Activation of Rac1 promotes hedgehog-mediated acquisition of the myofibroblastic phenotype in rat and human hepatic stellate cells

Catalpol inhibits hepatic stellate cell activation by reducing the formation and changing the contents of hepatocyte-derived extracellular vesicles

Hepatic stellate cell (HSC) activation is the central event in hepatic fibrosis. The cross-talk between HSCs and hepatocytes, which is mediated by extracellular vesicles (EVs), affects HSC activation. This study aimed to investigate whether Catalpol (CTP) attenuated hepatic fibrosis via modulating EVs. Mice were injected intraperitoneally with CCl4 for 4 weeks to induce hepatic fibrosis. They were gavaged with CTP daily. Mouse serum EVs were isolated and identified using nanoparticle tracking analysis and transmission electron microscopy. Mouse hepatocytes (AML12) and primary HSCs were used to investigate the cell-to-cell crosstalk. The autophagosome-autolysosome fusion was determined using the autophagic flux assay. Hepatic fibrosis was attenuated by CTP, with a decrease of the myofibroblast marker, alpha-smooth muscle actin. The CTP treatment lowered the serum EVs. The co-culture of HSCs and the EVs derived from the CTP-treated mice or hepatocytes reduced HSC proliferation and the expressions of ACTA2 and Col1a1. After the CCl4 treatment, the autophagosomes in AML12 cells were increased, while the autolysosomes were reduced. The decrease of autophagic cargo receptor SQSTM1 in the CTP group suggested that autophagic degradation was sustained. After inhibiting the endogenous Rac1-GTP of hepatocytes, the co-culture of EVs and HSCs reduced Rac1-GTP. The Rac1-GTP level in serum EVs from the CTP-treated mice was reduced in vivo. CTP inhibited autophagy in hepatocytes by reducing Rac1-GTP and thus affect the amount of Rac1-GTP in hepatocyte-derived EVs and the formation of EVs, which attenuated hepatic fibrosis via inhibiting HSC activation.

Cellular heterogeneity and plasticity during NAFLD progression

Nonalcoholic fatty liver disease (NAFLD) is a progressive liver disease that can progress to nonalcoholic steatohepatitis (NASH), NASH-related cirrhosis, and hepatocellular carcinoma (HCC). NAFLD ranges from simple steatosis (or nonalcoholic fatty liver [NAFL]) to NASH as a progressive form of NAFL, which is characterized by steatosis, lobular inflammation, and hepatocellular ballooning with or without fibrosis. Because of the complex pathophysiological mechanism and the heterogeneity of NAFLD, including its wide spectrum of clinical and histological characteristics, no specific therapeutic drugs have been approved for NAFLD. The heterogeneity of NAFLD is closely associated with cellular plasticity, which describes the ability of cells to acquire new identities or change their phenotypes in response to environmental stimuli. The liver consists of parenchymal cells including hepatocytes and cholangiocytes and nonparenchymal cells including Kupffer cells, hepatic stellate cells, and endothelial cells, all of which have specialized functions. This heterogeneous cell population has cellular plasticity to adapt to environmental changes. During NAFLD progression, these cells can exert diverse and complex responses at multiple levels following exposure to a variety of stimuli, including fatty acids, inflammation, and oxidative stress. Therefore, this review provides insights into NAFLD heterogeneity by addressing the cellular plasticity and metabolic adaptation of hepatocytes, cholangiocytes, hepatic stellate cells, and Kupffer cells during NAFLD progression.

Liver fibrosis in fish research: From an immunological perspective

Liver fibrosis is a pathological process whereby the liver is subjected to various acute and chronic injuries, resulting in the activation of hepatic stellate cells (HSCs), an imbalance of extracellular matrix generation and degradation, and deposition in the liver. This review article summarizes the current understanding of liver fibrosis in fish research. Liver fibrosis is a common pathological condition that occurs in fish raised in aquaculture. It is often associated with poor water quality, stressful conditions, and the presence of pathogens. The review describes the pathophysiology of liver fibrosis in fish, including the roles of various cells and molecules involved in the development and progression of the disease. The review also covers the various methods used to diagnose and assess the severity of liver fibrosis in fish, including histological analysis, biochemical markers, and imaging techniques. In addition, the article discusses the current treatment options for liver fibrosis in fish, including dietary interventions, pharmaceuticals, and probiotics. This review highlights the need for more in-depth research in this area to better understand the mechanisms by which liver fibrosis in fish occurs and to develop effective prevention and treatment strategies. Finally, improved management practices and the development of new treatments will be critical to the sustainability of aquaculture and the health of farmed fish.

A novel mechanistic approach for the anti-fibrotic potential of rupatadine in rat liver via amendment of PAF/NF-ĸB p65/TGF-β1 and hedgehog/HIF-1α/VEGF trajectories

Hepatic fibrosis is one of the major worldwide health concerns which requires tremendous research due to the limited outcomes of the current therapies. The present study was designed to assess, for the first time, the potential therapeutic effect of rupatadine (RUP) in diethylnitrosamine (DEN)-induced liver fibrosis and to explore its possible mechanistic actions. For the induction of hepatic fibrosis, rats were treated with DEN (100 mg/kg, i.p.) once weekly for 6 consecutive weeks, and on the 6th week, RUP (4 mg/kg/day, p.o.) was administered for 4 weeks. Treatment with RUP ameliorated changes in body weights, liver indices, liver function enzymes, and histopathological alterations induced by DEN. Besides, RUP amended oxidative stress, which led to the inhibition of PAF/NF-κB p65-induced inflammation, and, subsequently, prevention of TGF-β1 elevation and HSCs activation as indicated by reduced α-SMA expression and collagen deposition. Moreover, RUP exerted significant anti-fibrotic and anti-angiogenic effects by suppressing Hh and HIF-1α/VEGF signaling pathways. Our results highlight, for the first time, a promising anti-fibrotic potential of RUP in rat liver. The molecular mechanisms underlying this effect involve the attenuation of PAF/NF-κB p65/TGF-β1 and Hh pathways and, subsequently, the pathological angiogenesis (HIF-1α/VEGF).

Regulatory Functions and Mechanisms of Circular RNAs in Hepatic Stellate Cell Activation and Liver Fibrosis

Chronic liver injury induces the activation of hepatic stellate cells (HSCs) into myofibroblasts, which produce excessive amounts of extracellular matrix (ECM), resulting in tissue fibrosis. If the injury persists, these fibrous scars could be permanent and disrupt liver architecture and function. Currently, effective anti-fibrotic therapies are lacking; hence, understanding molecular mechanisms that control HSC activation could hold a key to the development of new treatments. Recently, emerging studies have revealed roles of circular RNAs (circRNAs), a class of non-coding RNAs that was initially assumed to be the result of splicing errors, as new regulators in HSC activation. These circRNAs can modulate the activity of microRNAs (miRNAs) and their interacting protein partners involved in regulating fibrogenic signaling cascades. In this review, we will summarize the current knowledge of this class of non-coding RNAs for their molecular function in HSC activation and liver fibrosis progression.

Circular RNAs in organ injury: recent development

Circular ribonucleic acids (circRNAs) are a class of long non-coding RNA that were once regarded as non-functional transcription byproducts. However, recent studies suggested that circRNAs may exhibit important regulatory roles in many critical biological pathways and disease pathologies. These studies have identified significantly differential expression profiles of circRNAs upon changes in physiological and pathological conditions of eukaryotic cells. Importantly, a substantial number of studies have suggested that circRNAs may play critical roles in organ injuries. This review aims to provide a summary of recent studies on circRNAs in organ injuries with respect to (1) changes in circRNAs expression patterns, (2) main mechanism axi(e)s, (3) therapeutic implications and (4) future study prospective. With the increasing attention to this research area and the advancement in high-throughput nucleic acid sequencing techniques, our knowledge of circRNAs may bring fruitful outcomes from basic and clinical research.

