The combined effect of fibrin formation and factor XIII A subunit Val34Leu polymorphism on the activation of factor XIII in whole plasma

Factor XIII levels, clot strength, and impact of fibrinogen concentrate in infants undergoing cardiopulmonary bypass: a mechanistic sub-study of the FIBCON trial

BACKGROUND

Acquired factor XIII (FXIII) deficiency after major surgery can increase postoperative bleeding. We evaluated FXIII contribution to clot strength and the effect of fibrinogen concentrate administration on FXIII activity in infants undergoing cardiac surgery using cardiopulmonary bypass.

METHODS

We conducted a prospectively planned, mechanistic sub-study, nested within the Fibrinogen Concentrate Supplementation in the Management of Bleeding During Paediatric Cardiopulmonary Bypass: A Phase 1B/2A, Open-Label Dose Escalation Study (FIBCON) trial, which investigated fibrinogen concentrate supplementation during cardiopulmonary bypass (ISRCTN: 50553029) in 111 infants (median age 6.4 months). The relationships between platelet number, fibrinogen concentration, and FXIII activity with rotational thromboelastometry clot strength (EXTEM-MCF) in blood taken immediately before cardiopulmonary bypass and after separation from bypass were estimated using multivariable linear regression. Changes in coagulation variables over time were quantified using a generalised linear model comparing three groups: fibrinogen concentrate-supplemented infants, placebo, and a third cohort with lower bleeding risk.

RESULTS

Overall, 48% of the variability (multivariable R²) in EXTEM-MCF clot strength was explained by three factors: the largest contribution was from FXIII activity (partial R²=0.21), followed by platelet number (partial R²=0.14), and fibrinogen concentration (partial R²=0.095). During cardiopulmonary bypass, mean platelet count fell by a similar amount in the three groups (-36% to -41%; interaction P=0.98). Conversely, fibrinogen concentration increased in all three groups: 132% in the fibrinogen concentrate-supplemented group, 26% in the placebo group, and 51% in the low-risk group. A similar increase was observed for FXIII activity (61%, 23%, and 25%, respectively; interaction P<0.0001).

CONCLUSIONS

FXIII contribution to clot strength is considerable in infants undergoing cardiac surgery. Fibrinogen concentrate supplementation also increased FXIII activity, and hence clot strength.

CLINICAL TRIAL REGISTRATION

ISRCTN: 50553029.

Coagulation Factor XIII Val34Leu Polymorphism in the Prediction of Premature Cardiovascular Events-The Results of Two Meta-Analyses

Background: Polymorphisms within the gene that encodes for coagulation factor XIII (FXIII) have been suggested to be involved in the pathogeneses of ischemic stroke (IS) and myocardial infarction (MI). The Val34Leu polymorphism is one of the most commonly analysed FXIII polymorphisms. However, studies on the role of the Val34Leu polymorphism in the aetiology of vascular diseases often show contradictory results. In the present meta-analysis, we aimed to pool data from available articles to assess the relationship between the FXIII Val34Leu polymorphism and the susceptibilities to IS of undetermined source and premature MI in patients aged below 55 years. Methods: We searched databases (PubMed, Embase, Google Scholar, SciELO, and Medline) using specific keywords (the last search was in January 2022). Eventually, 18 studies (627 cases and 1639 controls for IS; 2595 cases and 4255 controls for MI) met the inclusion criteria. Data were analysed using RevMan 5.4 and StatsDirect 3 link software. The relation between Val34Leu polymorphism and disease was analysed in five genetic models, i.e., dominant, recessive, additive, heterozygous, and allelic. Results: No relation between Val34Leu polymorphism and IS in young adults was observed in all analysed genetic models. For premature MI, significant pooled OR was found between the carrier state of the Leu allele (Val/Leu + Leu/Leu vs. Val/Val) and a lack of MI, suggesting its protective role (OR = 0.80 95%CI 0.64–0.99, p = 0.04). A similar finding was observed for the heterozygous model in MI (Val/Leu vs. Val/Val) (OR = 0.77 95%CI 0.61–0.98, p = 0.03). No relation was found for the recessive, additive, and allelic models in MI. Conclusions: In the population of young adults, no positive correlation was found between the FXIII Val34Leu polymorphism and IS of undetermined source in any of the analysed genetic models. In turn, the carrier state of the 34Leu allele as well as FXIII heterozygotes themselves were found to play a protective role in relation to premature MI.

