Increased adhesion to endothelial cells of erythrocytes from patients with polycythemia vera is mediated by laminin alpha5 chain and Lu/BCAM

Neuron-specific RNA-sequencing reveals different responses in peripheral neurons after nerve injury

Peripheral neurons are heterogeneous and functionally diverse, but all share the capability to switch to a pro-regenerative state after nerve injury. Despite the assumption that the injury response is similar among neuronal subtypes, functional recovery may differ. Understanding the distinct intrinsic regenerative properties between neurons may help to improve the quality of regeneration, prioritizing the growth of axon subpopulations to their targets. Here, we present a comparative analysis of regeneration across four key peripheral neuron populations: motoneurons, proprioceptors, cutaneous mechanoreceptors, and nociceptors. Using Cre/Ai9 mice that allow fluorescent labeling of neuronal subtypes, we found that nociceptors showed the greater regeneration after a sciatic crush, followed by motoneurons, mechanoreceptors, and, finally, proprioceptors. By breeding these Cre mice with Ribotag mice, we isolated specific translatomes and defined the regenerative response of these neuronal subtypes after axotomy. Only 20% of the regulated genes were common, revealing a diverse response to injury among neurons, which was also supported by the differential influence of neurotrophins among neuron subtypes. Among differentially regulated genes, we proposed MED12 as a specific regulator of the regeneration of proprioceptors. Altogether, we demonstrate that the intrinsic regenerative capacity differs between peripheral neuron subtypes, opening the door to selectively modulate these responses.

Retinal Vessel Analysis and Microvascular Abnormalities in Patients with Philadelphia-Negative Chronic Myeloproliferative Neoplasms

Background: Philadelphia-negative chronic myeloproliferative neoplasms are a group of clonal hematopoietic disorders including polycythemia vera, essential thrombocythemia, and primary myelofi-brosis. These neoplasms are characterized by an increased risk of thrombotic complications. Several studies have highlighted that the study of vessels of the retina offers the opportunity to visualize, in vivo, the damage to microcirculation that is common in various systemic pathologies. Methods: in our study, forty patients underwent an ophthalmological examination, using non-invasive imaging tech-niques, for analyses of their retinal vascularization. The objective was to correlate the findings ob-tained from this study of the retina with different markers of thrombotic risk, to demonstrate the usefulness of studying retinal vessels as a possible new prognostic biomarker of thrombotic risk in patients affected by Philadelphia-negative chronic myeloproliferative neoplasms. Results: retinal imaging demonstrated changes in the microcirculation, with a reduced vascular density of the deep and superficial capillary plexuses with respect to a normal group, and a correlation between retinal changes and blood parameters. Conclusions: additional research will allow us to determine whether retinal changes in individuals with chronic myeloproliferative neoplasms could be predictive of the development of thrombotic events in these subjects.

Exploring the Molecular Aspects of Myeloproliferative Neoplasms Associated with Unusual Site Vein Thrombosis: Review of the Literature and Latest Insights

Myeloproliferative neoplasms (MPNs) are the leading causes of unusual site thrombosis, affecting nearly 40% of individuals with conditions like Budd-Chiari syndrome or portal vein thrombosis. Diagnosing MPNs in these cases is challenging because common indicators, such as spleen enlargement and elevated blood cell counts, can be obscured by portal hypertension or bleeding issues. Recent advancements in diagnostic tools have enhanced the accuracy of MPN diagnosis and classification. While bone marrow biopsies remain significant diagnostic criteria, molecular markers now play a pivotal role in both diagnosis and prognosis assessment. Hence, it is essential to initiate the diagnostic process for splanchnic vein thrombosis with a JAK2 V617F mutation screening, but a comprehensive approach is necessary. A multidisciplinary strategy is vital to accurately determine the specific subtype of MPNs, recommend additional tests, and propose the most effective treatment plan. Establishing specialized care pathways for patients with splanchnic vein thrombosis and underlying MPNs is crucial to tailor management approaches that reduce the risk of hematological outcomes and hepatic complications.

Activated PRKCD-mediated neutrophil extracellular traps pathway may be the prothrombotic mechanism of neutrophils in polycythemia vera patients based on clinical retrospective analysis and bioinformatics study

Thrombosis is a major cause of morbimortality in patients with polycythemia vera (PV). Furthermore, neutrophils play a significant role in thrombosis, but their role in the pathogenetic mechanisms of PV is not well characterized. Therefore, we investigated the role and mechanisms by which neutrophils regulate thrombosis in PV patients. Univariate and multivariate logistic regression analysis of clinicopathological factors was performed to determine the independent risk factors of thrombosis in PV. Pearson's correlation analysis was performed to determine the relationship between absolute neutrophil count (ANC) and the hypercoagulable state in PV patients. Bioinformatics analysis of the GSE54644 dataset was used to identify hemostasis-related pathways in neutrophils of PV patients. Weighted gene co-expression network analysis (WGCNA) of the integrated dataset (GSE57793, GSE26049 and GSE61629) was used to identify neutrophils-related genes and pathways associated with thrombosis in PV. Ingenuity pathway analysis (IPA) was performed to identify the differentially activated pathways in PV patients with or without thrombosis using GSE47018 dataset. Our data showed increased ANC in PV patients. Multivariate logistic regression analysis showed that ANC was an independent risk factor for the thrombotic events in PV patients before or at diagnosis. ANC correlated with the hypercoagulable state in PV patients. Neutrophil extracellular traps (NETs) pathway was significantly enriched in the neutrophils of PV patients. IPA results demonstrated that PRKCD-mediated NETs pathway was hyperactivated in PV patients with thrombosis. In summary, ANC was an independent risk factor for the thrombotic events in PV patients before or at diagnosis, and PRKCD-mediated NETs pathway was aberrantly activated in the neutrophils of PV patients and was associated with the thrombotic events.

Red Blood Cell Contribution to Thrombosis in Polycythemia Vera and Essential Thrombocythemia

Polycythemia vera (PV) and essential thrombocythemia (ET) are myeloproliferative neoplasms (MPN) characterized by clonal erythrocytosis and thrombocytosis, respectively. The main goal of therapy in PV and ET is to prevent thrombohemorrhagic complications. Despite a debated notion that red blood cells (RBCs) play a passive and minor role in thrombosis, there has been increasing evidence over the past decades that RBCs may play a biological and clinical role in PV and ET pathophysiology. This review summarizes the main mechanisms that suggest the involvement of PV and ET RBCs in thrombosis, including quantitative and qualitative RBC abnormalities reported in these pathologies. Among these abnormalities, we discuss increased RBC counts and hematocrit, that modulate blood rheology by increasing viscosity, as well as qualitative changes, such as deformability, aggregation, expression of adhesion proteins and phosphatidylserine and release of extracellular microvesicles. While the direct relationship between a high red cell count and thrombosis is well-known, the intrinsic defects of RBCs from PV and ET patients are new contributors that need to be investigated in depth in order to elucidate their role and pave the way for new therapeutical strategies.

