Valine as a Metabolic Modulator of Hematopoiesis

项目总结/摘要 造血干细胞（HSC）可以说是研究得最好的成体干细胞群，并且也用于治疗癌症。 骨髓移植（BM）的临床应用。尽管作出了广泛的努力， BM维持HSC和血液稳态仍然难以捉摸。我的实验室已经开始探索氨基酸 作为造血的代谢调节剂，最近发现HSC高度依赖于缬氨酸。 此外，我们发现BM保持高浓度的氨基酸，约为50倍 高于外周血。限制缬氨酸的饮食甚至可以取代照射来调节小鼠的HSC 移植，为使用饮食方法进行BM调节提供了重要的概念验证。 结合起来，这些结果使我们提出氨基酸，特别是缬氨酸，是 BM HSC微环境。然而，几个关键问题仍然没有解决，包括缬氨酸如何调节 HSC的功能和氨基酸浓度如何在BM内调节。通过回答这些基本问题， 为了解决生物学问题，我们的目标是改进离体HSC扩增和BM移植方案。 在本研究计划中，我们将：（1）确定缬氨酸catalysts对HSC功能的贡献;（2）解剖HSC中的 在BM微环境中的缬氨酸催化剂和氨基酸摄取的需求;和（3）改善BM 通过调节氨基酸代谢调节移植条件和结果。在目标1中，我们将建立在新的 证据表明，缬氨酸催化剂调节HSC自我更新。虽然这一发现有助于理解为什么HSC 需要缬氨酸，HSC自我更新和缬氨酸catalysts途径之间的机制关系不是 清楚为了解决这一问题，我们将联合收割机代谢方法与体外和体内拯救试验相结合，以确定 所述缬氨酸分解代谢物具有“自我更新促进”活性。在鉴定出这些生物活性物质后， 代谢物，我们将能够进一步研究的作用机制，甚至可以提高前 体内HSC扩增。目标2将建立在此基础上与遗传方法来了解缬氨酸的重要性 正常BM功能中的钙离子。此外，我们将检验BM跨内皮氨基酸 转运负责维持高BM氨基酸浓度和维持造血。在 目的3，我们将应用我们对HSC/BM氨基酸调控的理解来优化我们的概念验证饮食。 BM调节方案。在造血系统内，T细胞和B细胞也高度依赖于 缬氨酸由于这些淋巴样细胞负责移植物排斥反应，我们将奋进利用它们的敏感性， 缬氨酸剥夺将我们的饮食调节方法扩展到异基因HSC移植。通过更好 了解淋巴细胞亚群的缬氨酸敏感性，我们甚至可以开发出方法， “擦除”有害的免疫记忆，如自身免疫性I型糖尿病。总之，该项目将 研究缬氨酸如何作为造血的调节剂以及BM如何调节氨基酸代谢， 目的是改善离体HSC扩增和BM移植。

PROJECT SUMMARY/ABSTRACT Hematopoietic stem cells (HSCs) are arguably the best-studied adult stem cell population and are also used in the clinic in a form of bone marrow (BM) transplantation. Despite extensive efforts, the mechanism of how the BM maintains HSCs and blood homeostasis remains elusive. My laboratory has begun to explore amino acids as metabolic modulators of hematopoiesis and recently found that HSCs are highly dependent on valine. Additionally, we have found that the BM maintains high concentrations of amino acids, approximately 50-fold higher than in the peripheral blood. A valine-restricted diet can even replace irradiation to condition mice for HSC transplantation, providing important proof-of-concept for the use of dietary approaches for BM conditioning. Combined, these results led us to propose that amino acids, and in particular valine, are key components of the BM HSC microenvironment. However, several key issues remain unresolved, including how valine modulates HSC function and how amino acid concentrations are regulated within the BM. By answering these basic biological questions, we aim to improve ex vivo HSC expansion and BM transplantation protocols. In this research plan, we will: (1) define the contribution of valine catabolism to HSC function; (2) dissect the requirements of valine catabolism and amino acid uptake in the BM microenvironment; and (3) improve BM transplantation conditioning and outcome by modulating amino acid metabolism. In Aim 1, we will build on new evidence that valine catabolism regulates HSC self-renewal. While this finding helps to understand why HSCs require valine, the mechanistic relationship between HSC self-renewal and the valine catabolism pathway is not clear. To address this, we will combine metabolic approaches with in vitro and in vivo rescue assays, to define which valine catabolite(s) have “self-renewal promoting” activity. After identifying these biologically active metabolites, we will be able to further investigate the mechanism of action and may even be able to improve ex vivo HSC expansion. Aim 2 will build on this with genetic approaches to understand the importance of valine catabolism in normal BM function. Additionally, we will test the hypothesis that BM trans-endothelial amino acid transport is responsible for maintaining high BM amino acid concentrations and sustaining hematopoiesis. In Aim 3, we will apply our understanding of HSC/BM amino acid regulation to optimize our proof-of-concept dietary BM conditioning protocols. Within the hematopoietic system, T cells and B cells are also highly dependent on valine. As these lymphoid cells are responsible for graft rejection, we will endeavor to utilize their sensitivity to valine deprivation to extend our dietary conditioning approach to allogeneic HSC transplantation. By better understanding the valine sensitivity of lymphoid subpopulations, we may even be able to develop methods to “wipe” harmful immunological memory, such as in autoimmune type I diabetes. In summary, this project will investigate how valine acts as a modulator of hematopoiesis and how the BM regulates amino acid metabolism, with the aim of improving ex vivo HSC expansion and BM transplantation.