Fibroblasts Derive from Hepatocytes in Liver Fibrosis via Epithelial to Mesenchymal Transition

Hepatic wound repair

Background

Human chronic liver diseases (CLDs) with different aetiologies rely on chronic activation of wound healing that represents the driving force for fibrogenesis progression (throughout defined patterns of fibrosis) to the end stage of cirrhosis and liver failure.

Issues

Fibrogenesis progression has a major worldwide clinical impact due to the high number of patients affected by CLDs, increasing mortality rate, incidence of hepatocellular carcinoma and shortage of organ donors for liver transplantation.

Basic science advances

Liver fibrogenesis is sustained by a heterogeneous population of profibrogenic hepatic myofibroblasts (MFs), the majority being positive for α smooth muscle actin (αSMA), that may originate from hepatic stellate cells and portal fibroblasts following a process of activation or from bone marrow-derived cells recruited to damaged liver and, in a method still disputed, by a process of epithelial to mesenchymal transition (EMT) involving cholangiocytes and hepatocytes. Recent experimental and clinical data have identified, at tissue, cellular and molecular level major profibrogenic mechanisms: (a) chronic activation of the wound-healing reaction, (b) oxidative stress and related reactive intermediates, and (c) derangement of epithelial-mesenchymal interactions.

Clinical care relevance

Liver fibrosis may regress following specific therapeutic interventions able to downstage or, at least, stabilise fibrosis. In cirrhotic patients, this would lead to a reduction of portal hypertension and of the consequent clinical complications and to an overall improvement of liver function, thus extending the complication-free patient survival time and reducing the need for liver transplantation.

Conclusion

Emerging mechanisms and concepts related to liver fibrogenesis may significantly contribute to clinical management of patients affected by CLDs.

Human gastrointestinal neoplasia-associated myofibroblasts can develop from bone marrow-derived cells following allogeneic stem cell transplantation

This study characterized the contribution of bone marrow-derived cells to human neoplasia and the perineoplastic stroma. The Australasian Bone Marrow Transplant Recipient Registry was used to identify solid organ neoplasia that developed in female recipients of male allogeneic stem cell transplants. Eighteen suitable cases were identified including several skin cancers, two gastric cancers, and one rectal adenoma. Light microscopy, fluorescence and chromogenic in situ hybridization, and immunohistochemistry were performed to determine the nature and origin of the neoplastic and stromal cells. In contrast to recent reports, donor-derived neoplastic cells were not detected. Bone marrow-derived neoplasia-associated myofibroblasts, however, were identified in the rectal adenoma and in a gastric cancer. Bone marrow-derived cells can generate myofibroblasts in the setting of human gastrointestinal neoplasia.

Less Smad2 is good for you! A scientific update on coffee's liver benefits

Scientists at the National Institutes of Health have reported that increased coffee consumption is associated with a slower progression of fibrogenesis in patients with chronic and particularly alcoholic liver disease and a reduced incidence of heptocellular carcinoma. However, a causal mechanistic explanation was pending. New results indicate that the methylxanthine caffeine--a major component of coffee and the most widely consumed pharmacologically active substance in the world--might be responsible for this phenomenon, because it inhibits the synthesis of connective tissue growth factor (CTGF/CCN2) in liver parenchymal and nonparenchymal cells, primarily by inducing degradation of Smad2 (and to a much lesser extent Smad3) and thus impairment of transforming growth factor beta (TGF-beta) signaling. CTGF and TGF-beta play crucial roles in the fibrotic remodeling of various organs, and, ultimately, carcinogenesis. This article summarizes the clinical-epidemiological observations as well as the pathophysiological background and provides suggestions for the therapeutic use of (methyl)xanthine derivatives in the management of fibro-/carcinogenic (liver) diseases.

Inflammation and EMT: an alliance towards organ fibrosis and cancer progression

Recent advances in our understanding of the molecular pathways that govern the association of inflammation with organ fibrosis and cancer point to the epithelial to mesenchymal transition (EMT) as the common link in the progression of these devastating diseases. The EMT is a crucial process in the development of different tissues in the embryo and its reactivation in the adult may be regarded as a physiological attempt to control inflammatory responses and to 'heal' damaged tissue. However, in pathological contexts such as in tumours or during the development of organ fibrosis, this healing response adopts a sinister nature, steering these diseases towards metastasis and organ failure. Importantly, the chronic inflammatory microenvironment common to fibrotic and cancer cells emerges as a decisive factor in the induction of the pathological EMT.

Rationale and targets for antifibrotic therapies

We have made striking progress in our understanding of the biochemistry and cell biology that underlies liver fibrosis and cirrhosis, including the development of strategies and agents to prevent and reverse fibrosis and incipient cirrhosis. However, translation of this knowledge into clinical practice has been hampered by the limitation of many in vitro and in vivo models to confirm mechanisms and to test antifibrotic agents, as well as the lack of sensitive methodologies to quantify the degree of liver fibrosis and the dynamics of fibrosis progression or reversal. Furthermore, while cirrhosis and subsequent decompensation are accepted hard clinical end-points, fibrosis and fibrosis progression alone are merely plausible surrogates for future clinical deterioration. This review focuses on basic mechanisms that underlay liver fibrosis progression and reversal and optimized strategies for preclinical antifibrotic drug development and validation. Therapies include several drugs that are of proven safety for other indications, agents that interfere with major fibrogenic or fibrolytic mechanisms, targeted drug delivery to the fibrogenic liver cells, and their potential combinations with hepatocyte or stem cell replenishment.

Hepatic tumor-stroma crosstalk guides epithelial to mesenchymal transition at the tumor edge

The tumor-stroma crosstalk is a dynamic process fundamental in tumor development. In hepatocellular carcinoma (HCC), the progression of malignant hepatocytes frequently depends on transforming growth factor (TGF)-beta provided by stromal cells. TGF-beta induces an epithelial to mesenchymal transition (EMT) of oncogenic Ras-transformed hepatocytes and an upregulation of platelet-derived growth factor (PDGF) signaling. To analyse the influence of the hepatic tumor-stroma crosstalk onto tumor growth and progression, we co-injected malignant hepatocytes and myofibroblasts (MFBs). For this, we either used in vitro-activated p19(ARF) MFBs or in vivo-activated MFBs derived from physiologically inflamed livers of Mdr2/p19(ARF) double-null mice. We show that co-transplantation of MFBs with Ras-transformed hepatocytes strongly enhances tumor growth. Genetic interference with the PDGF signaling decreases tumor cell growth and maintains plasma membrane-located E-cadherin and beta-catenin at the tumor-host border, indicating a blockade of hepatocellular EMT. We further generated a collagen gel-based three dimensional HCC model in vitro to monitor the MFB-induced invasion of micro-organoid HCC spheroids. This invasion was diminished after inhibition of TGF-beta or PDGF signaling. These data suggest that the TGF-beta/PDGF axis is crucial during hepatic tumor-stroma crosstalk, regulating both tumor growth and cancer progression.

