Hsieh Pin-Pen, Olsen Randy J, O'Malley Dennis P, Konoplev Sergej N, Hussong Jerry W, Dunphy Cherie H, Perkins Sherrie L, Cheng Liang, Lin Pei, Chang Chung-Che
Department of Pathology and Laboratory Medicine, The Methodist Hospital and the Methodist Hospital Research Institute, Houston, TX 77030, USA.
Mod Pathol. 2007 Sep;20(9):929-35. doi: 10.1038/modpathol.3800826. Epub 2007 Jul 20.
Extramedullary hematopoiesis (EMH) in the spleen is a characteristic feature of the chronic myeloproliferative disorders (CMPDs) and various other neoplastic or reactive myeloid conditions. However, the origin of these hematopoietic precursor cells and the molecular mechanisms underlying their development in the spleen is uncertain. The V617F mutation in the Janus Kinase 2 gene (JAK2(V617F)) was recently shown to be frequently and preferentially present in the peripheral blood and bone marrow cells of CMPD patients, and the resulting dysregulation of its downstream targets is important to CMPD pathogenesis. To determine the occurrence and potential role of JAK2(V617F) in splenic EMH cells, we studied splenectomy specimens from 47 patients with significant EMH. JAK2(V617F) was detected by real-time PCR melting curve analysis in 22 specimens, including 11/17 chronic idiopathic myelofibrosis, 7/7 polycythemia vera, 1/1 essential thrombocythemia, 1/3 CMPD unclassifiable, 1/5 chronic myelomonocytic leukemia, 0/5 chronic myelogenous leukemia, 1/3 myelodysplastic syndrome and 0/6 acute myeloblastic leukemia cases, whereas only the JAK2 wild-type allele was detected in the other 25. Nineteen of 20 cases with adequate bone marrow samples available for molecular examination demonstrated concordant JAK2 genotypes. Laser-capture microdissection was then used to enrich the EMH and non-EMH splenic cell fractions, confirming that the mutant alleles specifically originated from the EMH cells. Furthermore, megakaryocytes in the JAK2(V617F)-positive splenectomy specimens expressed higher levels of Bcl-xL, an antiapoptotic protein and downstream target of the JAK2/STAT5 pathway. Thus, JAK2(V617F) is frequently present in splenic EMH cells associated with CMPD, but it is rarely identified in splenic EMH cells associated with other myeloid disorders. Our results indicate that the precursor cells leading to extramedullary hematopoietic expansion in CMPD most likely originate from the transformed bone marrow clone. Also, dysregulation of downstream pathways such as Bcl-xL may be important to CMPD disease pathogenesis in the spleen.
脾脏中的髓外造血（EMH）是慢性骨髓增殖性疾病（CMPD）以及其他各种肿瘤性或反应性髓系疾病的一个特征性表现。然而，这些造血前体细胞的起源及其在脾脏中发育的分子机制尚不清楚。最近研究表明，Janus激酶2基因（JAK2(V617F)）中的V617F突变频繁且优先存在于CMPD患者的外周血和骨髓细胞中，其下游靶点的失调对CMPD发病机制至关重要。为了确定JAK2(V617F)在脾脏EMH细胞中的发生情况及其潜在作用，我们研究了47例有显著EMH的患者的脾切除标本。通过实时PCR熔解曲线分析在22个标本中检测到JAK2(V617F)，其中包括11/17例慢性特发性骨髓纤维化、7/7例真性红细胞增多症、1/1例原发性血小板增多症、1/3例无法分类的CMPD、1/5例慢性粒单核细胞白血病、0/5例慢性粒细胞白血病、1/3例骨髓增生异常综合征和0/6例急性髓细胞白血病病例，而在其他25个标本中仅检测到JAK2野生型等位基因。在20例有足够骨髓样本可进行分子检测的病例中，有19例显示JAK2基因型一致。然后使用激光捕获显微切割技术富集脾脏EMH和非EMH细胞组分，证实突变等位基因特异性起源于EMH细胞。此外，JAK2(V617F)阳性脾切除标本中的巨核细胞表达更高水平的Bcl-xL，Bcl-xL是一种抗凋亡蛋白，也是JAK2/STAT5途径的下游靶点。因此，JAK2(V617F)频繁存在于与CMPD相关的脾脏EMH细胞中，但在与其他髓系疾病相关的脾脏EMH细胞中很少发现。我们的结果表明，导致CMPD中髓外造血扩张的前体细胞很可能起源于转化的骨髓克隆。此外，诸如Bcl-xL等下游途径的失调可能对脾脏中CMPD疾病的发病机制很重要。
