IEX-1 as a potential biomarker for early detection of myelodysplastic syndromes

描述(由申请人提供)：本提案的总体目标是确定IEX-1(即时早期反应基因X-1)作为早期诊断骨髓增生异常综合征(MDS)或其进展为急性髓系白血病(AML)的生物标志物的潜力。MDS是一种造血干细胞(HSCs)的克隆性疾病，可能是由于控制HSCs分化、自我更新或增殖的基因突变积累所致。MDS患者HSCs异常高频率的基因改变可能部分归因于导致DNA突变的活性氧物种(ROS)的产生增加，这反过来可能导致获得额外的基因组变化和ROS形成。IEX-1通过靶向降解线粒体FoF1-ATP合酶抑制物(IF1)，参与调节线粒体ROS生成和氧化磷酸化之间的平衡。IEX-1的过度表达降低了IF1的表达水平，伴随着ROS产生的减少，保护细胞免受线粒体依赖的凋亡的影响。相反，IEX-1零突变稳定了IF1的表达，增加了细胞对凋亡的敏感性。根据IEX-1在HSCs存活和分化中的作用，IEX-1缺陷的HSCs表现出较高的凋亡率和增殖率，但其代谢率下降。此外，最近的一些研究表明，半数以上的MDS患者中IEX-1的表达存在下调，并且这种下调与疾病的进展和患者CD34+干细胞的凋亡水平有关。基于这些观察，我们假设IEX-1表达的放松对MDS的发展及其向AML的进展有重要贡献。我们将通过长期竞争性再种群分析来检验这一假说，以确定IEX-1是否或如何通过自主或外部方式促进MDS的发展。然后对重组的小鼠进行抗氧化剂处理，以恢复HSCs的自我更新能力。在目标2中，我们将把IEX-1基因敲除(KO)小鼠暴露在提供“二次打击”的放射或化疗中，使它们更容易受到放射或化疗诱导的DNA突变，从而发展成MDS/AML。治疗后IEX-1 KO小鼠对MDS/AML易感性的增加将表明IEX-1是导致HSC基因组不稳定的“多重打击”之一，因此可作为判断髓系疾病预后的生物标志物。这项研究还可能为疾病发展的机制提供新的见解，并有助于开发新的预防策略。

DESCRIPTION (provided by applicant): The overall objective of this proposal is to determine a potential of IEX-1 (Immediate Early responsive gene X-1) as a biomarker for the early diagnosis of myelodysplastic syndromes (MDS) or its progression to acute myeloid leukemia (AML). MDS is a clonal disorder of hematopoietic stem cells (HSCs) presumably resulting from the accumulation of mutations in genes that control the differentiation, self-renewal, or proliferation of HSCs. An unusual high frequency of genetic alterations in HSCs in MDS patients may be ascribed in part to increased production of reactive oxygen species (ROS) that causes DNA mutations, which could in turn lead to acquisition of additional genomic changes and ROS formation. IEX-1 takes part in regulating a balance between ROS generation and oxidative phosphorylation in mitochondria by targeting the inhibitor of mitochondrial FoF1-ATP synthase (IF1) to degradation. Over-expression of IEX-1 reduced the level of IF1 expression, concomitant with diminished ROS production, protecting cells from mitochondrion-dependent apoptosis. On the contrary, null mutation of IEX-1 stabilized IF1 expression and increased the susceptibility of cells to apoptosis. In accordance with a role of IEX-1 in the survival and differentiation of HSCs, IEX-1 deficient HSCs exhibited a high rate of apoptosis and proliferation but a decrease in their generation. Moreover, several studies recently showed that IEX-1 expression was deregulated in more than half of patients with MDS and the deregulation was correlated with the progression of the disease and the apoptosis level in CD34+ stem cells in the patients. Based on these observations, we hypothesize that deregulation of IEX-1 expression contributes significantly to the development of MDS and its progression to AML. We will test this hypothesis by long term competitive repopulation assays so as to determine whether or how IEX-1 contributes to MDS development via an autonomous or extrinsic fashion. The reconstituted mice will be then treated with anti-oxidant to restore the self-renewal capacity of HSCs. In aim 2, we will expose IEX-1 knockout (KO) mice to radiation or chemotherapy that offers a "second hit", rendering them more susceptible to radiation- or chemotherapy-induced DNA mutations and thus MDS/AML development. An increase in the susceptibility of IEX-1 KO mice to MDS/AML after the treatment will suggest that IEX-1 is one of the "multiple hits" causing the genomic instability in HSCs and can be thus used as a biomarker for the prognosis of myeloid disorders. The study may also provide new insights into the mechanism for the disease development and help to develop novel strategies to prevent it.