Glucocorticoid-induced down regulation of transforming growth factor-beta 1 in adult rat lung fibroblasts

Pathobiology of Airway Remodeling in Asthma: The Emerging Role of Integrins

Airway remodeling is a complex clinical feature of asthma that involves long-term disruption and modification of airway architecture, which contributes significantly to airway hyperresponsiveness (AHR) and lung function decline. It is characterized by thickening of the airway smooth muscle layer, deposition of a matrix below the airway epithelium, resulting in subepithelial fibrosis, changes within the airway epithelium, leading to disruption of the barrier, and excessive mucous production and angiogenesis within the airway wall. Airway remodeling contributes to stiffer and less compliant airways in asthma and leads to persistent, irreversible airflow obstruction. Current asthma treatments aim to reduce airway inflammation and exacerbations but none are targeted towards airway remodeling. Inhibiting the development of airway remodeling or reversing established remodeling has the potential to dramatically improve symptoms and disease burden in asthmatic patients. Integrins are a family of transmembrane heterodimeric proteins that serve as the primary receptors for extracellular matrix (ECM) components, mediating cell-cell and cell-ECM interactions to initiate intracellular signaling cascades. Cells present within the lungs, including structural and inflammatory cells, express a wide and varying range of integrin heterodimer combinations and permutations. Integrins are emerging as an important regulator of inflammation, repair, remodeling, and fibrosis in the lung, particularly in chronic lung diseases such as asthma. Here, we provide a comprehensive summary of the current state of knowledge on integrins in the asthmatic airway and how these integrins promote the remodeling process, and emphasize their potential involvement in airway disease.

Y It Matters—Sex Differences in Fetal Lung Development

Within this review, sex-specific differences in alveolar epithelial functions are discussed with special focus on preterm infants and the respiratory disorders associated with premature birth. First, a short overview about fetal lung development, the challenges the lung faces during perinatal lung transition to air breathing and respiratory distress in preterm infants is given. Next, clinical observations concerning sex-specific differences in pulmonary morbidity of human preterm infants are noted. The second part discusses potential sex-specific causes of pulmonary complications, including pulmonary steroid receptors and local lung steroid metabolism. With regard to pulmonary steroid metabolism, it is important to highlight which steroidogenic enzymes are expressed at which stage during fetal lung development. Thereafter, we review the knowledge concerning sex-specific aspects of lung growth and maturation. Special focus is given to alveolar epithelial Na+ transport as a driver of perinatal lung transition and the sex differences that were noted in this process.

Concomitant inhibition of primary equine bronchial fibroblast proliferation and differentiation by selective β2-adrenoceptor agonists and dexamethasone

Altered airway cell proliferation plays an important role in the pathogenesis of human bronchial asthma and chronic obstructive pulmonary disease (COPD) as well as the equine recurrent airway obstruction (RAO) with consistent changes, i.e. narrowing the airway wall, explained by proliferation and differentiation of fibroblasts. In permanent cell lines, it has been suggested that β2-adrenoceptor agonists and glucocorticoids regulate cell proliferation via the β2-adrenoceptor pathway; indeed, no study was carried out in fresh isolated primary equine bronchial fibroblasts (EBF). We characterized the β-adrenoceptors in EBF, and compared effects of long-acting (clenbuterol) and short-acting (salbutamol and isoproterenol) β2-agonists and dexamethasone on proliferation, differentiation and collagen synthesis. High density (Bmax; 5037±494 sites/cell) of β2-adrenoceptor subtype was expressed in EBF. β2-agonists inhibited concentration-dependently EBF proliferation with potency of clenbuterol>salbutamol »isoproterenol which was inhibited by ICI 118.551 and propranolol but not by CGP 20712A. In contrast, dexamethasone alone inhibited less EBF proliferation, but the effect was high when dexamethasone was combined with β2-agonists. Transforming growth factor-β1 (TGF-β1) increased transformation of fibroblasts into myofibroblasts, which was inhibited by clenbuterol and dexamethasone alone and drug combination resulted in high inhibition rate. Collagen synthesis in EBF was rather hampered by dexamethasone than by β-agonists. Collectively, the expression of β2-adrenoceptor subtype in EBF and the anti-proliferative effect of clenbuterol suggest that β2-adrenoceptors are growth inhibitory and anti-fibrotic in EBF. These β2-agonist effects in EBF were synergistically enhanced by dexamethasone, providing the additive effects of glucocorticoids to counteract airway remodelling and morbidity of asthma and RAO.