Long Noncoding RNA Metastasis-Associated Lung Adenocarcinoma Transcript 1 in Extracellular Vesicles Promotes Hepatic Stellate Cell Activation, Liver Fibrosis and β-Catenin Signaling Pathway

Evidence shows that the long noncoding RNA metastasis-associated lung adenocarcinoma transcript 1 (Lnc-MALAT1) is associated with activation of hepatic stellate cells (HSCs) and liver fibrosis in animal and in vitro studies. However, its roles in human liver fibrosis and the underlying mechanism in HSC activation are not yet defined. In our current study, the expression of Lnc-MALAT1 in the fibrotic liver tissues and in the plasma extracelllar vesicles (EVs) of liver fibrosis patients was detected by FISH and qRT-PCR. The results revealed that enhanced expression of Lnc-MALAT1 was co-localized with increased expression of the fibrotic markers (collagen I and α-SMA) and the Wnt/β-catenin signaling proteins (β-catenin, cyclinD1 and c-myc) in the fibrotic liver tissues. The level of Lnc-MALAT1 in the plasma EVs isolated from 60 liver fibrosis patients was significantly increased compared with that of the 46 control patients, and area under receiver operating curve (AUROC) analysis showed that plasma EVs-Lnc-MALAT1 was a potential diagnostic marker for liver fibrosis, especially for high liver fibrosis. Plasma EVs with highly expressed Lnc-MALAT1 derived from high liver fibrosis patients up-regulated the expression of the fibrotic markers and enhanced the Wnt/β-catenin signaling in human hepatic stellate cells LX-2, and the fibrogenic effects in LX-2 were inhibited by Lnc-MALAT1 knock-down. Interestingly, TGF-β1, a potent pro-fibrotic cytokine, promoted the expression of Lnc-MALAT1 in LX-2 and its pro-fibrotic effects were also abolished by siRNA for Lnc-MALAT1, suggesting that Lnc-MALAT1 probably functions as a common mediator in the activation and fibrogenesis of HSCs. Our results indicate that enhanced expression of Lnc-MALAT1 in the fibrotic liver stimulate the activation of HSCs and thus promote their fibrogenic activity. These results also provide evidences that Lnc-MALAT1 is a potential therapeutic target and plasma EVs-Lnc-MALAT1 is a potential diagnostic biomarker for liver fibrosis.

The Role of Rho GTPases During Fibroblast Spreading, Migration, and Myofibroblast Differentiation in 3D Synthetic Fibrous Matrices

Introduction

Connective tissue repair and mechanosensing are tightly entwined in vivo and occur within a complex three-dimensional (3D), fibrous extracellular matrix (ECM). Typically driven by activated fibroblasts, wound repair involves well-defined steps of cell spreading, migration, proliferation, and fibrous ECM deposition. While the role of Rho GTPases in regulating these processes has been explored extensively in two-dimensional cell culture models, much less is known about their role in more physiologic, 3D environments.

Methods

We employed a 3D, fibrous and protease-sensitive hydrogel model of interstitial ECM to study the interplay between Rho GTPases and fibrous matrix cues in fibroblasts during wound healing.

Results

Modulating fiber density within protease-sensitive hydrogels, we confirmed previous findings that heightened fiber density promotes fibroblast spreading and proliferation. The presence of matrix fibers furthermore corresponded to increased cell migration speeds and macroscopic hydrogel contraction arising from fibroblast generated forces. During fibroblast spreading, Rac1 and RhoA GTPase activity proved crucial for fiber-mediated cell spreading and contact guidance along matrix fibers, while Cdc42 was dispensable. In contrast, interplay between RhoA, Rac1, and Cdc42 contributed to fiber-mediated myofibroblast differentiation and matrix contraction over longer time scales.

Conclusion

These observations may provide insights into tissue repair processes in vivo and motivate the incorporation of cell-adhesive fibers within synthetic hydrogels for material-guided wound repair strategies.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12195-021-00698-5.

c-Myc affects hedgehog pathway via KCNQ1OT1/RAC1: A new mechanism for regulating HSC proliferation and epithelial-mesenchymal transition

BACKGROUND

This study aimed to probe into the potential mechanism of KCNQ1OT1 in liver fibrosis.

METHODS

The pathological changes in liver tissues were observed by Masson and hematoxylin-eosin (HE) staining. The proliferation or cell cycle of hepatic stellate cells (HSCs) was analyzed by MTT or flow cytometry. The expressions of epithelial markers E-cadherin, interstitial markers Snail and Vimentin, and hedgehog signaling pathway-related molecules Hhip, Shh, and Gli2 were detected by Western blot. The interaction or binding of c-Myc with the KCNQ1OT1 promoter was analyzed by dual-luciferase reporter gene or Chromatin immunoprecipitation (ChIP)-qPCR, and the interaction between KCNQ1OT1 and RAC1 was assessed by RNA immunoprecipitation and RNA pull-down. Moreover, the stability of RAC1 protein was detected by cycloheximide-chase and ubiquitination.

RESULTS

c-Myc and KCNQ1OT1 were up-regulated in liver fibrosis tissues and cells. After the interference with c-Myc in primary-1-Day HSCs, the down-regulated KCNQ1OT1 restrained HSC proliferation and EMT by down-regulating RAC1 expression and restraining the hedgehog pathway.

CONCLUSION

Our results indicated that the interference with c-Myc down-regulated RAC1 expression and restrained the hedgehog pathway by down-regulating KCNQ1OT1, thus restraining HSC proliferation and EMT in liver fibrosis.

The Role of the Hedgehog Pathway in Cholangiocarcinoma

Simple Summary

Cholangiocarcinoma (CCA) is one of the most refractory malignancies with a high mortality rate. Among all the pathways involved in CCA development, emerging evidence highlights Hedgehog (HH) signaling as a substantial player in CCA-genesis and development. The pro-tumoral function of HH provides potential therapeutic implications, and recently the use of HH inhibitors has paved the way for clinical application in various solid tumors. Targeting HH members, namely Hedgehog ligands, SMO transmembrane protein and GLI transcription factors may thus confer therapeutic options for the improvement of CCA treatment outcome.

Abstract

Cholangiocarcinoma (CCA) is a poorly treatable type of cancer and, along with hepatocellular carcinoma (HCC), is the predominant type of primitive liver cancer in adults. The lack of understanding of CCA biology has slowed down the identification of novel targets and the development of effective treatments. While tumors share some general characteristics, detailed knowledge of specific features is essential for the development of effectively tailored therapeutic approaches. The Hedgehog (HH) signaling cascade regulates stemness biology, embryonal development, tissue homeostasis, and cell proliferation and differentiation. Its aberrant activation has been associated with a variety of solid and hematological human malignancies. Several HH-inhibiting compounds have been indeed developed as potential anticancer agents in different types of tumors, with Smoothened and GLI inhibitors showing the most promising results. Beside its well-established function in other tumors, findings regarding the HH signaling in CCA are still controversial. Here we will give an overview of the most important clinical and molecular features of cholangiocarcinoma, and we will discuss the available evidence of the crosstalk between the HH signaling pathway and the cholangiocarcinoma cell biology.

Bioinformatic analysis of RHO family of GTPases identifies RAC1 pharmacological inhibition as a new therapeutic strategy for hepatocellular carcinoma

OBJECTIVE

The RHO family of GTPases, particularly RAC1, has been linked with hepatocarcinogenesis, suggesting that their inhibition might be a rational therapeutic approach. We aimed to identify and target deregulated RHO family members in human hepatocellular carcinoma (HCC).

DESIGN

We studied expression deregulation, clinical prognosis and transcription programmes relevant to HCC using public datasets. The therapeutic potential of RAC1 inhibitors in HCC was study in vitro and in vivo. RNA-Seq analysis and their correlation with the three different HCC datasets were used to characterise the underlying mechanism on RAC1 inhibition. The therapeutic effect of RAC1 inhibition on liver fibrosis was evaluated.

