EXOGENOUS GLYCOSAMINOGLYCANS (GAG) DIFFERENTIALLY MODULATE GAG SYNTHESIS BY ANCHORAGE-INDEPENDENT CULTURES OF THE OUTER CELLS FROM NEONATALRAT CALVARIA IN THE ABSENCE AND PRESENCE OF TGF-BETA

In anchorage-dependent (AD) cultures of the outer cell population (OCP ) from neonatal rat calvaria, transforming growth factor-beta(1) (TGF- beta) specifically upregulated the synthesis of chondroitin sulfate (C S) proteoglycan (PG) and uncoupled the inhibitory effect of increasing cell density on CS PG synthesis (reference #30). Utilizing the same c ell population, we have further examined the possibility that glycosam inoglycans (GAG) known to be synthesized and secreted by bone cells mi ght exert feedback effects on GAG synthesis and/or its stimulation by TGF-beta. Although addition of TGF-beta alone stimulated net synthesis of HA and CS in both AD and anchorage-independent (AI) cultures, sign ificant alterations of basal and TGF-beta-stimulated GAG synthesis by exogenous GAGs were observed only in AI cultures. In AI cultures exoge nously added hyaluronic acid (HA) markedly enhanced the basal synthesi s of HA and CS while heparin (H) suppressed the basal synthesis of HA, CS as well as dermatan sulfate (DS). Also, the addition of HA markedl y potentiated the stimulation by TGF-beta of HA and CS synthesis as di d heparan sulfate (HS) for CS and DS synthesis. H suppressed the stimu lation of the synthesis of HA, CS and DS by TGF-beta. Overall, our res ults indicate specific effects of individual GAGs on basal and TGF-bet a-stimulated GAG synthesis in OCP cultures. We suggest that some of th e GAGs in the OCP microenvironment (which with the exception of HA are covalently linked to protein cores of secreted PGs), acting in concer t with TGF-beta, may serve as an amplification system for upregulating GAG synthesis in the rapidly growing neonatal calvarium.