Cholangiocyte cilia are abnormal in syndromic and non-syndromic biliary atresia

Kidney ischemia/reperfusion injury causes cholangiocytes primary cilia disruption and abnormal bile secretion

BACKGROUND

Acute kidney injury (AKI) causes distant liver injury, to date, which causes poor outcomes of patients with AKI. Many studies have been performed to overcome AKI-associated liver injury. However, those studies have mainly focused on hepatocytes, and AKI-induced liver injury still remains a clinical problem. Here, we investigated the implication of cholangiocytes and their primary cilia which are critical in final bile secretion. Cholangiocyte, a lining cell of bile ducts, are the only liver epithelial cell containing primary cilium (a microtubule-based cell surface signal-sensing organelle).

METHODS

Cystathione γ-lyase (CSE, a transsulfuration enzyme) deficient and wild-type mice were subjected to kidney ischemia followed by reperfusion (KIR). Some mice were administered with N-acetyl-cysteine (NAC).

RESULTS

KIR damaged hepatocytes and cholagiocytes, disrupted cholangiocytes primary cilia, released the disrupted ciliary fragments into the bile, and caused abnormal bile secretion. Glutathione (GSH) and H2S levels in the livers were significantly reduced by KIR, resulting in increased the ratio oxidized GSH to total GSH, and oxidation of tissue and bile. CSE and cystathione β-synthase (CBS) expression were lowered in the liver after KIR. NAC administration increased total GSH and H2S levels in the liver and attenuated KIR-induced liver injuries. In contrast, Cse deletion caused the reduction of total GSH levels and worsened KIR-induced liver injuries, including primary cilia damage and abnormal bile secretion.

CONCLUSIONS

These results indicate that KIR causes cholangiocyte damage, cholangiocytes primary cilia disruption, and abnormal bile secretion through reduced antioxidative ability of the liver.

Biliary atresia

Biliary atresia (BA) is a progressive inflammatory fibrosclerosing disease of the biliary system and a major cause of neonatal cholestasis. It affects 1:5,000-20,000 live births, with the highest incidence in Asia. The pathogenesis is still unknown, but emerging research suggests a role for ciliary dysfunction, redox stress and hypoxia. The study of the underlying mechanisms can be conceptualized along the likely prenatal timing of an initial insult and the distinction between the injury and prenatal and postnatal responses to injury. Although still speculative, these emerging concepts, new diagnostic tools and early diagnosis might enable neoadjuvant therapy (possibly aimed at oxidative stress) before a Kasai portoenterostomy (KPE). This is particularly important, as timely KPE restores bile flow in only 50-75% of patients of whom many subsequently develop cholangitis, portal hypertension and progressive fibrosis; 60-75% of patients require liver transplantation by the age of 18 years. Early diagnosis, multidisciplinary management, centralization of surgery and optimized interventions for complications after KPE lead to better survival. Postoperative corticosteroid use has shown benefits, whereas the role of other adjuvant therapies remains to be evaluated. Continued research to better understand disease mechanisms is necessary to develop innovative treatments, including adjuvant therapies targeting the immune response, regenerative medicine approaches and new clinical tests to improve patient outcomes.

Pkd1l1-deficiency drives biliary atresia through ciliary dysfunction in biliary epithelial cells

BACKGROUND & AIMS

Syndromic biliary atresia is a cholangiopathy characterized by fibro-obliterative changes in the extrahepatic bile duct (EHBD) and congenital malformations including laterality defects. The etiology remains elusive and faithful animal models are lacking. Genetic syndromes provide important clues regarding the pathogenic mechanisms underlying the disease. We investigated the role of the gene Pkd1l1 in the pathophysiology of syndromic biliary atresia.

METHODS

Constitutive and conditional Pkd1l1 knockout mice were generated to explore genetic pathology as a cause of syndromic biliary atresia. We investigated congenital malformations, EHBD and liver pathology, EHBD gene expression, and biliary epithelial cell turnover. Biliary drainage was functionally assessed with cholangiography. Histology and serum chemistries were assessed after DDC (3,5-diethoxycarbony l-1,4-dihydrocollidine) diet treatment and inhibition of the ciliary signaling effector GLI1.

RESULTS

Pkd1l1-deficient mice exhibited congenital anomalies including malrotation and heterotaxy. Pkd1l1-deficient EHBDs were hypertrophic and fibrotic. Pkd1l1-deficient EHBDs were patent but displayed delayed biliary drainage. Pkd1l1-deficient livers exhibited ductular reaction and periportal fibrosis. After DDC treatment, Pkd1l1-deficient mice exhibited EHBD obstruction and advanced liver fibrosis. Pkd1l1-deficient mice had increased expression of fibrosis and extracellular matrix remodeling genes (Tgfα, Cdkn1a, Hb-egf, Fgfr3, Pdgfc, Mmp12, and Mmp15) and decreased expression of genes mediating ciliary signaling (Gli1, Gli2, Ptch1, and Ptch2). Primary cilia were reduced on biliary epithelial cells and altered expression of ciliogenesis genes occurred in Pkd1l1-deficient mice. Small molecule inhibition of the ciliary signaling effector GLI1 with Gant61 recapitulated Pkd1l1-deficiency.

CONCLUSIONS

Pkd1l1 loss causes both laterality defects and fibro-proliferative EHBD transformation through disrupted ciliary signaling, phenocopying syndromic biliary atresia. Pkd1l1-deficient mice function as an authentic genetic model for study of the pathogenesis of biliary atresia.

IMPACT AND IMPLICATIONS

The syndromic form of biliary atresia is characterized by fibro-obliteration of extrahepatic bile ducts and is often accompanied by laterality defects. The etiology is unknown, but Pkd1l1 was identified as a potential genetic candidate for syndromic biliary atresia. We found that loss of the ciliary gene Pkd1l1 contributes to hepatobiliary pathology in biliary atresia, exhibited by bile duct hypertrophy, reduced biliary drainage, and liver fibrosis in Pkd1l1-deficient mice. Pkd1l1-deficient mice serve as a genetic model of biliary atresia and reveal ciliopathy as an etiology of biliary atresia. This model will help scientists uncover new therapeutic approaches for patients with biliary atresia, while pediatric hepatologists should validate the diagnostic utility of PKD1L1 variants.

Biliary atresia: insights into mechanisms using a toxic model of the disease including Wnt and Hippo signaling pathways and microtubules

BACKGROUND

Mechanisms underlying bile duct injury in biliary atresia (BA) remain unclear and mechanisms of bile duct repair are unknown. This study aimed to explore the roles of microtubule instability and Wnt and Hippo signaling pathways in a biliatresone-induced BA model.

METHODS

Using primary murine neonatal cholangiocytes in both 2D and 3D cultures, and ex-vivo extra hepatic bile ducts (EHBD) which also has peri-cholangiocyte area, we analyzed injury and recovery processes. Injury was induced by the toxin biliatresone and recovery was induced by toxin wash-out.

RESULTS

Microtubule stabilizer paclitaxel prevented biliatresone-induced injury, both to cholangiocytes as well as reduced periductal αSMA stain, this process is mediated by decreased glutathione levels. RhoU and Wnt11 (Wnt signaling) and Pard6g and Amotl1 (Hippo signaling) are involved in both injury and recovery processes, with the latter acting upstream to Wnt signaling.

CONCLUSIONS

Early stages of biliatresone-induced EHBD injury in cholangiocytes and periductal structures are reversible. Wnt and Hippo signaling pathways play crucial roles in injury and recovery, providing insights into BA injury mechanisms and potential recovery avenues.