Direct contribution of epithelium to organ fibrosis: epithelial-mesenchymal transition

Fibrosis of epithelial parenchymal organs and end-stage organ failure represent the final common pathway of many chronic diseases and are a major determinant of morbidity and mortality worldwide. Fibrosis is a complex response initiated to protect the host from an injurious event; nevertheless, it leads to serious organ damage when it becomes independent from the initiating stimulus. It involves massive deposition of matrix by an expanded pool of fibrogenic cells, disruption of the normal tissue architecture, and parenchymal destruction. Fibroblasts, the effector cells of matrix production, when engaged in fibrogenesis, display the highly activated phenotype characteristic of myofibroblasts. These cells are present in a large number in sites with ongoing inflammation, reparative reaction, and fibrosis, but their origin has not yet been definitely elucidated. Although proliferation of preexisting stromal fibroblasts and, probably, recruitment of bone marrow-derived fibrogenic cells may account for a portion of them, emerging evidence seems to indicate that an important number of matrix-producing fibroblasts/myofibroblasts arises through a mechanism of epithelial-mesenchymal transition. Through this process, epithelial cells would lose intercellular cohesion and would translocate from the epithelial compartment into the interstitium where, gaining a full mesenchymal phenotype, they could participate in the synthesis of the fibrotic matrix. Epithelial-mesenchymal transition is induced by the integrated actions of many stimuli including transforming growth factor-beta and matrix-generated signals that are also known to be implicated in inflammation, repair responses, and fibrosis. The consequences of epithelial-mesenchymal transition in chronic fibrosing diseases could be two-fold as follows: on one hand, by supplementing new mesenchymal cells, it might feed the expanding pool of interstitial fibroblasts/myofibroblasts responsible for the matrix accumulation; on the other hand, it could cause loss of epithelial cells, thus, contributing to the parenchyma destruction seen in advanced fibrosis. Markers of epithelium undergoing epithelial-mesenchymal transition include loss of E-cadherin and cytokeratin; de novo expression of fibroblast-specific protein 1/S100A4, vimentin, and alpha-smooth muscle actin; basement membrane component loss; and production of interstitial-type matrix molecules such as fibronectin and type I/III collagen. Evidence of epithelial-mesenchymal transition has been reported in the kidney, lung, liver, eye, and serosal membranes suggesting that epithelial-mesenchymal transition could be involved in the pathogenesis of fibrotic disorders in these organs. Thus, because of its fibrogenic potential, the detection of epithelial-mesenchymal transition in biopsy specimens could be useful diagnostically and represent a new biomarker of progression in chronic fibrosing diseases.

Renal studies provide an insight into cardiac extracellular matrix remodeling during health and disease

The remodeling of a heart ventricle after myocardial infarction involves numerous inflammatory mediators that may trigger a long-lasting and a highly fibrogenic process. Likewise, in the kidney, acute and chronic injuries may lead to abnormal extracellular matrix deposition and eventually lead to the loss of renal function. Major breakthroughs have emerged during the last ten years with respect to the pathophysiology of matrix remodeling. Epithelial and endothelial cells are plastic, and able to engage in epithelial (or endothelial)-to-mesenchymal transition (EMT or EndMT), thus actively contributing to the fibrogenesis. Members of the fibrinolytic system were demonstrated to possess unsuspected properties and interact with receptors and integrins on endothelial and epithelial cells. Finally, a notion that stem cells could integrate into damaged tissue has recently emerged, which likely contributes to the tissue repair. In many aspects, the kidney and the heart share many common injury mechanisms. We envision that some of them will be accessible as common therapeutic targets in the future.

The basics of epithelial-mesenchymal transition

The origins of the mesenchymal cells participating in tissue repair and pathological processes, notably tissue fibrosis, tumor invasiveness, and metastasis, are poorly understood. However, emerging evidence suggests that epithelial-mesenchymal transitions (EMTs) represent one important source of these cells. As we discuss here, processes similar to the EMTs associated with embryo implantation, embryogenesis, and organ development are appropriated and subverted by chronically inflamed tissues and neoplasias. The identification of the signaling pathways that lead to activation of EMT programs during these disease processes is providing new insights into the plasticity of cellular phenotypes and possible therapeutic interventions.

The basics of epithelial-mesenchymal transition

The origins of the mesenchymal cells participating in tissue repair and pathological processes, notably tissue fibrosis, tumor invasiveness, and metastasis, are poorly understood. However, emerging evidence suggests that epithelial-mesenchymal transitions (EMTs) represent one important source of these cells. As we discuss here, processes similar to the EMTs associated with embryo implantation, embryogenesis, and organ development are appropriated and subverted by chronically inflamed tissues and neoplasias. The identification of the signaling pathways that lead to activation of EMT programs during these disease processes is providing new insights into the plasticity of cellular phenotypes and possible therapeutic interventions.

The etiology of liver damage imparts cytokines transforming growth factor beta1 or interleukin-13 as driving forces in fibrogenesis

It is unknown whether transforming growth factor beta1 (TGF-beta1) signaling uniformly participates in fibrogenic chronic liver diseases, irrespective of the underlying origin, or if other cytokines such as interleukin (IL)-13 share in fibrogenesis (e.g., due to regulatory effects on type I pro-collagen expression). TGF-beta1 signaling events were scored in 396 liver tissue samples from patients with diverse chronic liver diseases, including hepatitis B virus (HBV), hepatitis C virus (HCV), Schistosoma japonicum infection, and steatosis/steatohepatitis. Phospho-Smad2 staining correlated significantly with fibrotic stage in patients with HBV infection (n = 112, P < 0.001) and steatosis/steatohepatitis (n = 120, P < 0.01), but not in patients with HCV infection (n = 77, P > 0.05). In tissue with HBx protein expression, phospho-Smad2 was detectable, suggesting a functional link between viral protein expression and TGF-beta1 signaling. For IL-13, immunostaining correlated with fibrotic stage in patients with HCV infection and steatosis/steatohepatitis. IL-13 protein was more abundant in liver tissue lysates from three HCV patients compared with controls, as were IL-13 serum levels in 68 patients with chronic HCV infection compared with 20 healthy volunteers (72.87 +/- 26.38 versus 45.41 +/- 3.73, P < 0.001). Immunohistochemistry results suggest that IL-13-mediated liver fibrogenesis may take place in the absence of phospho-signal transducer and activator of transcription protein 6 signaling. In a subgroup of patients with advanced liver fibrosis (stage > or =3), neither TGF-beta nor IL-13 signaling was detectable.

CONCLUSION

Depending on the cause of liver damage, a predominance of TGF-beta or IL-13 signaling is found. TGF-beta1 predominance is detected in HBV-related liver fibrogenesis and IL-13 predominance in chronic HCV infection. In some instances, the underlying fibrogenic mediator remains enigmatic.

About coffee, cappuccino and connective tissue growth factor-Or how to protect your liver!?

