Barbui

De Stefano

Sands

Stephen T. Oh

Wolach

English

Oh, Stephen T

Digital Commons@Becker

Washington University School of MedicineDigital Commons@BeckerOpen Access Publications2018Neutralize the neutrophils! Neutrophil β1 /β2integrin activation contributes toJAK2-V617F–driven thrombosisStephen T. OhWashington University School of Medicine in St. LouisFollow this and additional works at: https://digitalcommons.wustl.edu/open_access_pubsThis Open Access Publication is brought to you for free and open access by Digital Commons@Becker. It has been accepted for inclusion in OpenAccess Publications by an authorized administrator of Digital Commons@Becker. For more information, please contact engeszer@wustl.edu.Recommended CitationOh, Stephen T., ,"Neutralize the neutrophils! Neutrophil β1 /β2 integrin activation contributes to JAK2-V617F–driven thrombosis."The Journal of Clinical Investigation.128,10. 4248-4250. (2018).https://digitalcommons.wustl.edu/open_access_pubs/7218The Journal of Clinical Investigation C OMM E N TA RY4 2 4 8 jci.org   Volume 128   Number 10   October 2018Neutralize the neutrophils! Neutrophil β1/β2  integrin activation contributes to  JAK2-V617F–driven thrombosisStephen T. OhDivision of Hematology, Washington University School of Medicine, St. Louis, Missouri, USA.Thrombosis in myeloproliferative neoplasmsPatients with myeloproliferative neoplasms (MPNs) exhibit a propensity for thrombo-sis, which leads to significant morbidity and mortality (1, 2). Both arterial (e.g., stroke, myocardial infarction) and venous (e.g., pul-monary embolism, deep vein thrombosis) systems can be affected, and unusual loca-tions can be involved, such as the splanchnic vasculature. The prevalence of thrombot-ic events has been reported to range from 10% to 29% in essential thrombocythemia (ET) and 34% to 39% in polycythemia vera (PV) patients (3). In one population-based study, the incidence of arterial and venous thrombosis in the first 3 months after MPN diagnosis was 3 and 10 times higher, respec-tively, compared with the incidence in indi-viduals without MPN (4).Established risk factors for thrombo-sis in MPNs include older age and prior history of thrombosis (5). As the defining feature of PV is erythrocytosis, increased RBC mass presumably is a primary fac-tor that drives thrombosis. Thus, current guidelines for PV patients recommend maintaining the hematocrit (HCT) at a level less than 45% (6). The importance of this specific target was validated by a study in which patients were randomized to two different treatment goals (HCT less than 45% versus HCT of 45%–50%) that demonstrated that the lower HCT goal associated with a lower likelihood of death from cardiovascular causes or major thrombotic events (7). In ET, the cardinal feature is excessive platelet production, although the degree of thrombocytosis (i.e., platelet count) has not been shown to correlate well with the risk of thrombosis (2). Current guidelines indicate that ET patients considered at high risk for throm-bosis should be treated with cytoreductive therapy (most commonly hydroxyurea) to normalize platelet count (6).A role for leukocytes in promoting MPN-associated thrombosis?MPN patients also commonly exhibit leu-kocytosis, and some studies have implicat-ed leukocytosis as an independent risk fac-tor for thrombosis (8–10). As noted above, cytoreductive therapies, such as hydroxy-urea, are commonly used to reduce the HCT and/or platelet count in PV and ET patients. However, it has been speculated that an important benefit of hydroxyurea may be to lower the white blood count (WBC), thereby mitigating a potential con-tribution of leukocytes to thrombus for-mation (11). Neutrophils specifically have been recently recognized as integral to thrombus initiation and progression. Pro-posed mechanisms by which leukocytes could contribute to thrombosis include the release of proteolytic enzymes by activat-ed neutrophils, as well as increased CD11b expression, leading to stronger attach-ment of leukocytes to the endothelium and platelets (1, 2). Abnormal generation of neutrophil extracellular traps (NETs), which contribute to coagulation and plate-let aggregation, has also recently been linked to the MPN-associated mutation JAK2-V617F and thrombosis (12).