1α,25-dihydroxyvitamin D3 stimulates human SOST gene expression and sclerostin secretion

Abstract

Sclerostin, the SOST gene product, is a negative regulator of bone formation and a positive regulator of bone resorption. In this study, treatment of human primary osteoblasts, including cells differentiated to an osteocyte-like stage, with 1α,25-dihydroxyvitaminD3 (1,25D) resulted in the dose-dependent increased expression of SOST mRNA. A similar effect was observed in human trabecular bone samples cultured ex vivo, and in osteocyte-like cultures of differentiated SAOS2 cells. Treatment of SAOS2 cells with 1,25D resulted in the production and secretion of sclerostin protein. In silico analysis of the human SOST gene revealed a single putative DR3-type vitamin D response element (VDRE) at position -6216 bp upstream of the transcription start site (TSS). This sequence was confirmed to have strong VDRE activity by luciferase reporter assays and electrophoretic mobility shift analysis (EMSA). Sequence substitution in the VDR/RXR half-sites abolished VDRE reporter activity and binding of nuclear proteins. A 6.3 kb fragment of the human proximal SOST promoter demonstrated responsiveness to 1,25D. The addition of the evolutionary conserved region 5 (ECR5), a known bone specific enhancer region, ahead of the 6.3 kb fragment increased basal promoter activity but did not increase 1,25D responsiveness. Site-specific mutagenesis abolished the responsiveness of the 6.3 kb promoter to 1,25D. We conclude that 1,25D is a direct regulator of human SOST gene and sclerostin protein expression, extending the pathways of control of sclerostin expression. At least some of this responsiveness is mediated by the identified classical VDRE however the nature of the transcriptional regulation by 1,25D warrants further investigation.

1,25-Dihydroxyvitamin D Alone Improves Skeletal Growth, Microarchitecture, and Strength in a Murine Model of XLH, Despite Enhanced FGF23 Expression

“…Both daily and biweekly 1,25D increased the expression of ANK, PHOSPHO1, and MGP, whereas FGF23Ab therapy increased only ANK expression. Expression of sclerostin (SOST), an inhibitor of bone formation that impairs the differentiation and mineralization of cultured osteoblasts, is known to be increased by 1,25D . FGF23Ab and biweekly 1,25D normalized the low sclerostin expression observed in untreated Hyp mice, whereas daily 1,25D induced SOST expression to threefold above that of WT mice (Supplemental Fig.…”

Hormonal Regulation of Osteocyte Perilacunar and Canalicular Remodeling in the Hyp Mouse Model of X-Linked Hypophosphatemia

“…(16) It is possible that the improvement in mineralization seen with 1,25D or FGF23Ab therapy, (16) leads to decreased lacunar size in Hyp mice. It has been shown that 1,25D stimulates SOST expression (48) and that sclerostin stimulates perilacunar matrix resorption (49) ; therefore, it is paradoxical that the increased SOST expression in treated Hyp mice is associated with improvement in lacunar size.…”

Analysis of SOST expression using large minigenes reveals the MEF2C binding site in the evolutionarily conserved region (ECR5) enhancer mediates forskolin, but not 1,25-dihydroxyvitamin D3 or TGFβ1 responsiveness

“… Addendum – While this manuscript was in revision, a report by Wijenayaka and colleagues [27] was published that concludes that Sost is up-regulated by 1,25(OH) 2 D 3 . …”