Titration of non-replicating adenovirus as a vector for transducing active TGF-beta1 gene expression causing inflammation and fibrogenesis in the lungs of C57BL/6 mice

Hypoxia Induces Alterations in the Circadian Rhythm in Patients with Chronic Respiratory Diseases

The function of the circadian cycle is to determine the natural 24 h biological rhythm, which includes physiological, metabolic, and hormonal changes that occur daily in the body. This cycle is controlled by an internal biological clock that is present in the body's tissues and helps regulate various processes such as sleeping, eating, and others. Interestingly, animal models have provided enough evidence to assume that the alteration in the circadian system leads to the appearance of numerous diseases. Alterations in breathing patterns in lung diseases can modify oxygenation and the circadian cycles; however, the response mechanisms to hypoxia and their relationship with the clock genes are not fully understood. Hypoxia is a condition in which the lack of adequate oxygenation promotes adaptation mechanisms and is related to several genes that regulate the circadian cycles, the latter because hypoxia alters the production of melatonin and brain physiology. Additionally, the lack of oxygen alters the expression of clock genes, leading to an alteration in the regularity and precision of the circadian cycle. In this sense, hypoxia is a hallmark of a wide variety of lung diseases. In the present work, we intended to review the functional repercussions of hypoxia in the presence of asthma, chronic obstructive sleep apnea, lung cancer, idiopathic pulmonary fibrosis, obstructive sleep apnea, influenza, and COVID-19 and its repercussions on the circadian cycles.

CFTR dysfunction in smooth muscle drives TGFβ dependent airway hyperreactivity

BACKGROUND

The primary underlying defect in cystic fibrosis (CF) is disrupted ion transport in epithelia throughout the body. It is unclear if symptoms such as airway hyperreactivity (AHR) and increased airway smooth muscle (ASM) volume in people with CF are due to inherent abnormalities in smooth muscle or are secondary to epithelial dysfunction. Transforming Growth Factor beta 1 (TGFβ) is an established genetic modifier of CF lung disease and a known driver of abnormal ASM function. Prior studies have demonstrated that CF mice develop greater AHR, goblet cell hyperplasia, and ASM hypertrophy after pulmonary TGFβ exposure. However, the mechanism driving these abnormalities in CF lung disease, specifically the contribution of CFTR loss in ASM, was unknown.

METHODS

In this study, mice with smooth muscle-specific loss of CFTR function (Cftrfl/fl; SM-Cre mice) were exposed to pulmonary TGFβ. The impact on lung pathology and physiology was investigated through examination of lung mechanics, Western blot analysis, and pulmonary histology.

RESULTS

Cftrfl/fl; SM-Cre mice treated with TGFβ demonstrated greater methacholine-induced AHR than control mice. However, Cftrfl/fl; SM-Cre mice did not develop increased inflammation, ASM area, or goblet cell hyperplasia relative to controls following TGFβ exposure.

CONCLUSIONS

These results demonstrate a direct smooth muscle contribution to CF airway obstruction mediated by TGFβ. Dysfunction in non-epithelial tissues should be considered in the development of CF therapeutics, including potential genetic therapies.

Is there a role for specialized pro-resolving mediators in pulmonary fibrosis?

Pulmonary fibrotic diseases are characterized by proliferation of lung fibroblasts and myofibroblasts and excessive deposition of extracellular matrix proteins. Depending on the specific form of lung fibrosis, there can be progressive scarring of the lung, leading in some cases to respiratory failure and/or death. Recent and ongoing research has demonstrated that resolution of inflammation is an active process regulated by families of small bioactive lipid mediators termed "specialized pro-resolving mediators." While there are many reports of beneficial effects of SPMs in animal and cell culture models of acute and chronic inflammatory and immune diseases, there have been fewer reports investigating SPMs and fibrosis, especially pulmonary fibrosis. Here, we will review evidence that resolution pathways are impaired in interstitial lung disease, and that SPMs and other similar bioactive lipid mediators can inhibit fibroblast proliferation, myofibroblast differentiation, and accumulation of excess extracellular matrix in cell culture and animal models of pulmonary fibrosis, and we will consider future therapeutic implications of SPMs in fibrosis.

Repetitive schistosoma exposure causes perivascular lung fibrosis and persistent pulmonary hypertension

BACKGROUND

Pulmonary hypertension (PH) can occur as a complication of schistosomiasis. In humans, schistosomiasis-PH persists despite antihelminthic therapy and parasite eradication. We hypothesized that persistent disease arises as a consequence of exposure repetition.

METHODS

Following intraperitoneal sensitization, mice were experimentally exposed to Schistosoma eggs by intravenous injection, either once or three times repeatedly. The phenotype was characterized by right heart catheterization and tissue analysis.

