Basic Fibroblast Growth Factor Inhibits Osteoclast Formation Induced by 1α,25-Dihydroxyvitamin D3 through Suppressing the Production of Osteoclast Differentiation Factor☆

Abstract Basic fibroblast growth factor (bFGF) inhibited osteoclast-like cell (OCL) formation in cocultures of mouse spleen cells with either osteoblasts or a stromal cell line, ST2, in the presence of 1α,25-dihydroxyvitamin D 3 [1,25(OH) 2 D 3 ]. bFGF directly acted on osteoblasts/stromal cells, but not osteoclast progenitors, to inhibit 1,25(OH) 2 D 3 -induced OCL formation. bFGF suppressed the mRNA expression of osteoclast differentiation factor (ODF) but did not affect that of osteoclastogenesis inhibitory factor (OCIF) in ST2 cells treated with 1,25(OH) 2 D 3 and dexamethasone. Enzyme-linked immunosorbent assay showed that bFGF hardly affected OCIF production in the treated ST2 cells. A genetically engineered soluble form of ODF, but not anti-OCIF neutralizing antibody, abolished bFGF-mediated inhibition of OCL formation. bFGF suppressed the binding of 125 I-labeled OCIF to both ST2 cells and osteoblasts treated with 1,25(OH) 2 D 3 . These findings indicate that bFGF inhibits 1,25(OH) 2 D 3 -induced OCL formation via suppression of ODF production by osteoblasts/stromal cells.