Genetic polymorphisms in CTLA4 and SLC4A2 are differentially associated with the pathogenesis of primary biliary cirrhosis in Japanese patients

Association of tuberculosis risk with genetic polymorphisms of the immune checkpoint genes PDCD1, CTLA-4, and TIM3

The immune checkpoint proteins were reported to involve to host resistance to Mycobacteria tuberculosis (Mtb). Here, we evaluated 11 single nucleotide polymorphisms (SNPs) in PDCD1, CTLA4, and HAVCR2 genes between participants with and without TB infection. Genomic DNA isolated from 285 patients with TB and 270 controls without TB infection were used to perform the genotyping assay. Odds ratios were used to characterize the association of 11 SNPs with TB risk. In this study, the various genotypes of the 11 SNPs did not differ significantly in frequency between the non-TB and TB groups. When patients were stratified by sex, however, men differed significantly from women in genotype frequencies at HAVCR2 rs13170556. Odds ratios indicated that rs2227982, rs13170556, rs231775, and rs231779 were sex-specifically associated with TB risk. In addition, the combinations of rs2227982/rs13170556 GA/TC in men and the A-C-C haplotype of rs231775-rs231777-rs231779 in women were significantly associated with TB risk. Our results indicate that rs2227982 in PDCD1 and rs13170556 in HAVCR2 are associated with increased TB susceptibility in men and that the CTLA4 haplotype appears protective against TB in women.

Primary biliary cholangitis: pathogenic mechanisms

PURPOSE OF REVIEW

Primary biliary cholangitis (PBC) is characterized by autoimmune damage of intrahepatic bile ducts associated with a loss of tolerance to mitochondrial antigens. PBC etiopathogenesis is intriguing because of different perplexing features, namely: a) although mitochondria are present in all cell types and tissues, the damage is mainly restricted to biliary epithelial cells (BECs); b) despite being an autoimmune disorder, it does not respond to immunosuppressive drugs but rather to ursodeoxycholic acid, a bile salt that induces HCO3- rich choleresis; c) the overwhelming female preponderance of the disease remains unexplained. Here we present an etiopathogenic view of PBC which sheds light on these puzzling facts of the disease.

RECENT FINDINGS

PBC develops in patients with genetic predisposition to autoimmunity in whom epigenetic mechanisms silence the Cl-/HCO3- exchanger AE2 in both cholangiocytes and lymphoid cells. Defective AE2 function can produce BECs damage as a result of decreased biliary HCO3- secretion with disruption of the protective alkaline umbrella that normally prevents the penetration of toxic apolar bile salts into cholangiocytes. AE2 dysfunction also causes increased intracellular pH (pHi) in cholangiocytes, leading to the activation of soluble adenylyl cyclase, which sensitizes BECs to bile salt-induced apoptosis. Recently, mitophagy was found to be inhibited by cytosolic alkalization and stimulated by acidification. Accordingly, we propose that AE2 deficiency may disturb mitophagy in BECs, thus, promoting the accumulation of defective mitochondria, oxidative stress and presentation of mitochondrial antigens to the immune cells. As women possess a more acidic endolysosomal milieu than men, mitophagy might be more affected in women in an AE2-defective background. Apart from affecting BECs function, AE2 downregulation in lymphocytes may also contribute to alter immunoregulation facilitating autoreactive T-cell responses.

SUMMARY

PBC can be considered as a disorder of Cl-/HCO3- exchange in individuals with genetic predisposition to autoimmunity.

Promoter hypermethylation of the AE2/SLC4A2 gene in PBC

Background & Aims

Patients with primary biliary cholangitis (PBC) exhibit reduced AE2/SLC4A2 gene expression in the liver and peripheral blood mononuclear cells (PBMCs). AE2 encodes a Cl^–/HCO₃^– exchanger involved in biliary bicarbonate secretion and intracellular pH regulation. Reduced AE2 expression in PBC may be pathogenic, as Ae2-knockout mice reproduce characteristic PBC features. Herein, we aimed to identify CpG-methylation abnormalities in AE2 promoter regions that might contribute to the reduced gene transcription in PBC livers and PBMCs.

Methods

CpG-cytosine methylation rates were interrogated at 1-base pair resolution in upstream and alternate AE2 promoter regions through pyrosequencing of bisulphite-modified genomic DNA from liver specimens and PBMCs. AE2a and alternative AE2b1 and AE2b2 mRNA levels were measured by real-time PCR. Human lymphoblastoid-T2 cells were treated with 5-aza-2´-deoxycytidine for demethylation assays.

