Compound heterozygous protein C deficiency in a family with venous thrombosis: Identification and in vitro study of p.Asp297His and p.Val420Leu mutations

Computational analysis of the functional and structural impact of the most deleterious missense mutations in the human Protein C

Protein C (PC) is a vitamin K-dependent factor that plays a crucial role in controlling anticoagulant processes and acts as a cytoprotective agent to promote cell survival. Several mutations in human PC are associated with decreased protein production or altered protein structure, resulting in PC deficiency. In this study, we conducted a comprehensive analysis of nonsynonymous single nucleotide polymorphisms in human PC to prioritize and confirm the most high-risk mutations predicted to cause disease. Of the 340 missense mutations obtained from the NCBI database, only 26 were classified as high-risk mutations using various bioinformatic tools. Among these, we identified that 12 mutations reduced the stability of protein, and thereby had the greatest potential to disturb protein structure and function. Molecular dynamics simulations revealed moderate alterations in the structural stability, flexibility, and secondary structural organization of the serine protease domain of human PC for five missense mutations (L305R, W342C, G403R, V420E, and W444C) when compared to the native structure that could maybe influence its interaction with other molecules. Protein-protein interaction analyses demonstrated that the occurrence of these five mutations can affect the regular interaction between PC and activated factor V. Therefore, our findings assume that these mutants can be used in the identification and development of therapeutics for diseases associated with PC dysfunction, although assessment the effect of these mutations need to be proofed in in-vitro.

Two heterozygous mutations associated with type I protein C deficiency in two Chinese independent families

To explore the pathogenesis of protein C (PC) deficiency in two independent families by mutations detection and bioinformatics analysis. The PC activity (PC:A) and PC antigen (PC:Ag) were detected by chromogenic substrate and ELISA, respectively. The PROC sequencing was performed to identify the mutational sites. The molecular pathogenesis of the mutations were studied by the conservation, bioinformatics and model analysis. The PC:A and PC:Ag of the proband 1 were observably reduced at 35 and 44%, respectively. Gene sequencing analysis revealed the p.Leu278Pro derived from a heterozygous c.833T>C point mutations in exon 9 of PROC gene. For proband 2, the PC:A and PC:Ag were decreased to 40 and 51%, respectively, caused p.Ala178Pro missense mutation by a heterozygous point mismatch of c.532G>C in exon 5 of PROC gene. Bioinformatics and model analysis indicated that it was the Leu278Pro and Ala178Pro that caused clinical PC deficiency (PCD). The heterozygous mutations Leu278Pro and Ala178Pro were observed in two independent families. The Leu278Pro mutation in the PROC gene has not been described elsewhere. The two mutations can both lead to the type I hereditary PCD, and probably be the major causes of PCD in the families.

Establishment of a new protein C detection system based on chromogenic substrate assay and its clinical diagnostic value for deep vein thrombosis

Background

Deficiency of protein C (PC) affects the balance between blood coagulation and fibrinolysis in the human body. Chromogenic‐based assay is recommended as the preferred screening method for detecting PC deficiency. We established a PC detection system based on the chromogenic substrate assay.

Methods

First, a kit for the determination of PC activity in plasma was elaborately developed and its reaction parameters on XL‐3200c were explored. Then, we evaluated its performance and collected specimens to compare the test results obtained with those of the Siemens detection system. Finally, the clinical diagnostic efficacy of this detection system for deep vein thrombosis (DVT) was assessed.

Results

Optimum conditions for PC detection were 0.25–0.1 U/ml protein C activator Protac^® and 2.5–1 mM Pefachrome^®PCa5297. The composition and concentration ranges of buffer substances and stabilizers in the kit were also explored. Satisfactory results were observed in performance evaluation. The test results of the newly built detection system were highly correlated with those of the Siemens detection system (R² = 0.9771 in the control group and R² = 0.9776 in the DVT group), and Bland‐Altman plots also showed high consistency between the two detection systems. In addition, the area under the curve (AUC) of the newly built PC detection system for DVT was 0.888, indicating this system could effectively improve the diagnostic sensitivity and specificity for DVT.

Conclusion

In this study, a sensitive, wide linear range and reliable PC activity detection system were established.

