Hepatic fibrosis is enhanced and accompanied by robust oval cell activation after chronic carbon tetrachloride administration to Egr-1-deficient mice

Early-immediate gene Egr1 is associated with TGFβ1 regulation of epigenetic reader Bromodomain-containing protein 4 via the canonical Smad3 signaling in hepatic stellate cells in vitro and in vivo

Upon chronic damage to the liver, multiple cytokines stimulate hepatic stellate cells (HSCs), causing the alterations of gene expression profiles and thus leading to HSC activation, a key step in liver fibrogenesis. Activated HSCs are the dominant contributors to liver fibrosis. Bromodomain containing protein 4 (BrD4), an important epigenetic reader, was demonstrated to concentrate on hundreds of enhancers associated with genes involved in multiple profibrotic pathways, thereby directing HSC activation and the fibrotic responses. The present studies were designed to examine the effect of transforming growth factor beta-1 (TGFβ1), the most potent pro-fibrotic cytokine, on BrD4 expression in HSCs and, if so, elucidated the underlying mechanisms in vitro and in vivo. The experiments employed the heterogeneous TGFβ1 knockout (TGFβ1^+/- ) mice, gene knockdown in vivo, and a model of thioacetamide (TAA)-induced liver injury. The results revealed that TGFβ1 enhanced BrD4 expression in HSCs, which was mediated, at least, by Smad3 signaling and early-immediate gene Egr1 (early growth response-1). TGFβ1-induced Smad3 signaling increased Egr1 expression and promoted Egr1 binding to BrD4 promoter at a site around -111 bp, promoting BrD4 expression. Egr1 knockdown reduced BrD4 expression in HSCs in a mouse model of TAA-induced liver injury and lessened liver fibrosis. Double fluorescence staining demonstrated a strong increase in BrD4 expression in activated HSCs in fibrotic areas of the human livers, paralleling the upregulation of p-Smad3 and Egr1. This research suggested novel molecular events underlying the roles of the master pro-fibrotic cytokine TGFβ1 in HSC activation and liver fibrogenesis.

Hepatic kinome atlas: An in-depth identification of kinase pathways in liver fibrosis of humans and rodents

BACKGROUND AND AIMS

Resolution of pathways that converge to induce deleterious effects in hepatic diseases, such as in the later stages, have potential antifibrotic effects that may improve outcomes. We aimed to explore whether humans and rodents display similar fibrotic signaling networks.

APPROACH AND RESULTS

We assiduously mapped kinase pathways using 340 substrate targets, upstream bioinformatic analysis of kinase pathways, and over 2000 random sampling iterations using the PamGene PamStation kinome microarray chip technology. Using this technology, we characterized a large number of kinases with altered activity in liver fibrosis of both species. Gene expression and immunostaining analyses validated many of these kinases as bona fide signaling events. Surprisingly, the insulin receptor emerged as a considerable protein tyrosine kinase that is hyperactive in fibrotic liver disease in humans and rodents. Discoidin domain receptor tyrosine kinase, activated by collagen that increases during fibrosis, was another hyperactive protein tyrosine kinase in humans and rodents with fibrosis. The serine/threonine kinases found to be the most active in fibrosis were dystrophy type 1 protein kinase and members of the protein kinase family of kinases. We compared the fibrotic events over four models: humans with cirrhosis and three murine models with differing levels of fibrosis, including two models of fatty liver disease with emerging fibrosis. The data demonstrate a high concordance between human and rodent hepatic kinome signaling that focalizes, as shown by our network analysis of detrimental pathways.

CONCLUSIONS

Our findings establish a comprehensive kinase atlas for liver fibrosis, which identifies analogous signaling events conserved among humans and rodents.

Inhibition of CBP/β-catenin signaling ameliorated fibrosis in cholestatic liver disease

Chronic cholestatic liver diseases are characterized by injury of the bile ducts and hepatocytes caused by accumulated bile acids (BAs) and inflammation. Wnt/β-catenin signaling is implicated in organ fibrosis; however, its role in cholestatic liver fibrosis remains unclear. Therefore, we explored the effect of a selective cAMP response element-binding protein-binding protein (CBP)/β-catenin inhibitor, PRI-724, on murine cholestatic liver fibrosis. PRI-724 suppressed liver fibrosis induced by multidrug resistance protein 2 knockout (KO), bile duct ligation, or a 3.5-diethoxycarbonyl-1.4-dihydrocollidine (DDC) diet; it also suppressed BA synthesis and macrophage infiltration. The expression of early growth response-1 (Egr-1), which plays a key role in BA synthesis, was increased in the hepatocytes of patients with cholestatic liver disease. PRI-724 inhibited Egr-1 expression induced by cholestasis, and adenoviral shEgr-1-mediated Egr-1 knockdown suppressed BA synthesis and fibrosis in DDC diet-fed mice, suggesting that PRI-724 exerts its effects, at least in part, by suppressing Egr-1 expression in hepatocytes. Hepatocyte-specific CBP KO in mice suppressed BA synthesis, liver injury, and fibrosis, whereas hepatocyte-specific KO of P300, a CBP homolog, exacerbated DDC-induced fibrosis. Intrahepatic Egr-1 expression was also decreased in hepatocyte-specific CBP-KO mice and increased in P300-KO mice, indicating that Egr-1 is located downstream of CBP/β-catenin signaling. Conclusion: PRI-724 inhibits cholestatic liver injury and fibrosis by inhibiting BA synthesis in hepatocytes. These results highlight the therapeutic effect of CBP/β-catenin inhibition in cholestatic liver diseases.

HMGB1 induced endothelial to mesenchymal transition in liver fibrosis: The key regulation of early growth response factor 1

BACKGROUND

Liver fibrosis has been the focus and difficulty of medical research in the world and its concrete pathogenesis remains unclear. This study aims to observe the high-mobility group box 1 (HMGB1)-induced hepatic endothelial to mesenchymal transition (EndoMT) during the development of hepatic fibrosis, and further to explore the crucial involvement of Egr1 in this process.

METHODS

Carbon tetrachloride (CCl₄), diosbulbin B (DB), N-acetyl-p-aminophenol (APAP) and bile duct ligation (BDL) were used to induce liver fibrosis in mice. Serum HMGB1 content, the occurrence of EndoMT and the production of extracellular matrix (ECM) in vitro and in vivo were detected by Western-blot.

RESULTS

The elevated serum HMGB1 content, the occurrence of EndoMT, the production of ECM and the activation of Egr1 were observed in mice with liver fibrosis induced by CCl₄, DB, APAP or BDL. HMGB1 induced EndoMT and ECM production in human hepatic sinusoidal endothelial cells (HHSECs), and then HHSECs lost the ability to inhibit the activation of hepatic stellate cells (HSCs). The hepatic deposition of collagen, the increased serum HMGB1 content and hepatic EndoMT were further aggravated in Egr1 knockout mice. Natural compound silymarin attenuated liver fibrosis in mice induced by CCl₄ via increasing Egr1 nuclear accumulation, decreasing serum HMGB1 content and inhibiting hepatic EndoMT.

