Myocardial autophagy activation and suppressed survival signaling is associated with insulin resistance in fructose-fed mice

Abstract

Fructose intake is linked with the increasing prevalence of insulin resistance and there is now evidence for a specific insulin-resistant cardiomyopathy. The aim of this study was to determine the cardiac-specific myocardial remodeling effects of high fructose dietary intake. Given the links between insulin signaling, reactive oxygen species generation and autophagy induction, we hypothesized that autophagy contributes to pathologic remodeling in the insulin-resistant heart, and in particular may be a feature of high fructose diet-induced cardiac phenotype. Male C57Bl/6 mice were fed a high fructose (60%) diet or nutrient-matched control diet for 12 weeks. Systemic and myocardial insulin-resistant status was characterized. Superoxide production (lucigenin) and cellular growth and death signaling pathways were examined in myocardial tissue. Myocardial structural remodeling was evaluated by measurement of heart weight indices and histological analysis of collagen deposition (picrosirius red). Fructose-fed mice exhibited hyperglycemia and glucose intolerance, but plasma insulin and blood pressure were unchanged. High fructose intake suppressed the myocardial Akt cell survival signaling coincident with increased cardiac superoxide generation (21% increase, p<0.05). Fructose feeding induced elevated autophagy (LC3B-II: LC3B-I ratio: 46% increase, p<0.05) but not apoptosis signaling (unchanged Bax-1:Bcl-2 ratio). Despite a 28% increase in interstitial fibrosis, no difference in heart weight was observed in fructose-fed mice. We provide the first evidence that myocardial autophagy activation is associated with systemic insulin resistance, and that high level fructose intake inflicts direct cardiac damage. Upregulated autophagy is associated with elevated cardiac superoxide production, suppressed cell survival signaling and fibrotic infiltration in fructose-fed mice. The novel finding that autophagy contributes to cardiac pathology in insulin resistance identifies a new therapeutic target for diabetic cardiomyopathy.