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in a Murine Model of Toluene Diisocyanate-Induced Asthma1
* Department of Internal Medicine, Airway Remodeling Laboratory, and
Department of Immunology, Chonbuk National University Medical School, Jeonju, South Korea
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Abstract |
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(PPAR) has been shown to play a critical role in the control of airway inflammatory responses. However, no data are available on the role of PPAR in TDI-induced asthma. We have used a mouse model for TDI-induced asthma to determine the effect of PPAR agonist, rosiglitazone, or pioglitazone, and PPAR on TDI-induced bronchial inflammation and airway remodeling. This study with the TDI-induced model of asthma revealed the following typical pathophysiological features: increased numbers of inflammatory cells of the airways, airway hyperresponsiveness, increased levels of Th2 cytokines (IL-4, IL-5, and IL-13), adhesion molecules (ICAM-1 and VCAM-1), chemokines (RANTES and eotaxin), TGF-
1, and NF-
B in nuclear protein extracts. In addition, the mice exposed to TDI developed features of airway remodeling, including thickening of the peribronchial smooth muscle layer, subepithelial collagen deposition, and increased airway mucus production. Administration of PPAR agonists or adenovirus carrying PPAR2 cDNA reduced the pathophysiological symptoms of asthma and decreased the increased levels of Th2 cytokines, adhesion molecules, chemokines, TGF-1, and NF-B in nuclear protein extracts after TDI inhalation. In addition, inhibition of NF-B activation decreased the increased levels of Th2 cytokines, adhesion molecules, chemokines, and TGF-1 after TDI inhalation. These findings demonstrate a protective role of PPAR in the pathogenesis of the TDI-induced asthma phenotype. |
Introduction |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionDisclosuresReferences |
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Peroxisome proliferator-activated receptors (PPARs) are transcriptional factors belonging to the ligand-activated nuclear receptor superfamily (10). They are ubiquitously expressed throughout the body. Three major types have been identified, namely PPAR
, PPAR
, and PPAR. PPAR is originally known to regulate adipocyte differentiation and lipid metabolism (11). However, accumulating evidence indicates that PPAR affects cell cycle, differentiation, and apoptosis (12). In addition, PPAR activation down-regulates synthesis and release of immunomodulatory cytokines from various cell types (13, 14). Previous studies have shown that PPAR is involved in airway inflammation and remodeling in asthma (15, 16, 17). PPAR expression is increased in the airway mucosa of asthmatics as compared with healthy subjects (16). Recent studies suggest the use of PPAR ligands for the possible treatment of bronchial asthma (17, 18). However, there are no data on the effect of PPAR on the hyperresponsiveness, inflammation, and remodeling of the airways in TDI-induced asthma.
In the present study, we used a murine model of TDI-induced asthma to evaluate the effect of PPAR agonist, rosiglitazone, or pioglitazone, and an adenovirus gene transfer vector expressing a PPAR2 cDNA (AdPPAR) on hyperresponsiveness, inflammation, and remodeling of the airways.
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionDisclosuresReferences |
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Female BALB/c mice, 8–10 wk of age and free of murine-specific pathogens, were obtained from the Korean Research Institute of Chemistry Technology. All experimental animals used in this study were under a protocol approved by the Institutional Animal Care and Use Committee of the Chonbuk National University Medical School. Mice were sensitized twice by two courses of intranasal administration of 20 µl of 3% TDI dissolved in ethyl acetate:olive oil (1:4) under light anesthesia (sodium pentobarbitone, 30 mg/kg, i.p.) once daily for 5 consecutive days with a 3-wk interval as previously described (19) with some modifications (Fig. 1). At 7 days after the second course of sensitization (day 38), mice were challenged via the airways with 1% TDI dissolved in ethyl acetate:olive oil (1:4) for 10 min by ultrasonic nebulization (NE-U12; Omron), and then repeated once a week for 4 wk (Fig. 1). As a control, mice were sensitized and challenged using the same protocol but using only the solvent, ethyl acetate:olive oil (1:4). Bronchoalveolar lavage (BAL) was performed at 48 h after the last challenge.
