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Gene therapy for cardiac cachexia?
International Journal of Cardiology 85 (2002) 185–191 www.elsevier.com / locate / ijcard
Gene therapy for cardiac cachexia? Nadia Rosenthal a , *, Antonio Musaro` b b
a Mouse Biology Programme, European Molecular Biology Laboratory ( EMBL), Monterotondo, Rome 00016, Italy Department of Histology and Medical Embryology, University of Rome ‘ La Sapienza’, Via A. Scarpa 14, Rome 00161, Italy
Abstract The prevention or attenuation of disease-related skeletal muscle degeneration has been a common goal in the treatment of cardiac cachexia. Cell-based therapies are complicated by insufficient numbers of autologous myoblasts and by ineffective incorporation into host muscle. Pharmacological administration of growth hormone in a variety of clinical conditions characterized by an increase in catabolic rate have been associated with increases in mortality and morbidity, resulting in a decrease in the clinical use of growth hormone and its downstream effector, insulin-like growth factor-1 and a decline in general research into anabolic treatment strategies. In mouse models, however, the selective expression of a muscle-specific transgene encoding a locally acting IGF-1 isoform induces muscle hypertrophy, prevents age- or disease-related atrophy, by increasing stem cell recruitment to injured or degenerating tissue. This gene-based approach avoids hypertrophic effects on distal organs such as the heart, and eliminates risk of possible neoplasms induced by inappropriate high expression levels of circulating IGF-1. The potential therapeutic role of locally expressed IGF-1 is discussed in the context of current strategies for the attenuation of cardiac cachexia. 2002 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Skeletal muscle degeneration; Cardiac cachexia; Autologous myoblasts; Growth hormone; Insulin-like growth factor-1; Gene-based therapy
Progressive muscle atrophy leading to cardiac cachexia has been increasingly appreciated as a powerful negative predictive factor in heart failure. Although the genetic defects responsible for muscle dysfunction in several inherited pathologies have been well characterised, the molecular basis of muscle wasting remains elusive. Subtle alterations in signalling pathways have been identified as leading to significant defects in muscle metabolism, yet the field has been stalled in devising successful therapeutic strategies for treatment of this debilitating and often fatal group of human ailments. The complexity of muscle types, the intimate relationship between structural integrity and mechanical function, and the sensitivity of skeletal muscle to metabolic perturbations have impeded rapid progress in successful *Corresponding author. E-mail address: [email protected] (N. Rosenthal).
clinical intervention. The relatively poor regenerative properties of striated muscle further compound the devastating effects of cachexia. Recent studies on the role of insulin-like growth factor-1 (IGF-1) in skeletal muscle growth and homeostasis have excited new interest in this important mediator of anabolic pathways and suggest promising new avenues for intervention in catabolic disease. IGF-1 controls growth and metabolism in several organs and tissues during both embryonic and post-natal development [1,2]. In the adult, IGF-1 has been implicated in many anabolic pathways in skeletal muscle, where it plays a central role during muscle regeneration [3–5]. A reduction in IGF-1 expression is associated with age-related osteopenic and sarcopenic disorders [6,7], presumably limiting the ability of tissues to effect repair. Since IGF-1 levels decline in both rodent and human senescent muscle, this growth factor has been considered a promising
0167-5273 / 02 / $ – see front matter 2002 Elsevier Science Ireland Ltd. All rights reserved. PII: S0167-5273( 02 )00253-X
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therapeutic agent in staving off advancing muscle weakness during ageing and promoting regeneration [8].
the ablation of IGF-1 gene expression in the liver produced little effect on postnatal growth, and suggesting that extrahepatic IGF-1 expression is sufficient to promote normal postnatal growth and homeostasis in skeletal muscle as well as in other tissues.
1. Unexpected complexity of IGF-1 proteins At the structural level, IGF-1 is related to insulin and shares a 50% amino acid identity. Unlike the insulin gene, the IGF-1 gene locus encodes multiple proteins with variable N- and C-terminal amino acid sequences, producing both locally acting isoforms with an autocrine / paracrine action, and circulating isoforms with endocrine effects. Although the IGF-1 gene is highly conserved in numerous species, its relatively large size (over 70 kb), combined with complex transcriptional and splicing patterns, has complicated its analysis, and the physiological differences between the function of local and circulating isoform of IGF-1 are not completely established. Although IGF-1 transcripts are not exclusively tissuerestricted, those that predominate in the liver are highly growth hormone responsive and as such are major endocrine effectors of GH [9]. By contrast, other specific isoforms of the IGF-1 gene product, produced by alternate promoter usage and splicing, are locally synthesized in skeletal muscle fibers themselves in response to stretch exercise as well as to injury. The functions of the proteins encoded by these different transcripts are widely debated [10–13] but a cohesive picture has yet to emerge. The complexity of IGF-1 signaling pathways uncovered by transgenic and gene targeting experiments has required a revision of earlier views, according to which IGF-1 operated as obligatory downstream effectors of growth hormone (GH) action, predominantly on the liver [14]. Although the ability of GH to stimulate tissue growth involves the activation of IGF-1 gene expression [15], IGF-1 can function in a GH-independent manner, since GH and GH-receptor knockout mice display relatively normal embryonic and post-natal characteristics [14]. In contrast, mice nullizygous for genes encoding either IGF-1 or its receptor tyrosine kinase receptor are defective in embryonic growth, exhibiting marked muscle hypoplasia at birth [3,4]. Exploitation of the ‘binary’(Cre / lox) transgenic mice has added new insights into the function of this IGF-1 [16–19], demonstrating that
2. The importance of IGF-1 isoforms Analyses of transgenic mice expressing different IGF-1 isoforms have provided insight into the role of local IGF-1 signaling in the physiology of striated muscle. By controlling the transcription of IGF-1 transgenes with different promoters it has been possible to characterize the role of the local and / or circulating form of IGF-1 on muscle cell and tissue function [20–25]. The fact that IGF-1 can act either as a circulating hormone or as a local growth factor has confounded previous analyses of animal models in which transgenic IGF synthesized in extra-hepatic tissues was released into the circulation [22]. Overexpression of one IGF-1 isoform in the heart prevented activation of cell death in the viable myocardium after infarction, limiting ventricular dilation, myocardial loading, cardiac hypertrophy, and diabetic cardiomyopathy, supporting the notion that constitutive over-expression of IGF-1 in cardiomyocytes protects them from apoptosis and hypertrophy in the normal and pathological heart [22,26–29]. In another study, over-expression of a different IGF-1-transgene in the heart induced physiological cardiac hypertrophy that progressed to maladaptive hypertrophy [30]. The transgenic IGF-1 model generated in this study demonstrated that short-term systolic performance benefit of increased IGF-1, but ultimately it diminishes systolic performance raising doubt about the therapeutic value of chronic IGF-1 administration. The discrepancies in these phenotypes underscore the normal physiological difference between IGF-1 isoform function. Promising a survival factor as IGF1 might be, substantial evidence supports its involvement in mitogenesis and neoplastic transformation [31–37], suggesting that this signaling pathway plays an important role in the process of tumor promotion. The neoplastic potential of at least certain IGF-1 isoforms is an obvious concern to be taken into account when designing IGF-therapeutic strategies for human pathologies, where the specific role of
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each IGF-1 isoform must be viewed in the appropriate tissue context.
