Identification and precursor frequency analysis of a common T cell epitope motif in mitochondrial autoantigens in primary biliary cirrhosis

A genome-wide association study identified PTPN2 as a population-specific susceptibility gene locus for primary biliary cholangitis

BACKGROUND AND AIMS

Previous genome-wide association studies (GWAS) have indicated the involvement of shared (population-nonspecific) and nonshared (population-specific) susceptibility genes in the pathogenesis of primary biliary cholangitis (PBC) among European and East-Asian populations. Although a meta-analysis of these distinct populations has recently identified more than 20 novel PBC susceptibility loci, analyses of population-specific genetic architecture are still needed for a more comprehensive search for genetic factors in PBC.

APPROACH AND RESULTS

Protein tyrosine phosphatase nonreceptor type 2 ( PTPN2) was identified as a novel PBC susceptibility gene locus through GWAS and subsequent genome-wide meta-analysis involving 2181 cases and 2699 controls from the Japanese population (GWAS-lead variant: rs8098858, p = 2.6 × 10 -8 ). In silico and in vitro functional analyses indicated that the risk allele of rs2292758, which is a primary functional variant, decreases PTPN2 expression by disrupting Sp1 binding to the PTPN2 promoter in T follicular helper cells and plasmacytoid dendritic cells. Infiltration of PTPN2-positive T-cells and plasmacytoid dendritic cells was confirmed in the portal area of the PBC liver by immunohistochemistry. Furthermore, transcriptomic analysis of PBC-liver samples indicated the presence of a compromised negative feedback loop in vivo between PTPN2 and IFNG in patients carrying the risk allele of rs2292758.

CONCLUSIONS

PTPN2 , a novel susceptibility gene for PBC in the Japanese population, may be involved in the pathogenesis of PBC through an insufficient negative feedback loop caused by the risk allele of rs2292758 in IFN-γ signaling. This suggests that PTPN2 could be a potential molecular target for PBC treatment.

Investigational farnesoid X receptor agonists for the treatment of primary biliary cholangitis

INTRODUCTION

Up to 40% of Primary biliary cholangitis (PBC) patients have a suboptimal response to Ursodeoxycholic acid (UDCA). Close to half of such patients show a remarkable improvement when additionally treated with Obeticholic acid (OCA) but have a dose-dependent increase of pruritus. This relative success of OCA, a first-in-class Farnesoid receptor (FXR) agonist, has positioned FXR as an attractive target for drug development. Novel candidates have since emerged, providing hope for this subgroup of patients who lack effective and safe treatments.

AREAS COVERED

We discussed the role of bile acids in PBC pathogenesis and how the FXR agonists provide therapeutic value by affecting bile acid synthesis and transport. Novel FXR agonists undergoing pre-clinical and clinical trials for PBC were enlisted via literature search by including the terms 'FXR agonists,' 'FXR PBC,' 'PBC clinical trials' on PubMed, MEDLINE via Ovid, and Clinicaltrials.gov.

EXPERT OPINION

Novel FXR agonists currently under investigation for PBC improve the disease surrogate markers in early trials. However, as with OCA, pruritus remains a concern with the newer drugs despite targeted chemical modifications to increase FXR specificity. Directing future resources toward studying the molecular mechanisms behind pruritus may lead to better drug design and efficacious yet safer drugs.

Regulatory T cells in inflamed liver are dysfunctional in murine primary biliary cholangitis

Primary biliary cholangitis (PBC) is a chronic autoimmune disease characterized by immune-mediated destruction of intrahepatic small bile ducts. CD8 T cells play a critical role in biliary destruction. However, regulatory T cells (Tregs) have also been identified in the portal tracts of PBC patients. This study tested the hypothesis that hepatic Tregs in PBC were dysfunctional in suppressing immune responses in disease by using our human PBC-like autoimmune cholangitis (AIC) mouse model induced by 2-octynoic acid-conjugated ovalbumin (2-OA-OVA). Our results showed that female and male mice immunized with 2-OA-OVA developed AIC; however, female AIC mice had more severe liver inflammation and fibrosis than male AIC mice. Levels of functional effector CD8 T cells and their chemoattractants, CXCL9 and CXCL10, in the liver were markedly elevated in female AIC mice than in male AIC mice. These results reinforce that CD8 T cells are the primary effector cells in PBC. The number of hepatic Tregs in AIC mice was also higher than in saline-treated mice, but there was no difference between male and female AIC mice. The suppressive function of AIC Tregs was evident despite a discrepancy in the changes in their co-inhibitory receptors and inhibitory cytokines. However, the expansion of hepatic Tregs by low-dose IL-2 treatment did not reduce immune responses to AIC, which may be due to the dysfunction of Tregs in inhibiting T cells. In conclusion, the function of Tregs in the inflamed liver of PBC was insufficient, and low-dose IL-2 treatment could not restore their function to suppress pathological immune responses. Transferring normal Tregs or directly targeting effector CD8 T cells may be beneficial for treating PBC.

Primary Biliary Cholangitis: Epidemiology, Diagnosis, and Presentation

Using ursodeoxycholic acid as a standard treatment and for its ability to test for antimitochondrial antibody to accelerate diagnosis, survival of primary biliary cholangitis patients has approached that of the general population, leading to a change in nomenclature from primary biliary cirrhosis to primary biliary cholangitis to more accurately describe the disease.

rs10924104 in the expression enhancer motif of CD58 confers susceptibility to human autoimmune diseases

CD58 plays roles in cell adhesion and co-stimulation with antigen presentation from major histocompatibility complex class II on antigen-presenting cells to T-cell antigen receptors on naïve T cells. CD58 reportedly contributes to the development of various human autoimmune diseases. Recently, genome-wide association studies (GWASs) identified CD58 as a susceptibility locus for autoimmune diseases such as systemic lupus erythematosus (SLE), multiple sclerosis (MS), and primary biliary cholangitis (PBC). However, the primary functional variant and molecular mechanisms of susceptibility to autoimmune diseases in the CD58 locus were not clarified. Here, rs10924104, located in the ZNF35-binding motif within the gene expression regulatory motif, was identified as the primary functional variant for SLE, MS, and PBC among genetic variants showing stronger linkage disequilibrium (LD) with GWAS-lead variants in the CD58 locus. Expression-quantitative trait locus (e-QTL) data for each distinct blood cell type and in vitro functional analysis using the CRISPR/Cas9 system corroborated the functional role of rs10924104 in the upregulation of CD58 transcription by the disease-risk allele. Additionally, the strength of disease susceptibility observed in the CD58 locus could be accounted for by the strength of LD between rs10924104 and each GWAS-lead variant. In conclusion, the present study demonstrated for the first time the existence of a shared autoimmune disease-related primary functional variant (i.e., rs10924104) that regulates the expression of CD58. Clarifying the molecular mechanism of disease susceptibility derived from such a shared genetic background is important for understanding human autoimmune diseases and human immunology.

Sequence of events leading to primary biliary cholangitis

Primary biliary cholangitis (PBC) is a chronic cholestatic liver disease that is observed more frequently in middle-aged women. This disorder is considered an autoimmune disease, since liver injury is sustained by the presence of self-directed antimitochondrial antibodies targeting the bile duct cells. The prognosis may vary depending on an early diagnosis and response to therapy. However, nearly a third of patients can progress to liver cirrhosis, thus requiring a liver transplant. Traditional immunosuppressive therapies, commonly employed for other autoimmune diseases, have limited effects on PBC. In fact, dramatic functional changes that occur in the biliary epithelium in the course of inflammation play a major role in perpetuating the injury. In this minireview, after a background on the disease and possible predisposing factors, the sequential cooperation of cellular/molecular events leading to end-stage PBC is discussed in detail. The rise and maintenance of the autoimmune process, as well as the response of the biliary epithelia during inflammatory injury, are key factors in the progression of the disease. The so-called "ductular reaction (DR)", intended as a reactive expansion of cells with biliary phenotype, is a process frequently observed in PBC and partially understood. However, recent findings suggest a strict relationship between this pathological picture and the progression to liver fibrosis, cell senescence, and loss of biliary ducts. All these issues (onset of chronic inflammation, changes in secretive and proliferative biliary functions, DR, and its relationship with other pathological events) are discussed in this manuscript in an attempt to provide a snapshot, for clinicians and researchers, of the most relevant and sequential contributors to the progression of this human cholestatic disease. We believe that interpreting this disorder as a multistep process may help identify possible therapeutic targets to prevent evolution to severe disease.

