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

Serum proteomic profiling of patients with compensated advanced chronic liver disease with and without clinically significant portal hypertension

INTRODUCTION

Portal hypertension (PH) drives the progression of liver cirrhosis to decompensation and death. Hepatic venous pressure gradient (HVPG) measurement is the standard of PH quantification, and HVPG≥10 mmHg defines clinically significant PH (CSPH). We performed proteomics-based serum profiling to search for a proteomic signature of CSPH in patients with compensated advanced chronic liver disease (cACLD).

MATERIALS AND METHODS

Consecutive patients with histologically confirmed cACLD and results of HVPG measurements were prospectively included. Serum samples were pooled according to the presence/absence of CSPH and analysed by liquid chromatography-mass spectrometry. Gene set enrichment analysis was performed, followed by comprehensive literature review for proteins identified with the most striking difference between the groups.

RESULTS

We included 48 patients (30 with, and 18 without CSPH). Protein CD44, involved in the inflammatory response, vascular endothelial growth factor C (VEGF-C) and lymphatic vessel endothelial hyaluronan receptor-1 (LYVE-1), both involved in lymphangiogenesis were found solely in the CSPH group. Although identified in both groups, proteins involved in neutrophil extracellular traps (NET) formation, as well as tenascin C, autotaxin and nephronectin which mediate vascular contractility and lymphangiogenesis were more abundant in CSPH.

DISCUSSION AND CONCLUSION

We propose that altered inflammatory response, including NET formation, vascular contractility and formation of new lymph vessels are key steps in PH development. Proteins such as CD44, VEGF-C, LYVE-1, tenascin C, Plasminogen activator inhibitor 1, Nephronectin, Bactericidal permeability-increasing protein, Autotaxin, Myeloperoxidase and a disintegrin and metalloproteinase with thrombospondin motifs-like protein 4 might be considered for further validation as potential therapeutic targets and candidate biomarkers of CSPH in cACLD.

Transcriptomic signatures of progressive and regressive liver fibrosis and portal hypertension

Persistent liver injury triggers a fibrogenic program that causes pathologic remodeling of the hepatic microenvironment (i.e., liver fibrosis) and portal hypertension. The dynamics of gene regulation during liver disease progression and early regression remain understudied. Here, we generated hepatic transcriptome profiles in two well-established liver disease models at peak fibrosis and during spontaneous regression after the removal of the inducing agents. We linked the dynamics of key disease readouts, such as portal pressure, collagen area, and transaminase levels, to differentially expressed genes, enabling the identification of transcriptomic signatures of progressive vs. regressive liver fibrosis and portal hypertension. These candidate biomarkers (e.g., Tcf4, Mmp7, Trem2, Spp1, Scube1, Islr) were validated in RNA sequencing datasets of patients with cirrhosis and portal hypertension, and those cured from hepatitis C infection. Finally, deconvolution identified major cell types and suggested an association of macrophage and portal hepatocyte signatures with portal hypertension and fibrosis area.

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.

Cellular Interactions and Crosstalk Facilitating Biliary Fibrosis in Cholestasis

Biliary fibrosis is seen in cholangiopathies, including primary biliary cholangitis (PBC) and primary sclerosing cholangitis (PSC). In PBC and PSC, biliary fibrosis is associated with worse outcomes and histologic scores. Within the liver, both hepatic stellate cells (HSCs) and portal fibroblasts (PFs) contribute to biliary fibrosis, but their roles can differ. PFs reside near the bile ducts and may be the first responders to biliary damage, whereas HSCs may be recruited later and initiate bridging fibrosis. Indeed, different models of biliary fibrosis can activate PFs and HSCs to varying degrees. The portal niche can be composed of cholangiocytes, HSCs, PFs, endothelial cells, and various immune cells, and interactions between these cell types drive biliary fibrosis. In this review, we discuss the mechanisms of biliary fibrosis and the roles of PFs and HSCs in this process. We will also evaluate cellular interactions and mechanisms that contribute to biliary fibrosis in different models and highlight future perspectives and potential therapeutics.

Identification of Hub Genes in Idiopathic Pulmonary Fibrosis and Their Association with Lung Cancer by Bioinformatics Analysis

BACKGROUND

Idiopathic pulmonary fibrosis (IPF) is a chronic, progressive, and irreversible disease with a high mortality rate worldwide. However, the etiology and pathogenesis of IPF have not yet been fully described. Moreover, lung cancer is a significant complication of IPF and is associated with increased mortality. Nevertheless, identifying common genes involved in developing IPF and its progression to lung cancer remains an unmet need. The present study aimed to identify hub genes related to the development of IPF by meta-analysis. In addition, we analyzed their expression and their relationship with patients' progression in lung cancer.

METHOD

Microarray datasets GSE24206, GSE21369, GSE110147, GSE72073, and GSE32539 were downloaded from Gene Expression Omnibus (GEO). Next, we conducted a series of bioinformatics analysis to explore possible hub genes in IPF and evaluated the expression of hub genes in lung cancer and their relationship with the progression of different stages of cancer.

RESULTS

A total of 1888 differentially expressed genes (DEGs) were identified, including 1105 upregulated and 783 downregulated genes. The 10 hub genes that exhibited a high degree of connectivity from the PPI network were identified. Analysis of the KEGG pathways showed that hub genes correlate with pathways such as the ECM-receptor interaction. Finally, we found that these hub genes are expressed in lung cancer and are associated with the progression of different stages of lung cancer.

CONCLUSIONS

Based on the integration of GEO microarray datasets, the present study identified DEGs and hub genes that could play an essential role in the pathogenesis of IPF and its association with the development of lung cancer in these patients, which could be considered potential diagnostic biomarkers or therapeutic targets for the disease.

Extracellular matrix and vascular dynamics in the kidney of a murine model for Marfan syndrome

Fibrillin-1 is a pivotal structural component of the kidney's glomerulus and peritubular tissue. Mutations in the fibrillin-1 gene result in Marfan syndrome (MFS), an autosomal dominant disease of the connective tissue. Although the kidney is not considered a classically affected organ in MFS, several case reports describe glomerular disease in patients. Therefore, this study aimed to characterize the kidney in the mgΔlpn-mouse model of MFS. Affected animals presented a significant reduction of glomerulus, glomerulus-capillary, and urinary space, and a significant reduction of fibrillin-1 and fibronectin in the glomerulus. Transmission electron microscopy and 3D-ultrastructure analysis revealed decreased amounts of microfibrils which also appeared fragmented in the MFS mice. Increased collagen fibers types I and III, MMP-9, and α-actin were also observed in affected animals, suggesting a tissue-remodeling process in the kidney. Video microscopy analysis showed an increase of microvessel distribution coupled with reduction of blood-flow velocity, while ultrasound flow analysis revealed significantly lower blood flow in the kidney artery and vein of the MFS mice. The structural and hemodynamic changes of the kidney indicate the presence of kidney remodeling and vascular resistance in this MFS model. Both processes are associated with hypertension which is expected to worsen the cardiovascular phenotype in MFS.

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.

