Bone Marrow Transplantation Center, The First Affiliated Hospital, School of Medicine, Zhejiang University, Hangzhou, Zhejiang Province, 310003, People's Republic of China.
Institute of Hematology, Zhejiang University, Hangzhou, 310003, China.
Stem Cell Res Ther. 2017 Dec 29;8(1):292. doi: 10.1186/s13287-017-0744-6.
Bone marrow mesenchymal stem cells (MSCs) are promising candidates for the treatment of various inflammatory disorders due to their profound immunomodulatory properties. However, the immunosuppressive capacity of MSCs needs activation by an inflammatory microenvironment, which may negatively impact the therapeutic effect because of increased immunogenicity. Here we explore the role of mammalian target of rapamycin (mTOR) signaling on the immunosuppressive capacity of MSCs, and its impact on immunogenicity in the inflammatory microenvironment.
Human bone marrow MSCs were cocultured with activated human peripheral blood mononuclear cells, CD4 T cells, and mouse splenocytes to evaluate the immunosuppressive function. Immunosuppressive factors were assessed by quantitative real-time polymerase chain reaction (PCR), Western blot, and enzyme-linked immunosorbent assay (ELISA). The expression of major histocompatibility complex (MHC) was detected by flow cytometry. Short hairpin (sh)RNA was used to downregulate tuberous sclerosis complex (TSC)2, TSC1, and cyclooxygenase (COX)-2 in MSCs.
Inhibition of mTOR signaling using rapamycin enhanced the immunosuppressive functions of MSCs, while prolonged exposure to rapamycin did not. The enhancement of the immunosuppressive function was independent of the inflammatory microenvironment, and occurred mainly through the upregulation of COX-2 and prostaglandin-E (PGE) expression. Furthermore, mTOR inhibition did not impact the immunogenicity of MSCs. However, the upregulated expression of MHC class II molecules by interferon (IFN)-γ was attenuated by mTOR inhibition, whereas TSC2 knockdown had the opposite effect.
These results reveal that the mTOR signaling pathway regulates MSC immunobiology, and short-term exposure to rapamycin could be a novel approach to improve the MSC-based therapeutic effect.
骨髓间充质干细胞（MSCs）由于其强大的免疫调节特性，有望成为治疗各种炎症性疾病的候选细胞。然而，MSCs 的免疫抑制能力需要炎症微环境的激活，这可能会由于免疫原性增加而对治疗效果产生负面影响。在这里，我们探讨了雷帕霉素靶蛋白（mTOR）信号通路对 MSCs 免疫抑制能力的作用及其对炎症微环境中免疫原性的影响。
将人骨髓 MSCs 与激活的人外周血单个核细胞、CD4 T 细胞和小鼠脾细胞共培养，以评估其免疫抑制功能。通过实时定量聚合酶链反应（PCR）、Western blot 和酶联免疫吸附试验（ELISA）评估免疫抑制因子。通过流式细胞术检测主要组织相容性复合体（MHC）的表达。使用短发夹（sh）RNA 下调 MSCs 中的结节性硬化复合物（TSC）2、TSC1 和环氧化酶（COX）-2。
使用雷帕霉素抑制 mTOR 信号增强了 MSCs 的免疫抑制功能，而长时间暴露于雷帕霉素则没有。这种免疫抑制功能的增强与炎症微环境无关，主要通过 COX-2 和前列腺素-E（PGE）表达的上调来实现。此外，mTOR 抑制并不影响 MSCs 的免疫原性。然而，IFN-γ 上调的 MHC Ⅱ类分子表达被 mTOR 抑制所减弱，而 TSC2 敲低则有相反的效果。
这些结果表明，mTOR 信号通路调节 MSC 免疫生物学，短期暴露于雷帕霉素可能是提高 MSC 治疗效果的一种新方法。