Results

AE2 promoters were found to be hypermethylated in PBC livers compared to normal and diseased liver specimens. Receiver operating characteristic (ROC) curve analysis showed that minimal CpG-hypermethylation clusters of 3 AE2a-CpG sites and 4 alternate-AE2b2-CpG sites specifically differentiated PBC from normal and diseased controls, with mean methylation rates inversely correlating with respective transcript levels. Additionally, in PBMCs a minimal cluster of 3 hypermethylated AE2a-CpG sites distinguished PBC from controls, and mean methylation rates correlated negatively with AE2a mRNA levels in these immune cells. Alternate AE2b2/AE2b1 promoters in PBMCs were constitutively hypermethylated, in line with absent alternative mRNA expression in diseased and healthy PBMCs. Demethylation assays treating lymphoblastoid-T2 cells with 5-aza-2´-deoxycytidine triggered AE2b2/AE2b1 expression and upregulated AE2a-promoter expression.

Conclusions

Disease-specific hypermethylation of AE2 promoter regions and subsequent downregulation of AE2-gene expression in the liver and PBMCs of patients with PBC might be critically involved in the pathogenesis of this complex disease.

Lay summary

Primary biliary cholangitis (PBC) is a chronic immune-associated cholestatic liver disease with unclear complex/multifactorial etiopathogenesis affecting mostly middle-aged women. Patients with PBC exhibit reduced expression of the AE2/SLC4A2 gene. Herein, we found that AE2 promoter regions are hypermethylated in the liver and peripheral blood mononuclear cells of patients with PBC. This increased methylation is associated with downregulated AE2-gene expression, which might contribute to the pathogenesis of PBC. Therefore, novel epigenetic targets may improve treatment in patients with PBC who respond poorly to current pharmacological therapies.

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Patients with PBC have higher AE2 CpG methylation in upstream AE2a and/or AE2b2/AE2b1 promoter regions in liver and PBMCs.

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Combined methylation rates of 2 minimal CpG-clusters in the liver and 1 minimal CpG-cluster in PBMCs specifically distinguished PBC from normal and diseased controls.

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Methylation rates of AE2 promoter regions inversely correlated with levels of respective AE2 mRNAs in liver and PBMCs.

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Alternate AE2b2/AE2b1 promoter regions were found to be densely methylated in both normal and diseased PBMC samples.

Role of Bile Acids and the Biliary HCO3- Umbrella in the Pathogenesis of Primary Biliary Cholangitis

The biliary HCO₃^- umbrella hypothesis states that human cholangiocytes and hepatocytes create a protective apical alkaline barrier against millimolar concentrations of potentially toxic glycine-conjugated bile salts in bile by secreting HCO₃^- into the bile duct lumen. This alkaline barrier may retain biliary bile salts in their polar, deprotonated, and membrane-impermeant state to avoid uncontrolled invasion of apolar toxic bile acids, which initiate apoptosis, autophagy and senescence. In primary biliary cholangitis, defects of the biliary HCO₃^- umbrella, leading to impaired biliary HCO₃^- secretion have been identified. Current medical therapies stabilize the putatively defective biliary HCO₃^- umbrella and improve long-term prognosis.

NELFCD and CTSZ loci are associated with jaundice-stage progression in primary biliary cholangitis in the Japanese population

Approximately 10–20% of patients with primary biliary cholangitis (PBC) progress to jaundice stage regardless of treatment with ursodeoxycholic acid and bezafibrate. In this study, we performed a GWAS and a replication study to identify genetic variants associated with jaundice-stage progression in PBC using a total of 1,375 patients (1,202 early-stage and 173 jaundice-stage) in a Japanese population. SNP rs13720, which is located in the 3′UTR of cathepsin Z (CTSZ), showed the strongest association (odds ratio [OR] = 2.15, P = 7.62 × 10⁻⁷) with progression to jaundice stage in GWAS. High-density association mapping at the CTSZ and negative elongation factor complex member C/D (NELFCD) loci, which are located within a strong linkage disequilibrium (LD) block, revealed that an intronic SNP of CTSZ, rs163800, was significantly associated with jaundice-stage progression (OR = 2.16, P = 8.57 × 10⁻⁸). In addition, eQTL analysis and in silico functional analysis indicated that genotypes of rs163800 or variants in strong LD with rs163800 influence expression levels of both NELFCD and CTSZ mRNA. The present novel findings will contribute to dissect the mechanism of PBC progression and also to facilitate the development of therapies for PBC patients who are resistant to current therapies.

Mouse models of SLC4-linked disorders of HCO3--transporter dysfunction

The SLC4 family Cl^-/[Formula: see text] cotransporters (NBCe1, NBCe2, NBCn1, and NBCn2) contribute to a variety of vital physiological processes including pH regulation and epithelial fluid secretion. Accordingly, their dysfunction can have devastating effects. Disorders such as epilepsy, hemolytic anemia, glaucoma, hearing loss, osteopetrosis, and renal tubular acidosis are all genetically linked to SLC4-family gene loci. This review summarizes how studies of Slc4-modified mice have enhanced our understanding of the etiology of SLC4-linked pathologies and the interpretation of genetic linkage studies. The review also surveys the novel disease signs exhibited by Slc4-modified mice which could either be considered to presage their description in humans, or to highlight interspecific differences. Finally, novel Slc4-modified mouse models are proposed, the study of which may further our understanding of the basis and treatment of SLC4-linked disorders of [Formula: see text]-transporter dysfunction.

