Update on primary sclerosing cholangitis genetics

Activation of the GPR35 pathway drives angiogenesis in the tumour microenvironment

OBJECTIVE

Primary sclerosing cholangitis (PSC) is in 70% of cases associated with inflammatory bowel disease. The hypermorphic T108M variant of the orphan G protein-coupled receptor GPR35 increases risk for PSC and ulcerative colitis (UC), conditions strongly predisposing for inflammation-associated liver and colon cancer. Lack of GPR35 reduces tumour numbers in mouse models of spontaneous and colitis associated cancer. The tumour microenvironment substantially determines tumour growth, and tumour-associated macrophages are crucial for neovascularisation. We aim to understand the role of the GPR35 pathway in the tumour microenvironment of spontaneous and colitis-associated colon cancers.

DESIGN

Mice lacking GPR35 on their macrophages underwent models of spontaneous colon cancer or colitis-associated cancer. The role of tumour-associated macrophages was then assessed in biochemical and functional assays.

RESULTS

Here, we show that GPR35 on macrophages is a potent amplifier of tumour growth by stimulating neoangiogenesis and tumour tissue remodelling. Deletion of Gpr35 in macrophages profoundly reduces tumour growth in inflammation-associated and spontaneous tumour models caused by mutant tumour suppressor adenomatous polyposis coli. Neoangiogenesis and matrix metalloproteinase activity is promoted by GPR35 via Na/K-ATPase-dependent ion pumping and Src activation, and is selectively inhibited by a GPR35-specific pepducin. Supernatants from human inducible-pluripotent-stem-cell derived macrophages carrying the UC and PSC risk variant stimulate tube formation by enhancing the release of angiogenic factors.

CONCLUSIONS

Activation of the GPR35 pathway promotes tumour growth via two separate routes, by directly augmenting proliferation in epithelial cells that express the receptor, and by coordinating macrophages' ability to create a tumour-permissive environment.

PSC associated inflammatory bowel disease: a distinct entity

INTRODUCTION

Primary sclerosing cholangitis (PSC) is a rare, chronic, and progressive cholestatic disease involving intra- and/or extrahepatic bile ducts. PSC in many patients results in end-stage liver diseases. Nearly 60% of the PSC patients suffer from concomitant inflammatory bowel diseases (IBDs). Classically, IBDs are divided into two principle types: Crohn's disease (CD) and ulcerative colitis (UC). However, with growing knowledge, PSC-associated IBD (PSC-IBD) seems to be a rather distinct entity with specific genetics, clinical, and microbiota characteristics.

AREAS COVERED

In this article, we aim to review the unique characteristics of PSC-IBD from clinical, genetic, and microbiota point of view.

EXPERT OPINION

PSC-IBD's unique characteristics contribute to the notion that it could be a distinct entity. Acknowledgment of PSC-IBD as a novel entity necessitates designing new clinical guidelines for diagnosis and developing novel therapies.

Genetic variants of UDP-glucuronosyltransferase 1A genes are associated with disease presentation and outcome in primary sclerosing cholangitis

BACKGROUND AND AIMS

Primary sclerosing cholangitis (PSC) is a progressive cholestatic liver disease without a curative medical therapy. The human UDP-glucuronosyltransferases 1A play a major role in the detoxification and elimination of bilirubin, bile acids and xenobiotics. Whether genetic UGT1A variants determine course and outcome of PSC has not yet been described.

METHODS

A large cohort of German PSC patients with a long-term-follow-up was genotyped for UGT1A variants including UGT1A1*28, UGT1A3-66 T>C and UGT1A7 p.N129K/p.R131K using TaqMan 5'-nuclease assays. Results were correlated with clinical characteristics and transplant-free survival.

