KGF prevents hyperoxia-induced reduction of active ion transport in alveolar epithelial cells

Characteristics of Passive Solute Transport across Primary Rat Alveolar Epithelial Cell Monolayers

Primary rat alveolar epithelial cell monolayers (RAECM) were grown without (type I cell-like phenotype, RAECM-I) or with (type II cell-like phenotype, RAECM-II) keratinocyte growth factor to assess passive transport of 11 hydrophilic solutes. We estimated apparent permeability (Papp) in the absence/presence of calcium chelator EGTA to determine the effects of perturbing tight junctions on "equivalent" pores. Papp across RAECM-I and -II in the absence of EGTA are similar and decrease as solute size increases. We modeled Papp of the hydrophilic solutes across RAECM-I/-II as taking place via heterogeneous populations of equivalent pores comprised of small (0.41/0.32 nm radius) and large (9.88/11.56 nm radius) pores, respectively. Total equivalent pore area is dominated by small equivalent pores (99.92-99.97%). The number of small and large equivalent pores in RAECM-I was 8.55 and 1.29 times greater, respectively, than those in RAECM-II. With EGTA, the large pore radius in RAECM-I/-II increased by 1.58/4.34 times and the small equivalent pore radius increased by 1.84/1.90 times, respectively. These results indicate that passive diffusion of hydrophilic solutes across an alveolar epithelium occurs via small and large equivalent pores, reflecting interactions of transmembrane proteins expressed in intercellular tight junctions of alveolar epithelial cells.

Paracrine stimulation of perinatal lung functional and structural maturation by mesenchymal stem cells

Background

Mesenchymal stem cells (MSCs) were shown to harbor therapeutic potential in models of respiratory diseases, such as bronchopulmonary dysplasia (BPD), the most common sequel of preterm birth. In these studies, cells or animals were challenged with hyperoxia or other injury-inducing agents. However, little is known about the effect of MSCs on immature fetal lungs and whether MSCs are able to improve lung maturity, which may alleviate lung developmental arrest in BPD.

Methods

We aimed to determine if the conditioned medium (CM) of MSCs stimulates functional and structural lung maturation. As a measure of functional maturation, Na⁺ transport in primary fetal distal lung epithelial cells (FDLE) was studied in Ussing chambers. Na⁺ transporter and surfactant protein mRNA expression was determined by qRT-PCR. Structural maturation was assessed by microscopy in fetal rat lung explants.

Results

MSC-CM strongly increased the activity of the epithelial Na⁺ channel (ENaC) and the Na,K-ATPase as well as their mRNA expression. Branching and growth of fetal lung explants and surfactant protein mRNA expression were enhanced by MSC-CM. Epithelial integrity and metabolic activity of FDLE cells were not influenced by MSC-CM. Since MSC’s actions are mainly attributed to paracrine signaling, prominent lung growth factors were blocked. None of the tested growth factors (VEGF, BMP, PDGF, EGF, TGF-β, FGF, HGF) contributed to the MSC-induced increase of Na⁺ transport. In contrast, inhibition of PI3-K/AKT and Rac1 signaling reduced MSC-CM efficacy, suggesting an involvement of these pathways in the MSC-CM-induced Na⁺ transport.

Conclusion

The results demonstrate that MSC-CM strongly stimulated functional and structural maturation of the fetal lungs. These effects were at least partially mediated by the PI3-K/AKT and Rac1 signaling pathway. Thus, MSCs not only repair a deleterious tissue environment, but also target lung cellular immaturity itself.

Keratinocyte growth factor promotes epithelial survival and resolution in a human model of lung injury

RATIONALE

Increasing epithelial repair and regeneration may hasten resolution of lung injury in patients with the acute respiratory distress syndrome (ARDS). In animal models of ARDS, keratinocyte growth factor (KGF) reduces injury and increases epithelial proliferation and repair. The effect of KGF in the human alveolus is unknown.

OBJECTIVES

To test whether KGF can attenuate alveolar injury in a human model of ARDS.

METHODS

Volunteers were randomized to intravenous KGF (60 μg/kg) or placebo for 3 days, before inhaling 50 μg LPS. Six hours later, subjects underwent bronchoalveolar lavage (BAL) to quantify markers of alveolar inflammation and cell-specific injury.

