极性蛋白Par3敲除改变GHR信号通路促进肝器官增大机制

Cell polarity signals are closely related to liver development, regeneration and size control, but the regulatory mechanisms are poorly understood. This project aims to explore the role and mechanism of Par3, a key cell polarity protein, on liver development and size control. Par3 liver specific knockout mice (Par3KO) showed significant liver enlargement. Failure of Par3/YAP or Par3/TAZ double knockout to reduce liver size indicates that it is independent on the Hippo pathway. However, it was unexpectedly found that Par3KO mice were more sensitive to growth hormone (GH) and eventually developed hepatocellular carcinoma. Interestingly, GH and its receptor (GHR) signaling pathways in Par3KO mice were fundamentally changed, resulting in abnormal cleavage of GHR, and the accumulation of GH and GHR extracellular domain (GHR-ED) in cytoplasm and nuclei. These findings suggest a new biological function of Par3: regulate liver development and size control by GH/GHR pathway. The project intends to construct Par3 and GHR double knockout mice to verify the biological significance of abnormal GH/GHR pathway and its correlation with hepatomegaly and hepatocellular carcinoma. By using organoid culture system and Par3 knockout hepatocytes to further explore the specific molecular mechanism, and elucidate the regulation and significance of Par3 cell polarity signals in liver development and size control.

细胞极性信号与肝脏发育和再生及代谢功能密切相关，但调控机制了解甚少。本项目拟探讨关键细胞极性蛋白质Par3对肝脏发育和大小的作用和机制。Par3肝脏特异性敲除小鼠（Par3KO）有显著肝器官增大。Par3/YAP或Par3/TAZ双敲除不能恢复肝脏大小说明不依赖于Hippo通路。但意外发现Par3KO小鼠对生长激素（GH）更敏感，最终发展成肝癌。有意思的是Par3KO小鼠肝细胞中GH及其受体（GHR）信号通路发生根本性改变，GHR剪切异常，GH与GHR细胞外区在细胞内和胞核的大量积累，这些提示Par3全新的生物学功能：调控GH/GHR信号通路参与肝脏发育和大小调控。项目拟构建Par3和GHR双敲除小鼠验证异常GH/GHR通路的生物学意义，及其与肝肿大和肝癌的相关性。利用类器官培养体系和Par3敲除肝细胞进一步探讨具体的分子机理，阐明Par3细胞极性信号在肝脏发育和大小调控的规律和意义。

肝脏是体内最大的代谢器官，高度极化的肝细胞和胆管细胞与其它非实质细胞形成的肝脏结构是其发挥生理功能（物质代谢和解毒等）的基础。然而我们对肝细胞极性调控和肝脏功能的关系还不是很了解。本项目主要以细胞极性蛋白Par3为研究对象，通过对Par3肝脏特异性敲除小鼠表型的全面分析，我们发现Par3缺失的肝脏会有肝肿大和肝癌的发生；结合RNAseq数据，Par3缺失导致生长激素受体（GHR）下调而生长激素结合蛋白（GHBP）上调，同时对生长激素（GH）更敏感。但令我们遗憾的是，肝脏GHR敲除不但没有减轻反而加重了肝肿大和肝癌，而且购买的全身GHR敲除小鼠出现问题，得不到纯和子代。面对挫折，我们发现Par3缺失引起的高胆汁酸血症可能是导致肝肿大的重要因素。综上所诉，本项目揭示了Par3在维持肝脏正常生理功能和抑制肝肿大肝癌中的新作用，为进一步理解细胞极性及其调控蛋白在肝脏疾病、肝再生和肝癌发生发展中的作用提供新的思路。本项目虽然刚开始按照计划推进，但遇到结果与预期不符以及购买的小鼠出问题等状况，导致考核指标未完成，主要的结果可能还需要一年左右来发表。