Abstract 846: Gsk3β Inhibition Is Required For Postconditioning To Modulate Mitochondrial Permeability Transition Pore Opening

Abstract

Introduction: Activation of the PI3kinase pathway and subsequent Inhibition of GSK3β by phosphorylation at serine-9 residue has recently been shown to protect against myocardial lethal reperfusion injury. Hypothesis: We hypothesized that GSK3β may play a key role in protection afforded by postconditioning. We used transgenic mice (Tg) that express a constitutively active (i.e. that cannot be inactivated by phosphorylation at serine 9) form of GSK-3β. Methods: Anesthetized WT and Tg mice underwent 60 minutes of coronary artery occlusion followed by 24 hrs of reperfusion (n=9/gr). At reflow, mice received either no intervention (controls: C-WT and C-Tg), postconditioning (postC) by 3 cycles of [1 min ischemia / 1 min reperfusion], or an IV bolus injection (1 minute before reflow) of either 10 mg/kg of cyclosporine A (CsA), a potent inhibitor of the mitochondrial permeability transition pore (mPTP) opening, or 70μg/kg of SB 216763 (SB), a specific inhibitor of GSK3β. Infarct size (%of area at risk) was measured by TTC staining. CRC, an index of Ca 2+ -induced mPTP opening in isolated mitochondria was measured by a fluorimetric approach. Results: PostC, CsA and SB significantly reduced infarct to 29%, 36% and 34% respectively (p<0.05 vs. C: 56±5%) in WT mice. In contrast, postC failed to significantly reduce infarct size in Tg mice (51±5%), while as expected CsA limited necrosis (36±6%). In WT, CRC was significantly decreased in C versus sham (75±14 nmol Ca 2+ /mg), but improved in postC, CsA and SB mice, averaging 155±31, 267±11 and 183±37 nmol Ca 2+ /mg respectively (p<0.05). In Tg mice, CRC was not significantly changed in postC versus control (139±44 nmol Ca 2+ /mg), but improved in CsA. Conclusion: These results suggest that inhibition of GSK3β is involved in postconditioning’s protection against infarction, likely by preventing mPTP opening during the first minutes of reperfusion.