A novel function of ionotropic gamma-aminobutyric acid receptors involving alveolar fluid homeostasis

Regulation of neutrophil migration in acute pulmonary inflammation by extraneuronal α1 gamma-aminobutyric acidA receptors

Acute pulmonary inflammation is a common disease on intensive care. Due to the lack of specific treatments, lethality is still very high. The ionotropic GABAA-receptors are known from the central nervous system (CNS) and have recently been detected in the lung. These receptors have been shown to influence inflammatory processes. Opposing data has been reported, where both, GABA site agonists and antagonists achieved anti-inflammatory effects. The distribution of the 19 known GABAA-receptor subunits (α1-6, β1-3, γ1-3, δ, ε, π, θ and ρ1-3) and their role in inflammation remain unclear. In murine models of LPS- and bacteria-induced inflammation, Muscimol (GABAA-receptor agonist) and Bicuculline (antagonist) were administered before the onset of inflammation. Transcription of GABAA-receptor subunits was evaluated by real-time polymerase chain reaction. Neutrophil counts and adhesion molecule expression in wild type and GABAα1 knock-in mice were determined by flow-cytometry. Myeloperoxidase, neutrophil extracellular traps and cytokines were determined. In a model of ventilator-induced lung injury, blood gas analysis was performed using arterial blood. A multiplex western blot was done to assess signaling proteins. Muscimol and Bicuculline inhibited neutrophil influx in the bronchoalveolar lavage but did not change neutrophil activation. Both altered surface expression of adhesion molecules on neutrophils and reduced release of interleukin-6 (IL-6). The increased α1 subunit expression on lung epithelium and endothelium after inflammation was abolished by Muscimol and Bicuculline. In GABAα1-knock-in mice the protective effects of both agents were no longer observed. Only Muscimol lowered protein extravasation, improved blood gas analysis and lung function. A multiplex assay ascribed these anti-inflammatory effects to the influence of the IL-6 and phosphoinositide 3-kinase signaling pathways. In conclusion, Muscimol and Bicuculline exert various protective effects in two murine models of acute pulmonary inflammation. The multiple effects of Muscimol were linked to the inhibition of the proinflammatory signaling pathways IL-6 and PI3K.

Regulation of Vascular Endothelial Growth Factor Signaling by Nicotine in a Manner Dependent on Acetylcholine-and/or β-Adrenergic-Receptors in Human Lung Cancer Cells

Simple Summary

Nicotine, a highly addictive component in cigarette smoke, facilitates tumorigenesis and the accelerated development of non-small cell lung cancer (NSCLC), which is known to account for ~80% of all lung cancer cases. This study sheds light on how the nicotine treatment of NSCLC cells regulates vascular endothelial growth factor (VEGF) signaling, known to be important in the progression of vascular disease and cancer, by acting through nicotinic acetylcholine receptors and by leading to the activation of β-adrenergic receptors through increased levels of the stress neurotransmitters, norepinephrine/noradrenaline, and epinephrine/adrenaline. Nicotine-induced activation of VEGF promoted the function of proteins involved in increased cell survival and suppressed the function of a crucial tumor suppressor, blocking cell death. This work expands our scientific knowledge of mechanisms employed by nicotine in regulating VEGF signaling in a manner dependent on the acetylcholine and/or β-adrenergic receptors, leading to lung cancer cell survival, and also provides significant insights into novel future therapeutic strategies to combat lung cancer.

Abstract

In addition to binding to nicotinic acetylcholine receptors (nAChRs), nicotine is known to regulate the β-adrenergic receptors (β-ARs) promoting oncogenic signaling. Using A549 (p53 wild-type) and H1299 (p53-null) lung cancer cells, we show that nicotine treatment led to: increased adrenaline/noradrenaline levels, an effect blocked by treatment with the α7nAChR inhibitor (α-BTX) but not by the β-blocker (propranolol) or the α4β2nAChR antagonist (DhβE); decreased GABA levels in A549 and H1299 cell media, an effect blocked by treatment with DhβE; increased VEGF levels and PI3K/AKT activities, an effect diminished by cell co-treatment with α-BTX, propranolol, and/or DhβE; and inhibited p53 activity in A549 cells, that was reversed, upon cell co-treatment with α-BTX, propranolol, and/or DhβE or by VEGF immunodepletion. VEGF levels increased upon cell treatment with nicotine, adrenaline/noradrenaline, and decreased with GABA treatment. On the other hand, the p53 activity decreased in A549 cells treated with nicotine, adrenaline/noradrenaline and increased upon cell incubation with GABA. Knockdown of p53 led to increased VEGF levels in the media of A549 cells. The addition of anti-VEGF antibodies to A549 and H1299 cells decreased cell viability and increased apoptosis; blocked the activities of PI3K, AKT, and NFκB in the absence or presence of nicotine; and resulted in increased p53 activation in A549 cells. We conclude that VEGF can be upregulated via α7nAChR and/or β-ARs and downregulated via GABA and/or p53 in response to the nicotine treatment of NSCLC cells.

