Wnt signaling genes in adipose tissue and skeletal muscle of humans with different degrees of insulin sensitivity

Abstract

Context: The β-catenin-dependent Wnt signaling plays a role in adipogenesis, myogenesis, and glucose homeostasis. Objective: The aim of this study was to assess adipose tissue and skeletal muscle expression of Wnt/β-catenin signaling genes in a young healthy population according to insulin sensitivity and its regulation by hyperinsulinemia and free fatty acids. Design: We examined 117 male volunteers. The participants were divided into subgroups of highinsulin sensitivity (IS) and low-IS on the basis of a 2-hour euglycemic clamp. In 20 subjects, the clamp was prolonged to 6 hours. After 1 week, another 6-hour clamp, with Intralipid/heparin infusion, was performed. Tissue biopsies were performed before each clamp and after 6-hour clamps. Additionally, we collected muscle biopsies from another group of 16 male subjects for cell cultures. Myotubes were treated with insulin separately and in combination with palmitate. Results: We found decreased adipose tissue WNT10B, FZD1/8, LRP5, DVL2, CTNN1B, TCF7L2, and AXIN2 and increased muscle WNT10B, FZD1/8, LRP6, DVL1, GSK3B, CTNNB1, TCF7L2, AXIN2, MYC, and CCND1 expression in the low-IS group. Hyperinsulinemia resulted in a decrease in adipose tissue FZD4, LRP5/6, TCF7L2, and AXIN2 and an increase in muscle FZD1/8, DVL1/2/3, TCF7L2, AXIN2, and MYC expression. These changes disappeared after free fatty acid elevation. In myotubes, insulin increased the expression of FZD1, DVL2, CTNNB1, and TCF7L2, whereas palmitate abolished these effects. Conclusions: The association of β-catenin-dependent Wnt signaling with insulin resistance is tissue specific. Observed changes might reflect a compensatory mechanism to increase muscle glucose uptake and to generate new fat cells in insulin-resistant conditions.