Growth arrest in A549 cells during hyperoxic stress is associated with decreased cyclin B1 and increased p21(Waf1/Cip1/Sdi1) levels

Superoxide dismutase 3 dysregulation in a murine model of neonatal lung injury

Bronchopulmonary dysplasia (BPD), a common chronic respiratory disease that occurs after premature birth, is believed to be secondary to oxidative damage from hyperoxia and inflammation, which leads to impaired alveolar formation and chronic lung dysfunction. We hypothesized that extracellular superoxide dismutase (SOD)3, an antioxidant uniquely targeted to the extracellular matrix (ECM) and alveolar fluid, might have a different response (down-regulation) to hyperoxic injury and recovery in room air (RA), thereby contributing to the persistent airspace injury and inflammation. We used a murine BPD model using postnatal hyperoxia (O2) (4 or 5 d) followed by short-term recovery (14 d) in RA, which mimics the durable effects after injury during alveolar development. This was associated with significantly increased mRNA expression for antioxidant genes mediated by nuclear factor erythroid 2-related factor (Nrf2) in the O2 (n = 4) versus RA group (n = 5). SOD3, an Nrf2-independent antioxidant, was significantly reduced in the O2-exposed mice compared with RA. Immunohistochemistry revealed decreased and disrupted SOD3 deposition in the alveolar ECM of O2-exposed mice. Furthermore, this distinct hyperoxic antioxidant and injury profile was reproducible in murine lung epithelial 12 cells exposed to O2. Overexpression of SOD3 rescued the injury measures in the O2-exposed cells. We establish that reduced SOD3 expression correlates with alveolar injury measures in the recovered neonatal hyperoxic lung, and SOD3 overexpression attenuates hyperoxic injury in an alveolar epithelial cell line. Such findings suggest a candidate mechanism for the pathogenesis of BPD that may lead to targeted interventions.

Differential concentration-specific effects of caffeine on cell viability, oxidative stress, and cell cycle in pulmonary oxygen toxicity in vitro

Caffeine is used to prevent bronchopulmonary dysplasia (BPD) in premature neonates. Hyperoxia contributes to the development of BPD, inhibits cell proliferation and decreases cell survival. The mechanisms responsible for the protective effect of caffeine in pulmonary oxygen toxicity remain largely unknown. A549 and MLE 12 pulmonary epithelial cells were exposed to hyperoxia or maintained in room air, in the presence of different concentrations (0, 0.05, 0.1 and 1mM) of caffeine. Caffeine had a differential concentration-specific effect on cell cycle progression, oxidative stress and viability, with 1mM concentration being deleterious and 0.05 mM being protective. Reactive oxygen species (ROS) generation during hyperoxia was modulated by caffeine in a similar concentration-specific manner. Caffeine at 1mM, but not at the 0.05 mM concentration decreased the G2 arrest in these cells. Taken together this study shows the novel funding that caffeine has a concentration-specific effect on cell cycle regulation, ROS generation, and cell survival in hyperoxic conditions.

Biphasic response of checkpoint control proteins in hyperoxia: exposure to lower levels of oxygen induces genome maintenance genes in experimental baboon BPD

Breathing high concentrations of oxygen (hyperoxia) causes lung injury and is associated with lung diseases such as bronchopulmonary dysplasia (BPD), respiratory distress syndrome and persistent pulmonary hypertension of the newborns. Hyperoxia (95-100 %O2) causes DNA damage and growth arrest of lung cells and consequently cells die by apoptosis or necrosis. Although supplemental oxygen therapy is clinically important, the level and duration of hyperoxic exposure that would allow lung cells to reenter the cell cycle remains unclear. We hypothesized that cells exposed to lower concentrations of hyperoxia will retain the capacity to enter cell cycle when recovered in room air. We employed varying concentrations of oxygen (21-95 %) to determine the response of lung cells to hyperoxia. Our results indicate that cells were growth arrested and failed to reenter the cell cycle when exposed to greater than 60 % oxygen. Cell cycle checkpoint proteins were increased in a biphasic manner, increasing until 70 % oxygen, but declined in greater than 90 % oxygen. Microarray analysis shows that there is significant decrease in the abundance of Cdks 6-8 and retinoblastoma protein (Rb), p107 and p130 in exposure to 90 % oxygen for 48 h. We further tested the effect of clinically relevant as needed oxygen [(pro-re-nata (prn)] in premature infant (125-days and 140-days) baboon model of BPD. The microarray results show that 6 or 14d PRN oxygen-exposed animals had induced expression of chromosomal maintenance genes (MCMs), genes related to anti-inflammation, proliferation, and differentiation.

