Caspase-11剪切GsdmD在促进急性肾损伤时肾小管上皮细胞释放白细胞介素-18中的作用及机制研究

Acute renal injury (AKI) is characterized by rapid decline in renal filtration and release of inflammatory cytokines. Excessive inflammatory response is a key risk factor for accelerating renal injury. Among the different inflammatory cytokines, the increase of interlukin-18 (IL-18) is the most obvious and even accepted as a diagnostic indicator of AKI. Renal tubule is the major target of AKI. Meanwhile, renal tubular epithelial cell is also the major source of inflammatory cytokines. Release of IL-18 induces renal injury by activating FasL/Fas receptor pathway and NF-kB, promoting TNF-a, MCP-1 expression and microphage filtration. However, renal epithelial cell normally can not secret IL-18 since IL-18 is lack of secretory signal domain. In our preliminary study, we observed that the cleavage of GsdmD was increased, meanwhile, caspase-11 was also increased. Based on the preliminary observation, we hypothesized that under the pathological condition of AKI, the expression of caspase-11 is increased. Caspase-11 promotes the cleavage of GsdmD, initiates its translocation to the membrane and then facilitates the release of IL-18. The release of large amount of IL-18 from renal epithelial cells accelerates renal injury. We plan to test the hypothesis in caspase-11 and GsdmD gene knockout mice and cultured renal tubular epithelial cells. The result of the study will provide new evidence for understanding the molecular mechanism of renal injury and explore the new strategy for the treatment of AKI.

过度的炎症反应是急性肾损伤（AKI）的重要特征，也是加剧肾损伤的关键。在众多炎症因子中，IL-18在AKI时升高最为显著，甚至可作为AKI的诊断指标。肾小管上皮细胞是AKI时肾损伤的关键部位，同时也是炎症因子的重要来源，而IL-18主要来源就是小管上皮。IL-18能通过激活FasL/Fas受体通路等多种方式加剧肾损伤。然而，由于IL-18缺乏细胞分泌的信号肽，正常情况下细胞并不具备分泌IL-18的能力，其分泌机制并未阐明。预实验结果显示，在AKI动物模型中GsdmD剪切增加，同时Caspase-11表达升高。基于前期观察，我们提出假说，AKI时caspase-11表达升高，通过剪切GsdmD，促使其N-端发生膜转位并形成膜孔，从而促进了肾小管上皮细胞IL-18释放。课题拟利用Caspase-11和GsdmD基因敲除小鼠建立的AKI模型，结合在培养的小管上皮细胞中研究对这一假说加以验证。

近年来急性肾损伤的发病率不断升高，由缺血/再灌和肾毒性药物引起的急性肾损伤的发病率升高尤为显著。肾小管上皮细胞的死亡丢失和强烈的炎性反应是这类急性肾损伤的重要特征。受本课题资助，课题研究结果显示，在缺血/再灌和顺铂诱导的急性肾损伤模型中，肾小管上皮细胞中Caspase-11表达水平显著升高，Caspase-11一方面通过剪切炎性因子前体使其活化，同时剪切GSDMD，促发GSDMD-N向细胞膜转位，GSDMD-N在细胞膜上寡聚化形成膜孔，触发小管上皮细胞发生由非经典通路引发的焦亡，同时促进细胞内活化的炎性因子释放，参与急性肾损伤时炎性反应的形成；敲除Caspase-11或GSDMD均能缓解缺血/再灌或顺铂诱导的急性肾损伤的发生。该研究成果为首次报道焦亡参与急性肾损伤的发生及炎性反应的形成。课题研究成果还显示，由Caspase-11剪切GSDMD引发的细胞焦亡参与糖尿病时足细胞焦亡发生，并参与糖尿病肾病的发生和发展；病理情况下Caspase-11的升高还可通过剪切Pannexin，引发细胞ATP释放，进而激活NLRP3炎性小体，参与急性肾损伤时炎性反应的形成，与经典炎性通路之间形成串话。