Cardiomyocyte Apoptosis In Response Research Articles

Nrf2 Promotes Inflammation in Early Myocardial Ischemia-Reperfusion via Recruitment and Activation of Macrophages.

Cardiomyocyte apoptosis in response to inflammation is a primary cause of myocardial ischemia-reperfusion injury (IRI). Nuclear factor erythroid 2 like 2 (Nrf2) reportedly plays an important role in myocardial IRI, but the underlying mechanism remains obscure. Expression data from the normal heart tissues of mice or heart tissues treated with reperfusion for 6 h after ischemia (IR6h) were acquired from the GEO database; changes in biological function and infiltrating immune cells were analyzed. The binding between the molecules was verified by chromatin immunoprecipitation sequencing. Based on confirmation that early myocardial ischemia-reperfusion (myocardial ischemia/reperfusion for 6 hours, IR6h) promoted myocardial apoptosis and inflammatory response, we found that Nrf2, cooperating with Programmed Cell Death 4, promoted transcription initiation of C-C Motif Chemokine Ligand 3 (Ccl3) in myocardial tissues of mice treated with IR6h. Moreover, Ccl3 contributed to the high signature score of C-C motif chemokine receptor 1 (Ccr1)-positive macrophages. The high signature score of Ccr1-positive macrophages leads to the release of pro-inflammatory factors interleukin 1 beta and interleukin 6. This study is the first to elucidate the damaging effect of Nrf2 via remodeling of the immune microenvironment in early myocardial ischemia-reperfusion, which provides us with new perspectives and treatment strategies for myocardial ischemia-reperfusion.

HIF-1/AKT Signaling-Activated PFKFB2 Alleviates Cardiac Dysfunction and Cardiomyocyte Apoptosis in Response to Hypoxia.

Myocardial infarction (MI) is the most prevalent disease with severe mortality, and hypoxia-induced cardiac injury and cardiomyocyte apoptosis are the significant and harmful consequences of this disease. The cross talk between hypoxia signaling and glycolysis energy flux plays a critical role in modulating MI-related heart disorder. However, the underlying mechanism remains unclear. Here, we aimed to explore the effect of a key glycolytic enzyme of 6-phosphofructo-2-kinase/fructose-2, 6-bisphosphatase 2 (PFKFB2) on cardiac dysfunction and apoptosis in response to hypoxia. Our data demonstrated that the mRNA and protein expression of PFKFB2 were significantly elevated in the MI mice. The MI treatment promoted the activation of PFKFB2 in vivo, as presented by the remarkably increased phosphorylation levels of PFKFB2. PFKFB2 depletion enhanced MI-induced cardiac dysfunction and cardiomyocyte apoptosis in the MI mouse model. Moreover, hypoxia treatment dramatically upregulated the expression and activation of PFKFB2 in a time-dependent manner in cardiomyocytes. Hypoxia-stimulated PFKFB2 relieved hypoxia-induced cardiomyocyte apoptosis in vitro. PFKFB2 activated the fructose-2, 6-bisphosphate (Fru-2, 6-p2) /PFK/anaerobic adenosine triphosphate (ATP) glycolysis energy flux in response to hypoxia in cardiomyocytes. Mechanically, hypoxia-activated PFKFB2 by stimulating the hypoxia-inducible factor 1 (HIF-1) /ATK signaling. Thus, we conclude that HIF-1/AKT axis-activated PFKFB2 alleviates cardiac dysfunction and cardiomyocyte apoptosis in response to hypoxia. Our finding presents a new insight into the mechanism by which HIF-1/AKT/PFKFB2 signaling modulates MI-related heart disorder under the hypoxia condition, providing potential therapeutic targets and strategy for hypoxia-related myocardial injury.

GSK3β and MCL-1 mediate cardiomyocyte apoptosis in response to high glucose.

