Begoña Hurtado

Molecular basis of protein S deficiency.

Protein S deficiency (PSD) has been the most difficult to study among the classical inherited thrombophilic factors. This is in part due to the peculiar biology of protein S (PS), which has an anticoagulant role but no enzymatic activity, and because it interacts with plasma components that function in both haemostasis and inflammation. Clinically, it also has been difficult to define and standardise valuable assays to determine PS status and implication in thrombosis. Despite these drawbacks, at present heterozygous PS deficiency is well established as an autosomal dominant trait associated with an increased risk of thrombosis from data on familial and population studies. Almost two-hundred mutations have been characterised in PROS1, and approximately 30% of them have been characterised in vitro, clarifying the mechanisms leading to PSD. Furthermore, recent studies on the presence of large deletions in PROS1 have increased the number of PSD associated to PROS1 mutations. Finally, the discovery of new functions for PS, both in the anticoagulant system as well as in the interaction with cellular components through receptor tyrosine kinases, is broadening the importance of this molecule in the context of biomedicine.

Association of specific haplotypes of GAS6 gene with stroke

The product of the growth arrest-specific gene 6 (GAS6), a ligand for tyrosine kinase receptors, is a vitamin K-dependent protein, structurally related to anticoagulant protein S. Gas6-deficient mice are protected against thrombosis, demonstrating the importance of this protein in the cardiovascular system. In a preliminary study on GAS6 polymorphisms and atherothrombotic disease we found an association between the AA genotype of the c.834 + 7G > A GAS6 polymorphism and stroke. In order to further explore this association by considering GAS6 haplotypes and the main stroke subtypes, 457 patients with ischemic stroke, 199 with hemorrhagic stroke and 150 asymptomatic controls were genotyped for eight GAS6 polymorphisms and other genetic markers in the same genome region. Association was measured by logistic regression analysis. The THESIAS program was used to measure linkage disequilibrium and haplotype frequencies. In univariate analysis, the GAS6 c.834 + 7AA genotype was found associated with decreased risk for stroke (OR: 0.59; 95%CI: 0.37-0.93). After adjustment for vascular risk factors, association was maintained when stroke subtypes affecting the microvasculature such as lacunar stroke and deep haemorrhage, were grouped together (OR: 0.44; 95%CI: 0.21-0.90). Furthermore, haplotype analysis revealed that association was even stronger when the c.834 + 7A allele was present in a specific haplotype (CACA) of four GAS6 polymorphisms. From these results we conclude that the A allele of the GAS6 c.834 + 7G > A polymorphism and more specifically, the CACA haplotype, is less prevalent in patients with stroke, suggesting a protective role for stroke of this haplotype.

Vitamin K-dependent proteins GAS6 and Protein S and TAM receptors in patients of systemic lupus erythematosus: correlation with common genetic variants and disease activity

IntroductionGrowth arrest-specific gene 6 protein (GAS6) and protein S (ProS) are vitamin K-dependent proteins present in plasma with important regulatory functions in systems of response and repair to damage. They interact with receptor tyrosine kinases of the Tyro3, Axl and MerTK receptor tyrosine kinase (TAM) family, involved in apoptotic cell clearance (efferocytosis) and regulation of the innate immunity. TAM-deficient mice show spontaneous lupus-like symptoms. Here we tested the genetic profile and plasma levels of components of the system in patients with systemic lupus erythematosus (SLE), and compare them with a control healthy population.MethodsFifty SLE patients and 50 healthy controls with matched age, gender and from the same geographic area were compared. Genetic analysis was performed in GAS6 and the TAM receptor genes on SNPs previously identified. The concentrations of GAS6, total and free ProS, and the soluble forms of the three TAM receptors (sAxl, sMerTK and sTyro3) were measured in plasma from these samples.ResultsPlasma concentrations of GAS6 were higher and, total and free ProS were lower in the SLE patients compared to controls, even when patients on oral anticoagulant treatment were discarded. Those parameters correlated with SLE disease activity index (SLEDAI) score, GAS6 being higher in the most severe cases, while free and total ProS were lower. All 3 soluble receptors increased its concentration in plasma of lupus patients.ConclusionsThe present study highlights that the GAS6/ProS-TAM system correlates in several ways with disease activity in SLE. We show here that this correlation is affected by common polymorphisms in the genes of the system. These findings underscore the importance of mechanism of regulatory control of innate immunity in the pathology of SLE.

