- Email: [email protected]
Mitochondrial dysfunction and heart disease
Mitochondrion 4 (2004) 621–628 www.elsevier.com/locate/mito
Mitochondrial dysfunction and heart disease Paul Rosenberg Department of Medicine, Duke University, Durham, NC 27710, USA Received 1 December 2003; accepted 12 July 2004
Abstract Several inherited and acquired disorders of mitochondria lead to defects in cardiac function as reflected in exercise intolerance, arrhythmias and heart failure. Manifestations of mitochondrial dysfunction is reflected in the abnormal mitochondrial proliferation, structure and ultimately as cytochrome C-induced apoptosis. How these defects are associated with disordered cytosolic events including SR calcium release and transcription has suggested a cross talk of mitochondria and cytosolic events that drive cardiomyocytes dysfunction. q 2004 Elsevier B.V. and Mitochondria Research Society. All rights reserved. Keywords: Mitochondria; Heart disease; Mutation; SR calcium; Calcineurin; PGC-1
Heart disease including myocardial infarction, arrhythmia and cardiomyopathy is the leading cause of morbidity and mortality in this country. Therapies designed to decrease mortality from heart disease have been very effective but have increased the number of patients living longer lives with debilitating disease. Therefore more recent research has focused on the energy demands of the myocardium, seeking to optimize heart function despite continued pathology. The energy expenditures required of the cardiomyocyte include contractile force production (75%), maintenance of internal stores of calcium (15%), and sarcolemmal ionic balance (10%), and the ATP needed for these functions is produced predominately in the mitochondria via oxidative phosphorylation (Katz, 1992). Recent interest focusing on mitochondrial dysfunction reflects the growing E-mail address: [email protected]
consensus that errors in metabolism often accompany and modify cardiomyocyte dysfunction (Shoffner and Wallace, 1992). Indeed, primary inherited mitochondrial diseases display a full spectrum of cardiac disorders including hypertrophic and dilated cardiomyopathies (Melov et al., 1999). The proliferation of mitochondria, which occupy 30–50% of the cell volume of the normal cardiomyocyte, is dysregulated in certain disease states such as chronic ischemia and cardiomyopathy (Arbustini et al., 1998). Mitochondrial dysfunction, reflected in the structure, function and number of mitochondria within the cardiomyocyte, leads to diminished energy production, loss of myocyte contractility, altered electrical properties and eventual cardiomyocyte cell death (Capetanaki, 2002). In addition emerging evidence suggests that mitochondria function within a ternary complex of organelles, including the sarcoplasmic reticulum and the myofibrillary complex, to coordinate
1567-7249/$ - see front matter q 2004 Elsevier B.V. and Mitochondria Research Society. All rights reserved. doi:10.1016/j.mito.2004.07.016
622
P. Rosenberg / Mitochondrion 4 (2004) 621–628
Fig. 1. Interaction of mitochondria with other organelles. Cytosolic localization by desmin position mitochondria in energy requiring areas. Nuclear factors (PGC-1, MEF2, NFAT) mediate the mitochondrial biogenesis. Calcium release channels coordinate oxidative capacity by influencing matrix dehydrogenases activity. Calcium dependent signaling including CamK and calcineurin function as effectors of mitochondrial function.
contractile activity (Hajnoczky et al., 2002). In this review, we will focus on the plasticity of mitochondrial phenotype, the interaction of mitochondria with other organelles (Fig. 1), and its role in the failing cardiomyocyte.
1. Mitochondrial structure Mitochondria are large organelles, approximately one micron in size, found in the cytosol of all cells. Mitochondrial metabolism is compartmentalized by a two-membrane system: the outer mitochondrial membrane (OMM) separates the cytosol from the intermembrane compartment. The inner mitochondrial membrane (IMM) separates the intermembrane compartment from the central matrix. The integrity of these membrane structures is essential for proper mitochondrial function. In addition, specialized domains within the membrane system provide interaction with the rest of the cell in order to coordinate its energy demands. The OMM is responsible for interfacing with the cytosol and its interactions with cytoskeletal elements are important for movement of mitochondria within a cell (Capetanaki, 2002). This mobility is essential for the distribution of mitochondria during cell division, differentiation, and possibly for positioning of mitochondria to cellular regions under intense demands for
energy. Mitochondria slide along actin filaments using kinesin and dynein dependent ATP hydrolysis. More recent studies in the heart have demonstrated the movement of mitochondria along intermediate filaments (Milner et al., 2000). In muscle mitochondria localize to either the intermyofibrillary or subsarcolemmal regions and these populations differ with respect to oxidative capacity. Mitochondria found among the myofilaments involved in muscle contraction provide ATP for the actinomyosin complex, whereas mitochondria found underneath sarcolemma function to maintain the membrane electrical potential (Williams and Rosenberg, 2002). The outer membrane is also involved in transport of proteins from the cytosol to the interior of mitochondria. Small molecules less than 15 kD are freely diffusible to the intermembranous space, however, larger molecules are actively transported into the intermembranous space and matrix at specialized regions of the outer membrane (Yaffe, 1999b). Fusion of the inner and outer mitochondria membranes establish contact sites (CS) that are involved in protein import through the transport outer membrane (TOM) and transport inner membrane (TIM) complexes. Preproteins with N-terminal mitochondrial targeting sequences are transported through the multifunctional receptor Tom22 and the pore forming Tom40 and then the TIM complex to reach their destination. Proteins destined for the matrix space are transported across both OM and IM via the TOM/TIM complex located at CS (Endo et al., 2003). Several studies indicate that CS are dynamic and correlate with oxygen utilization of the embryonic and ischemic heart (Bakker et al., 1994, 1995; Ziegelhoffer-Mihalovicova et al., 1998). In addition, under pathologic conditions of hypertrophy and cardiomyopathy, CS have been found to increase within cardiomyocytes (Bakker et al., 1994). Although the detailed mechanisms of signaling energy utilization and CS formation in the heart are not yet elucidated, cytosolic Ca2C transients have been implicated to provide crosstalk between cytosol and mitochondria (Moran et al., 1990; Bakker et al., 1994). CS are also home to the multiprotein complex called the permeability transition pore (mtPTP) which is an early regulator of apoptosis (Crompton, 2003). mtPTP consists of several proteins including
P. Rosenberg / Mitochondrion 4 (2004) 621–628
the voltage dependent anion channel (VDAC), an integral membrane protein in the OM, the adenine nucleotide translocator (ANT), and cyclophilin D, an immunophilin located in the central matrix (Lesnefsky et al., 2001a). Activation of the mtPTP leads to depolarization and release of cytochrome C into the cytosol to activate caspase dependent apoptosis. The mechanisms in place to prevent IMM depolarization and therefore apoptosis include the mitochondrial ATP-sensitive potassium channels (Weiss et al., 2003). MtATP-K channels offer cytoprotection, as channel agonists mimic ischemic preconditioning in which repeated short lived ischemic events initiate an adaptative response to protect the cell from further ischemia (Akao et al., 2003a,b). VDAC is a large conductance channel and in the open configuration is freely permeable to ions including calcium. It has recently been suggested that the level of VDAC expression may influence mitochondrial calcium signaling (Weiss et al., 2003). Although these gain of function studies indicate that VDAC contributes directly to the mitochondrial calcium content, other possible mechanisms of regulation would include its localization and therefore apposition to calcium release sites of the SR/ER. Prolonged opening of the mtPTP allowing calcium influx through VDAC can induce swelling of the central matrix leading to irreversible damage of the mitochondria and cytochrome C release (Hajnoczky et al., 2002). This prolonged opening may occur during ischemia/reperfusion injury when mtPTP is in a highly permeable state in response to reactive oxygen species (ROS), long chain fatty acids and calcium. Cyclosporin is a potent blocker of the mtPTP and may therefore preserve mitochondrial structure and function during ischemia/reperfusion. However its mechanism of action appears to be independent of its inhibition of calcineurin, a calcium regulated serine threonine phosphatase and may be mediated through cyclophilin D, another component of the mtPTP. The intermembrane space has an ionic composition similar to the cytosol (Lesnefsky et al., 2001b). Cytochrome C is located in the intermembranous space and functions in healthy mitochondria as a mobile electron carrier for the respiratory centers located in inner mitochondrial membrane. Release of cytochrome C into the cytosol initiates the caspase
623
dependent activation of apoptosis, and therefore proper maintenance of the CS and integrity of the two-membrane system are essential for mitochondrial function and cell survival. Recent work has demonstrated that cytochrome C physically associates with the calcium release channel inositol trisphosphate receptor (IP3R) and it is suggested that calcium is released from the IP3R pool for the calcium dependent signaling involved in cell death. In addition, previous reports have implicated the IP3R as a regulator in lymphocyte apoptosis and as a caspase target molecule (Boehning et al., 2003). Future work will determine the significance of calcium regulated apoptosis in the cardiomyocyte. The inner mitochondria membranes are highly folded structures that provide a barrier for the inner matrix from molecules found in the intermembranous space. The inner mitochondrial membranes fold into the matrix to form cristae. Here integral membrane proteins are found such as the five complexes of the respiratory chain including the electron transport chains (complexes I-IV), ATP synthase (complex V), and the ANT. Electron transport through the respiratory chain generates the electrochemical gradient necessary to produce ATP. Key components of the electrochemical gradient include the membrane potential of IMM (DJ) and the proton gradient (DpH) (Weiss et al., 2003). The IMM remains impermeant to calcium and ADP in order to maintain the large DJ and the integrity of the IM is essential to maintain the conditions required for aerobic metabolism including ATP/ADP exchange by the ANT (Portman, 2000). Striated muscles express a specific isoform of the ANT, which is down regulated in animal models of myocardial remodeling. In addition, mice lacking ANT-1 display respiratory chain abnormalities (complex III), exercise intolerance, and cardiac hypertrophy (Murdock et al., 1999; Ning et al., 2000). The inner matrix contains the machinery used in macromolecular synthesis which is required for mitochondria to replicate and function properly. Regulation of mitochondrial proliferation and genomic mutation rates are increasingly recognized as markers of mitochondrial diseases (Arbustini et al., 1998). Strategies designed to maintain the integrity of the two membrane system may ameliorate mitochondrial dysfunction.
