Abstract 212: Globular Domain of Adiponectin Attenuates Post-Ischemia Myocardial Oxidative/Nitrative Stress in an AMPK-Independent Fashion
Reduced plasma adiponectin (APN) level not only contributes to the increased incidence of MI in diabetic patients, but also plays a causative role in increased cardiac injury after MI in these patients. However, singling mechanisms by which APN achieves its cardioprotection remains incompletely understood. Here, we investigated the role of AMP activated protein kinase (AMPK), the molecule that transfers APN’s metabolic signaling, in APN’s cardioprotection. Male adult mice with cardiac specific overexpression of a dominant negative AMPK α2 subunit (AMPK-DN) or wild type (WT) littermates controls were subjected to 30 min of MI followed by reperfusion (R) and treated with vehicle (V) or globular domain of APN (gAPN, 2 μg/g) 10 min before R. Comparing with WT mice, MI/R caused greater cardiac injury including larger infarct size, more apoptosis and poorer cardiac function (P<0.05) in AMPK-DN mice. Treatment of WT mice with gAPN significantly attenuated MI/R injury (P<0.01). Most interestingly, although the metabolic regulatory effect of gAPN is completely lost in AMPK-DN mice, a significant portion of cardioprotection of gAPN retained in the transgenic animals. Specifically, treatment of AMPK-DN mice with gAPN reduced infarct size (54±4.7% vs. 81±3.6% in V group, P<0.01), decreased apoptosis (lesser TUNEL positive labeling, weaker DNA fragmentation, and lower caspase 3 activity. P value all <0.01) and improved cardiac function after MI/R (higher LVEF, lower LVEDP and higher dP/dtmax. P value all <0.01). To further delineate the mechanisms responsible for gAPN’s AMPK-independent cardioprotection, effect of gAPN on cardiac oxidative/nitrative stress following MI/R were examined. Treatment of AMPK-DN mice with gAPN reduced superoxide and nitric oxide overproduction, decreased peroxynitrite formation (from 0.38±0.04 to 0.23±0.02 ng/mg protein in WT and from 0.50±0.06 to 0.32±0.02 ng/mg protein in AMPK-DN mice), and inhibited NADPH oxidase and iNOS expression to the same extent as that seen in WT mice. Taken together, our results demonstrated for the first time that a significant portion of gAPN cardioprotection is not mediated by the traditional AMPK signaling pathway and that the anti-oxidative/anti-nitrative effects of gAPN are AMPK-independent.