Characterization of a Mouse Factor IX cDNA and Developmental Regulation of the Factor IX Gene Expression in Liver

Identification of zebrafish ortholog for human coagulation factor IX and its age-dependent expression

BACKGROUND

Coagulation factor IX (FIX) is a serine protease zymogen involved in the intrinsic blood coagulation pathway, and its deficiency causes hemophilia B. Zebrafish has three f9 genes, and the ortholog to human F9 is unknown.

OBJECTIVE

To identify the zebrafish ortholog to F9 using sequence analysis and piggyback knockdown technology.

METHODS

Gene and protein sequence analysis for three f9 genes, f9a, f9b, and f9l, present in the zebrafish genome was performed. In vivo and in vitro assays after knockdown of each gene and immunodepletion using specific antibodies were carried out.

RESULTS

Sequence analysis revealed that f9a and f9b are similar to human F9, whereas f9l is similar to human F10. RNA analysis showed an age-dependent increase in expression of all three genes. Zebrafish f9a gene knockdown and Fixa immunodepletion prolonged kinetic partial thromboplastin time (kPTT), whereas f9l knockdown and Fixl immunodepletion prolonged kPTT, kinetic prothrombin time, and kinetic Russell viper venom activation time. Laser-assisted venous thrombosis increased time to occlusion after f9a and f9l knockdown and antibody inhibition of Fixa and Fixl. Further, analysis of plasma proteins by mass spectrometry and immunohistochemistry detected all three proteins.

CONCLUSIONS

Our findings suggest that zebrafish f9a has functional activity similar to human F9. Fixl is functionally similar to Fx. The age-dependent increases of these factors are comparable to those observed in mice and humans. Thus, the zebrafish model could be used to study factors involved in increasing f9a expression during aging. It could also be used to test whether normal human Factor IX and Factor IX Leyden promoter work in zebrafish background.

An age-related homeostasis mechanism is essential for spontaneous amelioration of hemophilia B Leyden

Regulation of age-related changes in gene expression underlies many diseases. We previously discovered the first puberty-onset gene switch, the age-related stability element (ASE)/age-related increase element (AIE)-mediated genetic mechanism for age-related gene regulation. Here, we report that this mechanism underlies the mysterious puberty-onset amelioration of abnormal bleeding seen in hemophilia B Leyden. Transgenic mice robustly mimicking the Leyden phenotype were constructed. Analysis of these animals indicated that ASE plays a central role in the puberty-onset amelioration of the disease. Human factor IX expression in these animals was reproducibly nullified by hypophysectomy, but nearly fully restored by administration of growth hormone, being consistent with the observed sex-independent recovery of factor IX expression. Ets1 was identified as the specific liver nuclear protein binding only to the functional ASE, G/CAGGAAG, and not to other Ets consensus elements. This study demonstrates the clinical relevance of the first discovered puberty-onset gene switch, the ASE/AIE-mediated regulatory mechanism.

Genetic mechanisms of age regulation of protein C and blood coagulation

Blood coagulation activity in humans increases with age. We previously identified two genetic elements, age-related stability element (ASE; GAGGAAG) and age-related increase element (AIE; unique stretch of dinucleotide repeats), which were responsible for age-related stable and increasing expression patterns, respectively, and together recapitulated normal age regulation of the human factor IX (hFIX) gene. Here we report the age-regulatory mechanisms of human anticoagulant protein C (hPC), which shows an age-stable pattern of circulatory levels. The murine protein C gene showed an age-related stable expression pattern in general agreement with that of the hPC. Through longitudinal analyses of transgenic mice carrying hPC minigenes, the hPC gene was found to have a functional age-related stability element (hPC ASE; CAGGAAG) in the 5'-upstream proximal region but was found to lack any age-related increase element. Three other ASE-like sequences present in the hPC gene, GAGGAAA and (G/C)AGGATG, also bound nuclear proteins but were not active in the age regulation of the hPC gene. Functional hPC ASE and hFIX ASE were apparently generated through convergent evolution, and hFIX ASE can fully substitute for the hPC ASE in conferring age-related stable expression pattern of the hPC gene. In the presence of the hPC ASE, hFIX AIE can convert the age-stable expression pattern of the hPC gene to a hFIX-like age-related increase pattern. These results support the universality of ASE and AIE functions across different genes. Clearance of hPC protein from the circulation was not significantly affected by age. We now have established the basic mechanisms responsible for the age-related increase of blood coagulation activity.