3. Maintenance of ageing muscle mass and strength by local mIGF-1 expression Restricting the action of local IGF-1 isoforms with tissue-specific promoters has allowed the assessment of autocrine / paracrine roles in skeletal muscle throughout the life-span of transgenic animals, exclusive of possible endocrine effects on other tissues [21–25]. Even when expressed from a transgene under the control of strong skeletal muscle-restricted regulatory elements, a local IGF-1 isoform, termed mIGF-1 [25], remains in the muscle bed and does not enter the circulation, thereby avoiding hypertrophic effects on distal organs such as the heart, and eliminating risk of possible neoplasms induced by inappropriately high levels of circulating IGF-1. Mice carrying the mIGF-1 transgene exhibited normal muscle morphology during embryonic development and at birth, but by 5 weeks after birth the transgenic animals displayed marked skeletal muscle hypertrophy compared to their non-transgenic sibs [25]. The importance of appropriate IGF-1 isoform selection is further underscored by preliminary analysis of mouse lines generated with a second IGF-1 transgene. The IGF-1 isoform used (cIGF-1) differed from the mIGF-1 transgene only in a variant Cterminal peptide, which was presumably responsible for the dramatic phenotypic differences of cIGF-1 mice. These animals did not display pronounced muscle hypertrophy but had increased levels of circulating IGF-1, mild cardiac hypertrophy, an increased incidence of late onset neoplasia (L. Tsao and N. Rosenthal, manuscript in preparation). Thus, the choice of isoform is critical to the design of gene therapeutic strategies employing IGF-1. The increased muscle mass in mIGF-1 transgenic mice was associated with augmented force generation compared to age-matched wild-type littermates. Examination of 2-year-old animals revealed that whereas wild-type mice underwent characteristic muscle atrophy, expression of the mIGF-1 transgene was protective against normal loss of muscle mass during senescence. Thus, IGF-1 expression preserves both muscle integrity and the heterogeneity of myofibers,
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two fundamental parameters of muscle function. Over-expression of the mIGF-1 transgene also promoted and preserved the regenerative capacity of muscle tissues and the ability to repair damaged muscle during aging [25]. If mIGF-1 can overcome the normal inability of skeletal muscle to sustain regeneration and repair [38–40], it represents a potentially effective gene therapeutic strategy to combat muscle wasting. Preliminary results testing this approach are promising [41]. Introduction of mIGF-1 somatically using an adeno-associated-viral (AAV) vector permanently blocked age-related loss of muscle size and strength. Young adult muscles receiving virally delivered IGF1 exhibited muscle hypertrophy, while the functional properties of old muscles injected with the IGF-1 virus approached those of their younger uninjected counterparts. Changes in muscle mass and crosssectional area of mIGF-1 injected or transgenic muscles also translated into increased force production, as the consequence of a combination of satellite cell activation and an increase of protein synthesis [42]. In addition, age-related reduction in force production and loss of fast fibers, all of which are typical of ageing skeletal muscle, were prevented both by virally delivered and by transgenic IGF-1 gene expression [25,41]. Thus, it appears that supplemental mIGF-1 is able to attenuate the structural and functional consequences of muscle ageing, independent of its action during embryogenesis or early postnatal life.
4. Supplemental mIGF-1 prevents pathological muscle degeneration Since local persistent synthesis of supplemental IGF-1 could prevent the loss of muscle function that begins at mid adulthood in healthy individuals, it might also be beneficial in cases of neuromuscular pathologies where muscle degeneration is vastly accelerated. Indeed, supplemental mIGF-1 in a mouse model of Duchenne’s muscular dystrophy lacking the dystrophin protein (mdx) could preserve function of the diseased muscle [43]. In mdx mice expressing the mIGF-1 transgene, muscle mass increased by at least 40%, leading to similar increases in force generation compared to those from mdx mice. In addition,
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mIGF-1 expression significantly reduced fibrosis in diaphragms of aged mdx mice, and decreased myonecrosis when compared to age-matched mdx animals. Signaling pathways associated with muscle regeneration and protection against apoptosis were also significantly elevated. The mechanisms by which mIGF-1 maintains muscle integrity in the absence of dystrophin is still unclear, due to the multiple functions of dystrophin and dystrophin-binding proteins. In addition to its structural role, dystrophin regulates the intracellular Ca 21 homeostasis, alterations in which result in an imbalance between muscle protein synthesis and protein degradation culminating in necrosis, fibrosis, and shift in fiber content [44]. Exploitation of genetic and pharmacological manipulations has established a conclusive link between the action of IGF-1 and calcineurin, a serine / threonine phosphatase activated by Ca 21 / calmodulin [45,46]. Calcineurin has been recently implicated in hypertrophic cardiomyopathies [47], skeletal muscle differentiation [48], the specification of slow muscle phenotype [49]. In addition, hypertrophic myocytes expressing mIGF-1 activated calcineurin-mediated NFATc1 dephosphorylation and induction of GATA-2, a novel molecular marker of skeletal muscle hypertrophy [45]. It is therefore possible that mIGF-1 expression in the mdx mouse preserves muscle function in the absence of dystrophin by supplanting some of the calcium-mediated signaling functions of dystrophin. It remains to be seen whether these pathways are important in the ability of mIGF-1 to act as a survival factor in promoting muscle regenerative capacity and preventing muscle necrosis, even in genetically compromised muscle.
5. Stem cells to the rescue? Adult skeletal muscle retains the ability to regenerate after injury, activating the proliferation of resident satellite cells that participate in the reconstitution of damaged tissues. Decreased number of satellite cells, reduced proliferation and concomitant activation of wasting pathways compromise muscle regeneration [50]. A prevailing view has held that the limited capacity for self-renewal of the satellite cell population accounts for the relatively poor regenerative
capacity of skeletal muscle tissue, compared to other organs such as the liver or skin. However, recent studies have demonstrated that skeletal muscle contains another population of progenitor cells, identified as stem cells by cytofluorometric analysis as a side population (SP), on the basis of their Hoechst dye exclusion properties [51]. Originally isolated from haematopoietic tissues in the bone marrow, circulating stem cells can home to various tissues, differentiating into multiple cell types, including muscle [52–55] Although haematopoietic stem cells (HSC) can repopulate and improve the function of injured myocardial tissue [56,57], less is known about the potential of recruited stem cells to ameliorate the regenerative capacity of damaged skeletal muscle. Indeed, the transplantation of bone marrow-derived stem cells into the mdx dystrophic mouse model had a limited impact on muscle cell replacement [58]. If the regenerative capacity of skeletal muscle is at least partially dependent on its capacity to replenish its stem cell compartment, the poor recruitment of circulating stem cells may be one of the limiting factors for tissue repair. Preliminary evidence supports this concept (Musaro et al., submitted). Upon toxin-mediated injury of healthy muscle, stem cells increased in the bone marrow, revealing an unexpected response to distal trauma. Mononuclear cell populations expressing general stem cell markers, as well as specific haematopoietic cell markers, were enhanced in damaged muscles of mIGF-1 transgenic mice, implicating mIGF-1 as a powerful mediator of the regeneration response. When stem cell populations isolated from regenerating mIGF-1 muscles were cultured, they exhibited accelerated myogenic differentiation, suggesting that mIGF-1 enhances stem cell conversion to the myogenic lineage. This was confirmed by experiments in which primary myoblast cultures isolated from mIGF-1 transgenic muscle and co-cultured with bone marrow increased their conversion to the myogenic lineage. These results are consistent with a model in which mIGF-1 enhances homing of bone marrow-derived haematopoietic stem cells to sites of local injury, and accelerates their myogenic differentiation. Although the molecules by which muscle and bone marrow may communicate are not yet known, it is possible that local chemo-attractive signals are en-
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hanced by mIGF-1 expression, guiding circulating stem cell targets of injury. Whatever the mechanism underlying muscle regeneration, it is enhanced at every level in mIGF-1 transgenic mice, suggesting that supplemental mIGF-1 production affects a fundamental change in muscle metabolism that results in the replenishment of stem cells. It remains to be seen whether local mIGF-1 expression will be sufficient to counter the progressive loss of muscle mass and function in cachexia associated with chronic heart failure. However, mIGF-1 represents a promising candidate for gene therapeutic approaches to attenuate deficits in muscle function and plasticity through stem cell recruitment.
