Smooth muscle actin and myosin expression in cultured airway smooth muscle cells.

In this study, the expression of smooth muscle actin and myosin was examined in cultures of rat tracheal smooth muscle cells. Protein and mRNA analyses demonstrated that these cells express alpha- and gamma-smooth muscle actin and smooth muscle myosin and nonmuscle myosin-B heavy chains. The expression of the smooth muscle specific actin and myosin isoforms was regulated in the same direction when growth conditions were changed. Thus, at confluency in 1 or 10% serum-containing medium as well as for low-density cells (50-60% confluent) deprived of serum, the expression of the smooth muscle forms of actin and myosin was relatively high. Conversely, in rapidly proliferating cultures at low density in 10% serum, smooth muscle contractile protein expression was low. The expression of nonmuscle myosin-B mRNA and protein was more stable and was upregulated only to a small degree in growing cells. Our results provide new insight into the molecular basis of differentiation and contractile function in airway smooth muscle cells.

Tamoxifen induces TGF-beta 1 activity and apoptosis of human MCF-7 breast cancer cells in vitro.

We report here that the antiestrogen tamoxifen (TAM) induces cell death in human breast cancer cell line MCF-7. We assessed the type of cell death induced by TAM in this breast cancer cell line on the basis of morphological and biochemical characteristics. Dying cells showed morphological characteristics of apoptosis, such as chromatin condensation and nuclear disintegration. DNA isolated from these cells revealed a pattern of distinctive DNA bands on agarose gel. The DNA fragmentation in MCF-7 cells induced by TAM could also be detected by terminal deoxynucleotidyl transferase-mediated dUTP-biotin end labeling. Northern blot hybridization revealed a substantial increase in the amounts of TRPM-2 and TGF-beta 1 mRNAs in MCF-7 cells after treatment with TAM. In contrast, the mRNA level of the estrogen-induced pS2 gene was strongly suppressed. The biological activity of TGF-beta was increased at least fourfold in the media from MCF-7 cells treated with TAM. The results presented in this study suggest that TAM induces apoptosis of MCF-7 cells and it may be mediated by the secretion of active TGF-beta.

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.

Norepinephrine and ANG II stimulate secretion of TGF-beta by neonatal rat cardiac fibroblasts in vitro.

Transforming growth factor-beta (TGF-beta) is a ubiquitous growth-regulating protein that is capable of influencing the growth and function of heart cells in vitro. To better understand the role TGF-beta might play as a paracrine mediator of cardiac hypertrophy, the expression, secretion, and growth effects of TGF-beta were examined. Neonatal cardiac fibroblasts in vitro secreted latent TGF-beta 1 and TGF-beta 2 as high as 15 ng/10(6) cells. Angiotensin II (ANG II) and norepinephrine (NE) each augmented up to threefold the expression and secretion of latent TGF-beta 1 and TGF-beta 2 and also induced a shift in isoform predominance from beta 1 to beta 2. Each agent individually produced hypertrophic growth of neonatal cardiocytes and hyperplastic growth of cardiac fibroblasts. Paradoxically, the combination of NE and ANG II at intermediate and high concentrations resulted in less TGF-beta secretion (compared with either agent alone) and in hypertrophic growth of fibroblasts. These results suggest that the growth-promoting effects of ANG II and NE may in part be mediated via a paracrine stimulation of TGF-beta secretion.

Bronchoalveolar lavage fluid from immature rats with hyperoxia-induced airway remodeling is mitogenic for airway smooth muscle.