RESULTS

Following intraperitoneal sensitization, a single intravenous Schistosoma egg exposure resulted in a PH phenotype that peaked at 7-14 days, followed by spontaneous resolution. Three sequential exposures resulted in a persistent PH phenotype. Inflammatory cytokines were not significantly different between mice exposed to one or three egg doses, but there was an increase in perivascular fibrosis in those who received three egg doses. Significant perivascular fibrosis was also observed in autopsy specimens from patients who died of this condition.

CONCLUSIONS

Repeatedly exposing mice to schistosomiasis causes a persistent PH phenotype, accompanied by perivascular fibrosis. Perivascular fibrosis may contribute to the persistent schistosomiasis-PH observed in humans with this disease.

Cymbopogon winterianus Essential Oil Attenuates Bleomycin-Induced Pulmonary Fibrosis in a Murine Model

The essential oil of Cymbopogon winterianus (EOCW) is a natural product with antioxidant, anti-inflammatory, and antifibrotic properties. We studied the effect of EOCW in the progression of histological changes of pulmonary fibrosis (PF) in a rodent model. The oil was obtained by hydrodistillation and characterized using gas chromatography–mass spectrometry. Intratracheal instillation of bleomycin was performed in 30 rats to induce PF, while Sham animals were subjected to instillation of saline solution. The treatment was performed using daily oral administration of distilled water, EOCW at 50, 100, and 200 mg/kg, and deflazacort (DFC). After 28 days, hemogram and bronchoalveolar lavage fluid (BALF), tissue levels of malondialdehyde (MDA), superoxide dismutase (SOD), and catalase (CAT) were assayed. Histological grading of PF, immunohistochemical expression of α-smooth muscle actin (α-SMA), and transforming growth factor-β (TGF-β) were also analyzed. The EOCW major compounds were found to be citronellal, geraniol, and citronellol. EOCW significantly reduced inflammation in BALF, reduced MDA levels, and increased SOD activity. EOCW attenuated histological grading of PF and reduced immunohistochemical expression of α-SMA and TGF-β in a dose-dependent way, likely due to the reduction of oxidative stress, inflammation, and TGF-β-induced myofibroblast differentiation.

Subacute TGFβ Exposure Drives Airway Hyperresponsiveness in Cystic Fibrosis Mice through the PI3K Pathway

Cystic fibrosis (CF) is a lethal genetic disease characterized by progressive lung damage and airway obstruction. The majority of patients demonstrate airway hyperresponsiveness (AHR), which is associated with more rapid lung function decline. Recent studies in the neonatal CF pig demonstrated airway smooth muscle (ASM) dysfunction. These findings, combined with observed CF transmembrane conductance regulator (CFTR) expression in ASM, suggest that a fundamental defect in ASM function contributes to lung function decline in CF. One established driver of AHR and ASM dysfunction is transforming growth factor (TGF) β1, a genetic modifier of CF lung disease. Prior studies demonstrated that TGFβ exposure in CF mice drives features of CF lung disease, including goblet cell hyperplasia and abnormal lung mechanics. CF mice displayed aberrant responses to pulmonary TGFβ, with elevated PI3K signaling and greater increases in lung resistance compared with controls. Here, we show that TGFβ drives abnormalities in CF ASM structure and function through PI3K signaling that is enhanced in CFTR-deficient lungs. CF and non-CF mice were exposed intratracheally to an adenoviral vector containing the TGFβ1 cDNA, empty vector, or PBS only. We assessed methacholine-induced AHR, bronchodilator response, and ASM area in control and CF mice. Notably, CF mice demonstrated enhanced AHR and bronchodilator response with greater ASM area increases compared with non-CF mice. Furthermore, therapeutic inhibition of PI3K signaling mitigated the TGFβ-induced AHR and goblet cell hyperplasia in CF mice. These results highlight a latent AHR phenotype in CFTR deficiency that is enhanced through TGFβ-induced PI3K signaling.

Subacute TGFβ expression drives inflammation, goblet cell hyperplasia, and pulmonary function abnormalities in mice with effects dependent on CFTR function

Cystic fibrosis (CF) produces variable lung disease phenotypes that are, in part, independent of the CF transmembrane conductance regulator ( CFTR) genotype. Transforming growth factor-β (TGFβ) is the best described genetic modifier of the CF phenotype, but its mechanism of action is unknown. We hypothesized that TGFβ is sufficient to drive pathognomonic features of CF lung disease in vivo and that CFTR deficiency enhances susceptibility to pathological TGFβ effects. A CF mouse model and littermate controls were exposed intratracheally to an adenoviral vector containing the TGFβ1 cDNA (Ad-TGFβ), empty vector, or PBS only. Studies were performed 1 wk after treatment, including lung mechanics, collection of bronchoalveolar lavage fluid, and analysis of lung histology, RNA, and protein. CF and non-CF mice showed similar weight loss, inflammation, goblet cell hyperplasia, and Smad pathway activation after Ad-TGFβ treatment. Ad-TGFβ produced greater abnormalities in lung mechanics in CF versus control mice, which was uniquely associated with induction of phosphoinositide 3-kinase and mitogen-activated protein kinase signaling. CFTR transcripts were reduced, and epithelial sodium channel transcripts were increased in CF and non-CF mice, whereas the goblet cell transcription factors, forkhead ortholog A3 and SAM-pointed domain-containing ETS-like factor, were increased in non-CF but not CF mice following Ad-TGFβ treatment. Pulmonary TGFβ1 expression was sufficient to produce pulmonary remodeling and abnormalities in lung mechanics that were associated with both shared and unique cell signaling pathway activation in CF and non-CF mice. These results highlight the multifunctional impact of TGFβ on pulmonary pathology in vivo and identify cellular-response differences that may impact CF lung pathology.