Distinct immune surveillance in primary biliary cholangitis and primary sclerosing cholangitis is linked with discrete cholangiocarcinoma risk

Primary biliary cholangitis (PBC) and primary sclerosing cholangitis (PSC) are 2 major liver autoimmune diseases. PBC is common in women and primarily affects intrahepatic small bile duct epithelial cells, known as cholangiocytes. In contrast, PSC is dominant in men and primarily affects medium and big intrahepatic and extrahepatic bile duct epithelial cells. Cholangiocarcinoma (CCA) is a malignancy arising from cholangiocytes, and its incidence is increasing worldwide in both men and women. Numerous retrospective and clinical studies have suggested that PBC patients rarely develop CCA compared to PSC patients. CCA is accountable for the higher deaths in PSC patients due to ineffective therapies and our inability to diagnose the disease at an early stage. Therefore, it is paramount to understand the differences in immune surveillance mechanisms that render PBC patients more resistant while PSC patients are susceptible to CCA development. Here, we review several potential mechanisms contributing to differences in the susceptibility to CCA in PBC versus PSC patients.

Role of autoantibodies in the clinical management of primary biliary cholangitis

Primary biliary cholangitis (PBC) is a chronic cholestatic liver disease characterized by immune-driven destruction of small intrahepatic bile ducts leading a proportion of patients to hepatic failure over the years. Diagnosis at early stages in concert with ursodeoxycholic acid treatment has been linked with prevention of disease progression in the majority of cases. Diagnosis of PBC in a patient with cholestasis relies on the detection of disease-specific autoantibodies, including anti-mitochondrial antibodies, and disease-specific anti-nuclear antibodies targeting sp100 and gp210. These autoantibodies assist the diagnosis of the disease, and are amongst few autoantibodies the presence of which is included in the diagnostic criteria of the disease. They have also become important tools evaluating disease prognosis. Herein, we summarize existing data on detection of PBC-related autoantibodies and their clinical significance. Moreover, we provide insight on novel autoantibodies and their possible prognostic role in PBC patients.

CCL26 in primary biliary cholangitis - Is it a novel disease mediator?

AIM

To verify the role of CX3C chemokine ligand 1 - CX3C chemokine receptor 1 (CX3CL1-CX3CR1) pathway in the pathogenesis of primary biliary cholangitis (PBC). To explore whether CCL26, a novel functional ligand to CX3CR1, participates in the immunological mechanism of PBC.

METHODS

Fifty-nine PBC patients and 54 healthy controls were recruited. Enzyme-linked immunosorbent assay and flow cytometry were used to measure CX3CL1 and CCL26 concentrations in plasma and CX3CR1 expression on peripheral lymphocytes, respectively. Chemotactic effects of CX3CL1 and CCL26 toward lymphocytes were detected by Transwell cell migration assays. CX3CL1 and CCL26 expressions in liver were assessed by immunohistochemical staining. Effects of CX3CL1 and CCL26 on stimulating cytokine production from lymphocytes were evaluated using intracellular flow cytometry.

RESULTS

Significantly elevated CX3CL1 and CCL26 plasma concentration and CX3CR1 expression on CD4⁺ and CD8⁺ T cells were noted in PBC patients. CX3CL1 exhibited chemotactic activity toward CD8⁺ T, natural killer (NK) and NKT cells in a dose-dependent manner while such chemotactic effects were not detected for CCL26. In PBC patients, CX3CL1 and CCL26 were both increasingly expressed in biliary tracts and a concentration gradient of CCL26 in hepatocytes around portal areas was observed. Immobilized CX3CL1 could enhance interferon-γ production from T and NK cells while such effect was not exhibited by soluble CX3CL1 or CCL26.

CONCLUSIONS

CCL26 expression is significantly elevated in plasma and biliary duct of PBC patients, yet does not appear to attract CX3CR1-expressing immune cells. CX3CL1-CX3CR1 pathway promotes the infiltration of T, NK and NKT cells into bile ducts and forms a positive feedback loop with T-helper 1 type cytokines in PBC.

The Genetics of Primary Biliary Cholangitis: A GWAS and Post-GWAS Update

Primary biliary cholangitis (PBC) is a chronic, progressive cholestatic liver disease in which the small intrahepatic bile ducts are destroyed by autoimmune reactions. Among autoimmune diseases, which are polygenic complex traits caused by the combined contribution of genetic and environmental factors, PBC exhibits the strongest involvement of genetic heritability in disease development. As at December 2022, genome-wide association studies (GWASs) and associated meta-analyses identified approximately 70 PBC susceptibility gene loci in various populations, including those of European and East Asian descent. However, the molecular mechanisms through which these susceptibility loci affect the pathogenesis of PBC are not fully understood. This study provides an overview of current data regarding the genetic factors of PBC as well as post-GWAS approaches to identifying primary functional variants and effector genes in disease-susceptibility loci. Possible mechanisms of these genetic factors in the development of PBC are also discussed, focusing on four major disease pathways identified by in silico gene set analyses, namely, (1) antigen presentation by human leukocyte antigens, (2) interleukin-12-related pathways, (3) cellular responses to tumor necrosis factor, and (4) B cell activation, maturation, and differentiation pathways.

Roles of cuproptosis-related gene DLAT in various cancers: a bioinformatic analysis and preliminary verification on pro-survival autophagy

Background

Studies have shown that the expressions and working mechanisms of Dihydrolipoamide S-acetyltransferase (DLAT) in different cancers vary. It is necessary to analyze the expressions and regulatory roles of DLAT in tumors systematically.

Methods

Online public-platform literature on the relationships between DLAT expression levels and tumor prognosis, methylation status, genetic alteration, drug sensitivity, and immune infiltration has been reviewed. The literature includes such documents as The Cancer Genome Atlas (TCGA), Human Protein Atlas (HPA), Tumor Immune Estimation Resource 2.0 (TIMER2.0), Gene Expression Profiling Interactive Analysis 2 (GEPIA2) and Receiver Operating Characteristic plotter (ROC plotter). The molecular mechanisms of DLAT were explored with the Gene Set Enrichment Analysis (GSEA). The relationship between down-regulated DLAT and autophagy in two liver hepatocellular carcinoma (LIHC) cell lines was confirmed with the western blot method, colony formation assay, and transmission electron microscopy. Tissue microarrays were validated through the immunohistochemical staining of DLAT.

Results

DLAT is upregulated in the LIHC, lung adenocarcinoma (LUAD), lung squamous cell carcinoma (LUSC), and stomach adenocarcinoma (STAD) tumors but is down-regulated in the head and neck squamous cell carcinoma (HNSC) and kidney renal clear cell carcinoma (KIRC) tumors in comparison with normal tissues. For LIHC patients treated with 5-Fluorouracil and Lenvatinib, the DLAT levels of those in the drug-resistant group are significantly high. In LIHC cells, autophagy will be inhibited, and cell death will be induced when DLAT breaks down. Moreover, there exist positive correlations between DLAT expression levels and infiltration of B cells, DC cells, Tregs, and CD8+ T cells in kidney chromophobe (KICH), breast invasive carcinoma (BRCA), prostate adenocarcinoma (PRAD), LIHC and HPV+ HNSC. In LIHC, markers of Tregs are positively correlated with DLAT. Compared with those of normal tissues, the staining intensity of DLAT and the amount of Tregs marker CD49d in LIHC increase.

Conclusions

Through this study, the expressions of DLAT in various cancer types can be understood comprehensively. It suggests that DLAT may be a prognostic marker for LIHC, LUAD, LUSC, STAD and KIRC. A high DLAT expression in LIHC may promote tumorigenesis by stimulating autophagy and inhibiting anti-tumor immunity.