Glucocorticoid-related molecular signaling pathways regulating hippocampal neurogenesis

Stress and glucocorticoid hormones regulate hippocampal neurogenesis, but the molecular mechanisms underlying their effects are unknown. We, therefore, investigated the molecular signaling pathways mediating the effects of cortisol on proliferation, neuronal differentiation, and astrogliogenesis, in an immortalized human hippocampal progenitor cell line. In addition, we examined the molecular signaling pathways activated in the hippocampus of prenatally stressed rats, characterized by persistently elevated glucocorticoid levels in adulthood. In human hippocampal progenitor cells, we found that low concentrations of cortisol (100 nM) increased proliferation (+16%), decreased neurogenesis into microtubule-associated protein 2 (MAP2)-positive neurons (-24%) and doublecortin (Dcx)-positive neuroblasts (-21%), and increased differentiation into S100β-positive astrocytes (+23%). These effects were dependent on the mineralocorticoid receptor (MR) as they were abolished by the MR antagonist, spironolactone, and mimicked by the MR-agonist, aldosterone. In contrast, high concentrations of cortisol (100 μM) decreased proliferation (-17%) and neuronal differentiation into MAP2-positive neurons (-22%) and into Dcx-positive neuroblasts (-27%), without regulating astrogliogenesis. These effects were dependent on the glucocorticoid receptor (GR), blocked by the GR antagonist RU486, and mimicked by the GR-agonist, dexamethasone. Gene expression microarray and pathway analysis showed that the low concentration of cortisol enhances Notch/Hes-signaling, the high concentration inhibits TGFβ-SMAD2/3-signaling, and both concentrations inhibit Hedgehog signaling. Mechanistically, we show that reduced Hedgehog signaling indeed critically contributes to the cortisol-induced reduction in neuronal differentiation. Accordingly, TGFβ-SMAD2/3 and Hedgehog signaling were also inhibited in the hippocampus of adult prenatally stressed rats with high glucocorticoid levels. In conclusion, our data demonstrate novel molecular signaling pathways that are regulated by glucocorticoids in vitro, in human hippocampal progenitor cells, and by stress in vivo, in the rat hippocampus.

Perioperative conditions affect long-term hypertrophic scar formation

Corticosteroids are widely used as treatment for excessive scarring by intralesional injection with variable success rates. It is conceivable that systemically administered corticosteroids affect a wider range of inflammatory processes that influence wound healing and may be more successful in preventing hypertrophic scar formation. To study this presumption, we have used a standardized model of presternal scars caused by cardiothoracic surgery through a median sternotomy incision. During cardiac surgery with cardiopulmonary bypass, 1 mg/kg dexamethasone was administered preoperatively, and 0.5 mg/kg 8 hours postoperatively. The presternal scars were evaluated prospectively 2, 4, 6, 12, and 52 weeks postoperatively at standardized measuring points. The height and width of the scars were measured 12 and 52 weeks postoperatively using both a slide caliper and a 7.5-MHz ultrasound probe. Cardiopulmonary bypass was used in 31 of the 43 participants. Eleven patients (35%) in the dexamethasone group developed clinical hypertrophic scars compared with 4 patients (33%) in the control group. These differences were not statistically significant. However, cranial scars became significantly wider in the dexamethasone group compared with the control group (P = 0.04). Twelve weeks postoperatively scars were significantly higher in the dexamethasone group, both cranial (P = 0.05) and caudal (P = 0.03). The differences in scar width and height were mainly present in patients that developed hypertrophic scars. The present results suggest that administration of high-dose perioperative dexamethasone does not prevent hypertrophic scar formation. Its use together with the cardiopulmonary bypass, however, did affect scar dimensions negatively up to 52 weeks after surgery. These findings contribute to the concept of the involvement of perioperative immunologic responses in the etiology of hypertrophic scar formation.

