Expression of the Bcl-2 protein in nasal epithelia of F344/N rats during mucous cell metaplasia and remodeling

Expression of Apoptosis-Related Biomarkers in Inflamed Nasal Sinus Epithelium of Patients with Chronic Rhinosinusitis with Nasal Polyps (CRSwNP)—Evaluation at mRNA and miRNA Levels

In chronic upper respiratory tract diseases, increased cell proliferative activity is observed, which is coordinated by BCL-2 proteins and small non-coding RNAs. This study aimed to determine the expression of critical apoptosis markers at the mRNA and miRNA levels in patients with chronic rhinosinusitis with nasal polyps (CSRwNP). The study group consisted of ten patients with CSRwNP and ten healthy subjects. To detect in situ apoptosis in the maxillary sinus mucosa, TUNEL staining was performed. The expression of transcripts was determined by RT-qPCR and included the detection of markers associated with cell survival and apoptosis, i.e., BAX, p53, p21, CASP3, CASP9, c-MYC, CCND1, BRIC5, and APAF1. Levels of miR-17-5p, miR-145-5p, miR-146a-5p, and miR-203a-3p were also measured by RT-qPCR. The obtained results indicated increased apoptosis determined by a TUNEL assay in CSRwNP patients and accompanied by an increased expression of BAX, P21, P53, CASP3, CASP9, c-MYC, and APAF-1 transcripts and decreased mRNA levels of BCL-2 and BIRC5. Furthermore, the nasal sinus epithelium of patients with CSRwNP showed increased levels of miR-203a-3p while also showing a decreased expression of miR-17-5p and miR-145-5p. Our results showed that pro-apoptotic transcripts detected at mRNA and miRNA levels might be involved in the pathogenesis of chronic sinusitis with polyps. The identification of those key molecular mediators may be applicable for the specific diagnostic and/or development of targeted therapies for chronic sinusitis with polyps.

IL-13 in LPS-Induced Inflammation Causes Bcl-2 Expression to Sustain Hyperplastic Mucous cells

Exposure to lipopolysaccharides (LPS) causes extensive neutrophilic inflammation in the airways followed by mucous cell hyperplasia (MCH) that is sustained by the anti-apoptotic protein, Bcl-2. To identify inflammatory factor(s) that are responsible for Bcl-2 expression, we established an organ culture system consisting of airway epithelial tissue from the rat nasal midseptum. The highest Muc5AC and Bcl-2 expression was observed when organ cultures were treated with brochoalveolar lavage (BAL) fluid harvested from rats 10 h post LPS instillation. Further, because BAL harvested from rats depleted of polymorphonuclear cells compared to controls showed increased Bcl-2 expression, analyses of cytokine levels in lavages identified IL-13 as an inducer of Bcl-2 expression. Ectopic IL-13 treatment of differentiated airway epithelial cells increased Bcl-2 and MUC5AC expression in the basal and apical regions of the cells, respectively. When Bcl-2 was blocked using shRNA or a small molecule inhibitor, ABT-263, mucous cell numbers were reduced due to increased apoptosis that disrupted the interaction of Bcl-2 with the pro-apoptotic protein, Bik. Furthermore, intranasal instillation of ABT-263 reduced the LPS-induced MCH in bik +/+ but not bik -/- mice, suggesting that Bik mediated apoptosis in hyperplastic mucous cells. Therefore, blocking Bcl-2 function could be useful in reducing IL-13 induced mucous hypersecretion.