MEASUREMENTS AND MAIN RESULTS

KGF did not alter leukocyte infiltration or markers of permeability in response to LPS. KGF increased BAL concentrations of surfactant protein D, matrix metalloproteinase (MMP)-9, IL-1Ra, granulocyte-macrophage colony-stimulating factor (GM-CSF), and C-reactive protein. In vitro, BAL fluid from KGF-treated subjects inhibited pulmonary fibroblast proliferation, but increased alveolar epithelial proliferation. Active MMP-9 increased alveolar epithelial wound repair. Finally, BAL from the KGF-pretreated group enhanced macrophage phagocytic uptake of apoptotic epithelial cells and bacteria compared with BAL from the placebo-treated group. This effect was blocked by inhibiting activation of the GM-CSF receptor.

CONCLUSIONS

KGF treatment increases BAL surfactant protein D, a marker of type II alveolar epithelial cell proliferation in a human model of acute lung injury. Additionally, KGF increases alveolar concentrations of the antiinflammatory cytokine IL-1Ra, and mediators that drive epithelial repair (MMP-9) and enhance macrophage clearance of dead cells and bacteria (GM-CSF). Clinical trial registered with ISRCTN 98813895.

Alveolar epithelium: beyond the barrier

I am deeply honored to have been awarded an American Thoracic Society Recognition Award for Scientific Accomplishment for 2014. Over the last 20 years, it has become clear that the alveolar epithelium, my area of research focus, is not simply a gas exchange surface and barrier to leakage of fluid and protein into the alveoli, but is an active participant in the pathogenesis of a number of lung diseases, including pulmonary fibrosis. Recognition by this Award stimulates a review of the awardee's contributions to the field, as summarized in this perspective.

Palifermin for the protection and regeneration of epithelial tissues following injury: new findings in basic research and pre-clinical models

Keratinocyte growth factor (KGF) is a paracrine-acting epithelial mitogen produced by cells of mesenchymal origin, that plays an important role in protecting and repairing epithelial tissues. Pre-clinical data initially demonstrated that a recombinant truncated KGF (palifermin) could reduce gastrointestinal injury and mortality resulting from a variety of toxic exposures. Furthermore, the use of palifermin in patients with hematological malignancies reduced the incidence and duration of severe oral mucositis experienced after intensive chemoradiotherapy. Based upon these findings, as well as the observation that KGF receptors are expressed in many, if not all, epithelial tissues, pre-clinical studies have been conducted to determine the efficacy of palifermin in protecting different epithelial tissues from toxic injury in an attempt to model various clinical situations in which it might prove to be of benefit in limiting tissue damage. In this article, we review these studies to provide the pre-clinical background for clinical trials that are described in the accompanying article and the rationale for additional clinical applications of palifermin.

Growth factors and cytokines in acute lung injury

Cytokines and growth factors play an integral role in the maintenance of immune homeostasis, the generation of protective immunity, and lung reparative processes. However, the dysregulated expression of cytokines and growth factors in response to infectious or noxious insults can initiate and perpetuate deleterious lung inflammation and fibroproliferation. In this article, we will comprehensively review the contribution of individual cytokines and growth factors and cytokine networks to key pathophysiological events in human and experimental acute lung injury (ALI), including inflammatory cell recruitment and activation, alveolar epithelial injury and repair, angiogenesis, and matrix deposition and remodeling. The application of cytokines/growth factors as prognostic indicators and therapeutic targets in human ALI is explored.

Hyperoxia sensing: from molecular mechanisms to significance in disease

Oxygen therapy using mechanical ventilation with hyperoxia is necessary to treat patients with respiratory failure and distress. However, prolonged exposure to hyperoxia leads to the generation of excessive reactive oxygen species (ROS), causing cellular damage and multiple organ dysfunctions. As the lungs are directly exposed, hyperoxia can cause both acute and chronic inflammatory lung injury and compromise innate immunity. ROS may contribute to pulmonary oxygen toxicity by overwhelming redox homeostasis, altering signaling cascades that affect cell fate, ultimately leading to hyperoxia-induced acute lung injury (HALI). HALI is characterized by pronounced inflammatory responses with leukocyte infiltration, injury, and death of pulmonary cells, including epithelia, endothelia, and macrophages. Under hyperoxic conditions, ROS mediate both direct and indirect modulation of signaling molecules such as protein kinases, transcription factors, receptors, and pro- and anti-apoptotic factors. The focus of this review is to elaborate on hyperoxia-activated key sensing molecules and current understanding of their signaling mechanisms in HALI. A better understanding of the signaling pathways leading to HALI may provide valuable insights on its pathogenesis and may help in designing more effective therapeutic approaches.