RESULTS

Among the RHO family of GTPases we observed that RAC1 is upregulated, correlates with poor patient survival, and is strongly linked with a prooncogenic transcriptional programme. From a panel of novel RAC1 inhibitors studied, 1D-142 was able to induce apoptosis and cell cycle arrest in HCC cells, displaying a stronger effect in highly proliferative cells. Partial rescue of the RAC1-related oncogenic transcriptional programme was obtained on RAC1 inhibition by 1D-142 in HCC. Most importantly, the RAC1 inhibitor 1D-142 strongly reduce tumour growth and intrahepatic metastasis in HCC mice models. Additionally, 1D-142 decreases hepatic stellate cell activation and exerts an anti-fibrotic effect in vivo.

CONCLUSIONS

The bioinformatics analysis of the HCC datasets, allows identifying RAC1 as a new therapeutic target for HCC. The targeted inhibition of RAC1 by 1D-142 resulted in a potent antitumoural effect in highly proliferative HCC established in fibrotic livers.

miR‑375 affects the hedgehog signaling pathway by downregulating RAC1 to inhibit hepatic stellate cell viability and epithelial‑mesenchymal transition

MicroRNAs (miRNAs/miRs) are a class of non-coding RNAs that serve crucial roles in liver cancer and other liver injury diseases. However, the expression profile and mechanisms underlying miRNAs in liver fibrosis are not completely understood. The present study identified the novel miR-375/Rac family small GTPase 1 (RAC1) regulatory axis in liver fibrosis. Reverse transcription-quantitative PCR was performed to detect miR-375 expression levels. MTT, flow cytometry and western blotting were performed to explore the in vitro roles of miR-375. The dual-luciferase reporter gene assay was performed to determine the potential mechanism underlying miR-375 in liver fibrosis. miR-375 expression was significantly downregulated in liver fibrosis tissues and cells compared with healthy control tissues and hepatocytes, respectively. Compared with the pre-negative control group, miR-375 overexpression inhibited mouse hepatic stellate cell (HSC) viability and epithelial-mesenchymal transition, and alleviated liver fibrosis. The dual-luciferase reporter assay results demonstrated that miR-375 bound to RAC1. Moreover, the results indicated that miR-375 regulated the hedgehog signaling pathway via RAC1 to restrain HSC viability and EMT, thus exerting its anti-liver fibrosis function. The present study identified the miR-375/RAC1 axis as a novel regulatory axis associated with the development of liver fibrosis.

Circular RNA RSF1 promotes inflammatory and fibrotic phenotypes of irradiated hepatic stellate cell by modulating miR-146a-5p

The role of circular RNA (circRNA) in radiation-induced liver disease (RILD) remains largely unknown. In this study, Ras-related C3 botulinum toxin substrate 1 (RAC1) was elevated in irradiated human hepatic stellate cell (HSC) line LX2, the important effector cell mediating RILD. Overexpression of RAC1 promotes cell proliferation, proinflammatory cytokines production, and α-smooth muscle actin expression, which were blocked by microRNA (miR)-146a-5p mimics. CircRNA RSF1 (circRSF1) was upregulated in irradiated LX2 cells and predicted to harbor binding site for miR-146a-5p. Biotinylated-RNA pull down and dual-luciferase reporter detection confirmed the direct interaction of circRSF1 and miR-146a-5p. Enforced expression of circRSF1 increased RAC1 expression by acting as miR-146a-5p sponge to inhibit miR-146a-5p activity, and thus enhanced the cell viability, and promoted inflammatory and fibrotic phenotype of irradiated LX2 cells. These findings indicate a functional regulatory axis composing of circRSF1, miR-146a-5p, and RAC1 in irradiated HSC, which may provide attractive therapeutic targets for RILD.

The preventive effect of atorvastatin on liver fibrosis in the bile duct ligation rats via antioxidant activity and down-regulation of Rac1 and NOX1

Objectives

Atorvastatin is a cholesterol-lowering agent capable of inhibiting 3-hydroxy-3-methylglutaryl coenzyme A reductase. Recent studies have demonstrated new facets of atorvastatin, such as antioxidant and anti-fibrotic properties. We investigated the effect of atorvastatin on hepatic injury via the measurement of the antioxidant capacity and protein expression of NOX1, Rac1-GTP, and Rac1 in a rat biliary duct ligation (BDL) model.

Materials and Methods

This study is regarded as experimental interventional research in which a total of 32 adult male Wistar rats (200-250 g) were assigned to 4 groups (eight rats per group) as follows: Control group; Control + At group (15 mg\kg\day atorvastatin); BDL group, and BDL+ At group (15 mg\kg\day atorvastatin). Expression levels of Rac1, NOX1, and Rac1-GTP were determined by western blot analysis. Besides, specific biomarkers of oxidative stress in hepatic tissues of all animals were also analyzed.

Results

Atorvastatin reduced liver injury via a decrease in the expression of NOX1, Rac1-GTP, and Rac1 in the BDL group (P<0.05), while the increased contents of protein thiol groups were observed, and the protein carbonylation was decreased in atorvastatin-treated BDL rats compared to the BDL group (P<0.05). Also, administration of atorvastatin in the BDL group significantly lowered oxidative stress through increasing the activity of catalase and superoxide dismutase in comparison with the BDL group (P<0.05).

Conclusion

It seems that atorvastatin has potential advantages in mitigation of liver fibrosis by a decrease in the expression of NOX1, Rac1-GTP, and Rac1, along with, a reduction in oxidative stress of liver tissues in rats induced by BDL.

A Novel Synthetic Derivative of Phloroglucinol Inhibits Neuroinflammatory Responses Through Attenuating Kalirin Signaling Pathway in Murine BV2 Microglial Cells

Neuroinflammation has been implicated as an important factor in the neurodegenerative diseases, and multiple candidates with anti-inflammatory effects have been shown to be beneficial for the treatment of neurodegenerative diseases. Our previous study demonstrated that a novel synthetic phloroglucinol derivative from Lysidice rhodostegia roots (code name: Compound 21) exerted neuroprotective effect through suppressing neuroinflammation. The aim of this study was to reveal the underlying molecular mechanism. The results indicated that the anti-inflammatory effects of Compound 21 were mediated through suppression of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activation and the production of reactive oxygen species (ROS). Further study showed that this suppression on NADPH oxidase was mediated by inhibiting the translocation and activity of its subunit Rac1. It is well established that Rac1 activation is regulated by a variety of guanine nucleotide exchange factors (GEFs), so we tried to find out whether GEFs were involved in the anti-inflammatory effects of Compound 21. The results showed that Compound 21 treatment down-regulated the expression and activity of GEF Kalirin, thus modulating the activity of Rac1 GTPase. Altogether, our data suggested that Compound 21 exerted the anti-neuroinflammatory effect through suppressing Kalirin signaling pathways, decreasing Rac1-NADPH oxidase activation and the subsequent pro-inflammatory cytokine production. The present study provided solid evidence to support Compound 21 as a potential candidate of neuroinflammatory inhibitor. Moreover, our findings have shed new light on the role of Rac1 and GEF Kalirin in neuroinflammation, which provides potential targets for neuroinflammation-related diseases, such as neurodegenerative diseases.

Hedgehog signaling pathway regulates liver regeneration in the Fah-/- knockout mice model xenografted by human hepatocytes

BACKGROUND

The aim of this study is to evaluates the hypothesis that Hh pathway activation occurs in the Fah^-/- Nod/Scid mice model and plays a role in regulating liver regeneration after functional human hepatocytes xenograft.

METHODS

Fah^-/- Nod/Scid mice were established in Shandong Cancer Hospital affiliated to Shandong University. Xeno-regeneration of Fah^-/- Nod/Scid mice livers was then transplanted by human hepatocytes. Hh signaling pathway associated factors were detected by RT-PCR and western blot. All statistical calculations were carried out using the SPSS.16.0 software.

