Primary myelofibrosis (PMF) is a myeloproliferative neoplasm (MPN) characterized by clonal myeloproliferation, progressive bone marrow (BM) fibrosis, splenomegaly, and anemia. BM fibrosis was previously thought to be a reactive phenomenon induced by mesenchymal stromal cells that are stimulated by the overproduction of cytokines such as transforming growth factor (TGF)-β1. However, the involvement of neoplastic fibrocytes in BM fibrosis was recently reported. In this study, we showed that the vast majority of collagen- and fibronectin-producing cells in the BM and spleens of Jak2V617F-induced myelofibrosis (MF) mice were fibrocytes derived from neoplastic hematopoietic cells. Neoplastic monocyte depletion eliminated collagen- and fibronectin-producing fibrocytes in BM and spleen, and ameliorated most characteristic MF features in Jak2V617F transgenic mice, including BM fibrosis, anemia, and splenomegaly, while had little effect on the elevated numbers of megakaryocytes and stem cells in BM, and leukothrombocytosis in peripheral blood. TGF-β1, which was produced by hematopoietic cells including fibrocytes, promoted the differentiation of neoplastic monocytes to fibrocytes, and elevated plasma TGF-β1 levels were normalized by monocyte depletion. Collectively, our data suggest that neoplastic fibrocytes are the major contributor to BM fibrosis in PMF, and TGF-β1 is required for their differentiation.
Calreticulin ( CALR ) exon 9 frameshift mutations, commonly detected in essential thrombocythemia (ET) and primary myelofibrosis patients, activate signal transducer and activator of transcription (STAT) proteins in the presence of Myeloproliferative Leukemia Virus (MPL) and induce ET in vivo. Loss of the KDEL motif, an endoplasmic reticulum retention signal, and generation of many positively charged amino acids (AAs) in the mutated C-terminus are thought to be important for disease induction. To test this hypothesis, we generated mice harboring a Calr frameshift mutation using the CRISPR/Cas9 system. Deletion of 19-base pairs in exon 9 (c.1099-1117del), designated the del19 mutation, induced loss of the KDEL motif and generated many positively charged AAs, similar to human mutants. Calr del19 mice exhibited mild thrombocytosis, slightly increased megakaryocytes, and mild splenomegaly. In vitro experiments revealed that the murine CALR del19 mutant had a weaker ability to combine with murine MPL than the human CALR del52 mutant. Consequently, STAT5 activation was also very weak downstream of the murine mutant and murine MPL, and may be the reason for the mild disease severity. In summary, loss of the KDEL motif and positively charged AAs in the C-terminus of CALR is insufficient for MPL binding and ET development.
Mutations in JAK2, MPL, or CALR are detected in more than 80% of myeloproliferative neoplasm (MPN) patients and are thought to play a driver role in MPN pathogenesis via autosomal activation of the JAK-STAT signaling cascade. Mutant CALR binds to MPL, activates downstream MPL signaling cascades, and induces essential thrombocythemia in mice. However, embryonic lethality of Calr-deficient mice precludes determination of a role for CALR in hematopoiesis. To clarify the role of CALR in normal hematopoiesis and MPN pathogenesis, we generated hematopoietic cell-specific Calr-deficient mice. CALR deficiency had little effect on the leukocyte count, hemoglobin levels, or platelet count in peripheral blood. However, Calr-deficient mice showed some hematopoietic properties of MPN, including decreased erythropoiesis and increased myeloid progenitor cells in the bone marrow, and extramedullary hematopoiesis in the spleen. Transplantation experiments revealed that Calr haploinsufficiency promoted the self-renewal capacity of hematopoietic stem cells. We generated CALRdel52 mutant transgenic mice with Calr haploinsufficiency as a model that mimics human MPN patients and found that Calr haploinsufficiency restored the self-renewal capacity of hematopoietic stem cells damaged by CALR mutations. Only recipient mice transplanted with Lineage-Sca1+c-kit+ cells harboring both CALR mutation and Calr haploinsufficiency developed MPN in competitive conditions, showing that CALR haploinsufficiency was required for the onset of CALR-mutated MPNs.
AIMTo evaluate the efficacy and safety of a regimen containing sofosbuvir (SOF) and ledipasvir (LDV) in Japanese patients aged ≥ 75 years with hepatitis C genotype 1.METHODSThis multicenter, retrospective study consisted of 246 Japanese patients with HCV genotype 1 at nine centers in Miyazaki prefecture in Japan. Demographic, clinical, virological, and adverse effects (AE)-related data obtained during and after SOF/LDV therapy were collected from medical records. These patients were divided into two groups, younger (aged < 75 years) and elderly (aged ≥ 75 years). Virological data and AEs were analyzed by age group.RESULTSThe sustained virological response (SVR) rates at 12 wk after treatment were 99.2%, 99.4%, and 98.7% in the overall population and in patients aged < 75 and ≥ 75 years, respectively. Common AEs during therapy were headache, pruritus, constipation, and insomnia. These occurred in fewer than 10% of patients, and their incidence was not significantly different between the younger and elderly groups. Two patients discontinued treatment, one due to a skin eruption and the other due to cerebral bleeding.CONCLUSIONCompared with younger patients, elderly patients had a similar virological response and tolerance to SOF/LDV therapy.
Portal vein thrombosis is a rare, aggressive and life-threatening complication of liver cirrhosis (LC). Eltrombopag is effective for the treatment of chronic hepatitis with thrombocytopenia, and portal vein thrombosis at this time has rarely been reported. We describe the case of a 78-year-old woman who suffered from LC due to hepatitis C viral infection. The patient developed immune thrombocytopenic purpura (ITP) that was diagnosed on the basis of nasal bleeding, progressive severe thrombocytopenia, elevation of platelet-associated IgG (PAIgG), no response to the transfusion of platelets and no abnormal findings on bone marrow biopsy. Although we first administered prednisolone (0.5 mg/kg/day), there was no recovery of platelet function and the nasal bleeding persisted. Subsequently, we administered eltrombopag for refractory ITP at a dose of 12.5 mg/day, and the thrombocytopenia gradually improved. Fifty-four days after the start of eltrombopag therapy, she developed portal vein thrombosis. Eltrombopag was stopped immediately, and antithrombin III was administered for prophylaxis against further portal vein thrombosis. Despite these treatments, there were subsequent deep vein and pulmonary artery thromboses. We then administered heparin for recanalization of the thrombi. One month after the initiation of heparin, there was recanalization as well as improvements of the portal vein, deep vein and pulmonary artery thromboses. There was no further thrombosis progression after switching from heparin to warfarin therapy. Our case suggests that eltrombopag may increase the risk of portal vein thrombosis ; therefore, this drug must be used carefully in the treatment of ITP in patients with LC due to hepatitis C viral infection. 〔J Clin Exp Hematop 53(2) : 151-155, 2013〕
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