The Neuropeptide Galanin Is Up-Regulated during Cholestasis and Contributes to Cholangiocyte Proliferation

Exposure to Gulf war illness-related chemicals exacerbates alcohol- induced liver damage in rodents

Gulf War Illness (GWI) describes a series of symptoms suffered by veterans of the Gulf war consisting of cognitive, neurological and gastrointestinal dysfunctions. Two chemicals associated with GWI are the insecticide permethrin (PER) and the nerve gas prophylactic pyridostigmine-bromide (PB). In this study we assessed the effects of PER and PB exposure on pathology and subsequent alcohol (EtOH)-induced liver injury, and the influence of a macrophage depletor, PLX3397, on EtOH-induced liver damage in PER/PB- treated mice. Male C57BL/6 mice were injected daily with vehicle or PER/PB for 10 days, followed by 4 months recovery, then treatment with PLX3397 and a chronic-plus-single-binge EtOH challenge for 10 days. PER/PB exposure resulted in the protracted increase in liver transaminases in the serum and induced chronic low-level microvesicular steatosis and inflammation in GWI vs Naïve mice up to 4 months after cessation of exposure. Furthermore, prior exposure to PER/PB also resulted in exacerbated response to EtOH-induced liver injury, with enhanced steatosis, ductular reaction and fibrosis. The enhanced EtOH-induced liver damage in GWI-mice was attenuated by strategies designed to deplete macrophages in the liver. Taken together, these data suggest that exposure to GWI-related chemicals may alter the liver's response to subsequent ethanol exposure.

Galanin System in the Human Bile Duct and Perihilar Cholangiocarcinoma

BACKGROUND

Perihilar cholangiocarcinoma (pCCA) is characterised by poor outcomes. Early diagnosis is essential for patient survival. The peptide galanin (GAL) and its receptors GAL1-3 are expressed in various tumours. Detailed characterisation of the GAL system in pCCA is lacking. Our study sought to characterise GAL and GAL1-3 receptor (GAL1-3-R) expression in the healthy human bile duct, in cholestasis and pCCA.

METHODS

Immunohistochemical staining was performed in healthy controls (n = 5) and in the peritumoural tissues (with and without cholestasis) (n = 20) and tumour tissues of pCCA patients (n = 33) using validated antibodies. The score values of GAL and GAL1-3-R expression were calculated and statistically evaluated.

RESULTS

GAL and GAL1-R were expressed in various bile duct cell types. GAL2-R was only slightly but still expressed in almost all the examined tissues, and GAL3-R specifically in cholangiocytes and capillaries. In a small pCCA patient cohort (n = 18), high GAL expression correlated with good survival, whereas high GAL3-R correlated with poor survival.

CONCLUSIONS

Our in-depth characterisation of the GAL system in the healthy human biliary duct and pCCA in a small patient cohort revealed that GAL and GAL3-R expression in tumour cells of pCCA patients could potentially represent suitable biomarkers for survival.

Galanin ameliorates liver inflammation and fibrosis in mice by activating AMPK/ACC signaling and modifying macrophage inflammatory phenotype

Background and aims

Galanin is a naturally occurring peptide that plays a critical role in regulating inflammation and energy metabolism, with expression in the liver. The exact involvement of galanin in non-alcoholic fatty liver disease and related fibrosis remains controversial.

Methods

The effects of subcutaneously administered galanin were studied in mice with non-alcoholic steatohepatitis (NASH) induced by a high-fat and high-cholesterol diet for 8 weeks, and in mice with liver fibrosis induced by CCl4 for 7 weeks. The underlying mechanism was also studied in vitro on murine macrophage cells (J774A.1 and RAW264.7).

Results

Galanin reduced inflammation, CD68-positive cell count, MCP-1 level, and mRNA levels of inflammation-related genes in the liver of NASH mice. It also mitigated liver injury and fibrosis caused by CCl4. In vitro, galanin had anti-inflammatory effects on murine macrophages, including reduced phagocytosis and intracellular reactive oxygen species (ROS). Galanin also activated AMP-activated protein kinase (AMPK)/acetyl-CoA carboxylase (ACC) signaling.