Hyperoxia decreases glycolytic capacity, glycolytic reserve and oxidative phosphorylation in MLE-12 cells and inhibits complex I and II function, but not complex IV in isolated mouse lung mitochondria

High levels of oxygen (hyperoxia) are frequently used in critical care units and in conditions of respiratory insufficiencies in adults, as well as in infants. However, hyperoxia has been implicated in a number of pulmonary disorders including bronchopulmonary dysplasia (BPD) and adult respiratory distress syndrome (ARDS). Hyperoxia increases the generation of reactive oxygen species (ROS) in the mitochondria that could impair the function of the mitochondrial electron transport chain. We analyzed lung mitochondrial function in hyperoxia using the XF24 analyzer (extracellular flux) and optimized the assay for lung epithelial cells and mitochondria isolated from lungs of mice. Our data show that hyperoxia decreases basal oxygen consumption rate (OCR), spare respiratory capacity, maximal respiration and ATP turnover in MLE-12 cells. There was significant decrease in glycolytic capacity and glycolytic reserve in MLE-12 cells exposed to hyperoxia. Using mitochondria isolated from lungs of mice exposed to hyperoxia or normoxia we have shown that hyperoxia decreased the basal, state 3 and state3 μ (respiration in an uncoupled state) respirations. Further, using substrate or inhibitor of a specific complex we show that the OCR via complex I and II, but not complex IV was decreased, demonstrating that complexes I and II are specific targets of hyperoxia. Further, the activities of complex I (NADH dehydrogenase, NADH-DH) and complex II (succinate dehydrogenase, SDH) were decreased in hyperoxia, but the activity of complex IV (cytochrome oxidase, COX) remains unchanged. Taken together, our study show that hyperoxia impairs glycolytic and mitochondrial energy metabolism in in tact cells, as well as in lungs of mice by selectively inactivating components of electron transport system.

Effects of hyperoxia on transdifferentiation of primary cultured typeII alveolar epithelial cells from premature rats

Hyperoxia exposure is a significant risk factor for the impaired alveolarization characteristic of bronchopulmonary dysplasia. Type II alveolar epithelial cells (AECIIs) may serve as "alveolar stem cells" to transdifferentiate into type I alveolar epithelial cells (AECIs). Here, we show that hyperoxia is capable of inducing transdifferentiation of AECIIs in premature rats in vitro. Hyperoxia-induced transdifferentiation was characterized by typical morphological changes, inhibition of cellular proliferation, decline in expression rate of Ki67, accumulation of cells in the G(1) phase of the cell cycle, increased expression of AECI-specific protein aquaporin 5, and decreased expression of AECII-associated protein surfactant protein C. These results suggest that hyperoxia may induce transdifferentiation of AECIIs into AECIs and the transdifferentiation may be responsible for repairing early lung injury.

Deletion of caveolin-1 protects hyperoxia-induced apoptosis via survivin-mediated pathways

