Regulation of Adipogenesis and Key Adipogenic Gene Expression by 1, 25-Dihydroxyvitamin D in 3T3-L1 Cells

The functions of 1, 25-dihydroxyvitamin D (1, 25-(OH)(2)D-3) in regulating adipogenesis, adipocyte differentiation and key adipogenic gene expression were studied in 3T3-L1 preadipocytes. Five concentrations (0.01, 0.1, 1, 10, 100nM) of 1, 25-(OH)(2)D-3 were studied and lipid accumulation measured by Oil Red O staining and expression of adipogenic genes quantified using quantitative real-time PCR. Adipogenic responses to 1, 25-(OH)(2)D-3 were determined on 6, and 12 h, and days 1-10 after induction of adipogenesis by a hormonal cocktail with or without 1, 25-(OH)(2)D-3. In response to 1, 25-(OH)(2)D-3 (1, 10, and 100 nM), lipid accumulation and the expression of PPAR gamma, C/EBP alpha, FABP4 and SCD-1 were inhibited through day 10, and vitamin D receptor expression was inhibited in the early time points. The greatest inhibitory effect was upon expression of FABP4. Expression of SREBP-1c was only affected on day 2. The lowest concentrations of 1, 25-(OH)(2)D-3 tested did not affect adipocyte differentiation or adipogenic gene expression. The C/EBP alpha promoter activity response to 1, 25-(OH)(2)D-3 was also tested, with no effect detected. These results indicate that 1, 25-(OH)(2)D-3 inhibited adipogenesis via suppressing adipogenic-specific genes, and is invoked either during PPAR gamma activation or immediately up-stream thereof. Gene expression down-stream of PPAR gamma especially FABP4 was strongly inhibited, and we suggest that the role of 1, 25-(OH)(2)D-3 in regulating adipogenesis will be informed by further studies of adipogenic-specific gene promoter activity.