Repression of inflammasome by Francisella tularensis

描述（由申请方提供）：土拉热弗朗西丝菌（Ft）是一种革兰氏阴性细胞内病原体，可引起一种称为土拉菌血症的致命性疾病。基于其高毒性，过去在生物武器计划中的使用，以及在生物恐怖袭击中使用的潜力，疾病控制中心（CDC）将Ft列为A类选择剂。Ft的极端毒力是由于其能够破坏宿主的先天免疫应答。为了支持这一观点，我们的初步研究表明，强毒株Ft SchuS 4和活疫苗株（LVS），一个F。Holarctica对先天性免疫信号传导级联发挥抑制作用，导致非常低水平的促炎细胞因子，其与感染细胞的程序性死亡的显著延迟相关。然而，介导这些效应的机制和弗朗西斯菌因子尚不清楚。两种主要的先天免疫传感器，Toll样受体（TLR）和胞质Nod样受体（NLR）被激活，以响应特定的微生物组分。这些传感器的激活导致促炎细胞因子的诱导、先天免疫细胞向感染部位的募集、适应性免疫应答的产生和感染的消退。胞质NLR对病原体的识别激活了称为炎性体的多分子复合物的组装。炎性小体复合物激活半胱氨酸蛋白酶半胱氨酸蛋白酶1，半胱氨酸蛋白酶半胱氨酸炎性小体组装和半胱天冬酶-1活化也诱导快速形式的促炎性细胞死亡，称为焦亡。初步研究表明，F.土拉菌病能够抑制TLR和NLR介导的反应以及细胞火灾死亡。该建议旨在研究Ft强毒株抑制NLR依赖性反应的机制。我们的假设是，“炎性小体的主动抑制是Ft细胞内存活所必需的”。我们提出，通过抑制或延迟这种保护性宿主的先天免疫反应，Ft能够在细胞质中创建复制小生境，导致宿主巨噬细胞内不受控制的增殖。 该假设将通过特异性目的1进行测试，特异性目的1将建立Ft LVS和SchuS 4抑制炎性小体的关键位点，而在特异性目的2中，我们将鉴定Ft介导的炎性小体抑制的机制。Ft作为一个独特的模型来理解炎性小体介导的反应的复杂机制。这些研究的结果将确定Ft抑制炎性小体的机制，这是一种关键的宿主先天免疫防御机制。这些研究将推进我们对兔热病发病机制的认识，并将使我们更接近于实现确定有效治疗和药物开发靶点的最终目标。这一提议在理解兔热病的免疫发病机制方面向前迈出了一步。

DESCRIPTION (provided by applicant): Francisella tularensis (Ft) is a gram-negative intracellular pathogen that causes a fatal disease known as tularemia. Based on its high virulence, use in bioweapon programs in the past, and potential to be used in bioterror attacks, the Centers for Disease Control (CDC) have classified Ft as a Category A select agent. The extreme virulence of Ft is due to its ability to subvert host's innate immune response. In support of this notion, our preliminary studies demonstrate that the virulent strain Ft SchuS4 and Live Vaccine Strain (LVS), a derivative of F. holarctica exert suppressive effects on innate immune signaling cascades resulting in very low levels of pro-inflammatory cytokines associated with significant delay in the programmed death of the infected cells. However, the mechanisms and the Francisella factors mediating these effects are ill defined. Two major classes of innate immune sensors, Toll-like receptors (TLRs) and cytosolic Nod-like receptors (NLRs) are activated in response to specific microbial components. Activation of these sensors leads to induction of pro- inflammatory cytokines, recruitment of innate immune cells to the sites of infection, generation of an adaptive immune response and resolution of infection. Recognition of pathogens by cytosolic NLRs activates assembly of a multi-molecular complex termed as inflammasome. The inflammasome complex activates cysteine protease caspase1 which in-turn activates pro-forms of pro-inflammatory cytokines IL-1¿ and IL-18 to their mature active forms. Inflammasome assembly and caspase-1 activation also induces a rapid form of pro- inflammatory cell death, termed pyroptosis. Our preliminary studies demonstrate that F. tularensis is capable of suppressing both TLR and NLR-mediated responses and pyroptotic cell death. This proposal is aimed at investigating the mechanism by which virulent strains of Ft suppress NLR-dependent responses. Our hypothesis is that "active repression of the inflammasome is essentially required for intracellular survival of Ft". We propose that by repressing or delaying this protective host's innate immune response, Ft is able to create a replicative niche in the cytosol leading to uncontrolled proliferation within the host macrophages. This hypothesis will be tested via Specific aim 1 which will establish the key sites of repression of inflammasome by Ft LVS and SchuS4 while in Specific aim 2, we will identify the mechanisms of Ft mediated repression of inflammasome. Ft serves as a unique model to understand the intricate mechanisms of inflammasome mediated responses. The outcome from these studies will identify mechanism(s) employed by Ft to repress the inflammasome, a critical host innate immune defense mechanism. These studies will advance our knowledge of tularemia pathogenesis and will bring us closer to achieving the ultimate goal of identifying the targets for development of effective therapeutics and prophylactics. This proposal is a step ahead in understanding the immunopathogenesis of tularemia.