Search

Abstract Background Neutrophils play a crucial role in inflammation and in the increased thrombotic risk in myeloproliferative neoplasms (MPNs). We have investigated how neutrophil-specific expression of JAK2-V617F or CALRdel re-programs the functions of neutrophils. Methods Ly6G-Cre JAK2-V617F and Ly6G-Cre CALRdel mice were generated. MPN parameters as blood counts, splenomegaly and bone marrow histology were compared to wild-type mice. Megakaryocyte differentiation was investigated using lineage-negative bone marrow cells upon in vitro incubation with TPO/IL-1β. Cytokine concentrations in serum of mice were determined by Mouse Cytokine Array. IL-1α expression in various hematopoietic cell populations was determined by intracellular FACS analysis. RNA-seq to analyse gene expression of inflammatory cytokines was performed in isolated neutrophils from JAK2-V617F and CALR-mutated mice and patients. Bioenergetics of neutrophils were recorded on a Seahorse extracellular flux analyzer. Cell motility of neutrophils was monitored in vitro (time lapse microscopy), and in vivo (two-photon microscopy) upon creating an inflammatory environment. Cell adhesion to integrins, E-selectin and P-selection was investigated in-vitro. Statistical analysis was carried out using GraphPad Prism. Data are shown as mean ± SEM. Unpaired, two-tailed t-tests were applied. Results Strikingly, neutrophil-specific expression of JAK2-V617F, but not CALRdel, was sufficient to induce pro-inflammatory cytokines including IL-1 in serum of mice. RNA-seq analysis in neutrophils from JAK2-V617F mice and patients revealed a distinct inflammatory chemokine signature which was not expressed in CALR-mutant neutrophils. In addition, IL-1 response genes were significantly enriched in neutrophils of JAK2-V617F patients as compared to CALR-mutant patients. Thus, JAK2-V617F positive neutrophils, but not CALR-mutant neutrophils, are pathogenic drivers of inflammation in MPN. In line with this, expression of JAK2-V617F or CALRdel elicited a significant difference in the metabolic phenotype of neutrophils, suggesting a stronger inflammatory activity of JAK2-V617F cells. Furthermore, JAK2-V617F, but not CALRdel, induced a VLA4 integrin-mediated adhesive phenotype in neutrophils. This resulted in reduced neutrophil migration in vitro and in an inflamed vessel. This mechanism may contribute to the increased thrombotic risk of JAK2-V617F patients compared to CALR-mutant individuals. Conclusions Taken together, our findings highlight genotype-specific differences in MPN-neutrophils that have implications for the differential pathophysiology of JAK2-V617F versus CALR-mutant disease.

Background: Neutrophils play a crucial role in inflammation and in the increased thrombotic risk in myeloproliferative neoplasms (MPNs). We have investigated how neutrophil-specific expression of JAK2-V617F or CALRdel re-programs the functions of neutrophils. Methods: Ly6G-Cre JAK2-V617F and Ly6G-Cre CALRdel mice were generated. MPN parameters as blood counts, splenomegaly and bone marrow histology were compared to wild-type mice. Megakaryocyte differentiation was investigated using lineage-negative bone marrow cells upon in vitro incubation with TPO/IL-1β. Cytokine concentrations in serum of mice were determined by Mouse Cytokine Array. IL-1α expression in various hematopoietic cell populations was determined by intracellular FACS analysis. RNA-seq to analyse gene expression of inflammatory cytokines was performed in isolated neutrophils from JAK2-V617F and CALR-mutated mice and patients. Bioenergetics of neutrophils were recorded on a Seahorse extracellular flux analyzer. Cell motility of neutrophils was monitored in vitro (time lapse microscopy), and in vivo (two-photon microscopy) upon creating an inflammatory environment. Cell adhesion to integrins, E-selectin and P-selection was investigated in-vitro. Statistical analysis was carried out using GraphPad Prism. Data are shown as mean ± SEM. Unpaired, two-tailed t-tests were applied. Results: Strikingly, neutrophil-specific expression of JAK2-V617F, but not CALRdel, was sufficient to induce pro-inflammatory cytokines including IL-1 in serum of mice. RNA-seq analysis in neutrophils from JAK2-V617F mice and patients revealed a distinct inflammatory chemokine signature which was not expressed in CALR-mutant neutrophils. In addition, IL-1 response genes were significantly enriched in neutrophils of JAK2-V617F patients as compared to CALR-mutant patients. Thus, JAK2-V617F positive neutrophils, but not CALR-mutant neutrophils, are pathogenic drivers of inflammation in MPN. In line with this, expression of JAK2-V617F or CALRdel elicited a significant difference in the metabolic phenotype of neutrophils, suggesting a stronger inflammatory activity of JAK2-V617F cells. Furthermore, JAK2-V617F, but not CALRdel, induced a VLA4 integrin-mediated adhesive phenotype in neutrophils. This resulted in reduced neutrophil migration in vitro and in an inflamed vessel. This mechanism may contribute to the increased thrombotic risk of JAK2-V617F patients compared to CALR-mutant individuals. Conclusions: Taken together, our findings highlight genotype-specific differences in MPN-neutrophils that have implications for the differential pathophysiology of JAK2-V617F versus CALR-mutant disease. [ABSTRACT FROM AUTHOR]

