Genetics in biliary atresia

Impact of gallbladder hypoplasia on hilar hepatic ducts in biliary atresia

BACKGROUND

Biliary atresia (BA) is an intractable disease of unknown cause that develops in the neonatal period. It causes jaundice and liver damage due to the destruction of extrahepatic biliary tracts,. We have found that heterozygous knockout mice of the SRY related HMG-box 17 (Sox17) gene, a master regulator of stem/progenitor cells in the gallbladder wall, exhibit a condition like BA. However, the precise contribution of hypoplastic gallbladder wall to the pathogenesis of hepatobiliary disease in Sox17 heterozygous embryos and human BA remains unclear.

METHODS

We employed cholangiography and histological analyses in the mouse BA model. Furthermore, we conducted a retrospective analysis of human BA.

RESULTS

We show that gallbladder wall hypoplasia causes abnormal multiple connections between the hilar hepatic bile ducts and the gallbladder-cystic duct in Sox17 heterozygous embryos. These multiple hilar extrahepatic ducts fuse with the developing intrahepatic duct walls and pull them out of the liver parenchyma, resulting in abnormal intrahepatic duct network and severe cholestasis. In human BA with gallbladder wall hypoplasia (i.e., abnormally reduced expression of SOX17), we also identify a strong association between reduced gallbladder width (a morphometric parameter indicating gallbladder wall hypoplasia) and severe liver injury at the time of the Kasai surgery, like the Sox17-mutant mouse model.

CONCLUSIONS

Together with the close correlation between gallbladder wall hypoplasia and liver damage in both mouse and human cases, these findings provide an insight into the critical role of SOX17-positive gallbladder walls in establishing functional bile duct networks in the hepatic hilus of neonates.

Progress in Biomarkers Related to Biliary Atresia

Biliary atresia (BA) is a congenital cholestatic disease that can seriously damage children's liver function. It is one of the main reasons for liver transplantation in children. Early diagnosis of BA is crucial to the prognosis of patients, but there is still a lack of reliable non-invasive diagnostic methods. Additionally, as some children are in urgent need of liver transplantation, evaluating the stage of liver fibrosis and postoperative native liver survival in children with BA using a straightforward, efficient, and less traumatic method is a major focus of doctors. In recent years, an increasing number of BA-related biomarkers have been identified and have shown great potential in the following three aspects of clinical practice: diagnosis, evaluation of the stage of liver fibrosis, and prediction of native liver survival. This review focuses on the pathophysiological function and clinical application of three novel BA-related biomarkers, namely MMP-7, FGF-19, and M2BPGi. Furthermore, progress in well-known biomarkers of BA such as gamma-glutamyltransferase, circulating cytokines, and other potential biomarkers is discussed, aiming to provide a reference for clinical practice.

Role of the circular RNA regulatory network in the pathogenesis of biliary atresia

Circular RNAs (circRNAs) serve an essential role in the occurrence and development of cholangiocarcinoma, but the expression and function of circRNA in biliary atresia (BA) is not clear. In the present study, circRNA expression profiles were investigated in the liver tissues of patients with BA as well as in the choledochal cyst (CC) tissues of control patients using RNA sequencing. A total of 78 differentially expressed circRNAs (DECs) were identified between the BA and CC tissues. The expression levels of eight circRNAs (hsa_circ_0006137, hsa_circ_0079422, hsa_circ_0007375, hsa_circ_0005597, hsa_circ_0006961, hsa_circ_0081171, hsa_circ_0084665 and hsa_circ_0075828) in the liver tissues of the BA group and control group were measured using reverse transcription-quantitative polymerase chain reaction. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis demonstrated that the identified DECs are involved in a variety of biological processes, including apoptosis and metabolism. In addition, based on the GO and KEGG pathway enrichment analyses, it was revealed that target genes that can be affected by circRNAs regulatory network were enriched in the TGF-β signaling pathway, EGFR tyrosine kinase inhibitor resistance pathway and transcription factor regulation pathway as well as other pathways that may be associated with the pathogenesis of BA. The present study revealed that circRNAs are potentially implicated in the pathogenesis of BA and could help to find promising targets and biomarkers for BA.

