Association of a single nucleotide polymorphism in CPB2 encoding the thrombin-activable fibrinolysis inhibitor (TAF1) with blood pressure

Thrombin Activatable Fibrinolysis Inhibitor (TAFI): An Updated Narrative Review

Thrombin activatable fibrinolysis inhibitor (TAFI), a proenzyme, is converted to a potent attenuator of the fibrinolytic system upon activation by thrombin, plasmin, or the thrombin/thrombomodulin complex. Since TAFI forms a molecular link between coagulation and fibrinolysis and plays a potential role in venous and arterial thrombotic diseases, much interest has been tied to the development of molecules that antagonize its function. This review aims at providing a general overview on the biochemical properties of TAFI, its (patho)physiologic function, and various strategies to stimulate the fibrinolytic system by interfering with (activated) TAFI functionality.

Introgression, admixture, and selection facilitate genetic adaptation to high-altitude environments in cattle

Domestication and subsequent selection of cattle to form breeds and biological types that can adapt to different environments partitioned ancestral genetic diversity into distinct modern lineages. Genome-wide selection particularly for adaptation to extreme environments left detectable signatures genome-wide. We used high-density genotype data for 42 cattle breeds and identified the influence of Bos grunniens and Bos javanicus on the formation of Chinese indicine breeds that led to their divergence from India-origin zebu. We also found evidence for introgression, admixture, and migration in most of the Chinese breeds. Selection signature analyses between high-altitude (≥1800 m) and low-altitude adapted breeds (<1500 m) revealed candidate genes (ACSS2, ALDOC, EPAS1, EGLN1, NUCB2) and pathways that are putatively involved in hypoxia adaptation. Immunohistochemical, real-time PCR and CRISPR/cas9 ACSS2-knockout analyses suggest that the up-regulation of ACSS2 expression in the liver promotes the metabolic adaptation of cells to hypoxia via the hypoxia-inducible factor pathway. High altitude adaptation involved the introgression of alleles from high-altitude adapted yaks into Chinese Bos taurus taurus prior to their formation into recognized breeds and followed by selection. In addition to selection, adaptation to high altitude environments has been facilitated by admixture and introgression with locally adapted cattle populations.

Genetic markers: Potential candidates for cardiovascular disease

The effective prevention of cardiovascular disease depends upon the ability to recognize the high-risk individuals at an early stage of the disease or long before the development of adverse events. Evolving technologies in the fields of proteomics, metabolomics, and genomics have played a significant role in the discovery of cardiovascular biomarkers, but so far these methods have achieved the modest success. Hence, there is a crucial need for more reliable, suitable, and lasting diagnostic and therapeutic markers to screen the disease well in time to start the clinical aid to the patients. Gene polymorphisms associated with the cardiovascular disease play a decisive role in the disease onset. Therefore, the genetic marker evaluation to classify high-risk patients from low-risk patients trends an effective approach to patient management and care. Currently, there are no genetic markers available for extensive adoption as risk factors for coronary vascular disease, yet, there are numerous promising, biologically acceptable candidates. Many of these gene biomarkers, alone or in combination, can play an essential role in the prediction of cardiovascular risk. The present review highlights some putative emerging genetic biomarkers that could facilitate more authentic and fast diagnosis of CVD. This review also briefly describes few technological approaches employed in the biomarker search.

Integrative network analysis reveals molecular mechanisms of blood pressure regulation

Genome‐wide association studies (GWAS) have identified numerous loci associated with blood pressure (BP). The molecular mechanisms underlying BP regulation, however, remain unclear. We investigated BP‐associated molecular mechanisms by integrating BP GWAS with whole blood mRNA expression profiles in 3,679 individuals, using network approaches. BP transcriptomic signatures at the single‐gene and the coexpression network module levels were identified. Four coexpression modules were identified as potentially causal based on genetic inference because expression‐related SNPs for their corresponding genes demonstrated enrichment for BP GWAS signals. Genes from the four modules were further projected onto predefined molecular interaction networks, revealing key drivers. Gene subnetworks entailing molecular interactions between key drivers and BP‐related genes were uncovered. As proof‐of‐concept, we validated SH2B3, one of the top key drivers, using Sh2b3^−/− mice. We found that a significant number of genes predicted to be regulated by SH2B3 in gene networks are perturbed in Sh2b3^−/− mice, which demonstrate an exaggerated pressor response to angiotensin II infusion. Our findings may help to identify novel targets for the prevention or treatment of hypertension.

