NOD2-自噬通路调控失血性休克致敏全身炎症反应的作用机制

Patients who survived hemorrhagic shock (HS) are more susceptible to infection. An additional slight infection may cause severe systemic inflammation and lead to life-threatening multi-organ failure. Clarifying the mechanisms of HS-primed inflammation might be beneficial to clinical prognosis. NOD2 (Nucleotide binding oligomerization domain 2) plays an important role in the innate immune system and participates in the development of bacterial infection-induced systemic inflammatory response syndrome. Our previous studies found that HS could facilitate the release of HMGB1 which then bound to TLR4 (Toll-like receptor 4) to upregulate NOD2 expression in the "two-hit" model to mimic clinical findings. The elevated NOD2 levels enhanced MDP-induced macrophage activation which caused severe inflammation. Interestingly, we also found that HS-induced NOD2 upregulation could activate autophagy process. Autophagy was found to negatively regulate inflammation. The underlying mechanisms that NOD2 upregulation by HS causes both inflammation and anti-inflammation remain elusive. Our current study comprises the following 3 parts: (1) to determine the mechanisms that NOD2 induces greater inflammation in post-HS infection; (2) to investigate the role of NOD2-induced autophagy in regulation of anti-inflammation during post-HS infection; (3) to find how NOD2 and autophagy interact with and influence each other. Through these subprojects, we aim to test the hypothesis that NOD2-autophagy signaling pathway is essential for post-HS primed inflammation. The successful completion of the current study might provide a potential target to manage post-HS inflammatory process.

失血性休克后，机体对感染的反应增强，轻微感染即可引起全身炎症反应，导致多器官功能障碍，危及生命。阐明失血性休克致敏全身炎症反应的机制将有助于改善患者预后。NOD2作为固有免疫的重要组成部分，参与了感染致全身炎症反应的发生和转归。本课题组采用模拟临床的"二次打击"模型，发现失血性休克可通过HMGB1-TLR4通路上调巨噬细胞NOD2表达，导致细菌胞壁成分MDP引起的炎症反应增强。有趣的是，本课题组发现失血性休克导致的NOD2上调能够激活自噬，产生抗炎作用。但NOD2-自噬通路促炎/抗炎的双向调控机制尚不清楚。本课题拟在前期基础上，开展以下研究：①NOD2促进炎症反应的作用机制；②NOD2介导的自噬抗炎反应机制；③NOD2与自噬的相互调节机制。本课题的完成，有可能发现失血性休克致敏全身炎症反应的新机制，即NOD2-自噬通路在此疾病发生中具有双向调控作用，并为临床干预提供新的靶点。

研究背景:失血性休克是临床上常见的急重症，复苏后常发生全身炎症反应综合征，甚至发展为多器官功能衰竭。失血性休克后，机体对感染的反应增强， 轻微感染即可引起全身炎症反应，导致多器官功能障碍，危及生命。阐明失血性休克致敏全身炎症反应的机制将有助于改善患者预后。研究内容：本课题主要研究研究“二次打击”后 NOD2-自噬通路对炎症反应的影响和相关机制。重要结果：（1）HS/R通过HMGB1-TLR4信号通路特异性上调AM的NOD2表达。（2）HS/R上调AM的NOD2表达，使AM对MDP的反应性增强，“二次打击”处理后，小鼠AM的MIP2、MIF和TNF-α等早期炎症介质表达上调，可进一步活化巨噬细胞和诱导中性粒细胞聚集。“二次打击”处理后，小鼠肺泡中IL-1β的含量明显上升，TLR4、NOD2、NF-κB分子参与IL-1β成熟和释放，并且AM中NOD2分子介导对caspase-1活化，启动IL-1β成熟和释放。（3）NOD2 在“二次打击”中，上调AM自噬体形成，并且自噬体出现较晚，在刺激8小时开始出现，3-MA可以阻断“二次打击”对自噬的诱导作用，NOD2-/-小鼠对“二次打击”诱导自噬体形成无反应，证明NOD2 是介导细胞自噬体重要分子。（4）NOD2在“二次打击”后早期时相，促进肺炎症反应，在“二次打击”后晚期时相诱导自噬形成，抑制肺炎症反应，如果阻断自噬可加重肺损伤，降低小鼠的生存率，NOD2-/-可明显降低“二次打击”带来的肺损伤，因此NOD2信号通路是介导“二次打击”后ALI的重要调控机制。（5）NOD2在“二次打击”晚期时相，促进肺泡巨噬细胞自噬形成，诱导细胞凋亡，3-MA阻断自噬减少细胞凋亡或坏死细胞的清除，使炎症反应放大，加重肺损伤程度。科学意义：综上所述，本研究证实在HS/R+MDP“二次打击”过程中，NOD2信号通路在早期时相，促进炎症细胞活化、炎症因子的合成与分泌，从而促进炎症反应；在晚期时相通过促进自噬和诱导细胞凋亡抑制炎症反应。通过研究确定了 NOD2、自噬在 HS 致敏 SIRS 中的双向调控作用及机制，为调控 HS 致敏 SIRS 的炎症反应提供新的思路，为遏制“二次打击”后患者进入 SIRS-MODS 阶段提供新的靶点。