624
P. Rosenberg / Mitochondrion 4 (2004) 621–628
2. Mitochondrial proliferation and morphology Normal mitochondria are quite heterogeneous, with size and morphology varying according to the specific metabolic needs of a cell (Yaffe, 1999a). Increased proliferation is another mechanism used by cells to adapt to changing metabolic needs. Temperature, neurohormones (adrenergic and thyroid hormones) and dietary conditions represent established environmental cues that initiate mitochondrial biogenesis in many tissues (Wallace, 2001). The regulatory circuit governing control of mitochondria biogenesis includes the nuclear encoded transcription factors (NRF1-2) which coordinate the transcriptional control of nuclear encoded genes such as the respiratory control centers of the IMM (Chau et al., 1992). The NRFs also regulate the expression of the mitochondrial transcription factor A (mtTFA) which stimulates mitochondrial DNA replication and orders mitochondrial biogenesis (Larsson et al., 1998). More recent work has focused on the PPARg transcriptional coactivator-1 pathway in regulating mitochondrial biogenesis in striated muscle. PGC-1 is a transcriptional coactivator originally identified in thermogenic brown adipose tissue (Wu et al., 1999). The developmental expression of PGC-1 in the mammalian heart parallels the shift from glycolytic to oxidative metabolism (Lehman et al., 2000). In addition, conditions known to alter adult cardiac metabolism such as starvation, pressure overload, and exercise influences the level of PGC-1 in the heart (Irrcher et al., 2003). Finally, forced overexpression of PGC-1 restricted to the myocardium resulted in increased mitochondrial biogenesis as well as LCFA oxidation. Hearts from these transgenic mice display variable degrees of cardiac dysfunction from cardiac hypertrophy to a dilated cardiomyopathy (Lehman et al., 2000; Irrcher et al., 2003). A recent experiment to promote gain-of-function of CaMK revealed a previously unexpected link to the gene encoding PGC-1 (Wu et al., 2002). Many, if not all, nuclear genes encoding mitochondrial proteins are induced by the action of PGC-1, which appears to function as a master regulator of this large class of proteins. Forced expression of a constitutively active form of CaMKIV in both heart and skeletal muscle produced a variety of phenotypes, including hypertrophy, a shift in myosin isotype from fast to slower
forms, and a prominent increase in the fractional volume of mitochondria within the myocytes. These effects closely resemble the morphological and biochemical remodeling responses evoked by endurance exercise, and muscle isolated from CaMKIV transgenic mice exhibited resistance to fatigue during repeated stimulation, a prominent consequence of endurance training. Increased mitochondrial biogenesis in these models suggest that a tight coupling of PGC-1 and metabolic demand is required to achieve optimal metabolic homeostasis and may involve calcium dependent signaling pathways (Wu et al., 2002). Mitochondrial deficiency and dysfunction was recently noted to occur in the MEF2A null mice. These mice exhibited marked chamber dilation, particularly the right ventricle, and the animals died suddenly from conduction disorders. Ultrastructural analysis of adult hearts revealed disordered sarcomeric and intermyofibrillary mitochondrial content (Naya et al., 2002). In addition, MEF2a null mice demonstrated diminished mitochondrial biogenesis (Czubryt et al., 2003). Since CamK signaling influences both MEF2 function as well as mitochondrial biogenesis, it will be interesting to evaluate CamK signaling in these mice (Passier et al., 2000). The mitochondrial disorganization and sarcomere assembly of the MEF2A null mice is reminiscent of the desmin null mouse (Milner et al., 2000). In addition, experiments with transgenic MEF2 indicator mice demonstrate that the promoter of desmin is enriched in MEF2 binding sites (Naya et al., 1999). In these models of cardiac and mitochondrial dysfunction, it is unclear whether the mitochondrial defect reflects altered mitochondrial biogenesis as a primary event or as a secondary event involving the loss of desmin and its interaction with the mitochondrial OMM. Increasingly, receptors coupled to the G-proteins of the Gq class have been implicated in cardiac hypertrophy and cardiomyocyte apoptosis. Recently serotonin and its signaling cascade have been shown to influence cardiac hypertrophy and mitochondrial function. Transgenic overexpression of 5-HT2b receptor in the hearts of mice led to cardiac hypertrophy, induction of the fetal heart gene program, and mitochondrial proliferation. In contrast, mice lacking a functional 5-HT2b receptor died
P. Rosenberg / Mitochondrion 4 (2004) 621–628
prematurely from a dilated cardiomyopathy with associated abnormalities in mitochondrial ultrastructure and dysfunction of oxidative phosphorylation. In addition, the authors provide evidence that 5-HT2b signaling in these mouse models directly influences the expression of ANT-1 and Bcl-2/BAX. The cellular balance of these factors can lead to maladaptive responses including cardiac hypertrophy and apoptosis. Cardiomyocyte apoptosis has been offered as a mechanism to explain the pathologic consequences of ischemic/reperfusion injury. Myocardial tissue subjected to transient interruption of blood flow should recover full functional capacity (Crompton, 2000; Weiss et al., 2003). However, it has been long recognized that the myocyte dysfunction results not from interrupted flow but from the reperfusion as well. In fact, recent work has established the importance of mitochondria and the mtPTP in the reperfusion injury. The toxic events may include combination of cell necrosis and apoptosis and matrix calcium content seems to be an important mediator of this balance (Weiss et al., 2003). In addition to factors intrinsic to mitochondria, ischemic/reperfusion injury depends on cytosolic signaling pathways that target key mitochondria proteins including the ANT and Bcl-2. The calcineurin signaling pathway has been shown to localize and dephosphorylate bcl-2 and Bax, important apoptotic factors (Wang et al., 1999). More recently, elegant studies of ischemia/reperfusion provide direct evidence for calcineurin and NFAT transactivation in cellular apoptosis. Overexpression of an activated form of calcineurin prevented myocyte loss following ischemic injury (De Windt et al., 2000). Moreover, mice lacking cardiac calcineurin A were more susceptible to apoptosis resulting from ischemic injury via coronary artery ligation (Bueno et al., 2003). Although calcineurin offers cytoprotection to injured myocytes, mitochondria from mice carrying the activated calcineurin have defects in the respiratory chain including complexes I and IV and were associated with high levels of superoxide production (Sayen et al., 2003). Taken together, these results indicate that calcineurin provides cytoprotection to cardiomyocyte following ischemic injury; however the mechanism by which calcineurin offers protection remains to be defined. However support for the NFAT
625
transcription factors as the downstream effectors of calcineurin is growing. Blockade of NFAT activation through use of the VIVIT peptide in cardiomyocytes can ameliorate apoptosis in cultured cardiomyocyte models (Pu et al., 2003). Finally, NFAT3/4 null mice demonstrate the essential role of NFAT transactivation in heart formation and mitochondrial function. NFAT3/4-/-mice die during at E10.5 from cardiac failure. Ultrastructural analysis of cardiac mitochondria demonstrated abnormal cristae while biochemical analysis revealed deficiencies of complexes II and IV in the respiratory chain (Bushdid et al., 2003). Taken together these experiments demonstrate a role for signal transduction pathways, G-protein coupled receptors, and transcription factors (PGC-1, NFT, MEF-2) in coordinating the replication and biogenesis of mitochondria needed to match expanding cellular energy demands in cardiac disease states including ischemia/reperfusion injury, cardiac hypertrophy and cardiomyopathy. Indeed, endomyocardial biopsy specimens from patients with dilated cardiomyopathy displayed a variety of morphologic phenotypes including mitochondrial proliferation, variable matrix density, abnormal cristae number and morphology, and inclusion bodies (Arbustini et al., 1998). The mechanism regulating mitochondrial proliferation, and the connection between calcium activated signal transduction and mitochondrial function has been an area of intense interest. Understanding how changes in cytosolic calcium influence mitochondrial behavior will likely yield important insights into the mechanisms of mitochondrial diseases.
