Abstract 9138: Thioredoxin-Interacting Protein is a Regulator of Redox Homeostasis in Diabetic Cardiomyopathy

Abstract

Introduction: Although the precise pathogenesis of diabetic cardiac damage remains unclear, potential mechanisms include increased oxidative stress. Thioredoxin-interacting protein (Txnip) is a binding partner and an endogenous inhibitor of antioxidative thioredoxin. Txnip is a highly glucose-responsive gene that mediates cellular damage. Hypothesis: This study was designed to provide direct in vivo evidence that the specific molecular interaction between Txnip and thioredoxin controls redox balance in the diabetic heart. Methods and Results: High glucose increased Txnip expression, leading to decreased thioredoxin activities and oxidative stress in mouse embryonic fibroblasts. The Txnip-thioredoxin complex was observed in cells overexpressing wild-type Txnip but not in cells overexpressing Txnip Cys247-to-Ser mutant (C247S), showing that Txnip C247 is an essential cysteine for this interaction. Then, the role of the Txnip-thioredoxin interaction was evaluated in the diabetic heart, using our newly-developed cardiomyocyte-specific Txnip C247S “knock-in” mutant mice. Injections of streptozotocin in these animals induced type 1 diabetes. Prolonged hyperglycemia upregulated myocardial expression of Txnip both in Txnip C247S mutant mice and their littermate wild-type controls. Interestingly, loss of Txnip’s inhibition of thioredoxin in Txnip C247S mutant hearts increased reduced/oxidized glutathione (GSH/GSSG) ratio and decreased TUNEL-positive cardiomyocytes, indicative of less oxidative stress and apoptosis within the diabetic myocardium in Txnip C247S mutant animals. Echocardiographic assessments did not detect any functional differences in left ventricular (LV) parameters between genotypes both at baseline and under diabetic conditions. However, hemodynamic analyses with beta-adrenergic stimulation revealed a masked functional phenotype that Txnip C247S diabetic hearts had a higher LV contractile reserve than wild-type diabetic hearts. Conclusions: These data demonstrate that hyperglycemia-induced Txnip is responsible for cardiomyocyte damage in the diabetic heart through the direct inhibition of thioredoxin and increased oxidative stress.