Apoptosis (2009) 14:536–548 DOI 10.1007/s10495-008-0302-x
CELL DEATH AND DISEASE
Role of apoptosis in cardiovascular disease ˚ sa B. Gustafsson Youngil Lee Æ A
Published online: 14 January 2009 Ó Springer Science+Business Media, LLC 2009
Abstract Apoptosis plays a key role in the pathogenesis in a variety of cardiovascular diseases due to loss of terminally differentiated cardiac myocytes. Cardiac myocytes undergoing apoptosis have been identified in tissue samples from patients suffering from myocardial infarction, diabetic cardiomyopathy, and end-stage congestive heart failure. Apoptosis is a highly regulated program of cell death and can be mediated by death receptors in the plasma membrane, as well as the mitochondria and the endoplasmic reticulum. The cell death program is activated in cardiac myocytes by various stressors including cytokines, increased oxidative stress and DNA damage. Many studies have demonstrated that inhibition of apoptosis is cardioprotective and can prevent the development of heart failure. This review provides a current overview of the evidence of apoptosis in cardiovascular diseases and discusses the molecular pathways involved in cardiac myocyte apoptosis. Keywords Apoptosis Heart failure Death receptors Mitochondria Bcl-2
Introduction Cardiovascular disease is the leading cause of morbidity and mortality in the developed world. A multitude of recent studies suggest that loss of terminally differentiated cardiac myocytes contributes to development of heart failure. There are three morphologically and biochemically distinct ˚ . B. Gustafsson (&) Y. Lee A BioScience Center, San Diego State University, 5500 Campanile Drive, San Diego, CA 92182-4650, USA e-mail:
[email protected]
123
forms of cell death that occur in the heart; necrosis, apoptosis, and possibly autophagy. Autophagy is a cellular process that degrades long lived proteins and dysfunctional organelles [1]. Autophagy is characterized by sequestration of cytoplasm in double-membrane vesicles called autophagosomes. Autophagosomes subsequently fuse with lysosomes, leading to degradation of their content [1]. This process is important for cellular homeostasis, and is a survival response upregulated in response to stress or starvation. However, excess autophagy can lead to cell death due to excessive digestion of organelles and essential proteins [2]. Necrosis is a passive form of cell death caused by ATP depletion and rapid disruption of cell membrane integrity resulting in spillage of intracellular contents into interstitial and extracellular space, which initiates inflammation and induces damage to neighboring cells [3, 4]. In contrast, apoptosis is an energy requiring form of programmed cell death whereby damaged cells are removed without provoking inflammation. Apoptosis is characterized by chromatin condensation, DNA fragmentation, plasma membrane blebbing (i.e., externalization of phosphatidylserine), and cell shrinkage due to reduction in cytoplasm and organelles [5–7]. Finally, membrane-bound apoptotic bodies containing cytosol and processed organelles are formed and then removed by macrophages via phagocytosis [8]. It is now evident that apoptosis plays a key role in the pathogenesis of a variety of cardiovascular diseases. Studies have reported that apoptosis occurs in myocardial tissue samples from patients suffering from myocardial infarction, dilated cardiomyopathy and end-stage heart failure [9–12] as well as in animal models of ischemia– reperfusion injury [13–15]. Apoptosis is activated in cardiac myocytes by multiple stressors that are commonly seen in cardiovascular disease such as cytokine production
Apoptosis (2009) 14:536–548
[16, 17], increased oxidative stress [18], and DNA damage [19]. Apoptosis is a highly regulated program of cell death and inhibition of this process is cardioprotective under many conditions. Therefore, this process represents a potential target for therapeutic intervention to prevent heart failure. This review provides a current overview of the evidence and functional role of apoptosis in cardiovascular diseases and discusses the molecular pathways involved in cardiac myocyte apoptosis.
Evidence of apoptosis in cardiovascular diseases Cardiac cells undergoing apoptosis have been detected in many different diseases of the cardiovascular system including atherosclerosis, myocardial ischemia and reperfusion injury, diabetic cardiomyopathy, and chronic heart failure. Atherosclerotic vascular disease is a leading cause of myocardial infarction and heart failure, and a major factor in the development of acute coronary syndrome is disruption of an atherosclerotic plaque. It has been reported that macrophages and smooth muscle cells undergo apoptosis in unstable atherosclerotic plaques which can lead to rupture of the plaque and thrombosis [20]. Recently, Clarke et al. [21] demonstrated that vascular smooth muscle cell apoptosis during either atherogenesis or within established plaques of apolipoprotein (Apo) E(-/-) mice accelerated plaque growth and was associated with features of plaque vulnerability such as a thin fibrous cap and loss of collagen and matrix. In addition, it has been proposed that poor clearance of apoptotic macrophages may lead to accumulation of cellular debris within the lipid-rich core of atherosclerotic plaque, thus contributing to plaque progression and rupture. Rupture of atherosclerotic plaques and thrombus formation cause occlusion of coronary arteries which reduces the blood supply to the myocardium and leads to myocardial infarction and possibly death. Reperfusion is the treatment for acute myocardial infarction, but the reintroduction of oxygen can aggravate the tissue damage, a process called reperfusion injury [22]. Loss of cardiac cells in response to ischemia/reperfusion (I/R) injury was long considered to be due to necrotic cell death, but studies over the past decade have identified apoptosis as a significant component of cell loss during reperfusion after a myocardial infarction [9, 10, 14]. Apoptosis seems to occur primarily after reperfusion following ischemia, whereas prolonged ischemia leads to necrosis. There is also mounting evidence that apoptosis plays an important role in both acute and chronic loss of cardiac myocytes after a myocardial infarction. Studies have reported the presence of apoptotic cells in the border zone of the infarct and in remote myocardium in the early phase [9], as well as months after myocardial infarction
537
[23], suggesting that apoptosis plays a role in remodeling and development of heart failure after myocardial infarction. Since the regenerative capacity of the myocardium is limited, there is intense interest in the prevention of cardiomyocyte loss during ischemia and reperfusion. Moreover, diabetes is a rapidly growing epidemic in the Western world which is well known to increase the risk of developing cardiovascular disease [24]. Increased levels of apoptosis have been detected in the hearts of diabetic patients and animal models of diabetes, and the loss of myocytes has been implicated in the development of diabetic cardiomyopathy [25, 26]. In addition, it has been reported that the mortality of myocardial infarction in diabetic patients is more than double that of non-diabetic patients [27]. It appears that cardiac myocytes in the diabetic myocardium are more susceptible to apoptosis [25], suggesting that the higher sensitivity to MI is due to a higher loss of cardiac myocytes via apoptosis in response to the stress [28]. Also, Kuethe et al. [29] found that diabetic patients with dilated cardiomyopathy had significantly more apoptotic cells in the heart compared to patients without diabetes. The pathogenesis of diabetic cardiomyopathy is a complex process that is attributed to abnormal cellular metabolism and defects in organelles such as mitochondria, sarcolemma, and endoplasmic reticulum (ER) which leads to activation of apoptosis. Hyperglycemia appears to play a central role in the development of diabetic cardiomyopathy by inducing apoptosis of cardiac myocytes via increased levels of reactive oxygen and nitrogen species [30]. Using a mouse model of diabetes, Cai et al. [25] found that administration of insulin suppressed hyperglycemia and inhibited diabetes-induced apoptosis in the heart. Other studies have shown that suppression of myocardial cell death by antioxidants or inhibition of apoptotic signaling pathways result in a significant prevention of diabetic cardiotoxicity, suggesting that oxidative-stress mediated apoptosis plays an important role in the development of diabetic cardiomyopathy [31, 32]. There is also a connection between chronic heart failure and apoptosis. It has been reported that patients with advanced heart failure have higher rates of cardiac myocyte apoptosis than normal subjects, (0.08–0.25 vs. 0.001– 0.002%) [9, 10, 33]. Genetic and pharmacological studies from animal models suggest that apoptosis plays a crucial role in the development and progression of heart failure. Using transgenic mice that express a conditionally active caspase-8 in the heart, Wencker et al. [34] found that extremely low levels of chronic myocyte apoptosis were sufficient to cause a lethal dilated cardiomyopathy. Inhibition of cell death with a caspase inhibitor prevented left ventricular dilation and improved ventricular function. Thus, even if apoptosis occurs at a very low frequency after an insult such as I/R, it is a constant process and results in
123
538
progressive loss of myocytes, which gradually reduces the ability of the heart to maintain contractile function. As a result, the remaining myocytes are forced to work harder to compensate for the loss in contractility, which, in turn, may contribute to cardiac hypertrophy resulting in cardiomyopathy and heart failure.
Apoptotic signaling pathways in the heart The major pathways involved in apoptotic signaling in the heart involve the death receptor pathway, the mitochondrial and ER-stress death pathways. A schematic view of apoptotic cascades is shown in Fig. 1.
