Changes in serum citrullinated fibrinogen concentration associated with the phase of bacteremia patients.

BACKGROUND: Citrullinated fibrinogen (C-Fbg) has been detected in rheumatoid arthritis; however, few studies have reported the role of C-Fbg in other inflammatory diseases. This study aimed to clarify the changes in serum C-Fbg associated with the bacteremia phase. METHODS: We measured serum C-Fbg concentration in bacteremia patients. C-Fbg levels at each phase of bacteremia, classified by white blood cell (WBC) count and neutrophil left shift change, were compared with those of healthy control (HC). The correlation between C-Fbg concentration and certain inflammatory markers, or citrullinated histone H3 concentration was assessed. Multiple linear regression (MLR) analysis was used to examine the association of log C-Fbg with certain inflammatory markers. RESULT: Serum C-Fbg levels were significantly higher in bacteremia patients than in HC (p < 0.001) and positively correlated with WBC and neutrophil count. Further, C-Fbg levels were significantly higher in phases III and IV of bacteremia than in HC (p < 0.001). MLR analysis indicated that log C-Fbg had a stronger relationship with log neutrophil counts than other certain inflammatory markers (p < 0.01). CONCLUSION: Serum C-Fbg levels increased in bacteremia patients, and this was consistent with an influx of neutrophils into the blood stream in accordance with the bacteremia phase.

Importance of cystatin C and uric acid levels in the association of cardiometabolic risk factors in Japanese junior high school students.

BACKGROUND: Serum cystatin C (CysC), a novel marker of renal function, is associated with the components of metabolic syndrome in adults. Little is known about the utility of CysC and its association with cardiometabolic risks in young subjects. METHODS AND RESULTS: In a cohort of 454 Japanese junior high school students, the distribution of serum CysC levels and associated variables were analyzed. CysC levels were significantly higher in boys than in girls (0.92±0.10mg/L vs. 0.77±0.08mg/L, p<0.001). CysC was significantly correlated with serum creatinine (r=0.473, p<0.001), and serum uric acid (SUA) (r=0.546, p<0.001). Multivariable regression analysis revealed significant associations between CysC and SUA in all subjects (ß=0.241, p<0.001), and in boys and girls separately (ß=0.264 and 0.240, respectively, both p<0.001). Importantly, subjects with elevation of both serum CysC and SUA levels had the highest ratio of triglyceride to high-density lipoprotein cholesterol. CONCLUSIONS: CysC had significant associations with both creatinine and SUA in Japanese junior high school students. The concomitant elevation of serum CysC and SUA levels was associated with subclinical lipid metabolism dysregulation, and suggested the presence of cardiometabolic risk accumulation.

[A Case of Secondary Cryofibrinogenemia with Cholangiocarcinoma and Deep Venous Thrombosis].

Cryofibrinogen (CF) is a type of cryoprotein (CP) that can precipitate in cooled plasma but not in serum, and resolves upon warming. We identified a case of secondary cryofibrinogenemia with cholangiocarcinoma and deep venous thrombosis. The patient's cryocrit measured using a Wintrobe tube was 19% in sodium citrate plasma stored for 7 days at 4 degrees C. We performed quantitative analysis of plasma proteins (fibrinogen, IgG, IgA, IgM, C3, C4, α1-antitrypsin, and C-reactive protein) before and after precipitation for 12 hours at 4 degrees C. The plasma fibrinogen concentration decreased by 16.7% (120 mg/dL --> 100 mg/dL), whereas the others were unaffected by precipitation. The CP purified from the patient's plasma was washed three times with saline and subjected to Western blot and Sodium Dodecyl Sulfate Polyacrylamide Gel Electrophoresis (SDS-PAGE) analyses. Western blot analysis indicated that the purified CP was composed of not only fibrinogen but also fibronectin, α1-antitrypsin, α2-macroglobulin, coagulation factor VIII, and IgG, IgA, and IgM. Interestingly, SDS-PAGE analysis showed that the molecular weight of the patient's CF differed from that of purified normal fibrinogen (340 KDa) and consisted of several low-molecular-weight bands (50-250 KDa). From these results, we speculated that CF found in this case was a mixture of degradated fibrinogen and some plasma proteins. In summary, cryofibrinogenemia is a rare and under-recognized disease. Sample information in routine clinical practice is valuable to diagnose this disease.

