The effects and mechanisms of TBK1 on NLRC4 inflammasome
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摘要:
目的：探究TANK结合激酶1（TANK-binding kinase 1，TBK1）调控核苷结合寡聚化结构域样受体4（nucleotide-binding oligomerization domain-like receptor 4，NLRC4）炎症小体激活的作用及其机制。方法：在鼠伤寒沙门氏菌（Salmonella typhimurium， S.T）感染的永生化骨髓巨噬细胞（immortalized bone marrow derived macrophage，IBMDM）中，Western blot检测NLRC4炎症小体激活及其下游分子半胱天冬蛋白酶1（cysteine aspartic acid specific protease 1，Caspase-1）和Gasdermin D（GSDMD）的剪切情况； 乳酸脱氢酶检测试剂盒检测细胞培养基上清中乳酸脱氢酶的含量；蛋白质免疫共沉淀实验确定 TBK1 与 NLRC4的相互作用及其具体结构域；细胞免疫荧光实验确定TBK1与NLRC4的空间定位；GST pull-down实验确定TBK1与NLRC4是否存在直接相互作用；凋亡相关斑点样蛋白（apoptosis-associated speck-like protein containing a CARD，ASC）寡聚化检测实验验证NLRC4 炎症小体组装。构建S.T感染C57BL/6小鼠动物模型，观察小鼠生存情况。涂板计数腹腔灌洗液和肺的细菌负荷量；酶联免疫吸附试验（ELISA）检测腹腔灌洗液及血清中的肿瘤坏死因子（tumor necrosis factor，TNF）-α和白细胞介素（interleukin，IL）-1β的含量；流式细胞术检测腹腔灌洗液中的中性粒细胞比例。结果：在S.T感染的IBMDM中，抑制TBK1可减弱NLRC4炎症小体激活，NLRC4磷酸化水平下降，Caspase-1与GSDMD的剪切减少；TBK1与NLRC4存在相互作用，TBK1的N端与NLRC4的NACHT 结构域相互作用；TBK1与NLRC4存在空间上的共定位；TBK1可以磷酸化NLRC4的Ser533位点。S.T动物模型实验显示，抑制 TBK1活性可以显著提高小鼠的生存率；减低小鼠腹腔灌洗液和肺中的细菌负荷量；降低血清以及腹腔灌洗液中的IL-1β、TNF-α 的表达水平；减少腹腔灌洗液中的中性粒细胞比例。结论：TBK1与NLRC4相互作用，磷酸化NLRC4 Ser533位点，促进NLRC4 炎症小体的激活，为治疗相关疾病提供理论依据和新的潜在靶点。
Abstract:
Objective：To investigate the mechanism by which TANK binding kinase 1（TBK1）regulates the activation of nucleotide-binding oligomerization domain -like receptor 4（NLRC4）inflammasome. Methods：Western blot was used to detect the activation of NLRC4 inflammasome and their downstream molecules cysteine aspartic acid-specific protease 1（Caspase-1）and Gasdermin D （GSDMD）in immortalized bone marrow-derived macrophages（IBMDM）infected with Salmonella typhimurium（S.T）. A lactate dehydrogenase detection kit was used to detect the content of lactate dehydrogenase in the supernatant of cell culture medium. The interaction between TBK1 and NLRC4 and their specific interaction domain was determined through protein co -immunoprecipitation experiments. Cellular immunofluorescence assay was used to determine the spatial localization of TBK1 and NLRC4. The GST pull-down experiment confirmed the direct interaction between TBK1 and NLRC4. The assembly of NLRC4 inflammasome was verified using apoptosis-associated speck-like protein containing a CARD（ASC）oligomerization detection experiments. The S.T infected animal model of C57BL/6 mice was built and the survival of mice was observed. The bacterial load of lung tissues and peritoneal cavity-flushed fluid was analyzed through smear analysis. ELISA was used to detect the content of tunor necrosis factor（TNF）- α and interleukin（IL）-1β in peritoneal cavity -flushed fluid and serum. Flow cytometry was used to detect the proportion of neutrophils in peritoneal cavity-flushed fluid. Results：In S.T infected IBMDM，inhibiting TBK1 led to a weakened activation of NLRC4 inflammasomes，decreased phosphorylation levels of NLRC4，and reduced cleavage of Caspase-1 and GSDMD. There was an interaction between TBK1 and NLRC4，and the N-terminal of TBK1 interaced with the NACHT domain of NLRC4. TBK1 and NLRC4 had spatial co-localization. TBK1 phosphorylated the NLRC4 Ser533 site. S.T animal model experiments showed that inhibiting TBK1 activity significantly improved the survival rate of mice，weakened the bacterial load in the peritoneal cavity -flushed fluid and lung tissues of mice，reduced the content of IL-1β and TNF-α in serum and peritoneal cavity-flushed fluid，and reduced the proportion of neutrophils in peritoneal cavity -flushed fluid. Conclusion：TBK1 interacts with NLRC4，phosphorylates the NLRC4 Ser533 site，and promotes the activation of NLRC4 inflammasome，which providing a theoretical basis and new potential targets for treating related diseases.