Immunologic Responses and the Pathophysiology of Primary Biliary Cholangitis

Primary biliary cholangitis (PBC) is an autoimmune liver disease with a female predisposition and selective destruction of intrahepatic small bile ducts leading to nonsuppurative destructive cholangitis. It is characterized by seropositivity of antimitochondrial antibodies or PBC-specific antinuclear antibodies, progressive cholestasis, and typical liver histologic manifestations. Destruction of the protective bicarbonate-rich umbrella is attributed to the decreased expression of membrane transporters in biliary epithelial cells (BECs), leading to the accumulation of hydrophobic bile acids and sensitizing BECs to apoptosis. A recent X-wide association study reveals a novel risk locus on the X chromosome, which reiterates the importance of Treg cells.

rs2013278 in the multiple immunological-trait susceptibility locus CD28 regulates the production of non-functional splicing isoforms

Background

Ligation of CD28 with ligands such as CD80 or CD86 provides a critical second signal alongside antigen presentation by class II major histocompatibility complex expressed on antigen-presenting cells through the T cell antigen receptor for naïve T cell activation. A number of studies suggested that CD28 plays an important role in the pathogenesis of various human diseases. Recent genome-wide association studies (GWASs) identified CD28 as a susceptibility locus for lymphocyte and eosinophil counts, multiple sclerosis, ulcerative colitis, celiac disease, rheumatoid arthritis, asthma, and primary biliary cholangitis. However, the primary functional variant and molecular mechanisms of disease susceptibility in this locus remain to be elucidated. This study aimed to identify the primary functional variant from thousands of genetic variants in the CD28 locus and elucidate its functional effect on the CD28 molecule.

Results

Among the genetic variants exhibiting stronger linkage disequilibrium (LD) with all GWAS-lead variants in the CD28 locus, rs2013278, located in the Rbfox binding motif related to splicing regulation, was identified as a primary functional variant related to multiple immunological traits. Relative endogenous expression levels of CD28 splicing isoforms (CD28i and CD28Δex2) compared with full-length CD28 in allele knock-in cell lines generated using CRISPR/Cas9 were directly regulated by rs2013278 (P < 0.05). Although full-length CD28 protein expressed on Jurkat T cells showed higher binding affinity for CD80/CD86, both CD28i and CD28Δex2 encoded loss-of-function isoforms.

Conclusion

The present study demonstrated for the first time that CD28 has a shared disease-related primary functional variant (i.e., rs2013278) that regulates the CD28 alternative splicing that generates loss-of-function isoforms. They reduce disease risk by inducing anergy of effector T cells that over-react to autoantigens and allergens.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40246-022-00419-7.

Linking Human Betaretrovirus with Autoimmunity and Liver Disease in Patients with Primary Biliary Cholangitis

Primary biliary cholangitis (PBC) is an autoimmune liver disease characterized by the production of diagnostic antimitochondrial antibodies (AMA) reactive to the pyruvate dehydrogenase complex. A human betaretrovirus (HBRV) resembling mouse mammary tumor virus has been characterized in patients with PBC. However, linking the viral infection with the disease is not a straight-forward process because PBC is a complex multifactorial disease influenced by genetic, hormonal, autoimmune, environmental, and other factors. Currently, PBC is assumed to have an autoimmune etiology, but the evidence is lacking to support this conjecture. In this review, we describe different approaches connecting HBRV with PBC. Initially, we used co-cultivation of HBRV with biliary epithelial cells to trigger the PBC-specific phenotype with cell surface expression of cryptic mitochondrial autoantigens linked with antimitochondrial antibody expression. Subsequently, we have derived layers of proof to support the role of betaretrovirus infection in mouse models of autoimmune biliary disease with spontaneous AMA production and in patients with PBC. Using Hill’s criteria, we provide an overview of how betaretrovirus infection may trigger autoimmunity and propagate biliary disease. Ultimately, the demonstration that disease can be cured with antiviral therapy may sway the argument toward an infectious disease etiology in an analogous fashion that was used to link H. pylori with peptic ulcer disease.

The latest research trends in primary biliary cholangitis: a bibliometric analysis

The bibliometric analysis uses the citation count of an article to measure its impact in the scientific community, but no study has been undertaken to determine the most influential papers in the field of primary biliary cholangitis (PBC). This study aimed to investigate the global research interest regarding PBC in dentistry using a bibliometric approach. We searched the Web of Science Core Collection database to find the top 100 most cited (T100) articles focusing on PBC. The information about each article including citations, authors, journals, countries, institutions, and keywords was recorded for bibliometric analysis. The T100 articles related to PBC were published from 1983 to 2019 and were originated from 26 countries. A total of 805 different authors were from 342 different institutions, and articles written by them were published in 35 journals. The five most frequently occurring keywords were "biochemical response," "ursodeoxycholic acid," "primary biliary cirrhosis," "antimitochondrial antibody," and "autoimmunity." The T100 articles were classified into different research focuses: pathogenesis (41%), treatment (20%), prognosis (12%), epidemiology (9%), diagnosis (8%), and others (10%). These 100 articles included 32 observational studies, 29 basic research articles, 15 reviews, eight meta-analyses, 12 clinical trials, and four clinical guidelines. The 100 top-cited articles are marked with the leading countries, institutions, journals, hotspots, and development trends in the PBC field that could provide the foundation for further investigations.

Mitochondrial Proteins as Source of Cancer Neoantigens

In the past decade, anti-tumour immune responses have been successfully exploited to improve the outcome of patients with different cancers. Significant progress has been made in taking advantage of different types of T cell functions for therapeutic purposes. Despite these achievements, only a subset of patients respond favorably to immunotherapy. Therefore, there is a need of novel approaches to improve the effector functions of immune cells and to recognize the major targets of anti-tumour immunity. A major hallmark of cancer is metabolic rewiring associated with switch of mitochondrial functions. These changes are a consequence of high energy demand and increased macromolecular synthesis in cancer cells. Such adaptations in tumour cells might generate novel targets of tumour therapy, including the generation of neoantigens. Here, we review the most recent advances in research on the immune response to mitochondrial proteins in different cellular conditions.

E. coli and the etiology of human PBC: Antimitochondrial antibodies and spreading determinants

BACKGROUND AND AIMS

The increased frequency of urinary tract infections in patients with primary biliary cholangitis (PBC) and the cross-reactivity between the lipoyl domains (LD) of human pyruvate dehydrogenase complex (hPDC-E2) and Escherichia coli PDC-E2 (ePDC-E2) have long suggested a role of E. coli in causality of PBC. This issue, however, has remained speculative. We hypothesized that by generating specific constructs of human and E. coli PDC-E2, we would be able to assess the specificity of autoantibody responses and define whether exposure to E. coli in susceptible hosts is the basis for the antimitochondrial antibody (AMA) response.

APPROACH AND RESULTS

Importantly, the reactivity of hPDC-E2 LD (hPDC-E2LD) affinity-purified antibodies against hPDC-E2LD could only be removed by prior absorption with hPDC-E2LD and not ePDC-E2, suggesting the presence of unique human PDC-E2 epitopes distinct from E. coli PDC-E2. To identify the autoepitope(s) present in hPDC-E2LD, a more detailed study using a variety of PDC-E2 constructs was tested, including the effect of lipoic acid (LA) on ePDC-E2 conformation and AMA recognition. Individual recombinant ePDCE2 LD domains LD1, LD2 and LD3 did not react with either AMA or antibodies to LA (anti-LA), but in contrast, anti-LA was readily reactive against purified recombinant LD1, LD2, and LD3 expressed in tandem (LP); such reactivity increased when LP was precultured with LA. Moreover, when the three LD (LD1, LD2, LD3) domains were expressed in tandem in pET28a or when LD1 was expressed in another plasmid pGEX, they were lipoylated and reactive to PBC sera.