Novel heterozygous dysfibrinogenemia, Sumida (AαC472S), showed markedly impaired lateral aggregation of protofibrils and mildly lower functional fibrinogen levels.

INTRODUCTION: We encountered a 6-year-old girl with systemic lupus erythematosus. Although no bleeding or thrombotic tendency was detected, routine coagulation screening tests revealed slightly lower plasma fibrinogen levels, as determined by functional and antigenic measurements (functional/antigenic ratio=0.857), suggesting hypodysfibrinogenemia. MATERIALS AND METHODS: DNA sequence and functional analyses were performed on purified plasma fibrinogen, and recombinant variant fibrinogen was synthesized in Chinese hamster ovary cells based on the results obtained. RESULTS: DNA sequencing revealed a heterozygous AαC472S substitution (mature protein residue number) in the αC-domain. AαC472S fibrinogen indicated the presence of additional disulfide-bonded molecules, and markedly impaired lateral aggregation of protofibrils in spite of slightly lower functional plasma fibrinogen levels. Scanning electron microscopic observations showed a thin fiber fibrin clot, and t-PA and plasminogen-mediated clot lysis was similar to that of a normal control. Recombinant variant fibrinogen-producing cells demonstrated that destruction of the Aα442C-472C disulfide bond did not prevent the synthesis or secretion of fibrinogen, whereas the variant Aα chain of the secreted protein was degraded faster than that of the normal control. CONCLUSION: Our results suggest that AαC472S fibrinogen may cause dysfibrinogenemia, but not hypofibrinogenemia. The destruction and steric hindrance of the αC-domain of variant fibrinogen led to the impaired lateral aggregation of protofibrils and t-PA and plasminogen-mediated fibrinolysis, as well as several previously reported variants located in the αC-domain, and demonstrated the presence of disulfide-bonded molecules.

Recombinant γT305A fibrinogen indicates severely impaired fibrin polymerization due to the aberrant function of hole 'A' and calcium binding sites.

INTRODUCTION: We examined a 6-month-old girl with inherited fibrinogen abnormality and no history of bleeding or thrombosis. Routine coagulation screening tests showed a markedly low level of plasma fibrinogen determined by functional measurement and also a low level by antigenic measurement (functional/antigenic ratio=0.295), suggesting hypodysfibrinogenemia. MATERIALS AND METHODS: DNA sequence analysis was performed, and γT305A fibrinogen was synthesized in Chinese hamster ovary cells based on the results. We then functionally analyzed and compared with that of nearby recombinant γN308K fibrinogen. RESULTS: DNA sequence analysis revealed a heterozygous γT305A substitution (mature protein residue number). The γT305A fibrinogen indicated markedly impaired thrombin-catalyzed fibrin polymerization both in the presence or absence of 1mM calcium ion compared with that of γN308K fibrinogen. Protection of plasmin degradation in the presence of calcium ion or Gly-Pro-Arg-Pro peptide (analogue for so-called knob 'A') and factor XIIIa-catalyzed fibrinogen crosslinking demonstrated that the calcium binding sites, hole 'a' and D:D interaction sites were all markedly impaired, whereas γN308Kwas impaired at the latter two sites. Molecular modeling demonstrated that γT305 is localized at a shorter distance than γN308 from the high affinity calcium binding site and hole 'a'. CONCLUSION: Our findings suggest that γT305 might be important for construction of the overall structure of the γ module of fibrinogen. Substitution of γT305A leads to both dysfibrinogenemic and hypofibrinogenemic characterization, namely hypodysfibrinogenemia. We have already reported that recombinant γT305A fibrinogen was synthesized normally and secreted slightly, but was significantly reduced.

γ375W fibrinogen-synthesizing CHO cells indicate the accumulation of variant fibrinogen within endoplasmic reticulum.

