title: SYK regulates macrophage MHC-II expression via activation of autophagy in response to oxidized LDL.
abstract: Adaptive immunity, which plays an important role in the development of atherosclerosis, is mediated by major histocompatibility complex (MHC)-dependent antigen presentation. In atherosclerotic lesions, macrophages constitute an important class of antigen-presenting cells that activate adaptive immune responses to oxidized low-density lipoprotein (OxLDL). It has been reported that autophagy regulates adaptive immune responses by enhancing antigen presentation to MHC class II (MHC-II). In a previous study, we have demonstrated that SYK (spleen tyrosine kinase) regulates generation of reactive oxygen species (ROS) and activation of MAPK8/JNK1 in macrophages. Because ROS and MAPK8 are known to regulate autophagy, in this study we investigated the role of SYK in autophagy, MHC-II expression and adaptive immune response to OxLDL. We demonstrate that OxLDL induces autophagosome formation, MHC-II expression, and phosphorylation of SYK in macrophages. Gene knockout and pharmacological inhibitors of NOX2 and MAPK8 reduced OxLDL-induced autophagy. Using bone marrow-derived macrophages isolated from wild-type and myeloid-specific SYK knockout mice, we demonstrate that SYK regulates OxLDL-induced ROS generation, MAPK8 activation, BECN1-BCL2 dissociation, autophagosome formation and presentation of OxLDL-derived antigens to CD4(+) T cells. ldlr(-/-) syk(-/-) mice fed a high-fat diet produced lower levels of IgG to malondialdehyde (MDA)-LDL, malondialdehyde-acetaldehyde (MAA)-LDL, and OxLDL compared to ldlr(-/-) mice. These results provide new insights into the mechanisms by which SYK regulates MHC-II expression via autophagy in macrophages and may contribute to regulation of adaptive immune responses in atherosclerosis.
authors.affiliation: a Department of Medicine; University of California , San Diego; La Jolla , CA , USA.
authors.forename: Soo-Ho
authors.initials: SH
authors.lastname: Choi
authors.forename: Ayelet
authors.initials: A
authors.lastname: Gonen
authors.forename: Cody J
authors.initials: CJ
authors.lastname: Diehl
authors.forename: Jungsu
authors.initials: J
authors.lastname: Kim
authors.forename: Felicidad
authors.initials: F
authors.lastname: Almazan
authors.forename: Joseph L
authors.initials: JL
authors.lastname: Witztum
authors.forename: Yury I
authors.initials: YI
authors.lastname: Miller
mesh_terms: D000818:Animals; D001343:Autophagy / Q000187:drug effects*; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology; D000939:Epitopes / Q000276:immunology; D051638:Ether-A-Go-Go Potassium Channels / Q000378:metabolism; D000949:Histocompatibility Antigens Class II / Q000378:metabolism*; D006937:Hypercholesterolemia / Q000276:immunology / Q000473:pathology; D007074:Immunoglobulin G / Q000276:immunology; D047908:Intracellular Signaling Peptides and Proteins / Q000172:deficiency / Q000378:metabolism*; D008077:Lipoproteins, LDL / Q000494:pharmacology*; D008213:Lymphocyte Activation / Q000276:immunology; D008264:Macrophages / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D048055:Mitogen-Activated Protein Kinase 8; D000074662:NADPH Oxidase 2; D019255:NADPH Oxidases / Q000378:metabolism; D010084:Oxidation-Reduction / Q000187:drug effects; D011505:Protein-Tyrosine Kinases / Q000172:deficiency / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D000067996:RAW 264.7 Cells; D017382:Reactive Oxygen Species / Q000378:metabolism; D000072377:Syk Kinase; D015854:Up-Regulation / Q000187:drug effects
chemical_list: D000939:Epitopes; D051638:Ether-A-Go-Go Potassium Channels; D000949:Histocompatibility Antigens Class II; D007074:Immunoglobulin G; D047908:Intracellular Signaling Peptides and Proteins; C496887:Kcnh3 protein, mouse; D008077:Lipoproteins, LDL; D008562:Membrane Glycoproteins; D019253:Proto-Oncogene Proteins c-bcl-2; D017382:Reactive Oxygen Species; C099252:oxidized low density lipoprotein; C488842:Cybb protein, mouse; D000074662:NADPH Oxidase 2; D019255:NADPH Oxidases; D011505:Protein-Tyrosine Kinases; D000072377:Syk Kinase; C000606897:Syk protein, mouse; D048055:Mitogen-Activated Protein Kinase 8
keywords: 3MA, 3-methyladenine; APCs, antigen-presenting cells; BCR, B cell receptor; BMDM, bone marrow-derived macrophage; Baf, bafilomycin A1; DPI, diphenyleneiodonium; FCGR, Fc fragment of IgG; GFP, green fluorescent protein; HFD, high-fat diet; IL2, interleukin 2; ITAM, immunoreceptor tyrosine-based activation motif; IgG, immunoglobulin G; IgM, immunoglobulin M; LPS, lipopolysaccharide; MAA-LDL, malondialdehyde-acetaldehyde modified low density lipoprotein; MAP1LC3/LC3, microtubule-associated protein 1 light chain 3; MAPK, mitogen-activated protein kinase; MDA-LDL, malondialdehyde modified low density lipoprotein; MHC-II; MHC-II, major histocompatibility complex class II; NOX, NAPDH oxidase; OSE, oxidation specific epitopes; OxLDL; OxLDL, oxidized low density lipoprotein; PBS, phosphate-buffered saline; PIC, piceatannol; ROS; ROS, reactive oxygen species; SYK; SYK, spleen tyrosine kinase; TCR, T cell receptor; TLR4, toll-like receptor 4; TNF, tumor necrosis factor; autophagy; low affinity, receptor; mmLDL, minimally modified low density lipoprotein; oxidation-specific antibodies