RESULTS

About 331 patients with PSC were included in the study (69.9% male, mean age at diagnosis 32.6 years). Median transplant-free survival was 14.9 years. Patients with wild-type alleles of all three UGT1A genes had a longer transplant-free survival (17.2 vs. 14.4 years, P = .048) than patients carrying a homozygous or heterozygous SNP variant in at least one of the UGT1A1, UGT1A3 or UGT1A7 genes. Additionally, we found that patients carrying wild-type alleles of all three UGT1A genes had lower serum bilirubin (25 vs. 38 µmol/L, P = .02) and serum cholesterol (195 vs. 223 mg/dL), P = .035) at first presentation. Furthermore, inflammatory bowel disease was found to be associated with wild-type UGT1A alleles (82.2% vs. 68.4%, P = .046).

CONCLUSIONS

This large cohort shows an association with single nucleotide polymorphisms of the UGT1A1, UGT1A3 and UGT1A7 genes and outcome in PSC. Thus, UGT1A variants may represent a tool for the prognostic stratification of PSC patients and establish a link between disease progression and the regulation of detoxification by glucuronidation in PSC.

Fungi participate in the dysbiosis of gut microbiota in patients with primary sclerosing cholangitis

OBJECTIVE

Patients with primary sclerosing cholangitis (PSC) were previously shown to display a bacterial gut dysbiosis but fungal microbiota has never been examined in these patients. The aim of this study was to assess the fungal gut microbiota in patients with PSC.

DESIGN

We analysed the faecal microbiota of patients with PSC and concomitant IBD (n=27), patients with PSC and no IBD (n=22), patients with IBD and no PSC (n=33) and healthy subjects (n=30). Bacterial and fungal composition of the faecal microbiota was determined using 16S and ITS2 sequencing, respectively.

RESULTS

We found that patients with PSC harboured bacterial dysbiosis characterised by a decreased biodiversity, an altered composition and a decreased correlation network density. These alterations of the microbiota were associated with PSC, independently of IBD status. For the first time, we showed that patients with PSC displayed a fungal gut dysbiosis, characterised by a relative increase in biodiversity and an altered composition. Notably, we observed an increased proportion of Exophiala and a decreased proportion of Saccharomyces cerevisiae. Compared with patients with IBD and healthy subjects, the gut microbiota of patients with PSC exhibited a strong disruption in bacteria-fungi correlation network, suggesting an alteration in the interkingdom crosstalk.

CONCLUSION

This study demonstrates that bacteria and fungi contribute to gut dysbiosis in PSC.

Bile-Derived Organoids From Patients With Primary Sclerosing Cholangitis Recapitulate Their Inflammatory Immune Profile

Primary sclerosing cholangitis (PSC) is a heterogeneous and progressive fibroinflammatory cholangiopathy with no known etiology or effective treatment. Studies of PSC are limited due to difficulty in accessing the cholangiocyte, the small percentage of these cells in the liver, instability of in vitro culture systems, and reliance on samples from end-stage disease. Here, we demonstrate that stem cells can be isolated from the bile of PSC patients undergoing endoscopic retrograde cholangiopancreatography earlier in their clinical course and maintained long term in vitro as three-dimensional (3D) organoids that express a biliary genetic phenotype. Additionally, bile-derived organoids (BDOs) can be biobanked and samples obtained longitudinally over the course of the disease. These BDOs express known cholangiocyte markers including gamma glutamyl transferase, cytokeratin 19, epithelial cellular adhesion molecule, cystic fibrosis transmembrane conductance regulator, and anion exchanger 2. RNA sequence analysis identified 39 genes whose expression differed in organoids from PSC patients compared to non-PSC controls, including human leukocyte antigen DM alpha chain and chemokine (C-C motif) ligand 20 (CCL20), immune-related genes previously described in genome-wide association studies of PSC. Incubation of these BDOs with interleukin 17A or tumor necrosis factor alpha led to an immune-reactive phenotype with a significant increase in secretion of proinflammatory mediators, including CCL20, a T-cell chemoattractant. Conclusion: This study demonstrates that bile can be used as a source of biliary-like cells that can be maintained long term in vitro as 3D organoids; these BDOs retain features of cholangiopathies, including the ability to react to inflammatory stimuli by secreting chemokines and propagating an immune-reactive phenotype reflective of the pathogenesis of these diseases; thus, BDOs represent a platform for the study of the pathogenesis and therapy of cholangiopathies, particularly PSC.