CONCLUSIONS

In conclusion, our data are consistent with an exposure to E. coli that elicits specific antibody to ePDC-E2 resulting in determinant spreading and the classic autoantibody to hPDC-E2LD. We argue this is the first step to development of human PBC.

rs9459874 and rs1012656 in CCR6/FGFR1OP confer susceptibility to primary biliary cholangitis

Primary biliary cholangitis (PBC) is a chronic cholestatic autoimmune liver disease that appears to be strongly influenced by genetic factors. Recently, an international meta-analysis of genome-wide association studies (GWAS) identified CC-Motif Chemokine Receptor-6 (CCR6) and FGFR1 Oncogene-Partner (FGFR1OP) as PBC-susceptibility genes. However, the lead single nucleotide polymorphisms (SNPs) of CCR6/FGFR1OP showed low linkage disequilibrium with each other in East Asian and European populations. Additionally, the primary functional variants and the molecular mechanisms responsible for PBC-susceptibility remain unclear. Here, among the PBC-susceptibility SNPs identified by high-density association mapping in our previous meta-GWAS (Patients: n = 10,516; healthy controls: n = 20,772) within the CCR6/FGFR1OP locus, rs9459874 and rs1012656 were identified as primary functional variants. These functional variants accounted for the effects of GWAS-identified lead SNPs in CCR6/FGFR1OP. Additionally, the roles of rs9459874 and rs1012656 in regulating FGFR1OP transcription and CCR6 translation, respectively, were supported by expression quantitative trait loci (eQTL) analysis and gene editing technology using the CRISPR/Cas9 system. Immunohistochemistry showed higher expression of CCR6 protein in the livers of patients with PBC than in those of a non-diseased control. In conclusion, we identified primary functional variants in CCR6/FGFR1OP and revealed the molecular mechanisms by which these variants confer PBC-susceptibility in an eQTL-dependent or -independent manner. The approach in this study is applicable for the elucidation of the pathogenesis of other autoimmune disorders in which CCR6/FGFR1OP is known as a susceptibility locus, as well as PBC.

rs1944919 on chromosome 11q23.1 and its effector genes COLCA1/COLCA2 confer susceptibility to primary biliary cholangitis

Primary biliary cholangitis (PBC) is a chronic, progressive cholestatic liver disease in which intrahepatic bile ducts are destroyed by an autoimmune reaction. Our previous genome-wide association study (GWAS) identified chromosome 11q23.1 as a susceptibility gene locus for PBC in the Japanese population. Here, high-density association mapping based on single nucleotide polymorphism (SNP) imputation and in silico/in vitro functional analyses identified rs1944919 as the primary functional variant. Expression-quantitative trait loci analyses showed that the PBC susceptibility allele of rs1944919 was significantly associated with increased COLCA1/COLCA2 expression levels. Additionally, the effects of rs1944919 on COLCA1/COLCA2 expression levels were confirmed using genotype knock-in versions of cell lines constructed using the CRISPR/Cas9 system and differed between rs1944919-G/G clones and -T/T clones. To our knowledge, this is the first study to demonstrate the contribution of COLCA1/COLCA2 to PBC susceptibility.

Cholestatic liver disease: Practice guidelines from the Saudi Association for the Study of Liver diseases and Transplantation

Cholestatic liver diseases (CLDs) are a group of diseases characterized by jaundice and cholestasis as the main presentation with different complications, which have considerable impact on the liver and can lead to end-stage liver disease, cirrhosis, and liver-related complications. In the last few years, tremendous progress has been made in understanding the pathophysiology, diagnosis, and treatment of patients with these conditions. However, several aspects related to the management of CLDs remain deficient and unclear. Due to the lack of recommendations that can help in the management, treatment of those conditions, the Saudi Association for the Study of Liver diseases and Transplantation (SASLT) has created a task force group to develop guidelines related to CLDs management in order to provide a standard of care for patients in need. These guidelines provide general guidance for health care professionals to optimize medical care for patients with CLDs for both adult and pediatric populations, in association with clinical judgments to be considered on a case-by-case basis. These guidelines describe common CLDs in Saudi Arabia, with recommendations on the best approach for diagnosis and management of different diseases based on the Grading of Recommendation Assessment (GRADE), combined with a level of evidence available in the literature.

Immune system and cholangiocytes: A puzzling affair in primary biliary cholangitis

Primary biliary cholangitis (PBC) is a cholestatic liver disease characterized by the destruction of the small and medium bile ducts. Its pathogenesis is still unknown. Despite the genome wide association study findings, the therapies targeting the cytokines pathway, tested so far, have failed. The concept of the biliary epithelium as a key player of the PBC pathogenesis has emerged over the last few years. It is now well accepted that the biliary epithelial cells (BECs) actively participate to the genesis of the damage. The chronic stimulation of BECs via microbes and bile changes the cell phenotype toward an active state, which, across the production of proinflammatory mediators, can recruit, retain, and activate immune cells. The consequent immune system activation can in turn damage BECs. Thus, the crosstalk between both innate and adaptive immune cells and the biliary epithelium creates a paracrine loop responsible for the disease progression. In this review, we summarize the evidence provided in literature about the role of BECs and the immune system in the pathogenesis of PBC. We also dissect the relationship between the immune system and the BECs, focusing on the unanswered questions and the future potential directions of the translational research and the cellular therapy in this area.

Enhanced expression of miR-21 and miR-150 is a feature of anti-mitochondrial antibody-negative primary biliary cholangitis

Background & Aims

Anti-mitochondrial-autoantibodies (AMA) remain a hallmark of Primary Biliary Cholangitis (PBC) however approximately 10% of patients test negative for these antibodies. They do not differ in terms of biochemistry or clinical presentation from AMA positive ones. Epigenetics play a key role in immune signalling. Two microRNAs (miRs), namely, miR-21 and miR-150 are known to be involved in liver inflammation and fibrosis. The expression of those two microRNAs and their downstream targets were analyze in the context of AMA-status and the stage of liver fibrosis.

Methods

The relative levels of miR-21 and miR-150 and their target genes: cMyb, RAS-guanyl-releasing protein-1(RASGRP1), and DNA-methyltransferase-1(DNMT1) were determined by Real-Time PCR in serum, liver tissue and peripheral blood mononuclear cells (PBMCs) of patients with PBC.

Results

Serum expressions of miR-21 and miR-150 were significantly enhanced in AMA-negative patients, and they inversely correlated with disease-specific AMA titers in PBS patients. In PBMCs, an increased expression of miR-21 correlated with decreased levels of RASGRP1 and DNMT1 mRNAs whereas, the level of miR-150 remained comparable to controls; and cMyb mRNA was downregulated. In cirrhotic livers, the level of miR-21 was unchanged while miR-150 expression was increased.

Conclusion

This study convincingly report, that AMA-negative PBC is characterized by notable alternations of miR-21 and miR-150 and their downstream targets compared to AMA-positive patients underlining their possible importance in the induction of the disease and its progression to fibrosis.

The challenges of primary biliary cholangitis: What is new and what needs to be done

Primary Biliary Cholangitis (PBC) is an uncommon, chronic, cholangiopathy of autoimmune origin and unknown etiology characterized by positive anti-mitochondrial autoantibodies (AMA), female preponderance and progression to cirrhosis if left untreated. The diagnosis is based on AMA- or PBC-specific anti-nuclear antibody (ANA)-positivity in the presence of a cholestatic biochemical profile, histologic confirmation being mandatory only in seronegative cases. First-line treatment is ursodeoxycholic acid (UDCA), which is effective in preventing disease progression in about two thirds of the patients. The only approved second-line treatment is obeticholic acid. This article summarizes the most relevant conclusions of a meeting held in Lugano, Switzerland, from September 23rd-25th 2018, gathering basic and clinical scientists with various background from around the world to discuss the latest advances in PBC research. The meeting was dedicated to Ian Mackay, pioneer in the field of autoimmune liver diseases. The role of liver histology needs to be reconsidered: liver pathology consistent with PBC in AMA-positive individuals without biochemical cholestasis is increasingly reported, raising the question as to whether biochemical cholestasis is a reliable disease marker for both clinical practice and trials. The urgent need for new biomarkers, including more accurate markers of cholestasis, was also widely discussed during the meeting. Moreover, new insights in interactions of bile acids with biliary epithelia in PBC provide solid evidence of a role for impaired epithelial protection against potentially toxic hydrophobic bile acids, raising the fundamental question as to whether this bile acid-induced epithelial damage is the cause or the consequence of the autoimmune attack to the biliary epithelium. Strategies are needed to identify difficult-to-treat patients at an early disease stage, when new therapeutic approaches targeting immunologic pathways, in addition to bile acid-based therapies, may be effective. In conclusion, using interdisciplinary approaches, groundbreaking advances can be expected before long in respect to our understanding of the etiopathogenesis of PBC, with the ultimate aim of improving its treatment.