RESULTS

Fah^-/- mice were healthy and reproduced normally while treated with NTBC. NTBC-OFF Fah^-/- mice with HHT gradually gained weight by six weeks after human hepatocyte transplantation. NTBC-OFF Fah^-/- mice causes a progressive increase in ALT, AST, GGT and AP, which were used to monitor hepatocyte inflammation. However, liver function in NTBC-OFF Fah Fah^-/- mice with HHT returned to normal. Hedgehog pathway activation and Hh-target genes were enhanced follows human hepatocytes transplantation which indicated liver regeneration associated closely with Hh signaling pathway. Moreover, Hh signaling was inhibited by cyclopamine after HHT.

CONCLUSIONS

The current study provides novel evidence that Hedgehog signaling pathway regulation is required for optimal regeneration of NTBC OFF Fah^-/- mice with HHT.

Ursolic acid suppresses TGF-β1-induced quiescent HSC activation and transformation by inhibiting NADPH oxidase expression and Hedgehog signaling

Activation of quiescent hepatic stellate cells (q-HSCs) and their transformation to myofibroblasts (MFBs) is a key event in liver fibrosis. Hedgehog (Hh) signaling stimulates q-HSCs to differentiate into MFBs, and NADPH oxidase (NOX) may be involved in regulating Hh signaling. The author's preliminary study demonstrated that ursolic acid (UA) selectively induces apoptosis in activated HSCs and inhibits their proliferation in vitro via negative regulation of NOX activity and expression. However, the effect of UA on q-HSCs remains to be elucidated. The present study aimed to investigate the effect of UA on q-HSC activation and HSC transformation and to observe alterations in the NOX and Hh signaling pathways during q-HSC activation. q-HSC were isolated from adult male Sprague-Dawley rats. Following culture for 3 days, the cells were treated with or without transforming growth factor-β1 (TGF-β1; 5 µg/l); intervention groups were pretreated with UA (40 µM) or diphenyleneiodonium chloride (DPI; 10 µM) for 30 min prior to addition of TGF-β1. mRNA and protein expression of NOX and Hh signaling components and markers of q-HSC activation were examined by western blotting and reverse transcription-polymerase chain reaction. TGF-β1 induced activation of q-HSCs, with increased expression of α-smooth muscle actin (α-SMA) and type I collagen. In addition, expression of NOX subunits (gp91^phox, p67^phox, p22^phox, and Rac1) and Hh signaling components, including sonic Hh, sterol-4-alpha-methyl oxidase, and Gli family zinc finger 2, were upregulated in activated HSCs. Pretreatment of q-HSCs with UA or DPI prior to TGF-β1 significantly downregulated expression of NOX subunits and Hh signaling components and additionally inhibited expression of α-SMA and type I collagen, thereby preventing transformation to MFBs. UA inhibited TGF-β1-induced activation of q-HSCs and their transformation by inhibiting expression of NOX subunits and the downstream Hh pathway.

Thymosin beta-4 regulates activation of hepatic stellate cells via hedgehog signaling

The molecular mechanisms of thymosin beta-4 (TB4) involved in regulating hepatic stellate cell (HSC) functions remain unclear. Therefore, we hypothesize that TB4 influences HSC activation through hedgehog (Hh) pathway. HSC functions declined in a TB4 siRNA-treated LX-2. TB4 suppression down-regulated both integrin linked kinase (ILK), an activator of smoothened, and phosphorylated glycogen synthase kinase 3 beta (pGSK-3B), an inactive form of GSK-3B degrading glioblastoma 2 (GLI2), followed by the decreased expression of both smoothened and GLI2. A TB4 CRISPR also blocked the activation of primary HSCs, with decreased expression of smoothened, GLI2 and ILK compared with cells transfected with nontargeting control CRISPR. Double immunostaining and an immunoprecipitation assay revealed that TB4 interacted with either smoothened at the cytoplasm or GLI2 at the nucleus in LX-2. Smoothened suppression in primary HSCs using a Hh antagonist or adenovirus transduction decreased TB4 expression with the reduced activation of HSCs. Tb4-overexpressing transgenic mice treated with CCl₄ were susceptible to the development hepatic fibrosis with higher levels of ILK, pGSK3b, and Hh activity, as compared with wild-type mice. These findings demonstrate that TB4 regulates HSC activation by influencing the activity of Smoothened and GLI2, suggesting TB4 as a novel therapeutic target in liver disease.

Quercetin protects liver injury induced by bile duct ligation via attenuation of Rac1 and NADPH oxidase1 expression in rats

BACKGROUND

Bile duct ligation (BDL) and subsequent cholestasis are correlated with oxidative stress, hepatocellular injury and fibrosis. Quercetin is a flavonoid with antifibrotic, and hepatoprotective properties. However, the molecular mechanism underlying quercetin-mediated hepatoprotection is not fully understood. The current study was to evaluate mechanisms of hepatoprotective effect of quercetin in BDL rat model.

METHODS

We divided male Wistar rats into 4 groups (n=8 for each): sham, sham+quercetin (30 mg/kg per day), BDL, and BDL+quercetin (30 mg/kg per day). Four weeks later, the rats were sacrificed, the blood was collected for liver enzyme measurements and liver for the measurement of Rac1, Rac1-GTP and NOX1 mRNA and protein levels by quantitative PCR and Western blotting, respectively.

RESULTS

Quercetin significantly alleviated liver injury in BDL rats as evidenced by histology and reduced liver enzymes. Furthermore, the mRNA and protein expression of Rac1, Rac1-GTP and NOX1 were significantly increased in BDL rats compared with those in the sham group (P<0.05); quercetin treatment reversed these variables back toward normal (P<0.05). Another interesting finding was that the antioxidant markers e.g. superoxide dismutase and catalase were elevated in quercetin-treated BDL rats compared to BDL rats (P<0.05).

CONCLUSION

Quercetin demonstrated hepatoprotective activity against BDL-induced liver injury through increasing antioxidant capacity of the liver tissue, while preventing the production of Rac1, Rac1-GTP and NOX1 proteins.

Forskolin, a hedgehog signalling inhibitor, attenuates carbon tetrachloride-induced liver fibrosis in rats

BACKGROUND AND PURPOSE

Liver fibrosis is one of the leading causes of morbidity and mortality worldwide with very limited therapeutic options. Given the pivotal role of activated hepatic stellate cells in liver fibrosis, attention has been directed towards the signalling pathways underlying their activation and fibrogenic functions. Recently, the hedgehog (Hh) signalling pathway has been identified as a potentially important therapeutic target in liver fibrosis. The present study was designed to explore the antifibrotic effects of the potent Hh signalling inhibitor, forskolin, and the possible molecular mechanisms underlying these effects.

EXPERIMENTAL APPROACH

Male Sprague-Dawley rats were treated with either CCl₄ and/or forskolin for 6 consecutive weeks. Serum hepatotoxicity markers were determined, and histopathological evaluation was performed. Hepatic fibrosis was assessed by measuring α-SMA expression and collagen deposition by Masson's trichrome staining and hydroxyproline content. The effects of forskolin on oxidative stress markers (GSH, GPx, lipid peroxides), inflammatory markers (NF-κB, TNF-α, COX-2, IL-1β), TGF-β1 and Hh signalling markers (Ptch-1, Smo, Gli-2) were also assessed.

KEY RESULTS

Hepatic fibrosis induced by CCl₄ was significantly reduced by forskolin, as indicated by decreased α-SMA expression and collagen deposition. Forskolin co-treatment significantly attenuated oxidative stress and inflammation, reduced TGF-β1 levels and down-regulated mRNA expression of Ptch-1, Smo and Gli-2 through cAMP-dependent PKA activation.

