Increased levels of NETosis in myeloproliferative neoplasms are not linked to thrombotic events

The Proteome Content of Blood Clots Observed Under Different Conditions: Successful Role in Predicting Clot Amyloid(ogenicity)

A recent analysis compared the proteome of (i) blood clots seen in two diseases-sepsis and long COVID-when blood was known to have clotted into an amyloid microclot form (as judged by staining with the fluorogenic amyloid stain thioflavin T) with (ii) that of those non-amyloid clots considered to have formed normally. Such fibrinaloid microclots are also relatively resistant to fibrinolysis. The proteins that the amyloid microclots contained differed markedly both from the soluble proteome of typical plasma and that of normal clots, and also between the diseases studied (an acute syndrome in the form of sepsis in an ITU and a chronic disease represented by Long COVID). Many proteins in the amyloid microclots were low in concentration in plasma and were effectively accumulated into the fibres, whereas many other abundant plasma proteins were excluded. The proteins found in the microclots associated with the diseases also tended to be themselves amyloidogenic. We here ask effectively the inverse question. This is: can the clot proteome tell us whether the clots associated with a particular disease contained proteins that are observed uniquely (or are highly over-represented) in known amyloid clots relative to normal clots, and thus were in fact amyloid in nature? The answer is in the affirmative in a variety of major coagulopathies, viz., venous thromboembolism, pulmonary embolism, deep vein thrombosis, various cardiac issues, and ischaemic stroke. Galectin-3-binding protein and thrombospondin-1 seem to be especially widely associated with amyloid-type clots, and the latter has indeed been shown to be incorporated into growing fibrin fibres. These may consequently provide useful biomarkers with a mechanistic basis.

Molecular and Clinical Risk Factors Associated with Thrombosis and Bleeding in Myelofibrosis Patients

BACKGROUND

 The risk of thrombosis and bleeding in myelofibrosis (MF) has been historically underappreciated. We sought to investigate potential molecular and clinical risk factors for venous (VTE) and arterial (ATE) thrombotic events as well as bleeding episodes.

METHODS

 Data from 246 consecutive MF patients were analyzed. Driver mutations were tested in 191 patients.

RESULTS

 In total, 181 mutations were found in 177 MF patients: 118 (61.8%) patients showed JAK2-V617F, 50 patients (26.2%) showed CALR, and 6 patients (3.1%) showed MPL mutations. Two patients were JAK2-V617F and MPL positive and one patient was positive for all three genes. Fourteen (7.3%) patients were triple negative. The JAK2-V617F allele burden was assessed in 63 JAK2-V617F-mutated patients, revealing a median of 35.6% (range: 5.0-96.0). At the time of MF diagnosis and during follow-up, 84 thrombotic events (52 VTEs and 32 ATEs) were observed, corresponding to 6.6% of patients per year. A significant association was found between JAK2-V617F mutation (OR: 2.5, 95% CI: 1.1-5.6) and prior VTE (OR: 7.6, 95% CI: 2.1-27.1) with an increased risk of VTE. Patients with prefibrotic MF had a higher rate of ATE than patients with overt MF. Hemorrhagic events occurred in 34 (13.8%) patients, corresponding to 3.8% of patients per year. Fibrosis grade 3 was associated with bleeding risk (OR: 3.4, 95% CI: 1.2-9.2, p = 0.02).

CONCLUSIONS

 The presence of the JAK2-V617F mutation, regardless of allele burden, and prior thrombosis were strongly associated with an increased risk of VTE. Patients with prefibrotic MF might be considered at high risk for developing ATE.

Interferon-α Inhibits NET Formation in Neutrophils Derived from Patients with Myeloproliferative Neoplasms in a Neutrophil Sub-Population-Specific Manner

Neutrophils and neutrophil extracellular traps (NETs) contribute to thrombosis and hyperinflammation in myeloproliferative neoplasms (MPN). High-density neutrophils (HDNs) and low-density neutrophils (LDNs) have recently been characterized as distinct neutrophil sub-populations with distinct morphological and functional properties. We aim to study the kinetics of NET formation and inhibition with interferon-α (IFNα) in neutrophils derived from patients with MPN as compared to matched healthy controls. Ex vivo NET formation was assessed by neutrophil-elastase activity, neutrophil-associated nucleosomes, myeloperoxidase (MPO), and citrullinated histone H3 content. IFNα significantly inhibited NET formation in neutrophils derived from MPN patients. Neutrophil sub-population analysis demonstrated that HDNs drive the increase in NET formation as compared to LDNs in patients and in healthy controls and are effectively inhibited by IFNα, an effect that is lost in LDNs. In conclusion, we demonstrate that in MPN, HDNs drive excess NET formation and are more sensitive to IFNα inhibition. These observations uncover unique neutrophil sub-population biology and dynamics in MPN.

