小胶质细胞通过分泌IL-1β招募星形胶质细胞进而促进髓母细胞瘤发生的分子机理研究

Microglia and astrocytes play essential roles in multiple nerve system diseases. We previously found that, astrocytes are highly infiltrated in tumor microenvironment of medulloblastoma, ablation of astrocytes using transgenic mouse model could obviously decrease tumor volume, demonstrating an indispensible role for astrocytes in medulloblastoma tumorigenesis and tumor development. However, the molecular biological process of astrocytes recruitment by tumor microenvironment in medulloblastoma initiation and development are still not clear. We found that microglia and macrophagy are highly distributed in tumor microenvironment, and have a higher expression level of IL-1β at early stage of medulloblastoma. Meanwhile, inhibiting IL-1β signaling pathway could significantly attenuate astrocytes recruitment and tumor cell proliferation, suggesting that IL-1β secreted by microglia play important role in astrocytes recruitment and promotion of medulloblastoma tumorigenesis. Based on the previous results, we will further investigate the underlying molecular mechanism and tumor-promoting effects of astrocytes recruitment by microglia-secreted IL-1β in medulloblastoma, and examine the inhibitory effect on tumorigenesis and development of medulloblastoma by blocking recruitment of astrocytes, which could provide evidence for identification of novel therapeutic strategy targeting tumor microenvironment .

小胶质细胞与星形胶质细胞参与多种神经系统疾病的发病过程。我们前期研究表明，星形胶质细胞在髓母细胞瘤肿瘤微环境中高度浸润，通过转基因小鼠模型去除星形胶质细胞可显著缩小肿瘤体积，表明星形胶质细胞对髓母细胞瘤发生发展具有重要作用。但髓母细胞瘤肿瘤微环境招募星形胶质细胞进而促进肿瘤发生发展的分子生物学进程并不清楚。我们发现在髓母细胞瘤发生早期肿瘤微环境中，小胶质细胞和巨噬细胞等炎症相关细胞分布广泛且高表达IL-1β，干扰IL-1β信号通路可显著抑制星形胶质细胞募集与肿瘤细胞增殖。提示小胶质细胞分泌高水平的IL-1β在招募星形胶质细胞并促进髓母细胞瘤发生中发挥重要作用。本课题在此基础上，将深入研究髓母细胞瘤发生早期小胶质细胞通过分泌IL-1β招募星形胶质细胞进而促进肿瘤发生的分子机制，并观察星形胶质细胞募集被阻断后对髓母细胞瘤发生发展的抑制效果，从而为新型肿瘤微环境靶向治疗策略研发提供依据。

肿瘤微环境对肿瘤发生发展至关重要，肿瘤相关小胶质细胞（TAMs）是髓母细胞瘤（MB）肿瘤炎症微环境的主要基质细胞。但是TAMs诱导MB细胞增殖的作用机制还不清楚，开发靶向TAMs的药物也有待研究。我们利用Ptch1基因敲除的MB小鼠发现，TAMs在MB组织中含量非常丰富且通过分泌IL-1β促进MB细胞增殖。同时，我们利用自杀基因白喉毒素受体（DTR）和Ptch1条件性敲除系统构建CD11b-DTR/Math1-Cre/Ptch1fl/fl 转基因MB小鼠，从而可以在患MB小鼠体内特异的去除TAMs。利用该小鼠模型可以成功降低MB肿瘤内TAMs密度并显著抑制肿瘤生长，表明小胶质细胞对MB细胞增殖具有关键作用。接着，我们利用原代小胶质细胞和脑部炎症模型探索抑制TAMs活性的药物。实验发现，鹅不食草醇提物（ECM）及其有效成分6-OAP通过作用于NF-κB通路显著抑制小胶质细胞活化。ECM和6-OAP在小胶质细胞中可以降低炎症相关酶的表达并抑制IL-1β和TNF-α等炎症因子分泌，从而抑制脑部炎症进展。同时，我们也发现ECM联合顺铂可以显著的抑制NSCLC肿瘤生长，并达到协同抗肿瘤效果。从而提示，ECM及其有效成分可能具有抑制TAM活性和治疗MB的潜能。接着，我们利用上述转基因小鼠模型发现了可以特异靶向MB的药物土槿皮乙酸（PAB），PAB通过结合SMO受体抑制MB细胞内SHH通路活化并降低Gli1转录活性。PAB不仅抑制野生型SMO，还可以抑制突变耐药型SMO，从而可以作为新型MB治疗药物。另外，我们课题组研究发现天然化合物桦木酸通过靶向泛素连接酶抑制肿瘤生长转移。因此，我们课题组通过转基因小鼠明确了TAM在MB组织中的重要作用，并初步发现了可以抑制小胶质细胞和治疗MB的药物，为研发MB肿瘤治疗策略提供了重要理论依据。