Several epidemiological studies suggest that coffee drinking is inversely correlated with the risk of development of liver fibrosis. However, a causal, mechanistic explanation has long been pending. New results indicate that the methylxanthine caffeine, major component of coffee and the most widely consumed pharmacologically active substance in the world, might be responsible for this phenomenon as it, and even more potently its derived primary metabolite paraxanthine, inhibits transforming growth factor (TGF)-β-dependent and -independent synthesis of connective tissue growth factor (CTGF/CCN2) in liver parenchymal cells in vitro and in vivo. CTGF plays a crucial role in the fibrotic remodeling of various organs which has therefore frequently been proposed as therapeutic target in the management of fibrotic disorders. This article summarizes the clinical-epidemiological observations as well as the pathophysiological background of the antifibrotic effects of coffee consumption and provides suggestions for the therapeutic use of caffeine and its derived metabolic methylxanthines as potentially powerful drugs in patients with chronic fibrogenic liver disease by their inhibitory effect on (hepatocellular) CTGF synthesis.

[Liver fibrosis: from pathophysiology to therapeutic openings]

Understanding of liver fibrosis pathogenesis has undergone tremendous advances over the past twenty years. In this respect, demonstration of the reversibility of fibrosis was a major turnpoint. The panel of therapeutic targets is continuously expanding. Clinical development has however remained limited, heretofore, but should rapidly progress owing to the availability of accurate non-invasive methods for assessment of fibrosis, to improvement in the selection patients included in therapeutic trials, and to the development of cell specific targeting devices for agents at risk of adverse effects.

JunB mediates enhancer/promoter activity of COL1A2 following TGF-beta induction

Transcriptional control of the genes coding for collagen type I is regulated by a complex interaction between a distal enhancer and a proximal promoter. In this study, we have dissected the molecular mechanism of this interaction by defining a specific sequence within the enhancer that respond in fibroblasts to transforming growth factor-β (TGF-β). We show that TGF-β activates COL1A2 gene via a non-canonical (Smad-independent) signalling pathway, which requires enhancer/promoter co-operation. This interaction involves exchange of cJun/Jun B transcription factor occupancy of a critical enhancer site resulting in the stabilization of enhancer/promoter coalescence. Moreover, using transgenesis, we show that interference in this mechanism results in the abolition of COL1A2 fibroblast expression in vivo. These data are therefore relevant to the control of collagen type I in vivo both in embryonic development, in adult connective tissue homeostasis, and in tissue repair and scarring pathologies.

Contribution of epithelial-derived fibroblasts to bleomycin-induced lung fibrosis

RATIONALE

Lung fibroblasts are key mediators of fibrosis resulting in accumulation of excessive interstitial collagen and extracellular matrix, but their origins are not well defined.

OBJECTIVES

We aimed to elucidate the contribution of lung epithelium-derived fibroblasts via epithelial-mesenchymal transition (EMT) in the intratracheal bleomycin model.

METHODS

Primary type II alveolar epithelial cells were cultured from Immortomice and exposed to transforming growth factor-beta(1) and epidermal growth factor. Cell fate reporter mice that permanently mark cells of lung epithelial lineage with beta-galactosidase were developed to study EMT, and bone marrow chimeras expressing green fluorescent protein under the control of the fibroblast-associated S100A4 promoter were generated to examine bone marrow-derived fibroblasts. Mice were given intratracheal bleomycin (0.08 unit). Immunostaining was performed for S100A4, beta-galactosidase, green fluorescent protein, and alpha-smooth muscle actin.

MEASUREMENTS AND MAIN RESULTS

In vitro, primary type II alveolar epithelial cells undergo phenotypic changes of EMT when exposed to transforming growth factor-beta(1) and epidermal growth factor with loss of prosurfactant protein C and E-cadherin and gain of S100A4 and type I procollagen. In vivo, using cell fate reporter mice, approximately one-third of S100A4-positive fibroblasts were derived from lung epithelium 2 weeks after bleomycin administration. From bone marrow chimera studies, one-fifth of S100A4-positive fibroblasts were derived from bone marrow at this same time point. Myofibroblasts rarely derived from EMT or bone marrow progenitors.

CONCLUSIONS

Both EMT and bone marrow progenitors contribute to S100A4-positive fibroblasts in bleomycin-induced lung fibrosis. However, neither origin is a principal contributor to lung myofibroblasts.

The basics of epithelial-mesenchymal transition

The origins of the mesenchymal cells participating in tissue repair and pathological processes, notably tissue fibrosis, tumor invasiveness, and metastasis, are poorly understood. However, emerging evidence suggests that epithelial-mesenchymal transitions (EMTs) represent one important source of these cells. As we discuss here, processes similar to the EMTs associated with embryo implantation, embryogenesis, and organ development are appropriated and subverted by chronically inflamed tissues and neoplasias. The identification of the signaling pathways that lead to activation of EMT programs during these disease processes is providing new insights into the plasticity of cellular phenotypes and possible therapeutic interventions.

Connective tissue growth factor is a Smad2 regulated amplifier of transforming growth factor beta actions in hepatocytes--but without modulating bone morphogenetic protein 7 signaling

In vivo knockdown of connective tissue growth factor (CTGF/CCN2) was recently shown to attenuate the formation of experimental liver fibrosis. The secreted, cysteine-rich growth factor is proposed to adversely modulate the binding of profibrogenic transforming growth factor beta (TGF-beta) and its natural antagonist bone morphogenetic protein (BMP) to their cognate receptors in several cellular systems, but the functionality of CTGF in modulation of the TGF-beta/BMP signaling pathways is still unknown. This study aims at characterizing a potentially differential modulating role of CTGF on TGF-beta- and BMP7-dependent transactivation of reporter gene [Ad-(CAGA)(12)-MLP-luc, Ad-hCTGF-luc, and Ad-(BRE)(2)-luc reporter gene] expression in rat hepatocytes. In this context, emphasis is also placed on the differential roles of Smad2 and Smad3 in the TGF-beta-dependent transactivation of the endogenous CTGF gene and the CTGF gene reporter, as investigated following adenoviral infection of wild-type and dominant negative Smad2/3 or treatment with the specific inhibitor of Smad3 or ALK5-specific (SB-431542) inhibitor. In this analysis, we found (1) a selective transcriptional activation of the CTGF promoter by Smad2 (but not Smad3); (2) the failure of BMP7 to inhibit the transcriptional activation of the Smad3-selective (CAGA)(12)-luc reporter by TGF-beta, as well as the failure of TGF-beta to inhibit the transcriptional activation of the Smad5-selective (BRE)(2)-luc reporter by BMP7; and (3) the sensitization of hepatocytes toward TGF-beta type I receptor (ALK5)/Smad2 and Smad3-mediated TGF-beta signaling by CTGF, whereas BMP type I receptor (ALK1)/Smad5-mediated BMP7 signaling is not modulated.

CONCLUSION

CTGF acts as a Smad2-dependent sensitizer of TGF-beta actions that does not influence BMP7 signaling in hepatocytes.

Biomarkers for epithelial-mesenchymal transitions

Somatic cells that change from one mature phenotype to another exhibit the property of plasticity. It is increasingly clear that epithelial and endothelial cells enjoy some of this plasticity, which is easily demonstrated by studying the process of epithelial-mesenchymal transition (EMT). Published reports from the literature typically rely on ad hoc criteria for determining EMT events; consequently, there is some uncertainty as to whether the same process occurs under different experimental conditions. As we discuss in this Personal Perspective, we believe that context and various changes in plasticity biomarkers can help identify at least three types of EMT and that using a collection of criteria for EMT increases the likelihood that everyone is studying the same phenomenon - namely, the transition of epithelial and endothelial cells to a motile phenotype.

