Beneficial effects of AMP-activated protein kinase agonists in kidney ischemia-reperfusion: Autophagy and cellular stress markers

Abstract

Background: Kidney ischemia-reperfusion is a form of acute kidney injury resulting in a cascade of cellular events prompting rapid cellular damage and suppression of kidney function. A cellular response to ischemic stress is the activation of AMP-activated protein kinase (AMPK), where AMPK induces a number of homeostatic and renoprotective mechanisms, including autophagy. However, whether autophagy is beneficial or detrimental in ischemia-reperfusion remains controversial. We investigated the effects of agonist induction of AMPK activity on autophagy and cell stress proteins in the model of kidney ischemia-reperfusion. Methods: AMPK agonists, AICAR (0.1 g/kg) and metformin (0.3 g/kg), were administered 24 h prior to ischemia, with kidneys harvested at 24 h of reperfusion. Results: We observed a paradoxical decrease in AMPK activity accompanied by increases in mammalian target of rapamycin (mTOR) C1 activity and p62/SQSTM1 expression. These results led us to propose that AMPK and autophagy are insufficient to properly counter the cellular insults in ischemia-reperfusion. Agonist induction of AMPK activity with AICAR or metformin increased macroautophagy protein LC3 and normalized p62/SQSTM1 expression and mTOR activity. Ischemia-reperfusion increases in Beclin-1 and PINK1 expressions, consistent with increased mitophagy, were also mitigated with AMPK agonists. Stress-responsive and apoptotic marker expressions increase in ischemia-reperfusion and are significantly attenuated with agonist administration, as are early indicators of fibrosis. Conclusions: Our data suggest that levels of renoprotective AMPK activity and canonical autophagy are insufficient to maintain cellular homeostasis, contributing to the progression of ischemia-reperfusion injury. We further demonstrate that induction of AMPK activity can provide beneficial cellular effects in containing injury in ischemia-reperfusion.