6. Future therapeutic directions for cardiac cachexia The prolongation of skeletal muscle strength in neuromuscular disease has been the objective of numerous gene- and cell-based therapeutic approaches employing a variety of delivery systems, which can be a useful starting point for treating cachexia. The generation of appropriate experimental models is particularly important for the development of strategies to attenuate muscle wasting and promote myofiber survival in humans. Although to date a mouse model of muscle cachexia is lacking, currently available animal models of muscular dystrophy, neuromuscular degeneration and disuse atrophy can be employed in preliminary tests of new interventions for muscle wasting. Even if a cachectic animal model is developed, many significant hurdles remain in the efficient translation of pilot studies to clinical practice. In each case a careful consideration of both benefits and risks of treatment is warranted. As such the dramatic attenuation of age-related atrophy by expression of virally delivered mIGF-1 in normal mouse muscle [41] has yet to be tested in a pathological setting. Since the isoform used in these studies does not appear in the circulation, rather acting in locally to enhance the proliferative capacity of neighboring satellite cells in the muscle bed, it is unlikely to be a promising candidate for systemic rescue of cachectic muscle. The molecular and functional characterization of specific IGF-1 isoforms will facilitate the
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evaluation of IGF-1 action in the maintenance of tissue homeostasis, and may allow the development of appropriate therapies to attenuate the muscle wasting. The continued characterization of factors and molecular pathways that participate in the prevention of muscle catabolism, and in the promotion of muscle survival and plasticity, will be of critical importance in generating candidate genes for the attenuation of muscle wasting. Tissue remodeling is an important physiological process that allows skeletal myocytes to respond to environmental demands, promoting adaptive changes in cytoarchitecture and protein composition in response to a variety of stimuli. Extracellular agonists, receptors, protein kinases, intermediate molecules and transcription factors are all components of one or more signal transduction pathways promoting specific cellular responses in adult myocytes. Perturbations in these pathways can result in chronic protein degradation, one of the most devastating consequences of defects in muscle survival mechanisms. Blocking proteolytic pathways or inducing muscle regeneration with genetic or pharmacological intervention will require a detailed knowledge of the signaling mechanisms involved, and the extent to which blocking or enhancing these pathways will be detrimental to other physiological parameters such as motor innervation. Recent evidence that implicates a decline of IGF-1 levels in the skeletal muscles of precachectic heart failure patients [59] underscores the early systemic effects of cardiac malfunction. The potential feedback between skeletal muscle and other tissue types such as heart, adipose tissue and bone is a major potential complication that merits further study in the context of promoting muscle plasticity and survival in the clinic. Interventions in pathological muscle catabolism will require innovative manipulation of these feedback pathways, to target their actions to cachectic tissue. Finally, it may prove advantageous to combine gene therapeutic approaches to cardiac cachexia with cell-based therapies, which have recently enjoyed a renaissance following the demonstration that bone marrow stem cells are competent to contribute to skeletal muscle and vice versa [52,53]. To be effective, stem cells must integrate into host tissue in sufficient numbers and take over or at least induce appropriate physiological functions once grafted.
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Since the small number of muscle stem cells that can be isolated from normal muscle is a limiting factor, viable therapeutic strategies based on autologous material depend upon the development of methods to increase the resident muscle stem cell population or to increase the recruitment of haematopoietic stem cells. Another possibility to be explored is the capacity of stem cells to lodge in the injured organ and secrete as yet unknown factors to promote proliferation and repair in surrounding tissues. This potential remains to be rigorously tested, the possible paracrine action in stem cell-mediated regeneration holds great promise. The persistence of regenerative potential in the muscles of mIGF-1 transgenic mice, as well as the reversal of age-related muscle atrophy by infection of mature muscles with virally delivered mIGF-1, provides a possible venue for expanding mature stem cell populations either in situ or ex vivo. If this proves to be a general principle, stem cells might be engineered to express increased levels of these paracrine factors, acting as an efficient and easily administered delivery system for therapeutic molecules that reverse pathological tissue degeneration in cachectic tissues.
Acknowledgements The financial support of MDA, Telethon–Italy (grant no GP0098 / 01) and CNR-invecchiamento are gratefully acknowledged.
References [1] Stewart CE, Rotwein P. Growth, differentiation, and survival: multiple physiological functions for insulin-like growth factors. Physiol Rev 1996;76:1005–26. [2] Butler AA, LeRoith D. Minireview: tissue-specific versus generalized gene targeting of the igf1 and igf1r genes and their roles in insulin-like growth factor physiology. Endocrinology 2001;142:1685–8. [3] Liu J-L, Baker J, Perkins AS, Robertson EJ, Efstratiadis A. Mice carrying null mutations of the genes encoding insulin-like growth factors-I (IGF-1) and type 1 IGF receptor (IGF1r). Cell 1993;75:59– 72. [4] Powell-Braxton L, Hollingshead P, Warburton C et al. IGF-1 is required for normal embryonic growth in mice. Genes Dev 1993;7:2609–17.
[5] Florini JR, Ewton DZ, Coolican SA. Growth hormone and the Insulin-like growth factor system in myogenesis. Endocr Rev 1996;17:481–517. [6] Rosen CJ, Conover C. Growth hormone / insulin-like growth factor-I axis in aging: a summary of a National Institutes of Aging-Sponsored Symposium. J Clin Endocrinol Metab 1997;82:3919–22. [7] Rosen CJ, Pollak M. Circulating IGF-1: new perspectives for a new century. Trends Endocrinol Metab 1999;10:136–41. [8] Musaro A, Rosenthal N. Transgenic mouse models of muscle aging. Exp Gerontol 1999;34:147–56. [9] LeRoith D, Roberts Jr. CT. Insulin-like growth factor I (IGF-1): a molecular basis for endocrine versus local action? Mol Cell Endocrinol 1991;77:C57–61. [10] Bach MA, Roberts Jr. CT, Smith EP, LeRoith D. Alternative splicing produces messenger RNAs encoding insulin-like growth factor-I prohormones that are differentially glycosylated in vitro. Mol Endocrinol 1990;4:899–904. [11] Adamo ML, Neuenschwander S, LeRoith D, Roberts Jr. CT. Structure, expression, and regulation of the IGF-1 gene. Adv Exp Med Biol 1993;343:1–11. [12] LeRoith D, Roberts Jr. CT. Insulin-like growth factors. Ann NY Acad Sci 1993;692:1–9. [13] McKoy G, Ashley W, Mander J et al. Expression of insulin growth factor-1 splice variants and structural genes in rabbit skeletal muscle induced by stretch and stimulation. J Physiol 1999;516:583–92. [14] LeRoith D, Bondy C, Yakar S, Liu J-L, Butler A. The somatomedin hypothesis: 2001. Endocr Rev 2001;22:53–74. [15] Liu JL, LeRoith D. Insulin-like growth factor I is essential for postnatal growth in response to growth hormone. Endocrinology 1999;140:5178–84. [16] Liu JL, Grinberg A, Westphal H et al. Insulin-like growth factorI affects perinatal lethality and postnatal development in a gene dosage-dependent manner: manipulation using the Cre / loxP system in transgenic mice. Mol Endocrinol 1998;12:452–62. [17] Yakar S, Liu JL, Stannard B. Normal growth and development in the absence of hepatic insulin-like growth factor I. Proc Natl Acad Sci U S A 1999;96:7324–9. [18] Holzenberger M, Leneuve P, Hamard G et al. A targeted partial invalidation of the insulin-like growth factor I receptor gene in mice causes a postnatal growth deficit. Endocrinology 2000;141:2557–66. [19] Dietrich P, Dragatsis I, Xuan S, Zeitlin S, Efstratiadis A. Conditional mutagenesis in mice with heat shock promoter-driven cre transgenes. Mamm Genome 2000;11:196–205. [20] Mathews LS, Hammer RE, Behringer RR et al. Growth enhancement of transgenic mice expressing human insulin-like growth factor I. Endocrinology 1988;123:2827–33. [21] Coleman ME, DeMayo F, Yin KC et al. Myogenic vector expression of insulin-like growth factor I stimulates muscle cell differentiation and myofiber hypertrophy in transgenic mice. J Biol Chem 1995;270:12109–16. [22] Reiss K, Cheng W, Ferber A et al. Over-expression of insulin-like growth factor-1 in the heart is coupled with myocyte proliferation in transgenic mice. Proc Natl Acad Sci USA 1996;93:8630–5. [23] Renganathan M, Messi ML, Schwartz R, Delbono O. Over-expression of hIGF-1 exclusively in skeletal muscle increases the number of dihydropyridine receptors in adult transgenic mice. FEBS Lett 1997;417:13–6. [24] Criswell DS, Booth FW, DeMayo F, Schwartz RJ, Gordon SE, Fiorotto ML. Over-expression of IGF-1 in skeletal muscle of transgenic mice does not prevent unloading-induced atrophy. Am J Physiol 1998;275:E373–379. [25] Musaro` A, McCullagh K, Paul A et al. Localized Igf-1 transgene expression sustains hypertrophy and regeneration in senescent skeletal muscle. Nat Genet 2001;27:195–200.
