MALAT1/mascRNA双分子体系在调节巨噬细胞固有免疫应答及抗类风湿关节炎疾病中的作用和机制研究

Looking for inhibitors targeting multiple inflammatory cytokines with long-term safety represents a promising strategy for the treatment of patients with rheumatoid arthritis (RA) who fail to respond to currently available therapies. MALAT1 is an evolutionary conserved long noncoding RNA (lncRNA) enriched in the nucleus. Post-transcriptional processing of MALAT1 nascent transcript generates the mature form of this lncRNA, together with a cytoplasmic small noncoding RNA termed mascRNA. Earlier we showed that MALAT1 inhibits inflammatory cytokine production by macrophages through its interaction with NF-κB. A recent report also revealed that mascRNA negatively regulates the expression of immune-related genes including TNFα in macrophages, suggesting that both MALAT1 and mascRNA are involved in modulating innate immune responses. The purpose of this project is to address the mechanism underlying the regulation of innate immune responses by mascRNA, and investigate the relationship between nucleus-localized MALAT1 and cytoplasm-localized mascRNA in modulating innate immune responses. In addition, this project aims to define the functional element of MALAT1 responsible for NF-κB binding, and evaluate therapeutic values and mechanisms of action of this element and mascRNA in a disease model of RA. This project can help us gain insight into the mechanism by which the MALAT1-mascRNA two-molecule system exert its negative effect on inflammatory response, holding promise for developing novel treatment strategies against RA.

寻找安全的、靶向多个炎性细胞因子的抑制剂是治疗对现有药物没有响应的类风湿关节炎（RA）患者的有效途径。MALAT1是一种保守的核内长链非编码RNA，在其成熟过程中经转录后加工还生成位于胞浆的小分子非编码RNA“mascRNA”。前期工作表明MALAT1与NF-κB互作抑制巨噬细胞合成炎症因子，新近又有报道mascRNA也可抑制巨噬细胞中TNFα等免疫相关基因的表达，提示MALAT1、mascRNA均参与固有免疫应答。本项目拟揭示mascRNA调节固有免疫应答的机制，研究核内分布的MALAT1与胞质分布的mascRNA在调控巨噬细胞固有免疫应答过程中的相互关系；此外，本项目拟解析与NF-κB结合的MALAT1功能元件，并评价此功能元件和mascRNA对RA疾病模型的疗效及体内作用机制。本项目有助于阐释MALAT1/mascRNA双分子体系负调控炎症反应的新机制，同时为RA的治疗提供新思路。

固有免疫应答是机体清除病原体和受损细胞的一种保护性机制，但不受控制的免疫反应也会导致炎症以及自身免疫病如类风湿性关节炎(RA)。Toll样受体（TLR）是一类启动固有免疫应答、进化上保守的模式识别受体，TLR信号通路负调控机制的缺失与炎症性自身免疫病高度相关，因此TLR通路是治疗这类疾病的有效靶点。mascRNA是一种tRNA样小分子非编码RNA，来自于长链非编码RNA Malat1前体的转录后加工。我们发现，mascRNA参与TLR介导的固有免疫调控。mascRNA抑制巨噬细胞中LPS (TLR4配体)诱导的NF-κB和MAPK信号通路的活化以及炎性细胞因子的产生，而且外源性mascRNA可减轻LPS诱导的小鼠肺部炎症。 与之相反，mascRNA在体外和体内均增强TLR3配体poly(I:C)诱导的IRF3和STAT1的磷酸化以及干扰素刺激基因的转录。机制上，mascRNA促进TRAF6蛋白K48泛素化导致其经蛋白酶体途径降解，从而负调控TLR介导的MyD88依赖的炎症反应，同时正调控TRIF依赖的抗病毒应答。值得注意的是，mascRNA抑制炎症的功能独立于Malat1。我们还发现，hnRNP H/F蛋白可与mascRNA互作，参与对TLR介导的炎症反应的精细调控。因此，除蛋白、长链非编码RNA、miRNA之外，mascRNA可被视为一种新的能够对固有免疫进行正、负调节的因子，这种双重调节功能有望为某些免疫相关炎症性疾病如多发性硬化症、溃疡性结肠炎和炎症性关节炎甚至肿瘤的药物研发带来希望，因为mascRNA在抑制炎症因子的同时并不损害干扰素对这些炎性疾病和肿瘤的治疗作用。事实上，全身给予外源性mascRNA在RA小鼠模型中显示出抗炎和抗骨侵蚀疗效，提示mascRNA可能是治疗对现有药物没有响应的RA患者的潜在生物药物。