β1 and β2 integrin activation contributes to JAK2-V617F–mediated thrombosisβ1 and β2 integrins are essential media-tors of leukocyte adhesion to the endo-thelium. In this issue, Edelmann and colleagues hypothesized that in MPNs, abnormal integrin function on leukocytes could contribute to thrombus formation (13). Granulocytes isolated from JAK2-V617F knockin mice exhibited increased adhesion to VCAM1 and ICAM1, ligands for β1 and β2 integrin, respectively (Figure 1A). These findings are consistent with recent studies from the same group show-     Related Article: p. 4359Conflict of interest: The author has declared that no conflict of interest exists.Reference information: J Clin Invest. 2018;128(10):4248–4250. https://doi.org/10.1172/JCI123388.Thrombosis is a major problem for patients with myeloproliferative neoplasms (MPNs). Leukocytes have long been speculated to contribute to thrombotic development in MPNs, but the exact role of these cells has not been fully elucidated. In this issue of the JCI, Edelmann and colleagues demonstrate that granulocytes from mice expressing an MPN-associated JAK2 mutation (JAK2-V617F) exhibit enhanced adhesion to VCAM1- and ICAM1-coated surfaces. The increased adhesion was shown to be mediated by β1 (VLA-4) and β2 integrins, which are activated via inside-out signaling induced by JAK2-V617F. In a murine thrombosis model, administration of neutralizing antibodies targeting VLA-4 and β2 integrin reduced thrombosis, suggesting the intriguing possibility that targeting these pathways could have clinical relevance for MPN.The Journal of Clinical Investigation   C OMM E N TA RY4 2 4 9jci.org   Volume 128   Number 10   October 2018granulocyte adhesion to VCAM1 was also reduced following incubation with the PI3K inhibitor wortmannin. Similar reduc-tions in adhesion were obtained with the Ca2+ and Mg2+ chelator BAPTA/AM, as well as with knockdown of the Ca2+-dependent enzyme CalDAG-GEFI, which is involved in conversion of Rap1-GDP to Rap1-GTP. Together, these findings suggest a role for PI3K and CalDAG-GEFI signaling in Rap1 activation mediated by JAK2-V617F.To determine the contribution of β1 and β2 integrin activation to JAK2-V617F–induced thrombosis Edelmann et al. utilized an inferi-or vena cava (IVC) ligation model. Compared with JAK2-WT mice, JAK2-mutant mice exhibited a significant increase in thrombus size in response to partial IVC ligation that was dramatically reduced by injection of β1 and β2 integrin–blocking antibodies (Fig-ure 1A). These findings indicate that β1 and β2 integrins play an important role in JAK2-V617F–driven thrombosis, and suggest that targeting β1 and β2 integrin activation could potentially be efficacious clinically.PerspectiveTogether, these studies by Edelmann and colleagues highlight the role of neutrophils in MPN-associated thrombosis and shed light on the mechanism by which JAK2-V617F activates β1and β2 integrins to pro-mote thrombus formation. One outstand-ing question not addressed in this study is whether inhibition of JAK2 with agents, such as ruxolitinib, might impact β1 and β2 integrin activation driven by mutant JAK2. Regardless, the studies shown establish that blocking β1 and β2 integrin activation could mitigate JAK2-V617F–driven thrombosis. Agents that target various integrin subunits have shown promising activity in several inflammatory diseases, including multiple sclerosis and inflammatory bowel disease, although, integrin-targeting therapies have been associated with increased susceptibil-ity to infection (15, 16). Whether targeting β1 and β2 integrin activation as a means of preventing thrombosis in MPNs is a viable strategy merits further exploration.Address correspondence to: Stephen T. Oh, Division of Hematology, Washington Uni-versity School of Medicine, 660 S. Euclid Ave, Campus Box 8125, St. Louis, Missouri 63110, USA. Phone: 314.362.8846; Email: stoh@wustl.edu.ence in Rap1 expression is notable, since CALR-mutant MPN patients are known to be at lower risk for thrombosis compared with JAK2-mutant MPN patients.Activation of Rap1-GTP is associated with translocation to the plasma mem-brane, and JAK2-V617F expression was shown to promote Rap1 membrane relocal-ization. Moreover, GGTI-2147, a geranyl-geranyltransferase inhibitor that blocks the posttranslational modifications required for Rap1 activation and translocation to the plasma membrane, inhibited adhe-sion of JAK2-mutant (but not JAK2-WT) granulocytes to VCAM1. JAK2- mutant ing that granulocytes from JAK2-mutant