Tissue-specific effects of allergic rhinitis in mouse nasal epithelia

Allergic rhinitis (AR) can cause significant olfactory loss, but few studies have specifically investigated AR effects on olfactory and nasal respiratory tissues per se. To address this, we used a murine AR protocol employing nasal allergen infusion for both sensitization and challenges. Seven- to 11-week BALB/c mice were bilaterally infused with 1% ovalbumin (OVA) in phosphate-buffered saline (PBS) or PBS alone for 6 or 11 weeks, given single bilateral PBS or OVA infusions 24 h before sacrifice, or left untreated. High OVA-specific IgE serum levels and eosinophil infiltration confirmed AR induction. Olfactory (OE) and respiratory (RE) epithelia showed distinctly different responses, most conspicuously, massive eosinophil infiltration of immediately RE-subjacent lamina propria. In OE, such infiltration was minimal. Significant RE hypertrophy and hyperplasia also occurred, although OE organization was generally maintained and extensive disruption localized despite a 20% reduction in sensory neurons and globose basal cells after 11 weeks OVA. Pronounced Bowman's gland hypertrophy crowded both OE and olfactory nerve bundles. Cellular proliferation was widely distributed in RE but in OE was localized to normally thinner OE and RE-proximal OE, suggesting possible indirect RE influences. Terminal deoxynucleotide transferase (TdT) nick end labeling was greater in OE than RE and, in contrast to other effects, occurred with acute infusions and chronic PBS alone, often unilaterally. Following chronic OVA, AR-related bilateral increases appeared superimposed on those. These findings indicate AR effects on olfactory function may be complex, reflecting various levels of RE/OE responses and interactions.

Apoptosis and the airway epithelium

The airway epithelium functions as a barrier and front line of host defense in the lung. Apoptosis or programmed cell death can be elicited in the epithelium as a response to viral infection, exposure to allergen or to environmental toxins, or to drugs. While apoptosis can be induced via activation of death receptors on the cell surface or by disruption of mitochondrial polarity, epithelial cells compared to inflammatory cells are more resistant to apoptotic stimuli. This paper focuses on the response of airway epithelium to apoptosis in the normal state, apoptosis as a potential regulator of the number and types of epithelial cells in the airway, and the contribution of epithelial cell apoptosis in important airways diseases.

Differential rates of proliferation and apoptosis in nasal polyps correspond to alterations in DNA spatial distribution and nuclear polarization as observed by confocal microscopy

The study aimed to investigate the expression of p53, Bcl-2 and Ki-67 in relation to the histologic and nuclear qualitative and spatial characteristics of chronic rhinosinusitis with polyposis (CRP). Imprint smears obtained from surgically removed nasal polyps of 20 patients were studied. The polyps were classified according to their histological characteristics as: hyperplasia (simple and pronounced) and squamous metaplasia. The expression of p53, Bcl-2 and Ki-67 was assessed by immunocytochemistry. DNA spatial distribution and nuclear orientation were studied by staining with propidium iodide and examined by confocal microscopy. Positive immunoreaction for p53, Ki-67 and Bcl-2 was observed in 50, 65, and 50% of polyp's smears, respectively. For each diagnosis, the rates were simple hyperplasia 60, 80 and 30%, pronounced hyperplasia 80, 100 and 40%, metaplasia 0, 0 and 100%, respectively. Abnormal chromatin distribution and nuclear disorientation was observed in three cases of pronounced hyperplasia combined with positive immunoreaction for Ki-67 and p53 and negative immunoreaction for Bcl-2. CRP demonstrated different proliferation and apoptotic rates, according to their histology. Nuclear characteristics observed by confocal microscopy are associated with the immunocytochemical markers of proliferation and apoptosis.

Bcl-2 expression and p38MAPK activity in cells infected with influenza A virus: impact on virally induced apoptosis and viral replication

Previous reports have shown that various steps in the influenza A virus life cycle are impaired in cells expressing the antiapoptotic protein Bcl-2 (Bcl-2(+) cells). We demonstrated a direct link between Bcl-2 and the reduced nuclear export of viral ribonucleoprotein (vRNP) complexes in these cells. However, despite its negative impact on viral replication, Bcl-2 did not prevent host cells from undergoing virally triggered apoptosis. The protein's reduced antiapoptotic capacity was related to phosphorylation of its threonine 56 and serine 87 residues by virally activated p38MAPK. In infected Bcl-2(+) cells, activated p38MAPK was found predominantly in the cytoplasm, colocalized with Bcl-2, and both Bcl-2 phosphorylation and virally induced apoptosis were diminished by specific inhibition of p38MAPK activity. In contrast, in Bcl-2-negative (Bcl-2(-)) cells, which are fully permissive to viral infection, p38MAPK activity was predominantly nuclear, and its inhibition decreased vRNP traffic, phosphorylation of viral nucleoprotein, and virus titers in cell supernatants, suggesting that this kinase also contributes to the regulation of vRNP export and viral replication. This could explain why in Bcl-2(+) cells, where p38MAPK is active in the cytoplasm, phosphorylating Bcl-2, influenza viral replication is substantially reduced, whereas apoptosis proceeds at rates similar to those observed in Bcl-2(-) cells. Our findings suggest that the impact of p38MAPK on the influenza virus life cycle and the apoptotic response of host cells to infection depends on whether or not the cells express Bcl-2, highlighting the possibility that the pathological effects of the virus are partly determined by the cell type it targets.

