High-fat diet (HFD) induces insulin resistance but the actual role and source of reactive oxygen species (ROS) in this contest remains uncertain. In particular little is known about potential role of Nox2 in insulin resistance in skeletal muscle.
MATERIALS AND METHODS
Wild-type (WT) and Nox2 knockout (Nox2-KO) mice were fed up to 3 or 9 months either a standard-diet (SD: 5% fat) or a high-fat-diet (HFD: 45% fat). Before sacrifice mice were fasted and injected or not with 0.75 IU/kg insulin intraperitoneally, then gastrocnemius muscles were excised and frozen in liquid nitrogen or fixed in formalin.
Whole-body fat mass was measured by dual-energy X-ray absorptiometry. Serum levels of insulin and glucose were measured and HOMA index, an estimation of insulin resistance, was calculated. The same set of mice underwent insulin tolerance test and glucose tolerance test. For in vitro support C2C12, a murine myoblastic cell line, were cultured and treated with or without H2O2 (100 μM) or in presence of a standard concentration of glucose (5 mM) or a high concentration of glucose (HG, 25 mM) or palmitate (200 µM). Knockdown of Nox2 expression was performed using recombinant lentivirus containing shRNA to murine Nox2.
Nox2-KO mice fed HFD exhibited only modest changes in blood glucose, insulin level and HOMA-index and the absence of Nox2 was significantly protective against the development of glucose intolerance and insulin resistance. On a SD the decrease in glucose level after insulin injection occurs faster in Nox2-KO mice than in WT mice, this kinetic difference indicates that Nox2-KO mice are more sensitive to insulin than WT mice (Fig 1-3).
These data suggest that Nox2 mediates insulin resistance in skeletal muscle and its absence has a protective effect against insulin resistance induced by a HFD representing a new target for treatment of metabolic syndrome and its associated complications.