Anita A. Tseng

Phagocyte recognition and clearance of bacteria play essential roles in the host response to infection. In an on-going forward genetic screen, we identify the Drosophila melanogaster scavenger receptor Croquemort as a receptor for Staphylococcus aureus, implicating for the first time the CD36 family as phagocytic receptors for bacteria. In transfection assays, the mammalian Croquemort paralogue CD36 confers binding and internalization of Gram-positive and, to a lesser extent, Gram-negative bacteria. By mutational analysis, we show that internalization of S. aureus and its component lipoteichoic acid requires the COOH-terminal cytoplasmic portion of CD36, specifically Y463 and C464, which activates Toll-like receptor (TLR) 2/6 signaling. Macrophages lacking CD36 demonstrate reduced internalization of S. aureus and its component lipoteichoic acid, accompanied by a marked defect in tumor necrosis factor-alpha and IL-12 production. As a result, Cd36-/- mice fail to efficiently clear S. aureus in vivo resulting in profound bacteraemia. Thus, response to S. aureus requires CD36-mediated phagocytosis triggered by the COOH-terminal cytoplasmic domain, which initiates TLR2/6 signaling.

Macrophage internalization of modified lipoproteins is thought to play a critical role in the initiation of atherogenesis. Two scavenger receptors, scavenger receptor A (SR-A) and CD36, have been centrally implicated in this lipid uptake process. Previous studies showed that these receptors mediated the majority of cholesterol ester accumulation in macrophages exposed to oxidized LDL and that mice with deletions of either receptor exhibited marked reductions in atherosclerosis. This work has contributed to an atherosclerosis paradigm: scavenger receptor-mediated oxidized lipoprotein uptake is required for foam cell formation and atherogenesis. In this study, Apoe-/- mice lacking SR-A or CD36, backcrossed into the C57BL/6 strain for 7 generations, were fed an atherogenic diet for 8 weeks. Hyperlipidemic Cd36-/-Apoe-/- and Msr1-/-Apoe-/- mice showed significant reductions in peritoneal macrophage lipid accumulation in vivo; however, in contrast with previous reports, this was associated with increased aortic sinus lesion areas. Characterization of aortic sinus lesions by electron microscopy and immunohistochemistry showed abundant macrophage foam cells, indicating that lipid uptake by intimal macrophages occurs in the absence of CD36 or SR-A. These data show that alternative lipid uptake mechanisms may contribute to macrophage cholesterol ester accumulation in vivo and suggest that the roles of SR-A and CD36 as proatherosclerotic mediators of modified LDL uptake in vivo need to be reassessed.

Cell migration plays important roles in embryonic development and inflammation, and this process is highly regulated to ensure tissue homeostasis. A number of barriers exist to prevent the inappropriate migration of leukocytes into healthy peripheral tissues, including retention of these cells in the inactive state and maintenance of the integrity and charge of the vascular endothelium. However, active signals also are likely to exist that can repulse cells or abolish existing cell migration. One such paradigm exists in the developing nervous system, where neuronal migration is mediated by a balance between chemoattractive and chemorepulsive signals. The ability of the guidance molecule netrin-1 to repulse or abolish attraction of neuronal cells expressing the UNC5b receptor makes it an attractive candidate for the regulation of inflammatory cell migration. Here, we show that netrin-1 is expressed on vascular endothelium, where it is regulated by infection and inflammatory cytokines. The netrin-1 receptor UNC5b is strongly expressed by leukocytes, upon which netrin-1 acts as a potent inhibitor of migration to different chemotactic stimuli both in vivo and in vitro. These data suggest that endothelial expression of netrin-1 may inhibit basal cell migration into tissues and that its down-regulation with the onset of sepsis/inflammation may facilitate leukocyte recruitment.