STAT1 activation causes translocation of Bax to the endoplasmic reticulum during the resolution of airway mucous cell hyperplasia by IFN-gamma

Disruption of the normal resolution process of inflammation-induced mucous cell hyperplasia may lead to sustained mucous hypersecretion in chronic diseases. During prolonged exposure of mice to allergen, IFN-gamma reduces mucous cell hyperplasia, but the signaling responsible for the cell death is largely unknown. A brief phosphorylation of STAT1 by IFN-gamma was required for cell death in airway epithelial cells (AEC), and during prolonged exposure to allergen, mucous cell hyperplasia remained elevated in STAT1(-/-) but was resolved in STAT1(+/+) mice. Although IFN-gamma treatment of primary human AECs and other airway cell lines left Bax protein levels unchanged, it caused translocation of Bax from the cytosol to the endoplasmic reticulum (ER) but not to the mitochondria. Localization of Bax to the ER was observed in IFN-gamma-treated primary AECs isolated from STAT1(+/+) mice but not in cells from STAT1(-/-) mice. In addition, ER Bax was detected in mucous cells of STAT1(+/+) but not STAT1(-/-) airways of mice exposed to allergen for prolonged periods. IFN-gamma did not release cytochrome c from mitochondria but reduced ER calcium stores and dilated the ER, confirming that the IFN-gamma-induced cell death is mediated through changes localized in the ER. Collectively, these observations suggest that STAT1-dependent translocation of Bax to the ER is crucial for IFN-gamma-induced cell death of AECs and the resolution of allergen-induced mucous cell hyperplasia.

Intronic single-nucleotide polymorphisms in Bcl-2 are associated with chronic obstructive pulmonary disease severity

BACKGROUND AND OBJECTIVE

COPD is a multifactorial disease influenced by genetic and environmental factors, and gene-by-environmental interactions. There is considerable variability in the degree of airflow obstruction, moreover only 10-15% of chronic smokers develop COPD. These observations indicate that additional risk factors, possibly genetic, contribute to not only the susceptibility to COPD but also the development and severity of COPD. Recent paradigms highlight the presence and causal role of apoptosis in emphysema. There is a large amount of information on the genes involved in the regulation of apoptosis and one of the most studied is Bcl-2. The aim of this study was to investigate the genetic association of Bcl-2 gene with the level of lung function, that is, the severity, of COPD.

METHODS

The genetic association of Bcl-2 polymorphisms with lung function was investigated in 261 Japanese patients with COPD using 12 single-nucleotide polymorphisms (SNPs) in Bcl-2.

RESULTS

Four SNPs showed a significant association between the high and low lung function groups in a dominant trait comparison. Subsequent linkage-disequilibrium mapping and analyses of haplotype structure also showed a significant association between the level of lung function and two haplotypes comprised of the associated SNPs in Bcl-2.

CONCLUSIONS

Although the linkage between Bcl-2 gene and the susceptibility to COPD remains to be clarified, the findings of the current study indicate that Bcl-2 might be influencing the level of lung function, that is, the development and severity of COPD.

Roles of apoptosis in airway epithelia

The airway epithelium functions primarily as a barrier to foreign particles and as a modulator of inflammation. Apoptosis is induced in airway epithelial cells (AECs) by viral and bacterial infections, destruction of the cytoskeleton, or by exposure to toxins such as high oxygen and polycyclic hydrocarbons. Various growth factors and cytokines including TGF-beta, IFN-gamma, or the activators of the death receptors, TNF-alpha and FasL, also induce apoptosis in AECs. However, cell death is observed in maximally 15% of AECs after 24 h of treatment. Preincubation with IFN-gamma or a zinc deficiency increases the percentage of apoptotic AECs in response to TNF-alpha or FasL, suggesting that AECs have mechanisms to protect them from cell death. Apoptosis of AECs is a major mechanism in reducing cell numbers after hyperplastic changes in airway epithelia that may arise due to major injuries in response to LPS or allergen exposures. Resolution of hyperplastic changes or changes during prolonged exposure to an allergen is primarily regulated by the Bcl-2 family of proteins. Fas and FasL are both expressed in AECs, and their main function may be to control inflammation by inducing Fas-induced death in inflammatory cells without inducing apoptosis in neighboring cells. Furthermore, AECs engulf dying eosinophils to clear them by phagocytosis. Therefore, in the airway epithelium apoptosis serves three main roles: (1) to eliminate damaged cells; (2) to restore homeostasis following hyperplastic changes; and (3) to control inflammation, and thereby support the barrier and anti-inflammatory functions.