A review of hepatic fibrosis-associated histopathology in aged cadavers

This article reviews hepatic fibrosis-associated histopathology of aged cadavers (mean age 82 years). A study of 68 livers identified steatosis in 35.5%, central vein fibrosis in 49.2%, perisinusoidal fibrosis in 63.2%, portal tract fibrosis in 47.7%, septa formation in 44.1%, bridging fibrosis in 30.8%, and cirrhosis in 4.4% of the samples as well as one hepatocellular carcinoma and six metastatic tumors. Other studies have revealed that collagens I, III, IV, V, and VI and fibronectin constitute the matrices of fibrous central veins, perisinusoidal space, portal tracts, and septa. Elastin is rich in portal tracts and fibrous septa but absent from the perisinusoidal space. Hepatic stellate cells are ubiquitous in the liver parenchyma while myofibroblasts localize in fibrotic foci. Factor VIII-related antigen expression signals sinusoidal to systemic vascular endothelium transformation while collagen IV and laminin codistribution indicates formation of perisinusoidal membranes. Their coincidence reflects focalized capillarization of sinusoids in the aged liver. In response to fibrogenesis, hepatic progenitor cells residing in the canal of Hering in the periportal parenchyma undergo expansion and migration deep into the lobule. Concomitantly, intermediate hepatocyte-like cells increase in advanced fibrosis stages, which is possibly related to hepatic regeneration. Metabolic zonation of glutamine synthetase expands from the perivenous to non-perivenous parenchyma in fibrosis progression but its expression is lost in cirrhosis, while cytochrome P-4502E1 expression is maintained in centrilobular and midlobular zones in fibrosis progression and expressed in cirrhosis. Hence, cadaveric livers provide a platform for further investigation of hepatic histopathologies associated with the aging liver.

Construction and Evaluation of Recombinant Chimeric Fibrillin and Elastin Fragment in Human Mesenchymal Stem Cells

BACKGROUND

Diverse extracellular matrix (ECM) proteins physically interact with stem cells and regulate stem cell function. However, the large molecular weight of the natural ECM renders large-scale fabrication of a similar functional structure challenging.

OBJECTIVE

The objective of this study was to construct a low molecular weight and multifunctional chimeric form of recombinant ECM to stimulate mesenchymal stem cell (MSC) for tissue repair. We engineered Fibrillin-1PF14 fused to an elastin-like polypeptide to develop a new biomimetic ECM for stem cell differentiation and investigated whether this recombinant chimeric Fibrillin-Elastin fragment (rcFE) was effective on human nasal inferior turbinate-derived mesenchymal stem cells (hTMSCs).

METHODS

hTMSCs were grown in the medium supplemented with rcFE, then the effect of the protein was confirmed through cell adhesion assay, proliferation assay, and real-time PCR.

RESULTS

rcFE enhanced the adhesion activity of hTMSCs by 2.7-fold at the optimal concentration, and the proliferation activity was 2.6-fold higher than that of the control group (non-treatment rcFE). In addition, when smooth muscle cell differentiation markers were identified by real-time PCR, Calponin increased about 6-fold, α-actin about 9-fold, and MYH11 about 10-fold compared to the control group.

CONCLUSION

Chimeric rcFE enhanced cellular functions such as cell adhesion, proliferation, and smooth muscle differentiation of hTMSCs, suggesting that the rcFE can facilitate the induction of tissue regeneration.

Effects of Copper Nanoparticles on mRNA and Small RNA Expression in Human Hepatocellular Carcinoma (HepG2) Cells

With the advancement of nanotechnology, nanoparticles are widely used in many different industrial processes and consumer products. Copper nanoparticles (Cu NPs) are among the most toxic nanomaterials. We investigated Cu NPs toxicity in Human Hepatocellular carcinoma (HepG2) cells by examining signaling pathways, and microRNA/mRNA interactions. We compared the effects of exposures to Cu NPs at various concentrations and CuCl₂ was used as a control. The number of differentially expressed mRNA did not follow a linear dose-response relationship for either Cu NPs or CuCl₂ treatments. The most significantly altered genes and pathways by Cu NPs exposure were NRF2 (nuclear factor erythroid 2 related factor 2)-mediated oxidative stress response, protein ubiquitination, Tumor protein p53 (p53), phase I and II metabolizing enzymes, antioxidant proteins and phase III detoxifying gene pathways.Messenger RNA-microRNA interaction from MicroRNA Target Filter Analyses revealed more signaling pathways altered in Cu NPs treated samples than transcriptomics alone, including cell proliferation, DNA methylation, endoplasmic reticulum (ER) stress, apoptosis, autophagy, reactive oxygen species, inflammation, tumorigenesis, extracellular matrix/angiogenesis and protein synthesis. In contrast, in the control (CuCl₂) treated samples showed mostly changes in inflammation mainly through regulation of the Nuclear Factor Kappa-light-chain-enhancer of Activated B-cells (NFκB). Further, some RNA based parameters that showed promise as biomarkers of Cu NPs exposure including both well and lesser known genes: heme oxygenase 1 (HMOX1), heat shock protein, c-Fos proto-oncogene, DNA methyltransferases, and glutamate-cysteine ligase modifier subunit (GCLM, part of the glutathione synthesis pathway). The differences in signaling pathways altered by the Cu NPs and CuCl₂ treatments suggest that the effects of the Cu NPs were not the results of nanomaterial dissolution to soluble copper ions.

Proteomic Analysis Reveals Key Proteins in Extracellular Vesicles Cargo Associated with Idiopathic Pulmonary Fibrosis In Vitro

Idiopathic pulmonary fibrosis (IPF) is a chronic, progressive, irreversible, and highly fatal disease. It is characterized by the increased activation of both fibroblast and myofibroblast that results in excessive extracellular matrix (ECM) deposition. Extracellular vesicles (EVs) have been described as key mediators of intercellular communication in various pathologies. However, the role of EVs in the development of IPF remains poorly understood. This study aimed to characterize the differentially expressed proteins contained within EVs cargo derived from the fibroblast cell lines LL97A (IPF-1) and LL29 (IPF-2) isolated from lungs bearing IPF as compared to those derived from the fibroblast cell lines CCD8Lu (NL-1) and CCD19Lu (NL-2) isolated from healthy donors. Isolated EVs were subjected to label-free quantitative proteomic analysis by LC-MS/MS, and as a result, 331 proteins were identified. Differentially expressed proteins were obtained after the pairwise comparison, including all experimental groups. A total of 86 differentially expressed proteins were identified in either one or more comparison groups. Of note, proteins involved in fibrogenic processes, such as tenascin-c (TNC), insulin-like-growth-factor-binding protein 7 (IGFBP7), fibrillin-1 (FBN1), alpha-2 collagen chain (I) (COL1A2), alpha-1 collagen chain (I) (COL1A1), and lysyl oxidase homolog 1 (LOXL1), were identified in EVs cargo isolated from IPF cell lines. Additionally, KEGG pathway enrichment analysis revealed that differentially expressed proteins participate in focal adhesion, PI3K-Akt, and ECM–receptor interaction signaling pathways. In conclusion, our findings reveal that proteins contained within EVs cargo might play key roles during IPF pathogenesis.