CONCLUSION

Egr1 regulated the expression of HMGB1 that induced hepatic EndoMT, which plays an important role in the development of liver fibrosis.

GENERAL SIGNIFICANCE

This study provides a novel therapeutic strategy for the treatment of liver fibrosis in clinic.

Sex-Dependent Effects on Liver Inflammation and Gut Microbial Dysbiosis After Continuous Developmental Exposure to Trichloroethylene in Autoimmune-Prone Mice

Trichloroethylene (TCE) is a common environmental toxicant linked with hypersensitivity and autoimmune responses in humans and animal models. While autoimmune diseases are more common in females, mechanisms behind this disparity are not clear. Recent evidence suggests that autoimmunity may be increasing in males, and occupational studies have shown that TCE-mediated hypersensitivity responses occur just as often in males. Previous experimental studies in autoimmune-prone MRL^+/+ mice have focused on responses in females. However, it is important to include both males and females in order to better understand sex-disparity in autoimmune disease. In addition, because of an alarming increase in autoimmunity in adolescents, developmental and/or early life exposures to immune-enhancing environmental pollutants should also be considered. Using MRL^+/+ mice, we hypothesized that TCE would alter markers related to autoimmunity to a greater degree in female mice relative to male mice, and that TCE would enhance these effects. Mice were continuously exposed to either TCE or vehicle beginning at gestation, continuing during lactation, and directly in the drinking water. Both male and female offspring were evaluated at 7 weeks of age. Sex-specific effects were evident. Female mice were more likely than males to show enhanced CD4⁺ T cell cytokine responses (e.g., IL-4 and IFN-γ). Although none of the animals developed pathological or serological signs of autoimmune hepatitis-like disease, TCE-exposed female mice were more likely than males in either group to express higher levels of biomarkers in the liver related to regeneration/repair and proliferation. Levels of bacterial populations in the intestinal ileum were also altered by TCE exposure and were more prominent in females as compared to males. Thus, our expectations were correct in that young adult female mice developmentally exposed to TCE were more likely to exhibit alterations in immunological and gut/liver endpoints compared to male mice.

Matrine promotes hepatic oval cells differentiation into hepatocytes and alleviates liver injury by suppression of Notch signalling pathway

AIMS

Recent studies have shown that the hyperactive Notch pathway is involved in cirrhosis and hepatocellular carcinoma (HCC) development by regulating differentiation of hepatic oval cells (HOCs) into cancer cells. The aim of this study was to investigate whether matrine can alleviate liver injury and promote HOC differentiation into hepatocytes by suppression of Notch pathway.

MAIN METHODS

We evaluated the expression of Notch-1, Jagged-1, and Hes-1 in HCC tissue by immunohistochemistry. Stem cell characteristics of HOCs were evaluated by CCK-8, cell cycle, and apoptosis. The expression of Notch pathway, HOC markers and albumin (ALB) was detected by immunohistochemistry, QRT-PCR and western blotting. The effects of matrine in protecting liver in vivo were investigated in a rat Solt-Farber precancerous model.

KEY FINDINGS

We found an abnormal activated Notch pathway in HCC tissue, and the hyperactive Notch pathway was strongly associated with poor liver function in patients with cirrhosis with HCC. Using siNotch-1 to inhibit Notch pathway confirmed that Notch pathway could maintain stem cell characteristics of HOCs. Matrine inhibited stem cell characteristics of HOCs, the expression of Notch pathway and HOC markers but upregulated ALB. Matrine in combined with siNotch-1 RNA decreased the more potently inhibited HOC markers and Notch pathway. In rat Solt-Farber precancerous model, prophylactic application of matrine alleviated liver injury, downregulated Notch pathway and HOC markers, and upregulated ALB in a dose-dependent manner.

SIGNIFICANCE

Matrine could promote the differentiation of HOCs into hepatocytes by inhibiting the Notch signalling pathway and alleviate liver injury.

Soluble Klotho regulates bone differentiation by upregulating expression of the transcription factor EGR-1

Klotho is a transmembrane protein known to regulate aging and lifespan. Soluble Klotho (sKL), a truncated form of Klotho, regulates various cell signaling pathways, including bone development. Here, we investigated the relationship between sKL and the zinc finger transcription factor early growth response protein 1 (EGR-1) on bone formation. We find that sKL induces the expression of EGR-1 mRNA and protein. Through mutational analysis, we identify the 130 bp region on the EGR-1 promoter that is responsive to sKL overexpression. Additionally, sKL induces the expression of markers of bone differentiation (BMP2, RUNX2, ALP, COL1A, and osteocalcin) in osteoblast MC3T3 cells. EGR-1 siRNA decreases the bone mineralization induced by sKL or ascorbic acid/glycerol 2-phosphate in MC3T3 cells. Our results suggest that sKL may regulate bone development through EGR-1 expression.

Inhibition of Mast Cell Degranulation With Cromolyn Sodium Exhibits Organ-Specific Effects in Polycystic Kidney (PCK) Rats

Autosomal recessive polycystic kidney disease (ARPKD) is a monogenic disease characterized by development of hepatorenal cysts, pericystic fibrosis, and inflammation. Previous studies show that mast cell (MC) mediators such as histamine induce proliferation of cholangiocytes. We observed robust MC accumulation around liver cysts, but not kidney cysts, in polycystic kidney (PCK) rats (an animal model of ARPKD). Therefore, we hypothesized that MCs contribute to hepatic cyst growth in ARPKD. To test this hypothesis, we treated PCK rats with 1 of 2 different MC stabilizers, cromolyn sodium (CS) or ketotifen, or saline. The CS treatment decreased MC degranulation in the liver and reduced serum tryptase (an MC granule component). Interestingly, we observed an increase in liver to body weight ratio after CS treatment paralleled by a significant increase in individual cyst size. Hepatic fibrosis was not affected by CS treatment. The CS treatment increased hepatic cyst wall epithelial cell (CWEC) proliferation and decreased cell death. Ketotifen treatment also increased hepatic cyst size. In vitro, CS treatment did not affect proliferation of isolated hepatic CWECs from PCK rats. In contrast, CS decreased kidney to body weight ratio paralleled by a significant decrease in individual cyst size. The percentage of kidney to body weight ratio was strongly correlated with serum renin (an MC granule component). Ketotifen did not affect kidney cyst growth. Collectively, these data suggest that CS affects hepatic and renal cyst growth differently in PCK rats. Moreover, CS may be beneficial to renal cystic disease but may exacerbate hepatic cyst growth in ARPKD.

