The effect of class II transactivator mutations on bleomycin-induced lung inflammation and fibrosis.

IFN-γ expression increases during the inflammatory response after bleomycin injury in mice. IFN-γ deficiency attenuates lung inflammation and fibrosis. Because IFN-γ stimulates class II transactivator (CIITA) expression, which activates major histocompatibility class (MHC) II and represses collagen expression, it was hypothesized that CIITA mediates IFN-γ action after bleomycin injury. To test this hypothesis, two CIITA mouse lines, one carrying a mutation of the leucine-rich region of CIITA (CIITA C-/-) and one with a deletion extending into the GTP-binding domain (CIITA G-/-), were used. IFN-γ treatment of lung cells isolated from both strains of mice induced mutant CIITA expression, which did not activate MHC II transcription. Collagen expression was similar in both mutant mouse strains and comparable to C57BL/6 (wild-type) mice. When mice were exposed to intratracheal bleomycin, both strains of CIITA mutant mice retained body weight and altered inflammation at 14 days after bleomycin injury compared with bleomycin-treated wild-type mice. However, there was no difference in fibrosis as judged by histology, mRNA, and protein expression of lungs. Bronchoalveolar lavage cells from CIITA C-/- and C57BL/6 lungs were examined at 3, 7, and 14 days after bleomycin injury. CD4 mRNA expression in bronchoalveolar lavage cells was down-regulated, whereas IL-4 and IL-10 expression was up-regulated, in CIITA C-/- mice, indicating a diminished, skewed Th2 response. The expression of IFN-γ was the same in all mice tested. Combined, our data suggest that CIITA mutations altered the immune response without affecting fibrosis.

A human surfactant peptide-elastase inhibitor construct as a treatment for emphysema.

Two million Americans suffer from pulmonary emphysema, costing $2.5 billion/year and contributing to 100,000 deaths/year. Emphysema is thought to result from an imbalance between elastase and endogenous inhibitors of elastase, leading to tissue destruction and a loss of alveoli. Decades of research have still not resulted in an effective treatment other than stopping cigarette smoking, a highly addictive behavior. On the basis of our previous work, we hypothesize that small molecule inhibitors of human neutrophil elastase are ineffective because of rapid clearance from the lungs. To develop a long-acting elastase inhibitor with a lung pharmacodynamic profile that has minimal immunogenicity, we covalently linked an elastase inhibitor, similar to a trifluoro inhibitor that was used in clinical trials, to a 25-amino-acid fragment of human surfactant peptide B. We used this construct to prevent human neutrophil elastase-induced emphysema in a rodent model. The elastase inhibitor alone, although in a 70-fold molar excess to elastase in a mixture with <0.6% residual elastase activity, provided no protection from elastase-induced emphysema. Covalently combining an endogenous peptide from the target organ with a synthetic small molecule inhibitor is a unique way of endowing an active compound with the pharmacodynamic profile needed to create in vivo efficacy.

Lung lining fluid glutathione attenuates IL-13-induced asthma.

GGT(enu1) mice, deficient in gamma-glutamyl transferase and unable to metabolize extracellular glutathione, develop intracellular glutathione deficiency and oxidant stress. We used intratracheal IL-13 to induce airway inflammation and asthma in wild-type (WT) and GGT(enu1) mice to determine the effect of altered glutathione metabolism on bronchial asthma. WT and GGT(enu1) mice developed similar degrees of lung inflammation. In contrast, IL-13 induced airway epithelial cell mucous cell hyperplasia, mucin and mucin-related gene expression, epidermal growth factor receptor mRNA, and epidermal growth factor receptor activation along with airway hyperreactivity in WT mice but not in GGT(enu1) mice. Lung lining fluid (extracellular) glutathione was 10-fold greater in GGT(enu1) than in WT lungs, providing increased buffering of inflammation-associated reactive oxygen species. Pharmacologic inhibition of GGT in WT mice produced similar effects, suggesting that the lung lining fluid glutathione protects against epithelial cell induction of asthma. Inhibiting GGT activity in lung lining fluid may represent a novel therapeutic approach for preventing and treating asthma.

Induction of the myofibroblast phenotype following elastolytic injury to mouse lung.

The repair of alveolar structures following endotracheal administration of porcine pancreatic elastase (PPE) to mice involves the coordinated deposition of new matrix elements. We determined the induction of the myofibroblast phenotype following elastolytic injury to mouse lung by examining the expression of alpha-smooth muscle actin (alpha-SMA) by immunohistochemistry. We also examined elastin and alpha1(I) collagen mRNA expression by in situ hybridization. Changes in airspace dimensions were assessed by determining mean linear intercept. In untreated mice, alpha-SMA was localized to vascular structures and large airways, with no detectable expression in alveolar units. PPE induced alpha-SMA expression in damaged areas surrounding large vessels, in septal remnants, and in the opening ring of alveolar ducts. Elastin and alpha1(I) collagen mRNA expression were up-regulated in residual alveolar structures and septal walls. PPE dose-response studies indicated that alpha1(I) collagen and elastin mRNA expression were not induced in areas of normal lung adjacent to damaged lung. The administration of low dose PPE resulted in increased alpha-SMA protein and elastin mRNA expression in the cells comprising the opening ring of alveolar ducts. Our data suggest that repair mechanisms following elastolytic injury are confined to overtly damaged alveolar structures and involve the induction of the myofibroblast phenotype.

Elastase mediates the release of growth factors from lung in vivo.

