Integrin-mediated activation of transforming growth factor-beta(1) in pulmonary fibrosis

Phosphodiesterase 4 is overexpressed in keloid epidermal scars and its inhibition reduces keratinocyte fibrotic alterations

BACKGROUND

Epidermal remodeling and hypertrophy are hallmarks of skin fibrotic disorders, and keratinocyte to mesenchymal (EMT)-like transformations drive epidermis alteration in skin fibrosis such as keloids and hypertrophic scars (HTS). While phosphodiesterase 4 (PDE4) inhibitors have shown effectiveness in various fibrotic disorders, their role in skin fibrosis is not fully understood. This study aimed to explore the specific role of PDE4B in epidermal remodeling and hypertrophy seen in skin fibrosis.

METHODS

In vitro experiments examined the effects of inhibiting PDE4A-D (with Roflumilast) or PDE4B (with siRNA) on TGFβ1-induced EMT differentiation and dedifferentiation in human 3D epidermis. In vivo studies investigated the impact of PDE4 inhibition on HOCl-induced skin fibrosis and epidermal hypertrophy in mice, employing both preventive and therapeutic approaches.

RESULTS

The study found increased levels of PDE4B (mRNA, protein) in keloids > HTS compared to healthy epidermis, as well as in TGFβ-stimulated 3D epidermis. Keloids and HTS epidermis exhibited elevated levels of collagen Iα1, fibronectin, αSMA, N-cadherin, and NOX4 mRNA, along with decreased levels of E-cadherin and ZO-1, confirming an EMT process. Inhibition of both PDE4A-D and PDE4B prevented TGFβ1-induced Smad3 and ERK1/2 phosphorylation and mesenchymal differentiation in vitro. PDE4A-D inhibition also promoted mesenchymal dedifferentiation and reduced TGFβ1-induced ROS and keratinocyte senescence by rescuing PPM1A, a Smad3 phosphatase. In vivo, PDE4 inhibition mitigated HOCl-induced epidermal hypertrophy in mice in both preventive and therapeutic settings.

CONCLUSIONS

Overall, the study supports the potential of PDE4 inhibitors, particularly PDE4B, in treating skin fibrosis, including keloids and HTS, shedding light on their functional role in this condition.

Cellular Senescence: A Troy Horse in Pulmonary Fibrosis

Pulmonary fibrosis (PF) is a chronic interstitial lung disease characterized by myofibroblast abnormal activation and extracellular matrix deposition. However, the pathogenesis of PF remains unclear, and treatment options are limited. Epidemiological studies have shown that the average age of PF patients is estimated to be over 65 years, and the incidence of the disease increases with age. Therefore, PF is considered an age-related disease. A preliminary study on PF patients demonstrated that the combination therapy of the anti-senescence drugs dasatinib and quercetin improved physical functional indicators. Given the global aging population and the role of cellular senescence in tissue and organ aging, understanding the impact of cellular senescence on PF is of growing interest. This article systematically summarizes the causes and signaling pathways of cellular senescence in PF. It also objectively analyzes the impact of senescence in AECs and fibroblasts on PF development. Furthermore, potential intervention methods targeting cellular senescence in PF treatment are discussed. This review not only provides a strong theoretical foundation for understanding and manipulating cellular senescence, developing new therapies to improve age-related diseases, and extending a healthy lifespan but also offers hope for reversing the toxicity caused by the massive accumulation of senescence cells in humans.

Arginine Methylation of Integrin Alpha-4 Prevents Fibrosis Development in Alcohol-Associated Liver Disease

BACKGROUND & AIMS

Alcohol-associated liver disease (ALD) comprises a spectrum of disorders including steatosis, steatohepatitis, fibrosis, and cirrhosis. We aimed to study the role of protein arginine methyltransferase 6 (PRMT6), a new regulator of liver function, in ALD progression.

METHODS

Prmt6-deficient mice and wild-type littermates were fed Western diet with alcohol in the drinking water for 16 weeks. Mice fed standard chow diet or Western diet alone were used as a control.

RESULTS

We found that PRMT6 expression in the liver is down-regulated in 2 models of ALD and negatively correlates with disease severity in mice and human liver specimens. Prmt6-deficient mice spontaneously developed liver fibrosis after 1 year and more advanced fibrosis after high-fat diet feeding or thioacetamide treatment. In the presence of alcohol Prmt6 deficiency resulted in a dramatic increase in fibrosis development but did not affect lipid accumulation or liver injury. In the liver PRMT6 is primarily expressed in macrophages and endothelial cells. Transient replacement of knockout macrophages with wild-type macrophages in Prmt6 knockout mice reduced profibrotic signaling and prevented fibrosis progression. We found that PRMT6 decreases profibrotic signaling in liver macrophages via methylation of integrin α-4 at R464 residue. Integrin α-4 is predominantly expressed in infiltrating monocyte derived macrophages. Blocking monocyte infiltration into the liver with CCR2 inhibitor reduced fibrosis development in knockout mice and abolished differences between genotypes.