Gestational diabetes mellitus is a risk factor for congenital heart defects. Our previous results indicated that a decrease in myocardial cells and an increase in apoptotic cells leads to heart defects under hyperglycemia, but much work remains to elucidate this important mechanism of myocardial cell apoptosis induced by high glucose (HG). In this study, we found that a decrease in GSK3β phosphorylation on Ser9 occurred concomitantly with HG-induced cardiomyocyte apoptosis and in the heart tissues of the offspring of diabetic rats in vitro and in vivo. Decreases in GSK3β (Ser9) phosphorylation in response to HG were remarkably restored after treatment with SC79, an activator of the Akt signaling pathway. SB216763, an effective inhibitor of the GSK3β signaling pathway, suppressed HG-induced apoptosis in cardiomyocytes. Further studies showed a decrease in the expression of the anti-apoptotic protein MCL-1 was associated with GSK3β-mediated apoptosis. MCL-1 overexpression partly inhibits HG-induced apoptosis in cardiomyocytes. Herein, this study revealed the roles of GSK3β and MCL-1 in modulating HG-induced cardiomyocyte apoptosis and maternal diabetes-induced abnormalities.

Novel insights into the role of mitochondrial fusion and fission in cardiomyocyte apoptosis induced by ischemia/reperfusion.

As the main source of energy in the body, mitochondria are highly dynamic organelles, which are constantly going through fusion and fission. The fine balance of mitochondrial fusion and fission plays an important role in maintaining the stability of cardiomyocyte homeostasis. The processes of mitochondrial fusion and fission are very complex, which is mediated by fusion and fission proteins. Disruptions in these processes through controlling fusion and fission proteins affect mitochondrial functions and cardiomyocyte survival. Ischemia/reperfusion (I/R) can regulate the expression and post-translational modifications of fusion and fission proteins thereby inducing the abnormality of mitochondrial fusion and fission and cardiomyocyte apoptosis. Furthermore, intervention with the expression and function of fusion and fission proteins influences on cardiomyocyte apoptosis under I/R conditions. In this review, we focus on the current developments in the effects of mitochondrial fusion and fission on cardiomyocyte functions, the implications for cardiomyocyte apoptosis in response to I/R, and possible mechanisms. And we review their roles as a potential therapeutic target for treating I/R-induced cardiomyocyte injury.

Role of GAB1/PI3K/AKT signaling high glucose-induced cardiomyocyte apoptosis

Gestational diabetes mellitus (GDM) is a risk factor for abnormal heart development. Previous work showed that a decrease of myocardial cells and an increase of apoptotic cells leading to heart defects under hyperglycemia, and many genes and protein have been found to play important roles in cardiomyocyte apoptosis. However, there are still many blind nodes in HG-induced cardiac apoptosis. Our study showed that down-regulation of GAB1 occurred concurrently with HG-induced cardiomyocytes apoptosis and in the heart tissues of offspring of diabetic rats in vitro and in vivo. MTT and apoptosis assay showed GAB1 played a key role in mediating HG-induced apoptosis of cardiomyocytes. Down-regulation of XIAP and increased activities of Caspase3/7 was associated with GAB1-mediated cardiomyocyte apoptosis in response to HG treatment. Further study showed that the phosphorylation levels of AKT (Ser473) decreased after HG treatment. Over-expression of GAB1 resisted the reduction in AKT phosphorylation in response to HG. LY294002, which is an effective inhibitor of the PI3K/AKT signaling pathway, partly inhibited GAB1 to suppress apoptosis induced by HG in cardiomyocytes, and partly suppressed GAB1 to resist the decrease of XIAP in response to HG, indicating AKT signaling, XIAP, and Caspase3/7 participated in GAB1-mediated cardiomyocyte apoptosis in response to HG. Generally, we demonstrate a novel role of GAB1 and its down-stream signaling PI3K/AKT for modulating cardiomyocyte apoptosis in response to high glucose in vitro and vivo.