Keratinocyte growth factor expression is suppressed in early acute lung injury/acute respiratory distress syndrome by smad and c-Abl pathways

OBJECTIVE

Keratinocyte growth factor (KGF) is expressed primarily by fibroblasts, is important for alveolar epithelial proliferation/function, and protects against lung injury in multiple animal models. We wished to determine whether acute lung injury/acute respiratory distress syndrome (ALI/ARDS) alveolar fluid induces KGF and fibroblast genes important for alveolar repair.

DESIGN

A single-center cohort study enrolling patients between 2004 and 2006.

SETTING

A medical intensive care unit of a tertiary care medical center.

PATIENTS

Adult patients meeting the American-European Consensus Conference definition of ALI/ARDS.

INTERVENTIONS

Patients with ALI/ARDS were enrolled, and lavage fluid was collected within 48 hours of intubation. Lavage fluid was also collected from two control cohorts. The patients with ALI/ARDS were followed for 28 days or until death.

MEASUREMENT AND MAIN RESULTS

Fifteen patients with ALI/ARDS, five patients with cardiogenic edema, and five normal lung parenchyma controls were enrolled from 2004 to 2006. Primary normal human lung fibroblasts were incubated with bronchoalveolar lavage fluid and assessed for KGF, connective tissue growth factor, alpha-smooth muscle actin, and collagen 1 expression by real-time reverse transcriptase-polymerase chain reaction. Fibroblasts incubated with ALI/ARDS lavage fluid expressed 50% less KGF messenger RNA than those incubated with lavage fluid from CE patients (p < 0.01) and 33% than normal parenchymal controls (p < 0.03). Lavage fluid from patients with ALI/ARDS induced more connective tissue growth factor (p < 0.05), collagen 1 (p < 0.03), and alpha-smooth muscle actin (p < 0.04) than from CE patients. Preincubation of normal human lung fibroblasts with the transforming growth factor (TGF)-beta1 receptor/smad phosphorylation inhibitor SB431542 increased ALI/ARDS-induced KGF expression by 40% (p < 0.04). In cultured human lung fibroblasts, TGF-beta1 suppressed KGF messenger RNA and protein expression, which were reversed by SB431542 and by the c-Abl inhibitor, imatinib mesylate, but not by the p38 map kinase inhibitor, SB203580.

CONCLUSIONS

ALI/ARDS alveolar fluid suppresses KGF expression, in part, due to TGF-beta1. TGF-beta1 suppression of KGF requires both smad phosphorylation and c-Abl activation.

Characterization of mouse alveolar epithelial cell monolayers

We investigated the influence of extracellular matrix on transport properties of mouse alveolar epithelial cell (AEC) monolayers (MAECM) and transdifferentiation of isolated mouse alveolar epithelial type II (AT2) cells into an alveolar epithelial type I (AT1) cell-like phenotype. Primary mouse AT2 cells plated on laminin 5-coated polycarbonate filters formed monolayers with transepithelial resistance (R(T)) and equivalent short-circuit current (I(EQ)) of 1.8 kOmega.cm(2) and 5.3 microA/cm(2), respectively, after 8 days in culture. Amiloride (10 microM), ouabain (0.1 mM), and pimozide (10 microM) decreased MAECM I(EQ) to 40%, 10%, and 65% of its initial value, respectively. Sequential addition of pimozide and amiloride, in either order, revealed that their inhibitory effects are additive, suggesting that cyclic nucleotide-gated channels contribute to amiloride-insensitive active ion transport across MAECM. Ussing chamber measurements of unidirectional ion fluxes across MAECM under short-circuit conditions indicated that net absorption of Na(+) in the apical-to-basolateral direction is comparable to net ion flux calculated from the observed short-circuit current: 0.38 and 0.33 microeq.cm(-2).h(-1), respectively. Between days 1 and 9 in culture, AEC demonstrated increased expression of aquaporin-5 protein, an AT1 cell marker, and decreased expression of pro-surfactant protein-C protein, an AT2 cell marker, consistent with transition to an AT1 cell-like phenotype. These results demonstrate that AT1 cell-like MAECM grown on laminin 5-coated polycarbonate filters exhibit active and passive transport properties that likely reflect the properties of intact mouse alveolar epithelium. This mouse in vitro model will enhance the study of AEC derived from mutant strains of mice and help define important structure-function correlations.