CONCLUSIONS

Taken together, our data suggest that alcohol-mediated loss of Prmt6 contributes to alcohol-associated fibrosis development through reduced integrin methylation and increased profibrotic signaling in macrophages.

Integrin αVβ1 regulates procollagen I production through a non-canonical transforming growth factor β signaling pathway in human hepatic stellate cells

Hepatic stellate cells (HSCs) are thought to play key roles in the development of liver fibrosis. Extensive evidence has established the concept that αV integrins are involved in the activation of latent transforming growth factor β (TGF-β), a master regulator of the fibrotic signaling cascade. Based on mRNA and protein expression profiling data, we found that αVβ1 integrin is the most abundant member of the αV integrin family in either quiescent or TGF-β1-activated primary human HSCs. Unexpectedly, either a selective αVβ1 inhibitor, Compound 8 (C8), or a pan-αV integrin inhibitor, GSK3008348, decreased TGF-β1-activated procollagen I production in primary human HSCs, in which the role of β1 integrin was confirmed by ITGB1 siRNA. In contrast with an Activin receptor-like kinase 5 (Alk5) inhibitor, C8 and GSK3008348 failed to inhibit TGF-β1 induced SMAD3 and SMAD2 phosphorylation, but inhibited TGF-β-induced phosphorylation of ERK1/2 and STAT3, suggesting that αVβ1 integrin is involved in non-canonical TGF-β signaling pathways. Consistently, ITGB1 siRNA significantly decreased phosphorylation of ERK1/2. Furthermore, a selective inhibitor of MEK1/2 blocked TGF-β1 induced phosphorylation of ERK1/2 and decreased TGF-β1 induced procollagen I production, while a specific inhibitor of STAT3 had no effect on TGF-β1 induced procollagen I production. Taken together, current data indicate that αVβ1 integrin can regulate TGF-β signaling independent of its reported role in activating latent TGF-β. Our data further support that αVβ1 inhibition is a promising therapeutic target for the treatment of liver fibrosis.

Investigational drugs for idiopathic pulmonary fibrosis

INTRODUCTION

IPF is a specific form of chronic fibrosing interstitial pneumonia of unknown cause, characterized by progressive worsening in lung function and an unfavorable prognosis. Current concepts on IPF pathogenesis are based on a dysregulated wound healing response, leading to an over production of extracellular matrix. Based on recent research however, several other mechanisms are now proposed as potential targets for novel therapeutic strategies. Areas covered: This review analyzes the current investigational strategies targeting extracellular matrix deposition, tyrosine-kinase antagonism, immune and autoimmune response, and cell-based therapy. A description of the pathogenic rationale implied in each novel therapeutic approach is summarized. Expert opinion: New IPF drugs are being evaluated in the context of phase 1 and 2 clinical trials. Nevertheless, many drugs that have shown efficacy in preclinical studies, failed to exhibit the same positive effect when translated to humans. A possible explanation for these failures might be related to the known limitations of animal models of the disease. The recent development of 3D systems composed of cells from individual patients that recreate an ex-vivo model of IPF, could lead to significant improvements in disease pathogenesis and treatment. New drugs could be tested on more genuine models and clinicians could tailor therapy based on patient's response.

Uncoupling of the profibrotic and hemostatic effects of thrombin in lung fibrosis

Fibrotic lung disease, most notably idiopathic pulmonary fibrosis (IPF), is thought to result from aberrant wound-healing responses to repetitive lung injury. Increased vascular permeability is a cardinal response to tissue injury, but whether it is mechanistically linked to lung fibrosis is unknown. We previously described a model in which exaggeration of vascular leak after lung injury shifts the outcome of wound-healing responses from normal repair to pathological fibrosis. Here we report that the fibrosis produced in this model is highly dependent on thrombin activity and its downstream signaling pathways. Direct thrombin inhibition with dabigatran significantly inhibited protease-activated receptor-1 (PAR1) activation, integrin αvβ6 induction, TGF-β activation, and the development of pulmonary fibrosis in this vascular leak-dependent model. We used a potentially novel imaging method - ultashort echo time (UTE) lung magnetic resonance imaging (MRI) with the gadolinium-based, fibrin-specific probe EP-2104R - to directly visualize fibrin accumulation in injured mouse lungs, and to correlate the antifibrotic effects of dabigatran with attenuation of fibrin deposition. We found that inhibition of the profibrotic effects of thrombin can be uncoupled from inhibition of hemostasis, as therapeutic anticoagulation with warfarin failed to downregulate the PAR1/αvβ6/TGF-β axis or significantly protect against fibrosis. These findings have direct and important clinical implications, given recent findings that warfarin treatment is not beneficial in IPF, and the clinical availability of direct thrombin inhibitors that our data suggest could benefit these patients.

