Expression and cellular localization of fibrillin-1 in normal and pathological human liver

Exploring the metastasis-related biomarker and carcinogenic mechanism in liver cancer based on single cell technology

Background

Hepatocellular carcinoma (HCC) is a fatal primary malignancy characterized by high invasion and migration. We aimed to explore the underlying metastasis-related mechanism supporting the development of HCC.

Methods

The dataset of single cell RNA-seq (GSE149614) were collected for cell clustering by using the Seurat R package, the FindAllMarkers function was used to find the highly expression and defined the cell cluster. The WebGestaltR package was used for the GO and KEGG function analysis of shared genes, the Gene Set Enrichment Analysis (GSVA) was performed by clusterProfiler R package, the hTFtarget database was used to identify the crucial transcription factors (TFs), the Genomics of Drug Sensitivity in Cancer (GDSC) database was used for the drug sensitivity analysis. Finally, the overexpression and trans-well assay was used for gene function analysis.

Results

We obtained 9 cell clusters from the scRNA-seq data, including the nature killer (NK)/T cells, Myeloid cells, Hepatocytes, Epithelial cells, Endothelial cells, Plasma B cells, Smooth muscle cells, B cells, Liver bud hepatic cells. Further cell ecological analysis indicated that the Hepatocytes and Endothelial cell cluster were closely related to the cancer metastasis. Subsequently, the NDUFA4L2-Hepatocyte, GTSE1-Hepatocyte, ENTPD1-Endothelial and NDUFA4L2-Endothelial were defined as metastasis-supporting cell clusters, in which the NDUFA4L2-Hepatocyte cells was closely related to angiogenesis, while the NDUFA4L2-Endothelial was related with the inflammatory response and complement response. The overexpression and trans-well assay displayed that NDUFA4L2 exhibited clearly metastasis-promoting role in HCC progression.

Conclusion

We identified and defined 4 metastasis-supporting cell clusters by using the single cell technology, the specify shared gene was observed and played crucial role in promoting cancer progression, our findings were expected to provide new insight in control cancer metastasis.

Identification and expression analysis of Oxfibrillin gene involved in the regeneration process of Ophryotrocha xiamen (Annelida, Dorcilleidae)

Regeneration of lost body parts is a widespread phenomenon across annelids. However, the molecular inducers of the cell sources for this reparative morphogenesis have not been identified. We have identified a regeneration-related gene Oxfibrillin from the transcriptome analysis of a polychaeta, Ophryotrocha xiamen, which is found to be a well-suited model to study the mechanisms of regeneration. Fibrillins are large glycoproteins that assemble to form the microfibrils and regulate growth factors or other transfer processes. Here, we obtained the 31,274 bp genomic DNA sequences of Oxfibrillin. The coding sequence length was 5784 bp encoding 1927 amino acids with a VWD domain, EGF/cb-EGF domains, a TR domain, and a transmembrane domain. Oxfibrillin was positioned within the subgroup of invertebrates and showed low scores for homology to mammalian fibrillin. In gene expression analysis, Oxfibrillin genes were constantly upregulated during the early regeneration process and then remained stable until the formation of the complete tail which indicated that it might be a vital factor to affect posterior regeneration process. Therefore, the Oxfibrillin of O. xiamen might play important roles in the regeneration process.

The extracellular matrix glycoprotein fibrillin-1 in health and disease

Fibrillin-1 (FBN1) is a large, cysteine-rich, calcium binding extracellular matrix glycoprotein encoded by FBN1 gene. It serves as a structural component of microfibrils and provides force-bearing mechanical support in elastic and nonelastic connective tissue. As such, mutations in the FBN1 gene can cause a wide variety of genetic diseases such as Marfan syndrome, an autosomal dominant disorder characterized by ocular, skeletal and cardiovascular abnormalities. FBN1 also interacts with numerous microfibril-associated proteins, growth factors and cell membrane receptors, thereby mediating a wide range of biological processes such as cell survival, proliferation, migration and differentiation. Dysregulation of FBN1 is involved in the pathogenesis of many human diseases, such as cancers, cardiovascular disorders and kidney diseases. Paradoxically, both depletion and overexpression of FBN1 upregulate the bioavailability and signal transduction of TGF-β via distinct mechanisms in different settings. In this review, we summarize the structure and expression of FBN1 and present our current understanding of the functional role of FBN1 in various human diseases. This knowledge will allow to develop better strategies for therapeutic intervention of FBN1 related diseases.

Identification of signature of gene expression in biliary atresia using weighted gene co-expression network analysis

Biliary atresia (BA) is the most common cause of obstructive jaundice during the neonatal period. This study aimed to identify gene expression signature in BA. The datasets were obtained from the Gene Expression Omnibus database. Weighted gene co-expression network analysis identified a critical module associated with BA, whereas Gene Ontology (GO) enrichment analysis and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis revealed the functions of the essential modules. The high-connectivity genes in the most relevant module constructed protein-protein interaction networks via the string website and Cytoscape software. Hub genes screened by lasso regression consisted of a disease classification model using the randomforest method. Receiver operating characteristic curves were used to assess models' sensitivity and specificity and the model was verified using the internal and external validation sets. Ten gene modules were constructed by WGCNA, of which the brown module had a strong positive correlation with BA, comprising 443 genes. Functional enrichment analysis revealed that module genes were mainly involved in biological processes, such as extracellular matrix organization, cell adhesion, inflammatory response, and the Notch pathway (P < .001), whereas these genes were involved in the metabolic pathways and cell adhesion molecules (P < .001). Thirty-nine high-connectivity genes in the brown module constructed protein-protein interaction networks. keratin 7 (KRT7) and C-X-C motif chemokine ligand 8 (CXCL8) were used to construct a diagnostic model that had an accuracy of 93.6% and the area under the receiver operating curves for the model was 0.93. The study provided insight into the signature of gene expression and possible pathogenesis of BA; furthermore, it identified that the combination of KRT7 and CXCL8 could be a potential diagnostic model for BA.

Tissue mechanics coevolves with fibrillar matrisomes in healthy and fibrotic tissues

Fibrillar proteins are principal components of extracellular matrix (ECM) that confer mechanical properties to tissues. Fibrosis can result from wound repair in nearly every tissue in adults, and it associates with increased ECM density and crosslinking as well as increased tissue stiffness. Such fibrotic tissues are a major biomedical challenge, and an emerging view posits that the altered mechanical environment supports both synthetic and contractile myofibroblasts in a state of persistent activation. Here, we review the matrisome in several fibrotic diseases, as well as normal tissues, with a focus on physicochemical properties. Stiffness generally increases with the abundance of fibrillar collagens, the major constituent of ECM, with similar mathematical trends for fibrosis as well as adult tissues from soft brain to stiff bone and heart development. Changes in expression of other core matrisome and matrisome-associated proteins or proteoglycans contribute to tissue stiffening in fibrosis by organizing collagen, crosslinking ECM, and facilitating adhesion of myofibroblasts. Understanding how ECM composition and mechanics coevolve during fibrosis can lead to better models and help with antifibrotic therapies.

