Evidence that both 1alpha,25-dihydroxyvitamin D3 and 24-hydroxylated D3 enhance human osteoblast differentiation and mineralization.
Vitamin D plays a major role in the regulation of mineral homeostasis and affects bone metabolism. So far, detailed knowledge on the vitamin D endocrine system in human bone cells is limited. Here we investigated the direct effects of 1alpha,25-(OH)2D3 on osteoblast differentiation and mineralization. Also, we studied the impact of 24-hydroxylation, generally considered as the first step in the degradation pathway of vitamin D, as well as the role of the nuclear and presumed membrane vitamin D receptor (VDR). For this we used a human osteoblast cell line (SV-HFO) that has the potency to differentiate during culture forming a mineralized extracellular matrix in a 3-week period. Transcriptional analyses demonstrated that both 1alpha,25-(OH)2D3 and the 24-hydroxylated metabolites 24R,25-(OH)2D3 and 1alpha,24R,25-(OH)3D3 induced gene transcription. All metabolites dose-dependently increased alkaline phosphatase (ALP) activity and osteocalcin (OC) production (protein and RNA), and directly enhanced mineralization. 1Alpha,24R,25-(OH)3D3 stimulated ALP activity and OC production most potently, while for mineralization it was equipotent to 1alpha,25-(OH)2D3. The nuclear VDR antagonist ZK159222 almost completely blocked the effects of all metabolites. Interestingly, 1beta,25-(OH)2D3, an inhibitor of membrane effects of 1alpha,25-(OH)2D3 in the intestine, induced gene transcription and increased ALP activity, OC expression and mineralization. In conclusion, not only 1alpha,25-(OH)2D3, but also the presumed 24-hydroxylated "degradation" products stimulate differentiation of human osteoblasts. 1Alpha,25-(OH)2D3 as well as the 24-hydroxylated metabolites directly enhance mineralization, with the nuclear VDR playing a central role. The intestinal antagonist 1beta,25-(OH)2D3 acts in bone as an agonist and directly stimulates mineralization in a nuclear VDR-dependent way.
van Driel
M
M
Department of Internal Medicine, Erasmus MC, 3015 GE Rotterdam, The Netherlands.
Koedam
M
M
Buurman
C J
CJ
Roelse
M
M
Weyts
F
F
Chiba
H
H
Uitterlinden
A G
AG
Pols
H A P
HA
van Leeuwen
J P T M
JP
D015650:24,25-Dihydroxyvitamin D 3; D002113:Calcification, Physiologic; D002117:Calcitriol / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology*; D002454:Cell Differentiation; D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D006801:Humans; D006887:Hydroxycholecalciferols / Q000494:pharmacology*; D010006:Osteoblasts / Q000166:cytology / Q000187:drug effects* / Q000502:physiology*; D015675:Osteocalcin / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D018167:Receptors, Calcitriol / Q000037:antagonists & inhibitors / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic
D006887:Hydroxycholecalciferols; D012333:RNA, Messenger; D018167:Receptors, Calcitriol; D011993:Recombinant Fusion Proteins; C410228:ZK159222; C030711:24-hydroxyvitamin D3; D015675:Osteocalcin; D015650:24,25-Dihydroxyvitamin D 3; D002117:Calcitriol