Abstract 75: Insulin Modulates Cardioprotective Akt Signaling During Ischemia/Reperfusion Attenuating PHLPP-1 Phosphatase

Abstract

Introduction The recently discovered phosphatase PHLPP-1 directly dephosphorylates and inactivates Akt. Whether the suppression of Akt by PHLPP-1 may lead to myocardial ischemia intolerance in aged heart, has never been previously studied. Moreover, we unveiled that the cardioprotective effects of insulin in limiting ischemia/reperfusion(I/R) injury were Akt activation dependent. However,the role of insulin,regulating the endogenous negative regulator of Akt activity, remains largely unknown. In this study, an important role for insulin in intensifying Akt activity through attenuating PHLPP-1 and ameliorating myocardial injury following I/R in the senescent heart has been described. Methods and Results Young (3 M) and aged (20 M) rats were subjected to I (20 min) / R (4 h) in vivo . Insulin treatment during reperfusion significantly increased Akt phosphorylation(2.32 times) response to I/R and decreased the infarct size by 18±3%. Simultaneously, insulin treatment significantly suppressed the PHLPP-1 level by 65±5%. Insulin-induced Akt activation was impaired and the myocardial infarct was larger in I/R aged hearts compared with the young ones. The effect of Insulin attenuating PHLPP-1 to intensify Akt activity was impaired in aged ischemic hearts as compared to young ischemic hearts. In cultured rat ventricular myocytes, the inhibitory effects of insulin on cardiac PHLPP-1 were abolished by the proteasome inhibitor MG132. PHLPP-1 knockdown by small interfering RNA significantly enhances insulin-induced Akt phosphorylation and reduced simulated hypoxia/reoxygenation induced apoptosis. Moreover, swimming training (6 w) incresed insulin sensitivity in the senescent heart. The inhibitory effect of insulin on cardiac PHLPP-1 was partially reversed accompanying enhanced Akt phosphorylation. The tolerance of the aged heart to ischemic damage is also enhanced. Conclusions We conclude that PHLPP-1 may contribute to the aging-associated ischemic intolerance. Insulin acts as a crucial cardioprotective regulator by inhibiting physiological function of PHLPP-1 and thus enchancing Akt activity. For the first time,our results also indicated a new cardioprotective mechanism of insulin modulating ubiquitin-proteasome pathway of PHLPP-1.