Novel NIR-II fluorescent probes for biliary atresia imaging

Biliary atresia is a rare infant disease that predisposes patients to liver transplantation and death if not treated in time. However, early diagnosis is challenging because the clinical manifestations and laboratory tests of biliary atresia overlap with other cholestatic diseases. Therefore, it is very important to develop a simple, safe and reliable method for the early diagnosis of biliary atresia. Herein, a novel NIR-II fluorescence probe, HZL2, with high quantum yield, excellent biocompatibility, low cytotoxicity and rapid excretion through the liver and gallbladder was developed based on the oil/water partition coefficient and permeability. A simple fecal sample after injection of HZL2 can be used to efficiently identify the success of the mouse model of biliary atresia for the first time, allowing for an early diagnosis of the disease. This study not only developed a simple and safe method for the early diagnosis of biliary atresia with great potential in clinical translation but also provides a research tool for the development of pathogenesis and therapeutic medicines for biliary atresia.

Immune-mediated cholangiopathies in children: the need to better understand the pathophysiology for finding the future possible treatment targets

Cholangiopathies are defined as focal or extensive damage of the bile ducts. According to the pathogenetic mechanism, it may be immune-mediated or due to genetic, infectious, toxic, vascular, and obstructive causes. Their chronic evolution is characterized by inflammation, obstruction of bile flow, cholangiocyte proliferation, and progression toward fibrosis and cirrhosis. Immune-mediated cholangiopathies comprise primary sclerosing cholangitis (PSC), autoimmune cholangitis and IgG4-associated cholangitis in adults and biliary atresia (BA), neonatal sclerosing cholangitis (NSC) in children. The main purpose of this narrative review was to highlight the similarities and differences among immune-mediated cholangiopathies, especially those frequent in children in which cholangiocyte senescence plays a key role (BA, NSC, and PSC). These three entities have many similarities in terms of clinical and histopathological manifestations, and the distinction between them can be hard to achieve. In BA, bile duct destruction occurs due to aggression of the biliary cells due to viral infections or toxins during the intrauterine period or immediately after birth. The consequence is the activation of the immune system leading to severe inflammation and fibrosis of the extrahepatic biliary tract, lumen stenosis, and impairment of the biliary flow. PSC is characterized by inflammation and fibrosis of intra- and extrahepatic bile ducts, leading to secondary biliary cirrhosis. It is a multifactorial disease that occurs because of genetic predisposition [human leukocyte antigen (HLA) and non-HLA haplotypes], autoimmunity (cellular immune response, autoantibodies, association with inflammatory bowel disease), environmental factors (infections or toxic bile), and host factors (intestinal microbiota). NSC seems to be a distinct subgroup of childhood PSC that appears due to the interaction between genetic predisposition (HLA B8 and DR3) and the disruption of the immune system, validated by elevated IgG levels or specific antibodies [antinuclear antibody (ANA), anti-smooth muscle antibody (ASMA)]. Currently, the exact mechanism of immune cholangiopathy is not fully understood, and further data are required to identify individuals at high risk of developing these conditions. A better understanding of the immune mechanisms and pathophysiology of BA, NSC, and PSC will open new perspectives for future treatments and better methods of preventing severe evolution.

Biliary atresia and liver transplantation in the United States: A contemporary analysis

BACKGROUND

Biliary atresia (BA) remains the number one indication for paediatric liver transplantation (LT) worldwide but is an uncommon indication for older LT recipients. The impact of recent donor allocation changes, pervasive organ shortage and evolving LT practices on the BA LT population is unknown.

METHODS

We identified patients who underwent LT between January 2010 and December 2021 using the UNOS database. We compared clinical outcomes between patients with BA and those with non-BA cholestatic liver disease. Groups were stratified by age, <12 years (allocated via PELD system) and ≥12 years (allocated via MELD system). Waitlist outcomes were compared using competing-risk regression analysis, graft survival rates were compared using Kaplan-Meier time-to-event analysis and Cox proportional hazards modelling provided adjusted estimates.

RESULTS

There were 2754 BA LT waitlist additions and 2206 BA LTs (1937 <12 years [younger], 269 ≥12 years [older]). There were no differences in waitlist mortality between BA and non-BA cholestatic patients. Among BA LT recipients, there were 441 (20.0%) living-donor liver transplantations (LDLT) and 611 (27.7%) split deceased-donor LTs. Five-year graft survival was significantly higher among BA versus non-BA cholestatic patients in the older group (88.3% vs. 79.5%, p < .01) but not younger group (89.3% vs. 89.5%). Among BA LT recipients, improved graft outcomes were associated with LDLT (vs. split LT: HR: 2, 95% CI: 1.03-3.91) and higher transplant volume (volume >100 vs. <40 BA LTs: HR: 3.41, 95% CI: 1.87-6.2).

