Morphological characterisation of portal myofibroblasts and hepatic stellate cells in the normal dog liver

An Overview of Epithelial-to-Mesenchymal Transition and Mesenchymal-to-Epithelial Transition in Canine Tumors: How Far Have We Come?

Historically, pre-clinical and clinical studies in human medicine have provided new insights, pushing forward the contemporary knowledge. The new results represented a motivation for investigators in specific fields of veterinary medicine, who addressed the same research topics from different perspectives in studies based on experimental and spontaneous animal disease models. The study of different pheno-genotypic contexts contributes to the confirmation of translational models of pathologic mechanisms. This review provides an overview of EMT and MET processes in both human and canine species. While human medicine rapidly advances, having a large amount of information available, veterinary medicine is not at the same level. This situation should provide motivation for the veterinary medicine research field, to apply the knowledge on humans to research in pets. By merging the knowledge of these two disciplines, better and faster results can be achieved, thus improving human and canine health.

Liver tissue remodeling following ablation with irreversible electroporation in a porcine model

Irreversible electroporation (IRE) is a method of non-thermal focal tissue ablation characterized by irreversibly permeabilizing the cell membranes while preserving the extracellular matrix. This study aimed to investigate tissue remodeling after IRE in a porcine model, especially focusing on the extracellular matrix and hepatic stellate cells. IRE ablation was performed on 11 female pigs at 2,000 V/cm electric field strength using a versatile high-voltage generator and 3 cm diameter parallel-plate electrodes. The treated lobes were removed during surgery at 1, 3, 7, 14, and 21 days after IRE. Tissue remodeling and regeneration were assessed by histopathology and immunohistochemistry. Throughout the treated area, IRE led to extensive necrosis with intact collagenous structures evident until day 1. From then on, the necrosis progressively diminished while reparative tissue gradually increased. During this process, the reticulin framework and the septal fibrillar collagen remained in the necrotic foci until they were invaded by the reparative tissue. The reparative tissue was characterized by a massive proliferation of myofibroblast-like cells accompanied by a complete disorganization of the extracellular matrix with the disappearance of hepatic architecture. Hepatic stellate cell markers were associated with the proliferation of myofibroblast-like cells and the reorganization of the extracellular matrix. Between 2 and 3 weeks after IRE, the lobular architecture was almost completely regenerated. The events described in the present study show that IRE may be a valid model to study the mechanisms underlying liver regeneration after extensive acute injury.

Histologic, immunohistochemical, and scanning electron microscopic comparison of pre-iridal monocellular and fibrovascular membranes in normal and glaucomatous canine globes

OBJECTIVES

(i) To evaluate immunohistochemical labeling of pre-iridal monocellular and fibrovascular membranes and (ii) describe the light and scanning electron microscopic (SEM) characteristics of these membranes in glaucomatous and normal/control canine globes.

MATERIALS AND METHODS

All globes were evaluated with light microscopy. Immunohistochemical labeling for CD18, Smooth muscle actin (SMA), and CD117 was completed on 40 canine globes with congenital/anterior segment dysgenesis-associated glaucoma (n = 10), primary/goniodysgenesis-associated glaucoma (n = 10), secondary glaucoma (n = 10), and normal/control globes (n = 10). SEM was completed on 10 globes: 5 with monocellular membranes, 3 with fibrovascular membranes, and 2 without a histologically detectable membrane.

RESULTS

Monocellular membranes were detected in all normal/control globes with light microscopy and appeared to be morphologically very similar to those in diseased globes. CD18 labeling was detected in 9/10 monocellular membranes in normal/control globes, 15/23 monocellular, and 7/8 fibrovascular membranes in globes with glaucoma. SMA and CD117 labeling was not detected in monocellular membranes of normal/control globes. SMA was expressed in 10/23 monocellular and 7/8 fibrovascular membranes of glaucomatous globes. CD117 was expressed in 7/23 monocellular and 5/8 fibrovascular membranes of glaucomatous globes. SEM of monocellular membranes revealed a continuous sheet of mostly spindle cells and few individual round cells that extended over the anterior iris face in normal/control and all glaucomatous globes.

CONCLUSION

Pre-iridal monocellular membranes are a normal component of the anterior iris surface, and CD18 immunoreactivity suggests some cells within these are of leukocytic origin. SMA and CD117 labeling of monocellular membranes in glaucomatous, but not normal/control globes, suggest metaplastic cellular change secondary to intraocular pathology related to glaucoma.