We previously demonstrated that hyperoxia-exposed immature rats develop airway smooth muscle layer thickening; this remodeling appears partially attributable to smooth muscle hyperplasia. In this study, we tested the hypothesis that excess mitogenic activity for airway smooth muscle cells is present within the lungs of hyperoxia-exposed immature rats. We assessed the proliferative effect of bronchoalveolar lavage (BAL) fluid from air- and O2-exposed animals on cultured rat tracheal smooth muscle cells. BAL fluids from air- or O2-exposed immature rats increased DNA synthesis ([3H]-thymidine incorporation at 24 h of incubation) and cell number (compared with DMEM-treated control cells, at 2 days of incubation), but BAL fluid from O2-exposed animals had significantly greater mitogenic effects. This excess mitogenic activity was lipid inextractable and was ablated by trypsin digestion, indicating that at least one polypeptide growth factor was responsible; molecular sieve fractionation demonstrated a molecular weight of > 10 kD. Because platelet-derived growth factor (PDGF) has been identified in other models of hyperoxia exposure, we tested the further hypothesis that PDGF contributes to the observed excess mitogenic activity. Addition of neutralizing anti-PDGF antibodies to BAL-stimulated smooth muscle cultures did not reduce BAL fluid-induced mitogenesis. These data indicate that the lungs of O2-exposed rats contain excess mitogenic activity for airway smooth muscle, attributable to non-PDGF polypeptide growth factors. It is conceivable that this abnormal mitogenic activity contributes to O2-induced airway smooth muscle remodeling observed in immature rats in vivo.

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

Transforming growth factor-beta 1 mRNA and transforming growth factor beta activity are decreased with exposure of normal adult rat lung fibroblasts to dexamethasone. Dexamethasone caused a decrease in transforming growth factor-beta 1 mRNA within 2 hours, which was sustained at least over a 24-hour period. The decrease in transforming growth factor-beta 1 mRNA was dose related. Dexamethasone treatment of rat lung fibroblasts also resulted in a decrease of transforming growth factor beta activity as determined by the mink lung cell growth inhibition assay. These data indicate that glucocorticoids may regulate collagen synthesis at least in part through the mediation of transforming growth factor-beta 1 in rat lung fibroblasts.

Oxygen-induced changes in protein synthesis and cell proliferation in cultured lung slices.

Elevated fractions of inspired O2 induce significant remodeling of the airways and vasculature of the lung. The present study was undertaken to determine the direct effects of altered levels of O2 on protein synthesis and cell proliferation in lung tissue cultured in vitro. Rat lungs were inflated with low-melt agarose, cut transversely into 1-mm sections, and cultured in a serum-free medium for up to 7 days in the presence of 10, 21, 40, or 70% O2. Tissue structure integrity was maintained as assessed by light and electron microscopy. Fractional synthesis rates (FSR, %protein/day) of soluble protein from cultured lung homogenates demonstrated an O2 concentration-dependent response. Tissue cultured in the presence of 70% O2 exhibited the highest FSR. The FSR of tissue cultured in 21 or 40% O2 did not differ and demonstrated FSR values greater than tissue cultured in 10% O2. Cell proliferation was assessed histologically in parenchymal gas-exchange regions of lung slices cultured in the presence of 5-bromo-2'-deoxyuridine. Labeling indexes for tissue cultured in 21, 40, or 70% indicated an O2-dependent increase in cell proliferation after 3 days in culture followed by a return to baseline levels after 7 days. Tissue cultured in the presence of 10% O2 showed no change in cell proliferation over time. The data indicate a direct influence of O2 on lung cell growth and proliferation. Additionally, these studies show that this in vitro model may be suitable for further understanding of the mechanistic basis involved in proliferative events during lung injury.

Automated procedures for the quantitation of protein.

An entirely automated 96-well microplate-based system to perform procedures for the measurement of protein is described. This single instrument system utilizes a series of computer-controlled mechanical subsystems to move the plate, control incubations and dispense samples or reagents in order to perform the assay. This system allows the investigator to reproducibly perform these protein assays on large numbers of biological samples with minimal effort.

Hyperoxia inhibits proliferation of cultured rat tracheal smooth muscle cells.