Anti-Tissue Remodeling Effects of Corticosteroids

OBJECTIVES

Tissue remodeling often accompanies diseases such as COPD that are caused by or aggravated by tobacco exposure. Inhaled or systemic corticosteroids are frequently used for the treatment of these illnesses, and their beneficial effects are often ascribed to their anti-inflammatory properties. However, their role in tissue remodeling remains unclear. This study was designed to evaluate the role of corticosteroids in matrix expression in vitro.

DESIGN

We investigated the effects of the corticosteroid fluticasone propionate (FP) on the production of fibronectin by fibroblasts before and after stimulation by nicotine, a plant alkaloid found in tobacco. Fibronectin is an extracellular matrix glycoprotein found elevated in the alveolar lining fluid and airway walls of subjects with obstructive lung disease, and is considered a marker of tissue remodeling after injury.

RESULTS

FP, 1 micromol/L, inhibited the expression of fibronectin messenger RNA and protein in unstimulated NIH-3T3 cells and primary lung fibroblasts, as well as in fibroblasts stimulated with nicotine. The inhibitory effect of FP occurred at the level of gene transcription as demonstrated in lung fibroblasts expressing a construct containing the human fibronectin promoter connected to a luciferase reporter gene, but posttranscriptional effects also appeared involved. Electrophoresis mobility gel shift assays revealed that FP inhibited phosphorylation and DNA binding by the cyclic adenosine monophosphate response element binding protein, a transcription factor required for constitutive and nicotine-induced fibronectin expression.

CONCLUSIONS

Together, these data suggest that FP could diminish lung tissue remodeling by inhibiting the production of fibronectin in lung fibroblasts.

How do glucocorticoids compare to oligo decoys as inhibitors of collagen synthesis and potential toxicity of these therapeutics?

This article demonstrates how glucocorticoids decrease collagen synthesis. The parameters used to assess procollagen synthesis in our laboratory will be compared to those used by others. This article will note all the pertinent literature on the molecular mechanisms of this down regulation of procollagen synthesis. For example, what are the effects of glucocorticoids at the levels of transcription and translation of collagen mRNAs? Finally, we will define a molecular mechanism to inhibit Type I collagen synthesis by decreasing the binding of the TGF-beta activator protein complex to the TGF-beta element in the distal promoter of the proalpha1 Type I collagen gene, preventing the 2:1 ratio of alpha1 to alpha2 chains in the processed Type I collagen molecule. We will next ask "How do sense oligo decoys decrease Type I collagen synthesis at the in vivo and at the cell levels?" In primary fibrotic cell culture, the double-stranded phosphorothioate oligodeoxynucleotide decoys were more effective than their sense single-stranded counterparts. The molecular mechanism for the decrease in Type I collagen synthesis is the same as glucocorticoids, that is by decreasing the binding of the TGF-beta activator protein complex to the TGF-beta element in the distal promoter of the proalpha1 Type I collagen gene for the transcription of the proalpha1 mRNAs. The reason for using sense oligo decoys as anti-fibrotic agents as compared to the anti-fibrotic glucocorticoids, is that presently marketed and FDA approved glucocorticoids have many untoward side effects which the sense oligo decoys do not have.

