Alveolar type I cells protect rat lung epithelium from oxidative injury

Chelation therapy with 3,4,3-Li(1,2-HOPO) after pulmonary exposure to plutonium in rats

Internal exposure to plutonium can occur through inhalation for the nuclear worker, but also for the public if the radionuclide was released into the atmosphere in the context of a nuclear accident or terrorist attack. DieThylenetriaminePentaAcetic acid (DTPA) is currently still the only authorized chelator that can be used to decorporate internalized plutonium. The Linear HydrOxyPyridinOne-based ligand named 3,4,3-Li(1,2-HOPO) remains the most promising drug candidate to replace it in the hopes of improving chelating treatment. This study aimed to assess the efficacy of 3,4,3-Li(1,2-HOPO) in removing plutonium from rats exposed to the lungs, depending on the timing and route of treatment, and almost always compared to DTPA at a ten-fold higher dose used as a reference chelator. First, early intravenous injection or inhalation of 3,4,3-Li(1,2-HOPO) demonstrated superior efficacy over DTPA in preventing plutonium accumulation in liver and bone in rats exposed by injection or lung intubation. However, this superiority of 3,4,3-Li(1,2-HOPO) was much less pronounced with delayed treatment. In rats given plutonium in the lungs, the experiments also showed that 3,4,3-Li-HOPO reduced pulmonary retention of plutonium more effectively than DTPA only when the chelators were injected early but not at delayed times, while it was always the better of the two chelators when they were inhaled. Under our experimental conditions, the rapid oral administration of 3,4,3-Li(1,2-HOPO) was successful in preventing systemic accumulation of plutonium, but not in decreasing lung retention. Thus, after exposure to plutonium by inhalation, the best emergency treatment would be the rapid inhalation of a 3,4,3-Li(1,2-HOPO) aerosol to limit pulmonary retention of plutonium and prevent extrapulmonary deposition of plutonium in target systemic tissues.

Comparison of Local and Systemic DTPA Treatment Efficacy According to Actinide Physicochemical Properties Following Lung or Wound Contamination in the Rat

Purpose: In cases of occupational accidents in nuclear facilities or subsequent to terrorist activities, the most likely routes of internal contamination with alpha-particle emitting actinides, such as plutonium (Pu) and americium (Am), are by inhalation or following wounding. Following contamination, actinide transfer to the circulation and subsequent deposition in skeleton and liver depends primarily on the physicochemical nature of the compound. The treatment remit following internal contamination is to decrease actinide retention and in consequence potential health risks, both at the contamination site and in systemic retention organs as well as to promote elimination. The only approved drug for decorporation of Pu and Am is the metal chelator diethylenetriaminepentaacetic acid (DTPA). However, a limited efficacy of DTPA has been reported following contamination with insoluble actinides, irrespective of the contamination route. The objectives of this work are to evaluate the efficacy of prompt local and/or systemic DTPA treatment regimens following lung or wound contamination by actinides with differing solubility. The conclusions are drawn from retrospective analysis of experimental studies carried out over 10 years. Materials and Methods: Rat lungs or wounds were contaminated either with poorly soluble Mixed OXide (U, Pu O2) or more soluble forms of Pu (nitrate or citrate). DTPA treatment was administered promptly after contamination, locally to lungs by insufflation of a powder or inhalation of aerosolized solution or by injection directly into the wound site. Intravenous injections of DTPA were given either once or repeated in combination with the local treatment. Doses ranged from 1 to 30 µmol/kg. Animals were euthanized from day 7-21 and alpha activity levels were measured in urine, lungs, wound, bone and liver for determination of decorporation efficacy. Results: Different experiments confirmed that whatever the route of contamination, most of the activity is retained at the entry site after insoluble MOX contamination as compared with contamination with more soluble forms which results in very low activities reaching the systemic compartment and subsequent retention in bone and liver. Several DTPA treatment regimens were evaluated that had no significant effect on either lung or wound levels compared with untreated animals. In contrast, in all cases systemic retention (skeleton and liver) was reduced and urinary excretion were enhanced irrespective of the contamination route or DTPA treatment regimen. Conclusion: The present study demonstrates that despite limitation of retention in systemic organs, different DTPA protocols were ineffective in removing insoluble actinides deposited in lungs or wound site. For moderately soluble actinides, local or intravenous DTPA treatment reduced activity levels both at contamination and at systemic sites.

Hyperactivation of P2X7 receptors as a culprit of COVID-19 neuropathology

Scientists and health professionals are exhaustively trying to contain the coronavirus disease 2019 (COVID-19) pandemic by elucidating viral invasion mechanisms, possible drugs to prevent viral infection/replication, and health cares to minimize individual exposure. Although neurological symptoms are being reported worldwide, neural acute and long-term consequences of SARS-CoV-2 are still unknown. COVID-19 complications are associated with exacerbated immunoinflammatory responses to SARS-CoV-2 invasion. In this scenario, pro-inflammatory factors are intensely released into the bloodstream, causing the so-called "cytokine storm". Both pro-inflammatory factors and viruses may cross the blood-brain barrier and enter the central nervous system, activating neuroinflammatory responses accompanied by hemorrhagic lesions and neuronal impairment, which are largely described processes in psychiatric disorders and neurodegenerative diseases. Therefore, SARS-CoV-2 infection could trigger and/or worse brain diseases. Moreover, patients with central nervous system disorders associated to neuroimmune activation (e.g. depression, Parkinson's and Alzheimer's disease) may present increased susceptibility to SARS-CoV-2 infection and/or achieve severe conditions. Elevated levels of extracellular ATP induced by SARS-CoV-2 infection may trigger hyperactivation of P2X7 receptors leading to NLRP3 inflammasome stimulation as a key mediator of neuroinvasion and consequent neuroinflammatory processes, as observed in psychiatric disorders and neurodegenerative diseases. In this context, P2X7 receptor antagonism could be a promising strategy to prevent or treat neurological complications in COVID-19 patients.

Research on the Radiotoxicology of Plutonium Using Animals: Consideration of the 3Rs-Replace, Reduce, Refine

To characterize the health effects of incorporated plutonium, many experiments have been conducted using different animal models. These range from (1) applied (tissue uptake/retention determination, decorporation therapy efficacy), (2) fundamental (gene expression, cancer induction), and (3) dosimetry models. In recent years, the use of animals for scientific purposes has become a public concern. The application of the 3Rs - Replace (use of alternative methods or animals not considered capable of experiencing pain, suffering, and distress), Reduce (reduction in animal numbers), and Refine (better animal welfare and minimization of suffering, pain and distress) - has increased to address ethical concerns and legislative requirements. The introduction of novel non-animal technologies is also an important factor as complementary options to animal experimentation. In radiotoxicology research, it seems there is a natural tendency to Replace given the possibility of data reuse obtained from contamination cases in man and animal studies. The creation of "registries" and "repositories" for nuclear industry workers (civil and military) is now a rich legacy for radiotoxicological measurements. Similarly, Reduction in animal numbers can be achieved by good experimental planning with prior statistical analyses of animal numbers required to obtain robust data. Multiple measurements in the same animal over time (external body counting, excreta collection) with appropriate detection instruments also allow Reduction. In terms of Refinement, this has become "de rigueur" and a necessity given the societal and legal concerns for animal welfare. For research in radiotoxicology, particularly long-term studies, better housing conditions within the constraints of radiation protection issues for research workers are an important concern. These are all pertinent considerations for the 3Rs remit and future research in radiotoxicology.