Conclusion

Galanin ameliorates liver inflammation and fibrosis in mice, potentially by modifying macrophage inflammatory phenotype and activating AMPK/ACC signaling.

Current Perspectives of Neuroendocrine Regulation in Liver Fibrosis

Liver fibrosis is a complicated process that involves different cell types and pathological factors. The excessive accumulation of extracellular matrix (ECM) and the formation of fibrotic scar disrupt the tissue homeostasis of the liver, eventually leading to cirrhosis and even liver failure. Myofibroblasts derived from hepatic stellate cells (HSCs) contribute to the development of liver fibrosis by producing ECM in the area of injuries. It has been reported that the secretion of the neuroendocrine hormone in chronic liver injury is different from a healthy liver. Activated HSCs and cholangiocytes express specific receptors in response to these neuropeptides released from the neuroendocrine system and other neuroendocrine cells. Neuroendocrine hormones and their receptors form a complicated network that regulates hepatic inflammation, which controls the progression of liver fibrosis. This review summarizes neuroendocrine regulation in liver fibrosis from three aspects. The first part describes the mechanisms of liver fibrosis. The second part presents the neuroendocrine sources and neuroendocrine compartments in the liver. The third section discusses the effects of various neuroendocrine factors, such as substance P (SP), melatonin, as well as α-calcitonin gene-related peptide (α-CGRP), on liver fibrosis and the potential therapeutic interventions for liver fibrosis.

Neuromedin S Regulates Steroidogenesis through Maintaining Mitochondrial Morphology and Function via NMUR2 in Goat Ovarian Granulosa Cells

Neuromedin S (NMS) plays various roles in reproductive regulation, while the mechanism by which NMS regulates ovarian steroidogenesis remains unclear. In the current study, we confirmed the enhancement role of NMS in steroidogenesis in goat ovarian granulosa cells (GCs). To further explore the specific mechanism, we conducted a knockdown of NMUR2 in GCs followed by treatment with NMS and determined the effects of NMS treatment on mitochondrial morphology and function. The results found that NMS treatment increased the production of estrogen and up-regulated the expression of STAR, CYP11A1, 3BHSD, and CYP19A1, while the effects of NMS treatment were blocked by the knockdown of NMUR2 in goat GCs. Moreover, NMS treatment enhanced the fusion of mitochondria and up-regulated the expression of OPA1, MFN1, and MFN2, and increased mitochondrial membrane potential, the activity of respiratory chain enzymes and ATP production by maintaining a low expression level of mitochondrial unfolded protein response markers. The effects of NMS treatment on mitochondria were reversed by NMUR2 knockdown and NMS cotreatment. The possible mechanism of the results above was revealed by NMS treatment activating the Hippo pathway effector YAP1 and then managing the expression of phosphorylation PPARGC1A (Ser571). Together, these data showed that NMS promoted the fusion of mitochondria and protected mitochondrial function from mitochondrial unfolded protein response possibly via the NMUR2/YAP1/PPARGC1A pathway, thereby affecting the steroidogenesis of goat GCs. By elaborating the potential mechanism of NMS in regulating estrogen production in goat GCs, our results can serve as the mechanism reference for follicular growth and development.

Leptin Enhances Hepatic Fibrosis and Inflammation in a Mouse Model of Cholestasis

