AJP - Lung Columbus Instruments
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

Am J Physiol Lung Cell Mol Physiol 277: L511-L522, 1999;
1040-0605/99 $5.00
This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Wu, R.
Right arrow Articles by Tarkington, B.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Wu, R.
Right arrow Articles by Tarkington, B.
Vol. 277, Issue 3, L511-L522, September 1999

Differential expression of stress proteins in nonhuman primate lung and conducting airway after ozone exposure

Reen Wu1,2,3, Yu Hua Zhao3, Charles G. Plopper2,3, Mary Mann-Jong Chang3, Ken Chmiel3, John J. Cross3, Alison Weir2, Jerold A. Last1,3, and Brian Tarkington3

1 Division of Pulmonary and Critical Care Medicine; 2 Department of Veterinary Anatomy, Physiology, and Cell Biology; and 3 Center for Comparative Respiratory Biology and Medicine, University of California, Davis, California 95616


    ABSTRACT
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES

The presence of seven stress proteins including various heat shock proteins [27-kDa (HSP27), 60-kDa (HSP60), 70-kDa (HSP70) and its constitutive form HSC70, and 90-kDa (HSP90) HSPs] and two glucose-regulated proteins [75-kDa (GRP75) and 78-kDa (GRP78) GRPs] in ozone-exposed lungs of nonhuman primates and in cultured tracheobronchial epithelial cells was examined immunohistochemically by various monoclonal antibodies. Heat treatment (42°C) resulted in increased HSP70, HSP60, and HSP27 and slightly increased HSC70 and GRP75 but no increase in GRP78 in primary cultures of monkey tracheobronchial epithelial cells. Ozone exposure did not elevate the expression of these HSPs and GRPs. All of these HSPs including HSP90, which was undetectable in vitro, were suppressed in vivo in monkey respiratory epithelial cells after ozone exposure. Both GRP75 and GRP78 were very low in control cells, and ozone exposure in vivo significantly elevated these proteins. These results suggest that the stress mechanism exerted on pulmonary epithelial cells by ozone is quite different from that induced by heat. Furthermore, differences between in vitro and in vivo with regard to activation of HSPs and GRPs suggest a secondary mechanism in vivo, perhaps related to inflammatory response after ozone exposure.

oxidant injury; immunohistochemistry; air pollutants


    INTRODUCTION
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES

OZONE IS AN EXTREMELY REACTIVE oxidant gas. Its toxicity is complex because of the large number of biological systems that can be affected and the variable interactions between ozone and various cellular components (5, 8, 27). Lungs and conducting airways are primary sites of ozone toxicity. The primary sites of damage include the trachea, distal bronchioles, centriacinar region, and alveolar ducts (6, 12, 30). The extent of the damage in various anatomic sites appears to be more extensive in the trachea and distal bronchioles than in the bronchi; however, increasing the concentration of ozone exposure not only results in more severe lesions but also extends the lesions into the lung (1, 9, 31).

Despite these well-illustrated in vivo lesions, the biochemical toxicity of ozone and its stress effects on pulmonary cells, especially on target airway epithelial cells, remain unresolved. Since the discovery of the phenomenon by Ritossa (34), we have known that cells from all organisms respond to a variety of stresses by the rapid transcription and subsequent translation of a group of highly conserved proteins known as heat shock proteins (HSPs) (20) and glucose-regulated proteins (GRPs) (19), now collectively called stress proteins. Some of these stress proteins appear to function protectively in cells in response to different stress agents. For instance, GRPs are induced due to the stress related to glucose starvation or defects in glycoprotein processing (19, 21, 47). These GRPs are found largely at the cytosol of the stressed cells (21, 26). In contrast, some HSPs are translocated into the nucleus in response to stress. For instance, heat-induced 70-kDa HSP (HSP70) is found in nucleoli immediately after heat treatment (29, 45). This translocation is apparently related to the reassembly of damaged preribosomal ribonuclear proteins. Thus the induction of different sets of stress proteins may be related to the pathway of stress-induced response. In this study, we seek to elucidate the association between the synthesis of stress proteins and the stress that is induced by the exposure of airway epithelium to ozone both in vivo and in vitro. The correlation of the synthesis of some of these stress proteins with ozone toxicity and the recovery from injury in target airway epithelial cells may provide a biochemical clue to the nature of ozone toxicity in vivo.

Cohen et al. (4) have demonstrated an elevated synthesis of various HSPs in isolated guinea pig airway epithelial cells and alveolar macrophages induced by heat, sodium arsenite, and acidic gas but not by ozone or hydrogen peroxide. This result is consistent with the recent experiment by Sun et al. (39) in which the immortalized human bronchial epithelial cell line BEAS-2B was exposed to various concentrations of ozone in vitro. However, we have demonstrated an induced synthesis of a 45-kDa protein by ozone, and this induction appears to be dose dependent on ozone from 0.1 to 1.0 part/million (ppm). In contrast, this induction is not correlated with heat-induced HSP synthesis. Recently, both Wong et al. (50) and Su and Gordon (38), using Western blot analysis, have observed an enhanced HSP70 inducible form level in lung tissue extracts from rats and guinea pigs, respectively, after ozone exposure. This increase was also observed in the lavage fluid preparation from guinea pig lungs after ozone exposure (38). However, neither study revealed the cell type(s) responsible for the increase in HSP70 in the preparation.

Because stress proteins can also be induced by means other than heat treatment, such as metabolic starvation by glucose deprivation, it is important to extend the stress protein synthesis study to proteins other than via the heat-induced mechanism. In this study, we used monospecific monoclonal antibodies (MAbs) of seven stress proteins, including those of HSPs and GRPs, to examine the presence of these stress proteins in monkey airway tissues and primary cultures of airway epithelial cells after ozone exposure. We have observed a consistently enhanced presence of GRPs but not of HSPs in airway epithelial cells after ozone exposure in vivo. In contrast, ozone exposure in vitro had no effect on the level of HSP and GRP expression despite the observed enhancement of HSP expression by heat.