More Than Just a Barrier: The Immune Functions of the Airway Epithelium in Asthma Pathogenesis

Allergic bronchial asthma is a chronic disease of the airways that is characterized by symptoms like respiratory distress, chest tightness, wheezing, productive cough, and acute episodes of broncho-obstruction. This symptom-complex arises on the basis of chronic allergic inflammation of the airway wall. Consequently, the airway epithelium is central to the pathogenesis of this disease, because its multiple abilities directly have an impact on the inflammatory response and thus the formation of the disease. In turn, its structure and functions are markedly impaired by the inflammation. Hence, the airway epithelium represents a sealed, self-cleaning barrier, that prohibits penetration of inhaled allergens, pathogens, and other noxious agents into the body. This barrier is covered with mucus that further contains antimicrobial peptides and antibodies that are either produced or specifically transported by the airway epithelium in order to trap these particles and to remove them from the body by a process called mucociliary clearance. Once this first line of defense of the lung is overcome, airway epithelial cells are the first cells to get in contact with pathogens, to be damaged or infected. Therefore, these cells release a plethora of chemokines and cytokines that not only induce an acute inflammatory reaction but also have an impact on the alignment of the following immune reaction. In case of asthma, all these functions are impaired by the already existing allergic immune response that per se weakens the barrier integrity and self-cleaning abilities of the airway epithelium making it more vulnerable to penetration of allergens as well as of infection by bacteria and viruses. Recent studies indicate that the history of allergy- and pathogen-derived insults can leave some kind of memory in these cells that can be described as imprinting or trained immunity. Thus, the airway epithelium is in the center of processes that lead to formation, progression and acute exacerbation of asthma.

The APOE ε4 allele is associated with a reduction in FEV1/FVC in women: A cross-sectional analysis of the Long Life Family Study

INTRODUCTION

Murine studies have shown that apolipoprotein E modulates pulmonary function during development, aging, and allergen-induced airway disease. It is not known whether the polymorphic human APOE gene influences pulmonary function.

OBJECTIVES

We assessed whether an association exists between the polymorphic human APOE ε2, ε3, and ε4 alleles and pulmonary function among participants in the Long Life Family Study.

METHODS

Data from 4,468 Caucasian subjects who had genotyping performed for the APOE ε2, ε3, and ε4 alleles were analyzed, with and without stratification by sex. Statistical models were fitted considering the effects of the ε2 allele, defined as ε2/2 or ε2/3 genotypes, and the ε4 allele, defined as ε3/4 or ε4/4 genotypes, which were compared to the ε3/3 genotype.

RESULTS

The mean FEV1/FVC ratio (the forced expiratory volume in one second divided by the forced vital capacity) was lower among women with the ε4 allele as compared to women with the ε3/3 genotype or the ε2 allele. Carriage of the APOE ε4 allele was associated with FEV1/FVC, which implied lower values. Further analysis showed that the association primarily reflected women without lung disease who were older than 70 years. The association was not mediated by lipid levels, smoking status, body mass index, or cardiovascular disease.

CONCLUSIONS

This study for the first time identifies that the APOE gene is associated with modified lung physiology in women. This suggests that a link may exist between the APOE ε4 allele, female sex, and a reduction in the FEV1/FVC ratio in older individuals.

Plasma proteomics reveals gestational age-specific responses to mechanical ventilation and identifies the mechanistic pathways that initiate preterm lung injury

The preterm lung is particularly vulnerable to ventilator-induced lung injury (VILI) as a result of mechanical ventilation. However the developmental and pathological cellular mechanisms influencing the changing patterns of VILI have not been comprehensively delineated, preventing the advancement of targeted lung protective therapies. This study aimed to use SWATH-MS to comprehensively map the plasma proteome alterations associated with the initiation of VILI following 60 minutes of standardized mechanical ventilation from birth in three distinctly different developmental lung states; the extremely preterm, preterm and term lung using the ventilated lamb model. Across these gestations, 34 proteins were differentially altered in matched plasma samples taken at birth and 60 minutes. Multivariate analysis of the plasma proteomes confirmed a gestation-specific response to mechanical ventilation with 79% of differentially-expressed proteins altered in a single gestation group only. Six cellular and molecular functions and two physiological functions were uniquely enriched in either the extremely preterm or preterm group. Correlation analysis supported gestation-specific protein-function associations within each group. In identifying the gestation-specific proteome and functional responses to ventilation we provide the founding evidence required for the potential development of individualized respiratory support approaches tailored to both the developmental and pathological state of the lung.

High Nrf2 expression in alveolar type I pneumocytes is associated with low recurrences in primary spontaneous pneumothorax

Recurrent primary spontaneous pneumothorax (PSP) is a troublesome problem and a major concern for the patients. This study examined whether nuclear factor erythroid 2-related factor 2 (Nrf2) expression in alveolar type I pneumocytes was associated with the clinical manifestations of PSP patients including disease recurrence. Eighty-eight PSP patients who were managed with needlescopic video-assisted thoracoscopic surgery (NVATS) were included in this study. Immunohistochemistry (IHC) was assessed to determine Nrf2 expression in resected lung tissues and the results were correlated with clinicopathological characteristics by the chi-square or the Fisher's exact test. The prognostic value of Nrf2 for overall recurrence was evaluated by univariate and multivariable Cox regression model. The expression of Nrf2 was observed in type I pneumocytes of lung tissues from PSP patients by IHC. We found that low Nrf2 expression in PSP patients, especially in young (age ≤ 20, p = 0.033) and body mass index (BMI) ≥18 kg/m² (p = 0.019) groups, was significantly correlated with PSP recurrence. In the univariate and multivariate analyses, high Nrf2 expression was a significant protective factor for overall recurrence in PSP patients (univariate: p = 0.026; multivariate: p = 0.004). The expression level of Nrf2 in alveolar type I pneumocytes was a potential factor involved in PSP recurrence. Our findings suggest that elevated Nrf2 expression in PSP patients may be a promising way for reducing PSP recurrence.

