Targeting protein acetylation as a therapeutic approach for MDS

项目摘要 骨髓增生异常综合征(MDS)是一种以无效造血为特征的造血疾病， 外周血细胞减少和进展为急性髓系白血病(AML)的倾向。MDS遗骸 现有的非移植疗法无法治愈，这是60岁以上MDS患者的唯一选择。一个 越来越多的克隆分析研究提供了直接证据，表明在MDS中，整个骨骼的细胞 骨髓是从单个造血干细胞(HSC)或早期髓系祖细胞克隆而来。这些 据报道，异常的MDS造血干细胞和祖细胞(HSPC)抵抗治疗并导致 旧病复发。因此，更好地理解管理MDS HSPC维护的机制可以促进 针对MDS HSPC的治疗方法的发展。 DNA去甲基化酶四甲基胞嘧啶双加氧酶2(TET2)保护正常的HSCs 在血液系统恶性肿瘤中从转化为引发疾病的克隆。我们最近发现这种蛋白质 SIRT1的水平，这是一种有助于在应激条件下正常维持HSC的脱乙酰酶， MDS CD34+细胞显著减少，这是MDS HSPC高度浓缩的群体。使用损耗- 功能和诱变研究，我们发现了一种新的机制，即SIRT1缺乏导致TET2 高乙酰化，导致MDS细胞TET2功能障碍。我们还发现SIRT1的激活阻止了MDS 细胞以TET2依赖的方式增殖。重要的是，我们的初步研究还表明，TET2 低于正常SIRT1蛋白表达水平的人MDS标本的乙酰化水平增加。 基于这些发现，我们假设，在没有TET2突变的情况下，SIRT1缺乏会导致 由于不受调控的高乙酰化导致TET2功能障碍，使MDS HSPC得以维持，因此， SIRT1诱导的TET2去乙酰化可抑制MDS HSPC。为了检验我们的假设，我们将：1) 利用遗传小鼠模型确定SIRT1和TET2在MDS维持中的致病作用；2) 确定MDS细胞中SIRT1/TET2轴的上下游因素；以及3)确定 SIRT1单独激活或与目前一线治疗的去甲基化药物联合使用 年龄较大、高风险的MDS患者可以消融MDS HSPC。我们希望我们的研究将发现功能性 SIRT1和TET2之间的相互作用，并揭示这两个因素如何控制MDS HSPC的增长和自我更新。 这些研究将缩小与启动MDS的克隆如何获得增长优势相关的知识差距 在MDS的发展过程中，可能会找到更有效的消融MDS疾病的治疗策略- 通过靶向SIRT1来繁殖细胞。

Project Summary Myelodysplastic syndromes (MDS) are hematopoietic disorders characterized by ineffective hematopoiesis, peripheral cytopenias, and a propensity for progression to acute myeloid leukemia (AML). MDS remains incurable by existing nontransplant therapy, which is the only option for MDS patients over 60 years old. An increasing number of clonal-analysis studies provide direct evidence that, in MDS, cells of the entire bone marrow are clonally derived from a single hematopoietic stem cell (HSC) or early myeloid progenitor. These aberrant MDS hematopoietic stem and progenitor cells (HSPCs) reportedly resist therapy and expand causing relapse. Thus, improved understanding of mechanisms regulating MDS HSPCs maintenance could foster development of therapies targeting MDS HSPCs. The DNA demethylation enzyme Tet methylcytosine dioxygenase 2 (TET2) reportedly protects normal HSCs from transformation into disease-initiating clones in hematological malignancies. We recently found that protein levels of SIRT1, a deacetylase that contributes to normal HSC maintenance under stress conditions, significantly decreased in MDS CD34+ cells, a population highly enriched for MDS HSPCs. Using loss-of- function and mutagenesis studies, we identified a novel mechanism that SIRT1-deficiency induces TET2 hyperacetylation, leading to TET2 dysfunction in MDS cells. We also found that SIRT1 activation blocked MDS cell proliferation in a TET2-dependent manner. Importantly, our preliminary studies also show that TET2 acetylation levels increase in human MDS specimens expressing below normal SIRT1 protein levels. Based on these findings, we hypothesize that, in the absence of TET2 mutations, SIRT1-deficiency induces TET2 dysfunction due to unregulated hyperacetylation, enabling MDS HSPCs maintenance, and accordingly, that SIRT1-induced TET2 deacetylation could ablate MDS HSPCs. To test our hypothesis, we will: 1) determine the pathogenic roles of SIRT1 and TET2 in MDS maintenance using genetic mouse models; 2) define upstream and downstream factors of the SIRT1/TET2 axis in MDS cells; and 3) determine whether SIRT1 activation alone or in combination with a hypomethylating agent that is currently first-line treatment for older, high risk MDS patients can ablate MDS HSPCs. We expect that our studies will uncover functional interaction between SIRT1 and TET2 and reveal how both factors govern MDS HSPC growth and self-renewal. These studies will close the knowledge gap relevant to how MDS-initiating clones acquire a growth advantage during MDS development and may identify more effective therapeutic strategy for ablating MDS disease- propagating cells by targeting SIRT1.