Department of Medicine, University of Oklahoma Health Sciences Center, Oklahoma City, OK, United States.
Department of Microbiology and Immunology, University of Oklahoma Health Sciences Center, Oklahoma City, OK, United States.
Front Immunol. 2018 Nov 27;9:2751. doi: 10.3389/fimmu.2018.02751. eCollection 2018.
MicroRNA (miR) miR-155 modulates microglial activation and polarization, but its role in activation of microglia during bacterial brain infection is unclear. We studied miR-155 expression in brains of C57BL/6 (B6.WT) mice infected i.p. with the neuro-invasive bacterial pathogen (). Infected mice were treated with ampicillin starting 2 days (d) post-infection (p.i.) and analyzed 3d, 7d, and 14d p.i. Virulent strains EGD and 10403s upregulated miR-155 in whole brain 7 d p.i. whereas infection with avirulent, non-neurotropic Δ or Δ mutants did not. Similarly, infection with virulent but not mutated bacteria upregulated IFN-γ mRNA in the brain at 7 d p.i. Upregulation of miR-155 in microglia was confirmed by qPCR of flow cytometry-sorted CD45CD11b brain cells. Subsequently, brain leukocyte influxes and gene expression in sorted microglia were compared in -infected B6.WT and B6.Cg-Mir155tm1.1Rsky/J (B6.miR-155) mice. Brain influxes of Ly-6C monocytes and upregulation of IFN-related genes in microglia were similar to B6.WT mice at 3 d p.i. In contrast, by d 7 p.i. expressions of microglial IFN-related genes, including markers of M1 polarization, were significantly lower in B6.miR-155 mice and by 14 d p.i., influxes of activated T-lymphocytes were markedly reduced. Notably, CD45CD11b brain cells from B6.miR-155 mice isolated at 7 d p.i. expressed 2-fold fewer IFN-γ transcripts than did cells from B6.WT mice suggesting reduced IFN-γ stimulation contributed to dampened gene expression in B6.miR-155 microglia. Lastly, stimulation of 7 d p.i. brain cells with heat-killed induced greater production of TNF in B6.miR-155 microglia than in B6.WT microglia. Thus, miR-155 affects brain inflammation by multiple mechanisms during neuroinvasive infection. Peripheral miR-155 promotes brain inflammation through its required role in optimal development of IFN-γ-secreting lymphocytes that enter the brain and activate microglia. Microglial miR-155 promotes M1 polarization, and also inhibits inflammatory responses to stimulation by heat-killed , perhaps by targeting .
MicroRNA (miR) miR-155 调节小胶质细胞的激活和极化，但它在细菌脑感染中小胶质细胞激活中的作用尚不清楚。我们研究了 C57BL/6 (B6.WT) 小鼠脑内感染神经侵袭性细菌病原体 () 后 miR-155 的表达。感染后 2 天（d）开始用氨苄青霉素治疗，并在 3、7 和 14 天进行分析。毒力株 EGD 和 10403s 在 7 天感染时上调了整个大脑中的 miR-155，而感染无神经毒性的 Δ 或 Δ 突变体则没有。同样，感染毒力但非突变细菌在 7 天感染时上调了大脑中的 IFN-γ mRNA。通过流式细胞术分选的 CD45CD11b 脑细胞 qPCR 证实了小胶质细胞中 miR-155 的上调。随后，比较了 B6.WT 和 B6.Cg-Mir155tm1.1Rsky/J (B6.mir-155) 小鼠中感染后大脑白细胞流入和分选小胶质细胞中的基因表达。在感染后的 3 天，B6.WT 小鼠和 B6.mir-155 小鼠的 Ly-6C 单核细胞脑内流入和小胶质细胞中 IFN 相关基因的上调相似。相比之下，在第 7 天，B6.mir-155 小鼠小胶质细胞的 IFN 相关基因表达，包括 M1 极化标志物，显著降低，而在第 14 天，激活的 T 淋巴细胞的流入明显减少。值得注意的是，在 7 天感染时分离的 B6.mir-155 小鼠的 CD45CD11b 脑细胞表达的 IFN-γ 转录物比 B6.WT 小鼠的细胞少 2 倍，这表明 IFN-γ 刺激减少导致 B6.mir-155 小胶质细胞中的基因表达减弱。最后，与 B6.WT 小胶质细胞相比，热灭活的刺激 7 天感染的脑细胞产生了更多的 TNF 。因此，miR-155 通过多种机制在神经侵袭性感染期间影响大脑炎症。外周 miR-155 通过其在进入大脑并激活小胶质细胞的 IFN-γ 分泌淋巴细胞最佳发育中的必需作用，促进大脑炎症。小胶质细胞 miR-155 促进 M1 极化，并抑制对热灭活的反应，可能通过靶向 。
