Hypoxia-Induced Cytoskeleton Disruption in Alveolar Epithelial Cells

The Role of TPM3 in Protecting Cardiomyocyte from Hypoxia-Induced Injury via Cytoskeleton Stabilization

Ischemic heart disease (IHD) remains a major global health concern, with ischemia-reperfusion injury exacerbating myocardial damage despite therapeutic interventions. In this study, we investigated the role of tropomyosin 3 (TPM3) in protecting cardiomyocytes against hypoxia-induced injury and oxidative stress. Using the AC16 and H9c2 cell lines, we established a chemical hypoxia model by treating cells with cobalt chloride (CoCl2) to simulate low-oxygen conditions. We found that CoCl2 treatment significantly upregulated the expression of hypoxia-inducible factor 1 alpha (HIF-1α) in cardiomyocytes, indicating the successful induction of hypoxia. Subsequent morphological and biochemical analyses revealed that hypoxia altered cardiomyocyte morphology disrupted the cytoskeleton, and caused cellular damage, accompanied by increased lactate dehydrogenase (LDH) release and malondialdehyde (MDA) levels, and decreased superoxide dismutase (SOD) activity, indicative of oxidative stress. Lentivirus-mediated TPM3 overexpression attenuated hypoxia-induced morphological changes, cellular damage, and oxidative stress imbalance, while TPM3 knockdown exacerbated these effects. Furthermore, treatment with the HDAC1 inhibitor MGCD0103 partially reversed the exacerbation of hypoxia-induced injury caused by TPM3 knockdown. Protein-protein interaction (PPI) network and functional enrichment analysis suggested that TPM3 may modulate cardiac muscle development, contraction, and adrenergic signaling pathways. In conclusion, our findings highlight the therapeutic potential of TPM3 modulation in mitigating hypoxia-associated cardiac injury, suggesting a promising avenue for the treatment of ischemic heart disease and other hypoxia-related cardiac pathologies.

Nanopore-related cellular death through cytoskeleton depolymerization by drug-induced ROS

Prostate cancer (PCa) is a malignant tumor with a very high incidence which ranks second after lung cancer. Although there are many drugs available for the treatment of PCa, their effectiveness and anti-cancer mechanisms still need to be explored. Atomic force microscopy (AFM) could characterize minor morphological changes on cell surfaces, which provides an effective method to explore the interaction between drugs and cells at the nanometer level and further investigate the mechanisms for treating PCa. In our research, AFM visualized pore-like structures in the PC3M cell membrane after treatment with the eminent anticancer agent paclitaxel (PTX). The diameter, depth and number of these pores were in a concentration and time-dependent manner. Reactive oxygen species (ROS) was shown to depolymerize the actin cytoskeleton and make the membrane more sensitive to oxidative damage, thus inducing pore information. After pretreatment with a ROS scavenger, pore formation was prevented. AFM imaging technology provides a new evaluation method for drug-targeted therapy for cancer.

Metabolomic and Proteomic Identification of Serum Exosome for Hypoxic Preconditioning Participants

Background

In high-altitude areas, hypoxic stress can elicit a series of physiological responses in humans. Exosomes play important roles in both local and distal cellular communications.

Methods

We used ultraperformance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) and liquid chromatography-tandem mass spectrometry (LC-MS/MS) studies to analyze the differentially expressed metabolomics and proteomics in serum exosome of hypoxic preconditioning participants and control subjects in the hypoxic conditions.

Results

Fifty-seven military personnel were divided into hypoxic preconditioning group (n = 27) and control group (n = 30). One hundred thirty-six differentially expressed serum exosomal metabolites were found between the hypoxic preconditioning and control groups in the hypoxic conditions, and these differentially expressed metabolites were enriched in pathways related to lysine degradation, butanoate metabolism, GABAergic synapse, histidine metabolism, and linoleic acid metabolism. In addition, hypoxic preconditioning participants showed 102 excellent differential expressions of proteomics compared to controls, which involved actin cytoskeleton organization, hemostasis, complement and coagulation cascades, vesicle-medicated transport, wound healing, etc.

Conclusions

We revealed that the expression of exosomal metabolites and proteomics in hypoxic preconditioning participants was significantly different compared to controls in hypoxic conditions.

Lung Regeneration: Cells, Models, and Mechanisms

Lung epithelium, the lining that covers the inner surface of the respiratory tract, is directly exposed to the environment and thus susceptible to airborne toxins, irritants, and pathogen-induced damages. In adult mammalian lungs, epithelial cells are generally quiescent but can respond rapidly to repair of damaged tissues. Evidence from experimental injury models in rodents and human clinical samples has led to the identification of these regenerative cells, as well as pathological metaplastic states specifically associated with different forms of damages. Here, we provide a compendium of cells and cell states that exist during homeostasis in normal lungs and the lineage relationships between them. Additionally, we discuss various experimental injury models currently being used to probe the cellular sources-both resident and recruited-that contribute to repair, regeneration, and remodeling following acute and chronic injuries. Finally, we discuss certain maladaptive regeneration-associated cell states and their role in disease pathogenesis.

Impact of Sr2+ and hypoxia on 3D triple cultures of primary human osteoblasts, osteocytes and osteoclasts

An in vitro bone triple culture involving human primary osteoblasts, osteocytes and osteoclasts enables the investigation of bone healing factors, drugs or biomaterials in a model system for native bone tissue. The present study analyses the impact of Sr²⁺ as well as hypoxic cultivation (5% O₂ content or chemically induced by Co²⁺) on bone cells. The three cell types were cultivated together in the presence of 100 µM Sr²⁺, hypoxic conditions or in the presence of 75 µM Co²⁺. After cultivation the cell types were separated and analysed on mRNA and protein level individually. In response to Sr²⁺ osteoblasts showed a downregulation of IBSP expression and a stimulation of ALP activity. Osteocyte gene marker expression of PDPN, MEPE, RANKL, OPG, osteocalcin and likewise the amount of secreted osteocalcin was reduced in the presence of Sr²⁺. Activity of osteoclast-specific enzymes TRAP and CAII was enhanced compared to the Sr²⁺ free control. Hypoxic conditions induced by both 5% O₂ or a Co²⁺ treatment led to decreased DNA content of all bone cells and downregulated expression of osteoblast markers ALPL and IBSP as well as osteocyte markers PDPN, RANKL and OPG. In addition, Co²⁺ induced hypoxia decreased gene and protein expression of osteocalcin in osteocytes. In response to the Co²⁺ treatment, the TRAP gene expression and activity was increased. This study is the first to analyse the effects of Sr²⁺ or hypoxia on triple cultures with primary human bone cells. The investigated in vitro bone model might be suitable to reduce animal experiments in early stages of biomaterial and drug development.

Tandem Mass Tagging-Based Quantitative Proteomics Analysis Reveals Damage to the Liver and Brain of Hypophthalmichthys molitrix Exposed to Acute Hypoxia and Reoxygenation

Aquaculture environments frequently experience hypoxia and subsequent reoxygenation conditions, which have significant effects on hypoxia-sensitive fish populations. In this study, hepatic biochemical activity indices in serum and the content of major neurotransmitters in the brain were altered markedly after acute hypoxia and reoxygenation exposure in silver carp (Hypophthalmichthys molitrix). Proteomics analysis of the liver showed that a number of immune-related and cytoskeletal organization-related proteins were downregulated, the ferroptosis pathway was activated, and several antioxidant molecules and detoxifying enzymes were upregulated. Proteomics analysis of the brain showed that somatostatin-1A (SST1A) was upregulated, dopamine-degrading enzyme catechol O methyltransferase (COMT) and ferritin, heavy subunit (FerH) were downregulated, and the levels of proteins involved in the nervous system were changed in different ways. In conclusion, these findings highlight that hypoxia–reoxygenation has potential adverse effects on growth, locomotion, immunity, and reproduction of silver carp, and represents a serious threat to liver and brain function, possibly via ferroptosis, oxidative stress, and cytoskeleton destruction in the liver, and abnormal expression of susceptibility genes for neurodegenerative disorders in the brain. Our present findings provide clues to the mechanisms of hypoxia and reoxygenation damage in the brain and liver of hypoxia-sensitive fish. They could also be used to develop methods to reduce hypoxia or reoxygenation injury to fish.

