Department of Internal Medicine and Paediatrics, Ghent University, Ghent, Belgium.
VIB-UGent Center for Inflammation Research, VIB, Ghent, Belgium.
Cell Death Dis. 2023 Apr 21;14(4):282. doi: 10.1038/s41419-023-05801-4.
Citrobacter rodentium is an enteropathogen that causes intestinal inflammatory responses in mice reminiscent of the pathology provoked by enteropathogenic and enterohemorrhagic Escherichia coli infections in humans. C. rodentium expresses various virulence factors that target specific signaling proteins involved in executing apoptotic, necroptotic and pyroptotic cell death, suggesting that each of these distinct cell death modes performs essential host defense functions that the pathogen aims to disturb. However, the relative contributions of apoptosis, necroptosis and pyroptosis in protecting the host against C. rodentium have not been elucidated. Here we used mice with single or combined deficiencies in essential signaling proteins controlling apoptotic, necroptotic or pyroptotic cell death to reveal the roles of these cell death modes in host defense against C. rodentium. Gastrointestinal C. rodentium infections in mice lacking GSDMD and/or MLKL showed that both pyroptosis and necroptosis were dispensable for pathogen clearance. In contrast, while RIPK3-deficient mice showed normal C. rodentium clearance, mice with combined caspase-8 and RIPK3 deficiencies failed to clear intestinal pathogen loads. Although this demonstrated a crucial role for caspase-8 signaling in establishing intestinal host defense, Casp8Ripk3 mice remained capable of preventing systemic pathogen persistence. This systemic host defense relied on inflammasome signaling, as Casp8Ripk3 mice with combined caspase-1 and -11 deletion succumbed to C. rodentium infection. Interestingly, although it is known that C. rodentium can activate the non-canonical caspase-11 inflammasome, selectively disabling canonical inflammasome signaling by single caspase-1 deletion sufficed to render Casp8Ripk3 mice vulnerable to C. rodentium-induced lethality. Moreover, Casp8Ripk3 mice lacking GSDMD survived a C. rodentium infection, suggesting that pyroptosis was not crucial for the protective functions of canonical inflammasomes in these mice. Taken together, our mouse genetic experiments revealed an essential cooperation between caspase-8 signaling and GSDMD-independent canonical inflammasome signaling to establish intestinal and systemic host defense against gastrointestinal C. rodentium infection.
柠檬酸杆菌是一种肠道病原体，它会引起小鼠的肠道炎症反应，使人联想到人类中肠致病性和肠出血性大肠杆菌感染引起的病理学变化。柠檬酸杆菌表达多种毒力因子，针对参与执行细胞凋亡、坏死性凋亡和细胞焦亡的特定信号蛋白，这表明这些不同的细胞死亡模式中的每一种都发挥着宿主防御功能，而病原体旨在干扰这些功能。然而，凋亡、坏死性凋亡和细胞焦亡在保护宿主免受柠檬酸杆菌感染方面的相对贡献尚未阐明。在这里，我们使用了缺乏控制细胞凋亡、坏死性凋亡或细胞焦亡的必需信号蛋白的单一或组合缺失的小鼠，以揭示这些细胞死亡模式在宿主防御柠檬酸杆菌感染中的作用。缺乏 GSDMD 和/或 MLKL 的小鼠的胃肠道柠檬酸杆菌感染表明，细胞焦亡和坏死性凋亡对于清除病原体都是可有可无的。相比之下，虽然 RIPK3 缺陷型小鼠的柠檬酸杆菌清除能力正常，但同时缺乏 caspase-8 和 RIPK3 的小鼠则无法清除肠道病原体负荷。尽管这表明 caspase-8 信号在建立肠道宿主防御方面起着至关重要的作用，但 Casp8Ripk3 小鼠仍能够防止病原体在全身的持续存在。这种全身宿主防御依赖于炎症小体信号，因为同时缺乏 caspase-1 和 -11 的 Casp8Ripk3 小鼠会死于柠檬酸杆菌感染。有趣的是，尽管已知柠檬酸杆菌可以激活非经典的 caspase-11 炎症小体，但通过单一 caspase-1 缺失选择性地使经典炎症小体信号失活足以使 Casp8Ripk3 小鼠易受柠檬酸杆菌诱导的致死性影响。此外，缺乏 GSDMD 的 Casp8Ripk3 小鼠在柠檬酸杆菌感染后存活下来，这表明在这些小鼠中，细胞焦亡对于经典炎症小体的保护功能并不是至关重要的。总之，我们的小鼠遗传实验揭示了 caspase-8 信号与非依赖 GSDMD 的经典炎症小体信号之间的重要合作，以建立针对胃肠道柠檬酸杆菌感染的肠道和全身宿主防御。