Emerging Roles of Apolipoprotein E and Apolipoprotein A-I in the Pathogenesis and Treatment of Lung Disease

Emerging roles are being recognized increasingly for apolipoproteins in the pathogenesis and treatment of lung diseases on the basis of their ability to suppress inflammation, oxidative stress, and tissue remodeling, and to promote adaptive immunity and host defense. Apolipoproteins, such as apolipoprotein E (apoE) and apolipoprotein A-I (apoA-I), are important components of lipoprotein particles that facilitate the transport of cholesterol, triglycerides, and phospholipids between plasma and cells. ApoE-containing lipoprotein particles are internalized into cells by low-density lipoprotein receptors (LDLRs), whereas apoA-I can interact with the ATP-binding cassette subfamily A member 1 (ABCA1) transporter to efflux cholesterol and phospholipids out of cells. ApoE and apoA-I also mediate receptor-independent effects, such as binding to and neutralizing LPS. Both apoE and apoA-I are expressed by lung cells, which allows apoE/LDLR- and apoA-I/ABCA1-dependent pathways to modulate normal lung health and the pathogenesis of respiratory diseases, including asthma, acute lung injury, cancer, emphysema, pulmonary fibrosis, and pulmonary hypertension. Data from human studies and research using experimental murine model systems have shown that both apoE and apoA-I pathways play primarily protective roles in lung biology and respiratory disease. Furthermore, apolipoprotein mimetic peptides, corresponding to the LDLR-binding domain of apoE or the class A amphipathic α-helical structure of apoA-I, have antiinflammatory and antioxidant effects that attenuate the severity of lung disease in murine models. Thus, the development of inhaled apolipoprotein mimetic peptides as a novel treatment paradigm could represent a significant advance for patients with respiratory disease who do not respond to current therapies.

Analysis of genomic responses in a rat lung model treated with a humidifier sterilizer containing polyhexamethyleneguanidine phosphate

The antimicrobial biocide polyhexamethyleneguanidine (PHMG) phosphate is the main ingredient in the commercially available humidifier disinfectant. PHMG phosphate-based humidifier disinfectants can cause pulmonary fibrosis and induce inflammatory and fibrotic responses both in vivo and in vitro. However, toxicological mechanisms including genomic alterations induced by inhalation exposure to PHMG phosphate have not been elucidated. Therefore, this study evaluated the toxicological effects of the PHMG phosphate-containing humidifier disinfectant. We used DNA microarray to identify global gene expression changes in rats treated with PHMG phosphate-containing humidifier disinfectant for 4 weeks and 10 weeks. Functional significance of differentially expressed genes (DEGs) was estimated by gene ontology (GO) analysis. Four weeks post-exposure, 320 and 392 DEGs were identified in female and male rats, respectively (>2-fold, p<0.05). Ten weeks post-exposure, 1290 and 995 DEGs were identified in females and males, respectively. Of these, 119 and 556 genes overlapped between females and males at 4 weeks and 10 weeks, respectively, post-PHMG phosphate exposure. In addition, 21 genes were upregulated and 4 genes were downregulated in response to PHMG phosphate in a time-dependent manner. Thus, we predict that changes in genomic responses could be a significant molecular mechanism underlying PHMG phosphate toxicity. Further studies are required to determine the detailed mechanism of PHMG phosphate-induced pulmonary toxicity.

A Critical Role for P2X7 Receptor-Induced VCAM-1 Shedding and Neutrophil Infiltration during Acute Lung Injury

Pulmonary neutrophils are the initial inflammatory cells that are recruited during lung injury and are crucial for innate immunity. However, pathological recruitment of neutrophils results in lung injury. The objective of this study is to determine whether the novel neutrophil chemoattractant, soluble VCAM-1 (sVCAM-1), recruits pathological levels of neutrophils to injury sites and amplifies lung inflammation during acute lung injury. The mice with P2X7 receptor deficiency, or treated with a P2X7 receptor inhibitor or anti-VCAM-1 Abs, were subjected to a clinically relevant two-hit LPS and mechanical ventilation-induced acute lung injury. Neutrophil infiltration and lung inflammation were measured. Neutrophil chemotactic activities were determined by a chemotaxis assay. VCAM-1 shedding and signaling pathways were assessed in isolated lung epithelial cells. Ab neutralization of sVCAM-1 or deficiency or antagonism of P2X7R reduced neutrophil infiltration and proinflammatory cytokine levels. The ligands for sVCAM-1 were increased during acute lung injury. sVCAM-1 had neutrophil chemotactic activities and activated alveolar macrophages. VCAM-1 is released into the alveolar airspace from alveolar epithelial type I cells through P2X7 receptor-mediated activation of the metalloproteinase ADAM-17. In conclusion, sVCAM-1 is a novel chemoattractant for neutrophils and an activator for alveolar macrophages. Targeting sVCAM-1 provides a therapeutic intervention that could block pathological neutrophil recruitment, without interfering with the physiological recruitment of neutrophils, thus avoiding the impairment of host defenses.

Neonatal Type II Alveolar Epithelial Cell Transplant Facilitates Lung Reparation in Piglets With Acute Lung Injury and Extracorporeal Life Support

OBJECTIVES

Type II alveolar epithelial cells have potential for lung growth and reparation. Extracorporeal membrane oxygenation is used as life support for lung impairment resulting from acute respiratory distress syndrome. We hypothesized that intratracheal transplantation of isogeneic primary type II alveolar epithelial cells in combination with extracorporeal membrane oxygenation may facilitate lung reparation for acute lung injury (ALI).

DESIGN

A randomized, controlled experiment.

SETTING

An animal laboratory in a university pediatric center.

SUBJECTS

Twenty-eight 4- to 6-week young piglets, weighing 7-8 kg.

INTERVENTIONS

Type II alveolar epithelial cells from neonatal male piglet lungs were isolated, purified, cultured, and labeled with chemical stain PKH26. After 3-6 hours of induction of ALI by IV endotoxin and mechanical ventilation (MV), young female piglets were allocated to five groups (n = 5): ALI-MV, ALI treated with MV; ALI-EC, ALI treated with both MV and venovenous extracorporeal membrane oxygenation; ALI-EC-T, ALI-EC protocol plus intratracheal type II alveolar epithelial cell transplant; CON-MV, healthy animals treated with MV; and CON-EC-T, healthy animals treated with venovenous extracorporeal membrane oxygenation. After 24 hours, animals were weaned from treatment for recovery in the ensuing 14 days, with their lungs assessed for injury and reparation.