Late In-Stent Thrombosis After Carotid Artery Stenting for Symptomatic Internal Carotid Artery Stenosis in a Patient With JAK2 V617F-Positive Essential Thrombocythemia: An Illustrative Case Report

Essential thrombocythemia (ET) is a myeloproliferative disorder complicated by thrombosis in 13% of cases. The Janus kinase 2 (JAK2) V617Fmutation is present in 60% of ET cases, and it has recently been reported that the mutation itself is a significant contributor to ischemic stroke. Here, we present an illustrative case of late in-stent thrombosis following carotid artery stenting (CAS) in a patient with ET and the JAK2 V617F mutation presenting with symptomatic internal carotid artery (ICA) stenosis. An 80-year-old man with a history of JAK2 V617F-positive ET suffered from left upper motor weakness and numbness. Magnetic resonance imaging/magnetic resonance angiography revealed multiple acute cerebral infarctions scattered in the right frontal and parietal lobes and right ICA stenosis. Despite continued antiplatelet therapy, plaque size did not decrease. CAS was performed one month later; however, five months after the procedure, in-stent thrombus growth was observed, leading to severe stenosis despite administering antiplatelet or anticoagulant drugs. The thrombus was eventually resolved with increased doses of hydroxyurea and aspirin administration. In conclusion, controlling platelets and inflammation with hydroxyurea and aspirin may help improve the condition in case of rapid thrombosis due to the JAK2 V617F mutation, unlike other thromboses. This case highlights the importance of careful follow-up after CAS.

The Double-Edged Sword of Erythrocytes in Health and Disease via Their Adhesiveness

Their widespread presence throughout the vasculature, coupled with their reactivity, and thereby to their potential to release reactive oxidative species, or to utilize their anti-oxidative capacities, has promoted much discussion of the role(s) of red blood cells (RBCs) in the progression of health or, alternatively, a wide range of disease states. Moreover, these role(s) have been linked to the development of adhesiveness and, in fact, thereby to the essential pathway to their eventual clearance, e.g., by macrophages in the spleen. These disparate roles coupled with the mechanisms involved are reviewed and given. Following an analysis, novel perspectives are provided; these perspectives can lead to novel assays for identifying the potential for RBC adhesiveness as suggested herein. We describe this paradigm, that involves RBC adhesiveness, hemolysis, and ghost formation, with examples including, inter alia, the progression of atherosclerosis and the suppression of tumor growth along with other disease states.

Basal cell adhesion molecule promotes metastasis-associated processes in ovarian cancer

BACKGROUND

Basal cell adhesion molecule (BCAM) is a laminin α5 (LAMA5) binding membrane-bound protein with a putative role in cancer. Besides full-length BCAM1, an isoform lacking most of the cytoplasmic domain (BCAM2), and a soluble form (sBCAM) of unknown function are known. In ovarian carcinoma (OC), all BCAM forms are abundant and associated with poor survival, yet BCAM's contribution to peritoneal metastatic spread remains enigmatic.

METHODS

Biochemical, omics-based and real-time cell assays were employed to identify the source of sBCAM and metastasis-related functions of different BCAM forms. OC cells, explanted omentum and a mouse model of peritoneal colonisation were used in loss- and gain-of-function experiments.

RESULTS

We identified ADAM10 as a major BCAM sheddase produced by OC cells and identified proteolytic cleavage sites proximal to the transmembrane domain. Recombinant soluble BCAM inhibited single-cell adhesion and migration identically to membrane-bound isoforms, confirming its biological activity in OC. Intriguingly, this seemingly anti-tumorigenic potential of BCAM contrasts with a novel pro-metastatic function discovered in the present study. Thus, all queried BCAM forms decreased the compactness of tumour cell spheroids by inhibiting LAMA5 - integrin β1 interactions, promoted spheroid dispersion in a three-dimensional collagen matrix, induced clearance of mesothelial cells at spheroid attachment sites in vitro and enhanced invasion of spheroids into omental tissue both ex vivo and in vivo.

CONCLUSIONS

Membrane-bound BCAM as well as sBCAM shed by ADAM10 act as decoys rather than signalling receptors to modulate metastasis-related functions. While BCAM appears to have tumour-suppressive effects on single cells, it promotes the dispersion of OC cell spheroids by regulating LAMA5-integrin-β1-dependent compaction and thereby facilitating invasion of metastatic target sites. As peritoneal dissemination is majorly mediated by spheroids, these findings offer an explanation for the association of BCAM with a poor clinical outcome of OC, suggesting novel therapeutic options.

Splanchnic Vein Thrombosis in Myeloproliferative Neoplasms: Treatment Considerations and Unmet Needs

Patients who develop splanchnic vein thrombosis (SVT) in the setting of a myeloproliferative neoplasm (MPN) are at risk for complications including portal hypertension, bleeding, thrombosis, and death. Prompt multidisciplinary treatment is thus necessary to prevent long-term sequelae. However, optimal management strategies are not well established due to a paucity of data. In this review, we very briefly discuss the epidemiology, pathophysiology, and prognosis of MPN-SVT and then more comprehensively explore treatment considerations of MPN-SVT, including anticoagulation, endovascular/surgical intervention, and cytoreductive therapy. We will also highlight current gaps in our knowledge of MPN-SVT and conclude by suggesting future directions to optimize the treatment of MPN-SVT and improve outcomes.

Hyperviscosity syndromes; hemorheology for physicians and the use of microfluidic devices

PURPOSE OF REVIEW

Hyperviscosity syndromes can lead to significant morbidity and mortality. Existing methods to measure microcirculatory rheology are not readily available and limited in relevance and accuracy at this level. In this review, we review selected hyperviscosity syndromes and the advancement of their knowledge using microfluidic platforms.

RECENT FINDINGS

Viscosity changes drastically at the microvascular level as the physical properties of the cells themselves become the major determinants of resistance to blood flow. Current, outdated viscosity measurements only quantify whole blood or serum. Changes in blood composition, cell number, or the physical properties themselves lead to increased blood viscosity. Given the significant morbidity and mortality from hyperviscosity syndromes, new biophysical tools are needed and being developed to study microvascular biophysical and hemodynamic conditions at this microvascular level to help predict those at risk and guide therapeutic treatment.

SUMMARY

The use of 'lab-on-a-chip' technology continues to rise to relevance with point of care, personalized testing and medicine as customizable microfluidic platforms enable independent control of many in vivo factors and are a powerful tool to study microcirculatory hemorheology.

Prognostic Role of Cell Blood Count in Chronic Myeloid Neoplasm and Acute Myeloid Leukemia and Its Possible Implications in Hematopoietic Stem Cell Transplantation

Numerous prognostic indexes have been developed in hematological diseases based on patient characteristics and genetic or molecular assessment. However, less attention was paid to more accessible parameters, such as neutrophils, lymphocytes, monocytes, and platelet counts. Although many studies have defined the role of neutrophil-to-lymphocyte or platelet-to-lymphocyte in lymphoid malignancies, few applications exist for myeloid neoplasm or hematopoietic stem cell transplantation procedures. In this review, we synthesized literature data on the prognostic value of count blood cells in myeloid malignancies and hematopoietic stem cell transplantation in the context of classical prognostic factors and clinical outcomes.