Short course dexamethasone treatment following injury inhibits bleomycin induced fibrosis in rats

BACKGROUND

Corticosteroids are routinely used in patients with pulmonary fibrosis. The timing for initiation of treatment is likely to be crucial for corticosteroids to exert an antifibrotic effect. Experimental studies in animals have examined the effect of corticosteroid treatment starting before or at the time of lung injury. However, this is not representative of the human condition as treatment only begins after disease has been established. We examined the effect of a short course corticosteroid treatment starting 3 days after bleomycin induced lung injury on the development of pulmonary fibrosis.

METHODS

Bleomycin (1.5 mg/kg) was instilled intratracheally into rats to induce pulmonary fibrosis. The effect of a 3-day course of dexamethasone (0.5 mg/kg) initiated 3 days after bleomycin induced lung injury on cell proliferation and collagen deposition was examined by analysing bronchoalveolar lavage (BAL) fluid and lung tissue.

RESULTS

Treating bleomycin exposed animals after injury with dexamethasone for 3 days inhibited lung collagen deposition compared with animals exposed to bleomycin without dexamethasone treatment (15.2 (2.2) mg collagen/lung v 22.5 (2.1) mg/lung; p<0.05). Dexamethasone treatment reduced pulmonary parenchymal cell proliferation in bleomycin exposed rats but did not influence BAL fluid mitogenic activity for lung fibroblasts or alter the BAL fluid levels of the fibrogenic mediators transforming growth factor-beta(1), platelet derived growth factor-AB, and thrombin.

CONCLUSIONS

A 3 day course of dexamethasone treatment initiated 3 days after bleomycin induced lung injury reduces lung cell proliferation and collagen deposition by mechanisms other than through reduction of transforming growth factor-beta(1), platelet derived growth factor-AB, and thrombin levels in BAL fluid. We propose that an early short course treatment with dexamethasone may be useful in inhibiting pulmonary fibrosis.

Pharmacotherapy and airway remodelling in asthma?

Over the last few decades attention has largely focused on airway inflammation in asthma, but more recently it has been appreciated that there are important structural airway changes which have been grouped together under the term "airway remodelling". It is only now that questions have been asked about the impact of treatment on these structural changes. This review examines the nature of these structural airway changes, the mechanisms of their generation, their potential consequences, and what is known about the ability of anti-asthma treatments to modulate these changes.

Molecular basis of the alteration in skin collagen metabolism in response to in vivo dexamethasone treatment: effects on the synthesis of collagen type I and III, collagenase, and tissue inhibitors of metalloproteinases

BACKGROUND

Glucocorticoids are widely used for the treatment of various diseases, despite known side-effects such as skin atrophy. Many studies have shown that the status of collagen fibres in the skin is affected by glucocorticoid treatment. However, the molecular mechanism underlying the alteration of collagen metabolism in the skin by glucocorticoid treatment remains unknown.

OBJECTIVES

To characterize the molecular mechanisms related to the deterioration of the dermis in response to glucocorticoids, the status of two major types of collagen, collagenase, and tissue inhibitors of metalloproteinases (TIMPs) in the dorsal skin of rats was studied at the protein and mRNA levels.

METHODS

Samples of rat dorsal skin were obtained after daily (1 mg kg-1) subcutaneous injections of dexamethasone (DEX) for 8 days. mRNA levels of two types of collagen and of TIMPs were measured by a lysate RNase protection assay. mRNA levels of collagenase were measured by a quantitative polymerase chain reaction. Protein levels of collagen and collagenase were measured by an immunoblot analysis.

RESULTS

Levels of type I tropocollagen and type III tropocollagen were drastically reduced in response to DEX. The effects of DEX treatment were more severe on type III than type I collagen: it also produced a significant decrease in fibril collagen of type III collagen. DEX treatment was found to decrease both active and latent forms of collagenase as well as its mRNA levels. Among TIMPs, mRNA levels of TIMP-1 and TIMP-2 were decreased in response to DEX treatment, whereas those of TIMP-3 were not affected.