CONCLUSION

Liver transplant outcomes among BA patients are excellent, with LDLT and higher transplant centre volume associated with optimal graft outcomes.

Genetic Contributions to Biliary Atresia: A Developmental Cholangiopathy

Biliary atresia (BA) is the most prevalent serious liver disease of infancy and childhood, and the principal indication for liver transplantation in pediatrics. BA is best considered as an idiopathic panbiliary cholangiopathy characterized by obstruction of bile flow and consequent cholestasis presenting during fetal and perinatal periods. While several etiologies have been proposed, each has significant drawbacks that have limited understanding of disease progression and the development of effective treatments. Recently, modern genetic analyses have uncovered gene variants contributing to BA, thereby shifting the paradigm for explaining the BA phenotype from an acquired etiology (e.g., virus, toxin) to one that results from genetically altered cholangiocyte development and function. Herein we review recently reported genetic contributions to BA, highlighting the enhanced representation of variants in biological pathways involving ciliary function, cytoskeletal structure, and inflammation. Finally, we blend these findings as a new framework for understanding the resultant BA phenotype as a developmental cholangiopathy.

COL3A1, CXCL8, VCAN, THBS2, and COL1A2 are correlated with the onset of biliary atresia

BACKGROUND

Biliary atresia (BA) is a devastating progressive fibro inflammatory disorder in infants. The exact etiology of BA is still unclear. This study aimed screen key genes potentially associated with the occurrence of BA.

METHODS

All BA data was obtained from GSE46960 dataset. The limma package in R language was used for differentially expressed gene (DEG) analyses. gene ontology and Kyoto encyclopedia of genes and genomes enrichment analysis were performed on the screened DEGs, using "clusterProfiler" package. protein-protein interaction network was built based on STRING Cytoscape software (Bethesda, Rockville, MD). The logistic regression model was constructed based on the selected DEGs.

RESULTS

There were totally 78 DEGs in BA samples compared with normal samples, which were significantly enriched in 200 biological process terms, 37 molecular function terms, 17 cellular component terms, and 18 Kyoto encyclopedia of genes and genomes pathways. Among which, the top 10 genes with the highest importance in protein-protein interaction network were selected. Subsequently, on the basis of the stepwise regression method and 5-fold cross-validation, the logistic regression model constructed based on COL3A1, CXCL8, VCAN, THBS2, and COL1A2 was finally evidenced to predict the BA sample relatively reliably.

CONCLUSIONS

In conclusion, COL3A1, CXCL8, VCAN, THBS2, and COL1A2 are potentially crucial genes in BA. The logistic regression model constructed based on them could predict the BA sample relatively reliably.

Omphalocele and biliary atresia: chance or causality. A case report

To relate omphalocele and biliary atresia and investigate possible embryological correlations that justify the simultaneous occurrence. A female preterm newborn diagnosed as omphalocele; cesarean delivery, weight 2,500g, 46 XX karyotype. Initially, the newborn remained fasting and on parenteral nutrition, and enteral diet was introduced later, with good acceptance. On the 12^th day of life, the newborn presented direct hyperbilirubinemia, increased levels of liver enzymes and fecal acholia, with a presumptive diagnosis of biliary atresia. However, the ultrasound was inconclusive, due to anatomical changes resulting from omphalocele. A surgical approach was chosen on the 37^th day of life aiming to confirm diagnosis of biliary atresia and to repair omphalocele. During the surgical procedure, structural alterations compatible with biliary atresia were observed, later confirmed by pathological examination; a hepatoportoenterostomy was performed and the omphalocele was corrected. She evolved well in the postoperative period, with a decrease in direct bilirubin and liver enzymes, as well as resolution of fecal acholia, and was discharged in good clinical condition. This is a bizarre and extremely rare association, but the prognosis may be good when an early diagnosis is made and surgery performed, besides support and clinical management to prevent complications in the perioperative period. Although the pathogenesis of the diseases has not been fully defined yet, there is, to date, no direct relation between them. The association between omphalocele and biliary atresia is extremely uncommon, with only two published cases.

