Abstract
Abstract Individually, transforming growth factor beta (TGFβ) and 1,25-dihydroxyvitamin D 3 (1,25(OH) 2D 3) alter the growth and differentiation of normal and transformed osteoblast-like (OB) cells. Although recent evidence suggests interactions between TGFβ and 1,25(OH) 2D 3 may occur, little is known of the individual or combined effects of these hormones on the expression of the osteoblast phenotype at the cytochemical and biochemical levels in normal human OB (hOB) cells. Primary cultures of hOBs were treated with TGFβ (0.001– 10 ng/ml) and 1,25(OH) 2D 3 (0.1 p M−100 n M) either alone or in combination. TGFβ and 1,25(OH) 2D 3 stimulated spindle-shaped cells to become stellate in appearance and increased the number of cytoplasmic processes. TGFβ increased 3H-thymidine incorporation and 1,25(OH) 2D 3 reduced this effect. Conversely, procollagen type-I synthesis and secretion were increased in a dose-dependent manner in the presence of TGFβ but were not significantly affected in the presence of 1,25(OH) 2D 3. TGFβ and 1,25(OH) 2D 3 each marginally increased alkaline phosphatase (ALP) activity, but the combination synergistically increased ALP activity in a dose- and time-dependent manner at the cytochemical and biochemical level (three to tenfold over vehicle controls; n=12). In contrast, TGFβ reduced 1,25(OH) 2D 3-stimulated osteocalcin secretion. These data suggest that TGFβ stimulates hOB cells to actively produce collagen matrix and proliferate. The combination of TGFβ and 1,25(OH) 2D 3, however, produces a synergistic increase in ALP activity and maintenance of collagen synthesis. 1,25(OH) 2D 3 stimulation may induce cells to advance to an endstage where cell proliferation is reduced and osteocalcin expression is promoted. Interactions between TGFβ and 1,25(OH) 2D 3 may represent important steps in the regulation of osteoblast differentiation and matrix production.
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