title: Metabotropic glutamate receptor 5 modulates calcium oscillation and innate immune response induced by lipopolysaccharide in microglial cell.
abstract: Microglia, the primary immune cells in the brain, have been implicated as the predominant cells governing inflammation-mediated neuronal damage. In response to immunological challenges such as lipopolysaccharide (LPS), microglia are activated and subsequently inflammatory process is initiated as evidenced by the release of pro-inflammatory chemokines and cytokines. Here we show that Group I metabotropic glutamate receptor 5 (mGluR5) is involved in LPS-induced microglia activation. LPS triggered a similar pattern of [Ca2+]i oscillation in N9, Toll-like receptor 4 (TLR4)-mutant EOC 20, TLR4-wild-type and TLR4-deficient primary mouse microglia, suggesting that LPS-induced [Ca2+]i oscillation is independent of TLR4. The characteristics of [Ca2+]i oscillation induced by LPS are consistent with those observed in mGluR5 activation. In addition, mGluR5 antagonist 3-[(2-methyl-1,3-thiazol-4-yl)ethynyl]pyridine (MTEP) abolished LPS-induced [Ca2+]i oscillation. Immunocytochemistry demonstrated that LPS colocalizes with mGluR5 in microglia and the direct binding of LPS and mGluR5 was further validated by antibody-based fluorescence resonance energy transfer (FRET) technology. Activation of mGluR5 using a selective agonist (RS)-2-chloro-5-hydroxyphenylglycine (CHPG) significantly expanded LPS-induced nuclear factor-kappa B (NF-κB) activity and CHPG alone increased NF-κB activity as well. But, mGluR5 antagonist MTEP attenuated the actions of LPS, CHPG and the additive effect of LPS and CHPG in microglia. LPS induced tumor necrosis factor-α (TNF-α) secretion in N9 microglia, but not in TLR4-mutant EOC 20 and TLR4-deficient primary mouse microglia. CHPG reduced LPS-caused TNF-α production, but MTEP increased LPS-induced TNF-α production and blocked the effect of CHPG in N9 microglia. These data demonstrate that mGluR5 and TLR4 are two critical receptors that mediate microglia activation in response to LPS, suggesting that mGluR5 may represent a novel target for modulating microglia-dependent neuroinflammation.
authors.affiliation: State Key Laboratory of Trauma, Burn and Combined Injury, Chongqing, China; Department of Infection & Immunity, Research Institute of Surgery/Daping Hospital, Third Military Medical University, Chongqing, China.
authors.forename: F
authors.initials: F
authors.lastname: Liu
authors.affiliation: Department of Operating Room, Children's Hospital, Chongqing Medical University, Chongqing, China; Ministry of Education Key Laboratory of Child Development and Disorders, Children's Hospital, Chongqing Medical University, Chongqing, China.
authors.forename: R
authors.initials: R
authors.lastname: Zhou
authors.affiliation: Department of Anesthesiology, Research Institute of Surgery/Daping Hospital, Third Military Medical University, Chongqing, China.
authors.forename: H
authors.initials: H
authors.lastname: Yan
authors.affiliation: Department of Emergency Nursing, School of Nursing, Third Military Medical University, Chongqing, China.
authors.forename: H
authors.initials: H
authors.lastname: Yin
authors.affiliation: Department of Infection & Immunity, Research Institute of Surgery/Daping Hospital, Third Military Medical University, Chongqing, China.
authors.forename: X
authors.initials: X
authors.lastname: Wu
authors.affiliation: Department of Infection & Immunity, Research Institute of Surgery/Daping Hospital, Third Military Medical University, Chongqing, China.
authors.forename: Y
authors.initials: Y
authors.lastname: Tan
authors.affiliation: State Key Laboratory of Trauma, Burn and Combined Injury, Chongqing, China; Department of Infection & Immunity, Research Institute of Surgery/Daping Hospital, Third Military Medical University, Chongqing, China. Electronic address: leili1962@yahoo.com.
authors.forename: L
authors.initials: L
authors.lastname: Li
mesh_terms: D000818:Animals; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D002460:Cell Line; D007113:Immunity, Innate / Q000187:drug effects / Q000502:physiology*; D008070:Lipopolysaccharides / Q000494:pharmacology*; D051379:Mice; D017628:Microglia / Q000378:metabolism*; D016328:NF-kappa B / Q000378:metabolism*; D064529:Receptor, Metabotropic Glutamate 5 / Q000378:metabolism*; D051197:Toll-Like Receptor 4 / Q000378:metabolism*; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism
chemical_list: C578936:Grm5 protein, mouse; D008070:Lipopolysaccharides; D016328:NF-kappa B; D064529:Receptor, Metabotropic Glutamate 5; C493487:Tlr4 protein, mouse; D051197:Toll-Like Receptor 4; D014409:Tumor Necrosis Factor-alpha
keywords: Group I metabotropic glutamate receptor 5; NF-κB; Toll-like receptors; [Ca2+]i oscillation; lipopolysaccharide; microglia