棕榈酰化修饰调节FAT/CD36介导的肝细胞线粒体脂肪酸氧化的分子机制与非酒精性脂肪性肝病

Fatty acid translocase (FAT/CD36), a multifunctional membrane glycoprotein, which is closely related to long chain fatty acids (LCFA) transmembrane transport, plays an important role in the pathogenesis of non-alcoholic fatty liver disease (NAFLD). Palmitoylation of FAT/CD36 is a kind of protein modification in post-translation level and regulates FAT/CD36 localization and function. Our previous studies demonstrated that palmitoylation increased the translocations of FAT/CD36 from hepatocellular mitochondria to plasma membrane (especially lipid raft), as well as promoted fatty acid uptake and inhibited the fatty acid-driven oxygen consumption rate (palmitate-dependent OCR)，suggesting that FAT/CD36 palmitoylation may regulate fatty acid oxidation (FAO) in the mitochondria. However, the mechanism for palmitoylation FAT/CD36 regulating FAO is largely unknown. .We propose that palmitylation of hepatic FAT/CD36 mainly affects fatty acid oxidation in the mitochondria by two pathways: FAT/CD36 on plasma membrane /intracellular protein kinase-AMPK-ACC-CPT signaling pathway and FAT/CD36 on mitochondrial membrane /ACS-CPT signaling pathway. .We will examine this hypothesis in cultured hepatic cells with/without palmitoylation inhibitors and in mice carrying lentivirus vector with wild-type of FAT/CD36 or mutation of FAT/CD36 palmitoylation site, to reveal the roles of FAT/CD36 palmitoylation and its mediated signaling pathway of fatty acid oxidation, which could be a novel target for the prevention of NAFLD.

脂肪酸转运酶（FAT/CD36）是介导长链脂肪酸（LCFA）跨膜转运的多功能蛋白，与脂肪肝发生密切相关。我们前期发现：棕榈酰化修饰（一种蛋白质翻译后脂质共价修饰形式）可增加FAT/CD36在肝细胞膜定位、减少其在线粒体上滞留和LCFA依赖的耗氧率，提示棕榈酰化修饰FAT/CD36可能参与调节线粒体脂肪酸β氧化而影响肝脏脂肪酸代谢平衡，但其具体机制尚不清楚。我们推测：高脂血症下异常增加的棕榈酰化修饰致FAT/CD3定位改变，可分别通过干扰肝细胞膜和线粒体上FAT/CD36介导的两个环节酶系通路来抑制脂肪酸在线粒体的β氧化而导致脂肪肝发生。本项目拟应用多种体内外模型和技术，深入探讨棕榈酰化修饰调节FAT/CD36介导的肝细胞线粒体脂肪酸氧化的可能分子机制，从一个全新角度阐释脂肪肝发病机制，为针对FAT/CD36介导的脂肪酸氧化代谢通路中不同靶点的新药开发、寻找有效防治手段提供新的理论依据。

脂肪酸转运酶（FAT/CD36）是与脂肪酸摄取和代谢性炎症产生密切相关的膜糖蛋白，它在细胞膜及亚器的定位决定了其功能，在非酒精性脂肪性肝病（NAFLD）中扮演了重要角色。棕榈酰化修饰是蛋白质翻译后脂质共价修饰的一种形式，对蛋白质定位和功能有重要调节作用。本项目应用课题组已建立的多种实验技术，探讨棕榈酰化修饰如何调节肝细胞中FAT/CD36定位到线粒体上并调控脂肪酸进入线粒体进行氧化的过程，进而调节肝细胞脂肪酸的代谢，深入分析其与NAFLD发生发展的关系。通过一系列体内外实验，我们发现：NAFLD小鼠肝脏中FAT/CD36表达和棕榈酰化修饰增加，抑制FAT/CD36棕榈酰化保护小鼠免受NAFLD的损伤。同时抑制FAT/CD36棕榈酰化可增强FAT/CD36向线粒体的分布。进一步，我们发现抑制FAT/CD36棕榈酰化通过增加长链酰基辅酶A的产生，促进脂肪酸β-氧化。ACSL1是FAT/CD36介导的脂肪酸β-氧化增加过程所必需的。减少FAT/CD36棕榈酰化修饰促进了FAT/CD36和ACSL1之间的相互作用，并且促进了脂肪酸向线粒体的运输。因此，我们提出了一个重要的创新性理论：抑制FAT/CD36棕榈酰化促进FAT/CD36定位到线粒体，并增强FAT/CD36与ACSL1的相互作用。线粒体上去棕榈酰化的FAT/CD36可能作为长链脂肪酸和ACSL1之间的“分子桥梁”。FAT/CD36增加长链脂肪酸向ACSL1转运并催化产生更多的酰基辅酶A和酰基肉碱，由此促进脂肪酸进入线粒体基质进行β-氧化，减轻高脂饮食引起的肝细胞脂质积累。由于棕榈酰化修饰控制FAT/CD36的分布和功能，靶向FAT/CD36的棕榈酰化修饰位点可能成为治疗NAFLD及其他代谢性疾病的潜在策略。