Insulin and IGF1 signaling through the PI3K/AKT and MAPK/ERK pathways are essential for maintenance of brown and white adipose tissues (BAT and WAT), as shown by our previous results using adipocyte-specific and inducible IR/IGF1R knockout mice (Ai-DKO). Here, through a research to screen the genes essential for adipose tissues maintenance in WAT and BAT using Ai-DKO mice, we identified a reduction of α4, a protein phosphatase protector which regulate phosphorylation state, in Ai-DKO BAT. shRNA-mediated α4 knockdown (KD) altered insulin-stimulated phosphorylation status in BAT; decreased IRβ (Y1162/1163), IRS1 (Y612) and Akt (S473), with a mild change in ERK1/2 (T202/Y204) but increased ribosomal S6 protein (S235/236), suggesting α4 reduces S6 phosphorylation state via a unique pathway. Next, to investigate the impact of α4 in vivo, we created inducible adipocyte-specific α4 KO (Ai-α4 KO) mice with tamoxifen-inducible Cre-ERT2 transgene. Once induced α4 KO in adipocytes, the mice revealed extensive losses of adipocytes in SC-WAT and BAT depots with increased apoptotic cell death. Ai-α4 KO mice showed cold intolerance, severe diabetes, ectopic lipid accumulation in the liver, and pancreatic islet hyperplasia. RNA-seq showed a marked reduction of genes associated with mitochondrial fatty acid oxidation and increases with inflammatory cytokine pathways in Ai-α4 KO SC-WAT and BAT. WAT and BAT mass can recover after a few months in Ai-α4KO. Interestingly, lipidomics analysis displayed that the regenerated adipocytes showed unique lipid content in the Ai-α4KO. Thus, our model demonstrates that the tuning of phosphorylation status for insulin-dependent signaling by α4 is critical for maintaining and regeneration of white and brown adipose tissues.
M. Sakaguchi: None. S. Okagawa: None. Y. Okubo: None. S. Kitano: None. M. Igata: None. T. Kondo: None. E. Araki: Advisory Panel; Self; Abbott. Speaker’s Bureau; Self; ARKRAY, Astellas Pharma Inc., AstraZeneca, Eli Lilly Japan K.K., Merck & Co., Inc., Novo Nordisk Inc., WebMD LLC. Other Relationship; Self; Kowa Company, Ltd., Mitsubishi Tanabe Pharma Corporation, Novartis Pharma K.K., Sumitomo Dainippon Pharma Co., Ltd., Takeda Pharmaceutical Company Limited.
Japan Society for the Promotion of Science; Merck Sharp & Dohme Foundation; Takeda Foundation; Boehringer Ingelheim; Eli Lilly and Company