DENTAL ENAMEL FORMATION AND IMPLICATIONS FOR ORAL HEALTH AND DISEASE

Dental enamel is the hardest and most mineralized tissue in extinct and extant vertebrate species and provides maximum durability that allows teeth to function as weapons and/or tools as well as for food processing. Enamel development and mineralization is an intricate process tightly regulated by cells of the enamel organ called ameloblasts. These heavily polarized cells form a monolayer around the developing enamel tissue and move as a single forming front in specified directions as they lay down a proteinaceous matrix that serves as a template for crystal growth. Ameloblasts maintain intercellular connections creating a semi-permeable barrier that at one end (basal/proximal) receives nutrients and ions from blood vessels, and at the opposite end (secretory/apical/distal) forms extracellular crystals within specified pH conditions. In this unique environment, ameloblasts orchestrate crystal growth via multiple cellular activities including modulating the transport of minerals and ions, pH regulation, proteolysis, and endocytosis. In many vertebrates, the bulk of the enamel tissue volume is first formed and subsequently mineralized by these same cells as they retransform their morphology and function. Cell death by apoptosis and regression are the fates of many ameloblasts following enamel maturation, and what cells remain of the enamel organ are shed during tooth eruption, or are incorporated into the tooth's epithelial attachment to the oral gingiva. In this review, we examine key aspects of dental enamel formation, from its developmental genesis to the ever-increasing wealth of data on the mechanisms mediating ionic transport, as well as the clinical outcomes resulting from abnormal ameloblast function.

Genetic Polymorphisms of Cytotoxic T-Lymphocyte Antigen 4 in Primary Biliary Cholangitis: A Meta-Analysis

Background and Aim

The connection between gene polymorphisms of cytotoxic T-lymphocyte-associated protein 4 (CTLA4) and primary biliary cholangitis (PBC) is still vague and blurred. The purpose of this study is to precisely estimate the association of the polymorphisms of CTLA4 with the risk of PBC by using a meta-analysis.

Methods

PubMed and the Chinese National Knowledge Infrastructure (CNKI) database were used to search correlative literatures, and the documents which were about the relationships between the polymorphisms of CTLA4 (rs231775, rs231725, rs3087243, and rs5742909) and PBC were collected as of June 2016. The strength of correlation based on odds ratios (ORs) and its 95% confidence intervals (95%CIs) was computed by STATA.

Results

Generally, in rs231775, a significant risk was found in G allele, the value of OR was 1.32, and its 95%CI was 1.19 to 1.47. The same situation was found in A allele of rs231725, the value of OR was 1.33, and its 95%CI was 1.22 to 1.45. As genotypic level, different genotypic models were also found to have obvious relevance with PBC in rs231775 and rs231725. No obvious connections were found in other SNPs.

Conclusion

This study indicated that the polymorphisms of rs231775 and rs231725 would be the risk factors of PBC.

Using GWAS to identify genetic predisposition in hepatic autoimmunity

Primary biliary cirrhosis (PBC), primary sclerosing cholangitis (PSC) and autoimmune hepatitis (AIH) represent the three major hepatic autoimmune conditions. Patient morbidity and mortality remain high across these three diseases, and an unmet need for rational therapy exists. Disease understanding has focused on combining clinical and laboratory based science to provide better insights into the joint host and environmental factors necessary for the initiation, and perpetuation, of hepato-biliary inflammation. Twin studies, family studies, population studies and an inter-relationship with other autoimmune phenomena suggest a genetic component to risk for each disease. Until recently, understanding of this genetic risk has been limited to HLA haplotypes. Associations with risk-conferring and protective HLA haplotypes are present in all three diseases. Over the last few years, genome-wide association studies (GWAS), and related genetic association studies, have greatly increased understanding of the genetic risk signature of these three diseases and autoimmunity in general. Here we consider the rationale for GWAS in general and with specific reference to hepatic autoimmunity. We consider the process of GWAS, and highlight major findings to date. Potential functional implications of key findings are discussed including the IL-12/STAT4 pathway in PBC and the CD28/IL-2 pathway in PSC. We describe the marked pleiotropy demonstrated by PBC and PSC, which is consistent with other autoimmune diseases. Further, we focus on specific gene associations including SH2B3, which is common to all three diseases, and FUT2 in PSC, which represents a link between environment and genetics. We review attempts to translate GWAS findings into basic laboratory models including in vivo systems and highlight where clinical observations relate to genetics. Finally we describe deficiencies in GWAS to date and consider future study of genetics in hepatic autoimmunity.