CONCLUSIONS

These results suggest that DEX treatment strongly interferes with both the synthesis and degradation of type I collagen and, more drastically, type III collagen, the molecule that is known to play a major role in the initiation of wound healing. The present study may provide a molecular basis for the deterioration of skin function, impaired wound healing, and skin atrophy caused by glucocorticoid treatment.

Glucocorticoid-regulated gene expression during cutaneous wound repair

Glucocorticoids exert a deleterious effect on the wound healing process, which has been suggested to result from the anti-inflammatory action of these steroids. In addition, recent studies have demonstrated that glucocorticoids regulate the expression of various genes at the wound site which are likely to encode key players in the wound repair process. Using a murine full-thickness excisional wound healing model, we analyzed the effect of dexamethasone on the expression of various cytokines, growth factors, enzymes, and extracellular matrix molecules in normal and wounded skin. We demonstrate that the proinflammatory cytokines interleukin-1 alpha and -beta, tumor necrosis factor alpha, keratinocyte growth factor, transforming growth factors beta 1, beta 2, and beta 3 and their receptors, platelet-derived growth factors and their receptors, tenascin-C, stromelysin-2, macrophage metalloelastase, and enzymes involved in the generation of nitric oxide are targets of glucocorticoid action in wounded skin. These results indicate that anti-inflammatory steroids inhibit wound repair at least in part by influencing the expression of these key regulatory molecules.

Identification of sex-specific differences in surfactant synthesis in rat lung

Delayed lung maturation and lower levels of surfactant phosphatidylcholine have been previously identified in male fetuses compared with female fetuses in several species. We investigated the mechanisms for sex differences in surfactant content by examining parameters of phosphatidylcholine turnover and biosynthesis; the latter was evaluated by measuring metabolic steps within the biosynthetic pathway. Compared with male lung cells, freshly isolated lung cells from female fetuses contained higher levels of disaturated phosphatidylcholine, a marker of surfactant lipid. Female mixed monolayer cultures exhibited a 71% increase in choline incorporation into disaturated phosphatidylcholine compared with male cultures. Male cultures exhibited significantly greater release of [3H]-arachidonic acid into the medium compared with females, suggesting sex differences in phospholipase activity. However, pulse-chase studies showed no sex differences in degradation of disaturated phosphatidylcholine, which was confirmed by assays of phospholipase A2, phosphatidylcholine-specific phospholipase C, and phospholipase D. Female mixed lung cells, however, had greater rates of cellular choline transport and activity of cytidylyltransferase, the rate-regulatory enzyme for phosphatidylcholine synthesis. Separate studies showed that exposure of sex-specific pretype II cell cultures to cortisol-stimulated fibroblast-conditioned medium plus transforming growth factor-beta-neutralizing antibody stimulated cytidylyltransferase activity to a greater extent in male cells compared with female cells. These studies indicate that sex differences in surfactant phospholipid content are not due to differences in phospholipid turnover, but rather differential regulation of specific metabolic steps within the surfactant biosynthetic pathway. The data also support a role for transforming growth factor-beta as a negative regulator of a key surfactant biosynthetic enzyme within male lungs.

Perspective article: transforming growth factor-beta: crossroad of glucocorticoid and bleomycin regulation of collagen synthesis in lung fibroblasts

Fibrosis is a consequence of injury which is characterized by accumulation of excess collagen and other extracellular matrix components, resulting in the destruction of normal tissue architecture and function. Transforming growth factor-beta, a potent wound healing agent, has also been shown to be an agent that can produce fibrosis because it is a potent stimulator of collagen synthesis. Both glucocorticoids and bleomycin have recently been shown to affect collagen synthesis in opposite directions, by utilizing a common pathway of involving transforming growth factor-beta activator protein binding to the transforming growth factor-beta element. This article presents a mechanistic overview of collagen synthesis regulation by glucocorticoids and bleomycin through the transforming growth factor-beta pathway.