Targeted Drug Delivery to Hepatic Stellate Cells for the Treatment of Liver Fibrosis

Liver fibrosis is caused by excessive accumulation of extracellular matrix during chronic liver injuries. Although clinical evidence suggests that liver fibrosis can be reversed, there is no standard therapy for liver fibrosis. Moreover, there is a lack of diagnostic tools to detect early-stage liver fibrosis. Activation of hepatic stellate cells (HSCs) is the key step during liver fibrogenesis, and its mechanism has been extensively studied by various cell culture and animal models. Targeted delivery of therapeutic agents to activated HSCs is therefore critical for the successful treatment of liver fibrosis. A number of protein markers have been found to be overexpressed in activated HSCs, and their ligands have been used to specifically deliver various antifibrotic agents. In this review, we summarize these HSC-specific protein markers and their ligands for targeted delivery of antifibrotic agents.

Canine Idiopathic Chronic Hepatitis

The World Small Animal Veterinary Association's Liver Standardization Group produced standardized criteria for the histologic diagnosis of canine chronic hepatitis (CH). They define CH by the presence of hepatocellular apoptosis or necrosis, a variable mononuclear or mixed inflammatory cell infiltrate, regeneration, and fibrosis. There are variations in histologic appearance between breeds. Hepatic copper accumulation is an important cause of canine CH. However, where copper accumulation has been ruled out, dogs are said to have idiopathic CH. This article reviews theories regarding the etiopathogenesis of canine CH other than copper accumulation, and its clinical features, diagnostic findings, and management.

Sinusoidal endothelial cell and hepatic stellate cell phenotype correlates with stage of fibrosis in chronic liver disease in dogs

We evaluated the extent of hepatic fibrosis in chronic liver disease of dogs using a modification of Ishak's staging criteria for human chronic liver disease, and examined the association of stage of fibrosis with immunophenotypic markers of transdifferentiation of hepatic sinusoidal endothelial cells and hepatic stellate cells. Formalin-fixed, paraffin-embedded, hematoxylin and eosin-stained liver biopsy specimens from 45 case dogs with chronic liver disease and 55 healthy control dogs were scored for the presence and extent of fibrosis. This stage score for fibrosis strongly correlated with upregulated von Willebrand factor (vWF) expression in lobular sinusoidal endothelial cells (Spearman correlation coefficient [SCC] = 0.57, p < 0.05). Immunoreactivity for vWF factor was identified in 68.9% of case biopsies, varying in distribution from periportal to diffuse, whereas vWF immunoreactivity was identified in only 14.5% of control specimens, and was restricted to the immediate periportal sinusoids. The majority of both case and control biopsies exhibited similar prominent lobular perisinusoidal expression of alpha-smooth muscle actin (α-SMA). A minority of specimens (17.8% of case biopsies, 1.8% of control biopsies) exhibited low perisinoidal α-SMA expression, and there was a weak negative correlation between α-SMA expression and stage of fibrosis (SCC = -0.29, p = 0.0037). These results document a method for staging the severity of fibrosis in canine liver biopsies, and show a strong association between fibrosis and increased expression of vWF in hepatic sinusoidal endothelial cells.

Tenascin-C in Chronic Canine Hepatitis: Immunohistochemical Localization and Correlation with Necro-Inflammatory Activity, Fibrotic Stage, and Expression of Alpha-Smooth Muscle Actin, Cytokeratin 7, and CD3+ Cells