Collagen and elastic fibres in acute and chronic liver injury

The histological distinction between acute and chronic liver injury is a challenging aspect of liver histopathology. It is traditionally based on the interpretation of morphological changes to the extracellular matrix (ECM) at sites of hepatocyte loss using histochemical stains. Our aim was to investigate whether immunohistochemistry and multiplexing for collagen type (I & III) and elastic fibres and a modified Victoria blue method could be helpful. We studied 43 livers removed at transplantation for acute liver failure (ALF, 20 cases) or cirrhosis (23) plus 8 normal controls. In ALF the periportal ECM was normal in 2 cases, contained mainly collagen I associated with a ductular reaction in 6 cases, and delicate elastic strands in 11 cases. Periportal deposition of mainly collagen I and mature elastic fibres was observed in cirrhosis. In ALF the perisinusoidal ECM was intact in 4 cases, collapsed or condensed but of normal composition (predominantly collagen III) in 2 cases, and collapsed and condensed containing mostly collagen I in 17 cases (7 including delicate immature elastic strands). In contrast, bridging fibrous septa of cirrhosis contained abundant collagen 1 and bundles of mature elastin. We propose the use of a scale and the use of immunohistochemistry and multiplexing in additional to histochemical stains to characterise the ECM changes in acute and chronic liver injury.

Gastric Cancer Tumor Microenvironment Characterization Reveals Stromal-Related Gene Signatures Associated With Macrophage Infiltration

The tumor microenvironment (TME) has attracted attention owing to its essential role in tumor initiation, progression, and metastasis. With the emergence of immunotherapies for various cancers, and their high efficacy, an understanding of the TME in gastric cancer (GC) is critical. The aim of this study was to investigate the effect of various components within the GC TME, and to identify mechanisms that exhibit potential as therapeutic targets. The ESTIMATE algorithm was used to quantify immune and stromal components in GC samples, whose clinicopathological significance and relationship with predicted outcomes were explored. Low tumor mutational burden and high M2 macrophage infiltration, which are considered immune suppressive characteristics and may be responsible for unfavorable prognoses in GC, were observed in the high stromal group (HR = 1.585; 95% CI, 1.112–2.259; P = 0.009). Furthermore, weighted correlation network, differential expression, and univariate Cox analyses were used, along with machine learning methods (LASSO and SVM-RFE), to reveal genome-wide immune phenotypic correlations. Eight stromal-relevant genes cluster (FSTL1, RAB31, FBN1, ANTXR1, LRRC32, CTSK, COL5A2, and ENG) were identified as adverse prognostic factors in GC. Finally, using a combination of TIMER database and single-sample gene set enrichment analyses, we found that the identified genes potentially contribute to macrophage recruitment and polarization of tumor-associated macrophages. These findings provide a different perspective into the immune microenvironment and indicate potential prognostic and therapeutic targets for GC immunotherapies.

Hepatic Stellate Cells in Liver Tumor

Hepatocellular carcinoma and intrahepatic cholangiocarcinoma are the most common types of primary liver cancers. Moreover, the liver is the second most frequently involved organ in cancer metastasis after lymph nodes. The tumor microenvironment is crucial for the development of both primary and secondary liver cancers. The hepatic microenvironment consists of multiple cell types, including liver sinusoidal endothelial cells, Kupffer cells, natural killer cells, liver-associated lymphocytes, and hepatic stellate cells (HSCs). The microenvironment of a normal liver changes to a tumor microenvironment when tumor cells exist or tumor cells migrate to and multiply in the liver. Interactions between tumor cells and non-transformed cells generate a tumor microenvironment that contributes significantly to tumor progression. HSCs play a central role in the tumor microenvironment crosstalk. As this crosstalk is crucial for liver carcinogenesis and liver-tumor development, elucidating the mechanism underlying the interaction of HSCs with the tumor microenvironment could provide potential therapeutic targets for liver cancer.

Proteomics reveals a set of highly enriched proteins in epiretinal membrane compared with inner limiting membrane

Few data exist regarding the protein composition of idiopathic epiretinal membrane (iERM). In the present study we compared the proteome of epiretinal membrane of iERM with the proteome of the inner limiting membrane (ILM) of idiopathic macular hole (iMH). Twelve epiretinal membrane samples were obtained from patients with iERM undergoing therapeutic vitrectomy. Twelve ILM samples from patients with iMH were used as controls. Proteomic analysis was conducted with discovery-based label-free quantitative nano-liquid chromatography - tandem mass spectrometry (LFQ nLC-MS/MS). Verification of results was performed with targeted MS using selected reaction monitoring on a different set of samples. Discovery data were searched against the Uniprot Homo sapiens protein database using MaxQuant Software. Identified proteins were filtered with Perseus software. Bioinformatic analysis of the differences in protein expression between epiretinal membrane from iERM and ILM from iMH was performed using STRING. A total of 2,183 different proteins were identified. 357 proteins were found to be present in all samples. The protein profile of iERM was highly different from iMH with 62 proteins found at significantly higher levels in iERM. The proteins upregulated more than 10-fold in iERM were: fibrillin-1, tenascin, prolargin, biglycan, opticin, collagen alpha-1(II) chain, protein-glutamine gamma-glutamyltransferase 2, fibronectin, filamin-A, collagen alpha-2(IX) chain, spectrin alpha chain, transforming growth factor beta induced protein ig-h3, dihydropyrimidinase - related protein 3, endoplasmin and glutamate dehydrogenase 1. Proteins with high level in iERM consisted of proteins that especially localized to the actin cytoskeleton, the extracellular matrix and the mitochondrion. Analysis of all proteins indicated that the disease process in iERM at least in part can be characterized as skin formation with perturbation of nucleotide metabolism. Our study identified proteins that have not earlier been associated with iERM. Fifteen proteins are found at very high concentration, 10-fold or more, and amongst these four proteins, fibrillin-1, tenascin, prolargin and biglycan were found at more than a 100-fold higher content compared to ILM of iMH. These proteins may be potential therapeutic targets. Data are available via ProteomeXchange with identifier PXD014286.

Curcumin Suppresses Hepatic Stellate Cell-Induced Hepatocarcinoma Angiogenesis and Invasion through Downregulating CTGF

Microenvironment plays a vital role in tumor progression; we focused on elucidating the role of hepatic stellate cells (HSCs) in hepatocarcinoma (HCC) aggressiveness and investigated the potential protective effect of curcumin on HSC-driven hepatocarcinoma angiogenesis and invasion. Our data suggest that HSCs increase HCC reactive oxygen species (ROS) production to upregulate hypoxia-inducible factor-1α (HIF-1α) expression to promote angiogenesis, epithelial to mesenchymal transition (EMT) process and invasion. And HSCs could secrete soluble factors, such as interleukin-6 (IL-6), vascular endothelial cell growth factor (VEGF), and stromal-derived factor-1 (SDF-1) to facilitate HCC progression. Curcumin could significantly suppress the above HSC-induced effects in HCC and could abrogate ROS and HIF-1α expression in HCC. HIF-1α or connective tissue growth factor (CTGF) knockdown could abolish the aforementioned curcumin affection. Moreover, CTGF is a downstream gene of HIF-1α. In addition, nuclear factor E2-related factor 2 (Nrf2) and glutathione (GSH) are involved in curcumin protection of HCC. These data indicate that curcumin may induce ROS scavenging by upregulating Nrf2 and GSH, thus inhibiting HIF-1α stabilization to suppress CTGF expression to exhibit its protection on HCC. Curcumin has a promising therapeutic effect on HCC. CTGF is responsible for curcumin-induced protection in HCC.

