title: TLR2 is a primary receptor for Alzheimer's amyloid β peptide to trigger neuroinflammatory activation.
abstract: Microglia activated by extracellularly deposited amyloid β peptide (Aβ) act as a two-edged sword in Alzheimer's disease pathogenesis: on the one hand, they damage neurons by releasing neurotoxic proinflammatory mediators (M1 activation); on the other hand, they protect neurons by triggering anti-inflammatory/neurotrophic M2 activation and by clearing Aβ via phagocytosis. TLRs are associated with Aβ-induced microglial inflammatory activation and Aβ internalization, but the mechanisms remain unclear. In this study, we used real-time surface plasmon resonance spectroscopy and conventional biochemical pull-down assays to demonstrate a direct interaction between TLR2 and the aggregated 42-aa form of human Aβ (Aβ42). TLR2 deficiency reduced Aβ42-triggered inflammatory activation but enhanced Aβ phagocytosis in cultured microglia and macrophages. By expressing TLR2 in HEK293 cells that do not endogenously express TLR2, we observed that TLR2 expression enabled HEK293 cells to respond to Aβ42. Through site-directed mutagenesis of tlr2 gene, we identified the amino acids EKKA (741-744) as a critical cytoplasmic domain for transduction of inflammatory signals. By coexpressing TLR1 or TLR6 in TLR2-transgenic HEK293 cells or silencing tlrs genes in RAW264.7 macrophages, we observed that TLR2-mediated Aβ42-triggered inflammatory activation was enhanced by TLR1 and suppressed by TLR6. Using bone marrow chimeric Alzheimer's amyloid precursor transgenic mice, we observed that TLR2 deficiency in microglia shifts M1- to M2-inflammatory activation in vivo, which was associated with improved neuronal function. Our study demonstrated that TLR2 is a primary receptor for Aβ to trigger neuroinflammatory activation and suggested that inhibition of TLR2 in microglia could be beneficial in Alzheimer's disease pathogenesis.
authors.affiliation: Department of Neurology, University of the Saarland, 66421 Homburg/Saar, Germany.
authors.forename: Shirong
authors.initials: S
authors.lastname: Liu
authors.forename: Yang
authors.initials: Y
authors.lastname: Liu
authors.forename: Wenlin
authors.initials: W
authors.lastname: Hao
authors.forename: Lisa
authors.initials: L
authors.lastname: Wolf
authors.forename: Amanda J
authors.initials: AJ
authors.lastname: Kiliaan
authors.forename: Botond
authors.initials: B
authors.lastname: Penke
authors.forename: Claudia E
authors.initials: CE
authors.lastname: Rübe
authors.forename: Jochen
authors.initials: J
authors.lastname: Walter
authors.forename: Michael T
authors.initials: MT
authors.lastname: Heneka
authors.forename: Tobias
authors.initials: T
authors.lastname: Hartmann
authors.forename: Michael D
authors.initials: MD
authors.lastname: Menger
authors.forename: Klaus
authors.initials: K
authors.lastname: Fassbender
mesh_terms: D000544:Alzheimer Disease; D016229:Amyloid beta-Peptides / Q000276:immunology*; D000818:Animals; D002460:Cell Line; D006801:Humans; D008264:Macrophages; D051379:Mice; D008822:Mice, Transgenic; D017628:Microglia / Q000276:immunology*; D020078:Neurogenic Inflammation / Q000209:etiology*; D010587:Phagocytosis; D051194:Toll-Like Receptor 1; D051195:Toll-Like Receptor 2 / Q000276:immunology*; D051216:Toll-Like Receptor 6
chemical_list: D016229:Amyloid beta-Peptides; C495342:TLR2 protein, human; C493486:Tlr2 protein, mouse; C495369:Tlr6 protein, mouse; D051194:Toll-Like Receptor 1; D051195:Toll-Like Receptor 2; D051216:Toll-Like Receptor 6