CONCLUSION AND IMPLICATIONS

In our model, forskolin exerted promising antifibrotic effects which could be partly attributed to its antioxidant and anti-inflammatory effects, as well as to its inhibition of Hh signalling, mediated by cAMP-dependent activation of PKA.

MALAT1 functions as a competing endogenous RNA to mediate Rac1 expression by sequestering miR-101b in liver fibrosis

Emerging evidence shows that Metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) plays a pivotal role in cell proliferation, migration, and invasion in tumors. However, the biological role and underlying mechanism of MALAT1 in liver fibrosis remains undefined. In this study, up-regulation of MALAT1 was observed in fibrotic liver tissues and in activated hepatic stellate cells (HSCs). In addition, depletion of MALAT1 inhibited the activation of HSCs in vitro and attenuated collagen deposits in vivo. Our results demonstrated that MALAT1 expression is negatively correlated with microRNA-101b (miR-101b) expression. Furthermore, there was a negative feedback loop between the levels of MALAT1 and miR-101b. Luciferase reporter assay indicated that MALAT1 and RAS-related C3 botulinum substrate 1 (Rac1) are targets of miR-101b. We uncovered that MALAT1 regulates Rac1 expression through miR-101b as a competing endogenous RNA (ceRNA), thereby influencing the proliferation, cell cycle and activation of primary HSCs. Collectively, The ceRNA regulatory network may prompt a better understanding of liver fibrogenesis and contribute to a novel therapeutic strategy for liver fibrosis.

Pentoxifylline inhibits liver fibrosis via hedgehog signaling pathway

Infection of schistosomiasis japonica may eventually lead to liver fibrosis, and no effective antifibrotic therapies are available but liver transplantation. Hedgehog (HH) signaling pathway has been involved in the process and is a promising target for treating liver fibrosis. This study aimed to explore the effects of pentoxifylline (PTX) on liver fibrosis induced by schistosoma japonicum infection by inhibiting the HH signaling pathway. Phorbol12-myristate13-acetate (PMA) was used to induce human acute mononuclear leukemia cells THP-1 to differentiate into macrophages. The THP-1-derived macrophages were stimulated by soluble egg antigen (SEA), and the culture supernatants were collected for detection of activation of macrophages. Cell Counting Kit-8 (CCK-8) was used to detect the cytotoxicity of the culture supernatant and PTX on the LX-2 cells. The LX-2 cells were administered with activated culture supernatant from macrophages and(or) PTX to detect the transforming growth factor-β gene expression. The mRNA expression of shh and gli-1, key parts in HH signaling pathway, was detected. The mRNA expression of shh and gli-1 was increased in LX-2 cells treated with activated macrophages-derived culture supernatant, suggesting HH signaling pathway may play a key role in the activation process of hepatic stellate cells (HSCs). The expression of these genes decreased in LX-2 cells co-cultured with both activated macrophages-derived culture supernatant and PTX, indicating PTX could suppress the activation process of HSCs. In conclusion, these data provide evidence that PTX prevents liver fibrogenesis in vitro by the suppression of HH signaling pathway.

Pathogenesis of nonalcoholic steatohepatitis

Nonalcoholic steatohepatitis (NASH) is a severe form of nonalcoholic fatty liver disease and a risk factor for cirrhosis and hepatocellular carcinoma. The pathological features of NASH include steatosis, hepatocyte injury, inflammation, and various degrees of fibrosis. Steatosis reflects disordered lipid metabolism. Insulin resistance and excessive fatty acid influx to the liver are two important contributing factors. Steatosis is also likely associated with lipotoxicity and cellular stresses such as oxidative stress and endoplasmic reticulum stress, which result in hepatocyte injury. Inflammation and fibrosis are frequently triggered by various signals such as proinflammatory cytokines and chemokines, released by injuried hepatocytes and activated Kupffer cells. Although much progress has been made, the pathogenesis of NASH is not fully elucidated. The purpose of this review is to discuss the current understanding of NASH pathogenesis, mainly focusing on factors contributing to steatosis, hepatocyte injury, inflammation, and fibrosis.

Non-alcoholic steatohepatitis: emerging molecular targets and therapeutic strategies

Non-alcoholic fatty liver disease - the most common chronic liver disease - encompasses a histological spectrum ranging from simple steatosis to non-alcoholic steatohepatitis (NASH). Over the next decade, NASH is projected to be the most common indication for liver transplantation. The absence of an effective pharmacological therapy for NASH is a major incentive for research into novel therapeutic approaches for this condition. The current focus areas for research include the modulation of nuclear transcription factors; agents that target lipotoxicity and oxidative stress; and the modulation of cellular energy homeostasis, metabolism and the inflammatory response. Strategies to enhance resolution of inflammation and fibrosis also show promise to reverse the advanced stages of liver disease.

MicroRNA‑200a suppresses epithelial‑to‑mesenchymal transition in rat hepatic stellate cells via GLI family zinc finger 2

Hepatic stellate cells (HSCs) have an important role in liver fibrosis. Epithelial‑to‑mesenchymal transition (EMT), which is promoted by the Hedgehog (Hh) signaling pathway, is involved in the activation of HSCs. MicroRNAs (miRNAs/miRs) have been reported to be involved in the progression of liver fibrosis. A previous study indicated that the activation of HSCs was suppressed by miR‑200a via targeting transforming growth factor‑β2 and β‑catenin. However, whether miR‑200a is able to regulate the EMT in HSCs has remained elusive. The present study revealed that miR‑200a was decreased in vitro and in vivo during liver fibrosis. Furthermore, miR‑200a overexpression resulted in the inhibition of proliferation, α‑SMA expression and extracellular matrix production of activated HSCs. Of note, miR‑200a overexpression reduced myofibroblastic markers, including α‑SMA, type I collagen and desmin, and increased the epithelial cell marker E‑cadherin. These results were further confirmed by immunofluorescence staining. Further study showed that the expression of genes associated with Hh signaling, including Hhip, Shh and Gli1, were not affected by miR‑200a. However, Gli2, a downstream signaling protein of the Hh pathway, was inhibited by miR‑200a and confirmed as a target of miR‑200a using a dual luciferase reporter assay. In addition, the inhibition of the Hh pathway by miR‑200a resulted in an increase of BMP‑7 and Id2 as well as a reduction of Snai1 and S100A4. Collectively, the results of the present study demonstrated that miR‑200a suppressed the EMT process in HSCs, at least in part, via Gli2.

The Riddle of Nonalcoholic Fatty Liver Disease: Progression From Nonalcoholic Fatty Liver to Nonalcoholic Steatohepatitis

Nonalcoholic fatty liver (NAFL) is an emerging global epidemic which progresses to nonalcoholic steatohepatitis (NASH) and cirrhosis in a subset of subjects. Various reviews have focused on the etiology, epidemiology, pathogenesis and treatment of NAFLD. This review highlights specifically the triggers implicated in disease progression from NAFL to NASH. The integrating role of genes, dietary factors, innate immunity, cytokines and gut microbiome have been discussed.

Hedgehog signaling pathway as key player in liver fibrosis: new insights and perspectives

INTRODUCTION

Activation of hepatic stellate cells (HSCs) is a pivotal cellular event in liver fibrosis. Therefore, improving our understanding of the molecular pathways that are involved in these processes is essential to generate new therapies for liver fibrosis. Greater knowledge of the role of the hedgehog signaling pathway in liver fibrosis could improve understanding of the liver fibrosis pathogenesis.

AREAS COVERED

The aim of this review is to describe the present knowledge about the hedgehog signaling pathway, which significantly participates in liver fibrosis and HSC activation, and look ahead on new perspectives of hedgehog signaling pathway research. Moreover, we will discuss the different interactions with hedgehog signaling pathway-regulated liver fibrosis.

