Niacin is converted to NAD and NADP in tissues, whose products are involved in a number of cellular processes; and it is associated with the regulation of adipogenesis. In this study, we identified the molecular mechanism by which niacin promotes the adipogenesis in mouse 3T3-L1 cells. When the cells were cultured with niacin, the expression of adipogenic peroxisome proliferator-activated receptor γ, CCAAT enhancer binding protein (C/EBP)α, and their target genes was enhanced concomitant with an increase in triglyceride storage. Moreover, niacin suppressed the expression of cyclooxygenase-2 and decreased the production of prostaglandin (PG) F(2α) in the early phase of adipogenesis, which PG suppresses the progression of adipogenesis via the PGF(2α) receptor. Furthermore, niacin decreased the C/EBPβ level in the early phase of adipogenesis. These results indicate that niacin promoted adipogenesis by suppressing the production of the anti-adipogenic PGF(2α) through down-regulation of C/EBPβ-activated cyclooxygenase-2 expression in adipocytes.
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