CXCR7 attenuates the TGF-β-induced endothelial-to-mesenchymal transition and pulmonary fibrosis

Lung fibrosis is a progressive and often fatal lung disease characterized by fibroblast proliferation and excessive deposition of extracellular matrix in the lungs.

BRD4 mediates NF-κB-dependent epithelial-mesenchymal transition and pulmonary fibrosis via transcriptional elongation

Chronic epithelial injury triggers a TGF-β-mediated cellular transition from normal epithelium into a mesenchymal-like state that produces subepithelial fibrosis and airway remodeling. Here we examined how TGF-β induces the mesenchymal cell state and determined its mechanism. We observed that TGF-β stimulation activates an inflammatory gene program controlled by the NF-κB/RelA signaling pathway. In the mesenchymal state, NF-κB-dependent immediate-early genes accumulate euchromatin marks and processive RNA polymerase. This program of immediate-early genes is activated by enhanced expression, nuclear translocation, and activating phosphorylation of the NF-κB/RelA transcription factor on Ser276, mediated by a paracrine signal. Phospho-Ser276 RelA binds to the BRD4/CDK9 transcriptional elongation complex, activating the paused RNA Pol II by phosphorylation on Ser2 in its carboxy-terminal domain. RelA-initiated transcriptional elongation is required for expression of the core epithelial-mesenchymal transition transcriptional regulators SNAI1, TWIST1, and ZEB1 and mesenchymal genes. Finally, we observed that pharmacological inhibition of BRD4 can attenuate experimental lung fibrosis induced by repetitive TGF-β challenge in a mouse model. These data provide a detailed mechanism for how activated NF-κB and BRD4 control epithelial-mesenchymal transition initiation and transcriptional elongation in model airway epithelial cells in vitro and in a murine pulmonary fibrosis model in vivo. Our data validate BRD4 as an in vivo target for the treatment of pulmonary fibrosis associated with inflammation-coupled remodeling in chronic lung diseases.

Regulation of transforming growth factor-beta1 (TGF-β1)-induced pro-fibrotic activities by circadian clock gene BMAL1

BACKGROUND

BMAL1 is a transcriptional activator of the molecular clock feedback network. Besides its role in generating circadian rhythms, it has also been shown to be involved in the modulation of cell proliferation, autophagy and cancer cell invasion. However, the role of BMAL1 in pulmonary fibrogenesis is still largely unknown. In this study, we investigated the crosstalk between BMAL1 and the signaling transduction and cellular activities of TGF-β1, a key player in lung fibrogenesis.

METHODS

Lungs from wild type and TGF-β1-adenovirus-infected mice were harvested and homogenized for isolation of RNA and protein. RT-PCR and Western Blotting were employed to measure the expression level of clock genes and TGF-β1-induced downstream target genes. siRNA against human BMAL1 gene was transfected by using lipofectamine RNAiMAX to knockdown the endogenous BMAL1 in both lung epithelial cells and fibroblasts.

RESULTS

Our results showed that TGF-β1 is able to up-regulate BMAL1 expression in both lung epithelial cells and normal lung fibroblasts. In animal models of pulmonary fibrosis, BMAL1 expression was also significantly higher in adenovirus-TGF-β1-infected mice than in the control group. Interestingly, BMAL1 was mostly found in a deacetylated form in the presence of TGF-β1. Importantly, siRNA-mediated knockdown of BMAL1 significantly attenuated the canonical TGF-β1 signaling pathway and altered TGF-β1-induced epithelial-mesenchymal transition and MMP9 production in lung epithelial cells. In addition, BMAL1 knockdown inhibited the fibroblast to myofibroblast differentiation of normal human lung fibroblasts.

CONCLUSIONS

Our results indicate that activation of TGF-β1 promotes the transcriptional induction of BMAL1. Furthermore, BMAL1 is required for the TGF-β1-induced signaling transduction and pro-fibrotic activities in the lung.