Elastin in the Liver

A characteristic feature of liver cirrhosis is the accumulation of large amounts of connective tissue with the prevailing content of type I collagen. Elastin is a minor connective tissue component in normal liver but it is actively synthesized by hepatic stellate cells and portal fibroblasts in diseased liver. The accumulation of elastic fibers in later stages of liver fibrosis may contribute to the decreasing reversibility of the disease with advancing time. Elastin is formed by polymerization of tropoelastin monomers. It is an amorphous protein highly resistant to the action of proteases that forms the core of elastic fibers. Microfibrils surrounding the core are composed of fibrillins that bind a number of proteins involved in fiber formation. They include microfibril-associated glycoproteins (MAGPs), microfibrillar-associated proteins (MFAPs) and fibulins. Lysyl oxidase (LOX) and lysyl oxidase-like proteins (LOXLs) are responsible for tropoelastin cross-linking and polymerization. TGF-β complexes attached to microfibrils release this cytokine and influence the behavior of the cells in the neighborhood. The role of TGF-β as the main profibrotic cytokine in the liver is well-known and the release of the cytokines of TGF-β superfamily from their storage in elastic fibers may affect the course of fibrosis. Elastic fibers are often studied in the tissues where they provide elasticity and resilience but their role is no longer viewed as purely mechanical. Tropoelastin, elastin polymer and elastin peptides resulting from partial elastin degradation influence fibroblastic and inflammatory cells as well as angiogenesis. A similar role may be performed by elastin in the liver. This article reviews the results of the research of liver elastic fibers on the background of the present knowledge of elastin biochemistry and physiology. The regulation of liver elastin synthesis and degradation may be important for the outcome of liver fibrosis.

miR-486-5p inhibits cell growth of papillary thyroid carcinoma by targeting fibrillin-1

Previous studies have demonstrated that miR-486-5p functions as a tumor suppressor or oncogene in various types of cancer. In the present study, we showed that miR-486-5p was significantly down-regulated in papillary thyroid carcinoma (PTC) tissues and cell lines, whereas miR-486-5p down-regulation inhibited PTC cell proliferation and increased apoptosis. Conversely, under-expression of miR-486-5p enhanced PTC cell proliferation and decreased apoptosis. Fibrillin-1 (FBN1) was shown to be a direct target of miR-486-5p and inversely regulated by miR-486-5p. FBN1 silencing led to decreased PTC cell proliferation and enhanced apoptosis in vitro, similar to that mediated by miR-486-5p. Furthermore, miR-486-5p over-expression or FBN1 knock-down inhibited, while up-regulation of FBN1 boosted xenograft tumor formation in vivo. Our data suggest that miR-486-5p induces PTC cell growth inhibition and apoptosis by targeting and suppressing FBN1. Thus, miR-486-5p/FBN1 might provide a promising therapeutic target for PTC treatment.

TIMP-1 mediates TGF-β-dependent crosstalk between hepatic stellate and cancer cells via FAK signaling

Transforming growth factor-β (TGF-β) signaling plays a key role in progression and metastasis of HCC. This study was undertaken to gain the proof of concept of a small-molecule inhibitor of TGF-β type I receptor kinase, EW-7197 as a potent anti-cancer therapy for HCC. We identified tissue inhibitors of metalloproteinases-1 (TIMP-1) as one of the secreted proteins of hepatic stellate cells (HSCs) and a key mediator of TGF-β-mediated crosstalk between HSCs and HCC cells. TGF-β signaling led to increased expression of TIMP-1, which activates focal adhesion kinase (FAK) signaling via its interaction with CD63. Inhibition of TGF-β signaling using EW-7197 significantly attenuated the progression and intrahepatic metastasis of HCC in an SK-HEP1-Luc orthotopic-xenograft mouse model. In addition, EW-7197 inhibited TGF-β-stimulated TIMP-1 secretion by HSCs as well as the TIMP-1-induced proliferation, motility, and survival of HCC cells. Further, EW-7197 interrupted TGF-β-mediated epithelial-to-mesenchymal transition and Akt signaling, leading to significant reductions in the motility and anchorage-independent growth of HCC cells. In conclusion, we found that TIMP-1 mediates TGF-β-regulated crosstalk between HSCs and HCC cells via FAK signaling. In addition, EW-7197 demonstrates potent in vivo anti-cancer therapeutic activity and may be a potential new anti-cancer drug of choice to treat patients with liver cancer.

Hepatic stellate cells: central modulators of hepatic carcinogenesis

Hepatocellular carcinoma (HCC) represents the second most common cause of cancer-related death worldwide, and is increasing in incidence. Currently, our therapeutic repertoire for the treatment of HCC is severely limited, and therefore effective new therapies are urgently required. Recently, there has been increasing interest focusing on the cellular and molecular interactions between cancer cells and their microenvironment. HCC represents a unique opportunity to study the relationship between a diseased stroma and promotion of carcinogenesis, as 90 % of HCCs arise in a cirrhotic liver. Hepatic stellate cells (HSC) are the major source of extracellular proteins during fibrogenesis, and may directly, or via secreted products, contribute to tumour initiation and progression. In this review we explore the complex cellular and molecular interplay between HSC biology and hepatocarcinogenesis. We focus on the molecular mechanisms by which HSC modulate HCC growth, immune cell evasion and angiogenesis. This is followed by a discussion of recent progress in the field in understanding the mechanistic crosstalk between HSC and HCC, and the pathways that are potentially amenable to therapeutic intervention. Furthermore, we summarise the exciting recent developments in strategies to target HSC specifically, and novel techniques to deliver pharmaceutical agents directly to HSC, potentially allowing tailored, cell-specific therapy for HCC.

