Cardiac hypertrophy associated with myeloproliferative neoplasms in JAK2V617F transgenic mice
© Shi et al.; licensee BioMed Central Ltd. 2014
Received: 10 February 2014
Accepted: 15 March 2014
Published: 19 March 2014
Myeloproliferative neoplasms (MPNs) are blood malignancies manifested in increased production of red blood cells, white blood cells, and/or platelets. A major molecular lesion associated with the diseases is JAK2V617F, an activation mutation form of tyrosine kinase JAK2. Cardiovascular events represent the leading cause of morbidity and mortality associated MPNs, but the underlying mechanism is not well understood.
Previously, we generated JAK2V617F transgenic mice which displayed MPN-like phenotypes. In the present study, we further characterized these mice by analyzing the time course of MPN phenotype development and associated cardiac abnormalities. We performed detailed histochemical staining of cardiac sections.
JAK2V617F transgenic mice developed cardiomegaly as a subsequent event of increased blood cell production during the course of MPN phenotype development. The cardiomegaly is manifested in increased ventricular wall thickness and enlarged cardiomyocytes. Trichrome and reticulin staining revealed extensive collagen fibrosis in the heart of JAK2V617F transgenic mice. Thrombosis in the coronary artery and inflammatory cell infiltration into cardiac muscle were also observed in JAK2V617F transgenic mice, and the latter event was accompanied by fibrosis.
JAK2V617F-induced blood disorders have a major impact on heart function and lead to cardiac hypertrophy. JAK2V617F transgenic mice represent an excellent model system to study both hematological malignancies and cardiovascular diseases.
KeywordsMPN JAK2V617F Hematological malignancies Fibrosis Cardiomegaly Cardiac hypertrophy
Myeloproliferative neoplasms (MPNs) are chronic hematopoietic malignancies characterized by abnormal amplification of one or more myeloid lineages [1–3]. These diseases include polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF) [4, 5]. PV patients have increased production of all three types of blood cells, whereas ET patients mainly show elevations of platelets. Patients with PMF develop fibrous (scar-like) tissues in the bone marrow as a result of abnormal myeloid proliferation. MPNs mainly affect older people with an average onset of 55 years. So far, there is no effective cure for the diseases [6–9]. Complications associated with MPNs include thrombosis, hemorrhage, heart attacks, strokes, myeloid metaplasia, and acute leukemia. Strokes and heart attacks caused by these diseases are usually fatal. In fact, cardiovascular events represent the leading cause of morbidity and mortality in the course of PV and ET [10–12]. However, how the blood abnormality associated with MPNs leads to cardiac changes is not well understood.
JAK2V617F, a mutant form of tyrosine kinase JAK2, represents a major molecular defect in MPNs [13–17]. It is found in over 95% of PV and over 50% of ET and PMF cases [1–3, 18]. In early studies, we have generated JAK2V617F transgenic mice by using the vav-1 promoter which drives transgene expressions in the hematopoietic system. JAK2V617F transgenic mice display MPN-like phenotypes with increased levels of red blood cells, platelets, and white blood cells . These mice thus represent a model system to study MPNs and associated complications. In the present study, we investigated cardiac changes and remodeling during the course of MPN phenotype development in these mice. Our data demonstrate that JAK2V617F transgenic mice display cardiac hypertrophy manifest in increased ventricular wall thickness, enlarged cardiomyocytes, and formation of collagen fibrosis in the heart. Our study thus links a chronic blood malignancy directly to heart diseases.
JAK2V617F transgenic mice displayed cardiomegaly
JAK2V617F transgenic mice developed fibrosis in the heart
The most abundant extracellular matrix proteins in the heart are collagens, particularly the collagen type I and type III phenotypes [20, 21]. Our study thus revealed substantial accumulation of collagen fibrosis in the heart of JAK2V617F transgenic mice. This contributes to major cardiac remodeling and may significantly affect the heart function.
