探讨补体C3a受体信号在急性肾脏感染过程中的保护作用及其机制

Urinary tract infections (UTIs) caused by uropathogenic E. coli remain among the most common infectious diseases worldwide. Despite the antimicrobial therapy, frequent recurrence or persistence of infection and increase in antibiotic resistant highlight the need for improving our understanding of the pathogenic mechanisms of this disease and developing novel treatment strategies. Innate immunity plays important roles in host defence against bacterial infection, including kidney infection. The complement system is a major component of innate immunity. However, the roles of complement in kidney infection is a paradox, for example, most human uropathogenic strains are resistant to C5b-9 mediated killing, C5a and C3b haves been suggested to have pathogenic effects through interaction with their respective receptors on tubular epithelial cells. So far, it is unclear if complement has protective effects in kidney infection. Recent studies have demonstrated that C3a exerts protective roles in several pathological conditions such as inflammation and infection through its cognate receptor C3a receptor (C3aR). In this project, we propose to investigate protective roles of C3a-C3aR signalling in acute kidney infection and the involved molecular and cellular mechanisms. We will employ a well-established murine model of ascending UTI, using C3aR knockout (KO) mice as well as C3aR agonist to determine the protective roles of C3aR in acute kidney infection. We will generate bone marrow chimeras between wildtype and C3aR KO mice to define the relative importance of C3aR on infiltrating cells in conferring the protection. We will perform a series of ex vivo and in vitro experiments to examine the effects of C3aR signalling on phagocytes, in the context of the infection (i.e. phagocytic function, apoptosis, and cytokine production). The work will describe a previously unknown roles for C3a/C3aR in pyelonephritis, provide new insight into the mechanisms of host defence against UTI and has implications for developing novel therapies for prevention and treatment of this disease.

由大肠杆菌引起的泌尿系统感染是临床上常见问题，尽管抗生素可用于治疗,但感染反复发作以及出现抗生素耐药增多等是临床上面临的挑战。固有免疫在宿主抗感染免疫反应中发挥重要作用。补体系统是固有免疫的重要组成部分，但前期研究发现补体在肾脏感染中的作用与普遍预期矛盾。例如：大肠杆菌致病株对C5b-9介导的直接杀伤作用耐受，C5a和C3b与其相应受体作用可促进细菌入侵肾脏小管上皮细胞。目前尚不清楚补体活化是否在肾脏感染过程中也发挥保护作用。最新研究发现C3a受体信号在多种炎症、感染引起的病理损伤过程中发挥保护作用。在本项目中我们计划探讨C3a受体信号在急性肾脏感染过程中的保护作用及其机制。我们将使用受体敲除小鼠、受体激动剂以及上行性肾脏感染模型来明确C3a受体信号的保护作用，采用骨髓重构建立C3a受体嵌合小鼠以及细胞实验来探讨该过程所涉及的细胞、分子机制。我们的工作将有助于进一步认识肾脏感染的病理机制。

急性肾盂肾炎主要由尿路致病性大肠杆菌上行感染引起，严重病例可导致肾脏纤维化及慢性肾衰竭，引起败血症以及因全身感染而发的多器官功能衰竭。尽管抗生素对治疗有效，但感染的反复发作以及出现抗生素耐药增多等是临床上亟待解决的问题。因此有必要积极从改善宿主免疫的角度来探寻新的治疗策略。固有免疫系统在抗感染过程中发挥尤为重要作用。补体系统是固有免疫的重要组成部分，我们前期研究发现,补体活化小片段C5a通过与其受体（C5aR1）作用，促进组织炎症反应，加重感染引起的肾脏组织损伤，并在慢性肾脏感染模型中促进肾脏间质纤维化。这些工作主要强调了补体活化在肾脏感染过程中的致病作用。补体活化是否在肾脏感染中也发挥对宿主的保护作用目前尚不清楚，C3aR信号在泌尿系统感染过程中所起的作用尚未见报道。..在本研究中，项目组采用C3a受体敲除小鼠以及放射线外照射-骨髓移植技术建立受体嵌合小鼠，发现C3a-C3aR信号在急性肾脏感染过程中发挥重要抗感染保护作用。机制研究进一步发现C3aR信号主要通过促进吞噬功能以及调控巨噬细胞炎性细胞因子生成而发挥抗感染作用；使用C3aR激动剂特异性激活C3aR信号能够明显降低肾脏感染，提示本研究可能具有潜在的临床应用价值。..本研究初步揭示补体不同受体（C3aR，C5aR）在泌尿系统感染过程中发挥不同作用，由于补体抑制剂及补体受体拮抗剂开始在欧美进入II期临床试验, 我们的发现可能为针对不同补体受体靶向治疗反复发作的泌尿系统感染提供理论基础。

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