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C/EBPβ deficiency reshapes microglial gene expression

ABSTRACT: 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 of the various C/EBPβ expressing cell types in this neuroprotective effect 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. Mice with myeloid C/EBPβ deficiency were generated by crossing LysMCre and C/EBPβfl/fl mice . Primary microglial cultures from C/EBPβfl/fl (named here as WT) and LysMCre-C/EBPβfl/fl (named here as KO) mice were treated with lipopolysaccharide ± interferon γ (IFNγ) for 6 h and gene expression was analyzed by RNA sequencing. LysMCre-C/EBPβfl/fl mice showed an efficiency of C/EBPβ deletion of 100% in cultured microglia. 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. This study provides new data that support a central role for C/EBPβ in the biology of activated microglia.

ORGANISM(S): Mus musculus

PROVIDER: GSE90046 | GEO | 2017/06/13

SECONDARY ACCESSION(S): PRJNA354400

REPOSITORIES: GEO

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Project description:A synthetic analog of sphingosine named FTY720 (Fingolimod), phosphorylated by sphingosine kinase-2, interacts with sphingosine-1-phosphate (S1P) receptors expressed on various cells. FTY720 suppresses the disease activity of multiple sclerosis (MS) chiefly by inhibiting S1P-dependent egress of autoreactive T lymphocytes from secondary lymphoid organs, and possibly by exerting anti-inflammmatory and neuroprotective effects directly on brain cells. However, at present, biological effects of FTY720 on human microglia are largely unknown. We studied FTY720-mediated apoptosis of a human microglia cell line HMO6. The exposure of HMO6 cells to non-phosphorylated FTY720 (FTY720-non-P) induced apoptosis in a dose-dependent manner with IC50 of 10.6±2.0 microM, accompanied by the cleavage of caspase-7 and caspase-3 but not of caspase-9. The apoptosis was inhibited by Z-DQMD-FMK, a caspase-3 inhibitor, but not by Pertussis toxin, a Gi protein inhibitor, suramin, a S1P3/S1P5 inhibitor, or W123, a S1P1 competitive antagonist, although HMO6 expressed S1P1, S1P2, and S1P3. Furthermore, both phosphorylated FTY720 (FTY720-P) and SEW2871, a S1P1 selective agonist did not induce apoptosis of HMO6. Genome-wide gene expression profiling and molecular network analysis indicated activation of transcriptional regulation by sterol regulatory element-binding protein (SREBP) in FTY720-non-P-treated HMO6 cells. Western blot verified activation of SREBP2 in these cells, and apoptosis was enhanced by pretreatment with simvastatin, an activator of SREBP2, and by overexpression of the N-terminal fragment of SREBP2. These observations suggest that FTY720-non-P-induced apoptosis of HMO6 human microglia is independent of S1P receptor binding, and positively regulated by the SREBP2-dependent proapoptotic signaling pathway. The HMO6 cell line was established by immortalizing cultured microglia isolated from human embryonic telencephalon tissues with a retroviral vector PASK1.2 encoding v-myc oncogene (Nagai et al. Neurobiol. Dis. 8: 1057-1068, 2001). HMO6 cells express the markers of the microglia/macrophage lineage cells, including CD11b, CD68, CD86, HLA-ABC, HLA-DR, and ricinus communis agglutinin lectin-1 (RCA), serving as a model of human microglia both in vitro and in vivo. The cells were exposed for 2 hours to 10 microM FTY720-non-P dissolved in dimethyl sulfoxide (DMSO) or ethanol or exposed to the vehicle.

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C/EBPβ deficiency reshapes microglial gene expression

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