Liver secretin receptor predicts portoenterostomy outcomes and liver injury in biliary atresia

Biliary atresia (BA) is a chronic neonatal cholangiopathy characterized by fibroinflammatory bile duct damage. Reliable biomarkers for predicting native liver survival (NLS) following portoenterostomy (PE) surgery are lacking. Herein we explore the utility of 22 preidentified profibrotic molecules closely connected to ductular reaction (DR) and prevailing after successful PE (SPE), in predicting PE outcomes and liver injury. We used qPCR and immunohistochemistry in a BA cohort including liver samples obtained at PE (n = 53) and during postoperative follow-up after SPE (n = 25). Of the 13 genes over-expressed in relation to cholestatic age-matched controls at PE, only secretin receptor (SCTR) expression predicted cumulative 5-year NLS and clearance of jaundice. Patients in the highest SCTR expression tertile showed 34-55% lower NLS than other groups at 1-5 years after PE (P = 0.006-0.04 for each year). SCTR expression was also significantly lower [42 (24-63) vs 75 (39-107) fold, P = 0.015] among those who normalized their serum bilirubin after PE. Liver SCTR expression localized in cholangiocytes and correlated positively with liver fibrosis, DR, and transcriptional markers of fibrosis (ACTA2) and cholangiocytes (KRT7, KRT19) both at PE and after SPE. SCTR is a promising prognostic marker for PE outcomes and associates with liver injury in BA.

Biliary Atresia - emerging diagnostic and therapy opportunities

Biliary Atresia is a devastating pediatric cholangiopathy affecting the bile ducts of the liver. In this review, we describe recent progress in the understanding of liver development with a focus on cholangiocyte differentiation and how use of technical platforms, including rodent, zebrafish and organoid models, advances our understanding of Biliary Atresia. This is followed by a description of potential pathomechanisms, such as autoimmune responses, inflammation, disturbed apical-basal cell polarity, primary cilia dysfunction as well as beta-amyloid accumulation. Finally, we describe current and emerging diagnostic opportunities and recent translation breakthroughs for Biliary Atresia in the area of emerging therapy development, including immunomodulation and organoid-based systems for liver and bile duct repair.

Novel findings from family-based exome sequencing for children with biliary atresia

Biliary atresia (BA) is a progressive inflammation and fibrosis of the biliary tree characterized by the obstruction of bile flow, which results in liver failure, scarring and cirrhosis. This study aimed to explore the elusive aetiology of BA by conducting whole exome sequencing for 41 children with BA and their parents (35 trios, including 1 family with 2 BA-diagnosed children and 5 child-mother cases). We exclusively identified and validated a total of 28 variants (17 X-linked, 6 de novo and 5 homozygous) in 25 candidate genes from our BA cohort. These variants were among the 10% most deleterious and had a low minor allele frequency against the employed databases: Kinh Vietnamese (KHV), GnomAD and 1000 Genome Project. Interestingly, AMER1, INVS and OCRL variants were found in unrelated probands and were first reported in a BA cohort. Liver specimens and blood samples showed identical variants, suggesting that somatic variants were unlikely to occur during morphogenesis. Consistent with earlier attempts, this study implicated genetic heterogeneity and non-Mendelian inheritance of BA.

RNA Splicing: A Versatile Regulatory Mechanism in Pediatric Liver Diseases

With the development of high-throughput sequencing technology, the posttranscriptional mechanism of alternative splicing is becoming better understood. From decades of studies, alternative splicing has been shown to occur in multiple tissues, including the brain, heart, testis, skeletal muscle, and liver. This regulatory mechanism plays an important role in physiological functions in most liver diseases. Currently, due to the absence of symptoms, chronic pediatric liver diseases have a significant impact on public health. Furthermore, the progression of the disease is accelerated in children, leading to severe damage to their liver tissue if no precautions are taken. To this end, this review article summarizes the current knowledge of alternative splicing in pediatric liver diseases, paying special attention to liver damage in the child stage. The discussion of the regulatory role of splicing in liver diseases and its potential as a new therapeutic target is also included.

Identification of a wide spectrum of ciliary gene mutations in nonsyndromic biliary atresia patients implicates ciliary dysfunction as a novel disease mechanism

Background

Biliary atresia (BA) is the most common obstructive cholangiopathy in neonates, often progressing to end-stage cirrhosis. BA pathogenesis is believed to be multifactorial, but the genetic contribution, especially for nonsyndromic BA (common form: > 85%) remains poorly defined.