    MATERIALS AND METHODS
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES

Source of Monkeys, Tracheobronchial Tissues, and In Vitro Culture Conditions

Specific pathogen-free monkeys provided by the California Regional Primate Research Center at the University of California, Davis were used for both in vivo and in vitro ozone exposure and in vitro isolation of tracheobronchial epithelial (TBE) cells for primary culture. All procedures were approved by the University Animal Protocol Review Committee. These tissues were immersed in minimal essential medium and immediately delivered on ice to the laboratory. TBE cell isolation and culture conditions were carried out as previously described (23, 35). The isolated TBE cells were plated on a collagen gel substratum in Millicell inserts at a density of 1 × 104 cells/cm2 as previously described (39, 41, 49). After 4 days of incubation in the vitamin A (retinol; 1 µM)-supplemented, serum-free hormone-supplemented medium, the primary TBE cells were maintained biphasically in a well-humidified environment as previously described (39, 41). Four days later, a confluent culture was obtained and used subsequently for ozone exposure and heat (42°C) treatment.

In Vivo Ozone Exposure

Three healthy rhesus monkeys were exposed to chemically and biologically filtered air for 90 days, while three monkeys were exposed to 89 days of filtered air plus 1 day of 0.98 ppm ozone (8 h/day) and an additional three monkeys were exposed to 0.98 ppm ozone 8 h/day for 90 days. The animal housing, exposure, ozone generation, and monitoring were conducted according to standard procedures at the California Regional Primate Research Center Inhalation Exposure Facility (17). The animals were maintained with a 10:14-h light-dark cycle. At the end of the exposure, the animals were deeply anesthetized and their lungs were removed and fixed for paraffin block preparation as previously described (5, 31).

In Vitro Exposure and Heat Treatment

TBE cells cultured between the air phase and liquid medium, with no medium on the apical phase of epithelial cells, were exposed to either filtered air or ozone of various concentrations (0.1-1.0 ppm) as previously described (39-41). Ozone monitoring during exposure was carried out as previously described (40) with a computer-based data-acquisition system connected to the ozone analyzer. For heat treatment, the medium in the TBE cultures was replaced by freshly prewarmed (42°C) medium, and cultures that were under a medium-immersed condition were maintained at 42°C for several hours.

Determination of Injury on Cultured Cells by Ozone and Heat

Two colorimetric methods based on the metabolic activity of mitochondria were used in this study to assess cell injury after ozone exposure or heat (42°C) treatment. One method, developed by Mosmann (25), was based on the cleavage of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), which occurs in all living, metabolically active cells but not in cells that are not viable. The other method is based on the same principle with a water-soluble dye, Alamar blue, according to the manufacturer's suggested protocol (Alamar, Sacramento, CA) (39). The amount of color change in these two methods has been demonstrated to be directly proportional to the cell number, which was determined by a hemocytometer or an electronic Coulter counter. The viability assays based on these two methods are not only simpler but are also compatible with the traditional trypan blue dye exclusion method (41).

Sources of Antibodies and Immunoanalysis Methods

MAbs specific to seven stress proteins were obtained commercially. Clone G3.1, obtained from StressGen Biotechnologies, is of IgG1 class and specific to human 27-kDa HSP (HSP27) (3, 10). Clone 4B9/89, a product of Affinity BioReagents (Neshanic Station, NJ), is of IgG2a class and specific to human mitochondrial 60-kDa HSP (HSP60) (37). Clone C92F3A-5, an IgG1 class compound obtained from StressGen, is specific for the inducible form of human HSP70 (43, 48). Clone 1B5, obtained from StressGen, is of IgG1a class and specific for the constitutive form of HSP70, referred to as HSC70 (13, 18, 28). Clone 9D2, obtained from StressGen, is of IgG2a class and specific to human 90-kDa HSP (HSP90) (16). Clone 30A5, obtained from StressGen, is specific for 75-kDa GRP (GRP75) (22). Clone 10C3, obtained from StressGen, is specific for 78-kDa GRP (GRP78; BiP) and is of IgG2a class (44). These antibodies were used according to the manufacturers' suggested protocols. The antibodies were also used in both Western blot analysis and immunocytochemistry according to previous publications (14, 42). A Vectastain Elite ABC kit (Vector Laboratories, Burlingame, CA) was used for both immunohistochemical staining and Western blot analysis. In the Western blot analysis, an equal amount of protein (20 µg/lane) was loaded on a SDS-polyacrylamide gel for electrophoresis. To further verify the uniformity of protein loading, a parallel gel was stained with Commassie brilliant blue for a visual inspection. Protein concentration was determined by Bradford's (2) method (Bio-Rad, Hercules, CA). The control slides were stained in the absence of the primary antibody or with other unrelated MAbs.


    RESULTS
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES

Specificity of Antibodies and Induction of Stress Protein Synthesis In Vitro

Initially, we had to determine the specificity of these MAbs to stress proteins of monkey TBE cells because these antibodies were raised against human proteins. Using heat treatment, elevation of some of these stress proteins could be characterized. As shown by Western blot analysis (Figs. 1 and 2), six of seven antibodies used in this study [all except anti-HSP90 (clone 9D2)] reacted in only one protein band of monkey cell extract compared with the control cultures (Figs. 1E and 2B) in which the primary antibody was replaced by control mouse serum. The corresponding molecular masses of these single-protein bands were consistent with the human ones, suggesting the monospecific nature of these antibodies against the monkey stress proteins. Clone 9D2, an HSP90-specific MAb, did not stain any band over the bands found in control cultures (data not shown).


View larger version (55K):
[in this window]
[in a new window]
  		Fig. 1.   Western blot analysis of heat stress proteins (HSPs) in primary cultures of monkey tracheobronchial epithelial (TBE) cells during heat treatment. TBE cells were cultured in serum-free hormone-supplemented medium as described in text. After 8 days of incubation at 37°C, temperature was raised to 42°C for various lengths of time. Cells were lysed by SDS lysis buffer, and proteins were separated on SDS-polyacrylamide gel by electrophoresis. Protein gel was then electrophoretically blotted to a nitrocellulose membrane (38). Antibodies to 70-kDa HSP (HSP70; clone C92F3A-5; A), constitutive form of HSP70 (HSC70; clone 1B5; B), 60-kDa HSP (HSP60; clone 4B9/89; C), and 27-kDa HSP (HSP27; clone G3.1; D) and control mouse serum (E) were used to stain the membrane as previously described (42). S, standard molecular-mass proteins (nos. on left); 1, untreated cultures at 37°C; 2, cultures treated at 42°C for 4 h; 3, cultures treated at 42°C for 6 h; 4, cultures treated at 42°C for 8 h.