The pattern recognition receptor CD36 initiates a signaling cascade that promotes microglial activation and recruitment to β-amyloid deposits in the brain. In the present study we identify the focal adhesion-associated proteins p130Cas, Pyk2, and paxillin as novel members of the tyrosine kinase signaling pathway downstream of CD36 and show that assembly of this complex is essential for microglial migration. In primary microglia and macrophages exposed to β-amyloid, the scaffolding protein p130Cas is rapidly tyrosine-phosphorylated and co-localizes with CD36 to membrane ruffles contemporaneous with F-actin polymerization. These β-amyloid-stimulated events are not detected in CD36 null cells and are dependent on CD36 activation of Src family tyrosine kinases. Fyn, a Src kinase known to interact with CD36, co-precipitates with p130Cas and is an essential upstream intermediate in the signaling pathways leading to phosphorylation of the p130Cas substrate domain. Furthermore, the p130Cas-interacting kinase Pyk2 and the cytoskeletal adapter protein paxillin also demonstrate CD36-dependent phosphorylation, identifying these focal adhesion molecules as additional members of this β-amyloid signaling cascade. Disruption of this p130Cas complex by small interfering RNA silencing inhibits p44/42 mitogen-activated protein kinase phosphorylation and microglial migration, illustrating the importance of this pathway in microglial activation and recruitment. Together, these data are the first to identify the signaling cascade that directly links CD36 to the actin cytoskeleton and, thus, implicates it in diverse processes such as cellular migration, adhesion, and phagocytosis. The pattern recognition receptor CD36 initiates a signaling cascade that promotes microglial activation and recruitment to β-amyloid deposits in the brain. In the present study we identify the focal adhesion-associated proteins p130Cas, Pyk2, and paxillin as novel members of the tyrosine kinase signaling pathway downstream of CD36 and show that assembly of this complex is essential for microglial migration. In primary microglia and macrophages exposed to β-amyloid, the scaffolding protein p130Cas is rapidly tyrosine-phosphorylated and co-localizes with CD36 to membrane ruffles contemporaneous with F-actin polymerization. These β-amyloid-stimulated events are not detected in CD36 null cells and are dependent on CD36 activation of Src family tyrosine kinases. Fyn, a Src kinase known to interact with CD36, co-precipitates with p130Cas and is an essential upstream intermediate in the signaling pathways leading to phosphorylation of the p130Cas substrate domain. Furthermore, the p130Cas-interacting kinase Pyk2 and the cytoskeletal adapter protein paxillin also demonstrate CD36-dependent phosphorylation, identifying these focal adhesion molecules as additional members of this β-amyloid signaling cascade. Disruption of this p130Cas complex by small interfering RNA silencing inhibits p44/42 mitogen-activated protein kinase phosphorylation and microglial migration, illustrating the importance of this pathway in microglial activation and recruitment. Together, these data are the first to identify the signaling cascade that directly links CD36 to the actin cytoskeleton and, thus, implicates it in diverse processes such as cellular migration, adhesion, and phagocytosis. In Alzheimer disease the extracellular deposition of fibrillar β-amyloid incites a focal recruitment of microglia that is a hall-mark of senile plaques. Microglia are the primary immune effector cells of the central nervous system and, like other tissue macrophages, phagocytose exogenous or modified endogenous ligands and initiate an appropriate immune response. Activation of microglia by β-amyloid triggers the release of pro-inflammatory mediators, including cytokines, chemokines, and reactive oxygen species, which are believed to drive the chronic inflammation and neurotoxicity associated with Alzheimer disease (1Akiyama H. Barger S. Barnum S. Bradt B. Bauer J. Cole G.M. Cooper N.R. Eikelenboom P. Emmerling M. Fiebich B.L. Finch C.E. Frautschy S. Griffin W.S. Hampel H. Hull M. Landreth G. Lue L. Mrak R. Mackenzie I.R. McGeer P.L. O'Banion M.K. Pachter J. Pasinetti G. Plata-Salaman C. Rogers J. Rydel R. Shen Y. Streit W. Strohmeyer R. Tooyoma I. Van Muiswinkel F.L. Veerhuis R. Walker D. Webster S. Wegrzyniak B. Wenk G. Wyss-Coray T. Neurobiol. Aging. 