Fatty acid/branched-chain amino acid metabolism in hematopoietic stem cells

描述(申请人提供)：这项建议的长期目标是识别和表征影响造血干细胞(HSCs)新陈代谢和功能的分子和途径。具体地说，这项应用将检验支链氨基酸/脂肪酸(BCAA/FA)氧化在控制HSC功能中发挥关键作用的假设。造血干细胞的定义是其自我更新和产生多血细胞系的能力。在成人中，HSC群体生活在低氧的骨髓微环境中，并保持相对静止。肝星状细胞如何保持静止，但可以迅速重新编程，以便为随后的分化和动员做好准备，以维持体内平衡，这一点完全未知。虽然已有一些研究开始研究代谢与HSC功能之间的关系，但大多数研究集中在糖酵解和能量平衡方面，而没有研究脂肪和氨基酸分解代谢对HSC功能的贡献。我们先前已经证明，Cited2[CBP/p300-与谷氨酸(E)和富含天冬氨酸(D)的Tail 2相互作用的反式激活因子]的条件性敲除(KO)会导致HSC凋亡增加、静止丧失和周期增加，从而导致严重损害造血重建能力。我们最近使用从WT和Cited2 KO小鼠分离的LT-HSCs进行的全球代谢组学分析发现，支链氨基酸/脂肪酸(BCAA/FA)代谢是WT和Cited2 KO HSCs的主要代谢差异之一。近年来，一个未知的早幼粒细胞白血病-过氧化物酶体增殖物激活受体δ(PPAR-δ)-脂肪酸氧化(FAO)途径被证明在维持HSCs和控制细胞不对称分裂中起着关键作用。有趣的是，其他研究表明，Cited2与控制脂质代谢的PPAR核受体家族相互作用。此外，Cited2通过调节PGC-1α(PPAR-γ辅活化子-1α)的作用而发挥糖异生作用，可能成为治疗II型糖尿病的新靶点。由于Cited2与PPAR的分子和生物学联系以及Cited2和PML基因敲除小鼠(FAO)表型的重叠，这一多PI应用旨在通过两个子目标检验Cited2作为功能节点调控HSC功能的假设：1：确定影响Cited2基因敲除小鼠HSC功能的支链氨基酸和脂肪酸代谢中的中间产物。2：从机制上确定Cited2对HSCs中BCAA/FA氧化的调节作用。目前的应用代表了杨博士和霍佩尔之间的一项有针对性的协同新合作，以研究Cited2在造血干细胞支链氨基酸/脂肪酸氧化中的作用，这是一个未被探索的造血研究领域。这一发现可能为控制HSC细胞命运提供新的手段，并具有未来的治疗意义。因此，这项研究“紧紧聚焦于验证有望为发现开辟新途径的新概念和新方法”，并符合NIDDK的SIRE-II计划的使命。

DESCRIPTION (provided by applicant): The long-term goal of this proposal is to identify and characterize molecules and pathways that impact the metabolism and function of hematopoietic stem cells (HSCs). Specifically, the application will test the hypothesis that branched-chain amino acid/fatty acid (BCAA/FA) oxidation plays a critical role in controlling HSC functions. HSCs are defined by their ability to self-renew and to give rise to multi-lineages of blood cells. n adults, the HSC population resides in the hypoxic bone marrow microenvironment and remains relatively quiescent. How HSCs remain quiescent, but can rapidly reprogram themselves to be metabolically ready for subsequent differentiation and mobilization to maintain homeostasis is totally unknown. Although several studies have begun to investigate the relationship between metabolism and HSC function, most of the studies focused on glycolysis and energy homeostasis but not the contribution of lipid and amino acid catabolism on HSC functions. We have previously shown that conditional knockout (KO) of Cited2 [CBP/p300-interacting transactivators with glutamic acid (E) and aspartic acid (D)-rich tail 2] in the mouse results in increased HSC apoptosis, loss of quiescence and increased cycling, thus leading to severely impaired hematopoietic reconstitution capacity. Our recent global metabolomics analysis using LT-HSCs isolated from WT and Cited2 KO mice identified branched-chain amino acid/fatty acid (BCAA/FA) metabolism as one of the major metabolic differences between WT and Cited2 KO HSCs. Recently, a previously unknown promyelocytic leukemia (PML)-perioxisome proliferator-activated receptor δ (PPARδ)-fatty acid oxidation (FAO) pathway was shown to be crucial for the maintenance of HSCs and the control of asymmetric cell division. Interestingly, others have shown that Cited2 interacts with PPAR family of nuclear receptors that control lipid metabolism. In addition, Cited2 plays a role in gluconeogenesis through its regulation of PGC-1α (PPAR gamma coactivator-1α)actions and could be a novel therapeutic target for type II diabetes. Because of the molecular and biological link of Cited2 to PPAR and overlapping phenotypes of Cited2 and PML knockout mice (FAO), this multi-PI application intends to test the hypothesis that Cited2 acts as a functional node to modulate branched-chain amino acid and fatty acid metabolism in controlling HSC functions by two subaims: 1: To identify intermediates within the branched-chain amino acid and fatty acid metabolism that impact the function of HSCs from Cited2 knockout mice. 2: To determine mechanistically how Cited2 modulates the BCAA/FA oxidation in HSCs. The current application represents a focused synergistic new collaboration between Drs. Yang and Hoppel to investigate the role of Cited2 in BCAA/FA oxidation in HSCs, an under-explored research area in hematopoiesis. The findings may provide new means of controlling HSC cell fate with future therapeutic implications. The study therefore is "tightly focused and directed at validating novel concepts and approaches that promise to open up new pathways for discovery" and fits the mission of the SHINE-II program at NIDDK.