Red Blood Cell Morphodynamics in Patients with Polycythemia Vera and Stroke

Polycythemia vera (PV) is a Ph-negative myeloproliferative neoplasm (MPN) which is characterized by erythrocytosis and a high incidence of thrombotic complications, including stroke. The study aimed to evaluate red blood cell (RBC) morphodynamic properties in PV patients and their possible association with stroke. We enrolled 48 patients with PV in this cross-sectional study, 13 of which have a history of ischemic stroke. The control group consisted of 90 healthy subjects. RBC deformability and aggregation analysis were performed using a laser-assisted optical rotational red cell analyzer. The following parameters were calculated: aggregation amplitude (Amp), RBC rouleaux formation time constant (Tf), time of formation of three-dimensional aggregates (Ts), aggregation index (AI), rate of complete disaggregation (y-dis), and the maximal elongation of RBC (EImax). Statistical analysis was performed with the R programming language. There were significant differences in RBCs morphodynamics features between patients with PV and the control group. Lower EImax (0.47 (0.44; 0.51) vs. 0.51 (0.47; 0.54), p < 0.001) and γ-dis (100 (100; 140) vs. 140 (106; 188) s⁻¹, p < 0.001) along with higher amplitude (10.1 (8.6; 12.2) vs. 7.7 (6.6; 9.2), p < 0.001) was seen in patients with PV compared with control. A statistically significant difference between PV patients with and without stroke in aggregation amplitude was found (p = 0.03). A logistic regression model for stroke was built based on RBC morphodynamics which performed reasonably well (p = 0.01). RBC alterations may be associated with overt cerebrovascular disease in PV, suggesting a possible link between erythrocyte morphodynamics and increased risk of stroke.

Polycythemia vera presenting with pulmonary embolism and splenic infarction: a case report

Pulmonary embolism and splenic infarction are rare in patients with polycythemia vera. We herein describe a man in his early 60s whose main symptoms were chest tightness, cough, and sputum expectoration. Antibiotics, bronchodilators, and mucoactive agents did not improve his symptoms. Pulmonary artery computed tomography angiography showed pulmonary embolism, and abdominal computed tomography showed multiple hypodense foci in the spleen. Bone marrow aspiration cytology, biopsy, and genetic testing confirmed polycythemia vera. The patient’s symptoms were relieved after treatment with hydroxyurea and rivaroxaban. This case emphasizes that although pulmonary embolism and splenic infarction are relatively rare in patients with polycythemia vera, the possibility of polycythemia vera should be considered in clinical practice.

Red Blood Cells: Tethering, Vesiculation, and Disease in Micro-Vascular Flow

The red blood cell has become implicated in the progression of a range of diseases; mechanisms by which red cells are involved appear to include the transport of inflammatory species via red cell-derived vesicles. We review this role of RBCs in diseases such as diabetes mellitus, sickle cell anemia, polycythemia vera, central retinal vein occlusion, Gaucher disease, atherosclerosis, and myeloproliferative neoplasms. We propose a possibly unifying, and novel, paradigm for the inducement of RBC vesiculation during vascular flow of red cells adhered to the vascular endothelium as well as to the red pulp of the spleen. Indeed, we review the evidence for this hypothesis that links physiological conditions favoring both vesiculation and enhanced RBC adhesion and demonstrate the veracity of this hypothesis by way of a specific example occurring in splenic flow which we argue has various renderings in a wide range of vascular flows, in particular microvascular flows. We provide a mechanistic basis for membrane loss and the formation of lysed red blood cells in the spleen that may mediate their turnover. Our detailed explanation for this example also makes clear what features of red cell deformability are involved in the vesiculation process and hence require quantification and a new form of quantitative indexing.

The pathobiology of thrombosis, microvascular disease, and hemorrhage in the myeloproliferative neoplasms

Thrombotic, vascular, and bleeding complications are the most common causes of morbidity and mortality in the Philadelphia chromosome-negative myeloproliferative neoplasms (MPNs). In these disorders, circulating red cells, leukocytes, and platelets, as well as some vascular endothelial cells, each have abnormalities that are cell-intrinsic to the MPN driver mutations they harbor (eg, JAK2 V617F). When these cells are activated in the MPNs, their interactions with each other create a highly proadhesive and prothrombotic milieu in the circulation that predisposes patients with MPN to venous, arterial, and microvascular thrombosis and occlusive disease. Bleeding problems in the MPNs are caused by the MPN blood cell-initiated development of acquired von Willebrand disease. The inflammatory state created by MPN stem cells in their microenvironment extends systemically to amplify the clinical thrombotic tendency and, at the same time, preferentially promote further MPN stem cell clonal expansion, thereby generating a vicious cycle that favors a prothrombotic state in these diseases.

Pathogenesis of cardiovascular events in BCR-ABL1-negative myeloproliferative neoplasms

Thrombosis, both in arterial and venous territories, is the major complication of myeloproliferative neoplasms and is responsible for a high rate of morbidity and mortality. The currently accepted risk factors are an age over 60 years and a history of thrombosis. However, many complex mechanisms contribute to this increased prothrombotic risk, with involvement of all blood cell types, plasmatic factors, and endothelial cells. Besides, some cardiovascular events may originate from arterial vasospasm that could contribute to thrombotic complications. In this review, we discuss recent results obtained in mouse models in the light of data obtained from clinical studies. We emphasize on actors of thrombosis that are currently not targeted with current therapeutics but could be promising targets, i.e, neutrophil extracellular traps and vascular reactivity.

Lysophosphatidic Acid-Activated Calcium Signaling Is Elevated in Red Cells from Sickle Cell Disease Patients

(1) Background: It is known that sickle cells contain a higher amount of Ca2+ compared to healthy red blood cells (RBCs). The increased Ca2+ is associated with the most severe symptom of sickle cell disease (SCD), the vaso-occlusive crisis (VOC). The Ca2+ entry pathway received the name of Psickle but its molecular identity remains only partly resolved. We aimed to map the involved Ca2+ signaling to provide putative pharmacological targets for treatment. (2) Methods: The main technique applied was Ca2+ imaging of RBCs from healthy donors, SCD patients and a number of transgenic mouse models in comparison to wild-type mice. Life-cell Ca2+ imaging was applied to monitor responses to pharmacological targeting of the elements of signaling cascades. Infection as a trigger of VOC was imitated by stimulation of RBCs with lysophosphatidic acid (LPA). These measurements were complemented with biochemical assays. (3) Results: Ca2+ entry into SCD RBCs in response to LPA stimulation exceeded that of healthy donors. LPA receptor 4 levels were increased in SCD RBCs. Their activation was followed by the activation of Gi protein, which in turn triggered opening of TRPC6 and CaV2.1 channels via a protein kinase Cα and a MAP kinase pathway, respectively. (4) Conclusions: We found a new Ca2+ signaling cascade that is increased in SCD patients and identified new pharmacological targets that might be promising in addressing the most severe symptom of SCD, the VOC.

Prevention of recurrent thromboembolism in myeloproliferative neoplasms: review of literature and focus on direct oral anticoagulants

Myeloproliferative neoplasms (MPNs), including polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (MF) are stem cell clonal neoplasms characterized by expansion of late myeloid cells. Thrombosis risk is elevated in MPNs and contributes significantly to morbidity and mortality. Current consensus guidelines make no specific recommendations regarding anticoagulant choice for the treatment of venous thromboembolism (VTE) in MPNs, with most evidence supporting the use of vitamin K antagonists (VKAs) for secondary prophylaxis. However, direct oral anticoagulants (DOACs) are now increasingly being used, although with limited data on safety and efficacy in MPNs specifically. The widespread adoption of DOACs is based on new, high-quality evidence demonstrating safety and efficacy of DOAC treatment for cancer-associated VTE. However, these studies include few if any MPN patients, and MPNs have disease-specific considerations that may elevate thrombosis and bleeding risk. The purpose of this review is to discuss evidence behind current treatment recommendations for thrombosis in MPNs, with special attention to the use of DOACs.