3. Calcium and mitochondria More than any other tissue, cardiomyocytes utilize changes in intracellular calcium to affect cellular processes ranging from muscle contraction to gene transcription. Several lines of evidence have emerged to suggest that regulated calcium release directly influences mitochondrial function (Csordas et al., 2001). While some have focused on the nature of the relationship between the ER/SR and mitochondria in myocytes, others have pursued the dehydrogenases which are stimulated by calcium and include pyruvate dehydrogenase (PDH), mitochondrial NADP-isocitrate dehydrogenase (NADP-ICD), and oxoglutarate
626
P. Rosenberg / Mitochondrion 4 (2004) 621–628
dehydrogenase (Denton and McCormack, 1990). Recent work with a rodent model of cardiac hypertrophy has demonstrated that NADP-ICD is inactivated as an early step prior to cardiomyocyte dysfunction (Benderdour et al., 2003). This research will lead to an understanding of how reduced cardiac energy and contractile reserves interact in the cardiomyocyte subjected to pathologic stimuli. The uptake of cytosolic calcium into the mitochondrial matrix involves two transport mechanisms, OM calcium uptake by the VDAC and the IMM calcium uniporter (Hajnoczky et al., 2002). These transporters deliver large pulses of calcium to the inner matrix to regulate oxidative phosphorylation (Thomas et al., 1996). The calcium uniporter was characterized from isolated mitochondria and was believed to require high levels of cellular calcium—far beyond those observed with muscle contraction. Thus, for some time, mitochondria were believed to function as calcium buffer under conditions of cytosolic calcium overload (Denton and McCormack, 1990). More recently, local control has been offered to explain this paradox. Specialized regions of ER/SR in close contact with mitochondria transmit large calcium signals to mitochondria increasing calcium content in the central matrix. These microdomains do not require large evoked calcium responses that influence global cytosolic calcium. Instead, the spatial relationship of mitochondria and calcium release channel that is stable over time provide local control (Hajnoczky et al., 2000b). Interestingly, signal transmission from calcium release channels to mitochondria is optimized by oscillatory rather than tonic calcium signals (Hajnoczky et al., 1995). Thus, coupling of changes in cellular calcium with changes in ATP production may represent an important adaptation linking changes in contractility with oxidative metabolism. How local control is affected by processes such as ischemia and the failing cardiomyocyte may provide an essential link of disordered calcium homeostasis and cardiac energy reserves (Hajnoczky et al., 2000a; Brini, 2003). While most research has focused on the delivery of calcium form the cytosol to the mitochondria, a recent study demonstrates an intrinsic defect in mitochondrial calcium content from cells containing dysfunctional mitochondria (Brini et al., 1999). Here calcium transients were characterized from cells repopulated with mutant mitochondria from two mitochondrial
disease states. Cells carrying mitochodria from patients with myoclonic epilepsy (MERRF) displayed blunted mitochondrial calcium uptake in response IP3R activation. However, mitochondrial calcium uptake from patients with neurogenic muscle weakness, ataxia, and retinitis pigmentosa (NARP) paralleled those from control cells. The MERRF mutation involves a tRNA with global effects on macromolecular synthesis, whereas the NARP mutation leads to dysfunctional ATPase. Therefore, global dysfunction of mitochondria leads to an abnormal calcium response while a mutation of a specific target spares the mitochodrial machinery. Whether the dysfunctional calcium response involves the calcium uniporter or even the recently identified ryanodine receptor remains to be determined. Nevertheless, from this genetic complementation experiment the relevant molecules involved with mitochondria calcium signaling may be identified. 4. Conclusion Heart disease remains a major medical problem in this country, and emerging therapeutics designed to increase survival promises to increase number of patients suffering from chronic ischemic disease, heart failure and arrhythmias. Given that the manifestations of primary mitochondrial diseases share similar pathology with acquired heart disease, it is logical to direct research efforts to understand how mitochondrial dysfunction modulates the many known cellular responses in the cardiomyocyte. Growing research supports the view that mitochondria interface with other cellular organelles, most notably the ER/SR calcium stores and the myofilament. Mitochondria proliferation, structure, and mtDNA mutation rates are influenced by calcium dependent signaling pathways and are part of the adaptation to ischemia and reactive oxygen species. How cellular dysfunction is reflected among these organelles may provide an important understanding for future therapeutics. References Akao, M., O’Rourke, B., Kusuoka, H., Teshima, Y., Jones, S.P., Marban, E., 2003a. Differential actions of cardioprotective agents on the mitochondrial death pathway. Circ. Res. 92, 195–202.
P. Rosenberg / Mitochondrion 4 (2004) 621–628 Akao, M., O’Rourke, B., Teshima, Y., Seharaseyon, J., Marban, E., 2003b. Mechanistically distinct steps in the mitochondrial death pathway triggered by oxidative stress in cardiac myocytes. Circ. Res. 92, 186–194. Arbustini, E., Diegoli, M., Fasani, R., Grasso, M., Morbini, P., Banchieri, N., Bellini, O., Dal Bello, B., Pilotto, A., Magrini, G., Campana, C., Fortina, P., Gavazzi, A., Narula, J., Vigano, M., 1998. Mitochondrial DNA mutations and mitochondrial abnormalities in dilated cardiomyopathy. Am. J. Pathol. 153, 1501–1510. Bakker, A., Bernaert, I., De Bie, M., Ravingerova, T., Ziegelhoffer, A., Van Belle, H., Jacob, W., 1994. The effect of calcium on mitochondrial contact sites: a study on isolated rat hearts. Biochim. Biophys. Acta 1224, 583–588. Bakker, A., Goossens, F., De Bie, M., Bernaert, I., Van Belle, H., Jacob, W., 1995. The effect of ischemia and reperfusion on mitochondrial contact sites in isolated rat hearts. Histol. Histopathol. 10, 405–416. Benderdour, M., Charron, G., DeBlois, D., Comte, B., Des Rosiers, C., 2003. Cardiac mitochondrial NADPC-isocitrate dehydrogenase is inactivated through 4-hydroxynonenal adduct formation: an event that precedes hypertrophy development. J. Biol. Chem. 278, 45154–45159. Boehning, D., Patterson, R.L., Sedaghat, L., Glebova, N.O., Kurosaki, T., Snyder, S.H., 2003. Cytochrome c binds to inositol (1,4,5) trisphosphate receptors, amplifying calciumdependent apoptosis. Nat. Cell Biol. 5 (12), 1051–1061. Brini, M., 2003. Ca(2C) signalling in mitochondria: mechanism and role in physiology and pathology. Cell Calcium 34, 399–405. Brini, M., Pinton, P., King, M.P., Davidson, M., Schon, E.A., Rizzuto, R., 1999. A calcium signaling defect in the pathogenesis of a mitochondrial DNA inherited oxidative phosphorylation deficiency. Nat. Med. 5, 951–954. Bueno, O.F., Lips, D.J., Kaiser, R.A., Wilkins, B.J., Dai, Y.S., Glascock, B.J., Klevitsky, R., Hewett, T.E., Kimball, T.R., Aronow, B.J., Doevendans, P.A., Molkentin, J.D., 2003. Calcineurin A{beta} gene targeting predisposes the myocardium to acute ischemia-induced apoptosis and dysfunction. Circ. Res. 94, 91–99. Bushdid, P.B., Osinska, H., Waclaw, R.R., Molkentin, J.D., Yutzey, K.E., 2003. NFATc3 and NFATc4 are required for cardiac development and mitochondrial function. Circ. Res. 92, 1305–1313. Capetanaki, Y., 2002. Desmin cytoskeleton: a potential regulator of muscle mitochondrial behavior and function. Trends Cardiovasc. Med. 12, 339–348. Chau, C.M., Evans, M.J., Scarpulla, R.C., 1992. Nuclear respiratory factor 1 activation sites in genes encoding the gamma-subunit of ATP synthase, eukaryotic initiation factor 2 alpha, and tyrosine aminotransferase. Specific interaction of purified NRF-1 with multiple target genes. J. Biol. Chem. 267, 6999–7006. Crompton, M., 2000. Mitochondrial intermembrane junctional complexes and their role in cell death. J. Physiol. 529 (Pt 1), 11–21. Crompton, M., 2003. On the involvement of mitochondrial intermembrane junctional complexes in apoptosis. Curr. Med. Chem. 10, 1473–1484.