Influence of Hypoxia on the Epithelial-Pathogen Interactions in the Lung: Implications for Respiratory Disease

Under normal physiological conditions, the lung remains an oxygen rich environment. However, prominent regions of hypoxia are a common feature of infected and inflamed tissues and many chronic inflammatory respiratory diseases are associated with mucosal and systemic hypoxia. The airway epithelium represents a key interface with the external environment and is the first line of defense against potentially harmful agents including respiratory pathogens. The protective arsenal of the airway epithelium is provided in the form of physical barriers, and the production of an array of antimicrobial host defense molecules, proinflammatory cytokines and chemokines, in response to activation by receptors. Dysregulation of the airway epithelial innate immune response is associated with a compromised immunity and chronic inflammation of the lung. An increasing body of evidence indicates a distinct role for hypoxia in the dysfunction of the airway epithelium and in the responses of both innate immunity and of respiratory pathogens. Here we review the current evidence around the role of tissue hypoxia in modulating the host-pathogen interaction at the airway epithelium. Furthermore, we highlight the work needed to delineate the role of tissue hypoxia in the pathophysiology of chronic inflammatory lung diseases such as asthma, cystic fibrosis, and chronic obstructive pulmonary disease in addition to novel respiratory diseases such as COVID-19. Elucidating the molecular mechanisms underlying the epithelial-pathogen interactions in the setting of hypoxia will enable better understanding of persistent infections and complex disease processes in chronic inflammatory lung diseases and may aid the identification of novel therapeutic targets and strategies.

Curcumin prophylaxis refurbishes alveolar epithelial barrier integrity and alveolar fluid clearance under hypoxia

We have studied the prophylactic efficacy of curcumin to ameliorate the impairment of tight junction protein integrity and fluid clearance in lungs of rats under hypoxia. A549 cells wereexposed to 3 % O₂ for 1 h, 3 h, 6 h, 12 h, 24 h and 48 h and rats were exposed to 7620 m for 6 h. NF-κB, Hif-1α and their related genes, tight junction protein (TJ) (ZO-1, JAM-C, claudin-4 and claudin-5, claudin-18) expressions were determined in A549 cells and lungs of rats by western blotting, ELISA and their activity by reporter gene assay, siRNAp65 knock out. Tissue specific localization of tight junction protein was determined by immunohistochemistry and immunoflorescence. Further transmission electron microscopy (TEM) was used to visualize the TJ structures between pulmonary epithelial cells. Blood gas and hematological parameters were also assessed. Later we checked, whether prior treatment with curcumin can restore the altered alveolar epithelial barrier integrity that is compromised through inflammatory mediators under hypoxia, A549 cells were pre-treated (1 h) with 10 μM curcumin and rats with 50 mg curcumin/kg BW and exposed to hypoxia. Curcumin pre-treatment both in vitro and in vivo showed significant changes in TJ protein integrity, attenuated NF-κB activity with reduced expression of its regulatory genes in lung tissues, serum and bronchoalveolar lavage fluid (BALF) along with stabilized HIF-1α levels under hypoxia. NF-κB inhibitors MG132, SN50 or siRNA mediated p65 knock down significantly reduced the dextran FITC influx into the lungs. The present study indicates that, curcumin prophylaxis augments alveolar epithelial barrier integrity and alveolar fluid clearance under hypoxia.

Intermittent Hypoxia Increases the Severity of Bleomycin-Induced Lung Injury in Mice

Background

Severe obstructive sleep apnea (OSA) with chronic intermittent hypoxia (IH) is common in idiopathic pulmonary fibrosis (IPF). Here, we evaluated the impact of IH on bleomycin- (BLM-) induced pulmonary fibrosis in mice.

Methods

C57BL/6J mice received intratracheal BLM or saline and were exposed to IH (40 cycles/hour; FiO₂ nadir: 6%; 8 hours/day) or intermittent air (IA). In the four experimental groups, we evaluated (i) survival; (ii) alveolar inflammation, pulmonary edema, lung oxidative stress, and antioxidant enzymes; (iii) lung cell apoptosis; and (iv) pulmonary fibrosis.

Results

Survival at day 21 was lower in the BLM-IH group (p < 0.05). Pulmonary fibrosis was more severe at day 21 in BLM-IH mice, as assessed by lung collagen content (p = 0.02) and histology. At day 4, BLM-IH mice developed a more severe neutrophilic alveolitis, (p < 0.001). Lung oxidative stress was observed, and superoxide dismutase and glutathione peroxidase expression was decreased in BLM-IH mice (p < 0.05 versus BLM-IA group). At day 8, pulmonary edema was observed and lung cell apoptosis was increased in the BLM-IH group.

Conclusion

These results show that exposure to chronic IH increases mortality, lung inflammation, and lung fibrosis in BLM-treated mice. This study raises the question of the worsening impact of severe OSA in IPF patients.

Stabilization of hypoxia inducible factor by cobalt chloride can alter renal epithelial transport

Given the importance of the transcriptional regulator hypoxia-inducible factor-1 (HIF-1) for adaptive hypoxia responses, we examined the effect of stabilized HIF-1α on renal epithelial permeability and directed sodium transport. This study was motivated by histological analysis of cystic kidneys showing increased expression levels of HIF-1α and HIF-2α We hypothesize that compression induced localized ischemia-hypoxia of normal epithelia near a cyst leads to local stabilization of HIF-1α, leading to altered transepithelial transport that encourages cyst expansion. We found that stabilized HIF-1α alters both transcellular and paracellular transport through renal epithelial monolayers in a manner consistent with secretory behavior, indicating localized ischemia-hypoxia may lead to altered salt and water transport through kidney epithelial monolayers. A quantity of 100 μmol/L Cobalt chloride (CoCl₂) was used acutely to stabilize HIF-1α in confluent cultures of mouse renal epithelia. We measured increased transepithelial permeability and decreased transepithelial resistance (TER) when HIF-1α was stabilized. Most interestingly, we measured a change in the direction of sodium current, most likely corresponding to abnormal secretory function, supporting our positive-feedback hypothesis.

Mesenchymal stem cells reduce hypoxia-induced apoptosis in alveolar epithelial cells by modulating HIF and ROS hypoxic signaling

Distal lung diseases, such as pulmonary fibrosis or acute lung injury, are commonly associated with local alveolar hypoxia that may be deleterious through the stimulation of alveolar epithelial cell (AEC) apoptosis. In various murine models of alveolar injury, administration of allogenic human mesenchymal stem cells (hMSCs) exerts an overall protective paracrine effect, limiting lung inflammation and fibrosis. However, the precise mechanisms on lung cells themselves remain poorly understood. Here, we investigated whether hMSC-conditioned medium (hMSC-CM) would protect AECs from hypoxia-induced apoptosis and explored the mechanisms involved in this cytoprotective effect. Exposure of rat primary AECs to hypoxia (1.5% O₂ for 24 h) resulted in hypoxia-inducible factor (HIF)-1α protein stabilization, partly dependent on reactive oxygen species (ROS) accumulation, and in a twofold increase in AEC apoptosis that was prevented by the HIF inhibitor 3-(5'-hydroxymethyl-2'-furyl)-1-benzyl-indazole and the antioxidant drug N-acetyl cysteine. Incubation of AECs with hMSC-CM significantly reduced hypoxia-induced apoptosis. hMSC-CM decreased HIF-1α protein expression, as well as ROS accumulation through an increase in antioxidant enzyme activities. Expression of Bnip3 and CHOP, two proapoptotic targets of HIF-1α and ROS pathways, respectively, was suppressed by hMSC-CM, while Bcl-2 expression was restored. The paracrine protective effect of hMSC was partly dependent on keratinocyte growth factor and hepatocyte growth factor secretion, preventing ROS and HIF-1α accumulation.

