title: Long-lasting pro-inflammatory suppression of microglia by LPS-preconditioning is mediated by RelB-dependent epigenetic silencing.
abstract: Microglia, the innate immune cells of the central nervous system (CNS), react to endotoxins like bacterial lipopolysaccharides (LPS) with a pronounced inflammatory response. To avoid excess damage to the CNS, the microglia inflammatory response needs to be tightly regulated. Here we report that a single LPS challenge results in a prolonged blunted pro-inflammatory response to a subsequent LPS stimulation, both in primary microglia cultures (100 ng/ml) and in vivo after intraperitoneal (0.25 and 1mg/kg) or intracerebroventricular (5 μg) LPS administration. Chromatin immunoprecipitation (ChIP) experiments with primary microglia and microglia acutely isolated from mice showed that LPS preconditioning was accompanied by a reduction in active histone modifications AcH3 and H3K4me3 in the promoters of the IL-1β and TNF-α genes. Furthermore, LPS preconditioning resulted in an increase in the amount of repressive histone modification H3K9me2 in the IL-1β promoter. ChIP and knock-down experiments showed that NF-κB subunit RelB was bound to the IL-1β promoter in preconditioned microglia and that RelB is required for the attenuated LPS response. In addition to a suppressed pro-inflammatory response, preconditioned primary microglia displayed enhanced phagocytic activity, increased outward potassium currents and nitric oxide production in response to a second LPS challenge. In vivo, a single i.p. LPS injection resulted in reduced performance in a spatial learning task 4 weeks later, indicating that a single inflammatory episode affected memory formation in these mice. Summarizing, we show that LPS-preconditioned microglia acquire an epigenetically regulated, immune-suppressed phenotype, possibly to prevent excessive damage to the central nervous system in case of recurrent (peripheral) inflammation.
authors.affiliation: Department of Neuroscience, Section Medical Physiology, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands.
authors.forename: W
authors.initials: W
authors.lastname: Schaafsma
authors.affiliation: Department of Neuroscience, Section Medical Physiology, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands.
authors.forename: X
authors.initials: X
authors.lastname: Zhang
authors.affiliation: Department of Neuroscience, Section Medical Physiology, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands.
authors.forename: K C
authors.initials: KC
authors.lastname: van Zomeren
authors.affiliation: Department of Neuroscience, Section Medical Physiology, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands.
authors.forename: S
authors.initials: S
authors.lastname: Jacobs
authors.affiliation: Cellular Neurosciences, Max Delbrück Centre for Molecular Medicine, Berlin, Germany.
authors.forename: P B
authors.initials: PB
authors.lastname: Georgieva
authors.affiliation: Cellular Neurosciences, Max Delbrück Centre for Molecular Medicine, Berlin, Germany.
authors.forename: S A
authors.initials: SA
authors.lastname: Wolf
authors.affiliation: Cellular Neurosciences, Max Delbrück Centre for Molecular Medicine, Berlin, Germany.
authors.forename: H
authors.initials: H
authors.lastname: Kettenmann
authors.affiliation: Institute of Neuropathology, University of Göttingen, Göttingen, Germany.
authors.forename: H
authors.initials: H
authors.lastname: Janova
authors.affiliation: Institute of Neuropathology, University of Göttingen, Göttingen, Germany.
authors.forename: N
authors.initials: N
authors.lastname: Saiepour
authors.affiliation: Institute of Neuropathology, University of Göttingen, Göttingen, Germany; Universität Leipzig, Paul-Flechsig-Institut für Hirnforschung, Leipzig, Germany.
authors.forename: U-K
authors.initials: UK
authors.lastname: Hanisch
authors.affiliation: Center for Behavior and Neurosciences, University of Groningen, Groningen, The Netherlands.
authors.forename: P
authors.initials: P
authors.lastname: Meerlo
authors.affiliation: Department of Immunohematology and Blood Transfusion, Leiden University Medical Centre, The Netherlands; Department of Pathology, VU University Medical Center, Amsterdam, The Netherlands.
authors.forename: P J
authors.initials: PJ
authors.lastname: van den Elsen
authors.affiliation: Department of Neuroscience, Section Medical Physiology, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands.
authors.forename: N
authors.initials: N
authors.lastname: Brouwer
authors.affiliation: Department of Neuroscience, Section Medical Physiology, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands.
authors.forename: H W G M
authors.initials: HW
authors.lastname: Boddeke
authors.affiliation: Department of Neuroscience, Section Medical Physiology, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands. Electronic address: b.j.l.eggen@umcg.nl.
authors.forename: B J L
authors.initials: BJ
authors.lastname: Eggen
mesh_terms: D000818:Animals; D044127:Epigenesis, Genetic; D020868:Gene Silencing; D006657:Histones / Q000378:metabolism; D053583:Interleukin-1beta / Q000235:genetics / Q000378:metabolism; D008070:Lipopolysaccharides / Q000494:pharmacology*; D051379:Mice; D017628:Microglia / Q000187:drug effects / Q000378:metabolism*; D016328:NF-kappa B / Q000235:genetics / Q000378:metabolism; D011401:Promoter Regions, Genetic; D051841:Transcription Factor RelB / Q000378:metabolism*; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics / Q000378:metabolism
chemical_list: D006657:Histones; D053583:Interleukin-1beta; D008070:Lipopolysaccharides; D016328:NF-kappa B; C497594:Relb protein, mouse; D014409:Tumor Necrosis Factor-alpha; D051841:Transcription Factor RelB
keywords: Endotoxin tolerance; Epigenetic silencing; Innate immunity; Microglia