During fibrosis, the extracellular matrix (ECM) is continuously remodeled and increases in volume due to the production of various proteins. We studied the distribution of tenascin-C (TN-C) and the correlation of TN-C with the necro-inflammatory activity and expression of alpha–smooth muscle actin (α-SMA), cytokeratin 7 (CK7), and CD3+ T-lymphocytes in canine chronic hepatitis. This was analyzed using immunohistochemistry and semiquantitative scoring. We used 3 groups ( n = 19) of dogs: group 1 ( n = 5) with neonatal hepatitis/lobular dissecting hepatitis (NH/LDH), group 2 ( n = 8) with chronic hepatitis/cirrhosis (CH/CIRR), and group 3 ( n = 6) consisting of healthy animals. In normal livers, TN-C was localized in Disse's space and around bile ducts and blood vessels. In CH/CIRR livers, TN-C was localized at the periphery of the regenerating nodules and was conspicuous in the bridging fibrous bands. In NH/LDH, TN-C was diffusely distributed along the reticular fibers that dissected between single cells or groups of hepatocytes. α-SMA in the normal hepatic parenchyma showed an irregular distribution along the perisinusoidal linings. In other groups, α-SMA was increased in fibrotic septa and perisinusoidal linings. In normal livers, CK7 was positive in bile ducts. In other groups, CK7-expressing cells were conspicuous in the portal-parenchymal interface, the periphery of the regenerative nodules, and the degenerated parenchyma. The pattern of CD3+ lymphocytes was inversely proportional to that of TN-C. These results also showed that TN-C is strongly correlated with increased fibrotic stage, inflammatory activity, and expression of CK7 and α-SMA. TN-C, CK7, and CD3 expression did not differ between diagnostic groups.

Immunohistochemical study of hepatic fibropoiesis associated with canine visceral leishmaniasis

Hepatic fibropoiesis has been confirmed in canine visceral leishmaniasis. In fibrotic disease, hepatic stellate cells (HSC) play an important role in fibropoiesis, undergoing activation by TGF-β to acquire characteristics of myofibroblasts. These cells show extensive capacity for proliferation, motility, contractility, collagen synthesis and extracellular matrix component synthesis. The aim of this work was to identify markers of HSC activation in 10 symptomatic and 10 asymptomatic dogs naturally infected with Leishmania (Leishmania) infantum. Eight uninfected dogs were used as controls. Alpha-actin (α-SMA), vimentin and cytokeratin were investigated by immunohistochemistry as HSC markers. The cytokine TGF-β in tissue was also evaluated by immunohistochemistry. All infected dogs showed higher numbers of reticular fibres than controls. Fibropoiesis found in infected dogs was always associated with the presence of parasites and chronic granulomatous hepatitis. Positive correlation was found among fibropoiesis, parasite tissue load and expression of α-SMA. There was no correlation between fibropoiesis, vimentin and cytokeratin markers. The expression of cytokine TGF-β was higher in infected dogs than in controls, but not significantly different between symptomatic and asymptomatic dogs. These results confirm previous work describing the intense hepatic fibropoiesis in dogs naturally infected with Leishmania infantum, but now associated them with overexpression of TGF-β, where α-SMA may be a superior marker for activated HSC cells in CVL.

Viability, function and morphological integrity of precision-cut liver slices during prolonged incubation: Effects of culture medium

Precision-cut liver slices (PCLS) are an ex vivo model for metabolism and toxicity studies. However, data on the maintenance of the morphological integrity of the various cell types in the slices during prolonged incubation are lacking. Therefore, our aims were to characterize morphological and functional changes in rat PCLS during five days of incubation in a rich medium, RegeneMed®, and a standard medium, Williams' Medium E. Although cells of all types in the slices remain viable, profound changes in morphology were observed, which were more prominent in RegeneMed®. Slices underwent notable fibrosis, bile duct proliferation and fat deposition. Slice thickness increased, resulting in necrotic areas, while slice diameter decreased, possibly indicating cell migration. An increased proliferation of parenchymal and non-parenchymal cells (NPCs) was observed. Glycogen, albumin and Cyp3a1 were maintained albeit to a different level in two media. In conclusion, both hepatocytes and NPCs remain viable and functional, enabling five-day toxicity studies. Tissue remodeling and formation of a new capsule-like cell lining around the slices are evident after 3–4 days. The differences in effects between media emphasize the importance of media selection and of the recognition of morphological changes in PCLS, when interpreting results from toxicological or pharmacological studies.