Participation of liver stem cells in cholangiocarcinogenesis after aflatoxin B1 exposure of glutathione S-transferase A3 knockout mice

Aflatoxin B1, arguably the most potent human carcinogen, induces liver cancer in humans, rats, trout, ducks, and so on, but adult mice are totally resistant. This resistance is because of a detoxifying enzyme, mouse glutathione S-transferase A3, which binds to and inactivates aflatoxin B1 epoxide, preventing the epoxide from binding to DNA and causing mutations. Glutathione S-transferase A3 or its analog has not been detected in any of the sensitive species, including humans. The generation of a glutathione S-transferase A3 knockout (represented as KO or -/-) mice has allowed us to study the induction of liver cancer in mice by aflatoxin B1. In contrast to the induction of hepatocellular carcinomas in other species, aflatoxin B1 induces cholangiocarcinomas in GSTA3-/- mice. In other species and in knockout mice, the induction of liver cancer is preceded by extensive proliferation of small oval cells, providing additional evidence that oval cells are bipolar stem cells and may give rise to either hepatocellular carcinoma or cholangiocarcinoma depending on the nature of the hepatocarcinogen and the species of animal. The recent development of mouse oval cell lines in our laboratory from aflatoxin B1-treated GSTA3-/- mice should provide a new venue for study of the properties and potential of putative mouse liver stem cells.

Role of early growth response 1 in liver metabolism and liver cancer

The liver is an essential organ for nutrient and drug metabolism - possessing the remarkable ability to sense environmental and metabolic stimuli and provide an optimally adaptive response. Early growth response 1 (Egr1), an immediate early transcriptional factor which acts as a coordinator of the complex response to stress, is induced during liver injury and controls the expression of a wide range of genes involved in metabolism, cell proliferation, and role of Egr1 in liver injury and repair, deficiency of Egr1 delays liver regeneration process. The known upstream regulators of Egr1 include, but are not limited to, growth factors (e.g. transforming growth factor β1, platelet-derived growth factor, epidermal growth factor, hepatocyte growth factor), nuclear receptors (e.g. hepatocyte nuclear factor 4α, small heterodimer partner, peroxisome proliferator-activated receptor-γ), and other transcription factors (e.g. Sp1, E2F transcription factor 1). Research efforts using various animal models such as fatty liver, liver injury, and liver fibrosis contribute greatly to the elucidation of Egr1 function in the liver. Hepatocellular carcinoma (HCC) represents the second leading cause of cancer mortality worldwide due to the heterogeneity and the late stage at which cancer is generally diagnosed. Recent studies highlight the involvement of Egr1 in HCC development. The purpose of this review is to summarize current studies pertaining to the role of Egr1 in liver metabolism and liver diseases including liver cancer.

Reproductive age-associated fibrosis in the stroma of the mammalian ovary

Under normal physiological conditions, tissue remodeling in response to injury leads to tissue regeneration without permanent damage. However, if homeostasis between synthesis and degradation of extracellular matrix (ECM) components is altered, fibrosis - or the excess accumulation of ECM - can disrupt tissue architecture and function. Several organs, including the heart, lung and kidney, exhibit age-associated fibrosis. Here we investigated whether fibrosis underlies aging in the ovary - an organ that ages chronologically before other organs. We used Picrosirius Red (PSR), a connective tissue stain specific for collagen I and III fibers, to evaluate ovarian fibrosis. Using bright-field, epifluorescence, confocal and polarized light microscopy, we validated the specific staining of highly ordered PSR-stained fibers in the ovary. We next examined ovarian PSR staining in two mouse strains (CD1 and CB6F1) across an aging continuum and found that PSR staining was minimal in ovaries from reproductively young adult animals, increased in distinct foci in animals of mid-to-advanced reproductive age, and was prominent throughout the stroma of the oldest animals. Consistent with fibrosis, there was a reproductive age-associated increase in ovarian hydroxyproline content. We also observed a unique population of multinucleated macrophage giant cells, which are associated with chronic inflammation, within the ovarian stroma exclusively in reproductively old mice. In fact, several genes central to inflammation had significantly higher levels of expression in ovaries from reproductively old mice relative to young mice. These results establish fibrosis as an early hallmark of the aging ovarian stroma, and this altered microenvironment may contribute to the age-associated decline in gamete quality.

Gene expression profile after knockdown of USP18 in Hepg2.2.15 cells

In our previous work, we found that the expression of ubiquitin-specific protease 18 (USP18), also known as UBP43, is associated with the efficiency of interferon alpha (IFN-α) treatment in patients with chronic hepatitis B (CHB). To elucidate the influence of USP18 on hepatitis B virus (HBV) replication and the mechanism of this activity, we silenced USP18 by introducing short hairpin RNA (shRNA) into Hepg2.2.15 cells. To identify the changed genes and pathways in Hepg2.2.15-shRNA-USP18 cells, we performed a microarray gene expression analysis to compare the Hepg2.2.15 stably expressing USP18-shRNA cells versus control cells using the Affymetrix Human Transcriptome Array (HTA) 2.0 microarrays. Microarray analysis indicated that genes involved in regulation of thyroid hormone signaling pathway, complement, and coagulation cascades, PERK-mediated unfolded protein response, and insulin-like growth factor-activated receptor activity were significantly altered after USP18 knockdown for 72 h. Furthermore, genes involved in hepatocyte proliferation, liver fibrosis, such as cell cycle regulatory gene CCND1, were also altered after USP18 knockdown in Hepg2.2.15 cells. In conclusion, USP18 is critical for regulating the replication of HBV in Hepg2.2.15 cells, which suggest that USP18 may be a candidate target for HBV treatment.

Elk-3 Contributes to the Progression of Liver Fibrosis by Regulating the Epithelial-Mesenchymal Transition

Background/Aims

The role of Elk-3 in the epithelial-mesenchymal transition (EMT) during liver fibrogenesis remains unclear. Here, we determined the expression of Elk-3 in in vitro and in vivo models and in human liver fibrotic tissues. We also investigated the molecular relationships among Elk-3, early growth response-1 (Egr-1), and the mitogen activated protein kinases (MAPK) pathway during EMT in hepatocytes.

Methods

We established anin vitro EMT model in which normal mouse hepatocyte cell lines were treated with transforming growth factor (TGF)-β1 and a CCl₄-induced liver fibrosis model. Characteristics of EMT were determined by evaluating the expression levels of related markers. The expression of Elk-3 and its target Egr-1 were analyzed using Western blotting. Gene silencing of Elk-3 was performed using an siRNA knockdown system.

Results

The expression levels of mesenchymal markers were increased during TGF-β1-induced EMT of hepatocytes. The expression levels of Elk-3 and Egr-1 were significantly (p<0.05) increased during the EMT of hepatocytes, in CCl₄-induced mouse liver fibrotic tissues, and in human liver cirrhotic tissues. Silencing of Elk-3 and inhibition of the Ras-Elk-3 pathway with an inhibitor suppressed the expression of EMT-related markers. Moreover, Elk-3 expression was regulated by p38 MAPK phosphorylation during EMT.

Conclusions

Elk-3 contributes to the progression of liver fibrosis by modulating the EMT via the regulation of Egr-1 under MAPK signaling.