Methods

We conducted whole exome sequencing on 89 nonsyndromic BA trios to identify rare variants contributing to BA etiology. Functional evaluation using patients’ liver biopsies, human cell and zebrafish models were performed. Clinical impact on respiratory system was assessed with clinical evaluation, nasal nitric oxide (nNO), high speed video analysis and transmission electron microscopy.

Findings

We detected rare, deleterious de novo or biallelic variants in liver-expressed ciliary genes in 31.5% (28/89) of the BA patients. Burden test revealed 2.6-fold (odds ratio (OR) [95% confidence intervals (CI)]= 2.58 [1.15–6.07], adjusted p = 0.034) over-representation of rare, deleterious mutations in liver-expressed ciliary gene set in patients compared to controls. Functional analyses further demonstrated absence of cilia in the BA livers with KIF3B and TTC17 mutations, and knockdown of PCNT, KIF3B and TTC17 in human control fibroblasts and cholangiocytes resulted in reduced number of cilia. Additionally, CRISPR/Cas9-engineered zebrafish knockouts of KIF3B, PCNT and TTC17 displayed reduced biliary flow. Abnormally low level of nNO was detected in 80% (8/10) of BA patients carrying deleterious ciliary mutations, implicating the intrinsic ciliary defects.

Interpretation

Our findings support strong genetic susceptibility for nonsyndromic BA. Ciliary gene mutations leading to cholangiocyte cilia malformation and dysfunction could be a key biological mechanism in BA pathogenesis.

Funding

The study is supported by General Research Fund, HMRF Commissioned Paediatric Research at HKCH and Li Ka Shing Faculty of Medicine Enhanced New Staff Start-up Fund.

Biopsy-proven liver cirrhosis in young children: A 10-year cohort study

Young children with liver cirrhosis have a significantly high risk of mortality. However, there are few studies regarding early childhood-onset cirrhosis. This study aims to explore the causes, clinical findings and prognosis of biopsy-proven cirrhosis in infants, toddlers and preschoolers. We enroled young children with biopsy-proven cirrhosis from January 2010. Till January 2020, the study has been going on for 10 years. A total of 139 cirrhotic children were enrolled, including 87 boys and 52 girls. The median age at initially histological diagnosis of cirrhosis was 2 years old (range: 1 month-6 years). Sixty-two patients reported yellowish discoloration of sclera and/or skin as an initial symptom. Ninety-three patients had definite aetiologies while 46 had indeterminate causes. Among the confirmed cases, 31 had hepatitis B virus (HBV) infection, accounting for 33.3%. Subsequently, glycogen storage disease was diagnosed in 16 cases and Wilson disease in 14 cases. In these patients with HBV infection, nine finally achieved hepatitis B surface antigen (HBsAg) loss (29.0%) after effective antiviral therapy during the follow-up. Logistic regression revealed that baseline alanine aminotransferase (odds ratio 1.008, p = 0.028) was the independent predictor of HBsAg loss. Furthermore, one patient who underwent second biopsies showed histological reverse. HBV infection is an important cause of paediatric cirrhosis in our study. The pathogenesis of HBV-related cirrhosis in early childhood deserves further studies.

Down-regulation of STAT3 enhanced chemokine expression and neutrophil recruitment in biliary atresia

Biliary atresia (BA) is an immune-related disorder and signal transducer and activator of transcription 3 (STAT3) is a key signalling molecule in inflammation. The present study was designed to clarify the function of STAT3 in BA. STAT3 expression was examined in patients and a mouse BA model in which STAT3 levels were further altered with a specific inhibitor or activator. Neutrophil accumulation and the levels of the neutrophil chemoattractants (C-X-C motif) ligand 1 (CXCL1) and IL-8 were determined. The effects of STAT3 inhibition on IL-8 expression were examined in human biliary epithelial cell (BEC) cultures. Functional changes in liver STAT3+ neutrophils in the mouse model were analysed with 10× single cell RNA-seq methods. Results showed STAT3 and p-STAT3 expression was reduced in BA liver tissue compared with control samples. Administration of a STAT3 inhibitor increased jaundice and mortality and reduced body weight in BA mice. In contrast, the STAT3 activator ameliorated BA symptoms. Extensive neutrophil accumulation together with CXCL1 up-regulation, both of which were suppressed by an anti-CXCL1 antibody, were observed in the STAT3 inhibitor-treated group. Recombinant IL-8 administration increased disease severity in BA mice, and the STAT3 activator had the reverse effect. Inhibiting STAT3 increased apoptosis of human BECs together with up-regulated IL-8 expression. RNA-seq analysis revealed reduced the numbers of STAT3 expressing neutrophil in BA which was accompanied by marked enhanced interferon-related antiviral activities. In conclusion, STAT3 reduction, enhanced IL-8 and CXCL1 expression and promoted the accumulation of interferon-responsive neutrophils resulting in BEC damage in BA.