Proteolytic and nonproteolytic activation mechanisms result in conformationally and functionally different forms of coagulation factor XIII A

Factor XIIIA (FXIIIA) is a transglutaminase that cross-links intra- and extracellular protein substrates. FXIIIA is expressed as an inactive zymogen, and during blood coagulation, it is activated by removal of an activation peptide by the protease thrombin. No such proteolytic FXIIIA activation is known to occur in other tissues or the intracellular form of FXIIIA. For those locations, FXIIIA is assumed instead to undergo activation by Ca²⁺ ions. Previously, we demonstrated a monomeric state for active FXIIIA. Current analytical ultracentrifugation and kinetic experiments revealed that thrombin-activated FXIIIA has a higher conformational flexibility and a stronger affinity toward glutamine substrate than does nonproteolytically activated FXIIIA. The proteolytic activation of FXIIIA was further investigated in a context of fibrin clotting. In a series of fibrin cross-linking assays and scanning electron microscopy studies of plasma clots, the activation rates of FXIIIA V34X variants were correlated with the extent of fibrin cross-linking and incorporation of nonfibrous protein into the clot. Overall, the results suggest conformational and functional differences between active FXIIIA forms, thus expanding the understanding of FXIIIA function. Those differences may serve as a basis for developing therapeutic strategies to target FXIIIA in different physiological environments. ENZYMES: Factor XIIIA ( EC 2.3.2.13).

The interaction between fibrinogen and zymogen FXIII-A2B2 is mediated by fibrinogen residues γ390-396 and the FXIII-B subunits

Coagulation transglutaminase factor XIII (FXIII) exists in circulation as heterotetrameric proenzyme FXIII-A₂B₂ Effectively all FXIII-A₂B₂ circulates bound to fibrinogen, and excess FXIII-B₂ circulates in plasma. The motifs that mediate interaction of FXIII-A₂B₂ with fibrinogen have been elusive. We recently detected reduced binding of FXIII-A₂B₂ to murine fibrinogen that has γ-chain residues 390-396 mutated to alanines (Fibγ^390-396A). Here, we evaluated binding features using human components, including recombinant fibrinogen variants, FXIII-A₂B₂, and isolated FXIII-A₂ and -B₂ homodimers. FXIII-A₂B₂ coprecipitated with wild-type (γA/γA), alternatively-spliced (γ'/γ'), and αC-truncated (Aα251) fibrinogens, whereas coprecipitation with human Fibγ^390-396A was reduced by 75% (P <0001). Surface plasmon resonance showed γA/γA, γ'/γ', and Aα251 fibrinogens bound FXIII-A₂B₂ with high affinity (nanomolar); however, Fibγ^390-396A did not bind FXIII-A₂B₂ These data indicate fibrinogen residues γ390-396 comprise the major binding motif for FXIII-A₂B₂ Compared with γA/γA clots, FXIII-A₂B₂ activation peptide release was 2.7-fold slower in Fibγ^390-396A clots (P < .02). Conversely, activation of recombinant FXIII-A₂ (lacking FXIII-B₂) was similar in γA/γA and Fibγ^390-396A clots, suggesting fibrinogen residues γ390-396 accelerate FXIII-A₂B₂ activation in a FXIII-B₂-dependent mechanism. Recombinant FXIII-B₂ bound γA/γA, γ'/γ', and Aα251 with similar affinities as FXIII-A₂B₂, but did not bind or coprecipitate with Fibγ^390-396A FXIII-B₂ also coprecipitated with fibrinogen from FXIII-A-deficient mouse and human plasmas. Collectively, these data indicate that FXIII-A₂B₂ binds fibrinogen residues γ390-396 via the B subunits, and that excess plasma FXIII-B₂ is not free, but rather circulates bound to fibrinogen. These findings provide insight into assembly of the fibrinogen/FXIII-A₂B₂ complex in both physiologic and therapeutic situations.

