Preclinical insights into cholangiopathies: disease modeling and emerging therapeutic targets

Single-Cell Transcriptomic Profiling of Cholangiocyte Organoids Derived from Bile Ducts of Primary Sclerosing Cholangitis Patients

BACKGROUND AND AIMS

Primary sclerosing cholangitis (PSC) is a chronic inflammatory liver disorder without effective medical treatment which is characterized by inflammation and fibrotic structures around the bile ducts. Biliary epithelial cells (cholangiocytes) are the target and potential disease drivers in PSC, yet little is known if cholangiocytes from PSC patients differ from non-PSC controls. To characterize cholangiocytes at early rather than end-stage disease, cholangiocyte organoids (COs) were derived from diseased bile ducts of PSC patients and compared to organoids generated from disease controls.

METHODS

Cholangiocytes were obtained during endoscopic retrograde cholangiopancreatography (ERCP) brushing of diseased bile duct areas and expanded as organoids using previously established culture methods. Stable CO lines were analyzed for cell type identity, basic cholangiocyte function, and transcriptomic signature.

RESULTS

We demonstrate that cholangiocytes, derived from the damaged area within the bile ducts of PSC patients, can be expanded in culture without displaying functional or genetic disease-related features. We further show that COs from patients who later were diagnosed with dysplasia exhibit higher expression of the cancer-associated genes PGC, FXYD2, MIR4435-2HG, and HES1.

CONCLUSIONS

Our results demonstrate that PSC organoids are largely similar to control organoids after culture and highlight the significance of COs as a tool for regenerative medicine approaches as well as their potential for discovering new potential biomarkers for diagnosing cholangiocarcinoma.

Biliary fibrosis is an important but neglected pathological feature in hepatobiliary disorders: from molecular mechanisms to clinical implications

Fibrosis resulting from pathological repair secondary to recurrent or persistent tissue damage often leads to organ failure and mortality. Biliary fibrosis is a crucial but easily neglected pathological feature in hepatobiliary disorders, which may promote the development and progression of benign and malignant biliary diseases through pathological healing mechanisms secondary to biliary tract injuries. Elucidating the etiology and pathogenesis of biliary fibrosis is beneficial to the prevention and treatment of biliary diseases. In this review, we emphasized the importance of biliary fibrosis in cholangiopathies and summarized the clinical manifestations, epidemiology, and aberrant cellular composition involving the biliary ductules, cholangiocytes, immune system, fibroblasts, and the microbiome. We also focused on pivotal signaling pathways and offered insights into ongoing clinical trials and proposing a strategic approach for managing biliary fibrosis-related cholangiopathies. This review will offer a comprehensive perspective on biliary fibrosis and provide an important reference for future mechanism research and innovative therapy to prevent or reverse fibrosis.

Navigating the liver landscape: upcoming pharmacotherapies for primary sclerosing cholangitis

INTRODUCTION

Primary sclerosing cholangitis (PSC) is a bile duct disorder characterized by ductular reaction, hepatic inflammation, and liver fibrosis. The pathogenesis of PSC is still undefined, and treatment options for patients are limited. Previous clinical trials evaluated drug candidates targeting various cellular functions and pathways, such as bile acid signaling and absorption, gut bacteria and permeability, and lipid metabolisms. However, most of phase III clinical trials for PSC were disappointing, except vancomycin therapy, and there are still no established medications for PSC with efficacy and safety confirmed by phase IV clinical trials.

AREAS COVERED

This review summarizes the currently ongoing or completed clinical studies for PSC, which are phase II or further, and discusses therapeutic targets and strategies, limitations, and future directions and possibilities of PSC treatments. A literature search was conducted in PubMed and ClinicalTrials.gov utilizing the combination of the searched term 'primary sclerosing cholangitis' with other keywords, such as 'clinical trials,' 'antibiotics,' or drug names. Clinical trials at phase II or further were included for consideration.

EXPERT OPINION

Only vancomycin demonstrated promising therapeutic effects in the phase III clinical trial. Other drug candidates showed futility or inconsistent results, and the search for novel PSC treatments is still ongoing.

Novel preclinical developments of the primary sclerosing cholangitis treatment landscape

INTRODUCTION

Primary sclerosing cholangitis (PSC) is a chronic cholestatic liver disease associated with inflammation, fibrosis, and destruction of intra- and extrahepatic bile ducts. Despite substantial recent advances in our understanding of PSC, the only proven treatment of PSC is liver transplantation. There is an urgent unmet need to find medical therapies for this disorder.

AREAS COVERED

Multiple drugs are currently under evaluation as therapeutic options for this disease. This article summarizes the literature on the various novel therapeutic options that have been investigated and are currently under development for the treatment of PSC.