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The E1/E3-deleted replication-deficient recombinant adenovirus (Ad) was made using the AdEasy system (Quantum Biotech) described by He et al. (20).
Administration of rosiglitazone, pioglitazone, GW9662, Ad vectors, or BAY 11–7085
Rosiglitazone (1, 2.5, or 5 mg/kg body weight/day; GlaxoSmithKline) dissolved in distilled water or pioglitazone (1, 5, or 10 mg/kg body weight/day; Takeda Chemical Industries) dissolved in 0.05% DMSO and diluted with saline, was administered by oral gavage at 24-h interval on days 36–66, beginning 2 days before the first challenge as previously described (15) (Fig. 1). A selective antagonist of PPAR, GW9662 (0.5 mg/kg body weight/day; Cayman) dissolved in PBS was administered intratracheally six times to each animal on days 37, 40, 47, 54, 61, and 67, beginning 1 day before the first challenge as previously described (15). Ad vectors were administered intratracheally (109 PFU) six times to each animal on days 37, 40, 47, 54, 61, and 65, beginning 1 day before the first challenge. An inhibitor of NF-B activation, BAY 11–7085 (20 mg/kg body weight/day; BIOMOL) dissolved in DMSO and diluted with 0.9% NaCl, was administered by i.p. injection six times to each animal on days 37, 40, 47, 54, 61, and 67, beginning 1 day before the first challenge (21, 22).
Measurement of Th2 cytokines and TGF-1
Levels of IL-4, IL-5, IL-13, and TGF-1 were quantified in the supernatants of BAL fluids by enzyme immunoassays (IL-4 and IL-5 (Endogen); IL-13 and TGF-1 (R&D Systems)).
Western blot analysis
Protein expression levels were analyzed by Western blot analysis, as described previously (15). The blots were incubated with an anti-IL-4 Ab (Serotec), anti-IL-5 Ab (Santa Cruz Biotechnology), anti-IL-13 Ab (R&D Systems), anti-TGF-1 Ab (Santa Cruz Biotechnology), anti-ICAM-1 Ab (Santa Cruz Biotechnology), anti-VCAM-1 Ab (Santa Cruz Biotechnology), anti-RANTES Ab (Abcam), anti-eotaxin Ab (Abcam), anti-Akt Ab (Cell Signaling Technology), and anti-phosphorylated Akt (p-Akt) Ab (Cell Signaling Technology).
Cytosolic or nuclear protein extractions for analysis of NF-B p65 and PPAR
Cytosolic or nuclear extractions for analysis of NF-B p65 and PPAR were performed as described previously (15). The levels of these proteins were analyzed by Western blotting using Ab against NF-B p65 (Upstate Biotechnology) or PPAR (Santa Cruz Biotechnology).
Processing of lungs for histologic and image analysis
At 48 h after the last challenge, lungs were removed from the mice after sacrifice. The specimens were stained sequentially with H&E (Richard-Allan Scientific), periodic acid-Schiff (PAS), Masson’s trichrome stain, or -smooth muscle actin stain. Stained and immunostained slides were all quantified under identical light microscope conditions, including magnification (x20), gain, camera position, and background illumination (23).
Histology
For histological examination, 4-µm sections of fixed embedded tissues were cut on a Leica model 2165 rotary microtome (Leica Microsystems). The degree of peribronchial and perivascular inflammation was evaluated on a subjective scale of 0–3, as described elsewhere (24).
Quantitation of airway mucus expression
To quantitate the level of mucus expression in the airway, the number of PAS-positive and PAS-negative epithelial cells in individual bronchioles were counted as described previously (23, 25). Results are expressed as the percentage of PAS-positive cells per bronchiole, which is calculated from the number of PAS-positive epithelial cells per bronchiole divided by the total number of epithelial cells of each bronchiole.
Quantitation of peribronchial fibrosis
Two methods (trichrome staining and total lung collagen content) were used to quantify peribronchial fibrosis.
