The factor XIII V34L polymorphism accelerates thrombin activation of factor XIII and affects cross-linked fibrin structure

Associations Between 25-Hydroxyvitamin D and Total and γ' Fibrinogen and Plasma Clot Properties and Gene Interactions in a Group of Healthy Black South African Women

The role of 25-hydroxyvitamin D [25(OH)D] in reducing the risk of cardiovascular disease (CVD) has been recognized, but the mechanisms involved are unclear. Researchers have discovered a link between vitamin D and fibrinogen. Until now, data on the relationship between vitamin D and the γ' splice variant of fibrinogen and fibrin clot characteristics remain unexplored. In this study, 25(OH)D, total and γ' fibrinogen, as well as turbidimetrically determined plasma clot properties, were quantified, and fibrinogen and FXIII SNPs were genotyped in 660 Black, apparently healthy South African women. Alarmingly, 16 and 45% of the women presented with deficient and insufficient 25(OH)D, respectively. Total fibrinogen and maximum absorbance (as a measure of clot density) correlated inversely, whereas γ' fibrinogen correlated positively with 25(OH)D. γ' fibrinogen increased whereas maximum absorbance decreased over the deficient, insufficient, and sufficient 25(OH)D categories before and after adjustment for confounders. 25(OH)D modulated the association of the SNPs regarding fibrinogen concentration and clot structure/properties, but did not stand after correction for false discovery rate. Because only weak relationships were detected, the clinical significance of the findings are questionable and remain to be determined. However, we recommend vitamin D fortification and supplementation to reduce the high prevalence of this micronutrient deficiency and possibly to improve fibrinogen and plasma clot structure if the relationships are indeed clinically significant. There is a need for large cohort studies to demonstrate the relationship between vitamin D and cardiovascular and inflammatory risk factors as well as to uncover the molecular mechanisms responsible.

Factor XIII-A transglutaminase acts as a switch between preadipocyte proliferation and differentiation

Factor XIII-A (FXIII-A) transglutaminase (TG) was recently identified as a potential causative obesity gene in human white adipose tissue (WAT). Here, we have examined the role of TG activity and the role of protein crosslinking in adipogenesis. Mouse WAT and preadipocytes showed abundant TG activity arising from FXIII-A. FXIII-A was localized to the cell surface and acted as a negative regulator of adipogenesis by promoting assembly of fibronectin (FN) from plasma into preadipocyte extracellular matrix. This modulated cytoskeletal dynamics and maintained the preadipocyte state. FXIII-A-assembled plasma FN (pFN) matrix promoted preadipocyte proliferation and potentiated the proproliferative effects of insulin (INS) while suppressing the prodifferentiating INS signaling. FXIII-A-deficient mouse embryonic fibroblasts showed increased lipid accumulation and decreased proliferation as well as decreased pFN assembly into extracellular matrix. Thus, FXIII-A serves as a preadipocyte-bound proliferation/differentiation switch that mediates effects of hepatocyte-produced circulating pFN.

Transglutaminases and disease: lessons from genetically engineered mouse models and inherited disorders

The human transglutaminase (TG) family consists of a structural protein, protein 4.2, that lacks catalytic activity, and eight zymogens/enzymes, designated factor XIII-A (FXIII-A) and TG1-7, that catalyze three types of posttranslational modification reactions: transamidation, esterification, and hydrolysis. These reactions are essential for biological processes such as blood coagulation, skin barrier formation, and extracellular matrix assembly but can also contribute to the pathophysiology of various inflammatory, autoimmune, and degenerative conditions. Some members of the TG family, for example, TG2, can participate in biological processes through actions unrelated to transamidase catalytic activity. We present here a comprehensive review of recent insights into the physiology and pathophysiology of TG family members that have come from studies of genetically engineered mouse models and/or inherited disorders. The review focuses on FXIII-A, TG1, TG2, TG5, and protein 4.2, as mice deficient in TG3, TG4, TG6, or TG7 have not yet been reported, nor have mutations in these proteins been linked to human disease.

