Aging-Related Expression of Twinfilin-1 Regulates Cholangiocyte Biological Response to Injury.

Disorders of the biliary tree develop and progress differently according to patient age. It is currently not known whether the aging process affects the response to injury of cholangiocytes. The aim of this study was to identify molecular pathways associated with cholangiocyte aging and to determine their effects in the biological response to injury of biliary cells. A panel of microRNAs (miRs) involved in aging processes was evaluated in cholangiocytes of young and old mice (2 months and 22 months of age, respectively) and subjected to a model of sclerosing cholangitis. Intracellular pathways that are common to elevated miRs were identified by in silico analysis. Cell proliferation and senescence were evaluated in Twinfilin-1 (Twf1) knocked-down cells. In vivo, senescence-accelerated prone mice (Samp8, a model for accelerated aging), Twf1-/- , or their respective controls were subjected to DDC (3,5-diethoxycarbonyl-1,4-dihydrocollidine). Cholangiocytes from DDC-treated mice showed up-regulation of a panel of aging-related miRs. Twf1 was identified by in silico analysis as a common target of the up-regulated miRs. Twf1 expression was increased both in aged and diseased cholangiocytes, and in human cholangiopathies. Knock-down of Twf1 in cholangiocytes reduced cell proliferation. Senescence and senescence-associated secretory phenotype marker expression increased in Twf1 knocked-down cholangiocytes following pro-proliferative and pro-senescent (10-day lipopolysaccharide) stimulation. In vivo, Samp8 mice showed increased biliary proliferation, fibrosis, and Twf1 protein expression level, whereas Twf1-/- had a tendency toward lower biliary proliferation and fibrosis following DDC administration compared with control animals. Conclusion: We identified Twf1 as an important mediator of both cholangiocyte adaptation to aging processes and response to injury. Our data suggest that disease and aging might share common intracellular pathways.

Role of inflammation and proinflammatory cytokines in cholangiocyte pathophysiology.

Cholangiocytes, the epithelial cells lining the bile ducts, are an important subset of liver cells. They are involved in the modification of bile volume and composition, and respond to endogenous and exogenous stimuli. Along the biliary tree, two different kinds of cholangiocytes exist: small and large cholangiocytes. Each type has different features and biological role in physiologic and pathologic conditions, and their immunobiology is important for understanding biliary diseases. Cholangiocytes provide the first line of defence against luminal microbes in the hepatobiliary system. Indeed, they express a variety of pattern recognition receptors and may start an antimicrobial defence activating a set of intracellular signalling cascades. In response to injury, cholangiocytes that are normally quiescent become reactive and acquire a neuroendocrine-like phenotype with the release of proinflammatory mediators and antimicrobial peptides, which support biliary epithelial integrity. These molecules act in an autocrine/paracrine manner to modulate cholangiocyte biology and determine the evolution of biliary damage. Failure or dysregulation of such mechanisms may influence the progression of cholangiopathies, a group of diseases that selectively target biliary cells. In this review, we focus on the response of cholangiocytes in inflammatory conditions, with a particular focus on the mechanism driving cholangiocytes adaptation to damage. This article is part of a Special Issue entitled: Cholangiocytes in Health and Diseaseedited by Jesus Banales, Marco Marzioni, Nicholas LaRusso and Peter Jansen.

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.

Lack of NLRP3-inflammasome leads to gut-liver axis derangement, gut dysbiosis and a worsened phenotype in a mouse model of NAFLD.

Non-Alcoholic Fatty Liver Disease (NAFLD) represents the most common form of chronic liver injury and can progress to cirrhosis and hepatocellular carcinoma. A "multi-hit" theory, involving high fat diet and signals from the gut-liver axis, has been hypothesized. The role of the NLRP3-inflammasome, which senses dangerous signals, is controversial. Nlrp3-/- and wild-type mice were fed a Western-lifestyle diet with fructose in drinking water (HFHC) or a chow diet. Nlrp3-/--HFHC showed higher hepatic expression of PPAR γ2 (that regulates lipid uptake and storage) and triglyceride content, histological score of liver injury and greater adipose tissue inflammation. In Nlrp3-/--HFHC, dysregulation of gut immune response with impaired antimicrobial peptides expression, increased intestinal permeability and the occurrence of a dysbiotic microbiota led to bacterial translocation, associated with higher hepatic expression of TLR4 (an LPS receptor) and TLR9 (a receptor for double-stranded bacterial DNA). After antibiotic treatment, gram-negative species and bacterial translocation were reduced, and adverse effects restored both in liver and adipose tissue. In conclusion, the combination of a Western-lifestyle diet with innate immune dysfunction leads to NAFLD progression, mediated at least in part by dysbiosis and bacterial translocation, thus identifying new specific targets for NAFLD therapy.

Author Correction: Lack of NLRP3-inflammasome leads to gut-liver axis derangement, gut dysbiosis and a worsened phenotype in a mouse model of NAFLD.

A correction to this article has been published and is linked from the HTML version of this paper. The error has been fixed in the paper.