Abstract 1607: Zinc Protects Cardiac Cells from Reperfusion Injury by Inactivating Glycogen Synthase Kinase-3β
Although zinc has been demonstrated to be cardioprotective, the detailed cellular and molecular mechanisms that mediate the protection remain elusive. We aimed to test if exogenous zinc prevents cardiac reperfusion injury by inactivating glycogen synthase kinase 3β (GSK-3β). Treatment of cardiac H9c2 cells with ZnCl2 (10 μM) in the presence of zinc ionophore pyrithione for 20 min significantly enhanced GSK-3β phosphorylation at Ser9 (349 ± 55 % of the control), indicating that exogenous zinc can inactivate GSK-3β in cardiac cells. The effect of zinc on GSK-3β activity was blocked by PI3K inhibitor LY294002 (171 ± 36 % of control) but not by the mTOR inhibitor rapamycin or the PKC inhibitor chelerythrine, implying that PI3K but not mTOR or PKC accounts for the action of zinc. In support of this observation, zinc induced a significant increase in Akt but not mTOR phosphorylation. Further experiments found that zinc also increased mitochondrial GSK-3β phosphorylation. This may indicate an involvement of mitochondria in zinc’s action. ZnCl2 (10 μM) applied at reperfusion increased cell viability (69.1 ± 2.8 % vs. 27.5 ±3.5 % in control) in cells subjected to simulated ischemia/reperfusion, indicating that zinc can prevent reperfusion injury. However, zinc was not able to increase cell viability in cells transfected with the constitutively active GSK-3β (GSK-3β-S9A-HA) mutant (29.2 ± 2.9 %), suggesting that zinc prevents reperfusion injury by inactivating GSK-3β. Cells transfected with the catalytically inactive GSK-3β (GSK-3β-KM-HA) in the absence of zinc revealed a significant increase in cell viability (62.5 ± 3.7 %), strongly supporting the essential role of GSK-3β inactivation in cardioprotection. In conclusion, these data suggest that zinc prevents reperfusion injury by inactivating GSK-3β through the PI3K/Akt pathway.