2000; 21: 383-421Crossref PubMed Scopus (3585) Google Scholar). Microglia express multiple pattern recognition receptors that have been implicated in the innate immune response to β-amyloid, including three members of the scavenger receptor (SR) 2The abbreviations used are:SRscavenger receptorMAPKmitogen-activated protein (MAP) kinasePyk2proline-rich tyrosine kinase 2siRNAsmall inhibitory RNArevAβreverse Aβ42-1MCP-1monocyte chemotactic proteinLTB4leukotrienne B4TLRtoll-like receptorPBSphosphate-buffered saline 2The abbreviations used are:SRscavenger receptorMAPKmitogen-activated protein (MAP) kinasePyk2proline-rich tyrosine kinase 2siRNAsmall inhibitory RNArevAβreverse Aβ42-1MCP-1monocyte chemotactic proteinLTB4leukotrienne B4TLRtoll-like receptorPBSphosphate-buffered saline family, SR-A, SR-BI, and CD36 (2Husemann J. Loike J.D. Anankov R. Febbraio M. Silverstein S.C. Glia. 2002; 40: 195-205Crossref PubMed Scopus (298) Google Scholar). Although all of these SR pathways are thought to contribute to β-amyloid clearance by microglia, CD36 has uniquely been linked to a pro-inflammatory signaling cascade that initiates microglial activation and recruitment (3Moore K.J. El Khoury J. Medeiros L.A. Terada K. Geula C. Luster A.D. Freeman M.W. J. Biol. Chem. 2002; 277: 47373-47379Abstract Full Text Full Text PDF PubMed Scopus (287) Google Scholar, 4El Khoury J.B. Moore K.J. Means T.K. Leung J. Terada K. Toft M. Freeman M.W. Luster A.D. J. Exp. Med. 2003; 197: 1657-1666Crossref PubMed Scopus (368) Google Scholar, 5Bamberger M.E. Harris M.E. McDonald D.R. Husemann J. Landreth G.E. J. Neurosci. 2003; 23: 2665-2674Crossref PubMed Google Scholar). scavenger receptor mitogen-activated protein (MAP) kinase proline-rich tyrosine kinase 2 small inhibitory RNA reverse Aβ42-1 monocyte chemotactic protein leukotrienne B4 toll-like receptor phosphate-buffered saline scavenger receptor mitogen-activated protein (MAP) kinase proline-rich tyrosine kinase 2 small inhibitory RNA reverse Aβ42-1 monocyte chemotactic protein leukotrienne B4 toll-like receptor phosphate-buffered saline CD36 is highly expressed in both neonatal and adult microglia (6Coraci I.S. Husemann J. Berman J.W. Hulette C. Dufour J.H. Campanella G.K. Luster A.D. Silverstein S.C. El Khoury J. Am. J. Pathol. 2002; 160: 101-112Abstract Full Text Full Text PDF PubMed Scopus (327) Google Scholar) and has been shown to increase in the Alzheimer diseased brain (7Ricciarelli R. D'Abramo C. Zingg J.M. Giliberto L. Markesbery W. Azzi M. Biol. Med. PubMed Scopus Google Scholar). and have that β-amyloid to CD36 on microglia, and macrophages initiates cellular and the of (3Moore K.J. El Khoury J. Medeiros L.A. Terada K. Geula C. Luster A.D. Freeman M.W. J. Biol. Chem. 2002; 277: 47373-47379Abstract Full Text Full Text PDF PubMed Scopus (287) Google Scholar, 4El Khoury J.B. Moore K.J. Means T.K. Leung J. Terada K. Toft M. Freeman M.W. Luster A.D. J. Exp. Med. 2003; 197: 1657-1666Crossref PubMed Scopus (368) Google Scholar, 5Bamberger M.E. Harris M.E. McDonald D.R. Husemann J. Landreth G.E. J. Neurosci. 2003; 23: 2665-2674Crossref PubMed Google Scholar, B. J. C. Landreth G. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). of the tyrosine kinase signaling cascade downstream of CD36 has the Src family and as of the mitogen-activated protein kinase pathways and and reactive oxygen (3Moore K.J. El Khoury J. Medeiros L.A. Terada K. Geula C. Luster A.D. Freeman M.W. J. Biol. Chem. 2002; 277: 47373-47379Abstract Full Text Full Text PDF PubMed Scopus (287) Google Scholar, 4El Khoury J.B. Moore K.J. Means T.K. Leung J. Terada K. Toft M. Freeman M.W. Luster A.D. J. Exp. Med. 2003; 197: 1657-1666Crossref PubMed Scopus (368) Google Scholar, 5Bamberger M.E. Harris M.E. McDonald D.R. Husemann J. Landreth G.E. J. Neurosci. 