Department of Pulp Biology and Endodontics, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University (TMDU), Tokyo, Japan.
J Cell Physiol. 2019 Nov;234(11):21331-21341. doi: 10.1002/jcp.28737. Epub 2019 May 1.
microRNAs are small noncoding RNA molecules that regulate RNA silencing and posttranscriptional gene expression, and many microRNAs are involved in inflammatory processes. In particular, microRNA 21 (miR-21) is upregulated in inflammatory environment and reported to induce anti-inflammatory responses. However, the involvement of miR-21 in pulpal inflammation and the precise mechanisms of anti-inflammatory reactions induced by miR-21 remain unclear. We hypothesized that miR-21-5p expression is induced in lipopolysaccharide (LPS)-stimulated human dental pulp cells (hDPCs) and that miR-21-5p downregulates the proinflammatory cytokine expression in LPS-stimulated hDPCs. We found that miR-21-5p was upregulated in LPS-stimulated hDPCs concomitant with elevated proinflammatory cytokine expression and nuclear factor-kappa B (NF-κB) phosphorylation. miR-21-5p and cytokine expression were downregulated by BAY11-7085 and caffeic acid phenylethyl ester (CAPE), specific and potent NF-κB inhibitors. Enforced expression of miR-21-5p downregulated the Toll-like receptor (TLR)/NF-κB signaling via reducing the expression of TNF receptor-associated factor 6 (TRAF6) and programmed cell death 4 (PDCD4), which further induced the decrease of proinflammatory cytokine expression. hDPCs forcibly overexpressing miR-21-5p downregulated the LPS-induced expression of TNF receptor-associated factor 6 (TRAF6; a component of the Toll-like receptor [TLR]/NF-κB signaling pathway), programmed cell death 4 (PDCD4, a positive regulator of the TLR/NF-κB signaling pathway), and proinflammatory cytokines. In contrast, miR-21-5p inhibitor-transfected hDPCs upregulated the expression of TRAF6, PDCD4, and inflammatory cytokines following LPS stimulation. These findings suggest that miR-21-5p expression was induced by the NF-κB signaling pathway, which was in turn negatively regulated by miR-21-5p via downregulation of TRAF6 and PDCD4 expression in LPS-stimulated hDPCs.
microRNAs 是一种小的非编码 RNA 分子，可调节 RNA 沉默和转录后基因表达，许多 microRNAs 参与炎症过程。特别是 microRNA 21（miR-21）在炎症环境中上调，并报告诱导抗炎反应。然而，miR-21 在牙髓炎症中的参与以及 miR-21 诱导抗炎反应的确切机制尚不清楚。我们假设 miR-21-5p 在脂多糖（LPS）刺激的人牙髓细胞（hDPCs）中表达上调，并且 miR-21-5p 下调 LPS 刺激的 hDPCs 中促炎细胞因子的表达。我们发现，miR-21-5p 在 LPS 刺激的 hDPCs 中上调，同时促炎细胞因子表达和核因子-κB（NF-κB）磷酸化升高。miR-21-5p 和细胞因子表达通过特异性和有效的 NF-κB 抑制剂 BAY11-7085 和咖啡酸苯乙酯（CAPE）下调。miR-21-5p 的强制表达通过降低肿瘤坏死因子受体相关因子 6（TRAF6）和程序性细胞死亡 4（PDCD4）的表达来下调 Toll 样受体（TLR）/NF-κB 信号通路，从而进一步诱导促炎细胞因子表达的降低。强制过表达 miR-21-5p 的 hDPCs 下调 LPS 诱导的肿瘤坏死因子受体相关因子 6（TRAF6；TLR/NF-κB 信号通路的一个组成部分）、程序性细胞死亡 4（PDCD4，TLR/NF-κB 信号通路的正调节剂）和促炎细胞因子的表达。相反，miR-21-5p 抑制剂转染的 hDPCs 在 LPS 刺激后上调 TRAF6、PDCD4 和炎症细胞因子的表达。这些发现表明，miR-21-5p 的表达是由 NF-κB 信号通路诱导的，而 miR-21-5p 又通过下调 LPS 刺激的 hDPCs 中 TRAF6 和 PDCD4 的表达来负调控 NF-κB 信号通路。