Imetelstat shows activity in patients with myeloproliferative neoplasms, including primary myelofibrosis (PMF) and essential thrombocythemia. Here, we describe a case of prolonged disease stabilization by imetelstat treatment of a high-risk PMF patient enrolled into the clinical study MYF2001. We confirmed continuous shortening of telomere length (TL) by imetelstat treatment but observed emergence and expansion of a KRAST58I mutated clone during the patient’s clinical course. In order to investigate the molecular mechanisms involved in the imetelstat treatment response, we generated induced pluripotent stem cells (iPSC) from this patient. TL of iPSC-derived hematopoietic stem and progenitor cells, which was increased after reprogramming, was reduced upon imetelstat treatment for 14 days. However, while imetelstat reduced clonogenic growth of the patient’s primary CD34+ cells, clonogenic growth of iPSC-derived CD34+ cells was not affected, suggesting that TL was not critically short in these cells. Also, the propensity of iPSC differentiation toward megakaryocytes and granulocytes was not altered. Using human TF-1MPL and murine 32DMPL cell lines stably expressing JAK2V617F or CALRdel52, imetelstat-induced reduction of viability was significantly more pronounced in CALRdel52 than in JAK2V617F cells. This was associated with an immediate downregulation of JAK2 phosphorylation and downstream signaling as well as a reduction of hTERT and STAT3 mRNA expression. Hence, our data demonstrate that imetelstat reduces TL and targets JAK/STAT signaling, particularly in CALR-mutated cells. Although the exact patient subpopulation who will benefit most from imetelstat needs to be defined, our data propose that CALR-mutated clones are highly vulnerable. [ABSTRACT FROM AUTHOR]

Essential thrombocythemia (ET) is a blood cancer. ET is characterized by an overproduction of platelets that can lead to thrombosis formation. Platelet overproduction occurs in megakaryocytes through a signaling pathway that could involve JAK2, MPL, or CALR proteins. CALR mutations are associated with 25–30% of ET patients; CALR variants must be dimerized to induce ET. We classified these variants into five classes named A to E; classes A and B are the most frequent classes in patients with ET. The dynamic properties of these five classes using structural models of CALR's C-domain were analyzed using molecular dynamics simulations. Classes A, B, and C are associated with frameshifts in the C-domain. Their dimers can be stable only if a disulfide bond is formed; otherwise, the two monomers repulse each other. Classes D and E cannot be stable as dimers due to the absence of disulfide bonds. Class E and wild-type CALR have similar dynamic properties. These results suggest that the disulfide bond newly formed in classes A, B, and C may be essential for the pathogenicity of these variants. They also underline that class E cannot be directly related to ET but corresponds to human polymorphisms. [ABSTRACT FROM AUTHOR]

Essential thrombocythemia (ET) is a blood cancer. ET is characterized by an overproduction of platelets that can lead to thrombosis formation. Platelet overproduction occurs in megakaryocytes through a signaling pathway that could involve JAK2, MPL, or CALR proteins. CALR mutations are associated with 25–30% of ET patients; CALR variants must be dimerized to induce ET. We classified these variants into five classes named A to E; classes A and B are the most frequent classes in patients with ET. The dynamic properties of these five classes using structural models of CALR’s C-domain were analyzed using molecular dynamics simulations. Classes A, B, and C are associated with frameshifts in the C-domain. Their dimers can be stable only if a disulfide bond is formed; otherwise, the two monomers repulse each other. Classes D and E cannot be stable as dimers due to the absence of disulfide bonds. Class E and wild-type CALR have similar dynamic properties. These results suggest that the disulfide bond newly formed in classes A, B, and C may be essential for the pathogenicity of these variants. They also underline that class E cannot be directly related to ET but corresponds to human polymorphisms.

