Role of Caspase-8 in Yersinia virulence and host defense

描述(由申请人提供)：针对细菌感染的宿主免疫防御需要激活保守的信号通路，该通路上调炎性介质的产生以清除感染。许多细菌病原体抑制这些信号通路，以逃避宿主的免疫防御。这些病原体包括致病性耶尔森氏菌，它利用YopJ毒力因子来阻断NF-κB和MAPK信号转导。免疫防御是如何介导的，以对抗阻断免疫信号通路的病原体，目前仍知之甚少。阻断感染的巨噬细胞中的核因子-κB可导致细胞死亡，表现为细胞凋亡、下垂和坏死。令人惊讶的是，假结核或鼠疫耶尔森菌的细胞毒性增加导致细菌的毒力显著降低，这表明诱导细胞死亡可能是对耶尔森氏菌感染的一种宿主防御机制。我们的中心假设是，耶尔森氏菌阻断NF-κB和MAPK而触发的细胞死亡会导致促炎细胞死亡，从而提醒未受感染的邻近细胞感染的存在。然而，YopJ诱导细胞死亡的机制以及细胞死亡在免疫防御感染中的确切作用尚不清楚。在耶尔森氏菌感染过程中，多种半胱氨酸天冬氨酸酶被激活，但目前尚不清楚耶尔森氏菌诱导细胞死亡所需的特定因子(S)。我们的初步数据表明，caspsase-8在耶尔森氏菌诱导的细胞死亡和体内对耶尔森氏菌感染的宿主防御中是必需的。此外，caspase-8是caspase-1对耶尔森氏菌的反应所必需的，但不是对其他caspase-1激活刺激的反应。依赖于caspase-8的caspase-1激活是一种新的途径，能够使凋亡的caspase激活焦磷酸细胞死亡。然而，caspase-8依赖的caspase-1激活的分子机制仍不清楚。这是一个重要的问题，因为它可能在许多阻止关键的先天性免疫信号通路的病原体的反应中发挥作用，并且在导致caspase-8激活的病理刺激的背景下，我们提出了两个具体的目标来解决我们知识中的这一重要差距。首先，我们将定义依赖caspase-8激活caspase-1的分子基础，并剖析不同的细胞死亡途径在耶尔森氏菌诱导的细胞死亡中的相对贡献。其次，我们将确定caspase-8在耶尔森氏菌感染免疫防御中的作用。

DESCRIPTION (provided by applicant): Host immune defense against bacterial infection requires activation of conserved signaling pathways that upregulate production of inflammatory mediators to clear infection. Many bacterial pathogens inhibit these signaling pathways in order to evade host immune defenses. Such pathogens include the pathogenic Yersiniae which utilize the YopJ virulence factor to block NF-κB and MAPK signaling. How immune defense is mediated against pathogens that block immune signaling pathways remains poorly understood. NF-κB blockade in infected macrophages leads to cell death with characteristics of apoptosis, pyroptosis, and necrosis. Surprisingly, increasing cytotoxicity of Y. pseudotuberculosis or Y. pestis results in dramatically decreased virulence of the bacteria, suggesting that induction of cell death in response to Yersinia infection may be a host defense mechanism. Our central hypothesis is that cell death triggered in response to Yersinia blockade of NF-κB and MAPK leads to pro-inflammatory cell death that alerts uninfected neighboring cells to the presence of infection. However, the mechanisms of YopJ-induced cell death and the precise role of cell death in immune defense against infection remain unclear. Multiple caspases are activated during Yersinia infection, but no specific factor(s) are yet known that are required for Yersinia-induced cell death. Our preliminary data demonstrate that caspsase-8 is required for Yersinia-induced cell death, and for host defense in response to Yersinia infection in vivo. Furthermore, caspase-8 is required for caspase-1 processing in response to Yersinia, but not in response to other caspase-1 activating stimuli. Caspase-8-dependent caspase-1 activation is a novel pathway that enables an apoptotic caspase to activate a pyroptotic cell death. However, the molecular mechanism of caspase-8-dependent caspase-1 activation remains unknown. This is an important problem as it likely functions in response to many pathogens that block critical innate immune signaling pathways and in the context of pathological stimuli that lead to caspase-8 activation We propose two Specific Aims to address this important gap in our knowledge. First we will define the molecular basis of caspase-8-dependent activation of caspase-1, and dissect the relative contribution of distinct cell death pathways to Yersinia-induced cell death. Second, we will define the role of caspase-8 in immune defense against Yersinia infection.