Long-term acetaminophen treatment induced liver fibrosis in mice and the involvement of Egr-1

Acetaminophen (APAP)-induced acute liver injury has already been well studied. However, whether long-term administration of APAP will cause liver fibrosis is still not very clear. This study aims to investigate the liver fibrosis in mice induced by long-term APAP treatment and the involvement of early growth response 1 (Egr-1). C57BL/6 mice were orally given with APAP (200, 300mg/kg) for 2, 6 or 10 weeks, respectively. Liver hydroxyproline content, collagen deposition and inflammatory cells infiltration were increased in mice treated with APAP (200, 300mg/kg) for 6 or 10 weeks. Liver mRNA expression of collagen (COL)1a1, Col3a1, transforming growth factor-β (TGF-β) and serum contents of COL1, COL3, TGF-β were all increased in APAP-treated mice. Liver expression of α-smooth muscle actin (α-SMA) and phosphorylated ERK1/2 and Smad2/3 were all increased in APAP-treated mice. Furthermore, increased liver mRNA expression of Egr-1 and its subsequent nuclear translocation were found in APAP-treated mice. Egr-1 knock-out mice were further applied. APAP-induced liver fibrosis was found to be more serious in Egr-1 knock-out mice. N-acetyl-p-benzoquinoneimine (NAPQI), the APAP hepatotoxic metabolite, increased cellular mRNA expression of α-SMA, Col1a1, Col3a1, TGF-β, induced ERK1/2 and Smad2/3 phosphorylation and Egr-1 nuclear translocation in hepatic stellate LX2 cells. In conclusion, long-term administration of APAP induced liver fibrosis in mice, and Egr-1 was critically involved in this process. This study points out a warning and reference for patients with long-term APAP ingestion in clinic.

The progenitor cell dilemma: Cellular and functional heterogeneity in assistance or escalation of liver injury

Liver progenitor cells (LPCs) are quiescent cells that are activated during liver injury and thought to give rise to hepatocytes and cholangiocytes in order to support liver regeneration and tissue restitution. While hepatocytes are capable of self-renewal, during most chronic injuries the proliferative capacity of hepatocytes is inhibited, thus LPCs provide main source for regeneration. Despite extensive lineage tracing studies, their role and involvement in these processes are often controversial. Additionally, increasing evidence suggests that the LPC compartment consists of heterogeneous cell populations that are actively involved in cellular interactions with myeloid and lymphoid cells during regeneration. On the other hand, LPC expansion has been associated with an increased fibrogenic response, raising concerns about the therapeutic use of these cells. This review aims to summarize the current understanding of the identity, the cellular interactions and the key pathways affecting the biology of LPCs. Understanding the regulatory circuits and the specific role of LPCs is especially important as it could provide novel therapeutic platforms for the treatment of liver inflammation, fibrosis and regeneration.

Isolation and Enrichment of Liver Progenitor Subsets Identified by a Novel Surface Marker Combination

During chronic liver injuries, progenitor cells expand in a process called ductular reaction, which also entails the appearance of inflammatory cellular infiltrate and epithelial cell activation. The progenitor cell population during such inflammatory reactions has mostly been investigated using single surface markers, either by histological analysis or by flow cytometry-based techniques. However, novel surface markers identified various functionally distinct subsets within the liver progenitor/stem cell compartment. The method presented here describes the isolation and detailed flow cytometry analysis of progenitor subsets using novel surface marker combinations. Moreover, it demonstrates how the various progenitor cell subsets can be isolated with high purity using automated magnetic and FACS sorting-based methods. Importantly, novel and simplified enzymatic dissociation of the liver allows for the isolation of these rare cell populations with a high viability that is superior in comparison to other existing methods. This is especially relevant for further studying progenitor cells in vitro or for isolating high-quality RNA to analyze the gene expression profile.

Prospects for Adult Stem Cells in the Treatment of Liver Diseases

Hepatocytes constitute the main bulk of the liver and perform several essential functions. After injury, the hepatocytes have a remarkable capacity to regenerate and restore functionality. However, in some cases, the endogenous hepatocytes cannot replicate or restore the function, and liver transplantation, which is not exempt of complications, is required. Stem cells offer in theory the possibility of generating unlimited supply of hepatocytes in vitro due to their capacity to self-renew and differentiate when given the right cues. Stem cells isolated from an array of tissues have been investigated for their capacity to differentiate into hepatocyte-like cells in vitro and are employed in rescue experiments in vivo. Adult stem cells have gained in attractiveness over embryonic stem cells for liver cell therapy due to their origin, multipotentiality, and the possibility of autologous transplantation. This review deals with the promise and limitations of adult stem cells in clinically restoring liver functionality.

Organoids from adult liver and pancreas: Stem cell biology and biomedical utility

The liver and pancreas are critical organs maintaining whole body metabolism. Historically, the expansion of adult-derived cells from these organs in vitro has proven challenging and this in turn has hampered studies of liver and pancreas stem cell biology, as well as being a roadblock to disease modelling and cell replacement therapies for pathologies in these organs. Recently, defined culture conditions have been described which allow the in vitro culture and manipulation of adult-derived liver and pancreatic material. Here we review these systems and assess their physiological relevance, as well as their potential utility in biomedicine.

Moderate (2%, v/v) Ethanol Feeding Alters Hepatic Wound Healing after Acute Carbon Tetrachloride Exposure in Mice

Wound healing consists of three overlapping phases: inflammation, proliferation, and matrix synthesis and remodeling. Prolonged alcohol abuse can cause liver fibrosis due to deregulated matrix remodeling. Previous studies demonstrated that moderate ethanol feeding enhances liver fibrogenic markers and frank fibrosis independent of differences in CCl₄-induced liver injury. Our objective was to determine whether or not other phases of the hepatic wound healing response were affected by moderate ethanol after CCl₄ exposure. Mice were fed moderate ethanol (2% v/v) for two days and then were exposed to CCl₄ and euthanized 24–96 h later. Liver injury was not different between pair- and ethanol-fed mice; however, removal of necrotic tissue was delayed after CCl₄-induced liver injury in ethanol-fed mice. Inflammation, measured by TNFα mRNA and protein and hepatic Ly6c transcript accumulation, was reduced and associated with enhanced hepatocyte apoptosis after ethanol feeding. Hepatocytes entered the cell cycle equivalently in pair- and ethanol-fed mice after CCl₄ exposure, but hepatocyte proliferation was prolonged in livers from ethanol-fed mice. CCl₄-induced hepatic stellate cell activation was increased and matrix remodeling was prolonged in ethanol-fed mice compared to controls. Taken together, moderate ethanol affected each phase of the wound healing response to CCl₄. These data highlight previously unknown effects of moderate ethanol exposure on hepatic wound healing after acute hepatotoxicant exposure.

