Cholesterol regulation of Macrophage Inflammation and Vascular Diseases

 描述（由申请人提供）： 与肥胖相关的低度慢性炎症是包括2型糖尿病（T2 DM）和动脉粥样硬化在内的代谢疾病发展的根本原因。慢性炎症最重要的特征是其持续性和无法解决 导致体内平衡的恢复不足和代谢疾病的发展。与由损伤或感染引发的经典炎症相反，这种低度慢性炎症本质上是“无菌的”，没有病原体的直接参与，并且通常是无菌的。 由营养物和代谢过剩引发，因此也称为代谢性炎症，意味着代谢性引发的炎症。转移性炎症的特征在于异常的细胞因子产生，特别是白细胞介素-1 β（IL-1 β）和细胞因子网络的持续激活。 炎症通路。先天性免疫哨兵或巨噬细胞的慢性激活是这种异常细胞因子产生的基础，然而所涉及的细胞机制尚未完全确定。 来自巨噬细胞的IL-1 β的产生和分泌处于非常严格的调节下，这需要两种信号的协调，即信号1：诱导转录所需的细胞引发（通过NF-κ B B），和信号2：NLRP 3炎性体的激活，用于通过活性胱天蛋白酶-1蛋白水解切割pro-IL-1 β并分泌成熟IL-1 β。细胞脂质积累增加是肥胖的显著特征之一，细胞内脂质代谢，特别是胆固醇代谢，与巨噬细胞的炎症状态密切相关。例如，由于缺乏ABCA 1转运蛋白而不能有效地排出过量的胆固醇，增加了巨噬细胞的细胞因子产生并增加了炎症。同样，我们已经证明，通过巨噬细胞特异性转基因过表达胆固醇酯（CE）水解酶（CEH，一种水解细胞内储存的CE并限制胆固醇流出速率的酶）来降低巨噬细胞胆固醇含量导致血浆IL-1 β水平显著降低（>20倍）。然而，细胞胆固醇稳态和炎症通路之间的“串扰”的机制尚未建立。激活炎症途径所需的两种信号都依赖于细胞表面蛋白：通过细胞表面受体（例如，与膜脂筏或富含胆固醇的膜微结构域相关的NLR 4）是信号1和信号2所需的，或NLR 3激活由细胞表面相关离子通道调节的K+流出触发。由于这些细胞表面受体和通道的存在/功能取决于细胞/膜胆固醇或脂筏水平，我们假设CEH介导的细胞胆固醇含量的降低减弱了1）通过调节TLR 4信号传导的巨噬细胞的“引发”和2）通过细胞K+流出的变化的炎性体的“激活”，从而有益地调节巨噬细胞功能。我们提出以下目的来验证这一假设：目的1：阐明CEH介导的细胞胆固醇含量变化可以调节巨噬细胞“启动”或信号1的机制。目的2：阐明CEH通过细胞胆固醇消耗介导的“炎性体激活”或信号2的调节的潜在机制。目的3：评价CEH介导的信号1和信号2依赖的巨噬细胞活化的减弱在体内调节炎症中的作用。这些研究将确定巨噬细胞胆固醇含量的靶向降低将同时减轻多种代谢疾病，包括2型糖尿病和冠状动脉疾病（CAD）。此外，所使用的综合方法将定义疏水性胆固醇与炎症机制“通信”的途径，并确定未来可以作为潜在治疗靶点探索的分子机制（例如，调节K+流出）以调节其它基于无菌炎症的疾病。

 DESCRIPTION (provided by applicant): Low grade chronic inflammation associated with obesity is the underlying cause of the development of metabolic diseases including Type 2 diabetes (T2DM) and atherosclerosis. The most important characteristics of chronic inflammation are its persistence and inability to resolve resulting in lack of restoration of homeostasis and development of metabolic diseases. In contrast to classical inflammation which is triggered by an injury or infection, this low grade chronic inflammation is "sterile" in nature without a direct involvement of a pathogen and is often triggered by nutrients and metabolic surplus and hence also referred to as metaflammation meaning metabolically triggered inflammation. Metaflammation is characterized by abnormal cytokine production especially Interleukin-1 (IL-1) and persistent activation of a network of inflammatory pathways. Chronic activation of innate immune sentinels or macrophages underlies this abnormal cytokine production however the cellular mechanisms involved are not completely defined. The production and secretion of IL-1 from macrophages is under very tight regulation which requires coordination of two Signals, namely Signal 1: cellular priming required for inducing transcription (via NF-B), and Signal 2: activation of NLRP3 inflammasome for proteolytic cleavage of pro-IL-1 by active Caspase-1 and secretion of mature IL-1. Increase in cellular lipid accumulation is one of the prominent features of obesity and intracellular lipid metabolism, especially cholesterol metabolism, is tightly linked to the inflammatory status of macrophages. For example, inability to efficiently efflux excess cholesterol due to deficiency of ABCA1 transporter increases cytokine production from macrophages and increase inflammation. Consistently, we have demonstrated that reduction in macrophage cholesterol content by macrophage-specific transgenic over-expression of cholesterylester (CE) hydrolase (CEH, an enzyme that hydrolyzes intracellular stored CE and rate-limits cholesterol efflux) leads to a dramatic (>20 fold) reduction in plasma IL-1 levels. However, the mechanisms underlying the "crosstalk" between cellular cholesterol homeostasis and inflammatory pathways have not been established as yet. Both signals required for activation of inflammatory pathways depend on cell surface proteins: signaling via cell surface receptors (e.g., TLR4) associated with membrane lipid rafts or cholesterol- enriched membrane micro-domains is required for Signal 1 and Signal 2 or NLRP3 activation is triggered by K+ efflux regulated by cell surface-associated ion channels. Since the presence/function of these cell surface receptors and channels depends on the cellular/membrane cholesterol or lipid-raft levels, We hypothesize that CEH-mediated reduction in cellular cholesterol content attenuates 1) the "priming" of macrophages by modulating TLR4 signaling and 2) the "activation" of the inflammasome via changes in cellular K+ efflux and thereby beneficially modulates macrophage function. We propose the following Aims to test the hypothesis: Aim 1: To delineate the mechanisms by which CEH-mediated changes in cellular cholesterol content can modulate macrophage "priming" or Signal 1. Aim 2: To delineate the mechanisms underlying CEH-mediated modulation of "inflammasome activation" or Signal 2 via cellular cholesterol depletion. Aim 3: To evaluate the role of CEH-mediated attenuation of Signal 1 and Signal 2-dependent macrophage activation in modulating inflammation in vivo. These studies will establish that targeted reduction in macrophage cholesterol content would simultaneously attenuate multiple metabolic diseases including Type 2 Diabetes and Coronary Artery Disease (CAD). In addition, the comprehensive approach used will define the pathways by which hydrophobic cholesterol "communicates" with the inflammatory machinery and identify molecular mechanisms that can be explored as potential therapeutic targets in future (e.g., regulating K+ efflux) to modulate other sterile inflammation based diseases.