Galectin-1 inhibition attenuates profibrotic signaling in hypoxia-induced pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is characterized by lung remodeling arising from epithelial injury, aberrant fibroblast growth, and excessive deposition of extracellular matrix. Repeated epithelial injury elicits abnormal wound repair and lung remodeling, often associated with alveolar collapse and edema, leading to focal hypoxia. Here, we demonstrate that hypoxia is a physiological insult that contributes to pulmonary fibrosis (PF) and define its molecular roles in profibrotic activation of lung epithelial cells. Hypoxia increased transcription of profibrotic genes and altered the proteomic signatures of lung epithelial cells. Network analysis of the hypoxic epithelial proteome revealed a crosstalk between transforming growth factor-β1 and FAK1 (focal adhesion kinase-1) signaling, which regulated transcription of galectin-1, a profibrotic molecule. Galectin-1 physically interacted with and activated FAK1 in lung epithelial cells. We developed a novel model of exacerbated PF wherein hypoxia, as a secondary insult, caused PF in mice injured with subclinical levels of bleomycin. Hypoxia elevated expression of phosphorylated FAK1, galectin-1, and α-smooth muscle actin and reduced caspase-3 activation, suggesting aberrant injury repair. Galectin-1 inhibition caused apoptosis in the lung parenchyma and reduced FAK1 activation, preventing the development of hypoxia-induced PF. Galectin-1 inhibition also attenuated fibrosis-associated lung function decline. Further, galectin-1 transcript levels were increased in the lungs of IPF patients. In summary, we have identified a profibrotic role of galectin-1 in hypoxia signaling driving PF.

The impact of hypoxia on intestinal epithelial cell functions: consequences for invasion by bacterial pathogens

The maintenance of oxygen homeostasis in human tissues is mediated by several cellular adaptations in response to low-oxygen stress, called hypoxia. A decrease in tissue oxygen levels is initially counteracted by increasing local blood flow to overcome diminished oxygenation and avoid hypoxic stress. However, studies have shown that the physiological oxygen concentrations in several tissues are much lower than atmospheric (normoxic) conditions, and the oxygen supply is finely regulated in individual cell types. The gastrointestinal tract has been described to subsist in a state of physiologically low oxygen level and is thus depicted as a tissue in the state of constant low-grade inflammation. The intestinal epithelial cell layer plays a vital role in the immune response to inflammation and infections that occur within the intestinal tissue and is involved in many of the adaptation responses to hypoxic stress. This is especially relevant in the context of inflammatory disorders, such as inflammatory bowel disease (IBD). Therefore, this review aims to describe the intestinal epithelial cellular response to hypoxia and the consequences for host interactions with invading gastrointestinal bacterial pathogens.

HIF-1-Dependent TGM1 Expression is Associated with Maintenance of Airway Epithelial Junction Proteins

INTRODUCTION

Hypoxia has been implicated in the pathogenesis of many inflammatory and fibrotic lung diseases. The effect of hypoxia on epithelial junction protein expression is yet to be fully elucidated but evidence suggests a protective role for the hypoxia-inducible transcription factor HIF-1 in stabilising occludin. Transglutaminase 1 (TGM1) has been shown to stabilise endothelial and keratinocyte cell junctions, and while its expression and function have been mostly studied in the skin, recent studies have reported its expression in the lung. We hypothesised that TGM1 is a hypoxia-induced regulator of pulmonary epithelial junction protein stability, and the aim of this study was to investigate the regulation of TGM1 expression by hypoxia.

METHODS

Hypoxia-responsive genes were identified in human small airway epithelial cells (SAECs) by DNA microarray. TGM1 mRNA expression in SAECs was measured by quantitative real-time PCR. Protein expression of TGM1 and junction proteins was investigated by western blotting. Hypoxia-induced TGM1 was analysed by immunohistochemistry in vivo. The TGM1 gene promoter was investigated by luciferase assay.

RESULTS

In vitro exposure of SAECs to hypoxia induced a significant increase in TGM1 expression at both mRNA and protein levels. TGM1 was also significantly upregulated in hypoxic mouse lung epithelium. The hypoxia-responsive region was mapped to a HIF-1-responsive element. Inhibition of HIF-1 expression abolished hypoxia-induced promoter activation. Overexpression of TGM1 in lung epithelial cells or exposure of SAECs to hypoxia led to upregulated expression of junction proteins.

CONCLUSION

Herein we report that TGM1 is a HIF-1-regulated gene that is associated with the upregulation of airway epithelial junction proteins, supporting a protective role for HIF-1 in the lung. Interventions that augment the expression of TGM1 may provide useful therapeutic strategies for maintaining pulmonary epithelial integrity during lung injury.

Hypoxia Decreases Invasin-Mediated Yersinia enterocolitica Internalization into Caco-2 Cells

Yersinia enterocolitica is a major cause of human yersiniosis, with enterocolitis being a typical manifestation. These bacteria can cross the intestinal mucosa, and invade eukaryotic cells by binding to host β₁ integrins, a process mediated by the bacterial effector protein invasin. This study examines the role of hypoxia on the internalization of Y. enterocolitica into intestinal epithelial cells, since the gastrointestinal tract has been shown to be physiologically deficient in oxygen levels (hypoxic), especially in cases of infection and inflammation. We show that hypoxic pre-incubation of Caco-2 cells resulted in significantly decreased bacterial internalization compared to cells grown under normoxia. This phenotype was absent after functionally blocking host β₁ integrins as well as upon infection with an invasin-deficient Y. enterocolitica strain. Furthermore, downstream phosphorylation of the focal adhesion kinase was also reduced under hypoxia after infection. In good correlation to these data, cells grown under hypoxia showed decreased protein levels of β₁ integrins at the apical cell surface whereas the total protein level of the hypoxia inducible factor (HIF-1) alpha was elevated. Furthermore, treatment of cells with the HIF-1 α stabilizer dimethyloxalylglycine (DMOG) also reduced invasion and decreased β₁ integrin protein levels compared to control cells, indicating a potential role for HIF-1α in this process. These results suggest that hypoxia decreases invasin-integrin-mediated internalization of Y. enterocolitica into intestinal epithelial cells by reducing cell surface localization of host β₁ integrins.

The evidence for a role of vasospasm in the pathogenesis of cerebral malaria

Due to delay in treatment, cerebral malaria (CM) remains a significant complication of Plasmodium falciparum infection and is a common cause of death from malaria. In addition, more than 10 % of children surviving CM have neurological and long-term cognitive deficits. Understanding the pathogenesis of CM enables design of supportive treatment, reducing neurological morbidity and mortality. Vaso-occlusion and brain swelling appear to be leading to clinical features, neuronal damage and death in CM. It is proposed that parasitized red blood cells (pRBC), due to cytoadhesion to the endothelium and vasospasm induced by reduced bioavailability of nitric oxide, are causes. Stasis of blood flow and accumulation of pRBC may allow, after schizont rupture, for high concentration of products of haemolysis to accumulate, which leads to localized nitric oxide depletion, inducing adhesion molecules and cerebral vasospasm. Features consistent with an involvement of vasospasm are rapid reversibility of neurological symptoms, intermittently increased or absent flow in medium cerebral artery detectable on Doppler ultrasound and hemispheric reversible changes on cerebral magnetic resonance imaging in some patients. Clinical trials of treatment that can rapidly reduce cerebral vasospasm, including nitric oxide donors, inhaled nitric oxide, endothelin or calcium antagonists, or tissue plasminogen activators, are warranted.

G551D-CFTR needs more bound actin than wild-type CFTR to maintain its presence in plasma membranes

Cystic Fibrosis is due to mutations in the CFTR gene. The missense mutation G551D (approx. 5% of cases) encodes a CFTR chloride channel with normal cell surface expression but with an altered chloride channel activity, leading to a severe phenotype. Our aim was to identify specific interacting proteins of G551D-CFTR which could explain the channel defect. Wild-type CFTR (Wt-CFTR) was co-immunoprecipitated from stably transfected HeLa cells and resolved by 2D gel electrophoresis. Among the detected spots, one was expressed at a high level. Mass Spectrometry revealed that it corresponded to actin which is known to be involved in the CFTR's channel function. To assess whether actin could be involved in the altered G551D-CFTR function, its basal expression was studied. Because actin expression was the same in wt- and in G551D-CFTR expressing cells, its interaction with both wt- and G551D-CFTR was studied by co-immunoprecipitation, and we found that a higher amount of actin was bound onto G551D-CFTR than onto Wt-CFTR. The role of actin upon wt- and G551D-CFTR function was further studied by patch-clamp experiments after cytochalasin D treatment of the cells. We found a decrease of the very weak currents in G551D-CFTR expressing cells. Because a higher amount of actin is bound onto G551D-CFTR than onto Wt-CFTR, it is likely to be not involved in the mutated CFTR's defect. Nevertheless, because actin is necessary to maintain the very weak global currents observed in G551D-CFTR expressing HeLa cells, we conclude that more actin is necessary to maintain G551D-CFTR in the plasma membrane than for Wt-CFTR.

