High-fat load: mechanism(s) of insulin resistance in skeletal muscle

• Published in: International Journal of Obesity p. S31
• Main Authors: Fisher-Wellman, K H, Lark, D S, Neufer, P D
• Format: Journal Article
• Language: English
• Published: Nature Publishing Group 01.12.2012
• Subjects: Ceramides; Development and progression; Dietary fat; Electron transport; Fatty acids; Glucose; Insulin resistance; Metabolites; Obesity; Physiological aspects; Skeletal muscle; Type 2 diabetes
• ISSN: 0307-0565

Skeletal muscle from sedentary obese patients is characterized by depressed electron transport activity, reduced expression of genes required for oxidative metabolism, altered mitochondrial morphology and lower overall mitochondrial content. These findings imply that obesity, or more likely the metabolic imbalance that causes obesity, leads to a progressive decline in mitochondrial function, eventually culminating in mitochondrial dissolution or mitoptosis. A decrease in the sensitivity of skeletal muscle to insulin represents one of the earliest maladies associated with high dietary fat intake and weight gain. Considerable evidence has accumulated to suggest that the cytosolic ectopic accumulation of fatty acid metabolites, including diacylglycerol and ceramides, underlies the development of insulin resistance in skeletal muscle. However, an alternative mechanism has recently been evolving, which places the etiology of insulin resistance in the context of cellular/mitochondrial bioenergetics and redox systems biology. Overnutrition, particularly from high-fat diets, generates fuel overload within the mitochondria, resulting in the accumulation of partially oxidized acylcarnitines, increased mitochondrial hydrogen peroxide (H.sub.2O.sub.2) emission and a shift to a more oxidized intracellular redox environment. Blocking H.sub.2O.sub.2 emission prevents the shift in redox environment and preserves insulin sensitivity, providing evidence that the mitochondrial respiratory system is able to sense and respond to cellular metabolic imbalance. Mitochondrial H.sub.2O.sub.2 emission is a major regulator of protein redox state, as well as the overall cellular redox environment, raising the intriguing possibility that elevated H.sub.2O.sub.2 emission from nutrient overload may represent the underlying basis for the development of insulin resistance due to disruption of normal redox control mechanisms regulating protein function, including the insulin signaling and glucose transport processes.