EXPERT OPINION

The hedgehog pathway modulates several important aspects of function, including cell proliferation, activation and differentiation. Targeting the hedgehog pathway can be a promising direction in liver fibrosis treatment. We discuss new perspectives of hedgehog signaling pathway activation in liver fibrosis and HSC fate, including DNA methylation, methyl CpG binding protein 2, microRNA, irradiation and metabolism that influence hedgehog signaling pathway transduction. These findings identify the hedgehog pathway as a potentially important for biomarker development and therapeutic targets in liver fibrosis. Future studies are needed in order to find safer and more effective hedgehog-based drugs.

Role of innate immune response in non-alcoholic Fatty liver disease: metabolic complications and therapeutic tools

Non-alcoholic fatty liver disease (NAFLD) is currently the most common liver disease worldwide, both in adults and children. It is characterized by an aberrant lipid storage in hepatocytes, named hepatic steatosis. Simple steatosis remains a benign process in most affected patients, while some of them develop superimposed necroinflammatory activity with a non-specific inflammatory infiltrate and a progression to non-alcoholic steatohepatitis with or without fibrosis. Deep similarity and interconnections between innate immune cells and those of liver parenchyma have been highlighted and showed to play a key role in the development of chronic liver disease. The liver can be considered as an “immune organ” because it hosts non-lymphoid cells, such as macrophage Kupffer cells, stellate and dendritic cells, and lymphoid cells. Many of these cells are components of the classic innate immune system, enabling the liver to play a major role in response to pathogens. Although the liver provides a “tolerogenic” environment, aberrant activation of innate immune signaling may trigger “harmful” inflammation that contributes to tissue injury, fibrosis, and carcinogenesis. Pathogen recognition receptors, such as toll-like receptors and nucleotide oligomerization domain-like receptors, are responsible for the recognition of immunogenic signals, and represent the major conduit for sensing hepatic and non-hepatic noxious stimuli. A pivotal role in liver inflammation is also played by cytokines, which can initiate or have a part in immune response, triggering hepatic intracellular signaling pathways. The sum of inflammatory signals and deranged substrate handling induce most of the metabolic alteration traits: insulin resistance, obesity, diabetes, hyperlipidemia, and their compounded combined effects. In this review, we discuss the relevant role of innate immune cell activation in relation to NAFLD, the metabolic complications associated to this pathology, and the possible pharmacological tools.

CTHRC1 acts as a prognostic factor and promotes invasiveness of gastrointestinal stromal tumors by activating Wnt/PCP-Rho signaling

Gastrointestinal stromal tumors (GISTs) are the major gastrointestinal mesenchymal tumors with a variable malignancy ranging from a curable disorder to highly malignant sarcomas. Metastasis and recurrence are the main causes of death in GIST patients. To further explore the mechanism of metastasis and to more accurately estimate the recurrence risk of GISTs after surgery, the clinical significance and functional role of collagen triple helix repeat containing-1 (CTHRC1) in GIST were investigated. We found that CTHRC1 expression was gradually elevated as the risk grade of NIH classification increased, and was closely correlated with disease-free survival and overall survival in 412 GIST patients. In vitro experiments showed that recombinant CTHRC1 protein promoted the migration and invasion capacities of primary GIST cells. A luciferase reporter assay and pull down assay demonstrated that recombinant CTHRC1 protein activated noncanonical Wnt/PCP-Rho signaling but inhibited canonical Wnt signaling. The pro-motility effect of CTHRC1 on GIST cells was reversed by using a Wnt5a neutralizing antibody and inhibitors of Rac1 or ROCK. Taken together, these data indicate that CTHRC1 may serve as a new predictor of recurrence risk and prognosis in post-operative GIST patients and may play an important role in facilitating GIST progression. Furthermore, CTHRC1 promotes GIST cell migration and invasion by activating Wnt/PCP-Rho signaling, suggesting that the CTHRC1-Wnt/PCP-Rho axis may be a new therapeutic target for interventions against GIST invasion and metastasis.

S-adenosylmethionine inhibits the activated phenotype of human hepatic stellate cells via Rac1 and matrix metalloproteinases

OBJECTIVE

To investigate the effects of S-adenosylmethionine (SAM) on the proliferation, adhesion, migration, invasion and apoptosis of activated human hepatic stellate cells (HSCs) and to explore the relevant potential mechanisms.

METHODS

Human HSCs LX-2 were cultured with SAM. The proliferation and adhesion were detected by CCK-8. Cell apoptosis rate were analyzed by flow cytometry, and cell migration and invasion were tested by the transwell assay. The expression of Rac1 and MMP-2 was identified by real-time PCR or Western blotting, and activated Rac1 was detected by GST pull-down assay. The activity of MMP-2 and MMP-9 was analyzed by substrate zymography.

RESULTS

The proliferation of LX-2 cells was inhibited by SAM, exhibiting a dose-dependent manner. Cell apoptosis rate induced by SAM was remarkably increased. SAM decreased the adhesion, migration and invasion of LX-2 cells. The expression and activation of Rac1 in LX-2 cells were significantly suppressed by SAM. In contrast, the activity of MMP-2 and MMP-9 was enhanced by SAM. SAM attenuated the up-regulated expression of Smad3/4 and Rac1 induced by TGF-β1.

CONCLUSION

SAM inhibits the proliferation, adhesion, migration and invasion of LX-2 cells in vitro probably via attenuating the expression and activation of Rac1 and up-regulating MMP-2 and MMP-9 expression, which possibly provide a molecular basis for potential application of SAM in the therapy of liver fibrosis.

Attenuation of early liver fibrosis by pharmacological inhibition of smoothened receptor signaling

Hedgehog (Hh) signaling is involved in the pathogenesis of liver fibrosis. It has been previously shown that Hh-inhibitor cyclopamine (CYA) can reduce liver fibrosis in rats. However, CYA is not stable in vivo, which limits its clinical application. This study compares the antifibrotic potential of two known Hh antagonists, vismodegib (GDC-0449, abbreviated to GDC) and CYA. GDC is a synthetic molecule presently in clinical cancer trials and has been reported to be safe and efficacious. These drugs attenuated early liver fibrosis in common bile duct ligated rats, improved liver function, and prevented hepatic stellate cell (HSC) activation, thereby suppressing epithelial to mesenchymal transition (EMT). While both CYA and GDC increased the number of proliferating cell nuclear antigen positive liver cells in vivo, only CYA increased Caspase-3 expression in HSCs in rat livers, suggesting that while GDC and CYA effectively attenuate early liver fibrosis, their hepatoprotective effects may be mediated through different modes of action. Thus, GDC has the potential to serve as a new therapeutic agent for treating early liver fibrosis.

Differential effects of arsenic trioxide on chemosensitization in human hepatic tumor and stellate cell lines

BACKGROUND

Crosstalk between malignant hepatocytes and the surrounding peritumoral stroma is a key modulator of hepatocarcinogenesis and therapeutic resistance. To examine the chemotherapy resistance of these two cellular compartments in vitro, we evaluated a well-established hepatic tumor cell line, HepG2, and an adult hepatic stellate cell line, LX2. The aim was to compare the chemosensitization potential of arsenic trioxide (ATO) in combination with sorafenib or fluorouracil (5-FU), in both hepatic tumor cells and stromal cells.

METHODS

Cytotoxicity of ATO, 5-FU, and sorafenib, alone and in combination against HepG2 cells and LX2 cells was measured by an automated high throughput cell-based proliferation assay. Changes in survival and apoptotic signaling pathways were analyzed by flow cytometry and western blot. Gene expression of the 5-FU metabolic enzyme, thymidylate synthase, was analyzed by real time PCR.

RESULTS

Both HepG2 and LX2 cell lines were susceptible to single agent sorafenib and ATO at 24 hr (ATO IC(50): 5.3 μM in LX2; 32.7 μM in HepG2; Sorafenib IC(50): 11.8 μM in LX2; 9.9 μM in HepG2). In contrast, 5-FU cytotoxicity required higher concentrations and prolonged (48-72 hr) drug exposure. Concurrent ATO and 5-FU treatment of HepG2 cells was synergistic, leading to increased cytotoxicity due in part to modulation of thymidylate synthase levels by ATO. Concurrent ATO and sorafenib treatment showed a trend towards increased HepG2 cytotoxicity, possibly due to a significant decrease in MAPK activation in comparison to treatment with ATO alone.