MEASUREMENTS AND MAIN RESULTS

Lung injury for animals in ALI-MV was moderate to severe, whereas much milder injuries in ALI-EC-T and ALI-EC were found. More PKH26-labeled type II alveolar epithelial cells were detected by fluorescence in the lungs of ALI-EC-T than in CON-EC-T as further verified by the expression of messenger RNA of sex-determining region of Y chromosome. Electromicroscopically intact type II alveolar epithelial cells and prominent lattice-like tubular myelin were also found in ALI-EC-T and CON-MV but not in ALI-EC. The hydroxyproline level in lung tissue was significantly lower in ALI-EC-T than in ALI-EC and ALI-MV, with most of the lung histopathologic and pathobiologic manifestations in favor of ALI-EC-T.

CONCLUSIONS

The preliminary data suggested that type II alveolar epithelial cell transplant facilitated lung reparation for ALI in this model.

Wnt3a mitigates acute lung injury by reducing P2X7 receptor-mediated alveolar epithelial type I cell death

Acute lung injury (ALI) is characterized by pulmonary endothelial and epithelial cell damage, and loss of the alveolar–capillary barrier. We have previously shown that P2X7 receptor (P2X7R), a cell death receptor, is specifically expressed in alveolar epithelial type I cells (AEC I). In this study, we hypothesized that P2X7R-mediated purinergic signaling and its interaction with Wnt/β-catenin signaling contributes to AEC I death. We examined the effect of P2X7R agonist 2′-3′-O-(4-benzoylbenzoyl)-ATP (BzATP) and Wnt agonist Wnt3a on AEC I death in vitro and in vivo. We also assessed the therapeutic potential of Wnt3a in a clinically relevant ALI model of intratracheal lipopolysaccharide (LPS) exposure in ventilated mice. We found that the activation of P2X7R by BzATP caused the death of AEC I by suppressing Wnt/β-catenin signaling through stimulating glycogen synthase kinase-3β (GSK-3β) and proteasome. On the other hand, the activation of Wnt/β-catenin signaling by Wnt3a, GSK-3β inhibitor, or proteasome inhibitor blocked the P2X7R-mediated cell death. More importantly, Wnt3a attenuated the AEC I damage caused by intratracheal instillation of BzATP in rats or LPS in ventilated mice. Our results suggest that Wnt3a overrides the effect of P2X7R on the Wnt/β-catenin signaling to prevent the AEC I death and restrict the severity of ALI.

miR-375 regulates rat alveolar epithelial cell trans-differentiation by inhibiting Wnt/β-catenin pathway

Alveolar epithelial cell (AEC) trans-differentiation is a process where type II alveolar epithelial cells (AEC II) trans-differentiate into type I alveolar epithelial cells (AEC I) during lung recovery after various injuries, in which AEC I are damaged. This process is critical for lung tissue repair. MicroRNAs are a group of small RNAs that regulate gene expression at the post-transcriptional level. They have the potential to regulate almost every aspect of cell physiology. However, whether AEC trans-differentiation is regulated by microRNAs is completely unknown. In this study, we found that miR-375 was downregulated during AEC trans-differentiation. The overexpression of miR-375 with an adenoviral vector inhibited alveolar epithelial trans-differentiation as indicated by an increase in the AEC II marker, surfactant protein C, and decreases in the AEC I markers, T1α and advanced glycosylation end product-specific receptor. miR-375 also inhibited the Wnt/β-catenin pathway. The constitutively activation of Wnt/β-catenin signaling with a stabilized form of β-catenin blocked the miR-375 effects. Frizzled 8 was identified as a target of miR-375. In summary, our results demonstrate that miR-375 regulates AEC trans-differentiation through the Wnt/β-catenin pathway. This discovery may provide new targets for therapeutic intervention to benefit lung recovery from injuries.

GABA receptor ameliorates ventilator-induced lung injury in rats by improving alveolar fluid clearance

Introduction

Mechanical ventilators are increasingly used in critical care units. However, they can cause lung injury, including pulmonary edema. Our previous studies indicated that γ-aminobutyric acid (GABA) receptors are involved in alveolar-fluid homeostasis. The present study investigated the role of GABA receptors in ventilator-induced lung injury.

Methods

Adult female Sprague-Dawley rats were subjected to high-tidal-volume ventilation of 40 ml/kg body weight for 1 hour, and lung injuries were assessed.

Results

High-tidal-volume ventilation resulted in lung injury, as indicated by an increase in total protein in bronchoalveolar fluid, wet-to-dry ratio (indication of pulmonary edema), and Evans Blue dye extravasation (indication of vascular damage). Intratracheal administration of GABA before ventilation significantly reduced the wet-to-dry ratio. Further, histopathologic analysis indicated that GABA reduced ventilator-induced lung injury and apoptosis. GABA-mediated reduction was effectively blocked by the GABA_A-receptor antagonist, bicuculline. The GABA-mediated effect was not due to the vascular damage, because no differences in Evans Blue dye extravasation were noted. However, the decrease in alveolar fluid clearance by high-tidal-volume ventilation was partly prevented by GABA, which was blocked by bicuculline.

Conclusions

These results suggest that GABA reduces pulmonary edema induced by high-tidal-volume ventilation via its effects on alveolar fluid clearance and apoptosis.

Regulation of lung surfactant secretion by microRNA-150

P2X7 receptor (P2X7R) is a purinergic ion-channel receptor. We have previously shown that the activation of P2X7R in alveolar type I cells stimulates surfactant secretion in alveolar type II cells. In this study, we determined whether miR-150 regulates P2X7R-mediated surfactant secretion. The miR-150 expression level in alveolar type II cells was much higher than alveolar type I cells, which was inversely correlated with the P2X7R protein level. An adenovirus expressing miR-150 significantly reduced the P2X7R protein expression in E10 cells, an alveolar type I cell line. Furthermore, pre-treatment of E10 cells with the adenovirus reduced the surfactant secretion induced by E10 cell conditioned medium. Our study demonstrates that miR-150 regulates surfactant secretion through P2X7R.

Apolipoprotein mimetic peptides: a new approach for the treatment of asthma

New treatments are needed for severe asthmatics to improve disease control and avoid severe toxicities associated with oral corticosteroids. We have used a murine model of house dust mite (HDM)-induced asthma to identify steroid-unresponsive genes that might represent targets for new therapeutic approaches for severe asthma. This strategy identified apolipoprotein E as a steroid-unresponsive gene with increased mRNA expression in the lungs of HDM-challenged mice. Furthermore, apolipoprotein E functioned as an endogenous negative regulator of airway hyperreactivity and goblet cell hyperplasia in experimental HDM-induced asthma. The ability of apolipoprotein E, which is expressed by lung macrophages, to attenuate AHR, and goblet cell hyperplasia is mediated by low density lipoprotein (LDL) receptors expressed by airway epithelial cells. Consistent with this, administration of an apolipoprotein E mimetic peptide, corresponding to amino acids 130–149 of the LDL receptor-binding domain of the holo-apoE protein, significantly reduced AHR and goblet cell hyperplasia in HDM-challenged apoE^−/− mice. These findings identified the apolipoprotein E – LDL receptor pathway as a new druggable target for asthma that can be activated by administration of apoE-mimetic peptides. Similarly, apolipoprotein A-I may have therapeutic potential in asthma based upon its anti-inflammatory, anti-oxidative, and anti-fibrotic properties. Furthermore, administration of apolipoprotein A-I mimetic peptides has attenuated airway inflammation, airway remodeling, and airway hyperreactivity in murine models of experimental asthma. Thus, site-directed delivery of inhaled apolipoprotein E or apolipoprotein A-I mimetic peptides may represent novel treatment approaches that can be developed for asthma, including severe disease.