The footprint of TGF-β in airway remodeling of the mustard lung

Mustard lung is a major pulmonary complication in individuals exposed to sulfur mustard (SM) gas during the Iran-Iraq war. It shares common pathological and clinical features with some chronic inflammatory lung disorders, particularly chronic obstructive pulmonary disease (COPD). Airway remodeling, which is one of the main causes of lung dysfunction and the dominant phenomenon of chronic pulmonary diseases, is seen in the mustard lung. Among all mediators involved in the remodeling process, the transforming growth factor (TGF)-β plays a pivotal role in lung fibrosis and consequently in the airway remodeling. Regarding the high levels of this mediator detected in mustard lung patients, in the present study, we have discussed the possible roles of TGF-β in airway remodeling (including epithelial layer damage, subepithelial fibrosis and angiogenesis). Finally, based on TGF-β targeting, we have reviewed new airway remodeling therapeutic approaches.

Thiol-redox antioxidants protect against lung vascular endothelial cytoskeletal alterations caused by pulmonary fibrosis inducer, bleomycin: comparison between classical thiol-protectant, N-acetyl-L-cysteine, and novel thiol antioxidant, N,N'-bis-2-mercaptoethyl isophthalamide

Lung vascular alterations and pulmonary hypertension associated with oxidative stress have been reported to be involved in idiopathic lung fibrosis (ILF). Therefore, here, we hypothesize that the widely used lung fibrosis inducer, bleomycin, would cause cytoskeletal rearrangement through thiol-redox alterations in the cultured lung vascular endothelial cell (EC) monolayers. We exposed the monolayers of primary bovine pulmonary artery ECs to bleomycin (10 µg) and studied the cytotoxicity, cytoskeletal rearrangements, and the macromolecule (fluorescein isothiocyanate-dextran, 70,000 mol. wt.) paracellular transport in the absence and presence of two thiol-redox protectants, the classic water-soluble N-acetyl-L-cysteine (NAC) and the novel hydrophobic N,N'-bis-2-mercaptoethyl isophthalamide (NBMI). Our results revealed that bleomycin induced cytotoxicity (lactate dehydrogenase leak), morphological alterations (rounding of cells and filipodia formation), and cytoskeletal rearrangement (actin stress fiber formation and alterations of tight junction proteins, ZO-1 and occludin) in a dose-dependent fashion. Furthermore, our study demonstrated the formation of reactive oxygen species, loss of thiols (glutathione, GSH), EC barrier dysfunction (decrease of transendothelial electrical resistance), and enhanced paracellular transport (leak) of macromolecules. The observed bleomycin-induced EC alterations were attenuated by both NAC and NBMI, revealing that the novel hydrophobic thiol-protectant, NBMI, was more effective at µM concentrations as compared to the water-soluble NAC that was effective at mM concentrations in offering protection against the bleomycin-induced EC alterations. Overall, the results of the current study suggested the central role of thiol-redox in vascular EC dysfunction associated with ILF.

Adenoviral gene transfer of endothelin-1 in the lung induces pulmonary fibrosis through the activation of focal adhesion kinase

Endothelin-1 (ET-1) has been implicated in the development of pulmonary fibrosis, based on its capacity in vitro to promote extracellular matrix (ECM) production and contraction, and on studies showing elevated expression of ET-1 and its receptors in patients with pulmonary fibrosis. However, the in vivo fibrogenic effect of ET-1 is not well characterized. We used the adenoviral-mediated gene transfer of ET-1 to overexpress ET-1 transiently in murine lungs by intratracheal administration. An increased expression of ET-1 for 3 to 10 days after injection resulted in a moderate but reversible fibrotic response, peaking on Day 14 after infection and characterized by the deposition of ECM components, myofibroblast formation, and a significant inflammatory infiltrate, mainly in the peribronchiolar/perivascular region. Adenoviral-mediated ET-1 overexpression activated focal adhesion kinase (FAK) both in vitro, using primary murine lung fibroblasts, and in vivo, intratracheally administered in the lungs of mice. The inhibition of FAK with the compound PF-562,271 prevented ET-1-mediated collagen deposition and myofibroblast formation, thereby preventing the development of lung fibrosis. In conclusion, we demonstrate that the overexpression of ET-1 directly in the lungs of mice can initiate a fibrogenic response characterized by increased ECM deposition and myofibroblast formation, and that this effect of ET-1 can be prevented by inhibition of FAK. Our data suggest that the ET-1/FAK axis may contribute importantly to the pathogenesis of fibrotic disorders, and highlight FAK as a potential therapeutic target in these devastating diseases.

Ly6Chi monocytes direct alternatively activated profibrotic macrophage regulation of lung fibrosis

RATIONALE

Idiopathic pulmonary fibrosis (IPF) is a devastating disease. Antiinflammatory therapies, including corticosteroids, are of no benefit. The role of monocytes and macrophages is therefore controversial.

OBJECTIVES

To define the role of monocytes and macrophages during lung fibrogenesis and resolution, and explore the phenotype of the cells involved.