Human alveolar epithelial type II cells in primary culture

Alveolar epithelial type II (AEII) cells are a key structure and defender in the lung but also are the targets in many lung diseases, including acute respiratory distress syndrome, ventilator-induced lung injury, and pulmonary fibrosis. We sought to establish an optimized method for high yielding and long maintenance of characteristics of primary human AEII cells to facilitate the investigation of the mechanisms of lung diseases at the cellular and molecular levels. Adult human peripheral normal lung tissues of oncologic patients undergoing lung resection were collected. The AEII cells were isolated and identified by the expression of pro-surfactant protein (SP)C, epithelial sodium channel (αENaC) and cytokeratin (CK)-8, the lamellar bodies specific for AEII cells, and confirmed by the histology using electron microscopy. The phenotype of AEII cells was characterized by the expression of surfactant proteins (SP-A, SP-B, SP-C, SP-D), CK-8, KL-6, αENaC, and aquaporin (AQP)-3, which was maintained over 20 days. The biological activity of the primary human AEII cells producing SP-C, cytokines, and intercellular adhesion molecule-1 was vigorous in response to stimulation with tumor necrosis factor-α. We have modified previous methods and optimized a method for isolation of high purity and long maintenance of the human AEII cell phenotype in primary culture. This method provides an important tool for studies aiming at elucidating the molecular mechanisms of lung diseases exclusively in AEII cells.

Epoxyeicosatrienoic acids attenuating hypotonic-induced apoptosis of IMCD cells via γ-ENaC inhibition

Inner medulla collecting duct (IMCD) cells are the key part for urinary concentration. Hypotonic stress may trigger apoptosis of IMCD cells and induce renal injury. Epoxyeicosatrienoic acids (EETs) play an important role in anti-apoptosis, but their roles in hypotonic-induced apoptosis of IMCD cells are still unclear. Here we found increasing exogenous 11, 12-EET or endogenous EETs with Ad-CMV-CYP2C23-EGFP transfection decreased apoptosis of IMCD cells induced by hypotonic stress. Moreover, up-regulation of γ-ENaC induced by hypotonic stress was abolished by elevation of exogenous or endogenous EETs. Collectively, this study illustrated that EETs attenuated hypotonic-induced apoptosis of IMCD cells, and that regulation of γ-ENAC may be a possible mechanism contributing to the anti-apoptotic effect of EETs in response to hypotonic stress.

Hypoxia and the modulation of the actin cytoskeleton - emerging interrelations

Recent progress in understanding the influence of hypoxia on cell function has revealed new information about the interrelationship between the actin cytoskeleton and hypoxia; nevertheless, details remain cloudy. The dynamic regulation of the actin cytoskeleton during hypoxia is complex, varies in different cells and tissues, and also depends on the mode of hypoxia. Several molecular players and pathways are emerging that contribute to the modulation of the actin cytoskeleton and that affect the large repertoire of actin-binding proteins in hypoxia. This review describes and discusses the accumulated knowledge about actin cytoskeleton dynamics in hypoxia, placing special emphasis on the Rho family of small guanosine triphosphatases (Rho GTPases). Given that RhoA, Rac and Cdc42 are very well characterized, the review is focused on these family members of Rho GTPases. Notably, in several cell types and tissues, hypoxia, presumably via Rho GTPase signaling, induces actin rearrangement and actin stress fiber assembly, which is a prevalent modulation of the actin cytoskeleton in hypoxia.

High-altitude pulmonary edema

High-altitude pulmonary edema (HAPE), a not uncommon form of acute altitude illness, can occur within days of ascent above 2500 to 3000 m. Although life-threatening, it is avoidable by slow ascent to permit acclimatization or with drug prophylaxis. The critical pathophysiology is an excessive rise in pulmonary vascular resistance or hypoxic pulmonary vasoconstriction (HPV) leading to increased microvascular pressures. The resultant hydrostatic stress causes dynamic changes in the permeability of the alveolar capillary barrier and mechanical injurious damage leading to leakage of large proteins and erythrocytes into the alveolar space in the absence of inflammation. Bronchoalveolar lavage and hemodynamic pressure measurements in humans confirm that elevated capillary pressure induces a high-permeability noninflammatory lung edema. Reduced nitric oxide availability and increased endothelin in hypoxia are the major determinants of excessive HPV in HAPE-susceptible individuals. Other hypoxia-dependent differences in ventilatory control, sympathetic nervous system activation, endothelial function, and alveolar epithelial active fluid reabsorption likely contribute additionally to HAPE susceptibility. Recent studies strongly suggest nonuniform regional hypoxic arteriolar vasoconstriction as an explanation for how HPV occurring predominantly at the arteriolar level causes leakage. In areas of high blood flow due to lesser HPV, edema develops due to pressures that exceed the dynamic and structural capacity of the alveolar capillary barrier to maintain normal fluid balance. This article will review the pathophysiology of the vasculature, alveolar epithelium, innervation, immune response, and genetics of the lung at high altitude, as well as therapeutic and prophylactic strategies to reduce the morbidity and mortality of HAPE.

Up-regulation of stomatin expression by hypoxia and glucocorticoid stabilizes membrane-associated actin in alveolar epithelial cells

Stomatin is an important lipid raft-associated protein which interacts with membrane proteins and plays a role in the membrane organization. However, it is unknown whether it is involved in the response to hypoxia and glucocorticoid (GC) in alveolar epithelial cells (AEC). In this study we found that hypoxia and dexamethasone (dex), a synthetic GC not only up-regulated the expression of stomatin alone, but also imposed additive effect on the expression of stomatin in A549 cells, primary AEC and lung of rats. Then we investigated whether hypoxia and dex transcriptionally up-regulated the expression of stomatin by reporter gene assay, and found that dex, but not hypoxia could increase the activity of a stomatin promoter-driven reporter gene. Further deletion and mutational studies demonstrated that a GC response element (GRE) within the promoter region mainly contributed to the induction of stomatin by dex. Moreover, we found that hypoxia exposure did not affect membrane-associated actin, but decreased actin in cytoplasm in A549 cells. Inhibiting stomatin expression by stomatin siRNA significantly decreased dense of peripheral actin ring in hypoxia or dex treated A549 cells. Taken all together, these data indicated that dex and/or hypoxia significantly up-regulated the expression of stomatin in vivo and in vitro, which could stabilize membrane-associated actin in AEC. We suppose that the up-regulation of stomatin by hypoxia and dex may enhance the barrier function of alveolar epithelia and mediate the adaptive role of GC to hypoxia.

TNF-induced death signaling triggers alveolar epithelial dysfunction in acute lung injury

The ability of the alveolar epithelium to prevent and resolve pulmonary edema is a crucial determinant of morbidity and mortality in acute lung injury (ALI). TNF has been implicated in ALI pathogenesis, but the precise mechanisms remain undetermined. We evaluated the role of TNF signaling in pulmonary edema formation in a clinically relevant mouse model of ALI induced by acid aspiration and investigated the effects of TNF p55 receptor deletion, caspase-8 inhibition, and alveolar macrophage depletion on alveolar epithelial function. We found that TNF plays a central role in the development of pulmonary edema in ALI through activation of p55-mediated death signaling, rather than through previously well-characterized p55-mediated proinflammatory signaling. Acid aspiration produced pulmonary edema with significant alveolar epithelial dysfunction, as determined by alveolar fluid clearance (AFC) and intra-alveolar levels of the receptor for advanced glycation end-products. The impairment of AFC was strongly correlated with lung caspase-8 activation, which was localized to type 1 alveolar epithelial cells by flow cytometric analysis. p55-deficient mice displayed markedly attenuated injury, with improved AFC and reduced caspase-8 activity but no differences in downstream cytokine/chemokine production and neutrophil recruitment. Caspase-8 inhibition significantly improved AFC and oxygenation, whereas depletion of alveolar macrophages attenuated epithelial dysfunction with reduced TNF production and caspase-8 activity. These results provide in vivo evidence for a novel role for TNF p55 receptor-mediated caspase-8 signaling, without substantial apoptotic cell death, in triggering alveolar epithelial dysfunction and determining the early pathophysiology of ALI. Blockade of TNF-induced death signaling may provide an effective early-phase strategy for ALI.

