Inflammatory Stress Promotes Clonal Expansion of DNMT3A-mutant HSCs

摘要 髓系肿瘤，如骨髓增生异常综合征(MDS)，是由造血干细胞(HSCs)产生的，这些细胞获得了破坏关键HSC功能的基因突变。这些肿瘤中最常见的突变基因之一是从头DNA甲基转移酶DNMT3A。然而，DNMT3A突变可以在HSCs出现临床表现之前很久就发生。最近的研究表明，随着年龄的增长，占主导地位的HSC克隆通常含有髓系肿瘤特有的突变。这种现象被称为不确定潜力克隆性造血(CHIP)，但只有一小部分携带CHIP的人会继续发展为血癌。这表明，除了遗传因素外，一定还有其他因素在选择繁殖带有这些突变的HSCs的个体之间起不同的作用。我们的实验室感兴趣的是识别随着年龄变化的因素，这些因素可能会选择这些突变克隆的副产物，重点是炎症。我们的初步研究表明，诱导干扰素-γ(IFNG)反应的压力会产生一种选择Dnmt3突变的HSC生长的环境。虽然慢性IFNG信号对正常的造血干细胞是有害的，但DNMT3A突变的造血干细胞的功能在这种情况下被保留下来。因此，我们假设慢性IFNG提供了一种选择压力，有利于DNMT3A突变的HSCs作为机制驱动芯片的生长。我们认为，DNMT3A突变的HSC对慢性IFNG暴露的有害影响的抵抗力提供了一种机制，通过这种机制，随着时间的推移，野生型HSC在功能上会受到损害，并随着时间/年龄的推移而耗尽，从而获得克隆优势。鉴于这些具有挑衅性的结果，这项应用的目标是了解(A)DNMT3A突变的HSC抵抗IFNG有害影响的细胞和分子机制，以及(B)这对癌前HSC扩展到病理条件进展的影响。我们提出以下具体目标来解决这些问题； ？干扰素在DNMT3A突变型HSCs克隆扩增中的作用 ？DNMT3A突变型HSCs对IFNG的差异反应机制 ？炎症对DNMT3A突变的HSCs克隆进化的影响 这项工作的总体目标是确定炎症信号促进DNMT3A突变的HSC克隆在骨髓中扩张的机制，这可能为开发特定的干预策略提供理论基础，并对可能更容易出现疾病进展的CHIP个体进行分层。消除或选择性抑制新出现的DNMT3A突变的HSC克隆的方法可能为在突变细胞能够建立克隆显性并进化为疾病之前进行干预提供一个窗口。

ABSTRACT Myeloid neoplasms such as myelodysplastic syndromes (MDS) arise from hematopoietic stem cells (HSCs) that acquire genetic mutations which corrupt critical HSC functions. One of the most recurrently mutated genes in these neoplasms is the de novo DNA methyltransferase enzyme DNMT3A. However, DNMT3A mutations can occur in HSCs long before clinical presentation. Recent studies have shown that the HSC clones that predominate with age often contain mutations that are characteristic of myeloid neoplasms. This phenomenon is known as clonal hematopoiesis of indeterminate potential (CHIP), but only a small fraction of individuals with CHIP go on to develop a blood cancer. This suggests that in addition to genetics, there must be other factors that act differently between individuals which select for propagation of HSCs with these mutations. Our lab is interested in identifying factors that change with age which may select for outgrowth of these mutant clones, focusing on inflammation. Our preliminary studies show that stress which induces interferon gamma (IFNg) responses generates an environment that selects for the outgrowth of Dnmt3amutant HSCs. While chronic IFNg signaling is detrimental to normal HSCs, functionality of Dnmt3a-mutant HSCs is preserved in this setting. Thus, we hypothesize that chronic IFNg provides a selective pressure that favors the outgrowth of DNMT3A-mutant HSCs as a mechanism driving CHIP. We propose the resistance of Dnmt3a-mutant HSCs to the deleterious effects of chronic IFNg exposure presents a mechanism through which they can obtain clonal dominance over time as wild-type HSCs become functionally compromised and depleted over time / age. In light of these provocative results, the goal of this application is to understand (A) the cellular and molecular mechanisms through which Dnmt3a-mutant HSCs are resistant to the deleterious effects of IFNg, and (B) the impact of this for progression of pre-malignant HSC expansion to pathological conditions. We propose the following Specific Aims to address these questions; ? The role of IFNg in clonal expansion of Dnmt3a-mutant HSCs ? Mechanisms underlying the differential response of Dnmt3a-mutant HSCs to IFNg ? The impact of inflammation on clonal evolution of Dnmt3a-mutant HSCs The overall goal of this work is to determine the mechanisms by which inflammatory signals promote expansion of Dnmt3a-mutant HSC clones in the bone marrow, which could provide a rationale for development of specific intervening strategies and stratify individuals with CHIP who may be more “at-risk” for disease progression. Approaches to eliminate or selectively inhibit emerging DNMT3A-mutant HSC clones may provide a window for intervention before the mutant cells are able to establish clonal dominance and evolve to disease.