EXPERT OPINION

In the next decade, more than one drug will likely be approved for the treatment of the disease, and we will be looking at combination therapies for the optimal management of the disease.

MSC-derived exosomes attenuate hepatic fibrosis in primary sclerosing cholangitis through inhibition of Th17 differentiation

Primary sclerosing cholangitis (PSC) is an autoimmune cholangiopathy characterized by chronic inflammation of the biliary epithelium and periductal fibrosis, with no curative treatment available, and liver transplantation is inevitable for end-stage patients. Human placental mesenchymal stem cell (hpMSC)-derived exosomes have demonstrated the ability to prevent fibrosis, inhibit collagen production and possess immunomodulatory properties in autoimmune liver disease. Here, we prepared hpMSC-derived exosomes (ExoMSC) and further investigated the anti-fibrotic effects and detailed mechanism on PSC based on Mdr2-/- mice and multicellular organoids established from PSC patients. The results showed that ExoMSC ameliorated liver fibrosis in Mdr2-/- mice with significant collagen reduction in the preductal area where Th17 differentiation was inhibited as demonstrated by RNAseq analysis, and the percentage of CD4+IL-17A+T cells was reduced both in ExoMSC-treated Mdr2-/- mice (Mdr2-/--Exo) in vivo and ExoMSC-treated Th17 differentiation progressed in vitro. Furthermore, ExoMSC improved the hypersecretory phenotype and intercellular interactions in the hepatic Th17 microenvironment by regulating PERK/CHOP signaling as supported by multicellular organoids. Thus, our data demonstrate the anti-fibrosis effect of ExoMSC in PSC disease by inhibiting Th17 differentiation, and ameliorating the Th17-induced microenvironment, indicating the promising potential therapeutic role of ExoMSC in liver fibrosis of PSC or Th17-related diseases.

Development of Scaffold-Free Three-Dimensional Cholangiocyte Organoids to Study the Progression of Primary Sclerosing Cholangitis

Organoids are novel in vitro models to study intercellular cross talk between the different types of cells in disease pathophysiology. To better understand the underlying mechanisms driving the progression of primary sclerosing cholangitis (PSC), scaffold-free multicellular three-dimensional cholangiocyte organoids (3D-CHOs) were developed using primary liver cells derived from normal subjects and patients with PSC. Human liver samples from healthy donors and patients with PSC were used to isolate primary cholangiocytes [epithelial cell adhesion molecule (EpCam)+/ cytokeratin-19+], liver endothelial cells (CD31+), and hepatic stellate cells (HSCs; CD31-/CD68-/desmin+/vitamin A+). 3D-CHOs were formed using cholangiocytes, HSCs, and liver endothelial cells, and kept viable for up to 1 month. Isolated primary cell lines and 3D-CHOs were further characterized by immunofluorescence, quantitative RT-PCR, and transmission electron microscopy. Transcription profiles for cholangiocytes (SOX9, CFTR, EpCAM, AE, SCT, and SCTR), fibrosis (ACTA2, COL1A1, DESMIN, and TGFβ1), angiogenesis (PECAM, VEGF, CDH5, and vWF), and inflammation (IL-6 and TNF-α) confirmed PSC phenotypes of 3D-CHOs. Because cholangiocytes develop a neuroendocrine phenotype and express neuromodulators, confocal immunofluorescence was used to demonstrate localization of the neurokinin-1 receptor within cytokeratin-19+ cholangiocytes and desmin+ HSCs. Moreover, 3D-CHOs from patients with PSC confirmed PSC phenotypes with up-regulated neurokinin-1 receptor, tachykinin precursor 1, and down-regulated membrane metalloendopeptidase. Scaffold-free multicellular 3D-CHOs showed superiority as an in vitro model in mimicking PSC in vivo phenotypes compared with two-dimensional cell culture, which can be used in PSC disease-related research.

CCL24 regulates biliary inflammation and fibrosis in primary sclerosing cholangitis