Death receptor pathway in cardiovascular disease Apoptosis can be initiated through activation of the death receptor pathway (also called the extrinsic pathway) via a complex signal transduction from the plasma membrane leading to activation of the caspase cascade. The death receptors belong to the tumor necrosis factor/nerve growth factor receptor superfamily and are transmembrane proteins with an extracellular ligand-interacting domain, a transmembrane domain, and an intracellular death domain [35]. Binding of the corresponding ligand to the death receptor causes oligomerization and activation of the receptor. For instance, after Fas ligand (FasL) binding, Fas receptors undergo trimerization and recruit Fas-associated death domain (FADD). Fas/FADD complex binds to proFig. 1 Scheme of apoptotic signaling in cardiac myocytes. Apoptosis can be mediated via activation of death receptors, permeabilization of the outer mitochondrial membrane, or ER-stress
123
Apoptosis (2009) 14:536–548
caspase 8 leading to cleavage of the initiator pro-caspase 8 to active caspase 8. Activated caspase 8 propagates the apoptotic signal through a direct activation of executioner downstream caspases and via the release of cytochrome c by mitochondria. Several studies strongly suggest an important pathophysiological role for the death receptor pathway in the pathogenesis of heart failure. The best-characterized death receptors are Fas (also called CD95 or Apo1) and tumor necrosis factor receptor 1 (TNFR1). Both receptors are present in cardiac myocytes and have been implicated to contribute to cardiovascular disease. TRAIL is ligand for Death Receptor 4 and 5 (DR4 and DR5) and has also been reported to be released by cardiac myocytes [36], but not much is known about this ligand and its receptors in the heart. Patients with end-stage congestive heart failure have elevated circulating levels of TNF-a, the ligand for TNFR1 [37–39], and studies suggest that there is a relationship between the serum levels of TNF- a and the severity of heart failure [39, 40]. In addition, several studies have reported that cardiomyocytes can be an abundant source of TNF-a [41–43], and that failing human myocardium, but not nonfailing hearts, express high levels of TNF-a [44, 45]. Following I/R, there is a sustained increase of TNF-a both locally in the heart as well as in circulating levels in blood [43, 46]. The functional role of elevated levels of TNF-a has been investigated using transgenic mice overexpressing TNF-a specifically in the heart. For instance, cardiac specific overexpression of TNF-a in transgenic mice caused development of dilated cardiomyopathy and heart failure [16, 17], suggesting that increased levels of
Apoptosis (2009) 14:536–548
TNF-a is detrimental to the heart by activation of the death receptor pathway. In addition, both Fas and FasL expression are increased in myocytes exposed to hypoxia [47] and activation of the Fas pathway has been shown to induce apoptosis in cardiac myocytes [48]. There is also evidence suggesting that Fasmediated apoptosis is associated with myocarditis [49], myocardial reperfusion injury [50], and post-infarction ventricular remodeling [51]. For instance, Gomez et al. [52] recently reported that mice lacking functional Fas (lpr mice) had no difference in infarct size and apoptosis after I/R, suggesting that Fas plays a minor role in mediating acute I/R injury. Similarly, Li et al. [51] found that lpr mice and mice lacking Fas ligand (gld mice) had similar infarct sizes 2 days after myocardial infarction. Instead, this study found decreased apoptosis of granulation tissue cells which reduced post-infarct remodeling. Granulation tissue cells are removed via apoptosis to eventually make scar tissue [23]. Also, they found that infecting hearts with an adenovirus encoding soluble Fas, a competitive inhibitor of FasL, 3 days after a myocardial infarction improved cardiac function and survival. This suggests that the Fas pathway contributes to cell death in the later stages of an infarction. In contrast, two different studies found that the lpr mice were resistant to acute I/R injury and hearts had reduced infarct size and apoptosis compared to wild type [43, 50]. In support of this observation, vanadyl sulfate treatment caused decreased expression of FasL which correlated with reduced caspase-3 activation and cell death in an in vivo model of I/R, suggesting that the Fas pathway plays a key role in I/R-mediated apoptosis [53]. The reasons for the differences in the findings in these studies using the same mice are not clear and further studies are needed to clarify the role of Fas in acute I/R injury. In addition, monocyte chemoattractant protein-1 (MCP-1) plays a crucial role in initiating coronary heart disease by recruiting monocytes/macrophages to the vessel wall, and transgenic mice overexpressing MCP-1 in the heart manifest cardiac inflammation and develop heart failure. Interestingly, inhibition of FasL function through cardiac-specific expression of soluble Fas rescued the MCP-1 transgenic mice from developing heart failure, suggesting that the FasL derived from the infiltrating mononuclear cells causes death of cardiac cells resulting in the development of heart failure [54]. Clearly, Fas-mediated apoptosis plays a role in contributing to heart failure but further studies are needed to elucidate exactly how and under what conditions (chronic or acute) Fas activates apoptosis.
Mitochondrial death pathway in heart disease The primary function of mitochondria is to provide energy for the cell in the form of ATP through oxidative
539
phosphorylation. In cardiac myocytes, mitochondria constitute about 30% of cell volume and are located below the sarcolemma as well as in intermyofibrillar spaces. This ubiquitous presence and strategic location of mitochondria ensures efficient ATP supply and delivery to the continuously contracting myocyte. However, mitochondria can also contribute to cell death in response to intracellular stress such as increased oxidative stress, serum deprivation, and DNA damage. In response to stress, mitochondria release several pro-apoptotic factors such as cytochrome c, apoptosis inducing factor (AIF), endonuclease G (Endo G), second mitochondria-derived activator of caspases (Smac/ Diablo), and HtrA2/Omi, resulting in initiation of apoptosis. The mitochondrial death pathway appears to play a significant role in contributing to cell death particularly in I/R injury. Studies have reported that there is substantial release of cytochrome c and activation of caspase-9 after myocardial I/R injury [55–57]. Also, it has been reported that protecting mitochondrial integrity protects against I/R injury [56, 58–60]. The mitochondrial cell death pathway is regulated by the pro- and anti-apoptotic Bcl-2 proteins. These proteins share up to four conserved Bcl-2 homology (BH) domains. Anti-apoptotic Bcl-2 proteins, such as Bcl-2 and Bcl-XL, contain all four subtypes of BH domains (BH1-4) and promote cell survival. The pro-apoptotic Bcl-2 proteins contain one or three BH domains and therefore are divided into two structurally distinctive subfamilies: (1) multidomain proteins such as Bax and Bak that share three BH regions (BH1-3), and (2) BH3-only domain proteins such as Bnip3, Nix/Bnip3L, Bad, Bid, Noxa, and Puma [61, 62]. The anti-apoptotic members such as Bcl-2 and Bcl-XL are important in cell survival and protect cardiac myocytes against various stressors. For instance, overexpression of Bcl-XL in H9c2 cardiac cells protected against doxorubicin- and hypoxia-mediated apoptosis by preserving mitochondrial integrity [63], and Bcl-2 was shown to prevent p53-mediated apoptosis in cardiac myocytes [64]. Moreover, transgenic mice showing accelerated accumulation of mitochondrial DNA (mtDNA) mutations due to expression of an error-prone mtDNA polymerase specifically in the heart activated a strong prosurvival response by upregulation of Bcl-2 and Bcl-XL [65]. Transgenic mice overexpressing Bcl-2 in the heart have reduced I/R injury and fewer apoptotic cells compared to wild type mice, suggesting that the cardioprotective effect of Bcl-2 is via inhibition of the mitochondrial death pathway [60, 66, 67]. Bcl-2 has been reported to protect against cell death by preventing permeabilization of the outer mitochondrial membrane by inhibiting activation of pro-apoptotic Bax/ Bak [68]. For instance, mice null for desmin, a musclespecific member of the intermediate filament gene family, develop cardiomyopathy characterized by extensive
123
540
cardiomyocyte death, and subsequent heart failure [69]. Weisleder et al. [70] found that overexpression of Bcl-2 in the desmin null heart attenuated the cardiomyopathy phenotype by preventing mitochondrial defects. However, new protective functions for Bcl-2 have also been identified. During ischemia, the sodium calcium exchanger (NCX) operates in reverse to extrude Na? and as a result the cell becomes loaded with Ca2? [71]. Interestingly, Bcl-2 was reported to reduce NCX activity as well as increase resistance to permeability transition in the mitochondria by increasing the Ca2? threshold for mitochondrial permeability transition pore opening in heart mitochondria [72]. Bcl-2 also provides protection by inhibiting consumption of glycolytically generated ATP by the ATPase. During myocardial ischemia, mitochondrial ATP generation is inhibited and the F1F0-ATPase is running in reverse, thereby consuming ATP generated by glycolysis [73]. Interestingly, Imahashi et al. [74] found that Bcl-2 overexpression in the heart reduced the rate of ATP decline and decreased acidosis during ischemia. These studies suggest that the anti-apoptotic proteins can protect against cell death via multiple mechanisms and have attractive therapeutic potential to treat or prevent heart disease. The pro-apoptotic Bcl-2 proteins activate cell death by permeabilizing the outer mitochondrial membrane, which releases pro-apoptotic proteins such as cytochrome c and AIF from the intermembrane space. The pro-apoptotic BH3only proteins function as cellular stress sensors and integrate diverse cell death stimuli. For instance, Bnip3 is activated in response to increased oxidative stress [75], whereas Bad is activated in response to growth factor deprivation [76]. Activation of a BH3-only protein in response to a specific stress induces activation of downstream effectors Bax and/ or Bak either by directly interacting with these proteins or indirectly by sequestering anti-apoptotic Bcl-2/Bcl-XL [68]. Activation of Bax and/or Bak induce their oligomerization in the mitochondrial membrane and formation of a pore in the outer mitochondrial membrane which allows for release of proteins from the intermembrane space [68]. Bax and Bak are essential for cell death mediated via the mitochondrial pathway, and mouse embryonic fibroblast (MEFs) isolated from the Bax/Bak double knockout mouse are completely resistant to cell death by staurosporine, growth factor deprivation, and UV, as well as to overexpression of BH3only proteins such a tBid, Bad, and Bnip3 [75, 77, 79]. The pro-apoptotic Bcl-2 proteins have been widely implicated in cardiovascular disease. In the myocardial cells, Bax has been reported to be activated in response to oxidative stress [56] and simulated I/R [78, 80, 81]. Moreover, hearts of Bax deficient mice have reduced mitochondrial damage and infarcts size compared to wild type mice, suggesting that Bax is an important contributor to I/R injury [82]. The most studied BH3-only protein in the heart is Bnip3 which has