Major shifts in the spatio-temporal distribution of lung antioxidant enzymes during influenza pneumonia

With the incessant challenge of exposure to the air we breathe, lung tissue suffers the highest levels of oxygen tension and thus requires robust antioxidant defenses. Furthermore, following injury or infection, lung tissue faces the additional challenge of inflammation-induced reactive oxygen and nitrogen species (ROS/RNS). Little is known about the identity or distribution of lung antioxidant enzymes under normal conditions or during infection-induced inflammation. Using a mouse model of influenza (H1N1 influenza virus A/PR/8/34 [PR8]) in combination with bioinformatics, we identified seven lung-abundant antioxidant enzymes: Glutathione peroxidase 3 (Gpx3), Superoxide dismutase 3 (Sod3), Transferrin (Tf), peroxyredoxin6 (Prdx6), glutathione S-transferase kappa 1 (Gstk1), Catalase (Cat), and Glutathione peroxidase 8 (Gpx8). Interestingly, despite the demand for antioxidants during inflammation, influenza caused depletion in two key antioxidants: Cat and Prdx6. As Cat is highly expressed in Clara cells, virus-induced Clara cell loss contributes to the depletion in Cat. Prdx6 is also reduced due to Clara cell loss, however there is a coincident increase in Prdx6 levels in the alveoli, resulting in only a subtle reduction of Prdx6 overall. Analogously, Gpx3 shifts from the basement membranes underlying the bronchioles and blood vessels to the alveoli, thus maintaining balanced expression. Taken together, these studies identify key lung antioxidants and reveal their distribution among specific cell types. Furthermore, results show that influenza depletes key antioxidants, and that in some cases there is coincident increased expression, consistent with compensatory expression. Given that oxidative stress is known to be a key risk factor during influenza infection, knowledge about the antioxidant repertoire of lungs, and the spatio-temporal distribution of antioxidants, contributes to our understanding of the underlying mechanisms of influenza-induced morbidity and mortality.

Binase penetration into alveolar epithelial cellsdoes not induce cell death

Microbial ribonucleases possess a broad spectra of biological activities, demonstrating stimulating properties at low concentrations and cytotoxicity and genotoxicity at high concentrations. The mechanisms of their penetration into the cells are not clear so far. This research is aimed to the study of Bacillus intermedius RNase (binase) penetration in alveolar lung epithelial cells - pneumocytes of type II. Using immunofluorescence we have shown for the first time have internalization of binase by primary non-differentiated pneumocytes АТII. The enzyme did not penetrate in pneumocytes MLE-12, which also derived from type II cells. However, binase was cytotoxic towards tumor MLE-12 cells, but not АТII cells. The obtained results testified the higher sensitivity of tumor cells towards binase compared with normal cells, and also showed that penetration of the enzyme into alveolar cells did not directly correlated with the cell death.

Age-related differences in cigarette smoke extract-induced H2O2 production by lung endothelial cells

Cigarette smoke causes oxidative stress in the lung resulting in injury and disease. The purpose of this study was to determine if there were age-related differences in cigarette smoke extract (CSE)-induced production of reactive species in single and co-cultures of alveolar epithelial type I (AT I) cells and microvascular endothelial cells harvested from the lungs (MVECLs) of neonatal, young and old male Fischer 344 rats. Cultures of AT I cells and MVECLs grown separately (single culture) and together (co-culture) were exposed to CSE (1, 10, 50, 100%). Cultures were assayed for the production of intracellular reactive oxygen species (ROS), hydroxyl radical (OH), peroxynitrite (ONOO(-)), nitric oxide (NO) and extracellular hydrogen peroxide (H(2)O(2)). Single and co-cultures of AT I cells and MVECLs from all three ages produced minimal intracellular ROS in response to CSE. All ages of MVECLs produced H(2)O(2) in response to CSE, but young MVECLs produced significantly less H(2)O(2) compared to neonatal and old MVECLs. Interestingly, when grown as a co-culture with age-matched AT I cells, neonatal and old MVECLs demonstrated ~50% reduction in H(2)O(2) production in response to CSE. However, H(2)O(2) production in young MVECLs grown as a co-culture with young AT I cells did not change with CSE exposure. To begin investigating for a potential mechanism to explain the reduction in H(2)O(2) production in the co-cultures, we evaluated single and co-cultures for extracellular total antioxidant capacity. We also performed gene expression profiling specific to oxidant and anti-oxidant pathways. The total antioxidant capacity of the AT I cell supernatant was ~5 times greater than that of the MVECLs, and when grown as a co-culture and exposed to CSE (≥ 10%), the total antioxidant capacity of the supernatant was reduced by ~50%. There were no age-related differences in total antioxidant capacity of the cell supernatants. Gene expression profiling found eight genes to be significantly up-regulated or down-regulated. This is the first study to describe age-related differences in MVECLs exposed to CSE.

Purinergic P2X7 receptor regulates lung surfactant secretion in a paracrine manner

Alveolar epithelium is composed of alveolar epithelial cells of type I (AEC I) and type II (AEC II). AEC II secrete lung surfactant by means of exocytosis. P2X(7) receptor (P2X(7)R), a P2 purinergic receptor, has been implicated in the regulation of synaptic transmission and inflammation. Here, we report that P2X(7)R, which is expressed in AEC I but not AEC II, is a novel mediator for the paracrine regulation of surfactant secretion in AEC II. In primary co-cultures of AEC I and AEC II benzoyl ATP (BzATP; an agonist of P2X(7)R) increased surfactant secretion, which was blocked by the P2X(7)R antagonist Brilliant Blue G. This effect was observed in AEC II co-cultured with human embryonic kidney HEK-293 cells stably expressing rat P2X(7)R, but not when co-cultured with AEC I in which P2X(7)R was knocked down or in co-cultures of AEC I and AEC II isolated from P2X(7)R(-/-) mice. BzATP-mediated secretion involved P2Y(2) receptor signaling because it was reduced by the addition of the ATP scavengers apyrase and adenosine deaminase and the P2Y(2) receptor antagonist suramin. However, the stimulation with BzATP might also release other substances that potentially increase surfactant secretion as a greater stimulation of secretion was observed in AEC II incubated with BzATP when co-cultured with E10 or HEK-293-P2X(7)R cells than with ATP alone. P2X(7)R(-/-) mice failed to increase surfactant secretion in response to hyperventilation, pointing to the physiological relevance of P2X(7)R in maintaining surfactant homeostasis in the lung. These results suggest that the activation of P2X(7)R increases surfactant secretion by releasing ATP from AEC I and subsequently stimulating P2Y(2) receptors in AEC II.