Construction of oxygen and chemical concentration gradients in a single microfluidic device for studying tumor cell-drug interactions in a dynamic hypoxia microenvironment

Recent microfluidic advancements in oxygen gradients have greatly promoted controllable oxygen-sensitive cellular investigations at microscale resolution. However, multi-gradient integration in a single microfluidic device for tissue-mimicking cell investigation is not yet well established. In this study, we describe a method that can generate oxygen and chemical concentration gradients in a single microfluidic device via the formation of an oxygen gradient in a chamber and a chemical concentration gradient between adjacent chambers. The oxygen gradient dynamics were systematically investigated, and were quantitatively controlled using simple exchange between the aerial oxygen and the oxygen-free conditions in the gas-permeable polydimethylsiloxane channel. Meanwhile, the chemical gradient dynamics was generated using a special channel-branched device. For potential medical applications of the established oxygen and chemical concentration gradients, a tumor cell therapy assessment was performed using two antitumor drugs (tirapazamine and bleomycin) and two tumor cell lines (human lung adenocarcinoma A549 cells and human cervical carcinoma HeLa cells). The results of the proof-of-concept experiment indicate the dose-dependent antitumor effect of the drugs and hypoxia-induced cytotoxicity of tirapazamine. We demonstrate that the integration of oxygen and chemical concentration gradients in a single device can be applied to investigating oxygen- and chemical-sensitive cell events, which can also be valuable in the development of multi-gradient generating procedures and specific drug screening.

Divergence of tight and adherens junction factors in alveolar epithelium in pulmonary fibrosis

It has been proposed that an epithelial injury may be one of the multiple primary events in the pathogenesis of idiopathic pulmonary fibrosis (IPF). The aim of this study was to characterize the tight junction and adherens junction proteins in normal human lung, IPF, cryptogenic organizing pneumonia, and asbestosis. We determined the immunohistochemical cell-specific expression of tight junction proteins claudin-1, claudin-2, claudin-3, claudin-4, claudin-5, and claudin-7, as well as 3 adherens junction proteins, E-cadherin, N-cadherin, and β-catenin. We further analyzed the expression of claudin-1, claudin-3, and claudin-4 and E-cadherin, N-cadherin, and β-catenin at the transcriptional level by quantitative real-time reverse transcriptase polymerase chain reaction. The expression levels of both tight junction and adherens junction proteins were elevated in regenerative alveolar epithelium in pulmonary fibrosis as compared with the expression of these proteins in normal alveolar epithelium. In particular, the expression levels of claudins-1 and claudin-3 were clearly elevated in all diseases. Furthermore, the amounts of adherens junction proteins messenger RNAs (mRNAs) were also all increased in pulmonary fibroses in comparison with healthy controls, with N-cadherin showing the greatest increase in mRNA levels in all diseases. However, the amounts of claudin-1, claudin-3, and claudin-4 mRNAs in fibrotic lung were similar to or even lower than those measured in the healthy controls. It is possible that the diminished capacity to produce claudin mRNAs may be one explanation for poor repair capacity of alveolar epithelial cells in IPF.

In vitro assessment of epithelial electrical resistance in human esophageal and jejunal mucosae and in Caco-2 cell layers

OBJECTIVE

There is a need for a technique allowing studies of human mucosal specimens collected during different clinical conditions. This study elucidates if square wave pulse analysis discriminates between epithelial and transmural electrical resistance and if there is an association with transepithelial permeability of molecular probes.

METHODS

Mucosae from esophagus (surgical resections: n = 14; endoscopic biopsies: n = 15) and jejunum (n = 12) and Caco-2 cell monolayers were investigated in Ussing chambers. Transmural and epithelial electrical resistance were recorded by the use of standardized current pulses. Permeability was assessed using two fluorescein-labeled probes (weight 376 and 4000 Da).

RESULTS

Baseline epithelial electrical resistance was higher in esophageal mucosa (~280 Ω*cm(2)), than in jejunal (~10 Ω*cm(2)) and Caco-2 cells (~140 Ω*cm(2)). The subepithelial contribution to the transmural resistance was higher in jejunal preparations (+88%) and Caco-2 cells (+75%), than in esophageal (+30%). During hypoxia the subepithelial resistance was unchanged, whereas the epithelial resistance decreased significantly in jejunal mucosa and Caco-2 cells. These findings coincided with increased transepithelial probe permeability and signs of disturbed morphology. Esophageal epithelia were resistant to hypoxia. However, exposure to deoxycholic acid and trypsin abolished the esophageal epithelial resistance and increased probe permeability. Endoscopic esophageal biopsies from patients with erosive reflux disease exhibited significantly lower epithelial resistance and higher current than healthy subjects.

CONCLUSION

Square wave pulse analysis in Ussing chambers is suitable for assessment of epithelial electrical resistance that can reflect transepithelial permeability of molecular probes with known size. Moreover, the technique discriminated between healthy and reflux-diseased esophageal mucosal biopsies.

Vasodilator phosphostimulated protein (VASP) protects endothelial barrier function during hypoxia

The endothelial barrier controls the passage of solutes from the vascular space. This is achieved through active reorganization of the actin cytoskeleton. A central cytoskeletal protein involved into this is vasodilator-stimulated phosphoprotein (VASP). However, the functional role of endothelial VASP during hypoxia has not been thoroughly elucidated. We determined endothelial VASP expression through real-time PCR (Rt-PCR), immunhistochemistry, and Western blot analysis during hypoxia. VASP promoter studies were performed using a PGL3 firefly luciferase containing plasmid. Following approval by the local authorities, VASP ( -/- ) mice and littermate controls were subjected to normobaric hypoxia (8% O(2), 92% N(2)) after intravenous injection of Evans blue dye. In in vitro studies, we found significant VASP repression in human microvascular and human umbilical vein endothelial cells through Rt-PCR, immunhistochemistry, and Western blot analysis. The VASP promoter construct demonstrated significant repression in response to hypoxia, which was abolished when the binding of hypoxia-inducible factor 1 alpha was excluded. Exposure of wild-type (WT) and VASP ( -/- ) animals to normobaric hypoxia for 4 h resulted in an increase in Evans blue tissue extravasation that was significantly increased in VASP ( -/- ) animals compared to WT controls. In summary, we demonstrate here that endothelial VASP holds significant importance for endothelial barrier properties during hypoxia.

Lung oxidative damage by hypoxia

One of the most important functions of lungs is to maintain an adequate oxygenation in the organism. This organ can be affected by hypoxia facing both physiological and pathological situations. Exposure to this condition favors the increase of reactive oxygen species from mitochondria, as from NADPH oxidase, xanthine oxidase/reductase, and nitric oxide synthase enzymes, as well as establishing an inflammatory process. In lungs, hypoxia also modifies the levels of antioxidant substances causing pulmonary oxidative damage. Imbalance of redox state in lungs induced by hypoxia has been suggested as a participant in the changes observed in lung function in the hypoxic context, such as hypoxic vasoconstriction and pulmonary edema, in addition to vascular remodeling and chronic pulmonary hypertension. In this work, experimental evidence that shows the implied mechanisms in pulmonary redox state by hypoxia is reviewed. Herein, studies of cultures of different lung cells and complete isolated lung and tests conducted in vivo in the different forms of hypoxia, conducted in both animal models and humans, are described.

Expression of TMPRSS4 in non-small cell lung cancer and its modulation by hypoxia

Overexpression of TMPRSS4, a cell surface-associated transmembrane serine protease, has been reported in pancreatic, colorectal and thyroid cancers, and has been implicated in tumor cell migration and metastasis. Few reports have investigated both TMPRSS4 gene expression levels and the protein products. In this study, quantitative RT-PCR and protein staining were used to assess TMPRSS4 expression in primary non-small cell lung carcinoma (NSCLC) tissues and in lung tumor cell lines. At the transcriptional level, TMPRSS4 message was significantly elevated in the majority of human squamous cell and adenocarcinomas compared with normal lung tissues. Staining of over 100 NSCLC primary tumor and normal specimens with rabbit polyclonal anti-TMPRSS4 antibodies confirmed expression at the protein level in both squamous cell and adenocarcinomas with little or no staining in normal lung tissues. Human lung tumor cell lines expressed varying levels of TMPRSS4 mRNA in vitro. Interestingly, tumor cell lines with high levels of TMPRSS4 mRNA failed to show detectable TMPRSS4 protein by either immunoblotting or flow cytometry. However, protein levels were increased under hypoxic culture conditions suggesting that hypoxia within the tumor microenvironment may upregulate TMPRSS4 protein expression in vivo. This was supported by the observation of TMPRSS4 protein in xenograft tumors derived from the cell lines. In addition, staining of human squamous cell carcinoma samples for carbonic anhydrase IX (CAIX), a hypoxia marker, showed TMPRSS4 positive cells adjacent to CAIX positive cells. Overall, these results indicate that the cancer-associated TMPRSS4 protein is overexpressed in NSCLC and may represent a potential therapeutic target.