MiR-124 and miR-506 are involved in the decline of protein C in children with extra-hepatic portal vein obstruction

The deficiency of protein C (PROC) can be partly rescued by Rex shunt through restoring portal blood flow in children with extra-hepatic portal venous obstruction (EHPVO). However, the decline of PROC is still found in some patients with a normal portal blood flow after Rex shunt. The aim of this study was to identify the candidate miRNAs involving in the decline of PROC and their mechanism. The protein level of PROC was detected by the ELISA assay, and was compared between sick and healthy groups. The expressions of miRNAs and PROC mRNA were measured using qRT-PCR, and were compared between sick and healthy groups. The correlation between PROC and candidate miRNAs was analysed by a Pearson correlation analysis to identify the most significant miRNAs. The expression of PROC mRNA was detected by qRT-PCR in HL-7702 and LX-2 cells tansfected with miRNAs mimics or inhibitors and negative control (NC) mimics, which was compared among the different groups. The rates of liver cells’ proliferation and apoptosis were detected in HL-7702 and LX-2 cells tansfected with miRNAs mimics or inhibitors or with overexpressing PROC and negative control mimics by CKK8 assay and flow cytometry, which were compared among the different groups. The expressions of COX-2 and VEGF were measured by qRT-PCR, and were compared between the miRNAs groups and NC group. Western blot was assayed for detecting the protein levels of PROC, COX-2, VEGF, Bcl-2 and Bax, which were compared between the miRNAs groups and NC group. The expression of PROC mRNA was lower, and the expressions of miR-506-3p and miR-124-3p were higher in children with EHPVO than healthy group. PROC mRNA was negatively correlated with the expression of miR-506-3p and miR-124-3p. Compared to the NC group, the transcription activity of PROC was lower after exposure of miR-506 and miR-124 mimics in HL-7702 and LX-2 cells, but this phenomenon was reversed after inhibiting miR-506 and miR-124. The rate of cell proliferation was lower after exposure of miR-506 and miR-124 than the NC group, which was increased after inhibiting miR-506 and miR-124 in HL-7702 cells and overexpressing PROC in LX-2 cells. The apoptotic rate was higher after exposure of miR-506 and miR-124 than the NC group, which was decreased after inhibiting miR-506 and miR-124 in HL-7702 cells and overexpressing PROC in LX-2 cells. The mRNA levels of COX-2 and VEGF were significantly higher after exposure of miR-506 and miR-124 mimics than those in the NC group. The protein levels of PROC and Bcl-2 were down-regulated, and the levels of COX-2, Bax and VEGF were up-regulated after exposure of miR-506 and miR-124 in HL-7702 cells, but this phenomenon was reversed after inhibiting miR-506 and miR-124. MiR-506-3p and miR-124-3p may involve in the decline of PROC in protein and transcriptional level, in which the anti-proliferation and pro-apoptosis role of miR-506-3p and miR-124-3p for liver cells may involve in this mechanism.

Functional characterization of a loss-of-function mutant I324M of arginine vasopressin receptor 2 in X-linked nephrogenic diabetes insipidus

X-linked nephrogenic diabetes insipidus (X-linked NDI) is a rare inherited disease mainly caused by lost-of-function mutations in human AVPR2 gene encoding arginine vasopressin receptor 2 (V2R). Our focus of the current study is on exploration of the functional and biochemical properties of Ile324Met (I324M) mutation identified in a pedigree showing as typical recessive X-linked NDI. We demonstrated that I324M mutation interfered with the conformation of complex glycosylation of V2R. Moreover, almost all of the I324M-V2R failed to express on the cell surface due to being captured by the endoplasmic reticulum control system. We further examined the signaling activity of DDAVP-medicated cAMP and ERK1/2 pathways and the results revealed that the mutant receptor lost the ability in response to DDAVP stimulation contributed to the failure of accumulation of cAMP and phosphorylated ERK1/2. Based on the characteristics of molecular defects of I324M mutant, we selected two reagents (SR49059 and alvespimycin) to determine whether the functions of I324M-V2R can be restored and we found that both compounds can significantly “rescue” I324M mutation. Our findings may provide further insights for understanding the pathogenic mechanism of AVPR2 gene mutations and may offer some implications on development of promising treatments for patients with X-linked NDI.

