Department of Oral Biology, University of Florida, Gainesville, FL 32610, USA.
J Immunol. 2013 Feb 1;190(3):1250-63. doi: 10.4049/jimmunol.1103060. Epub 2012 Dec 21.
Innate immune response is the first defense against pathogens via recognition by various conserved pattern recognition receptors, such as TLRs, to initiate a rapid and strong cytokine alarm. TLR signaling-mediated cytokine production must be properly regulated to prevent pathological conditions deriving from overproduction of cytokines. In this study, the role of specific microRNAs in TLR-signaling pathway was investigated to reveal the cross-interaction and -regulation in the MyD88 pathway. In peptidoglycan (PGN)/TLR2-stimulated THP-1 monocytes, PBMCs, and primary macrophages showed rapid and dramatic miR-132 and miR-212 (miR-132/-212) upregulation. This newly identified response appeared earlier in time than the characteristic miR-146a response in LPS-TLR4 stimulation. The rapid induction of miR-132/-212 was transcription factor CREB dependent, and the sustained expression of miR-132/-212 was responsible for inducing tolerance to subsequent PGN challenge. Cross-tolerance was observed by TLR5 ligand flagellin and heat-killed or live bacteria resulting from miR-132/-212 upregulation. Mechanistically, IRAK4 was identified and validated as a target of miR-132/-212 by luciferase reporter assay and seed-sequence mutagenesis of the reporter. Transfection of miR-132 or miR-212 alone mimicked PGN tolerance in monocytes, whereas transfected specific miRNA inhibitors tampered the tolerance effect. During bacterial infection, PGN-mediated TLR2 signaling induces miR-132/-212 to downregulate IRAK4, an early component in the MyD88-dependent pathway, whereas LPS/TLR4-induced miR-146a downregulates downstream components of the same MyD88-dependent pathway. The identification of miR-132/-212 and miR-146a together to prevent damaging consequences from the overproduction of proinflammatory cytokines by targeting a common signaling pathway is significant and will provide insights into future design and development of therapeutics.
天然免疫反应是通过各种保守模式识别受体（如 TLRs）识别病原体的第一道防线，以启动快速而强烈的细胞因子警报。TLR 信号转导介导的细胞因子产生必须得到适当的调节，以防止细胞因子过度产生导致的病理状况。在这项研究中，研究了特定 microRNA 在 TLR 信号通路中的作用，以揭示 MyD88 通路中的交叉相互作用和调节。在肽聚糖（PGN）/TLR2 刺激的 THP-1 单核细胞、PBMC 和原代巨噬细胞中，miR-132 和 miR-212（miR-132/-212）迅速显著上调。这种新发现的反应比 LPS-TLR4 刺激中的特征性 miR-146a 反应更早出现。miR-132/-212 的快速诱导依赖于转录因子 CREB，而 miR-132/-212 的持续表达负责诱导对随后的 PGN 挑战的耐受。TLR5 配体鞭毛蛋白和热灭活或活菌引起的 miR-132/-212 上调导致交叉耐受。通过荧光素酶报告基因测定和报告基因的种子序列诱变鉴定并验证了 IRAK4 是 miR-132/-212 的靶标。单独转染 miR-132 或 miR-212 可模拟单核细胞中的 PGN 耐受，而转染特异性 miRNA 抑制剂则会干扰耐受效应。在细菌感染过程中，PGN 介导的 TLR2 信号诱导 miR-132/-212 下调 IRAK4，IRAK4 是 MyD88 依赖性途径中的早期组成部分，而 LPS/TLR4 诱导的 miR-146a 下调相同的 MyD88 依赖性途径的下游组成部分。miR-132/-212 和 miR-146a 的共同鉴定可防止通过靶向共同信号通路过度产生促炎细胞因子而产生破坏性后果，这具有重要意义，并将为未来治疗药物的设计和开发提供思路。
