Alterations of matrix- and cell-associated proteoglycans inhibit osteogenesis and growth response to fibroblast growth factor-2 in cultured rat mandibular condyle and calvaria

Matrix and cell surface proteoglycans (PGs) may play important roles in the control of cellular actions of heparan-binding growth factors such as fibr oblast growth factor (FGF) during chondrogenesis and osteogenesis. In this study, we used 4-methylumbelliferyl-beta-D-xyloside, an inhibitor of PG syn thesis, and sodium chlorate, a competitive inhibitor of glycoconjugate sulf ation, to determine the functional consequences of alterations of PG metabo lism on osteogenesis and on FGF actions in neonatal rat condyle and calvari a in vitro. Biochemical analysis showed that beta-D-xyloside (1 mM) or chlo rate (15 mM) treatment for 1-8 days inhibited cellular PG synthesis by 60-8 0% in condyle and calvaria, as evaluated by [S-35]sulfate incorporation. Hi stochemistry and immunohistochemistry showed that the inhibition of PG synt hesis by beta-D-xyloside resulted in reduced incorporation of chondroitin s ulfate into cartilage and bone matrix. This was associated with a 75% reduc tion in cell growth in condyle, determined by DNA synthesis, and in collage nous matrix synthesis in condyle and calvaria, evaluated by tritiated proli ne incorporation and type I collagen immunohistochemistry. Morphological an d quantitative autoradiographic analyses also showed that inhibition of PG synthesis by beta-B-xyloside blocked bone matrix formation by perichondral progenitor cells in condyles and by osteoblasts in calvaria. In addition, a lteration of PG metabolism blocked the mitogenic response to rhFGF-2 in cal varia. The data show that functional proteoglycans are essential for osteog enesis and for the growth response to FGF-2 during osteogenic differentiati on in vitro.