Persistent mucus accumulation: a consequence of delayed bronchial mucous cell apoptosis in RAO-affected horses?

This study examined the contribution of delayed apoptosis of bronchial mucous cells to mucus accumulation in equine recurrent airway obstruction (RAO). In pilot studies, Bcl-2, an apoptosis inhibitor, was detected in airway mucous cells of RAO-affected horses in remission and during acute disease, when most mucus was secreted. To study whether delayed apoptosis results in an increase in the number of mucous cells during disease recovery, six RAO-affected and six control horses were fed hay for 5 days to induce inflammation and then pellets for 7 days to partially resolve RAO before euthanasia. RAO-affected horses had more airway obstruction and luminal mucus than control horses under both management systems. At the time of euthanasia, RAO-affected horses had more inflammation and Bcl-2-positive bronchial mucous cells than control animals. In horses with >10 and <10 neutrophils per microliter of bronchoalveolar lavage fluid, >50% and <10% of mucous cells stained positive for Bcl-2, respectively. No differences in mucous cell number or amount of stored mucosubstance were observed between RAO-affected and control horses, but in RAO-affected animals, the amount of stored mucosubstance decreased as the number of neutrophils in bronchoalveolar lavage fluid increased. Because the number of mucous cells was similar in both groups of horses but only mucous cells of RAO-affected horses expressed Bcl-2 during recovery from acute disease, a conclusive role for Bcl-2 in prolonging bronchial mucous cell life could not be determined. Future studies are needed to compare horses that are kept in remission for prolonged periods when all mucous cells are fully developed.

Exacerbations of chronic obstructive pulmonary disease and chronic mucus hypersecretion

Chronic obstructive pulmonary disease (COPD) exacerbations are an important cause of the considerable morbidity and mortality found in COPD. COPD exacerbations increase with increasing severity of COPD, and some patients are prone to frequent exacerbations leading to hospital admission and readmission. These frequent exacerbations may have considerable impact on quality of life and activities of daily living. Factors that increase the risk for COPD exacerbations are associated with increased airway inflammation caused by common pollutants and bacterial and/or viral infections. These inflammatory responses cause mucus hypersecretion and, thereby, airway obstruction and associated exacerbations. While chronic mucus hypersecretion is a significant risk factor for frequent and severe exacerbations, patients with chronic mucus hypersecretion have a lower rate of relapse after initial treatment for acute exacerbation. The benefit of antibiotics for treatment of COPD exacerbations is small but significant. While the mechanisms of actions are not clear, mucolytic agents reduce the number of days of disability in subjects with exacerbations. Reducing mucous cell numbers in small airways could be a useful way to reduce chronic mucus hypersecretion. Our studies suggest that programmed cell death is crucial in the resolution of metaplastic mucous cells, and understanding these mechanisms may provide novel therapies to reduce the risk of COPD exacerbations.

Bcl-2 sustains increased mucous and epithelial cell numbers in metaplastic airway epithelium

Bcl-2, an inhibitor of apoptosis, is expressed in LPS-induced metaplastic goblet cells of rat airways. The present study investigated expression of Bcl-2 in airway mucous cells of persons with cystic fibrosis and tested in rats and mice whether its expression is responsible for sustaining metaplastic mucous cells. A significantly higher percentage of mucous cells expressed Bcl-2 in humans with cystic fibrosis compared with control subjects with no disease or subjects with other diseases. In LPS-instilled F344/N rats, the percentage of Bcl-2-positive mucous cells was decreased to background levels before the resolution of goblet cell metaplasia. Furthermore, intraperitoneal injection of rats with antisense oligonucleotides significantly reduced Bcl-2 expression and goblet cell metaplasia in nasal and pulmonary airway epithelia in rats. In contrast, sustained expression of Bcl-2 in transgenic mice by a metallothionein promoter caused increased LPS-induced goblet cell metaplasia over 8 days compared with wild-type mice. These studies demonstrate that Bcl-2 expression sustains goblet cell metaplasia in various species, that epithelial cell numbers are directly linked to the regulation of the numbers of goblet cells, and that downregulating Bcl-2 expression reduces goblet cell metaplasia.

