Mechanisms of NIrp3 inflammasome activation by mitochondrial dysfunction

描述(由申请人提供)：Nlrp3炎症小体与保护性和病理免疫反应都有关。它的适当激活触发了对流感病毒、金黄色葡萄球菌和白色念珠菌等入侵病原体的先天免疫反应，其过度反应是自体炎症综合征CAPS(低温比林相关周期性综合征)的基础。Nlrp3炎症体也由异常代谢条件触发，导致常见的衰弱疾病的发展，如痛风、II型糖尿病和动脉粥样硬化。我们已经在激活Nlrp3炎症体的途径中发现了一个新的步骤，揭示了以前未知的与外部凋亡途径的激活重叠。我们实验室的初步研究表明，与这些凋亡途径类似，Nlrp3炎症小体激活导致线粒体功能障碍，表现为线粒体内正常负电位的丧失。在细胞凋亡过程中，线粒体膜电位的这种丧失与线粒体脂类心磷脂从线粒体内膜到外膜的移位有关。这种运动伴随着心磷脂的氧化和它的结合伙伴细胞色素c的释放到膜间隙。线粒体膜外膜上的心磷脂招募并结合caspase-8，caspase-8进而驱动线粒体膜外孔的产生，通过这个孔，细胞色素c从系绳松散到心磷脂，穿过细胞质，通过以下方式触发免疫沉默的细胞死亡 细胞凋亡。我们现在表明，Nlrp3对线粒体心磷脂的这种结合需求和能力是相同的，以前的研究表明，Nlrp3在激活过程中迁移到线粒体。此外，线粒体膜电位的丧失也是Nlrp3炎症体激活所必需的，线粒体膜电位是细胞凋亡的决定性步骤。在这个方案中，我们特别剖析了心磷脂在Nlrp3激活中的作用，并确定了Nlrp3炎症小体激活在多大程度上反映了细胞凋亡。这些研究将确定这两条途径的分歧点，这不仅对促进我们对这一至关重要的炎症途径的理解很重要，而且因为一旦确定了这两条途径之间的转换，可能会被证明是治疗干预的目标。操纵这些途径不仅是为了改变Nlrp3的反应，而且也是因为有可能从凋亡途径切换到炎症途径，这可能有助于恶性肿瘤或隐蔽感染的发生。

DESCRIPTION (provided by applicant): The Nlrp3 inflammasome has been linked to both protective and pathologic immune responses. Its appropriate activation triggers the innate immune response to invading pathogens including influenza virus, Staphylococcus aureus and Candida albicans and its excessive response underlies the autoinflammatory syndromes CAPS (cryopyrin associated periodic syndromes). The Nlrp3 inflammasome is also triggered by abnormal metabolic conditions that lead to the development of common debilitating disorders such as gout, type II diabetes mellitus and atherosclerosis. We have identified a novel step in the pathway by which the Nlrp3 inflammasome is activated that reveals a previously unrecognized overlap with the activation of extrinsic apoptotic pathways. Preliminary studies in our lab show that similar to these apoptotic pathways Nlrp3 inflammasome activation induces mitochondrial dysfunction as demonstrated by a loss of the normal negative potential within the mitochondria. During apoptosis this loss of mitochondrial membrane potential is associated with the translocation of the mitochondrial lipid cardiolipin from its location on the inner mitochondril membrane to the outer membrane. This movement is accompanied by oxidation of cardiolipin and the release of its binding partner, cytochrome c, to the intermembrane space. Cardiolipin on the outer mitochondrial membrane recruits and binds caspase-8 that in turn drives the generation of an outer mitochondrial membrane pore through which cytochrome c, loose from its tether to cardiolipin, crosses to the cytosol and triggers immunologically silent cell death by apoptosis. We now show this requirement for and ability to bind mitochondrial cardiolipin is shared by Nlrp3, previously shown to migrate to the mitochondria during activation. Additionally, the loss of mitochondrial membrane potential, a defining step in apoptosis, is also required for Nlrp3 inflammasome activation. In this proposal we specifically dissect the role of cardiolipin in Nlrp3 activation and determine to what extent Nlrp3 inflammasome activation mirrors apoptosis. These studies will determine the point of divergence of these two pathways, important not only to advance our understanding of this vital inflammatory pathway but also because once identified this switch between pathways may prove to be a target for therapeutic intervention. Manipulation of these pathways is attractive not only for modifying Nlrp3 responses but also for the potential to switch from the apoptotic pathway to an inflammatory one as could be of benefit in the setting of malignancy or covert infections.