627
Csordas, G., Thomas, A.P., Hajnoczky, G., 2001. Calcium signal transmission between ryanodine receptors and mitochondria in cardiac muscle. Trends Cardiovasc Med. 11, 269–275. Czubryt, M.P., McAnally, J., Fishman, G.I., Olson, E.N., 2003. Regulation of peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC-1 alpha) and mitochondrial function by MEF2 and HDAC5. Proc. Natl Acad. Sci. USA 100, 1711–1716. Denton, R.M., McCormack, J.G., 1990. Ca2C as a second messenger within mitochondria of the heart and other tissues. Annu. Rev. Physiol. 52, 451–466. De Windt, L.J., Lim, H.W., Taigen, T., Wencker, D., Condorelli, G., Dorn 2nd., G.W., Kitsis, R.N., Molkentin, J.D., 2000. Calcineurin-mediated hypertrophy protects cardiomyocytes from apoptosis in vitro and in vivo: an apoptosis-independent model of dilated heart failure. Circ. Res. 86, 255–263. Endo, T., Yamamoto, H., Esaki, M., 2003. Functional cooperation and separation of translocators in protein import into mitochondria, the double-membrane bounded organelles. J. Cell Sci. 116, 3259–3267. Hajnoczky, G., Robb-Gaspers, L.D., Seitz, M.B., Thomas, A.P., 1995. Decoding of cytosolic calcium oscillations in the mitochondria. Cell 82, 415–424. Hajnoczky, G., Csordas, G., Madesh, M., Pacher, P., 2000a. Control of apoptosis by IP(3) and ryanodine receptor driven calcium signals. Cell Calcium 28, 349–363. Hajnoczky, G., Csordas, G., Madesh, M., Pacher, P., 2000b. The machinery of local Ca2C signalling between sarco-endoplasmic reticulum and mitochondria. J. Physiol. 529 (Pt 1), 69–81. Hajnoczky, G., Csordas, G., Yi, M., 2002. Old players in a new role: mitochondria-associated membranes, VDAC, and ryanodine receptors as contributors to calcium signal propagation from endoplasmic reticulum to the mitochondria. Cell Calcium 32, 363–377. Irrcher, I., Adhihetty, P.J., Sheehan, T., Joseph, A.M., Hood, D.A., 2003. PPARgamma coactivator-1alpha expression during thyroid hormone- and contractile activity-induced mitochondrial adaptations. Am. J. Physiol. Cell Physiol. 284, C1669–C1677. Katz, A., 1992. Physiology of the Heart, Farmington, CT 1992. Larsson, N.G., Wang, J., Wilhelmsson, H., Oldfors, A., Rustin, P., Lewandoski, M., Barsh, G.S., Clayton, D.A., 1998. Mitochondrial transcription factor A is necessary for mtDNA maintenance and embryogenesis in mice. Nat. Genet. 18, 231–236. Lehman, J.J., Barger, P.M., Kovacs, A., Saffitz, J.E., Medeiros, D.M., Kelly, D.P., 2000. Peroxisome proliferatoractivated receptor gamma coactivator-1 promotes cardiac mitochondrial biogenesis. J. Clin. Invest. 106, 847–856. Lesnefsky, E.J., Gudz, T.I., Moghaddas, S., Migita, C.T., IkedaSaito, M., Turkaly, P.J., Hoppel, C.L., 2001a. Aging decreases electron transport complex III activity in heart interfibrillar mitochondria by alteration of the cytochrome c binding site. J. Mol. Cell Cardiol. 33, 37–47. Lesnefsky, E.J., Moghaddas, S., Tandler, B., Kerner, J., Hoppel, C.L., 2001b. Mitochondrial dysfunction in cardiac disease: ischemia–reperfusion, aging, and heart failure. J. Mol. Cell Cardiol. 33, 1065–1089.
628
P. Rosenberg / Mitochondrion 4 (2004) 621–628
Melov, S., Coskun, P.E., Wallace, D.C., 1999. Mouse models of mitochondrial disease, oxidative stress, and senescence. Mutat. Res. 434, 233–242. Milner, D.J., Mavroidis, M., Weisleder, N., Capetanaki, Y., 2000. Desmin cytoskeleton linked to muscle mitochondrial distribution and respiratory function. J. Cell Biol. 150, 1283–1298. Moran, O., Sandri, G., Panfili, E., Stuhmer, W., Sorgato, M.C., 1990. Electrophysiological characterization of contact sites in brain mitochondria. J. Biol. Chem. 265, 908–913. Murdock, D.G., Boone, B.E., Esposito, L.A., Wallace, D.C., 1999. Up-regulation of nuclear and mitochondrial genes in the skeletal muscle of mice lacking the heart/muscle isoform of the adenine nucleotide translocator. J. Biol. Chem. 274, 14429–14433. Naya, F.J., Wu, C., Richardson, J.A., Overbeek, P., Olson, E.N., 1999. Transcriptional activity of MEF2 during mouse embryogenesis monitored with a MEF2-dependent transgene. Development 126, 2045–2052. Naya, F.J., Black, B.L., Wu, H., Bassel-Duby, R., Richardson, J.A., Hill, J.A., Olson, E.N., 2002. Mitochondrial deficiency and cardiac sudden death in mice lacking the MEF2A transcription factor. Nat. Med. 8, 1303–1309. Ning, X.H., Zhang, J., Liu, J., Ye, Y., Chen, S.H., From, A.H., Bache, R.J., Portman, M.A., 2000. Signaling and expression for mitochondrial membrane proteins during left ventricular remodeling and contractile failure after myocardial infarction. J. Am. Coll. Cardiol. 36, 282–287. Passier, R., Zeng, H., Frey, N., Naya, F.J., Nicol, R.L., McKinsey, T.A., Overbeek, P., Richardson, J.A., Grant, S.R., Olson, E.N., 2000. CaM kinase signaling induces cardiac hypertrophy and activates the MEF2 transcription factor in vivo. J. Clin. Invest. 105, 1395–1406. Portman, M.A., 2000. Adenine nucleotide translocator in heart. Mol. Genet. Metab. 71, 445–450. Pu, W.T., Ma, Q., Izumo, S., 2003. NFAT transcription factors are critical survival factors that inhibit cardiomyocyte apoptosis during phenylephrine stimulation in vitro. Circ. Res. 92, 725–731.
Sayen, M.R., Gustafsson, A.B., Sussman, M.A., Molkentin, J.D., Gottlieb, R.A., 2003. Calcineurin transgenic mice have mitochondrial dysfunction and elevated superoxide production. Am. J. Physiol. Cell Physiol. 284, C562–C570. Shoffner, J.M., Wallace, D.C., 1992. Heart disease and mitochondrial DNA mutations. Heart Dis. Stroke 1, 235–241. Thomas, A.P., Bird, G.S., Hajnoczky, G., Robb-Gaspers, L.D., Putney Jr., J.W., 1996. Spatial and temporal aspects of cellular calcium signaling. Faseb. J. 10, 1505–1517. Wallace, D.C., 2001. A mitochondrial paradigm for degenerative diseases and ageing. Novartis Found Symp., 235, 247–263; discussion 263–246. Wang, H.G., Pathan, N., Ethell, I.M., Krajewski, S., Yamaguchi, Y., Shibasaki, F., McKeon, F., Bobo, T., Franke, T.F., Reed, J.C., 1999. Ca2C-induced apoptosis through calcineurin dephosphorylation of BAD. Science 284, 339–343. Weiss, J.N., Korge, P., Honda, H.M., Ping, P., 2003. Role of the mitochondrial permeability transition in myocardial disease. Circ. Res. 93, 292–301. Williams, R.S., Rosenberg, P., 2002. Calcium-dependent gene regulation in myocyte hypertrophy and remodeling. Cold Spring Harb. Symp. Quant. Biol. 67, 339–344. Wu, Z., Puigserver, P., Andersson, U., Zhang, C., Adelmant, G., Mootha, V., Troy, A., Cinti, S., Lowell, B., Scarpulla, R.C., Spiegelman, B.M., 1999. Mechanisms controlling mitochondrial biogenesis and respiration through the thermogenic coactivator PGC-1. Cell 98, 115–124. Wu, H., Kanatous, S.B., Thurmond, F.A., Gallardo, T., Isotani, E., Bassel-Duby, R., Williams, R.S., 2002. Regulation of mitochondrial biogenesis in skeletal muscle by CaMK. Science 296, 349–352. Yaffe, M.P., 1999a. Dynamic mitochondria. Nat. Cell Biol. 1, E149–E150. Yaffe, M.P., 1999b. The machinery of mitochondrial inheritance and behavior. Science 283, 1493–1497. Ziegelhoffer-Mihalovicova, B., Kolar, F., Jacob, W., Tribulova, N., Uhrik, B., Ziegelhoffer, A., 1998. Modulation of mitochondrial contact sites formation in immature rat heart. Gen. Physiol Biophys. 17, 385–390.