BACKGROUND: Hepatic endoplasmic reticulum (ER) storage disease (HERSD) associated with hypofibrinogenemia has been reported in patients with four types of heterozygous γ-chain variant fibrinogen in the C terminal region. Of interest, substitution of γR375W induced hypofibrinogenemia and HERSD, whereas γR375G induced dysfibrinogenemia. OBJECTIVES: To analyze the synthesis of variant fibrinogen and morphological characteristics, we established variant fibrinogen-producing cells and compared them with wild-type fibrinogen-synthesizing cells. METHODS: The fibrinogen γ-chain expression vectors coding γ375W and γ375G were altered by oligonucleotide-directed mutagenesis and transfected into Chinese hamster ovary (CHO) cells. Synthesis of fibrinogen (media and cell lysates) was measured by ELISA for each cloned cell line and morphological characteristics were observed by immunofluorescence and transmission electron microscopy. RESULTS: The medium/cell lysate fibrinogen ratio of γ375W-CHO cells was markedly lower than that of the normal cells and γ375G-CHO cells. Immunostaining with anti-fibrinogen antibody showed only γ375W-CHO cells, but revealed two types of cells containing cytoplasmic inclusion bodies, scattered large-granular bodies and fibrous forms. Observation by confocal microscopy indicated that both inclusion bodies were colocalized with fibrinogen and ER-membrane protein; furthermore, transmission electron microscopic observation demonstrated dilatation of the ER by large-granular inclusion bodies and fibrous forms filled with regularly structured fibular materials within the dilated ER. CONCLUSION: These results demonstrated that assembled and non-secreted γ375W fibrinogen was accumulated in the dilated ER and aggregated variant fibrinogen was seen as regularly structured fibular materials, which was similar to the fingerprint-like pattern observed at inclusion bodies in patients' hepatocytes affected with HERSD.

[Polymorphism frequency of fibrinogen Bß-chain 448Arg and Lys, and the differences of plasma fibrinogen level and clotting function with three genotypes in Japanese].

The 448th residue in the fibrinogen Bß-chain molecule is known to be polymorphic (Arg/Lys, R/K), and its allele frequency was previously estimated to be R: 0.85 and K: 0.15 in the US. In the present study, we collected blood samples from 64 healthy individuals and examined the frequency of the fibrinogen Bß-chain 448 polymorphism in the Japanese population as well as the relationship between polymorphic types and the function and levels of fibrinogen. The polymorphic site was confirmed by MnlI restriction analysis and direct sequencing analysis for amplified 860 bp PCR products containing the Bß 448 residue. Fibrinogen plasma levels were estimated based on functional and immunological methods. Functional analyses were performed on the R/R, R/K, and K/K types using thrombin-catalyzed fibrin polymerization. The R/R type was detected in 48 out of 64 subjects, R/K in 15, and K/K in one. Therefore, the allele frequency was found to be R: 0.87 and K: 0.13 for the Bß 448 site, which was similar to that reported previously in the US. The polymorphism did not affect fibrinogen plasma levels. The results of the analysis on fibrin polymerization of the three types suggested that lateral aggregation may be significantly slower in the fibrinogen Bß-chain 448R/K and K/K types than in the R/R type. (Original).

Nonsense-mediated mRNA decay was demonstrated in two hypofibrinogenemias caused by heterozygous nonsense mutations of FGG, Shizuoka III and Kanazawa II.

