Osteoclastic Metabolism of 25(OH)-Vitamin D3: A Potential Mechanism for Optimization of Bone Resorption

摘要

The extrarenal synthesis of 1 ? ,25 dihydroxyvitamin D 3 (1,25D)has been demonstrated in a number of cell types including os-teoblasts and cells of the monocyte/macrophage lineage. Theskeleton appears responsive to serum levels of the 1,25D pre-cursor, 25 hydroxyvitamin D 3 (25D), in terms of bone mineral-ization parameters. The effect of metabolism of 25D into active1,25D by osteoclast lineage cells is unknown. We found thatCYP27B1 mRNA expression increased with exposure of humanperipheralbloodmononuclearcells(PBMCs)tomacrophagecol-ony-stimulating factor in the presence or absence of receptoractivator of nuclear factor- ? B ligand. Consistent with this, hu-man osteoclast cultures incubated with 25D produced measur-able quantities of 1,25D.