CONCLUSIONS

ATO differentially sensitizes hepatic tumor cells and adult hepatic stellate cells to 5-FU and sorafenib. Given the importance of both of these cell types in hepatocarcinogenesis, these data have implications for the rational development of anti-cancer therapy combinations for the treatment of hepatocellular carcinoma (HCC).

Mechanisms of disease progression in NASH: new paradigms

The incidence of nonalcoholic fatty liver disease is increasing at an astonishing rate in the US population. Although only a small proportion of these patients develop steatohepatitis (NASH), those who do have a greater likelihood of developing end-stage liver disease and complications. Research on liver fibrosis and NASH progression shows that hedgehog (Hh) is reactivated after liver injury to assist in liver repair and regeneration. When the process of tissue repair and regeneration is prolonged or when Hh ligand and related genes are aberrantly regulated and excessive, tissue repair goes awry and NASH progresses to cirrhosis and hepatocellular carcinoma.

Hedgehog pathway activation parallels histologic severity of injury and fibrosis in human nonalcoholic fatty liver disease

The Hedgehog (HH)-signaling pathway mediates several processes that are deregulated in patients with metabolic syndrome (e.g., fat mass regulation, vascular/endothelial remodeling, liver injury and repair, and carcinogenesis). The severity of nonalcoholic fatty liver disease (NAFLD) and metabolic syndrome generally correlate. Therefore, we hypothesized that the level of HH-pathway activation would increase in parallel with the severity of liver damage in NAFLD. To assess potential correlations between known histologic and clinical predictors of advanced liver disease and HH-pathway activation, immunohistochemistry was performed on liver biopsies from a large, well-characterized cohort of NAFLD patients (n = 90) enrolled in the Nonalcoholic Steatohepatitis Clinical Research Network (NASH CRN) Database 1 study. Increased HH activity (evidenced by accumulation of HH-ligand-producing cells and HH-responsive target cells) strongly correlated with portal inflammation, ballooning, and fibrosis stage (each P < 0.0001), supporting a relationship between HH-pathway activation and liver damage. Pathway activity also correlated significantly with markers of liver repair, including numbers of hepatic progenitors and myofibroblastic cells (both P < 0.03). In addition, various clinical parameters that have been linked to histologically advanced NAFLD, including increased patient age (P < 0.005), body mass index (P < 0.002), waist circumference (P < 0.0007), homeostatic model assessment of insulin resistance (P < 0.0001), and hypertension (P < 0.02), correlated with hepatic HH activity.

CONCLUSION

In NAFLD patients, the level of hepatic HH-pathway activity is highly correlated with the severity of liver damage and with metabolic syndrome parameters that are known to be predictive of advanced liver disease. Hence, deregulation of the HH-signaling network may contribute to the pathogenesis and sequelae of liver damage that develops with metabolic syndrome.

Myofibroblast differentiation and survival in fibrotic disease

During wound healing, contractile fibroblasts called myofibroblasts regulate the formation and contraction of granulation tissue; however, pathological and persistent myofibroblast activation, which occurs in hypertrophic scars or tissue fibrosis, results in a loss of function. Many reviews outline the cellular and molecular features of myofibroblasts and their roles in a variety of diseases. This review focuses on the origins of myofibroblasts and the factors that control their differentiation and prolonged survival in fibrotic tissues. Pulmonary fibrosis is used to illustrate many key points, but examples from other tissues and models are also included. Myofibroblasts originate mostly from tissue-resident fibroblasts, and also from epithelial and endothelial cells or other mesenchymal precursors. Their differentiation is influenced by cytokines, growth factors, extracellular matrix composition and stiffness, and cell surface molecules such as proteoglycans and THY1, among other factors. Many of these effects are modulated by cell contraction. Myofibroblasts resist programmed cell death, which promotes their accumulation in fibrotic tissues. The cause of resistance to apoptosis in myofibroblasts is under ongoing investigation, but many of the same stimuli that regulate their differentiation are involved. The contributions of oxidative stress, the WNT-β-catenin pathway and PPARγ to myofibroblast differentiation and survival are increasingly appreciated.

Hedgehog activity, epithelial-mesenchymal transitions, and biliary dysmorphogenesis in biliary atresia

Biliary atresia (BA) is notable for marked ductular reaction and rapid development of fibrosis. Activation of the Hedgehog (Hh) pathway promotes the expansion of populations of immature epithelial cells that coexpress mesenchymal markers and may be profibrogenic. We examined the hypothesis that in BA excessive Hh activation impedes ductular morphogenesis and enhances fibrogenesis by promoting accumulation of immature ductular cells with a mesenchymal phenotype. Livers and remnant extrahepatic ducts from BA patients were evaluated by quantitative reverse-transcription polymerase chain reaction (QRT-PCR) and immunostaining for Hh ligands, target genes, and markers of mesenchymal cells or ductular progenitors. Findings were compared to children with genetic cholestatic disease, age-matched deceased donor controls, and adult controls. Ductular cells isolated from adult rats with and without bile duct ligation were incubated with Hh ligand-enriched medium ± Hh-neutralizing antibody to determine direct effects of Hh ligands on epithelial to mesenchymal transition (EMT) marker expression. Livers from pediatric controls showed greater innate Hh activation than adult controls. In children with BA, both intra- and extrahepatic ductular cells demonstrated striking up-regulation of Hh ligand production and increased expression of Hh target genes. Excessive accumulation of Hh-producing cells and Hh-responsive cells also occurred in other infantile cholestatic diseases. Further analysis of the BA samples demonstrated that immature ductular cells with a mesenchymal phenotype were Hh-responsive. Treating immature ductular cells with Hh ligand-enriched medium induced mesenchymal genes; neutralizing Hh ligands inhibited this.

CONCLUSION

BA is characterized by excessive Hh pathway activity, which stimulates biliary EMT and may contribute to biliary dysmorphogenesis. Other cholestatic diseases show similar activation, suggesting that this is a common response to cholestatic injury in infancy.

N1-acetyl substituted pyrrolidine derivative CIP-A5: a novel compound that could ameliorate liver cirrhosis through modulation of hepatic stellate cell activity

(2S,4R)-methyl 1-acetyl-4-(N-(4-bromophenyl)sulfamoyloxy)pyrrolidine-2-carboxylate (CIP-A5) is the N1-acetyl substituted pyrrolidine derivative which was designed against the structure of matrix metalloproteinase (MMP-2) and MMP-9. CIP-A5 has been considered as a candidate compound for treatment of liver cirrhosis. In this study, we evaluated the efficacy of CIP-A5 on the activity of hepatic stellate cells. CIP-A5 prevented the transforming growth factor β (TGF-β)-induced proliferation of hepatic stellate HSC-T6 cells as estimated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. CIP-A5 stimulated MMPs activity as evidenced by an increase of degradation of succinylated gelatin. Gelatin zymography analysis showed that CIP-A5 stimulated the secretion and activity of MMP-2 and MMP-9 in HSC-T6 cells. This stimulatory effect on MMPs was verified by the observation of increased expression of MMP-2 and MMP-9 as evaluated by Western blot assay. At the same time, a significant decrease of the expression of tissue inhibitors of matrix metalloproteinases-1 (TIMP-1) was observed, suggesting a modulation of the balance of MMPs/TIMPs in hepatic stellate cells. CIP-A5 treatment also resulted in suppression of the profibrogenic cytokines, such as TGF-β, tumor necrosis factor alpha (TNF-α) and connective tissue growth factor (CTGF) in HSC-T6 cells. CIP-A5 did not have cytotoxicity to human normal hepatic cells. These results implied that CIP-A5 could selectively ameliorate the process of liver cirrhosis through modulation of activated hepatic stellate cell activity, which offers hope for prevention and treatment of this devastating end-stage liver disease.