METHODS

We used multiple in vivo depletional strategies, backed up by adoptive transfer techniques. Further studies were performed on samples from patients with IPF.

MEASUREMENTS AND MAIN RESULTS

Depletion of lung macrophages during fibrogenesis reduced pulmonary fibrosis as measured by lung collagen (P = 0.0079); fibrosis score (P = 0.0051); and quantitative polymerase chain reaction for surrogate markers of fibrosis Col1 (P = 0.0083) and a-smooth muscle actin (P = 0.0349). There was an associated reduction in markers of the profibrotic alternative macrophage activation phenotype, Ym1 (P = 0.0179), and Arginase 1. The alternative macrophage marker CD163 was expressed on lung macrophages from patients with IPF. Depletion of Ly6Chi circulating monocytes reduced pulmonary fibrosis (P = 0.0052) and the number of Ym1- positive alternatively activated lung macrophages (P = 0.0310). Their adoptive transfer during fibrogenesis exacerbated fibrosis (P = 0.0304); however, adoptively transferred CD45.1 Ly6Chi cells were not found in the lungs of recipient CD45.2 mice.

CONCLUSIONS

We demonstrate the importance of circulating monocytes and lung macrophages during pulmonary fibrosis, and emphasize the importance of the alternatively activated macrophage phenotype. We show that Ly6Chi monocytes facilitate the progression of pulmonary fibrosis, but are not obviously engrafted into lungs thereafter. Finally, we provide empirical data to suggest that macrophages may have a resolution-promoting role during the reversible phase of bleomycin-induced pulmonary fibrosis.

TGFβ signaling in lung epithelium regulates bleomycin-induced alveolar injury and fibroblast recruitment

The response of alveolar epithelial cells (AECs) to lung injury plays a central role in the pathogenesis of pulmonary fibrosis, but the mechanisms by which AECs regulate fibrotic processes are not well defined. We aimed to elucidate how transforming growth factor-β (TGFβ) signaling in lung epithelium impacts lung fibrosis in the intratracheal bleomycin model. Mice with selective deficiency of TGFβ receptor 2 (TGFβR2) in lung epithelium were generated and crossed to cell fate reporter mice that express β-galactosidase (β-gal) in cells of lung epithelial lineage. Mice were given intratracheal bleomycin (0.08 U), and the following parameters were assessed: AEC death by terminal deoxynucleotidyl transferase dUTP-mediated nick-end labeling assay, inflammation by total and differential cell counts from bronchoalveolar lavage, fibrosis by scoring of trichrome-stained lung sections, and total lung collagen content. Mice with lung epithelial deficiency of TGFβR2 had improved AEC survival, despite greater lung inflammation, after bleomycin administration. At 3 wk after bleomycin administration, mice with epithelial TGFβR2 deficiency showed a significantly attenuated fibrotic response in the lungs, as determined by semiquantitatve scoring and total collagen content. The reduction in lung fibrosis in these mice was associated with a marked decrease in the lung fibroblast population, both total lung fibroblasts and epithelial-to-mesenchymal transition-derived (S100A4(+)/β-gal(+)) fibroblasts. Attenuation of TGFβ signaling in lung epithelium provides protection from bleomycin-induced fibrosis, indicating a critical role for the epithelium in transducing the profibrotic effects of this cytokine.

Interstitial lung diseases in children

Interstitial lung disease (ILD) in infants and children comprises a large spectrum of rare respiratory disorders that are mostly chronic and associated with high morbidity and mortality. These disorders are characterized by inflammatory and fibrotic changes that affect alveolar walls. Typical features of ILD include dyspnea, diffuse infiltrates on chest radiographs, and abnormal pulmonary function tests with restrictive ventilatory defect and/or impaired gas exchange. Many pathological situations can impair gas exchange and, therefore, may contribute to progressive lung damage and ILD. Consequently, diagnosis approach needs to be structured with a clinical evaluation requiring a careful history paying attention to exposures and systemic diseases. Several classifications for ILD have been proposed but none is entirely satisfactory especially in children. The present article reviews current concepts of pathophysiological mechanisms, etiology and diagnostic approaches, as well as therapeutic strategies. The following diagnostic grouping is used to discuss the various causes of pediatric ILD: 1) exposure-related ILD; 2) systemic disease-associated ILD; 3) alveolar structure disorder-associated ILD; and 4) ILD specific to infancy. Therapeutic options include mainly anti-inflammatory, immunosuppressive, and/or anti-fibrotic drugs. The outcome is highly variable with a mortality rate around 15%. An overall favorable response to corticosteroid therapy is observed in around 50% of cases, often associated with sequelae such as limited exercise tolerance or the need for long-term oxygen therapy.

