Increased proton leak and SOD2 expression in myotubes from obese non-diabetic subjects with a family history of type 2 diabetes

Abstract

Muscle insulin resistance is linked to oxidative stress and decreased mitochondrial function. However, the exact cause of muscle insulin resistance is still unknown. Since offspring of patients with type 2 diabetes mellitus (T2DM) are susceptible to developing insulin resistance, they are ideal for studying the early development of insulin resistance. By using primary muscle cells derived from obese non-diabetic subjects with (FH+) or without (FH-) a family history of T2DM, we aimed to better understand the link between mitochondrial function, oxidative stress, and muscle insulin resistance. Insulin-stimulated glucose uptake and glycogen synthesis were normal in FH+ myotubes. Resting oxygen consumption rate was not different between groups. However, proton leak was higher in FH+ myotubes. This was associated with lower ATP content and decreased mitochondrial membrane potential in FH+ myotubes. Surprisingly, mtDNA content was higher in FH+ myotubes. Oxidative stress level was not different between FH+ and FH- groups. Reactive oxygen species content was lower in FH+ myotubes when differentiated in high glucose/insulin (25mM/150pM), which could be due to higher oxidative stress defenses (SOD2 expression and uncoupled respiration). The increased antioxidant defenses and mtDNA content in FH+ myotubes suggest the existence of compensatory mechanisms, which may provisionally prevent the development of insulin resistance.

Keywords: 2′,7′-dichlorfluorescein-diacetate; ANT; COX; CS; DCFH-DA; FCCP; FH; GSH; GSSG; HGI; IPAQ; IκKβ; JNK; LGI; Mitochondrial proton leak; Muscle; OCR; Oxidative phosphorylation; Oxidative stress; PPARγ; RMR; ROS; RQ; SOD2; T2DM; TMRE; UCP3; adenine nucleotide translocase; c-Jun N-terminal kinase; carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone; citrate synthase; cytochrome C oxidase; family history; high glucose, high insulin differentiation medium; inhibitor of NF-κB kinase; international physical activity questionnaire; low glucose, low insulin differentiation medium; manganese superoxide dismutase; oxidized glutathione; oxygen consumption rates; peroxisome proliferator-activated receptor γ; reactive oxygen species; reduced glutathione; respiratory quotient; resting metabolic rate; tetramethylrhodamine ethyl ester; type 2 diabetes mellitus; uncoupling protein 3.