MPN patients have increased adhesion to VCAM1 (14).Utilizing a conformation-specific anti-body for β1 integrins, Edelmann and col-leagues found that JAK2-V617F expression shifts β1 integrins from a closed, low-affinity confirmation to an open, high-affinity con-formation (Figure 1A). This conformation change occurred via integrin inside-out-side signaling that involves Rap1-GT-Pase. In granulocytes from calreticulin- mutant (CALR-mutant) MPN patients, Rap1 was activated to a lesser degree than in JAK2-V617F granulocytes. This differ-Figure 1. The myeloproliferative neoplasm–associated mutation JAK2-V617 promotes thrombus formation. (A) Neutrophils expressing JAK2-V617 have increased activation of β1 and β2 integrin, resulting in increased adhesion to VCAM and ICAM1 on the vascular endothelium and enhanced thrombus formation. JAK2-V617 enhances activation of Rap1, which then translocates to the plasma membrane, thereby inducing the inside-outside signaling that shifts β integrins from a closed, low-affinity confirmation to a high-affinity confirmation (inset). (B) Antibodies targeting β1 and β2 integrin reduce neutrophil adhesion, resulting in decreased thrombus formation.The Journal of Clinical Investigation C OMM E N TA RY4 2 5 0 jci.org   Volume 128   Number 10   October 2018bosis in polycythemia vera: a subanalysis of the CYTO-PV study. Blood. 2015;126(4):560–561. 12. Wolach O, et al. Increased neutrophil extracel-lular trap formation promotes thrombosis in myeloproliferative neoplasms. Sci Transl Med. 2018;10(436):eaan8292. 13. Edelmann B, et al. JAK2-V617F promotes venous thrombosis through β1/β2 integrin activation.  J Clin Invest. 2018;128(10):4359–4371. 14. Gupta N, et al. JAK2-V617F activates β1-inte-grin-mediated adhesion of granulocytes to vascular cell adhesion molecule 1. Leukemia. 2017;31(5):1223–1226. 15. Schwab N, Schneider-Hohendorf T, Wiendl H. Therapeutic uses of anti-α4-integrin (anti-VLA-4) antibodies in multiple sclerosis. Int Immunol. 2015;27(1):47–53. 16. Sands BE. Leukocyte anti-trafficking strategies: current status and future directions. Dig Dis. 2017;35(1–2):13–20.Compr Canc Netw. 2015;13(4):424–434. 6. Mesa RA, et al. NCCN Guidelines insights: myeloproliferative neoplasms, version 2.2018.  J Natl Compr Canc Netw. 2017;15(10):1193–1207. 7. Marchioli R, et al. Cardiovascular events and intensity of treatment in polycythemia vera.  N Engl J Med. 2013;368(1):22–33. 8. Landolfi R, et al. Leukocytosis as a major throm-botic risk factor in patients with polycythemia vera. Blood. 2007;109(6):2446–2452. 9. Barbui T, Carobbio A, Rambaldi A, Finazzi G. Perspectives on thrombosis in essential thrombo-cythemia and polycythemia vera: is leukocytosis a causative factor? Blood. 2009;114(4):759–763. 10. De Stefano V, et al. Leukocytosis is a risk factor for recurrent arterial thrombosis in young patients with polycythemia vera and essential thrombocythemia. Am J Hematol. 2010;85(2):97–100. 11. Barbui T, et al. White blood cell counts and throm- 1. Kroll MH, Michaelis LC, Verstovsek S. Mecha-nisms of thrombogenesis in polycythemia vera. Blood Rev. 2015;29(4):215–221. 2. Ball S, Thein KZ, Maiti A, Nugent K. Thrombosis in Philadelphia negative classical myelopro-liferative neoplasms: a narrative review on epidemiology, risk assessment, and pathophys-iologic mechanisms. J Thromb Thrombolysis. 2018;45(4):516–528. 3. Tefferi A, Elliott M. Thrombosis in myeloprolif-erative disorders: prevalence, prognostic factors, and the role of leukocytes and JAK2V617F. Semin Thromb Hemost. 2007;33(4):313–320. 4. Hultcrantz M, et al. Risk for arterial and venous thrombosis in patients with myeloproliferative neoplasms: a population-based cohort study. Ann Intern Med. 2018;168(5):317–325. 5. Stein BL, et al. Historical views, conventional approaches, and evolving management strat-egies for myeloproliferative neoplasms. J Natl 

Neutralize the neutrophils! Neutrophil β1 /β2 integrin activation contributes to JAK2-V617F–driven thrombosis

Crossref

Neutralize the neutrophils! Neutrophil β1/β2 integrin activation contributes to JAK2-V617F–driven thrombosis

https://digitalcommons.wustl.edu/cgi/viewcontent.cgi?article=8220&amp;context=open_access_pubs

Neutralize the neutrophils! Neutrophil β1 /β2 integrin activation contributes to JAK2-V617F–driven thrombosis

Abstract

Similar works

Full text

Available Versions

Digital Commons@Becker

Crossref