Antihypertension Induced by Tanshinone IIA Isolated from the Roots of Salvia miltiorrhiza

Tanshinone IIA is one of the active principles in danshen (Salvia miltiorrhiza Bge) widely used in treatment of cardiovascular disorders. We investigated the effect of danshen or tanshinone IIA on blood pressure and its possible mechanisms. An i.p. injection of danshen at 10 mg kg(-1) significantly lowered systolic blood pressure (SBP) of spontaneously hypertensive rats (SHRs) but failed to modify the SBP in normotensive Wistar-Kyoto rats (WKY). Oral administration of tanshinone IIA also decreased SBP in SHR but not in WKY. Tanshinone IIA produced a concentration-dependent relaxation in isolated SHR aortic rings precontracted with phenylephrine (10 nmol l(-1)) or potassium chloride (KCl) (40 mmol l(-1)). The relaxing effect of tanshinone IIA on tonic contraction of phenylephrine in isolated aortic rings without endothelium remained produced. Glibenclamide at concentration sufficient to block adenosine triphosphatase (ATP)-sensitive potassium (K(+)) channel attenuated this tanshinone IIA-induced relaxation that was not influenced by other inhibitors. We further investigated the effect of tanshinone IIA on the changes of intracellular calcium concentration ([Ca(2+)](i)) in cultured aortic smooth muscle (A7r5) cells using fura-2 as indicator. Tanshinone IIA decreased [Ca(2+)](i) elicited by phenylephrine (10 nmol l(-1)) or KCl (40 mmol l(-1)) in a concentration-dependent manner; glibenclamide, but not other inhibitors for K(+) channel, abated this effect. Our results suggest that tanshinone IIA acts as an active principle of danshen showing vasodilation through ATP-sensitive K(+) channel to lower [Ca(2+)](i).

Respiratory epithelial cells in innate immunity to influenza virus infection

Infection by influenza virus leads to respiratory failure characterized by acute lung injury associated with alveolar edema, necrotizing bronchiolitis, and excessive bleeding. Severe reactions to infection that lead to hospitalizations and/or death are frequently attributed to an exuberant host response, with excessive inflammation and damage to the epithelial cells that mediate respiratory gas exchange. The respiratory mucosa serves as a physical and chemical barrier to infection, producing mucus and surfactants, anti-viral mediators, and inflammatory cytokines. The airway epithelial cell layer also serves as the first and overwhelmingly primary target for virus infection and growth. This review details immune events during influenza infection from the viewpoint of the epithelial cells, secretory host defense mechanisms, cell death, and recovery.

Regulated gene expression in cultured type II cells of adult human lung

Alveolar type II cells have multiple functions, including surfactant production and fluid clearance, which are critical for lung function. Differentiation of type II cells occurs in cultured fetal lung epithelial cells treated with dexamethasone plus cAMP and isobutylmethylxanthine (DCI) and involves increased expression of 388 genes. In this study, type II cells of human adult lung were isolated at approximately 95% purity, and gene expression was determined (Affymetrix) before and after culturing 5 days on collagen-coated dishes with or without DCI for the final 3 days. In freshly isolated cells, highly expressed genes included SFTPA/B/C, SCGB1A, IL8, CXCL2, and SFN in addition to ubiquitously expressed genes. Transcript abundance was correlated between fetal and adult cells (r = 0.88), with a subset of 187 genes primarily related to inflammation and immunity that were expressed >10-fold higher in adult cells. During control culture, expression increased for 8.1% of expressed genes and decreased for approximately 4% including 118 immune response and 10 surfactant-related genes. DCI treatment promoted lamellar body production and increased expression of approximately 3% of probed genes by > or =1.5-fold; 40% of these were also induced in fetal cells. Highly induced genes (> or =10-fold) included PGC, ZBTB16, DUOX1, PLUNC, CIT, and CRTAC1. Twenty-five induced genes, including six genes related to surfactant (SFTPA/B/C, PGC, CEBPD, and ADFP), also had decreased expression during control culture and thus are candidates for hormonal regulation in vivo. Our results further define the adult human type II cell molecular phenotype and demonstrate that a subset of genes remains hormone responsive in cultured adult cells.

Regulatory T cell-mediated resolution of lung injury: identification of potential target genes via expression profiling

In animal models of acute lung injury (ALI), gene expression studies have focused on the acute phase of illness, with little emphasis on resolution. In this study, the acute phase of intratracheal lipopolysaccharide (IT LPS)-induced lung injury was similar in wild-type (WT) and recombinase-activating gene-1-deficient (Rag-1(-/-)) lymphocyte-deficient mice, but resolution was impaired and resolution-phase lung gene expression remained different from baseline only in Rag-1(-/-) mice. By focusing on groups of genes involved in similar biological processes (gene ontologies) pertinent to inflammation and the immune response, we identified 102 genes at days 4 and 10 after IT LPS with significantly different expression between WT and Rag-1(-/-) mice. After adoptive transfer of isolated CD4+CD25+Foxp3+ regulatory T cells (Tregs) to Rag-1(-/-) mice at the time of IT LPS, resolution was similar to that in WT mice. Of the 102 genes distinctly changed in either WT or Rag-1(-/-) mice from our 7 gene ontologies, 19 genes reverted from the Rag-1(-/-) to the WT pattern of expression after adoptive transfer of Tregs, implicating those 19 genes in Treg-mediated resolution of ALI.

Glycogen content is affected differently in acute pulmonary and extra-pulmonary lung injury

Acute respiratory distress syndrome (ARDS) is the most severe form of acute lung injury (ALI). The aim of the present study was to investigate whether paraquat-induced acute pulmonary and extra-pulmonary lung injury (ALI-P and ALI-EX, respectively), in rats, affects glycogen content in different tissues. This measurement could indicate performance limitations of tissues, a new biochemical aspect of ARDS. ALI-P and ALI-EX were induced by injection into the trachea (0.5 mg/kg) and intraperitoneally (20 mg/kg) 24 hours prior to tissue collection. The control groups (CTRL) received the same volume of saline. Glycogen content (mg/g tissue) from different tissues was measured using the anthrone reagent. Glycogen content in the heart and kidney was higher in the ALI-EX group than the CTRL-EX group. Glycogen content in the gastrocnemius muscle was lower in the ALI-EX group than the CTRL-EX group. However, there were no significant differences in glycogen content in the diaphragm in the ALI-EX and ALI-P groups or in the gastrocnemius, heart and kidney in the ALI-P group when compared to the respective controls. ALI-EX caused a greater thickening of the alveolar walls, more areas of atelectasis and a greater abundance of inflammatory cells in comparison to ALI-P. These results demonstrate that glycogen content in ALI, induced by an herbicide that is highly toxic to humans and animals, is altered in different tissues depending on the location of the injury.