Hedgehog signaling in the liver

Reactivation of Hedgehog (Hh), a morphogenic signaling pathway that controls progenitor cell fate and tissue construction during embryogenesis occurs during many types of liver injury in adult. The net effects of activating the Hedgehog pathway include expansion of liver progenitor populations to promote liver regeneration, but also hepatic accumulation of inflammatory cells, liver fibrogenesis, and vascular remodeling. All of these latter responses are known to be involved in the pathogenesis of cirrhosis. In addition, Hh signaling may play a role in primary liver cancers, such as cholangiocarcinoma and hepatocellular carcinoma. Study of Hedgehog signaling in liver cells is in its infancy. Additional research in this area is justified given growing experimental and clinical data supporting a role for the pathway in regulating outcomes of liver injury.

Osteopontin is induced by hedgehog pathway activation and promotes fibrosis progression in nonalcoholic steatohepatitis

Nonalcoholic steatohepatitis (NASH) is a leading cause of cirrhosis. Recently, we showed that NASH-related cirrhosis is associated with Hedgehog (Hh) pathway activation. The gene encoding osteopontin (OPN), a profibrogenic extracellular matrix protein and cytokine, is a direct transcriptional target of the Hh pathway. Thus, we hypothesize that Hh signaling induces OPN to promote liver fibrosis in NASH. Hepatic OPN expression and liver fibrosis were analyzed in wild-type (WT) mice, Patched-deficient (Ptc(+/-) ) (overly active Hh signaling) mice, and OPN-deficient mice before and after feeding methionine and choline-deficient (MCD) diets to induce NASH-related fibrosis. Hepatic OPN was also quantified in human NASH and nondiseased livers. Hh signaling was manipulated in cultured liver cells to assess direct effects on OPN expression, and hepatic stellate cells (HSCs) were cultured in medium with different OPN activities to determine effects on HSC phenotype. When fed MCD diets, Ptc(+/-) mice expressed more OPN and developed worse liver fibrosis (P < 0.05) than WT mice, whereas OPN-deficient mice exhibited reduced fibrosis (P < 0.05). In NASH patients, OPN was significantly up-regulated and correlated with Hh pathway activity and fibrosis stage. During NASH, ductular cells strongly expressed OPN. In cultured HSCs, SAG (an Hh agonist) up-regulated, whereas cyclopamine (an Hh antagonist) repressed OPN expression (P < 0.005). Cholangiocyte-derived OPN and recombinant OPN promoted fibrogenic responses in HSCs (P < 0.05); neutralizing OPN with RNA aptamers attenuated this (P < 0.05).

CONCLUSION

OPN is Hh-regulated and directly promotes profibrogenic responses. OPN induction correlates with Hh pathway activity and fibrosis stage. Therefore, OPN inhibition may be beneficial in NASH.

E-cadherin antagonizes transforming growth factor β1 gene induction in hepatic stellate cells by inhibiting RhoA-dependent Smad3 phosphorylation

Cadherins mediate cell-cell adhesion and catenin (ctn)-related signaling pathways. Liver fibrosis is accompanied by the loss of E-cadherin (ECAD), which promotes the process of epithelial-mesenchymal transition. Currently, no information is available about the inhibitory role of ECAD in hepatic stellate cell activation. Because of ECAD's potential for inhibiting the induction of transforming growth factor β1 (TGFβ1), we investigated whether ECAD overexpression prevents TGFβ1 gene induction; we also examined what the molecular basis could be. Forced expression of ECAD decreased α-smooth muscle actin and vimentin levels and caused decreases in the constitutive and inducible expression of the TGFβ1 gene and its downstream genes. ECAD overexpression decreased Smad3 phosphorylation, weakly decreased Smad2 phosphorylation, and thus inhibited Smad reporter activity induced by either treatment with TGFβ1 or Smad3 overexpression. Overexpression of a dominant negative mutant of ras homolog gene family A (RhoA) diminished the ability of TGFβ1 to elicit its own gene induction. Consistently, transfection with a constitutively active mutant of RhoA reversed the inhibition of TGFβ1-inducible or Smad3-inducible reporter activity by ECAD. Studies using the mutant constructs of ECAD revealed that the p120-ctn binding domain of ECAD was responsible for TGFβ1 repression. Consistently, ECAD was capable of binding p120-ctn, which recruited RhoA; this prevented TGFβ1 from increasing RhoA-mediated Smad3 phosphorylation. In the liver samples of patients with mild or severe fibrosis, ECAD expression reciprocally correlated with the severity of fibrosis.

CONCLUSION

Our results demonstrate that ECAD inhibits Smad3/2 phosphorylation by recruiting RhoA to p120-ctn at the p120-ctn binding domain, whereas the loss of ECAD due to cadherin switching promotes the up-regulation of TGFβ1 and its target genes, and facilitates liver fibrosis.

The role of Hedgehog signaling in fibrogenic liver repair

Repair of adult liver, like many tissues, involves the coordinated response of a number of different cell types. In adult livers, fibroblastic cells, ductular cells, inflammatory cells, and progenitor cells contribute to this process. Our studies demonstrate that the fates of such cells are dictated, at least in part, by Hedgehog, a fetal morphogenic pathway that was once thought to be active mainly during embryogenesis. Studies of injured adult human and rodent livers demonstrate that injury-related activation of the Hedgehog pathway modulates several important aspects of repair, including the growth of hepatic progenitor populations, hepatic accumulation of myofibroblasts, repair-related inflammatory responses, vascular remodeling, liver fibrosis and hepatocarcinogenesis. These findings identify the Hedgehog pathway as a potentially important target for biomarker development and therapeutic manipulation, and emphasize the need for further research to advance knowledge about how this pathway is regulated by and interacts with other signals that regulate adult liver repair.

Leptin promotes the myofibroblastic phenotype in hepatic stellate cells by activating the hedgehog pathway

Trans-differentiation of quiescent hepatic stellate cells (Q-HSCs), which exhibit epithelial and adipocytic features, into myofibroblastic-HSC (MF-HSCs) is a key event in liver fibrosis. Culture models demonstrated that Hedgehog (Hh) pathway activation is required for transition of epithelioid/adipocytic Q-HSCs into MF-HSCs. Hh signaling inhibits adiposity and promotes epithelial-to-mesenchymal transitions (EMTs). Leptin (anti-adipogenic, pro-EMT factor) promotes HSC trans-differentiation and liver fibrosis, suggesting that the pathways may interact to modulate cell fate. This study aimed to determine whether leptin activates Hh signaling and whether this is required for the fibrogenic effects of leptin. Cultures of primary HSCs from lean and fa/fa rats with an inherited ObRb defect were examined. Inhibitors of PI3K/Akt, JAK/STAT, and Hh signaling were used to delineate how ObRb activation influenced Hh signaling and HSC trans-differentiation. Fibrogenesis was compared in wild type and db/db mice (impaired ObRb function) to assess the profibrotic role of leptin. The results demonstrate that leptin-ObR interactions activate Hh signaling with the latter necessary to promote trans-differentiation. Leptin-related increases in Hh signaling required ObR induction of PI3K/Akt, which was sufficient for leptin to repress the epithelioid/adipocytic program. Leptin-mediated induction of JAK/STAT was required for mesenchymal gene expression. Leptin-ObRb interactions were not necessary for HSC trans-differentiation to occur in vitro or in vivo but are important because liver fibrogenesis was attenuated in db/db mice. These findings reveal that leptin activates Hh signaling to alter gene expression programs that control cell fate and have important implications for liver fibrosis and other leptin-regulated processes involving EMTs, including development, obesity, and cancer metastasis.