The immunogenetics of primary biliary cirrhosis: A comprehensive review

Primary biliary cirrhosis (PBC), a classic autoimmune liver disease, is characterised by a progressive T cell predominant lymphocytic cholangitis, and a serologic pattern of reactivity in the form of specific anti-mitochondrial antibodies (AMA). CD4+ T cells are particularly implicated by PBC's cytokine signature, the presence of CD4+ T cells specific to mitochondrial auto-antigens, the expression of MHC II on injured biliary epithelial cells, and PBC's coincidence with other similar T cell mediated autoimmune conditions. CD4+ T cells are also central to current animal models of PBC, and their transfer typically also transfers disease. The importance of genetic risk to developing PBC is evidenced by a much higher concordance rate in monozygotic than dizygotic twins, increased AMA rates in asymptomatic relatives, and disproportionate rates of disease in siblings of PBC patients, PBC family members and certain genetically defined populations. Recently, high-throughput genetic studies have greatly expanded our understanding of the gene variants underpinning risk for PBC development, so linking genetics and immunology. Here we summarize genetic association data that has emerged from large scale genome-wide association studies and discuss the evidence for the potential functional significance of the individual genes and pathways identified; we particularly highlight associations in the IL-12-STAT4-Th1 pathway. HLA associations and epigenetic effects are specifically considered and individual variants are linked to clinical phenotypes where data exist. We also consider why there is a gap between calculated genetic risk and clinical data: so-called missing heritability, and how immunogenetic observations are being translated to novel therapies. Ultimately whilst genetic risk factors will only account for a proportion of disease risk, ongoing efforts to refine associations and understand biologic links to disease pathways are hoped to drive more rational therapy for patients.

Autoantibody status and histological variables influence biochemical response to treatment and long-term outcomes in Japanese patients with primary biliary cirrhosis

AIM

The aim of the present study is to evaluate the factors influencing biochemical response to treatment and the value of biochemical response for predicting long-term outcomes in Japanese patients with primary biliary cirrhosis (PBC).

METHODS

Biochemical response to ursodeoxycholic acid (UDCA) or UDCA plus bezafibrate was defined as good (≤upper limit of normal [ULN]), fair (≤1.5 × ULN) or poor (>1.5 × ULN) at 2 years after initiation of UDCA treatment. Associations between various factors (including age, sex, autoantibody status and histological variables at baseline), biochemical response to treatment and long-term outcomes were evaluated in 164 Japanese PBC patients.

RESULTS

Anti-gp210 positivity and a higher bile duct loss score were significant risk factors for worse alkaline phosphatase (ALP) response (odds ratios [OR], 2.78 and 1.85, respectively). Age, anti-gp210 positivity and anticentromere positivity were significant risk factors for worse alanine aminotransferase (ALT) response (OR, 1.05, 4.0 and 2.77, respectively). Anti-gp210 positivity and a higher hepatitis score were significant risk factors for worse immunoglobulin (Ig)M response (OR, 2.10 and 2.06, respectively). Worse ALP and IgM response were significant risk factors for progression to late-stage disease without jaundice (OR, 2.27 and 2.32, respectively). Worse ALT response was a significant risk factor for progression to late-stage disease with persistent jaundice (OR, 11.11).

CONCLUSION

Biochemical response to treatment at 2 years, which is influenced by autoantibody status and histological variables at baseline, can predict long-term outcomes in Japanese patients with PBC.

Variations in genes involved in immune response checkpoints and association with outcomes in patients with resected colorectal liver metastases

In patients with colorectal liver metastases (CLM), liver resection offers the possibility of cure and long-term survival. The liver is a highly immunogenic organ harboring ~80% of the body's tissue macrophages. Emerging data demonstrate a critical role of the immune response for cancer treatment. We investigated variations within genes involved in immune response checkpoints and their association with outcomes in patients with CLM who underwent neoadjuvant chemotherapy including bevacizumab and liver resection. Single-nucleotide polymorphisms (SNPs) in nine genes (CCL2, CCR2, LAG3, NT5E, PDCD1, CD274, IDO1, CTLA4 and CD24) were analyzed in genomic DNA from 149 patients with resected bevacizumab-pretreated CLM by direct Sanger DNA sequencing, and correlated with response, recurrence-free survival (RFS), overall survival (OS), probability of cure and recurrence patterns. IDO1 (indoleamine 2, 3-dioxygenase) rs3739319 G>A and CD24 rs8734 G>A showed a significant difference in 3-year OS rates. In addition, IDO1 rs3739319 G>A was significantly associated with extrahepatic recurrence. Recursive partitioning analyses revealed that IDO1 rs3739319 G>A was the dominant SNP predicting RFS and OS. Our data suggest that variants within genes involved in immune response checkpoints are associated with outcomes in patients with resected CLM and might lead to improved treatment strategies modulating anti-tumor immune response by targeting novel immune checkpoints.