123
Apoptosis (2009) 14:536–548
been reported to contribute to acute I/R injury [58] and postinfarct remodeling [83]. Bnip3 is transcriptionally upregulated by hypoxia in neonatal cardiac myocytes via HIF-1a [84] and E2F-1 [85], and Frazier et al. [86] have reported that the Bnip3 protein is stabilized by acidosis. Recently, we reported that Bnip3 is activated by oxidative stress which promotes homodimerization and activation of Bnip3 in the myocardium [75]. Since apoptosis occurs mainly during reperfusion, these studies suggest that oxygen deprivation and acidosis promotes upregulation and stabilization of Bnip3, respectively, and that increased oxidative stress during reperfusion promotes homodimerization and activation of Bnip3 in the mitochondria. Bnip3 has been reported to activate downstream Bax/Bak [75] as well as induce opening of the mitochondrial permeability transition pore [87, 88]. In contrast, the Bnip3 homologue Nix/Bnip3L has been implicated in cardiac hypertrophy and development of cardiomyopathy [89]. Moreover, Bid is cleaved to its truncated and active form in response to I/R [55, 90], and Bad is upregulated in response to I/R [91]. Since ischemia and reperfusion induces multiple stress signals (oxygen deprivation, oxidative stress, DNA damage, growth factor deprivation etc.) in the cardiac myocyte, multiple BH3-only proteins are activated in response to I/R ensuring activation of the cell death program. Thus, the BH3-only proteins are important activators of the mitochondrial cell death pathway in response to myocardial infarction and pathological cardiac hypertrophy. Importantly, the relative level of the pro- and antiapoptotic Bcl-2 proteins determines whether a cell will survive or die following an apoptotic stimulus. It has been reported that there is a shift in the ratio of anti- to proapoptotic Bcl-2 proteins to proteins that promote apoptosis in the hearts of patients after a myocardial infarction, in severe dilated cardiomyopathy and ischemic heart disease [92–94]. In addition, there was a significant shift in the ratio of Bax to Bcl-XL during the transition from compensated hypertrophy to heart failure in a model of pressure overload which correlated with increased levels of cytochrome c in the cytosol and caspase-3 activation [95]. Although the ratio is shifted towards anti-apoptotic proteins, it may not activate apoptosis. However, the myocytes will have a lower threshold for additional stress and will induce apoptosis easier than a normal cell, making these hearts more susceptible to develop heart failure.
Permeabilization of the mitochondrial membrane Cytochrome c In healthy cells, the role of cytochrome c is to shuttle electrons from complex III to IV of the respiratory chain.
Apoptosis (2009) 14:536–548
However, during apoptosis, cytochrome c is released into the cytosol where it binds to Apaf-1 and dATP which induces a conformational change in Apaf-1 which recruits and subsequently activates caspases-9. The activated caspase-9 cleaves pro-caspases-3 to produce active effector caspase-3 which leads to the cleavage of cellular target proteins [96–98]. In addition, it has been reported that activated caspase-3 translocates to nucleus, then cleaves the DNA repairing enzyme, poly (ADP-ribose) polymerase (PARP) and activates endonucleases which cleave DNA. These events culminate in apoptotic cell death [96, 99, 100].
Apoptosis-inducing factor (AIF) AIF is a flavoprotein localized in the mitochondrial intermembrane space and is required for oxidative phosphorylation and for the assembly and/or stabilization of respiratory complex I [101]. AIF is essential for the maintenance of normal heart function, and inactivation of AIF results in dilated cardiomyopathy [102]. In addition, cardiac myocytes from Harlequin (Hq) mice, which has *80% reduction in AIF protein levels due to a proviral insertion in the first intron of the Aif gene, are sensitized to oxidative stress-induced cell death, and Hq hearts display more severe ischemic damage compared to wild-type hearts after acute ischemia/reperfusion injury [103]. AIF is anchored to the mitochondrial inner membrane via its N-terminus. However, upon induction of apoptosis, AIF is cleaved and released into the cytosol [104] where it then translocates to the nucleus and mediates chromatin condensation and large-scale DNA fragmentation [105]. Interestingly, it was recently reported that increased levels of mitochondrial Ca2? activated a mitochondrial calpain which cleaved membrane bound AIF. Permeabilization of the mitochondrial membrane resulted in release of the soluble AIF [104]. It is well known that I/R causes Ca2? overload of mitochondria [106], and reduction of mitochondrial Ca2? uptake has beneficial effects on cardiac function following I/R with improved functional recovery and reduced infarct size [107, 108]. Since it has been reported that I/R induces release of AIF [109, 110], it will be interesting to investigate whether this is due to processing and release of AIF by Ca2?-activated Calpain. Moreover, considering the fact that AIF functions as a NADH-oxidase involved in electron transport in complex I of the electron transport chain, loss of AIF from mitochondria may cause further mitochondrial dysfunction due to reduction in electron transport capacity. Thus, release of AIF not only initiates apoptosis, but also subsequently induces mitochondrial dysfunction which will ensure cell death.
541
Omi/HtrA2, Smac/Diablo, and endonuclease G (EndoG) Other apoptotic effectors are released from mitochondria, including the serine protease Omi/HtrA2, Smac/Diablo, and Endo G. Similar to cytochrome c-mediated activation of the caspase cascade, Smac/Diablo and Omi/HtrA2 are indirectly involved in caspase activation. For example, inhibitors of apoptosis proteins (IAPs) are endogenous inhibitors of caspases and are bound to caspase-3 and -9 under normal conditions [111, 112]. However, when released to cytosol, Smac/Diablo and Omi/HtrA2 prevent IAPs from inhibiting the caspases, resulting in activation of caspase-9 and -3. A role for Omi/HtrA2 in the heart was demonstrated by two studies where inhibition of Omi/ HtrA2 using ucf-101 reduced apoptosis and infarct size in mice as well as rat after in vivo I/R [113, 114]. Also, transgenic mice overexpressing IAP2 had reduced infarct size and fewer TUNEL-positive cells after I/R [115]. Endo G is a nuclear-encoded endonuclease and localized in the inner membrane space of mitochondria. Under normal conditions, Endo G plays a role in maintenance of mitochondria DNA by removing defective DNA [116]. However, similar to AIF once released, Endo G translocates to the nucleus where it cleaves DNA. Although few studies using Endo G-/- splenocytes and fibroblasts report that Endo G is not essential for nuclear DNA fragmentation and apoptosis, studies using intact heart or isolated cardiomyocytes demonstrate that Endo G plays a role in I/R-mediated cell death. For instance, Javadov et al. [117] reported that VAE-480, a specific Na?/H? exchanger-1 (NHE-1) inhibitor, reduced release of Endo G and I/R injury, suggesting that attenuation of Endo G release is cardioprotective. In addition, Bahi et al. [118] demonstrated that Endo G was released from mitochondria and induced DNA damage, and importantly when Endo G was downregulated using siRNA, DNA damage was significantly reduced in adult cardiomyocytes during I/R. Collectively, these studies suggest that Endo G is a critical contributor to DNA degradation during I/R.
Activation of the ER stress death pathway in the heart The ER is responsible for synthesis and folding of secreted proteins as well as Ca2? storage. Under normal conditions, there is a balance between import of newly unfolded proteins into the ER and secretion of folded mature proteins. When this balance is disturbed and there is an accumulation of protein aggregates in the ER lumen, the unfolded protein response (UPR) is activated in an attempt to restore ER homeostasis [119]. Aberrant Ca2? regulation can also activate the UPR. The UPR activates a transcriptional
123
542
program to increase the protein folding capacity of the ER, and the degradation of misfolded proteins, as well as suppress proteins synthesis in the cell [120]. Thus, the UPR is primarily an adaptive response to restore ER homeostasis and protect the cell from stress. However, if the stress is prolonged and overwhelming, the UPR activates a proapoptotic response instead which is independent of the mitochondria. Several recent studies have demonstrated a role for ER stress in cardiovascular disease. For instance, Okada et al. [121] found that pressure overload by aortic constriction induced extensive ER stress during progression from cardiac hypertrophy to heart failure. In addition, studies have reported that ER stress occurs in response to myocardial I/R [122, 123], and that enhanced ER stress is associated with the development of ischemic heart disease [124]. There is also evidence that ER stress-induced apoptosis is involved in pathogenesis of diabetes and heart failure [26], and ultrastructural analysis revealed swelling of the ER in diabetic myocardium [125]. Consistent with these observations, defective ER quality control in transgenic mice with mutant KDEL receptor (a receptor for ER chaperones) caused dilated cardiomyopathy [126]. These studies suggest that apoptosis mediated by ER stress may be a significant contributor to cardiovascular disease. Endoplasmic reticulum stress induces cell death via two different mechanisms. Under ER stress, activated caspase12 activates caspase-3, leading to apoptosis [119]. The second death-signaling pathway activated by ER stress is activation of a transcriptional program via upregulation of the transcription factor CHOP/GADD 153. CHOP activates transcription of genes encoding pro-apoptotic proteins including the BH3-only protein Puma [127]. Szegezdi et al. [122] found that during prolonged ischemia, the UPR switched to a pro-apoptotic response by activation of the ER stress death pathway with upregulation of the transcription factor CHOP, and activation of caspase-12 in neonatal cardiac myocytes. Studies in cardiac myocytes and the heart have demonstrated that increased CHOP expression during I/R contributed towards apoptosis, and inhibition of CHOP expression using a PKCd inhibitor significantly attenuated ER-mediated apoptosis [128]. This study suggests that translocation of PKCd to ER membrane induced the UPR, which led to upregulation of CHOP and subsequent apoptosis. In addition, Okada et al. [121] demonstrated that pharmacological intervention inducing ER stress increased CHOP expression and apoptosis in the heart. Interestingly, the BH3-only protein Puma was reported to be upregulated in isolated cardiac myocytes exposed to hypoxia/re-oxygensation, and genetic deletion of Puma reduced I/R-mediated cell death and decreased infarct size in Langendorff perfused hearts [129]. Recently, it was
123
Apoptosis (2009) 14:536–548
demonstrated that myocytes deficient in Puma or downregulation via siRNA were resistant to ER stress-induced apoptosis [130], suggesting that Puma is a critical component of ER-stress induced apoptosis in cardiac myocytes. The Bcl-2 proteins have been shown to localize to the ER where they can regulate the levels of Ca2? stored in the ER [131].