Podoplanin discriminates distinct stromal cell populations and a novel progenitor subset in the liver

Podoplanin/gp38(+) stromal cells present in lymphoid organs play a central role in the formation and reorganization of the extracellular matrix and in the functional regulation of immune responses. Gp38(+) cells are present during embryogenesis and in human livers of primary biliary cirrhosis. Since little is known about their function, we studied gp38(+) cells during chronic liver inflammation in models of biliary and parenchymal liver fibrosis and steatohepatitis. Gp38(+) cells were analyzed using flow cytometry and confocal microscopy, and the expression of their steady state and inflammation-associated genes was evaluated from healthy and inflamed livers. Gp38(+) cells significantly expanded in all three models of liver injury and returned to baseline levels during regression of inflammation. Based on CD133 and gp38 expression in the CD45(-)CD31(-)Asgpr1(-) liver cell fraction, numerous subsets could be identified that were negative for CD133 (gp38(hi)CD133(-), gp38(low)CD133(-), and gp38(-)CD133(-)). Moreover, among the CD133(+) cells, previously identified as progenitor population in injured liver, two subpopulations could be distinguished based on their gp38 expression (gp38(-)CD133(+) and CD133(+)gp38(+)). Importantly, the distribution of the identified subsets in inflammation illustrated injury-specific changes. Moreover, the gp38(+)CD133(+) cells exhibited liver progenitor cell characteristics similar to the gp38(-)CD133(+) population, thus representing a novel subset within the classical progenitor cell niche. Additionally, these cells expressed distinct sets of inflammatory genes during liver injury. Our study illuminates a novel classification of the stromal/progenitor cell compartment in the liver and pinpoints a hitherto unrecognized injury-related alteration in progenitor subset composition in chronic liver inflammation and fibrosis.

Constitutive Activation of the Nlrc4 Inflammasome Prevents Hepatic Fibrosis and Promotes Hepatic Regeneration after Partial Hepatectomy

TThe molecular mechanisms responsible for the development of hepatic fibrosis are not fully understood. The Nlrc4 inflammasome detects cytosolic presence of bacterial components, activating inflammatory cytokines to facilitate clearance of pathogens and infected cells. We hypothesized that low-grade constitutive activation of the Nlrc4 inflammasome may lead to induced hepatocyte proliferation and prevent the development of hepatic fibrosis. The gene of Nlrc4 contains two single nucleotide polymorphisms (SNPs), one located within the Nlrc4 promoter and one contained within exon 5. These SNPs regulate Nlrc4 gene transcription and activation as measured through gene reporter assays and IL-1β secretion. The 17C-6 mice have increased IL-1β in plasma after chronic carbon tetrachloride (CCl₄) administration compared to B6 mice. After two-thirds partial hepatectomy (2/3PH) 17C-6 mice have earlier restoration of liver mass with greater cyclin D1 protein and BrdU incorporation compared to B6 mice at several time points. These data reveal mild constitutive activation of the Nlrc4 inflammasome as the results of two SNPs, which leads to the stimulation of hepatocyte proliferation. The increased liver regeneration induces rapid liver mass recovery after hepatectomy and may prevent the development of hepatotoxin-induced liver fibrosis.

Bile acids and stellate cells

Hepatic stellate cells are mainly known for their contribution to fibrogenesis in chronic liver diseases, but their identity and function in normal liver remain unclear. They were recently identified as liver-resident mesenchymal stem cells (MSCs), which can differentiate not only into adipocytes and osteocytes, but also into liver epithelial cells such as hepatocytes and bile duct cells as investigated in vitro and in vivo. During hepatic differentiation, stellate cells and other MSCs transiently develop into liver progenitor cells with epithelial characteristics before hepatocytes are established. Transplanted stellate cells from the liver and pancreas are able to contribute to liver regeneration in stem cell-based liver injury models and can also home into the bone marrow, which is in line with their classification as MSCs. There is experimental evidence that bile acids support liver regeneration and are able to activate signaling pathways in hepatic stellate cells. For this reason, it is important to analyze the influence of bile acids on developmental fate decisions of hepatic stellate cells and other MSC populations.

Adaptive remodeling of the biliary tree: the essence of liver progenitor cell expansion

The liver progenitor cell population has long been thought to exist within the liver. However, there are no standardized criteria for defining the liver progenitor cells, and there has been intense debate about the origin of these cells in the adult liver. The characteristics of such cells vary depending on the disease model used and also on the method of analysis. Visualization of three-dimensional biliary structures has revealed that the emergence of liver progenitor cells essentially reflects the adaptive remodeling of the hepatic biliary network in response to liver injury. We propose that the progenitor cell exists as a subpopulation in the biliary tree and show that the appearance of liver progenitor cells in injured parenchyma is reflective of extensive remodeling of the biliary structure.

Regulation of mice liver regeneration by early growth response-1 through the GGPPS/RAS/MAPK pathway

BACKGROUND & AIMS

Liver regeneration (LR) consists of a series of complicated processes in which several transcription factors play important roles. Among them, the early growth response 1 gene (EGR-1) is rapidly induced in response to liver resection. Previous studies have shown that EGR-1-/- mice exhibit delayed hepatocellular mitotic progression after partial hepatectomy (PH). The mechanism underlying the EGR-1 regulated LR is still unknown. Our aim is to elucidate the underlying mechanism.

METHODS

Mice infected with adenoviral vectors expressing GFP, EGR-1 or dominant negative EGR-1 (dnEGR-1) were subjected to 2/3 PH. The serum starvation recovery cell model was chosen to mimic the regeneration process for the in vitro studies. Cell proliferation and signaling pathways downstream of geranylgeranyl diphosphate synthase (GGPPS) were examined in the regenerating liver and serum starvation recovery cell model.

RESULTS

Loss of function of EGR-1 significantly inhibited liver recovery and the expression of cyclin D1, cyclin E, and proliferating cell nuclear antigen (PCNA). The expression of GGPPS and the activity of the downstream RAS/MAPK pathway were inhibited in dnEGR-1-infected liver, which was consistent with the serum-induced cell model. In addition, loss of function of EGR-1 aggravated liver damage with increased serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels.

CONCLUSIONS

EGR-1-induced GGPPS plays a vital role in the LR after PH through the RAS/MAPK signaling.

Macrophage migration inhibitory factor is required for recruitment of scar-associated macrophages during liver fibrosis

Recruitment of peripheral monocytes to the liver is a key contributor to the response to injury. MIF can act as a chemokine and cytokine, regulating innate immune responses in many tissues and cell types. We hypothesized that MIF contributes to the progression of CCl4-induced hepatic fibrosis by regulating recruitment of SAM. SAMs dynamically regulate HSC activation and ECM degradation. To gain insight into the role of MIF in progression of liver fibrosis, we investigated markers of fibrosis and immune responses after chronic CCl4 administration to female C57BL/6 and MIF(-/-) mice. Chronic CCl4 exposure increased activation of HSC in WT mice, indicated by increased expression of αSMA mRNA and protein, as well as mRNA for collagen 1α1; these responses were blunted in female MIF(-/-) mice. Despite lower activation of HSC in MIF(-/-) mice, accumulation of ECM was similar in WT and MIF(-/-)mice, suggesting a decreased rate of ECM degradation. Recruitment of SAMs was lower in MIF(-/-) mice compared with WT mice, both in their initial inflammatory phenotype, as well as in the later phase as proresolution macrophages. The decreased presence of resolution macrophages was associated with lower expression of MMP13 in MIF(-/-) mice. Taken together, these data indicate that MIF-dependent recruitment of SAMs contributes to degradation of ECM via MMP13, highlighting the importance of appropriate recruitment and phenotypic profile of macrophages in the resolution of fibrosis.