Peribronchial trichrome staining. The area of peribronchial trichrome staining in a paraffin-embedded lung was outlined and quantified using a light microscope (Leica DM LB; Leica) attached to an image-analysis system (analySIS Pro version 3.2; Soft Imaging System). Results are expressed as the area of trichrome staining per micron length of basement membrane of bronchioles 150–200 µm of internal diameter. At least 10 bronchioles were counted in each slide.
Determination of total lung collagen content. The total lung collagen content was determined using the Sircol Collagen Assay kit (Biocolor) according to the manufacturer’s protocols.
Quantitation of peribronchial smooth muscle
For immunohistochemical detection of -smooth muscle actin, the lung sections were incubated with either a primary mAb directed against -smooth muscle actin (Sigma-Aldrich), or as a negative control mouse serum instead of the primary Ab. Results are expressed as the area of immunostaining per micron length of basement membrane of bronchioles 150–200 µm of internal diameter.
Determination of airway responsiveness
Airway responsiveness was assessed as a change in airway function after challenge with aerosolized methacholine via airways, as described elsewhere (26, 27). Each mouse was challenged with methacholine aerosol in increasing concentrations (2.5–50 mg/ml in saline). After each methacholine challenge, the data of airway resistance (RL) was continuously collected. Maximum values of RL were selected to express changes in airway function which was represented as a percentage change from baseline after saline aerosol.
Densitometric analyses and statistics
All immunoreactive signals were analyzed by densitometric scanning (Gel Doc XR; Bio-Rad). Data were expressed as mean ± SEM. Statistical comparisons were performed using one-way ANOVA followed by the Scheffe’s test. Significant differences between groups were determined using the unpaired Student t test. Statistical significance was set at p < 0.05.
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Results |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionDisclosuresReferences |
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on PPAR protein levels in lung tissues of TDI-sensitized and -challenged mice
Western blot analysis revealed that the levels of PPAR in nuclear protein extracts of lung tissues were increased at 48 h after the last TDI inhalation compared with the levels in the control mice (Fig. 2A). The increased PPAR levels in nuclear protein extracts of lung tissues were further increased by the administration of rosiglitazone or pioglitazone. In contrast, the levels of PPAR in cytosolic protein extracts of lung tissues were decreased at 48 h after the last TDI inhalation compared with the levels in the control mice. The decreased PPAR levels in cytosolic protein extracts of lung tissues were further decreased by the administration of rosiglitazone or pioglitazone. In addition, the levels of PPAR in nuclear protein extracts of lung tissues were increased in TDI-sensitized and -challenged mice treated with AdLacZ compared with the levels in the control mice on days 42, 49, 56, and 63 (Fig. 2B). The increased PPAR levels in nuclear protein extracts of lung tissues were further increased by the administration of AdPPAR on days 42, 49, 56, and 63.
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on cellular changes in BAL fluids
Numbers of total cells, lymphocytes, neutrophils, and eosinophils were significantly increased in the BAL fluid at 48 h after the last TDI inhalation compared with the levels in the control mice (Fig. 3A). The increased numbers of total cells, lymphocytes, neutrophils, and eosinophils in BAL fluids at 48 h after the last TDI inhalation were significantly reduced by the administration of rosiglitazone (5 mg/kg), pioglitazone (10 mg/kg), or AdPPAR in a dose-dependent manner. The inhibitory effect of rosiglitazone treatment on numbers of total cells, lymphocytes, neutrophils, and eosinophils in BAL fluids was abrogated when a PPAR antagonist, GW9662, was administered concomitantly with the agonist. These results indicate that rosiglitazone was mainly acting through PPAR in this model.
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on pathological changes of TDI-induced asthma
Histologic analyses revealed typical pathologic features of asthma in the TDI-exposed mice. Numerous inflammatory cells infiltrated around the bronchioles, the airway epithelium was thickened, and mucus and debris had accumulated in the lumen of bronchioles (Fig. 3C) as compared with the control (Fig. 3B). Mice treated with rosiglitazone (Fig. 3D) or AdPPAR (Fig. 3E) showed marked reductions in the thickening of airway epithelium, in the infiltration of inflammatory cells in the peribronchiolar region, in the number of inflammatory cells, and in the amount of debris in the airway lumen. In contrast, no significant changes were observed in AdLacZ-treated mice (Fig. 3F).