Exposure of the lung to elevated oxygen leads to structural and cellular injury followed by extensive tissue remodeling. In vitro models utilizing isolated cells exposed to hyperoxic conditions or exogenously added oxidants may be injurious or stimulatory depending on the specific cell type and level and duration of exposure. In the present study, proliferation of cultured rat tracheal smooth muscle cells was inhibited by oxygen concentrations of 40 and 70% compared with a "normoxic" concentration of 21%. Exposure to 70% oxygen had a hypertrophic effect on the cells, as indicated by increased cellular protein content, whereas cells exposed to 21% oxygen did not show increased protein content. Exogenously added oxidant, H2O2, resulted in complete inhibition of growth of tracheal smooth muscle cells at concentrations > 3 microM. Much higher concentrations of H2O2 were required to inhibit proliferation of vascular smooth muscle cells and rat lung fibroblasts. The heightened sensitivity of airway smooth muscle cells to oxygen and oxidants may be an important factor in the early events following hyperoxia-induced lung injury.

Bleomycin stimulates pro-alpha 1 (I) collagen promoter through transforming growth factor beta response element by intracellular and extracellular signaling.

The role of transforming growth factor beta as a mediator of the fibrogenic effect of bleomycin in lung has been investigated at the transcriptional level. Several constructs containing the rat pro-alpha 1 (I) collagen promoter fused to the chloramphenicol acetyltransferase gene were transfected into rat lung fibroblasts. Both bleomycin and transforming growth factor beta 1 increased promoter activity in fibroblasts transfected with constructs containing the transforming growth factor beta response element. Fibroblasts transfected with a deletion construct that lacks this response element did not respond to either bleomycin or transforming growth factor beta 1. Anti-transforming growth factor beta 1-neutralizing antibodies did not block the increase in promoter activity induced by bleomycin, suggesting intracellular signaling. Mutation of the transforming growth factor beta response element greatly reduced the bleomycin effect, which also infers intracellular signaling. In addition, plasmin added to the media greatly enhanced bleomycin stimulation of promoter activity demonstrating that transforming growth factor beta mediates the bleomycin effect through extracellular signaling.

Oxidant stress responses in human pleural mesothelial cells exposed to asbestos.

The generation of oxidants is a proposed mechanism of cell injury by asbestos fibers. To determine whether human pleural mesothelial cells (HMC) respond to asbestos and active oxygen species (AOS) by induction of antioxidant enzymes, cells obtained from pleural effusion were exposed to crocidolite or chrysotile asbestos or xanthine/xanthine oxidase (X/XO), a chemical-generating system of AOS. Gene expression of manganese-containing superoxide dismutase (MnSOD) and heme oxygenase (HO), endogenous enzymes involved in cell defense against oxidant stresses, was then determined. Dosage-dependent increases in steady-state mRNA levels of MnSOD and HO were observed in HMC exposed to asbestos or X/XO. However, increases in gene expression of MnSOD or HO did not occur in HMC after exposure to particulates such as polystyrene beads or riebeckite, the nonfibrous analog of crocidolite asbestos. Comparative experiments with human adult lung fibroblasts (HAL) showed less striking increases in mRNA levels of MnSOD and HO in response to asbestos, but steady-state mRNA levels for HO were increased more than fivefold in response to X/XO. To determine whether increases in mRNA levels of MnSOD were translated into protein, Western blot analyses were performed on HMC and HAL cells exposed to asbestos or X/XO. Slight increases in MnSOD immunoreactive protein were observed in HMC in response to both agents. In contrast, X/XO caused striking elevations in MnSOD protein levels in HAL cells. These results suggest that certain antioxidant enzymes are inducible in HMC after exposure to asbestos and other oxidants.

Variable expression of platelet-derived growth factor family proteins in acute lung injury.