2003; 23: 2665-2674Crossref PubMed Google Scholar). In of this signaling cascade by of CD36 or microglial of β-amyloid deposition in the the importance of this pathway in microglial recruitment and activation in Alzheimer disease (3Moore K.J. El Khoury J. Medeiros L.A. Terada K. Geula C. Luster A.D. Freeman M.W. J. Biol. Chem. 2002; 277: 47373-47379Abstract Full Text Full Text PDF PubMed Scopus (287) Google Scholar, 4El Khoury J.B. Moore K.J. Means T.K. Leung J. Terada K. Toft M. Freeman M.W. Luster A.D. J. Exp. Med. 2003; 197: 1657-1666Crossref PubMed Scopus (368) Google Scholar). with CD36, cells that not express this scavenger receptor the to β-amyloid, that CD36 recognition of this modified endogenous (6Coraci I.S. Husemann J. Berman J.W. Hulette C. Dufour J.H. Campanella G.K. Luster A.D. Silverstein S.C. El Khoury J. Am. J. Pathol. 2002; 160: 101-112Abstract Full Text Full Text PDF PubMed Scopus (327) Google Scholar). In CD36 has been shown to other including fibrillar of and L.A. T. El Khoury J.B. R. Moore K.J. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar, S. S. Full Text Full Text PDF PubMed Scopus Google Scholar, Moore K.J. PubMed Scopus Google Scholar). CD36 has been to β-amyloid as of a receptor complex SR-A, and the protein B. J. C. Landreth G. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar, J. Landreth G. J. Neurosci. PubMed Scopus Google Scholar). Although of a these receptors is of receptor the tyrosine signaling response to of these receptors has been shown to microglial of β-amyloid a that is used by the receptors and the receptor J. Landreth G. J. Neurosci. PubMed Scopus Google Scholar). Microglia are highly cells that cellular membrane migration, and phagocytosis. These processes are by in the of the actin cytoskeleton and the assembly and of focal the actin cytoskeleton to the extracellular and also as a for signaling pathways cellular including migration, and The scaffolding protein p130Cas in focal and, multiple a for the of and focal adhesion complex P. P. S. Biol. Full Text Full Text PDF PubMed Scopus Google Scholar). phosphorylation of the p130Cas substrate with proteins such as and focal adhesion with proline-rich tyrosine kinase 2 also known as and and the tyrosine and P. P. S. Biol. Full Text Full Text PDF PubMed Scopus Google Scholar). The assembly of these p130Cas as a kinase phosphorylation, of the actin and of and P. P. S. Biol. Full Text Full Text PDF PubMed Scopus Google Scholar). identify a focal adhesion signaling cascade by CD36 that phosphorylation of p130Cas links this receptor to the of the actin cytoskeleton to In macrophages and microglia, β-amyloid rapidly tyrosine phosphorylation of p130Cas and to membrane ruffles and with actin polymerization. p130Cas with CD36 in β-amyloid and of this receptor p130Cas phosphorylation and members of this p130Cas complex by β-amyloid the Src kinase Fyn, the kinase Pyk2, and the cytoskeletal of this complex small inhibitory RNA microglial and illustrating the importance of this pathway in the response to Together, these assembly of p130Cas as an essential of the β-amyloid signaling pathway that microglial cytoskeletal and reverse Aβ42-1 in and for and reverse Aβ42-1 as we (3Moore K.J. El Khoury J. Medeiros L.A. Terada K. Geula C. Luster A.D. Freeman M.W. J. Biol. Chem. 2002; 277: 47373-47379Abstract Full Text Full Text PDF PubMed Scopus (287) Google Scholar, 4El Khoury J.B. Moore K.J. Means T.K. Leung J. Terada K. Toft M. Freeman M.W. Luster A.D. J. Exp. Med. 2003; 197: 1657-1666Crossref PubMed Scopus (368) Google Scholar). of used as we (3Moore K.J. El Khoury J. Medeiros L.A. Terada K. Geula C. Luster A.D. Freeman M.W. J. Biol. Chem. 2002; 277: 47373-47379Abstract Full Text Full Text PDF PubMed Scopus (287) Google Scholar). in as and to for (3Moore K.J. El Khoury J. Medeiros L.A. Terada K. Geula C. Luster A.D. Freeman M.W. J. Biol. Chem. 2002; 277: 47373-47379Abstract Full Text Full Text PDF PubMed Scopus (287) Google Scholar). of used as and of in a with to and by the on and in with the of and the for the and of and microglia brain of as we (3Moore K.J. El Khoury J. Medeiros L.A. Terada K. Geula C. Luster A.D. Freeman M.W. J. Biol. Chem. 2002; 277: 47373-47379Abstract Full Text Full Text PDF PubMed Scopus (287) Google Scholar, I.S. Husemann J. Berman J.W. Hulette C. Dufour J.H. Campanella G.K. Luster A.D. Silverstein S.C. El Khoury J. Am. J. Pathol. 2002; 160: 101-112Abstract Full Text Full Text PDF PubMed Scopus (327) Google Scholar). The microglial and the as in with and (6Coraci I.S. Husemann J. Berman J.W. Hulette C. Dufour J.H. Campanella G.K. Luster A.D. Silverstein S.C. El Khoury J. Am. J. Pathol. 