Prevalence and risk factors for hypertension in hemophilia

Hypertension (HTN) is a major risk factor for intracranial hemorrhage. We, therefore, investigated the prevalence, treatment, and control of HTN in adult patients with hemophilia (PWH). PWH≥18 years (n=458) from 3 geographically different cohorts in the United States were evaluated retrospectively for HTN and risk factors. Results were compared with the nationally representative sample provided by the contemporary National Health and Nutrition Examination Survey (NHANES). PWH had a significantly higher prevalence of HTN compared with NHANES. Overall, the prevalence of HTN was 49.1% in PWH compared with 31.7% in NHANES. At ages 18 to 44, 45 to 64, 65 to 74, and ≥75 years, the prevalence of HTN for PWH was 31.8%, 72.6%, 89.7%, and 100.0% compared with 12.5%, 41.2%, 64.1%, and 71.7% in NHANES, respectively. Of treated hypertensive PWH, only 27.1% were controlled, compared with 47.7% in NHANES (all P<0.05). Age, body mass index, diabetes mellitus, and renal function were independently associated with HTN. Among patients with moderate or severe hemophilia there was a trend (≈1.5-fold) for higher odds of having HTN compared with patients with mild hemophilia. On the basis of these results, new care models for adult PWH and further studies for the causes of HTN in hemophilia are recommended.

Technologies in the Whole-Genome Age: MALDI-TOF-Based Genotyping

With the decipherment of the human genome, new questions have moved into the focus of today's research. One key aspect represents the discovery of DNA variations capable to influence gene transcription, RNA splicing, or regulating processes, and their link to pathology. Matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF-MS) is a powerful tool for the qualitative investigation and relative quantification of variations like single nucleotide polymorphisms, DNA methylation, microsatellite instability, or loss of heterozygosity. After its introduction into proteomics, efforts were made to adopt this technique to DNA analysis. Initially intended for peptide/protein analysis, it held several difficulties for application to nucleic acids. Today, MALDI-TOF-MS has reached worldwide acceptance and application in nucleic acid research, with a wide spectrum of methods being available. One of the most versatile approaches relies on primer extension to genotype single alleles, microsatellite repeat lengths or the methylation status of a given cytosine. Optimized methods comprising intelligent primer design and proper nucleotide selection for primer extension enabled multiplexing of reactions, rendering the analysis more economic due to parallel genotyping of several alleles in a single experiment. Laboratories equipped with MALDI-TOF-MS possess a universal technical platform for the analysis of a large variety of different molecules.

Curiouser and curiouser: recent advances in measurement of thrombin-activatable fibrinolysis inhibitor (TAFI) and in understanding its molecular genetics, gene regulation, and biological roles

The thrombin-activatable fibrinolysis inhibitor (TAFI) pathway defines a novel molecular connection between blood coagulation and both fibrinolysis and inflammation. TAFI is a plasma zymogen that can be activated by thrombin, the thrombin-thrombomodulin complex, or plasmin. The activated form of TAFI (TAFIa) attenuates fibrinolysis by removing the carboxyl-terminal lysine residues from partially degraded fibrin that mediate positive feedback in the fibrinolytic cascade. A role for TAFIa in modulating inflammation is suggested by the ability of this enzyme to down-regulate pericellular plasminogen activation and to inactivate the inflammatory peptides bradykinin and the anaphylatoxins C3a and C5a. The focus of this review is on recent advances in the clinical measurement of the TAFI pathway in human subjects and what this has revealed in terms of the molecular genetics of TAFI, the biological variation in plasma TAFI antigen levels, potential regulators of expression of the gene encoding TAFI, and the TAFI pathway as a risk factor for the development of vascular diseases. Although this field is in its infancy, much recent progress has been made and the available data suggest that the TAFI pathway is an intriguing new player in a variety of physiological and pathophysiological contexts.