Regulation of ENaC biogenesis by the stress response protein SERP1

Cystic fibrosis lung disease is caused by reduced Cl(-) secretion along with enhanced Na(+) absorption, leading to reduced airway surface liquid and compromised mucociliary clearance. Therapeutic strategies have been developed to activate cystic fibrosis transmembrane conductance regulator (CFTR) or to overcome enhanced Na(+) absorption by the epithelial Na(+) channel (ENaC). In a split-ubiquitin-based two-hybrid screening, we identified stress-associated ER protein 1 (SERP1)/ribosome-associated membrane protein 4 as a novel interacting partner for the ENaC β-subunit. SERP1 is induced during cell stress and interacts with the molecular chaperone calnexin, thus controlling early biogenesis of membrane proteins. ENaC activity was measured in the human airway epithelial cell lines H441 and A549 and in voltage clamp experiments with ENaC-overexpressing Xenopus oocytes. We found that expression of SERP1 strongly inhibits amiloride-sensitive Na(+) transport. SERP1 coimmunoprecipitated and colocalized with βENaC in the endoplasmic reticulum, together with the chaperone calnexin. In contrast to the inhibitory effects on ENaC, SERP1 appears to promote expression of CFTR. Taken together, SERP1 is a novel cochaperone and regulator of ENaC expression.

Claudins in lung diseases

Tight junctions are the most apically localized part of the epithelial junctional complex. They regulate the permeability and polarity of cell layers and create compartments in cell membranes. Claudins are structural molecules of tight junctions. There are 27 claudins known, and expression of different claudins is responsible for changes in the electrolyte and solute permeability in cells layers. Studies have shown that claudins and tight junctions also protect multicellular organisms from infections and that some infectious agents may use claudins as targets to invade and weaken the host's defense. In neoplastic diseases, claudin expression may be up- or downregulated. Since their expression is associated with specific tumor types or with specific locations of tumors to a certain degree, they can, in a restricted sense, also be used as tumor markers. However, the regulation of claudin expression is complex involving growth factors and integrins, protein kinases, proto-oncogens and transcription factors. In this review, the significance of claudins is discussed in lung disease and development.

Hypoxia increases transepithelial electrical conductance and reduces occludin at the plasma membrane in alveolar epithelial cells via PKC-ζ and PP2A pathway

During pulmonary edema, the alveolar space is exposed to a hypoxic environment. The integrity of the alveolar epithelial barrier is required for the reabsorption of alveolar fluid. Tight junctions (TJ) maintain the integrity of this barrier. We set out to determine whether hypoxia creates a dysfunctional alveolar epithelial barrier, evidenced by an increase in transepithelial electrical conductance (G(t)), due to a decrease in the abundance of TJ proteins at the plasma membrane. Alveolar epithelial cells (AEC) exposed to mild hypoxia (Po(2) = 50 mmHg) for 30 and 60 min decreased occludin abundance at the plasma membrane and significantly increased G(t). Other cell adhesion molecules such as E-cadherin and claudins were not affected by hypoxia. AEC exposed to hypoxia increased superoxide, but not hydrogen peroxide (H(2)O(2)). Overexpression of superoxide dismutase 1 (SOD1) but not SOD2 prevented the hypoxia-induced G(t) increase and occludin reduction in AEC. Also, overexpression of catalase had a similar effect as SOD1, despite not detecting any increase in H(2)O(2) during hypoxia. Blocking PKC-ζ and protein phosphatase 2A (PP2A) prevented the hypoxia-induced occludin reduction at the plasma membrane and increase in G(t). In summary, we show that superoxide, PKC-ζ, and PP2A are involved in the hypoxia-induced increase in G(t) and occludin reduction at the plasma membrane in AEC.

Oxygen regulation of the epithelial Na channel in the collecting duct

The PO(2) within the kidney changes dramatically from cortex to medulla. The present experiments examined the effect of changing PO(2) on epithelial Na channel (ENaC)-mediated Na transport in the collecting duct using the mpkCCD-c14 cell line. Decreasing ambient O(2) concentration from 20 to 8% decreased ENaC activity by 40%; increasing O(2) content to 40% increased ENaC activity by 50%. The O(2) effect required several hours to develop and was not mimicked by the acid pH that developed in monolayers incubated in low-O(2) medium. Corticosteroids increased ENaC activity at each O(2) concentration; there was no interaction. The pathways for O(2) and steroid regulation of ENaC are different since O(2) did not substantially affect Sgk1, α-ENaC, Gilz, or Usp2-45 mRNA levels, genes involved in steroid-mediated ENaC regulation. The regulation of ENaC activity by these levels of O(2) appears not to be mediated by changes in hypoxia-inducible factor-1α or -2α activity or a change in AMP kinase activity. Changes in O(2) concentration had minimal effect on α- or γ-ENaC mRNA and protein levels; there were moderate effects on β-ENaC levels. However, 40% O(2) induced substantially greater total β- and γ-ENaC on the apical surface compared with 8% O(2); both subunits demonstrated a greater increase in the mature forms. The α-ENaC subunit was difficult to detect on the apical surface, perhaps because our antibodies do not recognize the major mature form. These results identify a mechanism of ENaC regulation that may be important in different regions of the kidney and in responses to changes in dietary NaCl.

Cdk5 interacts with Hif-1α in neurons: a new hypoxic signalling mechanism?

The cyclin dependent kinase 5 (Cdk5)/p35 complex is essential for regulation of cell survival during development and in models of neuronal excitotoxicity. Dysregulation of Cdk5, by cleavage of its neuronal specific activators p35 and p39, has been implicated in various neurodegenerative disorders such as Alzheimer's disease, however targets of the complex that regulate neuronal survival physiologically and/or during pathogenesis are largely unknown. Since hypoxia is a key feature in the pathogenesis of several neuronal disorders we investigated a role for Cdk5/p35 in the neuronal hypoxic response. Our data show that hypoxia modulates the p35/Cdk5 complex in primary cortical neurons at the transcriptional and protein level. Furthermore hypoxic induction of Cdk5 activity correlates with Hif-1α stabilisation, and direct interaction between these proteins can occur. Importantly, we demonstrate that Cdk5-mediated signaling is involved in Hif-1α stabilisation since inhibition of Cdk5 by roscovitine abrogates Hif-1α accumulation and induces cell death. Taken together our results show that the Cdk5/p35 complex may significantly contribute to modulation of Hif-1α stabilisation and impact neuronal survival during oxygen deprivation. Thus this study highlights a new hypoxia-mediated signaling pathway and implicates the cytoskeleton as a potential regulator of Hif-1α.

Cytoskeletal regulation of epithelial barrier function during inflammation

Increased epithelial permeability is a common and important consequence of mucosal inflammation that results in perturbed body homeostasis and enhanced exposure to external pathogens. The integrity and barrier properties of epithelial layers are regulated by specialized adhesive plasma membrane structures known as intercellular junctions. It is generally believed that inflammatory stimuli increase transepithelial permeability by inducing junctional disassembly. This review highlights molecular events that lead to disruption of epithelial junctions during inflammation. We specifically focus on key mechanisms of junctional regulation that are dependent on reorganization of the perijunctional F-actin cytoskeleton. We discuss critical roles of myosin-II-dependent contractility and actin filament turnover in remodeling of the F-actin cytoskeleton that drive disruption of epithelial barriers under different inflammatory conditions. Finally, we highlight signaling pathways induced by inflammatory mediators that regulate reorganization of actin filaments and junctional disassembly in mucosal epithelia.

Induction of heme oxygenase-1, biliverdin reductase and H-ferritin in lung macrophage in smokers with primary spontaneous pneumothorax: role of HIF-1alpha

Background

Few data concern the pathophysiology of primary spontaneous pneumothorax (PSP), which is associated with alveolar hypoxia/reoxygenation. This study tested the hypothesis that PSP is associated with oxidative stress in lung macrophages. We analysed expression of the oxidative stress marker 4-HNE; the antioxidant and anti-inflammatory proteins heme oxygenase-1 (HO-1), biliverdin reductase (BVR) and heavy chain of ferritin (H-ferritin); and the transcription factors controlling their expression Nrf2 and HIF-1α, in lung samples from smoker and nonsmoker patients with PSP (PSP-S and PSP-NS), cigarette smoke being a risk factor of recurrence of the disease.