ˆCCL24 is a pro-fibrotic, pro-inflammatory chemokine expressed in several chronic fibrotic diseases. In the liver, CCL24 plays a role in fibrosis and inflammation, and blocking CCL24 led to reduced liver injury in experimental models. We studied the role of CCL24 in primary sclerosing cholangitis (PSC) and evaluated the potential therapeutic effect of blocking CCL24 in this disease. Multidrug resistance gene 2-knockout (Mdr2-/-) mice demonstrated CCL24 expression in liver macrophages and were used as a relevant experimental PSC model. CCL24-neutralizing monoclonal antibody, CM-101, significantly improved inflammation, fibrosis, and cholestasis-related markers in the biliary area. Moreover, using spatial transcriptomics, we observed reduced proliferation and senescence of cholangiocytes following CCL24 neutralization. Next, we demonstrated that CCL24 expression was elevated under pro-fibrotic conditions in primary human cholangiocytes and macrophages, and it induced proliferation of primary human hepatic stellate cells and cholangiocytes, which was attenuated following CCL24 inhibition. Correspondingly, CCL24 was found to be highly expressed in liver biopsies of patients with PSC. CCL24 serum levels correlated with Enhanced Liver Fibrosis score, most notably in patients with high alkaline phosphatase levels. These results suggest that blocking CCL24 may have a therapeutic effect in patients with PSC by reducing liver inflammation, fibrosis, and cholestasis.

Growth Hormone Signaling in Liver Diseases: Therapeutic Potentials and Controversies

Growth hormone (GH) and downstream insulin-like growth factor 1 (IGF1) signaling mediate growth and metabolism. GH deficiency causes short stature or dwarfism, and excess GH causes acromegaly. Although the association of GH/IGF1 signaling with liver diseases has been suggested previously, current studies are controversial and the functional roles of GH/IGF1 signaling are still undefined. GH supplementation therapy showed promising therapeutic effects in some patients, such as non-alcoholic fatty liver disease, but inhibition of GH signaling may be beneficial for other liver diseases, such as hepatocellular carcinoma. The functional roles of GH/IGF1 signaling and the effects of agonists/antagonists targeting this signaling may differ depending on the liver injury or animal models. This review summarizes current controversial studies of GH/IGF1 signaling in liver diseases and discusses therapeutic potentials of GH therapy.

Anti-Cholestatic Therapy with Obeticholic Acid Improves Short-Term Memory in Bile Duct-Ligated Mice

Patients with cholestatic liver disease, including those with primary biliary cholangitis, can experience symptoms of impaired cognition or brain fog. This phenomenon remains unexplained and is currently untreatable. Bile duct ligation (BDL) is an established rodent model of cholestasis. In addition to liver changes, BDL animals develop cognitive symptoms early in the disease process (before development of cirrhosis and/or liver failure). The cellular mechanisms underpinning these cognitive symptoms are poorly understood. Herein, the study explored the neurocognitive symptom manifestations, and tested potential therapies, in BDL mice, and used human neuronal cell cultures to explore translatability to humans. BDL animals exhibited short-term memory loss and showed reduced astrocyte coverage of the blood-brain barrier, destabilized hippocampal network activity, and neuronal senescence. Ursodeoxycholic acid (first-line therapy for most human cholestatic diseases) did not reverse symptomatic or mechanistic aspects. In contrast, obeticholic acid (OCA), a farnesoid X receptor agonist and second-line anti-cholestatic agent, normalized memory function, suppressed blood-brain barrier changes, prevented hippocampal network deficits, and reversed neuronal senescence. Co-culture of human neuronal cells with either BDL or human cholestatic patient serum induced cellular senescence and increased mitochondrial respiration, changes that were limited again by OCA. These findings provide new insights into the mechanism of cognitive symptoms in BDL animals, suggesting that OCA therapy or farnesoid X receptor agonism could be used to limit cholestasis-induced neuronal senescence.

Macrophages in cholangiopathies

PURPOSE OF REVIEW

Cholangiopathies are a heterogeneous class of liver diseases where cholangiocytes are the main targets of liver injury. Although available and emerging therapies mainly target bile acids (ursodeoxycholic acid/UDCA, 24-Norursodeoxycholic acid/norUDCA) and related signaling pathways (obeticholic acid, fibrates, FXR, and PPAR agonists), the mechanisms underlying inflammation, ductular reaction and fibrosis in cholestatic liver diseases remain poorly understood.

RECENT FINDINGS

Data from patients with cholestatic diseases, such as primary biliary cholangitis (PBC) or primary sclerosing cholangitis (PSC) as well as mouse models of biliary injury emphasize the role of immune cells in the pathogenesis of cholestatic disorders and indicate diverse functions of hepatic macrophages. Their versatile polarization phenotypes and their capacity to interact with other cell types (e.g. cholangiocytes, other immune cells) make macrophages central actors in the progression of cholangiopathies.

SUMMARY

In this review, we summarize recent findings on the response of hepatic macrophages to cholestasis and biliary injury and their involvement in the progression of cholangiopathies. Furthermore, we discuss how recent discoveries may foster the development of innovative therapies to treat patients suffering from cholestatic liver diseases, in particular, treatments targeting macrophages to limit hepatic inflammation.