N. Rosenthal, A. Musaro` / International Journal of Cardiology 85 (2002) 185 – 191 [26] Li Q, Li B, Wang X et al. Over-expression of insulin-like growth factor-1 in mice protects from myocyte death after infarction, attenuating ventricular dilation, wall stress, and cardiac hypertrophy. J Clin Invest 1997;100:1991–9. [27] Welch S, Plank D et al. Cardiac-specific IGF-1 expression attenuates dilated cardiomyopathy in tropomodulin-overexpressing transgenic mice. Circ Res 2002;90:641–8. [28] Li B, Setoguchi M, Wang X et al. Insulin-like growth factor-1 attenuates the detrimental impact of nonocclusive coronary artery constriction on the heart. Circ Res 1999;84:1007–19. [29] Kajstura J, Fiordaliso F, Andreoli AM et al. IGF-1 over-expression inhibits the development of diabetic cardiomyopathy and angiotensin II-mediated oxidative stress. Diabetes 2001;50:1414–24. [30] Delaughter MC, Taffet GE, Fiorotto ML, Entman ML, Schwartz RJ. Local insulin-like growth factor I expression induces physiologic, then pathologic, cardiac hypertrophy in transgenic mice. FASEB J 1999;13:1923–9. [31] Bol DK, Kiguchi K, Gimenez-Conti I, Rupp T, DiGiovanni J. Over-expression of insulin-like growth factor-1 induces hyperplasia, dermal abnormalities, and spontaneous tumor formation in transgenic mice. Oncogene 1997;14:1725–34. [32] Dyck MK, Ouellet M, Gagn M, Petitclerc D, Sirard MA, Pothier F. Testes-specific transgene expression in insulin-like growth factor-I transgenic mice. Mol Reprod Dev 1999;54:32–42. [33] Wilker E, Bol D, Kiguchi K, Rupp T, Beltran L, DiGiovanni J. Enhancement of susceptibility to diverse skin tumor promoters by activation of the insulin-like growth factor-1 receptor in the epidermis of transgenic mice. Mol Carcinog 1999;25:122–31. [34] DiGiovanni J, Bol DK, Wilker E et al. Constitutive expression of insulin-like growth factor-1 in epidermal basal cells of transgenic mice leads to spontaneous tumor promotion. Cancer Res 2000;60:1561–70. [35] DiGiovanni J, Kiguchi K, Frijhoff A et al. Deregulated expression of insulin-like growth factor 1 in prostate epithelium leads to neoplasia in transgenic mice. Proc Natl Acad Sci USA 2000;97:3455–60. [36] Weber MM, Fottner C, Wolf E. The role of the insulin-like growth factor system in adrenocortical tumourigenesis. Eur J Clin Invest 2000;30:69–75. [37] Dyck MK, Parlow AF, Senechal JF, Sirard MA, Pothier F. Ovarian expression of human insulin-like growth factor-I in transgenic mice results in cyst formation. Mol Reprod Dev 2001;59:178–85. [38] Carlson BM, Faulkner JA. Muscle transplantation between young and old rats: age of host determines recovery. Am J Physiol 1989;256:C1262–1266. [39] Carlson BM, Faulkner JA. Muscle regeneration in young and old rats: effects of motor nerve transection with and without marcaine treatment. J Gerontol A Biol Sci Med Sci 1998;53:B52–57. [40] Grounds MD. Age-associated changes in the response of skeletal muscle cells to exercise and regeneration. Ann NY Acad Sci 1998;854:78–91. [41] Barton-Davis ER, Shoturma DI, Musaro A, Rosenthal N, Sweeney HL. Viral mediated expression of insulin-like growth factor I blocks the aging-related loss of skeletal muscle function. Proc Natl Acad Sci USA 1998;95:15603–7.
191
[42] Barton-Davis ER, Shoturma DI, Sweeney HL. Contribution of satellite cells to IGF-1 induced hypertrophy of skeletal muscle. Acta Physiol Scand 1999;167:301–5. [43] Barton ER, Morris L, Musaro A, Rosenthal N, Sweeney HL. Muscle-specific expression of insulin like growth factor I counters muscle decline in mdx mice. J Cell Biol 2002;157:137–48. [44] Bodensteiner JB, Engel AG. Intracellular calcium accumulation in Duchenne dystrophy and other myopathies: a study of 567,000 muscle fibers in 114 biopsies. Neurology 1978;28:439–46. [45] Musaro` A, McCullagh KJ, Naya FJ, Olson EN, Rosenthal N. IGF-1 induces skeletal myocyte hypertrophy through calcineurin in association with GATA-2 and NF-ATc1. Nature 1999;400:581–5. [46] Crabtree GR. Generic signals and specific outcomes: signaling through Ca 21 , calcineurin, and NF-AT. Cell 1999;96:611–4. [47] McKinsey TA, Zhang CL, Lu J, Olson EN. Signal-dependent nuclear export of a histone deacetylase regulates muscle differentiation. Nature 2000;408:106–11. [48] Friday BB, Pavlath GK. A calcineurin- and NF-AT-dependent pathway regulates myf5 gene expression in skeletal muscle reserve cells. J Cell Sci 2001;114:203–10. [49] Lu J, McKinsey TA, Zhang CL, Olson EN. Regulation of skeletal myogenesis by association of the MEF2 transcription factor with class II histone deacetylases. Mol Cell 2000;6:233–44. [50] Heslop L, Morgan JE, Partridge TA. Evidence for a myogenic stem cell that is exhausted in dystrophic muscle. J Cell Sci 2000;113:2299–308. [51] Goodell MA, Brose K et al. Isolation and functional properties of murine hematopoietic stem cells that are replicating in vivo. J Exp Med 1996;183:1797–806. [52] Ferrari G, Cusella De Angelis MG, Coletta M et al. Skeletal muscle regeneration by bone marrow derived myogenic progenitors. Science 1998;279:1528–30. [53] Gussoni E, Soneoka Y, Strickland CD et al. Dystrophin expression in the mdx mouse restored by stem cell transplantation. Nature 1999;401:390–4. [54] Jackson KA, Majka SM et al. Regeneration of ischemic cardiac muscle and vascular endothelium by adult stem cells. J Clin Invest 2001;107:1395–402. [55] Krause DS, Theise ND et al. Multi-organ, multi-lineage engraftment by a single bone marrow-derived stem cell. Cell 2001;105:369–77. [56] Orlic D, Kajstura J et al. Mobilized bone marrow cells repair the infarcted heart, improving function and survival. Proc Natl Acad Sci USA 2001;98:10344–9. [57] Kocher AA, Schuster MD et al. Neovascularization of ischemic myocardium by human bone-marrow-derived angioblasts prevents cardiomyocyte apoptosis, reduces remodeling and improves cardiac function. Nat Med 2001;7:430–6. [58] Ferrari G, Stornaiuolo A et al. Failure to correct murine muscular dystrophy. Nature 2001;411:1014–5. [59] Hambrecht R, Schulze PC et al. Reduction of insulin-like growth factor-I expression in the skeletal muscle of noncachectic patients with chronic heart failure. J Am Coll Cardiol 2002;39:1175–81.
