title: TLR2 hypersensitivity of astrocytes as functional consequence of previous inflammatory episodes.
abstract: Precedent inflammatory episodes may drastically modify the function and reactivity of cells. We investigated whether priming of astrocytes by microglia-derived cytokines alters their subsequent reaction to pathogen-associated danger signals not recognized in the quiescent state. Resting primary murine astrocytes expressed little TLR2, and neither the TLR2/6 ligand fibroblast-stimulating lipopeptide-1 (FSL1) nor the TLR1/2 ligand Pam(3)CysSK(4) (P3C) triggered NF-κB translocation or IL-6 release. We made use of single-cell detection of NF-κB translocation as easily detectable and sharply regulated upstream indicator of an inflammatory response or of c-Jun phosphorylation to measure restimulation events in astrocytes under varying conditions. Cells prestimulated with IL-1β, with a TLR3 ligand, with a complete cytokine mix consisting of TNF-α, IL-1β, and IFN-γ, or with media conditioned by activated microglia responded strongly to FSL1 or P3C stimulation, whereas the sensitivity of the NF-κB response to other pattern recognition receptors was unchanged. This sensitization to TLR2 ligands was associated with an initial upregulation of TLR2, displayed a "memory" window of several days, and was largely independent of the length of prestimulation. The altered signaling led to altered function, as FSL1 or P3C triggered the release of IL-6, CCL-20, and CXCL-2 in primed cells, but not in resting astrocytes. These data confirmed the hypothesis that astrocytes exposed to activated microglia assume a different functional phenotype involving longer term TLR2 responsiveness, even after the initial stimulation by inflammatory mediators has ended.
authors.affiliation: Doerenkamp-Zbinden Chair of in vitro Toxicology and Biomedicine, University of Konstanz, D-78457 Konstanz, Germany.
authors.forename: Anja
authors.initials: A
authors.lastname: Henn
authors.forename: Susanne
authors.initials: S
authors.lastname: Kirner
authors.forename: Marcel
authors.initials: M
authors.lastname: Leist
mesh_terms: D000818:Animals; D001253:Astrocytes / Q000276:immunology* / Q000378:metabolism / Q000473:pathology*; D002460:Cell Line; D002478:Cells, Cultured; D016922:Cellular Senescence / Q000235:genetics / Q000276:immunology; D006967:Hypersensitivity / Q000276:immunology* / Q000378:metabolism* / Q000473:pathology; D016130:Immunophenotyping; D007249:Inflammation / Q000276:immunology / Q000378:metabolism / Q000473:pathology; D008024:Ligands; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D017628:Microglia / Q000276:immunology / Q000378:metabolism / Q000473:pathology; D019636:Neurodegenerative Diseases / Q000276:immunology / Q000378:metabolism / Q000473:pathology; D016192:Resting Phase, Cell Cycle / Q000235:genetics / Q000276:immunology; D051195:Toll-Like Receptor 2 / Q000172:deficiency / Q000378:metabolism / Q000502:physiology*
chemical_list: D008024:Ligands; C493486:Tlr2 protein, mouse; D051195:Toll-Like Receptor 2