Beta-amyloid deposition around hepatic bile ducts is a novel pathobiological and diagnostic feature of biliary atresia

BACKGROUND AND AIMS

Biliary atresia (BA) is a poorly understood and devastating obstructive bile duct disease of newborns. It is often diagnosed late, is incurable and frequently requires liver transplantation. In this study, we aimed to investigate the underlying pathogenesis and molecular signatures associated with BA.

METHODS

We combined organoid and transcriptomic analysis to gain new insights into BA pathobiology using patient samples and a mouse model of BA.

RESULTS

Liver organoids derived from patients with BA and a rhesus rotavirus A-infected mouse model of BA, exhibited aberrant morphology and disturbed apical-basal organization. Transcriptomic analysis of BA organoids revealed a shift from cholangiocyte to hepatocyte transcriptional signatures and altered beta-amyloid-related gene expression. Beta-amyloid accumulation was observed around the bile ducts in BA livers and exposure to beta-amyloid induced the aberrant morphology in control organoids.

CONCLUSION

The novel observation that beta-amyloid accumulates around bile ducts in the livers of patients with BA has important pathobiological implications, as well as diagnostic potential.

LAY SUMMARY

Biliary atresia is a poorly understood and devastating obstructive bile duct disease of newborns. It is often diagnosed late, is incurable and frequently requires liver transplantation. Using human and mouse 'liver mini-organs in the dish', we unexpectedly identified beta-amyloid deposition - the main pathological feature of Alzheimer's disease and cerebral amyloid angiopathy - around bile ducts in livers from patients with biliary atresia. This finding reveals a novel pathogenic mechanism that could have important diagnostic and therapeutic implications.

Recent developments in etiology and disease modeling of biliary atresia: a narrative review

Biliary atresia (BA) is a rare but severe fibroinflammatory disease of the extrahepatic and the intrahepatic bile ducts. Without prompt interventions, BA has fatal outcomes and is the most common indicator for pediatric liver transplantation (LTx). While the mainstay of treatment involves surgically correcting the extrahepatic biliary obstruction via Kasai hepato-portoenterostomy (KHPE), activation of a multitude of biological pathways and yet-to-be-determined etiology in BA continue to foster liver inflammation, cirrhosis and need for LTx. However, important caveats still exist in our understandings of the biliary pathophysiology, the rapidity of liver fibrosis and progression to liver failure, largely due to limited knowledge of the triggers of biliary injury and the inability to accurately model human BA. Although inconclusive, a large body of existing literature points to a potential viral infection in the early peri- or postnatal period as triggers of epithelial injury that perpetuates the downstream biliary disease. Further confounding this issue, are the lack of in-vivo and in-vitro models to efficiently recapitulate the cardinal features of BA, primarily liver fibrosis. To overcome these barriers in BA research, new directions in recent years have enabled (I) identification of additional triggers of biliary injury linked mostly to environmental toxins, (II) development of models to investigate liver fibrogenesis, and (III) translational research using patient-derived organoids. Here, we discuss recent advances that undoubtedly will stimulate future efforts investigating these new and exciting avenues towards mechanistic and drug discovery efforts and disease-preventive measures. The implications of these emerging scientific investigations and disease modeling in severe fibrosing cholangiopathies like BA are enormous and contribute substantially in our understandings of this rare but deadly disease. These findings are also expected to facilitate expeditious identification of translationally targetable pathways and bring us one step closer in treating an infant with BA, a population highly vulnerable to life-long liver related complications.