The role of skeletal muscle in liver glutathione metabolism during acetaminophen overdose

Marked alterations in systemic glutamate-glutamine metabolism characterize the catabolic state, in which there is an increased breakdown and decreased synthesis of skeletal muscle protein. Among these alterations are a greatly increased net release of glutamine (Gln) from skeletal muscle into blood plasma and a dramatic depletion of intramuscular Gln. Understanding the catabolic state is important because a number of pathological conditions with very different etiologies are characterized by its presence; these include major surgery, sepsis, trauma, and some cancers. Acetaminophen (APAP) overdose is also accompanied by dramatic changes in systemic glutamate-glutamine metabolism including large drops in liver glutathione (for which glutamate is a precursor) and plasma Gln. We have constructed a mathematical model of glutamate and glutamine metabolism in rat which includes liver, blood plasma and skeletal muscle. We show that for the normal rat, the model solutions fit experimental data including the diurnal variation in liver glutathione (GSH). We show that for the rat chronically dosed with dexamethasone (an artificial glucocorticoid which induces a catabolic state) the model can be used to explain empirically observed facts such as the linear decline in intramuscular Gln and the drop in plasma glutamine. We show that for the Wistar rat undergoing APAP overdose the model reproduces the experimentally observed rebound of liver GSH to normal levels by the 24-h mark. We show that this rebound is achieved in part by the action of the cystine-glutamate antiporter, an amino acid transporter not normally expressed in liver but induced under conditions of oxidative stress. Finally, we explain why supplementation with Gln, a Glu precursor, assists in the preservation of liver GSH during APAP overdose despite the fact that under normal conditions only Cys is rate-limiting for GSH formation.

Tumor microenviroment and hepatocellular carcinoma metastasis

The cross talk between tumor cells and the surrounding peritumoral stroma has been extensively studied as a dynamic system involving the processes of hepatocarcinogenesis, tumor invasion, and metastasis in recent few decades. Besides hepatocytes, liver tumor microenvironments are generally classified into cellular and noncellular components, including hepatic stellate cells, fibroblasts, immune, endothelial, mesenchymal stem cells, together with growth factors, cytokines, extracellular matrix, hormone as well as viruses et al. The noncellular components manipulate hepatocellular carcinoma invasion and metastasis by facilitating epithelial-mesenchymal transition, increasing proteolytic activity of matrix metalloproteinases, and regulating antitumor immunity, etc. Because the main cause of death in hepatocellular carcinoma patients is tumor progression with metastasis, a better understanding of the interplay between hepatocytes and their environment during tumor metastasis may be helpful for the discovery of novel molecular targets.

Identification of cell surface targets through meta-analysis of microarray data

High-resolution image guidance for resection of residual tumor cells would enable more precise and complete excision for more effective treatment of cancers, such as medulloblastoma, the most common pediatric brain cancer. Numerous studies have shown that brain tumor patient outcomes correlate with the precision of resection. To enable guided resection with molecular specificity and cellular resolution, molecular probes that effectively delineate brain tumor boundaries are essential. Therefore, we developed a bioinformatics approach to analyze micro-array datasets for the identification of transcripts that encode candidate cell surface biomarkers that are highly enriched in medulloblastoma. The results identified 380 genes with greater than a two-fold increase in the expression in the medulloblastoma compared with that in the normal cerebellum. To enrich for targets with accessibility for extracellular molecular probes, we further refined this list by filtering it with gene ontology to identify genes with protein localization on, or within, the plasma membrane. To validate this meta-analysis, the top 10 candidates were evaluated with immunohistochemistry. We identified two targets, fibrillin 2 and EphA3, which specifically stain medulloblastoma. These results demonstrate a novel bioinformatics approach that successfully identified cell surface and extracellular candidate markers enriched in medulloblastoma versus adjacent cerebellum. These two proteins are high-value targets for the development of tumor-specific probes in medulloblastoma. This bioinformatics method has broad utility for the identification of accessible molecular targets in a variety of cancers and will enable probe development for guided resection.

Proteomic analysis of extracellular matrix from the hepatic stellate cell line LX-2 identifies CYR61 and Wnt-5a as novel constituents of fibrotic liver

Activation of hepatic stellate cells (HSCs) and subsequent uncontrolled accumulation of altered extracellular matrix (ECM) underpin liver fibrosis, a wound healing response to chronic injury, which can lead to organ failure and death. We sought to catalogue the components of fibrotic liver ECM to obtain insights into disease etiology and aid identification of new biomarkers. Cell-derived ECM was isolated from the HSC line LX-2, an in vitro model of liver fibrosis, and compared to ECM from human foreskin fibroblasts (HFFs) as a control. Mass spectrometry analyses of cell-derived ECMs identified, with ≥99% confidence, 61 structural ECM or secreted proteins (48 and 31 proteins for LX-2 and HFF, respectively). Gene ontology enrichment analysis confirmed the enrichment of ECM proteins, and hierarchical clustering coupled with protein–protein interaction network analysis revealed a subset of proteins enriched to fibrotic ECM, highlighting the existence of cell type-specific ECM niches. Thirty-six proteins were enriched to LX-2 ECM as compared to HFF ECM, of which Wnt-5a and CYR61 were validated by immunohistochemistry in human and murine fibrotic liver tissue. Future studies will determine if these and other components may play a role in the etiology of hepatic fibrosis, serve as novel disease biomarkers, or open up new avenues for drug discovery.

The role of the myofibroblast in tumor stroma remodeling

Since its first description in wound granulation tissue, the myofibroblast has been recognized to be a key actor in the epithelial-mesenchymal cross-talk that plays a crucial role in many physiological and pathological situations, such as regulation of prostate development, ventilation-perfusion in lung alveoli or organ fibrosis. The presence of myofibroblasts in the stroma reaction to epithelial tumors is well established and many data are accumulating which suggest that the stroma compartment is an active participant in tumor onset and/or evolution. In this review we summarize the evidence in favor of this concept, the main mechanisms that regulate myofibroblast differentiation and function, as well as the biophysical and biochemical factors possibly involved in epithelial-stroma interactions, using liver carcinoma as main model, in view of achieving a better understanding of tumor progression mechanisms and of tools directed toward stroma as eventual therapeutic target.

Fascin, a novel marker of human hepatic stellate cells, may regulate their proliferation, migration, and collagen gene expression through the FAK-PI3K-Akt pathway

Fascin is a component of actin bundles and may regulate various cellular events. The expression and function of fascin in human hepatic stellate cells (HSCs) has remained largely uncharacterized. Fascin expression in human liver tissue was studied using immunohistochemistry. To identify cells expressing fascin, double immunofluorescent staining with vimentin, α-smooth muscle actin (α-SMA), or fibulin-2 was performed and analyzed with confocal microscopy. In culture experiments, fascin expression and the phosphorylation of focal adhesion kinase (FAK) and Akt in LX-2 cells, a cell line of human HSCs, were investigated using western blot. Specific siRNAs were used to reduce the expression of fascin in LX-2 cells. Proliferation and migration were assayed with a CyQuant assay kit and a Matrigel-coated culture insert system, respectively. Levels of matrix metalloproteinase (MMP)-2 and collagen mRNAs were examined using quantitative RT-PCR. Immunohistochemistry revealed the expression of fascin along sinusoids and overlapping with vimentin and α-SMA in both non-fibrotic and fibrotic liver tissue, but it was almost absent in periportal myofibroblastic cells and did not colocalize with fibulin-2, a marker of portal myofibroblasts. In addition, fascin immunoreactivity was almost undetectable in septa of fibrotic human liver tissue. The expression of fascin in LX-2 cells was confirmed using western blot. Two different specific siRNAs against fascin significantly reduced the number of viable LX-2 cells to 65% compared with control cultures and downregulated the mRNAs levels of types I and III collagen and MMP-2 to 62%, 65%, and 70% of control levels, respectively. This condition also reduced the migration activity of LX-2 cells to 46% of control cells and the phosphorylation level of both FAK and Akt. Fascin may be an excellent novel marker of human HSCs that distinguishes HSCs from periportal myofibroblasts. Fascin may regulate functions of human HSCs through the FAK-phosphoinositide 3-kinase-Akt pathway.