Effect of drug transporter pharmacogenetics on cholestasis

INTRODUCTION

The liver is the central place for the metabolism of drugs and other xenobiotics. In the liver cell, oxidation and conjugation of compounds take place, and at the same time, bile formation helps in extrusion of these compounds via the biliary route. A large number of transporters are responsible for drug uptake into the liver cell and excretion into bile or efflux to the sinusoidal blood.

AREAS COVERED

Genetic variants of these transporters and their transactivators contribute to changes in drug handling and are also responsible for cholestatic syndromes of different severity. This review summarizes the current knowledge regarding the influence of these genetic changes. The review covers progressive hereditary cholestatic syndromes as well as recurrent or transient cholestatic syndromes such as drug-induced liver injury, intrahepatic cholestasis of pregnancy, and benign recurrent intrahepatic cholestasis.

EXPERT OPINION

Polymorphisms in transporter genes are frequent. For clinically relevant cholestatic syndromes, it often requires a combination of genetic variants or acquired triggers such as pregnancy or drug treatment. In combination with other pathogenetic aspects, genetic variants in drug transporters may contribute to our understanding of not only cholestatic diseases such as primary sclerosing cholangitis or primary biliary cirrhosis, but also the natural course of chronic liver disease in general.

STAT4 gene polymorphisms are associated with susceptibility and ANA status in primary biliary cirrhosis

Recent genome-wide association studies suggest that genetic factors contribute to primary biliary cirrhosis (PBC) susceptibility. Although several reports have demonstrated that the interleukin (IL) 12 signaling pathway is involved in PBC pathogenesis, its precise genetic factors have not been fully clarified. Here, we performed an association analysis between IL12A, IL12RB, and signal transducer and activator of transcription 4 (STAT4) genetic variations and susceptibility to PBC. Single nucleotide polymorphisms (SNPs) were genotyped in 395 PBC patients and 458 healthy subjects of Japanese ethnicity and evaluated for associations with PBC susceptibility, anti-nuclear antibody (ANA) status, and anti-mitochondrial antibody (AMA) status. We detected significant associations with PBC susceptibility for several STAT4 SNPs (rs10168266; P = 9.4 × 10⁻³, rs11889341; P = 1.2 × 10⁻³, rs7574865; P = 4.0 × 10⁻⁴, rs8179673; P = 2.0 × 10⁻⁴, and rs10181656; P = 4.2 × 10⁻⁵). Three risk alleles (rs7574865; P = 0.040, rs8179673; P = 0.032, and rs10181656; P = 0.031) were associated with ANA status, but not with AMA positivity. Our findings confirm that STAT4 is involved in PBC susceptibility and may play a role in ANA status in the Japanese population.

Genetic polymorphisms of OCT-1 confer susceptibility to severe progression of primary biliary cirrhosis in Japanese patients

BACKGROUND

To identify the genetic factors involved in the pathogenesis of primary biliary cirrhosis (PBC), we focused on the organic cation transporter 1 (OCT1/SLC22A1), which is closely associated with phosphatidylcholine synthesis in hepatocytes.

METHODS

We selected four (rs683369, rs2282143, rs622342 and rs1443844) OCT-1 single nucleotide polymorphisms (SNPs), and genotyped these SNPs using the TaqMan probe method in 275 Japanese PBC patients and 194 gender-matched, healthy volunteers as controls.

RESULTS

The Chi-square test revealed that the rs683369 variant allele (G) was associated with insusceptibility to PBC development [P = 0.009, odds ratio (OR) 0.60, 95 % confidence interval (CI) 0.40-0.88] in an allele model, and that the rs683369 variant allele (G) was associated with jaundice-type progression in a minor allele dominant genotype model (P = 0.032, OR 3.10, 95 % CI 1.05-9.14). The OCT-1 rs2282143 variant (T) and rs622342 variant (C) were also associated with jaundice-type progression in a minor allele recessive genotype model (P = 0.0002, OR 10.58, 95 % CI 2.36-47.54, and P = 0.006, OR 7.84, 95 % CI 1.39-44.36, respectively). Furthermore, the association of OCT-1 rs683369 and rs622342 with susceptibility to jaundice-type progression was confirmed by a replication study with a distinct set of PBC patients who underwent liver transplantation.

CONCLUSIONS

The present study is the first report on the association of OCT-1 genetic polymorphisms with the overall development and jaundice-type progression of PBC.