ROCK1/p53/NOXA signaling mediates cardiomyocyte apoptosis in response to high glucose in vitro and vivo

Gestational diabetes mellitus is a risk factor for congenital heart defects; however, the molecular basis of the congenital heart anomalies remains obscure. Previous reports showed a positive correlation between abnormal cardiomyocyte apoptosis and ventricular wall thinness, one type of congenital heart anomaly. This work explored the expression pattern and molecular mechanism of the Rho-associated coiled-coil containing protein kinase 1 (ROCK1) gene in cardiomyocyte apoptosis and genesis of ventricular wall thinness. In this report, we found a marked increase in the number of apoptotic cardiomyocytes in response to high glucose (HG) treatment. Moreover, up-regulation of ROCK1 expression observed in diabetic offspring compared with controls was potentially associated with cardiomyocyte apoptosis and the ventricular wall thinness. Further investigation showed that p53 and NOXA protein levels increased during ROCK1-meidated apoptosis in response to HG. In response to HG, whereby ROCK1 phosphorylated p53 at Ser15 to up-regulate its protein level. Furthermore, we found that p53 mediated the expression of NOXA during HG-induced apoptosis, and histone acetyltransferase p300 participated in this process. These findings reveal a novel regulatory mechanism of ROCK1/p53/NOXA signaling in modulating cardiomyocyte apoptosis in vitro and maternal diabetes-induced congenital heart defects in vivo.

By Targeting Stat3 microRNA-17-5p Promotes Cardiomyocyte Apoptosis in Response to Ischemia Followed by Reperfusion

Background: Several studies have confirmed the role of microRNAs in regulating ischemia/reperfusion-induced cardiac injury (I/R-I). MiR-17-5p has been regarded as an oncomiR in the development of cancer. However, its potential role in cardiomyocytes has not been exploited. The aim of this study is to investigate the role of miR-17-5p in I/R-I and the underlying mechanism through targeting Stat3, a key surviving factor in cardiomyocytes. Methods: MTT (3-[4, 5-dimethylthiazol-2-yl]-2, 5 diphenyl tetrazolium bromide) assay was used to detect the cell viability. ELISA and TUNEL were performed to measure apoptosis of neonatal rat ventricular cardiomyocytes (NRVCs). Infarct area was estimated by TTC (triphenyltetrazolium chloride) and Evans blue staining. Western blot analysis was employed to detect the Stat3 and p-Stat3 levels and real-time RT-PCR was used to quantify miR-17-5p level. Results: The miR-17-5p level was significantly up-regulated in I/R-I mice and in NRVCs under oxidative stress. Overexpression of miR-17-5p aggravated cardiomyocyte injury with reduced cell viability and enhanced apoptotic cell death induced by H₂O₂, whereas inhibition of miR-17-5p by its antisense AMO-17-5p abrogated the deleterious changes. Moreover, the locked nucleic acid-modified antisense (LNA-anti-miR-17-5p) markedly decreased the infarct area and apoptosis induced by I/R-I in mice. Furthermore, overexpression of miR-17-5p diminished the p-Stat3 level in response to H₂O_2. The results from Western blot analysis and luciferase reporter gene assay confirmed Stat3 as a target gene for miR-17-5p. Conclusion: Upregulation of miR-17-5p promotes apoptosis induced by oxidative stress via targeting Stat3, accounting partially for I/R-I.

Glyceraldehyde-3-Phosphate Dehydrogenase Interacts with Proapoptotic Kinase Mst1 to Promote Cardiomyocyte Apoptosis

Mammalian sterile 20-like kinase 1 (Mst1) is a critical component of the Hippo signaling pathway, which regulates a variety of biological processes ranging from cell contact inhibition, organ size control, apoptosis and tumor suppression in mammals. Mst1 plays essential roles in the heart disease since its activation causes cardiomyocyte apoptosis and dilated cardiomyopathy. However, the mechanism underlying Mst1 activation in the heart remains unknown. In a yeast two-hybrid screen of a human heart cDNA library with Mst1 as bait, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) was identified as an Mst1-interacting protein. The interaction of GAPDH with Mst1 was confirmed by co-immunoprecipitation in both co-transfected HEK293 cells and mouse heart homogenates, in which GAPDH interacted with the kinase domain of Mst1, whereas the C-terminal catalytic domain of GAPDH mediated its interaction with Mst1. Moreover, interaction of Mst1 with GAPDH caused a robust phosphorylation of GAPDH and markedly increased the Mst1 activity in cells. Chelerythrine, a potent inducer of apoptosis, substantially increased the nuclear translocation and interaction of GAPDH and Mst1 in cardiomyocytes. Overexpression of GAPDH significantly augmented the Mst1 mediated apoptosis, whereas knockdown of GAPDH markedly attenuated the Mst1 activation and cardiomyocyte apoptosis in response to either chelerythrine or hypoxia/reoxygenation. These findings reveal a novel function of GAPDH in Mst1 activation and cardiomyocyte apoptosis and suggest that disruption of GAPDH interaction with Mst1 may prevent apoptosis related heart diseases such as heart failure and ischemic heart disease.