ADAMTSL5 is an epigenetically activated gene underlying tumorigenesis and drug resistance in hepatocellular carcinoma

BACKGROUND & AIMS

The tumour microenvironment shapes tumour growth through cellular communications that include both direct interactions and secreted factors. The aim of this study was to characterize the impact of the secreted glycoprotein ADAMTSL5, whose role in cancer has not been previously investigated, on hepatocellular carcinoma (HCC).

METHODS

ADAMTSL5 methylation status was evaluated through bisulfite sequencing, and publicly available data analysis. ADAMTSL5 RNA and protein expression were assessed in mouse models and HCC patient samples and compared to data from published datasets. Functional studies, including association of ADAMTSL5 depletion with responsiveness to clinically relevant drugs, were performed in cellular and in vivo models. Molecular alterations associated with ADAMTSL5 targeting were determined using proteomics, biochemistry, and reverse-transcription quantitative PCR.

RESULTS

Methylome analysis revealed hypermethylated gene body CpG islands at the ADAMTSL5 locus in both mouse and human HCC, correlating with higher ADAMTSL5 expression. ADAMTSL5 targeting interfered with tumorigenic properties of HCC cells in vitro and in vivo, whereas ADAMTSL5 overexpression conferred tumorigenicity to pre-tumoural hepatocytes sensitized to transformation by a modest level of MET receptor expression. Mechanistically, ADAMTSL5 abrogation led to a reduction of several oncogenic inputs relevant to HCC, including reduced expression and/or phosphorylation levels of receptor tyrosine kinases MET, EGFR, PDGFRβ, IGF1Rβ, or FGFR4. This phenotype was associated with significantly increased sensitivity of HCC cells to clinically relevant drugs, namely sorafenib, lenvatinib, and regorafenib. Moreover, ADAMTSL5 depletion drastically increased expression of AXL, accompanied by a sensitization to bemcentinib.

CONCLUSIONS

Our results point to a role for ADAMTSL5 in maintaining the function of key oncogenic signalling pathways, suggesting that it may act as a master regulator of tumorigenicity and drug resistance in HCC.

LAY SUMMARY

The environment of cancer cells has profound effects on establishment, progression, and response of a tumour to treatment. Herein, we show that ADAMTSL5, a protein secreted by liver cancer cells and overlooked in cancer so far, is increased in this tumour type, is necessary for tumour formation and supports drug resistance. Adamtsl5 removal conferred sensitivity of liver cancer cells to drugs used in current treatment. This suggests ADAMTSL5 as a potential marker in liver cancer as well as a possible drug target.

Human cathelicidin antimicrobial peptide LL-37 promotes lymphangiogenesis in lymphatic endothelial cells through the ERK and Akt signaling pathways

LL-37, the only member of the cathelicidin family of cationic antimicrobial peptides in humans has been shown to exhibit a wide variety of biological actions in addition to its antimicrobial activity. However, the lymphangiogenic effect of LL-37 has not been elucidated yet. In this study, we examined the effects of LL-37 on lymphangiogenesis and evaluated the underlying molecular mechanisms. LL-37 treatment significantly increased the migration and tube-like formation of human dermal lymphatic microvascular endothelial cells (HDLECs) and promoted the expression of lymphangiogenic factor in HDLECs. Treatment with LL-37 increased phosphorylation of ERK and Akt proteins in HDLECs, and pretreatment with ERK and Akt inhibitors significantly blocked the LL-37-induced HDLEC migration and tube-like formation. Furthermore, to investigate the involvement of formyl peptide receptor-like 1 (FPRL1) signaling in LL-37-induced lymphangiogenesis, HDLECs were treated with an FPRL1 antagonist. Pretreatment with the FPRL1 antagonist inhibited LL-37-induced phosphorylation of ERK and Akt proteins and attenuated LL-37-induced HDLEC migration and tube-like formation. These data indicated that LL-37 induces lymphangiogenesis in lymphatic endothelial cells via FPRL1, and the activation of the ERK and Akt-dependent signaling pathways.

Applying Non-Invasive Fibrosis Measurements in NAFLD/NASH: Progress to Date

Nonalcoholic fatty liver disease (NAFLD) has now become a worldwide health issue due to the obesity epidemic, affecting approximately 90% of the obese population and 15-40% of the general population. It is the most common form of chronic liver disease in the United States. NAFLD constitutes a spectrum of diseases ranging in severity from mild, such as fatty liver, progressing into nonalcoholic steatohepatitis (NASH), then fibrosis, and ending with cirrhosis. NASH and increasing fibrosis stage are associated with increased morbidity and mortality; the fibrosis stage is therefore a critical element of risk stratification needed to determine therapeutic approach and also the response to treatment. Liver biopsy is considered the 'gold standard' in the diagnosis of NAFLD. However, it is not practical for widespread clinical use because it is invasive, costly, and associated with complications including occasional death. These limitations have driven the development of noninvasive tests that can accurately predict the fibrosis stage in those with NAFLD. In this review, we provide a concise overview of different non-invasive measurements used for NAFLD/NASH.

Albumin self-modified liposomes for hepatic fibrosis therapy via SPARC-dependent pathways

Activated hepatic stellate cells (HSCs) have a central role in the progression of liver fibrosis and express a large amount of secreted protein, acidic and rich in cysteine (SPARC), a specific protein-binding protein. In this study, we reported the preparation and evaluation of naringenin (Nar) -loaded albumin self-modified liposomes (NaAlLs), which delivered Nar, a specific Smad3 inhibitor that blocked the TGF-β/Smad3 signaling pathway and played an anti-fibrosis role. After a series of characterization, it was found that NaAlLs had favorable dispersion (PDI < 0.15) with an average particle size of about 120 nm and high entrapment efficiency (>85%), albumin coated the surface of liposomes or embedded in phospholipid bilayer by interaction with the encapsulated naringenin and phospholipid molecules during the preparation of liposomes. The amount of albumin modified to the surface of NaAlLs by this method is not only more than that of the physical adsorption method, but also the binding force between albumin and liposomes is stronger. The albumin modified to the surface of NaAlLs greatly reduced the aggregation of liposomes and drug leakage and increased the stability of liposomes. More importantly, the uptake of NaAlLs by activated HSCs was 1.5 times higher than that of Nar-loaded liposomes (NaLs), suggesting that NaAlLs specifically increased targeting of activated HSCs via albumin and SPARC-dependent pathways. As expected, NaAlLs was more effective in improving liver fibrosis than the NaLs or the inclusion complex solution of Nar and Hydroxypropyl-β-cyclodextrin (NaICS). The results suggested that NaAlLs was a promising drug delivery system, which could target drug delivery to activated HSC for the treatment of liver fibrosis.

Activated hepatic stellate cells and portal fibroblasts contribute to cholestatic liver fibrosis in MDR2 knockout mice

BACKGROUND & AIMS

Chronic liver injury often results in the activation of hepatic myofibroblasts and the development of liver fibrosis. Hepatic myofibroblasts may originate from 3 major sources: hepatic stellate cells (HSCs), portal fibroblasts (PFs), and fibrocytes, with varying contributions depending on the etiology of liver injury. Here, we assessed the composition of hepatic myofibroblasts in multidrug resistance gene 2 knockout (Mdr2-/-) mice, a genetic model that resembles primary sclerosing cholangitis in patients.