Cellular and Molecular Aspects of Blood Cell-Endothelium Interactions in Vascular Disorders

In physiology and pathophysiology the molecules involved in blood cell–blood cell and blood cell–endothelium interactions have been identified. Platelet aggregation and adhesion to the walls belonging to vessels involve glycoproteins (GP), GP llb and GP llla and the GP Ib–IX–V complex. Red blood cells (RBCs) in normal situations have little interaction with the endothelium. Abnormal adhesion of RBCs was first observed in sickle cell anemia involving vascular cell adhesion molecule (VCAM)-1, α4β1, Lu/BCAM, and intercellular adhesion molecule (ICAM)-4. More recently RBC adhesion was found to be increased in retinal-vein occlusion (RVO) and in polycythemia vera (PV). The molecules which participate in this process are phosphatidylserine and annexin V in RVO, and phosphorylated Lu/BCAM and α5 laminin chain in PV. The additional adhesion in diabetes mellitus occurs due to the glycated RBC band 3 and the advanced glycation end-product receptors. The multiligand receptor binds advanced glycation end products (AGEs) or S100 calgranulins, or β-amyloid peptide. This receptor for advanced glycation end products is known as RAGE. The binding to RAGE-activated endothelial cells leads to an inflammatory reaction and a prothrombotic state via NADPH activation and altered gene expression. RAGE blockade is a potential target for drugs preventing the deleterious consequences of RAGE activation.

Ocular Manifestations in Patients with Philadelphia-Negative Myeloproliferative Neoplasms

The major complications of Philadelphia-negative (Ph-Negative) myeloproliferative neoplasms (MPNs) are thrombosis, haemorrhage and leukemic transformation. As systemic and haematological diseases, MPNs have the potential to affect many tissues and organs. Some complications lead to the diagnosis of MPNs, but other signs and symptoms are often misdiagnosed or neglected as a sign of MPN disease. Therefore, we reviewed the current literature to investigate and delineate the clinical manifestations seen in the eyes of Ph-negative MPN patients. We found that ocular manifestations are common among patients with MPNs. The most frequently described manifestations are due to the consequences of haematological abnormalities causing microvascular disturbances and hyperviscosity. More serious and vision-threatening complications as thrombotic events in the eyes have been repeatedly reported as well. These ocular symptoms may precede more serious extraocular complications. Accordingly, combined ophthalmological and haematological management have the potential to discover these diseases earlier and prevent morbidity and mortality in these patients. Furthermore, routine ophthalmological screening of all newly diagnosed MPN patients may be a preventive approach for early diagnosis and timely treatment of the ocular manifestations.

Increased von Willebrand factor levels in polycythemia vera and phenotypic differences with essential thrombocythemia

BACKGROUND

Acquired von Willebrand factor (VWF) deficiency was described in Philadelphia-negative myeloproliferative neoplasms, especially in essential thrombocythemia (ET). VWF phenotype in contemporary patients with polycythemia vera (PV) remains less explored.

OBJECTIVES

To characterize the VWF phenotype in PV and to compare VWF phenotype in PV with matched healthy subjects and ET patients.

PATIENTS/METHODS

We studied 48 PV patients, treated according to current recommendations (hematocrit ≤ 45%, on low-dose aspirin prophylaxis); 48 healthy and 41 subjects with ET, all sex, age, and blood group matched. We measured VWF antigen, activity, multimeric pattern, ADAMTS-13, and factor VIII (FVIII) antigen.

RESULTS

In patients with PV, VWF antigen and activity were significantly higher than in healthy subjects (antigen: 119[96-137] vs 93[79-107] IU/dL; activity: 114[95-128] vs 90[79-107] IU/dL, respectively, medians and interquartile, P < 0.01), with normal multimeric distribution. ADAMTS-13 levels were similar between patients with PV and healthy subjects. FVIII levels were higher in PV than in healthy subjects (141[119-169] versus 98[88-123] IU/dL, respectively, P < 0.01). By multivariable analysis, JAK2-p.V617F allelic burden, erythrocyte count, and male sex significantly predicted VWF antigen and activity levels. As compared to patients with ET, patients with PV showed similar VWF antigen levels but approximately 40% higher activity (79[49-104] vs 112[93-125] IU/dL, respectively, P < 0.01).

CONCLUSIONS

Patients with PV show increased VWF and FVIII levels, predicted by JAK2-p.V617F burden and erythrocyte count. At variance with ET, acquired VWF defect was not observed in PV. High VWF/FVIII levels may sustain the thrombotic diathesis of PV and may be investigated as biomarkers for risk stratification.

[Thrombosis and platelet dysfunction in myeloproliferative neoplasms]

Myeloproliferative neoplasms are acquired hematological malignancies, mainly affecting the adult and whose morbidity and mortality stems from haemostasis disorders. The most frequently encountered complications include thrombosis, affecting preferentially the arterial territory, but also atypical locations such as splanchnic vein thrombosis. The pathophysiology of these thromboses is complex and involves different actors: blood cells, endothelium and flow conditions. Numerous studies have been conducted to identify risk factors for thrombosis. To date, only two risk factors have been validated through prospective studies (age over 60 years old, history of thrombotic events) and allow classification of patients as "low risk" and "high risk" as the basis for current treatment recommendations. Haemorrhagic manifestations, less frequent than thrombosis, are mainly related to an alteration of primary haemostasis and are therefore manifested by mucocutaneous bleeding. In these patients, platelet dysfunctions and/or acquired Willebrand syndromes can be found. The pathophysiology of thrombosis and platelet dysfunction during myeloproliferative neoplasms remains to date partially unknown. In this review, we offer to focus on physiopathological mechanisms as well as the latest advances in their understanding.

[Pathogenesis of thrombosis in JAK2V617F myeloproliferative neoplasms]

BCR-ABL negative myeloproliferative neoplasms are acquired hematologic diseases characterized by blood cell proliferation and that include polycythemia vera (PV), essential thrombocytemia (ET) and primary myelofibrosis (PMF). Occurring of venous and arterial thrombosis is the main complication of these diseases. Risk factors for thrombosis are individuals older than 60 and history of thrombosis. The mechanisms leading to thrombosis are complex and involve several blood compartments, plasmatic factors and endothelial cells. Over the last years, new actors of thrombosis have been discovered.

Dimerization and phosphorylation of Lutheran/basal cell adhesion molecule are critical for its function in cell migration on laminin

Tumor cell migration depends on the interactions of adhesion proteins with the extracellular matrix. Lutheran/basal cell adhesion molecule (Lu/BCAM) promotes tumor cell migration by binding to laminin α5 chain, a subunit of laminins 511 and 521. Lu/BCAM is a type I transmembrane protein with a cytoplasmic domain of 59 (Lu) or 19 (Lu(v13)) amino acids. Here, using an array of techniques, including site-directed mutagenesis, immunoblotting, FRET, and proximity-ligation assays, we show that both Lu and Lu(v13) form homodimers at the cell surface of epithelial cancer cells. We mapped two small-XXX-small motifs in the transmembrane domain as potential sites for monomers docking and identified three cysteines in the cytoplasmic domain as being critical for covalently stabilizing dimers. We further found that Lu dimerization and phosphorylation of its cytoplasmic domain were concomitantly needed to promote cell migration. We conclude that Lu is the critical isoform supporting tumor cell migration on laminin 521 and that the Lu:Lu(v13) ratio at the cell surface may control the balance between cellular firm adhesion and migration.