View larger version (58K):
[in this window]
[in a new window]
  		Fig. 2.   Western blot analysis of glucose-regulated proteins (GRPs) in primary cultures of monkey TBE cells during heat treatment. Experiments were carried out as described in Fig. 1. A: 75-kDa GRP (GRP75; clone 30A5). B: control mouse serum. C: 78-kDa GRP (GRP78; clone 10C3). Note: a different Vectastain ABC kit from that used in A and B was used in C. S, standard molecular-mass proteins (nos. on left); 1, untreated cultures at 37°C; 2, cultures treated at 42°C for 4 h; 3, cultures treated at 42°C for 6 h; 4, cultures treated at 42°C for 8 h.

An elevation in the incubation temperature from 37 to 42°C significantly enhanced the abundance of HSP70 (Fig. 1A), HSP27 (Fig. 1D), and, to a lesser extent, HSP60 (Fig. 1C) as demonstrated by Western blot analysis. As a comparison, the constitutively expressed HSP70 form, HSC70, was only slightly elevated by the high-temperature treatment (Fig. 1B). In contrast to these HSPs, the response of GRPs to high-temperature treatment was either slight or nil. For GRP75, there was a slight elevation in the cells after heat treatment (Fig. 2A), whereas there was no obvious increase for GRP78 (BiP; Fig. 2C).

In contrast to the heat treatment, exposed cultured cells under the biphasic culture condition to ozone at 1 ppm for 90 min showed no significant increase or a decrease in the abundance of HSP27 (data not shown) or HSP70 (Fig. 3A). These results are consistent with the previous study (39) in an immortalized human bronchial epithelial cell line (BEAS-2B), which demonstrated an elevated synthesis of HSPs as analyzed by a two-dimensional SDS-PAGE system after heat but not after the ozone exposure treatment, even though both treatments injured cells substantially. A similar conclusion was obtained with GRPs. As shown in Fig. 3B, there was no effect on the GRP78 level in cultured cells after ozone exposure. This nonresponse phenomenon was not related to the protein loading because the loading was verified by Commassie blue staining (Fig. 3C). It is necessary to point out that these in vitro ozone exposure experiments have been repeated more than five times and on only one occasion have the levels of GRP75 and GRP78 been elevated by ozone (data not shown). The reason for this inconsistency in this particular experiment is not clear. Nevertheless, most studies have consistently demonstrated no change in the levels of stress proteins in monkey TBE cells in vitro by ozone.


View larger version (36K):
[in this window]
[in a new window]
  		Fig. 3.   Western blot analysis of stress proteins in primary cultures of monkey TBE cells after ozone exposure. Primary cells were cultured biphasically as described in text. On day 10, cultures with no liquid medium on apical side were exposed to filtered air (FA) or 1 part/million (ppm) ozone for 90 min. At various times after incubation, protein extracts were prepared from these cultures and subjected to Western blot analysis as described in Fig. 1. A: anti-HSP70 (clone C92F3A-4). B: anti-GRP78 (clone 10C3). C: gel stained with Commassie blue to demonstrate equal input of protein in each well of gel. S, standard molecular-mass proteins (nos. on left); 1, cultures before exposure; 2, cultures exposed to FA and 0-h postexposure incubation; 3, cultures exposed to ozone and 0-h postexposure incubation; 4, cultures exposed to FA and 24-h postexposure incubation; 5, cultures exposed to ozone and 24-h postexposure incubation.

Immunohistochemical Comparison of HSP Distribution In Vivo

Morphological lesions in monkey lungs after 0.98 ppm ozone exposure have been reported (1, 6, 9, 12, 30). With the use of the same set of tissue sources, except prepared in paraffin sections, an immunohistochemical comparison of stress protein distribution was carried out. For identifying stress protein-related antigens, MAbs monospecific to stress proteins, as demonstrated in the Western blot analysis, were used. The following analysis represents a summary from tissue sections prepared from three monkey lungs. Only representative pictures are presented.

Anti-HSP27 (clone G3.1). The labeling was heaviest in the epithelium and smooth muscle of the proximal bronchi and respiratory bronchioles in filtered-air control monkey lungs (Fig. 4, A and B, respectively). Labeling in the respiratory bronchioles included both the cuboidal and squamous epithelial populations. There was also focal labeling of epithelial and interstitial elements in the interalveolar septa. After either short-term (1-day) or long-term (90-day) exposure to ozone, there was a marked reduction in the expression of this protein in all compartments but primarily in the epithelium and interstitial compartments (Fig. 4, C-F). In the proximal bronchi, there was a restriction of the protein expression to the most apical boundaries of ciliated cells and to some of the low cuboidal cells (basal cells) adjacent to the basal lamina (data not shown). In the respiratory bronchioles, there was a reduction in the epithelial cells that reacted positively with this antibody and a reduction in the intensity in labeled cuboidal epithelium (Fig. 4D). This reduction was even more marked in animals exposed for a long time to ozone, with protein expression in the epithelium markedly reduced to very focal portions of some ciliated cells of proximal bronchi and to a very small number of cells in the respiratory bronchioles (Fig. 4, E and F). Binding to the smooth muscle of both blood vessels and peribronchial areas did not appear to be altered by ozone exposure.