IMPACT

Microtubule stabilization prevents cholangiocyte injury and lumen obstruction in a toxic model of biliary atresia (biliatresone induced). Early stages of biliatresone-induced injury, affecting both cholangiocytes and periductal structures, are reversible. Both Wnt and Hippo signaling pathways play a crucial role in bile duct injury and recovery, with a noted interplay between the two. Understanding mechanisms of cholangiocyte recovery is imperative to unveil potential therapeutic avenues.

Primary cilia as a targetable node between biliary injury, senescence and regeneration in liver transplantation

BACKGROUND & AIMS

Biliary complications are a major cause of morbidity and mortality in liver transplantation. Up to 25% of patients that develop biliary complications require additional surgical procedures, re-transplantation or die in the absence of a suitable regraft. Here, we investigate the role of the primary cilium, a highly specialised sensory organelle, in biliary injury leading to post-transplant biliary complications.

METHODS

Human biopsies were used to study the structure and function of primary cilia in liver transplant recipients that develop biliary complications (n = 7) in comparison with recipients without biliary complications (n = 12). To study the biological effects of the primary cilia during transplantation, we generated murine models that recapitulate liver procurement and cold storage, and assessed the elimination of the primary cilia in biliary epithelial cells in the K19CreERTKif3afl/fl mouse model. To explore the molecular mechanisms responsible for the observed phenotypes we used in vitro models of ischemia, cellular senescence and primary cilia ablation. Finally, we used pharmacological and genetic approaches to target cellular senescence and the primary cilia, both in mouse models and discarded human donor livers.

RESULTS

Prolonged ischemic periods before transplantation result in ciliary shortening and cellular senescence, an irreversible cell cycle arrest that blocks regeneration. Our results indicate that primary cilia damage results in biliary injury and a loss of regenerative potential. Senescence negatively impacts primary cilia structure and triggers a negative feedback loop that further impairs regeneration. Finally, we explore how targeted interventions for cellular senescence and/or the stabilisation of the primary cilia improve biliary regeneration following ischemic injury.

CONCLUSIONS

Primary cilia play an essential role in biliary regeneration and we demonstrate that senolytics and cilia-stabilising treatments provide a potential therapeutic opportunity to reduce the rate of biliary complications and improve clinical outcomes in liver transplantation.

IMPACT AND IMPLICATIONS

Up to 25% of liver transplants result in biliary complications, leading to additional surgery, retransplants, or death. We found that the incidence of biliary complications is increased by damage to the primary cilium, an antenna that protrudes from the cell and is key to regeneration. Here, we show that treatments that preserve the primary cilia during the transplant process provide a potential solution to reduce the rates of biliary complications.

Biliary atresia: the development, pathological features, and classification of the bile duct

Biliary atresia is an occlusive biliary disease involving intrahepatic and extrahepatic bile ducts. Its etiology and pathogenesis are unclear. There are many manifestations of bile duct involvement in biliary atresia, but little is known about its occurrence and development. In addition, different classification methods have been proposed in different periods of biliary atresia, each with its advantages and disadvantages. The combined application of biliary atresia classification will help to improve the survival rate of patients with native liver. Therefore, this article reviews the development, pathological features, and classification of intrahepatic and extrahepatic bile ducts in biliary atresia, to provide a reference for the study of the pathogenesis and the choice of treatment methods.

Pediatric Cholestatic Diseases: Common and Unique Pathogenic Mechanisms

Cholestasis is the predominate feature of many pediatric hepatobiliary diseases. The physiologic flow of bile requires multiple complex processes working in concert. Bile acid (BA) synthesis and excretion, the formation and flow of bile, and the enterohepatic reuptake of BAs all function to maintain the circulation of BAs, a key molecule in lipid digestion, metabolic and cellular signaling, and, as discussed in the review, a crucial mediator in the pathogenesis of cholestasis. Disruption of one or several of these steps can result in the accumulation of toxic BAs in bile ducts and hepatocytes leading to inflammation, fibrosis, and, over time, biliary and hepatic cirrhosis. Biliary atresia, progressive familial intrahepatic cholestasis, primary sclerosing cholangitis, and Alagille syndrome are four of the most common pediatric cholestatic conditions. Through understanding the commonalities and differences in these diseases, the important cellular mechanistic underpinnings of cholestasis can be greater appreciated.

Biliary atresia is associated with polygenic susceptibility in ciliogenesis and planar polarity effector genes

BACKGROUND & AIMS

Biliary atresia (BA) is poorly understood and leads to liver transplantation (LT), with the requirement for and associated risks of lifelong immunosuppression, in most children. We performed a genome-wide association study (GWAS) to determine the genetic basis of BA.

METHODS

We performed a GWAS in 811 European BA cases treated with LT in US, Canadian and UK centers, and 4,654 genetically matched controls. Whole-genome sequencing of 100 cases evaluated synthetic association with rare variants. Functional studies included whole liver transcriptome analysis of 64 BA cases and perturbations in experimental models.

RESULTS

A GWAS of common single nucleotide polymorphisms (SNPs), i.e. allele frequencies >1%, identified intronic SNPs rs6446628 in AFAP1 with genome-wide significance (p = 3.93E-8) and rs34599046 in TUSC3 at sub-threshold genome-wide significance (p = 1.34E-7), both supported by credible peaks of neighboring SNPs. Like other previously reported BA-associated genes, AFAP1 and TUSC3 are ciliogenesis and planar polarity effectors (CPLANE). In gene-set-based GWAS, BA was associated with 6,005 SNPs in 102 CPLANE genes (p = 5.84E-15). Compared with non-CPLANE genes, more CPLANE genes harbored rare variants (allele frequency <1%) that were assigned Human Phenotype Ontology terms related to hepatobiliary anomalies by predictive algorithms, 87% vs. 40%, p <0.0001. Rare variants were present in multiple genes distinct from those with BA-associated common variants in most BA cases. AFAP1 and TUSC3 knockdown blocked ciliogenesis in mouse tracheal cells. Inhibition of ciliogenesis caused biliary dysgenesis in zebrafish. AFAP1 and TUSC3 were expressed in fetal liver organoids, as well as fetal and BA livers, but not in normal or disease-control livers. Integrative analysis of BA-associated variants and liver transcripts revealed abnormal vasculogenesis and epithelial tube formation, explaining portal vein anomalies that co-exist with BA.

CONCLUSIONS

BA is associated with polygenic susceptibility in CPLANE genes. Rare variants contribute to polygenic risk in vulnerable pathways via unique genes.

IMPACT AND IMPLICATIONS

Liver transplantation is needed to cure most children born with biliary atresia, a poorly understood rare disease. Transplant immunosuppression increases the likelihood of life-threatening infections and cancers. To improve care by preventing this disease and its progression to transplantation, we examined its genetic basis. We find that this disease is associated with both common and rare mutations in highly specialized genes which maintain normal communication and movement of cells, and their organization into bile ducts and blood vessels during early development of the human embryo. Because defects in these genes also cause other birth defects, our findings could lead to preventive strategies to lower the incidence of biliary atresia and potentially other birth defects.

