Myeloid C/EBPβ deficiency reshapes microglial gene expression and is protective in experimental autoimmune encephalomyelitis

Background: ccaat/enhancer binding protein β (c/ebpβ) is a transcription factor that regulates the expression of important pro-inflammatory genes in microglia. mice deficient for c/ebpβ show protection against excitotoxic and ischemic cns damage,but the involvement in this neuroprotective effect of the various c/ebpβ-expressing cell types is not solved. since c/ebpβ-deficient microglia show attenuated neurotoxicity in culture,we hypothesized that specific c/ebpβ deficiency in microglia could be neuroprotective in vivo. in this study,we have tested this hypothesis by generating mice with myeloid c/ebpβ deficiency. methods: mice with myeloid c/ebpβ deficiency were generated by crossing lysmcre and c/ebpβfl/fl mice. primary microglial cultures from c/ebpβfl/fl and lysmcre-c/ebpβfl/fl mice were treated with lipopolysaccharide ± interferon γ (ifnγ) for 6 h,and gene expression was analyzed by rna sequencing. gene expression and c/ebpβ deletion were analyzed in vivo in microglia isolated from the brains of c/ebpβfl/fl and lysmcre-c/ebpβfl/fl mice treated systemically with lipolysaccharide or vehicle. mice of lysmcre-c/ebpβfl/fl or control genotypes were subjected to experimental autoimmune encephalitis and analyzed for clinical signs for 52 days. one- or two-way anova or kruskal-wallis with their appropriate post hoc tests were used. results: lysmcre-c/ebpβfl/fl mice showed an efficiency of c/ebpβ deletion in microglia of 100 and 90% in vitro and in vivo,respectively. these mice were devoid of female infertility,perinatal mortality and reduced lifespan that are associated to full c/ebpβ deficiency. transcriptomic analysis of c/ebpβ-deficient primary microglia revealed c/ebpβ-dependent expression of 1068 genes,significantly enriched in inflammatory and innate immune responses go terms. in vivo,microglial expression of the pro-inflammatory genes cybb,ptges,il23a,tnf and csf3 induced by systemic lipopolysaccharide injection was also blunted by c/ebpβ deletion. cns expression of c/ebpβ was upregulated in experimental autoimmune encephalitis and in multiple sclerosis samples. finally,lysmcre-c/ebpβfl/fl mice showed robust attenuation of clinical signs in experimental autoimmune encephalitis. conclusion: this study provides new data that support a central role for c/ebpβ in the biology of activated microglia,and it offers proof of concept for the therapeutic potential of microglial c/ebpβ inhibition in multiple sclerosis. © 2017 the author(s).