Genetic aspects of biliary atresia etiology

Biliary atresia (BA) is a cholestatic disorder of infancy that is fatal if untreated. Despite years of study the etiology of BA remains unknown. Three etiopathogenic mechanisms may be involved, such as immune dysregulation, environmental factors and genetic susceptibility. Genetic predisposition is being actively studied. Candidate genes associated with BA in certain populations, genes affecting the cholangiocyte cilia function, as well as genes involved in stress responses have been identified. However, the long-term follow-up of twins with BA suggests that genotype is not of paramount importance for the disease development. Both epigenetic patterns and postzygotic somatic mutations may contribute to etiology of the disease. Recently, some evidence is being accumulated on the possible genetic predisposition to certain outcome of Kasai portoenterostomy performed in patients with BA. However, the presence of a number of factors contributing to the development of the disease makes it difficult to identify the genetic markers.

Gallbladder wall abnormality in biliary atresia of mouse Sox17+/- neonates and human infants

Biliary atresia (BA) is characterized by the inflammation and obstruction of the extrahepatic bile ducts (EHBDs) in newborn infants. SOX17 is a master regulator of fetal EHBD formation. In mouse Sox17+/- BA models, SOX17 reduction causes cell-autonomous epithelial shedding together with the ectopic appearance of SOX9-positive cystic duct-like epithelia in the gallbladder walls, resulting in BA-like symptoms during the perinatal period. However, the similarities with human BA gallbladders are still unclear. In the present study, we conducted phenotypic analysis of Sox17+/- BA neonate mice, in order to compare with the gallbladder wall phenotype of human BA infants. The most characteristic phenotype of the Sox17+/- BA gallbladders is the ectopic appearance of SOX9-positive peribiliary glands (PBGs), so-called pseudopyloric glands (PPGs). Next, we examined SOX17/SOX9 expression profiles of human gallbladders in 13 BA infants. Among them, five BA cases showed a loss or drastic reduction of SOX17-positive signals throughout the whole region of gallbladder epithelia (SOX17-low group). Even in the remaining eight gallbladders (SOX17-high group), the epithelial cells near the decidual sites were frequently reduced in the SOX17-positive signal intensity. Most interestingly, the most characteristic phenotype of human BA gallbladders is the increased density of PBG/PPG-like glands in the gallbladder body, especially near the epithelial decidual site, indicating that PBG/PPG formation is a common phenotype between human BA and mouse Sox17+/- BA gallbladders. These findings provide the first evidence of the potential contribution of SOX17 reduction and PBG/PPG formation to the early pathogenesis of human BA gallbladders.This article has an associated First Person interview with the joint first authors of the paper.

TGF-β Signaling Plays a Pivotal Role During Developmental Biliary Atresia in Sea Lamprey (Petromyzon marinus)

Biliary atresia (BA) is a rare neonatal disease with unknown causes. Approximately 10% of BA cases develop in utero with other congenital defects that span a large spectrum of disease variations, including degeneration of the gall bladder and bile duct as well as malformation of the liver, intestines, and kidneys. Similar developmental alterations are manifested in a unique animal model, the sea lamprey (Petromyzon marinus), in which BA occurs naturally during metamorphosis. With the likelihood of conserved developmental mechanisms underlying organogenesis and degeneration, lamprey developmental BA may be a useful model to infer mechanisms underlying human embryonic BA. We reasoned that hepatobiliary transcriptomes regulate the transition between landmark stages of BA. Therefore, we examined sea lamprey hepatobiliary transcriptomes at four stages (M0, metamorphic stage 0 or larval stage, no BA; M2, metamorphic stage 2, onset of BA; M5, metamorphic stage 5, BA, and heightened hepatocyte proliferation and reorganization; and JV, juvenile, completion of BA) using messenger RNA sequencing and Kyoto Encyclopedia of Genes and Genomes pathway analyses. We found gene-expression patterns associated with the transition between these stages. In particular, transforming growth factor β (TGF-β), hedgehog, phosphatidylinositol-4,5-bisphosphate 3-kinase-Akt, Wnt, and mitogen-activated protein kinase pathways were involved during biliary degeneration. Furthermore, disrupting the TGF-β signaling pathway with antagonist or small interfering RNA treatments at the onset of BA delayed gall bladder and bile duct degeneration. Conclusion: Distinctive gene-expression patterns are associated with the degeneration of the biliary system during developmental BA. In addition, disrupting TGF-β signaling pathway at the onset of BA delayed biliary degeneration.