Coronary artery thrombosis and inflammatory cell infiltration were found in the heart of JAK2V617F transgenic mice
Real time PCR analyses revealed a minimal expression of transgenic JAK2V167F in the mouse heart
The cardiac hypertrophy observed in JAK2V617F mice is likely a consequence of MPN phenotype. However, there is a possibility that the JAK2V617F expression may directly affect cardiomyocytes. In fact, an earlier study revealed the presence of JAK2V617F in cardiomyocytes from a patient with MPNs and hypertrophic cardiomyopathy . To determine the expression of endogenous Jak2 and transgenic JAK2V617F in the heart, we performed real time PCR analysis with specific primers as described previously . Expression of these genes in hematopoietic tissues including bone marrow, peripheral blood, and spleen were included for comparison. Despite containing 26 copies of the JAK2V617F transgenic gene , mRNA transcripts of JAK2V617F were nearly 10-fold below the expression level of endogenous mouse Jak2 in the hematopoietic tissues. Mouse Jak2 was expressed at a substantial level in the heart, which is consistent with the crucial role of JAK2 in cardiomyogenesis . However, expression of transgenic JAK2V617F in the heart was much lower, about 200-fold below the level of mouse Jak2 in the heart or of JAKV617F in the hematopoietic tissues. This low-level JAK2V617F expression may be mainly attributable to the presence of residual blood cells in the cardiac blood vessels. The data thus demonstrate a minimal expression of JAK2V617F transgene in mouse heart cells. Although we cannot totally rule out the contribution of JAK2V617F expression in cardiomyocytes to the development of cardiac hypertrophy phenotypes, the possibility for this is very low.
Cardiomegaly can usually be caused by coronary artery diseases or high blood pressure (hypertension). On one hand, we observed the occurrence of thrombosis in the canary artery of JAK2V617F transgenic mouse heart. This can presumably cause myocardial ischemia thereby leading to cardiac enlargement, and the increased platelets in the transgenic mice may contribute a higher incidence of thrombotic events. On the other hand, hypertension may represent a more general phenotype in the transgenic mice. High red blood cells in these mice directly increase blood viscosity and thus raise the peripheral resistance. It has been well documented that high red blood cells and hematocrit lead to hypertension [27–30]. In fact, hypertension and thrombosis are common initial presentation and complications with MPN patients. Our data suggest these patients may also develop cardiomegaly.
Our study revealed substantial accumulation of collagen fibers in the heart of JAK2V617F transgenic mice. This can contribute significantly to cardiac hypertrophy in addition to increased cardiomyocyte size. Cardiac fibrosis is considered to be the key to understanding heart disease. Recent research points to several key signaling pathways involved in cardiac fibrosis, providing biomarkers and potential targets for intervention. The JAK2V617F transgenic mice serve as a good in vivo system to dissect these pathways and identify growth factors and cytokines that trigger the activation of these pathways. Among the extracellular matrix in the heart, collagens are the most abundant fibrillar proteins [20, 21]. Previous studies have mainly focused on type I collagen. Type I collagen can be detected by trichrome staining as shown in Figure 4, and it forms thick fibrils. However, type III collagen is also abundant in the heart but is seldom examined. Type III collagen forms so-called reticulin thin fibers. By using silver staining, we found a more profound change in the level of reticulin fibers in the extramyocyte space of hearts from JAK2V617F transgenic mice. Therefore, this method should be generally used to detect fibrosis in the heart. Reticulin fibers are also found in the liver, kidney and the spleen. Interestingly, JAK2V617F transgenic mice developed myelofibrosis in the bone marrow and spleen [1–3]. This is also recapitulated in JAK2V617F mice . The myelofibrosis is mainly caused by accumulation of reticulin fibers. We believe that the reticulin fibers found in the heart of JAK2V617F transgenic mice may be caused by a similar mechanism by which myelofibrosis is regulated.
