Molecular mechanism of 1,25-dihydroxyvitamin D sub(3) inhibition of adipogenesis in 3T3-L1 cells

• Published in: American journal of physiology: endocrinology and metabolism 2006-05, Vol.290 (5), p.E916-E924
• Main Authors: Kong, Juan, Li, Yan Chun
• Format: Article
• Language: English
• ISSN: 0193-1849; 1522-1555

We have investigated the molecular mechanism whereby 1,25-dihydroxyvitamin D sub(3) [1,25(OH) sub(2)D sub(3)] inhibits adipogenesis in vitro. 1,25(OH) sub(2)D sub(3) blocks 3T3-L1 cell differentiation into adipocytes in a dose-dependent manner; however, the inhibition is ineffective 24-48 h after the differentiation is initiated, suggesting that 1,25(OH) sub(2)D sub(3) inhibits only the early events of the adipogenic program. Treatment of 3T3-L1 cells with 1,25(OH) sub(2)D sub(3) does not block the mitotic clonal expansion or C/EBP beta induction; rather, 1,25(OH) sub(2)D sub(3) blocks the expression of C/EBP alpha , peroxisome proliferator-activated receptor- gamma (PPAR gamma ), sterol regulatory element-binding protein-1, and other downstream adipocyte markers. The inhibition by 1,25(OH) sub(2)D sub(3) is reversible, since removal of 1,25(OH) sub(2)D sub(3) from the medium restores the adipogenic process with only a temporal delay. Interestingly, although the vitamin D receptor (VDR) protein is barely detectable in 3T3-L1 preadipocytes, its levels are dramatically increased during the early phase of adipogenesis, peaking at 4-8 h and subsiding afterward throughout the rest of the differentiation program; 1,25(OH) sub(2)D sub(3) treatment appears to stabilize the VDR protein levels. Consistently, adenovirus-mediated overexpression of human (h) VDR in 3T3-L1 cells completely blocks the adipogenic program, confirming that VDR is inhibitory. Inhibition of adipocyte differentiation by 1,25(OH) sub(2)D sub(3) is ameliorated by troglitazone, a specific PPAR gamma antagonist; conversely, hVDR partially suppresses the transacting activity of PPAR gamma but not of C/EBP beta or C/EBP alpha . Moreover, 1,25(OH) sub(2)D sub(3) markedly suppresses C/EBP alpha and PPAR gamma mRNA levels in mouse epididymal fat tissue culture. Taken together, these data indicate that the blockade of 3T3-L1 cell differentiation by 1,25(OH) sub(2)D sub(3) occurs at the postclonal expansion stages and involves direct suppression of C/EBP alpha and PPAR gamma upregulation, antagonization of PPAR gamma activity, and stabilization of the inhibitory VDR protein.