Genetic mechanisms of age regulation of blood coagulation: factor IX model

Blood coagulation capacity increases with age in healthy individuals, apparently because of increases in the plasma concentration of most procoagulant factors. This phenomenon may play an important role in the advancing age-associated increase of cardiovascular diseases and thrombosis. Through longitudinal analyses of transgenic mice, we recently identified 2 critical age-regulatory elements, AE5' and AE3', which are together essential for age regulation of the normal human factor IX (hFIX) gene. AE5', present in the long interspersed repetitive element-derived sequence of the 5' upstream region, containing polyomavirus enhancer activator-3 or a closely related element, is responsible for age-stable expression of the gene and functions in a position-independent manner. AE3', present in the middle of the 3' untranslated region, is responsible for age-associated elevation of hFIX mRNA levels in the liver. Presence of both AE5' and AE3' is needed to recapitulate normal age regulation of the hFIX gene. Because factor IX clearance from the circulation is not significantly affected by age, age regulation of hFIX levels is achieved primarily by a combination of stabilization of gene transcription and age-dependent increases in the mRNA levels, which are presumably due to increasing mRNA stabilization. The stage is now set for further systematic studies of the genetic and molecular mechanisms of age regulation of other key coagulation and anticoagulation factors in hopes of understanding the overall age regulation of blood coagulation.

Genetic mechanisms of age regulation of human blood coagulation factor IX

Blood coagulation capacity increases with age in healthy individuals. Through extensive longitudinal analyses of human factor IX gene expression in transgenic mice, two essential age-regulatory elements, AE5' and AE3', have been identified. These elements are required and together are sufficient for normal age regulation of factor IX expression. AE5', a PEA-3 related element present in the 5' upstream region of the gene encoding factor IX, is responsible for age-stable expression of the gene. AE3', in the middle of the 3' untranslated region, is responsible for age-associated elevation in messenger RNA levels. In a concerted manner, AE5' and AE3' recapitulate natural patterns of the advancing age-associated increase in factor IX gene expression.

Prevention of vitamin K deficiency bleeding in newborns

Newborn babies are born vitamin K deficient; however, the deficiency is not sufficiently severe to cause a vitamin K deficiency coagulopathy and haemorrhagic disease of the newborn (HDN). Severe vitamin K deficiency can develop quickly in breast-fed newborns and can result in the appearance of classic HDN during the first week of life or late HDN during the first 2 months of life. Both forms of the disease can be severe, causing brain damage and death. Classic and late HDN are prevented by the intramuscular administration of vitamin K at birth. Oral prophylaxis prevents classic HDN but is ineffective in preventing late HDN. Despite proven effectiveness of intramuscular vitamin K prophylaxis there have been concerns about the need for, and safety of, this therapy. This review provides evidence that there is need for intramuscular vitamin K prophylaxis for all babies in order to eradicate haemorrhagic disease of the newborn and concludes that there is no evidence that this therapy is harmful.

Cloning of rat vitamin K-dependent gamma-glutamyl carboxylase and developmentally regulated gene expression in postimplantation embryos

Vitamin K-dependent carboxylase catalyzes the posttranslational modification of glutamate to gamma-carboxyglutamate (Gla) in its substrates, the vitamin K-dependent proteins (VKDPs). This modification is required for the activities of the VKDPs. Recent evidence demonstrates previously unrecognized roles for VKDPs as signaling molecules important in the regulation of cell growth, adhesion, and apoptosis, suggesting developmental functions for VKDPs and hence the carboxylase. The tissue distribution and functions of carboxylase in development are unknown. In this study, we isolated and characterized the full-length cDNA encoding the rat carboxylase and analyzed, at the cellular level, the expression of this gene in rat embryos by in situ hybridization. We demonstrate that the expression of this gene is highly regulated in a developmental and tissue-specific manner. Hepatocytes, the major site of synthesis of VKDPs of blood coagulation, express carboxylase mRNA late in gestation, in contrast to the central nervous system, mesenchymal, and skeletal tissues which express carboxylase mRNA early during rat embryogenesis. The tissue-specific temporal expression of the carboxylase gene during embryogenesis indicates that vitamin K-dependent carboxylation and the formation of Gla is developmentally regulated. These studies suggest that vitamin K-dependent carboxylation is an important modulator of embryonic VKDP function.