CXCL8 and its cognate receptors CXCR1/CXCR2 in primary myelofibrosis

BCR::ABL1 negative myeloproliferative neoplasms (MPN) form a distinct group of hematologic malignancies characterized by sustained proliferation of cells from multiple myeloid lineages. With a median survival of 16-35 months in patients with high-risk disease, primary myelofibrosis (PMF) is considered the most aggressive entity amongst all BCR::ABL1 MPN. Additionally, for a significant subset of patients, MPN evolve into secondary acute myeloid leukemia (AML), which has an even poorer prognosis compared to de novo AML. As the exact mechanisms of disease development and progression remain to be elucidated, current therapeutic approaches fail to prevent disease progression or transformation into secondary AML. As each MPN entity is characterized by sustained activation of various immune cells and raised cytokine concentrations within bone marrow (BM) and peripheral blood (PB), MPN may be considered to be typical inflammation-related malignancies. However, the exact role and consequences of increased cytokine concentrations within BM and PB plasma has still not been completely established. Up-regulated cytokines can stimulate cellular proliferation, or contribute to the development of an inflammation-related BM niche resulting in genotoxicity and thereby supporting mutagenesis. The neutrophil chemoattractant CXCL8 is of specific interest as its concentration is increased within PB and BM plasma of patients with PMF. Increased concentration of CXCL8 negatively correlates with overall survival. Furthermore, blockage of the CXCR1/2 axis appears to be able to reduce BM fibrosis and megakaryocyte dysmorphia in murine models. In this review, we summarize available evidence on the role of the CXCL8-CXCR1/2 axis within the pathogenesis of PMF, and discuss potential therapeutic modalities targeting either CXCL8 or its cognate receptors CXCR1/2.

Resveratrol and tetrahydroisoquinoline effects on neutrophil sensitivity to NETosis formation in low-risk essential thrombocythemia patients

INTRODUCTION

Recent studies scrutinize how NETosis (a unique cell death mechanism of neutrophil), impacts thrombosis patients with essential thrombocythemia (ET). This research evaluates the susceptibility of ET neutrophils to form NETs and tests two potential inhibitors, resveratrol (RSV) and tetrahydroisoquinoline (THIQ), in vitro.

METHODS

Platelet-rich plasma from low-risk ET patients was used, along with neutrophils from both patients and controls. NET formation assays, with or without RSV and THIQ treatment after LPS stimulation, were conducted in a CO2 incubator. Evaluation included flow cytometry and fluorescence microscopy for NET formation and ELISA for TNFα, IL8, and vWF:Ag levels in patient and control plasma.

RESULTS

Neutrophils from ET patients released more NETs than controls, confirmed by flow cytometry and fluorescence microscopy. Additionally, patients had significantly higher plasma levels of IL8 and TNFα compared to controls, while RSV was more effective than THIQ in reducing NETosis rates in these patients.

CONCLUSIONS

In ET patients, a platelet counts over 1 million indicates the need for preventive treatment against thrombotic events. Similarly, in this study, RSV and THIQ significantly reduced the rate of NETosis in ET patients with higher platelet counts, and this role was more prominent in the case of the second inhibitor (RSV).

ROP-ET: a prospective phase III trial investigating the efficacy and safety of ropeginterferon alfa-2b in essential thrombocythemia patients with limited treatment options

Interferon-based therapies, such as ropeginterferon alfa-2b have emerged as promising disease-modifying agents for myeloproliferative neoplasms (MPNs), including essential thrombocythemia (ET). Current ET treatments aim to normalize hematological parameters and reduce the thrombotic risk, but they do not modify the natural history of the disease and hence, have no impact on disease progression. Ropeginterferon alfa-2b (trade name BESREMi®), a novel, monopegylated interferon alfa-2b with an extended administration interval, has demonstrated a robust and sustained efficacy in polycythemia vera (PV) patients. Given the similarities in disease pathophysiology and treatment goals, ropeginterferon alfa-2b holds promise as a treatment option for ET. The ROP-ET trial is a prospective, multicenter, single-arm phase III study that includes patients with ET who are intolerant or resistant to, and/or are ineligible for current therapies, such as hydroxyurea (HU), anagrelide (ANA), busulfan (BUS) and pipobroman, leaving these patients with limited treatment options. The primary endpoint is a composite response of hematologic parameters and disease-related symptoms, according to modified European LeukemiaNet (ELN) criteria. Secondary endpoints include improvements in symptoms and quality of life, molecular response and the safety profile of ropeginterferon alfa-2b. Over a 3-year period the trial assesses longer term outcomes, particularly the effects on allele burden and clinical outcomes, such as disease-related symptoms, vascular events and disease progression. No prospective clinical trial data exist for ropeginterferon alfa-2b in the planned ET study population and this study will provide new findings that may contribute to advancing the treatment landscape for ET patients with limited alternatives. TRIAL REGISTRATION: EU Clinical Trials Register; EudraCT, 2023-505160-12-00; Registered on October 30, 2023.

