Romina Fiorotto

Purpose of review: Cystic fibrosis liver disease (CFLD) is a significant nonpulmonary complication of cystic fibrosis, affecting approximately 5–10% of patients. It encompasses a spectrum of hepatic abnormalities ranging from mild, transient elevations in liver enzymes to advanced CFLD (aCFLD), which is marked by clinically relevant portal hypertension due to cirrhotic or noncirrhotic liver pathology. This review focuses on aCFLD as the clinically meaningful form of the disease and summarizes recent mechanistic insights into its pathogenesis that may inform the development of targeted therapeutic strategies. Recent findings: CFLD pathogenesis has been traditionally linked to defective bile secretion. Emerging evidence, however, highlights additional contributors, including cholangiocyte immune dysregulation, gut dysbiosis, and intestinal barrier dysfunction, which together promote hepatic inflammation. Furthermore, recent studies underscore the role of vascular alterations independent of cirrhosis, specifically noncirrhotic portal hypertension, as the main clinical feature in aCFLD. These findings support a multifactorial, multihit model of disease in the pathogenesis of CFLD. Summary: The complex interplay of these factors suggests that effective treatment for aCFLD may require a multifaceted approach. Advances in understanding the gut-liver axis and vascular contributions provide new therapeutic targets. Future research should focus on validating these findings and evaluating the efficacy of cystic fibrosis transmembrane conductance regulator modulators and microbiome-targeted treatments in altering the course of CFLD.

Background and Aims: Cholangiopathies are an important cause of morbidity and mortality. Their pathogenesis and treatment remain unclear in part because of the lack of disease models relevant to humans. Three-dimensional biliary organoids hold great promise; however, the inaccessibility of their apical pole and the presence of extracellular matrix (ECM) limits their application. We hypothesized that signals coming from the extracellular matrix regulate organoids’ 3-dimensional architecture and could be manipulated to generate novel organotypic culture systems. Approach and Results: Biliary organoids were generated from human livers and grown embedded into Culturex Basement Membrane Extract as spheroids around an internal lumen (EMB). When removed from the EMC, biliary organoids revert their polarity and expose the apical membrane on the outside (AOOs). Functional, immunohistochemical, and transmission electron microscope studies, along with bulk and single-cell transcriptomic, demonstrate that AOOs are less heterogeneous and show increased biliary differentiation and decreased expression of stem cell features. AOOs transport bile acids and have competent tight junctions. When cocultured with liver pathogenic bacteria (Enterococcus spp.), AOOs secrete a range of proinflammatory chemokines (ie, MCP1, IL8, CCL20, and IP-10). Transcriptomic analysis and treatment with a beta-1-integrin blocking antibody identified beta-1-integrin signaling as a sensor of the cell-extracellular matrix interaction and a determinant of organoid polarity. Conclusions: This novel organoid model can be used to study bile transport, interactions with pathobionts, epithelial permeability, cross talk with other liver and immune cell types, and the effect of matrix changes on the biliary epithelium and obtain key insights into the pathobiology of cholangiopathies.

Congenital hepatic fibrosis (CHF), a genetic cholangiopathy characterized by fibropolycystic changes in the biliary tree, is caused by mutations in the PKHD1 gene, leading to defective fibrocystin (FPC), changes in planar cell polarity (PCP) and increased β‐catenin‐dependent chemokine secretion. In this study, we aimed at understanding the role of Scribble (a protein involved in PCP), Yes‐associated protein (YAP), and β‐catenin in the regulation of the fibroinflammatory phenotype of FPC‐defective cholangiocytes. Immunohistochemistry showed that compared with wild type (WT) mice, in FPC‐defective ( Pkhd1 ^del4/del4 ) mice nuclear expression of YAP/TAZ in cystic cholangiocytes, significantly increased and correlated with connective tissue growth factor (CTGF) expression and pericystic fibrosis, while Scribble expression on biliary cyst cells was markedly decreased. Cholangiocytes isolated from WT mice showed intense Scribble immunoreactivity at the membrane, but minimal nuclear expression of YAP, which conversely increased, together with CTGF, after small interfering RNA (siRNA) silencing of Scribble. In FPC‐defective cholangiocytes, inhibition of YAP nuclear import reduced β‐catenin nuclear expression, and CTGF, integrin β6, CXCL1, and CXCL10 mRNA levels, whereas inhibition of β‐catenin signaling did not affect nuclear translocation of YAP. Notably, siRNA silencing of Scribble and YAP in WT cholangiocytes mimics the fibroinflammatory changes of FPC‐defective cholangiocytes. Conditional deletion of β‐catenin in Pkhd1 ^del4/del4 mice reduced cyst growth, inflammation and fibrosis, without affecting YAP nuclear expression. In conclusion, the defective anchor of Scribble to the membrane facilitates the nuclear translocation of YAP and β‐catenin with gain of a fibroinflammatory phenotype. The Scribble/YAP/β‐catenin axis is a critical factor in the sequence of events linking the genetic defect to fibrocystic trait of cholangiocytes in CHF.

