Cholangiociliopathies: genetics, molecular mechanisms and potential therapies

Case report: Rare genetic liver disease - a case of congenital hepatic fibrosis in adults with autosomal dominant polycystic kidney disease

Congenital hepatic fibrosis (CHF) is considered to be a rare autosomal recessive hereditary fibrocystic liver disease, mainly found in children. However, cases of adult CHF with autosomal dominant polycystic kidney disease (ADPKD) caused by PKD1 gene mutation are extremely rare. We report a 31-year-old female patient admitted for esophageal and gastric variceal bleeding. Physical examination revealed significant splenomegaly, biochemical tests showed a slight increase in liver enzymes, and a decrease in platelet count. Imaging examinations showed significant dilatation of the common bile duct and intrahepatic bile ducts, as well as multiple renal cysts. Liver biopsy revealed enlarged portal areas, bridging fibrosis, and numerous variably shaped small bile ducts. Genetic testing identified two unique mutations in the PKD1 gene, identified as biallelic mutations compound heterozygous mutations composed of a mutation inherited from the father (c.8296 T > C) and one from the mother (c.9653G > C). Based on multiple test results, the patient was diagnosed with the portal hypertension type CHF associated with ADPKD. During her initial hospital stay, the patient underwent endoscopic treatment for gastrointestinal bleeding. To date, the patient has recovered well. Moreover, a significant reduction in varices was observed in a gastroscopy examination 18 months later.

Isolated polycystic liver disease in a child

INTRODUCTION

Polycystic liver disease (PCLD) is a genetic disorder characterized by the growth of >10 cysts in the liver. PCLD is associated with polycystic kidney disease (PKD) in 80-90%of cases (Kothadia et al., 2023 [1]). PCLD can occur in isolation though rarely in children. We present a case report of a child with symptomatic isolated PCLD.

CASE PRESENTATION

A 23-month old female child presented with a 17-month history of gradual increase in abdominal mass. She had acute onset of postprandial vomiting and shortness of breath while lying flat. On examination, she was irritable with massive abdominal distension. Liver function test done showed markedly elevated liver enzymes with preservation of liver synthesis function. Computed tomography (CT) scan showed a large intra-abdominal cyst and normal kidneys bilaterally. During laparotomy, we found multiple exophytic cysts arising from segment IVa of the liver. Hepatic resection was done successfully and patient recovered uneventfully. Histology showed Von Meyenburg complexes characteristic of PCLD.

CLINICAL DISCUSSION

The goal of management should be to counter symptomatology by intervening on developed cysts. The therapeutic options are individualized to address the symptoms and improve the patients' quality of life. Follow up of the patients is based on the presentation and intervention performed, during which period recurrence of cysts is assessed. Complete resection of the liver cysts is recommended to avoid the risk of cholangiocarcinoma.

CONCLUSION

Close follow up by physical examination, laboratory tests and imaging modalities is necessary to detect any recurring masses and malignancy transformation of the cysts to enable timely intervention.

NOTCH signalling - a core regulator of bile duct disease?

The Notch signalling pathway is an evolutionarily conserved mechanism of cell-cell communication that mediates cellular proliferation, fate determination and maintenance of stem/progenitor cell populations across tissues. Although it was originally identified as a critical regulator of embryonic liver development, NOTCH signalling activation has been associated with the pathogenesis of a number of paediatric and adult liver diseases. It remains unclear, however, what role NOTCH actually plays in these pathophysiological processes and whether NOTCH activity represents the reactivation of a conserved developmental programme that is essential for adult tissue repair. In this Review, we explore the concepts that NOTCH signalling reactivation in the biliary epithelium is a reiterative and essential response to bile duct damage and that, in disease contexts in which biliary epithelial cells need to be regenerated, NOTCH signalling supports ductular regrowth. Furthermore, we evaluate the recent literature on NOTCH signalling as a critical factor in progenitor-mediated hepatocyte regeneration, which indicates that the mitogenic role for NOTCH signalling in biliary epithelial cell proliferation has also been co-opted to support other forms of epithelial regeneration in the adult liver.

Autophagy promotes hepatic cystogenesis in polycystic liver disease by depletion of cholangiocyte ciliogenic proteins

BACKGROUNDS AND AIMS

Polycystic liver disease (PLD) is characterized by defective cholangiocyte cilia that regulate progressive growth of hepatic cysts. Because formation of primary cilia is influenced by autophagy through degradation of proteins involved in ciliogenesis, we hypothesized that ciliary defects in PLD cholangiocytes (PLDCs) originate from autophagy-mediated depletion of ciliogenic proteins ADP-ribosylation factor-like protein 3 (ARL3) and ADP-ribosylation factor-like protein 13B (ARL13B) and ARL-dependent mislocation of a ciliary-localized bile acid receptor, Takeda G-protein-coupled receptor 5 (TGR5), the activation of which enhances hepatic cystogenesis (HCG). The aims here were to determine whether: (1) ciliogenesis is impaired in PLDC, is associated with increased autophagy, and involves autophagy-mediated depletion of ARL3 and ARL13B; (2) depletion of ARL3 and ARL13B in PLDC cilia impacts ciliary localization of TGR5; and (3) pharmacological inhibition of autophagy re-establishes cholangiocyte cilia and ciliary localization of ARL3, ARL3B, and TGR5 and reduces HCG.

APPROACH AND RESULTS

By using liver tissue from healthy persons and patients with PLD, in vitro and in vivo models of PLD, and in vitro models of ciliogenesis, we demonstrated that, in PLDCs: ciliogenesis is impaired; autophagy is enhanced; ARL3 and ARL13B are ubiquitinated by HDAC6, depleted in cilia, and present in autophagosomes; depletion of ARL3 and ARL13B impacts ciliary localization of TGR5; and pharmacological inhibition of autophagy with mefloquine and verteporfin re-establishes cholangiocyte cilia and ciliary localization of ARL3, ARL13B, and TGR5 and reduces HCG.

CONCLUSIONS

The intersection between autophagy, defective cholangiocyte cilia, and enhanced HCG contributes to PLD progression and can be considered a target for therapeutic interventions.

Clinical features, concurrent disorders, and survival time in cats with suppurative cholangitis-cholangiohepatitis syndrome

OBJECTIVE

To characterize clinical features, comorbidities, frequency of bacterial isolation, and survival time in cats with suppurative cholangitis-cholangiohepatitis syndrome (S-CCHS).

ANIMALS

168 client-owned cats with S-CCHS.

PROCEDURES

Data were prospectively (1980 to 2019) collected regarding clinical features, comorbidities, bacterial infection, illness duration, and treatments. Variables were evaluated for associations with survival time.

RESULTS

Median age of cats was 10.0 years, with no breed or sex predilection observed. Common clinical features included hyporexia (82%), hyperbilirubinemia (80%), lethargy (80%), vomiting (80%), jaundice (67%), weight loss (54%), and hypoalbuminemia (50%). Comorbidities included extrahepatic bile duct obstruction (53%), cholelithiasis (42%), cholecystitis (40%), and ductal plate malformation (44%) as well as biopsy-confirmed inflammatory bowel disease (60/68 [88%]) and pancreatitis (41/44 [93%]). Bacterial cultures were commonly positive (69%) despite prebiopsy antimicrobial administration in most cats. Of surgically confirmed choleliths, diagnostic imaging identified only 58%. Among 55 cats with "idiopathic pancreatitis," 28 (51%) were documented to have transiting choleliths, and 20 had pancreatic biopsies confirming pancreatitis. Cholelithiasis (with or without bile duct obstruction) and cholecystectomy were associated with survival advantages. Survival disadvantages were found for leukocytosis, ≥ 2-fold increased alkaline phosphatase, and hyperbilirubinemia. Cholecystoenterostomy had no survival impact. Cats with ductal plate malformations were significantly younger at diagnosis and death than other cats. Chronic treatments with antimicrobials, S-adenosylmethionine, and ursodeoxycholic acid were common postbiopsy.