Gene therapy for cardiac cachexia? Nadia Rosenthal a , *, Antonio Musaro` b b
a Mouse Biology Programme, European Molecular Biology Laboratory ( EMBL), Monterotondo, Rome 00016, Italy Department of Histology and Medical Embryology, University of Rome ‘ La Sapienza’, Via A. Scarpa 14, Rome 00161, Italy
Abstract The prevention or attenuation of disease-related skeletal muscle degeneration has been a common goal in the treatment of cardiac cachexia. Cell-based therapies are complicated by insufficient numbers of autologous myoblasts and by ineffective incorporation into host muscle. Pharmacological administration of growth hormone in a variety of clinical conditions characterized by an increase in catabolic rate have been associated with increases in mortality and morbidity, resulting in a decrease in the clinical use of growth hormone and its downstream effector, insulin-like growth factor-1 and a decline in general research into anabolic treatment strategies. In mouse models, however, the selective expression of a muscle-specific transgene encoding a locally acting IGF-1 isoform induces muscle hypertrophy, prevents age- or disease-related atrophy, by increasing stem cell recruitment to injured or degenerating tissue. This gene-based approach avoids hypertrophic effects on distal organs such as the heart, and eliminates risk of possible neoplasms induced by inappropriate high expression levels of circulating IGF-1. The potential therapeutic role of locally expressed IGF-1 is discussed in the context of current strategies for the attenuation of cardiac cachexia. 2002 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Skeletal muscle degeneration; Cardiac cachexia; Autologous myoblasts; Growth hormone; Insulin-like growth factor-1; Gene-based therapy
Progressive muscle atrophy leading to cardiac cachexia has been increasingly appreciated as a powerful negative predictive factor in heart failure. Although the genetic defects responsible for muscle dysfunction in several inherited pathologies have been well characterised, the molecular basis of muscle wasting remains elusive. Subtle alterations in signalling pathways have been identified as leading to significant defects in muscle metabolism, yet the field has been stalled in devising successful therapeutic strategies for treatment of this debilitating and often fatal group of human ailments. The complexity of muscle types, the intimate relationship between structural integrity and mechanical function, and the sensitivity of skeletal muscle to metabolic perturbations have impeded rapid progress in successful *Corresponding author. E-mail address: [email protected] (N. Rosenthal).
clinical intervention. The relatively poor regenerative properties of striated muscle further compound the devastating effects of cachexia. Recent studies on the role of insulin-like growth factor-1 (IGF-1) in skeletal muscle growth and homeostasis have excited new interest in this important mediator of anabolic pathways and suggest promising new avenues for intervention in catabolic disease. IGF-1 controls growth and metabolism in several organs and tissues during both embryonic and post-natal development [1,2]. In the adult, IGF-1 has been implicated in many anabolic pathways in skeletal muscle, where it plays a central role during muscle regeneration [3–5]. A reduction in IGF-1 expression is associated with age-related osteopenic and sarcopenic disorders [6,7], presumably limiting the ability of tissues to effect repair. Since IGF-1 levels decline in both rodent and human senescent muscle, this growth factor has been considered a promising
0167-5273 / 02 / $ – see front matter 2002 Elsevier Science Ireland Ltd. All rights reserved. PII: S0167-5273( 02 )00253-X
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therapeutic agent in staving off advancing muscle weakness during ageing and promoting regeneration [8].
the ablation of IGF-1 gene expression in the liver produced little effect on postnatal growth, and suggesting that extrahepatic IGF-1 expression is sufficient to promote normal postnatal growth and homeostasis in skeletal muscle as well as in other tissues.
1. Unexpected complexity of IGF-1 proteins At the structural level, IGF-1 is related to insulin and shares a 50% amino acid identity. Unlike the insulin gene, the IGF-1 gene locus encodes multiple proteins with variable N- and C-terminal amino acid sequences, producing both locally acting isoforms with an autocrine / paracrine action, and circulating isoforms with endocrine effects. Although the IGF-1 gene is highly conserved in numerous species, its relatively large size (over 70 kb), combined with complex transcriptional and splicing patterns, has complicated its analysis, and the physiological differences between the function of local and circulating isoform of IGF-1 are not completely established. Although IGF-1 transcripts are not exclusively tissuerestricted, those that predominate in the liver are highly growth hormone responsive and as such are major endocrine effectors of GH [9]. By contrast, other specific isoforms of the IGF-1 gene product, produced by alternate promoter usage and splicing, are locally synthesized in skeletal muscle fibers themselves in response to stretch exercise as well as to injury. The functions of the proteins encoded by these different transcripts are widely debated [10–13] but a cohesive picture has yet to emerge. The complexity of IGF-1 signaling pathways uncovered by transgenic and gene targeting experiments has required a revision of earlier views, according to which IGF-1 operated as obligatory downstream effectors of growth hormone (GH) action, predominantly on the liver [14]. Although the ability of GH to stimulate tissue growth involves the activation of IGF-1 gene expression [15], IGF-1 can function in a GH-independent manner, since GH and GH-receptor knockout mice display relatively normal embryonic and post-natal characteristics [14]. In contrast, mice nullizygous for genes encoding either IGF-1 or its receptor tyrosine kinase receptor are defective in embryonic growth, exhibiting marked muscle hypoplasia at birth [3,4]. Exploitation of the ‘binary’(Cre / lox) transgenic mice has added new insights into the function of this IGF-1 [16–19], demonstrating that
2. The importance of IGF-1 isoforms Analyses of transgenic mice expressing different IGF-1 isoforms have provided insight into the role of local IGF-1 signaling in the physiology of striated muscle. By controlling the transcription of IGF-1 transgenes with different promoters it has been possible to characterize the role of the local and / or circulating form of IGF-1 on muscle cell and tissue function [20–25]. The fact that IGF-1 can act either as a circulating hormone or as a local growth factor has confounded previous analyses of animal models in which transgenic IGF synthesized in extra-hepatic tissues was released into the circulation [22]. Overexpression of one IGF-1 isoform in the heart prevented activation of cell death in the viable myocardium after infarction, limiting ventricular dilation, myocardial loading, cardiac hypertrophy, and diabetic cardiomyopathy, supporting the notion that constitutive over-expression of IGF-1 in cardiomyocytes protects them from apoptosis and hypertrophy in the normal and pathological heart [22,26–29]. In another study, over-expression of a different IGF-1-transgene in the heart induced physiological cardiac hypertrophy that progressed to maladaptive hypertrophy [30]. The transgenic IGF-1 model generated in this study demonstrated that short-term systolic performance benefit of increased IGF-1, but ultimately it diminishes systolic performance raising doubt about the therapeutic value of chronic IGF-1 administration. The discrepancies in these phenotypes underscore the normal physiological difference between IGF-1 isoform function. Promising a survival factor as IGF1 might be, substantial evidence supports its involvement in mitogenesis and neoplastic transformation [31–37], suggesting that this signaling pathway plays an important role in the process of tumor promotion. The neoplastic potential of at least certain IGF-1 isoforms is an obvious concern to be taken into account when designing IGF-therapeutic strategies for human pathologies, where the specific role of
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each IGF-1 isoform must be viewed in the appropriate tissue context.