Screening of candidate genes in fibroblasts derived from patients with Dupuytren's contracture using bioinformatics analysis

Our study aimed to identify candidate genes associated with Dupuytren's contracture (DC) and elucidate their roles in DC development. The microarray data of GSE21221 were downloaded from Gene Expression Omnibus database, including six samples from carpal tunnel-derived fibroblasts and six samples from DC-derived fibroblasts. The differentially expressed genes (DEGs) in DC samples were screened using limma package. GO annotation and KEGG pathway analyses were performed by DAVID online tool. Protein-protein interaction network and expression correlation network were constructed to identify crucial relationships between DEGs. Finally, candidate DC-associated genes were predicted based on comparative toxicogenomics database. A total of 529 DEGs (138 up- and 391 down-regulated) in DC-derived fibroblasts were screened and compared with carpal tunnel-derived fibroblasts. Only ten DC-associated genes, such as neurotrophin 3 (NTF3) and protein kinase C, epsilon (PRKCE), were further screened. In addition, NTF3 was significantly enriched in MAPK signaling pathway, in which other DEGs, such as nuclear receptor subfamily 4, group A, member 1 (NR4A1), fibroblast growth factor 22 (FGF22) and BDNF, were enriched. Besides, NTF3 could co-express with fibrillin 2 (FBN2), and PRKCE could co-express with zinc finger protein 516 (ZNF516), solute carrier organic anion transporter family, member 2A1 (SLCO2A1), chromosome 10 open reading frame 10 (C10orf10) and Kelch domain containing 7A (KLHDC7A). Our study indicates that these DEGs, including NTF3, FBN2, NR4A1, FGF22, BDNF, PRKCE, ZNF516, SLCO2A1, C10orf10 and KLHDC7A, may play important roles in DC development and serve as candidate molecular targets for treating DC.

Establishment and characterization of rat portal myofibroblast cell lines

The major sources of scar-forming myofibroblasts during liver fibrosis are activated hepatic stellate cells (HSC) and portal fibroblasts (PF). In contrast to well-characterized HSC, PF remain understudied and poorly defined. This is largely due to the facts that isolation of rodent PF for functional studies is technically challenging and that PF cell lines had not been established. To address this, we have generated two polyclonal portal myofibroblast cell lines, RGF and RGF-N2. RGF and RGF-N2 were established from primary PF isolated from adult rat livers that underwent culture activation and subsequent SV40-mediated immortalization. Specifically, Ntpdase2/Cd39l1-sorted primary PF were used to generate the RGF-N2 cell line. Both cell lines were functionally characterized by RT-PCR, immunofluorescence, immunoblot and bromodeoxyuridine-based proliferation assay. First, immortalized RGF and RGF-N2 cells are positive for phenotypic myofibroblast markers alpha smooth muscle actin, type I collagen alpha-1, tissue inhibitor of metalloproteinases-1, PF-specific markers elastin, type XV collagen alpha-1 and Ntpdase2/Cd39l1, and mesenchymal cell marker ecto-5’-nucleotidase/Cd73, while negative for HSC-specific markers desmin and lecithin retinol acyltransferase. Second, both RGF and RGF-N2 cell lines are readily transfectable using standard methods. Finally, RGF and RGF-N2 cells attenuate the growth of Mz-ChA-1 cholangiocarcinoma cells in co-culture, as previously demonstrated for primary PF. Immortalized rat portal myofibroblast RGF and RGF-N2 cell lines express typical markers of activated PF-derived myofibroblasts, are suitable for DNA transfection, and can effectively inhibit cholangiocyte proliferation. Both RGF and RGF-N2 cell lines represent novel in vitro cellular models for the functional studies of portal (myo)fibroblasts and their contribution to the progression of liver fibrosis.

Hypervitaminosis A-induced hepatic fibrosis in a cat

RATIONALE

The excessive intake of vitamin A in the form of vitamin concentrate, supplement or vitamin-rich liver can result in hypervitaminosis A in man and animals. Although osteopathologies resulting from chronic vitamin A intoxication in cats are well characterized, no information is available concerning feline hypervitaminosis A-induced liver disease.

CLINICAL SUMMARY

We report the first case of hepatic stellate cell lipidosis and hepatic fibrosis in a domestic cat that had been fed a diet based on raw beef liver. Radiographic examination revealed exostoses and ankylosis between vertebrae C1 and T7, compatible with deforming cervical spondylosis. Necropsy showed a slightly enlarged and light yellow to bronze liver. Microscopic and ultrastructural analyses of liver tissues revealed diffuse and severe liver fibrosis associated with hepatic stellate cell hyperplasia and hypertrophy. These cells showed immunopositive staining for α-smooth muscle actin and desmin markers. The necropsy findings of chronic liver disease coupled with osteopathology supported the diagnosis of hypervitaminosis A.