Novel Pathogenic DNAH5 Variants in Primary Ciliary Dyskinesia: Association with Visceral Heterotaxia and Neonatal Cholestasis

The dynein axonemal heavy chain 5 gene codes for a subunit of axonemal dynein necessary for ciliary motor function. Though research has elucidated the consequences of some variants in this gene, it is still unclear whether many variants in the DNAH5 locus are benign or pathogenic due to the rarity of primary ciliary dyskinesia (PCD, of which Kartagener's syndrome is a subset). Here, we introduce the case of an infant boy presenting with the classical findings of PCD along with visceral heterotaxia and neonatal cholestasis. Genetic testing indicated that the patient is a compound heterozygote with a pathogenic c.8498G > A (known as pathogenic) on the maternally derived allele and two variants of uncertain significance, c.1206T > A and c.7800T > G, on the paternally derived allele. As PCD is autosomal recessive, we conclude that one, or both, of these paternally derived variants are pathogenic. To our knowledge, this is the first time that the clinical implications of c.1206T > A (p.Asn402Lys) and c.7800T > G (p.Ile2600Met) are documented. Furthermore, we use this case as an example to recommend clinicians to assess for PCD and laterality defects when presented with severe infantile cholestasis. While the association of cholestasis with PCD is relatively uncommon, PCD is a risk factor for increased prevalence of biliary atresia and infections, both of which are known causes of cholestasis in early infancy.

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.

Genetic alterations and molecular mechanisms underlying hereditary intrahepatic cholestasis

Hereditary cholestatic liver disease caused by a class of autosomal gene mutations results in jaundice, which involves the abnormality of the synthesis, secretion, and other disorders of bile acids metabolism. Due to the existence of a variety of gene mutations, the clinical manifestations of children are also diverse. There is no unified standard for diagnosis and single detection method, which seriously hinders the development of clinical treatment. Therefore, the mutated genes of hereditary intrahepatic cholestasis were systematically described in this review.

Development of liver inflammatory injury in biliary atresia: from basic to clinical research

Biliary atresia (BA) is a severe cholangiopathy in infants. It is characterized by inflammatory fibro-obliteration of the intra- and extrahepatic bile ducts. Although the restoration of bile flow can be successful after Kasai operation, the rapid progression of liver fibrosis can continue, leading to cirrhosis. It is believed that the progression of liver fibrosis in BA is exacerbated by complicated mechanisms other than the consequence of bile duct obstruction. The fibrogenic cascade in BA liver can be divided into three stages, including liver inflammatory injury, myofibroblast activation, and fibrous scar formation. Recent studies have revealed that the activation of an immune response following bile duct injury plays an important role in promoting the inflammatory process, the releasing of inflammatory cytokines, and the development of fibrogenesis in BA liver. In this article, we summarized the evidence regarding liver inflammatory injury and the possible mechanisms that explain the rapid progression of liver fibrosis in BA.

Association analysis and functional follow-up identified common variants of JAG1 accounting for risk to biliary atresia

Background: Biliary atresia (BA) is a destructive, obliterative cholangiopathy characterized by progressive fibro-inflammatory disorder and obliteration of intra- and extrahepatic bile ducts. The Jagged1 (JAG1) gene mutations have been found in some isolated BA cases. We aim to explore the association of common variants in JAG1 with isolated BA risk in the Chinese Han population. Methods: We genotyped 31 tag single nucleotide polymorphisms covering the JAG1 gene region in 333 BA patients and 1,665 healthy controls from the Chinese population, and performed case-control association analysis. The expression patterns of JAG1 homologs were investigated in zebrafish embryos, and the roles of jag1a and jag1b in biliary development were examined by morpholino knockdown in zebrafish. Results: Single nucleotide polymorphisms rs6077861 [P _Allelic = 1.74 × 10^-4, odds ratio = 1.78, 95% confidence interval: 1.31-2.40] and rs3748478 (P _Allelic = 5.77 × 10^-4, odds ratio = 1.39, 95% confidence interval: 1.15-1.67) located in the intron region of JAG1 showed significant associations with BA susceptibility. The JAG1 homologs, jag1a and jag1b genes were expressed in the developing hepatobiliary duct of zebrafish, especially at 72 and 96 h postfertilization. Knockdown of both jag1a and jag1b led to poor biliary secretion, sparse intrahepatic bile duct network and smaller or no gallbladders compared with control embryos in the zebrafish model. Conclusion: Common genetic variants of JAG1 were associated with BA susceptibility. Knockdown of JAG1 homologs led to defective intrahepatic and extrahepatic bile ducts in zebrafish. These results suggest that JAG1 might be implicated in the etiology of BA.

Impact of Aberrant β-Catenin Pathway on Cholangiocarcinoma Heterogeneity

The poor prognosis of most cases of advanced cholangiocarcinoma (CCA) constitutes a severe problem in modern oncology, which is aggravated by the fact that the incidence of this liver cancer is increasing worldwide and is often diagnosed late, when surgical removal is not feasible. The difficulty of dealing with this deadly tumor is augmented by the heterogeneity of CCA subtypes and the complexity of mechanisms involved in enhanced proliferation, apoptosis avoidance, chemoresistance, invasiveness, and metastasis that characterize CCA. Among the regulatory processes implicated in developing these malignant traits, the Wnt/β-catenin pathway plays a pivotal role. Alteration of β-catenin expression and subcellular localization has been associated with worse outcomes in some CCA subtypes. This heterogeneity, which also affects cellular and in vivo models commonly used to study CCA biology and anticancer drug development, must be taken into account for CCA investigation to more accurately extrapolate basic laboratory research to the clinical situation. A better understanding of the altered Wnt/β-catenin pathway in relationship with the heterogeneous forms of CCA is mandatory for developing novel diagnostic tools and therapeutic strategies for patients suffering from this lethal disease.

Liver-restricted deletion of the biliary atresia candidate gene Pkd1l1 causes bile duct dysmorphogenesis and ciliopathy

BACKGROUND AND AIMS

A recent multicenter genetic exploration of the biliary atresia splenic malformation syndrome identified mutations in the ciliary gene PKD1L1 as candidate etiologic contributors. We hypothesized that deletion of Pkd1l1 in developing hepatoblasts would lead to cholangiopathy in mice.

APPROACH AND RESULTS

CRISPR-based genome editing inserted loxP sites flanking exon 8 of the murine Pkd1l1 gene. Pkd1l1Fl/Fl cross-bred with alpha-fetoprotein-Cre expressing mice to generate a liver-specific intrahepatic Pkd1l1 -deficient model (LKO). From embryonic day 18 through week 30, control ( Fl/Fl ) and LKO mice were evaluated with standard serum chemistries and liver histology. At select ages, tissues were analyzed using RNA sequencing, immunofluorescence, and electron microscopy with a focus on biliary structures, peribiliary inflammation, and fibrosis. Bile duct ligation for 5 days of Fl/Fl and LKO mice was followed by standard serum and liver analytics. Histological analyses from perinatal ages revealed delayed biliary maturation and reduced primary cilia, with progressive cholangiocyte proliferation, peribiliary fibroinflammation, and arterial hypertrophy evident in 7- to 16-week-old LKO versus Fl/Fl livers. Following bile duct ligation, cholangiocyte proliferation, peribiliary fibroinflammation, and necrosis were increased in LKO compared with Fl/Fl livers.

CONCLUSIONS

Bile duct ligation of the Pkd1l1 -deficient mouse model mirrors several aspects of the intrahepatic pathophysiology of biliary atresia in humans including bile duct dysmorphogenesis, peribiliary fibroinflammation, hepatic arteriopathy, and ciliopathy. This first genetically linked model of biliary atresia, the Pkd1l1 LKO mouse, may allow researchers a means to develop a deeper understanding of the pathophysiology of this serious and perplexing disorder, including the opportunity to identify rational therapeutic targets.

