Insulin and IGF1 signaling regulate function of brown and white adipose tissues. Recently we created adipocyte-specific inducible IR/IGF1R knockout mouse (Ai-DKO) and demonstrated the critical role of insulin signaling in maintenance of BAT and WAT. To further investigate downstream targets of these hormones regulating adipose tissue mass in adult animals, we compared gene expression patterns in WAT and BAT by using Ai-DKO mice, and found α4 expression was significantly reduced in Ai-DKO BAT but not in WAT compared with those of control. Knockdown of α4 in brown preadipocytecell lines using shRNA did not affect insulin-stimulated phosphorylation of IR, IRS1 or Akt; however, phosphorylation of ribosomal S6 protein was significantly increased in α4 KD cells after insulin stimulation. To investigate the impact of α4in mature adipocytesin vivo, we created inducible adipocyte-specific knockout of α4 gene (Ai-α4 KO) using floxed mice and mice carrying a tamoxifen-inducible Cre-ERT2transgene on the adiponectin promoter. Within 7 days, Ai-α4KO displayed an apparent decrease in SC-WAT and BAT mass, but not a significant effect on PG-WAT mass. Ai-α4 KO revealed extensive losses of adipocytes in SC-WAT and BAT depots with a significant increase in stromovascular cells in histological analysis with elevation of F4/80, TNF-α and IL-6, while no apparent changes were observed in PG-WAT. This appears to be due to a rapid development of an apoptotic process with increased TUNEL and cleaved caspase-3.Interestingly, Ai-α4KO showed marked reduction of BAT-associated functional gene UCP1 as well as PRDM16, Tfam and PGC1α mRNA compared to control. Consistent with these changes in mRNA and the decrease in BAT mass, Ai-α4 KO mice showed marked cold intolerance, glucose intolerance and insulin resistance. Thus, α4 is one of the components in control of insulin signaling and preferentially BAT mass, and has a unique role in regulating anti-apoptotic effect in brown adipocytes.
M. Sakaguchi: None. S. Okagawa: None. S. Kitano: None. T. Kondo: None. E. Araki: Research Support; Self; Astellas Pharma Inc., Boehringer Ingelheim Pharmaceuticals, Inc., Daiichi Sankyo Company, Limited, Novo Nordisk Inc., Takeda Pharmaceutical Company Limited. Speaker's Bureau; Self; Astellas Pharma Inc., Merck & Co., Inc., Novo Nordisk Inc., Ono Pharmaceutical Co., Ltd., Sanofi.
Japan Society for the Promotion of Science; Takeda Foundation; MSD Foundation; Kenzou Suzuki Foundation; Ono Foundation; Motida Foundation