Suppression of a broad spectrum of liver autoimmune pathologies by single peptide-MHC-based nanomedicines

Peptide-major histocompatibility complex class II (pMHCII)-based nanomedicines displaying tissue-specific autoantigenic epitopes can blunt specific autoimmune conditions by re-programming cognate antigen-experienced CD4+ T-cells into disease-suppressing T-regulatory type 1 (TR1) cells. Here, we show that single pMHCII-based nanomedicines displaying epitopes from mitochondrial, endoplasmic reticulum or cytoplasmic antigens associated with primary biliary cholangitis (PBC) or autoimmune hepatitis (AIH) can broadly blunt PBC, AIH and Primary Sclerosing Cholangitis in various murine models in an organ- rather than disease-specific manner, without suppressing general or local immunity against infection or metastatic tumors. Therapeutic activity is associated with cognate TR1 cell formation and expansion, TR1 cell recruitment to the liver and draining lymph nodes, local B-regulatory cell formation and profound suppression of the pro-inflammatory capacity of liver and liver-proximal myeloid dendritic cells and Kupffer cells. Thus, autoreactivity against liver-enriched autoantigens in liver autoimmunity is not disease-specific and can be harnessed to treat various liver autoimmune diseases broadly.

Immune response against tissue-specific antigens is a hallmark of autoimmunity. Here the authors show that a single autoantigen-based nanomedicine can ameliorate pathology in a broad range of liver autoimmunity models without impairing host defenses, suggesting organ-wide tolerization.

TCRβ repertoire of memory T cell reveals potential role for Escherichia coli in the pathogenesis of primary biliary cholangitis

BACKGROUND

Primary biliary cholangitis (PBC) is an organ-specific, T cell-mediated autoimmune disease which is characterized by the breakdown of self-tolerance to the highly conserved pyruvate dehydrogenase complex, especially the pyruvate dehydrogenase E2 complex (PDC-E2). However, the molecular mechanism of breakdown of self-tolerance is still unclear.

METHODS

A combination of multiplex-PCR and immune repertoire sequencing (IR-seq) was used for a standardized analysis of memory T cell receptor (TCR) β-chain repertoire of PBC patient and healthy volunteers. In vitro induction and expansion of human PDC-E2_163-176 (human PDC-E2)-specific T cells and E coli PDC-E2_{31-44/134-147/235-248} (E coli PDC-E2)-specific T cells, and identified the human (and E coli) PDC-E2-specific TCRβ repertoire by IR-seq.

RESULTS

Primary biliary cholangitis patients have shorter complementarity-determining region 3s (CDR3s), and higher degree of sequence overlap in the TCRβ repertoire of memory T cell. Moreover, altered insertion patterns and skewed TRBV segment usage were observed in PBC patients. With regard to the pathogenesis, the concentration of E coli was higher in PBC patients' faecal. The frequency of E coli (and human)-specific TCRs was higher in the memory TCRβ repertoire of PBC patients compared with healthy controls. Importantly, the TCRβ repertoire characteristics were almost identical between E coli PDC-E2-related TCRs and human PDC-E2-related TCRs, including the patterns of TRBV usage, CDR3 length and amino acid composition.

CONCLUSION

Our findings comprehensively revealed the TCRβ repertoire characterization of PBC patients, and provided a TCR molecular basis to understand the mechanism of cross-recognition between human PDC-E2 and E coli PDC-E2, and the imbalance of immune tolerance in PBC.

Immunological abnormalities in patients with primary biliary cholangitis

Primary biliary cholangitis (PBC), an autoimmune liver disease occurring predominantly in women, is characterized by high titers of serum anti-mitochondrial antibodies (AMAs) and progressive intrahepatic cholestasis. The immune system plays a critical role in PBC pathogenesis and a variety of immune cell subsets have been shown to infiltrate the portal tract areas of patients with PBC. Amongst the participating immune cells, CD4 T cells are important cytokine-producing cells that foster an inflammatory microenvironment. Specifically, these cells orchestrate activation of other immune cells, including autoreactive effector CD8 T cells that cause biliary epithelial cell (BEC) injury and B cells that produce large quantities of AMAs. Meanwhile, other immune cells, including dendritic cells (DCs), natural killer (NK) cells, NKT cells, monocytes, and macrophages are also important in PBC pathogenesis. Activation of these cells initiates and perpetuates bile duct damage in PBC patients, leading to intrahepatic cholestasis, hepatic damage, liver fibrosis, and eventually cirrhosis or even liver failure. Taken together, the body of accumulated clinical and experimental evidence has enhanced our understanding of the immunopathogenesis of PBC and suggests that immunotherapy may be a promising treatment option. Herein, we summarize current knowledge regarding immunological abnormalities of PBC patients, with emphasis on underlying pathogenic mechanisms. The differential immune response which occurs over decades of disease activity suggests that different therapies may be needed at different stages of disease.

Pathogen infections and primary biliary cholangitis

Primary biliary cholangitis (PBC) is a multi-factorial disease caused by the interaction of both genetic predisposition and environmental triggers. Bacterial infection has been investigated most intensively, both epidemiologically and experimentally, as a prime environmental aetiology in PBC. The association of recurrent history of urinary tract infection (UTI) with PBC has been frequently confirmed by several large-scale, case-control studies, despite variation in geographic area or case-finding methods. Escherichia coli is a predominant pathogen in most cases with UTI. Animal studies and molecular mimicry analysis between the human and E. coli E2 subunit of the 2-oxo-acid dehydrogenase complexes demonstrated that E. coli infection is a key factor in breaking immunological tolerance against the mitochondria, resulting in the production of anti-mitochondrial autoantibodies (AMA), the disease-specific autoantibodies of PBC. Novosphingobium aromaticivorans, a ubiquitous xenobiotic-metabolizing bacterium, is another candidate which may be involved in the aetiology of PBC. Meanwhile, improved environmental hygiene and increased prevalence of PBC, especially in males, may argue against the aetiological role of bacterial infection in PBC. Multiple mechanisms can result in the loss of tolerance to mitochondrial autoantigens in PBC; nonetheless, bacterial infection is probably one of the dominant pathways, especially in female patients. Notably, there is a rising prevalence of male patients with PBC. With increasing exposure to environmental xenobiotics in both genders, studies directed towards identifying the environmental culprit with systematically designed case-control studies are much needed to further determine the environmental factors and role of bacterial infections in PBC.

Evolution of our understanding of PBC

The discovery of mitochondrial autoantigens recognized by antimitochondrial antibodies (AMAs) in 1987 marked the dawn of a new era in primary biliary cholangitis (PBC) research. Since then, there has been substantial progress in our understanding of PBC partly bestowed by the development of innovative technologies in molecular biology, immunology, and genetics. Here, we review this evolutionary progress in understanding PBC. We now recognize that the epitopes of AMAs, CD4⁺, and CD8⁺ T cells are all mapped to the same region of the inner lipoyl domain of pyruvate dehydrogenase complex E2 subunit (PDC-E2), and that intrahepatic biliary epithelial cells (BECs) are exclusively targeted in PBC. BECs express PDC-E2 on apotopes in an immunologically intact form during apoptosis, but not other epithelial cells, which could explain the tissue specificity of PBC. In addition, genetic factors, environmental triggers, and epigenetic modifications play crucial roles in the development of PBC. Intact lipoylated PDC-E2, presumably after modification with xenobiotics such as 2-octynamide or 2-nonyamide that are abundantly present in the environment, is endocytosed by antigen-presenting cells and are presented to CD4⁺ or CD8⁺ T cells. An immune complex consisting of PDC-E2 and anti-PDC-E2 autoantibodies cross-present autoantigens in a more efficient manner. Finally, an adenylate uridine-rich element (ARE) Del -/- mouse model has been established, which presents a disease modeling human PBC, including female dominance as one of its most important features, and can be used to dissect the immunopathology of PBC. Expanding our knowledge of the pathology from a very early stage of the disease will provide the key to cure PBC.