Abstract Background Calreticulin (CALR) gene mutations are currently recommended as biomarkers in diagnosis of patients with myeloproliferative neoplasms (MPN) with Jak2 V617F negative phenotype. Our aim was to establish a rapid, low cost and sensitive assay for identification of CALR gene mutations and to validate the diagnostic performance of the established assay in a patient cohort with different clinical MPN phenotypes. Methods One hundred five Philadelphia-negative MPN patients, including polycythemia vera (PV), essential thrombocythaemia (ET), and primary myelofibrosis (PMF) were initially screened for JAK2 mutations by amplification-refractory mutation system (ARMS-PCR) methodology and were further subjected to detection of CALR gene mutations by our in-house assay, a PCR based amplicon length differentiation assay (PCR-ALDA). The PCR-ALDA methodology was compared with real time PCR and Sanger sequencing methods. Furthermore, the analytical sensitivity of the assay was established. Results PCR - ALDA approach was able to detect and discriminate the pseudo-positive samples containing more than 1% CALR mutant alleles. CALR mutations were not detected in 63 Jak2 V617F positive cases in all three methods. In contrast, amongst 42 Jak2 V617F negative cases, both PCR-ALDA and Sanger sequencing coherently identified 12 CALR mutants compared to 10 CALR mutants detected by real-time PCR method. Conclusion PCR-ALDA can be utilized as an easy-to-use, rapid, low cost and sensitive tool in the detection of CALR mutations in Philadelphia-negative MPN patients.

The article presents the study of three screening methods for the detection of calreticulin gene mutations. Topics include the detection of calreticulin (CALR) gene mutations for the diagnosis of Philadelphia‐chromosome negative chronic Myeloproliferative Neoplasms (Ph‐MPNs) by comparing several diagnostic methods, and first screening test for all patients was fragment analysis, and the samples resulted positive for mutations has subjected to Sanger sequencing.

Background and Aims Myeloproliferative neoplasms (MPN) are the leading cause of splanchnic vein thrombosis (SVT). Janus kinase 2 gene ( JAK2 ) V617F mutations are found in 80 to 90% of patients with SVT and MPN. Mutations of the calreticulin ( CALR ) gene have also been reported. However, as their prevalence ranges from 0 to 2%, the utility of routine testing is questionable. This study aimed to identify a group of patients with SVT at high risk of harboring CALR mutations and thus requiring this genetic testing. Methods CALR , JAK2 V617F and thrombopoietin receptor gene ( MPL ) mutations were analysed in a test cohort that included 312 patients with SVT. Criteria to identify patients at high risk of CALR mutations in this test cohort was used and evaluated in a validation cohort that included 209 patients with SVT. Results In the test cohort, 59 patients had JAK2 V617F , five had CALR and none had MPL mutations. Patients with CALR mutations had higher spleen height and platelet count than patients without these mutations. All patients with CALR mutations had a spleen height ⩾16 cm and platelet count >200×10 9 /L. These criteria had a positive predictive value of 56% (5/9) and a negative predictive value of 100% (0/233) for the identification of CALR mutations. In the validation cohort, these criteria had a positive predictive value of 33% (2/6) and a negative predictive value of 99% (1/96). Conclusion CALR mutations should be tested in patients with SVT, a spleen height ⩾16 cm, platelet count >200×10 9 /L, and no JAK2 V617F . This strategy avoids 96% of unnecessary CALR mutations testing. Lay summary: Mutations of the CALR gene are detected in 0 to 2% of patients with SVT, thus the utility of systematic CALR mutation testing to diagnose MPN is questionable. This study demonstrates that CALR mutations testing can be restricted to patients with SVT, a spleen height ⩾16 cm, a platelet count >200×10 9 /L, and no JAK2 V617F . This strategy avoids 96% of unnecessary CALR mutations testing. [ABSTRACT FROM AUTHOR]

