Identification of Therapeutic Targets in the Hematopoietic Vascular Niche

骨髓增生性肿瘤(MPN)是以干细胞扩张为特征的克隆性干细胞疾病。 以及成熟血细胞的过度生产。获得性激酶突变JAK2V617F在这些疾病中起着核心作用 疾病，但导致MPN干细胞扩增的确切分子机制尚不完全 理解，限制了当前治疗的有效性。血液学异常 微环境(生态位)开始被认为是生物多样性发展的一个重要因素 包括MPNS在内的恶性血液病。血管内皮细胞(ECs)是 造血龛和大多数造血干细胞位于一个骨髓血窦(“血管”)附近 利基“)。与正常骨髓相比，MPNS患者的特点是骨髓血管生成增加。 在这些患者中可以检测到携带JAK2V617F突变的内皮细胞。我们最近的工作证明了 携带JAK2V617F的血管壁龛不仅促进JAK2V617F突变干细胞的扩增 优先于JAK2WT干细胞，但也保护突变细胞免受致命辐射 骨髓移植的条件作用。干细胞必需的生态位因子CXCL12的水平 与JAK2WT ECs相比，携带JAK2V617F的ECs的维持性和存活率更高。此外, 我们发现，血小板生成素(TPO)及其受体MPL这两个干细胞活性的关键调节因子也是 MPL是MPN干细胞扩增和发育所必需的 携带JAK2V617F的血管壁龛的骨髓增殖性表型。拟议工作的目标 是为了确定JAK2V617F突变的生理效应和分子机制 造血血管壁龛促进MPN干细胞扩增。特别是，我们提出了以下建议 两个特定的目的：目的1)检验JAK2V617F突变改变血管壁龛功能以 促进MPN干细胞扩增和干细胞移植后疾病复发。CXCL12在细胞周期调控中的作用 将确定在MPN中携带JAK2V617F的血管壁龛功能。此外， 将评估JAK2V617F突变对人类血管内皮功能的影响。目的2)检验假设 JAK2V617F突变通过改变TPO/MPL信号改变了MPNS的血管龛功能。这个 这项研究计划的长期目标是确定造血细胞的分子和细胞功能 血管生态位在正常和肿瘤造血中的作用，并开发更有效的治疗策略 适用于患有MPNS和潜在的其他血液系统恶性肿瘤的患者。

The myeloproliferative neoplasms (MPNs) are clonal stem cell disorders characterized by stem cell expansion and overproduction of mature blood cells. The acquired kinase mutation JAK2V617F plays a central role in these disorders, but the precise molecular mechanisms responsible for MPN stem cell expansion are not fully understood, limiting the effectiveness of current treatments. Abnormalities of the hematopoietic microenvironment (niche) are beginning to be recognized as an important factor in the development of hematologic malignancies including MPNs. Endothelial cells (ECs) are an essential component of the hematopoietic niche and most hematopoietic stem cells reside adjacent to a marrow sinusoid (the “vascular niche”). Patients with MPNs are characterized by increased marrow angiogenesis compared to normal marrow and ECs carrying the JAK2V617F mutation can be detected in these patients. Our recent work demonstrated that the JAK2V617F-bearing vascular niche not only promotes the expansion of JAK2V617F-mutant stem cells in preference to JAK2WT stem cells but also protects the mutant cells from lethal irradiation administered during conditioning for marrow transplantation. The levels of CXCL12, an essential niche factor for stem cell maintenance and survival, are increased in JAK2V617F-bearing ECs compared to JAK2WT ECs. In addition, we found that thrombopoietin (TPO) and its receptor MPL, two key regulators of stem cell activity, are also important for the vascular niche function and MPL is essential for MPN stem cell expansion and the development of myeloproliferative phenotype in the JAK2V617F-bearing vascular niche. The objective of the proposed work is to determine the physiological effects and the molecular mechanisms by which the JAK2V617F mutation alters the hematopoietic vascular niche to promote MPN stem cell expansion. In particular, we propose the following two specific aims: Aim 1) To test the hypothesis that the JAK2V617F mutation alters vascular niche function to promote MPN stem cell expansion and disease relapse after stem cell transplantation. The roles of CXCL12 in JAK2V617F-bearing vascular niche function in MPNs will be determined. In addition, the effects of the JAK2V617F mutation on human vascular endothelium function will be assessed. Aim 2) To test the hypothesis that the JAK2V617F mutation changes vascular niche function in MPNs via altered TPO/MPL signaling. The long term goal of this research proposal is to define the molecular and cellular functions of the hematopoietic vascular niche in both normal and neoplastic hematopoiesis, and to develop more effective therapeutic strategies for patients with MPNs and potentially other hematologic malignancies.