We report two novel hypofibrinogenemias, Shizuoka III and Kanazawa II, which are caused by heterozygous mutations in FGG. Shizuoka III showed c.147delT and 147_149insACA in FGG exon 3 and a subsequent frameshift mutation, resulting in mature protein γ23X (native protein: γ49X), and Kanazawa II showed c.1205G>A in FGG exon 9, resulting in γ376X (native protein: γ402X). To determine whether the truncated γ-chains, γ23X and γ376X, were synthesized and participated in the assembly of fibrinogen, mutant-type cDNA vectors were transfected into Chinese hamster ovary (CHO) cells. Significant levels of mutant fibrinogen were not detected by ELISA in the culture media and cell lysates. Immunoblot analysis of cell lysates revealed that the mutant γ-chain of γ376X was observed but intact fibrinogen was not. On the other hand, mutant γ-chain was not observed in γ23X-expressing cells. To demonstrate the involvement of the mechanisms of nonsense-mediated mRNA decay (NMD), we cloned wild- and mutant-type mini-genes containing γ23 or γ376 codon and transfected these into CHO cell lines in the absence or presence of cycloheximide as an NMD inhibitor. mRNA levels were determined using real-time quantitative RT-PCR in CHO cells. In the absence of cycloheximide, levels of mRNAs transcribed from the mutant gene were lower than from the wild-type gene whereas, in the presence of cycloheximide, levels of mRNAs transcribed from the mutant gene increased dose-dependently. Finally, these results demonstrated that mRNAs containing γ23X or γ376X are degraded by the NMD system and translation of the truncated γ-chain polypeptide decrease in patients' hepatocytes, resulting in hypofibrinogenemias.

Successful living-related kidney transplantation in a boy with inherited dysfibrinogenemia.

In kidney transplantation, it is essential to avoid acute vascular complications, such as hemorrhage and renal vascular thrombosis, which may often lead to allograft loss. Inherited dysfibrinogenemia is a rare coagulation disorder with a wide spectrum of clinical manifestations, such as excessive bleeding and thrombosis. A 12-yr-old boy, previously diagnosed with renal hypodysplasia, was found to have reduced fibrinogen concentrations. Coagulation tests assessing surgical risk during kidney transplantation showed a discrepancy between functional and immunologic fibrinogen concentrations. Gene analysis confirmed inherited dysfibrinogenemia, with a heterozygous mutation in FGA (Aα Arg16His) in the patient and his mother. Based on the molecular and functional properties of the mutation, and a familial phenotype, in which his aunt had experienced a previous bleeding episode, the patient was considered at greater risk of bleeding than of thrombosis. The patient was administered fibrinogen concentrate before surgery, and kidney transplantation was performed with his father as the organ donor. The patient received additional prophylactic infusions of fibrinogen concentrate postoperatively, and his postoperative course was uneventful. Accurate diagnosis of dysfibrinogenemia, including gene analysis, is important for correctly managing patients with this coagulation disorder who are undergoing kidney transplantation.

siRNA down-regulation of FGA mRNA in HepG2 cells demonstrated that heterozygous abnormality of the Aα-chain gene does not affect the plasma fibrinogen level.

INTRODUCTION: We encountered two afibrinogenemia patients with homozygous and compound heterozygous FGA mutation. Of interest, the patients' parents, who are heterozygous, had normal levels of plasma fibrinogen; thus, we hypothesized that liver FGA mRNA levels were higher than those of FGB and/or FGG mRNA. MATERIALS AND METHODS: To test the hypothesis, we quantitated mRNA levels of a normal liver and a human hepatocyte cell line, HepG2 cells, and performed siRNA-mediated down-regulation of the fibrinogen gene in HepG2 cells. mRNA levels were determined using real-time quantitative RT- PCR for three normal livers and HepG2 cells. Down-regulation of FGA, FGB, or FGG in HepG2 cells was performed by the addition of siRNA corresponding to each of the three genes, and the mRNA levels determined in the cells and the secreted fibrinogen concentration in media. RESULTS: The mRNA level of normal human liver was FGA=FGB>FGG and the FGG mRNA level was about 2-fold lower than the others, that of HepG2 cells was FGA>FGG>FGB and FGA mRNA was approximately 2- or 4-fold higher than FGG mRNA and FGB mRNA. When FGA, FGB, or FGG mRNA expression levels were down-regulated by nearby 50%, fibrinogen concentrations in media were 78%, 49%, or 57% of the control, respectively. CONCLUSIONS: Our results suggest that FGG mRNA levels limit fibrinogen expression in normal liver and HepG2 cells and that 50% reduction of FGA mRNA levels would not limit fibrinogen expression in normal liver and HepG2 cells.

Fibrinopeptide A release is necessary for effective B:b interactions in polymerisation of variant fibrinogens with impaired A:a interactions.