Inflammation has a major role in cardiac hypertrophy. Importantly, we observed infiltration of inflammatory cells in the muscle of hearts from JAK2V617F transgenic mice. This inflammatory reaction may be triggered by a cell necrosis due to myocardial infarction. Necrotic cells release soluble factors that cause migration of inflammatory cells and fibroblasts to the site of injury for repairing. This further leads to fibrosis as seen in this study (Figure 7). Interestingly, we also found mast cells among the infiltrated inflammatory cells. Mast cells have a major role in the pathophysiology of cardiovascular disorders . Our data suggest that mast cells may promote fibrosis in the stressed and injured heart. We believe that the presence of JAK2V617F in these inflammatory cells further enhances their ability to infiltrate tissues thereby causing more profound damages. Identification of JAK2V617F has provided an excellent target for drug development. Many potent JAK2 inhibitors have been developed, and some have shown clinical benefits in treatment of myelofibrosis [31–34]. These inhibitors should also be useful for treating cardiovascular complications associated with MPNs.
We have demonstrated that JAK2V617F-induced MPNs can further lead to cardiac hypertrophy in mice. This has major implications for our understanding of complications that occur in MPN patients. Our data help to explain the high morbidity and mortality of MPN patients due to cardiovascular events. We have further demonstrated that the cardiac remodeling in JAK2V617F transgenic mice is manifest in fibrosis involving not only type I collagen but also type III reticulin fibers. By linking a hematological malignancy with heart diseases, JAK2V617F transgenic mice thus represent a unique model system to study cardiovascular diseases as well as blood disorders.
Materials and methods
JAK2V617F transgenic mice were generated as previously described . The JAK2V617F transgene is under the control of the vav-1 promoter which drives gene expression only in hematopoietic cells. These mice have been crossed with wild type C57BL/6 mice for over 10 generations. Homozygous line A JAK2V617F mice were used in this study. These mice carry 26 copies of the JAK2V617F transgene . Wild type C57BL/6 were purchased from The Jackson Laboratory and used as control together with non-transgenic siblings of JAK2V617F transgenic mice. At least 10 mice with about equal male and female representations were used for each control or experimental group. Animals were housed in ventilated cages under standard conditions. This study was carried out in strict accordance with the recommendations in the Guide for the Care and Use of Laboratory Animals of the National Institutes of Health.
Mouse tissue collection, fixation, and sectioning
Mice were weighed and put under deep anesthesia through inhalation of isoflurane. Terminal blood collection was performed by removing the eyeball from the socket . Hearts were then removed, blotted free of blood, and weighed. This is followed by fixation in 10% neutral buffered formalin overnight at room temperature and subsequent embedding in paraffin. Tissue sections (5 μm) were cut from various positions.
Histochemical staining, image acquisition, and digital quantification
Tissue sections were deparaffinized and then subjected to H&E, Masson’s trichrome, reticulin, and toluidine blue staining by using reagents and kits from Sigma-Aldrich following standard protocols. Slides were viewed with an Olympus BX-51 upright microscope equipped with U Plan Fluorite objectives. Images were acquired using a DP71 digital camera with the DP-BSW-V3.1 camera control software (Olympus) and were processed with the Adobe Photoshop software. Quantification of histochemical stain images was done by using the NIH ImageJ program. Cardiac sections from at least 10 mice per group were analyzed. The thickness at the obtuse margin of the left ventricle of each heart was measured, excluding trabeculations. Cardiomyocyte size was assessed by measuring cross-sectional area of cardiomyocytes from H&E-stained fields randomly selected.
Total RNA isolation and real time PCR analysis
Total RNAs were isolated from mouse tissues by using the RNeasy Mini kit (Qiagen), and single strand cDNAs were synthesized with equal amounts of total RNAs by using the QuantiTect reverse transcription kit from Qiagen. Real time PCR was performed with iQ SYBR Green Supermix (Bio-Rad) and primers specific for endogenous mouse Jak2, transgenic human JAK2V617F, and mouse glyceraldehyde-3-phosphate dehydrogenase (GAPDH) as previously described .
Statistical analyses were performed using the GraphPad program. Differences of samples between 2 groups were accessed using t tests. P values less than 0.05 (2-tailed) were considered significantly different.