Diagnostic and clinical significance of anti-centromere antibodies in primary biliary cirrhosis

Primary biliary cirrhosis (PBC) is an autoimmune disease of the liver characterised by biochemical evidence of cholestasis, elevated alkaline phosphatase levels and the presence of the highly disease specific anti-mitochondrial autoantibodies. Extra-hepatic autoimmune manifestations are common, including rheumatic disorders, such as systemic sclerosis (SSc). Notably, PBC is the most frequent autoimmune liver disease in SSc patients. Based on skin lesion extension, two major SSc disease subgroups are recognised: limited cutaneous SSc (lSSc) and diffuse cutaneous SSc. Anti-centromere antibody (ACA) positivity is highly characteristic of SSc, with up to 90% prevalence in lSSc patients. ACA has also been found in up to 30% of PBC patients and 80% of patients with a PBC/SSc overlap syndrome. The diagnostic and clinical significance of ACA positivity in patients with PBC without SSc has recently been under investigation, with several studies highlighting links to severe bile duct injury and portal hypertension. This review discusses the diagnostic and clinical relevance of ACA in patients with PBC, with or without SSc.

Association of genes involved in bile acid synthesis with the progression of primary biliary cirrhosis in Japanese patients

BACKGROUND

Patients with primary biliary cirrhosis (PBC) exhibit a variety of clinical manifestations and patterns of disease progression. The aim of this study was to identify genetic determinants of PBC progression.

METHODS

A total of 52 tag single nucleotide polymorphisms (SNPs) of 11 candidate genes involved in regulating bile acid synthesis were analyzed by polymerase chain reaction (PCR)-restriction fragment length polymorphism, -high resolution melting curve analysis, or -direct DNA sequencing in 315 Japanese patients with PBC.

RESULTS

In this study, four tag SNPs of CYP7A1 (rs1457043, rs8192870, rs3808607, and rs3824260), two tag SNPs of HNF4A (rs6017340 and 6031587), and one SNP of PPARGC1A (rs8192678) showed a significant association with PBC progression. In addition, a dual luciferase assay revealed that the polymorphism of rs3808607 in CYP7A1 altered the expression of CYP7A1 in HepG2. Specifically, the CYP7A1 promoter carrying the risk G allele for PBC progression induced higher expression of CYP7A1 under both the normal and cholestatic conditions in vitro as compared to another promoter carrying the non-risk T allele.

CONCLUSION

These results suggested that the genetic variants of CYP7A1 and its transcriptional activators (HNF4A and PPARGC1A) may activate bile acid synthesis, resulting in the accumulation of bile acids in hepatocytes and eventually leading to the predisposition to PBC progression. Thus, the regulation of CYP7A1 expression may represent an attractive therapeutic target for cholestatic liver diseases including PBC.

The SLC4 family of bicarbonate (HCO₃⁻) transporters

The SLC4 family consists of 10 genes (SLC4A1-5; SLC4A7-11). All encode integral membrane proteins with very similar hydropathy plots-consistent with 10-14 transmembrane segments. Nine SLC4 members encode proteins that transport HCO3(-) (or a related species, such as CO3(2-)) across the plasma membrane. Functionally, eight of these proteins fall into two major groups: three Cl-HCO3 exchangers (AE1-3) and five Na(+)-coupled HCO3(-) transporters (NBCe1, NBCe2, NBCn1, NBCn2, NDCBE). Two of the Na(+)-coupled transporters (NBCe1, NBCe2) are electrogenic; the other three Na(+)-coupled HCO3(-) transporters and all three AEs are electroneutral. In addition, two other SLC4 members (AE4, SLC4A9 and BTR1, SLC4A11) do not yet have a firmly established function. Most, though not all, SLC4 members are functionally inhibited by 4,4'-diisothiocyanatostilbene-2,2'-disulfonate (DIDS). SLC4 proteins play important roles many modes of acid-base homeostasis: the carriage of CO2 by erythrocytes, the transport of H(+) or HCO3(-) by several epithelia, as well as the regulation of cell volume and intracellular pH.

Association between cytotoxic T-lymphocyte antigen 4 gene polymorphisms and primary biliary cirrhosis in Chinese population: data from a multicenter study

BACKGROUND AND AIMS

The cytotoxic T-lymphocyte antigen 4 (CTLA4) gene polymorphisms have been shown to be associated with the risk of primary biliary cirrhosis (PBC). The study aimed to confirm the associations of CTLA4 gene polymorphisms with risk of PBC and patients' quality of life in Chinese population.

METHODS

A total of 312 female PBC patients from Chinese Han population were included as case, and 375 age-matched female healthy volunteers were included as control. Four single nucleotide polymorphisms (SNPs) including rs231775, rs3087243, rs231725, and rs5742909 were genotyped. The differences of genotype and allele distributions between PBC patients and healthy controls were assessed. The relationship between CTLA4 gene polymorphisms and healthy status of PBC patients were then investigated through comparisons of the domain scores of PBC-40 questionnaire between different genotype categories of each single nucleotide polymorphism.

