THE PROTEOGLYCAN DECORIN LINKS LOW-DENSITY LIPOPROTEINS WITH COLLAGENTYPE-I

Decorin is a small dermatan sulfate-rich proteoglycan which binds to c ollagen type I in vitro and in vivo. In atherosclerotic lesions the co ntents of low density lipoprotein (LDL), decorin, and collagen type I are increased, and ultrastructural studies have suggested an associati on between LDL and collagen in the lesions, To study interactions betw een LDL, decorin, and collagen type I, we used solid phase systems in which LDL was coupled to a Sepharose column, or in which LDL, decorin, or collagen type I was attached 60 microtiter wells, The interaction between LDL and decorin in the fluid phase was evaluated using a gel m obility shift as say, We found that LDL binds to decorin by ionic inte ractions. After treatment with chondroitinase ABC, decorin did not bin d to LDL, showing that the glycosaminoglycan side chain of decorin is essential for LDL binding, Acetylated and cyclohexanedione-treated LDL did not bind to decorin, demonstrating that both lysine and arginine residues of apoB-100 are necessary for the interaction. When collagen type I was attached to the microtiter plates, only insignificant amoun ts of LDL bound to the collagen. However, if decorin was first allowed to bind to the collagen, binding of LDL to the decorin-collagen compl exes was over 10-fold higher than to collagen alone. Thus, decorin can link LDL with collagen type I in vitro, which suggests a novel mechan ism for retention of LDL in collagen-rich areas of atherosclerotic les ions.