Hematoxylin and eosin.
This work was supported by grant no. 81270315 from National Natural Science Foundation of China (to P Yang) and grants from the National Institutes of Health (HL094591), Oklahoma Center for the Advancement of Science & Technology, and the MPN foundation (to ZJ Zhao).
- Levine RL, Gilliland DG: Myeloproliferative disorders. Blood. 2008, 112: 2190-2198. 10.1182/blood-2008-03-077966.PubMed CentralView ArticlePubMedGoogle Scholar
- Tefferi A: The history of myeloproliferative disorders: before and after Dameshek. Leukemia. 2008, 22: 3-13. 10.1038/sj.leu.2404946.View ArticlePubMedGoogle Scholar
- Campbell PJ, Green AR: The myeloproliferative disorders. N Engl J Med. 2006, 355: 2452-2466. 10.1056/NEJMra063728.View ArticlePubMedGoogle Scholar
- Kvasnicka HM, Thiele J: Prodromal myeloproliferative neoplasms: the 2008 WHO classification. Am J Hematol. 2010, 85: 62-69.PubMedGoogle Scholar
- Tefferi A, Thiele J, Orazi A, Kvasnicka HM, Barbui T, Hanson CA, Barosi G, Verstovsek S, Birgegard G, Mesa R, Reilly JT, Gisslinger H, Vannucchi AM, Cervantes F, Finazzi G, Hoffman R, Gilliland DG, Bloomfield CD, Vardiman JW: Proposals and rationale for revision of the World Health Organization diagnostic criteria for polycythemia vera, essential thrombocythemia, and primary myelofibrosis: recommendations from an ad hoc international expert panel. Blood. 2007, 110: 1092-1097. 10.1182/blood-2007-04-083501.View ArticlePubMedGoogle Scholar
- Tefferi A, Vainchenker W: Myeloproliferative neoplasms: molecular pathophysiology, essential clinical understanding, and treatment strategies. J Clin Oncol. 2011, 29: 573-582. 10.1200/JCO.2010.29.8711.View ArticlePubMedGoogle Scholar
- Finazzi G, Barbui T: How I treat patients with polycythemia vera. Blood. 2007, 109: 5104-5111. 10.1182/blood-2006-12-038968.View ArticlePubMedGoogle Scholar
- Beer PA, Erber WN, Campbell PJ, Green AR: How I treat essential thrombocythemia. Blood. 2011, 117: 1472-1482. 10.1182/blood-2010-08-270033.PubMed CentralView ArticlePubMedGoogle Scholar
- Tefferi A: How I treat myelofibrosis. Blood. 2011, 117: 3494-3504. 10.1182/blood-2010-11-315614.View ArticlePubMedGoogle Scholar
- Kim J, Haddad RY, Atallah E: Myeloproliferative neoplasms. Dis Mon. 2012, 58: 177-194. 10.1016/j.disamonth.2012.01.002.View ArticlePubMedGoogle Scholar
- Spivak JL: Polycythemia vera: myths, mechanisms, and management. Blood. 2002, 100: 4272-4290. 10.1182/blood-2001-12-0349.View ArticlePubMedGoogle Scholar
- Finazzi G, Barbui T: Risk-adapted therapy in essential thrombocythemia and polycythemia vera. Blood Rev. 2005, 19: 243-252. 10.1016/j.blre.2005.01.001.View ArticlePubMedGoogle Scholar
- Baxter EJ, Scott LM, Campbell PJ, East C, Fourouclas N, Swanton S, Vassiliou GS, Bench AJ, Boyd EM, Curtin N, Scott MA, Erber WN, Green AR, Cancer Genome Project: Acquired mutation of the tyrosine kinase JAK2 in human myeloproliferative disorders. Lancet. 2005, 365: 1054-1061. 10.1016/S0140-6736(05)71142-9.View ArticlePubMedGoogle Scholar