Organoids and Spheroids as Models for Studying Cholestatic Liver Injury and Cholangiocarcinoma

Cholangiopathies, such as primary sclerosing cholangitis, biliary atresia, and cholangiocarcinoma, have limited experimental models. Not only cholangiocytes but also other hepatic cells including hepatic stellate cells and macrophages are involved in the pathophysiology of cholangiopathies, and these hepatic cells orchestrate the coordinated response against diseased conditions. Classic two-dimensional monolayer cell cultures do not resemble intercellular cell-to-cell interaction and communication; however, three-dimensional cell culture systems, such as organoids and spheroids, can mimic cellular interaction and architecture between hepatic cells. Previous studies have demonstrated the generation of hepatic or biliary organoids/spheroids using various cell sources including pluripotent stem cells, hepatic progenitor cells, primary cells from liver biopsies, and immortalized cell lines. Gene manipulation, such as transfection and transduction can be performed in organoids, and established organoids have functional characteristics which can be suitable for drug screening. This review summarizes current methodologies for organoid/spheroid formation and a potential for three-dimensional hepatic cell cultures as in vitro models of cholangiopathies.

The role of bile acids in cholestatic liver injury

Clinical disorders that impair bile flow result in retention of bile acids and cholestatic liver injury, characterized by parenchymal cell death, bile duct proliferation, liver inflammation and fibrosis. However, the pathogenic role of bile acids in the development of cholestatic liver injury remains incompletely understood. In this review, we summarize the current understanding of this process focusing on the experimental and clinical evidence for direct effects of bile acids on each major cellular component of the liver: hepatocytes, cholangiocytes, stellate cells and immune cells. During cholestasis bile acids accumulated in the liver, causing oxidative stress and mitochondrial injury in hepatocytes. The stressed hepatocytes respond by releasing inflammatory cytokines through activation of specific signaling pathways and transcription factors. The recruited neutrophils and other immune cells then cause parenchymal cell death. In addition, bile acids also stimulate the proliferation of cholangiocytes and stellate cells that are responsible for bile duct proliferation and liver fibrosis. This review explores the evidence for bile acid involvement in these phenomena. The role of bile acid receptors, TGR5, FXR and the sphingosine-1-phosphate receptor 2 and the inflammasome are also examined. We hope that better understanding of these pathologic effects will facilitate new strategies for treating cholestatic liver injury.

Dual β-Catenin and γ-Catenin Loss in Hepatocytes Impacts Their Polarity through Altered Transforming Growth Factor-β and Hepatocyte Nuclear Factor 4α Signaling

Hepatocytes are highly polarized epithelia. Loss of hepatocyte polarity is associated with various liver diseases, including cholestasis. However, the molecular underpinnings of hepatocyte polarization remain poorly understood. Loss of β-catenin at adherens junctions is compensated by γ-catenin and dual loss of both catenins in double knockouts (DKOs) in mice liver leads to progressive intrahepatic cholestasis. However, the clinical relevance of this observation, and further phenotypic characterization of the phenotype, is important. Herein, simultaneous loss of β-catenin and γ-catenin was identified in a subset of liver samples from patients of progressive familial intrahepatic cholestasis and primary sclerosing cholangitis. Hepatocytes in DKO mice exhibited defects in apical-basolateral localization of polarity proteins, impaired bile canaliculi formation, and loss of microvilli. Loss of polarity in DKO livers manifested as epithelial-mesenchymal transition, increased hepatocyte proliferation, and suppression of hepatocyte differentiation, which was associated with up-regulation of transforming growth factor-β signaling and repression of hepatocyte nuclear factor 4α expression and activity. In conclusion, concomitant loss of the two catenins in the liver may play a pathogenic role in subsets of cholangiopathies. The findings also support a previously unknown role of β-catenin and γ-catenin in the maintenance of hepatocyte polarity. Improved understanding of the regulation of hepatocyte polarization processes by β-catenin and γ-catenin may potentially benefit development of new therapies for cholestasis.

Aging and the Biological Response to Liver Injury

Interest in understanding the aging process has recently risen in the scientific community. Aging, commonly defined as the functional decline in the function of organs and tissues, is indeed the major risk factor for the development of many chronic diseases, such as cardiovascular diseases, pathologies of nervous system, or cancer. To date, the influence of aging in the pathophysiology of liver and biliary diseases is not fully understood. Although liver cells have a high regenerative capacity, hepatocytes and cholangiocytes undergo extensive molecular changes in response to aging. Following time-dependent damage induced by aging, liver cells initially activate compensatory mechanisms that, if hyperstimulated, may lead to the decline of regenerative capacity and the development of pathologies. A deeper understanding of molecular aging has undoubtedly the potential to improve the clinical management of patients, possibly unveiling new pathways for selective drug treatment.