Antithrombotic properties of aspirin and resistance to aspirin: beyond strictly antiplatelet actions

Aspirin is effective in the prevention of cardiovascular events in high-risk patients. The primary established effect of aspirin on hemostasis is to impair platelet aggregation via inhibition of platelet thromboxane A(2) synthesis, thus reducing thrombus formation on the surface of the damaged arterial wall. Growing evidence also indicates that aspirin exerts additional antithrombotic effects, which appear to some extent unrelated to platelet thromboxane A(2) production. Aspirin can reduce thrombin generation with the subsequent attenuation of thrombin-mediated coagulant reactions such as factor XIII activation. Aspirin also acetylates lysine residues in fibrinogen resulting in increased fibrin clot permeability and enhanced clot lysis as well as directly promoting fibrinolysis with high-dose aspirin. The variable effectiveness of aspirin in terms of clinical outcomes and laboratory findings, which has been termed aspirin resistance, may be related to these additional antithrombotic effects that are altered when associated with common genetic polymorphisms such as the Leu33Pro beta(3)-integrin or Val34Leu factor XIII mutations. However, the clinical relevance of these observations is still unclear. Elucidation of the actual impacts of aspirin other than antiaggregation effects could be important in view of the widespread use of this drug in the prevention of thrombotic manifestations of atherosclerosis.

Parent-of-origin transmission of thrombophilic alleles to intrauterine growth-restricted newborns and transmission-ratio distortion in unaffected newborns

Findings on the role of thrombophilic polymorphisms in adverse pregnancy outcomes, particularly intrauterine growth restriction, are inconsistent. Such inconsistencies may be partly due to two types of effects which have not been considered before with regard to thrombophilic genes: parent-of-origin effects (imprinting) and transmission-ratio distortion effects (allele transmission differing from that expected in unaffected subjects). In this study of infants born at a Canadian hospital (1998-2000), the authors investigated both types of effects. Cases (n = 493) were defined as newborns whose birth weight for gestational age and sex was below the 10th percentile by national standards, and controls (n = 472) as newborns at or above the 10th percentile. Log-linear models were used to analyze the transmission of variant alleles among case- and control-parent trios. A single copy of a common polymorphism, Val34Leu in factor XIII, increased the risk of intrauterine growth restriction approximately 70% when the parent of origin was the father as opposed to the mother (p < 0.05). Among unaffected newborns, transmission of A1298C in the methylenetetrahydrofolate reductase gene (p < 0.005), transmission of the G1691A variant in factor V Leiden (p < 0.002), and transmission of the G20210A variant in the prothrombin (factor II) gene (p < 0.001) occurred significantly less often than expected (transmission-ratio distortion). Affected newborns also inherited the prothrombin G20210A variant significantly less often than expected. These results suggest that these three genes exhibit segregation distortion or reduce gestational survival.

The effect of dimethylbiguanide on thrombin activity, FXIII activation, fibrin polymerization, and fibrin clot formation

The antihyperglycemic drug dimethylbiguanide (DMB, also known as metformin) reduces the risk of cardiovascular complications in type 2 diabetes, although the mechanism(s) involved are unclear. DMB reduces glycosylation-related protein cross-linking, a process similar to fibrin cross-linking catalyzed by activated factor XIII (FXIII). To investigate whether the cardioprotective effect of DMB could be related to effects on clot stabilization, we studied the effects of DMB on FXIII, thrombin activity, and cleavage of fibrin(ogen). Activity of purified and plasma FXIII was inhibited by DMB. Analysis by mass spectrometry and FXIII-coupled magnetic particles excluded binding of DMB to FXIII. Thrombin-induced cleavage of the activation peptide from FXIII was inhibited in a dose-dependent manner, as was fibrinopeptide cleavage from fibrinogen. Ancrod-induced cleavage of fibrinopeptide A was not affected. DMB prolonged clotting time of normal plasma. Fiber thickness and pore size of fibrin clots, measured by permeation experiments and visualized by scanning electron microscopy, decreased significantly with DMB. No interactions between DMB and the active site of thrombin were found. Turbidity experiments demonstrated that DMB changed polymerization and lateral aggregation of protofibrils. These results suggest that DMB interferes with FXIII activation and fibrin polymerization, but not only by binding to thrombin on a different location than the active site. In patients on DMB therapy, FXIII antigen and activity levels in vivo were reduced over a 12-week period. These findings indicate that part of the cardioprotective effect of DMB in patients with type 2 diabetes may be attributed to alterations in fibrin structure/function.