- Levine RL, Wadleigh M, Cools J, Ebert BL, Wernig G, Huntly BJ, Boggon TJ, Wlodarska I, Clark JJ, Moore S, Adelsperger J, Koo S, Lee JC, Gabriel S, Mercher T, D’Andrea A, Fröhling S, Döhner K, Marynen P, Vandenberghe P, Mesa RA, Tefferi A, Griffin JD, Eck MJ, Sellers WR, Meyerson M, Golub TR, Lee SJ, Gilliland DG: Activating mutation in the tyrosine kinase JAK2 in polycythemia vera, essential thrombocythemia, and myeloid metaplasia with myelofibrosis. Cancer Cell. 2005, 7: 387-397. 10.1016/j.ccr.2005.03.023.View ArticlePubMedGoogle Scholar
- James C, Ugo V, Le Couédic JP, Staerk J, Delhommeau F, Lacout C, Garçon L, Raslova H, Berger R, Bennaceur-Griscelli A, Villeval JL, Constantinescu SN, Casadevall N, Vainchenker W: A unique clonal JAK2 mutation leading to constitutive signalling causes polycythaemia vera. Nature. 2005, 434: 1144-1148. 10.1038/nature03546.View ArticlePubMedGoogle Scholar
- Kralovics R, Passamonti F, Buser AS, Teo SS, Tiedt R, Passweg JR, Tichelli A, Cazzola M, Skoda RC: A gain-of-function mutation of JAK2 in myeloproliferative disorders. N Engl J Med. 2005, 352: 1779-1790. 10.1056/NEJMoa051113.View ArticlePubMedGoogle Scholar
- Zhao R, Xing S, Li Z, Fu X, Li Q, Krantz SB, Zhao ZJ: Identification of an acquired JAK2 mutation in polycythemia vera. J Biol Chem. 2005, 280: 22788-22792. 10.1074/jbc.C500138200.PubMed CentralView ArticlePubMedGoogle Scholar
- Zhao W, Gao R, Lee J, Xing S, Ho WT, Fu X, Li S, Zhao ZJ: Relevance of JAK2V617F positivity to hematological diseases–survey of samples from a clinical genetics laboratory. J Hematol Oncol. 2011, 4: 4-10.1186/1756-8722-4-4.PubMed CentralView ArticlePubMedGoogle Scholar
- Xing S, Wanting TH, Zhao W, Ma J, Wang S, Xu X, Li Q, Fu X, Xu M, Zhao ZJ: Transgenic expression of JAK2V617F causes myeloproliferative disorders in mice. Blood. 2008, 111: 5109-5117. 10.1182/blood-2007-05-091579.PubMed CentralView ArticlePubMedGoogle Scholar
- Nicoletti A, Michel JB: Cardiac fibrosis and inflammation: interaction with hemodynamic and hormonal factors. Cardiovasc Res. 1999, 41: 532-543. 10.1016/S0008-6363(98)00305-8.View ArticlePubMedGoogle Scholar
- Castellar A, Remedio RN, Barbosa RA, Gomes RJ, Caetano FH: Collagen and reticular fibers in left ventricular muscle in diabetic rats: Physical exercise prevents its changes?. Tissue Cell. 2011, 43: 24-28. 10.1016/j.tice.2010.11.001.View ArticlePubMedGoogle Scholar
- Kennedy S, Wu J, Wadsworth RM, Lawrence CE, Maffia P: Mast cells and vascular diseases. Pharmacol Ther. 2013, 138: 53-65. 10.1016/j.pharmthera.2013.01.001.View ArticlePubMedGoogle Scholar
- Jin X, Zhao W, Shi K, Ho WT, Zhao ZJ: Generation of a new congenic mouse strain with enhanced chymase expression in mast cells. PLoS One. 2013, 8: e84340-10.1371/journal.pone.0084340.PubMed CentralView ArticlePubMedGoogle Scholar
- Gattenlohner S, Ertl G, Einsele H, Kircher S, Muller-Hermelink HK, Marx A: Cardiac JAK2 mutation V617F in a patient with cardiomyopathy and myeloproliferative disease. Ann Intern Med. 2008, 149: 69-71. 10.7326/0003-4819-149-1-200807010-00027.View ArticlePubMedGoogle Scholar