Factor XIII-A subunit Val34Leu polymorphism in fatal atherothrombotic ischemic stroke

Factor XIII (FXIII) is a regulator of fibrinolysis and clot firmness. Val34Leu polymorphism of its potentially active A subunit (FXIII-A) leads to faster activation of FXIII, influences clot structure and provides a moderate protection against coronary artery disease. The effect of FXIII-A Val34Leu polymorphism on the risk of atherothrombotic ischemic stroke (AIS) has been investigated in a few studies with contradictory results. In all previous studies, only patients surviving AIS were enrolled and sex-specific effects were not explored. In this retrospective multicenter cohort, we investigated the effect of FXIII-A Val34Leu polymorphism on the risk of fatal AIS in women and men. DNA isolation and genetic determinations in the case of 316 patients who died of AIS were carried out on paraffin-embedded tissue specimens. Genetic analyses for population controls, patients with history of AIS and sex-matched controls were performed on extracted genomic DNA from peripheral blood leukocytes. The prevalence of homozygous wild-type, and heterozygous genotypes, Leu34 carriers and Leu34 allele was not different significantly between the patients with fatal AIS and their respective controls. Logistic regression analysis with age as co-variant demonstrated that in women, homozygous presentation of Leu34 allele represented a more than three-fold increased risk of AIS with fatal outcome. The results demonstrate that FXIII-A Val34Leu polymorphism does not influence the occurrence of AIS, but has an effect on the severity of its outcome. This effect is sex-specific and in homozygous women, the prothrombotic/antifibrinolytic effects of FXIII-A Val34Leu polymorphism seem to prevail.

Interaction of factor XIII subunits

Coagulation factor XIII (FXIII) is a heterotetramer consisting of 2 catalytic A subunits (FXIII-A2) and 2 protective/inhibitory B subunits (FXIII-B2). FXIII-B, a mosaic protein consisting of 10 sushi domains, significantly prolongs the lifespan of catalytic subunits in the circulation and prevents their slow progressive activation in plasmatic conditions. In this study, the biochemistry of the interaction between the 2 FXIII subunits was investigated. Using a surface plasmon resonance technique and an enzyme-linked immunosorbent assay-type binding assay, the equilibrium dissociation constant (Kd) for the interaction was established in the range of 10(-10) M. Based on the measured Kd, it was calculated that in plasma approximately 1% of FXIII-A2 should be in free form. This value was confirmed experimentally by measuring FXIII-A2 in plasma samples immunodepleted of FXIII-A2B2. Free plasma FXIII-A2 is functionally active, and when activated by thrombin and Ca(2+), it can cross-link fibrin. In cerebrospinal fluid and tears with much lower FXIII subunit concentrations, >80% of FXIII-A2 existed in free form. A monoclonal anti-FXIII-B antibody that prevented the interaction between the 2 subunits reacted with the recombinant combined first and second sushi domains of FXIII-B, and its epitope was localized to the peptide spanning positions 96 to 103 in the second sushi domain.