The GABA and GABA-Receptor System in Inflammation, Anti-Tumor Immune Responses, and COVID-19

GABA and GABA_A-receptors (GABA_A-Rs) play major roles in neurodevelopment and neurotransmission in the central nervous system (CNS). There has been a growing appreciation that GABA_A-Rs are also present on most immune cells. Studies in the fields of autoimmune disease, cancer, parasitology, and virology have observed that GABA-R ligands have anti-inflammatory actions on T cells and antigen-presenting cells (APCs), while also enhancing regulatory T cell (Treg) responses and shifting APCs toward anti-inflammatory phenotypes. These actions have enabled GABA_A-R ligands to ameliorate autoimmune diseases, such as type 1 diabetes (T1D), multiple sclerosis (MS), and rheumatoid arthritis, as well as type 2 diabetes (T2D)-associated inflammation in preclinical models. Conversely, antagonism of GABA_A-R activity promotes the pro-inflammatory responses of T cells and APCs, enhancing anti-tumor responses and reducing tumor burden in models of solid tumors. Lung epithelial cells also express GABA-Rs, whose activation helps maintain fluid homeostasis and promote recovery from injury. The ability of GABA_A-R agonists to limit both excessive immune responses and lung epithelial cell injury may underlie recent findings that GABA_A-R agonists reduce the severity of disease in mice infected with highly lethal coronaviruses (SARS-CoV-2 and MHV-1). These observations suggest that GABA_A-R agonists may provide off-the-shelf therapies for COVID-19 caused by new SARS-CoV-2 variants, as well as novel beta-coronaviruses, which evade vaccine-induced immune responses and antiviral medications. We review these findings and further advance the notions that (1) immune cells possess GABA_A-Rs to limit inflammation in the CNS, and (2) this natural "braking system" on inflammatory responses may be pharmacologically engaged to slow the progression of autoimmune diseases, reduce the severity of COVID-19, and perhaps limit neuroinflammation associated with long COVID.

A GABA-receptor agonist reduces pneumonitis severity, viral load, and death rate in SARS-CoV-2-infected mice

Gamma-aminobutyric acid (GABA) and GABA-receptors (GABA-Rs) form a major neurotransmitter system in the brain. GABA-Rs are also expressed by 1) cells of the innate and adaptive immune system and act to inhibit their inflammatory activities, and 2) lung epithelial cells and GABA-R agonists/potentiators have been observed to limit acute lung injuries. These biological properties suggest that GABA-R agonists may have potential for treating COVID-19. We previously reported that GABA-R agonist treatments protected mice from severe disease induced by infection with a lethal mouse coronavirus (MHV-1). Because MHV-1 targets different cellular receptors and is biologically distinct from SARS-CoV-2, we sought to test GABA therapy in K18-hACE2 mice which develop severe pneumonitis with high lethality following SARS-CoV-2 infection. We observed that GABA treatment initiated immediately after SARS-CoV-2 infection, or 2 days later near the peak of lung viral load, reduced pneumonitis severity and death rates in K18-hACE2 mice. GABA-treated mice had reduced lung viral loads and displayed shifts in their serum cytokine/chemokine levels that are associated with better outcomes in COVID-19 patients. Thus, GABA-R activation had multiple effects that are also desirable for the treatment of COVID-19. The protective effects of GABA against two very different beta coronaviruses (SARS-CoV-2 and MHV-1) suggest that it may provide a generalizable off-the-shelf therapy to help treat diseases induced by new SARS-CoV-2 variants and novel coronaviruses that evade immune responses and antiviral medications. GABA is inexpensive, safe for human use, and stable at room temperature, making it an attractive candidate for testing in clinical trials. We also discuss the potential of GABA-R agonists for limiting COVID-19-associated neuroinflammation.

