Ser9 phosphorylation of GSK-3β promotes aging in the heart through suppression of autophagy

Introduction: Glycogen synthase kinase-3β (GSK-3β) is a serine/threonine kinase and a negative regulator of cardiac hypertrophy. Phosphorylation of GSK-3β at Ser9 negatively regulates its kinase activity. The role of GSK-3β in cardiac aging remains poorly understood.Aim: The study aimed to elucidate the role of GSK-3β Ser9 phosphorylation in mediating cardiac aging and the underlying mechanism.Methods and Results: Phosphorylation of GSK-3β at Ser9 and the levels of β-catenin and Mcl-1 were increased in the mouse heart during aging, suggesting that GSK-3β is inactivated during aging in the heart. Age-induced cardiac hypertrophy, fibrosis, left ventricular dysfunction, and increases in cardiomyocyte apoptosis and senescence were all attenuated in constitutively active GSK-3βS9A knock-in (KI) mice compared to littermate wild type mice. Although autophagy is inhibited in the heart during aging, KI of GSK-3βS9A reversed the age-associated decline in autophagy in the mouse heart. GSK-3β directly phosphorylates Ulk1, a regulator of autophagy, at Ser913, thereby stimulating autophagy in cardiomyocytes. Ulk1Ser913A KI mice exhibited decreased autophagic flux and increased senescence in cardiomyocytes.Conclusion: Our results suggest that GSK-3β is inactivated during aging through Ser9 phosphorylation, which in turn plays an important role in mediating cardiac aging. GSK-3β promotes autophagy through phosphorylation of Ulk1 at Ser913, which in turn prevents aging in the heart.One sentence summary: Ser9 phosphorylation of GSK-3β promotes aging in the heart at least in part through decreases in Ulk1 phosphorylation at Ser913 and suppression of autophagy