TGF-β: Titan of Lung Fibrogenesis

Pulmonary fibrosis is characterized by epithelial cell injury, accumulation of myofibroblasts, and excessive deposition of collagen and other extracellular matrix elements, leading to loss of pulmonary function. Studies in both humans and animal models strongly suggest that TGF-β1 plays a pivotal role in the pathogenesis of pulmonary fibrosis. This review will first give an overview of TGF-β signaling and the effects of its inhibition on lung fibrogenesis. This overview includes information on TGF-β signal transduction pathways, the importance of TGF-β in the accumulation of myofibroblasts, the role of TGF-β in epithelial injury and apoptosis, the role of TGF-β in extracellular matrix remodeling, and the effects of inhibiting TGF-β signaling in animal models of lung fibrosis. Subsequently this review will highlight recent advances in two areas of particular interest to our research group: (1) TGF-β and proteoglycans; (2) TGF-β and histone deacetylases. Although our understanding of the role of TGF-β and its mechanisms of action in lung fibrogenesis has increased dramatically in recent years, there is still much to be learned about this important molecule, especially how TGF-β function is modulated in vivo, and its complex interactions with other factors expressed during lung injury and repair. Research in these areas will help identify novel therapeutic targets for the treatment of pulmonary fibrosis that will hopefully improve the prognosis of this devastating illness.

Adenovirus-mediated gene transfer of hIGF-IB in mouse lungs induced prolonged inflammation but no fibroproliferation

Pulmonary fibrosis (PF), the end stage of a variety of fibroproliferative lung diseases, is characterized by excessive lung mesenchymal cell activation and extracellular matrix deposition. Most PF is induced after repetitive or chronic lung inflammation; however, a significant portion of PF occurs without apparent inflammation. The mechanisms of fibroproliferation are poorly understood. Studies have shown that cytokines regulating inflammation and tissue repair processes play essential roles in the development of PF. Insulin-like growth factor I (IGF-I) has been shown to stimulate lung mesenchymal cell proliferation and extracellular matrix synthesis in vitro and is significantly elevated in patients with PF. In this study, we investigated whether human IGF-IB (hIGF-IB) expression in the lungs induces PF in a C57BL/6 mouse model. Mice were subjected to adenoviral gene transfer, and the effects of hIGF-IB expression on the lungs were examined 3, 7, 14, 21, and 42 days after gene delivery. hIGF-IB expression induced significant and prolonged inflammatory cell infiltration into the lungs, with an early neutrophil infiltration followed by a late macrophage infiltration. No significant fibroblast or matrix accumulation could be detected in the lungs of these mice. No significant collagen accumulation could be detected in vivo, despite in vitro evidence that hIGF-IB induces collagen mRNA expression in fibroblasts. Therefore, IGF-IB alone is not sufficient to induce fibrosis, and it is possible that a coactivator is required to induce significant fibroproliferation in vivo.

Transforming growth factor-beta1 induces heparan sulfate 6-O-endosulfatase 1 expression in vitro and in vivo

Transforming growth factor (TGF)-beta1 plays an important role in the development of pulmonary fibrosis. In this study we examined the relationship between TGF-beta1 stimulation and the expression of heparan sulfate (HS) 6-O-endosulfatase 1 (Sulf1) in cultured normal human lung fibroblasts (NHLFs) and in murine lungs in vivo. By removing 6-O-sulfates from specific HS intrachain sites on the cell surface, Sulf1 has been shown to modulate the activities of many HS binding growth factors and morphogens including fibroblast growth factor (FGF)-2. Real time reverse transcription-PCR analysis revealed that TGF-beta1 increased Sulf1 expression in NHLFs in a dose- and time-dependent manner which was accompanied by a decrease in 6-O-sulfated disaccharides as revealed by high performance liquid chromatography analysis. Decreased ERK activation after FGF-2 stimulation was observed in TGF-beta1-treated NHLFs compared with control cells without changes in HS-dependent FGF-2 binding or FGF-2.FR1c complex formation. To study the function of Sulf1, negative control or Sulf1-specific small interference RNA (siRNA)-transfected NHLFs were stimulated with TGF-beta1. Enhanced Smad2/3 phosphorylation and elevated total Smad2 protein level were observed in Sulf1 siRNA-transfected cells and were accompanied by enhanced expression of alpha-smooth muscle actin and fibronectin. In addition, Sulf1 siRNA transfection enhanced the anti-proliferative effect of TGF-beta1. Finally Sulf1 expression was up-regulated in the lungs of mice treated with adenovirus encoding active TGF-beta1. Taken together, our data indicate that Sulf1 is a TGF-beta1-responsive gene both in vitro and in vivo and may function as a negative regulator of TGF-beta1-induced fibrogenesis.

