Inhibition of p53 after acute myocardial infarction: Reduction of apoptosis is counteracted by disturbed scar formation and cardiac rupture
ABSTRACT Cardiomyocyte apoptosis, partially mediated through p53 signaling pathway, plays a crucial role in the progression of pathological remodeling and heart failure following myocardial infarction (MI). We hypothesized that pifithrin-alpha (PFTa), a synthetic p53 inhibitor, would suppress cardiac apoptosis through the disruption of p53-dependent transcriptional activation and thereby improve heart function in a mouse model of MI. In our experiments we show that PFTa blocked p53 transcriptional activity and attenuated H(2)O(2)-induced cardiac apoptosis in cultured neonatal rat cardiomyocytes. Additionally, administration of PFTa in mice after acute MI in vivo led to a significant reduction of cardiomyocyte apoptosis but in parallel caused an increase of infarct size and significantly reduced 7-day survival rate. Subsequent analysis revealed significantly reduced proliferation and cell number, diminished collagen deposition, and elevated MMP-2 activity at the infarct zone of PFTa-treated hearts. In homozygous p53 deficient mice (p53(-/-)), however, PFTa treatment did not interfere with scar formation and did not increase MMP-2 activity after MI. Collectively, our data suggest that although p53-inhibition through PFTa reduces cardiomyocyte apoptosis, in the setting of acute MI this assumed beneficial effect is severely counteracted by the adverse remodeling of the infarct zone. PFTa increases MMP-2 activity in a p53-dependent manner, which seems a major contributor to instability of the forming scar and consequently leads to infarct progression and ventricular rupture.
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ABSTRACT: β-adrenergic receptor stimulation plays an important role in cardiomyocyte stress responses, which may result in apoptosis and cardiovascular degeneration. We previously demonstrated that toxicity of the β-adrenergic agonist isoproterenol on H9c2 cardiomyoblasts depends on the stage of cell differentiation. We now investigate β-adrenergic receptor downstream signaling pathways and stress responses that explain the impact of muscle cell differentiation on hyper-β-adrenergic stimulation-induced cytotoxicity. When incubated with isoproterenol, differentiated H9c2 muscle cells have increased cytosolic calcium, cyclic-adenosine monophosphate content and oxidative stress, as well as mitochondrial depolarization, increased superoxide anion, loss of subunits from the mitochondrial respiratory chain, decreased Bcl-xL content, increased p53 and phosphorylated-p66Shc as well as activated caspase-3. Undifferentiated H9c2 cells incubated with isoproterenol showed increased Bcl-xL protein and increased superoxide dismutase 2 which may act as protective mechanisms. We conclude that the differentiation of H9c2 is associated with differential regulation of stress responses, which impact the toxicity of several agents, namely those acting through β-adrenergic receptors and resulting in mitochondrial disruption in differentiated cells only.The international journal of biochemistry & cell biology 08/2013; 45(11). DOI:10.1016/j.biocel.2013.08.006 · 4.24 Impact Factor
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ABSTRACT: Myocardial infarction leads to heart failure and death. Ischaemic preconditioning (PreC) and postconditioning (PostC) reduce infarct size in animal models and human. Zac1 was identified as the only gene related to apoptosis and jointly down-regulated upon PreC and PostC. The aim of our study was to investigate the role of Zac1 down-regulation during ischaemia-reperfusion (I/R) in vivo. C57BL/6 mice were submitted to myocardial I/R injury, PreC, or PostC protocols. QPCR and immunochemistry showed that Zac1 expression was down-regulated both at the transcriptional and the protein levels upon PreC and PostC. Zac1(-/-) Knockout mice (n = 7) developed smaller infarcts (54%) than Zac1(+/+) littermates (n = 8) and decreased apoptosis (61.7%) in the ischaemic part of the left ventricle during I/R (Zac1(-/-), n = 6 vs. Zac1(+/+), n = 7; P = 0.0012). Mutants showed under control conditions a decrease of 53.9% in mRNA of Daxx, a pro-apoptotic protein playing a key role in I/R injuries (4.81 ± 0.77, n = 4 Zac1(-/-) mice vs. 10.44 ± 3.5, n = 7 Zac1(+/+) mice; P = 0.0121). Our study shows for the first time that Zac1 is down-regulated both at the transcriptional and protein levels upon PreC and PostC in wild-type mice. Moreover, inactivation of Zac1 in vivo is associated with a decreased amount of Daxx transcripts and, upon I/R injury, decreased infarct size and apoptosis. Altogether, our results show that Zac1 down-regulation plays a key role during cardioprotection against I/R injury and support the concept that cardioprotection regulates a network of interacting pro-apoptotic genes including Zac1 and Daxx.Cardiovascular Research 11/2011; 94(2):351-8. DOI:10.1093/cvr/cvr310 · 5.81 Impact Factor
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ABSTRACT: The tumour suppressor BRCA1 is mutated in familial breast and ovarian cancer but its role in protecting other tissues from DNA damage has not been explored. Here we show a new role for BRCA1 as a gatekeeper of cardiac function and survival. In mice, loss of BRCA1 in cardiomyocytes results in adverse cardiac remodelling, poor ventricular function and higher mortality in response to ischaemic or genotoxic stress. Mechanistically, loss of cardiomyocyte BRCA1 results in impaired DNA double-strand break repair and activated p53-mediated pro-apoptotic signalling culminating in increased cardiomyocyte apoptosis, whereas deletion of the p53 gene rescues BRCA1-deficient mice from cardiac failure. In human adult and fetal cardiac tissues, ischaemia induces double-strand breaks and upregulates BRCA1 expression. These data reveal BRCA1 as a novel and essential adaptive response molecule shielding cardiomyocytes from DNA damage, apoptosis and heart dysfunction. BRCA1 mutation carriers, in addition to risk of breast and ovarian cancer, may be at a previously unrecognized risk of cardiac failure.Nature Communications 12/2011; 2:593. DOI:10.1038/ncomms1601 · 10.74 Impact Factor