Bile Acids and Biliary Fibrosis

Biliary fibrosis is the driving pathological process in cholangiopathies such as primary biliary cholangitis (PBC) and primary sclerosing cholangitis (PSC). Cholangiopathies are also associated with cholestasis, which is the retention of biliary components, including bile acids, in the liver and blood. Cholestasis may worsen with biliary fibrosis. Furthermore, bile acid levels, composition and homeostasis are dysregulated in PBC and PSC. In fact, mounting data from animal models and human cholangiopathies suggest that bile acids play a crucial role in the pathogenesis and progression of biliary fibrosis. The identification of bile acid receptors has advanced our understanding of various signaling pathways involved in regulating cholangiocyte functions and the potential impact on biliary fibrosis. We will also briefly review recent findings linking these receptors with epigenetic regulatory mechanisms. Further detailed understanding of bile acid signaling in the pathogenesis of biliary fibrosis will uncover additional therapeutic avenues for cholangiopathies.

Prominin-1 promotes restitution of the murine extrahepatic biliary luminal epithelium following cholestatic liver injury

BACKGROUND AND AIMS

Restitution of the extrahepatic biliary luminal epithelium in cholangiopathies is poorly understood. Prominin-1 (Prom1) is a key component of epithelial ciliary body of stem/progenitor cells. Given that intrahepatic Prom1-expressing progenitor cells undergo cholangiocyte differentiation, we hypothesized that Prom1 may promote restitution of the extrahepatic bile duct (EHBD) epithelium following injury.

APPROACH AND RESULTS

Utilizing various murine biliary injury models, we identified Prom1-expressing cells in the peribiliary glands of the EHBD. These Prom1-expressing cells are progenitor cells which give rise to cholangiocytes as part of the normal maintenance of the EHBD epithelium. Following injury, these cells proliferate significantly more rapidly to re-populate the biliary luminal epithelium. Null mutation of Prom1 leads to significantly >10-fold dilated peribiliary glands following rhesus rotavirus-mediated biliary injury. Cultured organoids derived from Prom1 knockout mice are comprised of biliary progenitor cells with altered apical-basal cellular polarity, significantly fewer and shorter cilia, and decreased organoid proliferation dynamics consistent with impaired cell motility.

CONCLUSIONS

We, therefore, conclude that Prom1 is involved in biliary epithelial restitution following biliary injury in part through its role in supporting cell polarity.

Biliary atresia & choledochal malformation--Embryological and anatomical considerations

The two main biliary pathologies in paediatric practice, biliary atresia and choledochal malformations (CM), have their origins within prenatal life. Nevertheless, the actual mechanisms remain elusive with many unanswered questions. The extrahepatic bile duct develops as a funnel-like structure emerging from the foregut from about 3-4 weeks of gestation into the mesenchyme of the septum transversum. The cranial elements of this contain hepatoblasts - the precursors to the two key cell lines that will become hepatocytes and biliary epithelial cells. The intrahepatic bile ducts develop separately and emerge from a complex process involving the ductal plate surrounding the in-growing portal venous system from about the 7-8^th week of gestation. A developmental defect at some point(s) in this process may be the cause of at least some variants of BA - the Biliary Atresia Splenic Malformation syndrome particularly - though evidence in the more common isolated BA is much more circumstantial. Similarly, some types of choledochal malformation, specifically the cystic type of CM, are invariably present during prenatal life although again an actual aetiological mechanism remains elusive.

Biallelic mutations of TTC12 and TTC21B were identified in Chinese patients with multisystem ciliopathy syndromes

Background

Abnormalities in cilia ultrastructure and function lead to a range of human phenotypes termed ciliopathies. Many tetratricopeptide repeat domain (TTC) family members have been reported to play critical roles in cilium organization and function.

Results

Here, we describe five unrelated family trios with multisystem ciliopathy syndromes, including situs abnormality, complex congenital heart disease, nephronophthisis or neonatal cholestasis. Through whole-exome sequencing and Sanger sequencing confirmation, we identified compound heterozygous mutations of TTC12 and TTC21B in six affected individuals of Chinese origin. These nonsynonymous mutations affected highly conserved residues and were consistently predicted to be pathogenic. Furthermore, ex vivo cDNA amplification demonstrated that homozygous c.1464 + 2 T > C of TTC12 would cause a whole exon 16 skipping. Both mRNA and protein levels of TTC12 were significantly downregulated in the cells derived from the patient carrying TTC12 mutation c.1464 + 2 T > C by real-time qPCR and immunofluorescence assays when compared with two healthy controls. Transmission electron microscopy analysis further identified ultrastructural defects of the inner dynein arms in this patient. Finally, the effect of TTC12 deficiency on cardiac LR patterning was recapitulated by employing a morpholino-mediated knockdown of ttc12 in zebrafish.

Conclusions

To the best of our knowledge, this is the first study reporting the association between TTC12 variants and ciliopathies in a Chinese population. In addition to nephronophthisis and laterality defects, our findings demonstrated that TTC21B should also be considered a candidate gene for biliary ciliopathy, such as TTC26, which further expands the phenotypic spectrum of TTC21B deficiency in humans.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40246-022-00421-z.

Current Understanding in the Clinical Characteristics and Molecular Mechanisms in Different Subtypes of Biliary Atresia

Biliary atresia is a severe obliterative cholangiopathy in early infancy that is by far the most common cause of surgical jaundice and the most common indicator for liver transplantation in children. With the advanced knowledge gained from different clinical trials and the development of research models, a more precise clinical classification of BA (i.e., isolated BA (IBA), cystic BA (CBA), syndromic BA (SBA), and cytomegalovirus-associated BA (CMVBA)) is proposed. Different BA subtypes have similar yet distinguishable clinical manifestations. The clinical and etiological heterogeneity leads to dramatically different prognoses; hence, treatment needs to be specific. In this study, we reviewed the clinical characteristics of different BA subtypes and revealed the molecular mechanisms of their developmental contributors. We aimed to highlight the differences among these various subtypes of BA which ultimately contribute to the development of a specific management protocol for each subtype.

Genetic Factors and Their Role in the Pathogenesis of Biliary Atresia

Biliary Atresia, a common basis for neonatal cholestasis and primary indication for Liver Transplantation, accounts for 60% of pediatric Liver Transplantations. While the pathogenesis of Biliary Atresia remains obscure, abnormalities within bile ducts and the liver, inflammation, fibrosis and cilia defects are thought to comprise the pathological basis for this condition. The findings of genetic variants in Biliary Atresia, such as Copy Number Variations and Single Nucleotide Polymorphism, are considered as essential factors in the development of this condition. In this review, we summarize and analyze these Biliary Atresia variants from a perspective of their pathological characteristics. In conclusion, such analyses may offer novel insights into the pathogenesis of Biliary Atresia and provide a foundation for future studies directed toward a better understanding and treatment of Biliary Atresia.

Diminution of the Primary Cilia From the Intrahepatic Cholangiocytes in a Pediatric Choledochal Cyst

Choledochal cyst (CC) is a cystic disease predominantly involving the extrahepatic biliary tree. Biliary atresia (BA), another disorder of the extrahepatic biliary tree, is sometimes considered to be in the same spectrum as pediatric CC. Recently, the absence and/or the structural abnormality of the primary cilia in the intrahepatic cholangiocytes have been implicated in the pathogenesis of BA. We aimed to evaluate the expression of primary ciliary proteins in the intrahepatic cholangiocytes in cases of pediatric CC and compare it with normal control and BA. We performed immunohistochemistry for primary ciliary proteins (acetylated-α-tubulin and double-cortin domain containing 2) on the liver biopsies of control liver (n=5), pediatric CC (n=13), and BA (n=14). We also compared the expression with various clinical, biochemical, histopathologic (portal fibroinflammation and ductal plate malformation), and immunohistochemical (proliferative index) data. There was significant loss of primary cilia from the intrahepatic cholangiocytes in cases of CC and BA as compared with the normal control by both immunostains (CC: P=0.003 and 0.001, respectively; BA: P=0.001 and 0.001, respectively). There was no significant difference between the CC and BA in terms of ciliary protein loss. The loss of the ciliary proteins occurred irrespective of the proliferative (MIB-1 labeling) index, portal fibroinflammation, or ductal plate malformation. The loss of cilia did not correlate with the clinical follow-up in cases of pediatric CC. The loss of primary cilia from the intrahepatic cholangiocytes may be crucial in the etiopathogenesis of pediatric CC.

