Conversion of death signal into survival signal by redox signaling.

Abstract

Reperfusion of ischemic myocardium produces reactive oxygen species (ROS) and results in apoptotic cell death and DNA fragmentation. Several redox-sensitive anti- and pro- apoptotic transcription factors including nuclear factor kappaB (NF-kappaB) and heterodimeric transcription factor AP-1 progressively and steadily increase in the heart as a function of the duration of ischemia and reperfusion. When the heart is adapted to ischemic stress by repeated short-term ischemia and reperfusion, NF-kappaB remains high, while AP-1 is lowered to almost baseline value. The anti-apoptotic gene Bcl-2 is downregulated in the ischemic/reperfused heart, while it is upregulated in the adapted myocardium. Cardioprotective abilities of the adapted myocardium are abolished when heart is pre-perfused with N-acetyl cysteine to scavenge ROS, suggesting a role of redox signaling. Mammalian heart is protected by several defense systems, which include, among others, the redox-regulated protein thioredoxin. Reperfusion of ischemic myocardium results in the downregulation of thioredoxin 1 (Trx 1) expression, which was upregulated in the adapted myocardium. The increased expression of Trx 1 is completely blocked with an inhibitor of Trx 1, cis-diammine-dichloroplatinum, which also abolished cardioprotection afforded by ischemic adaptation. The cardioprotective role of Trx 1 is further confirmed with transgenic mouse hearts overexpressing Trx 1. The Trx 1 mouse hearts displayed significantly improved post-ischemic ventricular recovery and reduced myocardial infarct size and apoptosis compared to the corresponding wild-type mouse hearts. The results of this study implicate a crucial role of redox signaling in transmitting anti-death signal.