Nlrp3 inflammasome signaling in immune responses to Candida albicans

描述(申请人提供)：白色念珠菌是一种成功的真菌共生，高度适应在宿主表面生存，如粘膜组织，在那里它无症状地定植在上皮表面。白念珠菌还可以引起严重的机会性感染，特别是在免疫功能低下的患者中，从黏膜皮肤念珠菌病到血液感染。即使有最佳的医疗护理，侵袭性真菌病仍有相当大的死亡率和发病率。为了开发针对真菌病原体的新的治疗方法，需要对控制病原体如白色念珠菌的先天和获得性免疫途径有详细的了解。在这项建议中，我们将研究核苷酸结合结构域富含亮氨酸重复序列(NLR)包含受体(NLR)家族成员Nlrp3在识别和应对感染白念珠菌中的作用。在巨噬细胞中，Nlrp3在一种称为炎症体的多蛋白复合体中被激活，对各种刺激做出反应。Nlrp3炎症体的激活最终导致半胱氨酸蛋白酶caspase-1的激活及其对促炎细胞因子的处理和分泌。白念珠菌以Nlrp3依赖的方式激活caspase-1，导致IL-12的释放。NLRP3基因缺陷的小鼠在体内也表现出对白色念珠菌感染的易感性增加。这项提案概述了三个新的目标，将检查参与白念珠菌激活Nlrp3的分子机制。在目标1中，将通过确定Nlrp3炎症体激活是否需要通过Syk/CARD9介导的信号来解决响应白色念珠菌的Nlrp3炎症体激活所需的初始启动步骤。在目标2中，我们将利用基因靶向的小鼠来确定活性氧和组织蛋白酶B是否在白色念珠菌诱导的Nlrp3炎症体的激活中起作用。我们还将鉴定在酵母-菌丝转换过程中表达的念珠菌特异性因子，这些因子可以直接被Nlrp3炎症体感受到。在目标3中，我们将研究Nlrp3炎症体如何在体内感染白念珠菌后形成后续的获得性免疫反应，特别是是否产生IL-17的Th17细胞的发展依赖于Nlrp3的存在。拟议研究的成功完成将提供对白色念珠菌如何激活Nlrp3炎症体的分子理解，并将大大增加我们对免疫系统如何控制真菌病原体的知识。此外，这些研究对白色念珠菌发病机制的新见解可能会为抗击这种病原体提供新的治疗方法。 公共卫生相关性：白色念珠菌是一种真菌病原体，可导致多种机会性感染，特别是在住院患者群体中，它导致了严重的发病率和死亡率。了解这种病原体如何与免疫系统相互作用并逃避免疫系统，将有助于我们找到治疗真菌感染的新靶点，因此与公众健康直接相关。我们的研究将集中在胞浆模式识别受体Nlrp3是如何被白色念珠菌激活的，以及这如何塑造宿主随后的免疫反应。此外，从拟议的研究中获得的信息也将有助于阐明其他真菌生物的致病机理。

DESCRIPTION (provided by applicant): C. albicans is a successful fungal commensal, highly adapted to survive on host surfaces such as mucosal tissue where it asymptomatically colonizes epithelial surfaces. C. albicans can also cause severe opportunistic infections particularly in immunocompromised patients ranging from mucocutaneous candidiasis to bloodstream infections. Even with optimal medical care there is still substantial mortality and morbidity associated with invasive fungal disease. In order to develop new therapeutic modalities directed at fungal pathogens a detailed understanding of the innate and adaptive immune pathways involved in control of pathogens such as C. albicans are required. In this proposal we will examine the role of the nucleotide-binding domain leucine-rich repeat containing receptor (NLR) family member Nlrp3 in recognition and response to infection with C. albicans. In macrophages Nlrp3 is activated in a multiprotein complex called the inflammasome in response to a wide variety of stimuli. The activation of the Nlrp3 inflammasome ultimately results in the activation of the cysteine protease caspase-1 and its processing and secretion of proinflammatory cytokines. C. albicans activates caspase-1 in an Nlrp3-dependent manner leading to the release of interleukin (IL)-12. Nlrp3-deficient mice also demonstrate increased susceptibility to infection with C. albicans in vivo. This proposal outlines three novel aims that will examine the molecular mechanism involved in activation of Nlrp3 by C. albicans. In Aim 1 the initial priming step required for Nlrp3 inflammasome activation in response to C. albicans will be addressed by determining if signaling mediated through Syk/Card9 is required for Nlrp3 inflammasome activation. In Aim 2 we will utilize gene targeted mice to determine if reactive oxygen species and cathepsin B play a role in C. albicans-induced activation of the Nlrp3 inflammasome. We will also identify Candida specific factors expressed during yeast-hyphae transition that are directly sensed by the Nlrp3 inflammasome. In Aim 3 we will examine how the Nlrp3 inflammasome shapes subsequent adaptive immune responses following in vivo infection with C. albicans and in particular if the development of IL-17 producing Th17 cells is dependent on the presence of Nlrp3. Successful completion of the proposed studies will provide a molecular understanding of how C. albicans activates the Nlrp3 inflammasome, and will substantially augment our knowledge of how the immune system controls fungal pathogens. Furthermore, new insights into the pathogenesis of C. albicans that result from these studies may suggest novel therapeutic approaches to combating this pathogen. PUBLIC HEALTH RELEVANCE: Candida albicans is a fungal pathogen that causes a wide variety of opportunistic infections, particularly in hospitalized patient populations where it is responsible for significant morbidity and mortality. Understanding how this pathogen interacts with and evades the immune system will help us identify new therapeutic targets to treat fungal infections and is hence directly relevant to public health. Our studies will focus on how the cytosolic pattern recognition receptor Nlrp3 is activated by Candida albicans and how this shapes subsequent immune responses by the host. In addition the information gained from the proposed studies will also shed light on the pathogenesis of other fungal organisms.