PRACTICAL RELEVANCE

As in human hepatology, if there is dietary evidence to support increased intake of vitamin A, then hypervitaminosis A should be considered in the differential diagnosis of chronic liver disease in cats.

Heparin modulation on hepatic nitric oxide synthase in experimental steatohepatitis

Nonalcoholic fatty liver disease (NAFLD) is considered to be a hepatic manifestation of metabolic syndrome, and has been etiologically associated with insulin resistance (IR). The histopathology of NAFLD ranges between simple steatosis and nonalcoholic steatohepatitis (NASH), with or without fibrosis. The aim of the present study was to examine the effect of heparin on steatohepatitis and hepatic-induced nitric oxide synthase (iNOS) expression in mice. Male mice were divided into four groups, which included the normal basal diet (control), high fat (HF) diet, HF diet + heparin (treatment group) and heparin control groups. After eight weeks from the initiation of the experiment, blood was collected and livers were harvested for biochemical analysis and histological studies. Serum levels of aspartate aminotransferase, alanine aminotransferase, hepatic triglyceride (TG) and hydroxyproline, as well as the IR, superoxide anion generation and mRNA expression of the hepatic iNOS enzyme were evaluated. Liver specimens were processed for histopathological and immunohistopathological evaluation. Heparin administration decreased the levels of the liver enzymes, IR, superoxide generation, hepatic TG, hydroxyproline and iNOS expression when compared with the HF diet group. These changes were associated with an improvement in inflammation and fibrosis observed via histopathological examination. Therefore, heparin treatment attenuates hepatic injury in steatohepatitis.

Interspecies comparison of stellate cell-containing macula flavae and vitamin A storage in vocal fold mucosa

The macula flavae (MF), populated by vitamin A-storing stellate cells (SCs), are believed to play a fundamental role in development, maintenance and repair of the vocal fold (VF) mucosa; however, to date, they have mostly been examined in observational human cadaver studies. Here, we conducted an interspecies comparison of MF and SC phenotype, as well as vitamin A quantification and localization, in human, pig, dog, rabbit and rat VF mucosae. MF containing vitamin A-positive SCs were only identified in human and rat specimens. Pig, dog and rabbit VF mucosae contained no discernable MF, but rather exhibited preferential vitamin A localization to mucous (pig), serous (dog) or mixed (rabbit) glands. This glandular vitamin A storage corresponded to exceedingly high concentrations of retinol in pig and dog mucosae, and retinyl ester in dog mucosa. These findings have significant implications for the presumed role of the MF and SCs in VF biology, the nature of vitamin A storage within the VF mucosa, and the selection of an appropriate animal model for future experimental studies.

Hepatic progenitor cells in canine and feline medicine: potential for regenerative strategies

New curative therapies for severe liver disease are urgently needed in both the human and veterinary clinic. It is important to find new treatment modalities which aim to compensate for the loss of parenchymal tissue and to repopulate the liver with healthy hepatocytes. A prime focus in regenerative medicine of the liver is the use of adult liver stem cells, or hepatic progenitor cells (HPCs), for functional recovery of liver disease. This review describes recent developments in HPC research in dog and cat and compares these findings to experimental rodent studies and human pathology. Specifically, the role of HPCs in liver regeneration, key components of the HPC niche, and HPC activation in specific types of canine and feline liver disease will be reviewed. Finally, the potential applications of HPCs in regenerative medicine of the liver are discussed and a potential role is suggested for dogs as first target species for HPC-based trials.

Potential of regenerative medicine techniques in canine hepatology

Liver cell turnover is very slow, especially compared to intestines and stomach epithelium and hair cells. Since the liver is the main detoxifying organ in the body, it does not come as a surprise that the liver has an unmatched regenerative capacity. After 70% partial hepatectomy, the liver size returns to normal in about two weeks due to replication of differentiated hepatocytes and cholangiocytes. Despite this, liver diseases are regularly encountered in the veterinary clinic. Dogs primarily present with parenchymal pathologies such as hepatitis. The estimated frequency of canine hepatitis depends on the investigated population and accounts for 1%-2% of our university clinic referral population, and up to 12% in a general population. In chronic and severe acute liver disease, the regenerative and replicative capacity of the hepatocytes and/or cholangiocytes falls short and the liver is not restored. In this situation, proliferation of hepatic stem cells or hepatic progenitor cells (HPCs), on histology called the ductular reaction, comes into play to replace the damaged hepatocytes or cholangiocytes. For unknown reasons the ductular reaction is often too little and too late, or differentiation into fully differentiated hepatocytes or cholangiocytes is hampered. In this way, HPCs fail to fully regenerate the liver. The presence and potential of HPCs does, however, provide great prospectives for their use in regenerative strategies. This review highlights the regulation of, and the interaction between, HPCs and other liver cell types and discusses potential regenerative medicine-oriented strategies in canine hepatitis, making use of (liver) stem cells.