The scores of peribronchial, perivascular, and total lung inflammation were significantly increased at 48 h after the last TDI inhalation compared with the scores in the control mice (Fig. 3G). The increased peribronchial, perivascular, and total lung inflammation after TDI inhalation were significantly decreased by the administration of rosiglitazone, pioglitazone, or AdPPAR. These results suggest that rosiglitazone, pioglitazone, and AdPPAR inhibit Ag-induced inflammation in the lungs. Supporting the observations, the inhibitory effect of rosiglitazone treatment on scores of peribronchial, perivascular, and total lung inflammation in lung tissues was abrogated when GW9662 was administered concomitantly with the agonist (Fig. 3G).
Effect of rosiglitazone, pioglitazone, GW9662 plus rosiglitazone, or AdPPAR on airway hyperresponsiveness
Airway responsiveness was assessed as a percent increase of RL in response to increasing doses of methacholine. In TDI-sensitized and -challenged mice, the dose-response curve of RL shifted to the left compared with that of control mice (Fig. 3, H and I). In addition, the RL produced by methacholine administration (at doses from 5 to 50 mg/ml) increased significantly in the TDI-sensitized and -challenged mice compared with the controls. TDI-sensitized and -challenged mice treated with rosiglitazone, pioglitazone, or AdPPAR showed a dose-response curve of RL that shifted to the right compared with that of untreated mice in a dose-dependent manner (Fig. 3I). These results indicate that rosiglitazone, pioglitazone, or AdPPAR treatment reduces TDI-induced airway hyperresponsiveness. The inhibitory effect of rosiglitazone treatment on airway hyperresponsiveness was abrogated when GW9662 was administered concomitantly with the agonist.
Effect of rosiglitazone, pioglitazone, GW9662 plus rosiglitazone, or AdPPAR on airway mucus expression
The percentage of airway epithelium which stained positively with PAS in mice repetitively challenged with TDI (Fig. 4, B and F) was significantly greater than in control non-TDI-challenged mice (Fig. 4, A and F). The administration of rosiglitazone (1, 2.5, and 5 mg/kg) (Fig. 4, C and F), pioglitazone (1, 5, and 10 mg/kg) (Fig. 4F), or AdPPAR (Fig. 4, D and F) to mice repetitively challenged with TDI significantly reduced the percentage of airway epithelium staining positively with PAS compared with untreated mice, whereas GW9662 plus rosiglitazone or AdLacZ did not (Fig. 4, E and F).
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on peribronchial collagen deposition
Mice exposed to repetitive TDI challenge (Fig. 5, B, F, and G) had a significant increase in the levels of peribronchial fibrosis compared with non-TDI-challenged mice (Fig. 5, A, F, and G) as assessed by trichrome staining and determination of total lung collagen content. The administration of rosiglitazone (2.5 and 5 mg/kg) (Fig. 5, C, F, and G), pioglitazone (10 mg/kg) (Fig. 5, F and G), or AdPPAR (Fig. 5, D, F, and G) to mice repetitively challenged with TDI significantly reduced the levels of peribronchial fibrosis compared with untreated mice, whereas GW9662 plus rosiglitazone or AdLacZ did not (Fig. 5, E, F, and G).
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on peribronchial -smooth muscle actin expression
Mice exposed to repetitive TDI challenge (Fig. 6, B and F) had a significant increase in the area of peribronchial -smooth muscle actin immunostaining compared with non-TDI-challenged mice (Fig. 6, A and F). The administration of rosiglitazone (1, 2.5, and 5 mg/kg) (Fig. 6, C and F), pioglitazone (5 and 10 mg/kg) (Fig. 6F), or AdPPAR (Fig. 6, D and F) to mice repetitively challenged with TDI significantly reduced the area of peribronchial -smooth muscle actin immunostaining compared with untreated mice, whereas GW9662 plus rosiglitazone or AdLacZ did not (Fig. 6, E and F).