Uncontrolled elastase activity is involved in the development of several types of lung disease. Previous reports demonstrated that growth factors are liberated from pulmonary matrix storage sites by elastase; however, release of these entities in vivo is not well defined. In the present study, we investigated the release of fibroblast growth factor-2 (FGF-2) and transforming growth factor-beta (TGF-beta), after intratracheal instillation of porcine pancreatic elastase into mice. We found that elastase promoted a time-dependent release of FGF-2 and TGF-beta1 from the lung into bronchoalveolar lavage (BAL) fluid. A large fraction of the TGF-beta1 in BAL fluid was in the active form (approximately 60%), suggesting that elastase might participate in the activation of TGF-beta1 from its latent form. Analysis of the levels of FGF-2 and TGF-beta1 in mouse blood indicated that the growth factors in BAL fluid were not entirely derived from blood. Moreover, elastase treatment of pulmonary fibroblasts cultures caused the release of TGF-beta1, suggesting that the TGF-beta1 in BAL fluid could have come from lung cells/matrix. Additional in vitro studies also indicated that TGF-beta1 plays a role in upregulating elastin mRNA levels. These data suggest that elastase releases growth factors from lung that participate in elastolytic injury responses.

Retinoic acid does not affect alveolar septation in adult FVB mice with elastase-induced emphysema.

BACKGROUND: Administration of ALL-TRANS retinoic acid (ATRA) to adult Sprague-Dawley rats with emphysema induced by porcine pancreatic elastase (PPE) reversed the emphysema perhaps by inducing new alveolar formation. OBJECTIVE: A study was conducted to determine whether ATRA can induce new alveolar septa and reverse the airspace enlargement caused in adult mice by PPE treatment. METHODS: 48 FVB mice were divided into 6 groups. Three groups received 15 microg of PPE in 0.1 ml of 0.9% saline and 3 groups received 0.1 ml of saline, intratracheally. Starting at day 22, the mice received 12 daily intraperitoneal injections of cottonseed oil, with or without ATRA (12.5 microg or 50 microg). The mice were killed for study 1 day after the last injection. RESULTS: Measurements of plasma and lung tissue ATRA levels showed statistically significant elevated levels after the 50-microg but not after the 12.5-microg doses of ATRA. In situ hybridization studies of elastin and alpha(1)(I) collagen mRNA expression in pulmonary parenchyma as well as in airways and blood vessels showed no effect of ATRA. Airspace size was determined by the mean linear intercept (Lm) method. The Lm of the groups receiving PPE and ATRA (46.2 +/- 4.1 microm, mean +/- SD) was not significantly different from the group receiving PPE and oil (47.8 +/- 6.0 microm). The Lm for groups receiving saline and ATRA (40.6 +/- 2.5 microm) were not significantly different from the group receiving saline and oil (41.0 +/- 2.7 microm). Comparison of the fixed lung volume data and calculated internal surface area also showed no differences between the control and ATRA-treated groups. CONCLUSION: ATRA treatment does not affect airspace size or expression of elastin or alpha(1)(I) collagen mRNA in adult FVB mice with PPE-induced emphysema.

Transcriptional regulation of pulmonary elastin gene expression in elastase-induced injury.

Previously we have shown that treatment of confluent, pulmonary fibroblast cultures with elastase results in upregulation of elastin mRNA and protein levels. In the present study we focused on determining the level at which elastin expression is upregulated after elastase exposure. We examined as models for this investigation elastin gene expression in primary pulmonary fibroblast cells during the transition from subconfluent to confluent cultures and in confluent, matrix-laden cultures treated briefly with elastase. In addition, we extended our studies to mice that were given an intratracheal dose of elastase; the effects on lung elastin mRNA and elastin promoter activity levels were measured and compared with results from in vitro cell models. The results demonstrate that upregulation of elastin gene expression during the transition of subconfluent to confluent cultures and after elastase injury is associated with an increase in the level of transcription both in vitro and in vivo. Furthermore, intratracheal administration of elastase to transgenic mice illustrates that the increased levels of elastin mRNA are accompanied by increased activity of the elastin gene promoter in cells spatially positioned near major sites of tissue injury.

Severity of elastase-induced emphysema is decreased in tumor necrosis factor-alpha and interleukin-1beta receptor-deficient mice.

A single intratracheal dose of porcine pancreatic elastase, which is cleared from the lung by 24 hours, was administered to wild-type, IL-1beta type 1 receptor-deficient, double TNF-alpha (type 1 and type 2) receptor-deficient, and combined TNF-alpha (type 1 receptor) plus IL-1beta receptor-deficient mice. The mean linear intercept (Lm) of saline-treated mice was 32(3) microm [mean(SE)]. For wild-type elastase-treated mice, Lm was 81(6) microm at 21 days versus 52(5) microm at 5 days after treatment, indicating that alveolar wall remodeling occurs long after the elastase injury. At 21 days, Lm values were 67(10), 62(3), and 39(5) microm in elastase-treated mice deficient in the IL-1beta receptor, double TNF-alpha receptors, and combined receptors, respectively. The level of apoptosis assessed by a terminal deoxynucleotidyl transferase-catalyzed in situ nick end-labeling assay was increased at 5 days after elastase treatment and was markedly and similarly attenuated in the IL-1beta, the double TNF-alpha, and the combined receptor-deficient mice. Our results indicate that inflammatory mediators exacerbate elastase-induced emphysema. We estimate that in the combined TNF-alpha + IL-1beta receptor-deficient mice, inflammation accounts for about 80% of the emphysema that develops after elastase treatment; decreased apoptosis of lung cells likely contributes to decreased severity of emphysema.