Red Blood Cells: Chasing Interactions

Human red blood cells (RBC) are highly differentiated cells that have lost all organelles and most intracellular machineries during their maturation process. RBC are fundamental for the nearly all basic physiologic dynamics and they are key cells in the body's respiratory system by being responsible for the oxygen transport to all cells and tissues, and delivery of carbon dioxide to the lungs. With their flexible structure RBC are capable to deform in order to travel through all blood vessels including very small capillaries. Throughout their in average 120 days lifespan, human RBC travel in the bloodstream and come in contact with a broad range of different cell types. In fact, RBC are able to interact and communicate with endothelial cells (ECs), platelets, macrophages, and bacteria. Additionally, they are involved in the maintenance of thrombosis and hemostasis and play an important role in the immune response against pathogens. To clarify the mechanisms of interaction of RBC and these other cells both in health and disease as well as to highlight the role of important key players, we focused our interest on RBC membrane components such as ion channels, proteins, and phospholipids.

Platelets as Mediators of Thromboinflammation in Chronic Myeloproliferative Neoplasms

Chronic myeloproliferative neoplasms (MPN) are stem cell disorders driven by mutations in JAK2, CALR, or MPL genes and characterized by myeloid proliferation and increased blood cell counts. They encompass three closely related conditions, including essential thrombocythemia, polycythemia vera, and primary myelofibrosis. Elevated levels of cytokines released by clonal and non-clonal cells generate a chronic proinflammatory state that contributes to disease pathogenesis. Thrombosis represents the most common cause of morbidity and mortality in MPN, although paradoxically, patients may also present with a bleeding diathesis. The mechanisms leading to thrombosis are complex and multiple and include increased blood cells together with qualitative abnormalities of red cells, leukocytes, and platelets that favor a prothrombotic activated phenotype. The functional interplay between blood cells, the clotting cascade, and dysfunctional endothelium contributes to hypercoagulability and this process is perpetuated by the effect of inflammatory cytokines. In addition to their well-known function in hemostasis, platelets contribute to innate immunity and inflammation and play a key role in MPN thromboinflammatory state. In vivo platelet activation leads to platelet aggregate formation and exposure of adhesion molecules which favor their interaction with activated neutrophils and monocytes leading to circulating platelet-leukocyte heterotypic aggregates. Platelets are recruited to the activated endothelium further enhancing the reciprocal activation of both cell types. Crosstalk between activated cells drives cytokine production, further fuelling the self-reinforcing thromboinflammatory loop. In addition, MPN platelets provide a procoagulant scaffold which triggers the coagulation cascade and platelet-derived microparticles amplify this response. Markers of platelet, leukocyte, endothelial and coagulation activation are increased in MPN patients although prospective studies are required to determine the potential value of these parameters for identifying patients at increased thrombotic risk. Thrombosis remains the main complication of MPN patients, with a high risk of recurrence despite adequate cytoreductive and antithrombotic treatment. Deeper insight into the mechanism favoring thrombosis development in this setting may lead to novel therapeutic approaches for MPN thrombosis. Considering the critical role of inflammation in the vascular risk, concomitant targeting of inflammatory pathways could potentially impact on primary or secondary prevention strategies.

Spatio-temporal dynamics of cerebral capillary segments with stalling red blood cells

Optical coherence tomography (OCT) allows label-free imaging of red blood cell (RBC) flux within capillaries with high spatio-temporal resolution. In this study, we utilized time-series OCT-angiography to demonstrate interruptions in capillary RBC flux in mouse brain in vivo. We noticed ∼7.5% of ∼200 capillaries had at least one stall in awake mice with chronic windows during a 9-min recording. At any instant, ∼0.45% of capillaries were stalled. Average stall duration was ∼15 s but could last over 1 min. Stalls were more frequent and longer lasting in acute window preparations. Further, isoflurane anesthesia in chronic preparations caused an increase in the number of stalls. In repeated imaging, the same segments had a tendency to stall again over a period of one month. In awake animals, functional stimulation decreased the observance of stalling events. Stalling segments were located distally, away from the first couple of arteriolar-side capillary branches and their average RBC and plasma velocities were lower than nonstalling capillaries within the same region. This first systematic analysis of capillary RBC stalls in the brain, enabled by rapid and continuous volumetric imaging of capillaries with OCT-angiography, will lead to future investigations of the potential role of stalling events in cerebral pathologies.

Oncogenic Deregulation of Cell Adhesion Molecules in Leukemia

Numerous cell⁻cell and cell⁻matrix interactions within the bone marrow microenvironment enable the controlled lifelong self-renewal and progeny of hematopoietic stem and progenitor cells (HSPCs). On the cellular level, this highly mutual interaction is granted by cell adhesion molecules (CAMs) integrating differentiation, proliferation, and pro-survival signals from the surrounding microenvironment to the inner cell. However, cell⁻cell and cell⁻matrix interactions are also critically involved during malignant transformation of hematopoietic stem/progenitor cells. It has become increasingly apparent that leukemia-associated gene products, such as activated tyrosine kinases and fusion proteins resulting from chromosomal translocations, directly regulate the activation status of adhesion molecules, thereby directing the leukemic phenotype. These observations imply that interference with adhesion molecule function represents a promising treatment strategy to target pre-leukemic and leukemic lesions within the bone marrow niche. Focusing on myeloid leukemia, we provide a current overview of the mechanisms by which leukemogenic gene products hijack control of cellular adhesion to subsequently disturb normal hematopoiesis and promote leukemia development.

Hematological Malignancies and Arterial Thromboembolism

Established guidelines exist for prevention and treatment of venous thromboembolism in hematological malignancies, but none for arterial thromboembolism. However, arterial and venous thromboembolism share the same provoking features—including altered procoagulant factors and defective fibrinolytic system. The morbidity for arterial thromboembolism is increasing in hematological malignancies, with the advent of immunomodulatory and targeted therapy. However, survival rate for hematological malignancy is improving. Consequently, as patients with hematological malignancies live longer, comorbidities including diabetes, hypertension and dyslipidemia, may accentuate arterial thrombosis. Thus far, the scientific literature on prophylaxis and treatment for arterial thromboembolism in hematological malignancies is limited. This review highlights the pathogenesis, incidence and clinical features of arterial thromboembolism in hematological malignancies.