Duration-dependent cytoprotective versus inflammatory effects of lung epithelial fibroblast growth factor-7 expression

Fibroblast growth factor-7 (FGF7) is a lung epithelial cell mitogen that is cytoprotective during injury. Transgenic mice that conditionally expressed FGF7 were used to dissect the mechanisms of FGF7 protection during lung injury. FGF7 improved survival when induced 3 days prior to acute lung injury. In contrast, FGF7 caused pulmonary inflammation and lung injury after 7 days or longer. Gene expression analysis of mouse lung mRNA identified mRNAs that contribute to the protective effects of FGF7. FGF7 improved survival during acute lung injury in adult mouse lung after short-term expression, but paradoxically induced inflammation and injury after persistent expression.

KGF promotes integrin alpha5 expression through CCAAT/enhancer-binding protein-beta

Keratinocyte growth factor (KGF) and alpha(5)beta(1)-integrin are not expressed in normal skin but they are both highly upregulated in the migrating epidermis during wound healing. Here we report that KGF increased alpha(5) mRNA and protein levels in epidermoid carcinoma cells and stratified bioengineered epidermis. Interestingly, KGF increased integrin alpha(5) in the basal as well as suprabasal cell epidermal layers. Promoter studies indicated that KGF-induced integrin alpha(5) promoter activation was dependent on the C/EBP transcription factor binding site. Accordingly, KGF induced sustained phosphorylation of C/EBP-beta that was dependent on activation of ERK1/2. In addition, a dominant negative form of C/EBP-beta inhibited alpha(5) promoter activity and blocking C/EBP-beta with siRNA diminished integrin alpha(5) expression. Taken together, our data indicate that KGF increased integrin alpha(5) expression by phosphorylating C/EBP-beta. Interestingly, KGF-induced upregulation of integrin alpha(5) was more pronounced in three-dimensional tissue analogues than in conventional two-dimensional culture suggesting that stratified epidermis may be useful in understanding the effects of growth factors in the local tissue microenvironment.

Cytokines in tolerance to hyperoxia-induced injury in the developing and adult lung

Cytokines are peptides that are produced by virtually every nucleated cell type in the body, possess overlapping biological activities, exert different effects at different concentrations, can either synergize or antagonize the effects of other cytokines, are regulated in a complex manner, and function via cytokine cascades. Hyperoxia-induced acute lung injury (HALI) is characterized by an influx of inflammatory cells, increased pulmonary permeability, and endothelial and epithelial cell injury/death. Some of these effects are orchestrated by cytokines. There are significant differences in the response of the developing versus the adult lung to hyperoxia. We review here cytokines (and select growth factors) that are involved in tolerance toward HALI in animal models. Increased cytokine expression and release have a cascade effect in HALI. IL-1 precedes the increase in IL-6 and CINC-1/IL-8 and this seems to predate the influx of inflammatory cells. Inflammatory cells in the alveolar space amplify the lung damage. Other cytokines that are primarily involved in this inflammatory response include IFN-gamma, MCP-1, and MIP-2. Certain cytokines (and growth factors) seem to ameliorate HALI by affecting cell death pathways. These include GM-CSF, KGF, IL-11, IL-13, and VEGF. There are significant differences in the type and temporal sequence of cytokine expression and release in the adult and newborn lung in response to hyperoxia. The newborn lung is greatly resistant to hyperoxia compared to the adult. The delayed increase in lung IL-1 and IL-6 in the newborn could induce protective factors that would help in the resolution of hyperoxia-induced injury. Designing a therapeutic approach to counteract oxygen toxicity in the adult and immature lung first needs understanding of the unique responses in each scenario.