Cross talk between the apoptotic pathways There is cross talk between the death receptor and mitochondrial cell death pathways. Activation of caspase 8 by the death receptor pathway directly activates executioner caspase-3, but also cleaves the BH3-only protein Bid at aspartate 60 to generate a 15 kDa truncated form (tBid) that facilitates release of cytochrome c from the mitochondria [132, 133]. The release of cytochrome c causes activation of caspase-9 which in turn also activates caspase-3, thus amplifying the death signal from the plasma membrane. The cross talk between the pathways via death receptor activation has been demonstrated in cardiac myocytes and the heart. For instance, Date et al. [134] found that overexpression of FasL activated both caspase-8 and -9 in neonatal cardiac myocytes. Moreover, cardiac restricted overexpression of TNF-a results in increased apoptosis and development of heart failure, but when these mice were crossed with transgenic mice overexpressing Bcl-2 in the heart cardiac myocytes apoptosis and LV remodeling was attenuated [135]. In addition, caspase-8 was activated, and Bid was cleaved to t-Bid, suggesting concurrent activation of both the death receptor and mitochondrial death pathways in the heart by TNF-a. In support of this, Bcl-2 overexpression only partially attenuated cardiomyocyte apoptosis and had no effect on extrinsic signaling. There have also been reports of cross-talk between the death receptor pathway and the ER-stress pathway. For instance, treatment of L929 cells with FasL induced processing of caspase-12 as well as activation of caspases-3, -7, and -9 [136]. In addition, Bajaj and Sharma [137] recently reported that TNF-a treatment caused activation of both caspase-3 and -12 in the HL-1 myocyte cell line. There is also evidence that there is communication between the ER and the mitochondrial death pathways. For instance, ER-targeted Bcl-2 was reported to inhibit mitochondrial membrane depolarization and cytochrome c release in apoptotic myelodysplastic syndrome erythroid precursor cells [138]. BAP31 is an ER-associated protein that is cleaved by caspase-8. The cleaved fragment directs proapoptotic signals between the ER and mitochondria by inducing release of Ca2? from the ER which gets taken up by the mitochondria [139]. In addition, the BH3-only
Apoptosis (2009) 14:536–548
protein Bik has been reported to localize to the mitochondria where it initiates release of Ca2? via activation of Bax/Bak in the ER membrane [140]. These studies suggest that the ER communicates with the mitochondria by releasing Ca2?.
Autophagy as a mediator of cell death Autophagy is an important cellular process involved in recycling of long-lived proteins and organelles. In the heart, autophagy is important to maintain homeostasis and disruption or a defect in this pathway leads to ventricular dysfunction and heat failure [141]. It is also an important survival response which is upregulated during starvation when the cells need to recycle amino acid and fatty acids. In the heart, autophagy is upregulated in response to ischemia/reperfusion [58, 142], and pressure overload [143]. However, the functional significance of increased autophagy in the heart is not clear and autophagy has been reported to protect against cell death as well be the cause of cell death [81, 142, 144]. Interestingly, recent studies suggest that there is cross talk between autophagy and apoptosis. Atg5, an essential autophagy protein, has been reported to activate apoptosis. Yousefi et al. [145] found that overexpression of Atg5 increased the cell’s susceptibility to apoptosis following stimulation with several death triggers, including anticancer drugs. They found that the death stimulation resulted in calpain-mediated cleavage of Atg5, and truncated Atg5 induced cytochrome c release and apoptosis. Overexpression of Bcl-2 protected against Atg5-mediated mitochondrial dysfunction. This suggests that Atg5 can serve as a molecular switch between autophagy and apoptosis, but it is not clear how truncated Atg5 triggers mitochondrial permeabilization. Another study reported that Atg5 associated with the Fas-associated death domain (FADD) protein to mediate IFN-c-induced cell death. In addition, a mutant of Atg5 (Atg5K130R), which was unable to activate autophagy, was able to induce cell death [146]. Similarly, calpainmediated truncated Atg5 was unable to promote autophagy, but induced apoptosis [145]. These two studies suggest that Atg5-mediated apoptosis does not require the formation of autophagosomes. Further investigations of this molecular link between autophagy and apoptosis are needed. Moreover, anti-apoptotic Bcl-2 family members and proapoptotic BH3-only proteins may participate in the inhibition and induction of autophagy, respectively. Beclin 1, an essential autophagy protein, is regulated by the Bcl-2 proteins. Under normal conditions, Bcl-2 and Bcl-XL suppress autophagy by associating with Beclin 1 through a BH3 domain in Beclin 1 and the BH3 binding groove of Bcl-2/ Bcl-XL [147]. The BH3-only proteins can disrupt the
543
interaction between Beclin 1 and Bcl-2/Bcl-XL to induce autophagy [148]. The BH3-only protein Bik was found to cause enhanced cell death with autophagic features in Bcl-2 deficient cells [149], and downregulation of Bcl-2 using siRNA induced autophagic cell death in MCF-7 cells [150]. This suggests that with a lack of Bcl-2, there is no break on Beclin-1 which can now be activated and induce excess autophagy. The BH3-only protein Bnip3 has been shown to be a potent inducer of autophagy in cardiac cells [58]. Bnip3 has been shown to interact with Bcl-2 and BclXL [151], but it is not known whether Bnip3 disrupts the interaction between Beclin 1 and Bcl-2/Bcl-XL. These studies suggest that there is cross talk between autophagy and apoptosis via Beclin 1 and Atg5. It is interesting that Beclin 1 contains a BH3-only domain, but it is not known whether it can act as a BH3-only protein and activate apoptosis. However, Beclin 1 heterozygous mice (Beclin 1?/-), which have reduced autophagy, also have reduced apoptosis and infarcts size after I/R injury [142], suggesting that Beclin 1 might activate apoptosis.