2002; 160: 101-112Abstract Full Text Full Text PDF PubMed Scopus (327) Google Scholar). macrophages by with as we L.A. T. El Khoury J.B. R. Moore K.J. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar, Medeiros L.A. T. Moore K.J. J. PubMed Scopus Google Scholar). signaling cells in the appropriate with in and in and as we (3Moore K.J. El Khoury J. Medeiros L.A. Terada K. Geula C. Luster A.D. Freeman M.W. J. Biol. Chem. 2002; 277: 47373-47379Abstract Full Text Full Text PDF PubMed Scopus (287) Google Scholar, L.A. T. El Khoury J.B. R. Moore K.J. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). of protein a of with of and with protein for with of p130Cas or and of protein for 2 proteins in and in of The on and by for p130Cas, and in and in and as we (3Moore K.J. El Khoury J. Medeiros L.A. Terada K. Geula C. Luster A.D. Freeman M.W. J. Biol. Chem. 2002; 277: 47373-47379Abstract Full Text Full Text PDF PubMed Scopus (287) Google Scholar, L.A. T. El Khoury J.B. R. Moore K.J. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). of protein on and proteins to a with and Pyk2 for in in other in in saline with for 2 with primary including p130Cas and p44/42 protein and and and CD36 (3Moore K.J. El Khoury J. Medeiros L.A. Terada K. Geula C. Luster A.D. Freeman M.W. J. Biol. Chem. 2002; 277: 47373-47379Abstract Full Text Full Text PDF PubMed Scopus (287) Google Scholar). in and with for an additional and exposed to or the on or in and with or for the cells in and with as J. L. J. PubMed Scopus Google Scholar, J. 23: PubMed Scopus Google Scholar). in and with p130Cas cells in and with in and with or or with CD36 or and an 2 the of p130Cas in microglia, the cells with or as L. S. K. S. D. D. J. S. L. M. K. R. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). cells and in with and for p130Cas silencing by of microglia by modified with a as we K. P. Moore K.J. S. PubMed Scopus Google Scholar). or p130Cas microglia in with and on in the and of monocyte chemotactic protein leukotrienne B4 or microglia with for or in the of the and cells in in the to for and the of cells the an with a expressed as chemotactic which by the of cells in the by the of cells in the a the we that β-amyloid to CD36 initiates a tyrosine signaling cascade in microglia and macrophages, including the phosphorylation of proteins of in (3Moore K.J. El Khoury J. Medeiros L.A. Terada K. Geula C. Luster A.D. Freeman M.W. J. Biol. Chem. 2002; 277: 47373-47379Abstract Full Text Full Text PDF PubMed Scopus (287) Google Scholar). in microglia, with not the reverse demonstrate a increase in tyrosine phosphorylation of a protein of this are 2 and to identify this and with signaling molecules of p130Cas, the protein and focal adhesion these p130Cas with the protein that tyrosine-phosphorylated in β-amyloid-stimulated cells not CD36 of the in the p130Cas a we demonstrate that a phosphorylation of in the central substrate of p130Cas that in cells with phosphorylation of the p130Cas substrate cellular of CD36, as phosphorylation in macrophages and microglia with a of this receptor and in the of in macrophages and microglia increase in of in cells by of the of by that the of in a pattern of focal not detected in macrophages and in cells CD36 Together, these data demonstrate a and for CD36 in the β-amyloid signaling pathway leading to phosphorylation of the adapter protein p130Cas in microglia, and The p130Cas cells CD36 with Src downstream signaling events including activation and reactive oxygen (3Moore K.J. El Khoury J. Medeiros L.A. Terada K. Geula C. Luster A.D. Freeman M.W. J. Biol. Chem. 2002; 277: 47373-47379Abstract Full Text Full Text PDF PubMed Scopus (287) Google Scholar, J.B. J.W. S. PubMed Scopus Google Scholar, B. Febbraio M. Silverstein Med. 2000; PubMed Scopus Google Scholar, Febbraio M. Silverstein Full Text Full Text PDF PubMed Scopus Google Scholar). Src the in the p130Cas substrate we with a of this kinase family, of Src kinase phosphorylation of p130Cas in identifying members of this kinase family as in this CD36 signaling cascade of p130Cas a of this scaffolding protein with Fyn, a Src kinase known to with CD36, that not by or with or and the immune on with and that p130Cas with in both and p130Cas protein a increase in tyrosine phosphorylation as by with the of p130Cas with kinase detected in or not the of p130Cas with kinase is essential