Genotype-Phenotype Relationships in a Large French Cohort of Subjects with Inherited Protein C Deficiency

Inherited protein C (PC) deficiency caused by mutations in the PROC gene is a well-known risk factor for venous thromboembolism. Few studies have investigated the relationship between PROC genotype and plasma or clinical phenotypes. We addressed this issue in a large retrospective cohort of 1,115 heterozygous carriers of 226 PROC pathogenic or likely pathogenic mutations. Mutations were classified in three categories according to their observed or presumed association with type I, type IIa, or type IIb PC deficiency. The study population comprised 876 carriers of type I category mutations, 55 carriers of type IIa category mutations, and 184 carriers of type IIb category mutations. PC anticoagulant activity significantly influenced risk of first venous thrombosis (p trend < 10^-4). No influence of mutation category on risk of whole or unprovoked thrombotic events was observed. Both PC anticoagulant activity and genotype significantly influenced risk of venous thrombosis. Effect of detrimental mutations on plasma phenotype was ambiguous in several carriers, whatever the mutation category. Altogether, our findings confirm that diagnosing PC inherited deficiency based on plasma measurement may be difficult but show that diagnosis can be improved by PROC genotyping.

The genetics of venous thromboembolism: a systematic review of thrombophilia families

Genetic risk factors are important for the occurrence and prognosis of venous thromboembolism (VTE). The studies of thrombophilia families are important for dissecting the genetic background of the thrombotic disease. We conducted the systematic review of all published family-based studies on VTE genetics across all racial groups through PubMed and Embase prior to 13th April 2020. This systematic review of 287 families (including 225 Caucasian families, 52 East Asian families, and families of other ethnicities) revealed a total of 21 different genes; the five most reported mutated genes were F5 (88/287, 30.7%), SERPINC1 (67/287, 23.3%), PROC (65/287, 22.6%), F2 (40/287, 13.9%) and PROS1 (48/287, 16.7%). For Caucasian families, F5 mutations were most frequently reported at 37.8% (85/225), while PROS1 mutations were most frequently reported, at 40.4% (21/52), for East Asian families (Chinese, Japanese and Korean). Factor V Leiden was reported more frequently in Caucasians than in East Asians. Missense mutations were reported frequently in the SERPINC1, PROC and PROS1 genes. In conclusion, our study found the most likely mutated genes associated with VTE among different ethnic groups and provided indications for VTE genetic testing and research in the future.

Pathogenic variants of PROC gene caused type I activity deficiency in a familial Chinese venous thrombosis

Pathogenic mutation of protein C (PROC) gene results into the deficiency of PROC activity. This study aimed to identify the pathogenic genetic variants and to explore the functional consequence in Chinese familial venous thrombosis (VTE). Whole exome sequencing was performed to identify the pathogenic variants of anticoagulant factors. Serum coagulation and anti‐coagulation factors activity were assayed to evaluate the genetic association. Functional study of PROC antigen secretion deficiency was conducted in VTE subjects and in vitro cell lines. One rare pathogenic variant (p.Ala178Pro) was identified in the four VTE subjects but not in the normal subjects from the family. An inframeshift variant (rs199469469) was also identified in a paediatric subject of the pedigree. Further evaluation of serum PROC activity levels in p.Ala178Pro variants VTE carriers showed significantly lower PROC activity compared to non‐carriers. Furthermore, in vitro study showed that the p.Ala178Pro mutant cells had a consistent reduction in concentration of PROC antigen. In conclusions, our study demonstrated the pathogenic variant (p.Ala178Pro) contributed to PROC type I activity deficiency, which may be due to decreased secretion of PROC.

Protein C deficiency (a novel mutation: ala291Thr) with systemic lupus erythematosus leads to the deep vein thrombosis

: The current study aims to explore the phenotype and genotype of a mutation Ala291Thr, which responsible for type I protein C (PC) deficiency in a Chinese woman. The PROC antigen was tested with chromogenic substrate method. PROC gene were amplified by PCR with direct sequencing. Bioinformatics and model analysis were used to study the harm of the mutation. PC activity (PC: A) levels of three members were reduced to 39, 57 and 56%, respectively, PC: antigen was decreased parallelly same as PC: A. Sequencing analysis showed proband with a novel heterozygous c.997G>A point mutation in exon 9 of PROC gene resulting in Ala291Thr. The Ala291Thr mutation is responsible for the decrease of PC: A, which is cross-reacting material negative deficiency and the first reported in the world. This mutation alone may not have significant clinical symptoms, whereas it will cause deep vein thrombosis when combined with systemic lupus erythematosus.

The clinical presentation and genotype of protein C deficiency with double mutations of the protein C gene

BACKGROUND

Severe protein C (PC) deficiency is a rare heritable thrombophilia leading to thromboembolic events during the neonatal period. It remains unclear how individuals with complete PC gene (PROC) defects develop or escape neonatal stroke or purpura fulminans (PF).