CLINICAL RELEVANCE

S-CCHS in cats was associated with bacterial infection and various comorbidities and may be confused with pancreatitis. Surgically correctable morbidities (ie, cholecystitis, cholecystocholelithiasis) and cholecystectomy provided a significant survival advantage.

Polycystic Liver Disease: Advances in Understanding and Treatment

Polycystic liver disease (PLD) is a group of genetic disorders characterized by progressive development of cholangiocyte-derived fluid-filled hepatic cysts. PLD is the most common manifestation of autosomal dominant and autosomal recessive polycystic kidney diseases and rarely occurs as autosomal dominant PLD. The mechanisms of PLD are a sequence of the primary (mutations in PLD-causative genes), secondary (initiation of cyst formation), and tertiary (progression of hepatic cystogenesis) interconnected molecular and cellular events in cholangiocytes. Nonsurgical, surgical, and limited pharmacological treatment options are currently available for clinical management of PLD. Substantial evidence suggests that pharmacological targeting of the signaling pathways and intracellular processes involved in the progression of hepatic cystogenesis is beneficial for PLD. Many of these targets have been evaluated in preclinical and clinical trials. In this review, we discuss the genetic, molecular, and cellular mechanisms of PLD and clinical and preclinical treatment strategies. Expected final online publication date for the Annual Review of Pathology: Mechanisms of Disease, Volume 17 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Autophagy-mediated reduction of miR-345 contributes to hepatic cystogenesis in polycystic liver disease

Background & Aims

Polycystic liver disease (PLD) is characterised by increased autophagy and reduced miRNA levels in cholangiocytes. Given that autophagy has been implicated in miRNA regulation, we tested the hypothesis that increased autophagy accounts for miRNA reduction in PLD cholangiocytes (PLDCs) and accelerated hepatic cystogenesis.

Methods

We assessed miRNA levels in cultured normal human cholangiocytes (NHCs), PLDCs, and isolated PLDC autophagosomes by miRNA-sequencing (miRNA-seq), and miRNA targets by mRNA-seq. Levels of miR-345 and miR-345-targeted proteins in livers of animals and humans with PLD, in NHCs and PLDCs, and in PLDCs transfected with pre-miR-345 were assessed by in situ hybridisation (ISH), quantitative PCR, western blotting, and fluorescence confocal microscopy. We also assessed cell proliferation and cyst growth in vitro, and hepatic cystogenesis in vivo.

Results

In total, 81% of miRNAs were decreased in PLDCs, with levels of 10 miRNAs reduced by more than 10 times; miR-345 was the most-reduced miRNA. In silico analysis and luciferase reporter assays showed that miR-345 targets included cell-cycle and cell-proliferation-related genes [i.e. cell division cycle 25A (CDC25A), cyclin-dependent kinase 6 (CDK6), E2F2, and proliferating cell nuclear antigen (PCNA)]; levels of 4 studied miR-345 targets were increased in PLDCs at both the mRNA and protein levels. Transfection of PLDCs with pre-miR-345 increased miR-345 and decreased the expression of miR-345-targeted proteins, cell proliferation, and cyst growth in vitro. MiR-345 accumulated in autophagosomes in PLDCs but not NHCs. Inhibition of autophagy increased miR-345 levels, decreased the expression of miR-345-targeted proteins, and reduced hepatic cystogenesis in vitro and in vivo.

Conclusion

Autophagy-mediated reduction of miR-345 in PLDCs (i.e. miRNAutophagy) accelerates hepatic cystogenesis. Inhibition of autophagy restores miR-345 levels, decreases cyst growth, and is beneficial for PLD.

Lay summary

Polycystic liver disease (PLD) is an incurable genetic disorder characterised by the progressive growth of hepatic cysts. We found that hepatic cystogenesis is increased when the levels of miR-345 in PLD cholangiocytes (PLDCs) are reduced by autophagy. Restoration of miR-345 in PLDCs via inhibition of autophagy decreases hepatic cystogenesis and thus, is beneficial for PLD.

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The miRNA profile is altered in PLD.

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MiR-345 is the most-reduced miRNA in PLDCs.

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The reduction of miR-345 increases PLDC proliferation and hepatic cystogenesis.

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MiR-345 in PLDCs is regulated by autophagy, termed ‘miRNAutophagy’.

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Restoration of miR-345 in PLDC is beneficial for PLD.

Use of a Comprehensive 66-Gene Cholestasis Sequencing Panel in 2171 Cholestatic Infants, Children, and Young Adults

OBJECTIVES

Cholestasis is caused by a wide variety of etiologies, often genetic in origin. Broad overlap in clinical presentations, particularly in newborns, renders prioritizing diagnostic investigations challenging. In this setting, a timely, comprehensive assessment using a multigene panel by a clinical diagnostic laboratory would likely prove useful. We summarize initial findings from a testing program designed to discover genetic causes of cholestasis.

METHODS

A neonatal/adult sequencing panel containing 66 genes (originally 57; nine added March 2017) relevant to cholestasis was used. A broad range of eligible patients were enrolled with current/history of cholestasis without an identified cause, or unexplained chronic liver disease. DNA sequencing utilized a custom-designed capture library, and variants were classified and reported as benign, likely benign, variant of unknown significance (VOUS), likely pathogenic (LP), or pathogenic (P), according to the clinical interpretation workflow at EGL Genetics (Tucker, GA).

RESULTS

A total of 2433 samples were submitted between February 2016 and December 2017; 2171 results were reported. Median turnaround time was 21 days. Results from the 2171 subjects (57% <1 year old) included 583 P variants, 79 LP variants, and 3117 VOUS; 166 P/LP variants and 415 VOUS were novel. The panel's overall diagnostic yield was 12% (n = 265/2171) representing 32 genes. The top five genetic diagnoses for the group, in order: JAG1 + NOTCH2 (Alagille syndrome), ABCB11, SERPINA1, ABCB4, and POLG.

CONCLUSIONS

These findings support the utility of comprehensive rapid multigene testing in diagnosing cholestasis and highlight the evolving understanding of genetic variants contributing to the pathogenesis of cholestasis.

New insights on the role of vascular endothelial growth factor in biliary pathophysiology

The family of vascular endothelial growth factors (VEGFs) includes 5 members (VEGF-A to -D, and placenta growth factor), which regulate several critical biological processes. VEGF-A exerts a variety of biological effects through high-affinity binding to tyrosine kinase receptors (VEGFR-1, -2 and -3), co-receptors and accessory proteins. In addition to its fundamental function in angiogenesis and endothelial cell biology, VEGF/VEGFR signalling also plays a role in other cell types including epithelial cells. This review provides an overview of VEGF signalling in biliary epithelial cell biology in both normal and pathologic conditions. VEGF/VEGFR-2 signalling stimulates bile duct proliferation in an autocrine and paracrine fashion. VEGF/VEGFR-1/VEGFR-2 and angiopoietins are involved at different stages of biliary development. In certain conditions, cholangiocytes maintain the ability to secrete VEGF-A, and to express a functional VEGFR-2 receptor. For example, in polycystic liver disease, VEGF secreted by cystic cells stimulates cyst growth and vascular remodelling through a PKA/RAS/ERK/HIF1α-dependent mechanism, unveiling a new level of complexity in VEFG/VEGFR-2 regulation in epithelial cells. VEGF/VEGFR-2 signalling is also reactivated during the liver repair process. In this context, pro-angiogenic factors mediate the interactions between epithelial, mesenchymal and inflammatory cells. This process takes place during the wound healing response, however, in chronic biliary diseases, it may lead to pathological neo-angiogenesis, a condition strictly linked with fibrosis progression, the development of cirrhosis and related complications, and cholangiocarcinoma. Novel observations indicate that in cholangiocarcinoma, VEGF is a determinant of lymphangiogenesis and of the immune response to the tumour. Better insights into the role of VEGF signalling in biliary pathophysiology might help in the search for effective therapeutic strategies.