Conclusion and perspective It is clear that apoptosis plays a critical role in pathogenesis of various cardiovascular diseases. Currently, three apoptotic pathways (death receptor, mitochondrial, and ERstress) have been identified in the heart to contribute to myocyte loss in various cardiovascular diseases. Since the regenerative capacity of the myocardium is limited, there is intense interest in the prevention of cardiomyocyte loss in cardiovascular diseases to prevent development of heart failure. Since apoptosis is a highly regulated process, it is a good potential target for therapeutic intervention. Inhibition of cardiac myocyte apoptosis using novel research technology including transgenic mice, gene deletion, recombinant proteins, and pharmacological inhibitors results in cardioprotection and prevention of heart failure. However, many important questions regarding the effect of each anti-apoptotic intervention remain to be answered. For instance, loss of mitochondrial membrane integrity is generally considered a point of no return in the cell death process. Therefore, inhibiting downstream effectors such as caspase-3 will delay, but not prevent cell death. Thus, it is essential to preserve mitochondrial integrity for effective therapy. Another complication is that multiple pro-apoptotic proteins can be activated in response to injury. For instance, multiple BH3-only proteins are activated during I/R, each of which would have to be targeted for effective therapy. In addition, it is not clear how much cross-talk there is between necrosis, apoptosis, and autophagy in the heart. Enhanced autophagy is often seen in cells where apoptosis is inhibited, and it is unknown whether inhibition
123
544
of apoptosis for cardioprotection against various heart diseases will subsequently lead to non-apoptotic cell death later. Although several potential therapeutic agents have been tested in animal models of I/R injury with success, nearly none of the specific anti-apoptotic agents have reached the stage of clinical research. Thus, a better understanding of the complex mechanisms associated with cardiac myocyte apoptosis is necessary to identify potential targets and to develop novel therapeutic strategies for cardiovascular diseases. Acknowledgments This manuscript was supported by a Scientist ˚ . B. G. Development Award from AHA, and NIH grant HL087023 to A
References 1. Reggiori F, Klionsky DJ (2005) Autophagosomes: biogenesis from scratch? Curr Opin Cell Biol 17:415–422. doi:10.1016/ j.ceb.2005.06.007 2. Kitsis RN, Peng CF, Cuervo AM (2007) Eat your heart out. Nat Med 13:539–541. doi:10.1038/nm0507-539 3. Schweichel JU, Merker HJ (1973) The morphology of various types of cell death in prenatal tissues. Teratology 7:253–266. doi:10.1002/tera.1420070306 4. Searle J, Kerr JF, Bishop CJ (1982) Necrosis and apoptosis: distinct modes of cell death with fundamentally different significance. Pathol Annu 17(Pt 2):229–259 5. Kerr JF (1971) Shrinkage necrosis: a distinct mode of cellular death. J Pathol 105:13–20. doi:10.1002/path.1711050103 6. Majno G, Joris I (1995) Apoptosis, oncosis, and necrosis. An overview of cell death. Am J Pathol 146:3–15 7. Rich T, Watson CJ, Wyllie A (1999) Apoptosis: the germs of death. Nat Cell Biol 1:E69–E71. doi:10.1038/11038 8. Savill J, Fadok V (2000) Corpse clearance defines the meaning of cell death. Nature 407:784–788. doi:10.1038/35037722 9. Olivetti G, Quaini F, Sala R et al (1996) Acute myocardial infarction in humans is associated with activation of programmed myocyte cell death in the surviving portion of the heart. J Mol Cell Cardiol 28:2005–2016. doi:10.1006/jmcc.1996.0193 10. Saraste A, Pulkki K, Kallajoki M, Henriksen K, Parvinen M, Voipio-Pulkki LM (1997) Apoptosis in human acute myocardial infarction. Circulation 95:320–323 11. Narula J, Haider N, Virmani R et al (1996) Apoptosis in myocytes in end-stage heart failure. N Engl J Med 335:1182–1189. doi:10.1056/NEJM199610173351603 12. Aharinejad S, Andrukhova O, Lucas T et al (2008) Programmed cell death in idiopathic dilated cardiomyopathy is mediated by suppression of the apoptosis inhibitor Apollon. Ann Thorac Surg 86:109–114. doi:10.1016/j.athoracsur.2008.03.057 discussion 114 13. Cheng W, Kajstura J, Nitahara JA et al (1996) Programmed myocyte cell death affects the viable myocardium after infarction in rats. Exp Cell Res 226:316–327. doi:10.1006/excr.1996. 0232 14. Gottlieb RA, Burleson KO, Kloner RA, Babior BM, Engler RL (1994) Reperfusion injury induces apoptosis in rabbit cardiomyocytes. J Clin Invest 94:1621–1628. doi:10.1172/JCI117504 15. Gao HK, Yin Z, Zhou N, Feng XY, Gao F, Wang HC (2008) Glycogen synthase kinase 3 inhibition protects the heart from acute ischemia–reperfusion injury via inhibition of inflammation and apoptosis. J Cardiovasc Pharmacol 52:286–292. doi: 10.1097/FJC.0b013e318186a84d
123
Apoptosis (2009) 14:536–548 16. Kubota T, McTiernan CF, Frye CS et al (1997) Dilated cardiomyopathy in transgenic mice with cardiac-specific overexpression of tumor necrosis factor-alpha. Circ Res 81:627–635 17. Bryant D, Becker L, Richardson J et al (1998) Cardiac failure in transgenic mice with myocardial expression of tumor necrosis factor-alpha. Circulation 97:1375–1381 18. Sayen MR, Gustafsson AB, Sussman MA, Molkentin JD, Gottlieb RA (2003) Calcineurin transgenic mice have mitochondrial dysfunction and elevated superoxide production. Am J Physiol Cell Physiol 284:C562–C570 19. Wang J, Silva JP, Gustafsson CM, Rustin P, Larsson NG (2001) Increased in vivo apoptosis in cells lacking mitochondrial DNA gene expression. Proc Natl Acad Sci USA 98:4038–4043. doi: 10.1073/pnas.061038798 20. Kockx MM, De Meyer GR, Muhring J, Jacob W, Bult H, Herman AG (1998) Apoptosis and related proteins in different stages of human atherosclerotic plaques. Circulation 97:2307– 2315 21. Clarke MC, Littlewood TD, Figg N et al (2008) Chronic apoptosis of vascular smooth muscle cells accelerates atherosclerosis and promotes calcification and medial degeneration. Circ Res 102:1529–1538. doi:10.1161/CIRCRESAHA.108. 175976 22. Matsumura K, Jeremy RW, Schaper J, Becker LC (1998) Progression of myocardial necrosis during reperfusion of ischemic myocardium. Circulation 97:795–804 23. Takemura G, Ohno M, Hayakawa Y et al (1998) Role of apoptosis in the disappearance of infiltrated and proliferated interstitial cells after myocardial infarction. Circ Res 82:1130– 1138 24. Kannel WB, Hjortland M, Castelli WP (1974) Role of diabetes in congestive heart failure: the Framingham study. Am J Cardiol 34:29–34. doi:10.1016/0002-9149(74)90089-7 25. Cai L, Li W, Wang G, Guo L, Jiang Y, Kang YJ (2002) Hyperglycemia-induced apoptosis in mouse myocardium: mitochondrial cytochrome C-mediated caspase-3 activation pathway. Diabetes 51:1938–1948. doi:10.2337/diabetes.51.6.1938 26. Li Z, Zhang T, Dai H et al (2007) Involvement of endoplasmic reticulum stress in myocardial apoptosis of streptozocin-induced diabetic rats. J Clin Biochem Nutr 41:58–67. doi:10.3164/jcbn. 2007008 27. Mukamal KJ, Nesto RW, Cohen MC et al (2001) Impact of diabetes on long-term survival after acute myocardial infarction: comparability of risk with prior myocardial infarction. Diabetes Care 24:1422–1427. doi:10.2337/diacare.24.8.1422 28. Backlund T, Palojoki E, Saraste A et al (2004) Sustained cardiomyocyte apoptosis and left ventricular remodelling after myocardial infarction in experimental diabetes. Diabetologia 47:325–330. doi:10.1007/s00125-003-1311-5 29. Kuethe F, Sigusch HH, Bornstein SR, Hilbig K, Kamvissi V, Figulla HR (2007) Apoptosis in patients with dilated cardiomyopathy and diabetes: a feature of diabetic cardiomyopathy? Horm Metab Res 39:672–676. doi:10.1055/s-2007-985823 30. Cai L, Kang YJ (2001) Oxidative stress and diabetic cardiomyopathy: a brief review. Cardiovasc Toxicol 1:181–193. doi: 10.1385/CT:1:3:181 31. Song Y, Wang J, Li Y et al (2005) Cardiac metallothionein synthesis in streptozotocin-induced diabetic mice, and its protection against diabetes-induced cardiac injury. Am J Pathol 167:17–26 32. Ye G, Metreveli NS, Ren J, Epstein PN (2003) Metallothionein prevents diabetes-induced deficits in cardiomyocytes by inhibiting reactive oxygen species production. Diabetes 52:777–783. doi:10.2337/diabetes.52.3.777 33. Guerra S, Leri A, Wang X et al (1999) Myocyte death in the failing human heart is gender dependent. Circ Res 85:856–866
Apoptosis (2009) 14:536–548 34. Wencker D, Chandra M, Nguyen K et al (2003) A mechanistic role for cardiac myocyte apoptosis in heart failure. J Clin Invest 111:1497–1504 35. Thorburn A (2004) Death receptor-induced cell killing. Cell Signal 16:139–144. doi:10.1016/j.cellsig.2003.08.007 36. Liao X, Wang X, Gu Y, Chen Q, Chen LY (2005) Involvement of death receptor signaling in mechanical stretch-induced cardiomyocyte apoptosis. Life Sci 77:160–174. doi:10.1016/j.lfs. 2004.11.029 37. Levine B, Kalman J, Mayer L, Fillit HM, Packer M (1990) Elevated circulating levels of tumor necrosis factor in severe chronic heart failure. N Engl J Med 323:236–241 38. Dutka DP, Elborn JS, Delamere F, Shale DJ, Morris GK (1993) Tumour necrosis factor alpha in severe congestive cardiac failure. Br Heart J 70:141–143. doi:10.1136/hrt.70.2.141 39. Ferrari R, Bachetti T, Confortini R et al (1995) Tumor necrosis factor soluble receptors in patients with various degrees of congestive heart failure. Circulation 92:1479–1486 40. Testa M, Yeh M, Lee P et al (1996) Circulating levels of cytokines and their endogenous modulators in patients with mild to severe congestive heart failure due to coronary artery disease or hypertension. J Am Coll Cardiol 28:964–971. doi:10.1016/ S0735-1097(96)00268-9 41. Giroir BP, Johnson JH, Brown T, Allen GL, Beutler B (1992) The tissue distribution of tumor necrosis factor biosynthesis during endotoxemia. J Clin Invest 90:693–698. doi:10.1172/ JCI115939 42. Kapadia S, Lee J, Torre-Amione G, Birdsall HH, Ma TS, Mann DL (1995) Tumor necrosis factor-alpha gene and protein expression in adult feline myocardium after endotoxin administration. J Clin Invest 96:1042–1052. doi:10.1172/JCI118090 43. Jeremias I, Kupatt C, Martin-Villalba A et al (2000) Involvement of CD95/Apo1/Fas in cell death after myocardial ischemia. Circulation 102:915–920 44. Torre-Amione G, Kapadia S, Lee J et al (1996) Tumor necrosis factor-alpha and tumor necrosis factor receptors in the failing human heart. Circulation 93:704–711 45. Doyama K, Fujiwara H, Fukumoto M et al (1996) Tumour necrosis factor is expressed in cardiac tissues of patients with heart failure. Int J Cardiol 54:217–225. doi:10.1016/0167-5273 (96)02607-1 46. Gilles S, Zahler S, Welsch U, Sommerhoff CP, Becker BF (2003) Release of TNF-alpha during myocardial reperfusion depends on oxidative stress and is prevented by mast cell stabilizers. Cardiovasc Res 60:608–616. doi:10.1016/j.cardiores. 2003.08.016 47. Tanaka M, Ito H, Adachi S et al (1994) Hypoxia induces apoptosis with enhanced expression of Fas antigen messenger RNA in cultured neonatal rat cardiomyocytes. Circ Res 75:426–433 48. Meldrum DR (1998) Tumor necrosis factor in the heart. Am J Physiol 274:R577–R595 49. Seko Y, Kayagaki N, Seino K, Yagita H, Okumura K, Nagai R (2002) Role of Fas/FasL pathway in the activation of infiltrating cells in murine acute myocarditis caused by Coxsackievirus B3. J Am Coll Cardiol 39:1399–1403. doi:10.1016/S0735-1097(02) 01776-X 50. Lee P, Sata M, Lefer DJ, Factor SM, Walsh K, Kitsis RN (2003) Fas pathway is a critical mediator of cardiac myocyte death and MI during ischemia–reperfusion in vivo. Am J Physiol Heart Circ Physiol 284:H456–H463 51. Li Y, Takemura G, Kosai K et al (2004) Critical roles for the Fas/Fas ligand system in postinfarction ventricular remodeling and heart failure. Circ Res 95:627–636. doi:10.1161/01.RES.000 0141528.54850.bd 52. Gomez L, Chavanis N, Argaud L et al (2005) Fas-independent mitochondrial damage triggers cardiomyocyte death after
545
53.