Factor XIIIa generation assay: a tool for studying factor XIII function in plasma

Triggering the extrinsic coagulation pathway in plasma and using a fluorogenic factor XIIIa (FXIIIa) substrate for continuously monitoring FXIIIa activity, an FXIIIa generation curve is obtained. The parameters area under the curve (AUC), time to peak (TTP), and concentration at peak (CP) were calculated. In dilutions of normal plasma in FXIII-deficient plasma, AUC and CP showed linear dose-response relationships, whereas TTP increased from 9.9 min for 25% FXIII to 11.6 min for 100% FXIII. Three FXIII-A preparations (rFXIII, rFXIII(V34L), and cellular FXIII [cFXIII]) showed a linear dose response for AUC and CP. The TTP increased slightly for rFXIII from 13.5 to 15.0 min, but surprisingly for cFXIII TTP increased concentration dependently from 13.5 to 28.7 min. Adding 5 μg/ml FXIII-B at a concentration of 1U of FXIII-A increased the AUC for rFXIII(V34L) and cFXIII by approximately 20% and accelerated TTP from 27.3 to 20.8 min for cFVIII, indicating a supportive function of FXIII-B in orientating cFXIII-A for thrombin cleavage. A commercial assay quantifying FXIII after complete activation in a restricted time window did not reveal differences in the cFXIII preparation with or without FXIII-B. The FXIIIa generation assay provides additional information about activation and function of FXIII. This advantage was underlined in experiments with an irreversible FXIIIa inhibitor.

Fibrinolysis alterations in infertile women during controlled ovarian stimulation: influence of BMI and genetic components

INTRODUCTION

Ovarian stimulation protocols have been described to induce prothrombotic phenotype through alterations of both coagulation and fibrinolysis pathways. We investigated fibrinolytic changes during ovarian stimulation through a global test (CLT) and PAI-1 and TAFI concentrations at different times of ovarian stimulation procedure, and the influence of polymorphisms in genes encoding for fibrinogen chains (FGA, FGB, FGG), t-PA (PLAT), TAFI (CBP2), FXIII (FXIIA1, FXIIIB), plasminogen (PLG) and PAI-1 (PAI1) on their intermediate phenotype.

MATERIALS AND METHODS

We evaluated fibrinolytic and genetic parameters in 110 infertile women undergoing ovarian stimulation procedure (in vitro fertilization, IVF or intracytoplasmic sperm injection, ICSI). All women were observed during the mid-luteal phase of cycle (T(0)) and on day 5 (T(1)), 7 (T(2)) and 9 (T(3)) of the ovarian stimulation.

RESULTS

Significant changes in fibrinolytic parameters from T(0) to T(3) of ovarian stimulation were found (CLT p=0.003; TAFI p=0.009 and PAI-1 p=0.003). CLT values, TAFI and PAI-1 concentrations significantly increased from baseline to T(1) (p<0.0001, p=0.01, p=0.005, respectively)(,) and decreased at T(2,) but remained higher than those at T(0). Moreover, at baseline overweight women showed longer CLT, higher TAFI and PAI-1 concentrations than normal weight women, as well as at T(1) two-fold longer CLT and higher PAI-1 concentrations were observed (p=0.001 and p=0.05, respectively). Significant differences of TAFI and PAI-1 concentrations during ovarian stimulation according to TAFI and PAI1 polymorphisms were observed.

CONCLUSIONS

This study shows alterations of fibrinolysis and suggests the contribution of TAFI and PAI1 genes in modulating fibrinolysis changes during the ovarian stimulation cycle.

Thrombomodulin-dependent effect of factor V Leiden mutation on the cross-linking of α2-plasmin inhibitor to fibrin and its consequences on fibrinolysis

INTRODUCTION

It has been shown that thrombomodulin (TM) considerably delays factor XIII (FXIII) activation and this effect is abrogated by Factor V Leiden (FV(Leiden)) mutation. The aim of the study was to explore the effect of TM on the cross-linking of α(2)-plasmin inhibitor (α(2)-PI) to fibrin in plasma samples of different FV genotypes and how this effect is related to the impaired fibrinolysis of FV(Leiden) carriers.