View larger version (120K):
[in this window]
[in a new window]
  		Fig. 4.   Immunohistochemical staining of monkey lung with anti-HSP27 (clone G3.1). Lung tissues after FA (A and B) and 0.98 ppm ozone exposure (C-F) were fixed, and paraffin sections were prepared. Immunostaining on these paraffin-sectioned slides was carried out as previously described (14). A: bronchus, FA. B: distal bronchiolar region, FA. C: bronchus, 8 h of ozone and 16-h postexposure incubation. D: distal bronchiolar region, 8 h of ozone and 16-h postexposure incubation. E: bronchus, 90 days of ozone (8 h/day) and 16-h postexposure incubation. F: distal bronchiolar region, 90 days of ozone (8 h/day) and 16-h postexposure incubation. Bars, 50 µm.

Anti-HSP60 (clone 4B9/89). In filtered-air control animals, HSP60 immunoreactivity was observed in all cellular and interstitial compartments. There was intense labeling of epithelial cells and interstitial elements, including smooth muscle and cartilage, and in both the endothelial and smooth muscle compartments of large vessels (Fig. 5A). All elements of the respiratory bronchioles and the gas-exchange parenchyma were also strongly labeled (Fig. 5B). Short-term exposure to ozone did not alter the distribution of this protein within the lung (Fig. 5, C and D). Long-term exposure, in contrast, significantly reduced the intensity of the labeling in the gas-exchange compartments, leaving only focal areas of intense staining in what appeared to be cuboidal cells of the interalveolar septa (Fig. 5, E and F). The epithelial and interstitial components of the respiratory bronchioles also had significantly reduced labeling, with the exception of the peribronchiolar smooth muscle. In the proximal bronchi, there was a redistribution of the antigen to the apical portions of ciliated cells. There was no alteration of labeling in large blood vessels in long-term exposed animals.


View larger version (103K):
[in this window]
[in a new window]
  		Fig. 5.   Immunohistochemical staining of monkey lung with anti-HSP60 (clone 4B9/89). Experiments were carried out as described in Fig. 4. A: bronchus, FA. B: distal bronchiolar region, FA. C: bronchus, 8 h of ozone and 16-h postexposure incubation. D: distal bronchiolar region, 8 h of ozone and 16-h postexposure incubation. E: bronchus, 90 days of ozone (8 h/day) and 16-h postexposure incubation. F: distal bronchiolar region, 90 days of ozone (8 h/day) and 16-h postexposure incubation. Bars, 50 µm.

Anti-HSP70 (clone C92F3A-5). In filtered-air control animals, a moderate level of reactivity was observed in the epithelial cells lining the conducting airways and respiratory bronchioles (Fig. 6, A and B, respectively). The predominant epithelial labeling occurred in the apex of the ciliated cell population and in the cuboidal cells of the respiratory bronchioles. There was some expression in the interstitial connective tissues surrounding the airways and in the chondrocytes of the peribronchial cartilage. In the distal airways, there was a low level of binding in most of the connective tissue elements and in what appeared to be the interstitium of the interalveolar septa. After short-term exposure to ozone, there appeared to be a minimal reduction in the expression of HSP70 antigen in the epithelium and connective tissue (Fig. 6, C and D). In the respiratory bronchioles, a large number of cuboidal cells that contained labeling for this protein were present (Fig. 6D). After long-term exposure to ozone, there was little change in the expression of this protein except for focal decreases in the labeling in bronchiolar epithelial cells (Fig. 6, E and F).


View larger version (120K):
[in this window]
[in a new window]
  		Fig. 6.   Immunohistochemical staining of monkey lung with anti-HSP70 (clone C92F3A-5). Experiments were carried out as described in Fig. 4. A: bronchus, FA. B: distal bronchiolar region, FA. C: bronchus, 8 h of ozone and 16-h postexposure incubation. D: distal bronchiolar region, 8 h of ozone and 16-h postexposure incubation. E: bronchus, 90 days of ozone (8 h/day) and 16-h postexposure incubation. F: distal bronchiolar region, 90 days of ozone (8 h/day) and 16-h postexposure incubation. Bars, 50 µm.

Anti-HSC70 (clone 1B5). The distribution of HSC70 in filtered-air control animals was similar to that observed for anti-HSP27 (clone G3.1; data not shown). The reduction and compartmental changes associated with short- and long-term exposure to ozone with clone G3.1 were also observed with clone 1B5.

Anti-HSP90 (clone 9D2). In filtered-air control animals, there was moderate reactivity for this protein in the epithelial cells of the proximal bronchi, but there was limited reactivity to the apexes of some ciliated cells, a moderately intense distribution in smooth muscle and connective tissue elements of both vessels and airways, and minimal labeling in the interalveolar septa (Fig. 7, A and B). After short-term exposure to ozone, there was no significant difference in the distribution of this protein compared with filtered-air control animals. After long-term exposure to ozone, there was a reduction in the expression of this protein throughout the parenchymal mass (Fig. 7, C and D). Little distribution change occurred in the proximal conducting airways, in either the epithelium or interstitial components, or in the large vessels and bronchiolar components of the respiratory bronchioles.


View larger version (99K):
[in this window]
[in a new window]
  		Fig. 7.   Immunohistochemical staining of monkey lung with anti-HSP90 (clone 9D2). Experiments were carried out as described in Fig. 4. A: bronchus, FA. B: distal bronchiolar region, FA. C: bronchus, 90 days of ozone (8 h/day) and 16-h postexposure incubation. D: distal bronchiolar region, 90 days of ozone (8 h/day) and 16-h postexposure incubation. Bars, 50 µm.

Immunohistochemical Comparison of GRP Distribution In Vivo

Anti-GRP75 (clone 30A5). In filtered-air control animals, the intensity of labeling for clone 30A5 was minimal (Fig. 8, A and B). There was a light density in the ciliated epithelial cells and in some cells of the cartilage. In the distal airways and the gas-exchange area, there was little labeling, with the exception of a slightly increased intensity in smooth muscle. After short-term exposure to ozone, there was an elevated intensity of labeling, primarily in the connective tissue of proximal airways (Fig. 8C). The intensity of labeling in the bronchial epithelium also increased at the apexes of ciliated cells, but the distribution of this labeling was not changed from that in the control animals. In the respiratory bronchioles (Fig. 8D), the epithelium on the nonalveolarized side showed intense labeling, and there was some increase in bronchiolar epithelial labeling in other parts of the respiratory bronchiole. There appeared to be some increase in the interstitial labeling of the interalveolar septa but not a major alteration in the peribronchial connective tissue distribution. In animals exposed long term to ozone, the intensity and distribution of labeling in the proximal bronchial epithelium did not change markedly from that of control or short-term exposed animals (Fig. 8, E and F). The primary difference was a decrease in the intensity of the interstitial labeling. In the distal airways, especially the respiratory bronchioles, there was a reduction in labeling in all compartments except the smooth muscle of blood vessels. No clearly definable labeling occurred in epithelial cells in either the respiratory bronchiole or gas-exchange area.