Dexamethasone is a novel potent inducer of connective tissue growth factor expression. Implications for glucocorticoid therapy

Due to its potent effect on fibroblast proliferation and extracellular matrix deposition, connective tissue growth factor (CTGF) seems to play an important role in the pathogenesis of fibrotic disease. Since glucocorticoids are frequently used for the therapy of these disorders, we determined a potential effect of these steroids on CTGF expression. In cultured fibroblasts, a striking induction of CTGF expression was observed after dexamethasone treatment and occurred in a time- and dose-dependent manner. This effect was obviously not mediated by the CTGF inducer transforming growth factor-beta1, since expression of this factor was down-regulated by the glucocorticoid. Most importantly, CTGF expression levels also increased substantially in various tissues and organs by systemic glucocorticoid treatment of mice. After cutaneous injury, a strong induction of CTGF expression was seen in the wounds of nontreated mice. However, no further increase in the levels of CTGF mRNA occurred in wounded skin compared with unwounded skin of glucocorticoid-treated animals, suggesting the presence of other factors in the wound that might compensate for the effect of the steroids. Tumor necrosis factor-alpha was identified as a possible mediator of this effect because this factor suppressed CTGF expression in cultured fibroblasts and also blocked the glucocorticoid-induced CTGF production by these cells. These findings indicate that glucocorticoids stimulate CTGF expression in normal tissues and organs but not in highly inflamed areas.

Identification of a glucocorticoid response element in the human transforming growth factor beta 1 gene promoter

TGF-beta 1, which has a stimulatory effect on dermal wound healing, has been implicated as the primary causative agent of fibrosis. Glucocorticoids such as dexamethasone normally inhibit wound healing and are capable of antagonizing the fibrotic effect of TGF-beta 1. Our data indicate the presence of a putative regulatory element responsive to glucocorticoids. Computer sequence analysis of the promoter region of the human TGF-beta 1 gene (Genbank Accession # J04431) revealed a consensus glucocorticoid response element, GRE (5'-AGAACA) located from (-1081) to (-1086) base pairs from the transcription start site. An oligonucleotide containing this site was obtained and labeled for use in gel mobility shift assays. The labeled oligonucleotide was found to bind both fetal rat skin nuclear extracts and purified recombinant glucocorticoid receptor. Unlabeled oligonucleotides containing a GRE from the rat procollagen type I promoter or a commercially supplied GRE competed effectively with the 32P-labeled GRE from the TGF-beta 1 promoter for binding to nuclear extracts. Addition of anti-glucocorticoid receptor revealed a supershifting of the labeled oligonucleotide-nuclear protein complex. These results indicate the presence of a putative GRE in the promoter region of the human TGF-beta 1 gene.

Circulating transforming growth factor beta 1 (TGF-beta1) in Guillain-Barré syndrome: decreased concentrations in the early course and increase with motor function

OBJECTIVE

To delineate the possible implication of the immunosuppressive cytokine transforming growth factor beta 1 (TGF-beta1) in the pathogenesis of Guillain-Barré syndrome. Guillain-Barré syndrome is a disorder that may implicate cytokines in its pathogenesis. TGF-beta1 is a potent anti-inflammatory cytokine occasionally shown to be regulated in the course of demyelinating disorders.

METHODS

The study measured circulating proinflammatory and anti-inflammatory cytokines from the progressing phase to early recovery in patients with Guillain-Barré syndrome. Plasma concentrations of TNF-alpha, IL-beta1, IL-2, IL-4, IL-6, IL-10, and TGF-beta1 were prospectively evaluated in 15 patients with Guillain-Barré syndrome every three days for the first 15 days after admission to hospital, and in 15 controls with non-inflammatory neurological diseases.

RESULTS

Concentrations of TGF-beta1 in plasma were decreased in 13115 patients (87 %) at day 1, remained low during progression and the plateau of paralysis (days 1-10), and then progressively increased up to control concentrations during early recovery (days 12-15). Concentrations of plasma TGF-beta1 correlated positively with motor function, the lowest values being e found in the most disabled patients. Concentrations of plasma TGF-beta1 were decreased before any treatment, and during treatment by either plasma exchange or intravenous immunoglobulins, plasma exchange being associated with a more pronounced decrease in TGF-beta1 at day 7. Circulating TNF-alpha concentrations were raised, as previously reported, when other cytokines were either randomly increased (IL-2, IL-6), or undetectable (IL-1, IL-4, IL-7, IL-10).