Leptin is an adipokine with roles in food intake and energy metabolism through its actions on neurons in the hypothalamus. The role of leptin in obesity and cardiovascular disorders is well documented. However, its influence on liver conditions such as cholestasis is poorly understood. The effects of exogenous leptin and leptin-neutralizing antibody on biliary hyperplasia, hepatic fibrosis, and inflammation in the multidrug resistance protein 2 knockout (Mdr2KO) mouse model of cholestasis were assessed by quantifying markers specific for cholangiocytes, activated hepatic stellate cells (HSCs), and cytokines. Serum and hepatic leptin were increased in Mdr2KO mice compared with FVB/NJ (FVBN) controls, and exogenous leptin enhanced biliary hyperplasia and liver fibrosis in Mdr2KO and FVBN mice. Leptin administration increased hepatic expression of C-C motif chemokine ligand 2 and IL-6 in Mdr2KO mice. In contrast, leptin-neutralizing antibody reduced intrahepatic bile duct mass and decreased HSC activation in Mdr2KO mice compared with FVBN controls. Sex-related differences were noted, with female Mdr2KO mice having more leptin than males. In cholangiocytes and LX2 cells in vitro, leptin increased phosphorylated Akt and stimulated cell proliferation. Leptin receptor siRNA and inhibitors of Akt phosphorylation impaired leptin-induced cell proliferation and proinflammatory cytokines. The current data suggest that leptin is abnormally increased in cholestatic mice, and excess leptin increases ductular reaction, hepatic fibrosis, and inflammation via leptin receptor-mediated phosphorylation of Akt in cholangiocytes and HSCs.

Novel Role of miR-18a-5p and Galanin in Rat Lung Ischemia Reperfusion-Mediated Response

Lung ischemia reperfusion (IR) is known to occur after lung transplantation or cardiac bypass. IR leads to tissue inflammation and damage and is also associated with increased morbidity and mortality. Various receptors are known to partake in activation of the innate immune system, but the downstream mechanism of tissue damage and inflammation is yet unknown. MicroRNAs (miRNAs) are in the forefront in regulating ischemia reperfusion injury and are involved in inflammatory response. Here, we have identified by high-throughput approach and evaluated a distinct set of miRNAs that may play a role in response to IR in rat lung tissue. The top three differentially expressed miRNAs were validated through quantitative PCRs in the IR rat lung model and an in vitro model of IR of hypoxia and reoxygenation exposed type II alveolar cells. Among the miRNAs, miR-18a-5p showed consistent downregulation in both the model systems on IR. Cellular and molecular analysis brought to light a crucial role of this miRNA in ischemia reperfusion. miR-18a-5p plays a role in IR-mediated apoptosis and ROS production and regulates the expression of neuropeptide Galanin. It also influences the nuclear localization of transcription factor: nuclear factor-erythroid 2-related factor (Nrf2) which in turn may regulate the expression of the miR-18a gene. Thus, we have not only established a rat model for lung IR and enumerated the important miRNAs involved in IR but have also extensively characterized the role of miR-18a-5p. This study will have important clinical and therapeutic implications for and during transplantation procedures.

Yes-associated protein regulates the hepatoprotective effect of vitamin D receptor activation through promoting adaptive bile duct remodeling in cholestatic mice

Mounting clinical evidence has revealed that the vitamin D receptor (VDR) is associated with cholestatic liver injury, although the functions of VDR in this condition remain largely unexplored. Here, we investigated the effects of VDR activation on bile duct ligation (BDL) mice, and the underlying mechanisms were further investigated. A low-calcemic VDR agonist, paricalcitol (PAL, 200 ng/kg), was intraperitoneally injected into BDL mice every other day for 5 days or 28 days. Liver histology, liver function indicators, cholangiocyte proliferation, fibrosis scores, and inflammation were evaluated. Mice treated with PAL were rescued from the decreased survival rate induced by BDL and liver damage was reduced. Mechanistically, PAL promoted cholangiocyte proliferation, which was likely conducive to proliferating bile duct maturation and increased branching of bile ducts. PAL treatment also increased the expression of Yes-associated protein (YAP) and its target protein epithelial cell adhesion molecule (EpCam) and decreased the level of inactive cytoplasmic phosphorylated YAP. YAP knockdown abrogated PAL-induced primary bile duct epithelial cell proliferation, confirmed with YAP inhibitor administration. In addition, BDL-induced liver fibrosis and inflammatory cell infiltration were reduced by PAL treatment at both day 5 and day 28 post-BDL. In conclusion, VDR activation mitigates cholestatic liver injury by promoting adaptive bile duct remodeling through cholangiocytic YAP upregulation. Because PAL is an approved clinical drug, it may be useful for treatment of cholestatic liver disease. © 2021 The Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Is Galanin a Promising Therapeutic Resource for Neural and Nonneural Diseases?