Comparison of vascular smooth muscle cells in canine great vessels

BACKGROUND

Elucidating the histological characteristics of normal vascular smooth muscle cells (VSMCs) is important for understanding mechanisms of development, disease etiology and the remodeling and/or regeneration process of the vessel. However, knowledge regarding VSMCs is focused primarily on the artery. Although the characteristics of each great vessel are documented, few studies have examined VSMCs in parallel within each great vessel. The present study focused on comparing characteristics of canine VSMCs within the aorta (Ao), branch pulmonary artery (bPA), main pulmonary artery (mPA) and inferior vena cava (IVC), simultaneously.

RESULTS

Western blot and immunohistochemistry were used to determine VSMC protein content for alpha smooth muscle actin (ASMA), calponin, myosin heavy chain (MHC) and its isozyme SM2, and non-muscle myosin heavy chain B (SMemb). Thickness and ratio of the VSMC layer were also measured. Expression levels of ASMA, calponin and SM2 significantly differed between vessels, except between mPA and either bPA, Ao and IVC vessels. Expression levels of MHC were significantly different in all vessels, whilst expression of SMemb was significantly different in the Ao compared with either bPA and mPA vessels. All vessels were significantly different with respect to total wall and VSMC layer thickness. The ratio between VSMC layer and total wall thickness was significantly different for each vessel, except between bPA and mPA vessels. Histological analysis of the IVC revealed that the VSMC layer does not line evenly and continuously through the long axis or transverse sections. With respect to the pulmonary artery, calponin was expressed to a greater extent in the mPA compared with the bPA (P < 0.01*). In contrast, MHC and SM2 were expressed to a greater extent in the bPA compared with the mPA (P < 0.01*). Differences in VSMC distribution indicate structural differences in the proximal and distal pulmonary artery bifurcation.

CONCLUSION

Our results show that the VSMC expression pattern in each great vessel is unique and suggestive of the developmental differences between great vessels. We believe this study provides basic data for the pathology, etiology and regenerative capability of the vessels.

The role of hepatic myofibroblasts in liver cirrhosis in fallow deer (Dama dama) naturally infected with giant liver fluke (Fascioloides magna)

Background

This paper describes liver cirrhosis in 35 fallow deer infected with the giant liver fluke, as well as the distribution, origin, and role of myofibroblasts in its development.

Results

In liver of infected deer, stripes of connective tissue are wound around groups of degenerated and regenerated liver lobuli. In the connective tissue, lymphocytes and macrophages which often contain parasite hematin are also present. The walls of the bile ducts are thickened, the epithelium multiplied with mucous metaplasia, and desquamated cells, parasite eggs and brown pigment are present in their lumen.

In the livers with cirrhosis, immunopositivity to α-SMA and desmin was observed in cells in portal and septal spaces, at the edge between fibrotic septa and the surrounding parenchyma and in perisinusoidal spaces. These cells vary in size, they are round, oval, spindle-shaped or irregular in shape, similar to vascular smooth muscle cells. The derangement of epithelial-mesenchymal interactions detected in chronic cholangiopathies is most probably the pro-fibrogenic mechanism in liver cirrhosis of fallow deer (Dama dama) infected with the giant liver fluke (Fascioloides magna).

Conclusion

Myofibroblasts, especially hepatic stellate cells (HSCs), play an important role in the synthesis of extracellular matrix components in the development of parasitic fibrosis and cirrhosis in the liver of fallow deer.