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.

A ZFYVE19 gene mutation associated with neonatal cholestasis and cilia dysfunction: case report with a novel pathogenic variant

Background

ZFYVE19 (Zinc Finger FYVE-Type Containing 19) mutations have most recently been associated to a novel type of high gamma-glutamyl transpeptidase (GGT), non-syndromic, neonatal-onset intrahepatic chronic cholestasis possibly associated to cilia dysfunction. Herein, we report a new case with further studies of whole exome sequencing (WES) and immunofluorescence in primary cilia of her cultured fibroblasts which confirm the observation.

Results

A now 5-year-old girl born to clinically healthy consanguineous Moroccan parents was assessed at 59 days of life due to severe cholestatic jaundice with increased serum bile acids and GGT, and preserved hepatocellular synthetic function. Despite fibrosis/cirrhosis and biliary ducts proliferation on liver biopsy suggested an extrahepatic biliary obstacle, normal intra-operatory cholangiography excluded biliary atresia. Under choleretic treatment, she maintained a clinically stable anicteric cholestasis but developped hyperlipidemia. After exclusion of the main causes of cholestasis by multiple tests, abnormal concentrations of sterols and WES led to a diagnosis of hereditary sitosterolemia (OMIM #618666), likely unrelated to her cholestasis. Further sequencing investigation revealed a homozygous non-sense mutation (p.Arg223Ter) in ZFYVE19 leading to a 222 aa truncated protein and present in both heterozygous parents. Immunofluorescence analysis of primary cilia on cultured skin fibroblasts showed a ciliary phenotype mainly defined by fragmented cilia and centrioles abnormalities.

Conclusions

Our findings are consistent with and expands the recent evidence linking ZFYVE19 to a novel, likely non-syndromic, high GGT-PFIC phenotype with neonatal onset. Due to the possible role of ZFYVE19 in cilia function and the unprecedented coexistence of a coincidental hereditary sterol disorder in our case, continuous monitoring will be necessary to substantiate type of liver disease progression and/or possible emergence of a multisystemic involvement. What mentioned above confirms that the application of WES in children with undiagnosed cholestasis may lead to the identification of new causative genes, widening the knowledge on the pathophysiology.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-021-01775-8.

The multisystem nature of isomerism: left isomerism complicated by Abernethy malformation and portopulmonary hypertension

Isomerism, also referred to as "heterotaxy" is a complex set of anatomic and functional perturbations. One of the most obvious manifestations of isomerism is the disturbance of organ arrangement, such that the thoracic organs are no longer asymmetric on the left and right. We report the case of a 14-year-old female in whom exercise-induced dyspnea led to a late diagnosis of left isomerism complicated by Abernethy malformation and portopulmonary hypertension. A comprehensive evaluation revealed two anatomic left lungs and hyparterial bronchi, bilateral left atria, an interrupted inferior caval vein with azygos continuation, multiple spleens, sinus node dysfunction, hepatic hypertrophy with focal nodular hyperplasia, and absence of the portal vein. Pulmonary vasodilator therapy was initiated resulting in clinical improvement. This case exhibits unique features including a late diagnosis of isomerism with Abernethy malformation and portopulmonary hypertension. The patient's presentation, medical workup, and future treatment emphasise the importance of multidisciplinary care in children with complex multisystem disease. We review the multiple cardiac and extracardiac manifestations of isomerism.

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.

Biliary-Atresia-Associated Mannosidase-1-Alpha-2 Gene Regulates Biliary and Ciliary Morphogenesis and Laterality

Background/Aims

Infectious and genetic factors are invoked, respectively in isolated biliary atresia (BA), or syndromic BA, with major extrahepatic anomalies. However, isolated BA is also associated with minor extrahepatic gut and cardiovascular anomalies and multiple susceptibility genes, suggesting common origins.

Methods

We investigated novel susceptibility genes with genome-wide association, targeted sequencing and tissue staining in BA requiring liver transplantation, independent of BA subtype. Candidate gene effects on morphogenesis, developmental pathways, and ciliogenesis, which regulates left-right patterning were investigated with zebrafish knockdown and mouse knockout models, mouse airway cell cultures, and liver transcriptome analysis.

Results

Single nucleotide polymorphisms in Mannosidase-1-α-2 (MAN1A2) were significantly associated with BA and with other polymorphisms known to affect MAN1A2 expression but were not differentially enriched in either BA subtype. In zebrafish embryos, man1a2 knockdown caused poor biliary network formation, ciliary dysgenesis in Kupffer’s vesicle, cardiac and liver heterotaxy, and dysregulated egfra and other developmental genes. Suboptimal man1a2 knockdown synergized with suboptimal EGFR signaling or suboptimal knockdown of the EGFR pathway gene, adenosine-ribosylation-factor-6, which had minimal effects individually, to reproduce biliary defects but not heterotaxy. In cultured mouse airway epithelium, Man1a2 knockdown arrested ciliary development and motility. Man1a2^–/– mice, which experience respiratory failure, also demonstrated portal and bile ductular inflammation. Human BA liver and Man1a2^–/– liver exhibited reduced Man1a2 expression and dysregulated ciliary genes, known to cause multisystem human laterality defects.

Conclusion

BA requiring transplantation associates with sequence variants in MAN1A2. man1a2 regulates laterality, in addition to hepatobiliary morphogenesis, by regulating ciliogenesis in zebrafish and mice, providing a novel developmental basis for multisystem defects in BA.

Systems Analysis of Biliary Atresia Through Integration of High-Throughput Biological Data

Biliary atresia (BA), blockage of the proper bile flow due to loss of extrahepatic bile ducts, is a rare, complex disease of the liver and the bile ducts with unknown etiology. Despite ongoing investigations to understand its complex pathogenesis, BA remains the most common cause of liver failure requiring liver transplantation in children. To elucidate underlying mechanisms, we analyzed the different types of high-throughput genomic and transcriptomic data collected from the blood and liver tissue samples of children suffering from BA. Through use of a novel integrative approach, we identified potential biomarkers and over-represented biological functions and pathways to derive a comprehensive network showing the dysfunctional mechanisms associated with BA. One of the pathways highlighted in the integrative network was hypoxia signaling. Perturbation with hypoxia inducible factor activator, dimethyloxalylglycine, induced the biliary defects of BA in a zebrafish model, serving as a validation for our studies. Our approach enables a systems-level understanding of human BA biology that is highlighted by the interaction between key biological functions such as fibrosis, inflammation, immunity, hypoxia, and development.

