MEKK2在固有免疫抗细菌感染中的调控机制

Mitogen-activated protein (MAPK) cascades are intracellular signaling networks existing in all eukaryotic cells. MAPKs are rapidly and transiently activated following immune receptor stimulation and control multiple steps of innate and adaptive immune responses. The molecular mechanisms that govern their activation and specificity during pathogenic bacteria-induced immune and inflammation responses remain unclear. MEKK2 is a member of the MAPK family. Although previous studies from many laboratories have established a major role of MEKK2 in innate immune responses, its function in host response to bacteria infection has not been fully studied. Using MEKK2 KO mice, we found that: 1) MEKK2 is activated by pathogenic bacteria. 2) MEKK2 deficient mice were impaired in endotoxin-induced septic shock in vivo. 3) Listeria monocytogenes（LM）infected MEKK2-deficient macrophages had decreased cytokines as compared to that in wild type cells. These preliminary results indicate that MEKK2 plays a central role in host defense against bacteria infection. The proposed studies are designed to elucidate the molecular mechanisms of MEKK2 signaling and function in innate immunity against bacterial infection. These studies will benefit the prevention and therapy for bacterial infection. Three Specific Aims are proposed: 1 Define the role of MEKK2 in host defense against bacteria infection. 2 Determine the role of MEKK2 in bacteria-mediated macrophage and dendritic cell. 3 Investigate the molecular mechanism of MEKK2 regulation by the immune receptors

MAPK级联是真核细胞普遍的胞内信号通路。免疫受体与配体结合后，MAPK迅速瞬时激活，通过调控炎症因子表达,启动固有和适应性免疫应答。在病原细菌引起免疫应答中，MAPK激活的分子机制尚不完全清楚。 MEKK2 隶属MAPK，MEKK2在免疫应答中起重要作用，但它在抗菌感染中的研究尚非常有限。利用MEKK2 KO小鼠，我们发现：1）细菌感染可以激活MEKK2。2）KO小鼠对内毒素引起的感染性休克有缺陷。3）李斯特菌感染后，KO 巨噬细胞生成细胞因子较少。因此，MEKK2可能在抗菌感染中起核心作用。本课题组将通过研究MEKK2在宿主抗菌感染过程中作用,以及其在巨噬细胞和树突状细胞对细菌反应中的作用,和免疫受体调控MEKK2的分子机制,为防治细菌感染提供新的思路。

固有免疫是机体抵抗外界微生物感染的重要途径，固有免疫依赖多种免疫细胞活化，其中广泛分布于机体组织的吞噬细胞在识别细菌特异抗原后能被迅速激活，是机体抵抗细菌感染的主要细胞群。巨噬细胞上TLR受体家族成员应激细菌信号刺激产生炎性应答并抵抗细菌感染，大量研究表明MAPK级联反应在介导TLR信号通路激活中具有核心作用，但其特异调控宿主抗菌反应的具体机理尚不清晰。. 在本项目支持下，我们通过研究MEKK2（MAPKKK）抗菌功能、效应细胞及分子机制三个层面分析了MAPK级联特异调控机体抗菌的机制。首先，利用细菌抗原诱导小鼠休克模型，我们揭示MEKK2具有刺激机体炎性反应抵抗细菌感染的作用；进一步我们利用肠炎模型在疾病状态下阐明MEKK2信号的这一抗菌反应最终有利肠炎减缓。接着，我们分析MEKK2信号在巨噬细胞中的功能机制，我们发现MEKK2缺陷的巨噬细胞分泌及表达细胞因子能力显著减弱，抵抗细菌所致凋亡能力受损，但分化不受干扰，说明MEKK2有助细菌刺激下巨噬细胞存活及炎性应答。最后，我们研究这一现象的具体分子机制。我们发现在细菌抗原刺激下，MEKK2介导的MAPK和NF-kB通路激活受损，这两条通路与炎性因子产生密切相关；有意思的是，应激不同细菌感染时这两条通路受损程度不同，提示MEKK2还介导其他更广谱且关键的机制促进巨噬细胞产生炎症因子。RNA-seq分析显示MEKK2敲除的巨噬细胞除MAPK信号受损外，细胞代谢也发生改变。鉴于细胞代谢与炎性反应的紧密联系，我们比较了MEKK2信号对巨噬细胞三种极化状态（M0、M1及M2）下的糖酵解影响，发现只在MEKK2缺陷的M1中糖酵解水平剧烈上升。. 综上所述，我们认为MEKK2调控巨噬细胞抵抗细菌感染的主要分子基础是经典MAPK/NF-kB通路及细胞代谢改变，这些工作将为未来针对MEKK2相关分子开发潜在药物提供理论基础。