Hyperoxia-induced lung injury is an established model that mimics human acute respiratory distress syndrome. Cell death is a prominent feature in lungs following prolonged hyperoxia. Caveolae are omega-shaped invaginations of the plasma membrane. Caveolin-1 (cav-1), a 22-kDa transmembrane scaffolding protein, is the principal structural component of caveolae. We have recently shown that deletion of cav-1 (cav-1-/-) protected against hyperoxia-induced cell death and lung injury both in vitro and in vivo; however, the mechanisms remain unclear. Survivin, a member of the inhibitor of apoptosis protein family, inhibits apoptosis in tumor cells. Although emerging evidence suggests that survivin is involved in wound healing, especially in vascular injuries, its role in hyperoxia-induced lung injury has not been investigated. Our current data demonstrated that hyperoxia induced apoptosis via suppressing survivin expression. Deletion of cav-1 abolished this suppression and subsequently protected against hyperoxia-induced apoptosis. Using "gain" and "loss" of function assays, we determined that survivin protected lung cells from hyperoxia-induced apoptosis via the inhibition of apoptosis executor caspase-3. Overexpression of survivin by deletion of cav-1 was regulated by Egr-1. Egr-1 functioned as a negative regulator of survivin expression. Deletion of cav-1 upregulated survivin via decreased Egr-1 binding of the survivin promoter region. Together, this study illustrates the effect of hyperoxia on survivin expression and the role of survivin in hyperoxia-induced apoptosis. We also demonstrate that deletion of cav-1 protects hyperoxia-induced apoptosis via modulation of survivin expression.

Effects of oxygen concentration and exposure time on cultured human airway epithelial cells

OBJECTIVES

To distinguish the direct effects of oxygen dose and exposure time on human airway epithelial cells. We hypothesized that progressive oxygen exposure would induce cell dysfunction and inflammation in a dose-dependent manner.

DESIGN

Interventional laboratory study.

SETTING

An academic medical research facility in the northeastern United States.

SUBJECTS

Calu-3 human airway epithelial cell culture.

INTERVENTIONS

Cells were cultured at a gas-liquid interface with the cells fed basolaterally with medium and grown to full confluence. The apical surfaces were then exposed to gas containing 21%, 40%, 60%, or 80% oxygen, 5% CO2, and balance nitrogen for 24 or 72 hrs.

MEASUREMENTS AND MAIN RESULTS

The effects of oxygen concentration and time-induced cellular change were examined by measuring transepithelial resistance of monolayers, cell viability by trypan blue exclusion, basolateral lactate concentration, histology of monolayer cross-sections, and cytospin slides, plus interleukin (IL)-6 and IL-8 secretion in apical surface fluid. Transepithelial resistance decreased in a dose- and time-dependent manner (p < .001), whereas cell viability was reduced only at 72 hrs and in all hyperoxic groups (p < .05). IL-6 secretion was elevated in all hyperoxic groups at 24 hrs (p < .001), and both IL-6 and IL-8 levels were greater in the 40% FiO2 group compared with all other groups at 72 hrs (p < .01).

CONCLUSIONS

In this model, airway epithelial cells demonstrate profound concentration and time-dependent responses to hyperoxic exposure with respect to cell physiology, viability, histology, and secretion of inflammatory mediators. This model might be a valuable tool for preliminary analysis of potentially protective therapies against hyperoxia-induced airway epithelial injury.

Inferring pairwise regulatory relationships from multiple time series datasets

MOTIVATION

Time series expression experiments have emerged as a popular method for studying a wide range of biological systems under a variety of conditions. One advantage of such data is the ability to infer regulatory relationships using time lag analysis. However, such analysis in a single experiment may result in many false positives due to the small number of time points and the large number of genes. Extending these methods to simultaneously analyze several time series datasets is challenging since under different experimental conditions biological systems may behave faster or slower making it hard to rely on the actual duration of the experiment.

RESULTS

We present a new computational model and an associated algorithm to address the problem of inferring time-lagged regulatory relationships from multiple time series expression experiments with varying (unknown) time-scales. Our proposed algorithm uses a set of known interacting pairs to compute a temporal transformation between every two datasets. Using this temporal transformation we search for new interacting pairs. As we show, our method achieves a much lower false-positive rate compared to previous methods that use time series expression data for pairwise regulatory relationship discovery. Some of the new predictions made by our method can be verified using other high throughput data sources and functional annotation databases.

AVAILABILITY

Matlab implementation is available from the supporting website: http://www.cs.cmu.edu/~yanxins/regulation_inference/index.html.