During acute lung injury, there is an outpouring of growth factors into the alveolar space that drive local repair and fibrosis. During the remodeling that follows the instillation of bleomycin via the trachea into the adult rat, at least two platelet-derived growth factor (PDGF)-like peptides are released sequentially into lung lining fluid. Groups of four to five animals were killed at 3, 6, 15, and 26 days after exposure to bleomycin and lungs lavaged with isotonic saline. PDGF-like peptides in epithelial lining fluid (ELF) were partially purified by cation exchange chromatography and concentrated. Isolated peptides were analyzed by immunoblotting to determine their molecular weight and immunologic identity. Western blots were probed with polyclonal antibodies to PDGF-BB and PDGF-AA. PDGF-like peptides of two distinct size classes (38-40 kD and 29 kD) were present in alveolar fluid from all rats with lung injury induced by bleomycin. No PDGF-like peptides were found in comparably prepared ELF from control animals. The 38-40 kD peptide was detected only with anti-PDGF-BB antibody; the 29 kD peptide was detected only with anti-PDGF-AA antibody. The presence of these two peptides varied independently with time after exposure to bleomycin. The 38-40 kD peptide was at peak levels at 3 to 6 days. In contrast, the 29 kD peptide was present at all times following injury but with far less variation over time. In parallel with these immunoassays for PDGF-like molecules, there was abundant growth-promoting activity for fibroblasts present in concentrated ELF during the course of injury.(ABSTRACT TRUNCATED AT 250 WORDS)

What is the relationship between hemolytic potential and fibrogenicity of mineral dusts?

The hemolytic reaction to a dust is often used as a potential indicator of fibrogenicity of silicon dioxide polymorphs. However, occasionally the hemolytic response may not correlate with the observed fibrotic response in vivo. For example, amorphous silicas are very hemolytic but have little or no fibrogenic activity. In our study, heat treatment was used to alter alpha-cristobalite, a known fibrogenic dust, to a more hydrophobic surface. Comparisons were made between heated and unheated alpha-cristobalite for hemolytic activity in vitro and for lung response in vivo. Heat treatment resulted in decreased hemolytic response, but no change in the fibrotic response occurred in vivo. In addition, the heat treatment resulted in increased initial dust accumulation, reduced short-term clearance, and enhanced long-term clearance in vivo. Increased inflammatory cell recruitment was also observed in lungs of animals exposed to alpha-cristobalite. Thus, whereas heat-induced surface changes in alpha-cristobalite markedly altered the hemolytic activity of the particles, no changes were observed in the fibrotic response.

Smooth muscle myosin regulation by serum and cell density in cultured rat lung connective tissue cells.

RNA and protein analyses were used to detect expression of SM1 and SM2 smooth muscle myosin heavy chain (MHC) in cultured adult rat lung connective tissue cells (RL-90). Smooth muscle MHC mRNA expression in confluent cells grown in 10% serum was approximately 50% of the level in adult stomach. Similar results were obtained in cells cultured at low density (25% confluency) in 1% serum. However, in low-density cultures transferred to 10% serum for 24 h, the level of MHC mRNA decreased to approximately 20% of that in adult stomach. Smooth muscle alpha-actin showed a pattern of expression similar to that for smooth muscle MHC. Expression of nonmuscle MHC-A mRNA was higher in all culture conditions compared to stomach. MHC-A mRNA expression was less in low-density cultures in low serum and increased when low-density cultures were transferred to 10% serum for 24 h. MHC-B mRNA expression was less in low- vs. high-density cultures. In contrast to MHC-A, however, MHC-B mRNA expression in low-density cultures was higher in low serum. Immunofluorescence and immunoblotting with SM1-specific antibody demonstrated the presence of the SM1 protein isoform as well as reactivity to a protein band migrating slightly faster than SM2. These results demonstrate that cultured rat lung connective tissue cells express smooth muscle MHC and that expression is modulated by culture conditions.

Patterns of secretion of transforming growth factor-alpha (TGF-alpha) in experimental silicosis. Acute and subacute effects of cristobalite exposure in the rat.