Epimorphin promotes human hepatocellular carcinoma invasion and metastasis through activation of focal adhesion kinase/extracellular signal-regulated kinase/matrix metalloproteinase-9 axis

The high incidence rate of hepatocellular carcinoma (HCC) is mainly the result of frequent metastasis and tumor recurrence. Unfortunately, the underlying molecular mechanisms driving HCC metastasis are still not fully understood. It has been demonstrated that tumor stroma cells contribute to primary tumor growth and metastasis. Within the HCC environment, activated hepatic stellate cells (HSCs) can release a number of molecules and enhance cancer cell proliferation and invasiveness in a paracrine manner. Here, for the first time, we demonstrate that epimorphin (EPM; also called syntaxin-2), an extracellular protein, is strongly elevated in activated HSCs within tumor stroma. We show that knockdown of EPM expression in HSCs substantially abolishes their effects on cancer cell invasion and metastasis. Ectopic expression of EPM in HCC cancer cells enhances their invasiveness; we demonstrate that the cells expressing EPM have markedly increased metastasis potential. Furthermore, EPM-mediated invasion and metastasis of cancer cells is found to require up-regulation of matrix metalloproteinase-9 (MMP-9) through the activation of focal adhesion kinase (FAK)/extracellular signal-regulated kinase (ERK) axis.

CONCLUSION

Our results show that EPM, secreted by activated HSCs within HCC stroma, promotes invasion and metastasis of cancer cells by activating MMP-9 expression through the FAK-ERK pathway.

[Expression of the elastic fibers components during the fœtal liver development]

Elastic fibers are composed of microfibrils containing fibrillin-1 and an elastic component, elastin. Microfibrils may not be associated with elastin. In the adult liver, fibrillin-1 and elastin are coexpressed within the stroma and portal tracts vessel walls. Fibrillin-1 is expressed alone around the bile ducts and within the Disse space. There is little work that has studied the elastic fiber organization during the fœtal liver development. Here, we studied the expression of fibrillin-1 and elastin by immunohistochemistry on 20 cases of fœtal liver. During the development of the portal tract, the two components are coexpressed on interstitial elastic fibers and within vessel walls. Fibrillin-1 is expressed alone around the bile structures during their maturation. Unlike adult liver, fibrillin-1 is expressed on thin and very irregular microfibrils within the Disse space. Our study shows that the elastic matrix development in the portal tract follows the development of the different structures, notably biliary structures. In the Disse space, microfibrils are not continuous. Their maturation may be in relation with the change of the hepatic blood flow after birth.

The tumor microenvironment in hepatocellular carcinoma: current status and therapeutic targets

A growing body of literature highlights the cross-talk between tumor cells and the surrounding peri-tumoral stroma as a key modulator of the processes of hepatocarcinogenesis, epithelial mesenchymal transition (EMT), tumor invasion and metastasis. The tumor microenvironment can be broadly classified into cellular and non-cellular components. The major cellular components include hepatic stellate cells, fibroblasts, immune, and endothelial cells. These cell types produce the non-cellular components of the tumor stroma, including extracellular matrix (ECM) proteins, proteolytic enzymes, growth factors and inflammatory cytokines. The non-cellular component of the tumor stroma modulates hepatocellular carcinoma (HCC) biology by effects on cancer signaling pathways in tumor cells and on tumor invasion and metastasis. Global gene expression profiling of HCC has revealed that the tumor microenvironment is an important component in the biologic and prognostic classification of HCC. There are substantial efforts underway to develop novel drugs targeting tumor-stromal interactions. In this review, we discuss the current knowledge about the role of the tumor microenvironment in pathogenesis of HCC, the role of the tumor microenvironment in the classification of HCC and efforts to develop treatments targeting the tumor microenvironment.

Human microvascular lymphatic and blood endothelial cells produce fibrillin: deposition patterns and quantitative analysis

Fibrillin microfibrils constitute a scaffold for elastin deposition in the wall of arteries and form the anchoring filaments that connect the lymphatic endothelium to surrounding elastic fibers. We previously reported that fibrillin is deposited in a honeycomb pattern in bovine arterial endothelial cells, which also deposit microfibril-associated glycoprotein (MAGP)-1, whereas thoracic duct endothelial cells form an irregular web. The present immunohistochemical study was designed to verify whether lymphatic and blood human dermal microvascular endothelial cells (HDMECs) isolated from human foreskin by the sequential use of a pan-endothelial marker, CD31, and the lymphatic specific marker, D2-40, deposit fibrillin and MAGP-1. In both cell types, fibrillin and MAGP-1 co-localized and were deposited with different patterns of increasing complexity co-existing in the same culture. Fibrillin microfibrils formed a wide-mesh honeycomb leaving fibrillin-free spaces that were gradually filled. This modality of fibrillin deposition, similar to that of bovine large artery endothelial cells, was basically the same in blood and lymphatic HDMECs. In some lymphatic HDMECs, fibrillin was initially deposited as uniformly scattered short fibrillin strands probably as a result of anchoring filaments carried over from the vessels of origin. Our findings show that blood and lymphatic endothelial cells participate in fibrillin deposition in human skin.

Portal fibroblasts: Underappreciated mediators of biliary fibrosis

Portal fibroblasts are an important yet often overlooked nonparenchymal cell population in the liver. They are distinct from hepatic stellate cells, yet like stellate cells differentiate in the setting of chronic injury to fibrogenic myofibroblasts, playing an important role in collagen production in the fibrotic liver. Portal fibroblasts (PFs) are located adjacent to bile duct epithelia and thus play a particularly significant role in biliary fibrosis. New data suggest that they may also have key functions independent of fibrogenesis. This review addresses the definition and characteristics of PFs as well as their signaling pathways, interactions with the biliary epithelium, and contributions to liver pathobiology.

CONCLUSION

PFs are an important and multifunctional nonparenchymal cell population in need of further study.

Activated hepatic stellate cells promote tumorigenicity of hepatocellular carcinoma

Liver cirrhosis is the main risk factor for the development of hepatocellular carcinoma (HCC). Activated hepatic stellate cells (HSC) are the effector cells of hepatic fibrosis and also infiltrate the HCC stroma where they might play a critical role in HCC progression. Here we aimed to analyze the effects of activated HSC on the proliferation and growth of HCC cell lines in vitro and in vivo. Conditioned media (CM) collected from HSC significantly induced proliferation and migration of HCC cells cultured in monolayers. In a 3-dimensional spheroid coculture system, HSC promoted HCC growth and diminished the extent of central necrosis. In accordance, in vivo simultaneous implantation of HSC and HCC cells into nude mice promoted tumor growth and invasiveness, and inhibited necrosis formation. As potential mechanism of the tumorigenic effects of HSC we identified activation of NFkappaB and extracellular-regulated kinase (ERK) in HCC cells, two signaling cascades that play a crucial role in HCC progression. In summary, our data indicate that stromal HSC promotes HCC progression and suggest the HSC-HCC interaction as an interesting tumor differentiation-independent target for therapy of this highly aggressive cancer.

