2-Methylene-19-nor-1α-hydroxyvitamin D3 analogs inhibit adipocyte differentiation and PPARγ2 gene transcription

The hormonally active form of vitamin D3, 1α,25-dihydroxyvitamin D3 (1,25(OH)2D3), prevents adipogenesis in the 3T3-L1 preadipocyte cell line. In this paper, both a shortened side-chain non-calcemic analog, (20S)-1α-hydroxy-2-methylene-19-nor-bishomopregnacalciferol (2MbisP), as well as a highly bone-selective compound, 2-methylene-19-nor-(20S)-1α-hydroxyvitamin D3 (2MD), are shown to completely prevent adipocyte differentiation in this cell line. 2MbisP is slightly less potent than 1,25(OH)2D3, whereas 2MD is approximately two orders of magnitude more potent that the parent hormone in preventing adipocyte differentiation. The ability to block differentiation requires binding to the vitamin D receptor. Both 1,25(OH)2D3 and the analogs prevent the induction of the C/EBPα and PPARγ2 transcription factors, which is necessary for terminal differentiation. In contrast, the normal increase in C/EBPβ protein that occurs shortly after the induction of differentiation occurs both in the presence and absence of vitamin D compounds, and the C/EBPβ protein appears functional with respect to DNA binding and nuclear localization. Transient transfection studies show that 1,25(OH)2D3 prevents transactivation through the 5′ region of the PPARγ2 promoter, and thus acts at the transcriptional level to inhibit the normal upregulation of PPARγ2 that occurs during the course of 3T3-L1 cell differentiation.