Fibrin polymerisation is mediated by interactions between knobs 'A' and 'B' exposed by thrombin cleavage, and holes 'a' and 'b'. We demonstrated markedly delayed thrombin-catalysed fibrin polymerisation, through B:b interactions alone, of recombinant γD364H -fibrinogen with impaired hole 'a'. To determine whether recombinant variant fibrinogens with no release of fibrinopeptide A (FpA) polymerise similarly to γD364H -fibrinogen, we examined two variant fibrinogens with substitutions altering knob 'A', Aα17A- and Aα17C-fibrinogen. We examined thrombin- or batroxobin-catalysed fibrinopeptide release by HPLC, fibrin clot formation by turbidity and fibrin clot structure by scanning electron microscopy (SEM) and compared the results of the variants with those for γ D364H-fibrinogen. Thrombin-catalysed FpA release of Aα17A-fibrinogen was substantially delayed and none observed for Aα17C-fibrinogen; fibrinopeptide B (FpB) release was delayed for all variants. All variant fibrinogens showed substantially impaired thrombin-catalysed polymerisation; for Aα17A-fibrinogen it was delayed less, and for Aα17C more than for γD364H -fibrinogen. No variants polymerised with batroxobin, which exposed only knob 'A'. The inhibition of variant fibrinogens' polymerisation was dose-dependent on the concentration of either GPRP or GHRP, and both peptides that block holes 'b'. SEM showed that the variant clots from Aα17A- and γD364H-fibrinogen had uniform, ordered fibres, thicker than normal, whereas Aα17C -fibrinogen formed less organised clots with shorter, thinner, and tapered ends. These results demonstrate that FpA release per se is necessary for effective B:b interactions during polymerisation of variant fibrinogens with impaired A:a interactions.

[Comparison of fibrinogen synthesis and secretion between novel variant fibrinogen, nagakute (gamma305Thr --> Ala), and other variants located in gamma305-308 residues].

We found and identified a novel heterozygous dysfibrinogenemia with gammaT305A (ACA --> GCA) mutation in a 6-month old boy. Since his plasma antigenic concentration of fibrinogen was 1.12g/l and less than the lower limit of the reference interval, we guessed that the production of a variant fibrinogen might be a partial defect. To clarify this speculation, we altered the gamma-chain expression vector, transfected it into Chinese Hamster Ovary(CHO) cells, and synthesized recombinant gammaT305A fibrinogen alongside three other variant fibrinogens, gammaS306P, gammaH307Y, and gammaN308K, and the wild type (gammaN) fibrinogen. Fibrinogen concentration ratio of culture media/cell lysates decreased in the order of gammaT305A-, gammaS306P-, gammaH307Y-CHO cells, all three being lower in comparison to the gammaN-CHO cells. Western blotting analyses indicated that all of variant gamma-chains were assembled into fibrinogen molecules in the cells. These data indicate the possibility that secretion of gamma T305A-fibrinogen is slightly impaired and variant fibrinogen is accumulated in the cell. Of interest, the secretion of gammaH307Y-fibrinogen was decreased the most, whereas that of the gammaN308K-CHO cells was not affected. The tertiary structure of the yC nodule indicated that gamma305T-gamma307H residues are located in the inside of the nodule. In contrast, that of gamma308N is located on surface of the nodule. In conclusion, our results showed the variant fibrinogen, gammaT305A, has characteristics not only of dysfibrinogenemia, but also might be hypofibrinogenemia, namely, hypo/dysfibrinogenemia. Furthermore, gamma306S-gamma307H residues of the gammaC nodule play crucial roles for protein synthesis and fibrin polymerization.

[Functional analysis for dysfibrinogenemias, Toyama and Adachi, which have a mutation of Aalpha16Arg-->His (CGT-->CAT) with aberrant fibrinopeptide A release].