BACKGROUND

Galanin (GAL) constitutes a family of neuropeptides composed of four peptides: (i) galanin (GAL), (ii) galanin-message associated peptide (GAMP), (iii) galanin-like peptide (GALP), and (iv) alarin. GAL contains 29/30 amino acids, and its biological action occurs through the interactions with its various receptors (GALR1, GALR2, and GALR3). The neuropeptide GAL regulates several physiological and pathophysiological functions in the central nervous system, the peripheral nervous system, and the peripheral organs. GAL is secreted mainly by oligodendrocytes, astrocytes, and the gastrointestinal tract, and its effect depends on the interaction with its different receptors. These receptors are expressed mainly in the central, peripheral nervous systems and the intestines.

OBJECTIVE

The present review evaluates the role of GAL family in inflammatory diseases. An overview is given of the signaling and pharmacological effects due to the interaction between GAL and GALR in different cell types. The potential use of GAL as a therapeutic resource is critically discussed.

CONCLUSION

GAL is suggested to have an anti-inflammatory function in some situations and a proinflammatory function in others. The literature on GAL is controversial and currently not conclusive. This could be due to the complexity of the metabolic network signaling induced by the interactions between GAL and GALR. In the next future, GAL might be a promising therapeutic resource for several diseases, but its practical use for disease control is presently not advisable.

Ghrelin reverses ductular reaction and hepatic fibrosis in a rodent model of cholestasis

The orexigenic peptide ghrelin (Ghr) stimulates hunger signals in the hypothalamus via growth hormone secretagogue receptor (GHS-R1a). Gastric Ghr is synthetized as a preprohormone which is proteolytically cleaved, and acylated by a membrane-bound acyl transferase (MBOAT). Circulating Ghr is reduced in cholestatic injuries, however Ghr's role in cholestasis is poorly understood. We investigated Ghr's effects on biliary hyperplasia and hepatic fibrosis in Mdr2-knockout (Mdr2KO) mice, a recognized model of cholestasis. Serum, stomach and liver were collected from Mdr2KO and FVBN control mice treated with Ghr, des-octanoyl-ghrelin (DG) or vehicle. Mdr2KO mice had lower expression of Ghr and MBOAT in the stomach, and lower levels of circulating Ghr compared to WT-controls. Treatment of Mdr2KO mice with Ghr improved plasma transaminases, reduced biliary and fibrosis markers. In the liver, GHS-R1a mRNA was expressed predominantly in cholangiocytes. Ghr but not DG, decreased cell proliferation via AMPK activation in cholangiocytes in vitro. AMPK inhibitors prevented Ghr-induced FOXO1 nuclear translocation and negative regulation of cell proliferation. Ghr treatment reduced ductular reaction and hepatic fibrosis in Mdr2KO mice, regulating cholangiocyte proliferation via GHS-R1a, a G-protein coupled receptor which causes increased intracellular Ca2+ and activation of AMPK and FOXO1, maintaining a low rate of cholangiocyte proliferation.

Coordinated Targeting of Galanin Receptors on Cholangiocytes and Hepatic Stellate Cells Ameliorates Liver Fibrosis in Multidrug Resistance Protein 2 Knockout Mice