Targeted Inactivation of the Coagulation Factor IX Gene Causes Hemophilia B in Mice

Hemophilia B is a leading target for gene therapy because current therapy is not optimal. Hence, a murine model of factor IX (F. IX) deficiency was generated to develop gene therapy strategies for hemophilia B. A targeting vector was created by replacing a 3.2-kb segment of the gene encompassing the catalytic domain with a phosphoglycerokinase promoter-driven neomycin resistant (neor) gene cassette. The transfected embryonic stem cell clones generated chimeric male mice, and germ line transmission of the inactivated F. IX gene was observed in their offsprings. Southern analysis confirmed the mutant genotype in hemizygous male and carrier female mice. F. IX transcripts were not detected in liver RNA isolated from hemizygous mice, and lower levels of F. IX mRNA were noted in carrier female mice when compared with those of normal litter mates. As expected, the mean F. IX coagulant titer of affected male mice was 2.8 U/dL (n = 10), while the mean F. IX titer of carrier female mice was 35 U/dL (n = 14), compared with 69 U/dL (n = 9) for the normal female mice and 92 U/dL (n = 22) for normal male and female litter mates. Further, the tail bleeding time of hemizygous mice was markedly prolonged (>3 hours) compared with those of normal and carrier female litter mates (15 to 20 minutes). Seven of 19 affected male mice died of exsanguination after tail snipping, and two affected mice died of umbilical cord bleeding. Currently, there are 10 affected mice surviving at 4 months of age. Aside from the factor IX defect, the carrier female and hemizygous male mice had no liver pathology by histologic examination, were fertile, and transmitted the F. IX gene mutation in the expected Mendelian frequency. Taken together, we have generated a F. IX knockout mouse for evaluation of novel gene therapy strategies for hemophilia B.

Androgen effects on factor IX expression: in-vitro and in-vivo studies in mice

A role for steroid hormones has been proposed for the post-pubertal factor IX increment of approximately 25% seen in both normal males and females, as well as in the post-pubertal phenotypic recovery seen in haemophilia B Leyden. We have evaluated androgen receptor binding to the factor IX promoter and have assessed transcriptional activation of the factor IX gene in hepatocytes through transient transfection studies and through expression of factor IX in a murine model of androgen insensitivity. Whereas transfection of the androgen receptor alone did not activate expression from the factor IX promoter, co-transfection with the CCAAT enhancer binding protein resulted in a synergistic 17-fold enhancement of transcriptional activity. Using liver nuclear extracts and recombinant androgen receptor protein we have confirmed binding of this protein to the factor IX proximal promoter and disruption of binding with a mutation at nucleotide -26. Finally, studies in normal and testicular feminized male mice showed different developmental patterns of factor IX expression. In normal mice, expression recapitulates that seen in humans, with early post-natal levels being approximately 50% of the adult values and with a post-pubertal increment of approximately 25%. In contrast, testicular feminized animals did not show a significant post-pubertal increment of factor IX. These studies provide further support for the role of androgen receptor binding to the factor IX promoter in regulating the developmental expression of factor IX.

gamma-Carboxyglutamic acids 36 and 40 do not contribute to human factor IX function