DNA synthesis and Bcl-2 expression during development of mucous cell metaplasia in airway epithelium of rats exposed to LPS

Exposure of pulmonary airways to environmental toxins and allergens may cause proliferation of airway epithelial cells and mucous cell metaplasia (MCM); however, it is unclear to what extent proliferating cells differentiate into mucus-storing cells and contribute to MCM. Our previous studies demonstrated that Bcl-2, an inhibitor of apoptosis with cell cycle regulatory functions, is expressed in metaplastic mucous cells. The purpose of the present study was to investigate the number of metaplastic mucous cells that are derived from proliferating epithelial cells and whether Bcl-2 has a role in cell cycle entry in these cells. Rats were intratracheally instilled with 100 microg of LPS from Pseudomonas aeruginosa in 500 microl of saline, and proliferating airway cells were labeled with bromodeoxyuridine (BrdU) by implanting a subcutaneous osmotic pump 24 h before instillation. The volume of stored mucosubstance and the number of mucous cells were increased 10- and 3-fold, respectively, from 24-48 h after instillation. The number of total epithelial cells per millimeter of basal lamina increased, and the number of serous cells per millimeter of basal lamina decreased during this time. Approximately 50% of Alcian blue-periodic acid Schiff-stained mucous cells were labeled with BrdU at 48 h after instillation, suggesting that one-half of the secretory cells were derived from proliferating cells. Furthermore, 50% of the Bcl-2-positive mucous cells were BrdU negative and therefore derived from nonproliferating, preexisting cells. Our findings demonstrate that preexisting and proliferating cells differentiate into mucous cells and compose LPS-induced metaplasia and that Bcl-2 does not have cell cycle regulatory function in these cells.

LPS-induced neutrophilic inflammation and Bcl-2 expression in metaplastic mucous cells

Our previous studies show that Bcl-2, a regulator of apoptosis, may be involved in the reduction of mucous cell metaplasia (MCM) during recovery from inflammatory responses. The present study was to determine whether neutrophilic inflammation mediates Bcl-2 expression in mucous cells. Rats were intratracheally instilled with 50-1000 microg of LPS. The number of neutrophils recovered by bronchoalveolar lavage (BAL) increased with the dose of LPS, and the percentage of Bcl-2-expressing cells increased with the numbers of neutrophils in the BAL. Depletion of neutrophils did not reduce MCM, but the percentage of Bcl-2-positive cells increased 1.8-fold in neutrophil-depleted compared with controls. Injection of rats with bezafibrate, an inducer of cytochrome P-450, doubled the number of neutrophils in the BAL, decreased MCM twofold compared with vehicle-injected controls, and reduced Bcl-2 expression. Bcl-2 mRNA levels decreased in a tracheal epithelial cell line treated with bezafibrate. These data demonstrate that Bcl-2 expression is independent of the number of neutrophils in the BAL and that bezafibrate may directly reduce Bcl-2 expression in epithelial cells.

Bax is crucial for IFN-gamma-induced resolution of allergen-induced mucus cell metaplasia

