title: Platelet phagocytosis and processing of beta-amyloid precursor protein as a mechanism of macrophage activation in atherosclerosis.
abstract: In human occluded saphenous vein grafts, we previously demonstrated cytotoxic foam cells, presumably derived from macrophages engulfing platelets. In the present study, we investigated whether platelet phagocytosis occurs in human atherosclerotic plaques, whether this activates macrophages, and whether the platelet constituent, amyloid precursor protein (APP), was involved. Immunohistochemistry documented the presence of APP, beta-amyloid peptide (Abeta, cleaved from APP), and platelets (CD9), along with inducible NO synthase (iNOS) and cyclooxygenase-2, two markers of macrophage activation, around microvessels in advanced human carotid artery plaques (n=18). Abeta colocalized with iNOS-expressing macrophages that were often surrounded by platelets. In vitro, murine J774 and human THP-1 macrophages were incubated with or without washed human platelets. Coincubation of macrophages and platelets led to platelet phagocytosis (electron and confocal microscopy) and formation of lipid-, APP-, and Abeta-containing foam cells. These expressed iNOS mRNA (reverse transcription-polymerase chain reaction) and protein and produced nitrite and tumor necrosis factor-alpha (ELISA). Macrophage pretreatment with 4-(2-aminoethyl)benzenesulfonyl fluoride, a protease inhibitor, reduced APP processing and inhibited NO biosynthesis induced by platelet phagocytosis but not by lipopolysaccharides. Human atherosclerotic plaques and J774 and THP-1 macrophages contained mRNA of the APP-cleaving enzyme beta-secretase. This is the first demonstration of Abeta, a peptide extensively studied in Alzheimer's disease, in human atherosclerotic plaques. It was present in activated iNOS-expressing perivascular macrophages that had phagocytized platelets. In vitro studies indicate that platelet phagocytosis leads to macrophage activation and suggest that platelet-derived APP is proteolytically processed to Abeta, resulting in iNOS induction. This represents a novel mechanism for macrophage activation in atherosclerosis.
authors.affiliation: Division of Pharmacology, University of Antwerp, Antwerp, Belgium. gdemeyer@uia.ua.ac.be
authors.forename: Guido R Y
authors.initials: GR
authors.lastname: De Meyer
authors.forename: Dieter M M
authors.initials: DM
authors.lastname: De Cleen
authors.forename: Susan
authors.initials: S
authors.lastname: Cooper
authors.forename: Michiel W M
authors.initials: MW
authors.lastname: Knaapen
authors.forename: Dominique M
authors.initials: DM
authors.lastname: Jans
authors.forename: Wim
authors.initials: W
authors.lastname: Martinet
authors.forename: Arnold G
authors.initials: AG
authors.lastname: Herman
authors.forename: Hidde
authors.initials: H
authors.lastname: Bult
authors.forename: Mark M
authors.initials: MM
authors.lastname: Kockx
mesh_terms: D000328:Adult; D016229:Amyloid beta-Peptides / Q000378:metabolism; D016564:Amyloid beta-Protein Precursor / Q000378:metabolism*; D000818:Animals; D001161:Arteriosclerosis / Q000235:genetics / Q000378:metabolism / Q000503:physiopathology*; D016282:Aspartic Acid Endopeptidases / Q000235:genetics; D001792:Blood Platelets / Q000502:physiology*; D002460:Cell Line; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D008262:Macrophage Activation / Q000187:drug effects; D008264:Macrophages / Q000378:metabolism / Q000502:physiology* / Q000648:ultrastructure; D008297:Male; D018613:Microscopy, Confocal; D008854:Microscopy, Electron; D008875:Middle Aged; D019001:Nitric Oxide Synthase / Q000378:metabolism; D052247:Nitric Oxide Synthase Type II; D010587:Phagocytosis / Q000502:physiology*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015842:Serine Proteinase Inhibitors / Q000494:pharmacology; D013450:Sulfones / Q000494:pharmacology
chemical_list: D016229:Amyloid beta-Peptides; D016564:Amyloid beta-Protein Precursor; D012333:RNA, Messenger; D015842:Serine Proteinase Inhibitors; D013450:Sulfones; C002010:4-(2-aminoethyl)benzenesulfonylfluoride; C496319:NOS2 protein, human; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; D016282:Aspartic Acid Endopeptidases