The gamma-carboxyglutamic acid (Gla) domains of the vitamin K-dependent blood coagulation proteins contain 10 highly conserved Gla residues within the first 33 residues, but factor IX is unique in possessing 2 additional Gla residues at positions 36 and 40. To determine their importance, factor IX species lacking these Gla residues were isolated from heterologously expressed human factor IX. Using ion-exchange chromatography, peptide mapping, mass spectrometry, and N-terminal sequencing, we have purified and identified two partially carboxylated recombinant factor IX species; factor IX/gamma 40E is uncarboxylated at residue 40 and factor IX/gamma 36,40E is uncarboxylated at both residues 36 and 40. These species were compared with the fully gamma-carboxylated recombinant factor IX, unfractionated recombinant factor IX, and plasma-derived factor IX. As monitored by anti-factor IX:Ca (II)-specific antibodies and by the quenching of intrinsic fluorescence, all these factor IX species underwent the Ca(II)-induced conformational transition required for phospholipid membrane binding and bound equivalently to phospholipid vesicles composed of phosphatidylserine, phosphatidylcholine, and phosphatidylethanolamine. Endothelial cell binding was also similar in all species, with half-maximal inhibition of the binding of 125I-labeled plasma-derived factor IX at concentrations of 2-6 nM. Functionally, factor IX/gamma 36,40E and factor IX/gamma 40E were similar to fully gamma-carboxylated recombinant factor IX and plasma-derived factor IX in their coagulant activity and in their ability to participate in the activation of factor X in the tenase complex both with synthetic phospholipid vesicles and activated platelets. However, Gla 36 and Gla 40 represent part of the epitope targeted by anti-factor IX:Mg(II)-specific antibodies because these antibodies bound factor IX preferentially to factor IX/gamma 36,40E and factor IX/gamma 40E. These results demonstrate that the gamma-carboxylation of glutamic acid residues 36 and 40 in human factor IX is not required for any function of factor IX examined.

Developmental expression of protein C and protein S in the rat

In order to better understand the expression of the Protein C/Protein S anticoagulant system, we have isolated and characterized cDNAs coding for rat Protein C and Protein S. These cDNAs were used in Northern analysis to determine tissue-specificity and developmental expression patterns for mRNAs coding for Proteins C and S. In rats, Protein C mRNA is expressed almost exclusively in liver with a small amount of expression in kidney, diaphragm, stomach, intestine, uterus and placenta. Protein C mRNA was not expressed in brain, heart, lung, spleen, small intestine, large intestine, ovary, or urinary bladder. In liver, Protein C mRNA is expressed at very low levels at prenatal day 18 and these levels increased to maximal levels by postnatal day 13. The size of the mRNA coding for rat Protein C is approximately 1.9 kb. Rat Protein S mRNA was expressed in all tissues examined: brain, heart, lung, diaphragm, liver, spleen, stomach, small intestine, large intestine, kidney, adrenal ovary, uterus, placenta, and urinary bladder. Interestingly, there were 4 bands hybridizing with the rat protein S cDNA that were evident in many of the tissues examined, corresponding to mRNA sizes of approximately 3.5, 2.6, 1.8, and 0.3 kb. There was a difference in tissue-specificity of each mRNA. The 1.8 kb band is generally the most prominent autoradiographic band in any tissue. From these results, it is evident that the expression of Protein C mRNA is similar to that of other vitamin K-dependent proteins. The expression of Protein S mRNA, however, is surprisingly complex and may include alternative splicing of mRNA to generate the various sizes evident on Northern analysis.

Haemophilia B caused by a missense mutation in the prepeptide sequence of factor IX

In the course of analysing mutation in the factor IX gene from 200 haemophilia B patients in Sweden and the UK, we have identified one patient with a prepeptide missense mutation. He has severe, antigen negative haemophilia, and complete analysis of his coding sequence reveals a single base transversion (A-->T) causing substitution of isoleucine by asparagine at position -30. This change disrupts the hydrophobic core of the prepeptide, a feature which is required for secretion. Thus, haemophilia in this patient is caused by a failure to secrete factor IX from the hepatocytes.

Characterization of a rabbit factor IX cDNA

A rabbit factor IX cDNA was isolated and characterized. The cDNA was 2,676 bp in length and contained the coding region for the leader peptide, the entire mature factor IX protein and a long 3' untranslated region. The deduced amino acid sequence shows a high degree of homology with the sequences of human factor IX and factor IX from other species. Northern blot analysis of liver RNA showed a single mRNA species of 2.8 kb for the rabbit factor IX.