Autoimmunity and Inflammation in CVID: a Possible Crosstalk between Immune Activation, Gut Microbiota, and Epigenetic Modifications

Common variable immunodeficiency (CVID) is the most common symptomatic primary immunodeficiency among adults and is characterized by a B cell dysfunction and increased risk of respiratory tract infections with encapsulated bacteria. However, a large proportion of patients also has inflammatory and autoimmune complications. It may seem like a paradox that immunodeficiency and inflammation/autoimmunity coexist within the same individuals. In this commentary, we propose that CVID immunopathogenesis involves an interplay of genes, environmental factors, and dysregulation of immune cells, where gut microbiota and gastrointestinal inflammation can both be important contributors or endpoints to the systemic immune activation seen in CVID, and where epigenetic mechanism may be the undiscovered link between these contributors. In our opinion, these pathways could represent novel targets for therapy in CVID directed against autoimmune and inflammatory manifestations that represent the most severe complications in these patients. Considering the heterogeneous nature of CVID, these mechanisms may not be present in all patients, and different complications may be triggered by different risk factors. CVID is really a variable disease and in the future there is clearly a need for a more personalized medicine based on both genotypic and phenotypic findings.

Inflammatory Bowel Disease and Primary Sclerosing Cholangitis: A Review of the Phenotype and Associated Specific Features

Primary sclerosing cholangitis (PSC) is a chronic, progressive cholestatic disease that is associated with inflammatory bowel disease (IBD) in approximately 70% of cases. Although the pathogenesis is still unknown for both diseases, there is increasing evidence to indicate that they share a common underlying predisposition. Herein, we review the epidemiology, diagnosis, disease pathogenesis, and specific clinical features of the PSC-IBD phenotype. Patients with PSC-IBD have a distinct IBD phenotype with an increased incidence of pancolitis, backwash ileitis, and rectal sparing. Despite often having extensive colonic involvement, these patients present with mild intestinal symptoms or are even asymptomatic, which can delay the diagnosis of IBD. Although the IBD phenotype has been well characterized in PSC patients, the natural history and disease behavior of PSC in PSC-IBD patients is less well defined. There is conflicting evidence regarding the course of IBD in PSC-IBD patients who receive liver transplantation and their risk of recurrent PSC. IBD may also be associated with an increased risk of cholangiocarcinoma in PSC patients. Overall, the PSC-IBD population has an increased risk of developing colorectal neoplasia compared to the conventional IBD population. Lifelong annual surveillance colonoscopy is currently recommended.

Emerging pharmacologic therapies for primary sclerosing cholangitis

PURPOSE OF REVIEW

The only currently approved treatment for primary sclerosing cholangitis (PSC) is liver transplantation, with a median time to transplant of 12-18 years after diagnosis. There are a number of emerging drugs that have the potential to meet this critically unmet need that will be summarized and discussed herein.

RECENT FINDINGS

Although the cause of PSC is unknown, there are a number of novel therapeutics under development. These drugs target presumed pathogenic mechanisms largely extrapolated from ex-vivo and in-vivo preclinical models, as well as translational observations.

SUMMARY

Future therapeutic strategies for PSC may include a multitude of complex pathogenic mechanisms encompassing pathways of immunomodulation, the microbiome and inflammation-related fibrosis.

