Valine as a Metabolic Modulator of Hematopoiesis

项目摘要/摘要 造血干细胞(HSCs)可以说是研究最深入的成体干细胞群体，也被用于 临床上采用了骨髓移植的形式。尽管做出了广泛的努力，但机制如何 BM维持HSCs，血液动态平衡仍然难以捉摸。我的实验室已经开始探索氨基酸 作为造血的代谢调节剂，最近发现造血干细胞高度依赖缬氨酸。 此外，我们还发现，BM保持较高的氨基酸浓度，大约是50倍 高于外周血中的含量。限制Valine的饮食甚至可以取代放射来为小鼠的HSC提供条件 移植，为使用饮食方法进行骨髓调节提供了重要的概念验证。 综上所述，这些结果使我们提出，氨基酸，特别是valine，是 BM HSC微环境。然而，几个关键问题仍然没有解决，包括valine如何调节 HSC的功能以及BM内氨基酸浓度是如何调节的。通过回答这些基本问题 在生物学问题上，我们的目标是改进HSC体外扩增和骨髓移植方案。 在这项研究计划中，我们将：(1)定义缬氨酸分解代谢对HSC功能的贡献；(2)解剖 BM微环境对Val分解代谢和氨基酸摄取的需求；以及(3)改善BM 通过调节氨基酸代谢来调节移植条件和预后。在目标1中，我们将在新的基础上 Valine分解代谢调节HSC自我更新的证据。虽然这一发现有助于理解为什么造血干细胞 需要valine，HSC自我更新和valine分解代谢途径之间的机制关系不是 安全。为了解决这一问题，我们将结合代谢方法与体外和体内救援试验，以确定 其中缬氨酸分解代谢产物(S)有“促进自我更新”的活动。在鉴定了这些生物活性之后 代谢物，我们将能够进一步研究其作用机制，甚至能够改善EX 体内HSC扩增。目标2将以此为基础，用遗传学方法来理解缬氨酸的重要性 正常骨髓功能中的分解代谢。此外，我们将检验BM反式内皮氨基酸的假设 运输负责维持较高的BM氨基酸浓度和维持造血。在……里面 目标3，我们将应用我们对HSC/BM氨基酸调节的理解来优化我们的概念验证饮食 BM调理方案。在造血系统中，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是移植物排斥反应的罪魁祸首，我们将努力利用它们对 剥夺缬氨酸将我们的饮食调节方法扩展到异基因造血干细胞移植。变得更好 了解淋巴系亚群对缬氨酸的敏感性，我们甚至可能开发出方法来 “清除”有害的免疫记忆，例如在自身免疫性I型糖尿病中。总而言之，这个项目将 研究Valine如何作为造血调节剂，以及BM如何调节氨基酸代谢， 旨在促进HSC的体外扩增和骨髓移植。

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.