Transforming growth factor-alpha (TGF-alpha) a cytokine having potent mitogenic activity for epithelial and mesenchymal cells, may play a role in the lung remodeling of silicosis. Lung macrophages are among the major cells producing TGF-alpha in a lung tissue. A pivotal event in the cascade of pathologic events leading to pulmonary silicosis is the interaction between inhaled silica and macrophages. TGF-alpha may be critical in directing the proliferation of type II pneumocytes that characterize silicosis. An inhalation model of brief exposure of pathogen-restricted male rats to 25 mg/M3 cristobalite, a highly reactive form of silicon dioxide was used to study experimental silicosis. This model is characterized by a rapid, intense, and sustained increase in macrophages, neutrophils, and lymphocytes in both alveolar and interstitial compartments of the lung. TGF-alpha was measured in an A431 cell proliferation assay made specific with the use of anti-TGF-alpha neutralizing antiserum in epithelial lining fluid (ELF) and conditioned media harvested from cultured alveolar and interstitial macrophages. Soluble TGF-alpha levels found in ELF were slightly elevated above control values during the exposure period, then increased 5-fold during the 20 weeks after the 8-day exposure period. Secretion of TGF-alpha by macrophages was elevated during exposure to cristobalite but then fell during the early post exposure period. Marked elevations in TGF-alpha secretion from both interstitial and alveolar macrophages (10- and 12-fold, respectively) occurred 8-16 weeks after cessation of exposure.(ABSTRACT TRUNCATED AT 250 WORDS)

Auto-induction of transforming growth factor-beta in human lung fibroblasts.

The type beta transforming growth factors (TGF-beta s) are a family of potent cytokines with diverse effects on proliferation, differentiation, turnover of extracellular matrix components, oncogene expression, and other aspects of cellular phenotype. Unlike lung fibroblasts of certain species, unstimulated human lung fibroblast lines produce little or no TGF-beta in culture. However, TGF-beta has been reported to autoregulate its own production in certain human tumor cells and in rodent cell lines. To test whether this phenomenon is operative in fibroblasts from normal human lung tissue, confluent cultures of IMR90 normal fetal lung fibroblasts were exposed to TGF-beta. Cultures were exposed briefly to purified TGF-beta 1 under serum-free conditions and secretion of newly synthesized TGF-beta over the ensuing 72 h was determined by immunoblotting and bioassays made specific with the use of neutralizing antibodies. Steady-state levels of mRNA for TGF-beta 1 were detected by Northern and slot blot hybridization analysis of total cellular RNA. The 2.5 kb TGF-beta 1 mRNA species rose within 1.5 h of exposure of IMR90 cells to TGF-beta 1 and reached maximal levels after 16 h. Increased levels of TGF-beta were detected in conditioned medium 9 h after the start of the exposure. Thereafter, TGF-beta continued to accumulate at an elevated rate (90 +/- 7 versus < or = 15 pg/10(6) cells/h in uninduced cells) for up to 72 h. As little as 1 ng/ml TGF-beta 1 auto-induced TGF-beta secretion.(ABSTRACT TRUNCATED AT 250 WORDS)

Complex cytokine modulation of a continuous line of mink lung epithelial cells (Mv1Lu).

The continuous mink lung epithelial cell line Mv1Lu has proven to be a sensitive reporter line in the bioassay for purified TGF-beta, exhibiting a sigmoid-shaped concentration-response relationship with an EC50 of 12 pM (0.3 ng/mL). Maximal inhibition of Mv1Lu cells generates a 75-95% decrement in the number of adherent cells. However, this bioassay is not specific for TGF-beta as originally claimed. Mv1Lu cells are sensitive to other cytokines and substances found in complex biological fluids. In this study the effects of other biological response modifiers in this assay were tested and several were found to have important growth modulatory capacities that confound the quantitation of TGF-beta. EGF, TGF-alpha, fibronectin, and IGF-I all induce Mv1Lu cell proliferation. In contrast, neither PDGF (-AA, -AB, -BB) nor endotoxin (< or = 10 micrograms/mL) affect Mv1Lu cell number. TGF-beta and TNF-alpha at high concentrations (> or = 10 ng/mL) are the only cytokines examined that inhibit Mv1Lu proliferation. TGF-beta decreases final cell number both by preventing mitosis and by inhibition of adherence of cells to the uncoated dish. Several strategies are suggested to assure the specificity of this otherwise convenient bioassay for TGF-beta.