Na,K-ATPase gene transfer increases liquid clearance during ventilation-induced lung injury

Mechanical ventilation with high tidal volumes (HVT) downregulates alveolar Na,K-ATPase function and impairs lung liquid clearance. We hypothesized that overexpression of Na,K-ATPase in the alveolar epithelium could counterbalance these changes and increase clearance in a rat model of mild ventilation-induced lung injury. We used a surfactant-based system to deliver 4 x 10(9) plaque-forming units of E1a-/E3- recombinant adenovirus containing either a rat beta1 Na,K-ATPase subunit cDNA (adbeta1) or no cDNA (adnull) to rat lungs 7 days before ventilation with a VT of approximately 40 ml/kg (peak airway pressure of less than 35 cm H2O) for 40 minutes. Lung liquid clearance and Na, K-ATPase activity and protein abundance were increased in HVT adbeta1-infected lungs as compared with sham and adnull-infected HVT lungs. These results suggest that Na,K-ATPase subunit gene overexpression in the alveolar epithelium increases Na,K-ATPase function and lung liquid clearance in a model of HVT. We provide here the first evidence that using a genetic approach improves active Na+ transport and thus liquid clearance in the setting of mild ventilation-induced lung injury.

Modulation of ion conductance and active transport by TGF-beta 1 in alveolar epithelial cell monolayers

Transforming growth factor-beta1 (TGF-beta 1) may be a critical mediator of lung injury and subsequent remodeling during recovery. We evaluated the effects of TGF-beta 1 on the permeability and active ion transport properties of alveolar epithelial cell monolayers. Rat alveolar type II cells plated on polycarbonate filters in defined serum-free medium form confluent monolayers and acquire the phenotypic characteristics of alveolar type I cells. Exposure to TGF-beta 1 (0.1-100 pM) from day 0 resulted in a concentration- and time-dependent decrease in transepithelial resistance (Rt) and increase in short-circuit current (Isc). Apical amiloride or basolateral ouabain on day 6 inhibited Isc by 80 and 100%, respectively. Concurrent increases in expression of Na+-K+-ATPase alpha 1- and beta 1-subunits were observed in TGF-beta 1-treated monolayers. No change in the alpha-subunit of the rat epithelial sodium channel (alpha-rENaC) was seen. Exposure of confluent monolayers to TGF-beta 1 from day 4 resulted in an initial decrease in Rt within 6 h, followed by an increase in Isc over 72-96 h. These results demonstrate that TGF-beta 1 modulates ion conductance and active transport characteristics of the alveolar epithelium, associated with increased Na+-K+-ATPase, but without a change in alpha-rENaC.

Keratinocyte growth factor pretreatment is associated with decreased macrophage inflammatory protein-2alpha concentrations and reduced neutrophil recruitment in acid aspiration lung injury

A two-hit model of acid aspiration was used to examine the effect of keratinocyte growth factor (KGF) on chemokine levels and neutrophil recruitment into the lung. Mice were subjected to cecal ligation and puncture and then either KGF or saline, intratracheally (i.t.). Forty-eight hours later, the mice were given i.t. acid. After 8 h, neutrophil counts in bronchoalveolar lavage (BAL) fluid were significantly decreased in animals pretreated with KGF (23 +/- 4 x 10(3)/mouse) compared with saline (74 +/- 2 x 10(3)/mouse). In addition, the BAL fluid IL-6 levels were decreased in the KGF-treated group (88+/- 44 pg/mL) compared with the saline group (166 +/- 34 pg/mL). To examine the mechanism behind the KGF-induced reduction in neutrophil influx, the murine chemokines KC and macrophage inflammatory protein (MIP)-2alpha were measured. KC levels in plasma and BAL fluid were not significantly different between the treatment groups. Likewise, levels of MIP-2alpha in plasma were not affected by KGF treatment. However, 8 h after acid aspiration, MIP-2alpha concentrations were significantly lower in the KGF-treated group. The ratio of MIP-2alpha in BAL fluid versus plasma was lower in the KGF group (0.72 +/- 0.28) than in the saline group at 3 h (2.23 +/- 0.93) and also significantly lower in the KGF group (3.02 +/- 0.78) compared with the saline group (6.23 +/- 1.19) at 8 h. In this study, KGF pretreatment after acid aspiration was associated with reduced neutrophil recruitment into the lung and a decrease in MIP-2alpha gradients between BAL fluid and plasma.