Biocompatible coupling of therapeutic fusion proteins to human erythrocytes

Carriage of drugs by red blood cells (RBCs) modulates pharmacokinetics, pharmacodynamics, and immunogenicity. However, optimal targets for attaching therapeutics to human RBCs and adverse effects have not been studied. We engineered nonhuman-primate single-chain antibody fragments (scFvs) directed to human RBCs and fused scFvs with human thrombomodulin (hTM) as a representative biotherapeutic cargo (hTM-scFv). Binding fusions to RBCs on band 3/glycophorin A (GPA; Wright b [Wr^b] epitope) and RhCE (Rh17/Hr0 epitope) similarly endowed RBCs with hTM activity, but differed in their effects on RBC physiology. scFv and hTM-scFv targeted to band 3/GPA increased membrane rigidity and sensitized RBCs to hemolysis induced by mechanical stress, while reducing sensitivity to hypo-osmotic hemolysis. Similar properties were seen for other ligands bound to GPA and band 3 on human and murine RBCs. In contrast, binding of scFv or hTM-scFv to RhCE did not alter deformability or sensitivity to mechanical and osmotic stress at similar copy numbers bound per RBCs. Contrasting responses were also seen for immunoglobulin G antibodies against band 3, GPA, and RhCE. RBC-bound hTM-scFv generated activated protein C (APC) in the presence of thrombin, but RhCE-targeted hTM-scFv demonstrated greater APC generation per bound copy. Both Wr^b- and RhCE-targeted fusion proteins inhibited fibrin deposition induced by tumor necrosis factor-α in an endothelialized microfluidic model using human whole blood. RhCE-bound hTM-scFv more effectively reduced platelet and leukocyte adhesion, whereas anti-Wr^b scFv appeared to promote platelet adhesion. These data provide a translational framework for the development of engineered affinity ligands to safely couple therapeutics to human RBCs.

Thrombospondin 1 (THBS1) Promotes Follicular Angiogenesis, Luteinization, and Ovulation in Primates

Angiogenesis is essential to both ovulation and the formation of the corpus luteum. The thrombospondin (THBS) family of glycoproteins plays diverse roles in regulation of angiogenesis, but the role of these vascular regulators in ovulation and luteinization remain to be elucidated. Using the cynomolgus macaque as a model for human ovulation, we demonstrated that levels of THBS1 mRNA and protein in preovulatory follicle granulosa cells increased after the ovulatory gonadotropin surge, with peak levels just before the expected time of ovulation. THBS1 treatment of monkey ovarian microvascular endothelial cells in vitro stimulated migration, proliferation, and capillary sprout formation, consistent with a pro-angiogenic action of THBS1. Injection of an anti-THBS1 antibody into monkey preovulatory follicles reduced rates of follicle rupture and oocyte release in response to an ovulatory gonadotropin stimulus when compared with control IgG-injected follicles. Interestingly, two of three oocytes from anti-THBS1 antibody injected follicles were germinal vesicle intact, indicating that meiosis failed to resume as anticipated. Follicles injected with anti-THBS1 antibody also showed reduced granulosa cell layer expansion, endothelial cell invasion, and capillary formation when compared to control IgG-injected follicles. Overall, these findings support a critical role for THBS1 in follicular angiogenesis, with implications for both successful ovulation and corpus luteum formation.

Endothelial glycocalyx regulates cytoadherence in Plasmodium falciparum malaria

Malaria is associated with significant microcirculation disorders, especially when the infection reaches its severe stage. This can lead to a range of fatal conditions, from cerebral malaria to multiple organ failure, of not fully understood pathogenesis. It has recently been proposed that a breakdown of the glycocalyx, the carbohydrate-rich layer lining the vascular endothelium, plays a key role in severe malaria, but direct evidence supporting this hypothesis is still lacking. Here, the interactions between Plasmodium falciparum infected red blood cells ( PfRBCs) and endothelial glycocalyx are investigated by developing an in vitro, physiologically relevant model of human microcirculation based on microfluidics. Impairment of the glycocalyx is obtained by enzymatic removal of sialic acid residues, which, due to their terminal location and net negative charge, are implicated in the initial interactions with contacting cells. We show a more than twofold increase of PfRBC adhesion to endothelial cells upon enzymatic treatment, relative to untreated endothelial cells. As a control, no effect of enzymatic treatment on healthy red blood cell adhesion is found. The increased adhesion of PfRBCs is also associated with cell flipping and reduced velocity as compared to the untreated endothelium. Altogether, these results provide a compelling evidence of the increased cytoadherence of PfRBCs to glycocalyx-impaired vascular endothelium, thus supporting the advocated role of glycocalyx disruption in the pathogenesis of this disease.

Expression of CD markers in JAK2V617F positive myeloproliferative neoplasms: Prognostic significance

Myeloproliferative neoplasms (MPNs) are clonal stem cell disorders characterized by the presence of JAK2^V617F mutation. Thrombohemorrhagic as well as autoimmune or inflammatory phenomena are common clinical outcomes of these disorders. Recent studies have shown that abnormality in frequency and function of blood cells manifested by an alteration in CD markers' expression patterns play a key role in these complications. So, there may be a relationship between CD markers' expressions and prognosis of JAK2^V617F positive MPNs. Therefore, in this review, we have focused on these abnormalities from the perspective of changing expressions of CD markers and assessment of the relationship between these changes with prognosis of JAK2^V617F positive MPNs. It can be stated that the abnormal expression of a large number of CD markers can be used as a prognostic biomarker for clinical outcomes including thrombohememorrhagic events, as well as autoimmune and leukemic transformation in JAK2^V617F positive MPNs. Considering the possible role of CD markers' expressions in JAK2^V617F MPNs prognosis, further studies are needed to confirm the relationship between the expression of CD markers with prognosis to be able to find an appropriate therapeutic approach via targeting CD markers.

Association of JAK2V617F mutation with thrombosis in Indian patients with Philadelphia negative chronic myeloproliferative neoplasms

Background

: It is still a matter of debate regarding the association of JAK2V617F mutation with thrombosis in BCR-ABL negative CMPN patients. The role of JAK2V617F mutation in increasing the thrombotic risk in CMPNs is yet unequivocal.

Aims

: To clarify the contribution of JAK2V617F mutation in thrombosis in CMPN patients.

Settings and Design

This retrospective study was done to evaluate role of JAK2V617F mutation in thrombosis in CMPNs.

Materials and Methods

65 CMPN patients (PV, ET and PMF) were analyzed for JAK2V617F mutation using ARMS-PCR and detailed history of thrombosis was recorded in these patients.

Statistical Analysis

P values were 2 tailed, and statistical significance was set at P < 0.05.

Results

: 46/65 were males and 19/65 were females [M: F: 2.4:1] with median age 46 years [range, 14-80 years]. Patients had median Hb 15.6 g/dl [range, 5.1-20.3], median TLC 10.7 × 10⁹/l [range 2.4-216] and platelet count 360 × 10⁹/l [range, 20-1859]. 32 were JAK2V617F positive and 33 were negative for this mutation. On comparing the prevalence of thrombosis in JAK2V617F positive patients with JAK2V617F negative patients, we observed that 20/32 (62.5%) JAK2V617F positive patients had thrombosis as compared to 16/33 (48%) in JAK2V617F negative patients (P = 0.04). We observed significant association of JAK2V617F mutation with thrombosis, however no association of this mutation with thrombosis was observed among the JAK2V617F negative patients.

Conclusion

Our study suggests that JAK2V617F mutation may increase the risk of thrombosis in CMPNs. This finding could lead to risk stratification, setting up the treatment strategy in CMPNs.

