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: The hyperacute rejection reaction of xenogeneic organs is supposed to be triggered by xenoreactive natural antibodies of the recipient organism. In an experimental set-up allowing for rapid medium exchange, primary cultures of spontaneously beating neonatal rat cardiomyocytes were challenged with dialyzed human serum containing xenoreactive natural antibodies. After adding the serum specimens, a reproducible pattern of disturbed contractility was observed: following an initial increase in beating frequency, spontaneous contractions stopped completely. This standstill was reversible in all experiments. No signs of permanent cytotoxicity were observed. The temporary cessation of contractions was prevented by raising extracellular calcium concentration, but not by extracellular electrical stimulation. After absorption of xenoreactive natural antibodies, cellular contractions ensued without interruption. Inactivated serum specimens produced similar effects on contractility, although the duration of the standstill period was significantly shorter. The same qualitative phenomenon occurred when sera of other xenogeneic species were used. These results point to a temporary functional disturbance of parenchymal cells by xenoreactive natural antibodies, whereas no chronic cytotoxicity was conspicuous in these experiments.Transplantation 01/1995; 58(12):1403-9. · 3.78 Impact Factor
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ABSTRACT: Myocyte cell loss is a prominent and important pathogenic feature of cardiac ischemia. We have used cultured neonatal rat cardiac myocytes exposed to prolonged hypoxia as an experimental system to identify critical factors involved in cardiomyocyte death. Exposure of myocytes to hypoxia for 48 h resulted in intranucleosomal cleavage of genomic DNA characteristic of apoptosis and was accompanied by increased p53 transactivating activity and protein accumulation. Expression of p21/WAF-1/CIP-1, a well-characterized target of p53 transactivation, also increased in response to hypoxia. Hypoxia did not cause DNA laddering or cell loss in cardiac fibroblasts. To determine whether the increase in p53 expression in myocytes was sufficient to induce apoptosis, normoxic cultures were infected with a replication-defective adenovirus expressing wild-type human p53 (AdCMV.p53). Infected cells expressed high intracellular levels of p53 protein and exhibited the morphological changes and genomic DNA fragmentation characteristic of apoptosis. In contrast, no genomic DNA fragmentation was observed in myocytes infected with the control virus lacking an insert (AdCMV.null) or in cardiac fibroblasts infected with AdCMV.p53. These results suggest that the intracellular signaling pathways activated by p53 might play a critical role in the regulation of hypoxia-induced apoptosis of cardiomyocytes.Journal of Clinical Investigation 07/1997; 99(11):2635-43. · 12.81 Impact Factor
- Circulation Research 08/1998; 83(1):15-26. · 11.86 Impact Factor