Department of Pharmacology and Experimental Neuroscience, University of Nebraska Medical Center, 42nd and Emile, Omaha, NE, 68198, USA.
Mol Cell Biochem. 2021 Nov;476(11):4139-4151. doi: 10.1007/s11010-021-04220-3. Epub 2021 Jul 27.
Toll-like receptors (TLRs) can contribute to central nervous system disease pathologies via recognition of microRNAs (miRNAs); however, it remains to be determined which miRNAs are able to activate this signaling. Here we report that numerous miRNAs induced the production of tumor necrosis factor alpha in multiple myeloid cell types, including microglia, and that this effect was abolished in cells deficient in TLR7. Examination of closely related miRNAs that differed in their ability to activate TLR7 resulted in the identification of a motif (UGCUUAU) in miR-20a-5p and specific nucleotides (all the uridines and surprisingly the cytosine as well) in a key area of miR-20a-5p and miR-148b-3p that were vital for the secretion of cytokines via TLR7 stimulation. A 10-nucleotide sequence including this motif was identified to be the shortest single-stranded RNA to signal via TLR7. An miRNA containing this motif induced the secretion of multiple proinflammatory molecules, which was dependent on the phosphoinositide 3-kinase, mitogen-activated protein kinase, and nuclear factor kappa-light-chain-enhancer of activated B cell signaling pathways. Wild-type mice administered miR-20a-5p, which contained this motif, demonstrated increased leukocyte migration. This effect was significantly ameliorated in TLR7-knockout mice, and mice administered miR-20b-5p, in which the motif was mutated, did not exhibit leukocyte migration. We provide a detailed analysis of miRNAs that activate endosomal TLR7 and identify key nucleotide features of a sequence motif recognized by TLR7.
Toll 样受体 (TLRs) 可通过识别 microRNAs (miRNAs) 促进中枢神经系统疾病病理学的发生；然而，目前尚不清楚哪些 miRNAs 能够激活这种信号。在这里，我们报告说，许多 miRNAs 可诱导多种骨髓细胞类型（包括小胶质细胞）产生肿瘤坏死因子-α，而在 TLR7 缺陷的细胞中，这种作用被消除。对在激活 TLR7 能力上存在差异的密切相关 miRNAs 的检查导致鉴定出 miR-20a-5p 中的一个基序 (UGCUUAU) 和 miR-20a-5p 和 miR-148b-3p 中的关键区域中的特定核苷酸（所有的尿嘧啶和令人惊讶的胞嘧啶）对于通过 TLR7 刺激细胞因子的分泌至关重要。鉴定出包括该基序的 10 个核苷酸序列是通过 TLR7 信号转导的最短单链 RNA。包含该基序的 miRNA 诱导多种促炎分子的分泌，这依赖于磷酸肌醇 3-激酶、丝裂原活化蛋白激酶和核因子 kappa-轻链增强子的 B 细胞信号通路。给予含有该基序的 miR-20a-5p 的野生型小鼠表现出白细胞迁移增加。在 TLR7 敲除小鼠中，这种作用显著改善，而给予 miR-20b-5p（其中该基序发生突变）的小鼠则未观察到白细胞迁移。我们对激活内体 TLR7 的 miRNAs 进行了详细分析，并确定了 TLR7 识别的序列基序的关键核苷酸特征。