3. Maintenance of ageing muscle mass and strength by local mIGF-1 expression Restricting the action of local IGF-1 isoforms with tissue-specific promoters has allowed the assessment of autocrine / paracrine roles in skeletal muscle throughout the life-span of transgenic animals, exclusive of possible endocrine effects on other tissues [21–25]. Even when expressed from a transgene under the control of strong skeletal muscle-restricted regulatory elements, a local IGF-1 isoform, termed mIGF-1 [25], remains in the muscle bed and does not enter the circulation, thereby avoiding hypertrophic effects on distal organs such as the heart, and eliminating risk of possible neoplasms induced by inappropriately high levels of circulating IGF-1. Mice carrying the mIGF-1 transgene exhibited normal muscle morphology during embryonic development and at birth, but by 5 weeks after birth the transgenic animals displayed marked skeletal muscle hypertrophy compared to their non-transgenic sibs [25]. The importance of appropriate IGF-1 isoform selection is further underscored by preliminary analysis of mouse lines generated with a second IGF-1 transgene. The IGF-1 isoform used (cIGF-1) differed from the mIGF-1 transgene only in a variant Cterminal peptide, which was presumably responsible for the dramatic phenotypic differences of cIGF-1 mice. These animals did not display pronounced muscle hypertrophy but had increased levels of circulating IGF-1, mild cardiac hypertrophy, an increased incidence of late onset neoplasia (L. Tsao and N. Rosenthal, manuscript in preparation). Thus, the choice of isoform is critical to the design of gene therapeutic strategies employing IGF-1. The increased muscle mass in mIGF-1 transgenic mice was associated with augmented force generation compared to age-matched wild-type littermates. Examination of 2-year-old animals revealed that whereas wild-type mice underwent characteristic muscle atrophy, expression of the mIGF-1 transgene was protective against normal loss of muscle mass during senescence. Thus, IGF-1 expression preserves both muscle integrity and the heterogeneity of myofibers,
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two fundamental parameters of muscle function. Over-expression of the mIGF-1 transgene also promoted and preserved the regenerative capacity of muscle tissues and the ability to repair damaged muscle during aging [25]. If mIGF-1 can overcome the normal inability of skeletal muscle to sustain regeneration and repair [38–40], it represents a potentially effective gene therapeutic strategy to combat muscle wasting. Preliminary results testing this approach are promising [41]. Introduction of mIGF-1 somatically using an adeno-associated-viral (AAV) vector permanently blocked age-related loss of muscle size and strength. Young adult muscles receiving virally delivered IGF1 exhibited muscle hypertrophy, while the functional properties of old muscles injected with the IGF-1 virus approached those of their younger uninjected counterparts. Changes in muscle mass and crosssectional area of mIGF-1 injected or transgenic muscles also translated into increased force production, as the consequence of a combination of satellite cell activation and an increase of protein synthesis [42]. In addition, age-related reduction in force production and loss of fast fibers, all of which are typical of ageing skeletal muscle, were prevented both by virally delivered and by transgenic IGF-1 gene expression [25,41]. Thus, it appears that supplemental mIGF-1 is able to attenuate the structural and functional consequences of muscle ageing, independent of its action during embryogenesis or early postnatal life.
4. Supplemental mIGF-1 prevents pathological muscle degeneration Since local persistent synthesis of supplemental IGF-1 could prevent the loss of muscle function that begins at mid adulthood in healthy individuals, it might also be beneficial in cases of neuromuscular pathologies where muscle degeneration is vastly accelerated. Indeed, supplemental mIGF-1 in a mouse model of Duchenne’s muscular dystrophy lacking the dystrophin protein (mdx) could preserve function of the diseased muscle [43]. In mdx mice expressing the mIGF-1 transgene, muscle mass increased by at least 40%, leading to similar increases in force generation compared to those from mdx mice. In addition,
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mIGF-1 expression significantly reduced fibrosis in diaphragms of aged mdx mice, and decreased myonecrosis when compared to age-matched mdx animals. Signaling pathways associated with muscle regeneration and protection against apoptosis were also significantly elevated. The mechanisms by which mIGF-1 maintains muscle integrity in the absence of dystrophin is still unclear, due to the multiple functions of dystrophin and dystrophin-binding proteins. In addition to its structural role, dystrophin regulates the intracellular Ca 21 homeostasis, alterations in which result in an imbalance between muscle protein synthesis and protein degradation culminating in necrosis, fibrosis, and shift in fiber content [44]. Exploitation of genetic and pharmacological manipulations has established a conclusive link between the action of IGF-1 and calcineurin, a serine / threonine phosphatase activated by Ca 21 / calmodulin [45,46]. Calcineurin has been recently implicated in hypertrophic cardiomyopathies [47], skeletal muscle differentiation [48], the specification of slow muscle phenotype [49]. In addition, hypertrophic myocytes expressing mIGF-1 activated calcineurin-mediated NFATc1 dephosphorylation and induction of GATA-2, a novel molecular marker of skeletal muscle hypertrophy [45]. It is therefore possible that mIGF-1 expression in the mdx mouse preserves muscle function in the absence of dystrophin by supplanting some of the calcium-mediated signaling functions of dystrophin. It remains to be seen whether these pathways are important in the ability of mIGF-1 to act as a survival factor in promoting muscle regenerative capacity and preventing muscle necrosis, even in genetically compromised muscle.
5. Stem cells to the rescue? Adult skeletal muscle retains the ability to regenerate after injury, activating the proliferation of resident satellite cells that participate in the reconstitution of damaged tissues. Decreased number of satellite cells, reduced proliferation and concomitant activation of wasting pathways compromise muscle regeneration [50]. A prevailing view has held that the limited capacity for self-renewal of the satellite cell population accounts for the relatively poor regenerative
capacity of skeletal muscle tissue, compared to other organs such as the liver or skin. However, recent studies have demonstrated that skeletal muscle contains another population of progenitor cells, identified as stem cells by cytofluorometric analysis as a side population (SP), on the basis of their Hoechst dye exclusion properties [51]. Originally isolated from haematopoietic tissues in the bone marrow, circulating stem cells can home to various tissues, differentiating into multiple cell types, including muscle [52–55] Although haematopoietic stem cells (HSC) can repopulate and improve the function of injured myocardial tissue [56,57], less is known about the potential of recruited stem cells to ameliorate the regenerative capacity of damaged skeletal muscle. Indeed, the transplantation of bone marrow-derived stem cells into the mdx dystrophic mouse model had a limited impact on muscle cell replacement [58]. If the regenerative capacity of skeletal muscle is at least partially dependent on its capacity to replenish its stem cell compartment, the poor recruitment of circulating stem cells may be one of the limiting factors for tissue repair. Preliminary evidence supports this concept (Musaro et al., submitted). Upon toxin-mediated injury of healthy muscle, stem cells increased in the bone marrow, revealing an unexpected response to distal trauma. Mononuclear cell populations expressing general stem cell markers, as well as specific haematopoietic cell markers, were enhanced in damaged muscles of mIGF-1 transgenic mice, implicating mIGF-1 as a powerful mediator of the regeneration response. When stem cell populations isolated from regenerating mIGF-1 muscles were cultured, they exhibited accelerated myogenic differentiation, suggesting that mIGF-1 enhances stem cell conversion to the myogenic lineage. This was confirmed by experiments in which primary myoblast cultures isolated from mIGF-1 transgenic muscle and co-cultured with bone marrow increased their conversion to the myogenic lineage. These results are consistent with a model in which mIGF-1 enhances homing of bone marrow-derived haematopoietic stem cells to sites of local injury, and accelerates their myogenic differentiation. Although the molecules by which muscle and bone marrow may communicate are not yet known, it is possible that local chemo-attractive signals are en-
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hanced by mIGF-1 expression, guiding circulating stem cell targets of injury. Whatever the mechanism underlying muscle regeneration, it is enhanced at every level in mIGF-1 transgenic mice, suggesting that supplemental mIGF-1 production affects a fundamental change in muscle metabolism that results in the replenishment of stem cells. It remains to be seen whether local mIGF-1 expression will be sufficient to counter the progressive loss of muscle mass and function in cachexia associated with chronic heart failure. However, mIGF-1 represents a promising candidate for gene therapeutic approaches to attenuate deficits in muscle function and plasticity through stem cell recruitment.