METHODS

In the plasma samples of fifteen individuals with different FV genotypes and in FV deficient plasma supplemented with wild type FV or FV(Leiden) coagulation was initiated by recombinant human tissue factor and phospholipids with or without recombinant human TM (rhTM). In the recovered clots the extent of α(2)-PI-fibrin cross-linking was evaluated by Western blotting and quantitative densitometry. The effect of rhTM on tissue plasminogen activator (tPA) induced clot lysis was measured by turbidimetric method.

RESULTS

rhTM significantly delayed the formation of α(2)-PI-fibrin α-chain heterodimers/oligomers in plasma samples containing wild type FV. This effect of rhTM was impaired in the presence of FV(Leiden). rhTM delayed tPA-induced clot lysis and this effect of rhTM was more pronounced in plasma containing FV(Leiden). When TAFIa was inhibited by potato carboxypeptidase inhibitor, rhTM accelerated clot lysis in the presence of wild type FV, which is explained by the delayed α(2)-PI-fibrin cross-linking. This effect of rhTM did not prevail in the presence of FV(Leiden).

CONCLUSION

FV(Leiden) abrogates the delaying effect of rhTM on α(2)-PI-fibrin cross-linking, which contributes to the impaired fibrinolysis observed in FV(Leiden) carriers.

Genetic predictors of response to photodynamictherapy

In Western countries, therapeutic management of patients affected by choroidal neovascularization (CNV) secondary to different typologies of macular degeneration represents a major health care problem. Age-related macular degeneration is the disease most frequently associated with CNV development. Schematically, CNVs can be distinguished into classic and occult subtypes, which are characterized by variable natural history and different responsiveness to some therapeutic procedures. At present, the dramatic vision loss due to CNV can be mainly treated by two interventional strategies, which are utilizable in either single or combined modalities: photodynamic therapy with verteporfin (PDT-V), and intravitreal administration of drugs acting against vascular endothelial growth factor. The combined use of PDT-V and anti-angiogenic drugs represents one of the most promising strategies against neovascular macular degeneration, but it unavoidably results in an expensive increase in health resource utilization. However, the positive data from several studies serve as a basis for reconsidering the role of PDT-V, which has undergone a renaissance prompted by the need for a more rational therapeutic approach toward CNV. New pharmacogenetic knowledge of PDT-V points to exploratory prospects to optimize the clinical application of this intriguing photothrombotic procedure. In fact, a Medline search provides data regarding the role of several single nucleotide polymorphisms (SNPs) as genetic predictors of CNV responsiveness to PDT-V. Specifically, correlations between SNPs and different levels of PDT-V efficacy have been detected by examining the gene variants influencing (i) thrombo-coagulative pathways, i.e. methylenetetrahydrofolate reductase (MTHFR) 677C>T (rs1801133), factor V (F5) 1691G>A (rs6025), prothrombin (F2) 20210G>A (rs1799963), and factor XIII-A (F13A1) 185G>T (rs5985); (ii) complement activation and/or inflammatory processes, i.e. complement factor H (CFH) 1277T>C (rs1061170), high-temperature requirement factor A1 (HTRA1) promoter -512G>A (rs11200638), and two variants of the C-reactive protein (CRP) gene (rs2808635 and rs876538); and (iii) production and bioavailability of vascular endothelial growth factor (VEGFA -2578C>A [rs699947] and rs2146323). This article critically evaluates both the clinical plausibility and the opportunity to utilize the most important SNP-response interactions of PDT-V for an effective upgrade of the current anti-CNV therapeutic scenario. In addition, the pharmacogenetics of a very severe post-PDT-V adverse event, i.e. a decrease in acute vision, is briefly discussed. A comprehensive appraisal of the findings reviewed in this article should be carefully considered to design future trials aimed at verifying (after proper genotypic stratification of the enrolled patients) whether these innovative pharmacogenetic approaches will be able to improve the multifaceted interventional management of neovascular macular degeneration.