An impaired biliary bicarbonate umbrella may be involved in dysregulated autophagy in primary biliary cholangitis

Dysregulated autophagy may be a central player in trehe pathogenesis of primary biliary cholangitis (PBC) by inducing autoimmune processes via abnormal expression of mitochondrial antigens such as pyruvate dehydrogenase complex, E2 component (PDC-E2) and also by inducing cellular senescence in biliary epithelial cells (BECs) in bile duct lesions in PBC. We examined the association of an impaired "biliary bicarbonate umbrella" due to dysfunction of anion exchanger 2 (AE2) with dysregulated autophagy and cellular senescence in PBC. The expression of AE2 was examined in cultured BECs treated with bile acids such as glycochenodeoxycholic acid (GCDC) and tauro-ursodeoxycholic acid (TUDCA), various cytokines (IL-4, IL-13, IFNγ, TNFα, TGFβ), and serum deprivation. The effect of AE2 knockdown using siRNA on autophagy, cell surface expression of PDC-E2, and cellular senescence was also examined. The expression of AE2 and its association with autophagy-related markers and senescent markers p16^INK4a and p21^WAF1/Cip1 were immunohistochemically determined in livers taken from the patients with PBC (n = 50) and 69 control diseased and normal livers. The expression of AE2 was significantly induced in the cultured BECs shortly treated with GCDC and other stresses, whereas it was significantly decreased in senescent BECs induced by GCDC and other stresses (p < 0.05). Dysregulated autophagy, cell surface expression of PDC-E2, and cellular senescence were significantly increased by knockdown of AE2 (p < 0.05). The expression of AE2 was significantly decreased in cholangitis in PBC, compared to control livers (p < 0.05). The decreased expression of AE2 was correlated with dysregulated autophagy, abnormal expression of PDC-E2, and cellular senescence in bile duct lesions in PBC. In conclusion, an impaired biliary bicarbonate umbrella may be involved in the pathogenesis of PBC by inducing dysregulated autophagy.

NI-0801, an anti-chemokine (C-X-C motif) ligand 10 antibody, in patients with primary biliary cholangitis and an incomplete response to ursodeoxycholic acid

NI-0801 is a fully human monoclonal antibody against chemokine (C-X-C motif) ligand 10 (CXCL10), which is involved in the recruitment of inflammatory T cells into the liver. The safety and efficacy of NI-0801 was assessed in patients with primary biliary cholangitis. In this open-label phase 2a study, patients with primary biliary cholangitis with an inadequate response to ursodeoxycholic acid received six consecutive intravenous administrations of NI-0801 (10 mg/kg) every 2 weeks. Patients were followed up for 3 months after the last infusion. Liver function tests, safety assessments, as well as pharmacokinetic and pharmacodynamic parameters were evaluated at different time points throughout the dosing period and the safety follow-up period. Twenty-nine patients were enrolled in the study and were treated with NI-0801. The most frequently reported adverse events included headaches (52%), pruritus (34%), fatigue (24%), and diarrhea (21%). No study drug-related serious adverse events were reported. NI-0801 administration did not lead to a significant reduction in any of the liver function tests assessed at the end of the treatment period (i.e., 2 weeks after final NI-0801 administration) compared to baseline. Conclusion: Despite clear pharmacologic responses in the blood, no therapeutic benefit of multiple administrations of NI-0801 could be demonstrated. The high production rate of CXCL10 makes it difficult to achieve drug levels that lead to sustained neutralization of the chemokine, thus limiting its targetability. (Hepatology Communications 2018;2:492-503).

Potential role of indoleamine 2,3-dioxygenase in primary biliary cirrhosis

Indoleamine 2,3-dioxygenase (IDO)-induced immunosuppression can be clinically beneficial for autoimmune diseases. Primary biliary cirrhosis (PBC) is characterized by autoimmune lesions of intrahepatic bile duct epithelial cells that may lead to irreversible cirrhosis or hepatocellular carcinoma. The present study assessed the expression and function of IDO in a cell culture model and in PBC patients. IDO expression was monitored in a human immortalized but non-malignant biliary epithelial cell (iBEC) line. Increased expression of IDO1/2 was observed in the iBECs following stimulation with interferon-γ (IFN-γ). The induction of IDO was IFN-γ-dependent, but was independent of the transforming growth factor-β (TGF-β) pathway. IDO enzymatic activity was observed in the supernatant of iBECs following stimulation with IFN-γ using colorimetric assays. A total of 47 serum samples from PBC patients were used to examine IDO activity by high-performance liquid chromatography, with samples from 24 healthy volunteers used as controls. Patients with PBC exhibited an increased rate of tryptophan to kynurenine conversion (P>0.01). Liver sections from patients with PBC (n=5) and those of healthy controls (n=5) were used for immunohistochemical studies. IDO expression was observed in biliary epithelial cells and in hepatocytes of PBC patients. Finally, the effect of tryptophan metabolites on human cluster of differentiation (CD) 4+ T cells in inducing polarization towards a regulatory T cell phenotype was examined. 3-Hydroxykynurenine significantly upregulated the fraction of CD4+ cells expressing forkhead box p3 (Foxp3). The results of the present study suggest a therapeutic opportunity for the management of PBC and indicate that tryptophan catabolism could serve as a potential biomarker to monitor disease progression.

miR-425 regulates inflammatory cytokine production in CD4+ T cells via N-Ras upregulation in primary biliary cholangitis

BACKGROUND & AIMS

Primary biliary cholangitis (PBC) is an autoimmune liver disease of unknown pathogenesis. Consequently, therapeutic targets for PBC have yet to be identified. CD4⁺ T cells play a pivotal role in immunological dysfunction observed in PBC, and therefore, microRNA (miRNA) and mRNA expression were analysed in CD4⁺ T cells, to investigate PBC pathogenesis and identify novel therapeutic targets.

METHODS

Integral miRNA and mRNA analysis of 14 PBC patients and ten healthy controls was carried out using microarray and quantitative real-time polymerase chain reaction (qRT-PCR), with gene set enrichment analysis. The functional analyses of miRNA were then assessed using reporter and miRNA-overexpression assays.

RESULTS

The integral analysis of miRNA and mRNA identified four significantly downregulated miRNAs (miR-181a, -181b, -374b, and -425) related to the T cell receptor (TCR) signalling pathway in CD4⁺ T cells of PBC. N-Ras, a regulator of the TCR signalling pathway, was found to be targeted by all four identified miRNAs. In addition, in vitro assays confirmed that decreased miR-425 strongly induced inflammatory cytokines (interleukin [IL]-2 and interferon [IFN]-γ) via N-Ras upregulation in the TCR signalling pathway.

CONCLUSION

The decreased expression of four miRNAs that dysregulate TCR signalling in PBC CD4⁺ T cells was identified. miR-425 was demonstrated as an inflammatory regulator of PBC via N-Ras upregulation. Therefore, the restoration of decreased miR-425 or the suppression of N-Ras may be a promising immunotherapeutic strategy against PBC.

LAY SUMMARY

Primary biliary cholangitis (PBC) is an autoimmune liver disease, but the causes are unknown. MicroRNAs are molecules known to regulate biological signals. In this study, four microRNAs were identified as being decreased in PBC patients, leading to activation of T cell receptor signalling pathways, involved in inflammation. One particular target, N-Ras, could be an attractive and novel immunotherapeutic option for PBC.

TRANSCRIPT PROFILING

Microarray data are deposited in GEO (GEO accession: GSE93172).

Toward solving the etiological mystery of primary biliary cholangitis

Primary biliary cholangitis (PBC) is considered a model autoimmune disease due to its signature anti‐mitochondrial antibody (AMA) autoantibody, female predominance, and relatively specific portal infiltration and cholestasis. The identification and cloning of the major mitochondrial autoantigens recognized by AMA have served as an immunologic platform to identify the earliest events involved in loss of tolerance. Despite the relatively high concordance rate in identical twins, genome‐wide association studies have not proven clinically useful and have led to suggestions of epigenetic events. To understand the natural history and etiology of PBC, several murine models have been developed, including spontaneous models, models induced by chemical xenobiotic immunization, and by “designer” mice with altered interferon metabolism. Herein, we describe five such models, including 1) NOD.c3c4 mice, 2) dominant negative form of transforming growth factor receptor type II mice, 3) interleukin‐2R α^−/− mice, 4) adenylate‐uridylate‐rich element Del^−/− mice, and 5) 2‐octynoic acid‐conjugated bovine serum albumin immunized mice. Individually there is no perfect murine model, but collectively the models point to loss of tolerance to PDC‐E2, the major mitochondrial autoantigen, as the earliest event that occurs before clinical disease is manifest. Although there is no direct association of AMA titer and PBC disease progression, it is noteworthy that the triad of PBC monocytes, biliary apotopes, and AMA leads to an intense proinflammatory cytokine burst. Further, the recurrence of PBC after liver transplantation indicates that, due to major histocompatibility complex restriction, disease activity must include not only adaptive immunity but also innate immune mechanisms. We postulate that successful treatment of PBC may require a personalized approach with therapies designed for different stages of disease. (Hepatology Communications 2017;1:275–287)

Proposed therapies in primary biliary cholangitis

Primary biliary cholangitis (PBC), previously known as primary biliary cirrhosis, is a model autoimmune disease with chronic cholestasis characterized by the hallmark of anti-mitochondrial antibodies and treated with ursodeoxycholic acid (UDCA). However, approximately 20-40% of patients incompletely respond to UDCA and have an increased risk of disease progression. Although there have been significant advances in the immunobiology of PBC, these have yet to be translated into newer therapeutic modalities. Current approaches to controlling the immune response include broad immunosuppression with corticosteroids as well as targeted therapies directed against T and B cells. In contrast, ameliorating cholestasis is the focus of other therapies in development, including obeticholic acid. In this article the authors will discuss ongoing clinical trials and, in particular, the rationale for choosing agents that may effectively target the aberrant immune response.