Intrathoracic distribution and transport of aerosolized silica in the rat.

Short-term exposure of rats to aerosols of the silicon dioxide, cristobalite, leads to pulmonary inflammation persisting several months. Clearance of particles occurs during the first two weeks after cessation of exposure, after which there is little additional clearance in the whole lung. In the present studies, quantitation of silica in lung compartments at selected times following exposure indicated movement of particles between the alveolar space and the lung tissue per se, with increased alveolar silica content associated with decreased silica content in the tissue compartment. Further, changes in the silica content in the alveolar compartment were generally associated with fluctuations in the alveolar macrophage population. Silica accumulated linearly in the mediastinal lymph nodes and thymus for several months after cessation of exposure, while negligible amounts were found in kidney, spleen, liver, and blood. A compartmental model was used to describe the distribution and translocation kinetics of the inhaled silica in the lung and extrapulmonary tissues.

Spontaneous production of PDGF A-chain homodimer by rat lung fibroblasts in vitro.

Platelet-derived growth factor (PDGF) is considered a decisive mediator of fibroblast growth and phenotype within the lung. The cellular sources of PDGF within the lung remain undefined. The ability of lung fibroblasts themselves to produce PDGF in vitro was therefore investigated. Northern and Western blot analyses revealed the expression of PDGF-A mRNA and secretion of A-chain containing proteins by fibroblasts derived from adult and fetal rat lung. PDGF-A gene or protein expression were below the limits of detection in two human lung fibroblast lines examined in a similar manner. PDGF-B transcripts or proteins were not detected in any lung fibroblast line examined. Conditioned medium (CM) was collected from these same lung fibroblast lines and tested for its ability to promote cell growth using human fetal lung fibroblasts as targets. Both adult and fetal rat lung fibroblasts were found to produce a potent and efficacious stimulus for cell growth. Growth-promoting activity in rat fibroblast-derived CM functioned as a "competence" factor and was partially inhibited by anti-PDGF antibody. Thus rat lung fibroblasts in vitro produce potent growth factors of which at least one appears to be PDGF-AA. Differences in the expression of PDGF-AA between rat and human lung fibroblasts exist. Growth factor-producing fibroblasts may play a role in lung repair and remodeling through production PDGF-AA in vivo.

Expression of antioxidant enzymes in rat lungs after inhalation of asbestos or silica.

Several studies indicate that active oxygen species play an important role in the development of pulmonary disease (asbestosis and silicosis) after exposure to mineral dust. The present study was conducted to determine if inhaled fibrogenic minerals induced changes in gene expression and activities of antioxidant enzymes (AOE) in rat lung. Two different fibrogenic minerals were compared, crocidolite, an amphibole asbestos fiber, and cristobalite, a crystalline silicon dioxide particle. Steady-state mRNA levels, immunoreactive protein, and activities of selected AOE were measured in lungs 1-10 days after initiation of exposure and at 14 days after cessation of a 10-day exposure period. Exposure to asbestos resulted in significant increases in steady-state mRNA levels of manganese-containing superoxide dismutase (MnSOD) at 3 and 9 days and of glutathione peroxidase at 6 and 9 days. An increase in steady-state mRNA levels of copper, zinc-containing superoxide dismutase (CuZnSOD), was observed at 6 days. Exposure to asbestos also resulted in overall increased enzyme activities of catalase, glutathione peroxidase and total superoxide dismutase in lung. In contrast, silica caused a dramatic increase in steady-state levels of MnSOD mRNA at all time periods and an increase in glutathione peroxidase mRNA levels at 9 days. Activities of AOE remained unchanged in silica-exposed lungs. In both models, increases in gene expression of MnSOD correlated with increased amounts of MnSOD immunoreactive protein in lung and the pattern and extent of inflammation. These data indicate that the profiles of AOE are dissimilar during the development of experimental asbestosis or silicosis and suggest different mechanisms of lung defense in response to these minerals.