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.
T. Kubota: None. M. Inoue: None. N. Kubota: None. I. Takamoto: None. K. Ueki: Speaker's Bureau; Self; Daiichi Sankyo Company, Limited, Eli Lilly and Company, Boehringer Ingelheim Pharmaceuticals, Inc., MSD K.K., Novo Nordisk Inc., Mitsubishi Tanabe Pharma Corporation, Kyowa Hakko Kirin Co., Ltd., Takeda. Research Support; Self; Takeda, Astellas, Novo Nordisk Inc. T. Yamauchi: Research Support; Self; Novo Nordisk Inc., Daiichi Sankyo Company, Limited, Sanofi, Takeda, Tanabe-Mitsubishi. T. Kadowaki: Consultant; Self; Novo Nordisk A/S, AstraZeneca, Merck Sharp & Dohme Corp.. Research Support; Self; Kissei Pharmaceutical Co., Ltd., Taisho Pharmaceutical Co., Ltd., Sanofi, Kyowa Hakko Kirin Co., Ltd., Novo Nordisk A/S, Astellas Pharma, Daiichi Sankyo Company, Limited, Takeda, Mitsubishi Tanabe Pharma Corporation, Ono Pharmaceutical Co., Ltd., Merck Sharp & Dohme Corp., Nippon Boehringer Ingelheim Co. Ltd.. Speaker's Bureau; Self; Astellas Pharma, AstraZeneca, Merck Sharp & Dohme Corp., Ono Pharmaceutical Co., Ltd., Takeda, Eli Lilly and Company, Nippon Boehringer Ingelheim Co. Ltd., Novo Nordisk A/S.