Mechanisms of cell death in oxidative stress

Reactive oxygen or nitrogen species (ROS/RNS) generated endogenously or in response to environmental stress have long been implicated in tissue injury in the context of a variety of disease states. ROS/RNS can cause cell death by nonphysiological (necrotic) or regulated pathways (apoptotic). The mechanisms by which ROS/RNS cause or regulate apoptosis typically include receptor activation, caspase activation, Bcl-2 family proteins, and mitochondrial dysfunction. Various protein kinase activities, including mitogen-activated protein kinases, protein kinases-B/C, inhibitor-of-I-kappaB kinases, and their corresponding phosphatases modulate the apoptotic program depending on cellular context. Recently, lipid-derived mediators have emerged as potential intermediates in the apoptosis pathway triggered by oxidants. Cell death mechanisms have been studied across a broad spectrum of models of oxidative stress, including H2O2, nitric oxide and derivatives, endotoxin-induced inflammation, photodynamic therapy, ultraviolet-A and ionizing radiations, and cigarette smoke. Additionally ROS generated in the lung and other organs as the result of high oxygen therapy or ischemia/reperfusion can stimulate cell death pathways associated with tissue damage. Cells have evolved numerous survival pathways to counter proapoptotic stimuli, which include activation of stress-related protein responses. Among these, the heme oxygenase-1/carbon monoxide system has emerged as a major intracellular antiapoptotic mechanism.

Analyses of variant human papillomavirus type-16 E5 proteins for their ability to induce mitogenesis of murine fibroblasts

BACKGROUND

Human papillomavirus type 16 (HPV-16) E5 protein co-operates with epidermal growth factor to stimulate mitogenesis of murine fibroblasts. Currently, little is known about which viral amino acids are involved in this process. Using sequence variants of HPV-16 E5 we have investigated their effects upon E5 transcription, cell-cycling and cell-growth of murine fibroblasts.

RESULTS

We demonstrate that: (i) introduction of Thr64 into the reference E5 sequence of HPV-16 abrogates mitogenic activity: both were poorly transcribed in NIH-3T3 cells; (ii) substitution of Leu44Val65 or, Thr37Leu44Val65 into the HPV-16 E5 reference backbone resulted in high transcription in NIH-3T3 cells, enhanced cell-cycle progression and high cell-growth; and, (iii) inclusion of Tyr8 into the Leu44Val65 backbone inhibited E5 induced cell-growth and repression of p21 expression, despite high transcription levels.

CONCLUSION

The effects of HPV-16 E5 variants upon mitosis help to explain why Leu44Val65 HPV-16 E5 variants are most prevalent in 'wild' pathogenic viral populations in the UK.

Oxidative stress response results in increased p21WAF1/CIP1 degradation in cystic fibrosis lung epithelial cells

Lung epithelium in cystic fibrosis (CF) patients is characterized by structural damage and altered repair due to oxidative stress. To gain insight into the oxidative stress-related damage in CF, we studied the effects of hyperoxia in CF and normal lung epithelial cell lines. In response to a 95% O2 exposure, both cell lines exhibited increased reactive oxygen species. Unexpectedly, the cyclin-dependent kinase inhibitor p21WAF1/CIP1 protein was undetectable in CF cells under hyperoxia, contrasting with increased levels of p21WAF1/CIP1 in normal cells. In both cell lines, exposure to hyperoxia led to S-phase arrest. Apoptotic features including nuclear condensation, DNA laddering, Annexin V incorporation, and elevated caspase-3 activity were not readily observed in CF cells in contrast to normal cells. Interestingly, treatment of hyperoxia-exposed CF cells with two proteasome inhibitors, MG132 and lactacystin, restored p21WAF1/CIP1 protein and was associated with an increase of caspase-3 activity. Moreover, transfection of p21WAF1/CIP1 protein in CF cells led to increased caspase-3 activity and was associated with increased apoptotic cell death, specifically under hyperoxia. Taken together, our data suggest that modulating p21WAF1/CIP1 degradation may have the therapeutic potential of reducing lung epithelial damage related to oxidative stress in CF patients.

