
autoimmune cytopenias: Results of a prospective multi-institutional trial. Blood. 2015.
AC C
60. Bishu K, Ogut O, Kushwaha S, et al. Anti-remodeling effects of rapamycin in experimental heart failure: Dose response and interaction with angiotensin receptor blockade. PLoS One. 2013;8(12):e81325.
61. Das A, Durrant D, Koka S, Salloum FN, Xi L, Kukreja RC. Mammalian target of rapamycin (mTOR) inhibition with rapamycin improves cardiac function in type 2 diabetic mice: Potential role of attenuated oxidative stress and altered contractile protein expression. J Biol Chem. 2014;289(7):4145-4160.
18
ACCEPTED MANUSCRIPT 62. Lamming DW, Ye L, Sabatini DM, Baur JA. Rapalogs and mTOR inhibitors as anti-aging therapeutics. J Clin Invest. 2013;123(3):980-989.
63. Chhajed PN, Dickenmann M, Bubendorf L, Mayr M, Steiger J, Tamm M. Patterns of
RI PT
pulmonary complications associated with sirolimus. Respiration. 2006;73(3):367-374.
64. Johnston O, Rose CL, Webster AC, Gill JS. Sirolimus is associated with new-onset diabetes in kidney transplant recipients. J Am Soc Nephrol. 2008;19(7):1411-1418.
SC
65. Drose S, Altendorf K. Bafilomycins and concanamycins as inhibitors of V-ATPases and
M AN U
P-ATPases. J Exp Biol. 1997;200(Pt 1):1-8.
66. Kolb PS, Ayaub EA, Zhou W, Yum V, Dickhout JG, Ask K. The therapeutic effects of 4phenylbutyric acid in maintaining proteostasis. Int J Biochem Cell Biol. 2015;61:45-52.
67. Berry SA, Lichter-Konecki U, Diaz GA, et al. Glycerol phenylbutyrate treatment in
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children with urea cycle disorders: Pooled analysis of short and long-term ammonia control and outcomes. Mol Genet Metab. 2014;112(1):17-24.
68. Carducci MA, Gilbert J, Bowling MK, et al. A phase I clinical and pharmacological
EP
evaluation of sodium phenylbutyrate on an 120-h infusion schedule. Clin Cancer Res.
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2001;7(10):3047-3055.
69. Bishu K, Ogut O, Kushwaha S, et al. Anti-remodeling effects of rapamycin in experimental heart failure: Dose response and interaction with angiotensin receptor blockade. PLoS One. 2013;8(12):e81325.
70. Yang L, Gao JY, Ma J, et al. Cardiac-specific overexpression of metallothionein attenuates myocardial remodeling and contractile dysfunction in l-NAME-induced experimental hypertension: Role of autophagy regulation. Toxicol Lett. 2015;237(2):121-132.
19
ACCEPTED MANUSCRIPT 71. Chen MC, Chang JP, Wang YH, Liu WH, Ho WC, Chang HW. Autophagy as a mechanism for myolysis of cardiomyocytes in mitral regurgitation. Eur J Clin Invest. 2011;41(3):299-307.
72. Munasinghe PE, Riu F, Dixit P, et al. Type-2 diabetes increases autophagy in the human
RI PT
heart through promotion of beclin-1 mediated pathway. Int J Cardiol. 2016;202:13-20.
73. Kanamori H, Takemura G, Goto K, et al. Autophagic adaptations in diabetic
cardiomyopathy differ between type 1 and type 2 diabetes. Autophagy. 2015;11(7):1146-
SC
1160.
M AN U
74. Ma MQ, Thapalia BA, Lin XH. A 6 hour therapeutic window, optimal for interventions targeting AMPK synergism and apoptosis antagonism, for cardioprotection against myocardial ischemic injury: An experimental study on rats. Am J Cardiovasc Dis. 2015;5(1):63-71.
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75. Huang Z, Han Z, Ye B, et al. Berberine alleviates cardiac ischemia/reperfusion injury by inhibiting excessive autophagy in cardiomyocytes. Eur J Pharmacol. 2015;762:1-10.
76. Wu X, He L, Chen F, et al. Impaired autophagy contributes to adverse cardiac
EP
remodeling in acute myocardial infarction. PLoS One. 2014;9(11):e112891.
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77. Maloyan A, Sayegh J, Osinska H, Chua BH, Robbins J. Manipulation of death pathways in desmin-related cardiomyopathy. Circ Res. 2010;106(9):1524-1532.
78. Yuan Y, Zhao J, Yan S, et al. Autophagy: A potential novel mechanistic contributor to atrial fibrillation. Int J Cardiol. 2014;172(2):492-494.
79. Garcia L, Verdejo HE, Kuzmicic J, et al. Impaired cardiac autophagy in patients developing postoperative atrial fibrillation. J Thorac Cardiovasc Surg. 2012;143(2):451-459.