Transforming growth factor-β: activation by neuraminidase and role in highly pathogenic H5N1 influenza pathogenesis

Transforming growth factor-beta (TGF-β), a multifunctional cytokine regulating several immunologic processes, is expressed by virtually all cells as a biologically inactive molecule termed latent TGF-β (LTGF-β). We have previously shown that TGF-β activity increases during influenza virus infection in mice and suggested that the neuraminidase (NA) protein mediates this activation. In the current study, we determined the mechanism of activation of LTGF-β by NA from the influenza virus A/Gray Teal/Australia/2/1979 by mobility shift and enzyme inhibition assays. We also investigated whether exogenous TGF-β administered via a replication-deficient adenovirus vector provides protection from H5N1 influenza pathogenesis and whether depletion of TGF-β during virus infection increases morbidity in mice. We found that both the influenza and bacterial NA activate LTGF-β by removing sialic acid motifs from LTGF-β, each NA being specific for the sialic acid linkages cleaved. Further, NA likely activates LTGF-β primarily via its enzymatic activity, but proteases might also play a role in this process. Several influenza A virus subtypes (H1N1, H1N2, H3N2, H5N9, H6N1, and H7N3) except the highly pathogenic H5N1 strains activated LTGF-β in vitro and in vivo. Addition of exogenous TGF-β to H5N1 influenza virus-infected mice delayed mortality and reduced viral titers whereas neutralization of TGF-β during H5N1 and pandemic 2009 H1N1 infection increased morbidity. Together, these data show that microbe-associated NAs can directly activate LTGF-β and that TGF-β plays a pivotal role protecting the host from influenza pathogenesis.

Strategies for treating idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is the most common and most lethal diffuse fibrosing lung disease, with a mortality rate that exceeds that of many cancers. Recently, there have been many clinical trials of novel therapies for IPF. The results have mostly been disappointing, although two treatment approaches have shown some efficacy. This Review describes the difficulties of treating IPF and the approaches that have been tried or are in development, and concludes with suggestions of future therapeutic targets and strategies.

Extracellular matrix-induced gene expression in human breast cancer cells

Extracellular matrix (ECM) molecules modify gene expression through attachment-dependent (focal adhesion-related) integrin receptor signaling. It was previously unknown whether the same molecules acting as soluble peptides could generate signal cascades without the associated mechanical anchoring, a condition that may be encountered during matrix remodeling and degradation and relevant to invasion and metastatic processes. In the current study, the role of ECM ligand-regulated gene expression through this attachment-independent process was examined. It was observed that fibronectin, laminin, and collagen type I and II induce Smad2 activation in MCF-10A and MCF-7 cells. This activation is not caused by transforming growth factor (TGF)-beta ligand contamination or autocrine TGF involvement and is 3- to 5-fold less robust than the TGF-beta1 ligand. The resulting nuclear translocation of Smad4 in response to ECM ligand indicates downstream transcriptional responses occurring. Coimmunoprecipitation experiments determined that collagen type II and laminin act through interaction with integrin alpha(2)beta(1) receptor complex. The ECM ligand-induced Smad activation (termed signaling crosstalk) resulted in cell type and ligand-specific transcriptional changes, which are distinct from the TGF-beta ligand-induced responses. These findings show that cell-matrix communication is more complex than previously thought. Soluble ECM peptides drive transcriptional regulation through corresponding adhesion and non-attachment-related processes. The resultant gene expressional patterns correlate with pathway activity and not by the extent of Smad activation. These results extend the complexity and the existing paradigms of ECM-cell communication to ECM ligand regulation without the necessity of mechanical coupling.

The role of epithelial integrin receptors in recognition of pulmonary pathogens

Integrins are a large family of heterodimeric transmembrane cell adhesion receptors. During the last decade, it has become clear that integrins significantly participate in various host-pathogen interactions involving pathogenic bacteria, fungi, and viruses. Many bacteria possess adhesins that can bind either directly or indirectly to integrins. However, there appears to be an emerging role for integrins beyond simply adhesion molecules. Given the conserved nature of integrin structure and function, and the diversity of the pathogens which use integrins, it appears that they may act as pattern recognition receptors important for the innate immune response. Several clinically significant bacterial pathogens target lung epithelial integrins, and this review will focus on exploring various structures and mechanisms involved in these interactions.

Latency associated peptide has in vitro and in vivo immune effects independent of TGF-beta1

Latency Associated Peptide (LAP) binds TGF-β1, forming a latent complex. Currently, LAP is presumed to function only as a sequestering agent for active TGF-β1. Previous work shows that LAP can induce epithelial cell migration, but effects on leukocytes have not been reported. Because of the multiplicity of immunologic processes in which TGF-β1 plays a role, we hypothesized that LAP could function independently to modulate immune responses. In separate experiments we found that LAP promoted chemotaxis of human monocytes and blocked inflammation in vivo in a murine model of the delayed-type hypersensitivity response (DTHR). These effects did not involve TGF-β1 activity. Further studies revealed that disruption of specific LAP-thrombospondin-1 (TSP-1) interactions prevented LAP-induced responses. The effect of LAP on DTH inhibition depended on IL-10. These data support a novel role for LAP in regulating monocyte trafficking and immune modulation.

