Role of Macrophage Glycosaminoglycans in the Cellular Catabolism of Oxidized LDL by Macrophages

Abstract

Abstract-Macrophage binding sites for oxidized LDL (Ox-LDL) include class A scavenger receptors (SR-As), the CD-36 molecule, and an additional but hitherto unidentified binding site. Because cell-surface glycosaminoglycans (GAGs) were previously shown to be involved in the cellular uptake of native LDL and lipoprotein(a), several strategies to assess the participation of heparan sulfate (HS) and chondroitin sulfate (CS) in macrophage catabolism of Ox-LDL were used. First, incubation of J-774 A.1 macrophage-like cells with either heparinase or chondroitinase, or with both enzymes together, reduced the binding, uptake, and degradation of 125 I-Ox-LDL by 20% to 45%, in comparison with control nontreated cells, while catabolism of 125 I-labeled acetylated LDL (Ac-LDL) and native LDL were unaffected. Second, the proteoglycan (PG) cellular content was increased by cell enrichment with exogenous GAGs or by using human monocyte-derived macrophages from two patients with Sanfilippo mucopolysaccharidosis, which are characterized by cellular HS accumulation. In these macrophages, cellular uptake of 125 I-Ox-LDL increased, while catabolism of 125 I-Ac-LDL and native LDL were unaffected. Experiments using conditioned media from control, heparinase-digested, or chondroitinase-digested macrophages indicated that neither secreted GAGs nor released digestion products played any role in Ox-LDL catabolism. To evaluate potential interactions between cell-surface GAGs and known receptors for Ox-LDL, we used excess unlabeled Ac-LDL to block SR-As or anti-CD-36 antibodies to block CD-36, and then examined the catabolism of 125 I-Ox-LDL by GAG-enriched or -depleted macrophages. Both excess unlabeled Ac-LDL and anti-CD-36 antibodies reduced 125 I-Ox-LDL catabolism, but only excess unlabeled Ac-LDL completely abolished the increase in 125 I-Ox-LDL catabolism on GAG enrichment of the cells, indicating a cooperation between exogenous GAGs and cell-surface SR-As in the catabolism of OX-LDL. Moreover, the addition of GAGases to macrophages that were preincubated with anti-CD-36 antibodies and excess Ac-LDL further reduced macrophage degradation of Ox-LDL in comparison with cells that were pretreated only with anti-CD-36 antibodies and Ac-LDL, indicating a more complex role for endogenous GAGs. Overall, these studies demonstrate a substantial contribution of macrophage-associated GAGs in the catabolism of Ox-LDL, which is mediated in part by a cooperation between GAGs and cell-surface SR-As. (Arterioscler Thromb Vasc Biol. 1998;18:542-553.) Key Words: proteoglycans Ⅲ oxidized LDL Ⅲ macrophages Ⅲ glycosaminoglycans Ⅲ mucopolysaccharidosis O xidatively modified LDL is likely to play an important contributory role in the development of atherosclerosis. Oxidized epitopes, including oxidized apoB, the major protein of Ox-LDL, have been demonstrated in human lesions. 1,2 Ox-LDL contains many biologically active molecules, such as lysophosphatidylcholine 3,4 and oxidized sterols, 5,6 that substantially alter the metabolism of arterial wall cells. Fu...

The Pathogenesis of Foam Cell Formation

“…Digestion of heparan sulfate and chondroitin sulfate could reduce degradation by 40%. 23 This affect was not seen at 10 g/mL but only at concentrations Ͼ25 g/mL. Perhaps some modified LDL is internalized by attachment to the plasma membrane via glycosaminoglycans, but stimulation of macropinocytosis by interaction with the scavenger receptor is necessary.…”

“…Recently glycosaminoglycans and proteoglycans have been shown to contribute to the catabolism of OxLDL. 23,24 One study showed a cooperation between glycosaminoglycans and cell-surface scavenger receptors (SR-As). Digestion of heparan sulfate and chondroitin sulfate could reduce degradation by 40%.…”

Pomegranate juice inhibits oxidized LDL uptake and cholesterol biosynthesis in macrophages

“…However, CD36 is not the only surface binding site that mediates the uptake of Ox-LDL by macrophages. Specifically, PJ could interact with other scavenger receptors such as SR-A (SR-AI, SR-AII) or with proteoglycans [37], which were also shown to mediate uptake of Ox-LDL by macrophages [38,39], resulting in interference of the cellular uptake of the lipoprotein. PJ polyphenols could also interfere with the uptake of Ox-LDL by interaction with macrophage surface phospholipids and/or kinases [40,41].…”

Dietary manganese affects the concentration, composition and sulfation pattern of heparan sulfate glycosaminoglycans in Sprague-Dawley rat aorta

“…In contrast to chondroitin sulfate proteoglycans (CSPGs), which play a role in LDL retention and modification in arterial intima (Pillarisetti 2000), HSPGs may act as potential receptors for atherogenic lipoproteins or facilitate the uptake of ligands by a process called ligand transfer to lipoprotein receptors, such as the LDL receptorrelated protein (LRP), which binds and internalizes aggregated LDL in human vascular smooth muscle cells (Edwards et al 1995;Albertini et al 1997). Thus, HSPGs are important for the accumulation of cholesterol esters in fibroblasts (Kaplan et al 1998). Additionally, an increase in sulfated GAGs rather than in non-sulfated, plays a critical role in enhancing blood vessel lipid deposition and accumulation (Li et al 1997).…”