Modeling toxicodynamic effects of trichloroethylene on liver in mouse model of autoimmune hepatitis

Chronic exposure to industrial solvent and water pollutant trichloroethylene (TCE) in female MRL+/+mice generates disease similar to human autoimmune hepatitis. The current study was initiated to investigate why TCE-induced autoimmunity targeted the liver. Compared to other tissues the liver has an unusually robust capacity for repair and regeneration. This investigation examined both time-dependent and dose-dependent effects of TCE on hepatoprotective and pro-inflammatory events in liver and macrophages from female MRL+/+mice. After a 12-week exposure to TCE in drinking water a dose-dependent decrease in macrophage production of IL-6 at both the transcriptional and protein level was observed. A longitudinal study similarly showed that TCE inhibited macrophage IL-6 production. In terms of the liver, TCE had little effect on expression of pro-inflammatory genes (Tnfa, Saa2 or Cscl1) until the end of the 40-week exposure. Instead, TCE suppressed hepatic expression of genes involved in IL-6 signaling (Il6r, gp130, and Egr1). Linear regression analysis confirmed liver histopathology in the TCE-treated mice correlated with decreased expression of Il6r. A toxicodynamic model was developed to estimate the effects of TCE on IL-6 signaling and liver pathology under different levels of exposure and rates of repair. This study underlined the importance of longitudinal studies in mechanistic evaluations of immuntoxicants. It showed that later-occurring liver pathology caused by TCE was associated with early suppression of hepatoprotection rather than an increase in conventional pro-inflammatory events. This information was used to create a novel toxicodynamic model of IL-6-mediated TCE-induced liver inflammation.

Toxicogenomic analysis reveals profibrogenic effects of trichloroethylene in autoimmune-mediated cholangitis in mice

Epidemiological studies suggest that exposure to environmental chemicals increases the risk of developing autoimmune liver disease. However, the identity of specific chemical perpetrators and the mechanisms whereby environmental chemicals modify liver disease is unclear. Previous studies link exposure to trichloroethylene (TCE) with the development of autoimmune liver disease and exacerbation of autoimmunity in lupus-prone MRL mice. In this study, we utilized NOD.c3c4 mice, which spontaneously develop autoimmune cholangitis bearing resemblance to some features of primary biliary cirrhosis. Nine-week-old female NOD.c3c4 mice were given TCE (0.5 mg/ml) or its vehicle (1% Cremophor-EL) in drinking water for 4 weeks. TCE had little effect on clinical chemistry, biliary cyst formation, or hepatic CD3+ T-cell accumulation. Hepatic microarray profiling revealed a dramatic suppression of early growth response 1 (EGR1) mRNA in livers of TCE-treated mice, which was verified by qPCR and immunohistochemical staining. Consistent with a reported link between reduced EGR1 expression and liver fibrosis, TCE increased hepatic type I collagen (COL1A1) mRNA and protein levels in livers of NOD.c3c4 mice. In contrast, TCE did not increase COL1A1 expression in NOD.ShiLtJ mice, which do not develop autoimmune cholangitis. These results suggest that in the context of concurrent autoimmune liver disease with a genetic basis, modification of hepatic gene expression by TCE may increase profibrogenic signaling in the liver. Moreover, these studies suggest that NOD.c3c4 mice may be a novel model to study gene-environment interactions critical for the development of autoimmune liver disease.

Peritumoral ductular reaction: a poor postoperative prognostic factor for hepatocellular carcinoma

Background

The role of ductular reaction (DR) in hepatocellular carcinoma (HCC) remains to be elucidated.

Methods

In this study, we tried to uncover possible effect by correlating peritumoral DR in a necroinflammatory microenvironment with postoperative prognosis in HCC. The expression of peritumoral DR/CK19 by immunohistochemistry, necroinflammation and fibrosis were assessed from 106 patients receiving curative resection for HCC. Prognostic values for these and other clinicopathologic factors were evaluated.

Results

Peritumoral DR significantly correlated with necroinflammation (r = 0.563, p = 3.4E-10), fibrosis (r = 0.435, p = 3.1E-06), AFP level (p = 0.010), HBsAg (p = 4.9E-4), BCLC stage (p = 0.003), TNM stage (p = 0.002), multiple nodules (p = 0.004), absence of tumor capsule (p = 0.027), severe microscopic vascular invasion (p = 0.031) and early recurrence (p = 0.010). Increased DR was significantly associated with decreased RFS/OS (p = 4.8E-04 and p = 2.6E-05, respectively) in univariate analysis and were identified as an independent prognostic factor (HR = 2.380, 95% CI = 1.250-4.534, p = 0.008 for RFS; HR = 4.294, 95% CI = 2.255-8.177, p = 9.3E-6 for OS) in multivariate analysis.

Conclusions

These results suggested that peritumoral DR in a necroinflammatory microenvironment was a poor prognostic factor for HCC after resection.

Kupffer cells in the liver

Kupffer cells are a critical component of the mononuclear phagocytic system and are central to both the hepatic and systemic response to pathogens. Kupffer cells are reemerging as critical mediators of both liver injury and repair. Kupffer cells exhibit a tremendous plasticity; depending on the local metabolic and immune environment, then can express a range of polarized phenotypes, from the proinflammatory M1 phenotype to the alternative/M2 phenotype. Multiple M2 phenotypes can be distinguished, each involved in the resolution of inflammation and wound healing. Here, we have provided an update on recent research that has contributed to the developing delineation of the contribution of Kupffer cells to different types of liver injury, with an emphasis on alcoholic and nonalcoholic liver diseases. These recent advances in our understanding of Kupffer cell function and regulation will likely provide new insights into the potential for therapeutic manipulation of Kupffer cells to promote the resolution of inflammation and enhance wound healing in liver disease.

Molecular basis of organ fibrosis: potential therapeutic approaches

Fibrosis, a non-physiological wound healing in multiple organs, is associated with end-stage pathological symptoms of a wide variety of vascular injury and inflammation related diseases. In response to chemical, immunological and physical insults, the body's defense system and matrix synthetic machinery respond to healing the wound and maintain tissue homeostasis. However, uncontrolled wound healing leads to scarring or fibrosis, a pathological condition characterized by excessive synthesis and accumulation of extracellular matrix proteins, loss of tissue homeostasis and organ failure. Understanding the actual cause of pathological wound healing and identification of igniter(s) of fibrogenesis would be helpful to design novel therapeutic approaches to control pathological wound healing and to prevent fibrosis related morbidity and mortality. In this article, we review the significance of a few key cytokines (TGF-β, IFN-γ, IL-10) transcriptional activators (Sp1, Egr-1, Smad3), repressors (Smad7, Fli-1, PPAR-γ, p53, Klotho) and epigenetic modulators (acetyltransferase, methyltransferases, deacetylases, microRNAs) involved in major matrix protein collagen synthesis under pathological stage of wound healing, and the potentiality of these regulators as therapeutic targets for fibrosis treatment. The significance of endothelial to mesenchymal transition (EndMT) and senescence, two newly emerged fields in fibrosis research, has also been discussed.

