Selenoprotein W deficiency does not affect oxidative stress and insulin sensitivity in the skeletal muscle of high-fat diet-fed obese mice.

Selenoprotein W (SelW) is a selenium-containing protein with a redox motif found abundantly in the skeletal muscle of rodents. Previous in vitro studies suggest that SelW plays an antioxidant role; however, relatively few in vivo studies have addressed the antioxidant role of SelW. Since oxidative stress is a causative factor for the development of insulin resistance in obese subjects, we hypothesized that if SelW plays a role as an antioxidant, SelW deficiency could aggravate the oxidative stress and insulin resistance caused by a high-fat diet. SelW deficiency did not affect insulin sensitivity and H2O2 levels in the skeletal muscle of control diet-fed mice. SelW levels in the skeletal muscle were decreased by high-fat diet feeding for 12 wk. High-fat diet induced obesity and insulin resistance and increased the levels of H2O2 and oxidative stress makers, which were not affected by SelW deficiency. High-fat diet feeding increased the expression of antioxidant enzymes; however, SelW deficiency did not affect the expression levels of antioxidants. These results suggest that SelW does not play a protective role against oxidative stress and insulin resistance in the skeletal muscle of high-fat diet-fed obese mice.

Selenoprotein W depletion in vitro might indicate that its main function is not as an antioxidative enzyme.

Examination of the antioxidative homeostasis in skeletal muscle cells in the presence or absence of selenoprotein W (SelW) is necessary to understand the importance of SelW in the antioxidative system. Depletion of SelW by RNA interference was achieved by introducing a synthetic small interfering RNA into the mouse skeletal muscle cell line C2C12 (C3H). Transfectant screening was performed by real-time reverse transcription-PCR, Western blotting, flow cytometry, fluorescence staining, cell viability, and glutathione assays. SelW expression and mRNA levels were downregulated by 62.1 and 72.4%, respectively. In addition, acute cytotoxicity and an apoptosis rate of approximately 36% in SelW-depleted cells demonstrated that RNA interference was successful. As compared with non-SelW-depleted cells, the enzyme activities of glutathione peroxidase, superoxide dismutase, and catalase and total antioxidative capability and glutathione level increased by 47.6, 103.0, 31.0, 205.6, and 30.0%, respectively (P < 0.05). Thus, SelW is important for the antioxidative system of muscle cells. Depletion of SelW, however, could be compensated by other intracellular antioxidative enzymes because oxidative stress was not the causative factor for apoptosis in SelW-depleted cells. Thus, the main function of SelW in muscle cells is not in the antioxidative system.