for phosphorylation, we macrophages with a of of in the p130Cas substrate in macrophages with identifying as a intermediate in the pathway leading to p130Cas phosphorylation of Pyk2 and in a CD36-dependent as a to and initiate such proteins are the focal adhesion kinase Pyk2 and the adapter paxillin that the membrane for signaling and In cells with Pyk2 and paxillin both rapidly and with a a of Pyk2 phosphorylation that not phosphorylation of this to Pyk2, paxillin a increase in tyrosine phosphorylation in response to These phosphorylation events with to p130Cas phosphorylation, and or in cells with Pyk2 and paxillin are the of of the additional in the CD36 signaling cascade and we phosphorylation of these focal adhesion molecules and in macrophages this response in macrophages and These data the p130Cas-interacting kinase Pyk2 and the cytoskeletal paxillin in the β-amyloid signaling cascade downstream of p130Cas to and F-actin assembly and membrane of p130Cas has been shown to to cytoskeletal and activation of the and P. P. S. Biol. Full Text Full Text PDF PubMed Scopus Google Scholar). the of p130Cas in and macrophages exposed to by In macrophages, p130Cas present in the of the of macrophages to p130Cas to membrane ruffles and the leading of the it with CD36 of p130Cas dependent on CD36 as p130Cas to membrane ruffles not detected in macrophages in microglia that this of p130Cas with actin of microglia of both p130Cas and F-actin has been in cells J. 23: PubMed Scopus Google we that β-amyloid the of p130Cas and of the of in microglia and macrophages and These and in of cells with β-amyloid of of p130Cas these in with F-actin as by These p130Cas have been associated with p130Cas phosphorylation, migration, and J. 23: PubMed Scopus Google Scholar, J. PubMed Scopus Google activation by β-amyloid of with F-actin polymerization. microglia exposed to for the by a for F-actin a or a of both p130Cas, demonstrate that the of p130Cas membrane ruffles and with the of F-actin of the of cells for p130Cas and F-actin in microglia with or for the of p130Cas cellular and of in of cells by or for p130Cas and the of p130Cas and of p130Cas and in in of p130Cas null microglia and macrophages H. H. T. R. T. T. K. K. T. M. Y. H. PubMed Scopus Google Scholar). to the of CD36 assembly of p130Cas we of p130Cas in microglia to study in focal microglia with p130Cas show a in p130Cas protein by as with or cells of p130Cas and not microglial of CD36 assembly of p130Cas microglial In silencing of p130Cas microglial migration. or microglia in to or microglia exposed to which we have shown are chemotactic Khoury J.B. Moore K.J. Means T.K. Leung J. Terada K. Toft M. Freeman M.W. Luster A.D. J. Exp. Med. 2003; 197: 1657-1666Crossref PubMed Scopus (368) Google Scholar). of these cells to or to a of the a increase in microglial increase in chemotactic in p130Cas microglia exposed to or The of p130Cas microglia to to these chemotactic the for this scaffolding protein in the signaling pathways cellular p130Cas has also been shown to upstream of the small and which signaling and extracellular kinase p44/42 P. P. S. Biol. Full Text Full Text PDF PubMed Scopus Google Scholar). p44/42 is known to a primary effector of we p130Cas for activation of this phosphorylation of p44/42 in p130Cas microglia and microglia show an of and response in p130Cas microglia, that p130Cas is a intermediate in the CD36 signaling cascade leading to p44/42 The recruitment of microglia to β-amyloid deposits and in senile are believed to a chronic response that promotes in Alzheimer disease (1Akiyama H. Barger S. Barnum S. Bradt B. Bauer J. Cole G.M. Cooper N.R. Eikelenboom P. Emmerling M. Fiebich B.L. Finch C.E. Frautschy S. Griffin W.S. Hampel H. Hull M. Landreth G. Lue L. Mrak R. Mackenzie I.R. McGeer P.L. O'Banion M.K. Pachter J. Pasinetti G. Plata-Salaman C. Rogers J. Rydel R. Shen Y. Streit W. Strohmeyer R. Tooyoma I. Van Muiswinkel F.L. Veerhuis R. Walker D. Webster S. Wegrzyniak B. Wenk G. Wyss-Coray T. Neurobiol. Aging. 