METHODS

Mdr2-/- mice expressing a collagen-GFP reporter were analyzed at different ages. Hepatic non-parenchymal cells isolated from collagen-GFP Mdr2-/- mice were sorted based on collagen-GFP and vitamin A. An NADPH oxidase (NOX) 1/4 inhibitor was administrated to Mdr2-/- mice aged 12-16 weeks old to assess the therapeutic approach of targeting oxidative stress in cholestatic injury.

RESULTS

Thy1+ activated PFs accounted for 26%, 51%, and 54% of collagen-GFP+ myofibroblasts in Mdr2-/- mice at 4, 8, and 16 weeks of age, respectively. The remaining collagen-GFP+ myofibroblasts were composed of activated HSCs, suggesting that PFs and HSCs are both activated in Mdr2-/- mice. Bone-marrow-derived fibrocytes minimally contributed to liver fibrosis in Mdr2-/- mice. The development of cholestatic liver fibrosis in Mdr2-/- mice was associated with early recruitment of Gr1+ myeloid cells and upregulation of pro-inflammatory cytokines (4 weeks). Administration of a NOX inhibitor to 12-week-old Mdr2-/- mice suppressed the activation of myofibroblasts and attenuated the development of cholestatic fibrosis.

CONCLUSIONS

Activated PFs and activated HSCs contribute to cholestatic fibrosis in Mdr2-/- mice, and serve as targets for antifibrotic therapy.

LAY SUMMARY

Activated portal fibroblasts and hepatic stellate cells, but not fibrocytes, contributed to the production of the fibrous scar in livers of Mdr2-/- mice, and these cells can serve as targets for antifibrotic therapy in cholestatic injury. Therapeutic inhibition of the enzyme NADPH oxidase (NOX) in Mdr2-/- mice reversed cholestatic fibrosis, suggesting that targeting NOXs may be an effective strategy for the treatment of cholestatic fibrosis.

Hepatic elastin content is predictive of adverse outcome in advanced fibrotic liver disease

AIMS

The aim of this study was to determine if elastin content in needle core native liver biopsies was predictive of clinical outcome in patients with chronic hepatitis C virus-related chronic liver disease.

METHODS AND RESULTS

Elastin contents in liver biopsies were determined by image analysis, technically validated in an independent centre, and correlated with outcome in patients with advanced (Ishak stage ≥5) chronic hepatitis C virus-related chronic liver disease. Elastin was robustly quantified in an operator-independent and laboratory-independent manner, with very strong correlation of elastin staining measured with two methods of image classification (rs = 0.873, P < 0.00001). Elastin content (but not absolute scar content or Ishak stage) was predictive for future clinical outcomes. In a cohort of patients without sustained virological response, the median hepatic elastin content was 3.4%, and 17 patients (57%) progressed to a liver-related clinical outcome; 11 of the 15 patients (73%) with a hepatic elastin content of >3.4% progressed to a clinical outcome, as compared with only six of 15 (40%) with an elastin content of <3.4%. The difference in time to outcome was significant.

CONCLUSIONS

We describe a simple and reproducible method for elastin quantification in liver biopsies that provides potentially valuable prognostic information to inform clinical management.

Maintaining Elastogenicity of Mesenchymal Stem Cell-Derived Smooth Muscle Cells in Two-Dimensional Culture

Abdominal aortic aneurysms (AAAs) are localized expansions of the abdominal aorta that grow slowly to rupture. AAA growth is driven by irreversible elastic matrix breakdown in the aorta wall by chronically upregulated matrix metalloproteases (MMPs). Since adult vascular smooth muscle cells (SMCs) poorly regenerate elastic matrix, we previously explored utility of bone marrow mesenchymal stem cells and SMCs derived therefrom (BM-SMCs) for this purpose. One specific differentiated phenotype (cBM-SMCs) generated on a fibronectin substrate in presence of exogenous transforming growth factor-β and platelet-derived growth factor exhibited superior elastogenicity versus other phenotypes, and usefully provided proelastogenic and antiproteolytic stimuli to aneurysmal SMCs. Since in vivo cell therapy demands large cell inoculates, these derived SMCs must be propagated in vitro while maintaining their superior elastogenic, proelastogenic, and antiproteolytic characteristics. In this work, we thus investigated the culture conditions that must be provided to this propagation phase, which ensure that the differentiated SMCs maintain their phenotype and matrix regenerative benefits. Our results indicate that our BM-SMCs retain their phenotype in long-term culture even in the absence of differentiation growth factors and fibronectin substrate, but these conditions must be continued to be provided during postdifferentiation propagation if they are to maintain their superior elastic matrix deposition, crosslinking, and fiber formation properties. Our study, however, showed that cells propagated under these conditions exhibit higher expression of MMP-2, but favorably, no expression of elastolytic MMP-9. Hence, the study outcomes provide crucial guidelines to maintain phenotypic stability of cBM-SMCs during their propagation in two-dimensional culture before their delivery to the AAA wall for therapy.

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.

Extracellular Matrix Molecular Remodeling in Human Liver Fibrosis Evolution

Chronic liver damage leads to pathological accumulation of ECM proteins (liver fibrosis). Comprehensive characterization of the human ECM molecular composition is essential for gaining insights into the mechanisms of liver disease. To date, studies of ECM remodeling in human liver diseases have been hampered by the unavailability of purified ECM. Here, we developed a decellularization method to purify ECM scaffolds from human liver tissues. Histological and electron microscopy analyses demonstrated that the ECM scaffolds, devoid of plasma and cellular components, preserved the three-dimensional ECM structure and zonal distribution of ECM components. This method has been then applied on 57 liver biopsies of HCV-infected patients at different stages of liver fibrosis according to METAVIR classification. Label-free nLC-MS/MS proteomics and computation biology were performed to analyze the ECM molecular composition in liver fibrosis progression, thus unveiling protein expression signatures specific for the HCV-related liver fibrotic stages. In particular, the ECM molecular composition of liver fibrosis was found to involve dynamic changes in matrix stiffness, flexibility and density related to the dysregulation of predominant collagen, elastic fibers and minor components with both structural and signaling properties. This study contributes to the understanding of the molecular bases underlying ECM remodeling in liver fibrosis and suggests new molecular targets for fibrolytic strategies.

Mitochondrial Molecular Pathophysiology of Nonalcoholic Fatty Liver Disease: A Proteomics Approach

Nonalcoholic fatty liver disease (NAFLD) is a chronic liver condition that can progress to nonalcoholic steatohepatitis, cirrhosis and cancer. It is considered an emerging health problem due to malnourishment or a high-fat diet (HFD) intake, which is observed worldwide. It is well known that the hepatocytes’ apoptosis phenomenon is one of the most important features of NAFLD. Thus, this review focuses on revealing, through a proteomics approach, the complex network of protein interactions that promote fibrosis, liver cell stress, and apoptosis. According to different types of in vitro and murine models, it has been found that oxidative/nitrative protein stress leads to mitochondrial dysfunction, which plays a major role in stimulating NAFLD damage. Human studies have revealed the importance of novel biomarkers, such as retinol-binding protein 4, lumican, transgelin 2 and hemoglobin, which have a significant role in the disease. The post-genome era has brought proteomics technology, which allows the determination of molecular pathogenesis in NAFLD. This has led to the search for biomarkers which improve early diagnosis and optimal treatment and which may effectively prevent fatal consequences such as cirrhosis or cancer.

