Abstract
Decorin is a small dermatan sulfate-rich proteoglycan which binds to collagen type I in vitro and in vivo. In atherosclerotic lesions the contents of low density lipoprotein (LDL), decorin, and collagen type I are increased, and ultrastructural studies have suggested an association between LDL and collagen in the lesions. To study interactions between 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 to microtiter wells. The interaction between LDL and decorin in the fluid phase was evaluated using a gel mobility shift assay. We found that LDL binds to decorin by ionic interactions. After treatment with chondroitinase ABC, decorin did not bind 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 amounts of LDL bound to the collagen. However, if decorin was first allowed to bind to the collagen, binding of LDL to the decorin-collagen complexes was over 10-fold higher than to collagen alone. Thus, decorin can link LDL with collagen type I in vitro, which suggests a novel mechanism for retention of LDL in collagen-rich areas of atherosclerotic lesions.
Highlights
Collagen is the major connective tissue component of atherosclerotic arteries, comprising up to 40% of the total protein in fibrous plaques and 60% in advanced lesions [6]
Interaction between low density lipoprotein (LDL) and Decorin—To study the ability of LDL to bind to decorin, 3H-LDL was added to microtiter wells coated with decorin
96% of the applied decorin bound to the LDL, and the bound decorin was released from the LDL at approximately 100 mM NaCl in a NaCl gradient, suggesting that decorin was bound to LDL via ionic interactions. In accord with this result, we found that, in the microtiter well binding assay, increasing concentrations of NaCl progressively decreased the binding of 35S-decorin to LDL-coated microtiter wells
Summary
(Received for publication, July 22, 1996, and in revised form, November 27, 1996). Markku O. Decorin is a small dermatan sulfate-rich proteoglycan which binds to collagen type I in vitro and in vivo. In atherosclerotic lesions the contents of low density lipoprotein (LDL), decorin, and collagen type I are increased, and ultrastructural studies have suggested an association between LDL and collagen in the lesions. Decorin can link LDL with collagen type I in vitro, which suggests a novel mechanism for retention of LDL in collagen-rich areas of atherosclerotic lesions. The present study concerns the interaction between native LDL and collagen type I in the absence and presence of decorin. In the absence of decorin, there was no significant interaction between LDL and collagen type I. When decorin was first allowed to bind to the immobilized collagen, significant amounts of LDL were bound to the decorin-collagen complexes formed.
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