Abstract 18545: GSK-3β Prevents Lipotoxicity in Obesity Cardiomyopathy Through Upregulation of ATGL

Abstract

Introduction: Obesity induces accumulation of lipids in cardiomyocytes, leading to cardiac dysfunction, termed lipotoxic cardiomyopathy. We have shown previously that GSK-3α promotes fatty acid uptake in the heart. In contrast, GSK-3β may mediate lipid catabolism. In this study, we aimed to elucidate the role of GSK-3β in lipolysis, primarily focusing on the post-translational regulation of FoxO1 and its association with ATGL, which is the first lipase to hydrolyze lipids. Methods: Wild-type (WT) and homozygous cardiac-specific GSK-3β knock-out (GSK-3β-cKO) mice were fed a normal diet (ND) or a high fat diet (HFD) for 3 months. Results: HFD consumption in WT mice activated GSK-3β in the heart, as indicated by decreases in Ser9-phosphorylated GSK-3β/total GSK-3β (0.5-fold, p<0.05 compared to ND consumption), and upregulated ATGL (2.4-fold, p<0.05) in the heart. Echocardiographic analyses showed preserved systolic and diastolic function in WT mice at this time point (LVEF: 56.3 ± 1.5 %, E/A: 2.06 ± 0.22, n = 13). However, ATGL was not increased (1.6-fold) and both systolic and diastolic dysfunction were observed (LVEF: 45.8 ± 1.5 %, p<0.01 compared to WT, E/A: 1.43 ± 0.20, p<0.05, n =12) in GSK-3β-cKO mice fed a HFD. GSK-3β overexpression in neonatal rat ventricular cardiomyocytes increased ATGL in a dose-dependent manner (p<0.05). FoxO1 knock-down on this background inhibited upregulation of ATGL, suggesting that GSK-3β-induced upregulation of ATGL is mediated through a FoxO1-dependent mechanism. Immunoprecipitation showed that GSK-3β interacts with FoxO1, while mass spectrometry analyses revealed that GSK-3β phosphorylates FoxO1 at 8 Serine/Threonine residues. A FoxO1 mutant in which Serine/Threonine residues at the GSK-3β phosphorylation sites are mutated to Alanine was excluded from the nucleus, and its overexpression prevented upregulation of ATGL in the presence of GSK-3β overexpression. Conclusions: GSK-3β is activated in the presence of HFD consumption in the heart, which may, in turn, prevent lipotoxic cardiomyopathy through phosphorylation of FoxO1 and upregulation of ATGL.