Expression of the vitamin K-dependent proteins GAS6 and protein S and the TAM receptor tyrosine kinases in human atherosclerotic carotid plaques

The GAS6/ProS-TAM system is composed of two vitamin K-dependent ligands (GAS6 and protein S) and their three protein tyrosine kinase receptors TYRO3, AXL and MERTK, known as the TAM receptors. The system plays a prominent role in conditions of injury, inflammation and repair. In murine models of atherosclerotic plaque formation, mutations in its components affect atherosclerosis severity. Here we used Taqman low-density arrays and immunoblotting to study mRNA and protein expression of GAS6, ProS and the TAM receptors in human carotid arteries with different degrees of atherosclerosis. The results show a clear down-regulation of the expression of AXL in atheroma plaques with respect to normal carotids that is matched by decreased abundance of AXL in protein extracts detected by immunoblotting. A similar decrease was observed in PROS1 mRNA expression in atherosclerotic carotids compared to the normal ones, but in this case protein S (ProS) was clearly increased in protein extracts of carotid arteries with increasing grade of atherosclerosis, suggesting that ProS is carried into the plaque. MERTK was also increased in atherosclerotic carotid arteries with respect to the normal ones, suggesting that the ProS-MERTK axis is functional in advanced human atherosclerotic plaques. MERTK was expressed in macrophages, frequently in association with ProS, while ProS was abundant also in the necrotic core. Our data suggest that the ProS-MERTK ligand-receptor pair was active in advanced stages of atherosclerosis, while AXL signalling is probably down-regulated.

Association study between polymorphims in GAS6-TAM genes and carotid atherosclerosis

Carotid atherosclerosis (CA) is one of the most common causes of stroke, and recent studies suggest that pathways initiated by the interaction of the plasma vitamin K-dependent protein GAS6 with the tyrosine kinase receptors TYRO3, AXL and MERTK (TAM) may have a relevant role in atherogenesis. Furthermore, our previous studies indicated an association between GAS6 and stroke. The aim of this study was to analyse the genetic association between SNPs and haplotypes in GAS6-TAM genes and CA. We performed a case-control study with 233 CA patients confirmed by nuclear magnetic resonance angiography and 202 patients who suffered from cardioembolic (non atherogenic) stroke. For all included subjects information on established risk factors was available. Genotyping of 16 selected tagSNPs was performed by real-time PCR, using either FRET or TaqMan probes. Adjusted logistic regression (LR) analyses indicated that rs2289743 in TYRO3 and rs869016 in MERTK were associated to CA, decreasing its risk (OR [95%CI]=0.39 [0.16-0.94] and OR [95%CI]=0.31 [0.14-0.69], respectively). Linkage disequilibrium results were consistent with the haplotype blocks described in HapMap and adjusted LR analyses revealed that the haplotype ACAA in MERTK , containing the minor allele of the associated SNP, was also associated to CA. No association was observed with GAS6 and AXL variants, which suggests that CA is not the mechanism underlying the reported association between GAS6 and stroke. The association between TYRO3 and MERTK variants and carotid atherosclerosis found in this study reinforces a physiological role of the GAS6-TAM pathway in atherogenesis.

GAS6 in systemic inflammatory diseases: with and without infection

Vitamin K-dependent proteins are not only essential regulators of blood coagulation. A recent paper in Critical Care describes the levels of the vitamin K-dependent GAS6 and the soluble form of its receptor Axl in plasma from patients with sepsis of systemic inflammation. The results confirm that GAS6 is elevated during septicemia, but the fact that inflammatory conditions without infection produce a similar effect suggests it is inflammation that induces the synthesis of GAS6, rather than the interactions with bacteria or other infectious agents. The soluble form of the GAS6 receptor Axl was induced less compared with the effect observed in GAS6. This is important as the two proteins form an inactive complex in plasma, suggesting that a functional GAS6 form could be synthesized under these conditions. GAS6 has been proposed as a broad regulator of the innate immune response. GAS6 synthesis is therefore likely to be a regulatory mechanism during systemic inflammation. Recent advances provide the necessary tools for further research, including genetic screenings of the components of this system.

Effect of the Gas6 c.834+7G>A Polymorphism and the Interaction of Known Risk Factors on AMD Pathogenesis in Hungarian Patients

Age-related macular degeneration (AMD) is the leading cause of blindness in the elderly in the developed world. Numerous genetic factors contribute to the development of the multifactorial disease. We performed a case-control study to assess the risk conferred by known and candidate genetic polymorphisms on the development of AMD. We searched for genetic interactions and for differences in dry and wet AMD etiology. We enrolled 213 patients with exudative, 67 patients with dry AMD and 106 age and ethnically matched controls. Altogether 12 polymorphisms in Apolipoprotein E, complement factor H, complement factor I, complement component 3, blood coagulation factor XIII, HTRA1, LOC387715, Gas6 and MerTK genes were tested. No association was found between either the exudative or the dry form and the polymorphisms in the Apolipoprotein E, complement factor I, FXIII and MerTK genes. Gas6 c.834+7G>A polymorphism was found to be significantly protective irrespective of other genotypes, reducing the odds of wet type AMD by a half (OR = 0.50, 95%CI: 0.26–0.97, p = 0.04). Multiple regression models revealed an interesting genetic interaction in the dry AMD subgroup. In the absence of C3 risk allele, mutant genotypes of both CFH and HTRA1 behaved as strongly significant risk factors (OR = 7.96, 95%CI: 2.39 = 26.50, p = 0.0007, and OR = 36.02, 95%CI: 3.30–393.02, p = 0.0033, respectively), but reduced to neutrality otherwise. The risk allele of C3 was observed to carry a significant risk in the simultaneous absence of homozygous CFH and HTRA1 polymorphisms only, in which case it was associated with a near-five-fold relative increase in the odds of dry type AMD (OR = 4.93, 95%CI: 1.98–12.25, p = 0.0006). Our results suggest a protective role of Gas6 c.834+7G>A polymorphism in exudative AMD development. In addition, novel genetic interactions were revealed between CFH, HTRA1 and C3 polymorphisms that might contribute to the pathogenesis of dry AMD.