Bile acids participate in the intestinal emulsion, digestion, and absorption of lipids and fat-soluble vitamins. When present in high concentrations, as in cholestatic liver diseases, bile acids can damage cells and cause inflammation. After the discovery of bile acids receptors about two decades ago, bile acids are considered signaling molecules. Besides regulating bile acid, xenobiotic, and nutrient metabolism, bile acids and their receptors have shown immunomodulatory properties and have been proposed as therapeutic targets for inflammatory diseases of the liver. This review focuses on bile acid–related signaling pathways that affect inflammation in the liver and provides an overview of the preclinical and clinical applications of modulators of these pathways for the treatment of cholestatic and autoimmune liver diseases.

Lack of a prompt and accurate diagnosis remains on top of the list of challenges faced by patients with rare liver diseases. Although rare liver diseases affect a significant percentage of the population as a group, when taken singularly they represent unique diseases and the approaches used for diagnosis of common liver diseases are insufficient. However, the development of new methods for the acquisition of molecular and clinical data (i.e., genomic, proteomics, metabolomics) and computational tools for their analysis and integration, together with advances in modeling diseases using stem cell-based technology [i.e., induced pluripotent stem cells (iPSCs) and tissue organoids] represent a promising and powerful tool to improve the clinical management of these patients. This is the goal of precision medicine, a novel approach of modern medicine that aims at delivering a specific treatment based on disease-specific biological insights and individual profile. This review will discuss the application and advances of these technologies and how they represent a new opportunity in hepatology.

Abnormal liver function tests (LFTs) are reported frequently in hospitalized coronavirus disease 2019 (COVID‐19) patients. A review of the literature shows that 46% of admitted COVID‐19 patients had elevated plasma aspartate aminotransferase (AST) and 35% had elevated alanine aminotransferase (ALT) levels on admission. Elevations of both AST and ALT are mostly below 5 times the upper reference limit and are associated with severe disease and increased inflammatory markers. AST and ALT elevations are more frequent in US patients compared to Chinese patients. Mild elevations in gamma‐glutamyltransferase (GGT), alkaline phosphatase (ALP) and total bilirubin are also reported, although less frequently. Significant impairment of liver function or overt liver failure as the cause of death in COVID‐19 rarely occur. There is no direct evidence of severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) hepatic infection, although a subset of hepatocytes and cholangiocytes express the host receptor utilized for cellular entry by SARS‐CoV‐2. The presence of pre‐existing liver disease in patients with elevated LFTs on admission has not been comprehensively assessed in most studies but is unlikely to account for all abnormalities in LFTs. Although abnormal LFTs are already frequently present upon admission before the start of treatment, drug‐induced liver injury should be taken into consideration, especially after the use of acetaminophen, lopinavir/ritonavir and remdesivir, which are potentially hepatotoxic. In conclusion, these initial observations suggest that the prevalence of abnormal LFTs is high in COVID‐19 patients, but that the clinical relevance is limited and that treatment is not required. The mechanisms underlying abnormal LFTs in COVID‐19 are likely multifactorial and related to a hyper‐inflammatory status and thrombotic microangiopathy that are observed in severe COVID‐19 disease.

Molecular and cellular research modalities for the study of liver pathologies have been tremendously improved over the recent decades. Advanced technologies offer novel opportunities to establish cell isolation techniques with excellent purity, paving the path for 2D and 3D microscopy and high-throughput assays (e.g., bulk or single-cell RNA sequencing). The use of stem cell and organoid research will help to decipher the pathophysiology of liver diseases and the interaction between various parenchymal and non-parenchymal liver cells. Furthermore, sophisticated animal models of liver disease allow for the in vivo assessment of fibrogenesis, portal hypertension and hepatocellular carcinoma (HCC) and for the preclinical testing of therapeutic strategies. The purpose of this review is to portray in detail novel in vitro and in vivo methods for the study of liver cell biology that had been presented at the workshop of the 8th meeting of the European Club for Liver Cell Biology (ECLCB-8) in October of 2018 in Bonn, Germany.

Chronic diseases of the biliary tree (cholangiopathies) represent one of the major unmet needs in clinical hepatology and a significant knowledge gap in liver pathophysiology. The common theme in cholangiopathies is that the target of the disease is the biliary tree. After damage to the biliary epithelium, inflammatory changes stimulate a reparative response with proliferation of cholangiocytes and restoration of the biliary architecture, owing to the reactivation of a variety of morphogenetic signals. Chronic damage and inflammation will ultimately result in pathological repair with generation of biliary fibrosis and clinical progression of the disease. The hallmark of pathological biliary repair is the appearance of reactive ductular cells, a population of cholangiocyte-like epithelial cells of unclear and likely mixed origin that are able to orchestrate a complex process that involves a number of different cell types, under joint control of inflammatory and morphogenetic signals. Several questions remain open concerning the histogenesis of reactive ductular cells, their role in liver repair, their mechanism of activation, and the signals exchanged with the other cellular elements cooperating in the reparative process. This review contributes to the current debate by highlighting a number of new concepts derived from the study of the pathophysiology of chronic cholangiopathies, such as congenital hepatic fibrosis, biliary atresia, and Alagille syndrome.