Murine models of pulmonary fibrosis

Human pulmonary fibrosis is characterized by alveolar epithelial cell injury, areas of type II cell hyperplasia, accumulation of fibroblasts and myofibroblasts, and the deposition of extracellular matrix proteins. The result is a progressive loss of normal lung architecture and impairment in gas exchange. Pertinent features of the human disease include temporal heterogeneity of the fibrotic lesions, progressive nature of the disease, development of fibrotic foci, and in some patients, a rapid worsening of symptoms known as an acute exacerbation. No current animal model recapitulates all of these cardinal manifestations of the human disease. However, investigations using murine models have led to the identification of many pathological cells and mediators that are believed to be important in human disease as well. In this review, we will summarize the characteristics, advantages, and disadvantages of many of the currently utilized murine models of pulmonary fibrosis.

Radioprotective effects of amifostine on acute and chronic esophageal injury in rodents

PURPOSE

This study was performed to evaluate the protective benefit of amifostine against esophageal injury from fractionated radiation in a rodent model.

METHODS

Fractionated or sham esophageal irradiation was administered to Fisher-344 rats for 5 consecutive daily fractions of 9 Gy using 150 kV X-rays. Animals received an intraperitoneal injection of amifostine or placebo 30 min before each fraction. Histopathologic analyses for mucosal thickness, submucosal collagen deposition, activation of macrophages, oxidative stress and expression/activation of integrinalphavbeta6 and transforming growth factor (TGF)-beta were performed 5 days and 10 weeks after irradiation.

RESULTS

Pre-RT mean mucosal thickness was 35 microm in both the placebo and the amifostine groups. Five days post-RT, mean mucosal thicknesses were 30 microm in the placebo group versus 37 microm in the amifostine group (p = 0.024). At 10 weeks post-RT, the group receiving amifostine experienced a significant decrease in tunica muscularis damage (p = 0.002), submucosal collagen deposition (p = 0.027), and macrophage accumulation (p = 0.026) when compared with the placebo group. The levels of immunoreactivity for oxidative stress, TGF-beta, and integrinalphavbeta6 were significantly decreased 10 weeks post-RT in the group receiving amifostine treatment compared with placebo group.

CONCLUSIONS

This study demonstrates that amifostine given before each radiation fraction protects against acute and chronic esophageal injury in a rodent model. Protection of the mucosal epithelium integrity by amifostine prevents integrinalphavbeta6 expression which reduces TGF-beta activation and subsequent development of chronic esophageal injury in this model. Further investigation is necessary to determine the clinical relevance of these findings.

Alphav beta6 integrin regulates renal fibrosis and inflammation in Alport mouse

The transforming growth factor (TGF)-beta-inducible integrin alpha v beta6 is preferentially expressed at sites of epithelial remodeling and has been shown to bind and activate latent precursor TGF-beta. Herein, we show that alpha v beta6 is overexpressed in human kidney epithelium in membranous glomerulonephritis, diabetes mellitus, IgA nephropathy, Goodpasture's syndrome, and Alport syndrome renal epithelium. To assess the potential regulatory role of alpha v beta6 in renal disease, we studied the effects of function-blocking alpha v beta6 monoclonal antibodies (mAbs) and genetic ablation of the beta6 subunit on kidney fibrosis in Col4A3-/- mice, a mouse model of Alport syndrome. Expression of alpha v beta6 in Alport mouse kidneys was observed primarily in cortical tubular epithelial cells and in correlation with the progression of fibrosis. Treatment with alpha v beta6-blocking mAbs inhibited accumulation of activated fibroblasts and deposition of interstitial collagen matrix. Similar inhibition of renal fibrosis was observed in beta6-deficient Alport mice. Transcript profiling of kidney tissues showed that alpha v beta6-blocking mAbs significantly inhibited disease-associated changes in expression of fibrotic and inflammatory mediators. Similar patterns of transcript modulation were produced with recombinant soluble TGF-beta RII treatment, suggesting shared regulatory functions of alpha v beta6 and TGF-beta. These findings demonstrate that alpha v beta6 can contribute to the regulation of renal fibrosis and suggest this integrin as a potential therapeutic target.

Expression of transforming growth factor beta (TGF-b1) by human preterm lung inflammatory cells

Using a previously published model of human BPD this study examines whether preterm lung inflammatory cells produce transforming growth factor beta 1 (TGF-beta1), a cytokine pivotal in pathogenesis of bronchopulmonary dysplasia (BPD), and whether TGF-beta1 expression is regulated by inflammation. Lung inflammatory cells (neutrophils and macrophages) recovered in the broncho-alveolar (BAL) fluid of premature infants intubated for respiratory distress after birth expressed TGF-b1 mRNA and protein. Total and bioactive TGF-beta1 were abundantly found in the BAL fluid of the same infants. In cell culture stimulation by lipopolysaccharide (LPS) did not result in any further expression of total or bioactive TGF-beta1 by neonatal lung inflammatory cells over constitutive concentrations. In conclusion, lung inflammatory cells from premature infants are a source of TGF-beta1 but LPS does not regulate TGF-b1 production in these cells.