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on NF-B p65 protein levels in lung tissues
Western blot analysis showed that levels of NF-B p65 in nuclear protein extracts from lung tissues were increased at 48 h after the last TDI inhalation compared with the levels in the control mice (Fig. 7A). The increased NF-B p65 levels in nuclear protein extracts were decreased by the administration of rosiglitazone, pioglitazone, or AdPPAR. No significant changes were observed in TDI-sensitized and -challenged mice treated with GW9662 plus rosiglitazone or AdLacZ. In contrast, the levels of NF-B p65 protein in cytosol fractions from lung tissues were decreased at 48 h after the last TDI inhalation as compared with the levels in the control mice. The decreased NF-B p65 protein levels in cytosol fractions from lung tissues were increased by the administration of rosiglitazone, pioglitazone, or AdPPAR. However, no significant changes were observed in TDI-sensitized and -challenged mice treated with GW9662 plus rosiglitazone or AdLacZ.
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The levels of p-Akt protein in the lung tissues were increased significantly at 48 h after the last TDI inhalation compared with the levels in the control mice (Fig. 7B). In contrast, no significant changes in total Akt protein levels were observed in any of the groups tested. The increased p-Akt but not Akt protein levels in the lung tissues at 48 h after TDI inhalation were significantly reduced by the administration of rosiglitazone, pioglitazone, or AdPPAR. However, no significant changes were observed in TDI-sensitized and -challenged mice treated with GW9662 plus rosiglitazone or AdLacZ.
Effect of rosiglitazone, pioglitazone, GW9662 plus rosiglitazone, or AdPPAR on levels of IL-4, IL-5, and IL-13 expression in lung tissues and BAL fluids
Western blot analysis revealed that IL-4, IL-5, and IL-13 protein levels in lung tissues were significantly increased at 48 h after the last TDI inhalation compared with the levels in the control mice (Fig. 8, A and B). The increased levels of these cytokines were significantly reduced by the administration of rosiglitazone, pioglitazone, or AdPPAR. No significant changes were observed in TDI-sensitized and -challenged mice treated with GW9662 plus rosiglitazone or AdLacZ. Consistent with the results obtained from the Western blot analysis, enzyme immunoassays showed that levels of IL-4, IL-5, and IL-13 in BAL fluids were significantly increased at 48 h after the last TDI inhalation compared with the levels in the control mice (Fig. 8C). The increased levels of these cytokines were significantly reduced by the administration of rosiglitazone, pioglitazone, or AdPPAR.
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on ICAM-1, VCAM-1, RANTES, and eotaxin expression in lung tissues
Western blot analysis showed that ICAM-1, VCAM-1, RANTES, and eotaxin protein levels in lung tissues were significantly increased at 48 h after the last TDI inhalation compared with the levels in the control mice (Fig. 9). The increased levels of these adhesion molecules and chemokines were significantly reduced by the administration of rosiglitazone, pioglitazone, or AdPPAR. In contrast, no significant changes were observed in TDI-sensitized and -challenged mice treated with GW9662 plus rosiglitazone or AdLacZ.
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on TGF-1 expression in lung tissues and BAL fluids
Western blot analysis showed that TGF-1 protein levels in lung tissues were significantly increased at 48 h after the last TDI inhalation compared with the levels in the control mice (Fig. 10, A and B). The increased TGF-1 levels were significantly reduced by the administration of rosiglitazone, pioglitazone, or AdPPAR. No significant changes were observed in TDI-sensitized and -challenged mice treated with GW9662 plus rosiglitazone or AdLacZ. Consistent with the results obtained from the Western blot analysis, enzyme immunoassays revealed that levels of TGF-1 in BAL fluids were significantly increased at 48 h after the last TDI inhalation compared with the levels in the control mice (Fig. 10C). The increased TGF-1 levels were significantly reduced by the administration of rosiglitazone, pioglitazone, or AdPPAR.