Abstract 16890: WW45 is Required for Mst1-Dependent Inactivation of YAP and Promotion of Myocardial Damage During Ischemia-Reperfusion

The mammalian homolog of Drosophila Hippo, Mst1, is a kinase which negatively regulates cardiomyocyte (CM) growth and survival. Mst1 promotes CM apoptosis in response to oxidative stress and mediates myocardial ischemia-reperfusion (I/R) injury. In Drosophila , the adaptor protein Salvador is required for activation and function of Hippo. We investigated the role of the mammalian homolog of Salvador, WW45, in the regulation of Mst1 activity in the heart. To address this issue, we studied the cardiac phenotype of cardiac-specific WW45 knock-out (W-cKO) mice. At baseline, W-cKO mice were characterized by a mild increase in LV weight/body weight compared to controls (3.44 ± 0.13 vs. 2.92 ± 0.10 mg/g; p<0.05) and normal cardiac function, suggesting that endogenous WW45 negatively regulates baseline growth of the heart. After I/R (30 minutes/24 hours), W-cKO mice exhibited a significantly smaller infarct size/area at risk than controls (20.4 ± 6.0 vs. 38.2 ± 4.5%; p<0.05). Interestingly, Mst1 activation, as evaluated by its phosphorylation status (Thr183), was significantly reduced in W-cKO mice both at baseline (0.5 ± 0.01 fold, p<0.05) and during reperfusion (0.37 ± 0.04 fold, p<0.05), indicating that WW45 is required for Mst1 activation. Co-immunoprecipitation analysis showed that WW45 physically interacts with Mst1 in CMs. We further evaluated whether downregulation of WW45 affects the phosphorylation status (Ser127) and the accumulation of Yes-associated protein (YAP), a transcription factor co-factor which promotes cellular growth and survival. YAP is phosphorylated by the Hippo pathway, and, upon its phosphorylation, YAP is exported from the nucleus and degraded. The level of YAP was increased in the hearts of W-cKO mice at baseline (2.6 ± 0.03 fold, p<0.05) and during reperfusion (4.2± 0.16 fold, p<0.05), and its relative phosphorylation status was decreased (-64% and -75%, p<0.05), indicating that WW45 positively regulates phosphorylation of YAP. There was a significant increase in nuclear localization of YAP during I/R in W-cKO CMs compared to in control CMs (2.2 ± 0.26 fold, p<0.05). In conclusion, our data suggest that endogenous WW45 is required for Mst1-dependent inactivation of YAP and promotion of myocardial damage during I/R.

Akt2 Regulates Cardiac Metabolism and Cardiomyocyte Survival

The Akt family of serine-threonine kinases participates in diverse cellular processes, including the promotion of cell survival, glucose metabolism, and cellular protein synthesis. All three known Akt family members, Akt1, Akt2 and Akt3, are expressed in the myocardium, although Akt1 and Akt2 are most abundant. Previous studies demonstrated that Akt1 and Akt3 overexpression results in enhanced myocardial size and function. Yet, little is known about the role of Akt2 in modulating cardiac metabolism, survival, and growth. Here, we utilize murine models with targeted disruption of the akt2 or the akt1 genes to demonstrate that Akt2, but not Akt1, is required for insulin-stimulated 2-[(3)H]deoxyglucose uptake and metabolism. In contrast, akt2(-/-) mice displayed normal cardiac growth responses to provocative stimulation, including ligand stimulation of cultured cardiomyocytes, pressure overload by transverse aortic constriction, and myocardial infarction. However, akt2(-/-) mice were found to be sensitized to cardiomyocyte apoptosis in response to ischemic injury, and apoptosis was significantly increased in the peri-infarct zone of akt2(-/-) hearts 7 days after occlusion of the left coronary artery. These results implicate Akt2 in the regulation of cardiomyocyte metabolism and survival.

