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 1 mg/kg) or intracere-broventricular (5 mu g) 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-10 and TNF-alpha genes. Furthermore, LPS preconditioning resulted in an increase in the amount of repressive histone modification H3K9me2 in the IL-1 beta promoter. ChIP and knock-down experiments showed that NF-kappa B subunit RelB was bound to the IL-1 beta 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. (C) 2015 Elsevier Inc. All rights reserved.
Original language | English |
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Pages (from-to) | 205-221 |
Number of pages | 17 |
Journal | Brain, Behavior, and Immunity |
Volume | 48 |
DOIs | |
Publication status | Published - Aug-2015 |
Keywords
- Microglia
- Innate immunity
- Endotoxin tolerance
- Epigenetic silencing
- ENDOTOXIN TOLERANCE
- CHROMATIN MODIFICATIONS
- COGNITIVE IMPAIRMENT
- RECEPTOR ACTIVATION
- CELL-DEATH
- TNF-ALPHA
- IN-VIVO
- HISTONE
- DISTINCT
- PHAGOCYTOSIS