Histological and immunohistochemical evaluations of lobular dissecting hepatitis in American cocker spaniel dogs

Histological and immunohistochemical evaluations of lobular dissecting hepatitis (LDH) were performed in nine American cocker spaniel dogs. Histological examination showed diffuse fibrosis with weak inflammatory reaction of extensive neutrophils, macrophages, lymphocytes and plasma cells. Immunohistochemical examination revealed that the myofibroblastic cells positive for anti-α-smooth muscle actin and anti-vimentin antibodies produced reticular and collagen fibers and brought about the dissection of hepatic cords and diffuse disappearance of hepatocytes. Reticular fibers invading between hepatocytes and the surrounding small group of hepatocytes were strongly positive for anti-collagen type III and anti-collagen type IV antibodies. The positivity to anti-fibronectin and anti-laminin antibodies was frequently continuous on the basement membrane of the sinusoids of the remaining hepatic cords and between the hepatocytes. Positive findings for anti-E-cadherin antibody were not observed between the hepatocytes showing positive findings for anti-collagen type III and anti-collagen type IV antibodies. These results may explain the expression of fibronectin and laminin that occurs prior to the invasion of reticular fibers between hepatocytes. The present study further suggests that expression of an extracellular matrix mainly containing fibronectin and laminin between the hepatocytes and proliferation of collagen fibers and reticular fibers have a major role in the rupture of the hepatic cords and disappearance of hepatocytes.

Cross-species immunohistochemical investigation of the activation of the liver progenitor cell niche in different types of liver disease

BACKGROUND

When hepatocyte replication during liver disease is insufficient for regeneration, liver progenitor cells (LPCs) are activated. The cells and stroma in the immediate environment of LPCs, together termed the LPC niche, are thought to play an important role in this activation. Among these cells are the hepatic stellate cells (HSCs)/myofibroblasts (MFs).

AIMS/METHODS

We assessed the activation of HSC/MFs and LPCs in relation to the histological location and extent of liver disease in immunohistochemically (double) stained serial sections. Markers of HSC/MFs [alpha-smooth muscle actin, glial fibrillary acidic protein (GFAP), neurotrophin 3 and neural-cell adhesion molecule], markers of LPCs (keratin 7 and keratin 19) and a proliferation marker (Ki67) were used. A very relevant spontaneous model to evaluate LPC niche activation in a translational approach seems to be the dog. Therefore, both human and canine liver diseases with different degree of fibrosis and disease activity were included.

RESULTS

In human and canine liver disease, type and extent of LPC niche activation depended on type and severity of disease (P<0.05) and corresponded to the main location of disease. Activated HSCs surrounded the activated LPCs. In chronic hepatitis and non-alcoholic steatohepatitis lobular-type HSCs were activated, while during biliary disease portal/septal MFs were mainly activated. In canine liver, GFAP further presented as an early marker of HSC activation. Activation of the LPCs correlated with disease location and severity (P<0.01), and was inversely related to hepatocyte proliferation, as was previously shown in man.

CONCLUSION

A shared involvement of HSC/MFs, LPCs and disease severity during hepatic disease processes is shown, which is highly similar in man and dog.

Pancreatic stellate/myofibroblast cells express G-protein-coupled melatonin receptor 1

In chronic pancreatitis and pancreatic cancer, progressive fibrosis with the accumulation of extracellular matrix occurs. The main extracellular matrix-producing cell types are retinoid-storing pancreatic stellate cells (PSCs) of mesenchymal origin. Similar to liver stellate cells, quiescent PSCs undergo activation and acquire a myofibroblast-like phenotype in response to pro-fibrogenic mediators (reactive oxygen species, cytokines and toxic metabolites). Activated PSCs differ in their differentiation stage and are characterized by the expression of glial fibrillary-acidic protein, alpha-smooth muscle actin, and nestin. As G-protein-coupled receptors were described to regulate PSC differentiation, we investigated tissue samples from patients with pancreatitis and ductal pancreatic adenocarcinoma for the expression of G-protein-coupled melatonin receptors MT1 and MT2 by double immunofluorescence staining. We show that MT1, but not MT2, is occasionally expressed in PSCs in normal tissue, while in the diseased tissue MT1 is found at high rates in activated PSCs at all stages, and, additionally, in ductal epithelial cells. It is speculated that MT1 activation by its ligand melatonin regulates proliferation and differentiation of PSCs. Prevention of myofibroblast formation by MT1 activation could explain favourable effects of the pineal hormone melatonin on the outcome of pancreatic fibrosis in animal models.