1749-P: Deficient Mitochondrial Activation in Type 2 Diabetic Human ß-Cells during Insulin Secretion

Glucose and cellular energy metabolism are central components of glucose sensing in pancreatic β-cells. Conceptually, β-cells operate by converting the rate of glucose metabolism into the rate of insulin secretion. We have identified a novel activation mechanism in healthy human β-cell mitochondria that plays a central role in setting this rate of metabolism during glucose-stimulated insulin secretion (GSIS). Using live islets and dispersed islet cell cultures originating from type 2 diabetic (T2D) and nondiabetic human cadavers, here we show the failure of this activation mechanism and a loss of bioenergetic control in β-cells from T2D individuals. Modular kinetic analysis of oxidative phosphorylation was used to measure pathway activities based on monitoring cell respiration, mitochondrial membrane potential (ΔψM) and NADH/NAD⁺. We observed an energization-dependent activation of glucose oxidation during GSIS in nondiabetic β-cells, and localized this to intramitochondrial NADH-producing pathways, excluding Ca²⁺-dependent activation. In T2D β-cells the activation of this activation was impaired. Chronic culturing of nondiabetic β-cells at elevated glucose concentration or in the presence of methylglyoxal recapitulated the suppression of activation observed in T2D β-cells. In high glucose-cultured nondiabetic and in standard-cultured T2D β-cells the magnitude of GSIS was highly variable between individuals, and often increased. GSIS correlated well and was predicted by ΔψM in nondiabetic β-cells, but this bioenergetic fine control was lost in T2D suggesting a rearrangement of stimulus-secretion coupling in T2D, where the role energetics reduces to permissive, and other coupling pathways become dominant with kinetic properties different from nondiabetic.