Interaction between macrophages, TGF-beta1, and the COX-2 pathway during the inflammatory phase of skeletal muscle healing after injury

Inflammation, an important phase of skeletal muscle healing, largely involves macrophages, TGF-beta1, and the COX-2 pathway. To improve our understanding of how these molecules interact during all phases of muscle healing, we examined their roles in muscle cells in vitro and in vivo. Initially, we found that depletion of macrophages in muscle tissue led to reduced muscle regeneration. Macrophages may influence healing by inducing the production of TGF-beta1 and PGE2 in different muscle cell types. We then found that the addition of TGF-beta1 induced PGE2 production in muscle cells, an effect probably mediated by COX-2 enzyme. It was also found that TGF-beta1 enhanced macrophage infiltration in wild-type mice after muscle injury. However, this effect was not observed in COX-2(-/-) mice, suggesting that the effect of TGF-beta1 on macrophage infiltration is mediated by the COX-2 pathway. Furthermore, we found that PGE2 can inhibit the expression of TGF-beta1. PGE2 and TGF-beta1 may be involved in a negative feedback loop balancing the level of fibrosis formation during skeletal muscle healing. In conclusion, our results suggest a complex regulatory mechanism of skeletal muscle healing. Macrophages, TGF-beta1, and the COX-2 pathway products may regulate one another's levels and have profound influence on the whole muscle healing process.

Laser capture microdissection reveals dose-response of gene expression in situ consequent to asbestos exposure

The genes that mediate fibroproliferative lung disease remain to be defined. Prior studies from our laboratory showed by in situ hybridization and immunohistochemistry that the genes coding for tumour necrosis factor alpha, transforming growth factor beta, the platelet-derived growth factor A and B isoforms, and alpha-1 pro-collagen are expressed in fibroproliferative lesions that develop quickly after asbestos inhalation. These five genes, along with matrix metalloproteinase 9, a collagenase found to be increased in several lung diseases, are known to control matrix production and cell proliferation in humans and animals. Here we show by laser capture microdissection that (i) The six genes are expressed at significantly higher levels in the asbestos-exposed mice when comparing the same anatomic regions 'captured' in unexposed mice. (ii) The bronchiolar-alveolar duct (BAD) junctions, where the greatest number of fibres initially deposit, were always significantly higher than the other anatomic regions for each gene. The first alveolar duct bifurcation (ADB) generally was higher than the second ADB, the ADBs were always significantly higher than the airway walls and pleura, and the airway walls and pleura were generally higher than the unexposed tissues. (iii) Animals exposed for 3 days always exhibited significantly higher levels of gene expression at the BAD junctions and ADBs than animals exposed for 2 days. To our knowledge, this is the first demonstration of a dose-response to a toxic particle in situ, and this response appears to be dependent on the number of fibres that deposits at the individual anatomic site.

Progressive pulmonary fibrosis is mediated by TGF-beta isoform 1 but not TGF-beta3

Tissue repair is a well-orchestrated biological process involving numerous soluble mediators, and an imbalance between these factors may result in impaired repair and fibrosis. Transforming growth factor (TGF)-beta is a key profibrotic element in this process and it is thought that its three isoforms act in a similar way. Here, we report that TGF-beta3 administered to rat lungs using transient overexpression initiates profibrotic effects similar to those elicited by TGF-beta1, but causes less severe and progressive changes. The data suggest that TGF-beta3 does not lead to inhibition of matrix degradation in the same way as TGF-beta1, resulting in non-fibrotic tissue repair. Further, TGF-beta3 is able to downregulate TGF-beta1-induced gene expression, suggesting a regulatory role of TGF-beta3. TGF-beta3 overexpression results in an upregulation of Smad proteins similar to TGF-beta1, but is less efficient in inducing the ALK 5 and TGF-beta type II receptor (TbetaRII). We provide evidence that this difference may contribute to the progressive nature of TGF-beta1-induced fibrotic response, in contrast to the limited fibrosis observed following TGF-beta3 overexpression. TGF-beta3 is important in "normal wound healing", but is outbalanced by TGF-beta1 in "fibrotic wound healing" in the lung.

Tumor necrosis factor-alpha induces transforming growth factor-beta1 expression in lung fibroblasts through the extracellular signal-regulated kinase pathway

Increased expression of transforming growth factor (TGF)-beta(1) and tumor necrosis factor (TNF)-alpha are thought to play important roles in the development of pulmonary fibrosis. We recently reported that TNF-alpha upregulates TGF-beta(1) expression in primary mouse lung fibroblasts (MLFs), a key cell population in fibrogenesis. In the present study, we have investigated signal transduction pathways involved in TNF-alpha upregulation of TGF-beta(1) in both primary MLFs and the Swiss 3T3 fibroblast cell line. Treatment of fibroblasts with TNF-alpha resulted in a significant increase in TGF-beta(1) protein as measured by ELISA. The increase in protein was preceded by a 200-400% increase in TGF-beta(1) mRNA detected by quantitative, real-time, reverse transcriptase-polymerase chain reaction. Western blot analysis showed that TNF-alpha activated the extracellular signal-regulated kinase (ERK), and inhibitors of the ERK-specific mitogen-activated protein kinase pathway (PD98059 or U0126) blocked TNF-alpha induction of TGF-beta(1) mRNA and protein. mRNA stability experiments showed that TNF-alpha increased the half-life of TGF-beta(1) mRNA to more than 24 h compared with approximately 15 h in unstimulated cells. Expression of constitutively active MEK1 that selectively phosphorylates ERK was sufficient for TGF-beta(1) mRNA stabilization in Swiss 3T3 fibroblasts. These results indicate that TNF-alpha activates the ERK-specific mitogen-activated protein kinase pathway leading to increased TGF-beta(1) production in fibroblasts, primarily via a post-transcriptional mechanism that involves stabilization of the TGF-beta(1) transcript.

