Cardioprotective effect of selenium via modulation of cardiac ryanodine receptor calcium release channels in diabetic rat cardiomyocytes through thioredoxin system

Increased oxidative stress contributes to heart dysfunction via impaired Ca²⁺ homeostasis in diabetes. Abnormal RyR2 function related with altered cellular redox state is an important factor in the pathogenesis of diabetic cardiomyopathy, while its underlying mechanisms remain poorly understood. In the present study, we used a streptozotocin-induced rat model of diabetic cardiomyopathy and tested a hypothesis that diabetes-related alteration in RyR2 function is related with ROS-induced posttranslational modifications. For this, we used heart preparations from either a diabetic rat or a sodium selenate (NaSe)-treated (0.3 mg/kg for 4 weeks) diabetic rat as well as either NaSe- (100 nmol/L) or thioredoxin (Trx; 5 μmol/L)-incubated (30 min) diabetic cardiomyocytes. Experimental approaches included imaging of intracellular free-Ca²⁺ ([Ca²⁺]_i) under both electrically stimulated and resting Fluo-3-loaded cardiomyocytes. RyR2-mediated SR-Ca²⁺ leak was significantly enhanced in diabetic cardiomyocytes, resulting in reduced amplitude and prolonged time courses of [Ca²⁺]_i transients compared to those of controls. Both SR-Ca²⁺ leak and [Ca²⁺]_i transients were normalized by treating diabetic rats with NaSe or by incubating diabetic myocytes with NaSe or Trx. Moreover, exposure of diabetic cardiomyocytes to antioxidants significantly improved [Ca²⁺]_i handling factors such as phosphorylation/protein levels of RyR2, amount of RyR2-bound FKBP12.6 and activities of both protein kinase A and CaMKII. NaSe treatment also normalized the oxidative stress/antioxidant defense biomarkers in plasma as well as Trx activity and nuclear factor-κB phosphorylation in the diabetic rat heart. Collectively, these findings suggest that redox modification through Trx-system besides the glutathione system contributes to abnormal function of RyR2s in hyperglycemic cardiomyocytes, presenting a potential therapeutic target for treating diabetics to preserve cardiac function.