Galanin (Gal) is a peptide with a role in neuroendocrine regulation of the liver. In this study, we assessed the role of Gal and its receptors, Gal receptor 1 (GalR1) and Gal receptor 2 (GalR2), in cholangiocyte proliferation and liver fibrosis in multidrug resistance protein 2 knockout (Mdr2KO) mice as a model of chronic hepatic cholestasis. The distribution of Gal, GalR1, and GalR2 in specific liver cell types was assessed by laser-capture microdissection and confocal microscopy. Galanin immunoreactivity was detected in cholangiocytes, hepatic stellate cells (HSCs), and hepatocytes. Cholangiocytes expressed GalR1, whereas HSCs and hepatocytes expressed GalR2. Strategies were used to either stimulate or block GalR1 and GalR2 in FVB/N (wild-type) and Mdr2KO mice and measure biliary hyperplasia and hepatic fibrosis by quantitative PCR and immunostaining of specific markers. Galanin treatment increased cholangiocyte proliferation and fibrogenesis in both FVB/N and Mdr2KO mice. Suppression of GalR1, GalR2, or both receptors in Mdr2KO mice resulted in reduced bile duct mass and hepatic fibrosis. In vitro knockdown of GalR1 in cholangiocytes reduced α-smooth muscle actin expression in LX-2 cells treated with cholangiocyte-conditioned media. A GalR2 antagonist inhibited HSC activation when Gal was administered directly to LX-2 cells, but not via cholangiocyte-conditioned media. These data demonstrate that Gal contributes not only to cholangiocyte proliferation but also to liver fibrogenesis via the coordinate activation of GalR1 in cholangiocytes and GalR2 in HSCs.

Preclinical insights into cholangiopathies: disease modeling and emerging therapeutic targets

INTRODUCTION

The common predominant clinical features of cholangiopathies such as primary sclerosing cholangitis (PSC), primary biliary cholangitis (PBC), and biliary atresia (BA) are biliary damage/senescence and liver fibrosis. Curative therapies are lacking, and liver transplantation is the only option. An understanding of the mechanisms and pathogenesis is needed to develop novel therapies. Previous studies have developed various disease-based research models and have identified candidate therapeutic targets. Areas covered: This review summarizes recent studies performed in preclinical models of cholangiopathies and the current understanding of the pathophysiology representing potential targets for novel therapies. A literature search was conducted in PubMed using the combination of the searched term 'cholangiopathies' with one or two keywords including 'model', 'cholangiocyte', 'animal', or 'fibrosis'. Papers published within five years were obtained. Expert opinion: Access to appropriate research models is a key challenge in cholangiopathy research; establishing more appropriate models for PBC is an important goal. Several preclinical studies have demonstrated promising results and have led to novel therapeutic approaches, especially for PSC. Further studies on the pathophysiology of PBC and BA are necessary to identify candidate targets. Innovative therapeutic approaches such as stem cell transplantation have been introduced, and those therapies could be applied to PSC, PBC, and BA.

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.

Mechanisms of cholangiocyte responses to injury

Cholangiocytes, epithelial cells that line the biliary epithelium, are the primary target cells for cholangiopathies including primary sclerosing cholangitis and primary biliary cholangitis. Quiescent cholangiocytes respond to biliary damage and acquire an activated neuroendocrine phenotype to maintain the homeostasis of the liver. The typical response of cholangiocytes is proliferation leading to bile duct hyperplasia, which is a characteristic of cholestatic liver diseases. Current studies have identified various signaling pathways that are associated with cholangiocyte proliferation/loss and liver fibrosis in cholangiopathies using human samples and rodent models. Although recent studies have demonstrated that extracellular vesicles and microRNAs could be mediators that regulate these messenger/receptor axes, further studies are required to confirm their roles. This review summarizes current studies of biliary response and cholangiocyte proliferation during cholestatic liver injury with particular emphasis on the secretin/secretin receptor axis. This article is part of a Special Issue entitled: Cholangiocytes in Health and Diseaseedited by Jesus Banales, Marco Marzioni, Nicholas LaRusso and Peter Jansen.

Recent advances in understanding bile duct remodeling and fibrosis

Cholestatic liver disease encompasses a detrimental group of diseases that are non-discriminatory in nature. These diseases occur over every age range from infancy (biliary atresia) to geriatrics (hepatitis). They also cover both genders in the form of primary sclerosing cholangitis in men and primary biliary cholangitis in women. Oftentimes, owing to the disease progression and extensive scarring, the treatment of last resort becomes a liver transplant. In this review, we will briefly discuss and explore new avenues of understanding in the progression of cholestatic liver disease and possible therapeutic targets for intervention. The greater our understanding into the idiopathic nature of cholestatic liver disease, the better our chances of discovering treatment options to halt or reverse the progression, reducing or eliminating the need for expensive and risky transplants.