Genetics of primary sclerosing cholangitis and pathophysiological implications

Primary sclerosing cholangitis (PSC) is a chronic disease leading to fibrotic scarring of the intrahepatic and extrahepatic bile ducts, causing considerable morbidity and mortality via the development of cholestatic liver cirrhosis, concurrent IBD and a high risk of bile duct cancer. Expectations have been high that genetic studies would determine key factors in PSC pathogenesis to support the development of effective medical therapies. Through the application of genome-wide association studies, a large number of disease susceptibility genes have been identified. The overall genetic architecture of PSC shares features with both autoimmune diseases and IBD. Strong human leukocyte antigen gene associations, along with several susceptibility genes that are critically involved in T-cell function, support the involvement of adaptive immune responses in disease pathogenesis, and position PSC as an autoimmune disease. In this Review, we survey the developments that have led to these gene discoveries. We also elaborate relevant interpretations of individual gene findings in the context of established disease models in PSC, and propose relevant translational research efforts to pursue novel insights.

Immunogenetics in primary sclerosing cholangitis

PURPOSE OF REVIEW

Primary sclerosing cholangitis (PSC) is a progressive biliary liver disorder strongly associated with inflammatory bowel disease (PSC-IBD). We summarize the genetics of PSC-IBD and highlight recent findings that further differentiate PSC-IBD as a unique disease.

RECENT FINDINGS

To date, genome-wide studies have uncovered 23 susceptibility loci for PSC-IBD, the majority of which have been previously reported as risk factors in other immune-mediated disorders. For most candidates, the pathological relationship to PSC-IBD remains largely unknown. Several candidate genes appear to be liver related but the large majority relate to immunity and reaffirm that alterations to immune function, trafficking, and tolerance are likely to influence susceptibility and presentation of PSC-IBD. Similar to most immune-mediated diseases, the strongest association in PSC-IBD resides within the human leukocyte antigen complex and suggests that disease-specific antigens drive pathogenic immune responses. Although genetic predisposition influences disease, genetic determinants account for less than 10% of total disease liability in PSC-IBD, clearly emphasizing the predominant role of environmental factors on disease susceptibility.

SUMMARY

Genetic studies define PSC-IBD as a unique disease to IBD mirroring clinical observations. Most risk loci harbour immune-related genes and disease variants are likely to perturb immune function, tolerance, and/or trafficking. Additional studies in patients and novel experimental systems are needed to identify the origin and impact of environmental factors in relation to genetic predisposition in PSC-IBD.

Opportunities and challenges of whole-genome and -exome sequencing

Recent advances in the development of sequencing technologies provide researchers with unprecedented possibilities for genetic analyses. In this review, we will discuss the history of genetic studies and the progress driven by next-generation sequencing (NGS), using complex inflammatory bowel diseases as an example. We focus on the opportunities, but also challenges that researchers are facing when working with NGS data to unravel the genetic causes underlying diseases.

Genetics in PSC: what do the "risk genes" teach us?

A role of genetics in primary sclerosing cholangitis (PSC) development is now firmly established. A total of 16 risk genes have been reported at highly robust ("genome-wide") significance levels, and ongoing efforts suggest that the list will ultimately be considerably longer. Importantly, this genetic risk pool so far accounts for less than 10 % of an estimated overall PSC susceptibility. The relative importance of genetic versus environmental factors (including gene-gene and gene-environment interactions) in remaining aspects of PSC pathogenesis is unknown, and other study designs than genome-wide association studies are needed to explore these aspects. For some of the loci, e.g. HLA and FUT2, distinct interacting environmental factors may exist, and working from the genetic associations may prove one valid path for determining the specific nature of environmental triggers. So far the biological implications for PSC risk genes are typically merely hypothesized based on previously published literature, and there is therefore a strong need for dedicated translational studies to determine their roles within the specific disease context of PSC. Apparently, most risk loci seem to involve in a subset of biological pathways for which genetic associations exist in a multitude of immune-mediated diseases, accounting for both inflammatory bowel disease as well as prototypical autoimmunity. In the present article, we will survey the current knowledge on PSC genetics with a particular emphasis on the pathophysiological insight potentially gained from genetic risk loci involving in this profound immunogenetic pleiotropy.

