Recombinant bone morphogenetic protein (BMP)-2 regulates costochondral growth plate chondrocytes and induces expression of BMP-2 and BMP-4 in a cell maturation-dependent manner

This study examined the effect of recombinant human bone morphogenetic protein‐2 on several parameters of growth, differentiation, and matrix synthesis and on the endogenous production of mRNA of bone morphogenetic proteins 2 and 4 by growth plate chondrocytes in culture. Chondrocytes from resting and growth zones were obtained from rat costochondral cartilage and cultured for 24 or 48 hours in medium containing 0.05‐100 ng/ml recombinant human bone morphogenetic protein‐2 and 10% fetal bovine serum. Incorporation of [3H]thymidine, cell number, alkaline phosphatase specific activity, incorporation of [3H]proline into collagenase‐digestible protein and noncollagenase‐digestible protein, and incorporation of [35S]sulfate were assayed as indicators of cell proliferation, differentiation, and extracellular matrix synthesis. mRNA levels T for bone morphogenetic proteins 2 andv4 were determined by Northern blot analysis. Recombinant human bone morphogenetic protein‐2 increased the incorporation of [3H]thymidine by quiescent resting‐zone and growth‐zone cells in a similar manner, whereas it had a differential effect on nonquiescent cultures. At 24 and 48 hours, 12.5‐100 ng/ml recombinant human bone morphogenetic protein‐2 caused a dose‐dependent increase in cell number and DNA synthesis in resting‐zone chondrocytes. No effect was seen in growth‐zone cell Recombinant human bone morphogenetic protein‐2 stimulated alkaline phosphatase specific activity in resting‐zone chondrocytes in a bimodal manner, causing significant increases between 0.2 and 0.8 ng/ml and again between 25 and 100 ng/ml. In contrast, alkaline phosphatase specific activity in growth‐zone chondrocytes was significantly increased only between 12.5 and 100 ng/ml. Recombinant human bone morphogenetic protein‐2 increased the production of both collagenase‐digestible protein and noncollagenase‐digestible protein by resting‐zone and growth‐zone cells, but incorporation of [35S]sulfate was unaffected. Administration of recombinant human bone morphogenetic protein‐2 also increased incorporation of [3H]uridine in both resting‐zone and growth‐zone chondrocytes; these cells produced mRNA for bone morphogenetic proteins 2 and 4. Bone morphogenetic protein‐2 mRNA levels in both resting‐zone and growth‐zone chondrocytes increased in the presence of recombinant human bone morphogenetic protein‐2; however, bone morphogenetic protein‐4 mRNA levels in growth‐zone cells decreased under its influence, and those in re