Human liver myofibroblasts during development and diseases with a focus on portal (myo)fibroblasts

Myofibroblasts are stromal cells mainly involved in tissue repair. These cells present contractile properties and play a major role in extracellular matrix deposition and remodeling. In liver, myofibroblasts are found in two critical situations. First, during fetal liver development, especially in portal tracts, myofibroblasts surround vessels and bile ducts during their maturation. After complete development of the liver, myofibroblasts disappear and are replaced in portal tracts by portal fibroblasts. Second, during liver injury, myofibroblasts re-appear principally deriving from the activation of local stromal cells such as portal fibroblasts and hepatic stellate cells or can sometimes emerge by an epithelial-mesenchymal transition process. After acute injury, myofibroblasts play also a major role during liver regeneration. While myofibroblastic precursor cells are well known, the spectrum of activation and the fate of myofibroblasts during disease evolution are not fully understood. Some data are in accordance with a possible deactivation, at least partial, or a disappearance by apoptosis. Despite these shadows, liver is definitively a pertinent model showing that myofibroblasts are pivotal cells for extracellular matrix control during morphogenesis, repair and fibrous scarring.

Correlation between Fibrillin-1 Degradation and mRNA Downregulation and Myofibroblast Differentiation in Cultured Human Dental Pulp Tissue

Myofibroblasts and extracellular matrix are important components in wound healing. Alpha-smooth muscle actin (α-SMA) is a marker of myofibroblasts. Fibrillin-1 is a major constituent of microfibrils and an extracellular-regulator of TGF-β1, an important cytokine in the transdifferentiation of resident fibroblasts into myofibroblasts. To study the correlation between changes in fibrillin-1 expression and myofibroblast differentiation, we examined alterations in fibrillin-1 and α-SMA expression in organotypic cultures of dental pulp in vitro. Extracted healthy human teeth were cut to 1-mm-thick slices and cultured for 7 days. In intact dental pulp, fibrillin-1 was broadly distributed, and α-SMA was observed in pericytes and vascular smooth muscle cells. After 7 days of culture, immunostaining for fibrillin-1 became faint concomitant with a downregulation in its mRNA levels. Furthermore, fibroblasts, odontoblasts and Schwann cells were immunoreactive for α-SMA with a significant increase in α-SMA mRNA expression. Double immunofluorescence staining was positive for pSmad2/3, central mediators of TGF-β signaling, and α-SMA. The administration of inhibitors for extracellular matrix proteases recovered fibrillin-1 immunostaining; moreover, fibroblasts lost their immunoreactivity for α-SMA along with a downregulation in α-SMA mRNA. These findings suggest that the expression of α-SMA is TGF-β1 dependent, and fibrillin-1 degradation and downregulation might be implicated in the differentiation of myofibroblasts in dental pulp wound healing.

Extracellular matrix and liver disease

SIGNIFICANCE

The extracellular matrix (ECM) is a dynamic microenvironment that undergoes continuous remodeling, particularly during injury and wound healing. Chronic liver injury of many different etiologies such as viral hepatitis, alcohol abuse, drug-induced liver injury, obesity and insulin resistance, metabolic disorders, and autoimmune disease is characterized by excessive deposition of ECM proteins in response to persistent liver damage.

CRITICAL ISSUES

This review describes the main collagenous and noncollagenous components from the ECM that play a significant role in pathological matrix deposition during liver disease. We define how increased myofibroblasts (MF) from different origins are at the forefront of liver fibrosis and how liver cell-specific regulation of the complex scarring process occurs.

RECENT ADVANCES

Particular attention is paid to the role of cytokines, growth factors, reactive oxygen species, and newly identified matricellular proteins in the regulation of fibrillar type I collagen, a field to which our laboratory has significantly contributed over the years. We compile data from recent literature on the potential mechanisms driving fibrosis resolution such as MF' apoptosis, senescence, and reversal to quiescence.

FUTURE DIRECTIONS

We conclude with a brief description of how epigenetics, an evolving field, can regulate the behavior of MF and of how new "omics" tools may advance our understanding of the mechanisms by which the fibrogenic response to liver injury occurs.

The portal fibroblast: not just a poor man's stellate cell

Portal fibroblasts, the resident fibroblasts of the portal tract, are found in the mesenchyme surrounding the bile ducts. Their roles in liver homeostasis and response to injury are undefined and controversial. Although portal fibroblasts almost certainly give rise to myofibroblasts during the development of biliary fibrosis, recent lineage tracing studies suggest that their contribution to fibrogenesis is limited compared with that of hepatic stellate cells. Other functions of portal fibroblasts include participation in the peribiliary stem cell niche, regulation of cholangiocyte proliferation, and deposition of specific matrix proteins. Portal fibroblasts synthesize elastin and other components of microfibrils; these may serve structural roles, providing stability to ducts and the vasculature under conditions of increased ductal pressure, or could regulate the bioavailability of the fibrogenic transforming growth factor β in response to injury. Viewing portal fibroblasts in the context of fibroblast populations throughout the body and studying their niche-specific roles in matrix deposition and epithelial regulation could yield new insights into their contributions in the normal and injured liver. Understanding the functions of portal fibroblasts will require us to view them as more than just an alternative to hepatic stellate cells in fibrosis.

Proteomic analysis of altered extracellular matrix turnover in bleomycin-induced pulmonary fibrosis

Fibrotic disease is characterized by the pathological accumulation of extracellular matrix (ECM) proteins. Surprisingly, very little is known about the synthesis and degradation rates of the many proteins and proteoglycans that constitute healthy or pathological extracellular matrix. A comprehensive understanding of altered ECM protein synthesis and degradation during the onset and progression of fibrotic disease would be immensely valuable. We have developed a dynamic proteomics platform that quantifies the fractional synthesis rates of large numbers of proteins via stable isotope labeling and LC/MS-based mass isotopomer analysis. Here, we present the first broad analysis of ECM protein kinetics during the onset of experimental pulmonary fibrosis. Mice were labeled with heavy water for up to 21 days following the induction of lung fibrosis with bleomycin. Lung tissue was subjected to sequential protein extraction to fractionate cellular, guanidine-soluble ECM proteins and residual insoluble ECM proteins. Fractional synthesis rates were calculated for 34 ECM proteins or protein subunits, including collagens, proteoglycans, and microfibrillar proteins. Overall, fractional synthesis rates of guanidine-soluble ECM proteins were faster than those of insoluble ECM proteins, suggesting that the insoluble fraction reflected older, more mature matrix components. This was confirmed through the quantitation of pyridinoline cross-links in each protein fraction. In fibrotic lung tissue, there was a significant increase in the fractional synthesis of unique sets of matrix proteins during early (pre-1 week) and late (post-1 week) fibrotic response. Furthermore, we isolated fast turnover subpopulations of several ECM proteins (e.g. type I collagen) based on guanidine solubility, allowing for accelerated detection of increased synthesis of typically slow-turnover protein populations. This establishes the presence of multiple kinetic pools of pulmonary collagen in vivo with altered turnover rates during evolving fibrosis. These data demonstrate the utility of dynamic proteomics in analyzing changes in ECM protein turnover associated with the onset and progression of fibrotic disease.