Pathogenesis of ventilator-induced lung injury: metabolomics analysis of the lung and plasma

INTRODUCTION

Nowadays,the mechanical ventilation (MV) aims to rest the respiratory muscles while providing adequate gas exchange, and it has been a part of basic life support during general anesthesia as well as in critically ill patients with and without respiratory failure. However, MV itself has the potential to cause or worsen lung injury, which is also known as ventilator-induced lung injury (VILI). Thus, the early diagnosis of VILI is of great importance for the prevention and treatment of VILI.

OBJECTIVE

This study aimed to investigate the metabolomes in the lung and plasma of mice receiving mechanical ventilation (MV).

METHODS

Healthy mice were randomly assigned into control group; (2) high volume tidal (HV) group (30 ml/kg); (3) low volume tidal (LV) group (6 ml/kg). After ventilation for 4 h, mice were sacrificed and the lung tissue and plasma were collected. The lung and plasma were processed for the metabolomics analysis. We also performed histopathological examination on the lung tissue.

RESULTS

We detected moderate inflammatory damage with alveolar septal thickening in the HV group compared with the normal and LV groups.The metabolomics analysis results showed MV altered the metabolism which was characterized by the dysregulation of γ-amino butyric acid (GABA) system and urea cycle (desregulations in plasma and lung guanidinosuccinic acid, argininosuccinic acid, succinic acid semialdehyde and lung GABA ), Disturbance of citric acid cycle (CAC) (increased plasma glutamine and lung phosphoenol pyruvate) and redox imbalance (desregulations in plasma and/or lung ascorbic acid, chenodeoxycholic acid, uric acid, oleic acid, stearidonic acid, palmitoleic acid and docosahexaenoic acid). Moreover, the lung and plasma metabolomes were also significantly different between LV and HV groups.

CONCLUSIONS

Some lung and plasma metabolites related to the GABA system and urea cycle, citric acid cycle and redox balance were significantly altered, and they may be employed for the evaluation of VILI and serve as targets in the treatment of VILI.

Disturbed lipid and amino acid metabolisms in COVID-19 patients

The Coronavirus disease 2019 (COVID-19) pandemic is overwhelming the healthcare systems. Identification of systemic reactions underlying COVID-19 will lead to new biomarkers and therapeutic targets for monitoring and early intervention in this viral infection. We performed targeted metabolomics covering up to 630 metabolites within several key metabolic pathways in plasma samples of 20 hospitalized COVID-19 patients and 37 matched controls. Plasma metabolic signatures specifically differentiated severe COVID-19 from control patients. The identified metabolic signatures indicated distinct alterations in both lipid and amino acid metabolisms in COVID-19 compared to control patient plasma. Systems biology-based analyses identified sphingolipid, tryptophan, tyrosine, glutamine, arginine, and arachidonic acid metabolism as mostly impacted pathways in COVID-19 patients. Notably, gamma-aminobutyric acid (GABA) was significantly reduced in COVID-19 patients and GABA plasma levels allowed for stratification of COVID-19 patients with high sensitivity and specificity. The data reveal large metabolic disturbances in COVID-19 patients and suggest use of GABA as potential biomarker and therapeutic target for the infection.

