Investigating the role of ARC in hematopoiesis and myeloproliferative neoplasms

描述（由申请人提供）：在造血过程中，造血干细胞（hsc）的后代开始沿着特定的细胞系分化，最终获得成熟的终末分化细胞的特征。在过去的几十年里，造血干细胞的鉴定和分离已经取得了很大的进展，然而，调节干细胞谱系承诺和分化的机制仍然不清楚。程序性细胞死亡在正常造血分化的调节中起着至关重要的作用，而这一细胞过程在血液恶性肿瘤中经常发生改变。在费城染色体阴性骨髓增殖性肿瘤（Ph- MPN）中，经常观察到细胞死亡途径的失调，暗示细胞死亡蛋白是导致肿瘤发生的潜在因素

DESCRIPTION (provided by applicant): During hematopoiesis, descendants of hematopoietic stem cells (HSCs) become committed to differentiate along specific cell lineages, eventually acquiring the characteristics of mature terminally differentiated cells. The identification and isolation of HSCs has advanced substantially over the past few decades, however, the mechanisms that regulate stem cell lineage commitment and differentiation are still obscure. Programmed cell death plays a crucial role in the regulation of normal hematopoietic differentiation, and this cellular process is frequently altered in hematologic malignancies. In Philadelphia chromosome negative myeloproliferative neoplasms (Ph- MPN), dysregulation of cell death pathways is frequently observed, implicating cell death proteins as potential factors in the pathogenesis of disease and targets for therapeutic intervention. Currently the molecular pathogenesis of Ph- MPNs is largely unknown. Recent studies have highlighted the importance of the anti-apoptotic protein apoptosis repressor with caspase recruitment domain (ARC) in human malignancies, however, the function of ARC in normal and malignant hematopoiesis has not been thoroughly investigated. Our work aims to identify the role of ARC in mouse and human hematopoietic stem and progenitor cells (HSPCs), and in the Ph- MPN primary myelofibrosis (PMF). Utilizing an ARC knockout (ARC [-/-]) mouse model for our investigation, we have found that aged ARC [-/-] mice exhibit significantly altered blood cell counts and splenomegaly with an expansion of myeloid and immature cells consistent with extramedullary hematopoiesis. ARC [-/-] bone marrow revealed reduced blood sinusoids and increased bone marrow fibrosis according to reticulin staining. Further analysis showed expansion of the bone marrow HSC compartment and in vitro methylcellulose colony assays revealed altered HSC differentiation capacity. The hematologic findings in ARC [-/-] mice are consistent with a novel mouse model of PMF. Additionally, the ARC [-/-] phenotype is transplantable into lethally irradiated congenic recipients. We hypothesize that ARC plays a critical role in mouse and human HSPC function and that loss of ARC may contribute to the pathogenesis of PMF. To characterize ARC in lineage commitment and differentiation of mouse and human HSPCs, we will utilize genetic murine models, stem cell transplantation, in vitro stem cell functional assays and in vivo xenotransplantation experiments. To elucidate the mechanism of ARC in HSCs, we will use transcriptional profiling to guide our investigation and identify molecular pathways critical to ARC function. Furthermore, we will quantitate ARC transcript levels in HSCs from patients with PMF to determine if ARC expression is relevant to the disease pathogenesis. PMF has the most severe morbidity and greatest mortality of the Ph-MPNs and the identification of novel mouse models and potential therapeutic targets is urgently required.