View larger version (121K):
[in this window]
[in a new window]
  		Fig. 8.   Immunohistochemical staining of monkey lung with anti-GRP75 (clone 30A5). Experiments were carried out as described in Fig. 4. A: bronchus, FA. B: distal bronchiolar region, FA. C: bronchus, 8 h of ozone and 16-h postexposure incubation. D: distal bronchiolar region, 8 h of ozone and 16-h postexposure incubation. E: bronchus, 90 day of ozone (8 h/day) and 16-h postexposure incubation. F: distal bronchiolar region, 90 days of ozone (8 h/day) and 16-h postexposure incubation. Bars, 50 µm.

Anti-GRP78/Bip (clone 10C3). In filtered-air control animals, there was minimal distribution of this antigen in the lungs (Fig. 9, A and B). There were small focal areas of labeling in the apexes of ciliated cells of the proximal bronchi and small focal distributions of immunoreactivity in the parenchyma. There was virtually no reactivity with the smooth muscle in either the blood vessels or airways or in the epithelial cells lining the respiratory bronchioles. After short-term exposure to ozone, there was a marked elevation in the intensity of immunoreactivity in both the proximal and distal airways (Fig. 9, C and D, respectively). Intense labeling was found in the apexes of all ciliated cells throughout the airway tree and what appeared to be the majority of basal cells in the proximal airways. The smooth muscle surrounding both the vessels and airways was also intensely labeled. In the respiratory bronchioles, virtually every epithelial cell expressed this protein whether they were cuboidal cells of the respiratory bronchioles or alveolar cells lining alveolar outpocketings. A small increase in density occurred in the peribronchiolar connective tissue as well, which appeared to be associated with both smooth muscle and connective tissue elements. No marked change, however, was found in expression in the parenchyma. After long-term exposure to ozone, the expression of this protein was reduced compared with animals exposed for a short term (Fig. 9, E and F). The change was most marked in the proximal bronchi where protein expression resembled that in the epithelium of filtered-air control animals. The primary difference in the proximal bronchi and blood vessels was that the labeling in the peribronchial smooth muscle and vascular smooth muscle resembled that observed in short-term exposed animals. In the respiratory bronchioles, there was a reduced intensity in the immunoreactivity in the peribronchiolar connective tissue and, to a certain extent, in some of the epithelial populations lining the air space. This was especially true for alveolar outpockets and for more distal portions of the respiratory bronchiole. There did not appear to be a significant difference in the distribution or intensity of this protein in the parenchyma after long-term exposure compared with either filtered-air control or acute short-term exposed animals.


View larger version (116K):
[in this window]
[in a new window]
  		Fig. 9.   Immunohistochemical staining of monkey lung with anti-GRP78 (clone 10C3). Experiments were carried out as described in Fig. 4. A: bronchus, FA. B: distal bronchiolar region, FA. C: bronchus, 8 h of ozone and 16-h postexposure incubation. D: distal bronchiolar region, 8 h of ozone and 16-h postexposure incubation. E: bronchus, 90 days of ozone (8 h/day) and 16-h postexposure incubation. F: distal bronchiolar region, 90 days of ozone (8 h/day) and 16-h postexposure incubation. Bars, 50 µm.


    DISCUSSION
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES

Stress proteins are a set of proteins characterized by the property that their levels within cells increase under a variety of stress conditions (24). Some of these stress proteins involve a chaperone function (7, 11), whereas others are still unresolved. In this study, seven MAbs specific to human stress proteins were used to illustrate the effects of ozone on stress protein synthesis in monkey lung tissues and cultured TBE cells. These antibodies were chosen because of their IgG class and their monospecificity toward a single stress protein. The specificities of these antibodies on monkey proteins were confirmed at the Western blot level except for anti-HSP90 (clone 9D2). We have observed that most heat-induced stress proteins other than HSP90, such as HSP27, HSP60, and HSP70, could be induced by heat under in vitro culture conditions. For HSP90, it was difficult to detect this protein in cultured cells by Western blot. This problem may be related to the use of dexamethasone in the culture medium. Because HSP90 is known to be bound to the glucocorticoid hormone receptor (36), the interactions between dexamethasone and the glucocorticoid hormone receptor might increase the turnover of HSP90 in cultured cells (35). In contrast to these HSPs, GRPs were not significantly elevated by heat. Unfortunately, our experiments with in vitro ozone exposure did not reveal any change in the levels of these stress proteins in cultured cells. This result is consistent with recent data by Sun et al. (39) in which newly synthesized proteins labeled by [35S]methionine were analyzed by two-dimensional gel electrophoresis. Using primary guinea pig tracheal epithelial cultures, Cohen et al. (4) have obtained similar results suggesting no inducible HSP synthesis by ozone in vitro. Here, we have further demonstrated no change in GRPs by ozone in culture.

In contrast to these in vitro observations, in vivo exposure with ozone on nonhuman primates caused significant changes in various stress proteins in lung tissues. We have observed a paradoxical difference in the expression of HSPs and GRPs in vivo in monkey lungs after ozone exposure. These results are best summarized in Table 1. After both short- and long-term exposures, the levels of various heat-induced proteins, HSP27, HSP60, and HSP70, decreased significantly, whereas the levels of heatless inducible stress proteins, GRP75 and GRP78, were obviously enhanced in lung tissues after ozone exposure. HSC70, the constitutive form of HSP70, which is not induced by heat but shares a similar function as HSP70, also decreased in lung tissues after ozone exposure. HSP90, a stress protein known to be bound to the glucocorticoid hormone receptor (36), was suppressed only under long-term exposure conditions. These results further support the notion that the regulations between the HSPs and GRPs are quite different. It is necessary to point out that the difference between the induction of HSPs and GRPs by different stress means has been noticed (19-21, 47). The in vivo results demonstrated in this study further confirm this notion, suggesting that the stress mechanism exerted by ozone on cells is quite different from that exerted by the high-temperature treatment.