Allergic airway responses cause proliferation of epithelial cells and mucus cell metaplasia (MCM), and the resolution of MCM involves reduction of cell numbers. The role of inflammation and apoptosis on this process was investigated in P-selectin +/+ and -/- mice sensitized and challenged with OVA by analyzing the expression and the role of regulators of apoptosis in metaplastic mucus cells. No differences were observed in MCM at 5 days of allergen exposure between +/+ and -/- mice, despite reduced IL-13 levels in -/- mice. Although IL-4 levels were similar in both -/- and +/+ mice, IL-13 and IL-5 levels had decreased and IFN-gamma levels were increased earlier in -/- compared with +/+ mice. MCM levels were decreased 4-fold at 7 days of allergen exposure in -/- mice and at 15 days in +/+ mice. The percentage of Bax-expressing mucus cells increased significantly at 7 days in -/- mice and at 10 days in +/+ mice. The Bax-positive mucus cells exhibited caspase-specific cleavage of cytokeratin 18. IFN-gamma caused Bax expression in IL-13-induced MCM in microdissected airway cultures. MCM remained significantly elevated in Bax -/- mice following 15 days of allergen exposure compared with +/+ mice, while the number of eosinophils was reduced in both Bax +/+ and -/- mice at 15 days. Together, these data demonstrate that reduced IL-13 levels were sufficient to elicit maximum MCM, that IFN-gamma induces Bax in metaplastic mucus cells, and that Bax plays a critical role in the resolution of MCM, but not in the resolution of eosinophils.

CCSP modulates airway dysfunction and host responses in an Ova-challenged mouse model

Clara cell secretory protein (CCSP) is synthesized by nonciliated bronchiolar cells in the lung and modulates lung inflammation to infection. To determine the role of CCSP in the host response to allergic airway disease, CCSP-deficient [(-/-)] mice were immunized twice with ovalbumin (Ova) and challenged by Ova (2 or 5 mg/m(3)) aerosol. After 2, 3, and 5 days of Ova aerosol challenge (6 h/day), airway reactivity was increased in CCSP(-/-) mice compared with wild-type [CCSP(+/+)] mice. Neutrophils were markedly increased in the bronchoalveolar lavage fluid of CCSP(-/-) Ova mice, coinciding with increased myeloperoxidase activity and macrophage inflammatory protein-2 levels. Lung histopathology and inflammation were increased in CCSP(-/-) compared with wild-type mice after Ova challenge. Mucus production, as assessed by histological staining, was increased in the airway epithelium of CCSP(-/-) Ova mice compared with that in CCSP(+/+) Ova mice. These data suggest a role for CCSP in airway reactivity and the host response to allergic airway inflammation and provide further evidence for the role of the airway epithelium in regulating airway responses in allergic disease.

Clinical and cellular effects of cytochrome P-450 modulators

Stress stimulates the hypothalamic-pituitary-adrenal axis and leads to elevated glucocorticoid hormones (GCs). GCs reduce inflammation and suppress responses mediated by cytokines, including fever and pulmonary inflammation. Besides cyclooxygenases and lipoxygenases, cytochrome P-450 enzymes (CYP), referred to as epoxygenases, are also involved in the metabolism of arachidonic acid, implicating epoxygenases in regulating inflammation and the generation of fever. Intraperitoneal injection of lipopolysaccharide (LPS) triggers fever in rats and mice, and administration of compounds known to induce CYP reduces LPS-induced fever, while inhibitors of CYP suppress fever. Consistent with these findings, inhibitors of CYP augment the elevation of LPS-induced prostaglandin E2 levels, an endogenous pyrogen, and administration of epoxygenase metabolites results in antipyresis. CYP inducers also reduce lung inflammation, the resulting mucous cell metaplasia, and the percentage of Bcl-2-positive mucous cells in rat airways after intratracheal instillation of LPS. Together, these observations indicate that CYP modulators may have therapeutic anti-inflammatory effects, and this pathway may be involved in stress-induced reduction of inflammation.

Bcl-2 in LPS- and allergen-induced hyperplastic mucous cells in airway epithelia of Brown Norway rats

Environmental toxins, infection, and allergens lead to a transient mucous cell hyperplasia (MCH) in airway epithelia; however, the mechanisms for reducing mucous cell numbers during recovery are largely unknown. This study investigated Bcl-2 expression in mucous cells induced by a neutrophilic or eosinophilic inflammatory response. Brown Norway rats intratracheally instilled with lipopolysaccharide (LPS) showed an inflammatory response characterized primarily by neutrophils. Secreted mucin was increased fourfold at 1 day, and the number of mucous cells was increased fivefold 2, 3, and 4 days post-LPS instillation compared with those in noninstilled rats. None of the mucous cells in non- or saline-instilled control animals expressed Bcl-2, whereas 20-30% of mucous cells were Bcl-2 positive 1 and 2 days post-LPS instillation. Brown Norway rats immunized and challenged with ovalbumin (OVA) for 2, 4, and 6 days showed an inflammatory response characterized primarily by eosinophils. Secreted mucin increased fivefold, and mucous cell number increased fivefold after 4 and 6 days of OVA exposure compared with water-immunized control rats challenged with OVA aerosols. Approximately 10-25% of mucous cells were Bcl-2 positive in OVA-immunized and -challenged rats. These data demonstrate Bcl-2 expression in hyperplastic mucous cells of Brown Norway rats regardless of the type of inflammatory response and indicate that apoptotic mechanisms may be involved in the resolution of MCHs.

