Mechanisms underlying antidiabetes effects of GLP-1 analogs such as liraglutide, collectively termed incretins, remain incompletely understood. While incretins boost insulin secretion, they also modulate the immune system and have anti-obesity effects. We discovered that prediabetic patients treated with incretins have increased thermogenic gene expression in supraclavicular adipose tissue (AT) . Interestingly, incretin-treated patients were found to have elevated levels of IL6 plasma, consistent with the observation that incretin treatment induces IL6 secretion by human monocytes. We hypothesized that incretins induce adipocyte browning via IL6 and used the mouse model to test if IL6 receptor (IL6Ra) signaling underlies the effects of the incretin-IL6 axis. We show that liraglutide transiently increases IL6 in circulation and ILRa signaling in AT while metronomic liraglutide treatment results in AT browning and improved glucose clearance in mice. IL6-blocking antibody treatment inhibited the thermogenic and antidiabetes effects of liraglutide. Based on the observation that IL6 induces thermogenic gene expression in cultured adipocytes, we hypothesized that the incretin-IL6 axis directly induces adipocyte browning. To test this, we generated mice with IL6Ra knockout in Pdgfrb-positive adipocyte progenitors (APC-KO) and in adipocytes (AD-KO) . We show that liraglutide-induced weight loss does not depend on IL6 signaling in the adipocyte lineage. However, both IL6Ra APC-KO and AD-KO mice failed to undergo thermogenic adipocyte browning and glucose utilization increase in response to liraglutide treatment. We conclude that the antidiabetes effects of metronomically administered incretins are mediated by transient upregulation of IL6, which activates canonical ILRa signaling and thermogenesis in adipocytes.
A.D.Gutierrez: None. Z.Gao: None. Y.Yu: None. M.Kolonin: n/a.
National Institutes of Health (NIDDK 5R21DK122234)