Abnormal response of osteoblasts from Hyp mice to 1,25-dihydroxyvitamin D3.
To further explore the hypothesis of an osteoblast inappropriate response to 1,25-(OH)2D3 in hypophosphatemic vitamin D-resistant rickets (HYP), osteoblasts were isolated from Hyp mice, the animal model for human HYP, and their response to a physiologic dose of 1,25-(OH)2D3 (10(-10) M) was investigated with respect to alkaline phosphatase (ALP) activity and cell proliferation, and compared to that of normal osteoblasts. Cells in secondary culture were incubated for 72 h while in log phase, with or without 1,25-(OH)2D3, at various medium phosphate (P) concentrations ranging from 0.5 to 4.5 mM. Stimulation of ALP activity and inhibition of cell proliferation was induced by 10(-10)M 1,25-(OH)2D3 in normal cells exposed to medium P concentration corresponding to serum levels observed in normal mice (2.1-2.7 mM P). By contrast, Hyp cells failed to respond to 1,25-(OH)2D3 in that range of P concentrations. Stimulation of ALP activity and inhibition of proliferation of mutant cells were evident at higher medium P concentrations (over 3 mM). 1,25-(OH)2D3 at the supraphysiologic level of 10(-9)M had no consistent effect on ALP activity in normal and Hyp mouse osteoblasts, but inhibited cell proliferation in cultures of both genotypes at all P concentrations tested. These results indicate that extracellular P modulates the action of 1,25-(OH)2D3 on osteoblasts, and that this modulation was altered in osteoblasts from Hyp mice. The failure of Hyp cells to respond to a physiologic dose of 1,25-(OH)2D3 upon normal P concentration may reflect the abnormal response of bone to 1,25-(OH)2D3 observed in Hyp mice and HYP patients.
Yamamoto
T
T
Shriners Hospital, Department of Surgery, Montreal, Quebec, Canada.
Ecarot
B
B
Glorieux
F H
FH
D000469:Alkaline Phosphatase / Q000378:metabolism*; D000818:Animals; D002117:Calcitriol / Q000494:pharmacology*; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D003470:Culture Media; D004247:DNA / Q000032:analysis; D007015:Hypophosphatemia, Familial / Q000378:metabolism*; D051379:Mice; D008807:Mice, Inbred BALB C; D010006:Osteoblasts / Q000166:cytology / Q000187:drug effects* / Q000201:enzymology; D010710:Phosphates / Q000097:blood* / Q000494:pharmacology
D003470:Culture Media; D010710:Phosphates; D004247:DNA; D000469:Alkaline Phosphatase; D002117:Calcitriol