Deletion of Sox9 in the liver leads to hepatic cystogenesis in mice by transcriptionally downregulating Sec63

Hepatic cysts are found in heterogeneous disorders with different pathogeneses, of which simple hepatic cysts and polycystic liver diseases are two major types. The process of hepatic cytogenesis for these two diseases is caused by defects in remodelling of the ductal plate during biliary tract development, which is called ductal plate malformation. SOX9 is a transcription factor participating in the process of bile duct development, and thus, its dysregulation may play important roles in hepatic cystogenesis. SEC63 encodes an endoplasmic reticulum membrane protein that is mutated in human autosomal dominant polycystic liver disease. However, the transcriptional regulation of SEC63 is largely unknown. In the present study, a liver-specific Sox9 knockout (Sox9^LKO ) mouse was generated to investigate the roles and underlying mechanism of SOX9 in hepatic cystogenesis. We found that hepatic cysts began to be observed in Sox9^LKO mice at 6 months of age. The number and size of cysts increased with age in Sox9^LKO mice. In addition, the characteristics of hepatic cytogenesis, including the activation of proliferation, absence of primary cilium, and disorder of polarity in biliary epithelial cells, were detected in the livers of Sox9^LKO mice. RNAi silencing of SOX9 in human intrahepatic biliary epithelial cells (HIBEpic) resulted in increased proliferation and reduced formation of the primary cilium. Moreover, Sec63 was downregulated in primary biliary epithelial cells from Sox9^LKO mice and SEC63 in HIBEpic transfected with siSOX9. Chromatin immunoprecipitation assays and luciferase reporter assays further demonstrated that SOX9 transcriptionally regulated the expression of SEC63 in biliary epithelial cells. Importantly, the overexpression of SEC63 in HIBEpic partially reversed the effects of SOX9 depletion on the formation of primary cilia and cell proliferation. These findings highlight the biological significance of SOX9 in hepatic cytogenesis and elucidate a novel molecular mechanism underlying hepatic cytogenesis. © 2021 The Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

MicroRNAs and Polycystic Kidney Disease

Important advances have been made regarding the diagnosis and management of polycystic kidney diseases. Care of patients with polycystic kidney diseases has moved beyond supportive care for complications and chronic kidney disease to new potentially disease-modifying therapies. Recently, the role of noncoding RNAs, in particular microRNAs, has been described in polycystic kidney diseases. microRNAs are involved in the regulation of gene expression, in which PKD1, PKD2, and other genes that contribute to the pathogenesis of polycystic kidney diseases are considerable participants. Seminal studies have highlighted the potential importance of microRNAs as new therapeutic targets and innovative diagnostic and/or prognostic biomarkers. Furthermore, an anti-miR-17 drug has advanced through preclinical autosomal dominant polycystic disease studies, and an anti-miR-21 drug has already cleared a phase 1 clinical trial. Most probably, new drugs in the microRNA research field will be yielded as a result of ongoing and planned therapeutic trials. To provide a foundation for understanding microRNA functions as a disease-modifying therapeutic drug in novel targeted therapies, in this narrative review we present an overview of the current knowledge of microRNAs in the pathogenesis of polycystic kidney diseases.

Review: Pathogenesis of cholestatic liver diseases

Cholestatic liver diseases (CLD) begin to develop after an impairment of bile flow start to affect the biliary tree. Cholangiocytes actively participate in the liver response to injury and repair and the intensity of this reaction is a determinant factor for the development of CLD. Progressive cholangiopathies may ultimately lead to end-stage liver disease requiring at the end orthotopic liver transplantation. This narrative review will discuss cholangiocyte biology and pathogenesis mechanisms involved in four intrahepatic CLD: Primary biliary cholangitis, primary sclerosing cholangitis, cystic fibrosis involving the liver, and polycystic liver disease.

Pathobiology of inherited biliary diseases: a roadmap to understand acquired liver diseases

Bile duct epithelial cells, also known as cholangiocytes, regulate the composition of bile and its flow. Acquired, congenital and genetic dysfunctions in these cells give rise to a set of diverse and complex diseases, often of unknown aetiology, called cholangiopathies. New knowledge has been steadily acquired about genetic and congenital cholangiopathies, and this has led to a better understanding of the mechanisms of acquired cholangiopathies. This Review focuses on findings from studies on Alagille syndrome, polycystic liver diseases, fibropolycystic liver diseases (Caroli disease and congenital hepatic fibrosis) and cystic fibrosis-related liver disease. In particular, knowledge on the role of Notch signalling in biliary repair and tubulogenesis has been advanced by work on Alagille syndrome, and investigations in polycystic liver diseases have highlighted the role of primary cilia in biliary pathophysiology and the concept of biliary angiogenic signalling and its role in cyst growth and biliary repair. In fibropolycystic liver disease, research has shown that loss of fibrocystin generates a signalling cascade that increases β-catenin signalling, activates the NOD-, LRR- and pyrin domain-containing 3 inflammasome, and promotes production of IL-1β and other chemokines that attract macrophages and orchestrate the process of pericystic and portal fibrosis, which are the main mechanisms of progression in cholangiopathies. In cystic fibrosis-related liver disease, lack of cystic fibrosis transmembrane conductance regulator increases the sensitivity of epithelial Toll-like receptor 4 that sustains the secretion of nuclear factor-κB-dependent cytokines and peribiliary inflammation in response to gut-derived products, providing a model for primary sclerosing cholangitis. These signalling mechanisms may be targeted therapeutically and they offer a possibility for the development of novel treatments for acquired cholangiopathies.

Magnetic resonance imaging of fibropolycystic liver disease: the spectrum of ductal plate malformations

Fibropolycystic liver diseases, also known as ductal plate malformations, are a group of associated congenital disorders resulting from abnormal development of the biliary ductal system. These disorders include congenital hepatic fibrosis, biliary hamartomas, polycystic liver disease, choledochal cysts and Caroli disease. Recently, it has been thought to include biliary atresia in this group of diseases, because ductal plate malformations could be implicated in the pathogenesis of this disease. Concomitant associated renal anomalies can also be present, such as autosomal recessive polycystic kidney disease (ARPKD), medullary sponge kidney and nephronophthisis. These disorders can be clinically silent or can cause abnormalities such as cholangitis, portal hypertension, gastrointestinal bleeding and infections. The different types of ductal plate malformations show typical findings at magnetic resonance (MR) imaging. A clear knowledge of the embryology and pathogenesis of the ductal plate plays a pivotal role to understand the characteristic imaging appearances of these complex diseases. Awareness of these MR imaging findings is central to the detecting and differentiating between various fibropolycystic liver diseases and is important to direct appropriate clinical management and prevent misdiagnosis.

Caroli's-type ductal plate malformation and a portosystemic shunt in a 4-month-old kitten

Case summary

A 4-month-old neutered male Russian Blue kitten had a 4 week history of hypersalivation and failure to thrive. In addition, there was a 2 week history of soft tissue swelling on the ventral abdomen, which had failed to improve with antimicrobial therapy. There were no significant physical examination or neurological deficits on examination; however, the cat had a quiet demeanour for its age. Postprandial bile acids were increased (32 µmol/l; reference interval <25 µmol/l). An abdominal CT scan revealed changes consistent with an extrahepatic portosystemic shunt and inflammation of fat of the ventral abdominal body wall. Surgical biopsy and culture of the subcutaneous swelling identified non-infectious steatitis. Ten weeks following initial presentation, surgical exploration, liver biopsy and ligation of the portosystemic shunt were performed. Liver biopsy was submitted to the Anatomical Pathology Laboratory of Cornell University Animal Health Diagnostic Center, New York, USA. Histopathology revealed a ductal plate malformation (Caroli’s type), as well as changes consistent with a portosystemic shunt.

