Impairment of M2a-Subtype Macrophage Activation by Il-4-Irs2 Pathway in Obesity

Introduction: M2a-subtype macrophage activation is known to be impaired in obesity, although the underlying mechanisms remain poorly understood.

Methods: We found that the phosphorylation levels of Irs2 by IL-4 were significantly reduced along with decreased Irs2 expression in macrophages of high-fat (HF) diet-fed mice. To investigate the role of Irs2 in the macrophages, we then generated myeloid cell-specific Irs2-deficient (MIrs2KO) mice.

Results: HF diet-fed MIrs2KO mice showed impairment of IL-4-induced M2a-subtype macrophage activation, resulting in insulin resistance. Expressions of the maker genes for M2a-subtype macrophages were downregulated by stabilization of the FoxO1/HDAC3/NCoR1 corepressor complex via impairment of the IL-4/Irs2 pathway. Furthermore, Irs2 expression was significantly suppressed by insulin treatment in macrophages, suggesting that chronic hyperinsulinemia downregulates macrophage Irs2 expression via insulin receptor (IR). Indeed, in myeloid cell-specific IR-deficient mice, the IL-4-Irs2 pathway was preserved in the macrophages due to the lack of IR-mediated downregulation of Irs2, resulting in a reduced degree of inflammation and insulin resistance.

Conclusion: These data suggest that in obesity, downregulation of macrophage Irs2 is induced by hyperinsulinemia, resulting in impaired IL-4-induced M2a-subtype macrophage activation, and insulin resistance.