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ACCEPTED MANUSCRIPT 80. Choi JC, Muchir A, Wu W, et al. Temsirolimus activates autophagy and ameliorates cardiomyopathy caused by lamin A/C gene mutation. Sci Transl Med. 2012;4(144):144ra102.
81. Kassiotis C, Ballal K, Wellnitz K, et al. Markers of autophagy are downregulated in failing
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human heart after mechanical unloading. Circulation. 2009;120(11 Suppl):S191-7.
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Table 1. Autophagy in several cardiac disease models cardiac disease model autophagy Heart failure Mouse69 70 Hypertension Mouse Pig70 70 Rat Mitral regurgitation Human71 72 Diabetic cardiomyopathy Human Mouse73 74 Myocardial infarct Rat Mouse75 Mouse76 77 Desmin-related cardiomyopathy Mouse Atrial fibrillation Dog78 78 Human Human71 79 Postoperative atrial fibrillation Human Dilated cardiomyopathy Mouse80 81 Human
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ACCEPTED MANUSCRIPT Table 2. Drugs with potential benefit in preventing age-related cardiac diseases and proteostatic loss, which are currently in clinical trials for human application.
GGA (teprenone)
HSP induction
IV
BGP-15 Rapamycin (sirolimus, temsirolimus, everolimus)
HSP induction Autophagy inducer
4PBA (buphenyl)
ER stress inhibitor
II II II I/II I I II II III I/II II II/III IV II/III I II I/II I II II I/II II/III
indication
Identifier (clinicaltrials.gov) Gastric ulcers NCT01190657 Gastritis NCT01547559 Gastric lesion NCT01397448 Diabetes Mellitus NCT01069965 Tuberous Sclerosis NCT01526356 Kidney transplantation NCT01014234 Autoimmune blood diseases NCT00392951 Leukemia NCT00780104 Sarcoma NCT00450320 Systemic lupus erythematosus NCT00779194 Breast cancer NCT01698918 Liver transplantation NCT01150097 Cystic Fibrosis NCT00590538 Pulmonary Tuberculosis NCT01580007 Maple Syrup Urine Disease NCT01529060 Diabetes NCT00533559 Urea Cycle Disorders NCT00947544 Lymphoma NCT00002909 HIV NCT01702974 Amyotrophic lateral sclerosis NCT00107770 Parkinson’s Disease NCT02046434 Brain Tumor NCT00006450 Huntington’s disease NCT00212316 Spinal muscular atrophy NCT00528268 Proteinuric nephropathies NCT02343094
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ACCEPTED MANUSCRIPT Figure legends
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Figure 1 The stress-responsive and protein degradation pathways of the proteostasis network. A Cellular stress induces ER stress (green lines), which drives the dissociation of HSPA5 from IRE1, PERK and ATF6. IRE1 splices XBP1 mRNA, resulting in an active XBP1 transcription factor. PERK phosphorylates eIF2α, resulting in a general protein translation block, and activates the transcription of genes related to ER stress, including transcription factor ATF4. ATF6 is translocated to the Golgi apparatus, where it is cleaved. XBP1, ATF4 and spliced ATF6 all translocate to the nucleus and bind to the promotor of genes of molecular chaperones involved in resolving ER stress. Cytosolic stress (grey lines) promotes the dissociation of HSP70 and HSP90 from HSF1, thereby activating the latter. Active HSF1 homotrimerizes and translocates to the nucleus as a transcription factor to promote expression of HSPs, which help to restore proteostasis. Mitochondrial stress (blue lines) inhibits the import of ATFS1 into the mitochondria, where it is degraded by mitochondrial proteases under normal conditions. The cytosolic accumulation of ATFS1 leads to the translocation of this transcription factor to the nucleus, where it binds to the promotor of genes involved in resolving mitochondrial stress. B The ubiquitin-proteasome system degrades single proteins. Folded proteins (green) can become misfolded (red) under stress conditions. Chaperones (HSPs) are induced to refold the protein. When refolding cannot be achieved, HSPs promote polyubiquitination of the misfolded protein and direct the complex to the proteasome. There, deubiquitinating (DUB) enzymes remove the polyubiquitin chain from the proteins, after which the protein is unfolded and degraded. C The autophagiclysosomal pathway degrades large proteins, aggregates and/or organelles. These are sequestered in double-layered membranes, called autophagosomes, which fuses with lysosomes, after which lysosomal hydrolases degrade the contents in to recyclable ATP, amino acids and fatty acids.
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Figure 2 Aging reduces proteostatic function and increases risk for cardiac diseases. A During aging the function of the pathways of the proteostasis network declines. Consequently, protein aggregation and risk for cardiac disease development increases. B Cardiac aging is associated with electrical and structural changes in the heart and a decline in the function of proteostatic pathways. This decline results in increased cellular stress. Due to a diminished stress response of the proteostatic pathway, cellular stress is detrimental for aged hearts and lead to development of cardiac diseases.
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