Dissecting the contribution of SREBPs and lipid biosynthesis to inflammasome function

 描述(申请人提供)：白介素1家族成员是感染后先天免疫反应中的关键炎性细胞因子。虽然IL-1对于正确防御病原体是必要的，但这种细胞因子的产生必须受到仔细的调控，以防止免疫病理。IL-1家族细胞因子释放的一个关卡是它们需要由被称为炎症体的多蛋白复合体进行翻译后处理，该复合体作为招募和激活蛋白酶caspase-1的平台。通过Toll样受体(TLRs)感应细胞外细菌会触发il1b mRNA的转录，但IL-1？直到炎症体传感器蛋白识别进入细胞内的细菌产物后才会释放。众所周知，I型干扰素(IFN-I)可以抑制炎症体的活性，这部分解释了它们长期以来被公认的免疫抑制能力，尽管其潜在的机制尚不清楚。诱导CH25H酶从胆固醇中产生25-羟基胆固醇(25-HC)，是干扰素-I介导的抑制炎性小体的关键成分。CH25H是巨噬细胞中受干扰素-I刺激的基因，CH25H缺失会导致Capase-1活性增加和IL-1？释放。25-HC是甾醇反应元件结合蛋白(SREBP)胆固醇生物合成途径的有效抑制者，CH25H缺陷的巨噬细胞在TLR刺激后还表现出SREBP途径的活性增加。巨噬细胞中SREBP激活所需的蛋白SCAP的缺失会导致炎症体活性降低。基于这些数据，我的目标是描述SREBP通路如何积极地调节炎性小体。具体地说，我建议确定SREBP蛋白在增强炎症体功能方面的必要性和充分性，并确定它们调节炎症体激活的哪个步骤(目标1)。我还建议检验SREBPs通过产生胆固醇来促进炎症体功能的假设(目标2)。

 DESCRIPTION (provided by applicant): Interleukin-1 family members are key inflammatory cytokines in the innate immune response to infection. While IL-1 is necessary for proper defense against pathogens, the production of this cytokine must be carefully regulated in order to prevent immunopathology. One checkpoint on the release of IL-1 family cytokines is their requirement for post-translational processing by a multi-protein complex known as the inflammasome, which serves as a platform for recruiting and activating the protease caspase-1. Sensing of extracellular bacteria by Toll-like receptors (TLRs) triggers the transcription of il1b mRNA, but IL-1ß is not released until inflammasome sensor proteins recognize bacterial products that have entered the cellular cytosolic compartment. Type I interferons (IFN-I) are known to inhibit inflammasome activity, which partially explains their long-recognized immunosuppressive capacity, although the underlying mechanisms have been unclear. Induction of the enzyme Ch25h, which produces 25-hydroxycholesterol (25-HC) from cholesterol, is a key component of IFN-I- mediated inhibition of inflammasomes. Ch25h is an IFN-I-stimulated gene in macrophages, and deletion of Ch25h results in increased capase-1 activity and release of IL-1ß. 25-HC is a potent suppressor of the Sterol Response Element Binding Protein (SREBP) cholesterol biosynthetic pathway, and Ch25h-deficient macrophages additionally display increased SREBP pathway activity after TLR stimulation. Deletion of SCAP, a protein required for SREBP activation, in macrophages results in decreased inflammasome activity. Based on these data, I aim to characterize how the SREBP pathway positively regulates inflammasomes. Specifically, I propose to determine the necessity and sufficiency of SREBP proteins in augmenting inflammasome function, and to define which step of inflammasome activation they regulate (Aim 1). I also propose to test the hypothesis that SREBPs promote inflammasome function via the production of cholesterol (Aim 2).