Polycystic Liver Diseases: Congenital Disorders of Cholangiocyte Signaling

doi:10.1053/j.gastro.2011.04.030

Gastroenterology

Volume 140, Issue 7, June 2011, Pages 1855-1859.e1

https://doi.org/10.1053/j.gastro.2011.04.030 Get rights and content

Polycystic liver diseases (PLD) are inherited disorders of the biliary epithelium, caused by genetic defects in proteins associated with intracellular organelles, mainly the endoplasmic reticulum and the cilium. PLD are characterized by the formation and progressive enlargement of multiple cysts scattered throughout the liver parenchyma, and include different entities, classified based on their pathology, inheritance pattern, involvement of the kidney and clinical features. PLD should be considered as congenital diseases of cholangiocyte signaling. Here, we will review the changes in signaling pathways involved in liver cyst formation and progression, and their impact on cholangiocyte physiology. Each pathway represents a potential target for therapies aimed at reducing disease progression.

Section snippets

Genetics of PLD

ADPKD is associated with mutations in 2 genes: “PKD1 or PKD2” which encode polycystin-1 (PC1) and polycystin-2 (PC2), respectively. PC1, a 460-kDA transmembrane protein, is localized in the primary cilium, plasma membrane, and adherens junctions. PC1 functions as a mechanoceptor that, sensing changes in apical flow, stimulates PC2-mediated Ca²⁺ signals.¹ In addition, cleaved fragments of the PC1 cytoplasmic tail, translocate to the nucleus and bind to β-catenin, preventing its transcriptional

Cellular Mechanisms of Liver Cyst Formation and Growth

In ADPKD and PCLD, liver cysts are scattered throughout the parenchyma, without connection to the biliary tree, which appears anatomically intact and without accompanying fibrosis. By contrast, in fibropolycystic diseases, liver cysts are connected to the biliary tree, which appear distorted and embedded in abundant fibrotic tissue. Cyst formation is not a common reaction of the biliary epithelium to liver damage. In response to obstructive cholestasis, the biliary epithelium generates multiple

Future Directions: PLD as Disorders of Cholangiocytes Signaling

There is convincing evidence that PLD are disorders of intracellular signaling; altered Ca²⁺ homeostasis, and increased production of cAMP being the main defects. Lower intracellular Ca²⁺ and higher cAMP levels have been consistently reported in cystic epithelia from ADPKD and ARPKD models.10, 23 The mechanistic relationship between defective polycystins/fibrocystin and the disorder of these second messengers is unclear. Here, we will provide a reasonable, yet speculative, working model based

Acknowledgments

The authors thank Carlo Spirli, PhD, for critically reading the manuscript.

