Titin and CK2α are New Intracellular Targets in Acute Insulin Application-Associated Benefits on Electrophysiological Parameters of Left Ventricular Cardiomyocytes From Insulin-Resistant Metabolic Syndrome Rats.

Abstract

Previous studies have demonstrated that a high-carbohydrate intake could induce metabolic syndrome (MetS) in male rats with marked cardiac functional abnormalities. In addition, studies mentioned some benefits of insulin application on these complications, but there are considerable disagreements among their findings. Therefore, we aimed to extend our knowledge on the in-vitro influence of insulin on left ventricular dysfunction and also in the isolated cardiomyocytes from MetS rats. At the organ function level, an acute insulin application (100-nM) provided an important beneficial effect on the left ventricular developed pressure in MetS rats. Furthermore, to treat the freshly isolated cardiomyocytes from MetS rats with insulin provided marked recoveries in elevated resting intracellular Ca2+-level, as well as significant prevention of prolonged action potential through an augmentation in depressed K+-channel currents. Insulin also normalized the cellular levels of increased ROS and phosphorylation of PKCα, together with normalizations of apoptotic markers in MetS cardiomyocytes through the insulin-mediated regulation of phospho-Akt. Since not only elevated PKCα-activity but also reductions in phospho-Akt are key modulators of titin-based cardiomyocyte stiffening in hyperglycemia, insulin treatment of the cardiomyocytes prevented the activation of titin via the above pathways. Furthermore, CK2α-activation and NOS-phosphorylation could be prevented with insulin treatment. Mechanistically, we found that impaired insulin signaling and elevated PKCα and CK2α activities, as well as depressed Akt phosphorylation, are key modulators of titin-based cardiomyocyte stiffening in MetS rats. We propose that restoring normal kinase activities and also increases in phospho-Akt by insulin can contribute marked recoveries in MetS heart function, indicating a promising approach to modulate titin-associated factors in heart dysfunction associated with type-2 diabetes mellitus. Graphical Abstract.