title: Endocytosis, partial degradation and release of heparan sulfate by elicited mouse peritoneal macrophages.
abstract: Interactions between glycosaminoglycans (GAGs) and low density lipoprotein (LDL) are thought to influence the progression of atherogenesis. In an effort to gauge whether macrophages mediate GAG-LDL interaction by GAG modification, we have investigated the endocytosis, degradation and retro-endocytosis of the GAG heparan sulfate (HS) by mouse peritoneal macrophages. Radiolabelled HS was produced by derivatization with sulfosuccinimidyl-3-(4-hydroxyphenyl) propionate and radio-iodination by the chloramine T method. The amount of 125I-HS internalized by cultures of thioglycollate-elicited macrophages rose over a 24 h time period in proportion to the amount of tracer added to the wells (2-2500 ng ml-1). Analysis of GAG molecular weight was performed using gel filtration chromatography and polyacrylamide gel electrophoresis. After a 24 h pulse period, the 125I-HS in the intracellular fraction of the cultured cells was of smaller molecular weight than for control material. During a 24 h cold chase, fragments of 125I-HS were released into the medium. These fragments had lower affinity for Polybrene-Sepharose but did not appear significantly N-desulfated as determined by low pH nitrous acid treatment. The NADPH oxidase inhibitor diphenylene iodonium, although minimizing basal and phorbol ester-triggered radical output, did not inhibit 125I-HS depolymerization. These data indicate that elicited macrophages can interact with and reduce the polymer length of HS without extensively desulfating the molecule. They are consistent with a mechanism by which the macrophage internalizes and partially degrades HS by endoglucuronidase activity rather than NADPH oxidase-generated free radicals, followed by release of the products into the extracellular milieu.
authors.affiliation: Heart Research Institute, Sydney, NSW, Australia.
authors.forename: M
authors.initials: M
authors.lastname: Thomson
mesh_terms: D000818:Animals; D001713:Biphenyl Compounds / Q000494:pharmacology; D002478:Cells, Cultured; D004705:Endocytosis; D005966:Glucuronidase / Q000378:metabolism*; D006497:Heparan Sulfate / Q000378:metabolism*; D008262:Macrophage Activation / Q000187:drug effects; D017737:Macrophages, Peritoneal / Q000378:metabolism*; D051379:Mice; D009247:NADH, NADPH Oxidoreductases / Q000037:antagonists & inhibitors; D019255:NADPH Oxidases; D009861:Onium Compounds / Q000494:pharmacology; D010703:Phorbol Esters / Q000494:pharmacology; D013481:Superoxides / Q000378:metabolism; D013864:Thioglycolates / Q000494:pharmacology
chemical_list: D001713:Biphenyl Compounds; D005966:Glucuronidase; D006497:Heparan Sulfate; D009247:NADH, NADPH Oxidoreductases; D019255:NADPH Oxidases; D009861:Onium Compounds; D010703:Phorbol Esters; D013481:Superoxides; D013864:Thioglycolates; C031291:diphenyliodonium