GR 63799X, an EP3 receptor agonist, induced S phase arrest and 3T6 fibroblast growth inhibition

The importance of arachidonic acid metabolites on the control of cell growth, particularly those derived from cyclooxygenase pathway has long been recognized. Recently, we observed that prostaglandin E(2) (PGE(2)) interaction with EP(1) and EP(4) receptors is involved in serum-induced 3T6 fibroblast growth due to their effect at various levels of the cell cycle machinery. This study shows that prostanoid EP(3) receptor was expressed in 3T6 fibroblast. We studied the role of EP(3) receptor agonist GR 63799X in serum-induced 3T6 cell proliferation. This was concentration-dependent inhibit (IC(50) approximately 10 microM) to a complete inhibition without any cytotoxic or proapoptotic effect. The prostanoid EP(3) receptor agonist treatment decreased the G(0)/G(1) and G(2)/M populations whereas cells were accumulated in S phase. This arrest in S phase was associated with a decrease in cyclin B levels and the enhancement of p21 expression. Our data show that EP(3) agonist decreases cAMP levels in our experimental conditions. Interestingly, the S arrest caused by prostanoid EP(3) receptor agonist seems to be cAMP dependent, at least in part, because forskolin treatment allowed S-arrested cells to progress through cell cycle and consequently growth. Thus, our results suggest that PGE(2) EP(3) receptor interaction may be involved in serum-induced 3T6 fibroblast growth due to their effects on cAMP levels and on cell cycle machinery of the S phase.

Dual and opposing roles of ERK in regulating G1 and S-G2/M delays in A549 cells caused by hyperoxia

This study explores the role of ERK activation in regulating G(1) and S-G(2)/M delays during hyperoxia. We demonstrate here that exposing A549 human alveolar type 2 adenocarcinoma cells to hyperoxia (95% O(2)) for 0.5-24 h time-dependently increases phospho-ERK, phospho-p53(Ser15), p53, and p21(CIP1) protein levels. Decreasing phospho-ERK with the pharmacological inhibitors, PD98059 and U0126, markedly suppresses hyperoxia-stimulated phospho-p53(Ser15), p53, and p21(CIP1), and also restores the hyperoxia-reduced kinase activities of cyclin D1/E1-Cdks. Our results suggest that ERK activation during hyperoxia contributes to the p53/p21-mediated G(1) checkpoint. However, inhibition of ERK signaling during hyperoxia further delays S-phase entry and progression. Hyperoxia induces significant expression of cyclin A/B1 and translocation of cyclin A into nuclei while marginally decreasing cyclin A/B1-Cdks kinase activities, which may be related to nuclear association with p21. Interestingly, inhibition of ERK signaling markedly suppresses the elevation of cyclin A/B1 proteins and cyclin A/B1-Cdks kinase activities during hyperoxia. Taken together, the results presented here suggest that hyperoxia-activated ERK acts upstream of p53 and p21 to suppress G(1)-Cdk activities; however, it is also required for induction of cyclin A/B1 and maintenance of cyclin A/B1-Cdk activities that oppose delays in S-phase entry and progression.

The effect of glutamine on A549 cells exposed to moderate hyperoxia

The use of high oxygen concentrations is frequently necessary in the treatment of acute respiratory distress syndrome (ARDS) and bronchopulmonary dysplasia (BPD). High oxygen concentrations, however, are detrimental to cell growth and cell survival. Glutamine (Gln) may be protective to cells during periods of stress and recently has been shown to increase survival in A549 cells exposed to lethal concentrations of oxygen (95% O2). We found that supplemental Gln enhances cell growth in A549 cells exposed to moderate concentrations of oxygen (60% O2). We therefore evaluated the effect of moderate hyperoxia on the cell cycle distribution of A549 cells. At 48 h there was no significant difference in the cell cycle distribution between 2 mM Gln cells in 60% O2 and 2 mM cells in room air. Furthermore, 2 mM Gln cells in 60% O2 had stable protein levels of cyclin B1 consistent with ongoing cell proliferation. In contrast, at 48 h, cells not supplemented with glutamine (Gln-) in 60% O2 had evidence of growth arrest by both flow cytometry (increased percentage of G1 cells) and by decreased protein levels of cyclin B1. G1 growth arrest in the Gln- cells exposed to 60% O2 was not, however, associated with induction of p21 protein. At 72 and 96 h, Gln- cells in 60% O2, began to demonstrate a partial loss of G1 checkpoint regulation and an increase in apoptosis, indicating an increased sensitivity to oxygen toxicity. Glutathione (GSH) concentrations were then measured. 2 mM Gln cells in 60% O2 were found to have higher concentrations of GSH compared to Gln- cells in 60% O2, suggesting that Gln confers protection to the cell during exposure to hyperoxia through up-regulation of GSH. When cells in 60% O2 were given higher concentrations of Gln (5 and 10 mM), cell growth at 96 h was increased compared to cells grown in 2 mM Gln (P<0.04). Clonal survival was also increased in cells exposed 60% O2 and supplemented with higher concentrations of Gln compared to Gln- cells in 60% O2. These studies suggest that supplemental glutamine may improve cell growth and cell viability and therefore may be beneficial to the lung during exposure to moderate concentrations of supplemental oxygen.

