Abstract 1165: The Interaction Between PKB/Akt, JNK and PTEN During Ischemia/Reperfusion of Insulin Resistant Heart
PKB/Akt is activated via PI3-kinase and PIP3, which in turn, are controlled by the phosphatase PTEN. In addition, the stress kinase JNK has been shown to phosphorylate PKB at the onset of reperfusion. We have shown that baseline PKB activation and insulin-induced glucose uptake are significantly reduced in cardiomyocytes of insulin-resistant rats. Based on the proposed interaction between JNK and PKB during early reperfusion, we hypothesize that JNK may be important in the functional recovery of the heart after ischemia/reperfusion and in impairment of PI3-K/PKB signaling in insulin resistance.
Methods: Obesity and insulin-resistance were induced by feeding rats a high calorie diet for 16 weeks (DIO). Hearts from DIO rats and age-matched controls were subjected to 15 min global ischemia in vitro, followed by 1, 5, 10 or 30 min reperfusion before freeze-clamping. Phosphorylation and expression of PKB, PTEN, JNK, p38MAPK and ERK were assessed by Western blot. N=6/group.
Results: DIO hearts showed improved functional recovery during reperfusion compared to controls (% recovery of aortic output: Controls 33.2±3.53% vs DIO 64.63±5.42; p<0.05). Except for PTEN phosphorylation which was significantly higher in DIO hearts after I min reperfusion, no activation of ERK, JNK or PKB was detected at this time in both groups. At both 5 and 10 min reperfusion, phosphorylation of JNKp46, JNKp54 and PKB (serine 473) was significantly higher in DIO hearts (fold increase from baseline: JNKp46: 5 min: control 4.38±0.5; DIO 7.14 ±0.37; 10 min: control 2.59± 0.28; DIO 4.28± 0.35, p<0.05; JNKp54: 5 min: control 3.91± 0.95, DIO 6.51± 0.22; 10 min: control 2.62 ±0.42; DIO 4.49 ±0.41, p<0.05; PKB: 5 min: control 2.51±0.19; DIO 3.37± 0.21; 10 min: control 3.26 ±0.21; DIO 4.3± 0.11; p<0.05). PTEN showed increased inactivation in DIO hearts (5 min: control 1.79±0.08; DIO 2.48±0.28; 10 min: control 1.79±0.17; DIO 3.42±0.75, p<0.05). However, at 30 min reperfusion activation of JNK and PKB was significantly less in the DIO hearts. ERK and p38MAPK did not differ.
Conclusion: Inactivation of PTEN and concomitant activation of JNK and PKB during early reperfusion of DIO insulin resistant hearts may play a pivotal role in improving function after ischemia.