Targeting Wnt and mTOR to expand hematopoietic stem cells

描述（由申请人提供）：造血干细胞（HSC）已经成为干细胞生物学研究的基本模型，并且是治疗造血恶性肿瘤和骨髓衰竭综合征的重要治疗方式。尽管造血干细胞的调控涉及多种信号通路，但这些信号如何在造血干细胞水平上整合以维持自我更新和谱系承诺之间的平衡仍然是造血干细胞研究中的一个主要问题。我们最近的研究表明，信号分子糖原合成酶激酶3 （GSK-3）在体内HSC稳态中起着关键作用。药理和遗传功能丧失研究表明，GSK-3抑制造血干细胞/祖细胞（HSPCs）中的两种不同途径，Wnt/ss-catenin和mTOR途径。GSK-3的抑制激活了HSPC的两条通路，其结果不同：Wnt信号的激活导致表型HSPC的扩增，而mTOR的激活导致HSPC衰竭。因此，GSK-3和mTOR的联合抑制在体内产生HSPC的净扩增，因为wnt刺激的HSPC扩增不再被mTOR介导的HSPC耗尽所平衡。这些观察结果表明GSK-3是HSC稳态的重要调节因子，并建议使用目前fda批准的药物在体内和体外扩大HSC的治疗策略，包括锂来抑制GSK-3和雷帕霉素/西罗莫司来抑制mTOR。我们的初步数据进一步表明，这种药物组合可以在缺乏造血细胞因子的情况下长期培养小鼠造血干细胞。因此，我们将在体内和离体条件下测试GSK-3和mTOR的同时抑制是否会扩展功能性hsc。如果成功，该项目将确定HSC稳态的关键调控节点，并将确定扩展HSC以改进HSCT治疗的方法。

DESCRIPTION (provided by applicant): Hematopoietic stem cells (HSC) have served as a fundamental model for the study of stem cell biology and as a vital therapeutic modality for the treatment of hematopoietic malignancies and bone marrow failure syndromes. Although multiple signaling pathways are implicated in the regulation of HSCs, how these signals are integrated at the level of the HSC to maintain the balance between self-renewal and lineage commitment remains a major question in HSC research. Our recent work has demonstrated that the signaling molecule glycogen synthase kinase-3 (GSK-3) plays a pivotal role in HSC homeostasis in vivo. Pharmacological and genetic loss of function studies reveal that GSK-3 suppresses two, distinct pathways in hematopoietic stem/progenitor cells (HSPCs), the Wnt/ss-catenin and mTOR pathways. Inhibition of GSK-3 activates both pathways in HSPCs-with distinct consequences: activation of Wnt signaling causes expansion of phenotypic HSPCs, whereas mTOR activation causes HSPC exhaustion. Thus, combined inhibition of GSK-3 and mTOR yields a net expansion of HSPCs in vivo, as Wnt-stimulated HSPC expansion is no longer balanced by mTOR-mediated HSPC depletion. These observations demonstrate that GSK-3 is an important regulator of HSC homeostasis and suggest a therapeutic strategy to expand HSCs in vivo and ex vivo using currently available FDA-approved agents, including lithium to inhibit GSK-3 and rapamycin/sirolimus to inhibit mTOR. Our preliminary data further indicate that this drug combination may allow long-term culture of mouse HSCs ex vivo in the absence of hematopoietic cytokines. We will therefore test whether simultaneous inhibition of GSK-3 and mTOR expands functional HSCs under both in vivo and ex vivo conditions. If successful, this project will define a critical regulatory node in HSC homeostasis and will identify approaches to expand HSCs for improved HSCT therapy. PUBLIC HEALTH RELEVANCE: This proposal investigates the regulation of blood forming cells and specifically how the body maintains the ability to produce a high volume of mature blood cells and at the same time maintains the population of cells in the bone marrow needed for new blood formation. The proposal explores new approaches to enhance blood formation for bone marrow transplantation and in patients with low blood counts due to disease or chemotherapy.