Identification of Polycystic Kidney Disease 1 Like 1 Gene Variants in Children With Biliary Atresia Splenic Malformation Syndrome

Biliary atresia (BA) is the most common cause of end-stage liver disease in children and the primary indication for pediatric liver transplantation, yet underlying etiologies remain unknown. Approximately 10% of infants affected by BA exhibit various laterality defects (heterotaxy) including splenic abnormalities and complex cardiac malformations-a distinctive subgroup commonly referred to as the biliary atresia splenic malformation (BASM) syndrome. We hypothesized that genetic factors linking laterality features with the etiopathogenesis of BA in BASM patients could be identified through whole-exome sequencing (WES) of an affected cohort. DNA specimens from 67 BASM subjects, including 58 patient-parent trios, from the National Institute of Diabetes and Digestive and Kidney Diseases-supported Childhood Liver Disease Research Network (ChiLDReN) underwent WES. Candidate gene variants derived from a prespecified set of 2,016 genes associated with ciliary dysgenesis and/or dysfunction or cholestasis were prioritized according to pathogenicity, population frequency, and mode of inheritance. Five BASM subjects harbored rare and potentially deleterious biallelic variants in polycystic kidney disease 1 like 1 (PKD1L1), a gene associated with ciliary calcium signaling and embryonic laterality determination in fish, mice, and humans. Heterozygous PKD1L1 variants were found in 3 additional subjects. Immunohistochemical analysis of liver from the one BASM subject available revealed decreased PKD1L1 expression in bile duct epithelium when compared to normal livers and livers affected by other noncholestatic diseases. Conclusion: WES identified biallelic and heterozygous PKD1L1 variants of interest in 8 BASM subjects from the ChiLDReN data set; the dual roles for PKD1L1 in laterality determination and ciliary function suggest that PKD1L1 is a biologically plausible, cholangiocyte-expressed candidate gene for the BASM syndrome.

A practical approach to the pathology of neonatal cholestatic liver disease

Navigating the complexities of interpreting a liver biopsy performed on a neonate with conjugated/direct hyperbilirubinemia can be an arduous task given these biopsies are infrequently encountered. The list of entities is long and yet there are only a few histologic patterns of liver injury. The first step for the pathologist is to determine the histologic pattern, which will guide further inquiry into the useful clinical information to have while evaluating the biopsy. Ultimately, the goal is to identify those conditions that will benefit from early intervention. We begin with a review of biliary development to help understand what findings may be physiologic versus pathologic, particularly in premature infants. Then we review eight cases that cover the three most common histologic patterns of injury in patients with neonatal cholestasis: biliary obstructive, neonatal hepatitis, and paucity of intrahepatic bile ducts. The entities that serve as prototypes for these histologic patterns are covered, including biliary atresia, idiopathic neonatal hepatitis, and Alagille syndrome, along with rarer entities that have histologic overlap. The cases with accompanying tables and algorithms are intended to help place the histologic findings in the context of the overall clinical work-up, including genetic testing.

Intrahepatic bile duct primary cilia in biliary atresia

AIM

The etiopathogenesis of non-syndromic biliary atresia (BA) is obscure. The primary aim was to investigate intrahepatic bile duct cilia (IHBC) in BA at diagnosis and its correlation with clinical outcome. The secondary aim was to analyze IHBC in routine paraffin-embedded liver biopsies using conventional scanning electron microscopy (SEM).

METHODS

Surgical liver biopsies taken at diagnosis from 22 BA infants (age range, 39-116 days) and from eight children with non-BA chronic cholestasis (age range, 162 days -16.8 years) were evaluated for IHBC by immunofluorescence (IF) and SEM. A minimum 18-month follow-up after surgery was available for all patients.

RESULTS

By IF, cilia were present in 6/8 (75%) non-BA but only in 3/22 (14%) BA cases, and cilia were reduced or absent in 19/22 (86%) BA and 2/8 (25%) non-BA livers (P < 0.01). In BA, cilia presence was found to be associated with clearance of jaundice at 6-month follow-up (P < 0.05). However, high overall survival rates with native liver, >90% at 12 months, and >70% at 24 months post-surgery, were recorded regardless of cilia presence/absence at diagnosis. Electron microscopy was able to detect bile ducts and cilia in routine liver biopsies, revealing significant abnormalities in 100% BA livers.

CONCLUSIONS

The presence of IHBC in BA livers at the diagnosis was associated with resolution of cholestasis, although was not predictive of short-term survival with native liver. Scanning electron microscopy represents a powerful new tool to study routine liver biopsies in biliary disorders. Cilia dysfunction in BA pathogenesis and/or disease progression warrants further investigation.

The cholangiocyte primary cilium in health and disease

Cholangiocytes, like most cells, express primary cilia extending from their membranes. These organelles function as antennae which detect stimuli from bile and transmit the information into cells regulating several signaling pathways involved in secretion, proliferation and apoptosis. The ability of primary cilia to detect different signals is provided by ciliary associated proteins which are expressed in its membrane. Defects in the structure and/or function of these organelles lead to cholangiociliopathies that result in cholangiocyte hyperproliferation, altered fluid secretion and absorption. Since primary cilia dysfunction has been observed in several epithelial tumors, including cholangiocarcinoma (CCA), primary cilia have been proposed as tumor suppressor organelles. In addition, the loss of cilia is associated with dysregulation of several molecular pathways resulting in CCA development and progression. Thus, restoration of the primary cilia may be a potential therapeutic approach for several ciliopathies and CCA.

SOX17 regulates cholangiocyte differentiation and acts as a tumor suppressor in cholangiocarcinoma

BACKGROUND & AIMS

Cholangiocarcinoma (CCA) is a biliary malignancy linked to genetic and epigenetic abnormalities, such as hypermethylation of SOX17 promoter. Here, the role of SOX17 in cholangiocyte differentiation and cholangiocarcinogenesis was studied.

METHODS

SOX17 expression/function was evaluated along the differentiation of human induced pluripotent stem cells (iPSC) into cholangiocytes, in the dedifferentiation process of normal human cholangiocytes (NHC) in culture and in cholangiocarcinogenesis. Lentiviruses for SOX17 overexpression or knockdown were used. Gene expression and DNA methylation profiling were performed.

RESULTS

SOX17 expression is induced in the last stage of cholangiocyte differentiation from iPSC and regulates the acquisition of biliary markers. SOX17 becomes downregulated in NHC undergoing dedifferentiation; experimental SOX17 knockdown in differentiated NHC downregulated biliary markers and promoted baseline and Wnt-dependent proliferation. SOX17 expression is lower in human CCA than in healthy tissue, which correlates with worse survival after tumor resection. In CCA cells, SOX17 overexpression decreased their tumorigenic capacity in murine xenograft models, which was related to increased oxidative stress and apoptosis. In contrast, SOX17 overexpression in NHC did not affect their survival but inhibited their baseline proliferation. In CCA cells, SOX17 inhibited migration, anchorage-independent growth and Wnt/β-catenin-dependent proliferation, and restored the expression of biliary markers and primary cilium length. In human CCA, SOX17 promoter was found hypermethylated and its expression inversely correlates with the methylation grade. In NHC, Wnt3a decreased SOX17 expression in a DNMT-dependent manner, whereas in CCA, DNMT1 inhibition or silencing upregulated SOX17.

CONCLUSIONS

SOX17 regulates the differentiation and maintenance of the biliary phenotype and functions as a tumor suppressor for CCA, being a potential prognostic marker and a promising therapeutic target.

LAY SUMMARY

Understanding the molecular mechanisms involved in the pathogenesis of CCA is key in finding new valuable diagnostic and prognostic biomarkers, as well as therapeutic targets. This study provides evidence that SOX17 regulates the differentiation and maintenance of the biliary phenotype, and its downregulation promotes their tumorigenic transformation. SOX17 acts as a tumor suppressor in CCA and its genetic, molecular and/or pharmacological restoration may represent a new promising therapeutic strategy. Moreover, SOX17 expression correlates with the outcome of patients after tumor resection, being a potential prognostic biomarker.