Elastin fibers display a versatile microfibril network in articular cartilage depending on the mechanical microenvironments

Elastin fibers are major extracellular matrix macromolecules that are critical in maintaining the elasticity and resilience of tissues such as blood vessels, lungs and skins. However, the role of elastin in articular cartilage is poorly defined. The present study investigated the organization of elastin fiber in articular cartilage, its relationship to collagen fibers and the architecture of elastin fibers from different mechanical environments by using a kangaroo model. Five morphologies of elastin fibers were identified: Straight fiber, straight fiber with branches, branching fibers directly associated with chondrocyte, wave fiber and fine elastin. The architecture of the elastin network varied significantly with cartilage depth. In the most superficial layer of tibial plateau articular cartilage, dense elastin fibers formed a distinctive cobweb-like meshwork which was parallel to the cartilage surface. In the superficial zone, elastin fibers were well organized in a preferred orientation which was parallel to collagen fibers. In the deep zone, no detectable elastin fiber was found. Moreover, differences in the organization of elastin fibers were also observed between articular cartilage from the tibial plateau, femoral condyle, and distal humerus. This study unravels the detailed microarchitecture of elastin fibers which display a well-organized three-dimensional versatile network in articular cartilage. Our findings imply that elastin fibers may play a crucial role in maintaining the integrity, elasticity, and the mechanical properties of articular cartilage, and that the local mechanical environment affects the architectural development of elastin fibers.

Tissue mechanics and fibrosis

Mechanical forces are essential to the development and progression of fibrosis, and are likely to be as important as soluble factors. These forces regulate the phenotype and proliferation of myofibroblasts and other cells in damaged tissues, the activation of growth factors, the structure and mechanics of the matrix, and, potentially, tissue patterning. Better understanding of the variety and magnitude of forces, the characteristics of those forces in biological tissues, and their impact on fibrosis in multiple tissues is needed and may lead to identification of important new therapeutic targets. This article is part of a Special Issue entitled: Fibrosis: Translation of basic research to human disease.

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.

Elastin accumulation is regulated at the level of degradation by macrophage metalloelastase (MMP-12) during experimental liver fibrosis

Elastin has been linked to maturity of liver fibrosis. To date, the regulation of elastin secretion and its degradation in liver fibrosis has not been characterized. The aim of this work was to define elastin accumulation and the role of the paradigm elastase macrophage metalloelastase (MMP-12) in its turnover during fibrosis. Liver fibrosis was induced by either intraperitoneal injections of carbon tetrachloride (CCl(4) ) for up to 12 weeks (rat and mouse) or oral administration of thioacetamide (TAA) for 1 year (mouse). Elastin synthesis, deposition, and degradation were investigated by immunohistochemistry, quantitative polymerase chain reaction (qPCR), western blotting, and casein zymography. The regulation of MMP-12 elastin degradation was defined mechanistically using CD11b-DTR and MMP-12 knockout mice. In a CCl(4) model of fibrosis in rat, elastin deposition was significantly increased only in advanced fibrosis. Tropoelastin expression increased with duration of injury. MMP-12 protein levels were only modestly changed and in coimmunoprecipitation experiments MMP-12 was bound in greater quantities to its inhibitor TIMP-1 in advanced versus early fibrosis. Immunohistochemistry and macrophage depletion experiments indicated that macrophages were the sole source of MMP-12. Exposure of CCl(4) in MMP-12(-/-) mice led to a similar degree of overall fibrosis compared to wildtype (WT) but increased perisinusoidal elastin. Conversely, oral administration of TAA caused both higher elastin accumulation and higher fibrosis in MMP-12(-/-) mice compared with WT.

CONCLUSION

Elastin is regulated at the level of degradation during liver fibrosis. Macrophage-derived MMP-12 regulates elastin degradation even in progressive experimental liver fibrosis. These observations have important implications for the design of antifibrotic therapies.

Liver fibrosis in elderly cadavers: localization of collagen types I, III, and IV, α-smooth muscle actin, and elastic fibers

We have shown a high prevalence of liver fibrosis in elderly cadavers with diverse causes of death by Sirius red stain; however, the various collagen types in these samples have yet to be evaluated. To further characterize the histopathology of the fibrotic lesions in the livers of these elderly cadavers, this study used immunohistochemistry and histochemistry to identify the principal collagens produced in liver fibrosis, fibrogenic cells and elastic fibers. Collagen I and III immunoreactions were found to colocalize in collagen fibers of fibrotic central veins, perisinusoidal fibrotic foci, portal tract stroma, and fibrous septa. α-Smooth muscle actin-expressing perisinusoidal hepatic stellate cells (HSCs), as well as perivenular, portal, and septal myofibroblasts, were closely associated with collagen fibers, reflecting their fibrogenic functions. HSCs and myofibroblasts were also noted to express collagen IV, which may contribute to production of basal lamina-like structures. In fibrotic livers, the sinusoidal lining showed variable immunostaining for collagen IV. Collagen IV immunostaining revealed vascular proliferation and atypical ductular reaction at the portal-septal parenchymal borders, as well as capillary-like vessels in the lobular parenchyma. While elastic fibers were absent in the space of Disse, they were found to codistribute with collagens in portal tracts, fibrous septa and central veins. Our combined assessment of collagen types, HSCs, myofibroblasts, and elastic fibers is significant in understanding the histopathology of fibrosis in the aging liver.

Hepatic stellate cells require a stiff environment for myofibroblastic differentiation

The myofibroblastic differentiation of hepatic stellate cells (HSC) is a critical event in liver fibrosis and is part of the final common pathway to cirrhosis in chronic liver disease from all causes. The molecular mechanisms driving HSC differentiation are not fully understood. Because macroscopic tissue stiffening is a feature of fibrotic disease, we hypothesized that mechanical properties of the underlying matrix are a principal determinant of HSC activation. Primary rat HSC were cultured on inert polyacrylamide supports of variable but precisely defined shear modulus (stiffness) coated with different extracellular matrix proteins or poly-L-lysine. HSC differentiation was determined by cell morphology, immunofluorescence staining, and gene expression. HSC became progressively myofibroblastic as substrate stiffness increased on all coating matrices, including Matrigel. The degree rather than speed of HSC activation correlated with substrate stiffness, with cells cultured on supports of intermediate stiffness adopting stable intermediate phenotypes. Quiescent cells on soft supports were able to undergo myofibroblastic differentiation with exposure to stiff supports. Stiffness-dependent differentiation required adhesion to matrix proteins and the generation of mechanical tension. Transforming growth factor-β treatment enhanced differentiation on stiff supports, but was not required. HSC differentiate to myofibroblasts in vitro primarily as a function of the physical rather than the chemical properties of the substrate. HSC require a mechanically stiff substrate, with adhesion to matrix proteins and the generation of mechanical tension, to differentiate. These findings suggest that alterations in liver stiffness are a key factor driving the progression of fibrosis.