Methodology/Principal Findings

mRNA was assessed by RT-PCR and proteins by western blot, immunohistochemistry and confocal laser analysis. 4-HNE, HO-1, BVR and H-ferritin were increased in macrophages from PSP-S as compared to PSP-NS and controls (C). HO-1 increase was associated with increased expression of HIF-1α mRNA and protein in alveolar macrophages in PSP-S patients, whereas Nrf2 was not modified. To understand the regulation of HO-1, BVR and H-ferritin, THP-1 macrophages were exposed to conditions mimicking conditions in C, PSP-S and PSP-NS patients: cigarette smoke condensate (CS) or air exposure followed or not by hypoxia/reoxygenation. Silencing RNA experiments confirmed that HIF-1α nuclear translocation was responsible for HO-1, BVR and H-ferritin induction mediated by CS and hypoxia/reoxygenation.

Conclusions/Significance

PSP in smokers is associated with lung macrophage oxidative stress. The response to this condition involves HIF-1α-mediated induction of HO-1, BVR and H-ferritin.

Cell migration in BeWo cells and the role of epithelial sodium channels

Cell migration/proliferation processes associated with wound healing were measured in BeWo cells at 6 h, when mitosis is still scarce. Cells were cultured in medium with 1% fetal bovine serum to minimize proliferation. BeWo cell migration covered 20.6 +/- 7.0%, 38.0 +/- 5.4%, 16.6 +/- 4.8% and 13.7 +/- 3.6% of the wound when cultivated under control, aldosterone (100 nM, 12 h), aldosterone plus amiloride (10 muM) and amiloride treatments, respectively. When BeWo cells were treated with aldosterone, there was an increase in wound healing (P < 0.05), which was prevented by adding the ENaC blocker amiloride (P < 0.05, n = 16). Immunocytochemistry studies showed that the three ENaC subunits showed greater expression at the leading edge of the wound 3 h after injury, supporting the notion that these proteins participate in a postinjury signal. Antisense oligonucleotides directed against the alpha-ENaC subunit decreased the migratory response of the cells compared to the sense treated cells or the cells without oligonucleotides (P < 0.001, n = 16): 30.2 +/- 3.7%, 17.6 +/- 1.3%, 27.5 +/- 1.5% and 20.2 +/- 1.5% reinvasion of the wound with aldosterone, aldosterone plus antisense, aldosterone plus sense treatments and control conditions, respectively. Aldosterone and amiloride influence wound healing in BeWo cells, probably by their effects upon ENaCs, transmitting a signal to the cell cytoplasm for the release of several agents that promote cell migration.

Normothermic ex vivo perfusion prevents lung injury compared to extended cold preservation for transplantation

Treatment of injured donor lungs ex vivo to accelerate organ recovery and ameliorate reperfusion injury could have a major impact in lung transplantation. We have recently demonstrated a feasible technique for prolonged (12 h) normothermic ex vivo lung perfusion (EVLP). This study was performed to examine the impact of prolonged EVLP on ischemic injury. Pig donor lungs were cold preserved in Perfadex for 12 h and subsequently divided into two groups: cold static preservation (CSP) or EVLP at 37 degrees C with Steen solution for a further 12 h (total 24 h preservation). Lungs were then transplanted and reperfused for 4 h. EVLP preservation resulted in significantly better lung oxygenation (PaO(2) 531 +/- 43 vs. 244 +/- 49 mmHg, p < 0.01) and lower edema formation rates after transplantation. Alveolar epithelial cell tight junction integrity, evaluated by zona occludens-1 protein staining, was disrupted in the cell membranes after prolonged CSP but not after EVLP. The maintenance of integrity of barrier function during EVLP translates into significant attenuation of reperfusion injury and improved graft performance after transplantation. Integrity of functional metabolic pathways during normothermic perfusion was confirmed by effective gene transfer and GFP protein synthesis by lung alveolar cells. In conclusion, EVLP prevents ongoing injury associated with prolonged ischemia and accelerates lung recovery.

Inflammation-associated repression of vasodilator-stimulated phosphoprotein (VASP) reduces alveolar-capillary barrier function during acute lung injury

Acute lung injury (ALI) is an inflammatory disorder associated with reduced alveolar-capillary barrier function, increased pulmonary vascular permeability, and infiltration of leukocytes into the alveolar space. Pulmonary function might be compromised, its most severe form being the acute respiratory distress syndrome. A protein central to physiological barrier properties is vasodilator-stimulated phosphoprotein (VASP). Given the fact that VASP expression is reduced during periods of cellular hypoxia, we investigated the role of VASP during ALI. Initial studies revealed reduced VASP expressional levels through cytokines in vitro. Studies in the putative human VASP promoter identified NF-kappaB as a key regulator of VASP transcription. This VASP repression results in increased paracellular permeability and migration of neutrophils in vitro. In a model of LPS-induced ALI, VASP(-/-) mice demonstrated increased pulmonary damage compared with wild-type animals. These findings were confirmed in a second model of ventilator-induced lung injury. Studies employing bone marrow chimeric animals identified tissue-specific repression of VASP as the underlying cause of decreased barrier properties of the alveolar-capillary barrier during ALI. Taken together these studies identify tissue-specific VASP as a central protein in the control of the alveolar-capillary barrier properties during ALI.

Calpain-mediated breakdown of cytoskeletal proteins contributes to cholecystokinin-induced damage of rat pancreatic acini

The cytosolic cysteine protease calpain is implicated in a multitude of cellular functions but also plays a role in cell damage. Our previous results suggest that an activation of calpain accompanied by a decrease in its endogenous inhibitor calpastatin may contribute to pancreatic damage during cerulein-induced acute pancreatitis. The present study aimed at the time course of secretagogue-induced calpain activation and cellular substrates of the protease. Isolated rat pancreatic acini were incubated with a supramaximal concentration of cholecystokinin (0.1 microM CCK) for 30 min in the presence or absence of the calpain inhibitor Z-Val-Phe methyl ester (100 microM ZVP). The activation of calpain and the expression of calpastatin and the actin cytoskeleton-associated proteins alphaII-spectrin, E-cadherin and vinculin were studied by immunoblotting. The cell damage was assessed by lactate dehydrogenase release and ultrastructural analysis including fluorescence-labelled actin filaments. Immediately after administration, CCK led to activation of both calpain isoforms, mu- and m-calpain. The protease activation was accompanied by a decrease in the E-cadherin level and formation of calpain-specific breakdown products of alphaII-spectrin. A calpain-specific cleavage product of vinculin appeared concomitantly with changes in the actin filament organization. No effect of CCK on calpastatin was found. Inhibition of calpain by ZVP reduced CCK-induced damage of the actin-associated proteins and the cellular ultrastructure including the actin cytoskeleton. The results suggest that CCK-induced acinar cell damage requires activation of calpain and that the actin cytoskeleton belongs to the cellular targets of the protease.

Physiological consequences of gill remodeling in goldfish (Carassius auratus) during exposure to long-term hypoxia

Goldfish (Carassius auratus) acclimated to 7 degrees C and exposed to hypoxia ( approximately 10 mmHg) for 7 days exhibited a pronounced remodeling of the gill consisting of the removal of an interlamellar cell mass (ILCM). Subsequent experiments were designed to assess the impact of gill remodeling and the associated increase in functional lamellar surface area on the distribution of branchial ionocytes and Cl(-) flux across the gill. Despite the increased functional lamellar surface area during hypoxia, there was no corresponding increase in Cl(-) loss or efflux of the extracellular marker polyethylene glycol (PEG 4000). However, when hypoxic fish were returned to normoxic water for 12 h, rates of Cl(-) and PEG efflux were markedly stimulated in keeping with an increased surface area for solute movement. Similarly, the rate of branchial Cl(-) uptake was reduced (105 +/- 22 vs. 45 +/- 8 micromol x kg(-1) x h(-1)) in normoxic and hypoxic fish, respectively, but then stimulated (345 micromol x kg(-1) x h(-1)) upon reestablishment of normoxic conditions. Hypoxia (7 days) was accompanied by a significant decrease in the total cross-sectional area of branchial ionocytes owing to a decrease in their numbers and individual sizes. Thus, despite experiencing an increase in functional lamellar surface area, hypoxic goldfish limit branchial Cl(-) loss likely by a hypoxia-mediated decrease in paracellular permeability. In normoxic fish, the ionocytes were largely confined to the outer edges of the ILCM. During hypoxia, preexisting ionocytes migrated with the shrinking ILCM, while a smaller proportion of newly differentiated cells appeared below the surface of the ILCM. The capacity to maintain a population of ionocytes in contact with the water is an appropriate strategy to retain ionoregulatory capabilities regardless of whether the lamellae are uncovered or covered.