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1 in lung tissues
Western blot analysis showed that IL-4, IL-5, IL-13, ICAM-1, VCAM-1, RANTES, eotaxin, and TGF-1 protein levels in the lung tissues were increased significantly at 48 h after the last TDI inhalation compared with the levels in the control mice (Fig. 11). The increased levels of these molecules were significantly reduced by the administration of BAY 11–7085.
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Discussion |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionDisclosuresReferences |
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has been shown to play a critical role in the control of airway inflammatory responses. This study with the TDI-induced model of asthma has revealed the following typical pathophysiological features in the lungs: increase in numbers of inflammatory cells of the airways, airway responsiveness, levels of Th2 cytokines (IL-4, IL-5, and IL-13), adhesion molecules (ICAM-1 and VCAM-1), chemokines (RANTES and eotaxin), TGF-1, and NF-B in nuclear protein extracts. In addition, the mice exposed to TDI developed features of airway remodeling, including thickening of the peribronchial smooth muscle layer, subepithelial collagen deposition, and increased airway mucus production. Administration of PPAR agonists or AdPPAR reduced the pathophysiological symptoms of asthma and decreased the increased levels of Th2 cytokines, adhesion molecules, chemokines, TGF-1, and NF-B in nuclear protein extracts after TDI inhalation. In addition, administration of NF-B inhibitor decreased the increased levels of Th2 cytokines, adhesion molecules, chemokines, and TGF-1 after TDI inhalation. These findings suggest that PPAR reduces airway inflammation, airway hyperresponsiveness, and airway remodeling.
Previous reports have demonstrated that activation of PPAR inhibits expression of various cytokines, airway hyperresponsiveness, airway remodeling, and activation of inflammatory cells which are increased by induction of asthma (17, 28). Consistent with these observations, our results have shown that administration of the PPAR agonists or AdPPAR substantially reduced expression of cytokines, airway hyperresponsiveness, airway inflammation, and airway remodeling in a murine model of occupational asthma. In addition, induction of asthma through TDI-challenge increased expression of PPAR itself, and administration of the agonists and AdPPAR further increased the receptor expression. Up-regulation of PPAR expression is also observed in human asthmatic airways (16). These findings indicate that regulation of PPAR expression may play a protective role in the induction and maintenance of TDI-induced asthma.
Intriguingly, our data have shown that the administration of AdPPAR without ligands resulted in the constitutive PPAR activation in TDI-induced asthma. Several studies have revealed that a range of substances produced by induction of asthma, such as 15-hydroxyeicosateraenoic acid or IL-4, can activate PPAR and enhance its expression (13, 29, 30, 31, 32). In addition, PPAR2 used in this study possesses ligand-dependent and considerable ligand-independent transactivation potential (33, 34, 35). Therefore, we suggest that the stimulation for AdPPAR by the increased several substances and cytokines produced in the airways of asthmatics and the ligand-independent activation of PPAR2 could be possible mechanisms for the constitutive PPAR activation by AdPPAR without ligands in our present asthmatic lungs.