Early growth response gene 1-mediated apoptosis is essential for transforming growth factor beta1-induced pulmonary fibrosis

Fibrosis and apoptosis are juxtaposed in pulmonary disorders such as asthma and the interstitial diseases, and transforming growth factor (TGF)-β₁ has been implicated in the pathogenesis of these responses. However, the in vivo effector functions of TGF-β₁ in the lung and its roles in the pathogenesis of these responses are not completely understood. In addition, the relationships between apoptosis and other TGF-β₁–induced responses have not been defined. To address these issues, we targeted bioactive TGF-β₁ to the murine lung using a novel externally regulatable, triple transgenic system. TGF-β₁ produced a transient wave of epithelial apoptosis that was followed by mononuclear-rich inflammation, tissue fibrosis, myofibroblast and myocyte hyperplasia, and septal rupture with honeycombing. Studies of these mice highlighted the reversibility of this fibrotic response. They also demonstrated that a null mutation of early growth response gene (Egr)-1 or caspase inhibition blocked TGF-β₁–induced apoptosis. Interestingly, both interventions markedly ameliorated TGF-β₁–induced fibrosis and alveolar remodeling. These studies illustrate the complex effects of TGF-β₁ in vivo and define the critical role of Egr-1 in the TGF-β₁ phenotype. They also demonstrate that Egr-1–mediated apoptosis is a prerequisite for TGF-β₁–induced fibrosis and remodeling.

Asbestos-derived reactive oxygen species activate TGF-beta1

Transforming growth factor-beta1 (TGF-beta1) is a potent peptide that inhibits epithelial and mesenchymal cell proliferation and stimulates the synthesis of extracellular matrix components. This cytokine is produced in a biologically latent complex bound to a latent-associated peptide (LAP), and it is the disassociation of this complex that regulates TGF-beta activity. A number of mechanisms have been shown to activate TGF-beta1. We show here that reactive oxygen species (ROS), generated by the iron in chrysotile or crocidolite asbestos, mediate the biological activity of TGF-beta1. Recombinant human latent TGF-beta1 was activated in a cell free system in the presence of asbestos and ascorbic acid. Latent TGF-beta1 was overexpressed in both A549 and mink lung epithelial cell lines through an adenovirus vector containing the full-length construct for porcine TGF-beta1. This latent TGF-beta1 was activated in a concentration-dependant fashion by introducing asbestos into the cell cultures. This activation was reduced significantly through the use of superoxide dismutase, catalase or deferoxamine. Amino-acid constituents of the LAP were oxidized as demonstrated by the appearance of carbonyls detected by Western analysis. The oxidized LAP could no longer form a complex with TGF-beta1. Our data support the postulate that ROS derived from asbestos provide a mechanism for activating TGF-beta1 in the alveolar environment by oxidizing amino acids in LAP.

Susceptibility to asbestos-induced and transforming growth factor-beta1-induced fibroproliferative lung disease in two strains of mice

Pulmonary fibrosis (PF) is caused by a number of inhaled agents, as well as by some drugs and toxic particles. The elaboration of certain peptide growth factors is thought to be key to the development of this disease process. In addition, genetic susceptibility plays a role in the development of PF. For instance, we have previously shown that the 129J strain of mice is resistant, whereas the C57BL/6 strain is highly susceptible, to asbestos-induced fibrosis. To pursue this further, in one mouse model, we crossed the 129J strain to the C57BL/6 strain to produce an F1 generation and subsequently backcrossed the F1 mice to the inbred founders. This backcross to the 129 inbred strain produced reverse similar 25% of the offspring with a phenotype that was protected from the fibrogenic effects of inhaled asbestos fibers. In the second model, both strains of mice were treated intratracheally with an adenovirus vector (AdV), which transduces expression of active transforming growth factor (TGF)-beta(1) in the lungs, producing fibroproliferative lung disease. Compared with C57 mice, a significant number of 129 strain mice exhibited at least a 1-wk delay in the fibroproliferative response to TGF-beta(1) expression at three concentrations of virus. These findings suggest that certain sequences in a gene or a cluster of genes in the 129 mouse strain impart a phenotype in which there is a delay in, or protection from, the development of lung fibrogenesis.