The Exposure of Phosphatidylserine Influences Procoagulant Activity in Retinal Vein Occlusion by Microparticles, Blood Cells, and Endothelium

The pathogenesis of hypercoagulability in retinal vein occlusion (RVO) is largely unknown. Whether the exposure of phosphatidylserine (PS) and microparticle (MPs) release will affect procoagulant activity (PCA) in RVO needs to be investigated. Objectives. To evaluate PS expression, circulating MPs, and the corresponding PCA in RVO patients. Twenty-five RVO patients were compared with 25 controls. PS-positive cells were detected by flow cytometry. Cell-specific MPs were measured by lactadherin for PS and relevant CD antibody. We explored PCA with coagulation time, purified coagulation complex assays, and fibrin production assays. In RVO, MPs from platelets, erythrocytes, leukocyte, and endothelial cells were increased and the exposure of PS was elevated significantly when compared with controls. In addition, we showed that circulating MPs in RVO patients were mostly derived from platelets, representing about 60-70% of all MPs, followed by erythrocytes and leukocytes. Moreover, PS exposure, ECs, and MPs in RVO lead to shortened clotting time with upregulation of FXa and thrombin formation obviously. Importantly, ECs treated with RVO serum which bounded FVa and FXa explicitly suggested the damage of retinal vein endothelial cells. Furthermore, lactadherin can inhibit the combination between PS and coagulation factors by approximately 70% and then exert an anticoagulant effect. In summary, circulating MPs and exposed PS from different cells may contribute to the increased PCA in patients with RVO. Lactadherin can be used for PS detection and an anticoagulant agent.

Erythrocytes from patients with myeloproliferative neoplasms and splanchnic venous thrombosis show greater expression of Lu/BCAM

INTRODUCTION

Lutheran/BCAM protein (Lu) on the surface of erythrocytes is key for their adhesion to the endothelium, and erythrocytes from individuals with JAK2V617F-mutated myeloproliferative neoplasms (MPN) have increased endothelial adhesion. Splanchnic vein thrombosis (SVT) is a devastating thrombotic complication of MPN, and frequently, the only diagnostic feature is the JAK2V617F mutation. We sought to examine whether erythrocytes from patients with JAK2V617F mutated SVT (MPN-SVT) exhibited increased Lu expression, thereby supporting a mechanistic contribution to the development of thrombosis.

METHODS

We report the validation of a novel flow cytometry assay for Lu expression on erythrocytes. We examined the expression of Lu on erythrocytes from a cohort of MPN patients with and without SVT, and healthy controls. Samples were obtained from 20 normal individuals, 22 with MPN (both JAK2V617F-mutated and wild-type) and 8 with JAK2V617F-mutated MPN-SVT.

RESULTS

Lu expression by erythrocytes from patients with MPN and MPN-SVT is significantly increased compared to erythrocytes from healthy individuals (P < .05), but there was no significant difference between patients with MPN-SVT and MPN.

CONCLUSIONS

Patients with MPN have increased expression of the red cell Lu/BCAM adhesion molecule. Further work is required to determine the role of the increased Lu/BCAM adhesion to the endothelium in the development of thrombosis in MPN of all genotypes.

Impact of hydroxycarbamide and interferon-α on red cell adhesion and membrane protein expression in polycythemia vera

Polycythemia vera is a chronic myeloproliferative neoplasm characterized by the JAK2V617F mutation, elevated blood cell counts and a high risk of thrombosis. Although the red cell lineage is primarily affected by JAK2V617F, the impact of mutated JAK2 on circulating red blood cells is poorly documented. Recently, we showed that in polycythemia vera, erythrocytes had abnormal expression of several proteins including Lu/BCAM adhesion molecule and proteins from the endoplasmic reticulum, mainly calreticulin and calnexin. Here we investigated the effects of hydroxycarbamide and interferon-α treatments on the expression of erythroid membrane proteins in a cohort of 53 patients. Surprisingly, while both drugs tended to normalize calreticulin expression, proteomics analysis showed that hydroxycarbamide deregulated the expression of 53 proteins in red cell ghosts, with overexpression and downregulation of 37 and 16 proteins, respectively. Within over-expressed proteins, hydroxycarbamide was found to enhance the expression of adhesion molecules such as Lu/BCAM and CD147, while interferon-α did not. In addition, we found that hydroxycarbamide increased Lu/BCAM phosphorylation and exacerbated red cell adhesion to its ligand laminin. Our study reveals unexpected adverse effects of hydroxycarbamide on red cell physiology in polycythemia vera and provides new insights into the effects of this molecule on gene regulation and protein recycling or maturation during erythroid differentiation. Furthermore, our study shows deregulation of Lu/BCAM and CD147 that are two ubiquitously expressed proteins linked to progression of solid tumors, paving the way for future studies to address the role of hydroxycarbamide in tissues other than blood cells in myeloproliferative neoplasms.

Glycophorin-C sialylation regulates Lu/BCAM adhesive capacity during erythrocyte aging

Lutheran/basal cell adhesion molecule (Lu/BCAM) is a transmembrane adhesion molecule expressed by erythrocytes and endothelial cells that can interact with the extracellular matrix protein laminin-α5. In sickle cell disease, Lu/BCAM is thought to contribute to adhesion of sickle erythrocytes to the vascular wall, especially during vaso-occlusive crises. On healthy erythrocytes however, its function is unclear. Here we report that Lu/BCAM is activated during erythrocyte aging. We show that Lu/BCAM-mediated binding to laminin-α5 is restricted by interacting, in cis, with glycophorin-C-derived sialic acid residues. Following loss of sialic acid during erythrocyte aging, Lu/BCAM is released from glycophorin-C and allowed to interact with sialic acid residues on laminin-α5. Decreased glycophorin-C sialylation, as observed in individuals lacking exon 3 of glycophorin-C, the so-called Gerbich phenotype, was found to correlate with increased Lu/BCAM-dependent binding to laminin-α5. In addition, we identified the sialic acid-binding site within the third immunoglobulin-like domain within Lu/BCAM that accounts for the interaction with glycophorin-C and laminin-α5. Last, we present evidence that neuraminidase-expressing pathogens, such as Streptococcus pneumoniae, can similarly induce Lu/BCAM-mediated binding to laminin-α5, by cleaving terminal sialic acid residues from the erythrocyte membrane. These results shed new light on the mechanisms contributing to increased adhesiveness of erythrocytes at the end of their lifespan, possibly facilitating their clearance. Furthermore, this work may contribute to understanding the pathology induced by neuraminidase-positive bacteria, because they are especially harmful to patients suffering from sickle cell disease and are associated with the occurrence of vaso-occlusive crises.

Complications and management of coagulation disorders in leukemia patients

Patients with leukemia are predisposed to various coagulation abnormalities. Thrombosis and bleeding continue to be a major cause of morbidity and mortality in leukemias. The pathophysiology of these disorders is unique, and not only the disease but also the treatment and other factors play a role. There has been an increase in the understanding of these disorders in leukemias. However, it is still difficult to predict when and which patients will have these complications. The evidence for the management of coagulation abnormalities in leukemias is still evolving and not as established as in solid malignancies. The management of these disorders is complex, and making clinical decisions is often challenging. In the era of specialization, where there are different hematologists looking after benign- and malignant-hematology patients, opinions of thrombosis experts are often sought by leukemia specialists. This review aims to bridge the gap in the knowledge of these disorders between these specialists.