RESULTS

The frequencies of G allele at rs231775 and A allele at rs231725 were both significantly increased in PBC patients when compared with normal controls (P < 0.001, odds ratio = 1.44, 95% confidence interval = 1.24-1.67 for rs231775; P < 0.001, odds ratio = 1.29, 95% confidence interval = 1.12-1.48 for rs231725). Besides, patients carrying A allele of rs3087243 had significantly lower score of fatigue domain than those carrying G allele (2.5 ± 0.8 vs 3.9 ± 1.3, P < 0.001).

CONCLUSIONS

This study revealed that CTLA4 gene polymorphism might be associated with susceptibility of PBC. G allele of rs231775 and A allele of rs231725 were significantly associated with the risk of PBC. In addition, patients carrying A allele of rs3087243 could have significantly better quality of life than those carrying G allele.

Recent advances in understanding the pathogenesis of primary biliary cirrhosis

Primary biliary cirrhosis (PBC) is a chronic progressive cholestatic autoimmune liver disease characterized by the destruction of small intrahepatic bile ducts and the presence of highly specific serum antimitochondrial antibodies (AMAs). The human leukocyte antigen (HLA) gene has been proved to have strongest association with PBC susceptibility, and non-HLA genes, including IL12A, IL12RB2, STAT4, IRF5-TNPO3, ORMDL3/IKZF3, MMEL1, SPIB, CTLA-4, FCRL3 and A2BP1, are also closely associated with PBC susceptibility. Four AMAs including anti-M2, anti-M4, anti-M8 and anti-M9, and antinuclear antibodies (ANAs), such as antinuclear dot antibodies (SP100, PML, NDP52, SP140), antinuclear pore antibodies (gp210, p62), antinuclear envelope antibodies (Lamin and Lamin B receptor), and anti-centromere antibodies, may also be involved in the pathogenesis of PBC. The imbalance between Th17 cells and regulatory T lymphocytes (Treg) may also play an important role in the pathogenesis of PBC. In addition, senescence, autophagy, apoptosis of biliary epithelial cells (BECs), and environmental factors, such as Epstein-Barr virus (EBV) infection and smoking, may also contribute to the pathogenesis of PBC. Understanding of the mechanisms responsible for the pathogenesis of PBC has important implications for the treatment of PBC.

Up-regulation of microRNA 506 leads to decreased Cl-/HCO3- anion exchanger 2 expression in biliary epithelium of patients with primary biliary cirrhosis

Cl(-) /HCO3- anion exchanger 2 (AE2) participates in intracellular pH homeostasis and secretin-stimulated biliary bicarbonate secretion. AE2/SLC4A2 gene expression is reduced in liver and blood mononuclear cells from patients with primary biliary cirrhosis (PBC). Our previous findings of hepatic and immunological features mimicking PBC in Ae2-deficient mice strongly suggest that decreased AE2 expression might be involved in the pathogenesis of PBC. Here, we tested the potential role of microRNA 506 (miR-506) - predicted as candidate to target AE2 mRNA - for the decreased expression of AE2 in PBC. Real-time quantitative polymerase chain reaction showed that miR-506 expression is increased in PBC livers versus normal liver specimens. In situ hybridization in liver sections confirmed that miR-506 is up-regulated in the intrahepatic bile ducts of PBC livers, compared with normal and primary sclerosing cholangitis livers. Precursor-mediated overexpression of miR-506 in SV40-immortalized normal human cholangiocytes (H69 cells) led to decreased AE2 protein expression and activity, as indicated by immunoblotting and microfluorimetry, respectively. Moreover, miR-506 overexpression in three-dimensional (3D)-cultured H69 cholangiocytes blocked the secretin-stimulated expansion of cystic structures developed under the 3D conditions. Luciferase assays and site-directed mutagenesis demonstrated that miR-506 specifically may bind the 3'untranslated region (3'UTR) of AE2 messenger RNA (mRNA) and prevent protein translation. Finally, cultured PBC cholangiocytes showed decreased AE2 activity, together with miR-506 overexpression, compared to normal human cholangiocytes, and transfection of PBC cholangiocytes with anti-miR-506 was able to improve their AE2 activity.

CONCLUSION

miR-506 is up-regulated in cholangiocytes from PBC patients, binds the 3'UTR region of AE2 mRNA, and prevents protein translation, leading to diminished AE2 activity and impaired biliary secretory functions. In view of the putative pathogenic role of decreased AE2 in PBC, miR-506 may constitute a potential therapeutic target for this disease.

