Mechanisms of Hematopoietic Stem Cell Transformation

描述（由申请人提供）：该项目的总体目标是揭示长期造血干细胞（HSCLT）如何在疾病条件下过量产生特定的成熟血细胞谱系。我们特别感兴趣的是确定从转化的HSCLT中异常产生髓系细胞的机制，以发现治疗髓系恶性肿瘤（如骨髓增生性肿瘤（MPN））的新分子靶点。这一建议是基于我们目前正在实验室开发的早期血液谱系规范的新模型，其中特定的HSCLT分化途径促进了独立于淋巴谱系的髓系细胞的产生。我们最近发现了两个新的髓偏多能祖细胞（mpp）群体，它们通常作为髓系扩增的短暂区室，但在MPN发育过程中异常扩增。我们提出，劫持这种髓细胞特异性HSCLT分化途径促进了mpn中髓细胞的过度产生，并预测其病理激活的阻断可能纠正疾病条件下异常的髓细胞产生。我们将使用人类慢性粒细胞白血病（CML）的诱导型Scl-tTA:TRE-BCR/ABL （tTA-BA）小鼠模型来验证这些假设，我们在实验室中对该模型进行了广泛的表征（Reynaud et al., 2011）。基于我们的初步数据和已经发表的结果，我们将研究控制HSCLT命运决定机制中的细胞内在失调，如Notch通路活性受损，如何与骨髓（BM）环境的变化（如促炎细胞因子水平升高）合作，推动MPN的发展。在Specific Aim 1中，我们将讨论异常激活HSCLT分化途径如何导致髓细胞扩张，并剖析Notch信号在这一过程中的作用。在Specific Aim 2中，我们将研究促炎信号在正常和疾病条件下如何控制HSCLT分化途径，并将探索与Notch信号的潜在串扰。在Specific Aim 3中，我们将测试通过阻断导致HSCLT异常激活的机制来操纵HSCLT分化途径是否可以代表一种治疗mpn的有效方法。我们将在小鼠中进行原理验证实验，并使用正常人类细胞和MPN患者样本验证关键发现。综上所述，这些方法将揭示早期血液谱系规范的变化如何促进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.