Introduction: Ischemic postconditioning represents a series of brief occlusions of blood flow before complete restoration of reperfusion after stroke, but the underlying protective mechanisms of postconditioning are not fully understood. The mTOR pathway plays a key role in cell growth and survival. We studied the hypothesis that mTOR pathway is involved in the protective effect of ischemic postconditioning.
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 performed until 21d after stroke. Peri-infarct tissues were collected for Western blotting and immunostaining. Molecular markers including Gap-43, synaptophysin, MAP-2, PSD-95, phosphorylated mTOR (p-MTOR) and 4EPB-1 in the mTOR pathway were 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. 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.
Conclusions: Ischemic postconditioning improved brain function by the enhanced mTOR activity, which is consistent with the improved expression of proteins related with synaptic function and brain plasticity.
Patient Care: This research show that postconditoning has protective effect again stroke through mTOR pathway, which will have a translational meaning for stroke therapy in clinic.
Learning Objectives: By the conclusion of this session, participants should be able to: 1) Describe the importance of mTOR pathway in postconditioning protective effect against stroke. 2) Discuss, in small groups, to show the potential relationship between mTOR pathway and postconditioning. 3) Identify an effective mechanism against brain ischemia for future clinical application.