2000; 21: 383-421Crossref PubMed Scopus (3585) Google Scholar). The microglial and activation in this disease are other tissue macrophages, microglia are with pattern recognition receptors that innate immune recognition and of or including modified and has shown that the scavenger receptor CD36 proteins and initiates a tyrosine signaling cascade that promotes including the recruitment of microglia to β-amyloid deposits in the brain (3Moore K.J. El Khoury J. Medeiros L.A. Terada K. Geula C. Luster A.D. Freeman M.W. J. Biol. Chem. 2002; 277: 47373-47379Abstract Full Text Full Text PDF PubMed Scopus (287) Google Scholar, 4El Khoury J.B. Moore K.J. Means T.K. Leung J. Terada K. Toft M. Freeman M.W. Luster A.D. J. Exp. Med. 2003; 197: 1657-1666Crossref PubMed Scopus (368) Google Scholar, 5Bamberger M.E. Harris M.E. McDonald D.R. Husemann J. Landreth G.E. J. Neurosci. 2003; 23: 2665-2674Crossref PubMed Google Scholar, B. J. C. Landreth G. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar, L.A. T. El Khoury J.B. R. Moore K.J. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). identify three members of this CD36 including p130Cas Pyk2 kinase and paxillin and demonstrate that these focal adhesion proteins cytoskeletal leading to cellular in response to β-amyloid and microglial migration. The of adhesion, and are complex events that of the by assembly and of focal and of the actin The assembly of p130Cas a for signaling these p130Cas is a scaffolding protein that the of that kinase phosphorylation and and focal adhesion assembly P. P. S. Biol. Full Text Full Text PDF PubMed Scopus Google Scholar). these p130Cas is a the actin cytoskeleton and in processes as diverse as migration, adhesion, and demonstrate that p130Cas, downstream of CD36, is also in microglial to β-amyloid, including in The of p130Cas in on the tyrosine phosphorylation of substrate and the assembly of p130Cas adhesion that drive actin and the recruitment of receptors for K. K. Full Text Full Text PDF PubMed Scopus Google Scholar, M. M. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar, K. L.A. C.E. Biol. PubMed Scopus Google Scholar). that with β-amyloid, p130Cas to membrane ruffles it with CD36 with the of In in microglia, p130Cas and of p130Cas in cells J. 23: PubMed Scopus Google Scholar, J. PubMed Scopus Google Scholar). with these β-amyloid rapidly phosphorylation of the in the p130Cas substrate and the cellular of this in a pattern of focal These signaling events are dependent CD36, as of this receptor phosphorylation of p130Cas and of In microglia, the silencing of p130Cas by these cytoskeletal microglial migration. Together, these data assembly of p130Cas in the of the to the p130Cas as a protein associated with in of p130Cas promotes J. 23: PubMed Scopus Google Scholar, J. PubMed Scopus Google Scholar, Biol. PubMed Scopus Google Scholar). of the Src family of have been shown to initiate signaling downstream of CD36 and are in the activation of and the of (3Moore K.J. El Khoury J. Medeiros L.A. Terada K. Geula C. Luster A.D. Freeman M.W. J. Biol. Chem. 2002; 277: 47373-47379Abstract Full Text Full Text PDF PubMed Scopus (287) Google Scholar, 5Bamberger M.E. Harris M.E. McDonald D.R. Husemann J. Landreth G.E. J. Neurosci. 2003; 23: 2665-2674Crossref PubMed Google Scholar, B. Febbraio M. Silverstein Med. 2000; PubMed Scopus Google Scholar, Febbraio M. Silverstein Full Text Full Text PDF PubMed Scopus Google Scholar, M.E. S. M. 2003; PubMed Scopus Google Scholar). to CD36 to the assembly and activation of p130Cas in response to β-amyloid, we the of Src kinases. that in p130Cas is associated with the Src kinase that is to CD36 B. Febbraio M. Silverstein Med. 2000; PubMed Scopus Google Scholar). phosphorylation of p130Cas is by of Src kinase or by of Together, these data directly CD36 activation of upstream of the phosphorylation of the p130Cas substrate domain. other the and cytoskeletal downstream of p130Cas are In with p130Cas the complex that membrane and Y. T. H. M. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar, Biol. 2000; PubMed Scopus Google Scholar). These events are for diverse processes such as adhesion, and migration. In of a for this pathway in the cellular response to β-amyloid, a signaling in CD36, shown to contribute to reactive oxygen and in and microglia exposed to β-amyloid B. J. C. Landreth G. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). with a we that β-amyloid rapidly phosphorylation of the kinase Pyk2 and substrate paxillin Landreth G.E. J. Neurosci. PubMed Google Scholar). These proteins upstream of and essential in the of and by macrophages as as other M. C. M. S. J. S. 2003; PubMed Scopus Google Scholar). phosphorylation of these proteins is not in the of CD36, that CD36 is an essential receptor for this response to Furthermore, silencing of the scaffolding protein to which Pyk2 and paxillin microglial migration, an essential for the of this complex in in the of the actin These data are the first to these focal molecules and cytoskeletal downstream of CD36 or as of a receptor including SR-A, or molecules also implicated in β-amyloid recognition J. Landreth G. J. Neurosci. PubMed Scopus Google to Although has on β-amyloid as a the of CD36 signaling to directly p130Cas and the cytoskeleton has an tyrosine phosphorylation of the p130Cas substrate has been shown to a in the of and of which demonstrate cellular to we in microglia and macrophages exposed to that phosphorylation of p130Cas, and the focal adhesion kinase as as the of as and J. 23: PubMed Scopus Google Scholar, J. PubMed Scopus Google Scholar). These data the that CD36 signaling in by endogenous or other known CD36 ligands such as a not in microglial activation also contribute to for assembly of p130Cas is in the of microglial and Activation of CD36 signaling has been linked to the of in response to β-amyloid, including and reactive oxygen species, in activation of signaling (3Moore K.J. El Khoury J. Medeiros L.A. Terada K. Geula C. Luster A.D. Freeman M.W. J. Biol. Chem. 2002; 277: 47373-47379Abstract Full Text Full Text PDF PubMed Scopus (287) Google Scholar, 4El Khoury J.B. 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M. 2003; PubMed Scopus Google Scholar, L. 2000; PubMed Google Scholar). in the by these ligands are including the of members of the Src and kinase family, and these are by The of p130Cas in activation in these CD36 signaling pathways is not we and have also that CD36 with the receptors to the signaling response to the J. J.M. K. Moore K.J. J. Biol. PubMed Scopus (327) Google Scholar, K. P. S. S. K. S. L. T. B. PubMed Scopus Google Scholar). family of pattern recognition receptors has to identify highly including and RNA S. K. PubMed Scopus Google Scholar). that CD36, and initiates signaling leading to the of essential for S. J. J.M. K. Moore K.J. J. Biol. PubMed Scopus (327) Google Scholar). of to of the CD36 signaling pathway in this such as p130Cas, and Pyk2, are also for of signaling and CD36 pathways to to modified endogenous ligands such as β-amyloid and these the importance of the of CD36 signaling as it contribute to a of with with

The macrophage scavenger receptor CD36 plays a key role in the initiation of atherosclerosis through its ability to bind to and internalize oxidized low-density lipoproteins (oxLDL). Prompted by recent findings that the CD36 receptor also recognizes amyloid fibrils formed by beta-amyloid and apolipoprotein C-II, we investigated whether the oxidation of low-density lipoproteins (LDL) generates characteristic amyloid-like structures and whether these structures serve as CD36 ligands. Our studies demonstrate that LDL oxidized by copper ions, 2,2-azobis(2-amidinopropane) dihydrochloride (AAPH), or ozone react with the diagnostic amyloid dyes thioflavin T and Congo Red and bind to serum amyloid P component (SAP), a universal constituent of physiological amyloid deposits. X-ray powder diffraction patterns for native LDL show a diffuse powder diffraction ring with maximum intensity corresponding to an atomic spacing of approximately 4.7 A, consistent with the spacing between beta-strands in a beta-sheet. Ozone treatment of LDL generates an additional diffuse powder diffraction ring with maximum intensity indicating a spacing of approximately 9.8 A. This distance is consistent with the presence of cross-beta-structure, a defining characteristic of amyloid. Evidence that these cross-beta-amyloid structures in oxLDL are recognized by macrophages is provided by the observation that SAP strongly inhibits the association and internalization of (125)I-labeled copper-oxidized LDL by peritoneal macrophages. The ability of SAP to bind to amyloid-like structures in oxLDL and prevent lipid uptake by macrophages highlights the potential importance of these structures and suggests an important preventative role for SAP in foam cell formation and early-stage atherosclerosis.