54.
55.
56.
57.
58.
59.
60.
61. 62.
63.
64.
65.
66.
67.
68.
69.
ischemia–reperfusion. Am J Physiol Heart Circ Physiol 289:H2153–H2158. doi:10.1152/ajpheart.00165.2005 Bhuiyan MS, Takada Y, Shioda N, Moriguchi S, Kasahara J, Fukunaga K (2008) Cardioprotective effect of vanadyl sulfate on ischemia/reperfusion-induced injury in rat heart in vivo is mediated by activation of protein kinase B and induction of FLICE-inhibitory protein. Cardiovasc Ther 26:10–23 Niu J, Azfer A, Deucher MF, Goldschmidt-Clermont PJ, Kolattukudy PE (2006) Targeted cardiac expression of soluble FAS prevents the development of heart failure in mice with cardiacspecific expression of MCP-1. J Mol Cell Cardiol 40:810–820. doi:10.1016/j.yjmcc.2006.03.010 Scarabelli TM, Stephanou A, Pasini E et al (2002) Different signaling pathways induce apoptosis in endothelial cells and cardiac myocytes during ischemia/reperfusion injury. Circ Res 90:745–748. doi:10.1161/01.RES.0000015224.07870.9A Gustafsson AB, Tsai JG, Logue SE, Crow MT, Gottlieb RA (2004) Apoptosis repressor with caspase recruitment domain protects against cell death by interfering with Bax activation. J Biol Chem 279:21233–21238. doi:10.1074/jbc.M400695200 Chen M, Won DJ, Krajewski S, Gottlieb RA (2002) Calpain and mitochondria in ischemia/reperfusion injury. J Biol Chem 277:29181–29186. doi:10.1074/jbc.M204951200 Hamacher-Brady A, Brady NR, Logue SE et al (2007) Response to myocardial ischemia/reperfusion injury involves Bnip3 and autophagy. Cell Death Differ 14:146–157. doi:10.1038/sj.cdd. 4401936 Iliodromitis EK, Lazou A, Kremastinos DT (2007) Ischemic preconditioning: protection against myocardial necrosis and apoptosis. Vasc Health Risk Manag 3:629–637 Imahashi K, Schneider MD, Steenbergen C, Murphy E (2004) Transgenic expression of Bcl-2 modulates energy metabolism, prevents cytosolic acidification during ischemia, and reduces ischemia/reperfusion injury. Circ Res 95:734–741. doi:10.1161/ 01.RES.0000143898.67182.4c Danial NN, Korsmeyer SJ (2004) Cell death: critical control points. Cell 116:205–219. doi:10.1016/S0092-8674(04)00046-7 Huang DC, Strasser A (2000) BH3-Only proteins-essential initiators of apoptotic cell death. Cell 103:839–842. doi:10.1016/ S0092-8674(00)00187-2 Reeve JL, Szegezdi E, Logue SE et al (2007) Distinct mechanisms of cardiomyocyte apoptosis induced by doxorubicin and hypoxia converge on mitochondria and are inhibited by Bcl-xL. J Cell Mol Med 11:509–520. doi:10.1111/j.1582-4934.2007.00042.x Kirshenbaum LA, de Moissac D (1997) The bcl-2 gene product prevents programmed cell death of ventricular myocytes. Circulation 96:1580–1585 Zhang D, Mott JL, Chang SW, Stevens M, Mikolajczak P, Zassenhaus HP (2005) Mitochondrial DNA mutations activate programmed cell survival in the mouse heart. Am J Physiol Heart Circ Physiol 288:H2476–H2483. doi:10.1152/ajpheart. 00670.2004 Brocheriou V, Hagege AA, Oubenaissa A et al (2000) Cardiac functional improvement by a human Bcl-2 transgene in a mouse model of ischemia/reperfusion injury. J Gene Med 2:326–333. doi:10.1002/1521-2254(200009/10)2:5\326::AID-JGM133[3.0. CO;2-1 Chen Z, Chua CC, Ho YS, Hamdy RC, Chua BH (2001) Overexpression of Bcl-2 attenuates apoptosis and protects against myocardial I/R injury in transgenic mice. Am J Physiol Heart Circ Physiol 280:H2313–H2320 Gustafsson AB, Gottlieb RA (2007) Bcl-2 family members and apoptosis, taken to heart. Am J Physiol Cell Physiol 292:C45– C51 Milner DJ, Taffet GE, Wang X et al (1999) The absence of desmin leads to cardiomyocyte hypertrophy and cardiac dilation
123
546
70.
71.
72.
73.
74.
75.
76.
77.
78.
79.
80.
81.
82.
83.
84.
85.
86.
Apoptosis (2009) 14:536–548 with compromised systolic function. J Mol Cell Cardiol 31:2063–2076. doi:10.1006/jmcc.1999.1037 Weisleder N, Taffet GE, Capetanaki Y (2004) Bcl-2 overexpression corrects mitochondrial defects and ameliorates inherited desmin null cardiomyopathy. Proc Natl Acad Sci USA 101:769–774. doi:10.1073/pnas.0303202101 Karmazyn M, Moffat MP (1993) Role of Na?/H? exchange in cardiac physiology and pathophysiology: mediation of myocardial reperfusion injury by the pH paradox. Cardiovasc Res 27:915–924. doi:10.1093/cvr/27.6.915 Zhu L, Yu Y, Chua BH, Ho YS, Kuo TH (2001) Regulation of sodium–calcium exchange and mitochondrial energetics by Bcl2 in the heart of transgenic mice. J Mol Cell Cardiol 33:2135– 2144. doi:10.1006/jmcc.2001.1476 Rouslin W, Erickson JL, Solaro RJ (1986) Effects of oligomycin and acidosis on rates of ATP depletion in ischemic heart muscle. Am J Physiol 250:H503–H508 Imahashi K, Schneider M, Steenbergen C, Murphy E (2004) BCL-2 reduces acidification and the fall in ATP during Ischaemia. Cardiovasc J S Afr 15:S3 Kubli DA, Quinsay MN, Huang C, Lee Y, Gustafsson AB (2008) Bnip3 functions as a mitochondrial sensor of oxidative stress during myocardial ischemia and reperfusion. Am J Physiol Heart Circ Physiol 295(5):H2025–H2031 Zha J, Harada H, Yang E, Jockel J, Korsmeyer SJ (1996) Serine phosphorylation of death agonist BAD in response to survival factor results in binding to 14–3-3 not BCL-X(L). Cell 87:619– 628. doi:10.1016/S0092-8674(00)81382-3 Wei MC, Zong WX, Cheng EH et al (2001) Proapoptotic BAX and BAK: a requisite gateway to mitochondrial dysfunction and death. Science 292:727–730. doi:10.1126/science.1059108 Kubli DA, Ycaza JE, Gustafsson AB (2007) Bnip3 mediates mitochondrial dysfunction and cell death through Bax and Bak. Biochem J 405:407–415. doi:10.1042/BJ20070319 Zong WX, Lindsten T, Ross AJ, MacGregor GR, Thompson CB (2001) BH3-only proteins that bind pro-survival Bcl-2 family members fail to induce apoptosis in the absence of Bax and Bak. Genes Dev 15:1481–1486. doi:10.1101/gad.897601 Capano M, Crompton M (2006) Bax translocates to mitochondria of heart cells during simulated ischaemia: involvement of AMP-activated and p38 mitogen-activated protein kinases. Biochem J 395:57–64. doi:10.1042/BJ20051654 Hamacher-Brady A, Brady NR, Gottlieb RA (2006) Enhancing macroautophagy protects against ischemia/reperfusion injury in cardiac myocytes. J Biol Chem 281:29776–29787. doi:10.1074/ jbc.M603783200 Hochhauser E, Kivity S, Offen D et al (2003) Bax ablation protects against myocardial ischemia–reperfusion injury in transgenic mice. Am J Physiol Heart Circ Physiol 284:H2351– H2359 Diwan A, Krenz M, Syed FM et al (2007) Inhibition of ischemic cardiomyocyte apoptosis through targeted ablation of Bnip3 restrains postinfarction remodeling in mice. J Clin Invest 117:2825–2833. doi:10.1172/JCI32490 Bruick RK (2000) Expression of the gene encoding the proapoptotic Nip3 protein is induced by hypoxia. Proc Natl Acad Sci USA 97:9082–9087. doi:10.1073/pnas.97.16.9082 Yurkova N, Shaw J, Blackie K et al (2008) The cell cycle factor E2F-1 activates Bnip3 and the intrinsic death pathway in ventricular myocytes. Circ Res 102:472–479. doi:10.1161/ CIRCRESAHA.107.164731 Frazier DP, Wilson A, Graham RM, Thompson JW, Bishopric NH, Webster KA (2006) Acidosis regulates the stability, hydrophobicity, and activity of the BH3-only protein Bnip3. Antioxid Redox Signal 8:1625–1634. doi:10.1089/ars.2006.8. 1625