MicroRNAs: target recognition and regulatory functions

MicroRNAs (miRNAs) are endogenous approximately 23 nt RNAs that play important gene-regulatory roles in animals and plants by pairing to the mRNAs of protein-coding genes to direct their posttranscriptional repression. This review outlines the current understanding of miRNA target recognition in animals and discusses the widespread impact of miRNAs on both the expression and evolution of protein-coding genes.

Fibulin-5 is involved in phlebosclerosis of major portal vein branches associated with elastic fiber deposition in idiopathic portal hypertension

AIM

In cases of idiopathic portal hypertension (IPH), the deposition of elastic fibers in the major portal vein branches and peripheral portal tracts is a common and characteristic histological finding, which may be related to the disease's pathogenesis. This study aimed to clarify the mechanism of this portal fibroelastosis.

METHODS

The expression of fibulin-5 and fibrillin-1, proteins essential for elastogenesis, was examined in IPH livers (n = 15) using immunohistochemistry. Liver specimens obtained from patients with chronic viral hepatitis (CVH)/liver cirrhosis (LC) (n = 12) and normal/subnormal livers (n = 10) were used as controls.

RESULTS

In IPH livers, immunohistochemical labeling of fibulin-5 was observed in the major portal vein branches in eight cases (53%), and the distribution corresponded to that of elastic fibers in the vessel walls, while the peripheral portaltracts totally lacked fibulin-5 in spite of the presence of dense elastic fibers. In CVH/LC and normal livers, fibulin-5 expression was absent or faint throughout the sections. Fibrillin-1 was detected in the connective tissue of the hilar region and peripheral portal tracts in IPH, CVH/LC and normal livers, with the expression varying greatly among cases.

CONCLUSIONS

These results suggest that fibulin-5, rather than fibrillin-1, expressed in the major portal vein branches of IPH livers is related to phlebosclerosis, leading to an increase in presinusoidal vascular resistance and portal hypertension. In addition, the mechanism of fibroelastosis may differ between the major portal vein branches and peripheral portal tracts of IPH livers.

Transforming growth factor-beta and substrate stiffness regulate portal fibroblast activation in culture

Myofibroblasts derived from portal fibroblasts are important fibrogenic cells in the early stages of biliary fibrosis. In contrast to hepatic stellate cells, portal fibroblasts have not been well studied in vitro, and little is known about their myofibroblastic differentiation. In this article we report the isolation and characterization of rat portal fibroblasts in culture. We demonstrate that primary portal fibroblasts undergo differentiation to alpha-smooth muscle actin-expressing myofibroblasts over 10-14 days. Marker analysis comparing portal fibroblasts to hepatic stellate cells demonstrated that these are distinct populations and that staining with elastin and desmin can differentiate between them. Portal fibroblasts expressed elastin at all stages in culture but never expressed desmin, whereas hepatic stellate cells consistently expressed desmin but never elastin. Immunostaining of rat liver tissue confirmed these results in vivo. Characterization of portal fibroblast differentiation in culture demonstrated that these cells required transforming growth factor-beta (TGF-beta): cells remained quiescent in the presence of a TGF-beta receptor kinase inhibitor, whereas exogenous TGF-beta1 enhanced portal fibroblast alpha-smooth muscle actin expression and stress fiber formation. In contrast, platelet-derived growth factor inhibited myofibroblastic differentiation. Portal fibroblasts were also dependent on mechanical tension for myofibroblastic differentiation, and cells cultured on polyacrylamide supports of variable stiffness demonstrated an increasingly myofibroblastic phenotype as stiffness increased.

CONCLUSION

Portal fibroblasts are morphologically and functionally distinct from hepatic stellate cells. Portal fibroblast myofibroblastic differentiation can be modeled in culture and requires both TGF-beta and mechanical tension.

Expression of mRNAs related to connective tissue metabolism in rat hepatic stellate cells and myofibroblasts

Hepatic stellate cells (HSC) and liver myofibroblasts (MFB) are two cell populations most likely responsible for the synthesis of most connective tissue components in fibrotic liver. They differ in their origin and location, and possibly in patterns of gene expression. Normal and carbon tetrachloride-cirrhotic livers from rats were used to isolate HSC. Liver was perfused with pronase and collagenase solutions, followed by centrifugation of the cell suspension on a density gradient. HSC were quiescent 2 days after plating on plastic but they became activated after another 5 days in culture. When the culture was passaged 5 times, its character changed profoundly as HSC were replaced by MFB. Microarray analysis was used to determine gene expression in quiescent HSC, activated HSC and MFB. The expression of 49 genes coding for connective tissue proteins, proteoglycans, metalloproteinases and their inhibitors, growth factors and cellular markers was determined. The pattern of gene expression changed during HSC activation and there were distinct differences between HSC and MFB. Little difference between normal cells and cells isolated from cirrhotic liver was found.

Fibrillin expression and localization in various types of carcinomas of the thyroid gland

Fibrillin is an extracellular matrix (ECM) glycoprotein, a main component of microfibrills, suggested to support cell attachment and to impact cell differentiation and migration. The aim of this study was to investigate fibrillin-1 expression in thyroid carcinomas at mRNA and protein level, since ECM proteins are suggested to be of great importance for the metastatic potential of carcinomas. RNA was extracted from 13 thyroid carcinoma cell lines and RT-PCR analysis with gene-specific primers revealed fibrillin-1 mRNA expression in all cell lines, with highest expression in the follicular carcinoma cell line WRO and lowest expression in the two anaplastic cell lines (APO, FRO). Furthermore, we investigated fibrillin-1 expression by immumohistochemistry in a commercially available tissue microarray including 50 thyroid carcinomas as well as in archival tissue from 33 thyroid carcinomas. Fibrillin-1 demonstrated a cytoplasmic location in the neoplastic cells of almost all carcinomas apart from the follicular ones. The most intense staining was observed in papillary carcinomas with some evidence of a slight increased intensity in advanced stages. Our data indicate that fibrillin-1 is strongly expressed by the neoplastic cells of thyroid carcinomas in different degree in the various histologic types and might be implicated in cell-stroma interaction in terms of signaling, attachment and migration.