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Liver progenitor cells may construct cysts having heterogeneous gene expression of liver-enriched transcription factors in mice with conditional knockout of the Hhex gene
2022, Biochemical and Biophysical Research Communications
The deletion of the Hhex (Hematopoietically expressed homeobox) gene causes agenesis of the liver and polycystic liver disease depending on its timing. The present study was undertaken to determine the role of the Hhex gene in not only signaling cascades to cyst and abnormal bile duct formation but also the liver progenitor contribution to cystic development. Liver-specific Hhex knockout mice (Alb-Cre/Hhex^loxP/loxP) in adult stages were used. Wild-type and conditional knockout (cKO) livers were immunohistologically compared for cell growth, and gene expression of liver functions, biliary markers and cystic markers. In Hhex cKO livers, cyst formation and dilated intrahepatic bile ducts were noted, which resembled the histology of the von Meyenburg complex. Ki67 immunohistochemistry showed that the growth activity in bile ducts and cysts of cKO livers was elevated compared with that of wild-type livers. There were far fewer liver progenitor cells or bile ductule cells around portal veins of cKO livers than in wild-type livers. Several liver-enriched transcription factors, including Foxa1 and Foxa2, were heterogeneously expressed in bile ducts and cysts of cKO livers whereas their expression in wild-type bile ducts was comparatively homogeneous. PC1 and PC2 immunohistochemistry revealed their up-regulation in cysts of cKO livers. These data indicate that Hhex is not only required for proper bile duct morphogenesis, but is also involved in cyst formation through promoted cell growth. Liver progenitor cells may form cysts. Unbalanced expression of liver-enriched transcription factors might be involved in cyst formation. Hhex cKO mice may be a good animal model for hepatic cystic diseases.
Autophagy-mediated reduction of miR-345 contributes to hepatic cystogenesis in polycystic liver disease
2021, JHEP Reports
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.
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.
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.
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.
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.
New insights on the role of vascular endothelial growth factor in biliary pathophysiology
2021, JHEP Reports
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.
Cholangiocyte death in ductopenic cholestatic cholangiopathies: Mechanistic basis and emerging therapeutic strategies
2019, Life Sciences
Citation Excerpt :
First, proliferating cholangiocytes secrete a number of mediators, such as cytokines, chemokines, and other profibrogenic factors, that act via paracrine mechanisms to stimulate myofibroblast activation, migration, and proliferation, thus promoting liver fibrosis [96]. Second, the stimuli needed to activate otherwise quiescent cholangiocytes may trigger uncontrolled cholangiocyte hyperproliferation in susceptible individuals, resulting in liver diseases associated with growth-promoting effects, such as polycystic liver diseases [246] and cholangiocarcinoma [247]. This therapeutic approach may be particularly dangerous in diseases with a high lifetime risk of developing cholangiocarcinoma, such as PSC and CF-associated liver disease, especially if associated with an adjuvant antiapoptotic therapeutic strategy [248].
Among hepatic diseases, cholestatic ductopenic cholangiopathies are poorly studied, and they are rarely given the importance they deserve, especially considering their high incidence in clinical practice. Although cholestatic ductopenic cholangiopathies have different etiologies and pathogenesis, all have the same target (the cholangiocyte) and similar mechanistic basis of cell death. Cholestatic cholangiopathies are characterized, predominantly, by obstructive or functional damage in the biliary epithelium, resulting in an imbalance between proliferation and cholangiocellular death; this leads to the progressive disappearance of bile ducts, as has been shown to occur in primary sclerosing cholangitis, primary biliary cholangitis, low-phospholipid-associated cholelithiasis syndrome, cystic fibrosis-related liver disease, and drug-induced ductopenia, among other biliary disorders. This review summarizes the features of the more common ductopenic syndromes and the cellular mechanisms involved in cholengiocellular death, with focus on the main forms of cholangiocyte death described so far, namely apoptosis, autophagy, necrosis, and necroptosis. It also emphasizes the importance to study in depth the molecular mechanisms of cholengiocyte death to make possible to counteract them with therapeutic purposes. These therapeutic strategies are limited in number and efficacy at present, and this is why it is important to find complementary, safe strategies to stimulate cholangiocellular proliferation in order favor bile duct replenishment as well. Successful in finding appropriate treatments would prevent the patient from having liver transplantation as the only therapeutic alternative.
The mitochondrial uncoupling protein 2 gene is causal for the spontaneous polycystic liver diseases in mice
2018, Mitochondrion
Citation Excerpt :
Since Pkd1 interacts with Pkd2, Prkcsh and Sec63 (Fedeles et al., 2011), it points towards that Ucp2 is closely related with the gene network (a predicted gene network was shown in the supplementary Fig. 3). The gene products of Pkd1 and Pkd2 are polycystin-1 (PC1) and polycystin-2 (PC2 or TRPP2), respectively and are co-localized in the cilium (Strazzabosco and Somlo, 2011). In ADPLD patients, 20% of them carry mutations in PRKCSH (up to 15%), SEC63 or LRP5 (Perugorria et al., 2014).
Polycystic liver diseases (PCLDs) are autosomal dominant disorders. To date, 3 genes are known to be associated with the disease, SEC63 and PRKCSH and LRP5. Here, we report that mice deficient in the mitochondrial uncoupling protein 2 gene (Ucp2^−/−) spontaneously developed PCLDs when they were over 12 months old. Macroscopical observation, blood chemistry as well as histopathological analysis demonstrated the PCLDs found in Ucp2^−/− mice were very similar to the findings in human PCLDs. This is the first report describing the gene encoding mitochondrial protein is causative for PCLDs. UCP2 may be a biomarker of the PCLDs in humans.
Pathophysiologic implications of innate immunity and autoinflammation in the biliary epithelium
2018, Biochimica et Biophysica Acta - Molecular Basis of Disease
Citation Excerpt :
The function of FPC is still unknown, and a variety of cellular functions, including proliferation, differentiation, tubulogenesis, planar cell polarity and cell-matrix interaction seem to be influenced by FPC. Biliary cysts, which originate from the abnormal remodeling of the fetal ductal plate structures, progressively enlarge in association with a dense fibrosis and a portal inflammatory infiltrate [38,39]. In this pathogenetic sequence, in sharp contrast with acquired cholangiopathies where portal fibrosis is associated with cell necrosis or apoptosis, an overt necroinflammation of the biliary epithelium is typically absent [39].
The most studied physiological function of biliary epithelial cells (cholangiocytes) is to regulate bile flow and composition, in particular the hydration and alkalinity of the primary bile secreted by hepatocytes. After almost three decades of studies it is now become clear that cholangiocytes are also involved in epithelial innate immunity, in inflammation, and in the reparative processes in response to liver damage. An increasing number of evidence highlights the ability of cholangiocyte to undergo changes in phenotype and function in response to liver damage. By participating actively to the immune and inflammatory responses, cholangiocytes represent a first defense line against liver injury from different causes. Indeed, cholangiocytes express a number of receptors able to recognize pathogen- or damage-associated molecular patterns (PAMPs/DAMPs), such as Toll-like receptors (TLR), which modulate their pro-inflammatory behavior. Cholangiocytes can be both the targets and the initiators of the inflammatory process. Derangements of the signals controlling these mechanisms are at the basis of the pathogenesis of different cholangiopathies, both hereditary and acquired, such as cystic fibrosis-related liver disease and sclerosing cholangitis. This article is part of a Special Issue entitled: Cholangiocytes in Health and Diseaseedited by Jesus Banales, Marco Marzioni, Nicholas LaRusso and Peter Jansen.

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: Conflicts of interest The authors disclose no conflicts.

: Funding Supported by NIH DK079005, by Yale University Liver Center (NIH DK34989) and PKD Foundation to MS; DK51041 and DK54053 to S.S.

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Mini-Reviews and PerspectivePolycystic Liver Diseases: Congenital Disorders of Cholangiocyte Signaling