内质网应激对巨核细胞生成中凋亡相关let-7b的时空调控及其在慢性ITP中的作用研究

Deficient megakaryocytopoiesis is a major mechanism of chronic immune thrombocytopenia (ITP). Fine-tuning of apoptosis plays an important role in megakaryocytopoiesis. It was reported that let-7b can induce apoptosis of liver cancer, lung cancer and other tumor cells, and endoplasmic reticulum stress is closely related to regulation of miRNA level and apoptosis. Our preliminary data showed that over-expression of let-7b in megakaryocyte promoted apoptosis, whereas induced endoplasmic reticulum stress led to an increase in let-7b expression. During megakaryocytopoiesis, let-7b gradually increased and accumulated in the endoplasmic reticulum with the maturation of megakaryocytes in a time and space-dependent manner. While chronic ITP plasma treatment led to a large amount of early activation of endoplasmic reticulum stress and the premature apoptosis of megakaryocytes. It is speculated that the massive activation of endoplasmic reticulum stress in chronic ITP leads to uncontrolled spatial and temporal expression of let-7b, premature apoptosis of megakaryocytes, and subsequent deficient megakaryocytopoiesis. Based on the previous work, this project aims to further investigate the specific mechanism of let-7b regualtion by endoplasmic reticulum stress , and explore the role of space-time expression of let-7b by endoplasmic reticulum stress in chronic ITP through the combination of methods in molecular, cell biology and mouse models. Through the above research, this project will help to understand the pathogenesis of chronic ITP and provide a theoretical basis for a new treatment.

巨核细胞生成缺陷是慢性ITP发病的重要机制。细胞凋亡在巨核细胞生成中发挥重要作用。研究发现，let-7b可促进肝癌、肺癌等肿瘤细胞发生细胞凋亡，内质网应激与miRNA表达和细胞凋亡的调节密切相关。项目组预实验发现，过表达let-7b导致巨核细胞凋亡显著增加，诱导内质网应激促进let-7b表达；巨核细胞生成中let-7b的表达呈时空变化，随巨核细胞成熟逐渐升高并在内质网聚集；慢性ITP血浆处理导致内质网应激提前大量激活，巨核细胞发生过早细胞凋亡。我们推测慢性ITP中内质网应激的提前激活，导致let-7b时空表达失控，巨核细胞发生过早细胞凋亡及生成缺陷。本项目拟在前期工作基础上，结合分子、细胞生物学和动物模型，进一步研究巨核细胞生成中内质网应激对let-7b时空表达的调控机制、内质网应激调节let-7b表达在慢性ITP中作用及干预策略，为阐明慢性ITP的发病机制、建立新的治疗策略提供理论依据。

血小板生成减少是免疫性血小板减少症（ITP）的重要机制之一。内质网应激和细胞凋亡在巨核细胞血小板生成中发挥重要作用，而let-7b等多种microRNAs与细胞凋亡密切相关。根据既往研究和前期数据，我们推测ITP中内质网应激的异常激活可能通过调控凋亡相关Let-7b的表达导致巨核细胞凋亡紊乱。本项目中我们研究了巨核细胞生成中内质网应激对let-7b时空表达的调控机制以及内质网应激调节let-7b表达在慢性ITP中作用，发现：慢性ITP患者骨髓未成熟巨核细胞凋亡显著增加；慢性ITP血浆处理导致内质网应激提前大量激活，巨核细胞发生过早细胞凋亡；内质网应激促进let-7b表达及巨核细胞凋亡；机制上，内质网应激抑制AGO2介导的let-7b释放从而提高let-7b胞内水平，后者通过靶向抑制抗凋亡基因Bcl-xL导致巨核细胞凋亡。然而ITP小鼠模型中，干预内质网应激对血小板生成无明显作用。本项目揭示了ITP中内质网应激与巨核细胞凋亡间新的调控机制，这可能为研究慢性ITP的发病机制和建立治疗策略提供新的思路。