The αvβ6 integrin plays a role in compromised epidermal wound healing

The alphavbeta6 integrin is an exclusively epithelial integrin that is highly expressed during fetal development. In adult tissue, alphavbeta6 integrin is expressed during inflammation, carcinogenesis, and in wound healing. We previously reported that alphavbeta6 integrin is highly expressed in poorly healing human wounds and its over-expression is associated with chronic wounds in a mouse model. The objective of this study was to investigate the role of alphavbeta6 integrin in compromised wound healing induced by hydrocortisone treatment or aging by using young and old mice deficient in or overexpressing the beta6 integrin subunit in the epidermis. Untreated aged beta6 integrin-deficient (beta6-/-) animals showed a significant delay in wound healing when compared to their age-matched controls or younger beta6-/- mice. The most significant delay was observed at the stages where granulation tissue deposition was occurring. Hydrocortisone treatment significantly delayed wound healing in wild-type and beta6 integrin-deficient mice in comparison with the untreated controls. However, hydrocortisone treatment in beta6 integrin overexpressing animals did not cause a significant delay in wound healing. The results of this study suggest that alphavbeta6 integrin plays an important role in wound healing in animals compromised by either age or stress mimicked by hydrocortisone.

Regulation of Fibrosis by the Immune System

Inflammation and fibrosis are two inter-related conditions with many overlapping mechanisms. Three specific cell types, macrophages, T helper cells, and myofibroblasts, each play important roles in regulating both processes. Following tissue injury, an inflammatory stimulus is often necessary to initiate tissue repair, where cytokines released from resident and infiltrating leukocytes stimulate proliferation and activation of myofibroblasts. However, in many cases this drive stimulates an inappropriate pro-fibrotic response. In addition, activated myofibroblasts can take on the role of traditional APCs, secrete pro-inflammatory cytokines, and recruit inflammatory cells to fibrotic foci, amplifying the fibrotic response in a vicious cycle. Moreover, inflammatory cells have been shown to play contradictory roles in initiation, amplification, and resolution of fibrotic disease processes. The central role of the macrophage in contributing to the fibrotic response and fibrotic resolution is only beginning to be fully appreciated. In the following review, we discuss the fibrotic disease process from the context of the immune response to injury. We review the major cellular and soluble factors controlling these responses and suggest ways in which more specific and, hopefully, more effective therapies may be derived.

Opposing regulatory roles of complement factor 5 in the development of bleomycin-induced pulmonary fibrosis

The mechanisms of idiopathic pulmonary fibrosis pathogenesis, a chronic and progressive interstitial lung disease, remain elusive. The complement system, a crucial arm of the innate immune response, plays a pivotal role in several pathological disorders; however, the contribution of individual complement components to lung fibrosis has not yet been examined. Complement factor 5 (C5) and its cleavage product C5a are critical mediators in inflammatory diseases. Thus, to evaluate the role of C5 in lung fibrosis, we compared congenic C5-sufficient and C5-deficient mice in a well-characterized murine model of bleomycin-induced pulmonary fibrosis. C5-deficient mice had an exaggerated inflammatory phenotype compared with C5-sufficient mice during acute bleomycin-induced lung injury. These findings suggest a protective and anti-inflammatory role for C5, which was linked to the regulation of matrix metalloproteinases involved in cell migration. In contrast, C5 had a detrimental effect during chronic stages of bleomycin-induced injury, indicating a profibrotic role for C5. This deleterious activity for C5 was associated with expression of the fibrogenic cytokine TGF-beta1 and matrix metalloproteinase-3, an important mediator in fibroblast contraction. Altogether, our data reveal novel and opposing roles for C5 in both inflammation and tissue repair. Furthermore, these findings provide insight into the development of new therapeutic strategies for idiopathic pulmonary fibrosis patients.

The protective effect of recombinant human keratinocyte growth factor on radiation-induced pulmonary toxicity in rats

PURPOSE

Radiation-induced lung toxicity is a significant dose-limiting side effect of radiotherapy for thoracic tumors. Recombinant human keratinocyte growth factor (rHuKGF) has been shown to be a mitogen for type II pneumocytes. The purpose of this study was to determine whether rHuKGF prevents or ameliorates the severity of late lung damage from fractionated irradiation in a rat model.

METHODS AND MATERIALS

Female Fisher 344 rats were irradiated to the right hemithorax with a dose of 40 Gy/5 fractions/5 days. rHuKGF at dose of 5 mg/kg or 15 mg/kg was given via a single intravenous injection 10 min after the last fraction of irradiation. Animals were followed for 6 months after irradiation.