α6-Containing GABAA Receptors: Functional Roles and Therapeutic Potentials

GABAA receptors containing the α6 subunit are highly expressed in cerebellar granule cells and less abundantly in many other neuronal and peripheral tissues. Here, we for the first time summarize their importance for the functions of the cerebellum and the nervous system. The cerebellum is not only involved in motor control but also in cognitive, emotional, and social behaviors. α6βγ2 GABAA receptors located at cerebellar Golgi cell/granule cell synapses enhance the precision of inputs required for cerebellar timing of motor activity and are thus involved in cognitive processing and adequate responses to our environment. Extrasynaptic α6βδ GABAA receptors regulate the amount of information entering the cerebellum by their tonic inhibition of granule cells, and their optimal functioning enhances input filtering or contrast. The complex roles of the cerebellum in multiple brain functions can be compromised by genetic or neurodevelopmental causes that lead to a hypofunction of cerebellar α6-containing GABAA receptors. Animal models mimicking neuropsychiatric phenotypes suggest that compounds selectively activating or positively modulating cerebellar α6-containing GABAA receptors can alleviate essential tremor and motor disturbances in Angelman and Down syndrome as well as impaired prepulse inhibition in neuropsychiatric disorders and reduce migraine and trigeminal-related pain via α6-containing GABAA receptors in trigeminal ganglia. Genetic studies in humans suggest an association of the human GABAA receptor α6 subunit gene with stress-associated disorders. Animal studies support this conclusion. Neuroimaging and post-mortem studies in humans further support an involvement of α6-containing GABAA receptors in various neuropsychiatric disorders, pointing to a broad therapeutic potential of drugs modulating α6-containing GABAA receptors. SIGNIFICANCE STATEMENT: α6-Containing GABAA receptors are abundantly expressed in cerebellar granule cells, but their pathophysiological roles are widely unknown, and they are thus out of the mainstream of GABAA receptor research. Anatomical and electrophysiological evidence indicates that these receptors have a crucial function in neuronal circuits of the cerebellum and the nervous system, and experimental, genetic, post-mortem, and pharmacological studies indicate that selective modulation of these receptors offers therapeutic prospects for a variety of neuropsychiatric disorders and for stress and its consequences.

Mapping the metabolomic and lipidomic changes in the Bleomycin model of pulmonary fibrosis in young and aged mice

Alterations in metabolic pathways were recently recognized as potential underlying drivers of idiopathic pulmonary fibrosis (IPF), translating into novel therapeutic targets. However, knowledge of metabolic and lipid regulation in fibrotic lungs is limited. To comprehensively characterize metabolic perturbations in the bleomycin mouse model of IPF, we analyzed the metabolome and lipidome by mass spectrometry. We identified increased tissue turnover and repair, evident by enhanced breakdown of proteins, nucleic acids and lipids and extracellular matrix turnover. Energy production was upregulated, including glycolysis, the tricarboxylic acid cycle, glutaminolysis, lactate production and fatty acid oxidation. Higher eicosanoid synthesis indicated inflammatory processes. Because the risk of IPF increases with age, we investigated how age influences metabolomic and lipidomic changes in the bleomycin-induced pulmonary fibrosis model. Surprisingly, except for cytidine, we did not detect any significantly differential metabolites or lipids between old and young bleomycin-treated lungs. Together, we identified metabolomic and lipidomic changes in fibrosis that reflect higher energy demand, proliferation, tissue remodeling, collagen deposition and inflammation, which might serve to improve diagnostic and therapeutic options for fibrotic lung diseases in the future.

Editor's choice: Using bleomycin-induced lung injury as a mouse model for idiopathic pulmonary fibrosis, this study identifies metabolomic and lipidomic changes in fibrosis reflecting higher energy demand, proliferation, tissue remodeling, collagen deposition and inflammation.

Simvastatin attenuates acute lung injury by activation of A2B adenosine receptor

To explore the protective mechanism of simvastatin in acute lung injury (ALI), the lipopolysaccharide (LPS) induced (5 mg/kg) ALI rat model was used to examine the effects of simvastatin. Following simvastatin treatment, the histopathological evaluation of lung tissues was made using hematoxylin and eosin (H&E) staining. Also, myeloperoxidase (MPO) activity and the levels of tumor necrosis factor-alpha (TNF-α), interleukin-1 beta (IL-1β), and IL-10 were determined by ELISA. Blood gas analyses of arterial blood samples were performed to assess the pulmonary gas exchange. Moreover, the neutrophil count and total protein content were determined in the bronchoalveolar lavage (BAL) fluid. The ratio of wet lung to dry lung (W/D) and the alveolar fluid clearance (AFC) were calculated to estimate the severity of edema. Lastly, the levels of A2BAR, CFTR, claudin4, and claudin18 were also measured by qRT-PCR and Western blotting. Simvastatin treatment, in a dose-related manner, markedly improved the lung histological injury and decreased the levels of TNF-α, IL-1β, and increased IL-10 in LPS induced ALI. Also, pulmonary neutrophil count was alleviated. Besides, a decreased ratio of W/D lung also confirmed the simvastatin intervention. Notably, simvastatin reduced the levels of A2BAR, CFTR, and claudin18 but upregulated claudin4 in lung tissues. Additionally, treatment with PSB1115, an antagonist of A2BAR, countered the protective effect of simvastatin in ALI. Our study demonstrates that simvastatin has a protective effect against LPS-induced ALI by activating A2BAR and should be exploited as a novel therapeutic target for the treatment of ALI.