We found and identified four heterozygous dysfibrinogenemias with AalphaR16H(CGT-->CAT) mutation in two families by coagulation tests and direct sequence analysis for PCR-amplified DNA fragments. Two dysfibrinogens were designated as fibrinogen Toyama and Adachi, according to the place of residence of proposituses, respectively. Patients' fibrinogen purified from plasma using immunoaffinity-chromatography was subjected to thrombin- or batroxobin-catalyzed fibrin polymerization, fibrinopeptide A (FPA) release, and clottability test. AalphaR16H-fibrinogen showed impaired thrombin or batroxobin-catalyzed fibrin polymerization in comparison with normal control fibrinogen. It is interesting that the period of protofibril formation of Toyama propositus was longest in those of four affected people. The clottability of AalphaR16H-fibrinogen was 66-70% with thrombin and higher than with batroxobin, 35-50%. In the same condition with fibrin polymerization, thrombin and batroxobin did not cleave the Aalpha16H-17G peptide-bonding, resulting in no release of variant FPA. From these results, we speculated that elongation of the two-stranded protofibril formation would be terminated by participation of the heterodimer fibrinogen molecules composed with a normal and an aberrant Aalpha-chain, and it would result in a decrease in fibrin polymerization. We speculated that the difference in the extent of impairment of fibrin polymerization among the patients might be caused by the different amount of heterodimers. Moreover, we also speculated that batroxobin-induced clottability was lower than thrombin-induced clottability, because batroxobin cannot induce the so-called "B-knob-b-hole" interaction, which enhances fibrin formation.

Molecular analysis of afibrinogenemic mutations caused by a homozygous FGA1238 bp deletion, and a compound heterozygous FGA1238 bp deletion and novel FGA c.54+3A>C substitution.

We identified two afibrinogenemic girls in two Japanese families and performed molecular analysis to clarify the mechanisms of fibrinogen defects. Genetic analyses were performed by PCR amplification of the fibrinogen gene and DNA sequence analysis. To analyze the mechanisms of mature fibrinogen defects in plasma, we cloned minigenes from the proposita's PCR-amplified DNA, transfected them into CHO cells, and sequenced the cDNA amplified with the RT reaction followed by PCR. Sequence analyses indicated that one was caused by a homozygous 1238 bp deletion of the fibrinogen Aα-chain gene (FGAΔ1238) and the other was a compound heterozygous FGAΔ1238 and novel FGA c.54+3A>C substitution. The minigene corresponding to FGAΔ1238 generates two aberrant mRNAs, both of which may induce a frameshift and terminate prematurely. In contrast, the minigene corresponding to FGA c.54+3A>C generates two aberrant mRNAs, one of which may induce a frameshift and terminate prematurely, and the other uses a cryptic 5' splice site in exon 1, resulting in the deletion of six amino acids in signal peptides. Molecular analyses of both genetic variants suggest that the lack of a mature Aα-chain, impaired assembly, and/or secretion of the fibrinogen molecule may lead to afibrinogenemia.

[SNP-specific mismatched PCR for embryonic DNA detection using blood from pregnant mothers].

BACKGROUND: Although prenatal diagnoses are performed using amniotic fluid cells, chorionic villus, or cord blood, these methods are hazardous for pregnant woman and the fetus. To determine a procedure for safe prenatal diagnosis, we have developed a sensitive method to analyze SNPs and we evaluated the possibility to detect fetal DNA in the maternal blood. METHODS: GeneScan analysis was performed by using mismatched specific primers for 5 SNP types and fluorescein amidite (FAM) labeled primers, and Real-time PCR analysis was also performed by using mismatched specific primers for the same SNP type and probes labeled with FAM and black hole quencher. DNA from healthy volunteers' blood was used for a primary examination to establish procedures, and DNA from 200 microl of blood from pregnant women, their partners and children were used for detection of fetal DNA and/or typing and selection of SNPs. RESULTS: To evaluate the sensitivity of this method, mixing tests of DNA containing a SNP nucleotide and its counterpart indicated the sensitivities were 10(-1)-10(-3) for GeneScan analysis and 10(-1)-10(-4) for Real-time PCR analysis. Fetal DNA (rs3769393-A and G) was detected in blood from pregnant women (GG-type mother: 2 out of 2, AA-type mother: 1 out of 2) only at 18 and/or 28 gestation weeks by Real-time PCR analysis. However, 4 SNPs measured by Real-time PCR analysis and 5 SNPs examined by GeneScan analysis were not detected in all women in different gestation periods. CONCLUSIONS: We established a SNP detection method using GeneScan and Real-time PCR analysis. The latter detected fetal DNA in 200 microl of blood in only some pregnant women. We speculate that using a large amount of DNA from nucleated erythrocytes in 20 ml of blood will improve the detection rate of fetal DNA.

