Binding of platelet‐derived growth factor and low density lipoproteins to glycosaminoglycan species produced by human arterial smooth muscle cells

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Abstract
The platelet‐derived growth factor (PDGF) binds via a defined amino acid sequence to heparin (Fager et al., 1992, In Vitro Cell. Dev. Biol., 28A:176–180) and the protein moiety of low density lipoproteins (LDL; apo B‐100) via a similar sequence to chondroitin sulfate (Camejo et al., 1988, Arteriosclerosis Thromb., 8:368–377). In this study, synthetic oligopeptides were used to explore the capacity of smooth muscle cell‐derived glycosaminoglycans to bind to the critical sequences of PDGF and apo B‐100. In vitro, proliferating human arterial smooth muscle cells synthesized twice as much proteoglycans as did quiescent cells. The dominating glycosaminoglycan side chains were chondroitin and heparan sulfates in secreted and cell‐associated proteoglycans, respectively. The chondroitin sulfate‐rich proteoglycans had a higher molecular size and were to a larger extent secreted into the culture medium than the heparan and dermatan sulfate‐rich proteoglycans. Heparan, dermatan, and chondroitin sulfates bound to the PDGF‐derived oligopeptide with affinities similar to those of heparin. However, while heparan and dermatan sulfates both inhibited DNA synthesis in human arterial smooth muscle cells, chondroitin sulfate had no such inhibitory effect. Like the PDGF‐derived oligopeptide, the apo B‐100‐derived oligopeptide bound to these glycosaminoglycans. At the same time, both oligopeptides displaced bound LDL from chondroitin sulfate in vitro and released the block on DNA synthesis in smooth muscle cells that heparin induced in culture. Thus, chondroitin, dermatan, and heparan sulfates produced by arterial smooth muscle cells may bind LDL and PDGF competitively in atherogenesis but only heparan and dermatan sulfates inhibit cellular DNA synthesis. LDL and PDGF deposition may occur by binding to similar binding sites on glycosaminoglycans derived from smooth muscle cells within atherosclerotic lesions.

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