Colitis-associated colon cancer: Is it in your genes?

Colitis-associated colorectal cancer (CA-CRC) is the cause of death in 10%-15% of inflammatory bowel disease (IBD) patients. CA-CRC results from the accumulation of mutations in intestinal epithelial cells and progresses through a well-characterized inflammation to dysplasia to carcinoma sequence. Quantitative estimates of overall CA-CRC risks are highly variable ranging from 2% to 40% depending on IBD severity, duration and location, with IBD duration being the most significant risk factor associated with CA-CRC development. Recently, studies have identified IBD patients with similar patterns of colonic inflammation, but that differ with respect to CA-CRC development, suggesting a role for additional non-inflammatory risk factors in CA-CRC development. One suggestion is that select IBD patients carry polymorphisms in various low penetrance disease susceptibility genes, which pre-dispose them to CA-CRC development, although these loci have proven difficult to identify in human genome-wide association studies. Mouse models of CA-CRC have provided a viable alternative for the discovery, validation and study of individual genes in CA-CRC pathology. In this review, we summarize the current CA-CRC literature with a strong focus on genetic pre-disposition and highlight an emerging role for mouse models in the search for CA-CRC risk alleles.

Primary sclerosing cholangitis - the Norwegian experience

Research related to primary sclerosing cholangitis (PSC) has since 1980 been a major activity at the Oslo University Hospital Rikshospitalet. The purpose of this publication is to describe the development of this research, the impact of this research on the clinical handling of the patients, and finally to describe what we believe are the most urgent, remaining problems to be solved. During the early years, our research dealt primarily with clinical aspects of the disease. The concomitant inflammatory bowel disease (IBD) seen in most patients with PSC was a major interest and we also started looking into genetic associations of PSC. Prognosis, malignancy development and treatment with special emphasis on transplantation have later been dealt with. These activities has had impact on several aspects of PSC management; when and how to diagnose PSC and variant forms of PSC, how to handle IBD in PSC and how to deal with the increased rate of malignancy? The problems remaining to be solved are many. What is the role of the gut and the gut microbiota in the development of PSC? Do the PSC patients have an underlying disturbance in the bile homeostasis? And how does the characteristic type of fibrosis in PSC develop? The genetic studies have supported a role for the adaptive immune system in the disease development, but how should this be dealt with? Importantly, the development of malignancy in PSC is still not understood, and we lack appropriate medical treatment for our patients.

Genetics of liver disease: From pathophysiology to clinical practice

Paralleling the first 30 years of the Journal of Hepatology we have witnessed huge advances in our understanding of liver disease and physiology. Genetic advances have played no small part in that. Initial studies in the 1970s and 1980s identified the strong major histocompatibility complex associations in autoimmune liver diseases. During the 1990 s, developments in genomic technologies drove the identification of genes responsible for Mendelian liver diseases. Over the last decade, genome-wide association studies have allowed for the dissection of the genetic susceptibility to complex liver disorders, in which also environmental co-factors play important roles. Findings have allowed the identification and elaboration of pathophysiological processes, have indicated the need for reclassification of liver diseases and have already pointed to new disease treatments. In the immediate future genetics will allow further stratification of liver diseases and contribute to personalized medicine. Challenges exist with regard to clinical implementation of rapidly developing technologies and interpretation of the wealth of accumulating genetic data. The historical perspective of genetics in liver diseases illustrates the opportunities for future research and clinical care of our patients.

Distinctive inflammatory bowel disease phenotype in primary sclerosing cholangitis

AIM: To review the current literature for the specific clinical characteristics of inflammatory bowel disease (IBD) associated with primary sclerosing cholangitis (PSC).