Functional characterization of twelve natural PROS1 mutations associated with anticoagulant protein S deficiency

The molecular mechanisms by which PROS1 mutations result in protein S deficiency are still unknown for many mutations. Findings of this study indicate that the main mechanism for the deficiency associated with mutations that generate a premature termination codon is not the synthesis of a truncated protein, but the exclusion of the mutated allele. Background The molecular mechanisms by which PROS1 mutations result in protein S deficiency are still unknown for many of the mutations, particularly for those that result in a premature termination codon. The aim of this study was to analyze the functional relevance on mRNA and protein expression of 12 natural PROS1 mutations associated with protein S deficiency. Design and Methods Five mutations were nonsense, three were small frameshift deletions, one was c.258,259AG>GT at the 3’ end of exon 3, one was p.M640T and the last two were c.-7C>G and p.L15H, found in double heterozygosis as [c.-7C>G;44T>A].The apparently neutral variant p.R233K was also analyzed. PROS1 cDNA was assessed by reverse transcriptase polymerase chain reaction of platelet mRNA. Expression of mutant proteins was determined by site-directed mutagenesis and analyses of transiently transfected PROS1 mutants in COS-7 cells. Results Only cDNA from the normal allele was observed from the five nonsense mutations, the frameshift deletion c.1731delT and from c.258,259AG>GT. Both the normal and the mutated alleles were observed from [c.-7C>G;44T>A], c.187,188delTG and p.M640T. Transient expression analyses of PROS1 mutants whose mRNA was normally expressed revealed greatly reduced secretion of p.L15H and c.1272delA, mild secretion values of p.M640T and normal secretion levels of c.-7C>G and, as expected, p.R233K. Conclusions Whereas the main cause of quantitative protein S deficiency associated with missense mutations is defective synthesis, stability or secretion of the mutated protein, the main mechanism for the deficiency associated with mutations that generate a premature termination codon is not the synthesis of a truncated protein, but the exclusion of the mutated allele, probably by nonsense-mediated mRNA decay.

Role of sodium tungstate as a potential antiplatelet agent.

Purpose Platelet inhibition is a key strategy in the management of atherothrombosis. However, the large variability in response to current strategies leads to the search for alternative inhibitors. The antiplatelet effect of the inorganic salt sodium tungstate (Na2O4W), a protein tyrosine phosphatase 1B (PTP1B) inhibitor, has been investigated in this study. Methods Wild-type (WT) and PTP1B knockout (PTP1B−/−) mice were treated for 1 week with Na2O4W to study platelet function with the platelet function analyzer PFA-100, a cone-and-plate analyzer, a flat perfusion chamber, and thrombus formation in vivo. Human blood aliquots were incubated with Na2O4W for 1 hour to measure platelet function using the PFA-100 and the annular perfusion chamber. Aggregometry and thromboelastometry were also performed. Results In WT mice, Na2O4W treatment prolonged closure times in the PFA-100 and decreased the surface covered (%SC) by platelets on collagen. Thrombi formed in a thrombosis mice model were smaller in animals treated with Na2O4W (4.6±0.7 mg vs 8.9±0.7 mg; P<0.001). Results with Na2O4W were similar to those in untreated PTP1B−/− mice (5.0±0.3 mg). Treatment of the PTP1B−/− mice with Na2O4W modified only slightly this response. In human blood, a dose-dependent effect was observed. At 200 μM, closure times in the PFA-100 were prolonged. On denuded vessels, %SC and thrombi formation (%T) decreased with Na2O4W. Neither the aggregating response nor the viscoelastic clot properties were affected. Conclusion Na2O4W decreases consistently the hemostatic capacity of platelets, inhibiting their adhesive and cohesive properties under flow conditions in mice and in human blood, resulting in smaller thrombi. Although Na2O4W may be acting on platelet PTP1B, other potential targets should not be disregarded.

First case of protein S deficiency due to a translocation t(3;21)(q11.2;q22)

Begona Hurtado1*; Marga Nadal1*; Ester Margarit2; Aurora Sanchez2; Nerea Abasolo1; Nadia Garcia1; Pere Domenech3; Nuria Sala1 1Laboratori de Recerca Translacional, Institut Catala d’Oncologia ICO-IDIBELL, L’Hospitalet de Llobregat, Barcelona, Spain; 2Servei de Bioquimica i Genetica Molecular, Hospital Clinic and CIBERER (Centre for Biomedical Research on Rare Diseases), Barcelona, Spain; 3Unitat de Trombosi i Hemostasia, Hospital Universitari de Bellvitge, Barcelona, Spain Case Report