Mutations in DCDC2 (doublecortin domain containing protein 2) in neonatal sclerosing cholangitis

BACKGROUND & AIMS

Neonatal sclerosing cholangitis (NSC) is a severe neonatal-onset cholangiopathy commonly leading to liver transplantation (LT) for end-stage liver disease in childhood. Liver biopsy findings histopathologically resemble those in biliary atresia (BA); however, in NSC extrahepatic bile ducts are patent, whilst in BA their lumina are obliterated. NSC is commonly seen in consanguineous kindreds, suggesting autosomal recessive inheritance.

METHODS

From 29 NSC patients (24 families) identified, DNA was available in 24 (21 families). Thirteen (7 male) patients (12 families) of consanguineous parentage were selected for whole exome sequencing. Sequence variants were filtered for homozygosity, pathogenicity, minor allele frequency, quality score, and encoded protein expression pattern.

RESULTS

Four of 13 patients were homozygous and two were compound heterozygous for mutations in the doublecortin domain containing 2 gene (DCDC2), which encodes DCDC2 protein and is expressed in cholangiocyte cilia. Another 11 patients were sequenced: one (with one sibling pair) was compound heterozygous for DCDC2 mutations. All mutations were protein-truncating. In available liver tissue from patients with DCDC2 mutations, immunostaining for human DCDC2 and the ciliary protein acetylated alpha-tubulin (ACALT) showed no expression (n=6) and transmission electron microscopy found that cholangiocytes lacked primary cilia (n=5). DCDC2 and ACALT were expressed in NSC patients without DCDC2 mutations (n=22). Of the patients carrying DCDC2 mutations, one died awaiting LT; five came to LT, of whom one died 2years later. The other 4 are well.

CONCLUSION

Among 24 NSC patients with available DNA, 7 had mutations in DCDC2 (6 of 19 families). NSC patients in substantial proportion harbour mutations in DCDC2. Their disease represents a novel liver-based ciliopathy.

LAY SUMMARY

Neonatal sclerosing cholangitis (NSC) is a rare genetic form of liver disease presenting in infancy. Through next generation sequencing we identified mutations in the gene encoding for doublecortin domain containing 2 (DCDC2) protein in a group of NSC children. DCDC2 is a signalling and structural protein found in primary cilia of cholangiocytes. Cholangiocytes are the cells forming the biliary system which is the draining system of the liver.

Methylation Microarray Studies Highlight PDGFA Expression as a Factor in Biliary Atresia

Biliary atresia (BA) is a progressive fibro-inflammatory disorder that is the leading indication for liver transplantation in children. Although there is evidence implicating genetic, infectious, environmental, and inflammatory causes, the etiology of BA remains unknown. We have recently reported that cholangiocytes from BA patients showed decreased DNA methylation relative to disease- and non-disease controls, supporting a potential role for DNA hypomethylation in BA etiopathogenesis. In the current study, we examined the methylation status of specific genes in human BA livers using methylation microarray technology. We found global DNA hypomethylation in BA samples as compared to disease- and non-disease controls at specific genetic loci. Hedgehog pathway members, SHH and GLI2, known to be upregulated in BA, were both hypomethylated, validating this approach as an investigative tool. Another region near the PDGFA locus was the most significantly hypomethylated in BA, suggesting potential aberrant expression. Validation assays confirmed increased transcriptional and protein expression of PDGFA in BA livers. We also show that PDGF-A protein is specifically localized to cholangiocytes in human liver samples. Injection of PDGF-AA protein dimer into zebrafish larvae caused biliary developmental and functional defects. In addition, activation of the Hedgehog pathway caused increased expression of PDGF-A in zebrafish larvae, providing a previously unrecognized link between PDGF and the Hedgehog pathway. Our findings implicate DNA hypomethylation as a specific factor in mediating overexpression of genes associated with BA and identify PDGF as a new candidate in BA pathogenesis.

Identification of a plant isoflavonoid that causes biliary atresia

Biliary atresia (BA) is a rapidly progressive and destructive fibrotic disorder of unknown etiology affecting the extrahepatic biliary tree of neonates. Epidemiological studies suggest that an environmental factor, such as a virus or toxin, is the cause of the disease, although none have been definitively established. Several naturally occurring outbreaks of BA in Australian livestock have been associated with the ingestion of unusual plants by pregnant animals during drought conditions. We used a biliary secretion assay in zebrafish to isolate a previously undescribed isoflavonoid, biliatresone, from Dysphania species implicated in a recent BA outbreak. This compound caused selective destruction of the extrahepatic, but not intrahepatic, biliary system of larval zebrafish. A mutation that enhanced biliatresone toxicity mapped to a region of the zebrafish genome that has conserved synteny with an established human BA susceptibility locus. The toxin also caused loss of cilia in neonatal mouse extrahepatic cholangiocytes in culture and disrupted cell polarity and monolayer integrity in cholangiocyte spheroids. Together, these findings provide direct evidence that BA could be initiated by perinatal exposure to an environmental toxin.

Manifestations of bodily isomerism

We report the findings present in 49 postmortem specimens from patients with so-called heterotaxy, concentrating on those found in the extracardiac systems of organs. Also known as bodily isomerism, we suggest that it is important to segregate the syndromes into their isomeric subtypes to be able to make inferences regarding likely extracardiac and intracardiac findings to allow for proper surveillance. We demonstrate that this is best done on the basis of the atrial appendages, which were isomeric in all the hearts obtained from the specimens available for our inspection. The abdominal organs do not demonstrate isomerism, and they show variable features when compared to the isomeric atrial appendages.

Functional and structural features of cholangiocytes in health and disease

Cholangiocytes are the epithelial cells that line the bile ducts. Along the biliary tree, two different kinds of cholangiocytes exist; small and large cholangiocytes. Each type has important differences in their biological role in physiological and pathological conditions. In response to injury, cholangiocytes become reactive and acquire a neuroendocrine-like phenotype with the secretion of a number of peptides. These molecules act in an autocrine/paracrine fashion to modulate cholangiocyte biology and determine the evolution of biliary damage. The failure of such mechanisms is believed to influence the progression of cholangiopathies, a group of diseases that selectively target biliary cells. Therefore, the understanding of mechanisms regulating cholangiocyte response to injury is expected to foster the development of new therapeutic options to treat biliary diseases. In the present review, we will discuss the most recent findings in the mechanisms driving cholangiocyte adaptation to damage, with particular emphasis on molecular pathways that are susceptible of therapeutic intervention. Morphogenic pathways (Hippo, Notch, Hedgehog), which have been recently shown to regulate biliary ontogenesis and response to injury, will also be reviewed. In addition, the results of ongoing clinical trials evaluating new drugs for the treatment of cholangiopathies will be discussed.

Genetic contributors and modifiers of biliary atresia

To date, the etiology and pathogenic underpinning of the progression of the most prevalent serious neonatal liver disease, biliary atresia, remains elusive. This disease presents as an aggressive form of neonatal cholestasis characterized by the destruction and obliteration of the extrahepatic bile ducts within the first few weeks of life and a rapid progression of biliary fibrosis, likely due to unremitting cholestasis and retention of biliary constituents including bile acids. In ∼5% of patients, biliary atresia is associated with laterality features, suggesting a genetic underpinning to a disease that begins soon after birth. However, biliary atresia does not occur within families and twins are discordant, indicating an absence of strict mendelian inheritance. Despite this, genes related to bile duct dysmorphogenesis/ciliopathies overlapping with features of biliary atresia in both humans and nonhuman model systems have been proposed. Taken together, strict genetic etiologies leading to a common pathway of a neonatal cholangiopathy resulting in biliary atresia remain elusive. Contributions from fibrogenesis- and inflammation-based studies suggest that early engagement of these pathways contributes to disease progression, but a recent double-blind study did not suggest any benefit from early use of corticosteroids. However, there are genetic contributions to the adaptation and response to cholangiopathies and cholestasis that may be present in certain populations that likely impact upon the response to hepatoportoenterostomy and subsequent biliary tract function. Studies utilizing next generation sequencing technologies (e.g., exome analysis) are ongoing in several laboratories around the world; they are expected to provide insights into genetic contributions to biliary atresia outcomes. Altogether, combinations of exome sequencing and large population studies are expected to reveal causative and modifying genes relevant to patients with biliary atresia as a means to provide therapeutic targets and potential opportunities for genetic screening.