Directed expression of Cre in alveolar epithelial type 1 cells

Pulmonary alveolar epithelium is comprised of two morphologically and functionally distinct cell types, alveolar epithelial type (AT) I and AT2 cells. Genetically modified mice with cell-specific Cre/loxP-mediated knockouts of relevant genes in each respective cell type would be useful to help elucidate the relative contributions of AT1 versus AT2 cells to alveolar homeostasis. Cre has previously been efficiently expressed in AT2 cells in mouse lung with the surfactant protein (SP)-C promoter; however, no transgenic mouse expressing Cre in AT1 cells has so far been available. To develop an AT1 cell-specific transgenic Cre mouse, we generated a knockin of a Cre-IRES-DsRed cassette into exon 1 of the endogenous aquaporin 5 (Aqp5) gene, a gene expressed specifically in AT1 cells in the distal lung epithelium, resulting in the mouse line, Aqp5-Cre-IRES-DsRed (ACID). Endogenous Aqp5 and transgenic Cre in ACID mice showed a very similar pattern of tissue distribution by RT-PCR. To analyze Cre activity, ACID was crossed to two Cre reporter strains, R26LacZ and mT/mG. Double-transgenic offspring demonstrated reporter gene expression in a very high fraction of AT1 cells in the distal lung, whereas AT2 cells were negative. As expected, variable reporter expression was detected in several other tissues where endogenous Aqp5 is expressed (e.g., submandibular salivary gland and stomach). ACID mice should be of major utility in analyzing the functional contribution of AT1 cells to alveolar epithelial properties in vivo with Cre/loxP-mediated gene deletion technology.

MCP-1 antibody treatment enhances damage and impedes repair of the alveolar epithelium in influenza pneumonitis

Recent studies have demonstrated an essential role of alveolar macrophages during influenza virus infection. Enhanced mortalities were observed in macrophage-depleted mice and pigs after influenza virus infection, but the basis for the enhanced pathogenesis is unclear. This study revealed that blocking macrophage recruitment into the lungs in a mouse model of influenza pneumonitis resulted in enhanced alveolar epithelial damage and apoptosis, as evaluated by histopathology, immunohistochemistry, Western blot, RT-PCR, and TUNEL assays. Abrogation of macrophage recruitment was achieved by treatment with monoclonal antibody against monocyte chemoattractant protein-1 (MCP-1) after sub-lethal challenge with mouse-adapted human influenza A/Aichi/2/68 virus. Interestingly, elevated levels of hepatocyte growth factor (HGF), a mitogen for alveolar epithelium, were detected in bronchoalveolar lavage samples and in lung homogenates of control untreated and nonimmune immunoglobulin (Ig)G-treated mice after infection compared with anti-MCP-1-treated infected mice. The lungs of control animals also displayed strongly positive HGF staining in alveolar macrophages as well as alveolar epithelial cell hyperplasia. Co-culture of influenza virus-infected alveolar epithelial cells with freshly isolated alveolar macrophages induced HGF production and phagocytic activity of macrophages. Recombinant HGF added to mouse lung explants after influenza virus infection resulted in enhanced BrdU labeling of alveolar type II epithelial cells, indicating their proliferation, in contrast with anti-HGF treatment showing significantly reduced epithelial regeneration. Our data indicate that inhibition of macrophage recruitment augmented alveolar epithelial damage and apoptosis during influenza pneumonitis, and that HGF produced by macrophages in response to influenza participates in the resolution of alveolar epithelium.

Gene expression analysis after prenatal tracheal ligation in fetal rat as a model of stimulated lung growth

PURPOSE

Prenatal tracheal occlusion or ligation (TL) has been proven to accelerate lung growth, but the mechanism of this is poorly understood. To increase understanding of the biological mechanisms involved in growth stimulation after TL in the fetal lung, we performed Global gene expression analysis using microarray technology.

MATERIAL AND METHODS

Sprague-Dawley rats underwent surgery on gestational day 19. After a small hysterotomy, the trachea was mobilized and tied. As controls, we used littermates to manipulated fetuses. On day 21, fetuses were removed and lungs harvested. Global gene expression analysis was performed using Affymetrix Platform and the RAE 230 set arrays (Affymetrix Inc, Santa Clara, Calif). For validation of microarray data, we performed real time polymerase chain reaction (PCR) of the most significant upregulated or downregulated genes, combined with immunohistochemical (IHC) analysis of lung sections.

RESULTS

In the group that underwent TL, several growth factors had an increased expression including connective tissue growth factor (CTGF), insulin-like growth factor 1 (IGF-1), and fibroblast growth factor 18 (FGF-18). Some of the genes that were downregulated in the group that underwent TL compared with controls were surfactant protein A (SP-A), apolipoprotein E (Apo-E), and phospholipase group II A2 (plg2a2). These results could be confirmed with real time PCR and IHC studies.

DISCUSSION

Tracheal occlusion or ligation is a well-documented stimulator of fetal lung growth, and the present study provides novel insights into the underlying molecular mechanisms, with increased expression of genes and proteins with growth factor activity. One of these growth factors, CTGF, has never been previously described in this model. Also, decreased levels of genes involved in surfactant metabolism were observed, providing molecular insights into the decreased surfactant production that is known to occur in TL. Increased understanding of the molecular mechanisms that control lung growth may be the key to develop novel therapeutic techniques to stimulate prenatal and/or postnatal lung growth.

Age-related changes in the expression and oxidation of bronchoalveolar lavage proteins in the rat

The incidence and severity of many lung diseases change with age. Some diseases, such as pneumonia, occur with increased frequency in children and the elderly. Proteins obtained by bronchoalveolar lavage (BAL) serve as the first line of defense against inhaled toxins and pathogens. Age-related changes in BAL protein expression and oxidative modification were examined in juvenile (1 mo), young adult (2 mo), and aged (18 mo) F344 rats using two-dimensional difference gel electrophoresis (2D-DIGE), matrix-assisted laser desorption ionization-time of flight/time of flight (MALDI-ToF/ToF) tandem mass spectrometry, and carbonyl immunoblotting. Using 2D-DIGE, we detected 563 protein spots, and MALDI-ToF/ToF identified 204 spots comprising 31 proteins; 21 changed significantly (17 increases) between juvenile and young adult or aged rats, but for 12 of these proteins, levels had a biphasic pattern, and levels in aged rats were less than in young adults. Relative carbonylation was determined by comparison of immunostaining with total protein staining on each oxidized protein blot. We found that aged rats had significantly increased oxidation in 13 proteins compared with juvenile rats. Many of the proteins altered in expression or oxidation level had functions in host defense, redox regulation, and protein metabolism. We speculate that low levels of expression of host defense proteins in juvenile rats and decreases in levels of these proteins between young adult and aged rats may predispose these groups to pneumonia. In addition, we have shown age-related increases in protein oxidation that may compromise host defense function in aged rats.

