1,25-dihydroxyvitamin D3 influences cellular homocysteine levels in murine preosteoblastic MC3T3-E1 cells by direct regulation of cystathionine β-synthase

✍ Scribed by Carsten Kriebitzsch; Lieve Verlinden; Guy Eelen; Natasja M van Schoor; Karin Swart; Paul Lips; Mark B Meyer; J Wesley Pike; Steven Boonen; Carsten Carlberg; Victor Vitvitsky; Roger Bouillon; Ruma Banerjee; Annemieke Verstuyf

• Publisher: American Society for Bone and Mineral Research
• Year: 2011
• Tongue: English
• Weight: 321 KB
• Volume: 26
• Category: Article
• ISSN: 0884-0431
• DOI: 10.1002/jbmr.493

✦ Synopsis

High homocysteine (HCY) levels are a risk factor for osteoporotic fracture. Furthermore, bone quality and strength are compromised by elevated HCY owing to its negative impact on collagen maturation. HCY is cleared by cystathionine b-synthase (CBS), the first enzyme in the transsulfuration pathway. CBS converts HCY to cystathionine, thereby committing it to cysteine synthesis. A microarray experiment on MC3T3-E1 murine preosteoblasts treated with 1,25-dihydroxyvitamin D 3 [1,25(OH) 2 D 3 ] revealed a cluster of genes including the cbs gene, of which the transcription was rapidly and strongly induced by 1,25(OH) 2 D 3 . Quantitative real-time PCR and Western blot analysis confirmed higher levels of cbs mRNA and protein after 1,25(OH) 2 D 3 treatment in murine and human cells. Moreover, measurement of CBS enzyme activity and quantitative measurements of HCY, cystathionine, and cysteine concentrations were consistent with elevated transsulfuration activity in 1,25(OH) 2 D 3 -treated cells. The importance of a functional vitamin D receptor (VDR) for transcriptional regulation of cbs was shown in primary murine VDR knockout osteoblasts, in which upregulation of cbs in response to 1,25(OH) 2 D 3 was abolished. Chromatin immunoprecipitation on chip and transfection studies revealed a functional vitamin D response element in the second intron of cbs. To further explore the potential clinical relevance of our ex vivo findings, human data from the Longitudinal Aging Study Amsterdam suggested a correlation between vitamin D status [25(OH)D 3 levels] and HCY levels. In conclusion, this study showed that cbs is a primary 1,25(OH) 2 D 3 target gene which renders HCY metabolism responsive to 1,25(OH) 2 D 3 .