Invited review: lung edema clearance: role of Na(+)-K(+)-ATPase

Acute hypoxemic respiratory failure is a consequence of edema accumulation due to elevation of pulmonary capillary pressures and/or increases in permeability of the alveolocapillary barrier. It has been recognized that lung edema clearance is distinct from edema accumulation and is largely effected by active Na(+) transport out of the alveoli rather than reversal of the Starling forces, which control liquid flux from the pulmonary circulation into the alveolus. The alveolar epithelial Na(+)-K(+)-ATPase has an important role in regulating cell integrity and homeostasis. In the last 15 yr, Na(+)-K(+)-ATPase has been localized to the alveolar epithelium and its contribution to lung edema clearance has been appreciated. The importance of the alveolar epithelial Na(+)-K(+)-ATPase function is reflected in the changes in the lung's ability to clear edema when the Na(+)-K(+)-ATPase is inhibited or increased. An important focus of the ongoing research is the study of the mechanisms of Na(+)-K(+)-ATPase regulation in the alveolar epithelium during lung injury and how to accelerate lung edema clearance by modulating Na(+)-K(+)-ATPase activity.

Lung epithelial fluid transport and the resolution of pulmonary edema

The discovery of mechanisms that regulate salt and water transport by the alveolar and distal airway epithelium of the lung has generated new insights into the regulation of lung fluid balance under both normal and pathological conditions. There is convincing evidence that active sodium and chloride transporters are expressed in the distal lung epithelium and are responsible for the ability of the lung to remove alveolar fluid at the time of birth as well as in the mature lung when pathological conditions lead to the development of pulmonary edema. Currently, the best described molecular transporters are the epithelial sodium channel, the cystic fibrosis transmembrane conductance regulator, Na+-K+-ATPase, and several aquaporin water channels. Both catecholamine-dependent and -independent mechanisms can upregulate isosmolar fluid transport across the distal lung epithelium. Experimental and clinical studies have made it possible to examine the role of these transporters in the resolution of pulmonary edema.

Transepithelial sodium and water transport in the lung. Major player and novel therapeutic target in pulmonary edema

Active transepithelial transport of sodium from the airspaces to the lung interstitium is a primary mechanism driving alveolar fluid clearance. This mechanism depends on sodium uptake by amiloride-sensitive sodium channels on the apical membrane of alveolar type II cells followed by extrusion of sodium on the basolateral surface by the Na-K-ATPase. Injury to the alveolar epithelium can disrupt the integrity of the alveolar barrier or downregulate ion transport pathways thus reducing net alveolar fluid reabsorption, and enhancing the extent of alveolar edema. Endogenous catecholamines upregulate alveolar fluid clearance in several experimental models of acute lung injury, but this upregulation is short-term and often not sufficient to counterbalance alveolar flooding. There is new evidence, however, that pharmacological treatment with beta-adrenergic agonists and/or epithelial growth factors may induce a more sustained stimulation of alveolar fluid reabsorption and in turn facilitate recovery from experimental pulmonary edema. Similar results have been achieved experimentally by gene transfer enhancing the abundance of sodium transporters in the alveolar epithelium. Clinical studies show that impaired alveolar fluid transport mechanisms contribute to the development, severity and outcome of pulmonary edema in humans. Very recent data suggest that mechanisms that augment transepithelial sodium transport and enhance the clearance of alveolar edema may lead to more effective prevention or treatment for pulmonary edema and acute lung injury.