Non-invasive biomarkers for monitoring the fibrogenic process in liver: A short survey

The clinical course of chronic liver diseases is significantly dependent on the progression rate and the extent of fibrosis, i.e. the non-structured replacement of necrotic parenchyma by extracellular matrix. Fibrogenesis, i.e. the development of fibrosis can be regarded as an unlimited wound healing process, which is based on matrix (connective tissue) synthesis in activated hepatic stellate cells, fibroblasts (fibrocytes), hepatocytes and biliary epithelial cells, which are converted to matrix-producing (myo-)fibroblasts by a process defined as epithelial-mesenchymal transition. Blood (non-invasive) biomarkers of fibrogenesis and fibrosis can be divided into class I and class II analytes. Class I biomarkers are those single tests, which are based on the pathophysiology of fibrosis, whereas class II biomarkers are mostly multiparametric algorithms, which have been statistically evaluated with regard to the detection and activity of ongoing fibrosis. Currently available markers fulfil the criteria of ideal clinical-chemical tests only partially, but increased understanding of the complex pathogenesis of fibrosis offers additional ways for pathophysiologically well based serum (plasma) biomarkers. They include TGF-β-driven marker proteins, bone marrow-derived cells (fibrocytes), and cytokines, which govern pro- and anti-fibrotic activities. Proteomic and glycomic approaches of serum are under investigation to set up specific protein or carbohydrate profiles in patients with liver fibrosis. These and other novel parameters will supplement or eventually replace liver biopsy/histology, high resolution imaging analysis, and elastography for the detection and monitoring of patients at risk of developing liver fibrosis.

Elevated concentrations of 15-deoxy-Delta12,14-prostaglandin J2 in chronic liver disease propose therapeutic trials with peroxisome proliferator activated receptor gamma-inducing drugs

BACKGROUND/AIMS

Current knowledge confers a crucial role to connective tissue growth factor (CTGF/CCN2) in hepatic fibrogenesis. Hepatocytes are likely to be the major cellular source of CTGF in the liver in which CTGF is sensitively upregulated by TGF-beta. Recently, we demonstrated that the methylxanthine derivate caffeine leads to an upregulation of peroxisome proliferator activated receptor gamma (PPARgamma) expression in hepatocytes, thus sensitizing these cells to the well-known inhibitory effect of 15-deoxy-Delta(12,14)-prostaglandin J(2) (15-d-PGJ(2)) on CTGF expression. However, upregulation of the receptor alone is not sufficient per se; its physiological ligand 15-d-PGJ(2) is required to exert an inhibitory effect on transforming growth factor-beta (TGF-beta) target genes such as CTGF.

METHODS

This study compared serum concentrations of 15-d-PGJ(2) in Caucasian patients with fibrotic liver diseases (n=289), Caucasian controls (n=136) and Caucasian non-liver disease (NLD) sick (n=307), as well as of Chinese patients with hepatocellular carcinoma (HCC) (n=43) and Chinese healthy controls (n=63) in order to characterize their suitability for therapeutic approaches with PPARgamma-inducing (i.e. CTGF inhibitory) drugs such as caffeine.

RESULTS

The presented data showed that Caucasian patients with ongoing hepatic fibrogenesis (mean 6.2+/-5.9 microg/L) displayed strikingly higher serum concentrations of 15-d-PGJ(2) than healthy probands (mean 2.3+/-1.0) and Caucasian patients with NLD (mean 2.7+/-1.4 microg/L). Similar results were found in Chinese patients with fully developed HCC (mean 1.3+/-0.7 microg/L) compared with Chinese healthy controls (mean 0.4+/-0.2 microg/L).

CONCLUSIONS

In conclusion, our data thus proposed an increased suitability of these patient groups for therapeutic approaches with drugs inducing PPARgamma expression, such as methylxanthine derivates.

Research progress in mechanisms of intestinal fibrosis in Crohn's disease

The relationship between fibrosis and normal repair are not understood. Acute injury may cause normal mesenchymal cells to convert to fibrogenic phenotype that may lead to fibrosis when inappropriately sustained. Crohn's disease (CD)-associated fibrosis results from chronic transmural inflammation. Intestinal inflammation in CD is transmural, often associated with extracellular matrix changes, luminal narrowing and stricture formation. But the pathogenesis of stricture formation remains unclear. Current therapies do not alter its progression to intestinal fibrosis and obstruction. The aim of this review is to discuss the current understanding of fibrogenesis in CD.

Intestinal fibrosis in IBD--a dynamic, multifactorial process

Intestinal fibrosis is a common and potentially serious complication of IBD that results from the reaction of intestinal tissue to the damage inflicted by chronic inflammation. The traditional view that fibrosis is inevitable or irreversible in patients with IBD is progressively changing in light of improved understanding of the cellular and molecular mechanisms that underlie the pathogenesis of fibrosis in general, and, in particular, intestinal fibrosis. These mechanisms are complex and dynamic, and involve multiple cell types, interconnected cellular events and a large number of soluble factors. In addition, owing to a breakdown of the epithelial barrier during inflammation of the gut, luminal bacterial products induce an innate immune response, which is triggered by activation of immune and nonimmune cells alike. Comprehension of the mechanisms of intestinal fibrosis will create a conceptual and practical framework that could achieve the specific blockade of fibrogenic pathways, allow for the estimation of risk of fibrotic complications, permit the detection of early fibrotic changes and, eventually, enable the development of treatments customized to the type and stage of each patient's IBD.

Asbestos-induced lung diseases: an update

Asbestos causes asbestosis (pulmonary fibrosis caused by asbestos inhalation) and malignancies (bronchogenic carcinoma and mesothelioma) by mechanisms that are not fully elucidated. Despite a dramatic reduction in asbestos use worldwide, asbestos-induced lung diseases remain a substantial health concern primarily because of the vast amounts of fibers that have been mined, processed, and used during the 20th century combined with the long latency period of up to 40 years between exposure and disease presentation. This review summarizes the important new epidemiologic and pathogenic information that has emerged over the past several years. Whereas the development of asbestosis is directly associated with the magnitude and duration of asbestos exposure, the development of a malignant clone of cells can occur in the setting of low-level asbestos exposure. Emphasis is placed on the recent epidemiologic investigations that explore the malignancy risk that occurs from nonoccupational, environmental asbestos exposure. Accumulating studies are shedding light on novel mechanistic pathways by which asbestos damages the lung. Attention is focused on the importance of alveolar epithelial cell (AEC) injury and repair, the role of iron-derived reactive oxygen species (ROS), and apoptosis by the p53- and mitochondria-regulated death pathways. Furthermore, recent evidence underscores crucial roles for specific cellular signaling pathways that regulate the production of cytokines and growth factors. An evolving role for epithelial-mesenchymal transition (EMT) is also reviewed. The translational significance of these studies is evident in providing the molecular basis for developing novel therapeutic strategies for asbestos-related lung diseases and, importantly, other pulmonary diseases, such as interstitial pulmonary fibrosis and lung cancer.