Ghrelin inhibits interleukin-8 production induced by hydrogen peroxide in A549 cells via NF-kappaB pathway

Ghrelin, a novel growth hormone-releasing peptide, can influence appetite and induce positive energy balances. Previous studies have reported that ghrelin ameliorated inflammatory responses of the heart, liver and pancreas. We examined whether ghrelin inhibits the proinflammatory cytokine interleukin-8 production induced by hydrogen peroxide (H2O2) in human lung epithelia cell line A549 and which mechanism is related with this effect of ghrelin. A549 cells were preincubated with vehicle or ghrelin (0.1 to 1000 ng/mL) in a concentration-dependent manner and then H2O2 (0 to 50 microM) was added. The interleukin-8 released by A549 in the medium was determined by ELISA, the mRNA expressions of interleukin-8 and ghrelin receptor were detected by RT-PCR. We also examined the phosphorylation of NF-kappaB/p65 protein and the degradation of inhibitory protein-kappaB (I-kappaB) in A549 by western blot analysis, the NF-kappaB DNA-binding activity by electrophoretic mobility shift assay, and then detected the generation of reactive oxygen species (ROS) in A549 by nitroblue tetrazolium reduction assay. Cells treated with H2O2 (50 microM) exhibited significantly higher interleukin-8 production and ghrelin receptor mRNA expression compared with cells treated with vehicle alone (P < 0.05). Ghrelin inhibited H2O2-induced interleukin-8 production by A549 at both mRNA and protein levels in a concentration-dependent manner (P < 0.05). Moreover, ghrelin attenuated H2O2-triggered NF-kappaB activation dependent on I-kappaB degradation dose-dependently in A549, but the intracellular ROS level after application of H2O2 was not affected by ghrelin (1000 ng/mL). Together, these results suggest that ghrelin inhibits H2O2-induced interleukin-8 production in A549 cells by targeting on NF-kappaB pathway, but not by directly scavenging intracellular ROS.

Redox regulation of epithelial sodium channels examined in alveolar type 1 and 2 cells patch-clamped in lung slice tissue

The alveolar surface of the lung is lined by alveolar type 1 (AT1) and type 2 (AT2) cells. Using single channel patch clamp analysis in lung slice preparations, we are able to uniquely study AT1 and AT2 cells separately from intact lung. We report for the first time the Na+ transport properties of type 2 cells accessed in live lung tissue (as we have done in type 1 cells). Type 2 cells in lung tissue slices express both highly selective cation and nonselective cation channels with average conductances of 8.8 +/- 3.2 and 22.5 +/- 6.3 picosiemens, respectively. Anion channels with 10-picosiemen conductance are also present in the apical membrane of type 2 cells. Our lung slice studies importantly verify the use of cultured cell model systems commonly used in lung epithelial sodium channel (ENaC) studies. Furthermore, we identify novel functional differences between the cells that make up the alveolar epithelium. One important difference is that exposure to the nitric oxide (NO) donor, PAPA-NONOate (1.5 microm), significantly decreases average ENaC NPo in type 2 cells (from 1.38 +/- 0.26 to 0.82 +/- 0.16; p < 0.05 and n = 18) but failed to alter ENaC activity in alveolar type 1 cells. Elevating endogenous superoxide (O2.) levels with Ethiolat, a superoxide dismutase inhibitor, prevented NO inhibition of ENaC activity in type 2 cells, supporting the novel hypothesis that O2. and NO signaling plays an important role in maintaining lung fluid balance.

Expression and biological activity of ABCA1 in alveolar epithelial cells

The mechanisms used by alveolar type I pneumocytes for maintenance of the lipid homeostasis necessary to sustain these large squamous cells are unknown. The processes may involve the ATP-binding cassette transporter A1 (ABCA1), a transport protein shown to be crucial in apolipoprotein A-I (apoA-I)-mediated mobilization of cellular cholesterol and phospholipid. Immunohistochemical data demonstrated the presence of ABCA1 in lung type I and type II cells and in cultured pneumocytes. Type II cells isolated from rat lungs and cultured for 5 days in 10% serum trans-differentiated toward cells with a type I-like phenotype which reacted with the type I cell-specific monoclonal antibody VIIIB2. Upon incubation of the type I-like pneumocytes with agents that up-regulate the ABCA1 gene (9-cis-retinoic acid [9cRA] and 22-hydroxycholesterol [22-OH, 9cRA/22-OH]), ABCA1 protein levels were enhanced to maximum levels after 8 to 16 hours and remained elevated for 24 hours. In the presence of apoA-I and 9cRA/22-OH, efflux of radioactive phospholipid and cholesterol from pneumocytes was stimulated 3- to 20-fold, respectively, over controls. Lipid efflux was inhibited by Probucol. Sucrose density gradient analysis of the media from stimulated cells incubated with apoA-I identified heterogeneous lipid particles that isolated at a density between 1.063 and 1.210 g/ml, with low or high apoA-I content. Thus, pneumocytes with markers for the type I phenotype contained functional ABCA1 protein, released lipid to apoA-I protein, and were capable of producing particles resembling nascent high-density lipoprotein, indicating an important role for ABCA1 in the maintenance of lung lipid homeostasis.

In vitro transdifferentiation of human fetal type II cells toward a type I-like cell

For alveolar type I cells, phenotype plasticity and physiology other than gas exchange await further clarification due to in vitro study difficulties in isolating and maintaining type I cells in primary culture. Using an established in vitro model of human fetal type II cells, in which the type II phenotype is induced and maintained by adding hormones, we assessed for transdifferentiation in culture toward a type I-like cell with hormone removal for up to 144 h, followed by electron microscopy, permeability studies, and RNA and protein analysis. Hormone withdrawal resulted in diminished type II cell characteristics, including decreased microvilli, lamellar bodies, and type II cell marker RNA and protein. There was a simultaneous increase in type I characteristics, including increased epithelial cell barrier function indicative of a tight monolayer and increased type I cell marker RNA and protein. Our results indicate that hormone removal from cultured human fetal type II cells results in transdifferentiation toward a type I-like cell. This model will be useful for continued in vitro studies of human fetal alveolar epithelial cell differentiation and phenotype plasticity.