Hypothetical scheme describing the mechanism of autophagy under ischemia and reperfusion. Under ischemia, O2 and nutrient supplies are decreased and the intracellular ATP level is reduced, causing activation of AMPK. These stimuli lead to autophagy, which may be protective. On the other hand, upon reperfusion, activation of AMPK is no longer observed. Instead, expression of Beclin 1 is markedly upregulated. Simultaneously, increased oxidative stress and ER stress may occur. These stimuli induce autophagy, which could be detrimental.