Relevance and novel information

Ductal plate malformations are rarely described in the veterinary literature. To our knowledge this is the first reported case of Caroli’s-type malformation in a cat. There are no biochemical changes that allow for differentiation of ductal plate malformations from other hepatopathies. Liver biopsy is required for a definitive diagnosis.

Therapeutic Targets in Polycystic Liver Disease

Polycystic liver diseases (PLD) are a group of genetic disorders initiated by mutations in several PLD-related genes and characterized by the presence of multiple cholangiocyte-derived hepatic cysts that progressively replace liver tissue. PLD co-exists with Autosomal Dominant Polycystic Kidney Disease (ADPKD) and Autosomal Recessive PKD as well as occurs alone (i.e., Autosomal Dominant Polycystic Liver Disease [ADPLD]). PLD associated with ADPKD and ARPKD belong to a group of disorders known as cholangiociliopathies since many disease-causative and disease-related proteins are expressed in primary cilia of cholangiocytes. Aberrant expression of these proteins in primary cilia affects their structures and functions promoting cystogenesis. Current medical therapies for PLD include symptomatic management and surgical interventions. To date, the only available drug treatment for PLD patients that halt disease progression and improve quality of life are somatostatin analogs. However, the modest clinical benefits, need for long-term maintenance therapy, and the high cost of treatment justify the necessity for more effective treatment options. Substantial evidence suggests that experimental manipulations with components of the signaling pathways that influence cyst development (e.g., cAMP, intracellular calcium, receptor tyrosine kinase, transient receptor potential cation channel subfamily V member 4 (TRPV4) channel, mechanistic target of rapamycin (mTOR), histone deacetylase (HDAC6), Cdc25A phosphatase, miRNAs and metalloproteinases) attenuate growth of hepatic cysts. Many of these targets have been evaluated in pre-clinical trials suggesting their value as potential new therapies. This review outlines the current clinical and preclinical treatment strategies for PLD.

Primary Cilia in Tumor Biology: The Primary Cilium as a Therapeutic Target in Cholangiocarcinoma

Cilia are microtubule-based organelles, which are ubiquitously expressed in epithelial cells. Cholangiocytes, the epithelial cells lining the biliary tree, have primary cilia extending from their apical plasma membrane into the ductal lumen, where the cilia function as multisensory organelles transducing environmental cues into the cell interior. The decrease or loss of primary cilia has been described in several malignancies, including cholangiocarcinoma, suggesting that the loss of cilia is a common occurrence in neoplastic transformation. In this short review, we describe the expression of cilia in several cancers, explore the mechanisms and consequences of ciliary loss, and discuss the potential use of the primary cilia as therapeutic targets.

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.

Increased YAP Activation Is Associated With Hepatic Cyst Epithelial Cell Proliferation in ARPKD/CHF

Autosomal recessive polycystic kidney disease/congenital hepatic fibrosis (ARPKD/CHF) is a rare but fatal genetic disease characterized by progressive cyst development in the kidneys and liver. Liver cysts arise from aberrantly proliferative cholangiocytes accompanied by pericystic fibrosis and inflammation. Yes-associated protein (YAP), the downstream effector of the Hippo signaling pathway, is implicated in human hepatic malignancies such as hepatocellular carcinoma, cholangiocarcinoma, and hepatoblastoma, but its role in hepatic cystogenesis in ARPKD/CHF is unknown. We studied the role of the YAP in hepatic cyst development using polycystic kidney (PCK) rats, an orthologous model of ARPKD, and in human ARPKD/CHF patients. The liver cyst wall epithelial cells (CWECs) in PCK rats were highly proliferative and exhibited expression of YAP. There was increased expression of YAP target genes, Ccnd1 (cyclin D1) and Ctgf (connective tissue growth factor), in PCK rat livers. Extensive expression of YAP and its target genes was also detected in human ARPKD/CHF liver samples. Finally, pharmacological inhibition of YAP activity with verteporfin and short hairpin (sh) RNA-mediated knockdown of YAP expression in isolated liver CWECs significantly reduced their proliferation. These data indicate that increased YAP activity, possibly through dysregulation of the Hippo signaling pathway, is associated with hepatic cyst growth in ARPKD/CHF.

An update on the pathophysiology and management of polycystic liver disease

Polycystic liver disease (PLD) is characterized by the presence of multiple cholangiocyte-derived hepatic cysts that progressively replace liver tissue. They are classified as an inherited ciliopathy /cholangiopathy as pathology exists at the level of the primary cilia of cholangiocytes. Aberrant expression of the proteins in primary cilia can impair their structures and functions, thereby promoting cystogenesis. Areas covered: This review begins by looking at the epidemiology of PLD and its natural history. It then describes the pathophysiology and corresponding potential treatment strategies for PLD. Expert commentary: Traditionally, therapies for symptomatic PLD have been limited to symptomatic management and surgical interventions. Such techniques are not completely effective, do not alter the natural history of the disease, and are linked with high rate of re-accumulation of cysts. As a result, there has been a push for drugs targeted at abnormal cellular signaling cascades to address deregulated proliferation, cell dedifferentiation, apoptosis and fluid secretion. Currently, the only available drug treatments that halt disease progression and improve quality of life in PLD patients are somatostatin analogues. Numerous preclinical studies suggest that targeting components of the signaling pathways that influence cyst development can ameliorate growth of hepatic cysts.

Diagnostic and therapeutic potentials of microRNAs in cholangiopathies

Cholangiopathies are a group of rare, devastating diseases that arise from damaged cholangiocytes, the cells that line the intra- and extra-hepatic bile ducts of the biliary epithelium. Cholangiopathies result in significant morbidity and mortality and are a major cause of liver transplantation. A better understanding of the underlying pathogenesis that influences cholangiocyte dysregulation and cholangiopathy progression is necessary, considering the dismal prognosis associated with these diseases. MicroRNAs are a class of small, non-coding RNAs that regulate post-transcriptional mRNA expression of specific genes. The role of microRNAs has expanded to include the initiation and development of many diseases, including cholangiopathies. Understanding microRNA regulation of cholangiopathies may provide diagnostic and therapeutic benefit for these diseases. In this review, the authors primarily focus on studies published within the last five years that help determine the diagnostic and therapeutic potential of microRNAs in cholangiopathies.

Using zebrafish to model liver diseases-Where do we stand?

Purpose of Review

The liver is the largest internal organ and performs both exocrine and endocrine function that is necessary for survival. Liver failure is among the leading causes of death and represents a major global health burden. Liver transplantation is the only effective treatment for end-stage liver diseases. Animal models advance our understanding of liver disease etiology and hold promise for the development of alternative therapies. Zebrafish has become an increasingly popular system for modeling liver diseases and complements the rodent models.

Recent Findings

The zebrafish liver contains main cell types that are found in mammalian liver and exhibits similar pathogenic responses to environmental insults and genetic mutations. Zebrafish have been used to model neonatal cholestasis, cholangiopathies, such as polycystic liver disease, alcoholic liver disease, and non-alcoholic fatty liver disease. It also provides a unique opportunity to study the plasticity of liver parenchymal cells during regeneration.

Summary

In this review, we summarize the recent work of building zebrafish models of liver diseases. We highlight how these studies have brought new knowledge of disease mechanisms. We also discuss the advantages and challenges of using zebrafish to model liver diseases.

