HES1 inhibits adipogenesis of porcine mesenchymal stem cells via transcriptional repression of FAD24

Adipogenesis, the development from preadipocytes or mesenchymal stem cells (MSCs) to mature adipocytes, is regulated by a network of signaling pathways and transcription factors. The involvement of Notch signaling and its effector HES1 in adipogenesis has been investigated in several studies with conflicting results. The underlying mechanisms remain unclear because of the lack of information about HES1 target genes during adipocyte differentiation. As a novel gene transiently up-regulated in early adipogenesis, FAD24 functions as a positive regulator of adipocyte differentiation in both preadipocytes and MSCs. In the present study, we report that the expression level of FAD24 is inversely associated with that of HES1 in porcine MSCs after adipogenic induction. Enforced overexpression of HES1 in MSCs during the early stage of adipogenesis significantly repressed the transcription of FAD24 (P < 0.01) and the other pro-adipogenic genes (P < 0.05), resulting in reduced intracellular lipid accumulation. Sequence analysis showed that porcine FAD24 harbors an evolutionarily conserved HES1 binding site in its proximal promoter region. Functional HES1, but not its dominant-negative mutant, markedly reduced the promoter activity of FAD24 (P < 0.01). Site-directed mutation and chromatin immunoprecipitation further confirmed that HES1 inhibits FAD24 transcription by direct binding to the promoter. Taken together, we identified FAD24 as a novel downstream target of HES1 during adipogenesis. Our data suggest that HES1-mediated repression of FAD24 transcription at the early stage of adipocyte differentiation may contribute to the impaired adipogenesis induced by the Notch-HES1 signaling pathway.