METHODS: A systematical review for clinical characteristics of IBD in PSC was performed by conducting a broad search for “primary sclerosing cholangitis” in Pubmed. “Clinical characteristics” were specified into five predefined subthemes: epidemiology of IBD in PSC, characteristics of IBD in PSC (i.e., location, disease behavior), risk of colorectal cancer development, IBD recurrence and de novo disease after liver transplantation for PSC, and safety and complications after proctocolectomy with ileal pouch-anal anastomosis. Papers were selected for inclusion based on their relevance to the subthemes, and were reviewed by two independent reviewers. Only full papers relevant to PSC-IBD were included. Additionally the references of recent reviews for PSC (< 5 years old) were scrutinized for relevant articles.

RESULTS: Initial literature search for PSC yielded 4704 results. After careful review 65 papers, comprising a total of 11406 PSC-IBD patients, were selected and divided according to subtheme. Four manuscripts overlapped and were included in two subthemes. Prevalence of IBD in PSC shows a large variance, ranging from 46.5% to 98.7% with ulcerative colitis (UC) being the most common type (> 75%). The highest IBD rates in PSC are found in papers reviewing both endoscopic and histological data for IBD diagnosis. Although IBD in PSC is found to be a quiescent disease, pancolitis occurs often, with rates varying from 35% to 95%. Both backwash ileitis and rectal sparing are observed infrequently. The development of dysplasia or colorectal carcinoma is increased in PSC-IBD; the cumulative 10 years risk varying between 0% and 11%. Exacerbation of IBD is common after liver transplantation for PSC and de novo disease is seen in 1.3% to 31.3% of PSC-IBD patients. The risk for development of pouchitis in PSC-IBD is found to be significant, affecting 13.8% to 90% of the patients after proctocolectomy with ileo anal-pouch anastomosis.

CONCLUSION: IBD in primary sclerosing cholangitis represents a distinct phenotype that differs from UC and Crohn’s disease and therefore requires specialized management.

Gain of Function Mutations of PIK3CD as a Cause of Primary Sclerosing Cholangitis

Gain of function (GOF) mutation in the p110δ catalytic subunit of the phosphatidylinositol-3-OH kinase (PIK3CD) is the cause of a primary immunodeficiency (PID) characterized by recurrent sinopulmonary infections and lymphoproliferation. We describe a family of two adults and three children with GOF mutation in PIK3CD, all with recurrent sinopulmonary infections and varied infectious and non-infectious complications. The two adults have Primary Sclerosing Cholangitis (PSC) without evidence of Cryptosporidium parvum infection and have required liver transplantation. PSC is a novel phenotype of GOF mutation in PIK3CD.

Hepatobiliary manifestations of inflammatory bowel disease

Patients with inflammatory bowel diseases (IBDs) may present with several hepatic abnormalities. Some of these liver diseases are benign and only require observation, whereas others may cause liver failure and require liver transplantation. The aim of this review was to present and summarize the latest evidence on the most common liver diseases seen in patients with IBD. These manifestations can be divided in to 3 groups: those that are seen in association with IBD, those that are due to metabolic and physiologic changes induced by the IBD and those that are secondary to the drugs used in the treatment of IBD. Primary sclerosing cholangitis is one of the most common hepatobiliary manifestations of IBD that is more prevalent in patients with ulcerative colitis. There is no approved medical treatment for primary sclerosing cholangitis and about 50% of patients will require liver transplantation within 10 to 15 years from the time of diagnosis. Among the drugs that are commonly used in the treatment of IBD, thiopurines and methotrexate impose the higher risk of hepatotoxicity. In most cases, dose adjustment and avoidance of hepatotoxins will normalize the liver tests and discontinuation of the drug is required in a minority of cases. Reactivation of hepatitis B virus during immunosuppressive therapy is a major concern and adequate screening and vaccination is warranted. The approach to a patient with IBD who presents with abnormal liver chemistries can be challenging not only because 2 or more conditions can co-exist but also because management must be individualized.