SIRT1 (NAD+-dependent deacetylase) plays a suppressive role during the late stages of adipogenesis. However, the effects of SIRT1 on the early phases of adipogenic differentiation from embryonic stem cells (ESCs) are poorly understood. We employed Sirt1+/+ and Sirt1-/- mouse embryonic stem cells (mESCs) to evaluate the role of SIRT1 during the early stage mESC differentiation to adipocytes in response to retinoic acid (RA) treatment. Treatment with EX527 (a SIRT1 inhibitor) during the early phase and SIRT1 knockout both significantly diminished differentiation to mature adipocytes. Expressions of marker genes of preadipocytes, brown adipocytes, and brite cells were significantly lower in Sirt1-/- mESCs than in Sirt1+/+ mESCs. Furthermore, SIRT1 knockout reduced RA-induced RA receptor (RAR)α and RARβ mRNA and protein expressions during early adipocyte differentiation. Nuclear receptor corepressor 1 (NCOR1), a negative regulator of RAR signaling, expression, and acetylation levels were higher in Sirt1-/- than in Sirt1+/+ mESCs. After RA treatment, chromatin immunoprecipitation assays using an antibody against NCOR1, revealed that NCOR1 binding to RARβ promoters was significantly lower in Sirt1-/- mESCs than in Sirt1+/+ mESCs, and luciferase reporter assays showed SIRT1 knockdown decreased RA-induced RARα activity. Taken together, these observations show SIRT1 is required during the early phase of mESC adipogenesis and that SIRT1 deficiency inhibits adipogenesis by increasing NCOR1 acetylation and down-regulating the expressions of RARα and RARβ.
Keywords: Adipogenesis; Embryonic stem cell; NCOR1; SIRT1.
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