Author Correction: The role of the secretin/secretin receptor axis in inflammatory cholangiocyte communication via extracellular vesicles

Recent Advances in Intrahepatic Biliary Epithelial Heterogeneity

Biliary epithelium (i.e., cholangiocytes) is a heterogeneous population of epithelial cells in the liver, which line small and large bile ducts and have individual responses and functions dependent on size and location in the biliary tract. We discuss the recent findings showing that the intrahepatic biliary tree is heterogeneous regarding (1) morphology and function, (2) hormone expression and signaling (3), response to injury, and (4) roles in liver regeneration. This review overviews the significant characteristics and differences of the small and large cholangiocytes. Briefly, it outlines the in vitro and in vivo models used in the heterogeneity evaluation. In conclusion, future studies addressing biliary heterogeneity's role in the pathogenesis of liver diseases characterized by ductular reaction may reveal novel therapeutic approaches.

Human Cholangiocytes Form a Polarized and Functional Bile Duct on Hollow Fiber Membranes

Liver diseases affect hundreds of millions of people worldwide; most often the hepatocytes or cholangiocytes are damaged. Diseases of the biliary tract cause severe patient burden, and cholangiocytes, the cells lining the biliary tract, are sensitive to numerous drugs. Therefore, investigations into proper cholangiocyte functions are of utmost importance, which is restricted, in vitro, by the lack of primary human cholangiocytes allowing such screening. To investigate biliary function, including transepithelial transport, cholangiocytes must be cultured as three-dimensional (3D) ductular structures. We previously established murine intrahepatic cholangiocyte organoid-derived cholangiocyte-like cells (CLCs) and cultured them onto polyethersulfone hollow fiber membranes (HFMs) to generate 3D duct structures that resemble native bile ducts at the structural and functional level. Here, we established an efficient, stepwise method for directed differentiation of human intrahepatic cholangiocyte organoids (ICOs) into CLCs. Human ICO-derived CLCs showed key characteristics of cholangiocytes, such as the expression of structural and functional markers, formation of primary cilia, and P-glycoprotein-mediated transport in a polarized fashion. The organoid cultures exhibit farnesoid X receptor (FXR)-dependent functions that are vital to liver bile acid homeostasis in vivo. Furthermore, human ICO-derived CLCs cultured on HFMs in a differentiation medium form tubular architecture with some tight, confluent, and polarized monolayers that better mimic native bile duct characteristics than differentiated cultures in standard 2D or Matrigel-based 3D culture plates. Together, our optimized differentiation protocol to obtain CLC organoids, when applied on HFMs to form bioengineered bile ducts, will facilitate studying cholangiopathies and allow developing therapeutic strategies.

Liver fluke granulin promotes extracellular vesicle-mediated crosstalk and cellular microenvironment conducive to cholangiocarcinoma

Crosstalk between malignant and neighboring cells contributes to tumor growth. In East Asia, infection with the liver fluke is a major risk factor for cholangiocarcinoma (CCA). The liver fluke Opisthorchis viverrini secretes a growth factor termed liver fluke granulin, a homologue of the human progranulin, which contributes significantly to biliary tract fibrosis and morbidity. Here, extracellular vesicle (EV)-mediated transfer of mRNAs from human cholangiocytes to naïve recipient cells was investigated following exposure to liver fluke granulin. To minimize the influence of endogenous progranulin, its cognate gene was inactivated using CRISPR/Cas9-based gene knock-out. Several progranulin-depleted cell lines, termed ΔhuPGRN-H69, were established. These lines exhibited >80% reductions in levels of specific transcript and progranulin, both in gene-edited cells and within EVs released by these cells. Profiles of extracellular vesicle RNAs (evRNA) from ΔhuPGRN-H69 for CCA-associated characteristics revealed a paucity of transcripts for estrogen- and Wnt-signaling pathways, peptidase inhibitors and tyrosine phosphatase related to cellular processes including oncogenic transformation. Several CCA-specific evRNAs including MAPK/AKT pathway members were induced by exposure to liver fluke granulin. By comparison, estrogen, Wnt/PI3K and TGF signaling and other CCA pathway mRNAs were upregulated in wild type H69 cells exposed to liver fluke granulin. Of these, CCA-associated evRNAs modified the CCA microenvironment in naïve cells co-cultured with EVs from ΔhuPGRN-H69 cells exposed to liver fluke granulin, and induced translation of MAPK phosphorylation related-protein in naïve recipient cells in comparison with control recipient cells. Exosome-mediated crosstalk in response to liver fluke granulin promoted a CCA-specific program through MAPK pathway which, in turn, established a CCA-conducive disposition.

Biology, Pathophysiological Role, and Clinical Implications of Exosomes: A Critical Appraisal

Exosomes are membrane-enclosed entities of endocytic origin, which are generated during the fusion of multivesicular bodies (MVBs) and plasma membranes. Exosomes are released into the extracellular milieu or body fluids; this process was reported for mesenchymal, epithelial, endothelial, and different immune cells (B-cells and dendritic cells), and was reported to be correlated with normal physiological processes. The compositions and abundances of exosomes depend on their tissue origins and cell types. Exosomes range in size between 30 and 100 nm, and shuttle nucleic acids (DNA, messenger RNAs (mRNAs), microRNAs), proteins, and lipids between donor and target cells. Pathogenic microorganisms also secrete exosomes that modulate the host immune system and influence the fate of infections. Such immune-modulatory effect of exosomes can serve as a diagnostic biomarker of disease. On the other hand, the antigen-presenting and immune-stimulatory properties of exosomes enable them to trigger anti-tumor responses, and exosome release from cancerous cells suggests they contribute to the recruitment and reconstitution of components of tumor microenvironments. Furthermore, their modulation of physiological and pathological processes suggests they contribute to the developmental program, infections, and human diseases. Despite significant advances, our understanding of exosomes is far from complete, particularly regarding our understanding of the molecular mechanisms that subserve exosome formation, cargo packaging, and exosome release in different cellular backgrounds. The present study presents diverse biological aspects of exosomes, and highlights their diagnostic and therapeutic potentials.

Inflammation and the Gut-Liver Axis in the Pathophysiology of Cholangiopathies

Cholangiocytes, the epithelial cells lining the bile ducts, represent the unique target of a group of progressive diseases known as cholangiopathies whose pathogenesis remain largely unknown. In normal conditions, cholangiocytes are quiescent and participate to the final bile volume and composition. Following exogenous or endogenous stimuli, cholangiocytes undergo extensive modifications of their phenotype. Reactive cholangiocytes actively proliferate and release a set of proinflammatory molecules, which act in autocrine/paracrine manner mediating the cross-talk with other liver cell types and innate and adaptive immune cells. Cholangiocytes themselves activate innate immune responses against gut-derived microorganisms or bacterial products that reach the liver via enterohepatic circulation. Gut microbiota has been implicated in the development and progression of the two most common cholangiopathies, i.e., primary sclerosing cholangitis (PSC) and primary biliary cholangitis (PBC), which have distinctive microbiota composition compared to healthy individuals. The impairment of intestinal barrier functions or gut dysbiosis expose cholangiocytes to an increasing amount of microorganisms and may exacerbate inflammatory responses thus leading to fibrotic remodeling of the organ. The present review focuses on the complex interactions between the activation of innate immune responses in reactive cholangiocytes, dysbiosis, and gut permeability to bacterial products in the pathogenesis of PSC and PBC.