Bcl-2 Phosphorylation Triggers Autophagy Switch and Reduces Mitochondrial Damage in Limb Remote Ischemic Conditioned Rats After Ischemic Stroke

Autophagy, an important intracellular degradation pathway, has been reported to clear impaired mitochondria and reduce mitochondria-mediated injury in ischemic disease. Our study and other recent investigations have shown that AKT-dependent autophagy contributes to the neuroprotection afforded by limb remote ischemic conditioning (RIC) in experimental stroke. However, how AKT triggers RIC-based autophagy and whether RIC-afforded autophagy is beneficial for mitochondrial function after cerebral ischemia remains unclear. The disruption of the Bcl-2/Beclin1 complex has been reported to trigger autophagy formation in the condition of Bcl-2 phosphorylation at Ser70. We investigated whether Bcl-2 phosphorylation triggers RIC-based autophagy and thereby confers RIC-induced neuroprotection against mitochondrial injury, using a transient cerebral ischemic rat model. We demonstrated that rats undergoing RIC treatment 30 min after the onset of ischemia (I-30) and at reperfusion (R-0) significantly upregulated Bcl-2 phosphorylation. Immunoprecipitation revealed that RIC increased dissociation of the Bcl-2/Beclin1 complex, leading to a higher level of autophagy than in ischemia/reperfusion rats. Furthermore, AKT activation was shown to play a critical role in regulating Bcl-2-mediated autophagy, as an AKT inhibitor (LY294002, AKTi) administered 30 min prior to ischemia significantly suppressed Bcl-2 phosphorylation and Bcl-2/Beclin1 complex dissociation, thereby reducing autophagy in RIC rats. Blocking Bcl-2 phosphorylation-dependent autophagy with AKTi suppressed RIC-afforded protection on mitochondrial potential and mitochondrial-dependent cell death effector pathway. These findings indicate that Bcl-2 phosphorylation and thereby Bcl-2/Beclin1 complex disruption play a crucial role in triggering autophagy and reducing mitochondrial damage in RIC rats after cerebral ischemia and require the involvement of the AKT activation.