Long-lasting effects of chronic ozone exposure on rat nasal epithelium

Ozone, the principal oxidant pollutant in photochemical smog, causes airway epithelial injury in the upper and lower respiratory tract of laboratory animals. We have recently reported that long-term inhalation exposure to ozone causes mucous-cell metaplasia (MCM) in the surface epithelium lining the nasal airways of F344 rats. The principal objective of the present study was to determine the persistence of ozone-induced MCM in the nasal epithelium after the end of a chronic exposure. Male F344/N rats were exposed to 0, 0.25, or 0.5 ppm ozone, for 8 h/d, 7 d/wk for 13 wk. Animals were killed 8 h, 4 wk, or 13 wk after the end of the chronic exposure. Ozone-related alterations in the nasal epithelium were qualitatively and quantitatively characterized through histochemistry, image analysis, and morphometric techniques. Some rats were exposed for an additional 8 h to 0.5 ppm ozone at 13 wk after the end of the chronic exposure to determine whether previous ozone exposure results in persistent changes in the sensitivity of nasal epithelium to acute injury. At the end of the chronic exposure, hyperplasia was present in the nasal epithelium of rats exposed to 0.25 and 0.5 ppm ozone. By 13 wk postexposure, this proliferative alteration was still evident only in the rats exposed to 0.5 ppm ozone. Ozone-induced MCM with associated intraepithelial mucosubstances was evident only in the nasal tissues of rats exposed to 0.5 ppm ozone. Though attenuated, these alterations in the nasal mucous apparatus were still detectable at 13 wk after the end of the exposure. At this same time after the chronic exposure, an acute (8 h) exposure to 0.5 ppm ozone induced an additional increase of mucosubstances in the nasal epithelium of rats previously exposed to 0.5 ppm ozone, but not in rats chronically exposed to 0 or 2.5 ppm ozone. The persistent nature of the ozone-induced MCM in rats documented in this report suggests that ozone exposure may have the potential to induce similar long-lasting alterations in the airways of humans.

Endotoxin potentiates ozone-induced mucous cell metaplasia in rat nasal epithelium

People are exposed to a combination of environmental pollutants throughout their lives. Repeated exposures of one common pollutant, ozone, have been reported to cause the development of mucous cell metaplasia in the nasal transitional epithelium (NTE) of rats. The present study was designed to test the hypothesis that exposure to bacterial endotoxin, another toxicant ubiquitous to the environment, potentiates this metaplastic response in rat NTE. Rats were exposed to 0 or 0.5 ppm ozone 8 h/day for 3 days. After ozone exposure, rats were intranasally instilled with saline containing 0 or 100 micrograms endotoxin once daily for 2 days. Rats were killed 6 h or 3 days after the last intranasal instillation. Nasal tissue was processed for light microscopy and image analysis, or for isolation of total RNA. Mucous cell metaplasia was not detected in air/endotoxin-exposed rats, was observed in ozone/saline-exposed rats, and was most severe in ozone/endotoxin-exposed rats. At 6 h after instillation, amounts of intraepithelial mucosubstances (IM) were 4-fold greater in NTE of ozone/endotoxin-exposed rats as compared to controls. These IM levels were similar to those of ozone/saline-exposed rats. Mucin-specific mRNA (rMuc-5AC) levels were elevated in all treatment groups at this timepoint. At 3 days after instillation, amounts of IM in ozone/endotoxin-exposed rats were 10-fold greater than in controls and 5-fold greater than in ozone/saline-exposed rats. rMuc-5AC mRNA levels remained elevated in the ozone/endotoxin-exposed rats. Despite the fact that bacterial endotoxin alone does not cause a phenotypic change in rat NTE, it can augment the mucous cell metaplasia induced by a previous exposure to ozone.