CONCLUSIONS

Down regulation of TGF-beta1 in the early course of Guillain-Barré syndrome could participate in neural inflammation.

Dexamethasone abrogates the fibrogenic effect of transforming growth factor-beta in rat granuloma and granulation tissue fibroblasts

Administration of TGF-beta, a fibrogenic inflammatory growth factor, promotes fibrosis and scarring. Dexamethasone, an anti-inflammatory steroid, inhibits wound healing and reduces fibrosis. The current studies were initiated to determine whether the co-administration of dexamethasone was able to abrogate the fibrogenic effect of TGF-beta. Polyvinyl alcohol sponges were implanted subcutaneously on the abdominal area of rats and directly injected with vehicle, dexamethasone, TGF-beta, or dexamethasone plus TGF-beta. Dexamethasone was able to block the fibrogenic effect of TGF-beta. Collagen and noncollagen protein synthesis was measured as a function of TGF-beta or dexamethasone concentrations in fibroblasts isolated from granulation tissue. Addition of dexamethasone to cultures treated simultaneously with TGF-beta blocked the fibrogenic response of TGF-beta. To study the molecular regulation of collagen gene expression by TGF-beta or dexamethasone, fibroblasts derived from granulation tissue were stably transfected with the ColCat 3.6 plasmid, which contains the rat pro alpha1(I) collagen promoter linked to the chloramphenicol acetyltransferase (CAT) gene. Dexamethasone decreased CAT activity whereas TGF-beta increased the activity of this reporter gene. The increase in CAT activity observed with TGF-beta treatment was significantly decreased when dexamethasone was added to the cultures, although CAT activity did not return to control level. Since collagen synthesis in fibroblasts treated simultaneously with dexamethasone and TGF-beta1 was found to be the same as that of untreated samples, the data indicate that there is a dexamethasone-mediated posttranscriptional regulation of pro alpha1(I) collagen mRNA. These studies demonstrate that at the in vivo level, the cellular level, and the molecular level, dexamethasone is able to block the fibrogenic effect of TGF-beta.

Modulation of silica-induced pulmonary toxicity by dexamethasone-containing liposomes

Human exposure to silica (SI) is of great occupational concern because it is marked by pulmonary inflammation and fibrosis. Our objective was to determine if early pharmacological intervention altered the inflammatory and fibrotic responses to silica in rats. Male Fisher-344 rats received intratracheal (IT) instillations of the anti-inflammatory steroid, dexamethasone (DEX), incorporated into a novel liposomal (LIP) delivery system (DEX-LIP), or buffer as control (HBSS) on Day-1 and every fourth day until euthanization. On Day 0, the DEX-LIP group received IT instillations of SI (10 mg/100g body wt, DEX-LIP-SI); half of the HBSS group received SI (10 mg/100g body wt, HBSS-SI) and the other half saline (HBSS-SAL). On Day 10 or 20, bronchoalveolar lavage (BAL) was performed for cellular, biochemical, and functional analyses of inflammation and damage. HBSS-SI rats had significant elevations in the neutrophil cell count over HBSS-SAL rats at both times. DEX-LIP treatment markedly reduced these values, indicating that DEX-LIP protected against SI-induced inflammation. In contrast, DEX-LIP did not protect against biochemical (albumin concentration, and beta-glucuronidase and lactate dehydrogenase activities) and functional (luminol-dependent chemiluminescence) indices of SI-induced damage. At Day 20, the DEX-LIP treatment significantly reduced the SI-induced increase in right lung/total body weight ratio and right lung hydroxyproline content, a biochemical index of fibrosis. This attenuation of fibrosis was confirmed histopathologically on preserved left lungs from these same animals. These results show that administration of liposomes containing dexamethasone attenuated SI-induced pulmonary inflammation and fibrosis in rats, and that this protection is independent of some biochemical and functional parameters of damage.

