磷酸戊糖途径介导的粒细胞免疫训练在脓毒症二次感染中的作用机制研究

Tissue damage caused by the secondary infection greatly increased the risk of death of terminal patients with sepsis. In the secondary infection, the overactive immune response of neutrophils is one of the leading cause of tissue damage. Recently, scientists found that the innate immune cells can be “immune trained” by the first encounterment of pathogen and get memory. This effect strengthens the innate immune cells to response more intensively in the secondary infection. Previously, we have found that the immune trained neutrophils caused inflammatory damage of tissue during the secondary infection of sepsis; more importantly, the enhanced pentose-phophate pathway (PPP) of glucose metabolism is the unique features of trained neutrophils. We hypothesized that the PPP is activated by Akt1/mTOR/c-Myc signaling pathway and regulates neutrophil training, which leading to an overactivation of immune system and tissue damage in the secondary infection of sepsis. We aim to clarify the function of neutrophil training in tissue damage with the CLP-LPS secondary infection model, to illustrate the regulatory mechanisms of PPP on neutrophil training in vivo and in vitro, and to explore the regulatory mechanisms of Akt/mTOR pathway on PPP. Our program will illuminate the mechanism of neutrophil immune training in the levels of metabolic pathway and signaling pathway, and will provide new target for alleviate the immune injury caused by the secondary infection of sepsis.

继发感染造成的组织器官损伤大大增加了脓毒症晚期患者的死亡风险。继发感染时，粒细胞免疫反应过度活化是造成组织损伤的重要原因之一。新近发现，天然免疫细胞具有“免疫训练”效应，能对初次病原刺激产生记忆，再次遇到病原时免疫反应增强。申请人前期研究发现，粒细胞免疫训练是导致二次感染时器官炎性损伤的主要机制；更为重要的是，糖代谢磷酸戊糖途径增强是粒细胞免疫训练的独特特征。据此提出：Akt1/mTOR/c-Myc通路激活磷酸戊糖途径，调控粒细胞免疫训练，在二次感染时过度活化，引起组织损伤。本项目拟采用脓毒症二次感染小鼠模型，明确粒细胞免疫训练在组织损伤中的作用；通过体内、体外实验阐明磷酸戊糖途径调控粒细胞免疫训练的机制；采用mTOR功能缺陷小鼠，探讨Akt/mTOR通路对磷酸戊糖途径和免疫训练的调控机制。从代谢途径和信号通路两个层面明确粒细胞免疫训练的机制，为减轻脓毒症二次感染组织损伤提供新的治疗靶点。

脓毒症通常诱导免疫低反应状态，增加继发感染和晚期死亡的发生率。最新研究表明，暴露于某些微生物成分会触发单核细胞和巨噬细胞的训练免疫，以保护宿主免受继发感染的伤害。本项目中，我们研究了脓毒症继发感染如何诱导强烈的固有免疫反应。我们使用盲肠结扎穿孔术（CLP）脓毒症小鼠模型，发现粒细胞，而不是单核细胞或巨噬细胞，表现出训练免疫的典型特征。经过训练的粒细胞具有比初次感染更强的免疫应答水平，能够保护宿主免受非相关细菌感染；然而，由于免疫训练的粒细胞能够促进强烈的炎症反应，尤其是分泌大量TNF-α等炎性细胞因子，从而导致严重的肺损伤。机制上，我们发现两种机制独立地参与了粒细胞的免疫训练：1)代谢重塑。磷酸戊糖途径、糖酵解代谢以及脂肪酸合成增强，促进了粒细胞免疫训练；2)表观遗传重编程。TLR4下游NF-kB和MAPK信号通路的抑制性基因Socs1和Irak3（编码IRAK-M）启动子区H3k27ac、H3k9ac水平降低，基因转录受抑制，导致该通路异常活化，从而引起更强烈的炎症反应。通过对免疫训练的粒细胞进行代谢干预和表观遗传调控干预等，证实磷酸戊糖途径增强、Socs1和Irak3启动子区组蛋白去乙酰化修饰增强是引起粒细胞免疫训练的关键原因。本项目研究成果揭示了粒细胞免疫训练造成脓毒症二次感染器官损伤的新机制，为改善二次感染器官损伤、降低病死率提供一种新的治疗思路。