Transcription factor EGR1 directs tendon differentiation and promotes tendon repair

Tendon formation and repair rely on specific combinations of transcription factors, growth factors, and mechanical parameters that regulate the production and spatial organization of type I collagen. Here, we investigated the function of the zinc finger transcription factor EGR1 in tendon formation, healing, and repair using rodent animal models and mesenchymal stem cells (MSCs). Adult tendons of Egr1-/- mice displayed a deficiency in the expression of tendon genes, including Scx, Col1a1, and Col1a2, and were mechanically weaker compared with their WT littermates. EGR1 was recruited to the Col1a1 and Col2a1 promoters in postnatal mouse tendons in vivo. Egr1 was required for the normal gene response following tendon injury in a mouse model of Achilles tendon healing. Forced Egr1 expression programmed MSCs toward the tendon lineage and promoted the formation of in vitro-engineered tendons from MSCs. The application of EGR1-producing MSCs increased the formation of tendon-like tissues in a rat model of Achilles tendon injury. We provide evidence that the ability of EGR1 to promote tendon differentiation is partially mediated by TGF-β2. This study demonstrates EGR1 involvement in adult tendon formation, healing, and repair and identifies Egr1 as a putative target in tendon repair strategies.

Genetic resistance to liver fibrosis on A/J mouse chromosome 17

BACKGROUND

Because the histological and biochemical progression of liver disease is similar in alcoholic steatohepatitis (ASH) and nonalcoholic steatohepatitis (NASH), we hypothesized that the genetic susceptibility to these liver diseases would be similar. To identify potential candidate genes that regulate the development of liver fibrosis, we studied a chromosome substitution strain (CSS-17) that contains chromosome 17 from the A/J inbred strain substituted for the corresponding chromosome on the C57BL/6J (B6) genetic background. Previously, we identified quantitative trait loci (QTLs) in CSS-17, namely obesity-resistant QTL 13 and QTL 15 (Obrq13 and Obrq15, respectively), that were associated with protection from diet-induced obesity and hepatic steatosis on a high-fat diet.

METHODS

To test whether these or other CSS-17 QTLs conferred resistance to alcohol-induced liver injury and fibrosis, B6, A/J, CSS-17, and congenics 17C-1 and 17C-6 were either fed Lieber-DeCarli ethanol (EtOH)-containing diet or had carbon tetrachloride (CCl4 ) administered chronically.

RESULTS

The congenic strain carrying Obrq15 showed resistance from alcohol-induced liver injury and liver fibrosis, whereas Obrq13 conferred susceptibility to liver fibrosis. From published deep sequencing data for chromosome 17 in the B6 and A/J strains, we identified candidate genes in Obrq13 and Obrq15 that contained single-nucleotide polymorphisms (SNPs) in the promoter region or within the gene itself. NADPH oxidase organizer 1 (Noxo1) and NLR family, CARD domain containing 4 (Nlrc4) showed altered hepatic gene expression in strains with the A/J allele at the end of the EtOH diet study and after CCl4 treatment.

CONCLUSIONS

Aspects of the genetics for the progression of ASH are unique compared to NASH, suggesting that the molecular mechanisms for the progression of disease are at least partially distinct. Using these CSSs, we identified 2 candidate genes, Noxo1 and Nlrc4, which modulate genetic susceptibility in ASH.

Egr-1: new conductor for the tissue repair orchestra directs harmony (regeneration) or cacophony (fibrosis)

Fibroblasts and myofibroblasts are the key effector cells executing physiological tissue repair leading to regeneration on the one hand, and pathological fibrogenesis leading to chronic fibrosing conditions on the other. Recent studies identify the multifunctional transcription factor early growth response-1(Egr-1) as an important mediator of fibroblast activation triggered by diverse stimuli. Egr-1 has potent stimulatory effects on fibrotic gene expression, and aberrant Egr-1 expression or function is associated with animal models of fibrosis and human fibrotic disorders, including emphysema, pulmonary fibrosis, pulmonary hypertension and systemic sclerosis. Pharmacological suppression or genetic targeting of Egr-1 blocks fibrotic responses in vitro and ameliorates experimental fibrosis in the skin and lung. In contrast, Egr-1 appears to act as a negative regulator of hepatic fibrosis in mouse models, suggesting a context-dependent role in fibrosis. The Egr-1-binding protein Nab2 is an endogenous inhibitor of Egr-1-mediated signalling and abrogates the stimulation of fibrotic responses induced by transforming growth factor-β (TGFβ). Moreover, mice deficient in Nab2 show excessive collagen accumulation in the skin. These observations highlight a previously unsuspected fundamental physiological function for the Egr-1-Nab2 signalling axis in regulating fibrogenesis, and suggest that Egr-1 may be a potential novel therapeutic target in human diseases complicated by fibrosis. This review summarizes recent advances in understanding the regulation and complex functional role of Egr-1 and its related proteins and inhibitors in pathological fibrosis.

Bmi1 is required for hepatic progenitor cell expansion and liver tumor development

Bmi1 is a polycomb group transcriptional repressor and it has been implicated in regulating self-renewal and proliferation of many types of stem or progenitor cells. In addition, Bmi1 has been shown to function as an oncogene in multiple tumor types. In this study, we investigated the functional significance of Bmi1 in regulating hepatic oval cells, the major type of bipotential progenitor cells in adult liver, as well as the role of Bmi1 during hepatocarcinogenesis using Bmi1 knockout mice. We found that loss of Bmi1 significantly restricted chemically induced oval cell expansion in the mouse liver. Concomitant deletion of Ink4a/Arf in Bmi1 deficient mice completely rescued the oval cell expansion phenotype. Furthermore, ablation of Bmi1 delayed hepatocarcinogenesis induced by AKT and Ras co-expression. This antineoplastic effect was accompanied by the loss of hepatic oval cell marker expression in the liver tumor samples. In summary, our data demonstrated that Bmi1 is required for hepatic oval cell expansion via deregulating the Ink4a/Arf locus in mice. Our study also provides the evidence, for the first time, that Bmi1 expression is required for liver cancer development in vivo, thus representing a promising target for innovative treatments against human liver cancer.