Dual actions of the Galpha(q) agonist Pasteurella multocida toxin to promote cardiomyocyte hypertrophy and enhance apoptosis susceptibility.

Previous attempts to delineate the consequences of Galpha (q) activation in cardiomyocytes relied largely on molecular strategies in cultures or transgenic mice. Modest levels of wild-type Galpha(q) overexpression induce stable cardiac hypertrophy, whereas intense Galpha(q) stimulation induces cardiomyocyte apoptosis. The precise mechanism(s) whereby traditional targets of Galpha (q) subunits that induce hypertrophy also trigger cardiomyocyte apoptosis is not obvious and is explored with recombinant Pasteurella multocida toxin (rPMT, a Galpha(q) agonist). Cells cultured with rPMT display cardiomyocyte enlargement, sarcomeric organization, and increased atrial natriuretic factor expression in association with activation of phospholipase C, novel protein kinase C (PKC) isoforms, extracellular signal-regulated protein kinase (ERK), and (to a lesser extent) JNK/p38-MAPK. rPMT stimulates the ERK cascade via epidermal growth factor (EGF) receptor transactivation in cardiac fibroblasts, but EGF receptor transactivation plays no role in ERK activation in cardiomyocytes. Surprisingly, rPMT (or novel PKC isoform activation by PMA) decreases basal Akt phosphorylation; rPMT prevents Akt phosphorylation by EGF or IGF-1 and functionally augments cardiomyocyte apoptosis in response to H2O2. These results identify a Galpha(q)-PKC pathway that represses basal Akt phosphorylation and impairs Akt stimulation by survival factors. Because inhibition of Akt enhances cardiomyocyte susceptibility to apoptosis, this pathway is predicted to contribute to the transition from hypertrophy to cardiac decompensation and could be targeted for therapy in heart failure.

Calcineurin, Mitochondrial Membrane Potential, and Cardiomyocyte Apoptosis

Mitochondria comprise ≈30% of the total intracellular volume within a mammalian cardiomyocyte.1 2 Not surprisingly, subtle alterations in mitochondrial function or membrane potential can have a dramatic influence on cardiomyocyte energy production and, ultimately, the health of an individual cell. Indeed, cellular injury or stress stimulation directly elicits alterations in mitochondrial architecture, membrane potential, and oxidative capacity, which are associated with an irreversible loss of mitochondrial matrix contents and integral membrane protein constituents such as cytochrome c oxidase.3 The release of cytochrome c and/or mitochondrial permeability transition directly mediates cellular apoptosis through calcium-sensitive proteases or through coupling proteins that coordinate the activation of caspases and DNA fragmentation enzymes.3 Given the high intracellular content of mitochondria in cardiomyocytes and the unabated requirement for high-energy phosphate carriers to maintain ionic gradients and active force generation, coordinated disturbances in mitochondrial function can dramatically affect cell survival. Recent investigation has suggested an emerging paradigm whereby stress-responsive intracellular signaling pathways directly and indirectly influence mitochondrial membrane potential, oxidative capacity, and the coupling of apoptosis initiating factors. For example, stress-responsive signaling through the c-Jun N-terminal kinases (JNKs) has been shown to initiate apoptosis in certain cell types by directly influencing proteins within the mitochondrial membranes.4 In addition, increased expression of the mitochondrial stabilizing Bcl proteins can be transcriptionally regulated through stress-responsive signaling pathways, which subsequently antagonize mitochondrial dysfunction and cytochrome c release.5 Activation of the intracellular kinase Akt also directly antagonizes mitochondrial-directed apoptosis by phosphorylating the mitochondrial destabilizing protein Bad, reducing cytochrome c release and caspase activation.6 Lastly, activation of nuclear factor-κB (NF-κB) signaling induces expression of stress-adaptive proteins such as Bcl-2, antioxidants, and calcium-regulating proteins.7 In general, signaling pathways such as the stress- and mitogen-activated protein kinases (SAPKs and MAPKs), protein kinase C (PKC), Akt, NF-κB, and the …