人脑小胶质细胞/巨噬细胞的区域极化机制及其胶质瘤抑制性免疫微环境的形成作用

As an immune privileged site, the brain’s regional immune system has been less studied except for some immune functions of microglias. Human glioma is the most common malignant tumor of the central nervous system, and the efficacy of the traditional therapy such as operation and chemoradiotherapy is poor. By further study into the transformation of M1 and M2 subtype of microglia/macrophage, we can have a better understanding of the tumorigenesis and immune escape of glioma. Tumor infiltrating tumor-associated microglia/macrophages (GAMs) account for the maximum proportion among the entire immunosuppressive cells population and the hypoxia environment in glioma can promote the polarization of the GAMs to M2 subtype. The tumor early infiltrating GAMs are mainly induced from the innate microglia of the brain. As the tumor progression, plenty of peripheral mononuclear cells pass through the incomplete blood brain barrier during tumor neovascularization then induced into glioma infiltrating GAMs. However, the mechanism of the recruitment of M2 GAMs by glioma cells remains unclear. We regard the collection of M2 GAMs by glioma as three coherent stages: early-stage inherent recruit, medium-term peripheral recruit, and late-stage malignant accumulation. Then, we would explore the recruitment mechanism of the innate microglia and peripheral mononuclear cells' motility, and indicate what role does tumor hypoxia microenvironment play in recruitment and M2 polarization of GAMs. More importantly, we would try to find the molecular target of M2 subtype GAMs in its immunosuppressive function. This project will enrich the immune escape theory of glioma and provide new ideas for immunotherapy of glioma.

人脑作为“免疫特免器官”其区域免疫特性研究较少，仅涉及小胶质细胞的某些天然免疫功能。脑胶质瘤是最常见的中枢神经系统恶性肿瘤，传统疗法效果差。通过深入解析人脑小胶质细胞/巨噬细胞的M1/M2互转极化机制，有助于了解脑胶质瘤发生和逃逸关键因素。胶质瘤相关小胶质细胞/巨噬细胞（GAMs）是胶质瘤微环境中最多的免疫抑制细胞，肿瘤低氧状态可诱导其M2极化。早期GAMs主要来自脑内固有小胶质细胞，随着肿瘤进展，外周单核细胞可浸润至胶质瘤区域并被诱导为GAMs，目前胶质瘤细胞募集GAMs的细胞动力学机制仍不清楚。本课题将胶质瘤对GAMs的募集分为早期固有招募、中期外周招募和晚期恶性积聚三个阶段，从细胞运动角度分别研究胶质瘤招募GAMs的过程，阐述低氧在胶质瘤募集GAMs及M2极化过程中的作用，寻找逆转M2型GAMs相关免疫抑制作用的靶点。本课题将丰富胶质瘤免疫逃逸理论，为人脑胶质瘤的免疫治疗提供新思路。

人脑作为“免疫特免器官”其区域免疫特性研究较少，仅涉及小胶质细胞的某些天然免疫功能。脑胶质瘤是最常见的中枢神经系统恶性肿瘤，传统疗法效果差。通过深入解析人脑小胶质细胞/巨噬细胞的M1/M2互转极化机制，有助于了解脑胶质瘤发生和逃逸关键因素。胶质瘤相关小胶质细胞/巨噬细胞（TAMs）是胶质瘤微环境中最多的免疫抑制细胞，肿瘤低氧状态可诱导其M2极化。早期TAMs主要来自脑内固有小胶质细胞，随着肿瘤进展，外周单核细胞可浸润至胶质瘤区域并被诱导为TAMs。随着本项目研究进展，我们发现低氧可以通过TGF-α介导的RTK/PI3K通路促进骨膜蛋白（POSTN）的表达，进而促进TAM的招募。并进一步在体外实验证明了低氧环境及低氧培养下胶质瘤上清会使TAMs向M2型极化，且低氧诱导因子（HIF）抑制剂吖啶黄（ACF）的应用可以通过抑制低氧条件下TAM中M-CSFR及低氧胶质瘤中TGF-β的上调，对TAM向M2型极化起到部分抑制的作用，并在体内实验证明了ACF可以抑制肿瘤进展。除上述基于肿瘤微环境中细胞因子作用网络的相关研究研究成果外，课题组还针对肿瘤微环境中的外泌体（exosome）相关RNA调控网络进行了深入探讨。课题组研究发现，人脑胶质瘤细胞能够分泌大量胶质瘤相关外泌体（GDEs），且低氧微环境能够显著促进其分泌，胶质瘤外泌体不仅能够通过microRNA-1246相关通路促进肿瘤相关巨噬细胞的增殖和M2极化，还能显著促进肿瘤相关的MDSCs增殖和免疫抑制能力，产生更广泛的免疫抑制效应。进一步深入研究发现，胶质瘤外泌体相关的多条microRNA相关的信号通路介导了MDSCs免疫抑制能力的上调，进一步促进了肿瘤相关巨噬细胞的M2极化。课题组最终阐明了其中最关键外泌体相关调控机制为miR-21/PTEN、miR-10a/RORα、miR-29a/Hbp1、miR-92a/Prkar1a、和miR-1246/RAP1通路。这些数据揭示了肿瘤低氧微环境促进肿瘤抑制性免疫微环境形成的新机制，也为脑胶质瘤的相关免疫辅助疗法提供了重要的的治疗靶点。