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.

The elastic network of articular cartilage: an immunohistochemical study of elastin fibres and microfibrils

The elastic network of articular cartilage was investigated by immunohistochemistry using specific antibodies to elastin and fibrillin-1. Articular cartilage was dissected from defined regions of bovine metacarpophalangeal joints. Elastin fibres and microfibrils were dual-immunostained by labelling with distinct fluorescent dyes. A conventional fluorescence microscope combined with a polarized light filter was used to study the organization and degree of colocalization of elastin fibres, microfibrils and of the collagen network. We observed an elaborately organized elastic network. In the uppermost superficial zone, where few cells were present, elastin fibres and microfibrils formed a dense three dimensional network showing some degree of colocalization. The thickness and organization of this elastic network varied dramatically from region to region and was most extensive in the metacarpal palmar region. In the middle and deep zones, very few elastin fibres were observed but microfibrils formed a network in the inter-territorial matrix and dense network around the cells. Our finding of a three dimensional network of dense, well organized elastin fibres and microfibrils in the surface zone of the articular cartilage matrix, and a dense network of microfibrils around the cells deeper into the tissue suggests the elastic network could play both a mechanical and a biological role in articular cartilage.

Transforming growth factor-(beta)s and mammary gland involution; functional roles and implications for cancer progression

During rodent mammary gland involution there is a dramatic increase in the expression of the transforming growth factor-beta isoform, TGF-beta3. The TGF-betas are multifunctional cytokines which play important roles in wound healing and in carcinogenesis. The responses that are activated in the remodeling of the gland during involution have many similarities with the wound healing process and have been postulated to generate a mammary stroma that provides a microenvironment favoring tumor progression. In this review we will discuss the putative role of TGF-beta during involution, as well as its effects on the mammary microenvironment and possible implications for pregnancy-associated tumorigenesis.

Foxl1 is a marker of bipotential hepatic progenitor cells in mice

The liver contains a population of small bipotential facultative progenitor cells that reconstitute liver function when mature hepatocytes or cholangiocytes are unable to proliferate. Mesenchymal markers, including members of the forkhead transcription factor gene family, have been detected in hepatic progenitor cells. The winged helix transcription factor Foxl1 localizes to mesenchymal cells in the intestine; however, its expression in the liver has not been reported. We found that Foxl1 is expressed in rare cells in the normal liver but is dramatically induced in the livers of mice that have undergone bile duct ligation or were fed a 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC)-containing or choline-deficient, ethionine-supplemented diet. In addition, we employed genetic lineage tracing using a Foxl1-Cre transgenic mouse crossed with the Rosa26R lacZ reporter line to demonstrate that Foxl1-Cre-expressing cells are present within the periportal region shortly after injury. These cells give rise to both hepatocytes [marked by hepatocyte nuclear factor 4 alpha (HNF-4alpha) expression] and cholangiocytes (marked by CK19 expression), indicating that these cells are derived from Foxl1-Cre-expressing cells. Foxl1-Cre-expressing cells are distinct from hepatic stellate cells, portal fibroblasts, and myofibroblasts, although they are located in close proximity to portal fibroblasts. These results demonstrate that the early Foxl1-Cre lineage cell gives rise to both cholangiocytes and hepatocytes after liver injury and suggest the potential for progenitor-portal fibroblast cell interactions.

CONCLUSION

We propose that Foxl1 is a bona fide marker of the facultative progenitor cell in the mouse liver.

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.

Increased stiffness of the rat liver precedes matrix deposition: implications for fibrosis

Liver fibrosis, the response to chronic liver injury, results from the activation of mesenchymal cells to fibrogenic myofibroblasts. We have recently shown that two key myofibroblast precursor populations, hepatic stellate cells and portal fibroblasts, undergo activation in culture in response to increasing substrate stiffness. We therefore hypothesized that alterations in liver stiffness precede myofibroblast activation and fibrosis in vivo as well. To test this hypothesis, we induced fibrosis in rats by twice weekly injections of carbon tetrachloride (CCl(4)) and then killed the animals at various time points ranging from 3 to 70 days after the initiation of injury. The shear storage modulus of the whole liver was measured on fresh tissue; fixed and frozen tissue from the same livers was used to quantify fibrosis. We observed that liver stiffness increased immediately and continued to increase, leveling out by day 28. Fibrosis, measured histologically by trichrome staining as well as by quantitative sirius red staining, increased with time, although these increases were delayed relative to changes in stiffness. There was no direct correlation between stiffness and fibrosis at early or late time points. Treatment of a second cohort of rats with the lysyl oxidase inhibitor, beta-aminopropionitrile (BAPN), partially prevented early increases in liver stiffness. We concluded that increases in liver stiffness precede fibrosis and potentially myofibroblast activation. Liver stiffness appears to result from matrix cross-linking and possibly other unknown variables in addition to matrix quantity. We suggest that increased liver stiffness may play an important role in initiating the early stages of fibrosis.

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.

Increased expression of latent TGF-ß binding protein-1 and fibrillin-1 in human uterine leiomyomata

We compared latent TGF-ss binding protein-1 (LTBP-1) and fibrillin-1 (FBN-1) expression in leiomyomata and myometrium, correlated with leiomyomata size. We studied in vivo and in vitro effects of ovarian steroids using matched leiomyomata and myometrium samples from both phases of the menstrual cycle. Leiomyomata were divided into small (<or=2 cm), medium (3-5 cm) and large (>or=6 cm) groups. We validated LTBP-1 and FBN-1 expression using QPCR, western blot and immunohistochemistry. LTBP-1 and FBN-1 mRNA and protein expressions were higher in the medium-sized group compared with myometrium in the proliferative phase (P = 0.01; P = 0.01). FBN-1 mRNA expression was higher in the secretory phase (P = 0.01). LTBP-1 mRNA and protein expression was higher in the medium group compared with the small and large groups in the proliferative phase (P = 0.04; P = 0.04). No differences between groups were seen in FBN-1 expression in either phase. 17Beta-estradiol (E2) increased mRNA and protein expression of LTBP-1 and FBN-1 in cultured leiomyoma smooth muscle cells (LSMC) (P < 0.05). No change in FBN-1 and LTBP-1 expression was observed when cells were treated with E2 plus progesterone. Estrogen may be involved in LTBP-1 and FBN-1 expression in leiomyomata. Extracellular matrix metabolism may be different in medium-sized leiomyoma.