Hepatic myofibroblasts: a heterogeneous population of multifunctional cells in liver fibrogenesis

Hepatic myofibroblasts constitute a heterogeneous population of highly proliferative, pro-fibrogenic, pro-inflammatory, pro-angiogenic and contractile cells that sustain liver fibrogenesis and then fibrotic progression of chronic liver diseases of different aetiology to the common advanced-stage of cirrhosis. These alpha-smooth muscle actin-positive myofibroblast-like cells, according to current literature, mainly originate by a process of activation and trans-differentiation that involves either hepatic stellate cells or fibroblasts of portal areas. Hepatic myofibroblasts can also originate from bone marrow-derived cells, including mesenchymal stem cells or circulating fibrocytes able to engraft chronically injured liver, as well as, in certain conditions, by a process of epithelial to mesenchymal transition involving hepatocytes and cholangiocytes. Hepatic myofibroblasts may have also additional crucial roles in modulating immune response and in the cross talk with hepatic progenitor (stem) cells as well as with malignant cells of either primary hepatocellular carcinomas or of metastatic cancers.

Connective tissue growth factor and cardiac fibrosis

Cardiac fibrosis is a major pathogenic factor in a variety of cardiovascular diseases and refers to an excessive deposition of extracellular matrix components in the heart, which leads to cardiac dysfunction and eventually overt heart failure. Evidence is accumulating for a crucial role of connective tissue growth factor (CTGF) in fibrotic processes in several tissues including the heart. CTGF orchestrates the actions of important local factors evoking cardiac fibrosis. The central role of CTGF as a matricellular protein modulating the fibrotic process in cardiac remodelling makes it a possible biomarker for cardiac fibrosis and a potential candidate for therapeutic intervention to mitigate fibrosis in the heart.

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.

Liver cancer-derived hepatitis C virus core proteins shift TGF-beta responses from tumor suppression to epithelial-mesenchymal transition

Background

Chronic hepatitis C virus (HCV) infection and associated liver cirrhosis represent a major risk factor for hepatocellular carcinoma (HCC) development. TGF-β is an important driver of liver fibrogenesis and cancer; however, its actual impact in human cancer progression is still poorly known. The aim of this study was to investigate the role of HCC-derived HCV core natural variants on cancer progression through their impact on TGF-β signaling.

Principal Findings

We provide evidence that HCC-derived core protein expression in primary human or mouse hepatocyte alleviates TGF-β responses in terms or growth inhibition or apoptosis. Instead, in these hepatocytes TGF-β was still able to induce an epithelial to mesenchymal transition (EMT), a process that contributes to the promotion of cell invasion and metastasis. Moreover, we demonstrate that different thresholds of Smad3 activation dictate the TGF-β responses in hepatic cells and that HCV core protein, by decreasing Smad3 activation, may switch TGF-β growth inhibitory effects to tumor promoting responses.

Conclusion/Significance

Our data illustrate the capacity of hepatocytes to develop EMT and plasticity under TGF-β, emphasize the role of HCV core protein in the dynamic of these effects and provide evidence for a paradigm whereby a viral protein implicated in oncogenesis is capable to shift TGF-β responses from cytostatic effects to EMT development.

The cardiotonic steroid hormone marinobufagenin induces renal fibrosis: implication of epithelial-to-mesenchymal transition

We recently demonstrated that the cardiotonic steroid marinobufagenin (MBG) induced fibrosis in rat hearts through direct stimulation of collagen I secretion by cardiac fibroblasts. This stimulation was also responsible for the cardiac fibrosis seen in experimental renal failure. In this study, the effect of MBG on the development of renal fibrosis in rats was investigated. Four weeks of MBG infusion triggered mild periglomerular and peritubular fibrosis in the cortex and the appearance of fibrotic scars in the corticomedullary junction of the kidney. MBG also significantly increased the protein levels and nuclear localization of the transcription factor Snail in the tubular epithelia. It is known that activation of Snail is associated with epithelial-to-mesenchymal transition (EMT) during renal fibrosis. To examine whether MBG alone can trigger EMT, we used the porcine proximal tubular cell line LLC-PK1. MBG (100 nM) caused LLC-PK1 cells grown to confluence to acquire a fibroblast-like shape and have an invasive motility. The expressions of the mesenchymal proteins collagen I, fibronectin, and vimentin were increased twofold. However, the total level of E-cadherin remained unchanged. These alterations in LLC-PK1 cells in the presence of MBG were accompanied by elevated expression and nuclear translocation of Snail. During the time course of EMT, MBG did not have measurable inhibitory effects on the ion pumping activity of its natural ligand, Na(+)-K(+)-ATPase. Our data suggest that the MBG may be an important factor in inducing EMT and, through this mechanism, elevated levels of MBG in chronic renal failure may play a role in the progressive fibrosis.

BMP-7 does not protect against bleomycin-induced lung or skin fibrosis

Bone morphogenic protein (BMP)-7 is a member of the BMP family which are structurally and functionally related, and part of the TGFβ super family of growth factors. BMP-7 has been reported to inhibit renal fibrosis and TGFβ1-induced epithelial-mesenchymal transition (EMT), in part through negative interactions with TGFβ1 induced Smad 2/3 activation. We utilized in vivo bleomycin-induced fibrosis models in the skin and lung to determine the potential therapeutic effect of BMP-7. We then determined the effect of BMP-7 on TGFβ1-induced EMT in lung epithelial cells and collagen production by human lung fibroblasts. We show that BMP-7 did not affect bleomycin-induced fibrosis in either the lung or skin in vivo; had no effect on expression of pro-fibrotic genes by human lung fibroblasts, either at rest or following exposure to TGFβ1; and did not modulate TGFβ1 -induced EMT in human lung epithelial cells. Taken together our data indicates that BMP-7 has no anti-fibrotic effect in lung or skin fibrosis either in vivo or in vitro. This suggests that the therapeutic options for BMP-7 may be confined to the renal compartment.

Epithelial cell alpha3beta1 integrin links beta-catenin and Smad signaling to promote myofibroblast formation and pulmonary fibrosis

Pulmonary fibrosis, in particular idiopathic pulmonary fibrosis (IPF), results from aberrant wound healing and scarification. One population of fibroblasts involved in the fibrotic process is thought to originate from lung epithelial cells via epithelial-mesenchymal transition (EMT). Indeed, alveolar epithelial cells (AECs) undergo EMT in vivo during experimental fibrosis and ex vivo in response to TGF-beta1. As the ECM critically regulates AEC responses to TGF-beta1, we explored the role of the prominent epithelial integrin alpha3beta1 in experimental fibrosis by generating mice with lung epithelial cell-specific loss of alpha3 integrin expression. These mice had a normal acute response to bleomycin injury, but they exhibited markedly decreased accumulation of lung myofibroblasts and type I collagen and did not progress to fibrosis. Signaling through beta-catenin has been implicated in EMT; we found that in primary AECs, alpha3 integrin was required for beta-catenin phosphorylation at tyrosine residue 654 (Y654), formation of the pY654-beta-catenin/pSmad2 complex, and initiation of EMT, both in vitro and in vivo during the fibrotic phase following bleomycin injury. Finally, analysis of lung tissue from IPF patients revealed the presence of pY654-beta-catenin/pSmad2 complexes and showed accumulation of pY654-beta-catenin in myofibroblasts. These findings demonstrate epithelial integrin-dependent profibrotic crosstalk between beta-catenin and Smad signaling and support the hypothesis that EMT is an important contributor to pathologic fibrosis.

