间充质干细胞调节表观调控因子EZH2治疗肝衰竭的分子机制研究

Liver failure is liver tissue injury mediated by dysfunction of the immune system and the subsequent massive liver cell necrosis. Mesenchymal stem cells (MSC) are multipotent stromal cells with immunomodulatory capacity which could be utilized to treat liver failure. Our previous studies have found that MSC inhibit liver failure by inducing the generation of regulatory dendritic cells (DC). However, the molecular mechanisms by which MSC regulate the immune system and take part in tissue repair during liver failure remain to be resolved. Our preliminary study found that expression of epigenetic regulator EZH2 was significantly reduced in liver DC and hepatic stem cells during acute liver failure. However, MSC transplantation upregulated the expression of EZH2 in both cells which might be associated with immunomodulation and hepatic stem cell activation. Therefore, based on patients with liver failure and animal models, this program aims to investigate the pathological mechanism of EZH2 in promoting liver failure, and reveal the regulatory effect of EZH2 in MSC-based immunomodulation and hepatic stem cell activation. Most importantly, this program trys to uncover the key mechanism by which MSC inhibit liver failure. Altogether, this program aims to provide a novel strategy for the clinical immunological diagnosis and treatment of liver failure.

肝衰竭是肝脏免疫紊乱及继发大量肝细胞坏死导致的肝损伤。间充质干细胞(MSC)具有多向分化修复组织的能力又具有其它干细胞不具备的免疫调节特性，恰针对肝衰竭病理机制，符合有效治疗肝衰竭的需求。我们既往研究发现MSC是通过诱导调节性树突状细胞(DC)产生，抑制了免疫紊乱导致的肝衰竭，进一步明晰其免疫调控分子机制及损伤修复机制是MSC治疗肝衰竭中亟需解决的重要科学问题。我们前期研究发现急性肝衰竭小鼠肝脏DC及肝干细胞表达的表观调控因子EZH2显著降低，MSC输注后EZH2表达显著升高，并与免疫调控和肝干细胞动员增殖有关。由此，本项目拟以肝衰竭患者标本和疾病模式动物，研究肝衰竭发病中EZH2介导的病理机制；揭示MSC治疗通过调控EZH2，实现抑制免疫紊乱和促进肝干细胞修复损伤的双重作用；阐明MSC治疗肝衰竭的核心机制，形成干预新策略。为临床肝衰竭免疫学诊断新指标和治疗新靶点的建立提供理论和实验依据。

本项目以研究MSC 治疗肝衰竭的机制为主线，阐明肝衰竭发病机制中表观调控分子EZH2 的作用，揭示MSC调控EZH2对DC介导的免疫调节和组织内在干细胞参与修复损伤的作用及分子机制，为形成MSC干预治疗肝衰竭的新策略，研发新的治疗肝衰竭的靶向药物提供理论和实验依据。明晰了EZH2及催化产物H3K27me3在肝衰竭中的表达在肝衰竭机体和小鼠肝衰竭模型机体内中明显增高，且与机体促炎因子TNF的表达水平相关。证实采用抑制EZH2可以解肝衰竭机体疾病进展。其治疗机制主要是抑制EZH2减少ALF小鼠肝脏CD4+ T细胞的数量，抑制Th1型细胞因子IFN-γ，EZH2能够促进树突状细胞的成熟，增强DC对T细胞的作用。抑制EZH2能显著增加LPS引起PTEN水平的减低，显著增加LPS引起磷酸化AKT的减少，肝衰竭机体中EZH2和H3K27me的增高；抑制EZH2对肝衰竭机体的缓解与PTEN-ATK-NF-B通路密切相关。乙型肝炎病毒HBV可诱导小鼠肝脏自噬小体的形成，HBV感染细胞水平可产生自噬，但自噬并不能清除病毒。HBV通过抑制Rab7而阻止自噬小体与溶酶体的融合。分析肝脏干细胞（肝脏卵圆细胞）与微环境之间的交互作用，证实微环境中星状细胞通过产生Laminin对卵圆细胞具有促增殖作用；肝脏组织干细胞（间充质干细胞MSCs）作为外源移植治疗细胞缓解肝衰竭的核心治疗机制，抑制肝损伤小鼠肝脏中Th1细胞分化并促进Tregs产生，MSCs诱导DC前体向调节性DCs分化。我们的发现为表观调控分子 EZH2在肝衰竭发病机制中的作用，揭示 MSC调控 EZH2对 DC介导的免疫调节和组织内在干细胞参与修复损伤的分子机制拓展了新思路。为临床肝衰竭免疫学诊断新指标和治疗新靶点的建立，研发新的治疗肝衰竭的靶向药物提供理论和实验依据。