RESULTS

The breathing rate increased beginning at 6 weeks and reached a peak at 14 weeks after irradiation. The average breathing frequencies in the irradiated groups with rHuKGF (5 mg/kg and 15 mg/kg) treatment were significantly lower than that in the group receiving radiation without rHuKGF (116.5 +/- 1.0 and 115.2 +/- 0.8 vs 123.5 +/- 1.2 breaths/min, p < 0.01). The severity of lung fibrosis and the level of immunoreactivity of integrin alphavbeta6, TGFbeta1, type II TGFbeta receptor, Smad3, and phosphorylated Smad2/3 were significantly decreased only in the group receiving irradiation plus high-dose rHuKGF treatment compared with irradiation plus vehicle group, suggesting a dose response for the effect of rHuKGF.

CONCLUSIONS

This study is the first to demonstrate that rHuKGF treatment immediately after irradiation protects against late radiation-induced pulmonary toxicity. These results suggest that restoration of the integrity of the pulmonary epithelium via rHuKGF stimulation may downregulate the TGF-beta-mediated fibrosis pathway. These data also support the use of rHuKGF in a clinical trial designed to prevent radiation-induced lung injury.

Increase in p21 expression independent of the p53 pathway in bleomycin-induced lung fibrosis

Although a number of animal models have been used to study the pathogenesis of lung disease, to date few studies have looked at changed in the expression of cell cycle regulatory genes. We have studied the variation in the expression of p21, p53, p27 and PCNA in bleomycin-induced lung fibrosis using animal mouse models using immuno-histochemistry and gene-expression analysis. No difference in the p53, PCNA and p27 expressions were observed from the bleomycin-induced fibrosis when compared to saline-induced non-fibrotic lungs. Although no difference in nuclear p21 expression was observed, the level of cytoplasmic p21 expression was found to be higher in fibrotic lungs at day 14 after bleomycin injection. p21 expression was found to increase independent of p53 in fibrotic lungs at 14 days after bleomycin induction.

Syk tyrosine kinase participates in beta1-integrin signaling and inflammatory responses in airway epithelial cells

The protein tyrosine kinase Syk is critically involved in immunoreceptor signaling in hematopoietic cells. Recent studies demonstrate Syk expression in nonhematopoietic cells, including fibroblasts, endothelial cells, hepatocytes, and breast epithelium. However, the role of Syk in these cells is uncertain. We hypothesized that Syk is expressed in respiratory epithelial cells (EC) and that it functions as a signaling molecule involved in inflammatory responses in the epithelium. With the use of immunohistochemistry, Western blot, PCR, and laser scanning confocal microscopy, Syk was detected in human, rat, and mouse bronchial epithelium in situ and in cultured human bronchial EC in primary cells and the cell lines HS-24 and BEAS-2B. Syk-dependent signaling pathways in EC were initiated by engagement of beta1-integrin receptors. Stimulation of beta1-integrin receptors by fibronectin or antibody cross-linking caused redistribution of Syk from a cytoplasmic to plasma membrane localization. In stimulated cells, Syk and beta1-integrin colocalized. In addition, following beta1-integrin receptor engagement, tyrosine phosphorylation of Syk was observed. Expression of the intercellular adhesion molecule-1 (ICAM-1) and production of IL-6, both important molecules in lung inflammation, was downregulated in EC treated with Syk small interfering RNA or Syk inhibitor piceatannol. We propose that Syk is involved in signaling pathways induced by integrin engagement in airway EC. Syk-mediated signaling regulates IL-6 and ICAM-1 expression and may be important in the pathophysiology of lung inflammation.

Activation of latent transforming growth factor beta 1 and inhibition of matrix metalloprotease activity by a thrombospondin-like tripeptide linked to elaidic acid

Impaired wound healing and skin aging are characterized by neutral protease-mediated destruction of matrix macromolecules associated with disturbance in tissue repair. We synthesized a fatty acyl-peptide derivative at aims to simultaneously activate latent TGF-beta through its peptide domain, KFK, and inhibit MMPs through its lipophilic moiety, elaidic acid. Elaidyl-KFK as well as KFK were shown to activate LAP-TGF-beta both in vitro, using a solid phase assay with immobilized LAP-TGF-beta, and ex vivo using human dermal fibroblasts cultures. In both assays, as much as up to 10% of LAP-TGF-beta added could be recovered as active form. KQK, KQFK as well as their lipopeptide counterparts were inactive. Elaidyl-KFK-mediated LAP-TGF-beta activation led to up-regulation of collagen and TIMP-1 production and down regulation of PMA-induced MMP-1 expression in fibroblasts cultures. Those effects could be suppressed by supplementing cell culture medium with blocking TGF-beta antibody. Elaidyl-KFK inhibited MMP-2, MMP-9, MMP-3, MMP-1, in vitro with IC(50) equal to 1.2, 1.0, 0.24 and 8.9 microM, respectively. Its ex vivo inhibitory capacity, as assessed using skin tissue sections, towards the elastin-degrading capacity of MMP-9 was even more pronounced. At a 1 microM concentration, the lipopeptide decreased by up to 80% enzyme activity. Thus, "Lipospondin," i.e. elaidyl-KFK might be considered as a promising model compound to prevent age-associated dermal alterations.