Eryptosis in health and disease: A paradigm shift towards understanding the (patho)physiological implications of programmed cell death of erythrocytes

During the course of their natural ageing and upon injury, anucleate erythrocytes can undergo an unconventional apoptosis-like cell death, termed eryptosis. Eryptotic erythrocytes display a plethora of morphological alterations including volume reduction, membrane blebbing and breakdown of the membrane phospholipid asymmetry resulting in phosphatidylserine externalization which, in turn, mediates their phagocytic recognition and clearance from the circulation. Overall, the eryptosis machinery is tightly orchestrated by a wide array of endogenous mediators, ion channels, membrane receptors, and a host of intracellular signaling proteins. Enhanced eryptosis shortens the lifespan of circulating erythrocytes and confers a procoagulant phenotype; this phenomenon has been tangibly implicated in the pathogenesis of anemia, deranged microcirculation, and increased prothrombotic risk associated with a multitude of clinical conditions. Herein, we reviewed the molecular mechanisms dictating eryptosis and erythrophagocytosis and critically analyzed the current evidence leading to the pathophysiological ramifications of eryptotic cell death in the context of human disease.

Antagonists of the system L neutral amino acid transporter (LAT) promote endothelial adhesivity of human red blood cells

The system L neutral amino acid transporter (LAT; LAT1, LAT2, LAT3, or LAT4) has multiple functions in human biology, including the cellular import of S-nitrosothiols (SNOs), biologically active derivatives of nitric oxide (NO). SNO formation by haemoglobin within red blood cells (RBC) has been studied, but the conduit whereby a SNO leaves the RBC remains unidentified. Here we hypothesised that SNO export by RBCs may also depend on LAT activity, and investigated the role of RBC LAT in modulating SNO-sensitive RBC-endothelial cell (EC) adhesion. We used multiple pharmacologic inhibitors of LAT in vitro and in vivo to test the role of LAT in SNO export from RBCs and in thereby modulating RBC-EC adhesion. Inhibition of human RBC LAT by type-1-specific or nonspecific LAT antagonists increased RBC-endothelial adhesivity in vitro, and LAT inhibitors tended to increase post-transfusion RBC sequestration in the lung and decreased oxygenation in vivo. A LAT1-specific inhibitor attenuated SNO export from RBCs, and we demonstrated LAT1 in RBC membranes and LAT1 mRNA in reticulocytes. The proadhesive effects of inhibiting LAT1 could be overcome by supplemental L-CSNO (S-nitroso-L-cysteine), but not D-CSNO or L-Cys, and suggest a basal anti-adhesive role for stereospecific intercellular SNO transport. This study reveals for the first time a novel role of LAT1 in the export of SNOs from RBCs to prevent their adhesion to ECs. The findings have implications for the mechanisms of intercellular SNO signalling, and for thrombosis, sickle cell disease, and post-storage RBC transfusion, when RBC adhesivity is increased.

Platelet-independent adhesion of calcium-loaded erythrocytes to von Willebrand factor

Adhesion of erythrocytes to endothelial cells lining the vascular wall can cause vaso-occlusive events that impair blood flow which in turn may result in ischemia and tissue damage. Adhesion of erythrocytes to vascular endothelial cells has been described in multiple hemolytic disorders, especially in sickle cell disease, but the adhesion of normal erythrocytes to endothelial cells has hardly been described. It was shown that calcium-loaded erythrocytes can adhere to endothelial cells. Because sickle erythrocyte adhesion to ECs can be enhanced by ultra-large von Willebrand factor multimers, we investigated whether calcium loading of erythrocytes could promote binding to endothelial cells via ultra-large von Willebrand factor multimers. We used (immunofluorescent) live-cell imaging of washed erythrocytes perfused over primary endothelial cells at venular flow rate. Using this approach, we show that calcium-loaded erythrocytes strongly adhere to histamine-stimulated primary human endothelial cells. This adhesion is mediated by ultra-large von Willebrand factor multimers. Von Willebrand factor knockdown or ADAMTS13 cleavage abolished the binding of erythrocytes to activated endothelial cells under flow. Platelet depletion did not interfere with erythrocyte binding to von Willebrand factor. Our results reveal platelet-independent adhesion of calcium-loaded erythrocytes to endothelium-derived von Willebrand factor. Erythrocyte adhesion to von Willebrand factor may be particularly relevant for venous thrombosis, which is characterized by the formation of erythrocyte-rich thrombi.

Ph(-) myeloproliferative neoplasm red blood cells display deregulation of IQGAP1-Rho GTPase signaling depending on CALR/JAK2 status

Besides genetic abnormalities in MPN patients, several studies have reported alterations in protein expression that could contribute towards the clinical phenotype. However, little is known about protein modifications in Ph^- MPN erythrocytes. In this context, we used a quantitative mass spectrometry proteomics approach to study the MPN erythrocyte proteome. LC-MS/MS (LTQ Orbitrap) analysis led to the identification of 51 and 86 overexpressed proteins in Polycythemia Vera and Essential Thrombocythemia respectively, compared with controls. Functional comparison using pathway analysis software showed that the Rho GTPase family signaling pathways were deregulated in MPN patients. In particular, IQGAP1 was significantly overexpressed in MPNs compared with controls. Additionally, Western-blot analysis not only confirmed IQGAP1 overexpression, but also showed that IQGAP1 levels depended on the patient's genotype. Moreover, we found that in JAK2V617F patients IQGAP1 could bind RhoA, Rac1 and Cdc42 and consequently recruit activated GTP-Rac1 and the cytoskeleton motility protein PAK1. In CALR(+) patients, IQGAP1 was not overexpressed but immunoprecipitated with RhoGDI. In JAK2V617F transduced Ba/F3 cells we confirmed JAK2 inhibitor-sensitive overexpression of IQGAP1/PAK1. Altogether, our data demonstrated alterations of IQGAP1/Rho GTPase signaling in MPN erythrocytes dependent on JAK2/CALR status, reinforcing the hypothesis that modifications in erythrocyte signaling pathways participate in Ph^- MPN pathogenesis.

Scanning Electron Microscopy Reveals Two Distinct Classes of Erythroblastic Island Isolated from Adult Mammalian Bone Marrow

Erythroblastic islands are multicellular clusters in which a central macrophage supports the development and maturation of red blood cell (erythroid) progenitors. These clusters play crucial roles in the pathogenesis observed in animal models of hematological disorders. The precise structure and function of erythroblastic islands is poorly understood. Here, we have combined scanning electron microscopy and immuno-gold labeling of surface proteins to develop a better understanding of the ultrastructure of these multicellular clusters. The erythroid-specific surface antigen Ter-119 and the transferrin receptor CD71 exhibited distinct patterns of protein sorting during erythroid cell maturation as detected by immuno-gold labeling. During electron microscopy analysis we observed two distinct classes of erythroblastic islands. The islands varied in size and morphology, and the number and type of erythroid cells interacting with the central macrophage. Assessment of femoral marrow isolated from a cavid rodent species (guinea pig, Cavis porcellus) and a marsupial carnivore species (fat-tailed dunnarts, Sminthopsis crassicaudata) showed that while the morphology of the central macrophage varied, two different types of erythroblastic islands were consistently identifiable. Our findings suggest that these two classes of erythroblastic islands are conserved in mammalian evolution and may play distinct roles in red blood cell production.