EFFECTS OF TRANSFORMING GROWTH-FACTOR-BETA (TGF-BETA) AND 1,25 DIHYDROXYVITAMIN D-3 ON THE FUNCTION, CYTOCHEMISTRY AND MORPHOLOGY OF NORMAL HUMAN OSTEOBLAST-LIKE CELLS

Individually, transforming growth factor beta (TGF beta) and 1,25-dihydroxyvitamin D-3 (1,25(OH)(2)D-3) alter the growth and differentiation of normal and transformed osteoblast-like (OB) cells. Although recent evidence suggests interactions between TGF beta and 1,25(OH)(2)D-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 TGF beta (0.001-10 ng/ml) and 1,25(OH)(2)D-3 (0.1 pM-100 nM) either alone or in combination. TGF beta and 1,25(OH)(2)D-3 stimulated spindle-shaped cells to become stellate in appearance and increased the number of cytoplasmic processes. TGF beta increased H-3-thymidine incorporation and 1,25(OH)(2)D-3 reduced this effect. Conversely, procollagen type-I synthesis and secretion were increased in a dose-dependent manner in the presence of TGF beta but were not significantly affected in the presence of 1,25(OH)(2)D-3 TGF beta and 1,25(OH)(2)D-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, TGF beta reduced 1,25(OH)(2)D-3-stimulated osteocalcin secretion. These data suggest that TGF beta stimulates hOB cells to actively produce collagen matrix and proliferate. The combination of TGF beta and 1,25(OH)(2)D-3, however, produces a synergistic increase in ALP activity and maintenance of collagen synthesis. 1,25(OH)(2)D-3 stimulation may induce cells to advance to an endstage where cell proliferation is reduced and osteocalcin expression is promoted. Interactions between TGF beta and 1,25(OH)(2)D-3 may represent important steps in the regulation of osteoblast differentiation and matrix production.