非酒精性脂肪肝病进程中肠源性神经酰胺代谢网络的跨器官调控机制和新药研究

Nonalcoholic fatty liver disease (NAFLD) is the most common chronic and progressive liver disease in China with rapidly increasing prevalence. Non-alcoholic steatohepatitis (NASH) is a subset of NAFLD, characterized by necroinflammation and fibrosis with concurrent fat accumulation in the liver. However, there are no approved therapies for NASH. Thus, there is an urgent need to develop preventive strategies against NASH. It is well established that there is a positive relationship between ceramide levels and NASH in humans and mice. Intestinal ceramides promote the development and progression of NASH via gut-liver axis. Therefore, understanding the role of intestinal ceramide metabolism in the inter-organ regulation of NASH is crucial for the discovery of new NASH therapies. In this project, we hypothesize that nSMase2-based intestinal sphingomyelin-ceramide synthesis and metabolism is constantly activated in the pathogenesis of NASH, leading to the excessive accumulation of ceramides and the metabolite S1P in the portal vein, which are then transported to the liver and stimulate the lipogenesis in the hepatocytes, trigger the innate immune response in Kupffer cells, and ultimately promote liver fibrosis by activating stellate cells. We intent to systematically analyze the temporal and spatial dynamics of intestinal sphingomyelin-ceramide regulation network by means of multi-omics, including lipidomics and transcriptomics, identify the key regulators for NASH, and uncover the molecular mechanism by which ceramide regulates the signalings in hepatocytes, Kupffer cells and stellate cells. By validating the pivotal role of intestinal nSMase2 in the pathogenesis of NASH, we also plan to develop novel lead compounds targeting nSMase2 and SphK1. This project aims to benefit our understanding on the gut-liver axis in the regulation of NASH, discover novel targets and develop first-in-Class drugs for the treatment of NASH.

随着人们生活水平的提高，非酒精性脂肪肝病（NAFLD），特别是非酒精性脂肪肝炎（NASH）在我国的发病呈急剧上升趋势，然而至今尚无有效药物获批上市。越来越多的研究发现肝脏代谢功能的紊乱往往伴随着神经酰胺水平的升高，我们的前期工作也提示肠源性神经酰胺可以通过肠-肝轴促进NASH的发生发展，因此深入研究肠源性神经酰胺代谢网络在NASH进程中的作用，对于寻找治疗NASH的新药物靶标具有重要意义。在前期研究的基础上，本课题拟系统解析NASH进程中肠源性神经酰胺代谢网络的时空动态变化调控规律，通过多组学技术发现核心可调控节点，揭示肠源性神经酰胺跨器官调控肝实质、Kupffer和星状细胞的分子机制，并验证肠中性鞘磷脂酶2（nSMase2）和鞘氨醇激酶1（SphK1）作为潜在药物靶标在NASH进程中的重要作用。项目研究对于揭示肠-肝轴在NASH中的新机制、发现NASH的新药靶和原创新药具有重要科学价值。

非酒精性脂肪肝病已成为我国最常见的慢性肝脏疾病，可从单纯性脂肪肝（NAFL）进展为非酒精性脂肪性肝炎（NASH）、肝纤维化、肝硬化和肝癌，NAFLD已成为危害公共健康的一大问题。NASH以脂肪变性、炎症和纤维化为主要特征，迄今为止尚无治疗药物获批上市，因此迫切需要发现和确证新的NASH药物靶标。神经酰胺被认为是引起肝脏脂毒性的重要脂质，我们的前期工作发现肠道FXR-神经酰胺代谢轴可以跨器官参与NASH的发生发展。在本项目资助下，我们进一步完善了“肠道菌-胆汁酸-肠FXR-神经酰胺”代谢轴跨器官改善NASH的作用机制，并发现了1个非胆汁酸结构的肠FXR拮抗剂F6作为候选化合物，它被证明能改善不同NASH小鼠模型的脂质蓄积、炎症浸润和纤维化。在此基础上，我们进一步发现肠FXR主要通过调控中性鞘磷脂酶2（nSMase2，由基因SMPD3编码）参与NASH进程。既往研究认为从头合成途径是NAFL肝中神经酰胺的主要来源，然而我们通过对临床和动物样品中鞘磷脂-神经酰胺代谢网络分析，证明了nSMase2催化的鞘磷脂酶水解是NASH阶段神经酰胺的主要来源，该途径异常活化可能是NAFL向NASH转变的趋动因素。综合应用基因敲除、过表达小鼠和小分子抑制剂，我们阐明了nSMase2促进NASH进展的全新机制，即脂毒性激活nSMase2，从而促进肝细胞分泌S1P，激活Kupffer和肝星状细胞等非实质细胞，加剧脂质损伤并最终导致肝脏炎症和纤维化。本项目确证了肠FXR、肝脏nSMase2和S1P受体是治疗NASH的潜在药物靶标，为NASH治疗提供新的科学依据，并获得1个候选化合物正在进行系统临床前评价，有望于2023年申报临床。在本项目资助下，在Cell Stem Cell、Hepatology、Kidney International等杂志上发表研究论文10篇，获得1个候选化合物，申请中国专利2项，获中国专利授权1项，培养硕士研究生2名，博士研究生1名，博士后2名。

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