Mitochondrial dysfunction and heart disease Paul Rosenberg Department of Medicine, Duke University, Durham, NC 27710, USA Received 1 December 2003; accepted 12 July 2004
Abstract Several inherited and acquired disorders of mitochondria lead to defects in cardiac function as reflected in exercise intolerance, arrhythmias and heart failure. Manifestations of mitochondrial dysfunction is reflected in the abnormal mitochondrial proliferation, structure and ultimately as cytochrome C-induced apoptosis. How these defects are associated with disordered cytosolic events including SR calcium release and transcription has suggested a cross talk of mitochondria and cytosolic events that drive cardiomyocytes dysfunction. q 2004 Elsevier B.V. and Mitochondria Research Society. All rights reserved. Keywords: Mitochondria; Heart disease; Mutation; SR calcium; Calcineurin; PGC-1
Heart disease including myocardial infarction, arrhythmia and cardiomyopathy is the leading cause of morbidity and mortality in this country. Therapies designed to decrease mortality from heart disease have been very effective but have increased the number of patients living longer lives with debilitating disease. Therefore more recent research has focused on the energy demands of the myocardium, seeking to optimize heart function despite continued pathology. The energy expenditures required of the cardiomyocyte include contractile force production (75%), maintenance of internal stores of calcium (15%), and sarcolemmal ionic balance (10%), and the ATP needed for these functions is produced predominately in the mitochondria via oxidative phosphorylation (Katz, 1992). Recent interest focusing on mitochondrial dysfunction reflects the growing E-mail address: [email protected]
consensus that errors in metabolism often accompany and modify cardiomyocyte dysfunction (Shoffner and Wallace, 1992). Indeed, primary inherited mitochondrial diseases display a full spectrum of cardiac disorders including hypertrophic and dilated cardiomyopathies (Melov et al., 1999). The proliferation of mitochondria, which occupy 30–50% of the cell volume of the normal cardiomyocyte, is dysregulated in certain disease states such as chronic ischemia and cardiomyopathy (Arbustini et al., 1998). Mitochondrial dysfunction, reflected in the structure, function and number of mitochondria within the cardiomyocyte, leads to diminished energy production, loss of myocyte contractility, altered electrical properties and eventual cardiomyocyte cell death (Capetanaki, 2002). In addition emerging evidence suggests that mitochondria function within a ternary complex of organelles, including the sarcoplasmic reticulum and the myofibrillary complex, to coordinate
1567-7249/$ - see front matter q 2004 Elsevier B.V. and Mitochondria Research Society. All rights reserved. doi:10.1016/j.mito.2004.07.016
622
P. Rosenberg / Mitochondrion 4 (2004) 621–628
Fig. 1. Interaction of mitochondria with other organelles. Cytosolic localization by desmin position mitochondria in energy requiring areas. Nuclear factors (PGC-1, MEF2, NFAT) mediate the mitochondrial biogenesis. Calcium release channels coordinate oxidative capacity by influencing matrix dehydrogenases activity. Calcium dependent signaling including CamK and calcineurin function as effectors of mitochondrial function.
contractile activity (Hajnoczky et al., 2002). In this review, we will focus on the plasticity of mitochondrial phenotype, the interaction of mitochondria with other organelles (Fig. 1), and its role in the failing cardiomyocyte.
1. Mitochondrial structure Mitochondria are large organelles, approximately one micron in size, found in the cytosol of all cells. Mitochondrial metabolism is compartmentalized by a two-membrane system: the outer mitochondrial membrane (OMM) separates the cytosol from the intermembrane compartment. The inner mitochondrial membrane (IMM) separates the intermembrane compartment from the central matrix. The integrity of these membrane structures is essential for proper mitochondrial function. In addition, specialized domains within the membrane system provide interaction with the rest of the cell in order to coordinate its energy demands. The OMM is responsible for interfacing with the cytosol and its interactions with cytoskeletal elements are important for movement of mitochondria within a cell (Capetanaki, 2002). This mobility is essential for the distribution of mitochondria during cell division, differentiation, and possibly for positioning of mitochondria to cellular regions under intense demands for
energy. Mitochondria slide along actin filaments using kinesin and dynein dependent ATP hydrolysis. More recent studies in the heart have demonstrated the movement of mitochondria along intermediate filaments (Milner et al., 2000). In muscle mitochondria localize to either the intermyofibrillary or subsarcolemmal regions and these populations differ with respect to oxidative capacity. Mitochondria found among the myofilaments involved in muscle contraction provide ATP for the actinomyosin complex, whereas mitochondria found underneath sarcolemma function to maintain the membrane electrical potential (Williams and Rosenberg, 2002). The outer membrane is also involved in transport of proteins from the cytosol to the interior of mitochondria. Small molecules less than 15 kD are freely diffusible to the intermembranous space, however, larger molecules are actively transported into the intermembranous space and matrix at specialized regions of the outer membrane (Yaffe, 1999b). Fusion of the inner and outer mitochondria membranes establish contact sites (CS) that are involved in protein import through the transport outer membrane (TOM) and transport inner membrane (TIM) complexes. Preproteins with N-terminal mitochondrial targeting sequences are transported through the multifunctional receptor Tom22 and the pore forming Tom40 and then the TIM complex to reach their destination. Proteins destined for the matrix space are transported across both OM and IM via the TOM/TIM complex located at CS (Endo et al., 2003). Several studies indicate that CS are dynamic and correlate with oxygen utilization of the embryonic and ischemic heart (Bakker et al., 1994, 1995; Ziegelhoffer-Mihalovicova et al., 1998). In addition, under pathologic conditions of hypertrophy and cardiomyopathy, CS have been found to increase within cardiomyocytes (Bakker et al., 1994). Although the detailed mechanisms of signaling energy utilization and CS formation in the heart are not yet elucidated, cytosolic Ca2C transients have been implicated to provide crosstalk between cytosol and mitochondria (Moran et al., 1990; Bakker et al., 1994). CS are also home to the multiprotein complex called the permeability transition pore (mtPTP) which is an early regulator of apoptosis (Crompton, 2003). mtPTP consists of several proteins including
P. Rosenberg / Mitochondrion 4 (2004) 621–628
the voltage dependent anion channel (VDAC), an integral membrane protein in the OM, the adenine nucleotide translocator (ANT), and cyclophilin D, an immunophilin located in the central matrix (Lesnefsky et al., 2001a). Activation of the mtPTP leads to depolarization and release of cytochrome C into the cytosol to activate caspase dependent apoptosis. The mechanisms in place to prevent IMM depolarization and therefore apoptosis include the mitochondrial ATP-sensitive potassium channels (Weiss et al., 2003). MtATP-K channels offer cytoprotection, as channel agonists mimic ischemic preconditioning in which repeated short lived ischemic events initiate an adaptative response to protect the cell from further ischemia (Akao et al., 2003a,b). VDAC is a large conductance channel and in the open configuration is freely permeable to ions including calcium. It has recently been suggested that the level of VDAC expression may influence mitochondrial calcium signaling (Weiss et al., 2003). Although these gain of function studies indicate that VDAC contributes directly to the mitochondrial calcium content, other possible mechanisms of regulation would include its localization and therefore apposition to calcium release sites of the SR/ER. Prolonged opening of the mtPTP allowing calcium influx through VDAC can induce swelling of the central matrix leading to irreversible damage of the mitochondria and cytochrome C release (Hajnoczky et al., 2002). This prolonged opening may occur during ischemia/reperfusion injury when mtPTP is in a highly permeable state in response to reactive oxygen species (ROS), long chain fatty acids and calcium. Cyclosporin is a potent blocker of the mtPTP and may therefore preserve mitochondrial structure and function during ischemia/reperfusion. However its mechanism of action appears to be independent of its inhibition of calcineurin, a calcium regulated serine threonine phosphatase and may be mediated through cyclophilin D, another component of the mtPTP. The intermembrane space has an ionic composition similar to the cytosol (Lesnefsky et al., 2001b). Cytochrome C is located in the intermembranous space and functions in healthy mitochondria as a mobile electron carrier for the respiratory centers located in inner mitochondrial membrane. Release of cytochrome C into the cytosol initiates the caspase
623
dependent activation of apoptosis, and therefore proper maintenance of the CS and integrity of the two-membrane system are essential for mitochondrial function and cell survival. Recent work has demonstrated that cytochrome C physically associates with the calcium release channel inositol trisphosphate receptor (IP3R) and it is suggested that calcium is released from the IP3R pool for the calcium dependent signaling involved in cell death. In addition, previous reports have implicated the IP3R as a regulator in lymphocyte apoptosis and as a caspase target molecule (Boehning et al., 2003). Future work will determine the significance of calcium regulated apoptosis in the cardiomyocyte. The inner mitochondria membranes are highly folded structures that provide a barrier for the inner matrix from molecules found in the intermembranous space. The inner mitochondrial membranes fold into the matrix to form cristae. Here integral membrane proteins are found such as the five complexes of the respiratory chain including the electron transport chains (complexes I-IV), ATP synthase (complex V), and the ANT. Electron transport through the respiratory chain generates the electrochemical gradient necessary to produce ATP. Key components of the electrochemical gradient include the membrane potential of IMM (DJ) and the proton gradient (DpH) (Weiss et al., 2003). The IMM remains impermeant to calcium and ADP in order to maintain the large DJ and the integrity of the IM is essential to maintain the conditions required for aerobic metabolism including ATP/ADP exchange by the ANT (Portman, 2000). Striated muscles express a specific isoform of the ANT, which is down regulated in animal models of myocardial remodeling. In addition, mice lacking ANT-1 display respiratory chain abnormalities (complex III), exercise intolerance, and cardiac hypertrophy (Murdock et al., 1999; Ning et al., 2000). The inner matrix contains the machinery used in macromolecular synthesis which is required for mitochondria to replicate and function properly. Regulation of mitochondrial proliferation and genomic mutation rates are increasingly recognized as markers of mitochondrial diseases (Arbustini et al., 1998). Strategies designed to maintain the integrity of the two membrane system may ameliorate mitochondrial dysfunction.
