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.

Renoprotective Effects of Metformin are Independent of Organic Cation Transporters 1 & 2 and AMP-activated Protein Kinase in the Kidney

“…As AMPK has been suggested to be implicated in the renoprotective effects of metformin34, we next tested the potential role of AMPK in the 3dUUO model of renal damage using AMPK-β1 −/− mice. The AMPK-β1 −/− model was used for these experiments because KO mouse was found to practically ablate the expression of AMPK active enzyme in mouse kidney35.…”

Physiological Expression of AMPKγ2 Mutation Causes Wolff-Parkinson-White Syndrome and Induces Kidney Injury in Mice

“…It had been reported that AMPK and autophagy were activated in renal cells under stress conditions, which can cause programmed cell death (44). On the other hand, supraphysiologically activating AMPK by AICAR and metformin was reported to exert a beneficial effect in kidney ischemia-reperfusion (45). Although the underlying mechanism for why AMPK␥2 RG , but not AMPK␥2 NI , mice showed kidney injury is not fully understood, we speculate that the kidney injury might be associated with the higher baseline activity of AMPK␥2 RG and the "loss of AMP response" of AMPK␥2 RG , in which cellular AMP cannot bind to one of the binding domains in AMPK ␥-subunit (3).…”

Autophagy in acute kidney injury

“…Although overexpression of both BNIP3 and sestrin 2 induced autophagy as measured by LC3-II formation, only BNIP3 selectively induced mitophagy as visualized by confocal and electron microscopy 72 . The expression of PINK, a marker of mitophagy, was increased during renal ischemia-reperfusion injury 73 . Another study has shown that mitophagy in the kidneys of a rat fed low-calorie diet was markedly increased and ameliorated oxidative damage compared to that of high-calorie fed rats 74 .…”