123
87. Regula KM, Ens K, Kirshenbaum LA (2002) Inducible expression of BNIP3 provokes mitochondrial defects and hypoxia-mediated cell death of ventricular myocytes. Circ Res 91:226–231. doi:10.1161/01.RES.0000029232.42227.16 88. Vande VC, Cizeau J, Dubik D et al (2000) BNIP3 and genetic control of necrosis-like cell death through the mitochondrial permeability transition pore. Mol Cell Biol 20:5454–5468. doi: 10.1128/MCB.20.15.5454-5468.2000 89. Diwan A, Wansapura J, Syed FM, Matkovich SJ, Lorenz JN, Dorn GW II (2008) Nix-mediated apoptosis links myocardial fibrosis, cardiac remodeling, and hypertrophy decompensation. Circulation 117:396–404. doi:10.1161/CIRCULATIONAHA. 107.727073 90. Chen M, He H, Zhan S, Krajewski S, Reed JC, Gottlieb RA (2001) Bid is cleaved by calpain to an active fragment in vitro and during myocardial ischemia/reperfusion. J Biol Chem 276:30724–30728. doi:10.1074/jbc.M103701200 91. Murriel CL, Churchill E, Inagaki K, Szweda LI, Mochly-Rosen D (2004) Protein kinase Cdelta activation induces apoptosis in response to cardiac ischemia and reperfusion damage: a mechanism involving BAD and the mitochondria. J Biol Chem 279:47985–47991. doi:10.1074/jbc.M405071200 92. Latif N, Khan MA, Birks E et al (2000) Upregulation of the Bcl2 family of proteins in end stage heart failure. J Am Coll Cardiol 35:1769–1777. doi:10.1016/S0735-1097(00)00647-1 93. Di Napoli P, Taccardi AA, Grilli A et al (2003) Left ventricular wall stress as a direct correlate of cardiomyocyte apoptosis in patients with severe dilated cardiomyopathy. Am Heart J 146:1105–1111. doi:10.1016/S0002-8703(03)00445-9 94. Baldi A, Abbate A, Bussani R et al (2002) Apoptosis and postinfarction left ventricular remodeling. J Mol Cell Cardiol 34:165–174. doi:10.1006/jmcc.2001.1498 95. Sharma AK, Dhingra S, Khaper N, Singal PK (2007) Activation of apoptotic processes during transition from hypertrophy to heart failure in guinea pigs. Am J Physiol Heart Circ Physiol 293:H1384–H1390. doi:10.1152/ajpheart.00553.2007 96. Li P, Nijhawan D, Budihardjo I et al (1997) Cytochrome c and dATP-dependent formation of Apaf-1/caspase-9 complex initiates an apoptotic protease cascade. Cell 91:479–489. doi: 10.1016/S0092-8674(00)80434-1 97. Acehan D, Jiang X, Morgan DG, Heuser JE, Wang X, Akey CW (2002) Three-dimensional structure of the apoptosome: implications for assembly, procaspase-9 binding, and activation. Mol Cell 9:423–432. doi:10.1016/S1097-2765(02)00442-2 98. Jiang X, Wang X (2000) Cytochrome c promotes caspase-9 activation by inducing nucleotide binding to Apaf-1. J Biol Chem 275:31199–31203. doi:10.1074/jbc.C000405200 99. Pacher P, Szabo C (2007) Role of poly(ADP-ribose) polymerase 1 (PARP-1) in cardiovascular diseases: the therapeutic potential of PARP inhibitors. Cardiovasc Drug Rev 25:235–260. doi: 10.1111/j.1527-3466.2007.00018.x 100. de Boer RA, van Veldhuisen DJ, van der Wijk J et al (2000) Additional use of immunostaining for active caspase 3 and cleaved actin and PARP fragments to detect apoptosis in patients with chronic heart failure. J Card Fail 6:330–337. doi: 10.1054/jcaf.2000.20457 101. Vahsen N, Cande C, Briere JJ et al (2004) AIF deficiency compromises oxidative phosphorylation. EMBO J 23:4679– 4689. doi:10.1038/sj.emboj.7600461 102. Joza N, Oudit GY, Brown D et al (2005) Muscle-specific loss of apoptosis-inducing factor leads to mitochondrial dysfunction, skeletal muscle atrophy, and dilated cardiomyopathy. Mol Cell Biol 25:10261–10272. doi:10.1128/MCB.25.23.10261-10272. 2005 103. van Empel VP, Bertrand AT, van der Nagel R et al (2005) Downregulation of apoptosis-inducing factor in harlequin mutant mice
Apoptosis (2009) 14:536–548
104.
105.
106.
107.
108.
109.
110.
111.
112.
113.
114.
115.
116.
117.
118.
119.
sensitizes the myocardium to oxidative stress-related cell death and pressure overload-induced decompensation. Circ Res 96:e92–e101. doi:10.1161/01.RES.0000172081.30327.28 Norberg E, Gogvadze V, Ott M et al (2008) An increase in intracellular Ca(2?) is required for the activation of mitochondrial calpain to release AIF during cell death. Cell Death Differ 15(12):1857–1864 Daugas E, Susin SA, Zamzami N et al (2000) Mitochondrionuclear translocation of AIF in apoptosis and necrosis. FASEB J 14:729–739 Halestrap AP (2006) Calcium, mitochondria and reperfusion injury: a pore way to die. Biochem Soc Trans 34:232–237. doi: 10.1042/BST20060232 Garcia-Rivas Gde J, Carvajal K, Correa F, Zazueta C (2006) Ru360, a specific mitochondrial calcium uptake inhibitor, improves cardiac post-ischaemic functional recovery in rats in vivo. Br J Pharmacol 149:829–837. doi:10.1038/sj.bjp.0706932 Wang J, Zhang Z, Hu Y et al (2007) SEA0400, a novel Na(?)/ Ca(2 ?) exchanger inhibitor, reduces calcium overload induced by ischemia and reperfusion in mouse ventricular myocytes. Physiol Res 56:17–23 Kim GT, Chun YS, Park JW, Kim MS (2003) Role of apoptosisinducing factor in myocardial cell death by ischemia–reperfusion. Biochem Biophys Res Commun 309:619–624. doi: 10.1016/j.bbrc.2003.08.045 Song ZF, Ji XP, Li XX, Wang SJ, Wang SH, Zhang Y (2008) Inhibition of the activity of poly (ADP-ribose) polymerase reduces heart ischaemia/reperfusion injury via suppressing JNKmediated AIF translocation. J Cell Mol Med 12:1220–1228. doi: 10.1111/j.1582-4934.2008.00183.x Roy N, Deveraux QL, Takahashi R, Salvesen GS, Reed JC (1997) The c-IAP-1 and c-IAP-2 proteins are direct inhibitors of specific caspases. EMBO J 16:6914–6925. doi:10.1093/emboj/ 16.23.6914 Deveraux QL, Takahashi R, Salvesen GS, Reed JC (1997) Xlinked IAP is a direct inhibitor of cell-death proteases. Nature 388:300–304. doi:10.1038/40901 Liu HR, Gao E, Hu A et al (2005) Role of Omi/HtrA2 in apoptotic cell death after myocardial ischemia and reperfusion. Circulation 111:90–96. doi:10.1161/01.CIR.0000151613.90994.17 Bhuiyan MS, Fukunaga K (2007) Inhibition of HtrA2/Omi ameliorates heart dysfunction following ischemia/reperfusion injury in rat heart in vivo. Eur J Pharmacol 557:168–177. doi: 10.1016/j.ejphar.2006.10.067 Chua CC, Gao J, Ho YS et al (2007) Overexpression of IAP-2 attenuates apoptosis and protects against myocardial ischemia/ reperfusion injury in transgenic mice. Biochim Biophys Acta 1773:577–583 Ikeda S, Ozaki K (1997) Action of mitochondrial endonuclease G on DNA damaged by L-ascorbic acid, peplomycin, and cisdiamminedichloroplatinum (II). Biochem Biophys Res Commun 235:291–294. doi:10.1006/bbrc.1997.6786 Javadov S, Choi A, Rajapurohitam V, Zeidan A, Basnakian AG, Karmazyn M (2008) NHE-1 inhibition-induced cardioprotection against ischaemia/reperfusion is associated with attenuation of the mitochondrial permeability transition. Cardiovasc Res 77:416–424. doi:10.1093/cvr/cvm039 Bahi N, Zhang J, Llovera M, Ballester M, Comella JX, Sanchis D (2006) Switch from caspase-dependent to caspase-independent death during heart development: essential role of endonuclease G in ischemia-induced DNA processing of differentiated cardiomyocytes. J Biol Chem 281:22943–22952. doi: 10.1074/jbc.M601025200 Szegezdi E, Logue SE, Gorman AM, Samali A (2006) Mediators of endoplasmic reticulum stress-induced apoptosis. EMBO Rep 7:880–885. doi:10.1038/sj.embor.7400779