                              
View this table:
[in this window]
[in a new window]
  		Table 1.   Summary of stress protein expression in monkey lung after ozone exposure

Because the level of HSPs in airway epithelial cells was not affected by a direct exposure of airway epithelial cells to ozone in vitro, the in vivo phenomenon of a decrease in HSPs is likely due to an indirect mechanism exerted by ozone toxicity. At present, it is still difficult to elucidate the toxic mechanism of ozone in vivo because ozone is highly reactive and can react with many biological materials (5, 8, 27). Pryor (32) and Pryor and Church (33) have suggested that ozone cannot penetrate deep into the lumen of airways. Furthermore, it is known that most respiratory epithelial cells in vivo are covered by a layer of extracellular fluids. It is therefore likely that whatever reaction occurs between ozone and the lining fluids may be responsible for this in vivo HSP decrease phenomenon. In addition to this possibility, neutrophil influx to the airway lumen commonly occurs after ozone exposure (15), and the effect of neutrophils on stress protein synthesis is not clear. We do know that neutrophils under the influence of cytokines are able to produce myeloperoxidase, and the presence of myeloperoxidase in the airway lumen will cause significant oxidative stress on tissues.

The suppression of HSP-like antigens in monkey lungs and conducting airways by ozone is quite different from that seen in rat (50) and guinea pig (38) experiments, which showed an enhanced HSP70 expression in lung tissue extracts and lavage fluid by ozone exposure. This difference is difficult to explain because different species and sample preparations are involved. Because neither rat (50) nor guinea pig (38) studies revealed the cell type(s) responsible for the enhancement, it is possible that cell types other than pulmonary epithelial cells are responsible for the increase in HSP70 in these rodent animals by ozone. It is interesting to note that HSP70 enhancement in guinea pigs by ozone is more pronounced in the lavage fluid preparation compared with that in the lung tissue extract (38). This result may further suggest a significant contribution from the inflammatory cells to the elevated HSP70 presence in these lung tissue extract preparations. Alternatively, the lung tissue extracts in these rodent animal experiments may include a contribution from the exfoliated lung epithelial cell population, which was not fixed and included in the paraffin sections of the lung tissue preparation in the present study.

In contrast to HSP, the regulation of GRPs by ozone is quite different (Table 1). We notice that both GRP75 and GRP78 are very low in vivo in monkey lung tissues of control animals maintained under filtered-air conditions but are elevated in animals after ozone exposure. However, similar to HSP, this in vivo phenomenon could not be duplicated in culture. This failure could be related either to the difference in the in vitro and in vivo responses of cells to stress or to a different stress-induced mechanism as described in the HSP system above. However, we noticed that cultured TBE cells expressed an unusually high level of GRPs. This high level of GRP expression in cultured cells may interfere with the inducibility of cells by ozone treatment. Because the cultured condition is relatively anaerobic, it is possible that the elevated expression of GRPs may be related to this anoxic condition that increases glucose depletion by increased glycolysis (19, 21, 47).

It has been observed that there are at least three classes of induced mechanisms for GRPs (19, 46). The first class, which includes such inhibitors of glycoprotein processing as tunicamycin, castanospermine, and glucosamine, can induce expression of GRPs but not of HSPs. The second class, including amino acid analogs and heavy metals, simultaneously induces the synthesis of both HSPs and GRPs. The third class, including the calcium ionophore A-23187 and the glucose analog 2-deoxyglucose, coordinately induces the synthesis of GRPs and represses HSP expression. For the induction of GRP synthesis, a transcriptional mechanism is postulated, whereas in the depression of HSPs, a posttranscriptional mechanism is proposed (46). We have observed that ozone effects in vivo on stress proteins are similar to those of the third class of inducer. These results are consistent with the notion that the modes of induction of stress proteins in airway epithelial cells are probably complex and interrelated.


    ACKNOWLEDGEMENTS

We thank Dr. Gary Konas for reviewing and editing this manuscript before its submission.


    FOOTNOTES

The research was supported by National Institute of Environmental Health Sciences Grants ES-00628, ES-06553, ES-06230, ES-05707, and ES-09701; National Heart, Lung, and Blood Institute Grant HL-35635; and California Tobacco Disease-Related Research Program Grant 7RT-0149.

The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.

Address for reprint requests and other correspondence: R. Wu, Center for Comparative Respiratory Biology and Medicine, Univ. of California, Davis, Surge 1, Rm. 1121, One Shields Ave., Davis, CA 95616 (E-mail: rwu{at}ucdavis.edu).

Received 28 October 1998; accepted in final form 7 May 1999.


    REFERENCES
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES

1.   Barr, B. C., D. M. Hyde, C. G. Plopper, and D. L. Dungworth. Distal airway remodeling in rats chronically exposed to ozone. Am. Rev. Respir. Dis. 137: 924-938, 1988[Medline].

2.   Bradford, M. M. A rapid and sensitive method for the quantitation of micrograph quantities of protein utilizing the principle of protein-dye binding. Anal. Biochem. 72: 248-254, 1976[Medline].

3.   Ciocca, D. R., D. J. Adams, R. J. Bjercke, D. P. Edwards, and W. L. McGuire. Immunohistochemical detection of an estrogen-regulated protein by monoclonal antibodies. Cancer Res. 42: 4256-4258, 1982[Abstract/Free Full Text].

4.   Cohen, D. S., E. Palmer, W. J. Welch, and D. Sheppard. The response of guinea pig airway epithelial cells and alveolar macrophages to environmental stress. Am. J. Respir. Cell Mol. Biol. 5: 133-143, 1991.