Analysis of allelic differential expression in human white blood cells

Allelic variation of gene expression is common in humans, and is of interest because of its potential contribution to variation in heritable traits. To identify human genes with allelic expression differences, we genotype DNA and examine mRNA isolated from the white blood cells of 12 unrelated individuals using oligonucleotide arrays containing 8406 exonic SNPs. Of the exonic SNPs, 1983, located in 1389 genes, are both expressed in the white blood cells and heterozygous in at least one of the 12 individuals, and thus can be examined for differential allelic expression. Of the 1389 genes, 731 (53%) show allele expression differences in at least one individual. To gain insight into the regulatory mechanisms governing allelic expression differences, we analyze a set of 60 genes containing exonic SNPs that are heterozygous in three or more samples, and for which all heterozygotes display differential expression. We find three patterns of allelic expression, suggesting different underlying regulatory mechanisms. Exonic SNPs in three of the 60 genes are monoallelically expressed in the human white blood cells, and when examined in families show expression of only the maternal copy, consistent with regulation by imprinting. Approximately one-third of the genes have the same allele expressed more highly in all heterozygotes, suggesting that their regulation is predominantly influenced by cis-elements in strong linkage disequilibrium with the assayed exonic SNP. The remaining two-thirds of the genes have different alleles expressed more highly in different heterozygotes, suggesting that their expression differences are influenced by factors not in strong linkage disequilibrium with the assayed exonic SNP.

Thrombin activatable fibrinolysis inhibitor (TAFI)--how does thrombin regulate fibrinolysis?

The thrombin-catalysed conversion of plasma fibrinogen into fibrin and the development of an insoluble fibrin clot are the final steps of the coagulation cascade during haemostasis. A delicate balance between coagulation and fibrinolysis determines the stability of the fibrin clot. Thrombin plays a central role in this process, it not only forms the clot but it is also involved in stabilizing the clot by activating thrombin activatable fibrinolysis inhibitor (TAFI). Activated TAFI protects the fibrin clot against lysis. Here we will discuss the mechanisms for regulation of fibrinolysis by thrombin. The role of the coagulation system for the generation of thrombin and for the activation of TAFI implies that defects in thrombin generation will directly affect the protection of clots against lysis. Thus, defects in activation of TAFI might contribute to the severity of bleeding disorders. Vice versa an increased activation of TAFI due to an increased rate of thrombin generation might lead to thrombotic disorders. Specific inhibitors of activated TAFI or inhibitors that interfere with the generation of thrombin might provide novel therapeutic strategies for thrombolytic therapy. Besides having a role in the regulation of fibrinolysis, TAFI may also have an important function in the regulation of inflammation, wound healing and blood pressure.

GENETIC POLYMORPHISMS AND SEPSIS

Sepsis is a polygenic and complex syndrome that is initiated by infection and is characterized by a systemic inflammatory response. Genetic polymorphisms in the immune response to infection have been shown to be associated with clinical outcomes. Functional and association studies involving genetic polymorphisms in essential genes, including Toll-like receptors, cytokines, and coagulation factors, have provided important insights into the mechanisms involved in the pathogenesis of sepsis-induced organ dysfunction. The advancement of high-throughput single nucleotide polymorphism (SNP) genotyping will provide valuable information on the interaction of multiple allelic variants and clinical outcome. More precise categorization of patients based on genetic background is likely to lead to individualized targeted treatment. Future therapeutic trials as well as actual treatment regimens for patients with sepsis are likely to be designed to target specific genotypes and associated cellular responses, maximizing clinical response and patient safety.

Mutation detection using ligase chain reaction in passivated silicon-glass microchips and microchip capillary electrophoresis

The ligase chain reaction (LCR) following PCR is one of the most sensitive and specific methods for detecting mutations, especially single nucleotide polymorphisms (SNPs). Performing LCR in microchips remains a challenge because of the inhibitory effect of the internal surfaces of silicon-glass microchips. We have tested a dynamic polymer-based surface passivation method for LCR conducted in oxide-coated silicon-glass microchips. The combination of polyvinylpyrrolidone 40 (PVP-40) at 0.75% (w/v) with an excess of the ligase produced successful LCR in the silicon-glass microchips, with yields of ligated primers comparable to reactions performed in conventional reaction tubes. Ligated primers were detected and quantified simply and conveniently using microchip capillary electrophoresis.

Thrombin activatable fibrinolysis inhibitor (TAFI) at the interface between coagulation and fibrinolysis

The thrombin-catalysed conversion of plasma fibrinogen into fibrin and the development of an insoluble fibrin clot are the final steps of the coagulation cascade during haemostasis. A delicate balance between coagulation and fibrinolysis determines the stability of the fibrin clot. Thrombin Activatable Fibrinolysis Inhibitor (TAFI) plays an important role in this process. TAFI is activated by thrombin and protects the fibrin clot against lysis. The role of TAFI in bleeding and thrombotic disorders is discussed as well as its novel emerging role in wound healing and inflammation.