Gene expression during chemically induced liver fibrosis: effect of halofuginone on TGF-beta signaling

Hepatic fibrosis is associated with the activation of stellate cells (HSCs), the major source of extracellular matrix (ECM) proteins. Transforming growth factor-beta (TGF-beta), signaling via Smad3, is the most profibrogenic cytokine and the major promoter of ECM synthesis. Halofuginone, an inhibitor of liver fibrosis, inhibits TGF-beta-dependent Smad3 phosphorylation in human HSCs in culture. We have used transcriptional profiling to evaluate the effect of halofuginone on gene expression during the progression of thioacetamide (TAA)-induced liver fibrosis in the rat and have focused on genes that are associated with TGF-beta. TAA treatment causes alterations in the expression of 7% of liver genes. Halofuginone treatment prevents the changes in the expression of 41% of these genes and results in the inhibition of HSC activation and collagen synthesis. During the early stages of the disease, halofuginone affects genes involved in alcohol, lipid, protein, and phosphate metabolism and cell adhesion and, at later stages, in the cell cycle (cell development, differentiation, cell proliferation, and apoptosis). The activation of TGF-beta-dependent genes, such as tartrate-resistant acid phosphatase, its putative substrate osteopontin, stellate cell activation-association protein, and fibrillin-1, during chemically induced fibrosis is prevented by halofuginone. This study thus highlights the role of TGF-beta signaling in liver fibrosis and especially its potential for pharmacological intervention. Halofuginone, which has demonstrated efficacy and tolerance in animals and humans, could become an effective and novel therapy for liver fibrosis.

Identification of vitamin A-free cells in a stellate cell-enriched fraction of normal rat liver as myofibroblasts

Myofibroblasts (MFs) as well as hepatic stellate cells (HSCs) are known to be involved in liver fibrogenesis. Quiescent HSCs (qHSCs) in culture have been thought to differentiate to replicative activated HSCs (aHSCs). In this study a qHSC-enriched fraction isolated by Nycodenz-isodensity centrifugation was separated with a fluorescence-activated cell sorter, which revealed the presence of a small fraction (occupancy rate=0.4%) of cells that did not show vitamin A-autofluorescence under ultraviolet (UV)-irradiation (UV- cells). The remaining vitamin A-containing cells were autofluorescent (UV+) and originally expressed markers of qHSCs, and, in culture, did not grow, lost vitamin A, and expressed markers of aHSCs. UV- cells showed morphology of MFs, and, in culture, grew to form colonies and expressed markers of MFs. These results indicated that UV+ and UV- cells represent qHSCs and MFs, respectively, and that aHSCs have no growth potential and are a cell-type distinct from proliferative MFs. Gene expression profiles of UV- cells (MFs) newly identified gremlin as one of MF-preferential genes and its proteins were localized around fibrotic septa in rat and human livers. In addition, we suggested that the qHSC-enriched fraction included approximately 6% of liver MFs.

Metastatic potential of melanomas defined by specific gene expression profiles with no BRAF signature

The molecular biology of metastatic potential in melanoma has been studied many times previously and changes in the expression of many genes have been linked to metastatic behaviour. What is lacking is a systematic characterization of the regulatory relationships between genes whose expression is related to metastatic potential. Such a characterization would produce a molecular taxonomy for melanoma which could feasibly be used to identify epigenetic mechanisms behind changes in metastatic behaviour. To achieve this we carried out three separate DNA microarray analyses on a total of 86 cultures of melanoma. Significantly, multiple testing correction revealed that previous reports describing correlations of gene expression with activating mutations in BRAF or NRAS were incorrect and that no gene expression patterns correlate with the mutation status of these MAPK pathway components. Instead, we identified three different sample cohorts (A, B and C) and found that these cohorts represent melanoma groups of differing metastatic potential. Cohorts A and B were susceptible to transforming growth factor-beta (TGFbeta)-mediated inhibition of proliferation and had low motility. Cohort C was resistant to TGFbeta and demonstrated high motility. Meta-analysis of the data against previous studies linking gene expression and phenotype confirmed that cohorts A and C represent transcription signatures of weakly and strongly metastatic melanomas, respectively. Gene expression co-regulation suggested that signalling via TGFbeta-type and Wnt/beta-catenin pathways underwent considerable change between cohorts. These results suggest a model for the transition from weakly to strongly metastatic melanomas in which TGFbeta-type signalling upregulates genes expressing vasculogenic/extracellular matrix remodelling factors and Wnt signal inhibitors, coinciding with a downregulation of genes downstream of Wnt signalling.

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.

Fibrillin-1 regulates mesangial cell attachment, spreading, migration and proliferation

The microfibrillar protein fibrillin-1 is present in many organs, including the vasculature, eye, and dermis, and is thought to convey structural anchorage and elastic strength. Fibrillin-1 is also a component of the mesangial matrix. To assess the functional relevance of fibrillin-1 for cell-matrix interactions in the glomerulus, we studied the attachment, spreading, migration and proliferation of mesangial cells on fibrillin-1 and the regulation of fibrillin-1 in experimental anti-Thy1.1 nephritis displaying mesangial cell migration and proliferation in vivo. During the acute phase of experimental Thy1.1 nephritis, glomerular fibrillin-1 messenger ribonucleic acid expression and protein immunoreactivity were significantly induced as compared to controls. In a hexosaminidase-based adhesion assay, mesangial cells showed concentration-dependent attachment to fibrillin-1, similar to what was observed for fibronectin. The cell attachment was Arg-Gly-Asp dependent. Further, fibrillin-1 significantly promoted spreading and focal contact formation detected by immunostaining for vinculin. Mesangial cell migration, assessed by a transmigration assay, and proliferation, measured by a 5-bromo-2'-deoxy-uridine incorporation assay, were augmented by fibrillin-1. In diabetic mice underexpressing fibrillin-1, glomerular cell proliferation, determined by counting proliferating cell nuclear antigen-positive cells in renal sections, was significantly lower than in diabetic control mice. We conclude that fibrillin-1 promotes mesangial cell attachment, spreading, migration, and proliferation. We speculate that fibrillin-1 may thus contribute to mesangial hypercellularity during glomerular disease.

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.

Global analysis of host tissue gene expression in the invasive front of colorectal liver metastases

Host cell reactions are a crucial determinant for tumor invasion. We analyzed on a genomewide scale gene expression differences between microdissected tissues taken from unaffected liver tissue of a human colorectal tumor (LS174) growing in the livers of nude mice and tissue from the host part of the invasive front. Due to the low degree of interspecies cross-hybridization of 15% as determined on Affymetrix microarrays, our xenograft model allowed for the distinction of genes of murine versus human origin even if the respective tissues could not be isolated separately. Using the gene ontology (GO) classification, we were able to determine patterns of up- and downregulated genes in the liver part of the invasive front. We observed a pronounced overrepresentation, e.g., of the GO terms "extracellular matrix," "cell communication," "response to biotic stimulus," "structural molecule activity" and "cell growth," indicating a very pronounced host cell response to tumor invasion. On the single gene level, hepatic stellate cell (HSC) activation markers were overrepresented in the liver part of the invasion front. Immunohistochemistry and qPCR confirmed an activation of HSC as well as an increased number of HSC in the invasive front as compared to the noninvaded liver tissue. In summary, our data demonstrate the feasibility of an interspecies differential gene expression approach on a genomewide scale.