Chronic palmitic acid-induced lipotoxicity correlates with defective trafficking of ATP sensitive potassium channels in pancreatic β cells

Abstract

Lipotoxicity is associated with a high level of fatty acid accumulation in pancreatic β-cells. An overload of free fatty acids contributes to pancreatic β-cell apoptosis and dysfunction. Insulin secretion involves sequential ionic events upon glucose stimulation. ATP sensitive potassium (KATP) channels serve as glucose sensors and effectively initiate glucose-stimulated insulin secretion. This study investigated the effects of lipotoxicity on the trafficking of KATP channels in pancreatic β cells using chronic palmitic acid –injected mice and treated insulinoma cells. The chronic palmitic acid -injected mice displayed type II diabetic characteristics. The pancreatic sections of these mice exhibited a decrease in the expression of KATP channels. We then tested the time and dose effects of palmitic acid on the cell viability of INS-1 cells. We observed a significant decrease in the surface expression of KATP channels after 72 h of treatment with 0.4 mM palmitic acid. In addition, this treatment induced pancreatic β-cell apoptosis by increasing cleaved caspase 3 protein level. Our results demonstrated cotreatment with glibenclamide, the sulfonylurea compounds for type II diabetes mellitus, in palmitic acid -treated cells reduces cell death and recovers the glucose stimulated insulin secretion through increasing the surface expression of KATP channels. Importantly, glibenclamide also improved glucose tolerance, triglyceride concentration, and insulin sensitivity in the palmitic acid-injected mice. In conclusion, an increase in the surface expression of KATP channels restores insulin secretion, reduces pancreatic β-cell’s apoptosis, highlighting correct trafficking of KATP channels is important in survival of β-cells during lipotoxicity.