A novel natural mutation AαPhe98Ile in the fibrinogen coiled-coil affects fibrinogen function

Development of Transient Recombinant Expression and Affinity Chromatography Systems for Human Fibrinogen

Fibrin forms the structural scaffold of blood clots and has great potential for biomaterial applications. Creating recombinant expression systems of fibrinogen, fibrin’s soluble precursor, would advance the ability to construct mutational libraries that would enable structure–function studies of fibrinogen and expand the utility of fibrin as a biomaterial. Despite these needs, recombinant fibrinogen expression systems, thus far, have relied on the time-consuming creation of stable cell lines. Here we present tests of a transient fibrinogen expression system that can rapidly generate yields of 8–12 mg/L using suspension HEK Expi293^TM cells. We report results from two different plasmid systems encoding the fibrinogen cDNAs and two different transfection reagents. In addition, we describe a novel, affinity-based approach to purifying fibrinogen from complex media such as human plasma. We show that using a high-affinity peptide which mimics fibrin’s knob ‘A’ sequence enables the purification of 50–75% of fibrinogen present in plasma. Having robust expression and purification systems of fibrinogen will enable future studies of basic fibrin(ogen) biology, while paving the way for the ubiquitous use of fibrin as a biomaterial.

Arachidonic acid causes lysis of blood cells and ADP-dependent platelet activation responses in platelet function tests

The use of arachidonic acid (AA) to stimulate platelets is considered as a specific approach to study aspirin treatment efficacy. However, very high concentrations of AA are used, and it has been previously reported that AA can induce cell lysis in other settings. Several clinical studies have reported decreased responses to AA in whole blood tests in the presence of clopidogrel. Our aim was to investigate whether unspecific effects contribute to AA-induced aggregation and platelet activation in light transmission aggregometry (LTA) in platelet-rich plasma (PRP), and in assays using whole blood, multiple electrode aggregometry (MEA, Multiplate®), and flow cytometry. We report that cell lysis, especially of red blood cells, does occur at concentrations of AA used in the clinical tests and that ADP is very important for the AA-induced platelet activation responses. In flow cytometry, very limited platelet activation was detected before reaching AA concentrations in the millimolar range, where cell lysis also occurred, making it problematic to develop a reliable flow cytometry assay using AA as reagent. We conclude that cell lysis and ADP release contribute to AA-induced platelet responses, most markedly in whole blood assays. This finding could potentially explain some differences between studies comparing methods using whole blood and PRP and also how clopidogrel treatment could influence AA-induced aggregation results in previously published studies. Our findings highlight some issues with AA as reagent for platelet activation, which also have an impact on how platelet activation assays using AA should be interpreted.

A novel fibrinogen mutation: FGA g. 3057 C > T (p. Arg104 > Cys) impairs fibrinogen secretion

Background

Abnormal fibrinogens can be caused by clinically silent hereditary mutations. A new case was detected accidentally in an 11-year-old girl when routine pre-operative coagulation tests were performed for nasal turbinate surgery.

Methods

The fibrinogen genes FGA, FGG and FGB were sequenced using standard protocols. The kinetics of fibrin formation were followed by turbidity at 350 nm. Purified fibrinogen was incubated with plasmin, and the degradation products analyzed by SDS/PAGE. The formation of fibrinogen-albumin complexes was analyzed by immunobloting. Fibrin structure was examined in a Nikon Eclipse TE 2000-U laser microscope. Secretion of the variant protein was analyzed directly by reverse phase-electrospray time of flight-mass spectrometry (TOF-MS).

Results

DNA sequencing revealed a novel heterozygous g. 3057 C > T mutation in the FGA that predicts a p. Arg104 > Cys substitution, in the proband and her father. Both patients were asymptomatic with low functional and antigen fibrinogen concentrations. The proband's plasma fibrinogen polymerization was almost normal, with a 12% decrease in the final turbidity, while, the father's fibrin formation had a diminished slope and final turbidity (2.5× and 40%, respectively). Aα Arg104 is located at a plasmin cleavage site in the coiled-coil region of fibrinogen. However, the father's fibrinogen plasmin degradation was normal. Although the exchanged Cys introduces an unpaired -SH, immunoblotting showed no fibrinogen-albumin complexes. Furthermore, the plasma clot structure observed by confocal microscopy appeared almost normal. TOF-MS showed that the variant Aα chain was underrepresented in plasma and made up only about 25% of the total.

Conclusions

The low expression of the Aα Arg104 > Cys chain in circulation could account for the observed hypodysfibrinogenemia.

Fibrin nanostructures for biomedical applications

Fibrin is a versatile biopolymer that has been extensively used in tissue engineering. In this paper fibrin nanostructures prepared using a technique based on the catalytic effect of fibrin-bound thrombin are presented. This technique enables surface-attached thin fibrin networks to form with precisely regulated morphology without the development of fibrin gel in bulk solution. Moreover, the influence of changing the polymerization time, along with the antithrombin III and heparin concentrations on the morphology of fibrin nanostructures was explored. The binding of bioactive molecules (fibronectin, laminin, collagen, VEGF, bFGF, and heparin) to fibrin nanostructures was confirmed. These nanostructures can be used for the surface modification of artificial biomaterials designed for different biomedical applications (e.g. artificial vessels, stents, heart valves, bone and cartilage constructs, skin grafts, etc.) in order to promote the therapeutic outcome.

Two novel mutations in the fibrinogen γ nodule

INTRODUCTION

Congenital dysfibrinogenemia and hypofibrinogenemia are rare diseases characterized by inherited abnormality in the fibrinogen molecule, resulting in functional defects (dysfibrinogenemia) or low fibrinogen plasma levels (hypofibrinogenemia).

MATERIALS AND METHODS

We have described two abnormal fibrinogens - fibrinogen Hranice (γ Phe204Val) and Praha IV (γ Ser313Gly). The carrier of the Hranice mutation was a 40-year-old female with low fibrinogen levels. The carrier of the Praha IV mutation was a 42-year-old man with a history of idiopathic thrombosis, low functional fibrinogen levels, and a prolonged thrombin time.

RESULTS

Fibrin polymerization kinetics measurement was normal in both cases (after the addition of either thrombin or reptilase), as well as was fibrinolysis. Scanning electron microscopy and confocal microscopy revealed significantly wider fibers in both cases, when compared with fibers prepared from healthy control samples. Although both cases are situated in the γ-nodule, they manifested differently. While the γ Ser313Gly mutation manifested as dysfibrinogenemia with a thrombotic background, the γ Phe204Val mutation manifested as hypofibrinogenemia without clinical symptoms. The mutation sites of both fibrinogens are in highly conserved regions of the fibrinogen γ chains. γ Ser313 is situated in a class 16:18 β hairpin and is involved in hydrogen bonding with γ Asp320. γ Phe204 is situated in an inverse γ turn and may be involved in π-π interactions.

CONCLUSIONS

Both mutations cause conformational changes in fibrinogen, which lead either to impaired fibrinogen assembly (fibrinogen Hranice) or abnormal fibrinogen function (fibrinogen Praha IV).