The vitamin D receptor (VDR) is expressed in human adipocytes and is transiently induced during early adipogenesis in mesenchymal progenitor cell models. VDR null mice exhibit enhanced energy expenditure and reduced adiposity even when fed high fat diets. Adipocyte-specific transgenic-expression of human VDR in mice enhances adipose tissue mass, indicating that VDR activation in adipocytes enhances lipid storage in vivo. In these studies, we conducted genomic profiling and differentiation assays in primary cultures of human adipose-derived mesenchymal progenitor cells to define the role of the VDR and its ligand 1,25-dihydroxyvitamin D3 (1,25D) in adipogenesis. In the presence of adipogenic media, 1,25D promoted lipid accumulation and enhanced the expression of FABP4, FASN, and PPARγ. Mesenchymal cells derived from 6-month old VDR null mice exhibited impaired adipogenesis ex vivo but differentiation was restored by stable expression of human VDR. STEAP4, a gene that encodes a metalloreductase linked to obesity, insulin sensitivity, metabolic homeostasis and inflammation, was highly induced in human adipose cells differentiated in the presence of 1,25D but was minimally affected by 1,25D in undifferentiated precursors. These studies provide a molecular basis for recent epidemiological associations between vitamin D status, body weight and insulin resistance which may have relevance for prevention or treatment of metabolic syndrome and obesity.
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