The common bile duct ligation in rat: A relevant in vivo model to study the role of mechanical stress on cell and matrix behaviour

Common bile duct ligation leads to bile accumulation and liver fibrosis. In this model, little attention has been dedicated to the modification of the common bile duct. We have studied by histochemistry and immunohistochemistry, 3 and 5 days after ligation, the connective tissue modifications of the common bile duct wall. After bile duct ligation, compared with normal bile duct, a strong increase of the bile duct diameter, due to bile stasis, and a thickness of the bile duct wall were observed; numerous myofibroblasts expressing alpha-smooth muscle actin appeared in parallel with the detection of many proliferating connective tissue cells. These myofibroblasts secreted very early high amount of elastic fibre components, elastin and fibrillin-1. Elastic fibre increase was also observed close to the epithelial cell layer. Procollagen type III deposition was also induced 3 days after ligation but decreased thereafter, underlining that myofibroblasts modify their synthesis of extracellular matrix components to comply with the request. We show here that common bile duct ligation represents an invaluable model to study myofibroblastic differentiation and extracellular matrix adaptation produced by an acute mechanical stress.

B cells: no longer bystanders in liver fibrosis

Cytokines secreted by cells that mediate the innate and adaptive immune responses play a critical role in regulating the synthesis of ECM components by fibroblasts. Overexpression and deposition of ECM components are dominant features of fibrotic diseases, including hepatic fibrosis. The contribution of CD4+ Th2 cells to hepatic fibrosis has been well described. Now, in this issue of the JCI, Novobrantseva et al. provide data to suggest that hepatic B cells also play a role in liver injury (see the related article beginning on page 3072). In a carbon tetrachloride-induced mouse model of hepatic fibrosis, T cell-deficient mice developed severe liver fibrosis; however, in B cell-deficient animals, hepatic fibrosis was attenuated. This study provides new insight into our understanding of the cells involved in mediating the adaptive immune response that leads to hepatic fibrosis.

Differential gene expression profiles in the steatosis/fibrosis model of rat liver by chronic administration of carbon tetrachloride

Global gene expression profile was analyzed by microarray analysis of rat liver RNA after chronic carbon tetrachloride (CCl(4)) administration. Rats received 0.5 ml CCl(4)/kg three times a week, and the liver samples were obtained after 0, 30, 60, and 90 days of injection. Histopathologic studies of liver tissues enabled the classification of the CCl(4) effect into mild and severe fatty liver/steatosis (30 and 60 days, respectively) and fibrosis/cirrhosis (90 days) stages. The expression levels of 4,900 clones on a custom rat gene microarray were analyzed and the results were confirmed by semi-quantitative RT-PCR. Four hundred thirty-eight clones were differentially expressed with more than a 1.625-fold difference (which equals 0.7 in log2 scale) at one or more time points. Multiple genes involved in lipid metabolism and ribosome biogenesis showed differential transcript levels upon chronic CCl(4) administration, which was previously seen in acute rat model as well. In addition, a total of 149 clones were identified as fibrosis/cirrhosis-specific genes by either fold changes or Significance Analysis of Microarrays. In conclusion, we report microarray analysis results in rat liver upon chronic CCl(4) administration with a full chronological profile that not only covered fatty liver/steatosis but also later points of fibrosis/cirrhosis. These data will provide the insight of specific gene expression profiles that is implicated in the multistep process of fatty liver/steatosis and fibrosis/cirrhosis after chronic hepatotoxin exposure.

Enhanced expression of fibrillin-1, a constituent of the myocardial extracellular matrix in fibrosis

Fibrillin-1 localization in the myocardium and the modulation of its expression in cardiac fibrosis were examined. In normal rat hearts, fibrillin-1 was abundant throughout the myocardium as thin fibers that crossed over the perimysium and around arteries. After cardiac fibrosis was induced in rats by either 14-day ANG II infusion or 21-day DOCA-salt treatment [a high endothelin-1 (ET-1) model], fibrillin-1 immunostaining was stronger in the interstitium (2.8-fold and 4.4-fold increases, respectively, in each model), extended between myocytes, and accumulated in microscopic scars and in the perivascular area of both ventricles. mRNA analysis confirmed its enhanced ventricular expression in both groups of rats (2.5-fold and 6.6-fold increments, respectively, in each model). In 1B normotensive and 2C hypertensive transgenic mice, two lines expressing an ANG II fusion protein in cardiac myocytes, strong fibrillin-1 immunoreactivity was observed in the interstitium and around arteries (3.7-fold and 7-fold increases, respectively). ANG II and transforming growth factor-beta1 enhanced fibrillin-1 synthesis by cardiac fibroblasts. Some fibrillin-1 fragments interacted with RGD-dependent integrins, including alpha(8)beta(1)-integrin, of cardiac fibroblasts but not necessarily through the RGD motif. Our findings illustrate that fibrillin-1 is an important constituent of the myocardium. In vitro and in vivo evidence suggests that ANG II can directly induce fibrillin-1 expression in cardiac fibroblasts. This protein can thus contribute to reactive and reparative processes.

Portal tract fibrogenesis in the liver

The portal area is the 'main entrance' and one of the two main exits of the liver lobule. Through the main entrance portal and arterial blood reach the liver sinusoids. Through the exit the bile flows towards the duodenum. The three main structures, portal vein and artery with their own wall (and vascular smooth muscle cells) and bile duct with its basal membrane, are surrounded by loose myofibroblasts and by the first layer of hepatocytes and non-parenchymal cells. Chronic diseases of the liver can lead to development of liver cirrhosis, characterized by formation of fibrotic septa which can be portal-portal in the case of the chronic biliary damage or portal-central in the case of the chronic viral hepatitis. Central-central septa can also be observed under other pathological conditions. When damaging noxae are introduced to the liver, inflammatory cells are first recruited to the portal field, the first layer of hepatocytes may be destroyed (enlargement of the portal field) and portal (myo)fibroblasts become activated. A similar reaction may take place when the target of inflammation is the bile duct with consecutive reduction of the bile flow, activation of the portal (myo)fibroblasts, proliferation of bile ducts and destruction of the hepatocytes around the portal field. Increased matrix deposition may be the consequence. During the past years several publications dealt with the pathomechanisms of portal fibrogenesis as well as with its resolution. One of the most intriguing observations was that it is not hepatic stellate cells of the hepatic sinusoid, but portal (myo)fibroblasts which rapidly acquire the phenotype of 'activated' (myo)fibroblasts in the early stages of cholestatic fibrosis. These may also become the main mesenchymal cells of the porto-portal or porto-central fibrotic septa. This article reviews the similarities as well as differences between the mesenchymal cells of the portal tract and of the fibrotic septa vs 'activated' stellate cells of the hepatic sinusoids, and discusses the debate over their relative contributions to liver fibrogenesis.