6. Future therapeutic directions for cardiac cachexia The prolongation of skeletal muscle strength in neuromuscular disease has been the objective of numerous gene- and cell-based therapeutic approaches employing a variety of delivery systems, which can be a useful starting point for treating cachexia. The generation of appropriate experimental models is particularly important for the development of strategies to attenuate muscle wasting and promote myofiber survival in humans. Although to date a mouse model of muscle cachexia is lacking, currently available animal models of muscular dystrophy, neuromuscular degeneration and disuse atrophy can be employed in preliminary tests of new interventions for muscle wasting. Even if a cachectic animal model is developed, many significant hurdles remain in the efficient translation of pilot studies to clinical practice. In each case a careful consideration of both benefits and risks of treatment is warranted. As such the dramatic attenuation of age-related atrophy by expression of virally delivered mIGF-1 in normal mouse muscle [41] has yet to be tested in a pathological setting. Since the isoform used in these studies does not appear in the circulation, rather acting in locally to enhance the proliferative capacity of neighboring satellite cells in the muscle bed, it is unlikely to be a promising candidate for systemic rescue of cachectic muscle. The molecular and functional characterization of specific IGF-1 isoforms will facilitate the
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evaluation of IGF-1 action in the maintenance of tissue homeostasis, and may allow the development of appropriate therapies to attenuate the muscle wasting. The continued characterization of factors and molecular pathways that participate in the prevention of muscle catabolism, and in the promotion of muscle survival and plasticity, will be of critical importance in generating candidate genes for the attenuation of muscle wasting. Tissue remodeling is an important physiological process that allows skeletal myocytes to respond to environmental demands, promoting adaptive changes in cytoarchitecture and protein composition in response to a variety of stimuli. Extracellular agonists, receptors, protein kinases, intermediate molecules and transcription factors are all components of one or more signal transduction pathways promoting specific cellular responses in adult myocytes. Perturbations in these pathways can result in chronic protein degradation, one of the most devastating consequences of defects in muscle survival mechanisms. Blocking proteolytic pathways or inducing muscle regeneration with genetic or pharmacological intervention will require a detailed knowledge of the signaling mechanisms involved, and the extent to which blocking or enhancing these pathways will be detrimental to other physiological parameters such as motor innervation. Recent evidence that implicates a decline of IGF-1 levels in the skeletal muscles of precachectic heart failure patients [59] underscores the early systemic effects of cardiac malfunction. The potential feedback between skeletal muscle and other tissue types such as heart, adipose tissue and bone is a major potential complication that merits further study in the context of promoting muscle plasticity and survival in the clinic. Interventions in pathological muscle catabolism will require innovative manipulation of these feedback pathways, to target their actions to cachectic tissue. Finally, it may prove advantageous to combine gene therapeutic approaches to cardiac cachexia with cell-based therapies, which have recently enjoyed a renaissance following the demonstration that bone marrow stem cells are competent to contribute to skeletal muscle and vice versa [52,53]. To be effective, stem cells must integrate into host tissue in sufficient numbers and take over or at least induce appropriate physiological functions once grafted.
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Since the small number of muscle stem cells that can be isolated from normal muscle is a limiting factor, viable therapeutic strategies based on autologous material depend upon the development of methods to increase the resident muscle stem cell population or to increase the recruitment of haematopoietic stem cells. Another possibility to be explored is the capacity of stem cells to lodge in the injured organ and secrete as yet unknown factors to promote proliferation and repair in surrounding tissues. This potential remains to be rigorously tested, the possible paracrine action in stem cell-mediated regeneration holds great promise. The persistence of regenerative potential in the muscles of mIGF-1 transgenic mice, as well as the reversal of age-related muscle atrophy by infection of mature muscles with virally delivered mIGF-1, provides a possible venue for expanding mature stem cell populations either in situ or ex vivo. If this proves to be a general principle, stem cells might be engineered to express increased levels of these paracrine factors, acting as an efficient and easily administered delivery system for therapeutic molecules that reverse pathological tissue degeneration in cachectic tissues.
Acknowledgements The financial support of MDA, Telethon–Italy (grant no GP0098 / 01) and CNR-invecchiamento are gratefully acknowledged.
References [1] Stewart CE, Rotwein P. Growth, differentiation, and survival: multiple physiological functions for insulin-like growth factors. Physiol Rev 1996;76:1005–26. [2] Butler AA, LeRoith D. Minireview: tissue-specific versus generalized gene targeting of the igf1 and igf1r genes and their roles in insulin-like growth factor physiology. Endocrinology 2001;142:1685–8. [3] Liu J-L, Baker J, Perkins AS, Robertson EJ, Efstratiadis A. Mice carrying null mutations of the genes encoding insulin-like growth factors-I (IGF-1) and type 1 IGF receptor (IGF1r). Cell 1993;75:59– 72. [4] Powell-Braxton L, Hollingshead P, Warburton C et al. IGF-1 is required for normal embryonic growth in mice. Genes Dev 1993;7:2609–17.
[5] Florini JR, Ewton DZ, Coolican SA. Growth hormone and the Insulin-like growth factor system in myogenesis. Endocr Rev 1996;17:481–517. [6] Rosen CJ, Conover C. Growth hormone / insulin-like growth factor-I axis in aging: a summary of a National Institutes of Aging-Sponsored Symposium. J Clin Endocrinol Metab 1997;82:3919–22. [7] Rosen CJ, Pollak M. Circulating IGF-1: new perspectives for a new century. Trends Endocrinol Metab 1999;10:136–41. [8] Musaro A, Rosenthal N. Transgenic mouse models of muscle aging. Exp Gerontol 1999;34:147–56. [9] LeRoith D, Roberts Jr. CT. Insulin-like growth factor I (IGF-1): a molecular basis for endocrine versus local action? Mol Cell Endocrinol 1991;77:C57–61. [10] Bach MA, Roberts Jr. CT, Smith EP, LeRoith D. Alternative splicing produces messenger RNAs encoding insulin-like growth factor-I prohormones that are differentially glycosylated in vitro. Mol Endocrinol 1990;4:899–904. [11] Adamo ML, Neuenschwander S, LeRoith D, Roberts Jr. CT. Structure, expression, and regulation of the IGF-1 gene. Adv Exp Med Biol 1993;343:1–11. [12] LeRoith D, Roberts Jr. CT. Insulin-like growth factors. Ann NY Acad Sci 1993;692:1–9. [13] McKoy G, Ashley W, Mander J et al. Expression of insulin growth factor-1 splice variants and structural genes in rabbit skeletal muscle induced by stretch and stimulation. J Physiol 1999;516:583–92. [14] LeRoith D, Bondy C, Yakar S, Liu J-L, Butler A. The somatomedin hypothesis: 2001. Endocr Rev 2001;22:53–74. [15] Liu JL, LeRoith D. Insulin-like growth factor I is essential for postnatal growth in response to growth hormone. Endocrinology 1999;140:5178–84. [16] Liu JL, Grinberg A, Westphal H et al. Insulin-like growth factorI affects perinatal lethality and postnatal development in a gene dosage-dependent manner: manipulation using the Cre / loxP system in transgenic mice. Mol Endocrinol 1998;12:452–62. [17] Yakar S, Liu JL, Stannard B. Normal growth and development in the absence of hepatic insulin-like growth factor I. Proc Natl Acad Sci U S A 1999;96:7324–9. [18] Holzenberger M, Leneuve P, Hamard G et al. A targeted partial invalidation of the insulin-like growth factor I receptor gene in mice causes a postnatal growth deficit. Endocrinology 2000;141:2557–66. [19] Dietrich P, Dragatsis I, Xuan S, Zeitlin S, Efstratiadis A. Conditional mutagenesis in mice with heat shock promoter-driven cre transgenes. Mamm Genome 2000;11:196–205. [20] Mathews LS, Hammer RE, Behringer RR et al. Growth enhancement of transgenic mice expressing human insulin-like growth factor I. Endocrinology 1988;123:2827–33. [21] Coleman ME, DeMayo F, Yin KC et al. Myogenic vector expression of insulin-like growth factor I stimulates muscle cell differentiation and myofiber hypertrophy in transgenic mice. J Biol Chem 1995;270:12109–16. [22] Reiss K, Cheng W, Ferber A et al. Over-expression of insulin-like growth factor-1 in the heart is coupled with myocyte proliferation in transgenic mice. Proc Natl Acad Sci USA 1996;93:8630–5. [23] Renganathan M, Messi ML, Schwartz R, Delbono O. Over-expression of hIGF-1 exclusively in skeletal muscle increases the number of dihydropyridine receptors in adult transgenic mice. FEBS Lett 1997;417:13–6. [24] Criswell DS, Booth FW, DeMayo F, Schwartz RJ, Gordon SE, Fiorotto ML. Over-expression of IGF-1 in skeletal muscle of transgenic mice does not prevent unloading-induced atrophy. Am J Physiol 1998;275:E373–379. [25] Musaro` A, McCullagh K, Paul A et al. Localized Igf-1 transgene expression sustains hypertrophy and regeneration in senescent skeletal muscle. Nat Genet 2001;27:195–200.
