Metabolic control of normal and malignant hematopoiesis

项目总结/摘要 异柠檬酸脱氢酶（IDH）酶的体细胞突变有助于急性胰腺炎的发病机制。 通过产生“癌代谢物”D-2-羟基戊二酸， （D-2HG）。D-2 HG通过抑制α-酮戊二酸（α-Ketoglutarate，KKG）依赖性的 调节染色质结构和基因表达的酶。突变型IDH的小分子抑制剂 酶是有前途的AML新疗法，但其疗效仍限于AML患者亚组。 IDH突变。这就提出了一个问题，即类似的代谢畸变是否有助于 IDH-野生型AML中的白血病发生。有趣的是，2 HG是一种手性分子，可以以D-或L-构型存在。 对映体。尽管癌症相关的IDH突变体只产生D-2 HG，但生物化学研究表明， 表明L-2 HG可以作为许多PKG依赖酶的~10倍更有效的抑制剂起作用， 包括染色质修饰剂和低氧诱导因子（HIF）稳定性的调节剂。然而，生物 L-2 HG的来源和活性知之甚少。我们发现了一种代谢途径， 没有IDH突变的正常和恶性细胞响应氧限制选择性地产生L-2 HG （又称缺氧）通过乳酸脱氢酶（LDHA）催化的不寻常的反应。我们证明了 缺氧诱导的L-2 HG增强HIF的稳定性，增加抑制性染色质修饰，并阻断HIF的表达。 干/祖细胞的分化。这些发现表明，L-2 HG可能解释，至少部分， 缺氧小生境、HIF和LDHA在平衡干细胞自我更新和分化中的重要性 造血干/祖细胞（HSPC）和白血病干细胞。因此我们 假设L-2 HG作为一种代谢信号，将缺氧小生境与 维持正常造血干细胞和白血病干细胞。这一假设将严格 有三个具体目标。目的1将明确L-2 HG调节的分子机制， 体外血细胞分化。在这个目的中，我们将确定L-2 HG对基因表达的影响， 染色质结构，并确定这些输入如何平衡HSPC干细胞和谱系分化。目的 2将确定L-2 HG如何在体内控制正常和恶性造血。该目标将使用 允许组织特异性、诱导性操纵L-2 HG的新型基因工程小鼠模型 水平，以剖析L-2 HG在正常造血和白血病中的作用。目标3将阐明 L-2 HG在人白血病中的致癌机制和治疗潜力在本章中，我们将使用primary AML生物标本和患者来源的异种移植物，以确定导致L- 2 HG在AML亚组中的作用，并评估消耗L-2 HG是否提供了治疗人类AML的有希望的策略。 这些研究将为正常和恶性干细胞的代谢控制提供基本的见解。 细胞生物学和扩大代谢靶向疗法对白血病和其他癌症的适用性。

PROJECT SUMMARY/ABSTRACT Somatic mutations in the isocitrate dehydrogenase (IDH) enzymes contribute to the pathogenesis of acute myeloid leukemia (AML) and other malignancies via production of the ‘oncometabolite’ D-2-hydroxyglutarate (D-2HG). D-2HG blocks differentiation of malignant cells by inhibiting alpha-ketoglutarate (KG)-dependent enzymes that regulate chromatin structure and gene expression. Small molecule inhibitors of mutant IDH enzymes are promising new therapies for AML, but their efficacy remains limited to the subset of patients with IDH mutations. This raises the question as to whether analogous metabolic aberrations might contribute to leukemogenesis in IDH-wildtype AML. Intriguingly, 2HG is a chiral molecule that can exist in either the D- or L- enantiomer. Although cancer-associated IDH mutants exclusively produce D-2HG, biochemical studies indicate that L-2HG can function as a ~10-fold more potent inhibitor of many KG-dependent enzymes, including chromatin modifiers and regulators of hypoxia-inducible factor (HIF) stability. However, biological sources and activities of L-2HG have been poorly understood. We identified a metabolic pathway wherein normal and malignant cells without IDH mutations selectively produce L-2HG in response to oxygen limitation (a.k.a. hypoxia) through an unusual reaction catalyzed by lactate dehydrogenase (LDHA). We show that hypoxia-induced L-2HG enhances stability of HIF, increases repressive chromatin modifications, and blocks differentiation of stem/progenitor cells. These findings suggest that L-2HG might account, at least in part, for the importance of hypoxic niches, HIF, and LDHA in balancing self-renewal and differentiation of stem cell populations, including hematopoietic stem/progenitor cells (HSPC) and leukemia stem cells. Thus, we hypothesize that L-2HG functions as a metabolic signal that couples hypoxic niches to the maintenance of normal blood stem cells and leukemia stem cells. This hypothesis will be rigorously addressed in three Specific Aims. Aim 1 will define the molecular mechanisms by which L-2HG regulates blood cell differentiation in vitro. In this Aim, we will define the effects of L-2HG on gene expression and chromatin structure and determine how these inputs balance HSPC stemness and lineage differentiation. Aim 2 will determine how L-2HG functions to control normal and malignant hematopoiesis in vivo. This Aim will use novel genetically engineered mouse models that allow for tissue-specific, inducible manipulation of L-2HG levels in order to dissect the role of L-2HG in normal hematopoiesis and leukemia. Aim 3 will elucidate the oncogenic mechanisms and therapeutic potential of L-2HG in human leukemia. In this Aim, we will use primary AML biospecimens and patient-derived xenografts to determine the mechanisms that lead to deregulated L- 2HG in a subset of AML and assess whether depleting L-2HG offers a promising strategy to treat human AML. The proposed studies will offer fundamental insights into the metabolic control of normal and malignant stem cell biology and expand the applicability of metabolic targeted therapies for leukemia and other cancers.