Na transport proteins are expressed by rat alveolar epithelial type I cells

Despite a presumptive role for type I (AT1) cells in alveolar epithelial transport, specific Na transporters have not previously been localized to these cells. To evaluate expression of Na transporters in AT1 cells, double labeling immunofluorescence microscopy was utilized in whole lung and in cytocentrifuged preparations of partially purified alveolar epithelial cells (AEC). Expression of Na pump subunit isoforms and the alpha-subunit of the rat (r) epithelial Na channel (alpha-ENaC) was evaluated in isolated AT1 cells identified by their immunoreactivity with AT1 cell-specific antibody markers (VIIIB2 and/or anti-aquaporin-5) and lack of reactivity with antibodies specific for AT2 cells (anti-surfactant protein A) or leukocytes (anti-leukocyte common antigen). Expression of the Na pump alpha(1)-subunit in AEC was assessed in situ. Na pump subunit isoform and alpha-rENaC expression was also evaluated by RT-PCR in highly purified (approximately 95%) AT1 cell preparations. Labeling of isolated AT1 cells with anti-alpha(1) and anti-beta(1) Na pump subunit and anti-alpha-rENaC antibodies was detected, while reactivity with anti-alpha(2) Na pump subunit antibody was absent. AT1 cells in situ were reactive with anti-alpha(1) Na pump subunit antibody. Na pump alpha(1)- and beta(1)- (but not alpha(2)-) subunits and alpha-rENaC were detected in highly purified AT1 cells by RT-PCR. These data demonstrate that AT1 cells express Na pump and Na channel proteins, supporting a role for AT1 cells in active transalveolar epithelial Na transport.

Extracellular glutathione inhibits oxygen-induced permeability changes in alveolar epithelial monolayers

Exposure to high fractional inspired oxygen for 24 h increases permeability of the alveolar epithelium, contributing to the clinical manifestations of oxygen toxicity. Utilizing a model of the alveolar epithelium in which isolated rat type II cells form polarized monolayers on polycarbonate filters [transepithelial resistance (R(t)) > 1 k Omega x cm(2) by day 4], we evaluated the ability of reduced glutathione (GSH) to ameliorate these changes. On day 4, apical fluid was replaced with culture medium containing 1) no additives, 2) GSH (500 microM), or 3) GSH (500 microM) + glutathione reductase (0.5 U/ml) + nicotinamide adenine dinucleotide phosphate (250 microM). Monolayers were exposed (for 24 h) to room air (control) or 95% O(2), each containing 5% CO(2). After 24 h of hyperoxia, R(t) for condition 1 decreased by 45% compared with control (P < 0.001). In conditions 2 and 3, R(t) did not decrease significantly (P = not significant). Hyperoxia-induced decreases in active ion transport were observed for conditions 1 and 2 (P < 0.05), but not for condition 3 (P = not significant). These findings indicate that extracellular GSH may protect the alveolar epithelium against hyperoxia-induced injury. Addition of glutathione reductase and nicotinamide adenine dinucleotide phosphate may further augment these protective effects of GSH.

Keratinocyte growth factor protects against Pseudomonas aeruginosa-induced lung injury

We have previously reported that keratinocyte growth factor (KGF) attenuates alpha-naphthylthiourea-induced lung injury by upregulating alveolar fluid transport. The objective of this study was to determine the effect of KGF pretreatment in Pseudomonas aeruginosa pneumonia. A 5% bovine albumin solution with 1 microCi of (125)I-labeled human albumin was instilled into the air spaces 4 or 24 h after intratracheal instillation of P. aeruginosa, and the concentration of unlabeled and labeled proteins in the distal air spaces over 1 h was used as an index of net alveolar fluid clearance. Alveolocapillary barrier permeability was evaluated with an intravascular injection of 1 microCi of (131)I-albumin. In early pneumonia, KGF increased lung liquid clearance (LLC) compared with that in nonpretreated animals. In late pneumonia, LLC was significantly reduced in the absence of KGF but increased above the control value with KGF. KGF pretreatment increased the number of polymorphonuclear cells recovered in the bronchoalveolar lavage fluid and decreased bacterial pulmonary translocation. In conclusion, KGF restores normal alveolar epithelial fluid transport during the acute phase of P. aeruginosa pneumonia and LLC in early and late pneumonia. Host response is also improved as shown by the increase in the alveolar cellular response and the decrease in pulmonary translocation of bacteria.