Melatonin and circadian rhythms in liver diseases: Functional roles and potential therapies

Circadian rhythms and clock gene expressions are regulated by the suprachiasmatic nucleus in the hypothalamus, and melatonin is produced in the pineal gland. Although the brain detects the light through retinas and regulates rhythms and melatonin secretion throughout the body, the liver has independent circadian rhythms and expressions as well as melatonin production. Previous studies indicate the association between circadian rhythms with various liver diseases, and disruption of rhythms or clock gene expression may promote liver steatosis, inflammation, or cancer development. It is well known that melatonin has strong antioxidant effects. Alcohol drinking or excess fatty acid accumulation produces reactive oxygen species and oxidative stress in the liver leading to liver injuries. Melatonin administration protects these oxidative stress-induced liver damage and improves liver conditions. Recent studies have demonstrated that melatonin administration is not limited to antioxidant effects and it has various other effects contributing to the management of liver conditions. Accumulating evidence suggests that restoring circadian rhythms or expressions as well as melatonin supplementation may be promising therapeutic strategies for liver diseases. This review summarizes recent findings for the functional roles and therapeutic potentials of circadian rhythms and melatonin in liver diseases.

Neuroendocrine Changes in Cholangiocarcinoma Growth

Cholangiocarcinoma (CCA) is a highly aggressive malignancy that emerges from the biliary tree. There are three major classes of CCA-intrahepatic, hilar (perihilar), or distal (extrahepatic)-according to the location of tumor development. Although CCA tumors are mainly derived from biliary epithelia (i.e., cholangiocytes), CCA can be originated from other cells, such as hepatic progenitor cells and hepatocytes. This heterogeneity of CCA may be responsible for poor survival rates of patients, limited effects of chemotherapy and radiotherapy, and the lack of treatment options and novel therapies. Previous studies have identified a number of neuroendocrine mediators, such as hormones, neuropeptides, and neurotransmitters, as well as corresponding receptors. The mediator/receptor signaling pathways play a vital role in cholangiocyte proliferation, as well as CCA progression and metastases. Agonists or antagonists for candidate pathways may lead to the development of novel therapies for CCA patients. However, effects of mediators may differ between healthy or cancerous cholangiocytes, or between different subtypes of receptors. This review summarizes current understandings of neuroendocrine mediators and their functional roles in CCA.

Aging-Related Molecular Pathways in Chronic Cholestatic Conditions

Aging is commonly defined as the time-dependent functional decline of organs and tissues. Average life expectancy has increased considerably over the past century and is estimated to increase even further, consequently also the interest in understanding the aging processes. Although aging is not a disease, it is the major risk factor for the development of many chronic diseases. Pathologies, such as Primary Biliary Cholangitis (PBC) and Primary Sclerosing Cholangitis (PSC) are cholestatic liver diseases characterized by chronic inflammation, biliary damage and ultimately liver fibrosis, targeting specifically cholangiocytes. To date, the influence of aging in these biliary diseases is not fully understood. Currently, liver transplantation is the only solution because of lacking in efficiently therapies. Although liver cells have a high regenerative capacity, they undergo extensive molecular changes in response to aging. Following time-dependent damage induced by aging, the cells initially activate protective compensatory processes that, if hyperstimulated, can lead to the decline of regenerative ability and the development of pathologies. Recent studies have introduced novel therapeutic tools for cholangiopathies that have showed to have promising potential as novel therapies for PSC and PBC and for the development of new drugs. The recent advancements in understanding of molecular aging have undoubtedly the potential to unveil new pathways for selective drug treatments, but further studies are needed to deepen their knowledge.

UDCA, NorUDCA, and TUDCA in Liver Diseases: A Review of Their Mechanisms of Action and Clinical Applications

Bile acids (BAs) are key molecules in generating bile flow, which is an essential function of the liver. In the last decades, there have been great advances in the understanding of BA physiology, and new insights have emerged regarding the role of BAs in determining cell damage and death in several liver diseases. This new knowledge has helped to better delineate the pathophysiology of cholestasis and the adaptive responses of hepatocytes to cholestatic liver injury as well as of the mechanisms of injury of biliary epithelia. In this context, therapeutic approaches for liver diseases using hydrophilic BA (i.e., ursodeoxycholic acid, tauroursodeoxycholic, and, more recently, norursodeoxycholic acid), have been revamped. In the present review, we summarize current experimental and clinical data regarding these BAs and its role in the treatment of certain liver diseases.