Role of Akt Signaling in Mitochondrial Survival Pathway Triggered by Hypoxic Preconditioning

Abstract

Background-The signaling pathways that control ischemia/reperfusion-induced cardiomyocyte apoptosis in heart have not been fully defined. In this study, we investigated whether Akt signaling has a role in the antiapoptotic pathways of preconditioning against hypoxia/reoxygenation (H/R). Methods and Results-Primary cultures of adult rat ventricular myocytes (ARVMs) were subjected to preconditioning (PC) by exposing the cells to 10 minutes of hypoxia followed by 30 minutes of reoxygenation. Non-PC and PC myocytes were subjected to 90 minutes of hypoxia followed by 120 minutes of reoxygenation. Hypoxic-PC protected the myocytes from subsequent H/R injury, as evidenced by decreased apoptosis and LDH release and increased cell viability. H/R-induced cytochrome c release and activation of caspase-3 and -9 were blocked by PC. This protective effect was inhibited by treating the cells with LY294002 (50 mol/L), a PI3 kinase inhibitor, for 10 minutes before and during PC. PC also induced phosphorylation of Akt and BAD. Protein levels of Bcl-2 in mitochondria were maintained in PC. ARVMs were infected with either a control adenovirus (Adeno lac-Z), an adenovirus expressing dominantnegative Akt, or an adenovirus expressing constitutively active Akt. Ectopic overexpression of constitutively active Akt protected ARVMs from apoptosis induced by hypoxia/reoxygenation compared with Adeno lac-Z. In contrast, dominant negative Akt overexpression abolished the antiapoptotic effect of PC. Conclusions-Our data demonstrated that in adult cardiomyocytes, the antiapoptotic effect of PC against H/R requires Akt signaling leading to phosphorylation of BAD, inhibition of cytochrome c release, and prevention of caspase activation.

Identification of a receptor-independent activator of G protein signaling (AGS8) in ischemic heart and its interaction with Gβγ

“…Adaptation of the myocardium to ischemia involves alteration of several signaling pathways (i.e., ERK1͞2, AKT, protein kinase C, and͞or phospholipase C) involved in collateral growth (32,33), apoptosis (33,34), energy metabolism (33,35), and the development of a ''preconditioned'' myocardium. G␤␥ signaling is clearly involved in many aspects of such signaling pathways (36)(37)(38)(39). AGS8 provides an unexpected mechanism for regulation of the G protein activation cycle and is specifically induced in the heart in response to transient repetitive ischemia and͞or hypoxia.…”

Therapeutic Potential of HDL in Cardioprotection and Tissue Repair

“…This ratio is a marker of increased cardiomyocyte survival probability (Condorelli et al 1999). Furthermore, apo A-I transfer normalised the diabetes-reduced phosphorylation of the pro-survival protein kinase B Akt (Montanari et al 2005;Uchiyama et al 2004) and of its effector eNOS to levels found in non-diabetic hearts ). This finding was further corroborated by experiments in cardiomyocytes.…”

Ca2+ Dysregulation Induces Mitochondrial Depolarization and Apoptosis

“…Another condition that could accentuate the susceptibility of the mitochondria to elevated Ca 2ϩ is the diminished Akt activity that we previously reported occurred as early as 8 h after virus removal and contributed to Q209L-induced apoptosis (15). Akt has been shown to contribute to preservation of mitochondrial integrity in ischemic preconditioning and in response to ischemia reperfusion (32)(33)(34). Thus, both the increased ROS and the decreased Akt that occur in the intact cell would likely render the mitochondria more susceptible to disruption.…”