Fibrillin-1 expression in normal and fibrotic rat liver and in cultured hepatic fibroblastic cells: modulation by mechanical stress and role in cell adhesion

Fibrillin-1, together with elastin, is the main component of elastic fibers found throughout the extracellular space and responsible for the biomechanical properties of most tissues and organs. In this work, fibrillin-1 expression and modulation were explored in experimental rat liver fibrosis and in vitro; furthermore, the role of fibrillin-1 fragments on cell adhesion was analyzed. Fibrosis was induced by subjecting rats to common bile duct ligation for 72 h and 7 days or carbon tetrachloride (CCl(4)) treatment for 2 and 6 weeks. Immunohistochemistry showed that, after bile duct ligation, fibrillin-1, elastin, and alpha-smooth muscle actin colocalized in the developing portal connective tissue. In CCl(4)-treated animals, a similar colocalization was observed in septa; however, elastin deposition was not observed around activated alpha-smooth muscle actin-positive stellate cells of the parenchyma. Treatment with the profibrogenic mediator transforming growth factor-beta1 (TGF-beta1) greatly increased the fibrillin-1 expression of cultured liver fibroblasts. The level of fibrillin-1 expression was significantly higher in cells grown in restrained (stressed) collagen lattices compared with those grown in unrestrained collagen lattices. Cell adhesion on the C-terminal fragment of fibrillin-1 containing the RGD sequence (rF6H) slightly increased (between 0.3 and 2.5 microg/ml) and decreased at higher concentrations, while adhesion on the N-terminal fragment of fibrillin-1 (rF16) was dose-dependently decreased. In addition, the rF16 fragment decreased cell adhesion to fibronectin. In conclusion, our study illustrates the important deposition of fibrillin-1 that occurs in two mechanistically distinct settings of liver fibrogenesis. Furthermore, the induction of fibrillin-1 expression by TGF-beta1 and mechanical stress, and the antiadhesive properties of fibrillin-1 fragments suggest important implications for physiological and pathological fibrillin-1 catabolism during tissue remodeling.

Expression of fibrillin-1 in focal nodular hyperplasia of the liver: a role in microcirculation adaptability

Introduction

It has been suggested that the elastic network plays an important role in the tissue response to mechanical stress. The components of the elastic network have been poorly studied in liver diseases. Therefore, in this work, the expression and distribution of fibrillin-1 and elastin were studied in hepatic focal nodular hyperplasia and compared with surrounding liver and hepatocellular adenoma.

Methods

Immunohistochemical studies for fibrillin-1 and elastin were performed on unfixed cryostat sections of focal nodular hyperplasia (22 cases), hepatocellular adenoma (15 cases) and surrounding liver (34 cases).

Results

Surrounding normal liver showed only a continuous, thin and regular immunostaining of fibrillin-1 in the space of Disse, whereas elastin was nearly absent. In focal nodular hyperplasia, fibrillin-1 was more strongly expressed in the perisinusoidal space, compared with surrounding liver; in contrast, in adenomas fibrillin-1 immunostaining was irregular and very low in perisinusoidal space, more intense in peliotic areas.

Conclusions

In focal nodular hyperplasia, the increased microfibrillar network containing fibrillin-1 in the space of Disse could reflect an adaptation of the sinusoidal wall to an increased arterial blood flow in sinusoids. In hepatocellular adenoma, the different patterns of fibrillin-1 could be related to the heterogeneity of the arterial vascularization and to the frequent necrotico-hemorrhagic changes. This study comparing the elastic network in two types of lesions with vascularization abnormalities and in the surrounding liver provides interesting new data for understanding the structural role of fibrillin-1 in the space of Disse.

Mesenchymal cells in the liver--one cell type or two?

The wall of the liver sinusoid is made of highly specialized cells, the hepatic stellate cells (HSC) which together with the sinusoidal endothelial cells represent a loose barrier to the corpusculate part of the blood flowing through the liver. Quiescent stellate cells (quiescent HSC) store Vitamin A; "activated" stellate cells become involved in the reaction to acute or chronic noxae damaging the liver parenchyma. Activated HSC show increased protein synthesis capacity, increased DNA-synthesis and acquire a myofibroblast-like phenotype. Under similar conditions liver myofibroblasts (MF) of the portal field and of the pericentral area may also become "activated" by increasing protein synthesis, DNA synthesis and cell division. They express the fibulin-2 gene and produce large amounts of IL-6. In contrast to "activated" HSC they do not undergo spontaneous apoptosis in vitro and do not express the CD95-ligand gene. So far no definite prove has been found for a "transdifferentiation" of HSC to myofibroblasts. On the contrary an increasing amount of data support the conviction that HSC and MF represent two similar but not identical cell populations the latter being comparable to those of other organs.

Tropoelastin expression is up-regulated during activation of hepatic stellate cells and in the livers of CCl(4)-cirrhotic rats

BACKGROUND/AIMS

Activated hepatic stellate cells (HSC) are regarded as the principal cells synthesizing extracellular matrix components in fibrotic liver. Elastin content is increased in cirrhotic livers, but the cellular source is not known. Contribution of HSC to the production of elastin was investigated.

METHODS

Expression of elastin in CCl(4)-cirrhotic rat liver was studied by immunohistochemistry and in situ hybridization, liver myofibroblasts were identified in histological sections by alpha-smooth muscle actin (alpha-SMA) staining. LightCycler PCR and Northern blotting were used to detect tropoelastin mRNA in isolated HSC; tropoelastin protein was detected in the cells and in cell-conditioned medium by Western blotting.

RESULTS

HSC, isolated from normal rat liver, displayed increasing tropoelastin mRNA expression during transdifferentiation in culture. Expression of tropoelastin mRNA was accompanied by the production of tropoelastin protein in vitro. Increased levels of tropoelastin transcripts were found in the connective tissue septa of CCl(4)-cirrhotic rats and co-localized with alpha-SMA positive cells. Immunohistochemistry demonstrated elastin presence in the septa.

CONCLUSION

HSC express tropoelastin and its expression increases during transdifferentiation to myofibroblast-like cells.

Abnormal hepatic expression of fibrillin-1 in children with cholestasis

Fibrillin-1, one of the main constituents of microfibrils, is present in normal adult liver and overexpressed in fibrotic area around cirrhotic nodules and hepatocellular carcinoma. In this work fibrillin-1 expression was studied by immunohistochemistry in liver samples from children with various cholestatic diseases corresponding to paucity of intrahepatic bile ducts, biliary atresia, congenital hepatic fibrosis, Byler's disease, mitochondrial cytopathy, sclerosing cholangitis, or choledochal cyst. As controls, histologically normal liver samples were used. In control liver, as in adult, fibrillin-1 was expressed in vessel walls, sinusoids, and portal connective tissue, particularly at the interface with the limiting hepatocytic plate and close to the basement membrane of bile ducts. In paucity of intrahepatic bile ducts without fibrosis, the fibrillin-1 distribution was similar to controls. In cholestatic diseases associated with severe fibrosis, such as biliary atresia, congenital hepatic fibrosis, Byler's disease, mitochondrial cytopathy, or sclerosing cholangitis, an enhanced deposition of fibrillin-1 was observed in portal connective tissue and fibrous septa. The strong fibrillin-1 expression close to the basement membrane of biliary structures was lost in cholestatic diseases, except biliary atresia. Finally, in normal and pathologic tissues, fibrillin-1 was co-localized with its putative receptor alphaVbeta3 in sinusoids but not around biliary structures.