The molecular landscape of patients with myelofibrosis (MF) includes 'phenotypic driver' and 'subclonal' mutations. The three driver ( JAK2, MPL and CALR)-mutated genes currently represent major diagnostic criteria, unlike subclonal mutations that are not specific for the disease and occur in other myeloid neoplasms. Recent data indicate that selected mutations deserve prognostic significance allowing to identify categories of patients with different survival and risk of leukemia. This review focuses on current knowledge regarding genotype-prognostic correlates in MF, however, with the understanding that this is a rapid moving field and no definite recommendations for the clinicians can be done yet. [ABSTRACT FROM AUTHOR]

Résumé Les syndromes myéloprolifératifs « non LMC » comprennent la polyglobulie de Vaquez (PV), la thrombocytémie essentielle (TE) et la myélofibrose primitive (MFP). La PV et la TE sont des maladies d’évolution lente alors que la MFP est une maladie plus sévère. À terme, la gravité des SMP est liée au risque d’évolution vers une transformation hématologique et, initialement, la morbidité est liée aux complications vasculaires. La découverte de la mutation V617F de JAK2 a amélioré les connaissances sur la physio-pathologie des SMP et en a modifié le diagnostic. La mise en évidence des mutations de CALR et de MPL permet, à l’heure actuelle, de disposer d’un marqueur moléculaire dans 90% des cas. Avec le développement du séquençage de nouvelle génération, d’autres mutations sont détectées dont le rôle est encore mal connu, mais qui sont parfois associées à un pronostic péjoratif. Dix ans après JAK2 V617F, et avec l’arrivée des thérapies ciblées, l’identification des patients avec un mauvais pronostic est un des enjeux dans les SMP. Summary Philadelphia negative myeloproliferative neoplasms (MPN) include polycythemia vera (PV), essential thrombocythemia (ET) and primary myelofibrosis (PMF). PV and ET are very chronic diseases while MFP is a more severe one. Long-term prognosis of MPN is related to the risk of hematologic transformation, but initial morbidity is mainly related to vascular complications. The discovery of the JAK2 V617F mutation has improved our knowledge on the pathophysiology of MPN and has changed diagnosis algorithms. With the recent discovery of CALR and MPL mutations, a molecular marker is currently found in 90% of cases. With the development of next-generation sequencing, other mutations are detected whose role is still poorly known, but which may be associated with a poor prognosis. Ten years after JAK2 V617F, and in the targeted therapies era, the identification of poor prognosis patients is one of the challenges in MPN. [ABSTRACT FROM AUTHOR]

The article discusses CALR exon 9 mutational analysis into the molecular diagnostic algorithm for various myeloproliferative neoplasms (MPN) in post-allogeneic stem cell transplantation. Topics discussed include screening for evidence of CALR exon 9 mutations by DNA fragment analysis, utility of MPN-specific mutations to monitor disease kinetics post-Allogeneic Stem Cell Transplantation (ASCT) and persistence and eradication of CALR mutations that correlate with the clinical course.

Calreticulin (CALR) is a chaperone present in the endoplasmic reticulum, which is involved in the quality control of N-glycosylated proteins and storage of calcium ions. In 2013, the C-terminal mutation in CALR was identified in half of the patients with essential thrombocythemia and primary myelofibrosis who did not have a JAK2 or MPL mutation. The results of 8 years of intensive research are changing the clinical practice associated with treating myeloproliferative neoplasms (MPNs). The presence or absence of CALR mutations and their mutation types already provide important information for diagnosis and treatment decision making. In addition, the interaction with the thrombopoietin receptor MPL, which is the main mechanism of transformation by CALR mutation, and the expression of the mutant protein on the cell surface have a great potential as targets for molecular-targeted drugs and immunotherapy. This chapter presents recent findings on the clinical significance of the CALR mutation and the molecular basis by which this mutation drives MPNs., (Copyright © 2021 Elsevier Inc. All rights reserved.)

A letter to the editor in response to the articles "Incidence of CALR mutations in patients with splanchnic vein thrombosis" by K. Haslam and S.E. Langabeer and "Detection of the CALR mutation in the diagnosis of splanchnic vein thrombosis" by M. Roques published in previous issues is presented.

The article focuses on research related to Splanchnic vein thrombosis (SVT), a complication of myloproliferative neoplasms associated with several gene mutations. It discusses the increased incidences of CALR gene mutations in SVT patients and states that the research study was conducted on patients with different sites of thrombosis including portal vein thrombosis (PVT), renal vein thrombosis (RVT) and splenic vein thrombosis (SpVT).