624
P. Rosenberg / Mitochondrion 4 (2004) 621–628
2. Mitochondrial proliferation and morphology Normal mitochondria are quite heterogeneous, with size and morphology varying according to the specific metabolic needs of a cell (Yaffe, 1999a). Increased proliferation is another mechanism used by cells to adapt to changing metabolic needs. Temperature, neurohormones (adrenergic and thyroid hormones) and dietary conditions represent established environmental cues that initiate mitochondrial biogenesis in many tissues (Wallace, 2001). The regulatory circuit governing control of mitochondria biogenesis includes the nuclear encoded transcription factors (NRF1-2) which coordinate the transcriptional control of nuclear encoded genes such as the respiratory control centers of the IMM (Chau et al., 1992). The NRFs also regulate the expression of the mitochondrial transcription factor A (mtTFA) which stimulates mitochondrial DNA replication and orders mitochondrial biogenesis (Larsson et al., 1998). More recent work has focused on the PPARg transcriptional coactivator-1 pathway in regulating mitochondrial biogenesis in striated muscle. PGC-1 is a transcriptional coactivator originally identified in thermogenic brown adipose tissue (Wu et al., 1999). The developmental expression of PGC-1 in the mammalian heart parallels the shift from glycolytic to oxidative metabolism (Lehman et al., 2000). In addition, conditions known to alter adult cardiac metabolism such as starvation, pressure overload, and exercise influences the level of PGC-1 in the heart (Irrcher et al., 2003). Finally, forced overexpression of PGC-1 restricted to the myocardium resulted in increased mitochondrial biogenesis as well as LCFA oxidation. Hearts from these transgenic mice display variable degrees of cardiac dysfunction from cardiac hypertrophy to a dilated cardiomyopathy (Lehman et al., 2000; Irrcher et al., 2003). A recent experiment to promote gain-of-function of CaMK revealed a previously unexpected link to the gene encoding PGC-1 (Wu et al., 2002). Many, if not all, nuclear genes encoding mitochondrial proteins are induced by the action of PGC-1, which appears to function as a master regulator of this large class of proteins. Forced expression of a constitutively active form of CaMKIV in both heart and skeletal muscle produced a variety of phenotypes, including hypertrophy, a shift in myosin isotype from fast to slower
forms, and a prominent increase in the fractional volume of mitochondria within the myocytes. These effects closely resemble the morphological and biochemical remodeling responses evoked by endurance exercise, and muscle isolated from CaMKIV transgenic mice exhibited resistance to fatigue during repeated stimulation, a prominent consequence of endurance training. Increased mitochondrial biogenesis in these models suggest that a tight coupling of PGC-1 and metabolic demand is required to achieve optimal metabolic homeostasis and may involve calcium dependent signaling pathways (Wu et al., 2002). Mitochondrial deficiency and dysfunction was recently noted to occur in the MEF2A null mice. These mice exhibited marked chamber dilation, particularly the right ventricle, and the animals died suddenly from conduction disorders. Ultrastructural analysis of adult hearts revealed disordered sarcomeric and intermyofibrillary mitochondrial content (Naya et al., 2002). In addition, MEF2a null mice demonstrated diminished mitochondrial biogenesis (Czubryt et al., 2003). Since CamK signaling influences both MEF2 function as well as mitochondrial biogenesis, it will be interesting to evaluate CamK signaling in these mice (Passier et al., 2000). The mitochondrial disorganization and sarcomere assembly of the MEF2A null mice is reminiscent of the desmin null mouse (Milner et al., 2000). In addition, experiments with transgenic MEF2 indicator mice demonstrate that the promoter of desmin is enriched in MEF2 binding sites (Naya et al., 1999). In these models of cardiac and mitochondrial dysfunction, it is unclear whether the mitochondrial defect reflects altered mitochondrial biogenesis as a primary event or as a secondary event involving the loss of desmin and its interaction with the mitochondrial OMM. Increasingly, receptors coupled to the G-proteins of the Gq class have been implicated in cardiac hypertrophy and cardiomyocyte apoptosis. Recently serotonin and its signaling cascade have been shown to influence cardiac hypertrophy and mitochondrial function. Transgenic overexpression of 5-HT2b receptor in the hearts of mice led to cardiac hypertrophy, induction of the fetal heart gene program, and mitochondrial proliferation. In contrast, mice lacking a functional 5-HT2b receptor died
P. Rosenberg / Mitochondrion 4 (2004) 621–628
prematurely from a dilated cardiomyopathy with associated abnormalities in mitochondrial ultrastructure and dysfunction of oxidative phosphorylation. In addition, the authors provide evidence that 5-HT2b signaling in these mouse models directly influences the expression of ANT-1 and Bcl-2/BAX. The cellular balance of these factors can lead to maladaptive responses including cardiac hypertrophy and apoptosis. Cardiomyocyte apoptosis has been offered as a mechanism to explain the pathologic consequences of ischemic/reperfusion injury. Myocardial tissue subjected to transient interruption of blood flow should recover full functional capacity (Crompton, 2000; Weiss et al., 2003). However, it has been long recognized that the myocyte dysfunction results not from interrupted flow but from the reperfusion as well. In fact, recent work has established the importance of mitochondria and the mtPTP in the reperfusion injury. The toxic events may include combination of cell necrosis and apoptosis and matrix calcium content seems to be an important mediator of this balance (Weiss et al., 2003). In addition to factors intrinsic to mitochondria, ischemic/reperfusion injury depends on cytosolic signaling pathways that target key mitochondria proteins including the ANT and Bcl-2. The calcineurin signaling pathway has been shown to localize and dephosphorylate bcl-2 and Bax, important apoptotic factors (Wang et al., 1999). More recently, elegant studies of ischemia/reperfusion provide direct evidence for calcineurin and NFAT transactivation in cellular apoptosis. Overexpression of an activated form of calcineurin prevented myocyte loss following ischemic injury (De Windt et al., 2000). Moreover, mice lacking cardiac calcineurin A were more susceptible to apoptosis resulting from ischemic injury via coronary artery ligation (Bueno et al., 2003). Although calcineurin offers cytoprotection to injured myocytes, mitochondria from mice carrying the activated calcineurin have defects in the respiratory chain including complexes I and IV and were associated with high levels of superoxide production (Sayen et al., 2003). Taken together, these results indicate that calcineurin provides cytoprotection to cardiomyocyte following ischemic injury; however the mechanism by which calcineurin offers protection remains to be defined. However support for the NFAT
625
transcription factors as the downstream effectors of calcineurin is growing. Blockade of NFAT activation through use of the VIVIT peptide in cardiomyocytes can ameliorate apoptosis in cultured cardiomyocyte models (Pu et al., 2003). Finally, NFAT3/4 null mice demonstrate the essential role of NFAT transactivation in heart formation and mitochondrial function. NFAT3/4-/-mice die during at E10.5 from cardiac failure. Ultrastructural analysis of cardiac mitochondria demonstrated abnormal cristae while biochemical analysis revealed deficiencies of complexes II and IV in the respiratory chain (Bushdid et al., 2003). Taken together these experiments demonstrate a role for signal transduction pathways, G-protein coupled receptors, and transcription factors (PGC-1, NFT, MEF-2) in coordinating the replication and biogenesis of mitochondria needed to match expanding cellular energy demands in cardiac disease states including ischemia/reperfusion injury, cardiac hypertrophy and cardiomyopathy. Indeed, endomyocardial biopsy specimens from patients with dilated cardiomyopathy displayed a variety of morphologic phenotypes including mitochondrial proliferation, variable matrix density, abnormal cristae number and morphology, and inclusion bodies (Arbustini et al., 1998). The mechanism regulating mitochondrial proliferation, and the connection between calcium activated signal transduction and mitochondrial function has been an area of intense interest. Understanding how changes in cytosolic calcium influence mitochondrial behavior will likely yield important insights into the mechanisms of mitochondrial diseases.
