Mechanisms of Insulin Resistance in Humans

Insulin resistance in skeletal muscle is a characteristic abnormality in obesity and the metabolic syndrome and a major factor responsible for the development of type 2 diabetes. Although the mechanisms responsible for muscle insulin resistance are largely unclear, lipid oversupply is an important factor. Among numerous potential mechanisms whereby lipid oversupply may cause muscle insulin resistance, current evidence points towards inflammation as being critical. Recent studies in animals, however, indicate that the inflammatory response in skeletal muscles may require the presence of circulating pro-inflammatory factors suggesting that the inflammation induced insulin resistance in skeletal muscles may be a secondary event. More specifically, activation of Nuclear Factor-Kappa B(NF-kB), and inflammatory master switch that drives the production of numerous pro-inflammatory cytokines in fat and liver, has been implicated in causing insulin resistance in skeletal muscles by increasing circulating pro-inflammatory cytokines. In contrast, animal studies have found that activation of NF-KB directly in skeletal muscles has no or little effect on its insulin sensitivity but does produce other abnormalities such as increased proteasome activity. The study shall therefore be undertaken to determine to what extent lipid-induced inflammation and insulin resistance in skeletal muscles requires the presence of circulating proinflammatory factors in humans.