Role of the JAK2V617F mutation in the pathophysiology of thrombosis in myeloproliferative diseases

Janus激酶JAK 2（JAK 2 V617 F）的散发性突变Val 617 Phe与Bcr/Bcr阴性骨髓增生性疾病（MPD）相关：真性红细胞增多症（PV）、原发性血小板增多症（ET）和原发性骨髓纤维化（PMF）。这些是克隆性造血干细胞疾病，其特征在于特定造血谱系（PV中的红细胞、ET中的巨核细胞以及PMF中的粒细胞和巨核细胞）的增殖，而不阻断细胞成熟。JAK 2 V617 F是一种导致生长因子超敏反应的功能获得性突变，已在大多数PV患者和约60%的ET和PMF患者中检测到。血栓形成在约30%的患者中显示出MPD，并且是发病率和死亡率的主要原因。高达40%的ET和PV患者发生血栓形成。缺血性卒中比急性冠状动脉综合征和外周动脉疾病更常见。静脉血栓形成的发生率也随着内脏静脉血栓形成（即消化血管床的）的特别高的频率而增加。MPD血栓形成素质的潜在机制仍然很难理解。怀疑血小板和内皮细胞特性受损，但迄今尚未证实。临床研究确定高龄、既往血栓形成史、白细胞增多和JAK 2 V617 F状态是MPD患者血栓形成的风险因素。JAK 2 V617 F对MPD患者血小板功能的影响的直接评估受到突变克隆的异质性延伸和频繁使用血栓预防性治疗的限制。由于缺乏组织样本，很难对MPD中的内皮细胞进行广泛的研究。最近描述的小鼠模型中，JAK 2 V617 F表达是诱导型和组织特异性提供了一个有吸引力的替代方案，以确定这种突变对止血functions. Aim的影响我们的项目是阐明JAK 2 V617 F有利于动脉，静脉和微循环血栓形成的具体机制。该策略基于使用表达JAK 2 V617 F的培养细胞、JAK 2 V617 F患者的血液和血管样本以及几种转基因小鼠模型。已经确定了五项任务：（1）确定JAK 2 V617 F在患者中的细胞定位和表型结果;（2）分析JAK 2 V617 F的体外功能结果;（3）使用不同的小鼠血栓形成模型评估JAK 2 V617 F的体内功能结果并确定所涉及的精确机制;（4）评估JAK 2 V617 F在凝血激活中的潜在作用;（5）通过确定最近发现的钙网蛋白（CALR）突变在患有肝或门静脉血栓形成的患者中的患病率以及携带该突变的新的遗传修饰小鼠的发展来准备未来的研究。这可能会导致新的治疗方法和MPD患者血栓形成风险的标志物的识别。

The sporadic mutation Val617Phe of the Janus kinase JAK2 (JAK2V617F) is associated with the Bcr/Abl-negative myeloproliferative disorders (MPDs): polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF). These are clonal hematopoietic stem cell disorders characterized by the proliferation of particular hematopoietic lineages (erythroid in PV, megakaryocytic in ET, and granulocytic and megakaryocytic in PMF) without blockage in cell maturation. JAK2V617F is a gain of function mutation leading to growth factors hypersensitivity and has been detected in most PV patients and in ~60% of ET and PMF patients. Thrombosis reveals MPD in about 30% of patients and is a major cause of morbidity and mortality. Up to 40% of ET and PV patients develop thrombosis. Ischemic stroke is more frequent than acute coronary syndrome and peripheral artery disease. Incidence of vein thrombosis is also increased with a particularly high frequency of splanchnic vein thrombosis (i.e. of the digestive vascular bed). The mechanisms underlying the MPD thrombotic diathesis are still largely elusive. Impairment of platelet and endothelial cell properties is suspected but so far not demonstrated. Clinical studies identified advanced age, prior history of thrombosis, leukocytosis and the JAK2V617F status as risk factors for thrombosis in MPD patients. The direct assessment of the effect of JAK2V617F on platelet function in MPD patients is limited by the heterogeneous extension of the mutant clone and the frequent use of prophylactic treatment for thrombosis. An extensive study of endothelial cells in MPDs is difficult to achieve due to the scarcity of tissue samples. The recently described mouse models in which JAK2V617F expression is inducible and tissue-specific offer an attractive alternative to determine the impact of this mutation on haemostatic functions.The aim of our project is to elucidate the specific mechanisms by which JAK2V617F favours arterial, venous and microcirculatory thrombosis. The strategy is based on the use of cultured cells expressing JAK2V617F, of blood and vascular samples from patients with JAK2V617F and on several transgenic mouse models. Five tasks have been identified: (1) determine the cellular localization and phenotypic consequences of JAK2V167F in patients; (2) analyse functional consequences of JAK2V617F in vitro; (3) assess the functional consequences of JAK2V617F using different mouse models of thrombosis in vivo and determine the precise mechanisms involved; (4) evaluate the potential role of JAK2V617F in the activation of coagulation; (5) prepare future studies by determining the prevalence of the very recently discovered calreticulin (CALR) mutations in patients with thrombosis of hepatic or portal vein and development of new genetically modified mice harbouring this mutation. This could lead to the identification of new therapeutic approaches and of markers for thrombotic risk in MPD patients.