Emerging drugs for the treatment of Primary Biliary Cholangitis

INTRODUCTION

Primary biliary cholangitis (PBC) is an autoimmune chronic disease of the liver that can progress to cirrhosis and hepatocellular carcinoma. It affects approximately 1 in 4,000 with a 10:1 female to male ratio. The diagnosis of PBC can be made based on serum antimitochondrial antibodies (AMA) in a patient with abnormally high serum alkaline phosphatase after ruling out other causes of cholestasis and biliary obstruction. Genome-wide association studies have revealed several human leukocyte antigen (HLA) and non-HLA risk loci in PBC, and complex environmental-host immunogenetic interactions are believed to underlie the etiopathogenesis of the disease. Fatigue and pruritus are the most common and often problematic symptoms; although often mild, these can be severe and life-alternating in a subset of patients. Ursodeoxycholic acid (UDCA) is the only drug approved by the United States Food and Drug Administration for the treatment of PBC. Clinical trials have shown that UDCA significantly improves transplant-free survival. However, nearly 40% of PBC patients do not respond adequately to PBC and are at higher risk for serious complications when compared to PBC patients with complete response to UDCA.

AREAS COVERED

Here we provide a detailed discussion regarding novel therapeutic agents and potential areas for further investigation in PBC-related research.

EXPERT OPINION

Results of ongoing clinical trials and emerging treatment paradigms for PBC will likely further improve medical management of this disorder in the near future.

Dual Roles of IFN-γ and IL-4 in the Natural History of Murine Autoimmune Cholangitis: IL-30 and Implications for Precision Medicine

Primary biliary cirrhosis (PBC) is a progressive autoimmune liver disease with a long natural history. The pathogenesis of PBC is thought to be orchestrated by Th1 and/or Th17. In this study, we investigated the role of CD4⁺ helper T subsets and their cytokines on PBC using our previous established murine model of 2-OA-OVA immunization. We prepared adeno-associated virus (AAV)-IFN-γ and AAV-IL-4 and studied their individual influences on the natural history of autoimmune cholangitis in this model. Administration of IFN-γ significantly promotes recruitment and lymphocyte activation in the earliest phases of autoimmune cholangitis but subsequently leads to downregulation of chronic inflammation through induction of the immunosuppressive molecule IL-30. In contrast, the administration of IL-4 does not alter the initiation of autoimmune cholangitis, but does contribute to the exacerbation of chronic liver inflammation and fibrosis. Thus Th1 cells and IFN-γ are the dominant contributors in the initiation phase of this model but clearly may have different effects as the disease progress. In conclusion, better understanding of the mechanisms by which helper T cells function in the natural history of cholangitis is essential and illustrates that precision medicine may be needed for patients with PBC at various stages of their disease process.

Cirrhosis and autoimmune liver disease: Current understanding

Primary biliary cirrhosis (PBC), primary sclerosing cholangitis (PSC) and autoimmune hepatitis (AIH) constitute the classic autoimmune liver diseases (AILDs). While AIH target the hepatocytes, in PBC and PSC the targets of the autoimmune attack are the biliary epithelial cells. Persistent liver injury, associated with chronic AILD, leads to un-resolving inflammation, cell proliferation and the deposition of extracellular matrix proteins by hepatic stellate cells and portal myofibroblasts. Liver cirrhosis, and the resultant loss of normal liver function, inevitably ensues. Patients with cirrhosis have higher risks or morbidity and mortality, and that in the decompensated phase, complications of portal hypertension and/or liver dysfunction lead to rapid deterioration. Accurate diagnosis and monitoring of cirrhosis is, therefore of upmost importance. Liver biopsy is currently the gold standard technique, but highly promising non-invasive methodology is under development. Liver transplantation (LT) is an effective therapeutic option for the management of end-stage liver disease secondary to AIH, PBC and PSC. LT is indicated for AILD patients who have progressed to end-stage chronic liver disease or developed intractable symptoms or hepatic malignancy; in addition, LT may also be indicated for patients presenting with acute liver disease due to AIH who do not respond to steroids.

The management of autoimmunity in patients with cholestatic liver diseases

Cholestatic liver diseases are rare diseases that often lead to cirrhosis and its consequent complications. In addition to liver-related morbidity, patients with cholestatic liver diseases often suffer from autoimmune diseases that affect several organs and tissues. The robust and efficient data collection and collaboration between hepatologists and rheumatologists have led to significant advancements in understanding the relationship between the cholestatic liver diseases and associated autoimmune diseases. In this paper, we discuss the cholestatic liver diseases (primary biliary cirrhosis, primary sclerosing cholangitis and immunoglobulin G4 associated cholangitis) and associated autoimmune diseases.

Hydrophobic bile acids suppress expression of AE2 in biliary epithelial cells and induce bile duct inflammation in primary biliary cholangitis

Understanding the mechanisms of chronic inflammation in primary biliary cholangitis (PBC) is essential for successful treatment. Earlier work has demonstrated that patients with PBC have reduced expression of the anion exchanger 2 (AE2) on biliary epithelial cells (BEC) and deletion of AE2 gene has led to a PBC-like disorder in mice. To directly address the role of AE2 in preventing PBC pathogenesis, we took advantage of our ability to isolate human BEC and autologous splenic mononuclear cells (SMC). We studied the influence of hydrophobic bile acids, in particular, glycochenodeoxycholic acid (GCDC), on AE2 expression in BEC and the subsequent impact on the phenotypes of BEC and local inflammatory responses. We demonstrate herein that GCDC reduces AE2 expression in BEC through induction of reactive oxygen species (ROS), which enhances senescence of BEC. In addition, a reduction of AE2 levels by either GCDC or another AE2 inhibitor upregulates expression of CD40 and HLA-DR as well as production of IL-6, IL-8 and CXCL10 from BEC in response to toll like receptor ligands, an effect suppressed by inhibition of ROS. Importantly, reduced AE2 expression enhances the migration of autologous splenic mononuclear cells (SMC) towards BEC. In conclusion, our data highlight a key functional role of AE2 in the maintenance of the normal physiology of BEC and the pathogenic consequences of reduced AE2 expression, including abnormal intrinsic characteristics of BEC and their production of signal molecules that lead to the chronic inflammatory responses in small bile ducts.

It is time to change primary biliary cirrhosis (PBC): New nomenclature from "cirrhosis" to "cholangitis", and upcoming treatment based on unveiling pathology

Primary biliary cirrhosis (PBC) is a chronic, organ-specific, autoimmune liver disease characterized by progressive cholestasis, eventually leading to cirrhosis. Several lines of evidence have revealed a crucial role of adaptive as well as innate immune responses in the etiopathogenesis of PBC, and more recently, the biology of bile duct cells and genome-wide association studies (GWAS) demonstrated several key molecules and pathways in this enigmatic disease. Although ursodeoxycholic acid (UDCA) has been the only approved drug for PBC with clinical evidences for improvement of long-term outcomes, a substantial population have suboptimal responses to UDCA, resulting in unfavorable outcomes. In this regard, second-line treatment for patients refractory to UDCA is strongly awaited. In Japan, bezafibrate (BF) has been frequently used for this purpose, yet recent clinical trials failed to clearly demonstrate clinical efficacy of BF. Novel pharmacotherapies targeted to key molecules and pathways in PBC are upcoming. Finally, we sincerely call on all members of the Japan Society of Hepatology to use from this moment on the name "primary biliary cholangitis" for the disease known by its abbreviation PBC, in keeping with a very recent global agreement.