Previous studies have demonstrated that the molecular mechanisms of PPAR-dependent anti-inflammatory responses are based on 1) the interaction of PPARs with various transcription factors stimulating inflammation, such as NF-B, AP-1, C/EBP, STAT, and NF-AT, 2) the formation of complexes between PPARs and transcriptional coactivators and corepressors, and 3) the ability of PPARs to modulate the activity of different kinases involved in various proinflammatory pathways (36, 37, 38, 39, 40, 41, 42, 43, 44, 45). NF-B plays a critical role in immune and inflammatory responses, including asthma (46, 47, 48, 49, 50, 51, 52, 53). In addition, several studies have also shown that PI3K activation enhances NF-B signaling through production of phosphatidylinositol 3,4,5-triphosphate which leads to the stimulation of several downstream targets, including the serine/threonine protein kinase Akt (54, 55, 56, 57). Determination of NF-B protein levels in nuclear extracts and p-Akt protein levels in the lung tissues has revealed that these protein levels were substantially increased in our present TDI-induced model of asthma, suggesting that NF-B and PI3K are activated. It is known that activation of this transcription factor induces a variety of inflammatory genes that are abnormally expressed in asthma. These genes include cytokines, chemokines, growth factor, and adhesion molecules (58, 59). We have also assessed whether these genes are up-regulated in the TDI-induced asthma model. As expected, expression of Th2 cytokines, adhesion molecules, chemokines, and TGF-1 was significantly increased after TDI challenge. Administration of rosiglitazone, pioglitazone, or AdPPAR resulted in significant reduction in NF-B activity as well as in expression of these Th2 cytokines, adhesion molecules, chemokines, and TGF-1. We have also shown that the increased p-Akt but not Akt protein levels in lung tissues after TDI inhalation were significantly reduced by the administration of rosiglitazone, pioglitazone, or AdPPAR. In addition, we have demonstrated that blocking of NF-B activation by BAY 11–7085 decreased the increased levels of Th2 cytokines, adhesion molecules, chemokines, and TGF-1 after TDI inhalation in our murine model. These findings suggest that a protective role of PPAR in the pathogenesis of the TDI-induced asthma is at least mediated through an NF-B-dependent mechanism.
IL-4, IL-5, and IL-13 are cytokines produced primarily by activated Th2 cells and promote airway inflammation, mucus metaplasia, subepithelial fibrosis, airway obstruction, and airway hyperresponsiveness (60, 61, 62, 63). TGF- is a profibrotic cytokine, and the TGF- isoforms are implicated in the extracellular matrix changes observed in fibrosis. In vitro, TGF- has been shown to secrete a number of extracellular matrix proteins, including collagen types I and III, fibronectin, tenascin, and proteoglycans via stimulation of fibroblasts (64, 65, 66, 67, 68, 69, 70). In addition, expression of TGF- is increased in the airways of patients with asthma and seems to correlate with disease severity and degree of subepithelial fibrosis (71). Consistent with these previous findings, in the present TDI-induced model of asthma, our results have shown that expression of cytokines and growth factor was increased after TDI challenge. Administration of PPAR agonists or AdPPAR to TDI-induced mice decreased the increased expression of Th2 cytokines and TGF-1.
In conclusion, our results have demonstrated that PPAR agonists or AdPPAR reversed all pathophysiological symptoms of TDI-induced asthma examined and reduced the increased levels of various Th2 cytokines, adhesion molecules, chemokines, and TGF-1 in TDI-induced asthma. Hence, the PPAR agonist may have therapeutic potential for the treatment of occupational asthma.
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Acknowledgments |
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Disclosures |
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Footnotes |
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1 This work was supported by a grant from the National Research Laboratory Program of the Korea Science and Engineering Foundation, by a Korea Research Foundation Grant funded by the Korea Government (MOEHRD, Basic Research Promotion Fund, KRF-2005-201-E00014), by a grant of the Korea Health 21 R&D Project, Ministry of Health and Welfare, Republic of Korea (A060169) (to Y.C.L.), and also by a grant from the Korea Health 21 R&D Project (0412-CR03-0704-0001) (to S.J.P.). 
2 K.S.L. and S.J.P. contributed equally to this work.
3 Address correspondence and reprint requests to Dr. Yong Chul Lee, Department of Internal Medicine, Chonbuk National University Medical School, San 2-20 Geumam-dong, deokjin-gu, Jeonju, Jeonbuk 561-180, South Korea. E-mail address: leeyc{at}chonbuk.ac.kr
4 Abbreviations used in this paper: TDI, toluene diisocyanate; PPAR, peroxisome proliferator-activated receptor; BAL, bronchoalveolar lavage; Ad, adenovirus; p-Akt, phosphorylated Akt; PAS, periodic acid-Schiff; RL, airway resistance; AdPPAR, adenoviruses carrying PPAR2 cDNA.
Received for publication April 19, 2006. Accepted for publication July 27, 2006.
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References |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionDisclosuresReferences |
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, p < 0.05 vs EO+TDI+ROSI.