Intestinal fibrosis in inflammatory bowel disease - Current knowledge and future perspectives

BACKGROUND AND AIMS

Intestinal fibrosis is a common complication of IBD that can become seriously symptomatic and may require surgical intervention if stricture formation ensues. This review discusses existing and developing knowledge of intestinal fibrosis and its implications for therapy.

METHODS

Review of the literature, personal communications, unpublished observations.

RESULTS

Known mechanisms of intestinal fibrosis include fibroblast proliferation and migration, activation of stellate cells, and extraintestinal fibroblast recruitment. However, novel mechanisms are being uncovered, including epithelial-to-mesenchymal transition, endothelial-to-mesenchymal transition, pericyte differentiation, and fibrocyte recruitment. Most of the traditional and novel mechanisms underlying intestinal fibrosis are associated to the presence of chronic inflammation, but is also possible that fibrosis develops independently of persistent immune activation in the gut. At the moment, the development of preventive, non-interventional, and more effective management of intestinal fibrosis is hampered by the lack of a greater knowledge of its basic pathophysiology and predisposing factors.

CONCLUSIONS

It is reasonable to expect that therapy of IBD-associated fibrosis will radically improve once the underlying mechanisms are better understood, and therapeutic modalities will emerge that prevent or reverse this complication of IBD.

Activation of TGF-beta within cultured hepatocytes and in liver injury leads to intracrine signaling with expression of connective tissue growth factor

Recently, synthesis and secretion of connective tissue growth factor (CTGF)/CYR61/CTGF/NOV-family member 2 (CCN2) in cultures of hepatocytes were shown, which are sensitively up-regulated by exogenous TGF-beta. In this study TGF-beta-dependent CTGF/CCN2 expression in hepatocytes cultured under completely TGF-beta-free conditions was analysed by Western-blots, metabolic labelling, and CTGF-reporter gene assays. In alkaline phosphatase monoclonal anti-alkaline phosphatase complex (APAAP)-staining of cultured hepatocytes it was demonstrated that latent TGF-beta within the hepatocytes becomes rapidly detectable during culture indicating an intracellular demasking of the mature TGF-beta antigen. Subsequent signaling to theCTGF/CCN2 promoter occurs via p-Smad2, whereas p-Smad3 does not seem to be involved. Cycloheximide did not abolish the rapid immunocytochemical appearance of mature TGF-beta, but calpain inhibitors partially suppressed intracellular TGF-beta activation and subsequently CTGF up-regulation. Calpain treatment had the reverse effect. None of the inhibitors of extracellular TGF-beta signalling was effective in the reduction of spontaneous CTGF synthesis, but intracellularly acting Alk 4-/Alk 5-specific inhibitor SB-431542 was able to diminish CTGF expression. The assumption that latent intracellular TGF-beta is activated by calpains during culture-induced stress or injurious conditions in the liver in vivo was further validated by a direct effect of calpains on the activation of recombinant latent TGF-beta. In conclusion, these data are the first to suggest the possibility of intracrine TGF-beta signalling due to calpain-dependent intracellular proteolytic activation leading to transcriptional activation of CTGF/CCN2 as a TGF-beta-sensitive reporter gene. This mechanism might be deleterious for keeping long-term hepatocyte cultures due to TGF-beta-induced apoptosis and, further, might be of relevance for induction of apoptosis or epithelial-mesenchymal transition of hepatocytes in injured liver.

Current and future anti-fibrotic therapies for chronic liver disease

Chronic injury results in a wound healing response that eventually leads to fibrosis. The response is generalized, with features common among multiple organ systems. In the liver, various different types of injury lead to fibrogenesis, implying a common pathogenesis. Although several specific therapies for patients who have different liver diseases have been successfully developed, including antiviral therapies for those who have hepatitis B and hepatitis C virus infection, specific and effective antifibrotic therapy remains elusive. Over the past 2 decades, great advances in the understanding of fibrosis have been made and multiple mechanisms underlying hepatic fibrogenesis uncovered. Elucidation of these mechanisms has been of fundamental importance in highlighting novel potential therapies. Preclinical studies have indicated several putative therapies that might abrogate fibrogenesis. This article emphasizes mechanisms underlying fibrogenesis and reviews available and future therapeutics.

Intracrine signalling of activin A in hepatocytes upregulates connective tissue growth factor (CTGF/CCN2) expression

BACKGROUND/AIMS

Up to now, the effect of activin A on the expression of the important transforming growth factor (TGF)-beta downstream modulator connective tissue growth factor (CTGF) is not known, but might be of relevance for the functional effects of this cytokine on several liver cell types.

METHODS

In this study, activin A-dependent CTGF expression in hepatocytes (PC) primed by exogenous activin A and in PC maintained under complete activin-free culture conditions was analysed by Western blots, metabolic labelling, gene silencing, reverse transcriptase-polymerase chain reaction (RT-PCR) and CTGF reporter gene assays. This study was supplemented by immunocytochemical staining of activin A and CTGF in PC of injured liver.

RESULTS

Using alkaline phosphatase alpha-alkaline phosphatase staining, it is demonstrated that activin A becomes increasingly detectable during the course of CCl(4)-liver damage. Addition of activin A to cultured PC induced CTGF protein expression via phosphorylation of Smad2 and Smad3. This induction can be inhibited by the antagonist follistatin and alpha-activin A antibody respectively. When PC were cultured under serum(i.e. activin A)-free culture conditions, a time-dependent increase of activin expression during the course of the culture was proven by RT-PCR. Silencing of inhibin beta(A) gene expression under serum-free conditions by small interfering RNAs greatly suppressed CTGF synthesis and the phosphorylations of Smad2 and Smad3. However, both the extracellularly acting follistatin and the alpha-activin A antibody could not inhibit spontaneous CTGF expression, which, however, was achieved by the cell-permeable TGF-beta Alk4/Alk5 receptor-kinase-inhibitor SB431542.

CONCLUSIONS

In conclusion, the results point to activin A as an inducer of CTGF synthesis in PC. Intracellular activin A contributes to spontaneous CTGF expression in PC independent of exogenous activin A, which is proposed to occur via Alk4/Alk5-receptors. The findings might be important for many actions of activin A on the liver.