Heterozygous Bß-chain C-terminal 12 amino acid elongation variant, BßX462W (Kyoto VI), showed dysfibrinogenemia.

A heterozygous patient with dysfibrinogenemia with slight bleeding and no thrombotic complications was diagnosed with fibrinogen Kyoto VI (K-VI). To elucidate the genetic mutation(s) and characterize the variant protein, we performed the following experiments and compared with identical and similar variants that have already been reported. The proposita's PCR-amplified DNA was analyzed by sequencing and her purified plasma fibrinogen underwent SDS-PAGE followed by immunoblotting, fibrin polymerization, and scanning electron microscopic observation of fibrin clot and fibers. Sequence analyses showed that K-VI fibrinogen substituted W (TGG) for terminal codon (TAG), resulting in 12 amino acid elongation 462-473 (WSPIRRFLLFCM) in the Bß-chain. Protein analyses indicated that the presence of some albumin-binding variant fibrinogens and a dimeric molecule of variant fibrinogens reduced fibrin polymerization, with a thinner fiber and aberrant fibrin network. These results are almost the same as for the identical variant of Magdeburg, however, different from the similar variant of Osaka VI [12 amino acid elongation 462-473 (KSPIRRFLLFCM) in the Bß-chain] in the presence of variant forms and clot structure. We speculate the side-chain difference at 462 residues, W in K-VI, K in Osaka VI, and/or the difference in the presence of disulfide bridged forms of variant fibrinogens, led to the notable difference in the fibrin bundle network. Although a strong evolutional and structural association between Bß-chain and γ-chain molecules is established, the corresponding recombinant 15 residue elongation variants of the fibrinogen γ-chain showed reduced assembly and secretion.

[Role of fibrinogen Bbeta-chain D-region 454-458 residues for assembly and secretion of intact fibrinogen].

BACKGROUND: To examine the role of fibrinogen Bbeta-chain D region in the assembly and/or secretion of multichain protein, we synthesized eight variant fibrinogens with truncated Bbeta-chains in the C terminal region, terminating with 454, 455, 456 or 458 residues, and with substitution at Bbeta-455Arg by Lys, Ile, Ala or Asp in Chinese hamster ovary (CHO) cells. METHODS: A fibrinogen Bbeta-chain expression vector was altered and transfected into CHO cells that expressed normal human fibrinogen Aalpha- and gamma-chains. Expressed fibrinogens of cell lysates and culture media of the established cell lines were subjected to ELISA and immunoblot analysis. RESULTS: The CHO cells synthesized eight variant Bbeta-chains and assembled these into fibrinogen except for Bbeta-454 and Bbeta-455Asp. However, in the cell lysates, concentrations of these variant fibrinogens were lower than that in wild type cells. These assembled variant fibrinogens were secreted into the culture medium, and the levels in culture media were also lower than that in the medium of wild type cells. Significant differences in the mean ratios of fibrinogen concentration in medium to that in cell lysate were not observed between the variant type cells and the wild type cells. CONCLUSIONS: Residues of the Bbeta-chain D domain are essential for fibrinogen assembly, especially the Bbeta-455 residue was critical. The present study indicated that the structure of the fibrinogen Bbeta-chain C terminal D region is necessary for fibrinogen assembly, but not for secretion.

[Assembly and secretion of mutant fibrinogens with variant gamma-chain C terminal region (gamma313-gamma345)].