3. Calcium and mitochondria More than any other tissue, cardiomyocytes utilize changes in intracellular calcium to affect cellular processes ranging from muscle contraction to gene transcription. Several lines of evidence have emerged to suggest that regulated calcium release directly influences mitochondrial function (Csordas et al., 2001). While some have focused on the nature of the relationship between the ER/SR and mitochondria in myocytes, others have pursued the dehydrogenases which are stimulated by calcium and include pyruvate dehydrogenase (PDH), mitochondrial NADP-isocitrate dehydrogenase (NADP-ICD), and oxoglutarate
626
P. Rosenberg / Mitochondrion 4 (2004) 621–628
dehydrogenase (Denton and McCormack, 1990). Recent work with a rodent model of cardiac hypertrophy has demonstrated that NADP-ICD is inactivated as an early step prior to cardiomyocyte dysfunction (Benderdour et al., 2003). This research will lead to an understanding of how reduced cardiac energy and contractile reserves interact in the cardiomyocyte subjected to pathologic stimuli. The uptake of cytosolic calcium into the mitochondrial matrix involves two transport mechanisms, OM calcium uptake by the VDAC and the IMM calcium uniporter (Hajnoczky et al., 2002). These transporters deliver large pulses of calcium to the inner matrix to regulate oxidative phosphorylation (Thomas et al., 1996). The calcium uniporter was characterized from isolated mitochondria and was believed to require high levels of cellular calcium—far beyond those observed with muscle contraction. Thus, for some time, mitochondria were believed to function as calcium buffer under conditions of cytosolic calcium overload (Denton and McCormack, 1990). More recently, local control has been offered to explain this paradox. Specialized regions of ER/SR in close contact with mitochondria transmit large calcium signals to mitochondria increasing calcium content in the central matrix. These microdomains do not require large evoked calcium responses that influence global cytosolic calcium. Instead, the spatial relationship of mitochondria and calcium release channel that is stable over time provide local control (Hajnoczky et al., 2000b). Interestingly, signal transmission from calcium release channels to mitochondria is optimized by oscillatory rather than tonic calcium signals (Hajnoczky et al., 1995). Thus, coupling of changes in cellular calcium with changes in ATP production may represent an important adaptation linking changes in contractility with oxidative metabolism. How local control is affected by processes such as ischemia and the failing cardiomyocyte may provide an essential link of disordered calcium homeostasis and cardiac energy reserves (Hajnoczky et al., 2000a; Brini, 2003). While most research has focused on the delivery of calcium form the cytosol to the mitochondria, a recent study demonstrates an intrinsic defect in mitochondrial calcium content from cells containing dysfunctional mitochondria (Brini et al., 1999). Here calcium transients were characterized from cells repopulated with mutant mitochondria from two mitochondrial
disease states. Cells carrying mitochodria from patients with myoclonic epilepsy (MERRF) displayed blunted mitochondrial calcium uptake in response IP3R activation. However, mitochondrial calcium uptake from patients with neurogenic muscle weakness, ataxia, and retinitis pigmentosa (NARP) paralleled those from control cells. The MERRF mutation involves a tRNA with global effects on macromolecular synthesis, whereas the NARP mutation leads to dysfunctional ATPase. Therefore, global dysfunction of mitochondria leads to an abnormal calcium response while a mutation of a specific target spares the mitochodrial machinery. Whether the dysfunctional calcium response involves the calcium uniporter or even the recently identified ryanodine receptor remains to be determined. Nevertheless, from this genetic complementation experiment the relevant molecules involved with mitochondria calcium signaling may be identified. 4. Conclusion Heart disease remains a major medical problem in this country, and emerging therapeutics designed to increase survival promises to increase number of patients suffering from chronic ischemic disease, heart failure and arrhythmias. Given that the manifestations of primary mitochondrial diseases share similar pathology with acquired heart disease, it is logical to direct research efforts to understand how mitochondrial dysfunction modulates the many known cellular responses in the cardiomyocyte. Growing research supports the view that mitochondria interface with other cellular organelles, most notably the ER/SR calcium stores and the myofilament. Mitochondria proliferation, structure, and mtDNA mutation rates are influenced by calcium dependent signaling pathways and are part of the adaptation to ischemia and reactive oxygen species. How cellular dysfunction is reflected among these organelles may provide an important understanding for future therapeutics. References Akao, M., O’Rourke, B., Kusuoka, H., Teshima, Y., Jones, S.P., Marban, E., 2003a. Differential actions of cardioprotective agents on the mitochondrial death pathway. Circ. Res. 92, 195–202.
P. Rosenberg / Mitochondrion 4 (2004) 621–628 Akao, M., O’Rourke, B., Teshima, Y., Seharaseyon, J., Marban, E., 2003b. Mechanistically distinct steps in the mitochondrial death pathway triggered by oxidative stress in cardiac myocytes. Circ. Res. 92, 186–194. Arbustini, E., Diegoli, M., Fasani, R., Grasso, M., Morbini, P., Banchieri, N., Bellini, O., Dal Bello, B., Pilotto, A., Magrini, G., Campana, C., Fortina, P., Gavazzi, A., Narula, J., Vigano, M., 1998. Mitochondrial DNA mutations and mitochondrial abnormalities in dilated cardiomyopathy. Am. J. Pathol. 153, 1501–1510. Bakker, A., Bernaert, I., De Bie, M., Ravingerova, T., Ziegelhoffer, A., Van Belle, H., Jacob, W., 1994. The effect of calcium on mitochondrial contact sites: a study on isolated rat hearts. Biochim. Biophys. Acta 1224, 583–588. Bakker, A., Goossens, F., De Bie, M., Bernaert, I., Van Belle, H., Jacob, W., 1995. The effect of ischemia and reperfusion on mitochondrial contact sites in isolated rat hearts. Histol. Histopathol. 10, 405–416. Benderdour, M., Charron, G., DeBlois, D., Comte, B., Des Rosiers, C., 2003. Cardiac mitochondrial NADPC-isocitrate dehydrogenase is inactivated through 4-hydroxynonenal adduct formation: an event that precedes hypertrophy development. J. Biol. Chem. 278, 45154–45159. Boehning, D., Patterson, R.L., Sedaghat, L., Glebova, N.O., Kurosaki, T., Snyder, S.H., 2003. Cytochrome c binds to inositol (1,4,5) trisphosphate receptors, amplifying calciumdependent apoptosis. Nat. Cell Biol. 5 (12), 1051–1061. Brini, M., 2003. Ca(2C) signalling in mitochondria: mechanism and role in physiology and pathology. Cell Calcium 34, 399–405. Brini, M., Pinton, P., King, M.P., Davidson, M., Schon, E.A., Rizzuto, R., 1999. A calcium signaling defect in the pathogenesis of a mitochondrial DNA inherited oxidative phosphorylation deficiency. Nat. Med. 5, 951–954. Bueno, O.F., Lips, D.J., Kaiser, R.A., Wilkins, B.J., Dai, Y.S., Glascock, B.J., Klevitsky, R., Hewett, T.E., Kimball, T.R., Aronow, B.J., Doevendans, P.A., Molkentin, J.D., 2003. Calcineurin A{beta} gene targeting predisposes the myocardium to acute ischemia-induced apoptosis and dysfunction. Circ. Res. 94, 91–99. Bushdid, P.B., Osinska, H., Waclaw, R.R., Molkentin, J.D., Yutzey, K.E., 2003. NFATc3 and NFATc4 are required for cardiac development and mitochondrial function. Circ. Res. 92, 1305–1313. Capetanaki, Y., 2002. Desmin cytoskeleton: a potential regulator of muscle mitochondrial behavior and function. Trends Cardiovasc. Med. 12, 339–348. Chau, C.M., Evans, M.J., Scarpulla, R.C., 1992. Nuclear respiratory factor 1 activation sites in genes encoding the gamma-subunit of ATP synthase, eukaryotic initiation factor 2 alpha, and tyrosine aminotransferase. Specific interaction of purified NRF-1 with multiple target genes. J. Biol. Chem. 267, 6999–7006. Crompton, M., 2000. Mitochondrial intermembrane junctional complexes and their role in cell death. J. Physiol. 529 (Pt 1), 11–21. Crompton, M., 2003. On the involvement of mitochondrial intermembrane junctional complexes in apoptosis. Curr. Med. Chem. 10, 1473–1484.