The Immunogenetics of Autoimmune Cholestasis

The immune-mediated hepatobiliary diseases, primary biliary cirrhosis and primary sclerosing cholangitis are relatively rare, albeit and account for a significant amount of liver transplant activity and liver-related mortality globally. Precise disease mechanisms are yet to be described although a contributory role of genetic predisposition is firmly established. In addition to links with the major histocompatibility complex, a number of associations outside this region harbor additional loci which underscore the fundamental role of breaks in immune tolerance and mucosal immunogenicity in the pathogenesis of autoimmune biliary disease. We provide an overview of these key discoveries before discussing putative avenues of therapeutic exploitation based on existing findings.

Making Sense of Autoantibodies in Cholestatic Liver Diseases

Primary biliary cirrhosis (PBC) and primary sclerosing cholangitis (PSC) are the most common chronic cholestatic liver diseases (CLD) in adults and are associated with immune mechanisms. PBC is considered a model autoimmune disease, and more than 90% of patients present very specific autoantibodies against mitochondrial antigens. Whether PSC should be considered an autoimmune or merely immune-mediated disease is still under debate. This review addresses the clinical relevance of autoantibodies in CLD and their pathogenic mechanisms and illustrates the technology available for appropriate autoantibody detection.

Xenobiotics and loss of tolerance in primary biliary cholangitis

Data from genome wide association studies and geoepidemiological studies established that a combination of genetic predisposition and environmental stimulation is required for the loss of tolerance in primary biliary cholangitis (PBC). The serologic hallmark of PBC are the presence of high titer anti-mitochondrial autoantibodies (AMA) that recognize the lipoyl domain of the mitochondrial pyruvate dehydrogenase E2 (PDC-E2) subunit. Extensive efforts have been directed to investigate the molecular basis of AMA. Recently, experimental data has pointed to the thesis that the breaking of tolerance to PDC-E2 is a pivotal event in the initial etiology of PBC, including environmental xenobiotics including those commonly found in cosmetics and food additives, suggesting that chemical modification of the PDC-E2 epitope may render its vulnerable to become a neo-antigen and trigger an immune response in genetically susceptible hosts. Here, we will discuss the natural history, genetics and immunobiology of PBC and structural constraints of PDC-E2 in AMA recognition which makes it vulnerable to chemical modification.

New therapies for primary biliary cirrhosis

Primary biliary cirrhosis (PBC) is a rare inflammatory liver disease for which ursodeoxycholic acid (UDCA) is the only therapy approved by the U.S. Food and Drug Administration. Patients with a biochemical response to UDCA therapy have a similar survival rate compared to the general population. However, up to 40% of PBC patients do not achieve a complete response to UDCA, have an increased risk of liver-related death and liver transplantation, and represent a persistent medical need for new therapies. Several novel drugs have recently been studied and show potential efficacy in PBC. Obeticholic acid, a farnesoid X receptor agonist, has been tested in phase II trials and initial results after 1 year in a phase III international trial suggest that it may be effective in achieving a biochemical response in approximately 40% of patients who do not completely respond to UDCA. Several small studies on fibrates have suggested that they may have efficacy, but larger studies are needed. Surprisingly, results of immunomodulators and biologics have not yet been able to demonstrate efficacy, but new approaches have shown promise in animal models and their translation to human clinical trials are awaited.

Natural killer cells regulate T cell immune responses in primary biliary cirrhosis

The hallmark of primary biliary cirrhosis (PBC) is the presence of autoreactive T- and B-cell responses that target biliary epithelial cells (BECs). Biliary cell cytotoxicity is dependent upon initiation of innate immune responses followed by chronic adaptive, as well as bystander, mechanisms. Critical to these mechanisms are interactions between natural killer (NK) cells and BECs. We have taken advantage of the ability to isolate relatively pure viable preparations of liver-derived NK cells, BECs, and endothelial cells, and studied interactions between NK cells and BECs and focused on the mechanisms that activate autoreactive T cells, their dependence on interferon (IFN)-γ, and expression of BEC major histocompatibility complex (MHC) class I and II molecules. Here we show that at a high NK/BEC ratio, NK cells are cytotoxic for autologous BECs, but are not dependent on autoantigen, yet still activate autoreactive CD4(+) T cells in the presence of antigen presenting cells. In contrast, at a low NK/BEC ratio, BECs are not lysed, but IFN-γ production is induced, which facilitates expression of MHC class I and II molecules on BEC and protects them from lysis upon subsequent exposure to autoreactive NK cells. Furthermore, IFN-γ secreted from NK cells after exposure to autologous BECs is essential for this protective function and enables autoreactive CD4(+) T cells to become cytopathic.

CONCLUSIONS

NK cell-mediated innate immune responses are likely critical at the initial stage of PBC, but also facilitate and maintain the chronic cytopathic effect of autoantigen-specific T cells, essential for progression of disease.

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.

A possible involvement of endoplasmic reticulum stress in biliary epithelial autophagy and senescence in primary biliary cirrhosis

BACKGROUND

Deregulated autophagy followed by cellular senescence in biliary epithelial cells (BECs) may be closely related to the abnormal expression of mitochondrial antigens and following autoimmune pathogenesis in primary biliary cirrhosis (PBC). We examined an involvement of endoplasmic reticulum (ER) stress in the deregulated autophagy and cellular senescence in PBC.

METHODS

We examined the degree of ER stress using markers; glucose-regulated protein 78 (GRP78) and protein disulfide isomerases (PDI), autophagy and cellular senescence in cultured BECs treated with an ER stress inducer, tunicamycin (TM), glycochenodeoxycholic acid (GCDC), and palmitic acid (PA), and the effect of pretreatment with tauroursodeoxycholic acid (TUDCA). We examined the expression of PDI and GRP78 in livers taken from the patients with PBC (n = 43) and 75 control livers.

RESULTS

The expression of ER stress markers was significantly increased in cultured BECs treated with TM, GCDC or PA in BECs (p < 0.05), and pretreatment with TUDCA significantly suppressed the induced ER stress (p < 0.05). Autophagy, deregulated autophagy, and cellular senescence were induced in BECs treated with TM, GCDC, or PA. Pretreatment with TUDCA further increased autophagy in BECs treated with PA and suppressed cellular senescence caused by treatments with TM, GCDC, or PA (p < 0.05). A granular expression of PDI and GRP78 was significantly more extensive in small bile ducts in PBC, compared with control livers (p < 0.05). The expression of GRP78 was seen in senescent BECs in PBC.

CONCLUSIONS

ER stress may play a role in the pathogenesis of deregulated autophagy and cellular senescence in biliary epithelial lesions in PBC.

Immunological potential of cytotoxic T lymphocyte antigen 4 immunoglobulin in murine autoimmune cholangitis

Cytotoxic T lymphocyte antigen 4 (CTLA-4) immunoglobulin (Ig) is an important regulator of T cell activation and a fusion protein directed at CD80 and CD86; it blocks co-stimulatory signalling and T cell activation. We have taken advantage of a murine model of human primary biliary cirrhosis (PBC), mice expressing a transforming growth factor (TGF)-β receptor II dominant negative (dnTGF-βRII) transgene to address the potential therapeutic efficacy of CTLA-4 Ig. To mimic patients with PBC at different stages or duration of disease, we treated mice with either CTLA-4 Ig or control IgG three times weekly from 3 to 12 or 24 weeks of age, or from 12 to 24 weeks of age. CTLA-4 Ig treatment from 3 weeks of age significantly reduced liver inflammation to 12 weeks of age. Treatment initiated at 12 weeks of age also ameliorated the autoimmune cholangitis at 24 weeks of age. However, in mice treated at 3 weeks of age, suppression of liver inflammation was not sustained and colitis was aggravated when treatment was extended to 24 weeks of age. Our data indicate that, in dnTGF-βRII mice, CTLA-4 Ig treatment has short-term beneficial effects on autoimmune cholangitis, but the effect varies according to duration of treatment and the time in which therapy was initiated. Further dissection of the events that lead to the reduction in therapeutic effectiveness of CTLA-4 Ig will be critical to determining whether such efforts can be applied to human PBC.