Mechanisms of Hematopoietic Stem Cell Transformation

描述(由申请人提供)：这个项目的总体目标是揭示长期造血干细胞(HSCLT)在疾病条件下如何过度产生特定的成熟血细胞谱系。特别是，我们感兴趣的是确定转化的HSCLT异常产生髓系细胞的机制，以揭示治疗髓系恶性肿瘤(如骨髓增生性肿瘤)的新的分子靶点。这一建议是基于我们实验室目前正在开发的一种新的早期血统规范模型，在该模型中，特定的HSCLT分化途径促进了独立于淋巴系的髓系细胞的产生。我们最近发现了两个新的髓系偏向多能祖细胞(MPP)群体，它们通常作为髓系扩增的暂时性间隔，但在MPN发育过程中异常扩张。我们认为，这种髓系特异的HSCLT分化途径的劫持刺激了MPN中髓系细胞的过度生产，并预测阻断其病理激活可能纠正疾病条件下异常的髓系细胞产生。我们将使用我们在实验室中广泛描述的人类慢性粒细胞白血病(CML)的诱导性SCL-TTA：TRE-BCR/ABL(TTA-BA)小鼠模型来检验这些假设(Reynaud等人，2011年)。基于我们的初步数据和已发表的结果，我们将调查在控制HSCLT命运决定的机制中，细胞内在的去调控，如Notch途径活性受损，如何与骨髓(BM)环境的变化，如促炎细胞因子水平的增加，来推动MPN的发展。在特定的目标1中，我们将阐述HSCLT分化通路的异常激活如何导致髓系扩张，并将剖析Notch信号在这一过程中的作用。在特定的目标2中，我们将研究促炎信号如何在正常和疾病条件下控制HSCLT分化途径，并将探索与Notch信号的潜在串扰。在特定的目标3中，我们将测试通过阻断导致HSCLT分化通路异常激活的机制来操纵HSCLT分化通路是否可以代表一种治疗MPN的有效方法。我们将在小鼠身上进行原理验证实验，并使用正常人类细胞和MPN患者样本来验证关键发现。综上所述，这些方法将揭示早期血统规范的变化如何有助于MPN的发展，并为临床使用基于HSC的抗分化疗法治疗髓系恶性肿瘤提供理论依据。

DESCRIPTION (provided by applicant): The overall goal of this project is to unravel how long-term hematopoietic stem cells (HSCLT) overproduce specific lineages of mature blood cells in disease conditions. In particular, we are interested in identifying the mechanisms responsible for the aberrant production of myeloid cells from transformed HSCLT to uncover novel molecular targets for the treatment of myeloid malignancies such as myeloproliferative neoplasms (MPN). This proposal is based on a novel model of early blood lineage specification we are currently developing in our laboratory in which specific HSCLT differentiation pathways facilitate the production of myeloid cells independently of the lymphoid lineage. We recently discovered two new populations of myeloid-biased multipotent progenitors (MPPs) that normally serve as transient compartments of myeloid amplification but are aberrantly expanded during MPN development. We propose that the hijacking of this myeloid-specific HSCLT differentiation pathway fuels the overproduction of myeloid cells in MPNs, and predict that blockade of its pathological activation may correct aberrant myeloid cell production in disease conditions. We will test these hypotheses using an inducible Scl-tTA:TRE-BCR/ABL (tTA-BA) mouse model of human chronic myelogenous leukemia (CML) that we have extensively characterized in our laboratory (Reynaud et al., 2011). Based on our preliminary data and already published results, we will investigate how cell intrinsic deregulations in the mechanisms controlling HSCLT fate decisions, such as impaired Notch pathway activity, cooperate with changes in the bone marrow (BM) environment, such as increased levels of pro-inflammatory cytokines, to drive MPN development. In Specific Aim 1, we will address how aberrant activation of HSCLT differentiation pathways leads to myeloid expansion, and will dissect the role of Notch signaling in this process. In Specific Aim 2, we will investigate how pro-inflammatory signals control HSCLT differentiation pathways in both normal and disease conditions, and will probe for potential crosstalk with Notch signaling. In Specific Aim 3, we will test whether manipulating HSCLT differentiation pathways by blocking the mechanisms responsible for their aberrant activation could rep- resent a valid approach to treat MPNs. We will perform proof-of-principle experiments in mice and validate key findings using normal human cells and MPN patient samples. Taken together, these approaches will uncover how changes in early blood lineage specification contribute to MPN development, and provide rationales for the clinical use of HSC-based anti-differentiation therapies to treat myeloid malignancies.