Abstract 3126: Ischemic Postconditioning Facilitates Brain Recovery After Stroke by Promoting mTOR Activity

Abstract

Introduction: Ischemic postconditioning represents a series of brief occlusions of blood flow before complete restoration of reperfusion after brain stroke. We have shown that ischemic postconditioning reduces infarct size in focal ischemia in rats and improves neurological deficits, but the underlying protective mechanisms are not fully understood. The mammalian target of rapamycin (mTOR) pathway plays a key role in cell growth, differentiation and survival. We studied the hypothesis that the mTOR pathway is involved in the protective effect of ischemic postconditioning and brain recovery after stroke in rats. Methods: Focal ischemia was induced by 30 min of bilateral CCA occlusion and permanent distal MCA occlusion in rats. Ischemic postconditioning was induced by 3 cycles of 30 sec reperfusion and 10 sec occlusion at the end of stroke. Rapamycin, an mTOR inhibitor, was injected into the left lateral ventricle 1 hour before stroke onset. For the behavior test, home cage and vibrissa-elicited limb use tests were used and performed until 21d after stroke. Peri-infarct tissues were collected 1 and 3 weeks after stroke for Western blotting and immunostaining. Molecular markers related with synaptic transmission and neuronal growth and plasticity, including Gap-43, synaptophysin, MAP-2 and PSD-95 proteins were detected. Protein levels of phosphorylated mTOR (p-MTOR) and 4EPB-1 in the mTOR pathway, and the upstream molecule, Akt, were also measured. Results: Ischemic postconditioning improved neurological function when measured 2 weeks after stroke (n=6, p<0.05), and reduced brain injury size by 34.2% (P<0.05). These protective effects were abolished by rapamycin treatment. The results of Western blotting showed that postconditioning substantially promoted the protein level of Gap-43, MAP-2 and PSD-95, but not synaptophysin. Rapamycin significantly inhibited Gap-43 levels at 1 and 3 weeks after stroke, and inhibited Map-2 level at 1 week (P<0.05). Postconditioning significantly increased the protein levels of p-Akt, p-mTOR, p-4EBP-1 compared with control ischemia (p<0.05) at 1 week after stroke injury. Rapamycin attenuated p-mTOR levels 1 and 3 weeks after stroke, and inhibited p-4EBP-1 level at 1 week (p<0.05), but had no effects on the expression level of p-Akt and Akt. Conclusion: Ischemic postconditioning improved brain function, which is consistent with the improved expression of proteins related with synaptic function and brain plasticity. This protection appears to be achieved by the enhanced mTOR activity.