Plasma fibronectin in myeloproliferative disorders and chronic granulocytic leukaemia

Revisiting Circulating Extracellular Matrix Fragments as Disease Markers in Myelofibrosis and Related Neoplasms

Philadelphia chromosome-negative chronic myeloproliferative neoplasms (MPNs) arise due to acquired somatic driver mutations in stem cells and develop over 10-30 years from the earliest cancer stages (essential thrombocythemia, polycythemia vera) towards the advanced myelofibrosis stage with bone marrow failure. The JAK2V617F mutation is the most prevalent driver mutation. Chronic inflammation is considered to be a major pathogenetic player, both as a trigger of MPN development and as a driver of disease progression. Chronic inflammation in MPNs is characterized by persistent connective tissue remodeling, which leads to organ dysfunction and ultimately, organ failure, due to excessive accumulation of extracellular matrix (ECM). Considering that MPNs are acquired clonal stem cell diseases developing in an inflammatory microenvironment in which the hematopoietic cell populations are progressively replaced by stromal proliferation-"a wound that never heals"-we herein aim to provide a comprehensive review of previous promising research in the field of circulating ECM fragments in the diagnosis, treatment and monitoring of MPNs. We address the rationales and highlight new perspectives for the use of circulating ECM protein fragments as biologically plausible, noninvasive disease markers in the management of MPNs.

EDA fibronectin-TLR4 axis sustains megakaryocyte expansion and inflammation in bone marrow fibrosis

The fibronectin EDA isoform sustains bone marrow fibrosis, binding to TLR4 on megakaryocytes and inducing NF-κB activation and IL-6 release. In primary myelofibrosis patients, the bone marrow fibrosis correlates with increased levels of fibronectin EDA isoform in plasma.

The fibronectin EDA isoform (EDA FN) is instrumental in fibrogenesis but, to date, its expression and function in bone marrow (BM) fibrosis have not been explored. We found that mice constitutively expressing the EDA domain (EIIIA^+/+), but not EDA knockout mice, are more prone to develop BM fibrosis upon treatment with the thrombopoietin (TPO) mimetic romiplostim (TPO^high). Mechanistically, EDA FN binds to TLR4 and sustains progenitor cell proliferation and megakaryopoiesis in a TPO-independent fashion, inducing LPS-like responses, such as NF-κB activation and release of profibrotic IL-6. Pharmacological inhibition of TLR4 or TLR4 deletion in TPO^high mice abrogated Mk hyperplasia, BM fibrosis, IL-6 release, extramedullary hematopoiesis, and splenomegaly. Finally, developing a novel ELISA assay, we analyzed samples from patients affected by primary myelofibrosis (PMF), a well-known pathological situation caused by altered TPO signaling, and found that the EDA FN is increased in plasma and BM biopsies of PMF patients as compared with healthy controls, correlating with fibrotic phase.

Comprehensive Gene expression meta-analysis and integrated bioinformatic approaches reveal shared signatures between thrombosis and myeloproliferative disorders

Thrombosis is a leading cause of morbidity and mortality in patients with myeloproliferative disorders (MPDs), particularly polycythemia vera (PV) and essential thrombocythemia (ET). Despite the attempts to establish a link between them, the shared biological mechanisms are yet to be characterized. An integrated gene expression meta-analysis of five independent publicly available microarray data of the three diseases was conducted to identify shared gene expression signatures and overlapping biological processes. Using INMEX bioinformatic tool, based on combined Effect Size (ES) approaches, we identified a total of 1,157 differentially expressed genes (DEGs) (697 overexpressed and 460 underexpressed genes) shared between the three diseases. EnrichR tool's rich library was used for comprehensive functional enrichment and pathway analysis which revealed "mRNA Splicing" and "SUMO E3 ligases SUMOylate target proteins" among the most enriched terms. Network based meta-analysis identified MYC and FN1 to be the most highly ranked hub genes. Our results reveal that the alterations in biomarkers of the coagulation cascade like F2R, PROS1, SELPLG and ITGB2 were common between the three diseases. Interestingly, the study has generated a novel database of candidate genetic markers, pathways and transcription factors shared between thrombosis and MPDs, which might aid in the development of prognostic therapeutic biomarkers.

Composition of immune complexes and their relation to plasma fibronectin in chronic myeloproliferative disorders

High concentrations of circulating immune complexes were detected by polyethylene glycol precipitation in 11 of 20 patients with myelofibrosis secondary to chronic myeloproliferative disease. Circulating immune complexes showed a positive correlation with plasma IgG concentrations both in patients and controls. Covariance analysis of the two groups showed significantly increased polyethylene glycol precipitable IgG in patients when adjusted for plasma IgG concentrations, indicating that the patients had significantly increased concentrations of complexed IgG. The immune complexes contained IgG, C3, and fibronectin and were inversely correlated with plasma fibronectin concentrations, suggesting that this major non-specific opsonin is important for the normal clearance of immune complexes. Therapeutic plasmapheresis efficiently removed circulating complexes and produced an increase in plasma fibronectin. This suggests that plasmapheresis may be useful for controlling immune complex mediated complications of these disorders.

Plasma Fibronectin in Hemoblastosis

Fibronection (FN) is a glycoprotein whose plasma concentrations are reduced in many pathological conditions. In patients with hemoblastosis plasma FN was correlated with some clinical and biological parameters (stage of the disease, hepatosplenomegaly, infections and DIC), in order to assess its value as a tumor marker. The results suggest a poor relationship between FN levels and the course of the disease. However, the behaviour of the protein in relation with treatment was dynamic.