627
Csordas, G., Thomas, A.P., Hajnoczky, G., 2001. Calcium signal transmission between ryanodine receptors and mitochondria in cardiac muscle. Trends Cardiovasc Med. 11, 269–275. Czubryt, M.P., McAnally, J., Fishman, G.I., Olson, E.N., 2003. Regulation of peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC-1 alpha) and mitochondrial function by MEF2 and HDAC5. Proc. Natl Acad. Sci. USA 100, 1711–1716. Denton, R.M., McCormack, J.G., 1990. Ca2C as a second messenger within mitochondria of the heart and other tissues. Annu. Rev. Physiol. 52, 451–466. De Windt, L.J., Lim, H.W., Taigen, T., Wencker, D., Condorelli, G., Dorn 2nd., G.W., Kitsis, R.N., Molkentin, J.D., 2000. Calcineurin-mediated hypertrophy protects cardiomyocytes from apoptosis in vitro and in vivo: an apoptosis-independent model of dilated heart failure. Circ. Res. 86, 255–263. Endo, T., Yamamoto, H., Esaki, M., 2003. Functional cooperation and separation of translocators in protein import into mitochondria, the double-membrane bounded organelles. J. Cell Sci. 116, 3259–3267. Hajnoczky, G., Robb-Gaspers, L.D., Seitz, M.B., Thomas, A.P., 1995. Decoding of cytosolic calcium oscillations in the mitochondria. Cell 82, 415–424. Hajnoczky, G., Csordas, G., Madesh, M., Pacher, P., 2000a. Control of apoptosis by IP(3) and ryanodine receptor driven calcium signals. Cell Calcium 28, 349–363. Hajnoczky, G., Csordas, G., Madesh, M., Pacher, P., 2000b. The machinery of local Ca2C signalling between sarco-endoplasmic reticulum and mitochondria. J. Physiol. 529 (Pt 1), 69–81. Hajnoczky, G., Csordas, G., Yi, M., 2002. Old players in a new role: mitochondria-associated membranes, VDAC, and ryanodine receptors as contributors to calcium signal propagation from endoplasmic reticulum to the mitochondria. Cell Calcium 32, 363–377. Irrcher, I., Adhihetty, P.J., Sheehan, T., Joseph, A.M., Hood, D.A., 2003. PPARgamma coactivator-1alpha expression during thyroid hormone- and contractile activity-induced mitochondrial adaptations. Am. J. Physiol. Cell Physiol. 284, C1669–C1677. Katz, A., 1992. Physiology of the Heart, Farmington, CT 1992. Larsson, N.G., Wang, J., Wilhelmsson, H., Oldfors, A., Rustin, P., Lewandoski, M., Barsh, G.S., Clayton, D.A., 1998. Mitochondrial transcription factor A is necessary for mtDNA maintenance and embryogenesis in mice. Nat. Genet. 18, 231–236. Lehman, J.J., Barger, P.M., Kovacs, A., Saffitz, J.E., Medeiros, D.M., Kelly, D.P., 2000. Peroxisome proliferatoractivated receptor gamma coactivator-1 promotes cardiac mitochondrial biogenesis. J. Clin. Invest. 106, 847–856. Lesnefsky, E.J., Gudz, T.I., Moghaddas, S., Migita, C.T., IkedaSaito, M., Turkaly, P.J., Hoppel, C.L., 2001a. Aging decreases electron transport complex III activity in heart interfibrillar mitochondria by alteration of the cytochrome c binding site. J. Mol. Cell Cardiol. 33, 37–47. Lesnefsky, E.J., Moghaddas, S., Tandler, B., Kerner, J., Hoppel, C.L., 2001b. Mitochondrial dysfunction in cardiac disease: ischemia–reperfusion, aging, and heart failure. J. Mol. Cell Cardiol. 33, 1065–1089.
628
P. Rosenberg / Mitochondrion 4 (2004) 621–628
Melov, S., Coskun, P.E., Wallace, D.C., 1999. Mouse models of mitochondrial disease, oxidative stress, and senescence. Mutat. Res. 434, 233–242. Milner, D.J., Mavroidis, M., Weisleder, N., Capetanaki, Y., 2000. Desmin cytoskeleton linked to muscle mitochondrial distribution and respiratory function. J. Cell Biol. 150, 1283–1298. Moran, O., Sandri, G., Panfili, E., Stuhmer, W., Sorgato, M.C., 1990. Electrophysiological characterization of contact sites in brain mitochondria. J. Biol. Chem. 265, 908–913. Murdock, D.G., Boone, B.E., Esposito, L.A., Wallace, D.C., 1999. Up-regulation of nuclear and mitochondrial genes in the skeletal muscle of mice lacking the heart/muscle isoform of the adenine nucleotide translocator. J. Biol. Chem. 274, 14429–14433. Naya, F.J., Wu, C., Richardson, J.A., Overbeek, P., Olson, E.N., 1999. Transcriptional activity of MEF2 during mouse embryogenesis monitored with a MEF2-dependent transgene. Development 126, 2045–2052. Naya, F.J., Black, B.L., Wu, H., Bassel-Duby, R., Richardson, J.A., Hill, J.A., Olson, E.N., 2002. Mitochondrial deficiency and cardiac sudden death in mice lacking the MEF2A transcription factor. Nat. Med. 8, 1303–1309. Ning, X.H., Zhang, J., Liu, J., Ye, Y., Chen, S.H., From, A.H., Bache, R.J., Portman, M.A., 2000. Signaling and expression for mitochondrial membrane proteins during left ventricular remodeling and contractile failure after myocardial infarction. J. Am. Coll. Cardiol. 36, 282–287. Passier, R., Zeng, H., Frey, N., Naya, F.J., Nicol, R.L., McKinsey, T.A., Overbeek, P., Richardson, J.A., Grant, S.R., Olson, E.N., 2000. CaM kinase signaling induces cardiac hypertrophy and activates the MEF2 transcription factor in vivo. J. Clin. Invest. 105, 1395–1406. Portman, M.A., 2000. Adenine nucleotide translocator in heart. Mol. Genet. Metab. 71, 445–450. Pu, W.T., Ma, Q., Izumo, S., 2003. NFAT transcription factors are critical survival factors that inhibit cardiomyocyte apoptosis during phenylephrine stimulation in vitro. Circ. Res. 92, 725–731.
Sayen, M.R., Gustafsson, A.B., Sussman, M.A., Molkentin, J.D., Gottlieb, R.A., 2003. Calcineurin transgenic mice have mitochondrial dysfunction and elevated superoxide production. Am. J. Physiol. Cell Physiol. 284, C562–C570. Shoffner, J.M., Wallace, D.C., 1992. Heart disease and mitochondrial DNA mutations. Heart Dis. Stroke 1, 235–241. Thomas, A.P., Bird, G.S., Hajnoczky, G., Robb-Gaspers, L.D., Putney Jr., J.W., 1996. Spatial and temporal aspects of cellular calcium signaling. Faseb. J. 10, 1505–1517. Wallace, D.C., 2001. A mitochondrial paradigm for degenerative diseases and ageing. Novartis Found Symp., 235, 247–263; discussion 263–246. Wang, H.G., Pathan, N., Ethell, I.M., Krajewski, S., Yamaguchi, Y., Shibasaki, F., McKeon, F., Bobo, T., Franke, T.F., Reed, J.C., 1999. Ca2C-induced apoptosis through calcineurin dephosphorylation of BAD. Science 284, 339–343. Weiss, J.N., Korge, P., Honda, H.M., Ping, P., 2003. Role of the mitochondrial permeability transition in myocardial disease. Circ. Res. 93, 292–301. Williams, R.S., Rosenberg, P., 2002. Calcium-dependent gene regulation in myocyte hypertrophy and remodeling. Cold Spring Harb. Symp. Quant. Biol. 67, 339–344. Wu, Z., Puigserver, P., Andersson, U., Zhang, C., Adelmant, G., Mootha, V., Troy, A., Cinti, S., Lowell, B., Scarpulla, R.C., Spiegelman, B.M., 1999. Mechanisms controlling mitochondrial biogenesis and respiration through the thermogenic coactivator PGC-1. Cell 98, 115–124. Wu, H., Kanatous, S.B., Thurmond, F.A., Gallardo, T., Isotani, E., Bassel-Duby, R., Williams, R.S., 2002. Regulation of mitochondrial biogenesis in skeletal muscle by CaMK. Science 296, 349–352. Yaffe, M.P., 1999a. Dynamic mitochondria. Nat. Cell Biol. 1, E149–E150. Yaffe, M.P., 1999b. The machinery of mitochondrial inheritance and behavior. Science 283, 1493–1497. Ziegelhoffer-Mihalovicova, B., Kolar, F., Jacob, W., Tribulova, N., Uhrik, B., Ziegelhoffer, A., 1998. Modulation of mitochondrial contact sites formation in immature rat heart. Gen. Physiol Biophys. 17, 385–390.