The use of Yes-associated protein expression in the diagnosis of persistent neonatal cholestatic liver disease

Although physiologic jaundice of neonates is common, persistent neonatal cholestasis is life-threatening and has multiple etiologies. Among these etiologies, biliary atresia (BA) requires rapid diagnosis and treatment. In diagnosing BA, the surgical pathologist must recognize subtle histologic changes, often with only a small core liver biopsy. To aid in the differential diagnosis of neonatal cholestasis, we investigated Yes-associated protein (YAP), a regulator of organ size and bile duct development. We examined whether a YAP immunostain can highlight emerging hepatobiliary epithelium in BA (n = 28) versus other causes of persistent cholestasis (non-BA; n = 15) and thus serve as a useful diagnostic marker in persistent neonatal jaundice. We show significantly (P < .01) more high-grade (<2) fibrosis and ductular proliferation among BA versus non-BA cases. Likewise, there was significantly more high-grade (2-3/3) cytoplasmic and nuclear YAP staining in BA (97% and 89%) versus non-BA (20% and 13%). High-grade nuclear YAP staining was both sensitive (88%) and specific (87%) for the diagnosis of BA. In contrast to neonatal cholestasis, the differences in YAP localization in cholestatic/obstructed versus nonobstructed adult livers were not significant. Lastly, we found that pharmacologic inhibition of the YAP complex in both cholangiocyte and cholangiocarcinoma cell lines blocked compensatory bile duct proliferation, an early marker of BA that requires nuclear YAP expression, in a time- and dose-dependent manner. In summary, we show that YAP expression modulates both bile duct proliferation and liver damage/fibrosis while acting as a sensitive and specific marker in the differential diagnosis of persistent neonatal cholestasis.

Extrahepatic cholangiocyte cilia are abnormal in biliary atresia

OBJECTIVES

Biliary atresia (BA) is a rapidly progressive form of biliary fibrosis affecting neonates. We previously reported that primary cilia on the intrahepatic cholangiocytes of patients with both syndromic and nonsyndromic BA were structurally abnormal. Our objective was to determine whether extrahepatic cholangiocytes in human biliary atresia, intrahepatic and extrahepatic cholangiocytes of rhesus rotavirus (RRV)-infected neonatal mice, and RRV-infected primary neonatal extrahepatic cholangiocytes also demonstrate ciliary abnormalities.

METHODS

The livers of neonatal BALB/c mice injected with RRV that developed jaundice, human extrahepatic bile duct samples obtained at time of hepatoportoenterostomy, and RRV-infected primary neonatal cholangiocytes were stained with antibodies against acetylated α tubulin to identify primary cilia.

RESULTS

Extrahepatic cholangiocytes from RRV-treated mice demonstrated minimal loss of primary cilia at day 3 but almost complete loss at day 8 and partial loss at day 12. No changes were seen in mouse intrahepatic bile ducts at any of the time points. In the human BA samples, primary cilia were almost completely absent from extrahepatic duct cholangiocytes. There were, however, abundant cilia in the peribiliary glands adjacent to extrahepatic ducts in the BA sample. Cilia in RRV-infected primary neonatal cholangiocytes were significantly decreased compared with controls.

CONCLUSIONS

Primary cilia are selectively lost from neonatal extrahepatic but not intrahepatic cholangiocytes after RRV infection in BALB/c mice. The cilia are also decreased in RRV-infected primary cholangiocytes and the extrahepatic ducts from human patients with BA. This suggests that ciliary abnormalities are part of the pathophysiology of BA.

Sox17 haploinsufficiency results in perinatal biliary atresia and hepatitis in C57BL/6 background mice

Congenital biliary atresia is an incurable disease of newborn infants, of unknown genetic causes, that results in congenital deformation of the gallbladder and biliary duct system. Here, we show that during mouse organogenesis, insufficient SOX17 expression in the gallbladder and bile duct epithelia results in congenital biliary atresia and subsequent acute 'embryonic hepatitis', leading to perinatal death in ~95% of the Sox17 heterozygote neonates in C57BL/6 (B6) background mice. During gallbladder and bile duct development, Sox17 was expressed at the distal edge of the gallbladder primordium. In the Sox17(+/-) B6 embryos, gallbladder epithelia were hypoplastic, and some were detached from the luminal wall, leading to bile duct stenosis or atresia. The shredding of the gallbladder epithelia is probably caused by cell-autonomous defects in proliferation and maintenance of the Sox17(+/-) gallbladder/bile duct epithelia. Our results suggest that Sox17 plays a dosage-dependent function in the morphogenesis and maturation of gallbladder and bile duct epithelia during the late-organogenic stages, highlighting a novel entry point to the understanding of the etiology and pathogenesis of human congenital biliary atresia.

Bile canalicular abnormalities in the early phase of a mouse model of sclerosing cholangitis

BACKGROUND

The bile canaliculus is the smallest and first biliary channel and is formed by two or three adjacent hepatocytes. Previous studies of chronic cholangiopathies such as primary sclerosing cholangitis have focused on the bile ductules. However, little is known about the pathological alterations in bile canaliculi in the early phase of cholangiopathies.

AIM

To characterize the bile canalicular morphology in the early phase of sclerosing cholangitis we used 3,5-diethoxycarbonyl-1,4-dihydrocollidine-induced mouse model of sclerosing cholangitis.

METHODS

Mice were fed a diet with 3,5-diethoxycarbonyl-1,4-dihydrocollidine (0.1%). Serum biochemical, histological, immunohistochemical, and electron microscopic analyses were performed 1, 2, 4, and 7 days after feeding.

RESULTS

All experimental groups showed significantly increased serum aspartate aminotransferase, alanine aminotransferase, and alkaline phosphatase levels. From day 1, bile canalicular abnormalities such as dilatation and meandering and loss of microvilli were observed. After bile canalicular abnormalities had appeared, substantial infiltration of inflammatory cells was observed amongst the necrotic cells and periductal region. After these inflammatory changes, cholangiocytes proliferated in the portal area and formed ductular reactions. Finally, periductal fibrosis appeared.

CONCLUSION

This study provides novel evidence of the occurrence of bile canalicular abnormalities during the early phase of sclerosing cholangitis.

Biliary atresia: clinical aspects

Biliary atresia (BA) remains an enigmatic disease with a degree of etiologic heterogeneity. A number of variants can be defined clinically, and these include the syndromic group (typically BA splenic malformation), cystic BA, and cytomegalovirus (CMV) IgM +ve associated BA. The remainder, and still the largest group, may be termed isolated BA(.) There is a wide variation in incidence across the globe from 1 in 5000 in Taiwan to 1 in 20,000 live births in Northern Europe, although the reasons for such a disparity remain obscure. Management remains primarily surgical with an attempt to restore bile flow by resection of extrahepatic biliary remnants and a reconstruction portoenterostomy (the Kasai procedure), reserving liver transplantation for those where this fails or complications of chronic liver disease supervene. Clearance of jaundice to normal values has been achieved in 40%-55% of cases in large series from around the world, with an expectation of 5-year native liver survival of similar proportions.