Cellular sources of extracellular matrix in hepatic fibrosis

The deposition of increased and abnormal extracellular matrix is the hallmark of liver fibrosis. Hepatic stellate cells are well known as the major source of the fibrillar collagens and other components of the liver scar, but are now appreciated to be only one of many potentially fibrogenic cell populations in the diseased liver. Portal fibroblasts and circulating mesenchymal cells derived from the bone marrow are also important sources of matrix proteins in fibrosis. Recent data suggest that hepatocytes and biliary epithelial cells undergo an epithelial to mesenchymal transition, similarly assuming a fibrogenic phenotype. Sinusoidal endothelial cells and hepatocytes produce specific matrix proteins important in liver health and disease. The future challenge will be to define more explicitly the roles of these different fibrogenic cell populations in fibrosis in a disease-specific way.

Fibrosis and cirrhosis reversibility - molecular mechanisms

The concept that liver fibrosis is a dynamic process with potential for regression as well as progression has emerged in parallel with clinical evidence for remodeling of fibrotic extracellular matrix in patients who can be effectively treated for their underlying cause of liver disease. This article reviews recent discoveries relating to the cellular and molecular mechanisms that regulate fibrosis regression, with emphasis on studies that have used experimental in vivo models of liver disease. Apoptosis of hepatic myofibroblasts is discussed. The functions played by transcription factors, receptor-ligand interactions, and cell-matrix interactions as regulators of the lifespan of hepatic myofibroblasts are considered, as are the therapeutic opportunities for modulating these functions. Growth factors, proteolytic enzymes, and their inhibitors are discussed in detail.

Pharmacological application of caffeine inhibits TGF-beta-stimulated connective tissue growth factor expression in hepatocytes via PPARgamma and SMAD2/3-dependent pathways

BACKGROUND/AIMS

Epidemiological studies suggest that coffee drinking is inversely correlated with the risk of development of liver fibrosis but the molecular basis is unknown.

METHODS

We investigated the pharmacological mechanisms involved in caffeine-dependent regulation of CTGF expression, an important modulator protein of fibrogenic TGF-beta, in rat hepatocytes using Western-blot, co-immunoprecipitations, reporter-gene-assays and ELISAs.

RESULTS

It is demonstrated that caffeine, similar to 8-Br-cAMP, suppresses CTGF expression, decreases SMAD2 protein levels and inhibits SMAD1/3-phosphorylation. The SMAD2 level can be restored by a proteasome inhibitor. Additionally, caffeine leads to an up-regulation of PPARgamma expression, that enhances the inhibitory effect of the natural PPARgamma agonist 15-PGJ(2) on CTGF expression by inducing a dissociation of the SMAD2/3-CBP/p300-transcriptional complex.

CONCLUSIONS

We show that caffeine strongly down-modulates TGF-beta-induced CTGF expression in hepatocytes by stimulation of degradation of the TGF-beta effector SMAD 2, inhibition of SMAD3 phosphorylation and up-regulation of the PPARgamma-receptor. Long-term caffeinization might be an option for anti-fibrotic trials in chronic liver diseases.

Nuclear cathepsin F regulates activation markers in rat hepatic stellate cells

Activation of hepatic stellate cells during liver fibrosis is a major event facilitating an increase in extracellular matrix deposition. The up-regulation of smooth muscle alpha-actin and collagen type I is indicative of the activation process. The involvement of cysteine cathepsins, a class of lysosomal cysteine proteases, has not been studied in conjunction with the activation process of hepatic stellate cells. Here we report a nuclear cysteine protease activity partially attributed to cathepsin F, which co-localizes with nuclear speckles. This activity can be regulated by treatment with retinol/palmitic acid, known to reduce the hepatic stellate cell activation. The treatment for 48 h leads to a decrease in activity, which is coupled to an increase in cystatin B and C transcripts. Cystatin B knockdown experiments during the same treatment confirm the regulation of the nuclear activity by cystatin B. We demonstrate further that the inhibition of the nuclear activity by E-64d, a cysteine protease inhibitor, results in a differential regulation of smooth muscle alpha-actin and collagen type I transcripts. On the other hand, cathepsin F small interfering RNA transfection leads to a decrease in nuclear activity and a transcriptional down-regulation of both activation markers. These findings indicate a possible link between nuclear cathepsin F activity and the transcriptional regulation of hepatic stellate cell activation markers.

Fibrogenesis of parenchymal organs

Fibrosis of parenchymal organs is caused by prolonged injury, deregulation of the normal processes of wound healing, and extensive deposition of extracellular matrix (ECM) proteins. The current review will focus on common features of fibrogenesis in parenchymal organs, and will briefly discuss common features and differences in the pathophysiology of fibrosis. Comparison of hepatic, renal, and pulmonary fibrosis has identified several common mechanisms. Common themes include a critical role for the cytokine transforming growth factor beta and the generation of reactive oxygen species. Activated myofibroblasts are the common cell type that produce the excessive fibrous scar and may originate from endogenous cells such as hepatic stellate cells or fibroblasts, from the bone marrow such as fibrocytes, or from the transition of epithelial cells to mesenchymal cells. These concepts open new prospects for multidisciplinary research and the development of new therapies for fibrosis.

Fibrotic myofibroblasts manifest genome-wide derangements of translational control

Background

As a group, fibroproliferative disorders of the lung, liver, kidney, heart, vasculature and integument are common, progressive and refractory to therapy. They can emerge following toxic insults, but are frequently idiopathic. Their enigmatic propensity to resist therapy and progress to organ failure has focused attention on the myofibroblast–the primary effector of the fibroproliferative response. We have recently shown that aberrant beta 1 integrin signaling in fibrotic fibroblasts results in defective PTEN function, unrestrained Akt signaling and subsequent activation of the translation initiation machinery. How this pathological integrin signaling alters the gene expression pathway has not been elucidated.

Results

Using a systems approach to study this question in a prototype fibrotic disease, Idiopathic Pulmonary Fibrosis (IPF); here we show organized changes in the gene expression pathway of primary lung myofibroblasts that persist for up to 9 sub-cultivations in vitro. When comparing IPF and control myofibroblasts in a 3-dimensional type I collagen matrix, more genes differed at the level of ribosome recruitment than at the level of transcript abundance, indicating pathological translational control as a major characteristic of IPF myofibroblasts. To determine the effect of matrix state on translational control, myofibroblasts were permitted to contract the matrix. Ribosome recruitment in control myofibroblasts was relatively stable. In contrast, IPF cells manifested large alterations in the ribosome recruitment pattern. Pathological studies suggest an epithelial origin for IPF myofibroblasts through the epithelial to mesenchymal transition (EMT). In accord with this, we found systems-level indications for TGF-β -driven EMT as one source of IPF myofibroblasts.

Conclusions

These findings establish the power of systems level genome-wide analysis to provide mechanistic insights into fibrotic disorders such as IPF. Our data point to derangements of translational control downstream of aberrant beta 1 integrin signaling as a fundamental component of IPF pathobiology and indicates that TGF-β -driven EMT is one source for IPF myofibroblasts.