Adenovirus-mediated transfer of an Na+/K+-ATPase beta1 subunit gene improves alveolar fluid clearance and survival in hyperoxic rats

Pulmonary edema is cleared via active Na(+) transport by alveolar epithelial Na(+)/K(+)-ATPases and Na(+) channels. Rats exposed to acute hyperoxia have a high mortality rate, decreased Na(+)/K(+)-ATPase function, and decreased alveolar fluid clearance (AFC). We hypothesized that Na(+)/K(+)-ATPase subunit gene overexpression could improve AFC in rats exposed to hyperoxia. We delivered 4 x 10(9) PFU of recombinant adenoviruses containing rat alpha(1) and beta(1) Na(+)/K(+)-ATPase subunit cDNAs (adalpha(1) and adbeta(1), respectively) to rat lungs 7 days prior to exposure to 100% O(2) for 64 hr. As compared with controls and ad alpha(1), AFC in the adbeta(1) rats was increased by >300%. Permeability for large solutes was less in the ad beta(1) than in the other hyperoxia groups. Glutathione oxidation, but not superoxide dismutase activity, was increased only in the adbeta(1) group. Survival through 14 days of hyperoxia was 100% in the adbeta(1) group but was not different from hyperoxic controls in animals given adalpha(1). Our data show that overexpression of a beta(1) Na(+)/K(+)-ATPase subunit augments AFC and improves survival in this model of acute lung injury via antioxidant-independent mechanisms. Conceivably, restoration of AFC via gene transfer of Na(+)/K(+)-ATPase subunit genes may prove useful for the treatment of acute lung injury and pulmonary edema.

Continuous enteral nutrition attenuates pulmonary edema in rats exposed to 100% oxygen

Adult rats exposed to hyperoxia develop anorexia, weight loss, and a lung injury characterized by pulmonary edema and decreased lung liquid clearance. We hypothesized that maintenance of nutrition during hyperoxia could attenuate hyperoxia-induced pulmonary edema. To test this hypothesis, we enterally fed adult male Sprague-Dawley rats via gastrostomy tubes and exposed them to oxygen (inspired O(2) fraction >0.95) for 64 h. In contrast to controls, enterally fed hyperoxic animals did not lose weight and had smaller pleural effusions and wet-to-dry weight ratios (a measure of lung edema) that were not different from room air controls. Enterally fed rats exposed to hyperoxia had increased levels of mRNA for the Na(+)-K(+)-ATPase alpha(1)- and beta(1)-subunits and glutathione peroxidase. These findings suggest that maintenance of nutrition during an oxidative lung injury reduces lung edema, perhaps by allowing for continued expression and function of protective proteins such as the Na(+)-K(+)-ATPase.

Conditional expression of fibroblast growth factor-7 in the developing and mature lung

Effects of fibroblast growth factor-7 (FGF-7) on lung morphogenesis, respiratory epithelial cell differentiation, and proliferation were assessed in transgenic mice in which the human FGF-7 cDNA was controlled by a conditional promoter under the direction of regulatory elements from either the human surfactant protein-C (SP-C) or rat Clara cell secretory protein (ccsp) genes. Expression of FGF-7 was induced in respiratory epithelial cells of the fetal lung by administration of doxycycline to the dam. Prenatally, doxycycline induced FGF-7 mRNA in respiratory epithelial cells in both Sp-c and Ccsp transgenic lines, increasing lung size and causing cystadenomatoid malformation. Postnatally, mice bearing both Ccsp-rtta and (Teto)(7)-cmv-fgf-7 transgenes survived, and lung morphology was normal. Induction of FGF-7 expression by doxycycline in the Ccsp-rtta x (Teto)(7)-cmv-fgf-7 mice caused marked epithelial cell proliferation, adenomatous hyperplasia, and pulmonary infiltration with mononuclear cells. Epithelial cell hyperplasia caused by FGF-7 was largely resolved after removal of doxycycline. Surfactant proteins, TTF-1, and aquaporin 5 expression were conditionally induced by doxycycline. The Sp-c-rtta and Ccsp-rtta activator mice provide models in which expression is conditionally controlled in respiratory epithelial cells in the developing and mature lung, altering lung morphogenesis, differentiation, and proliferation.