1 Institute of Hematology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China. 2 Division of Radiation Health, Department of Pharmaceutical Sciences and Winthrop P. Rockefeller Cancer Institute, University of Arkansas for Medical Sciences, Little Rock, AR. 3 Institute of Pediatrics, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China. 4 Address correspondence to: Lingbo Liu, M.D., Ph.D., Institute of Hematology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei 430022, China and Daohong Zhou, M.D., Division of Radiation Health, Department of Pharmaceutical Sciences and Winthrop P. Rockefeller Cancer Institute, University of Arkansas for Medical Sciences, 4301 West Markham, #607, Little Rock, AR 72205.
Transplantation. 2014 Jan 15;97(1):20-9. doi: 10.1097/TP.0b013e3182a7fcf8.
The mammalian target of rapamycin (mTOR) is an important regulator of hematopoietic stem cell (HSC) self-renewal and its overactivation contributes to HSC premature exhaustion in part via induction of HSC senescence. Inhibition of mTOR with rapamycin has the potential to promote long-term hematopoiesis of ex vivo expanded HSCs to facilitate the clinical application of HSC transplantation for various hematologic diseases.
A well-established ex vivo expansion system for mouse bone marrow HSCs was used to investigate whether inhibition of overactivated mTOR with rapamycin can promote long-term hematopoiesis of ex vivo expanded HSCs and to elucidate the mechanisms of action of rapamycin.
HSC-enriched mouse bone marrow LSK cells exhibited a time-dependent activation of mTOR after ex vivo expansion in a serum-free medium supplemented with stem cell factor, thrombopoietin, and Flt3 ligand. The overactivation of mTOR was associated with induction of senescence but not apoptosis in LSK cells and a significant reduction in the ability of HSCs to produce long-term hematopoietic reconstitution. Inhibition of overactivated mTOR with rapamycin promoted ex vivo expansion and long-term hematopoietic reconstitution of HSCs. The increase in long-term hematopoiesis of expanded HSCs is likely attributable in part to rapamycin-mediated up-regulation of Bmi1 and down-regulation of p16, which prevent HSCs from undergoing senescence during ex vivo expansion.
These findings suggest that mTOR plays an important role in the regulation of HSC self-renewal in vitro and inhibition of mTOR hyperactivation with rapamycin may represent a novel approach to promote ex vivo expansion and their long-term hematopoietic reconstitution of HSCs.
哺乳动物雷帕霉素靶蛋白（mTOR）是造血干细胞（HSC）自我更新的重要调节剂，其过度激活部分通过诱导 HSC 衰老导致 HSC 过早耗竭。用雷帕霉素抑制 mTOR 有可能促进体外扩增的 HSCs 的长期造血，从而促进 HSC 移植在各种血液疾病中的临床应用。
使用成熟的体外扩增小鼠骨髓 HSC 系统来研究雷帕霉素抑制过度激活的 mTOR 是否可以促进体外扩增的 HSCs 的长期造血，并阐明雷帕霉素的作用机制。
富含 HSC 的小鼠骨髓 LSK 细胞在无血清培养基中体外扩增时，mTOR 呈时间依赖性激活，该培养基中添加了干细胞因子、血小板生成素和 Flt3 配体。mTOR 的过度激活与 LSK 细胞衰老的诱导有关，但与凋亡无关，并且 HSCs 产生长期造血重建的能力显著降低。用雷帕霉素抑制过度激活的 mTOR 可促进 HSCs 的体外扩增和长期造血重建。扩增的 HSCs 长期造血增加可能部分归因于雷帕霉素介导的 Bmi1 上调和 p16 下调，这可防止 HSCs 在体外扩增过程中发生衰老。
这些发现表明 mTOR 在体外调节 HSC 自我更新中起重要作用，用雷帕霉素抑制 mTOR 过度激活可能代表一种促进 HSCs 体外扩增及其长期造血重建的新方法。