Platelets and neutrophils cooperate to induce increased neutrophil extracellular trap formation in JAK2V617F myeloproliferative neoplasms

BACKGROUND

Neutrophils participate in the pathogenesis of thrombosis through the formation of neutrophil extracellular traps (NETs). Thrombosis is the main cause of morbidity and mortality in patients with myeloproliferative neoplasms (MPNs). Recent studies have shown an increase in NET formation (NETosis) both in patients with JAK2V617F neutrophils and in mouse models, and reported the participation of NETosis in the pathophysiology of thrombosis in mice.

OBJECTIVES

This study investigated whether JAK2V617F neutrophils are sufficient to promote thrombosis or whether their cooperation with other blood cell types is necessary.

METHODS

NETosis was studied in PF4iCre;Jak2V617F/WT mice expressing JAK2V617F in all hematopoietic lineages, as occurs in MPNs, and in MRP8Cre;Jak2V617F/WT mice in which JAK2V617F is expressed only in leukocytes.

RESULTS

In PF4iCre;Jak2V617F/WT mice, an increase in NETosis and spontaneous lung thrombosis abrogated by DNAse administration were observed. The absence of spontaneous NETosis or lung thrombosis in MRP8Cre;Jak2V617F/WT mice suggested that mutated neutrophils alone are not sufficient to induce thrombosis. Ex vivo experiments demonstrated that JAK2V617F-mutated platelets trigger NETosis by JAK2V617F-mutated neutrophils. Aspirin treatment in PF4iCre;Jak2V617F/WT mice reduced NETosis and reduced lung thrombosis. In cytoreductive-therapy-free patients with MPN treated with aspirin, plasma NET marker concentrations were lower than that in patients with MPN not treated with aspirin.

CONCLUSION

Our study demonstrates that JAK2V617F neutrophils alone are not sufficient to promote thrombosis; rather, platelets cooperate with neutrophils to promote NETosis in vivo. A new role for aspirin in thrombosis prevention in MPNs was also identified.

Putative Role of Neutrophil Extracellular Trap Formation in Chronic Myeloproliferative Neoplasms

Myeloproliferative neoplasms (MPNs) are hematologic malignancies characterized by gene mutations that promote myeloproliferation and resistance to apoptosis via constitutively active signaling pathways, with Janus kinase 2-signal transducers and the activators of transcription (JAK-STAT) axis as a core part. Chronic inflammation has been described as a pivot for the development and advancement of MPNs from early stage cancer to pronounced bone marrow fibrosis, but there are still unresolved questions regarding this issue. The MPN neutrophils are characterized by upregulation of JAK target genes, they are in a state of activation and with deregulated apoptotic machinery. Deregulated neutrophil apoptotic cell death supports inflammation and steers them towards secondary necrosis or neutrophil extracellular trap (NET) formation, a trigger of inflammation both ways. NETs in proinflammatory bone marrow microenvironment induce hematopoietic precursor proliferation, which has an impact on hematopoietic disorders. In MPNs, neutrophils are primed for NET formation, and even though it seems obvious for NETs to intervene in the disease progression by supporting inflammation, no reliable data are available. We discuss in this review the potential pathophysiological relevance of NET formation in MPNs, with the intention of contributing to a better understanding of how neutrophils and neutrophil clonality can orchestrate the evolution of a pathological microenvironment in MPNs.

Casting a NET on cancer: the multiple roles for neutrophil extracellular traps in cancer

PURPOSE OF REVIEW

The role of the innate immune system has become widely appreciated in cancer and cancer-associated disorders. Neutrophils, the most abundant circulating leukocytes, have prognostic value in determining cancer progression and survival. One of the ways by which neutrophils negatively impact outcome is by formation of neutrophil extracellular traps (NETs) which result in release of nuclear chromatin and bioactive proteins into the extracellular space. Here, we review the evidence for NETs contributions to cancer progression, metastasis, and cancer-associated thrombosis (CAT).

RECENT FINDINGS

NETs are increased across several cancer types and predict progression and adverse outcome. Several preclinical and clinical observations implicate NETs in promoting tumor growth, angiogenesis and metastasis via distinct pathways. Furthermore, NETs are shown to contribute to resistance to immunotherapy. NETs also emerge as key players in the prothrombotic phenotype associated with cancer that can result in potentially life-threatening arterial and venous thrombosis. Recent mechanistic insights expose several potential targets to inhibit NET formation and disrupt the interaction between NETs and tumor cells.

SUMMARY

Clinical and translational insights highlight the central role of NETs in cancer progression and metastasis, disease resistance and CAT. Targeting NETs and NET-associated pathways may represent a novel approach to treat cancer.