5.   Cross, C. E., P. A. Motchnik, B. A. Bruener, D. A. Jones, H. Kaur, B. N. Ames, and B. Halliwell. Oxidative damage to plasma constituents by ozone. FEBS Lett. 298: 269-272, 1992[Medline].

6.   Dungworth, D. L. Noncarcinogenic responses of the respiratory tract to inhaled toxicants. In: Concepts in Inhalation Toxicology, edited by R. O. McClellan, and R. F. Henderson. New York: Hemisphere, 1989, p. 273-298.

7.   Ellis, R. J. The molecular chaperone concept. Semin. Cell Biol. 1: 1-9, 1990[Medline].

8.   Elstner, E. F, and W. Osswald. Air pollution: involvement of oxygen radicals (a mini review). Free Radic. Res. Commun. 12: 795-807, 1991.

9.   Fujinaka, L. E., D. M. Hyde, C. G. Plopper, W. S. Tyler, D. L. Dungworth, and L. O. Lollini. Respiratory bronchiolitis following long-term ozone exposure in bonnet monkeys: a morphometric study. Exp. Lung Res. 8: 167-190, 1985[Medline].

10.   Fuqua, S. A. W., M. Blum-Salingaros, and W. L. McGuire. Induction of the estrogen-regulated "24K" protein by heat shock. Cancer Res. 49: 4126-4129, 1989[Abstract/Free Full Text].

11.   Gething, M. J., and J. Sambrook. Protein folding in the cell. Nature 355: 33-45, 1992[Medline].

12.   Harkema, J. R., C. G. Plopper, D. M. Hyde, J. A. St. George, D. W. Wilson, and D. L. Dungworth. Response of macaque bronchiolar epithelium to ambient concentrations of ozone. Am. J. Pathol. 143: 857-866, 1993[Abstract].

13.   Hattori, H., O. Kaneda, B. Lokeshwar, A. Laszlo, and K. Ohtsuka. A stress-inducible 40 kDa protein (HSP 40): purification by modified two dimensional gel electrophoresis and co-localization with HSC 70 (p73) in heat-shock HeLa cells. J. Cell Sci. 104: 629-638, 1993[Abstract].

14.   Huang, T. H., J. A. St. George, C. G. Plopper, and R. Wu. Keratin protein expression during the development of conducting airway epithelium in nonhuman primates. Differentiation 41: 78-86, 1989[Medline].

15.   Hyde, D. M., W. C. Hubbard, V. Wong, R. Wu, K. Pinkerton, and C. G. Plopper. Ozone-induced acute tracheobronchial epithelial injury: relationship to granulocyte emigration in the lung. Am. J. Respir. Cell Mol. Biol. 6: 481-497, 1992.

16.   Lai, B. T., N. W. Chin, A. E. Stanek, W. Keh, and K. W. Lanks. Quantitation and intracellular localization of the 85K heat shock protein by using monoclonal and polyclonal antibodies. Mol. Cell. Biol. 4: 2802-2810, 1984[Abstract/Free Full Text].

17.   Last, J. A., J. E. Gerriets, and D. M. Hyde. Synergistic effects on rat lungs of mixtures of oxidant air pollutants (ozone or nitrogen dioxide) and respirable aerosols. Am. Rev. Respir. Dis. 128: 539-544, 1983[Medline].

18.   Laszlo, A., and G. C. Li. Heat-resistant variants of Chinese hamster fibroblasts altered in the expression of heat shock protein. Proc. Natl. Acad. Sci. USA 82: 8029-8033, 1985[Abstract/Free Full Text].

19.   Lee, A. S. Mammalian stress response: induction of the glucose regulated protein family. Curr. Opin. Cell Biol. 4: 267-273, 1992[Medline].

20.   Lindquist, S. The heat-shock response. Annu. Rev. Biochem. 55: 1151-1191, 1986[Medline].

21.   Little, E., M. Ramakrishnan, B. Roy, G. Gazit, and A. S. Lee. The glucose-regulated proteins (GRP78 and GRP94): functions, gene regulation and applications. Crit. Rev. Eukaryot. Gene Expr. 4: 1-18, 1994[Medline].

22.   Manning-Krieg, U. C., P. E. Scherer, and G. Schatz. Sequential action of mitochondria chaperones in protein import into the matrix. EMBO J. 10: 3273-3280, 1991[Medline].

23.   Martin, W. R., C. Brown, Y. J. Zhang, and R. Wu. Growth and differentiation of primary tracheal epithelial cells in culture: regulation by extracellular calcium. J. Cell. Physiol. 147: 138-148, 1991[Medline].

24.   Morimoto, R. I., A. Tissieres, and C. Georgopoulus. Stress Proteins in Biology and Medicine. Cold Spring Harbor, NY: Cold Spring Harbor Laboratory, 1990.

25.   Mosmann, T. Rapid colorimetric assay for cellular growth and survival. Application to proliferation and cytotoxicity assays. J. Immunol. Methods 65: 55-63, 1985.

26.   Munro, S., and H. R. B. Pelham. An HSP70-like protein in the ER: identity with the 78 kd glucose-regulated protein and immunoglobulin heavy chain binding proteins. Cell 46: 291-300, 1986[Medline].

27.   Mustafa, M. G. Biochemical basis of ozone toxicity. Free Radic. Biol. Med. 9: 245-265, 1990[Medline].

28.   Ohtsuka, K., and A. Laszlo. The relationship between hsp70 localization and heat resistance. Exp. Cell Res. 202: 507-518, 1992[Medline].

29.   Pelham, H. R. B. HSP70 accelerates the recovery of nucleolar morphology after heat shock. EMBO J. 3: 3095-3100, 1984[Medline].

30.   Plopper, C. G. Pulmonary bronchiolar epithelial cytotoxicity: microanatomical considerations. In: Metabolic Activation and Toxicity of Chemical Agents to Lung Tissue and Cells, edited by T. E. Gram. New York: Pergamon, 1993, p. 1-24.

31.   Plopper, C. G., F. P. Chu, C. J. Haselton, J. Peake, J. Wu, and K. E. Pinkerton. Dose-dependent tolerance to ozone. I. Tracheobronchial epithelial reorganization in rats after 20 months' exposure. Am. J. Pathol. 144: 404-420, 1994[Abstract].