Hepatic fibrogenesis: from within and outwith

Liver disease is now the fifth commonest cause of death in the United Kingdom and the incidence is increasing. Chronic injury to the liver typically due to toxic insult, viral infection, immunological or metabolic diseases usually results in a stereotypical response with both parenchymal regeneration and wound healing. Chronic hepatic injury results in liver fibrosis with eventual progression to cirrhosis and end stage liver disease. At this point the majority of the clinical complications arise such as portal hypertension and the development of liver cancer. If the causative disease can be effectively treated the liver can regenerate and at the least partial resolution of liver fibrosis may occur. Unfortunately, unless the primary disease can be eradicated there are no specific anti-fibrotic treatments in routine clinical use. This highlights the urgent need to both increase our understanding of the mechanisms of hepatic fibrogenesis and to develop novel therapies to arrest or reverse the fibrotic process. This article initially outlines the main cellular pathway of fibrogenesis within the liver-the activation of the quiescent hepatic stellate cell into an activated myofibroblast phenotype, resulting in the production of fibrillar collagen. We will then discuss newly emerging sources of scar forming cells during hepatic injury together with the role of hepatic macrophages which have a regulatory function in both the formation and resolution of liver fibrosis.

Targeting liver myofibroblasts: a novel approach in anti-fibrogenic therapy

Chronic liver disease results in a liver-scarring response termed fibrosis. Excessive scarring leads to cirrhosis, which is associated with high morbidity and mortality. The only treatment for liver cirrhosis is liver transplantation; therefore, much attention has been directed toward therapies that will slow or reverse fibrosis. Although anti-fibrogenic therapies have been shown to be effective in experimental animal models, licensed therapies have yet to emerge. A potential problem for any anti-fibrogenic therapy in the liver is the existence of the body’s major drug metabolising cell (the hepatocyte) adjacent to the primary fibrosis-causing cell, the myofibroblast. This article reviews the development of a human recombinant single-chain antibody (scAb) that binds to the surface of myofibroblasts. This antibody binds specifically to myofibroblasts in fibrotic mouse livers. When conjugated with a compound that stimulates myofibroblast apoptosis, the antibody directs the specific apoptosis of myofibroblasts with greater specificity and efficacy than the free compound. The antibody also reduces the adverse effect of liver macrophage apoptosis and—in contrast to the free compound—reversed fibrosis in the sustained injury model used. These data suggest that specifically stimulating the apoptosis of liver myofibroblasts using a targeting antibody has potential in the treatment of liver fibrosis.

Connective tissue growth factor: a fibrogenic master switch in fibrotic liver diseases

Connective tissue growth factor (CTGF=CCN2), one of six members of cysteine-rich, secreted, heparin-binding proteins with a modular structure, is recognized as an important player in fibrogenic pathways as deduced from findings in non-hepatic tissues and emerging results from liver fibrosis. Collectively, the data show strongly increased expression in fibrosing tissues and transforming growth factor (TGF-beta)-stimulated expression in hepatocytes, biliary epithelial cells and stellate cells. Functional activity as a mediator of fibre-fibre, fibre-matrix and matrix-matrix interactions, as an enhancer of profibrogenic TGF-beta and several secondary effects owing to TGF-beta enhancement, and as a down-modulator of the bioactivity of bone morphogenetic protein-7 has been proposed. By changing the activity ratio of TGF-beta to its antagonist bone-morphogenetic protein-7, CTGF is proposed as a fibrogenic master switch for epithelial-mesenchymal transition. Consequently, knockdown of CTGF considerably attenuates experimental liver fibrosis. The spill-over of CTGF from the liver into the blood stream proposes this protein as a non-invasive reporter of TGF-beta bioactivity in this organ. Indeed, CTGF-levels in sera correlate significantly with fibrogenic activity. The data suggest CTGF as a multifaceted regulatory protein in fibrosis, which offers important translational aspects for diagnosis and follow-up of hepatic fibrogenesis and as a target for therapeutic interventions. In addition, CTGF-promoter polymorphism might be of importance as a prognostic genetic marker to predict the progression of fibrosis.

Hepatic fibrogenesis in response to chronic liver injury: novel insights on the role of cell-to-cell interaction and transition

Hepatic fibrosis represents the wound-healing response process of the liver to chronic injury, independently from aetiology. Advanced liver fibrosis results in cirrhosis that can lead to liver failure, portal hypertension and hepatocellular carcinoma. Currently, no effective therapies are available for hepatic fibrosis. After the definition of hepatic stellate cells (HSCs) as the main liver extracellular matrix-producing cells in the 1980s, the subsequent decade was dedicated to determine the role of specific cytokines and growth factors. Fibrotic progression of chronic liver diseases can be nowadays considered as a dynamic and highly integrated process of cellular response to chronic liver injury. The present review is dedicated to the novel mechanisms of cellular response to chronic liver injury leading to hepatic myofibroblasts' activation. The understanding of the cellular and molecular pathways regulating their function is crucial to counteract therapeutically the organ dysfunction caused by myofibroblasts' activation.

Pancreatic ductal adenocarcinoma: cellular origin, signaling pathways and stroma contribution

Pancreatic cancer has a very poor prognosis, in part due to its diagnosis at late stages of the disease and to limited response to chemotherapy and radiotherapy. The vast majority of pancreatic cancers are classified as pancreatic ductal adenocarcinomas (PDACs). Despite advances in knowledge on the cellular origin of PDAC or the involvement of signal transduction pathways therein, many questions remain unanswered. In this review, we summarize recent findings and current hypotheses regarding these two questions. Since pancreatitis is a risk factor for human PDAC, and the latter proceeds with an intense fibrotic reaction, we also analyze the role of the stroma in PDAC progression. An improved understanding of these key aspects for PDAC ontogeny will open new avenues for tumor prevention, early detection, and improved therapy.

EMT and proteinuria as progression factors

Tubulointerstitial fibrosis is an integral part of the structural changes of the kidney in chronic progressive renal failure. The accumulation of the extracellular matrix in the tubulointerstitial space is mediated mainly by myofibroblasts. These are derived from resident interstitial fibroblasts, tubular epithelial cells, periadventitial cells, and possibly also mesenchymal stem cells and endothelial cells. Fibrosis is usually preceded by tubulointerstitial infiltration of mononuclear inflammatory cells. Proteinuria is one of several mechanisms of primary glomerular or vascular disease to transmit the disease process to the interstitial space. Increased protein filtration may have direct toxic effects on tubular epithelial cells, induce chemokine and cytokine secretion and result in increased expression of adhesion molecules, all contributing to the influx of mononuclear cells. Inflammatory cells in return secrete cytokines, which stimulate resident fibroblasts and tubular epithelial cells to differentiate into matrix-producing cells. The phenotypic conversion of primary epithelial cells into mesenchymal cells, termed epithelial-mesenchymal transition (EMT), has been studied in great detail in recent years. Several signal transduction pathways of this process have been clarified and may eventually result in novel therapeutic approaches. The severity of proteinuria and the extent of EMT have both been associated with the decline in renal function in clinical studies. Limiting proteinuria results in a slower decline of renal function deterioration, whereas reducing EMT has had beneficial effects in a number of animal studies, including those indicating reversal of fibrotic lesions. However, the association between proteinuria and EMT and vice versa is far from clear and has not been carefully studied.