BACKGROUND: It has been reported that the structure of the fibrinogen gamma-chain C terminal (D) region (140-411 residues) has important functions in fibrinogen assembly and/or secretion. Variant fibrinogens, gamma313S>N, gamma336M>I, gamma341A>D, and gamma345N>D have been reported as hypofibrinogenemias or dysfibrinogenemias. To study the assembly and secretion of the variant fibrinogens containing aberrant D regions, we established CHO cells producing these four fibrinogens. METHODS: A fibrinogen gamma-chain expression vector was altered and transfected into CHO cells that expressed normal human fibrinogen Aalpha and Bbeta-chains. Cell lysates and culture media of the selected cell lines were subjected to ELISA and immunoblot analysis. RESULTS: The CHO cells synthesized mutant gamma-chains and assembled these into fibrinogen, although these variant fibrinogens were barely secreted into the culture media. In the cell lysates, however, concentrations of these variant fibrinogens were higher than the normal levels. CONCLUSIONS: The present study indicated that the tertiary structure of the fibrinogen gamma-chain C terminal region between 313 and 345 is necessary for fibrinogen secretion. These findings suggest that reduced levels of fibrinogen secretion lead to the hypofibrinogen in the patients and secreted fibrinogens might show dysfibrinogenemia.

A C-terminal amino acid substitution in the gamma-chain caused by a novel heterozygous frameshift mutation (Fibrinogen Matsumoto VII) results in hypofibrinogenaemia.

We found a novel hypofibrinogenemia designated as Matsumoto VII (M-VII), which is caused by a heterozygous nucleotide deletion at position g.7651 in FGG and a subsequent frameshift mutation in codon 387 of the gamma-chain. This frameshift results in 25 amino acid substitutions, late termination of translation with elongation by 15 amino acids, and the introduction of a canonical glycosylation site. Western blot analysis of the patient's plasma fibrinogen visualised with anti-gamma-chain antibody revealed the presence of two extra bands. To identify the extra bands and determine which of the above-mentioned alterations caused the assembly and/or secretion defects in the patient, 11 variant vectors that introduced mutations into the cDNA of the gamma-chain or gamma'-chain were transfected into Chinese hamster ovary cells. In vitro expression of transfectants containing gammaDelta7651A and gammaDelta7651A/399T (gammaDelta7651A with an amino acid substitution of 399Asn by Thr and a variant lacking the canonical glycosylation site) demonstrated a reduction in secretion to approximately 20% of the level seen in the transfectants carrying the normal gamma-chain. Furthermore, results from other transfectants demonstrated that eight aberrant residues between 391 and 398 of the M-VII variant, rather than the 15 amino acid extension or the additional glycosylation, are responsible for the reduced levels of assembly and secretion of M-VII variant fibrinogen. Finally, the results of this study and our previous reports demonstrate that the fibrinogen gamma-chain C-terminal tail (388-411) is not necessary for protein assembly or secretion, but the aberrant amino acid sequence observed in the M-VII variant (especially 391-398) disturbs these functions.

In vitro transcription of compound heterozygous hypofibrinogenemia Matsumoto IX; first identification of FGB IVS6 deletion of 4 nucleotides and FGG IVS3-2A>G causing abnormal RNA splicing.

BACKGROUND: We reported a case of hypofibrinogenemia Matsumoto IX (M IX) caused by a novel compound heterozygous mutation involving an FGB IVS6 deletion of 4 nucleotides (Delta4b) (three T, one G; between FGB IVS6-10 and -16) and FGG IVS3-2A/G, which are both identified for the first time. To examine the transcription of mRNA from the M IX gene, we cloned the wild-type and mutant genes into expression vectors. METHODS: The vectors were transfected into CHO cells and transiently produced wild-type, Bbeta- or gamma-mRNA in the cells. The mRNAs amplified with RT-PCR were analyzed by agarose gel electrophoresis and nucleotide sequencing. RESULTS: The RT-PCR product from FGB IVS6Delta4b showed aberrant mRNA that included both introns 6 and 7, and that from FGG IVS3-2G showed two aberrant mRNAs, a major one including intron 3 and a minor in which intron 3 was spliced by a cryptic splice site in exon 4. We speculated that the aberrant mRNAs are degraded before translation into proteins, and/or translated variant chains are subjected to quality control and degraded in the cytoplasm. CONCLUSION: The reduced plasma fibrinogen level of the M IX patient was caused by abnormal RNA splicing of one or both of the FGB and FGG genes.