An enzyme immunoassay to measure canine circulating fibronectin

A competitive enzyme immunoassay has been used to detect and quantitate fibronectin in canine plasma. In this test, purified fibronectin, bound to microtiter plates, competes with plasma fibronectin for the conjugated antibody, rabbit-anticanine, fibronectin-horseradish peroxidase. The assay could detect fibronectin in purified standards from 58 ng/ml to 580 microgram/ml. The range of 1-100 microgram/ml was linear for plasma samples diluted 1:10, allowing samples with fibronectin concentrations from 10-1000 microgram/ml to be easily measured by this method. The mean normal fibronectin concentration of 132 dogs, by this method, was determined to be 320 +/- 74 microgram/ml.

Fibronectin: applications to clinical medicine

In summary, the role of fibronectin in clinical medicine is not yet certain. Correlation of sepsis and organ failure with decreased fibronectin levels is still to some degree questionable; controlled clinical trials are urgently needed. The risk of hepatitis, AIDS, and other transfusion-transmitted diseases must be balanced by data substantiating the clinical efficacy of fibronectin therapy. To date, no results from controlled trials using purified fibronectin have been reported. Final judgement must be reserved pending results of appropriate human studies. It is likely, however, that even if fibronectin is proven to be clinically useful, the patient population which will achieve some benefit from its use will be restricted to septic and/or critically ill patients. As noted by Mosher and Grossman however, physicians treating such patients would likely welcome any new and effective therapeutic intervention.

Changes in plasma fibronectin during donor apheresis and therapeutic plasma exchange

Changes in plasma levels of the opsonic glycoprotein fibronectin were studied during machine apheresis in 32 healthy plasma donors and 18 patients undergoing a total of 86 therapeutic plasma exchanges. Donation of 500 ml of plasma at 3-monthly intervals produced a 10% immediate decrease in plasma fibronectin with no evidence of a long-term affect on levels of this protein. One plasma volume exchange with fibronectin-poor plasma protein fraction produced subnormal plasma fibronectin levels in 98% of post-exchange samples. Efficiency of exchange was significantly lower in patients with paraproteinaemia, probably reflecting increased plasma volume in such patients. Daily plasma exchange produced progressive depletion of plasma fibronectin (index of recovery 0.68) whereas levels were maintained close to the initial value with longer exchange intervals, except in the more severely ill patients. Reduction of plasma fibronectin by plasma exchange may increase susceptibility to infection and reduce the efficacy of this procedure when the object of exchange is to reverse reticuloendothelial blockade.

Plasma thrombospondin in patients with chronic renal failure, liver disease and splenectomy

Thrombospondin (TSP), is a major constituent of human blood platelet alpha-granules. Stimulation of platelets causes the release of TSP in parallel with other alpha-granule constituents such as beta-thromboglobulin (beta-TG) and platelet factor 4 (PF4) but the thrombospondin plasma in vivo half life is significantly greater than beta-TG and PF4. The aim of this study was to assay TSP levels in plasma of patients with chronic renal failure (CRF), liver disease (LD) and following splenectomy. The TSP values were then compared to the patients plasma levels of two traditional markers of platelet activation, beta-TG and PF4, and to fibronectin (FN) and von Willebrand factor (VIII:vWF). Plasma TSP levels (67.6 +/- 16.9 ng/ml) assayed in 14 CRF patients were significantly higher (p less than 0.05) than those measured in 28 donors (55.5 +/- 11.7 ng/ml). No correlation was observed, in CRF patients, between the TSP level and PF4 (2.5 +/- 1.5 ng/ml), beta-TG (131.1 +/- 21 ng/ml), FVIII:vWF (252 +/- 85%), or FN (102 +/- 33%) plasma levels. The TSP plasma level in CRF patients was significantly correlated (p less than 0.02) with that of fibrinopeptide A (4.1 +/- 1.9 ng/ml). Although the beta-TG (23.5 +/- 6.9 ng/ml) and PF4 (2.9 +/- 2 ng/ml) plasma levels in six LD patients were normal, the TSP levels (82.5 +/- 39.1 ng/ml) were significantly increased (p less than 0.01). Thrombospondin plasma levels (77.1 +/- 20.1 ng/ml) in 14 patients having undergone splenectomy were significantly increased (p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in plasma fibronectin during allogeneic bone marrow transplantation

Plasma fibronectin concentrations were measured serially in nine patients undergoing allogeneic bone marrow transplantation. Concentrations were reduced by conditioning treatment and episodes of bacterial infection. Acute graft versus host disease may exacerbate or prolong this process. Reduced plasma fibronectin concentrations impair the function of the mononuclear phagocyte system and the maintenance of capillary endothelial integrity and may thus contribute to the morbidity and mortality in patients undergoing bone marrow transplantation.

Fibronectin assays and their clinical application: a review

Cold insoluble globulin (fibronectin) was discovered 30 years ago but recently there has been a remarkable growth of knowledge concerning its interaction with the cell cytoskeleton and its role in cell-cell and cell-matrix adhesion. The protein is also a major plasma opsonin with a role in regulating fixed macrophage activity and it is this area in which clinical applications are now beginning to develop. Methods are discussed for measuring the concentration of the protein and its opsonic function in vitro, and for the evaluation of fixed macrophage function in vivo. Also discussed are the metabolism of the protein, the implications of opsonin depletion in patients with serious injury or infection and the attempts to reverse this with plasma protein replacement therapy.