Increased apoptosis and expression of p21 and p53 in premature infant baboon model of bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) is a major complication of premature infants who receive prolonged ventilatory support. The pathophysiology of BPD involves oxidant injury, baro/volutrauma, and disordered lung repair. Exposure of premature lung that is poorly adapted for air breathing (>3% oxygen in fetal lung) to a higher concentration of oxygen can cause significant oxidant injury. Cell growth and differentiation of the developing lung require selective and ordered cell division. As hyperoxia can increase the expression of cell-cycle checkpoints that can cause growth arrest of lung cells, in this report we examined the expression of checkpoint proteins p53 and p21 in a premature infant the baboon model of BPD. Additionally, we also determined whether enhanced apoptosis occurs in baboon BPD model. We have shown that p53 and p21 expression are increased in 125-day as well as 140-day premature baboons with BPD. We also demonstrate increased apoptosis in lung tissue of premature baboons with BPD. These results demonstrate that cell growth inhibition is a likely factor in the evolution of BPD. Additionally, lung cells may undergo increased apoptosis that can impair the repair process in the postventilatory recovery period.

Altered expression of cyclins and cdks in premature infant baboon model of bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) is a chronic lung disease of premature infants, which results in substantial morbidity. The pathophysiology of BPD includes oxidant injury, baro/volutrauma, and disordered lung repair. As lung development, differentiation, and repair require cell division, we hypothesized dysregulation of the cell cycle in oxygen exposure of premature infants that may contribute to the evolution of BPD. In this investigation, we studied the expression of cyclins and cyclin-dependent kinases (cdks) that regulate transition from G1 and G2 phases of the cell cycle. We report here that expression of cyclin D1, cyclin E, and cyclin A is modulated in premature baboons in respiratory distress. In addition, the expression of cdk1 or cdk4 was also modulated in these premature animals. The phosphorylation of retinoblastoma protein was progressively decreased in 125-day animals and in 140-day animals exposed to 6 or 14 days of PRN oxygen. These results indicate that due to altered cyclin and cdk expression, the repair of injured epithelium may proceed in a disordered manner that is characteristic of BPD. Thus, altered cell cycle regulation may be an important factor in the evolution of BPD.

Hyperoxia activates the ATR-Chk1 pathway and phosphorylates p53 at multiple sites