Cytotoxic T-lymphocyte associated antigen-4 gene polymorphisms and primary biliary cirrhosis: a systematic review

BACKGROUND AND AIM

The cytotoxic T-lymphocyte antigen 4 (CTLA4) is an inhibitory receptor expressed on activated and regulatory T lymphocytes. Polymorphisms could have remarkable effects on susceptibility to autoimmunity. However, the associations between CTLA-4 polymorphisms and primary biliary cirrhosis (PBC) remain ambiguous. The aim of this meta-analysis is to determine more precise estimations of the relationship.

METHODS

From literature retrieval from PubMed, Web of Science, Science Direct, and the Chinese National Knowledge Infrastructure (CNKI) Database, the publications on the associations between rs231775, rs3087243, rs5742909, rs231725 and rs11571317 polymorphisms of CTLA4 and PBC through June 2011 were collected. Odds ratios (OR) with 95% confidence intervals (95% CI) were calculated in fixed or random model, I(2) was calculated to examine heterogeneity, and funnel plots were plotted to examine small study effects with Revman 5.1 and Stata 11.

RESULTS

Overall, a significantly increased risk was found for G versus A allele for rs231775 (OR = 1.28, 95% CI = 1.17-1.41). For rs3087243, a significant association was found for AA versus GG genotype (OR = 0.66; 95% CI = 0.55-0.80). When subgroup analysis by ethnicity was performed, the same association was only found in Caucasians. For rs231725, the OR values (95% CI) for GG versus AA, GA versus AA and G versus A allele were 0.52 (0.40-0.68), 0.74 (0.60-0.92) and 0.73 (0.61-0.88). No significant associations were found for other polymorphisms.

CONCLUSION

The G allele of rs231775 is a risk factor for PBC, while AA genotype of rs3087243 and GG, GA and G allele of rs231725 show negative associations with PBC.

Polymorphisms of genes related to endothelial cells are associated with primary biliary cirrhosis patients of Cretan origin

BACKGROUND

Primary biliary cirrhosis (PBC) is an organ specific autoimmune disease of still unidentified genetic etiology. We have shown that endothelins (ETs), produced by the liver endothelial cells are increased in PBC and may play a major pathogenetic role.

AIMS

To study gene polymorphisms related to the endothelial cells (eNOS, EDN-1 genes) and, to investigate whether the previously reported association of CTLA4 gene polymorphisms is replicated in a genetically homogeneous Greek population.

PATIENTS AND METHODS

Genomic DNA was extracted from 100 PBC patients (83 females, 93% AMA+, 74/100 Ludwig stage I-II) and 158 healthy controls. eNOS, CTLA4 and ET1 polymorphisms were determined by PCR-RFLPs analysis.

RESULTS

Both eNOS intron4 VNTR and eNOS exon7 G894T SNP were significantly associated with increased risk in PBC. EDN-11 rs2071942 "A" and rs5370 "T" alleles appeared a tendency for association with disease progression. No association was found between PBC and the CTLA4 SNPs analyzed.

CONCLUSIONS

We demonstrated that eNOS, a gene related to the liver endothelium function is associated with PBC. Contrarily, the important in adaptive immunity gene CTLA4 was not associated with the disease in the homogeneous population analyzed. These results are compatible partially with our previous hypothesis that defects of the liver endothelial system, leading to endothelin overproduction, may be a fundamental early pathogenetic mechanism in PBC.

Etiopathogenesis of primary biliary cirrhosis: an overview of recent developments

Substantial advancements in the field of primary biliary cirrhosis (PBC) research have broadened our understanding of this enigmatic disease. Genome-wide studies have identified several new candidate genes involved in the immunoregulatory process, particularly those responsible for antigen presentation and lymphocyte signaling. Examples include the HLA class-II region and genes implicated in IL12-JAK/STAT signaling, and the NF-κB and TNF signaling pathways. Environmental triggers appear to disrupt the pre-existing, unstable immune tolerance in genetically susceptible individuals, and molecular mimics of the PBC-specific autoantigen (PDC) may be derived from microbes or xenobiotic compounds, which modify native proteins, making them immunogenic. Although the vast majority of patients with PBC are AMA-positive, a variety of disease-specific antinuclear antibodies have been recognized in conferring a worse clinical outcome. There has also been a revived interest in the role of antibody-secreting B cells in murine models suggesting that depletion of these cells paradoxically exacerbates cholangiopathy. Biliary specificity in PBC is most likely driven by the uniqueness of cholangiocyte apoptosis in which the PDC-E2 autoantigen undergoes differential glutathiolation. Cholangiocytes also possess the ability to phagocytose neighboring apoptotic cells, present intact immunoreactive antigen, and undergo attack from autoantibodies, the innate immune system, and autoreactive lymphocytes. Cellular senescence and a lack of functioning T-regulatory cells are proposed mechanisms by which this multi-lineage process is thought to be enhanced. This review summarizes these key advances as the true complexities of the disease process begin to be unraveled.