Cellular mechanisms of NLRP3 activation by ALCAT1 in diet-induced obesity

肥胖导致慢性“无菌”炎症，这与胰岛素抵抗有关， 其他代谢并发症。NLRP 3（NLR家族pyrin domain containing 3）是一种细胞内蛋白质， 传感器，用于检测微生物感染和代谢应激的各种“危险”信号。激活 NLRP 3炎性小体通过促进caspase 1依赖性介导宿主防御反应 IL-1β和其他促炎细胞因子的释放。有趣的是，NLRP 3的激活 炎性小体也与饮食诱导的“无菌”炎症和胰岛素抵抗有关。 肥胖症（DIO），但导致肥胖症中NLRP 3激活的“危险”信号仍然难以捉摸。 朊病毒是一种错误折叠的蛋白质，能够将其错误折叠的形状自我传递到 相同蛋白质的正常变体。该领域的最新进展已确定了240多个 非传染性朊病毒样蛋白。尽管这些蛋白质中的一些与 在神经退行性疾病的发病机制中，令人惊讶的是， 大多数朊病毒样蛋白可能与人类健康和疾病有关。这里我们 我建议研究一种新的途径，通过这种途径，一种假定的朊病毒样蛋白调节NLRP 3 在DIO中激活。该途径由ALCAT 1酶介导，ALCAT 1酶是第一个酰基辅酶A依赖性的酶。 溶血心磷脂酰基转移酶。我们在该领域的开创性工作 表明ALCAT 1通过催化与年龄相关的代谢疾病的发展， 心磷脂（CL）与极长链多不饱和脂肪酸，如 二十二碳六烯酸（DHA）。DHA的富集使CL对氧化敏感 活性氧（ROS）损伤（CL-Ox），导致CL耗竭和线粒体 代谢性疾病中的功能障碍。值得注意的是，我们的初步研究还发现了一个关键的 ALCAT 1在将DIO与NLRP 3激活（作为推定的朊病毒样蛋白）联系起来中的作用，包括1） ALCAT 1在氧化应激反应中形成朊病毒样蛋白聚集体， 通过N-末端的朊病毒样结构域; 2）脂肪组织中ALCAT 1的表达显著增加， DIO上调;和3）脂肪细胞中ALCAT 1的靶向缺失显著减弱 通过防止巨噬细胞浸润在白色脂肪组织中激活NLRP 3。所有这些 令人兴奋的发现让我们假设ALCAT 1促进DIO中NLRP 3的激活， 一种假定的朊病毒样蛋白，将通过三个特定目的进行测试：AIM 1将确定 ALCAT 1是否通过线粒体功能障碍促进NLRP 3活化; AIM 2是否通过线粒体功能障碍促进NLRP 3活化; 确定ALCAT 1促进NLRP 3作为朊病毒样激活的分子机制 AIM 3将评估ALCAT 1是否与脂肪组织中的细胞衰老相关， DIO小鼠的慢性炎症。成功完成拟议的研究不仅将 验证ALCAT 1作为慢性炎症的新型药物靶点，但也提供了概念证明 研究靶向酶用于治疗肥胖及其相关并发症。

Obesity causes chronic “sterile” inflammation, which is implicated in insulin resistance and other metabolic complications. NLRP3 (NLR family pyrin domain containing 3) is an intracellular sensor for various “danger” signals from microbial infection and metabolic stress. Activation of NLRP3 inflammasomes elicits host defense responses by promoting caspase 1-dependent release of IL-1β and other pro-inflammatory cytokines. Intriguingly, activation of NLRP3 inflammasomes is also implicated in “sterile” inflammation and insulin resistance in diet-induced obesity (DIO), yet the “danger” signals that lead to NLRP3 activation in obesity remains elusive. Prions are misfolded proteins that are capable of self-transmitting their misfolded shape onto normal variants of the same protein. Recent progress in the field has identified more than 240 non-infectious prion-like proteins in mammals. Although a few of these proteins are well implicated in the pathogenesis of neurodegenerative diseases, surprisingly little information is known about majority of the prion-like proteins’ potential involvement in human health and disease. Here, we propose to investigate a novel pathway by which a putative prion-like protein regulates NLRP3 activation in DIO. This pathway is mediated by the ALCAT1 enzyme, the first acyl-CoA dependent lysocardiolipin acyltransferase previously identified by us. Our groundbreaking work in the field shows that ALCAT1 promotes the development of age-related metabolic diseases by catalyzing pathological remodeling of cardiolipin (CL) with very long-chain polyunsaturated fatty acids, such as docosahexaenoic acid (DHA). Enrichment of DHA renders CL highly sensitive to oxidative damage (CL-Ox) by reactive oxygen species (ROS), leading to CL depletion and mitochondrial dysfunction in metabolic diseases. Remarkably, our preliminary studies also identified a pivotal role of ALCAT1 in linking DIO to NLRP3 activation as a putative prion-like protein, including 1) ALCAT1 forms prion-like protein aggregates in response to oxidative stress, which is mediated by a prion-like domain at the N-terminus; 2) ALCAT1 expression in adipose tissue is dramatically upregulated by DIO; and 3)Targeted deletion of ALCAT1 in adipocytes significantly attenuates NLRP3 activation by preventing macrophage infiltration in white adipose tissue. Together, these exciting findings let us to hypothesize that ALCAT1 promotes NLRP3 activation in DIO as a putative prion-like protein, which will be tested by three Specific Aims: AIM 1 will determine whether ALCAT1 promotes NLRP3 activation through mitochondrial dysfunction; AIM 2 will identify molecular mechanisms by which ALCAT1 promotes NLRP3 activation as a prion-like protein; and AIM 3 will assess whether ALCAT1 links cellular senescence in adipose tissue to chronic inflammation in DIO mice. Successful completion of the proposed studies will not only validate ALCAT1 as a novel drug target of chronic inflammation, but also provide proof of concept studies of targeting the enzyme for the treatment of obesity and its related complications.