Macrophage plasma membrane chondroitin sulfate proteoglycan binds oxidizedlow-density lipoprotein

Lipoprotein interactions with macrophage proteoglycans (PGs) is believed to play an important role in the cellular uptake of lipoproteins and in macro phage cholesterol accumulation. Recently, we have shown the participation o f macrophage plasma membrane glycosaminoglycans (GAGs) in the cellular upta ke of oxidized LDL (Ox-LDL). The aim of the present study was to identify t he specific cell surface proteoglycans involved in this interaction. J-774 A.1 macrophage-like cell line plasma membrane proteoglycans were isolated b y anion exchange chromatography from cells that were prelabeled with [S-35] sodium sulfate. Using Sepharose 6B chromatography, cell surface major prote oglycans were identified as chondroitin sulfate (CS) proteoglycans (77%) an d heparan sulfate (HS) proteoglycans (23%). Binding rates of these S-35-lab eled proteoglycans to Ox-LDL and to native LDL were analyzed by their abili ty to bind lipoproteins coupled to a CnBr-activated Sepharose CL-4B chromat ography. Of the total labeled cell surface proteoglycans added to the colum n, 57% were bound to the Sepharose-coupled Ox-LDL, whereas 73% of the cell surface proteoglycans were bound to the Sepharose-coupled native LDL. Bindi ng of the plasma membrane macrophage S-35-labeled proteoglycans to Ox-LDL w as inhibited by adding increasing concentrations of non-labeled chondroitin sulfate, or by pretreatment of the S-35-labeled proteoglycans fraction wit h chondroitinase ABC. In contrast, neither the addition of non-labeled hepa ran sulfate, nor pretreatment of the labeled proteoglycans fraction with he parinase III, had any significant effect on proteoglycan binding to Ox-LDL. These findings were further supported by using mutant cells characterized by specific glycosaminoglycan deficiencies. Ox-LDL binding and degradation by mutant 745 CHO cells which are characterized by a deficiency in both hep aran sulfate and chondroitin sulfate, was decreased by 28 and 27% respectiv ely, compared to the binding of Ox-LDL to the wild-type CHO cells. Ox-LDL b inding and degradation by mutant 677 CHO cells, which lack heparan sulfate but have increased levels of chondroitin sulfate, however, was found to be increased by 29 and 19%, respectively, compared to Ox-LDL binding to the wi ld-type CHO cells. Finally, analysis of the cell surface proteoglycans in m acrophages that were subjected to oxidative stress, by their preincubation with angiotensin II, exhibited a 51-59% increase in their cell surface prot eoglycan content, with a major effect on chondroitin sulfate proteoglycans. The present study thus demonstrated that Ox-LDL can specifically bind to m acrophage surface chondroitin sulfate proteoglycans, and the macrophage con tent of this proteoglycan is increased under oxidative stress. The interact ion between macrophage chondroitin sulfate proteoglycans and Ox-LDL can con tribute to enhanced uptake of Ox-LDL with the formation of cholesterol-load ed foam cells, and accelerated atherosclerosis. (C) 2000 Elsevier Science I reland Ltd. All rights reserved.