Deficiency of Subsarcolemmal Mitochondria in Obesity and Type 2 Diabetes

TLDR

Subsarcolemmal mitochondrial deficits may contribute to muscle insulin resistance in type 2 diabetes. The study tests a novel hypothesis that mitochondrial dysfunction in skeletal muscle of type 2 diabetes is subcellularly distributed. Muscle biopsies from 11 type 2 diabetic, 12 obese nondiabetic, and 8 lean volunteers were used to isolate subsarcolemmal and intermyofibrillar mitochondria by differential centrifugation and digestion. Subsarcolemmal mitochondria from type 2 diabetic muscle exhibited a seven‑fold decrease in electron transport chain activity versus lean controls, whereas intermyofibrillar activity was similar to obese subjects but lower than lean, indicating a selective functional impairment despite modest mtDNA reductions.

Abstract

The current study addresses a novel hypothesis of subcellular distribution of mitochondrial dysfunction in skeletal muscle in type 2 diabetes. Vastus lateralis muscle was obtained by percutaneous biopsy from 11 volunteers with type 2 diabetes; 12 age-, sex-, and weight-matched obese sedentary nondiabetic volunteers; and 8 lean volunteers. Subsarcolemmal and intermyofibrillar mitochondrial fractions were isolated by differential centrifugation and digestion techniques. Overall electron transport chain activity was similar in type 2 diabetic and obese subjects, but subsarcolemmal mitochondria electron transport chain activity was reduced in type 2 diabetic subjects (0.017 ± 0.003 vs. 0.034 ± 0.007 units/mU creatine kinase [CK], P = 0.01) and sevenfold reduced compared with lean subjects (P < 0.01). Electron transport chain activity in intermyofibrillar mitochondria was similar in type 2 diabetic and obese subjects, though reduced compared with lean subjects. A reduction in subsarcolemmal mitochondria was confirmed by transmission electron microscopy. Although mtDNA was lower in type 2 diabetic and obese subjects, the decrement in electron transport chain activity was proportionately greater, indicating functional impairment. Because of the potential importance of subsarcolemmal mitochondria for signal transduction and substrate transport, this deficit may contribute to the pathogenesis of muscle insulin resistance in type 2 diabetes.