Inhibition of apoptosis protects mice from ethanol-mediated acceleration of early markers of CCl4 -induced fibrosis but not steatosis or inflammation

BACKGROUND

Correlative evidence indicates that apoptosis is associated with the progression of alcoholic liver disease. If apoptosis contributes to ethanol (EtOH)-induced steatohepatitis and/or fibrosis, then mice deficient in Bid, a key pro-apoptotic Bcl-2 family member, or mice treated with a pan-caspase inhibitor (VX166) should be resistant to EtOH-induced liver injury.

METHODS

This hypothesis was tested in mice using a model of chronic, heavy EtOH-induced liver injury, as well as in a model in which moderate EtOH feeding accelerated the appearance of early markers of hepatic fibrosis in response to acute carbon tetrachloride (CCl(4) ) exposure.

RESULTS

Chronic EtOH feeding to mice increased TUNEL- and cytokeratin-18-positive cells in the liver, as well as the expression of receptor-interacting protein kinase 3 (RIP3), a marker of necroptosis. In this model, Bid-/- mice or wild-type mice treated with VX166 were protected from EtOH-induced apoptosis, but not EtOH-induced RIP3 expression. Bid deficiency or inhibition of caspase activity did not protect mice from EtOH-induced increases in plasma alanine and aspartate amino transferase activity, steatosis, or mRNA expression of some inflammatory cytokines. Moderate EtOH feeding to mice enhanced the response of mice to acute CCl(4) exposure, resulting in increased expression of α-smooth muscle actin and accumulation of extracellular matrix protein. VX166-treatment attenuated EtOH-mediated acceleration of these early indicators of CCl(4) -induced hepatic fibrosis, decreasing the expression of α-smooth muscle actin, and the accumulation of extracellular matrix protein.

CONCLUSIONS

EtOH-induced apoptosis of hepatocytes was mediated by Bid. Apoptosis played a critical role in the accelerating the appearance of early markers of CCl(4) -induced fibrosis by moderate EtOH but did not contribute to EtOH-induced hepatocyte injury, steatosis, or expression of mRNA for some inflammatory cytokines.

Liver precursor cells increase hepatic fibrosis induced by chronic carbon tetrachloride intoxication in rats

Hepatic fibrosis, the major complication of virtually all types of chronic liver damage, usually begins in portal areas, and its severity has been correlated to liver progenitor cells (LPC) expansion from periportal areas, even if the primary targets of injury are intralobular hepatocytes. The aim of this study was to determine the potential fibrogenic role of LPC, using a new experimental model in which rat liver fibrosis was induced by chronic carbon tetrachloride (CCl(4)) administration for 6 weeks, in combination with chronic acetylaminofluorene treatment (AAF), which promotes activation of LPC compartment. Treatment with CCl(4) alone caused a significant increase in serum transaminase activity as well as liver fibrosis initiating around central veins and leading to formation of incomplete centro-central septa with sparse fibrogenic cells expressing α-smooth muscle actin (αSMA). In AAF/CCl(4)-treated animals, the fibrogenic response was profoundly worsened, with formation of multiple porto-central bridging septa leading to cirrhosis, whereas hepatocellular necrosis and inflammation were similar to those observed in CCl(4)-treated animals. Enhanced fibrosis in AAF/CCl(4) group was accompanied by ductule forming LPC expanding from portal areas, αSMA-positive cells accumulation in the fibrotic areas and increased expression of hepatic collagen type 1, 3 and 4 mRNA. Moreover, CK19-positive LPC expressed the most potent fibrogenic cytokine transforming growth factor-β (TGFβ) without any expression of αSMA, desmin or fibroblast-specific protein-1, demonstrating that LPC did not undergo an epithelial-mesenchymal transition. In this new experimental model, LPC, by expressing TGFβ, contributed to the accumulation of αSMA-positive myofibroblasts in the ductular reaction leading to enhanced fibrosis but also to disease progression and to a fibrotic pattern similar to that observed in humans.

Early growth response factor-1 limits biliary fibrosis in a model of xenobiotic-induced cholestasis in mice

Hepatic expression of the transcription factor early growth response-1 (Egr-1) is increased in livers of patients with cholestatic liver disease. Bile acid induction of inflammatory genes in hepatocytes is Egr-1 dependent, and Egr-1 expression is increased in livers of mice after bile duct ligation. Of importance, Egr-1 deficiency reduces liver inflammation and injury in that model. However, it is not known whether Egr-1 promotes inflammation in other models of cholestasis. We tested the hypothesis that Egr-1 contributes to liver inflammation in mice exposed chronically to the bile duct epithelial cell (BDEC) toxicant alpha-naphthylisothiocyanate (ANIT). Egr-1-knockout (Egr-1(-/-)) mice and wild-type mice were fed a diet containing 0.025% ANIT for 2 weeks. Expression of Egr-1 mRNA and protein was significantly increased in livers of mice fed ANIT diet. Egr-1 deficiency did not significantly affect ANIT diet-induced hepatocellular injury, inflammatory gene induction, BDEC hyperplasia, or hepatic neutrophil accumulation. In contrast, the deposition of Type 1 collagen was significantly increased in livers of Egr-1(-/-) mice fed ANIT diet compared with wild-type mice fed ANIT diet. Interestingly, this increase in liver fibrosis occurred in association with elevated expression of the β6 integrin (Itgb6) gene, suggesting the potential for increased local activation of transforming growth factor beta. Taken together, the results indicate that Egr-1 does not contribute to liver injury or inflammation in mice fed a diet containing ANIT. Rather, these studies indicate that Egr-1 deficiency worsens liver fibrosis in conjunction with enhanced expression of the profibrogenic Itgb6 gene.

Role of early growth response 1 in liver injury

Liver injury is a sophisticated pathophysiological process caused by many factors. Currently, the role of early growth response 1 (EGR1) in liver injury is still controversial. Some studies show that EGR1 can amplify the systemic inflammatory response and promote apoptosis in galactosamine/lipopolysaccharide-induced acute liver injury and alpha-naphthylisothiocyanate (ANIT)-induced intrahepatic cholestasis as well as other non-liver injuries, while some other studies indicate that EGR1 protects the liver from CCl₄ exposure by regulating the expression of inducible nitric oxide synthase, cyclooxygenase-2, and tumor necrosis factor-α-regulated genes that have hepatoprotective function.

Animal models for the study of liver fibrosis: new insights from knockout mouse models

Fibrosis arises as part of a would-healing response that maintains organ structure and integrity following tissue damage but also contributes to a variety of human pathologies such as liver fibrosis. Liver fibrosis is an abnormal response of the liver to persistent injury with the excessive accumulation of collagenous extracellular matrices. Currently there is no effective treatment, and many patients end up with a progressive form of the disease, eventually requiring a liver transplant. The clarification of mechanisms underlying pathogenesis of liver fibrosis and the development of effective therapy are of clinical importance. Experimental animal models, in particular targeted gene knockouts (loss of function) in mice, have become a powerful resource to address the molecular mechanisms or significance of the targeted gene in hepatic functions and diseases. This review will focus on the recent advances in knowledge obtained from genetically engineered mice that provide novel insights into the pathophysiology of liver fibrosis.