Reperfusion-activated Akt kinase prevents apoptosis in transgenic mouse hearts overexpressing insulin-like growth factor-1

Hearts of wild-type and insulin-like growth factor-1 overexpressing (Igf-1( +/-)) transgenic mice were subjected to Langendorff perfusions and progress ive periods of ischemia followed by reperfusion. Apoptosis was measured by DNA nucleosomal cleavage and a hairpin probe labeling assay to detect singl e-base overhang. Transgenic hearts subjected to 20 minutes of ischemia and 4 hours of reperfusion (I/R) sustained a rate of apoptosis of 1.8+/-0.3% co mpared with 4.6+/-1.1% for wild-type controls (n=4; P<0.03). Phosphorylatio n of the protein kinase Akt/protein kinase B was elevated 6.2-fold in trans genic hearts at baseline and increased another 4.4-fold within 10 minutes o f reperfusion, remaining elevated for up to 2 hours. I/R activated Akt in w ild-type hearts but to a lesser extent (1.6+/-0.3-fold). Pretreatment of tr ansgenic hearts with wortmannin immediately before and during ischemia elim inated reperfusion-mediated activation of Akt and neutralized the resistanc e to apoptosis. The stress-activated kinase p38 was also activated during i schemia and reperfusion in both wild-type and transgenic hearts. Perfusion with the p38 inhibitor SB203580 (10 <mu>mol/L) blocked both p38 activation and phosphorylation of Akt and differentially modulated apoptosis in wild-t ype and transgenic hearts. Pretreatment with SB203580 reduced apoptosis in wild-type hearts but increased apoptosis in transgenic hearts. These result s demonstrate that Akt phosphorylation during I/R is modulated by IGF-1 and prevents apoptosis in hearts that overexpress the IGF-1 transgene.