Comparison of effects of different heparins on thrombin activatable fibrinolysis inhibitor in hemodialyzed patients

BACKGROUND

Thrombin activatable fibrinolysis inhibitor (TAFI) is a regulator of endogenous fibrinolysis. Heparin is used routinely during dialysis sessions to prevent clot formation in the extracorporeal circuit; therefore the aim of the study was to assess whether unfractionated heparin or low-molecular-weight heparins affect TAFI concentration and activity in hemodialyzed patients.

METHODS

Dalteparin (n = 16) or enoxaparin (n = 25) were administered before the second hemodialysis session in the week in a single dose, whereas unfractionated heparin (n = 18) was given first as a bolus, then in a pump. We also evaluated thrombin activity (thrombin-antithrombin complexes, prothrombin fragments 1 + 2), TAFI activator, thrombomodulin, a catalyzer of TAFI activation and a marker of endothelial cell injury, and the degree of plasmin generation (plasmin-antiplasmin complexes).

RESULTS

TAFI concentration, activity and markers of ongoing coagulation, i.e. prothrombin fragments 1 + 2 and thrombin-antithrombin complexes, were significantly higher in patients anticoagulated with unfractionated heparin when compared to both enoxaparin and dalteparin groups. Thrombin-antithrombin complexes, plasmin-antiplasmin complexes, prothrombin fragments 1 + 2, and thrombomodulin did not differ between patients anticoagulated with dalteparin and enoxaparin.

CONCLUSIONS

Our results suggest that low-molecular-weight heparins influence TAFI and other hemostatic parameters in hemodialyzed patients to a lesser degree than unfractionated heparin. Increased TAFI is possibly due to thrombin appearance during hemodialysis with unfractionated heparin.

Thrombin activatable fibrinolysis inhibitor: Not just an inhibitor of fibrinolysis

OBJECTIVE

To review the activation of thrombin activatable fibrinolysis inhibitor (TAFI) and activity of activated TAFI (TAFIa) as it relates to the regulation of both fibrinolytic and proinflammatory substances.

DATA SOURCE

Published articles and reviews (from PubMed, published between 1962 and 2003) on experimental studies of coagulation, fibrinolysis, and inflammation.

DATA SYNTHESIS AND CONCLUSIONS

The principal physiologic role of TAFI is still a matter of debate. Although TAFI activation can result from proteolysis by a number of proteases, the most likely physiologic activators are thrombin (in complex with the cofactor thrombomodulin) and plasmin (in complex with polysaccharide cofactors). The activated enzyme, TAFIa, displays carboxypeptidase B-like activity and probably regulates both fibrinolysis and inflammation in response to injury and infection. At present, there is limited understanding of the role that TAFI plays in the interrelationships between coagulation, fibrinolysis, and inflammation. Although the potential therapeutic value of TAFIa inhibition/TAFI activation awaits further investigation, the data gathered to date suggest that, like activated protein C, TAFIa may play a pivotal role in regulating the crosstalk between coagulation, fibrinolysis, and inflammation.

Thrombin activatable fibrinolysis inhibitor, a potential regulator of vascular inflammation

The latent plasma carboxypeptidase thrombin-activable fibrinolysis inhibitor (TAFI) is activated by thrombin/thrombomodulin on the endothelial cell surface, and functions in dampening fibrinolysis. In this study, we examined the effect of activated TAFI (TAFIa) in modulating the proinflammatory functions of bradykinin, complement C5a, and thrombin-cleaved osteopontin. Hydrolysis of bradykinin and C5a and thrombin-cleaved osteopontin peptides by TAFIa was as efficient as that of plasmin-cleaved fibrin peptides, indicating that these are also good substrates for TAFIa. Plasma carboxypeptidase N, generally regarded as the physiological regulator of kinins, was much less efficient than TAFIa. TAFIa abrogated C5a-induced neutrophil activation in vitro. Jurkat cell adhesion to osteopontin was markedly enhanced by thrombin cleavage of osteopontin. This was abolished by TAFIa treatment due to the removal of the C-terminal Arg168 by TAFIa from the exposed SVVYGLR alpha 4 beta 1 integrin-binding site in thrombin-cleaved osteopontin. Thus, thrombin cleavage of osteopontin followed by TAFIa treatment may sequentially up- and down-modulate the pro-inflammatory properties of osteopontin. An engineered anticoagulant thrombin, E229K, was able to activate endogenous plasma TAFI in mice, and E229K thrombin infusion effectively blocked bradykinin-induced hypotension in wild-type, but not in TAFI-deficient, mice in vivo. Our data suggest that TAFIa may have a broad anti-inflammatory role, and its function is not restricted to fibrinolysis.