Gene expression profile in human late radiation enteritis obtained by high-density cDNA array hybridization

Late radiation enteritis is a sequela of radiation therapy to the abdomen. The pathogenic process is poorly understood at the molecular level. cDNA array analysis was used to provide new insights into the pathogenesis of this disorder. Gene profiles of six samples of fibrotic bowel tissue from patients with radiation enteritis and six healthy bowel tissue samples from patients without radiation enteritis were compared using membrane-based arrays containing 1314 cDNAs. Results were confirmed with real-time RT-PCR and Western blot analysis. Array analysis identified many differentially expressed genes involved in fibrosis, stress response, inflammation, cell adhesion, intracellular and nuclear signaling, and metabolic pathways. Increased expression of genes coding for proteins involved in the composition and remodeling of the extracellular matrix, along with altered expression of genes involved in cell- to-cell and cell-to-matrix interactions, were observed mainly in radiation enteritis samples. Stress, inflammatory responses, and antioxidant metabolism were altered in radiation enteritis as were genes coding for recruitment of lymphocytes and macrophages. The Rho/HSP27 (HSPB1)/zyxin pathway, involved in tissue contraction and myofibroblast transdifferentiation, was also altered in radiation enteritis, suggesting that this pathway could be related to the fibrogenic process. Our results provide a global and integrated view of the alteration of gene expression associated with radiation enteritis. They suggest that radiation enteritis is a dynamic process involving constant remodeling of each structural component of the intestinal tissue, i.e. the mucosa, the mesenchyme, and blood vessels. Functional studies will be necessary to validate the present results.

Expression of transforming growth factor beta (TGF-beta1) in human epithelial alveolar cells: a pro-inflammatory mediator independent pathway

Regulation of transforming growth factor beta 1 (TGF-beta1) expression remains unclear. Inflammation has been inferred to play a major role in stimulating TGF-beta1 production since high concentrations of TGF-beta1 have been found in the lungs of patients with various diffuse inflammatory lung diseases. To establish an association between inflammation and TGF-beta1 expression, human alveolar epithelial (A549) cells were co-cultured with lipopolysaccharide (LPS), Tumor necrosis factor alpha (TNFalpha), Interleukin 1 beta (IL-1beta) and Interleukin 8 (IL-8) for 12 hours. Total and bioactive TGF-beta1 protein were then measured. A549 cells transiently transfected with a plasmid containing the TGF-beta1 promoter linked to a luciferase reported gene were then co-cultured with the same inflammatory peptides for 12 hours and TGF-beta1 promoter activity determined. Nuclear transcription factors AP-1 (c-jun) or NF-kappa (p65, p50 and p105) were over expressed in A549 cells transiently transfected with the TGF-beta1 promoter and TGF-beta1 promoter activity subsequently measured. Stimulation with inflammatory signals LPS, TNFalpha, IL-1beta, IL-8 resulted in no increase of total or bioactive TGF-beta1 activity above constitutive concentrations in vitro. TGF-beta1 promoter activity was also unchanged from baseline levels in response to the same inflammatory peptides. Expression of c-jun however led to significant increases of TGF-beta1 promoter activity over constitutive levels. In contrast p65 and p105 expression resulted in inhibition of TGF-beta1 promoter activity below baseline levels. We conclude that in a human alveolar epithelial cell line, inflammation does not regulate TGF-beta1 expression. These studies suggest that in lung pathologies such as asthma, lung fibrosis and CLD, TGF-beta1 production may involve pathways independent of inflammatory mediators LPS, TNFalpha, IL-1beta and IL-8.

The role of chemokines in the pathogenesis of scleroderma

PURPOSE OF REVIEW

The triad of pathologic changes that defines systemic sclerosis (scleroderma) includes immune system activation with autoimmunity; an obliterative, proliferative small vessel vasculopathy; and fibrosis. Available data suggest that several cytokines, including chemokines, contribute to the development of scleroderma complications. This review focuses on chemokines and their contribution to tissue fibrosis and pulmonary hypertension in scleroderma.

RECENT FINDINGS

Proteins and mRNAs for monocyte chemoattractant protein-1; pulmonary and activation-regulated chemokine; macrophage inflammatory protein-1, regulated upon activation normal T cell expressed and secreted; interleukin-8; and transforming growth factor-beta have been found in increased amounts in blood or involved tissue from scleroderma patients. These factors are likely to contribute directly to tissue damage in scleroderma through several pathways, including stimulation of extracellular matrix production, induction of TGF-beta production and activation, and chemoattraction of T cells and nonspecific inflammatory cells into tissues.

SUMMARY

Multiple chemokines are part of the pathologic network that causes tissue damage in scleroderma, and, as such, may provide therapeutic targets in scleroderma.

[Interstitial lung disease]

Molecular investigation into the physiopathology of interstitial lung diseases has gained special interest through the trials carried out in the last decade. These trials seem to point at the role played by certain molecules, such as cytokines (transforming growth factor, platelet derived growth factor) and integrins, in the processes that lead to pulmonary fibrosis during the course of interstitial lung disease. They also demonstrate the important role that angiotensin II plays in increasing the secretion of transforming growth factor by several cells. The above-mentioned studies allow new therapeutic approaches to be considered which will possibly improve the serious prognosis of such diseases once they have reached the last stage of their course: pulmonary fibrosis.

