Role of Akt signaling in mitochondrial survival pathway triggered by hypoxic preconditioning.
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).


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 micromol/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 dominant-negative 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.
Uchiyama
Takamichi
T
Cardiovascular Research Center, University of Connecticut School of Medicine, Farmington, CT 06030-1110, USA.
Engelman
Richard M
RM
Maulik
Nilanjana
N
Das
Dipak K
DK
D000818:Animals; D017209:Apoptosis; D002352:Carrier Proteins / Q000378:metabolism; D020169:Caspases / Q000378:metabolism; D015687:Cell Hypoxia; D002478:Cells, Cultured / Q000502:physiology / Q000648:ultrastructure; D002867:Chromones / Q000494:pharmacology; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006352:Heart Ventricles / Q000166:cytology; D019157:Ischemic Preconditioning, Myocardial; D008297:Male; D008929:Mitochondria, Heart / Q000502:physiology*; D009025:Morpholines / Q000494:pharmacology; D015425:Myocardial Reperfusion; D032383:Myocytes, Cardiac / Q000502:physiology* / Q000648:ultrastructure; D018384:Oxidative Stress; D010100:Oxygen / Q000494:pharmacology; D010766:Phosphorylation; D011499:Protein Processing, Post-Translational; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000502:physiology*; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000502:physiology*; D051057:Proto-Oncogene Proteins c-akt; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D011993:Recombinant Fusion Proteins / Q000502:physiology; D015398:Signal Transduction; D051025:bcl-Associated Death Protein
C494821:Bad protein, rat; D002352:Carrier Proteins; D002867:Chromones; D004791:Enzyme Inhibitors; D009025:Morpholines; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D011993:Recombinant Fusion Proteins; D051025:bcl-Associated Death Protein; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C494920:Akt1 protein, rat; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D020169:Caspases; D010100:Oxygen