Poly(ADP-ribose) polymerase-1-dependent cardiac myocyte cell death during heart failure is mediated by NAD+ depletion and reduced Sir2α deacetylase activity

Robust activation of poly(ADP-ribose) polymerase-1 (PARP) by oxidative stress has been implicated as a major cause of caspase-independent-myocyte cell death contributing to heart failure. Here, we show that depletion of myocyte NAD levels and the subsequent reduction of Sir2 alpha deacetylase activity are the sequential steps contributing to PARP-mediated myocyte cell death. In both failing hearts and cultured cardiac myocytes, the increased activity of PARP was associated with depletion of cellular NAD levels and reduced Sir2 alpha deacetylase activity. Myocyte cell death induced by PARP activation was prevented by repletion of cellular NAD levels either by adding NAD directly to the culture medium or by overexpressing NAD biosynthetic enzymes. The beneficial effect of NAD repletion was seen, however, only when Sir2 alpha was intact. Knocking down Sir2 alpha levels by small interfering RNA eliminated this benefit, indicating that Sir2 alpha is a downstream target of NAD replenishment leading to cell protection. NAD repletional so prevented loss of the transcriptional regulatory activity of the Sir2 alpha catalytic core domain resulting from PARP activation. We also show that PARP activation and the concomitant reduction of Sir2 alpha activity in failing hearts regulate the post-translational acetylation of p53. These data demonstrate that, in stressed cardiac myocytes, depletion of cellular NAD levels forms a link between PARP activation and reduced Sir2 alpha deacetylase activity, contributing to myocyte cell death during heart failure.