32.   Pryor, W. A. How far does ozone penetrate into the pulmonary air/tissue boundary before it reacts? Free Radic. Biol. Med. 12: 83-88, 1992[Medline].

33.   Pryor, W. A., and D. F. Church. Aldehydes, hydrogen peroxide, and organic radicals as mediators of ozone toxicity. Free Radic. Biol. Med. 11: 41-46, 1991[Medline].

34.   Ritossa, F. A new puffing pattern induced by temperature shock and DNP in Drosophila. Experientia 18: 571-573, 1962.

35.   Robinson, C. B., and R. Wu. Culture of conducting airway epithelial cells in serum-free medium. J. Tissue Cult. Methods 13: 95-102, 1991.

36.   Schuh, S., W. Yonemoto, J. Brugge, V. J. Bauer, R. M. Reihl, W. P. Sullivan, and D. O. Toft. A 90,000 dalton binding protein common to both steroid receptors and the Rous sarcoma virus transforming protein, pp60v-src. J. Biol. Chem. 260: 14292-14296, 1985[Abstract/Free Full Text].

37.   Sharif, M., J. G. Worrall, B. Singh, R. S. Gupta, P. M. Lydyard, C. Lambert, J. McCulloch, and G. A. Rook. The development of monoclonal antibodies to human mitochondrial 60-kd heat-shock protein, and their use in studying the expression of the protein in rheumatoid arthritis. Arthritis Rheum. 35: 1427-1433, 1992[Medline].

38.   Su, W. Y., and T. Gordon. In vivo exposure to ozone produces an increase in a 72-kDa heat shock protein in guinea pigs. J. Appl. Physiol. 83: 707-711, 1997[Abstract/Free Full Text].

39.   Sun, W., R. Wu, and J. A. Last. Coordinated expression of a 45 kd protein and ozone toxicity in a human bronchial epithelial cell line. Am. J. Respir. Cell Mol. Biol. 10: 673-682, 1994[Abstract].

40.   Tarkington, B. K., T. R. Duvall, and J. A. Last. Ozone exposure of cultured cells and tissues. Methods Enzymol. 234: 257-265, 1994[Medline].

41.   Tarkington, B. K., R. Wu, W. M. Sun, K. J. Nikula, D. W. Wilson, and J. A. Last. In vitro exposure of tracheobronchial epithelial cells and of tracheal explants to ozone. Toxicology 88: 51-68, 1994[Medline].

42.   Towbin, H., T. Staehelin, and J. Gordon. Electrophoretic transfer of proteins from polyacrylamide gel to nitrocellulose sheets: procedure and some applications. Proc. Natl. Acad. Sci. USA 76: 4350-4354, 1979[Abstract/Free Full Text].

43.   Vass, K., W. J. Welch, and T. S. Nowak, Jr. Localization of 70-kDa stress protein induction in gerbil brain after ischemia. Acta Neuropathol. (Berl.) 77: 128-135, 1988[Medline].

44.   Vaux, D., J. Tooze, and S. Fuller. Identification by anti-idiotype antibodies of an intracellular membrane protein that recognizes a mammalian endoplasmic reticulum retention signal. Nature 345: 495-502, 1990[Medline].

45.   Velazquez, J. M., and S. Lindquist. HSP70: nuclear concentration during environmental stress and cytoplasmic storage during recovery. Cell 36: 655-662, 1984[Medline].

46.   Watowich, S. S., and R. I. Morimoto. Complex regulation of heat shock- and glucose-responsive genes in human cells. Mol. Cell. Biol. 8: 393-405, 1988[Abstract/Free Full Text].

47.   Welch, W. J., J. I. Garrels, G. P. Thomas, J. J. Lin, and J. R. Feramisco. Biochemical characterization of the mammalian stress proteins and identification of two stress proteins as glucose- and Ca2+-ionophore-regulated proteins. J. Biol. Chem. 258: 7102-7111, 1983[Abstract/Free Full Text].

48.   Welch, W. J., and J. P. Suhan. Cellular and biochemical events in mammalian cells during and after recovery from physiological stress. J. Cell Biol. 103: 2035-2052, 1986[Abstract/Free Full Text].

49.   Whitcutt, J. M., K. B. Adler, and R. Wu. A biphasic culture system for maintaining polarity of differentiation of cultured respiratory tract epithelial cells. In Vitro Cell. Dev. Biol. 24: 420-428, 1988[Medline].

50.   Wong, C. G., M. Bonakdar, W. J. Mautz, and M. T. Kleinman. Chronic inhalation exposure to ozone and nitric acid elevates stress-inducible heat shock protein 70 in the rat lung. Toxicology 107: 111-119, 1996[Medline].

Am J Physiol Lung Cell Mol Physiol 277(3):L511-L522
0002-9513/99 $5.00 Copyright © 1999 the American Physiological Society


This article has been cited by other articles:


Home page
 Toxicol SciHome page
M. Yu, K. E. Pinkerton, and H. Witschi
Short-Term Exposure to Aged and Diluted Sidestream Cigarette Smoke Enhances Ozone-Induced Lung Injury in B6C3F1 Mice
Toxicol. Sci., January 1, 2002; 65(1): 99 - 106.
[Abstract] [Full Text] [PDF]

Home page
 Am. J. Respir. Crit. Care Med.Home page
K. YONEDA, K. PECK, M. M.-J. CHANG, K. CHMIEL, Y.-P. SHER, J. CHEN, P.-C. YANG, Y. CHEN, and R. WU
Development of High-density DNA Microarray Membrane for Profiling Smoke- and Hydrogen Peroxide-induced Genes in a Human Bronchial Epithelial Cell Line
Am. J. Respir. Crit. Care Med., November 15, 2001; 164(10): S85 - 89.
[Abstract] [Full Text] [PDF]

This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Wu, R.
Right arrow Articles by Tarkington, B.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Wu, R.
Right arrow Articles by Tarkington, B.

HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
Visit Other APS Journals Online