Overexpression of Aquaporin 1 on cysts of patients with polycystic liver disease

BACKGROUND AND OBJECTIVE

Polycystic liver disease (PCLD) represents a group of genetic disorders that include autosomal dominant polycystic kidney disease (ADPKD) and isolated polycystic liver disease (iPCLD). There is currently no definitive treatment except for liver transplantation. The aim of this study was to assess the expression level of aquaporin 1 (AQP1) on the PCLD cysts with different sizes and provide the potential therapeutic target.

METHODS

We collected 3 normal bile ducts, and recruited 8 patients with simple liver cyst disease, 24 patients with ADPKD, and 17 patients with iPCLD. AQP1 expression in different types of cyst walls and in normal bile ducts was detected using real time quantitative PCR, western blot and immunofluorescence staining. We also compared AQP1 expression levels in cysts of different sizes. Besides, ionic concentrations, pH and osmolality of cyst fluid were analyzed.

RESULTS

The results showed that AQP1 expression in PCLD cysts was significantly higher than that in simple liver cysts and the normal bile ducts. In addition, a comparable increasing trend was found in cysts of smaller sizes to cysts of larger sizes. pH values, the sodium and chloride concentrations were higher in cyst fluid than that in the serum.

CONCLUSIONS

AQP1 was overexpressed in cystic cholangiocytes. A tendency of increased AQP1 protein expression in correlation with the cyst size was also found. These observations offered a direction into the molecular mechanisms of cyst expansion and maybe provide new treatment strategies to reduce fluid secretion into liver cysts.

Portal hypertension in polycystic liver disease patients does not affect wait-list or immediate post-liver transplantation outcomes

AIM

To establish the impact of portal hypertension (PH) on wait-list/post-transplant outcomes in patients with polycystic liver disease (PCLD) listed for liver transplantation.

METHODS

A retrospective single-centre case controlled study of consecutive patients listed for liver transplantation over 12 years was performed from our centre. PH in the PCLD cohort was defined by the one or more of following parameters: (1) presence of radiological or endoscopic documented varices from our own centre or the referral centre; (2) splenomegaly (> 11 cm) on radiology in absence of splenic cysts accounting for increased imaging size; (3) thrombocytopenia (platelets < 150 × 10⁹/L); or (4) ascites without radiological evidence of hepatic venous outflow obstruction from a single cyst.

RESULTS

Forty-seven PCLD patients (F: M = 42: 5) were listed for liver transplantation (LT) (single organ, n = 35; combined liver-kidney transplantation, n = 12) with 19 patients (40.4%) having PH. When comparing the PH group with non-PH group, the mean listing age (PH group, 50.6 (6.4); non-PH group, 47.1 (7.4) years; P = 0.101), median listing MELD (PH group, 12; non-PH group, 11; P = 0.422) median listing UKELD score (PH group, 48; non-PH group, 46; P = 0.344) and need for renal replacement therapy (P = 0.317) were similar. In the patients who underwent LT alone, there was no difference in the duration of ICU stay (PH, 3 d; non-PH, 2 d; P = 0.188), hospital stay length (PH, 9 d; non-PH, 10 d; P = 0.973), or frequency of renal replacement therapy (PH, 2/8; non-PH, 1/14; P = 0.121) in the immediate post-transplantation period.

CONCLUSION

Clinically apparent portal hypertension in patients with PCLD listed for liver transplantation does not appear to have a major impact on wait-list or peri-transplant morbidity.

Lin28 and let-7: roles and regulation in liver diseases

The diagnosis and treatment of liver disease remain a major health concern worldwide because of the diverse etiologies of this disease. For this reason, new therapeutic targets are greatly needed to halt the progression of this damaging disease. Upon initiation of liver injury by viral infection, autoimmune disease or toxin, and/or hepatitis, chronic disease may develop, which can progress to cirrhosis, hepatocellular carcinoma (HCC), cholangiocarcinoma, liver failure, or death. The Lin28/lethal-7 (let-7) molecular switch has emerged as a central regulator of multiorgan injuries and cancer development. Lin28 is a stem cell marker vital to initiation or maintenance of a stem cell phenotype. Lin28 has not been extensively studied in the liver, despite its ability to induce tissue regeneration via reprogramming of oxidative enzymes in other tissues and its involvement with numerous upstream regulators and downstream targets in liver disease. Theoretically, overexpression of Lin28 in certain forms of liver disease could be a potential treatment that aids in liver regeneration. Alternatively, Lin28 has been implicated numerous times in the progression of diverse cancer types and is associated with increased severity of disease. In this case, Lin28 could be a potential inhibitory target to prevent malignant transformation in the liver. This review seeks to characterize the role of Lin28 in liver disease.

Ductal Plate Malformation in the Liver of Boxer Dogs: Clinical and Histological Features

Ductal plate malformations (DPMs) represent developmental biliary disorders with a wide phenotypic spectrum. This study characterizes DPM in 30 Boxer dogs. Median age was 1.5 (range, 0.3-10.0) years, with 12 dogs <1 year. Clinical features included increased serum levels of liver enzymes (28), gastrointestinal signs (16), poor body condition (14), abdominal effusion (9), and hepatic encephalopathy (2). Additional malformations included gallbladder atresia (8), atrophied left liver (2), absent quadrate lobe with left-displaced gallbladder (1), portal vasculature atresia (left liver, 1), intrahepatic portosystemic shunt (1), and complex intrahepatic arteriovenous malformation (1). All dogs had portal tracts dimensionally expanded by a moderate-to-severe multiple small bile duct phenotype embedded in abundant extracellular matrix; 80% displayed variable portal-to-portal bridging. Quantitative analysis confirmed significantly increased fibrillar collagen and a 3-fold increased portal tract area relative to 6 Boxer and 10 non-Boxer controls. Biliary phenotype was dominated by tightly formed CK19-positive ductules, typically 10 to 15 μm in diameter, with 3 to >30 profiles per portal tract, reduced luminal apertures, and negative Ki-67 immunoreactivity. CK19-positive biliary epithelium intersected directly with zone 1 hepatocytes as a signature feature when considered with other DPM characteristics. Phenotypic variation included a multiple small bile duct phenotype (all dogs), predominantly thin-walled sacculated ducts (4), well-formed saccular ducts (4), and sacculated segmental, interlobular, and intralobular ducts (Caroli malformation, 2 dogs, one with bridging portal fibrosis). Histologic evidence of portal venous hypoperfusion accompanied increased biliary profiles in every case. We propose that this spectrum of disorders be referred to as DPM with appropriate modifiers to characterize the unique phenotypes.

Aortic coarctation and carotid artery aneurysm in a patient with Hardikar syndrome: Cardiovascular implications for affected individuals

Hardikar syndrome is a multiple congenital anomaly syndrome first characterized in 1992 by Hardikar et al. to describe two individuals with cholestasis, cleft lip/palate, retinal pigmentation, intestinal abnormalities, and genitourinary anomalies. Between 1992 and 2002, four individuals with Hardikar syndrome were reported in the literature. The fourth individual [Maluf et al. (2002), Transplantation 74:1058-1061; Poley and Proud (2008) Am J Med Genet Part A 146A:2473-2479], who had progressive cholestatic liver disease ultimately requiring liver transplantation, has continued to be followed at our institution. Recently, at the age of 14 years, during an evaluation for refractory hypertension, she was found to have developed coarctation of the aorta that was treated with aortic angioplasty and stenting, dramatically improving her hypertension. Further vascular investigation also revealed a small aneurysm of her carotid artery requiring neurosurgical evaluation and anticoagulant therapy. To our knowledge, these vascular anomalies have not been reported in Hardikar syndrome and the high association of congenital heart disease in the individuals with Hardikar syndrome has not been further addressed. Herein, we discuss this additional clinical information, speculate briefly on possible molecular etiologies, and discuss potential cardiac surveillance recommendations. We hope that broadening the known phenotype of this very rare disorder will further aid clinicians in their management and surveillance for these individuals.