Hyperoxia has been shown to cause DNA damage resulting in growth arrest of cells in p53-dependent, as well as p53-independent, pathways. Although H2O2 and other peroxides have been shown to induce ataxia telangiectasia-mutated (ATM)-dependent p53 phosphorylation in response to DNA damage, the signal transduction mechanisms in response to hyperoxia are currently unknown. Here we demonstrate that hyperoxia phosphorylates the Ser15 residue of p53 independently of ATM. Hyperoxia phosphorylated p53 (Ser15) in DNA-dependent protein kinase null (DNA-PK-/-) cells, indicating that it may not depend on DNA-PK for phosphorylation of p53 (Ser15). We show that Ser37 and Ser392 residues of p53 are also phosphorylated in an ATM-independent manner in hyperoxia. In contrast, H2O2 did not phosphorylate Ser37 in either ATM+/+ or ATM-/- cells. Furthermore, H2O2 failed to phosphorylate Ser15 in ATM-/- cells. Additionally, overexpression of kinase-inactive ATM-and-Rad3-related (ATR) in HEK293T cells diminished Ser15, Ser37, and Ser392 phosphorylation compared with vector-only transfected cells. In contrast, wild-type ATR overexpression did not diminish Ser15, Ser37, or Ser392 phosphorylation. We also show that checkpoint kinase 1 (Chk1) is phosphorylated on Ser345 in response to hyperoxia, which could be inhibited by caffeine or wortmannin, potent inhibitors of phosphoinositide 3-kinase-related kinases. Hyperoxia also phosphorylated Chk1 in ATM+/+ as well as in ATM-/- cells, demonstrating an ATM-independent mechanism in Chk1 phosphorylation. Together, our data suggest that hyperoxia activates the ATR-Chk1 pathway and phosphorylates p53 at multiple sites in an ATM-independent manner, which is different from other forms of oxidative stress such as H2O2 or UV light.

The pathobiological mechanisms of emphysema models: what do they have in common?

Emphysema results from a multi-step, complex, process of lung destruction. This review aims at organizing the available information concerning the animal models of emphysema as to which step of the pathogenesis they address. The experimental models have been classified as to whether they are based on: (a) pharmacological, (b) environmental, or (c) genetic manipulations to induce emphysema and whether they are: (a) triggers or initiators of emphysema, (b) modifiers of lung predisposition to further damage by trigger factors, or (c) mediators of lung tissue destruction.

Protection of lungs from hyperoxic injury: gene expression analysis of cyclosporin A therapy

We have previously shown that cyclosporin A (CsA), an inhibitor of protein phosphatase 2B (calcineurin), attenuates hyperoxia-induced reductions in murine lung compliance. CsA protected against hyperoxia-induced changes in neutrophil infiltration, capillary congestion, edema, and hyaline membrane formation. Gene expression studies were conducted to identify the gene expression patterns underlying the protective effects of CsA during hyperoxic lung injury. After 72 h of simultaneous treatment with >95% oxygen and CsA (50 mg x kg(-1) x day(-1)), RNA was isolated from murine lungs. RNA from treated and untreated lungs was reverse transcribed to cDNA, competitively hybridized, and used to probe 8,734 complimentary DNAs on the Incyte mouse GEM 1 array. Several known genes and expressed sequence tags (ESTs) showed increased (GenBank accession numbers: AA125385, AA241295, W87197, syntaxin, and cyclin G) or decreased [AA036517, AA267567, AA217009, W82577, uteroglobin, stromal cell-derived factor 1, and surfactant protein C (SP-C)] expression after hyperoxia. Hyperoxia-stimulated reductions in SP-C gene expression were confirmed through Northern blot analysis. The increase in gene expression of one expressed sequence tag (AA125385) with hyperoxia was reversed by CsA treatment. Sequence data demonstrated that this EST has high homology to murine cyclin B1. Western blot analysis did not demonstrate any changes in distal lung cyclin B1 expression after hyperoxia. Protein expression of cyclin B1 in the distal lung was observed in the endothelial cells, bronchiolar epithelial cells, and both the type I and type II alveolar epithelial cells. Further analysis of cyclin B1 may elucidate the protective actions of CsA in hyperoxic injury.

Role of cyclins in epithelial response to oxidants

Oxidants are involved in a large variety of pulmonary diseases. Among the various cell types that compose the respiratory system, the epithelial cells appear to be a major target for oxidative stress. When cells are exposed to DNA-damaging agents such as oxidants, a feedback control is activated that acts as a brake on the cell cycle to inhibit entry into the S phase until DNA repair is completed. Progression through the G1 phase and the G1-S transition involves sequential assembly and activation of key regulators of the cell cycle machinery, the cyclin-dependent kinases (CDKs). Activity of the CDKs is regulated by several mechanisms, which include the CDK inhibitors (CKIs). The CKI p21(CIP1) appears to play an important role in the response of epithelial cells to oxidants.