Abstract 93: Sestrin2 Mediates the LKB1-AMPK Signaling Cascade in the Ischemic Heart
Background: AMP-activated Protein Kinase (AMPK) has emerged as a pertinent stress-activated kinase shown to have substantial cardioprotective capabilities against myocardial ischemia/reperfusion (I/R) injury. The regulation of AMPK in the ischemic and reperfused heart is critical to the development of new therapeutic strategies. We hypothesized that a novel stress-inducible protein, sestrin2, mediates AMPK activation in the ischemic heart.
Methods and Results: C57BL/6 mice were subjected to left anterior descending coronary artery occlusion for different time points of ischemia and I/R in order to detect the signaling activity in the left ventricle. The kinetics of AMPK phosphorylation at Thr172 of the α catalytic subunit appears brief and bell-shaped, peaking around 10 min (3.6-fold vs. sham, p<0.01), decreasing with prolonged ischemia, and leveling off to basal levels upon reperfusion. Intriguingly, at 10 min of ischemia, there was also a robust increase in p53 accumulation compared to basal conditions. Consequently, sestrin2 a p53-inducible protein, accumulates at the peak of ischemic AMPK activation (10 min, 2.5-fold vs. sham, p<0.05). Respective left ventricle lysates were immunoprecipitated with sestrin2 and the immunoblots revealed that sestrin2 forms a complex with AMPK during I/R, moreover, AMPKα2 is the predominant isoform that interact with sestrin2 as compared to AMPKα1 isoform during I/R. Interestingly, LKB1, an upstream AMPK kinase becomes significantly associated with sestrin2 (5 min), while there is a dramatic interaction between sestrin2 and p-AMPK (Thr172) (10 min), suggesting the interaction of LKB1 with sestrin2 initiates the phosphorylation of AMPK in this complex. Furthermore, sestrin2 knock out hearts demonstrate impaired ischemic AMPK activation and higher sensitivity to I/R-induced injury as compared to wild type hearts (p<0.01).
Conclusions:Here we show for the first time evidence of a unique mechanism that sestrin2 is a stress-induced scaffold protein that mediates the activation of AMPK in the ischemic myocardium via a time-dependent interaction with LKB1. Moreover, sestrin2 deficiency leads to blunted ischemic AMPK activation and increased sensitivity to ischemic insults.
- © 2012 by American Heart Association, Inc.