The Cholangiopathies

Cholangiocytes (ie, the epithelial cells that line the bile ducts) are an important subset of liver cells. They are actively involved in the modification of bile volume and composition, are activated by interactions with endogenous and exogenous stimuli (eg, microorganisms, drugs), and participate in liver injury and repair. The term cholangiopathies refers to a category of chronic liver diseases that share a central target: the cholangiocyte. The cholangiopathies account for substantial morbidity and mortality given their progressive nature, the challenges associated with clinical management, and the lack of effective medical therapies. Thus, cholangiopathies usually result in end-stage liver disease requiring liver transplant to extend survival. Approximately 16% of all liver transplants performed in the United States between 1988 and 2014 were for cholangiopathies. For all these reasons, cholangiopathies are an economic burden on patients, their families, and society. This review offers a concise summary of the biology of cholangiocytes and describes a conceptual framework for development of the cholangiopathies. We also present the recent progress made in understanding the pathogenesis of and how this knowledge has influenced therapies for the 6 common cholangiopathies-primary biliary cirrhosis, primary sclerosing cholangitis, cystic fibrosis involving the liver, biliary atresia, polycystic liver disease, and cholangiocarcinoma-because the latest scientific progress in the field concerns these conditions. We performed a search of the literature in PubMed for published papers using the following terms: cholangiocytes, biliary epithelia, cholestasis, cholangiopathy, and biliary disease. Studies had to be published in the past 5 years (from June 1, 2009, through May 31, 2014), and non-English studies were excluded.

Screening analysis of candidate gene mutations in a kindred with polycystic liver disease

AIM: To find potential mutable sites by detecting mutations of the candidate gene in a kindred with polycystic liver disease (PCLD).

METHODS: First, we chose a kindred with PCLD and obtained five venous blood samples of this kindred after the family members signed the informed consent form. In the kindred two cases were diagnosed with PCLD, and the left three cases were normal individuals. All the blood samples were preserved at -85 °C. Second, we extracted the genomic DNA from the venous blood samples of the kindred using a QIAamp DNA Mini Kit and then performed long-range polymerase chain reaction (PCR) with different primers. The exons of PKD1 were all sequenced with the forward and reverse primers to ensure the accuracy of the results. Next, we purified the PCR products and directly sequenced them using Big Dye Terminator Chemistry version 3.1. The sequencing reaction was conducted with BiomekFX (Beckman). Finally, we analyzed the results.

RESULTS: A total of 42 normal exons were identified in detecting mutations of the PKD1 gene. A synonymous mutation occurred in exon 5. The mutation was a homozygous T in the proband and was C in the reference sequence. This mutation was located in the third codon and did not change the amino acid encoded by the codon. Missense mutations occurred in exons 11 and 35. These mutations were located in the second codon; they changed the amino acid sequence and existed in the dbSNP library. A nonsense mutation occurred in exon 15. The mutation was a heterozygous CT in the proband and was C in the reference sequence. This mutation was located in the first codon and resulted in a termination codon. This mutation had an obvious influence on the encoded protein and changed the length of the protein from 4303 to 2246 amino acids. This was a new mutation that was not present in the dbSNP library.

CONCLUSION: The nonsense mutation of exon 15 existed in the proband and in the third individual. Additionally, the proband was heterozygous for this mutation, so the mutable site was a pathogenic mutation.

MicroRNAs and benign biliary tract diseases

Cholangiocytes, the epithelial cells lining the biliary tree, represent only a small portion of the total liver cell population (3-5%), but they are responsible for the secretion of up to 40% of total daily bile volume. In addition, cholangiocytes are the target of a diverse group of liver diseases affecting the biliary tract, the cholangiopathies; for most of these conditions, the pathological mechanisms are unclear. MicroRNAs (miRNAs) are small, noncoding RNAs that posttranscriptionally regulate gene expression. Thus, it is not surprising that altered miRNA profiles underlie the dysregulation of several proteins involved in the pathobiology of the cholangiopathies, as well as showing promise as diagnostic and prognostic tools. Here the authors review recent work relevant to the role of miRNAs in the etiopathogenesis of several of the cholangiopathies (i.e., fibroinflammatory cholangiopathies and polycystic liver diseases), discuss their value as prognostic and diagnostic tools, and provide suggestions for further research.

TGR5 in the Cholangiociliopathies

A plasma membrane-bound G protein-coupled receptor, TGR5, that transmits bile acid signaling into a cellular response primarily via the cAMP pathway is expressed in human and rodent cholangiocytes and is localized to multiple, diverse subcellular compartments, including primary cilia. Ciliary-associated TGR5 plays an important role in cholangiocyte physiology and may contribute to a group of liver diseases referred to as the 'cholangiociliopathies', which include polycystic liver disease (PLD) and, possibly, cholangiocarcinoma and primary sclerosing cholangitis. Based on our observations that (1) ciliated and nonciliated cholangiocytes respond to TGR5 activation differently (i.e. the level of cAMP increases in nonciliated cholangiocytes but decreases in ciliated cells) and (2) hepatic cysts are derived from cholangiocytes that are characterized by both malformed cilia and increased cAMP levels, we hypothesized that TGR5-mediated cAMP signaling in cystic cholangiocytes contributes to hepatic cystogenesis. Indeed, our studies show that TGR5 is overexpressed and mislocalized in cystic cholangiocytes, and when activated by ligands, results in increased intracellular cAMP levels, cholangiocyte hyperproliferation and cyst growth. Our studies also show that genetic elimination of TGR5 in an animal model of PLD inhibits hepatic cystogenesis. Collectively, these data suggest the involvement of TGR5 in PLD and that TGR5 targeting in cystic cholangiocytes may have therapeutic potential.

Calcium signaling in cilia and ciliary-mediated intracellular calcium signaling: are they independent or coordinated molecular events?

A primary cilium is a solitary, slender, non-motile protuberance of structured microtubules (9+0) enclosed by plasma membrane. Housing components of the cell division apparatus between cell divisions, primary cilia also serve as specialized compartments for calcium signaling and hedgehog signaling pathways. Specialized sensory cilia such as retinal photoreceptors and olfactory cilia use diverse ion channels. An ion current has been measured from primary cilia of kidney cells, but the responsible genes have not been identified. The polycystin proteins (PC and PKD), identified in linkage studies of polycystic kidney disease, are candidate channels divided into two structural classes 11-transmembrane proteins (PKD1, PKD1L1 and PKD1L2) remarkable for a large extracellular amino terminus of putative cell adhesion domains and a G-protein-coupled receptor proteolytic site, and the 6-transmembrane channel proteins (PKD2, PKD2L1 and PKD2L2; TRPPs). Evidence indicates that the PKD1 proteins associate with the PKD2 proteins via coiled-coil domains. Here we use a transgenic mouse in which only cilia express a fluorophore and use it to record directly from primary cilia, and demonstrate that PKD1L1 and PKD2L1 form ion channels at high densities in several cell types. In conjunction with an accompanying manuscript, we show that the PKD1L1-PKD2L1 heteromeric channel establishes the cilia as a unique calcium compartment within cells that modulates established hedgehog pathways.

MicroRNAs in Cholangiopathies

Cholangiocytes, the cells lining bile ducts, comprise a small fraction of the total cellular component of the liver, yet perform the essential role of bile modification and transport of biliary and blood constituents. Cholangiopathies are a diverse group of biliary disorders with the cholangiocyte as the target cell; the etiopathogenesis of most cholangiopathies remains obscure. MicroRNAs are small non-coding RNAs that post-transcriptionally regulate gene expression. These small RNAs may not only be involved in the etiopathogenesis of disease, but are showing promise as diagnostic and prognostic tools. In this brief review, we summarize recent work regarding the role of microRNAs in the etiopathogenesis of several cholangiopathies, and discuss their utility as prognostic and diagnostic tools.

