Abstract 13179: GSK-3β Differentially Regulates Myocardial Injury During Ischemia and Reperfusion Through Stimulation of Autophagy
Increasing lines of evidence suggest that inhibition of GSK-3 mediates cardioprotective effects of preconditioning, postconditioning, and other interventions. However, underlying mechanisms of cardioprotection afforded by GSK-3 inhibition remain to be elucidated. We studied the molecular mechanism mediating the effects of GSK-3β inhibition/activation upon myocardial injury during prolonged ischemia (PI) and ischemia-reperfusion (IR). After PI (2 hr), the infarct size was significantly increased by specific inhibition of GSK-3β with dominant negative GSK-3β in transgenic mice (Tg-DnGSK, 41.6±4.7% vs. 32.7±3.9%, p<0.05) and in heterozygous GSK-3β KO mice (GSK-3β+/-, 47.2±4.7% vs. 32.2±2.7%, p<0.05), but was significantly decreased by activation of GSK-3β in constitutively active GSK-3β knock-in mice (βKI, 24.5±0.8% vs. 35.4±2.7%, p<0.05). In contrast, after IR, the infarct size was significantly reduced by inhibition of GSK-3β in Tg-DnGSK (26.5±3.3% vs. 42.6±2.4%, p<0.05) and GSK-3β+/- (35.4±2.7% vs. 45.9±1.6%, p<0.05), but was significantly enhanced by activation of GSK-3β in βKI (61.4±7.5% vs. 39.2±3.1%, p<0.05). Both at baseline and after PI or IR, the phosphorylation level of S6K was increased in Tg-DnGSK but was decreased in βKI, indicating that inhibition of GSK-3β stimulates mTOR signaling. After PI or IR, there were significantly fewer GFP-LC3 dots in DnGSK-3β/GFP-LC3 bigenic mice than in GFP-LC3 transgenic mice, an effect which was abolished by rapamycin, indicating that GSK-3β inhibition decreased autophagy through an mTOR-dependent mechanism. Moreover, rapamycin abolished both the detrimental effects of GSK-3β inhibition on PI injury and the protective effects of GSK-3β inhibition on IR injury while restoring autophagy in Tg-DnGSK mice. Importantly, the influence of rapamycin on the effects of GSK-3β inhibition on myocardial injury was reversed by inhibition of autophagy in beclin 1+/- mice. These results suggest that regulation of autophagy through mTOR plays an important role in mediating the effects of GSK-3β modulation upon myocardial injury. Collectively, our results suggest that inhibition of GSK-3β exacerbates ischemic injury but protects against IR injury by stimulating mTOR and reducing autophagy.
- © 2010 by American Heart Association, Inc.