Factor XIII, clot structure, thrombosis

Blood coagulation factor XIII (FXIII) is a tetrameric protein consisting of two catalytic A (FXIII-A) and two carrier/inhibitory B (FXIII-B) subunits. It is a zymogen, which becomes transformed into an active transglutaminase (FXIIIa) in the final phase of coagulation cascade by thrombin and Ca(2+). FXIII is essential for hemostasis, its deficiency results in severe bleeding diathesis. FXIIIa mechanically stabilizes fibrin by cross-linking its α-, and γ-chains. It also protects newly formed fibrin from fibrinolysis, primarily by cross-linking α(2)-plasmin inhibitor to fibrin. Beside the above prothrombotic effects, it is involved in limiting thrombus growth by down-regulating platelet adhesion to fibrin. Elevated FXIII level seems to be a gender-specific risk factor of both coronary artery disease and peripheral arterial disease, it represents an increased risk only in females. The association of FXIII level with the risk of ischemic stroke and venous thromboembolism was investigated only in a few studies from which no clear conclusion could be drawn. Among the FXIII subunit polymorphisms, concerning their effect on the risk of thrombotic diseases, only FXIII-A p.Val34Leu was investigated extensively. Meta-analyses of reported data suggest that this polymorphism provides a moderate protection against coronary artery disease and venous thromboembolism, but not against ischemic stroke. Gene-gene and gene-environmental interactions might modify its effect. Further studies are required to explore the effect of other FXIII subunit polymorphism on the risk of thrombotic diseases.

Factor XIII: a coagulation factor with multiple plasmatic and cellular functions

Factor XIII (FXIII) is unique among clotting factors for a number of reasons: 1) it is a protransglutaminase, which becomes activated in the last stage of coagulation; 2) it works on an insoluble substrate; 3) its potentially active subunit is also present in the cytoplasm of platelets, monocytes, monocyte-derived macrophages, dendritic cells, chondrocytes, osteoblasts, and osteocytes; and 4) in addition to its contribution to hemostasis, it has multiple extra- and intracellular functions. This review gives a general overview on the structure and activation of FXIII as well as on the biochemical function and downregulation of activated FXIII with emphasis on new developments in the last decade. New aspects of the traditional functions of FXIII, stabilization of fibrin clot, and protection of fibrin against fibrinolysis are summarized. The role of FXIII in maintaining pregnancy, its contribution to the wound healing process, and its proangiogenic function are reviewed in details. Special attention is given to new, less explored, but promising fields of FXIII research that include inhibition of vascular permeability, cardioprotection, and its role in cartilage and bone development. FXIII is also considered as an intracellular enzyme; a separate section is devoted to its intracellular activation, intracellular action, and involvement in platelet, monocyte/macrophage, and dendritic cell functions.

Thrombomodulin-dependent effect of factor VLeiden mutation on factor XIII activation

INTRODUCTION

Factor V Leiden mutation (FV(Leiden)) is associated with impaired down-regulation of activated FV procoagulant activity and loss of FV anticoagulant function that result in an increased risk of venous thromboembolism. As the downstream effects of FV(Leiden) on clot formation and fibrinolyis have only partially been revealed, we investigated its effect on the activation of factor XIII (FXIII) and the cross-linking of fibrin.

METHODS

In the plasma samples of fifteen healthy individuals with known FV genotypes coagulation was initiated by recombinant human tissue factor and phospholipids with or without recombinant human thrombomodulin (rhTM). FV deficient plasma supplemented with purified wild type FV or FV(Leiden) were also investigated. Clots were recovered and analyzed by SDS-PAGE and quantitative densitometric evaluation of Western blots.

RESULTS

rhTM considerably delayed the activation of FXIII in the plasma from FV wild type individuals. This effect of rhTM was significantly impaired in the plasma from FV(Leiden) carriers. The results were confirmed in experiments with FV deficient plasma supplemented by FV prepared from wild type individuals or FV(Leiden) homozygotes. Fibrin γ-chain dimerization was also considerably delayed by rhTM in plasma samples from individuals without Leiden mutation, but not in plasma samples from FV(Leiden) heterozygotes or homozygotes. The difference between heterozygotes and homozygotes was not statistically significant.