Liver involvement in children with ciliopathies

Abnormalities in primary cilia lead to diseases called ciliopathies. Multiple organ involvement is the norm since primary cilia are present in most cells. When cholangiocyte cilia are abnormal, ductal plate malformation ensues leading to such conditions as congenital hepatic fibrosis, Caroli disease or syndrome, or other fibrocystic disease.

Polycystic liver disease: ductal plate malformation and the primary cilium

Polycystic livers are found in autosomal dominant polycystic kidney disease (ADPKD), caused by polycystic kidney disease (PKD)1 and PKD2 mutations in virtually all cases, and in isolated polycystic liver disease (PCLD), where 20% of cases are caused by mutations in Protein kinase C substrate 80K-H (PRKCSH) or SEC63. Loss of heterozygosity in single hepatoblasts leads to underlying cystogenic ductal plate malformations. Crucially, actual components driving this development remain elusive. Recent advances have unraveled the roles of transforming growth factor (TGF)-β, Notch and Wnt signaling, transcriptional regulators such as hepatocyte nuclear factor (HNF)6 and HNF1β, as well as cilium function in hepatobiliary organogenesis. In polycystic liver disease, mutation or defective co-translational processing of key elements required for primary cilium formation have been implicated. This review recapitulates liver patterning factors in hepatobiliary development and extracts molecular players in hepatic cystogenesis.

HDAC6 is overexpressed in cystic cholangiocytes and its inhibition reduces cystogenesis

Polycystic liver disease (PLD) is a member of the cholangiopathies, a group of liver diseases in which cholangiocytes, the epithelia lining of the biliary tree, are the target cells. PLDs are caused by mutations in genes involved in intracellular signaling pathways, cell cycle regulation, and ciliogenesis, among others. We previously showed that cystic cholangiocytes have abnormal cell cycle profiles and malfunctioning cilia. Because histone deacetylase 6 (HDAC6) plays an important role in both cell cycle regulation and ciliary disassembly, we examined the role of HDAC6 in hepatic cystogenesis. HDAC6 protein was increased sixfold in cystic liver tissue and in cultured cholangiocytes isolated from both PCK rats (an animal model of PLD) and humans with PLD. Furthermore, pharmacological inhibition of HDAC6 by Tubastatin-A, Tubacin, and ACY-1215 decreased proliferation of cystic cholangiocytes in a dose- and time-dependent manner, and inhibited cyst growth in three-dimensional cultures. Importantly, ACY-1215 administered to PCK rats diminished liver cyst development and fibrosis. In summary, we show that HDAC6 is overexpressed in cystic cholangiocytes both in vitro and in vivo, and its pharmacological inhibition reduces cholangiocyte proliferation and cyst growth. These data suggest that HDAC6 may represent a potential novel therapeutic target for cases of PLD.

Pasireotide is more effective than octreotide in reducing hepatorenal cystogenesis in rodents with polycystic kidney and liver diseases

In polycystic liver (PLD) and kidney (PKD) diseases, increased cyclic adenosine monophosphate (cAMP) levels trigger hepatorenal cystogenesis. A reduction of the elevated cAMP by targeting somatostatin receptors (SSTRs) with octreotide (OCT; a somatostatin analog that preferentially binds to SSTR2) inhibits cyst growth. Here we compare the effects of OCT to pasireotide (PAS; a more potent somatostatin analog with broader receptor specificity) on: (1) cAMP levels, cell cycle, proliferation, and cyst expansion in vitro using cholangiocytes derived from control and PCK rats (a model of autosomal recessive PKD [ARPKD]), healthy human beings, and patients with autosomal dominant PKD (ADPKD); and (2) hepatorenal cystogenesis in vivo in PCK rats and Pkd2(WS25/-) mice (a model of ADPKD). Expression of SSTRs was assessed in control and cystic cholangiocytes of rodents and human beings. Concentrations of insulin-like growth factor 1 (IGF1) and vascular endothelial growth factor (VEGF) (both involved in indirect action of somatostatin analogs), and expression and localization of SSTRs after treatment were evaluated. We found that PAS was more potent (by 30%-45%) than OCT in reducing cAMP and cell proliferation, affecting cell cycle distribution, decreasing growth of cultured cysts in vitro, and inhibiting hepatorenal cystogenesis in vivo in PCK rats and Pkd2(WS25/-) mice. The levels of IGF1 (but not VEGF) were reduced only in response to PAS. Expression of SSTR1 and SSTR2 (but not SSTR3 and SSTR5) was decreased in cystic cholangiocytes compared to control. Although both OCT and PAS increased the immunoreactivity of SSTR2, only PAS up-regulated SSTR1; neither drug affected cellular localization of SSTRs.

CONCLUSION

PAS is more effective than OCT in reducing hepatorenal cystogenesis in rodent models; therefore, it might be more beneficial for the treatment of PKD and PLD.

Ciliary subcellular localization of TGR5 determines the cholangiocyte functional response to bile acid signaling

TGR5, the G protein-coupled bile acid receptor that transmits bile acid signaling into a cell functional response via the intracellular cAMP signaling pathway, is expressed in human and rodent cholangiocytes. However, detailed information on the localization and function of cholangiocyte TGR5 is limited. We demonstrated that in human (H69 cells) and rat cholangiocytes, TGR5 is localized to multiple, diverse subcellular compartments, with its strongest expression on the apical plasma, ciliary, and nuclear membranes. To evaluate the relationship between ciliary TGR5 and the cholangiocyte functional response to bile acid signaling, we used a model of ciliated and nonciliated H69 cells and demonstrated that TGR5 agonists induce opposite changes in cAMP and ERK levels in cells with and without primary cilia. The cAMP level was increased in nonciliated cholangiocytes but decreased in ciliated cells. In contrast, ERK signaling was induced in ciliated cholangiocytes but suppressed in cells without cilia. TGR5 agonists inhibited proliferation of ciliated cholangiocytes but activated proliferation of nonciliated cells. The observed differential effects of TGR5 agonists were associated with the coupling of TGR5 to Gαi protein in ciliated cells and Gαs protein in nonciliated cholangiocytes. The functional responses of nonciliated and ciliated cholangiocytes to TGR5-mediated bile acid signaling may have important pathophysiological significance in cilia-related liver disorders (i.e., cholangiociliopathies), such as polycystic liver disease. In summary, TGR5 is expressed on diverse cholangiocyte compartments, including a primary cilium, and its ciliary localization determines the cholangiocyte functional response to bile acid signaling.

The zebrafish as a model to study polycystic liver disease

In the polycystic liver diseases (PLD), genetic defects initiate the formation of cysts in the liver and kidney. In rodent models of PLD (i.e., the PCK rat and Pkd2(WS25/-) mouse), we have studied hepatorenal cystic disease and therapeutic approaches. In this study, we employed zebrafish injected with morpholinos against genes involved in the PLD, including sec63, prkcsh, and pkd1a. We calculated the liver cystic area, and based on our rodent studies, we exposed the embryos to pasireotide [1 μM] or vitamin K3 [100 μM] and assessed the endoplasmic reticulum (ER) in cholangiocytes in embryos treated with 4-phenylbutyrate (4-PBA). Our results show that (a) morpholinos against sec63, prkcsh, and pkd1a eliminate expression of the respective proteins; (b) phenotypic body changes included curved tail and the formation of hepatic cysts in zebrafish larvae; (c) exposure of embryos to pasireotide inhibited hepatic cystogenesis in the zebrafish models; and (d) exposure of embryos to 4-PBA resulted in the ER in cholangiocytes resolving from a curved to a smooth appearance. Our results suggest that the zebrafish model of PLD may provide a means to screen drugs that could inhibit hepatic cystogenesis.

