TSP1-STAT3-PD-L1通路促进骨肉瘤细胞免疫逃逸和肺转移机制研究

Lung metastasis is the main reason for the failure of osteosarcoma treatment. Immune escape is closely related to lung metastasis of osteosarcoma. Programmed death receptor 1 (PD-L1) is one of the major proteins that mediates immune escape. Previously our research group found that thrombospondin 1 (TSP1) was highly enriched in lung metastaic tumor. Inhibition TSP1 protein expression in osteosarcoma cells can partially restore the T lymphocytes proliferation, reduce T lymphocytes apoptosis and suppress lung metastasis. Therefore, we speculate that TSP1 protein expression by osteosarcoma cells could inhibit T lymphocyte and thus promote the immune escape and lung metastasis of osteosarcoma cells. Furthermore, we found that TSP1 protein significantly upregulated the expression of PD-L1 in osteosarcoma cells and activated STAT3 pathway. Thus we speculate that TSP1 protein can upregulate the expression of PD-L1 in osteosarcoma cells by activating STAT3 pathway, and inhibit the proliferation and function of T lymphocytes through PD-L1/PD-1 pathway. This project will explore the role of PD-L1 expression induced by TSP1 in T lymphocytes inhibition, immune escape of osteosarcoma cells and lung metastasis through the tibial orthotopic lung metastasis model of osteosarcoma. Exploring the mechanism of STAT3 pathway involved in the upregulation of PD-L1 expression by TSP1 would provide a theoretical basis for TSP1 protein to promote the immune escape and lung metastasis of osteosarcoma cells, and provide new ideas for the clinical immune treatment of osteosarcoma.

肺转移是骨肉瘤治疗失败的主要原因，免疫逃逸和骨肉瘤肺转移关系密切，程序性死亡受体1（PD-L1）是介导免疫逃逸的主要蛋白之一。本课题组前期发现血小板反应蛋白1 (TSP1)在骨肉瘤肺转移灶中高度富集，抑制骨肉瘤细胞表达TSP1可以部分恢复T淋巴细胞的增殖和减少凋亡，抑制骨肉瘤细胞肺转移，因此本研究猜测TSP1可以抑制T淋巴细胞从而促进骨肉瘤细胞的免疫逃逸和肺转移。此外TSP1可以上调骨肉瘤细胞PD-L1的表达和激活STAT3通路，因此本研究猜测TSP1通过激活STAT3通路上调骨肉瘤细胞PD-L1的表达和抑制T淋巴细胞。本项目将通过胫骨原位骨肉瘤肺转移模型，探讨TSP1诱导的PD-L1表达在T淋巴细胞抑制和骨肉瘤细胞免疫逃逸以及肺转移中的作用；探索STAT3通路参与TSP1上调PD-L1表达的机制，为TSP1促进骨肉瘤细胞的免疫逃逸和肺转移提供理论基础，并为临床骨肉瘤免疫治疗提供新的思路。

肺转移是骨肉瘤治疗失败的主要原因，免疫逃逸和骨肉瘤肺转移关系密切，程序性死亡受体1（PD-L1）是介导免疫逃逸的主要蛋白之一。本项目将通过体外淋巴细胞和骨肉瘤细胞共培养实验和胫骨原位骨肉瘤肺转移模型，探讨血小板反应蛋白1 (Thrombospondin-1, TSP1或THBS1)诱导的PD-L1表达在CD8+T淋巴细胞功能抑制和骨肉瘤细胞免疫逃逸以及肺转移中的作用；探索STAT3通路参与TSP1上调PD-L1表达的机制。我们发现TSP1蛋白可以调节骨肉瘤细胞PD-L1的表达，体外TSP1蛋白可以诱导CD8+T凋亡和抑制增值，PD-L1/PD1通路部分参与TSP1的免疫抑制效应，TSP1蛋白通过STAT3信号通路调节骨肉瘤细胞PD-L1的表达。动物实验表明TSP1蛋白可以通过抑制肿瘤免疫促进骨肉瘤细胞的增长， 抑制骨肉瘤细胞TSP1蛋白的表达可以通过恢复抗肿瘤免疫抑制骨肉瘤细胞肺转移。本研究为TSP1蛋白促进骨肉瘤细胞的免疫逃逸和肺转移提供理论基础，并为临床骨肉瘤的治疗提供新的思路和实验依据。