Transforming growth factors beta1, beta2, and beta3 and their receptors are differentially regulated during normal and impaired wound healing

A series of studies has shown that application of transforming growth factor beta (TGF-beta) to a wound has a beneficial effect, especially in animals with wound healing disorders. In this study we have investigated the regulation of TGF-beta1, beta2, and beta3 and their receptors during the repair process. We found a large induction of all three TGF-beta isoforms and also of TGF-beta types I and II receptors, although the time course of induction and the absolute expression levels were different for these genes. Furthermore, each TGF-beta isoform had distinct sites of expression in the wound. Systemic treatment with glucocorticoids significantly altered the expression levels of TGF-betas and TGF-beta receptors. Whereas expression of TGF-beta1, TGF-beta2, and TGF-beta type II receptor was suppressed by glucocorticoids in normal and wounded skin, expression of TGF-beta3 and TGF-beta receptor type I mRNA was stimulated. These findings provide an explanation for the beneficial effect of exogenous TGF-beta in the treatment of impaired wound healing in glucocorticoid-treated animals. Furthermore, they suggest that a disturbed balance between the levels of the three TGF- beta isoforms and their receptors might underlie the wound healing defect seen in glucocorticoid-treated animals.

Glucocorticoids coordinately regulate type I collagen pro alpha 1 promoter activity through both the glucocorticoid and transforming growth factor beta response elements: a novel mechanism of glucocorticoid regulation of eukaryotic genes

Glucocorticoids have previously have shown to decrease Type I collagen synthesis in vivo and in fibroblast cell culture. Several studies have demonstrated that glucocorticoids decrease Type I procollagen gene expression. These latter studies have included uridine incorporation into pro alpha 1 (I) and pro alpha 2 (I) mRNAs and nuclear run-off experiments. Using the ColCat 3.6 plasmid, which contains part of the 5' flanking region of the pro alpha 1 (I) collagen gene and the reporter gene, chloramphenicol acetyltransferase, the present studies demonstrate by stable transfection of fetal rat skin fibroblasts that dexamethasone down regulates the promoter activity of the pro alpha 1 (I) collagen gene. The glucocorticoid-mediated down-regulation of procollagen gene expression was demonstrated using the ColCat 3.6, 2.4, 1.7, or 0.9 plasmid. In addition, competitive oligonucleotide transfection experiments and site specific mutation of the glucocorticoid response element (GRE) in the whole ColCat 3.6 plasmid did not eliminate the effect. The possibility existed that another cis-element in the 5' flanking region of the pro alpha 1 (I) collagen gene was also required for the collagen glucocorticoid-mediated down-regulation of procollagen gene expression, since TGF-beta has been shown to stimulate in a decrease of transforming growth factor-beta (TGF-beta) secretion into the media. Gel mobility studies demonstrated that glucocorticoid treatment of rat skin fibroblasts decreased glucocorticoid receptor binding to the GRE and TGF-beta activator protein to the TGF-beta element which were brought back to control values by coordinate exogenous TGF-beta treatment. Thus the interaction of these TGF-beta molecules with cellular membrane receptors and subsequent transduction is dramatically decreased resulting in less signals to regulate collagen gene expression. These data indicate that glucocorticoids coordinately regulate procollagen gene expression through both the GRE and TGF-beta elements. Depression of procollagen gene expression by glucocorticoids through the TGF-beta element is mediated by decreased TGF-beta secretion, possibly involving a secondary effect on regulatory protein(s) encoded by noncollagenous protein gene(s). The present studies provide the basis for a novel mechanism of glucocorticoid-mediator regulation of eukaryotic genes containing the TGF-beta element.