N. Rosenthal, A. Musaro` / International Journal of Cardiology 85 (2002) 185 – 191 [26] Li Q, Li B, Wang X et al. Over-expression of insulin-like growth factor-1 in mice protects from myocyte death after infarction, attenuating ventricular dilation, wall stress, and cardiac hypertrophy. J Clin Invest 1997;100:1991–9. [27] Welch S, Plank D et al. Cardiac-specific IGF-1 expression attenuates dilated cardiomyopathy in tropomodulin-overexpressing transgenic mice. Circ Res 2002;90:641–8. [28] Li B, Setoguchi M, Wang X et al. Insulin-like growth factor-1 attenuates the detrimental impact of nonocclusive coronary artery constriction on the heart. Circ Res 1999;84:1007–19. [29] Kajstura J, Fiordaliso F, Andreoli AM et al. IGF-1 over-expression inhibits the development of diabetic cardiomyopathy and angiotensin II-mediated oxidative stress. Diabetes 2001;50:1414–24. [30] Delaughter MC, Taffet GE, Fiorotto ML, Entman ML, Schwartz RJ. Local insulin-like growth factor I expression induces physiologic, then pathologic, cardiac hypertrophy in transgenic mice. FASEB J 1999;13:1923–9. [31] Bol DK, Kiguchi K, Gimenez-Conti I, Rupp T, DiGiovanni J. Over-expression of insulin-like growth factor-1 induces hyperplasia, dermal abnormalities, and spontaneous tumor formation in transgenic mice. Oncogene 1997;14:1725–34. [32] Dyck MK, Ouellet M, Gagn M, Petitclerc D, Sirard MA, Pothier F. Testes-specific transgene expression in insulin-like growth factor-I transgenic mice. Mol Reprod Dev 1999;54:32–42. [33] Wilker E, Bol D, Kiguchi K, Rupp T, Beltran L, DiGiovanni J. Enhancement of susceptibility to diverse skin tumor promoters by activation of the insulin-like growth factor-1 receptor in the epidermis of transgenic mice. Mol Carcinog 1999;25:122–31. [34] DiGiovanni J, Bol DK, Wilker E et al. Constitutive expression of insulin-like growth factor-1 in epidermal basal cells of transgenic mice leads to spontaneous tumor promotion. Cancer Res 2000;60:1561–70. [35] DiGiovanni J, Kiguchi K, Frijhoff A et al. Deregulated expression of insulin-like growth factor 1 in prostate epithelium leads to neoplasia in transgenic mice. Proc Natl Acad Sci USA 2000;97:3455–60. [36] Weber MM, Fottner C, Wolf E. The role of the insulin-like growth factor system in adrenocortical tumourigenesis. Eur J Clin Invest 2000;30:69–75. [37] Dyck MK, Parlow AF, Senechal JF, Sirard MA, Pothier F. Ovarian expression of human insulin-like growth factor-I in transgenic mice results in cyst formation. Mol Reprod Dev 2001;59:178–85. [38] Carlson BM, Faulkner JA. Muscle transplantation between young and old rats: age of host determines recovery. Am J Physiol 1989;256:C1262–1266. [39] Carlson BM, Faulkner JA. Muscle regeneration in young and old rats: effects of motor nerve transection with and without marcaine treatment. J Gerontol A Biol Sci Med Sci 1998;53:B52–57. [40] Grounds MD. Age-associated changes in the response of skeletal muscle cells to exercise and regeneration. Ann NY Acad Sci 1998;854:78–91. [41] Barton-Davis ER, Shoturma DI, Musaro A, Rosenthal N, Sweeney HL. Viral mediated expression of insulin-like growth factor I blocks the aging-related loss of skeletal muscle function. Proc Natl Acad Sci USA 1998;95:15603–7.
191
[42] Barton-Davis ER, Shoturma DI, Sweeney HL. Contribution of satellite cells to IGF-1 induced hypertrophy of skeletal muscle. Acta Physiol Scand 1999;167:301–5. [43] Barton ER, Morris L, Musaro A, Rosenthal N, Sweeney HL. Muscle-specific expression of insulin like growth factor I counters muscle decline in mdx mice. J Cell Biol 2002;157:137–48. [44] Bodensteiner JB, Engel AG. Intracellular calcium accumulation in Duchenne dystrophy and other myopathies: a study of 567,000 muscle fibers in 114 biopsies. Neurology 1978;28:439–46. [45] Musaro` A, McCullagh KJ, Naya FJ, Olson EN, Rosenthal N. IGF-1 induces skeletal myocyte hypertrophy through calcineurin in association with GATA-2 and NF-ATc1. Nature 1999;400:581–5. [46] Crabtree GR. Generic signals and specific outcomes: signaling through Ca 21 , calcineurin, and NF-AT. Cell 1999;96:611–4. [47] McKinsey TA, Zhang CL, Lu J, Olson EN. Signal-dependent nuclear export of a histone deacetylase regulates muscle differentiation. Nature 2000;408:106–11. [48] Friday BB, Pavlath GK. A calcineurin- and NF-AT-dependent pathway regulates myf5 gene expression in skeletal muscle reserve cells. J Cell Sci 2001;114:203–10. [49] Lu J, McKinsey TA, Zhang CL, Olson EN. Regulation of skeletal myogenesis by association of the MEF2 transcription factor with class II histone deacetylases. Mol Cell 2000;6:233–44. [50] Heslop L, Morgan JE, Partridge TA. Evidence for a myogenic stem cell that is exhausted in dystrophic muscle. J Cell Sci 2000;113:2299–308. [51] Goodell MA, Brose K et al. Isolation and functional properties of murine hematopoietic stem cells that are replicating in vivo. J Exp Med 1996;183:1797–806. [52] Ferrari G, Cusella De Angelis MG, Coletta M et al. Skeletal muscle regeneration by bone marrow derived myogenic progenitors. Science 1998;279:1528–30. [53] Gussoni E, Soneoka Y, Strickland CD et al. Dystrophin expression in the mdx mouse restored by stem cell transplantation. Nature 1999;401:390–4. [54] Jackson KA, Majka SM et al. Regeneration of ischemic cardiac muscle and vascular endothelium by adult stem cells. J Clin Invest 2001;107:1395–402. [55] Krause DS, Theise ND et al. Multi-organ, multi-lineage engraftment by a single bone marrow-derived stem cell. Cell 2001;105:369–77. [56] Orlic D, Kajstura J et al. Mobilized bone marrow cells repair the infarcted heart, improving function and survival. Proc Natl Acad Sci USA 2001;98:10344–9. [57] Kocher AA, Schuster MD et al. Neovascularization of ischemic myocardium by human bone-marrow-derived angioblasts prevents cardiomyocyte apoptosis, reduces remodeling and improves cardiac function. Nat Med 2001;7:430–6. [58] Ferrari G, Stornaiuolo A et al. Failure to correct murine muscular dystrophy. Nature 2001;411:1014–5. [59] Hambrecht R, Schulze PC et al. Reduction of insulin-like growth factor-I expression in the skeletal muscle of noncachectic patients with chronic heart failure. J Am Coll Cardiol 2002;39:1175–81.