磷脂酶PLA2G4C调控脂滴形成的机制及在HCV相关肝脂肪病变中的作用

Hepatic steatosis featured with lipid droplet (LD) accumulation in liver cell is a frequent histological finding in patients with chronic hepatitis C virus infection. Though LD accumulation was observed in HCV infected cells in vitro and LD was considered to be the assembly site of HCV virion, it’s still not clear how HCV induces LD accumulation and hepatic steatosis. A member of phospholipase, PLA2G4C, which is upregulated by HCV infection, was proved to be involved in HCV genomic RNA replication by modulating the membranous web formation. Further evidence showed that PLA2G4C is required in LD formation as well as HCV virion assembly, suggesting a role of PLA2G4C in HCV induced LD accumulation and HCV related hepatic steatosis. In this project, we will analyze the function and structure foundation of PLA2G4C in different stages of LD formation (including the neutral lipid synthesis, LD structure formation, growth and maturation, LD consumption) induced by HCV and oleate. The mechanism of LD formation and HCV virion assembly modulated by PLA2G4C will be studied. Further, we will analyze the involvement of PLA2G4C in HCV replication and HCV associated hepatic steatosis in the chronic HCV infection mouse model. Taken together, this project could shed light on the mechanism of HCV associated hepatic steatosis and provide new treatment strategy.

脂滴是丙型肝炎病毒（HCV）包装的场所，慢性HCV感染会导致肝脏脂滴堆积而发生脂肪肝，但HCV诱导脂滴形成及脂肪肝发生的机制尚不清晰。前期项目已证实HCV感染上调的宿主因子PLA2G4C调控HCV诱导的膜网结构形成而参与病毒RNA复制；进一步研究发现干扰PLA2G4C影响脂滴的发生，提示PLA2G4C通过调控脂滴形成而参与HCV包装，并在HCV诱导的脂滴增多及HCV相关肝脂肪病变的发生中具有重要作用。本项目将分析在生理及HCV感染条件下PLA2G4C在脂滴形成中的作用，解析其在中性脂合成、脂滴形态发生、生长成熟及脂滴消耗环节中的功能及结构基础，阐明其在病毒感染状态下调控脂滴生成和HCV病毒粒子组装的机理及联系；并进一步利用我们建立的HCV持续感染小鼠模型验证PLA2G4C在HCV复制及HCV相关肝脂肪病变中的作用。本项目可望揭示脂滴形成及HCV相关肝脂肪病变发生的新机理。

在发现受HCV感染上调的宿主因子PLA2G4C可调控HCV诱导的膜网结构形成从而参与病毒RNA复制的基础上，进一步研究发现干扰PLA2G4C影响脂滴的发生，研究证实PLA2G4C调节脂代谢重要转录因子SRBP-1c的表达和活性，并增加细胞总脂质含量；具体分析PLA2G4C的结构发现其260-292aa决定了PLA2G4C在脂滴的定位并参与诱导脂滴生成，同时其磷脂酶活性也为诱导脂滴生成的关键因素；而PLA2G4C诱导脂滴生成的功能与其对HCV病毒包装的影响直接相关。同时发现PLA2G4C包被的脂滴体积增大、运动速率降低，并且与ER结构相连，说明PLA2G4C参与ER-LD的连接；而在HCV感染过程中PLA2G4C参与了膜网结构即复制复合体与脂滴的密切连接，从而影响病毒复制。在高脂喂食小鼠中发现，PLA2G4C参与脂肪肝的发生，说明HCV感染诱导的PLA2G4C表达为其诱导脂肪肝发生的机制之一。总之，项目证实PLA2G4C诱导细胞脂滴的生成，并影响脂滴与膜网结构（复制复合体）的紧密相邻，从而参与HCV装配过程；PLA2G4C为HCV诱导脂肪肝发生的重要因素。