547 120. Xu C, Bailly-Maitre B, Reed JC (2005) Endoplasmic reticulum stress: cell life and death decisions. J Clin Invest 115:2656– 2664. doi:10.1172/JCI26373 121. Okada K, Minamino T, Tsukamoto Y et al (2004) Prolonged endoplasmic reticulum stress in hypertrophic and failing heart after aortic constriction: possible contribution of endoplasmic reticulum stress to cardiac myocyte apoptosis. Circulation 110:705–712. doi:10.1161/01.CIR.0000137836.95625.D4 122. Szegezdi E, Duffy A, O’Mahoney ME et al (2006) ER stress contributes to ischemia-induced cardiomyocyte apoptosis. Biochem Biophys Res Commun 349:1406–1411. doi:10.1016/ j.bbrc.2006.09.009 123. Thuerauf DJ, Marcinko M, Gude N, Rubio M, Sussman MA, Glembotski CC (2006) Activation of the unfolded protein response in infarcted mouse heart and hypoxic cultured cardiac myocytes. Circ Res 99:275–282. doi:10.1161/01.RES.0000233 317.70421.03 124. Azfer A, Niu J, Rogers LM, Adamski FM, Kolattukudy PE (2006) Activation of endoplasmic reticulum stress response during the development of ischemic heart disease. Am J Physiol Heart Circ Physiol 291:H1411–H1420. doi:10.1152/ajpheart. 01378.2005 125. Jackson CV, McGrath GM, Tahiliani AG, Vadlamudi RV, McNeill JH (1985) A functional and ultrastructural analysis of experimental diabetic rat myocardium.Manifestation of a cardiomyopathy. Diabetes 34:876–883. doi:10.2337/diabetes.34. 9.876 126. Hamada H, Suzuki M, Yuasa S et al (2004) Dilated cardiomyopathy caused by aberrant endoplasmic reticulum quality control in mutant KDEL receptor transgenic mice. Mol Cell Biol 24:8007–8017. doi:10.1128/MCB.24.18.8007-8017.2004 127. Breckenridge DG, Germain M, Mathai JP, Nguyen M, Shore GC (2003) Regulation of apoptosis by endoplasmic reticulum pathways. Oncogene 22:8608–8618. doi:10.1038/sj.onc.1207108 128. Qi X, Vallentin A, Churchill E, Mochly-Rosen D (2007) deltaPKC participates in the endoplasmic reticulum stressinduced response in cultured cardiac myocytes and ischemic heart. J Mol Cell Cardiol 43:420–428. doi:10.1016/j.yjmcc. 2007.07.061 129. Toth A, Jeffers JR, Nickson P et al (2006) Targeted deletion of puma attenuates cardiomyocyte death and improves cardiac function during ischemia-reperfusion. Am J Physiol Heart Circ Physiol 291(1):H52–H60 130. Nickson P, Toth A, Erhardt P (2007) PUMA is critical for neonatal cardiomyocyte apoptosis induced by endoplasmic reticulum stress. Cardiovasc Res 73:48–56. doi:10.1016/j.cardiores.2006. 10.001 131. Scorrano L, Oakes SA, Opferman JT et al (2003) BAX and BAK regulation of endoplasmic reticulum Ca2?: a control point for apoptosis. Science 300:135–139. doi:10.1126/science.1081208 132. Luo X, Budihardjo I, Zou H, Slaughter C, Wang X (1998) Bid, a Bcl2 interacting protein, mediates cytochrome c release from mitochondria in response to activation of cell surface death receptors. Cell 94:481–490. doi:10.1016/S0092-8674(00)81589-5 133. Li H, Zhu H, Xu CJ, Yuan J (1998) Cleavage of BID by caspase 8 mediates the mitochondrial damage in the Fas pathway of apoptosis. Cell 94:491–501. doi:10.1016/S00928674(00)81590-1 134. Date T, Mochizuki S, Belanger AJ et al (2003) Differential effects of membrane and soluble Fas ligand on cardiomyocytes: role in ischemia/reperfusion injury. J Mol Cell Cardiol 35:811– 821. doi:10.1016/S0022-2828(03)00139-1 135. Haudek SB, Taffet GE, Schneider MD, Mann DL (2007) TNF provokes cardiomyocyte apoptosis and cardiac remodeling through activation of multiple cell death pathways. J Clin Invest 117:2692–2701. doi:10.1172/JCI29134
123
548 136. Kalai M, Lamkanfi M, Denecker G et al (2003) Regulation of the expression and processing of caspase-12. J Cell Biol 162:457–467. doi:10.1083/jcb.200303157 137. Bajaj G, Sharma RK (2006) TNF-alpha-mediated cardiomyocyte apoptosis involves caspase-12 and calpain. Biochem Biophys Res Commun 345:1558–1564. doi:10.1016/j.bbrc.2006. 05.059 138. Gyan E, Frisan E, Beyne-Rauzy O et al (2008) Spontaneous and Fas-induced apoptosis of low-grade MDS erythroid precursors involves the endoplasmic reticulum. Leukemia 22:1864–1873. doi:10.1038/leu.2008.172 139. Breckenridge DG, Stojanovic M, Marcellus RC, Shore GC (2003) Caspase cleavage product of BAP31 induces mitochondrial fission through endoplasmic reticulum calcium signals, enhancing cytochrome c release to the cytosol. J Cell Biol 160:1115–1127. doi:10.1083/jcb.200212059 140. Mathai JP, Germain M, Shore GC (2005) BH3-only BIK regulates BAX, BAK-dependent release of Ca2? from endoplasmic reticulum stores and mitochondrial apoptosis during stressinduced cell death. J Biol Chem 280:23829–23836. doi:10.1074/ jbc.M500800200 141. Nakai A, Yamaguchi O, Takeda T et al (2007) The role of autophagy in cardiomyocytes in the basal state and in response to hemodynamic stress. Nat Med 13:619–624. doi:10.1038/ nm1574 142. Matsui Y, Takagi H, Qu X et al (2007) Distinct roles of autophagy in the heart during ischemia and reperfusion: roles of AMP-activated protein kinase and Beclin 1 in mediating autophagy. Circ Res 100:914–922. doi:10.1161/01.RES.0000 261924.76669.36 143. Zhu H, Tannous P, Johnstone JL et al (2007) Cardiac autophagy is a maladaptive response to hemodynamic stress. J Clin Invest 117:1782–1793. doi:10.1172/JCI27523
123
Apoptosis (2009) 14:536–548 144. Yan L, Vatner DE, Kim SJ et al (2005) Autophagy in chronically ischemic myocardium. Proc Natl Acad Sci USA 102:13807–13812. doi:10.1073/pnas.0506843102 145. Yousefi S, Perozzo R, Schmid I et al (2006) Calpain-mediated cleavage of Atg5 switches autophagy to apoptosis. Nat Cell Biol 8:1124–1132. doi:10.1038/ncb1482 146. Pyo JO, Jang MH, Kwon YK et al (2005) Essential roles of Atg5 and FADD in autophagic cell death: dissection of autophagic cell death into vacuole formation and cell death. J Biol Chem 280:20722–20729. doi:10.1074/jbc.M413934200 147. Pattingre S, Tassa A, Qu X et al (2005) Bcl-2 antiapoptotic proteins inhibit Beclin 1-dependent autophagy. Cell 122:927– 939. doi:10.1016/j.cell.2005.07.002 148. Maiuri MC, Criollo A, Tasdemir E et al (2007) BH3-only proteins and BH3 mimetics induce autophagy by competitively disrupting the interaction between Beclin 1 and Bcl-2/Bcl-X(L). Autophagy 3:374–376 149. Rashmi R, Pillai SG, Vijayalingam S, Ryerse J, Chinnadurai G (2008) BH3-only protein BIK induces caspase-independent cell death with autophagic features in Bcl-2 null cells. Oncogene 27:1366–1375. doi:10.1038/sj.onc.1210783 150. Akar U, Chaves-Reyez A, Barria M et al (2008) Silencing of Bcl-2 expression by small interfering RNA induces autophagic cell death in MCF-7 breast cancer cells. Autophagy 4:669–679 151. Ray R, Chen G, Vande VC et al (2000) BNIP3 heterodimerizes with Bcl-2/Bcl-X(L) and induces cell death independent of a Bcl-2 homology 3 (BH3) domain at both mitochondrial and nonmitochondrial sites. J Biol Chem 275:1439–1448. doi: 10.1074/jbc.275.2.1439
