1,25-Dihydroxyvitamin D3 inhibits synthesis and enhances degradation of proteoglycans in osteoblastic cells.

The effects of 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3), an active form of vitamin D3, on the metabolism of proteoglycans by an osteoblastic cell line MC3T3-E1 were studied. Cells metabolically labeled with [35S]sulfate and/or [3H]glucosamine synthesized large and small dermatan sulfate proteoglycans and heparan sulfate proteoglycan. The incorporation of [35S]sulfate into proteoglycans for 1 h was reduced by 1,25-(OH)2D3 in a dose-dependent manner with a maximum reduction of 40% obtained at 10(-8)M 1,25-(OH)2D3. This effect was observed for all the proteoglycans with the decrease for the large dermatan sulfate proteoglycan most prominent. Treatment with 1,25-(OH)2D3 did not influence the degree of sulfation nor the molecular size of the glycosaminoglycan chains. Thus, the change in the incorporation of [35S] sulfate reflects net change in the synthesis of proteoglycans. When cells were treated with beta-D-xyloside, 1,25-(OH)2D3 also inhibited net synthesis of dermatan sulfate glycosaminoglycan chains on this exogenous substrate suggesting that it decreases the capacity of the cells for glycosaminoglycan synthesis. The incorporation of [3H]glucosamine into hyaluronic acid was also inhibited up to 70% by 10(-8) M 1,25-(OH)2D3. Treatment with 24,25-dihydroxyvitamin D3 did not cause significant changes in the proteoglycan synthesis. Degradation of proteoglycans associated with the cell layer was enhanced by treatment with 1,25-(OH)2D3 at 10(-8) M. Proteoglycans exogenously added to the culture were also degraded with a cell-mediated process which was stimulated by treatment with 10(-8) M 1,25-(OH)2D3. These results demonstrate that 1,25-(OH)2D3 reduces the synthesis and stimulates the degradation of proteoglycans in osteoblastic cells in culture.