Injury and repair in lung and airways

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are common causes of morbidity and mortality in the intensive care unit. ALI/ARDS occurs as a result of systemic inflammation, usually triggered by a microorganism. Activation of leukocytes and release of proinflammatory mediators from multiple cellular sources result in both local and distant tissue injury. Tumor necrosis factor-alpha and interleukin-1 beta are the best characterized of the proinflammatory cytokines contributing to ALI/ARDS and subsequent fibrosis. The ultimate clinical course of ALI/ARDS often is determined by the ability of the injured lung to repopulate the alveolar epithelium with functional cells. Death may occur when fibrosis predominates the healing response, as it results in worsening lung compliance and oxygenation. The rodent bleomycin model of lung fibrosis allows the use of molecular tools to dissect the cellular and subcellular processes leading to fibrosis. The elements of this response may provide therapeutic targets for the prevention of this devastating complication of ALI/ARDS.

Occurrence of an activated, profibrotic pattern of gene expression in lung CD8+ T cells from scleroderma patients

OBJECTIVE

Pulmonary fibrosis is a major cause of death in scleroderma patients. Previous studies have shown an increase in CD8+ T cells in the lungs of scleroderma patients. In the present study, we sought to determine whether activated CD8+ T cells contribute to pulmonary fibrosis in scleroderma patients through the production and activation of profibrotic mediators.

METHODS

CD8+ cells were isolated from bronchoalveolar lavage fluid obtained from 19 scleroderma patients and 7 healthy subjects. The phenotype of these cells was determined using DNA array technology. Expression of selected genes was confirmed in real-time polymerase chain reaction and enzyme-linked immunosorbent assay experiments.

RESULTS

Hierarchical clustering of gene expression profiles revealed 2 groups of subjects. Group 1 consisted of 11 patients (8 with and 3 without lung inflammation). Group 2 consisted of 15 subjects (7 healthy controls and 2 patients with and 6 without lung inflammation). Gene expression in group 1 indicated T cell activation, a type 2 phenotype, production of profibrotic factors and matrix metalloproteinases, and reduced activation-induced cell death. Increased expression of beta6 integrin messenger RNA by CD8+ T cells in group 1 suggested the possibility that these T cells might induce cell-contact-dependent activation of latent transforming growth factor beta (TGFbeta).

CONCLUSION

A subset of scleroderma patients at higher risk of progressive lung disease have activated, long-lived CD8+ T cells in their lungs that could promote fibrosis directly, through production of profibrotic factors such as interleukin-4 and oncostatin M, as well as indirectly, through activation of TGFbeta.

Temporal response and localization of integrins beta1 and beta3 in the heart after myocardial infarction: regulation by cytokines

BACKGROUND

Integrins are involved in structural remodeling and tissue repair. This study aimed to elucidate the role of the beta-integrins in cardiac remodeling after myocardial infarction (MI).

METHODS AND RESULTS

The MI model was created by ligation of the left anterior descending coronary artery in rats. We detected cardiac integrins beta1 and beta3 gene expression (quantitative in situ hybridization) and protein production (Western blot and immunohistochemistry) and potential regulation by tumor necrosis factor (TNF) using neonatal ventricular myocytes and TNF-/- knockout mice. Integrins beta1 and beta3 gene expression and protein production were low in sham-operated hearts. After MI, the beta1 and beta3 mRNA and proteins were significantly increased at the site of MI at day 3, reached a peak at day 7, and gradually declined thereafter. Integrin beta1A localized primarily in fibroblasts and inflammatory cells, beta1D localized in myocytes, and integrin beta3 was associated primarily with endothelial and smooth muscle cells in peri-infarct vessels. In cultured myocytes, there was isoform transition from the adult beta1D to the fetal beta1A on exposure to TNF-alpha. This was confirmed in vivo in the peri-infarct myocytes, but the transition was voided in TNF-/--knockout mice.

CONCLUSIONS

Integrins beta1 and beta3 are significantly activated in the infarcted myocardium. Integrin beta1 is active particularly at sites of inflammation and fibrosis, whereas integrin beta3 localizes to vessels in the peri-infarct zone in a temporally coordinated manner. Integrin beta1D to beta1A isoform transition in myocytes is regulated by TNF-alpha.

The integrin alphaVbeta6 binds and activates latent TGFbeta3

Transforming growth factors-beta (TGFbeta1, 2 and 3) are secreted in a complex with their propeptides (latency-associated peptide 1 (LAP1), 2 and 3). TGFbeta signaling requires the dissociation of LAP and TGFbeta, a process termed latent TGFbeta activation. This process is a critical but incompletely understood step in the regulation of TGFbeta function. In particular, the extent to which activation mechanisms differ among the three TGFbeta isoforms is relatively unexplored. We show here that alphaVbeta6 binds and activates latent TGFbeta3.