Evidence from human and zebrafish that GPC1 is a biliary atresia susceptibility gene

BACKGROUND & AIMS

Biliary atresia (BA) is a progressive fibroinflammatory disorder of infants involving the extrahepatic and intrahepatic biliary tree. Its etiology is unclear but is believed to involve exposure of a genetically susceptible individual to certain environmental factors. BA occurs exclusively in the neonatal liver, so variants of genes expressed during hepatobiliary development could affect susceptibility. Genome-wide association studies previously identified a potential region of interest at 2q37. We continued these studies to narrow the region and identify BA susceptibility genes.

METHODS

We searched for copy number variants that were increased among patients with BA (n = 61) compared with healthy individuals (controls; n = 5088). After identifying a candidate gene, we investigated expression patterns of orthologues in zebrafish liver and the effects of reducing expression, with morpholino antisense oligonucleotides, on biliary development, gene expression, and signal transduction.

RESULTS

We observed a statistically significant increase in deletions at 2q37.3 in patients with BA that resulted in deletion of one copy of GPC1, which encodes glypican 1, a heparan sulfate proteoglycan that regulates Hedgehog signaling and inflammation. Knockdown of gpc1 in zebrafish led to developmental biliary defects. Exposure of the gpc1 morphants to cyclopamine, a Hedgehog antagonist, partially rescued the gpc1-knockdown phenotype. Injection of zebrafish with recombinant Sonic Hedgehog led to biliary defects similar to those of the gpc1 morphants. Liver samples from patients with BA had reduced levels of apical GPC1 in cholangiocytes compared with samples from controls.

CONCLUSIONS

Based on genetic analysis of patients with BA and zebrafish, GPC1 appears to be a BA susceptibility gene. These findings also support a role for Hedgehog signaling in the pathogenesis of BA.

Photoreceptor sensory cilia and ciliopathies: focus on CEP290, RPGR and their interacting proteins

Ciliopathies encompass a broad array of clinical findings associated with genetic defects in biogenesis and/or function of the primary cilium, a ubiquitous organelle involved in the transduction of diverse biological signals. Degeneration or dysfunction of retinal photoreceptors is frequently observed in diverse ciliopathies. The sensory cilium in a photoreceptor elaborates into unique outer segment discs that provide extensive surface area for maximal photon capture and efficient visual transduction. The daily renewal of approximately 10% of outer segments requires a precise control of ciliary transport. Here, we review the ciliopathies with associated retinal degeneration, describe the distinctive structure of the photoreceptor cilium, and discuss mouse models that allow investigations into molecular mechanisms of cilia biogenesis and defects. We have specifically focused on two ciliary proteins - CEP290 and RPGR - that underlie photoreceptor degeneration and syndromic ciliopathies. Mouse models of CEP290 and RPGR disease, and of their multiple interacting partners, have helped unravel new functional insights into cell type-specific phenotypic defects in distinct ciliary proteins. Elucidation of multifaceted ciliary functions and associated protein complexes will require concerted efforts to assimilate diverse datasets from in vivo and in vitro studies. We therefore discuss a possible framework for investigating genetic networks associated with photoreceptor cilia biogenesis and pathology.

MicroRNAs in biliary diseases

Cholangiopathies are a group of diseases primarily or secondarily affecting bile duct cells, and result in cholangiocyte proliferation, regression, and/or transformation. Their etiopathogenesis may be associated with a broad variety of causes of different nature, which includes genetic, neoplastic, immune-associated, infectious, vascular, and drug-induced alterations, or being idiopathic. miRNAs, small non-coding endogenous RNAs that post-transcriptionally regulate gene expression, have been associated with pathophysiological processes in different organs and cell types, and are postulated as potential targets for diagnosis and therapy. In the current manuscript, knowledge regarding the role of miRNAs in the development and/or progression of cholangiopathies has been reviewed and the most relevant findings in this promising field of hepatology have been highlighted.

Polycystic liver disease: a clinical review

Polycystic liver disease rarely occurs in isolation as part of autosomal dominant polycystic liver disease, but more commonly, it exists as an extra-renal manifestation of autosomal dominant polycystic kidney disease. The pathogenesis of polycystic liver disease involves defects in the primary cilium of the cholangiocyte, with genetic mutations that impair key proteins integral to the complex functioning of cilia. While most patients are asymptomatic and require no intervention aside from reassurance and genetic counseling, in a minority of patients, polycystic liver disease creates a myriad of symptoms from the compressive effects of enlarged cysts, and can even cause malnutrition and liver decompensation in the severest of cases. In patients with symptomatic disease, a variety of interventional radiology or surgical techniques can be considered, including aspiration with sclerotherapy of a dominant cyst, fenestration, segmental hepatic resection, and even liver transplantation. Although there are no curative medical options for polycystic liver disease, somatostatin analogs hold promise and have shown minimal efficacy in human studies. However, further research is needed to develop more efficacious medical treatments.

Cilia in vertebrate development and disease

Through the combined study of model organisms, cell biology, cell signaling and medical genetics we have significantly increased our understanding of the structure and functions of the vertebrate cilium. This ancient organelle has now emerged as a crucial component of certain signaling and sensory perception pathways in both developmental and homeostatic contexts. Here, we provide a snapshot of the structure, function and distribution of the vertebrate cilium and of the pathologies that are associated with its dysfunction.

Inhibition of Cdc25A suppresses hepato-renal cystogenesis in rodent models of polycystic kidney and liver disease

BACKGROUND & AIMS

In polycystic kidney disease and polycystic liver disease (PLD), the normally nonproliferative hepato-renal epithelia acquire a proliferative, cystic phenotype that is linked to overexpression of cell division cycle 25 (Cdc25)A phosphatase and cell-cycle deregulation. We investigated the effects of Cdc25A inhibition in mice and rats via genetic and pharmacologic approaches.

METHODS

Cdc25A(+/-) mice (which have reduced levels of Cdc25A) were cross-bred with polycystic kidney and hepatic disease 1 (Pkhd1(del2/del2)) mice (which have increased levels of Cdc25A and develop hepatic cysts). Cdc25A expression was analyzed in livers of control and polycystic kidney (PCK) rats, control and polycystic kidney 2 (Pkd2(ws25/-)) mice, healthy individuals, and patients with PLD. We examined effects of pharmacologic inhibition of Cdc25A with vitamin K3 (VK3) on the cell cycle, proliferation, and cyst expansion in vitro; hepato-renal cystogenesis in PCK rats and Pkd2(ws25/-)mice; and expression of Cdc25A and the cell-cycle proteins regulated by Cdc25A. We also examined the effects of the Cdc25A inhibitor PM-20 on hepato-renal cystogenesis in Pkd2(ws25/-) mice.

RESULTS

Liver weights and hepatic and fibrotic areas were decreased by 32%-52% in Cdc25A(+/-):Pkhd1(del2/del2) mice, compared with Pkhd1(del2/del2) mice. VK3 altered the cell cycle and reduced proliferation of cultured cholangiocytes by 32%-83% and decreased growth of cultured cysts by 23%-67%. In PCK rats and Pkd2(ws25/-) mice, VK3 reduced liver and kidney weights and hepato-renal cystic and fibrotic areas by 18%-34%. PM-20 decreased hepato-renal cystogenesis in Pkd2(ws25/-) mice by 15%.

CONCLUSIONS

Cdc25A inhibitors block cell-cycle progression and proliferation, reduce liver and kidney weights and cyst growth in animal models of polycystic kidney disease and PLD, and might be developed as therapeutics for these diseases.