The effect of endothelin-1 on alveolar fluid clearance and pulmonary edema formation in the rat

BACKGROUND

Endothelin-1 (ET-1) is thought to play a pivotal role in pulmonary edema formation. The underlying mechanisms remain uncertain but may include alterations in capillary pressure and vascular permeability. There are no studies investigating whether ET-1 also affects alveolar fluid clearance which is the primary mechanism for the resolution of pulmonary edema. Therefore, we performed this study to clarify effects of ET-1 on alveolar reabsorption and fluid balance in the rat lung.

METHODS

Alveolar fluid clearance was measured in fluid instilled rat lungs using a 5% albumin solution with or without ET-1 (10(-7) M) and/or amiloride (100 microM). Net alveolar fluid balance, time course of edema formation, pulmonary capillary pressure, and alveolar permeability to albumin were measured in the isolated, ventilated, constant pressure perfused rat lung with or without ET-1 (0.8 nM) added to the perfusate.

RESULTS

In the fluid-instilled lung, ET-1 reduced alveolar fluid clearance by about 65%, an effect that was related to a decrease in amiloride-sensitive transepithelial Na(+) transport (P < 0.001). The ET-1-induced inhibition was completely prevented by the endothelin B receptor antagonist BQ788 (P = 0.006), whereas the endothelin A receptor antagonist BQ123 had no effect (P = 0.663). In the isolated, ventilated, perfused rat lung ET-1 caused a net accumulation of alveolar fluid by about 20% (P = 0.011 vs control), whereas lungs of control rats cleared about 20% of the instilled fluid. ET-1 increased pulmonary capillary pressure (+9.4 cm H(2)O), decreased perfusate flow (-81%), accelerated lung weight gain and reduced lung survival time (P < 0.001). Permeability to albumin was not significantly affected by ET-1 (P = 0.24).

CONCLUSION

ET-1 inhibits alveolar fluid clearance of anesthetized rats by inhibition of amiloride-sensitive epithelial Na(+) channels. The inhibitory effect of ET-1 results from activation of the endothelin B receptor. These findings suggest a mechanism by which ET-1, in addition to increasing capillary pressure, contributes to pulmonary edema formation.

Gene regulation in the adaptive process to hypoxia in lung epithelial cells

Lung alveolar epithelial cells are normally very well oxygenated but may be exposed to hypoxia in many pathological conditions such as pulmonary edema, acute respiratory distress syndrome, chronic obstructive pulmonary diseases, or in some environmental conditions such ascent to high altitude. The ability of alveolar epithelial cells to cope with low oxygen tensions is crucial to maintain the structural and functional integrity of the alveolar epithelium. Alveolar epithelial cells appear to be remarkably tolerant to oxygen deprivation as they are able to maintain adequate cellular ATP content during prolonged hypoxic exposure when mitochondrial oxidative phosphorylation is limited. This property mostly relies on the ability of the cells to rapidly modify their gene expression program, stimulating the expression of genes involved in anaerobic energy supply and repressing expression of genes involved in some ATP-consuming cellular processes. This adaptive strategy of the cells is mostly, but not entirely, dependent on the expression of hypoxia-inducible factors (HIFs), known to be responsible for orchestrating a large number of hypoxia-sensitive genes. This review focuses on the role of HIF isoforms expressed in alveolar epithelial cells exposed to hypoxia and on the specific hypoxic gene regulation that takes place in alveolar epithelial cells either through HIF-dependent or -independent pathways.

In vitro hypoxia impairs beta2-adrenergic receptor signaling in primary rat alveolar epithelial cells

Hypoxia inhibits beta(2)-adrenergic receptor (beta(2)-AR) signaling in a variety of tissues, but effects in alveolar epithelium are unclear. We therefore examined the effect of 24 h of hypoxia on beta(2)-AR function in primary rat alveolar epithelial [alveolar type II (ATII)] cells. ATII cells were isolated, cultured to confluence, and incubated in normoxia or hypoxia (3% O(2)) for 24 h. Hypoxia decreased maximal terbutaline-stimulated cAMP production by 37%; potency of terbutaline was not affected. Reoxygenation (3 h) reversed this effect. Density of beta(2)-AR assessed by (-)-[(125)I]iodocyanopindolol binding was decreased in hypoxia (-22%). Hypoxia did not affect terbutaline binding affinity to beta(2)-AR. Hypoxia decreased G(s) protein levels by 27%, whereas no change was observed in G(i1/2), G(i3), and Gbeta subunits. Forskolin-stimulated cAMP production was not inhibited by hypoxia. Pertussis toxin (PTX; 0.5 microg/ml, 2 h), an inhibitor of G(i/o) proteins, restored terbutaline-stimulated cAMP production of hypoxic ATII cells to normoxic control values. Cholera toxin (CTX)-stimulated G(s) protein activity did not change in hypoxia. Hypoxia increased the sensitivity of beta(2)-AR to desensitization. These results indicate that despite the decrease in G(s) protein level G(s) protein was still functional and that hypoxia impairs beta(2)-AR signaling due to an increased activity of G(i/o) proteins.

MgcRacGAP interacts with HIF-1alpha and regulates its transcriptional activity

HIF-1alpha is the inducible subunit of the dimeric transcription factor HIF-1 (Hypoxia Inducible Factor 1). It is induced by hypoxia and hypoxia-mimetics in most cell types, as well as non-hypoxic signals such as growth factors, cytokines and oncogenes, often in a cell specific manner. HIF-1 is present in virtually all cells of higher eukaryotes and its function is of great biomedical relevance since it is highly involved in development, tumor progression and tissue ischemia. Intracellular signaling to HIF-1alpha, as well as its further action, involves its participation in numerous protein complexes. Using the yeast two-hybrid system we have identified MgcRacGAP (male germ cell Rac GTPase Activating Protein) as a HIF-1alpha interacting protein. The MgcRacGAP protein is a regulator of Rho proteins, which are principally involved in cytoskeletal organization. We have verified specific binding of HIF-1alpha and MgcRacGAP in vitro and in vivo in mammalian cells. We have additionally shown that MgcRacGAP overexpression inhibits HIF-1alpha transcriptional activity, without lowering HIF-1alpha protein levels, or altering its subcellular localization. Moreover, this inhibition is dependent on the MgcRacGAP domain that interacts with HIF-1alpha. In conclusion, our findings demonstrate that HIF-1alpha function is negatively affected by its interaction with MgcRacGAP.

Identification of vasodilator-stimulated phosphoprotein (VASP) as an HIF-regulated tissue permeability factor during hypoxia

Increased tissue permeability is commonly associated with hypoxia of many origins. Since hypoxia-inducible factor (HIF) represents a predominant hypoxia signaling mechanism, we compared hypoxia-elicited changes in tissue barrier function in mice conditionally lacking intestinal epithelial hypoxia-inducible factor-1alpha (hif1a). Somewhat surprisingly, these studies revealed that mutant hif1a mice were protected from hypoxia-induced increases in intestinal permeability in vivo. Guided by microarray analysis of tissues derived from these mutant hif1a mice, we identified HIF-1-dependent repression of vasodilator-stimulated phosphoprotein (VASP), a molecule known to be important in the control of cytoskeletal dynamics, including barrier function. Studies at the mRNA and protein level confirmed hypoxia-elicited repression of VASP in murine tissue, cultured epithelia and endothelia, as well as human saphenous vein ex vivo. Targeted repression of VASP by siRNA recapitulated our findings with hypoxia and directed overexpression of VASP abolished hypoxia-induced barrier dysfunction. Studies in the cloned human VASP promoter revealed hypoxia-dependent transcriptional repression, and functional studies by chromatin immunoprecipitation (ChIP) and site-directed mutagenesis revealed hypoxia-dependent binding of HIF-1alpha to the human VASP promoter. These studies identify HIF-1-dependent repression of VASP as a control point for hypoxia-regulated barrier dysfunction.