- Foshay K, Rodriguez G, Hoel B, Narayan J, Gallicano GI: JAK2/STAT3 directs cardiomyogenesis within murine embryonic stem cells in vitro. Stem Cells. 2005, 23: 530-543. 10.1634/stemcells.2004-0293.View ArticlePubMedGoogle Scholar
- Ogilvy S, Elefanty AG, Visvader J, Bath ML, Harris AW, Adams JM: Transcriptional regulation of vav, a gene expressed throughout the hematopoietic compartment. Blood. 1998, 91: 419-430.PubMedGoogle Scholar
- Letcher RL, Chien S, Pickering TG, Sealey JE, Laragh JH: Direct relationship between blood pressure and blood viscosity in normal and hypertensive subjects. Role of fibrinogen and concentration. Am J Med. 1981, 70: 1195-1202. 10.1016/0002-9343(81)90827-5.View ArticlePubMedGoogle Scholar
- Fowkes FG, Lowe GD, Rumley A, Lennie SE, Smith FB, Donnan PT: The relationship between blood viscosity and blood pressure in a random sample of the population aged 55 to 74 years. Eur Heart J. 1993, 14: 597-601. 10.1093/eurheartj/14.5.597.View ArticlePubMedGoogle Scholar
- Cinar Y, Demir G, Paç M, Cinar AB: Effect of hematocrit on blood pressure via hyperviscosity. Am J Hypertens. 1999, 12: 739-743. 10.1016/S0895-7061(99)00011-4.View ArticlePubMedGoogle Scholar
- Ciuffetti G, Schillaci G, Lombardini R, Pirro M, Vaudo G, Mannarino E: Prognostic impact of low-shear whole blood viscosity in hypertensive men. Eur J Clin Invest. 2005, 35: 93-98. 10.1111/j.1365-2362.2005.01437.x.View ArticlePubMedGoogle Scholar
- Verstovsek S, Kantarjian H, Mesa RA, Pardanani AD, Cortes-Franco J, Thomas DA, Estrov Z, Fridman JS, Bradley EC, Erickson-Viitanen S, Vaddi K, Levy R, Tefferi A: Safety and efficacy of INCB018424, a JAK1 and JAK2 inhibitor, in myelofibrosis. N Engl J Med. 2010, 363: 1117-1127. 10.1056/NEJMoa1002028.View ArticlePubMedGoogle Scholar
- Mesa RA, Cortes J: Optimizing management of ruxolitinib in patients with myelofibrosis: the need for individualized dosing. J Hematol Oncol. 2013, 6: 79-10.1186/1756-8722-6-79.PubMed CentralView ArticlePubMedGoogle Scholar
- Randhawa J, Ostojic A, Vrhovac R, Atallah E, Verstovsek S: Splenomegaly in myelofibrosis—new options for therapy and the therapeutic potential of Janus kinase 2 inhibitors. J Hematol Oncol. 2012, 5: 43-10.1186/1756-8722-5-43.PubMed CentralView ArticlePubMedGoogle Scholar
- Talpaz M, Paquette R, Afrin L, Hamburg SI, Prchal JT, Jamieson K, Terebelo HR, Ortega GL, Lyons RM, Tiu RV, Winton EF, Natrajan K, Odenike O, Claxton D, Peng W, O’Neill P, Erickson-Viitanen S, Leopold L, Sandor V, Levy RS, Kantarjian HM, Verstovsek S: Interim analysis of safety and efficacy of ruxolitinib in patients with myelofibrosis and low platelet counts. J Hematol Oncol. 2013, 6: 81-10.1186/1756-8722-6-81.PubMed CentralView ArticlePubMedGoogle Scholar
- Hoff J: Methods of blood collection in the mouse. Lab Anim. 2000, 29: 47-53.Google Scholar
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.