PROCEDURE

We studied the onset of disease and the genotype of 22 PC-deficient patients with double mutations in PROC based on our cohort (n = 12) and the previous reports (n = 10) in Japan.

RESULTS

Twenty-two patients in 20 unrelated families had 4 homozygous and 18 compound heterozygous mutations. Sixteen newborns presented with PF (n = 11, 69%), intracranial thromboembolism and hemorrhage (n = 13, 81%), or both (n = 8, 50%), with most showing a plasma PC activity of <10%. Six others first developed overt thromboembolism when they were over 15 years of age, showing a median PC activity of 31% (range: 19-52%). Fifteen of the 22 patients (68%) had the five major mutations (G423VfsX82, V339M, R211W, M406I, and F181V) or two others (E68K and K193del) that have been reported in Japan. Three of the six late-onset cases, but none of the 16 neonatal cases, had the K193del mutation, which has been reported to be the most common variant of Chinese thrombophilia. A novel mutation of A309V was determined in a family of two patients with late onset.

CONCLUSIONS

The genotype of double-PROC mutants might show less diversity than heterozygous mutants in terms of the timing of the onset of thrombophilia (newborn onset or late onset).

A protein C and plasminogen compound heterozygous mutation and a compound heterozygote of protein C in two related Chinese families

Hereditary protein C (PC) deficiency and congenital plasminogen (PLG) deficiency are both factors of thrombophilia which were caused by PC and PLG gene mutations with the characteristics of activity and antigen decreasing inconsonantly. To illustrate the connection between gene mutations and the corresponding deficiencies of PC and PLG, we studied two related cases. The proband 1 showed a cranial venous sinus thrombosis with reduced activities of PC and PLG, 55 and 56%, respectively. And the proband 2 was his asymptomatic nephew who had a reduced PC activity of 27%. All the PC genes (PROC) and PLG genes were amplified by PCR with direct sequencing. Then these detected mutations were analyzed by conservation, bioinformatics, and model. Genetic analysis detected two compound heterozygous missense mutations: the proband 1 carried a p.Gly86Asp in PC and a p.Ala601Thr in PLG, whereas the proband 2 took two mutations of PC (p.Gly86Asp and p.Arg147Trp). All conservation, bioinformatics prediction, and model analysis results indicated that these mutations probably affected the structures and stabilities of the matching proteins. We speculated that the three mutations are responsible for the reduction of PC activity and PLG activity. Furthermore, the p.Gly86Asp of PC has been detected for the first time in the world.

Two novel compound heterozygous mutations associated with types I and II protein C deficiency with unusual phenotypes

INTRODUCTION

We diagnosed two Chinese hereditary PC deficiency families and identified two novel compound heterozygous mutations (p.Arg194Cys/Gly324Ser and p.Glu274X/Asp297His) in the protein C (PROC) gene. The probands were classified as types I and II PC deficiency. The aim of this article is to access the influence of the mutations on PC activity, antigen and protein structure, and to evaluate whether there is abnormal PC localization.

MATERIALS AND METHODS

Genomic DNA of all family members was extracted, PCR amplified, and sequenced. The mutant PC expression plasmids were constructed. Expression assays, intracellular localization, and molecular modeling were performed.

RESULTS

Proband 1, a type II PC defect, harbored a compound heterozygous mutation, p.Arg194Cys/Gly324Ser in the PROC gene, underwent two thromboembolic events. Expression assays indicated that the p.Arg194Cys mutant lead to decreased PC activity and normal PC Ag levels. Intracellular localization showed that both p.Arg194Cys and p.Gly324Ser co-localized with the endoplasmic reticuli and the Golgi apparatus. Molecular modeling suggested that the p.Gly324Ser mutation disturbed the interaction between the heavy and light chains of the PC protein. Proband 2, a type I PC defect, harbored a compound heterozygous PROC gene mutation, p.Glu274X/Asp297His, presented with recurrent spontaneous abortion and right popliteal vein thrombosis. Expression results were in accordance with the PC changes of the patient, and existed in defective PC transport. Structural model suggested p.Glu274X lead to disulfide bond between heavy and light chain cannot form.

CONCLUSIONS

Our results confirm that two novel compound heterozygous PROC gene mutations are causative on the two PC deficiency families.