CONCLUSION

The highly diminished delaying effect of TM on FXIII activation and on the cross-linking of fibrin in FV(Leiden) carriers might represent a novel mechanism contributing to the increased thrombosis risk of these individuals.

Factor XIII: novel structural and functional aspects

Factor (F)XIII is a protransglutaminase that, in addition to maintaining hemostasis, has multiple plasmatic and intracellular functions. Its plasmatic form (pFXIII) is a tetramer of two potentially active A (FXIII-A) and two inhibitory/carrier B (FXIII-B) subunits, whereas its cellular form (cFXIII) is a dimer of FXIII-A. FXIII-A belongs to the family of transglutaminases (TGs), which show modest similarity in the primary structure, but a high degree of conservatism in their domain and sub-domain secondary structure. FXIII-A consists of an activation peptide, a β-sandwich, a catalytic and two β-barrel domains. FXIII-B is a glycoprotein consisting of 10 repetitive sushi domains each held together by two internal disulfide bonds. The structural elements of FXIII-A involved in the interaction with FXIII-B have not been elucidated; in FXIII-B the first sushi domain seems important for complex formation. In the circulation pFXIII is bound to the fibrinogen γ'-chain through its B subunit. In the process of pFXIII activation first thrombin cleaves off the activation peptide from FXIII-A, then in the presence of Ca(2+) FXIII-B dissociates and FXIII-A becomes transformed into an active transglutaminase (FXIIIa). The activation is highly accelerated by the presence of fibrin(ogen). cFXIII does not require proteolysis for intracellular activation. The three-dimensional structure of FXIIIa has not been resolved. Based on analogies with transglutaminase-2, a three-dimensional structure of FXIIIa was developed by molecular modeling, which shows good agreement with the drastic structural changes demonstrated by biochemical studies. The structural requirements for enzyme-substrate interaction and for transglutaminase activity are also reviewed.

Predictive role of C677T MTHFR polymorphism in variable efficacy of photodynamic therapy for neovascular age-related macular degeneration

Age-related macular degeneration (AMD) complicated by subfoveal choroidal neovascularization (CNV) is the leading cause of severe central blindness in developed countries. AMD-related CNVs are distinguishable in classic and occult subtypes, characterized by variable natural history and different responsiveness to therapeutic procedures. Combined and repeated use of photodynamic therapy with verteporfin (PDT-V) and antiangiogenic drugs represents the most promising strategy against neovascular AMD, but it is unavoidably associated with mounting health-resource utilization. Predictive correlations between peculiar coagulation-balance gene variants and different levels of post-PDT-V benefit have recently been documented in Caucasians with AMD-related CNVs. In particular, methylenetetrahydrofolate reductase C677T substitution, a common thrombophilic folate pathway genotypic polymorphism, influences a better CNV responsiveness to PDT-V in classic- but not in occult-CNV cases. These pharmacogenetic findings indicate the opportunities to optimize the eligibility criteria of PDT-V and/or to perform this intriguing therapy in a customized manner, for finally minimizing the socio-economic burden of neovascular AMD.

Inactive and highly active, proteolytically processed transglutaminase-5 in epithelial cells

Transglutaminases (TGs) are Ca(2+)-dependent enzymes capable of catalyzing transamidation of glutamine residues to form intermolecular isopeptide bonds. These enzymes are involved in various biological phenomena, including blood coagulation, wound healing, cell death, tissue repair, and terminal differentiation of keratinocytes. Among the TG-family members, TG5 is one of the latest identified enzymes and therefore the less characterized at the functional level. In this work, we reported that TG5 is proteolytically processed in the baculovirus expression system and in mammal epithelial cells. Similar to other members of the TG family-TG1, TG3, and factor XIIIa -, TG5 full-length enzyme has very low enzymatic activity, while the 53-kDa proteolytically processed form is highly active.