DNA methylation in chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD), a complex disease with polygenetic tendency, is one of the most important health problems in the world. Recently, in the study of the pathogenesis of the COPD, epigenetic changes caused by environmental factors, such as DNA methylation, started to attract more attention than genetic factors. In this review, we discuss the main features of DNA methylation, such as DNA methyltransferases and the methylation sites that modulate the DNA methylation level, and their roles in COPD progression. Finally, to promote new ideas for the prevention and treatment of COPD, we focus on the potential of DNA methylation as a COPD therapeutic target.

GABAA-Receptor Agonists Limit Pneumonitis and Death in Murine Coronavirus-Infected Mice

There is an urgent need for new approaches to limit the severity of coronavirus infections. Many cells of the immune system express receptors for the neurotransmitter γ-aminobutyric acid (GABA), and GABA-receptor (GABA-R) agonists have anti-inflammatory effects. Lung epithelial cells also express GABA-Rs, and GABA-R modulators have been shown to limit acute lung injuries. There is currently, however, no information on whether GABA-R agonists might impact the course of a viral infection. Here, we assessed whether clinically applicable GABA-R agonists could be repurposed for the treatment of a lethal coronavirus (murine hepatitis virus 1, MHV-1) infection in mice. We found that oral GABA administration before, or after the appearance of symptoms, very effectively limited MHV-1-induced pneumonitis, severe illness, and death. GABA treatment also reduced viral load in the lungs, suggesting that GABA-Rs may provide a new druggable target to limit coronavirus replication. Treatment with the GABA_A-R-specific agonist homotaurine, but not the GABA_B-R-specific agonist baclofen, significantly reduced the severity of pneumonitis and death rates in MHV-1-infected mice, indicating that the therapeutic effects were mediated primarily through GABA_A-Rs. Since GABA and homotaurine are safe for human consumption, they are promising candidates to help treat coronavirus infections.

The Emerging Roles of π Subunit-Containing GABAA Receptors in Different Cancers

Cancer is one of the leading causes of death in both developed and developing countries. Due to its heterogenous nature, it occurs in various regions of the body and often goes undetected until later stages of disease progression. Feasible treatment options are limited because of the invasive nature of cancer and often result in detrimental side-effects and poor survival rates. Therefore, recent studies have attempted to identify aberrant expression levels of previously undiscovered proteins in cancer, with the hope of developing better diagnostic tools and pharmaceutical options. One class of such targets is the π-subunit-containing γ-aminobutyric acid type A receptors. Although these receptors were discovered more than 20 years ago, there is limited information available. They possess atypical functional properties and are expressed in several non-neuronal tissues. Prior studies have highlighted the role of these receptors in the female reproductive system. New research focusing on the higher expression levels of these receptors in ovarian, breast, gastric, cervical, and pancreatic cancers, their physiological function in healthy individuals, and their pro-tumorigenic effects in these cancer types is reviewed here.

GABA administration prevents severe illness and death following coronavirus infection in mice

There is an urgent need for new treatments to prevent and ameliorate severe illness and death induced by SARS-CoV-2 infection in COVID-19 patients. The coronavirus mouse hepatitis virus (MHV)-1 causes pneumonitis in mice which shares many pathological characteristics with human SARS-CoV infection. Previous studies have shown that the amino acid gamma-aminobutyric acid (GABA) has anti-inflammatory effects. We tested whether oral treatment with GABA could modulate the MHV-1 induced pneumonitis in susceptible A/J mice. As expected, MHV-1-inoculated control mice became severely ill (as measured by weight loss, clinical score, and the ratio of lung weight to body weight) and >60% of them succumbed to the infection. In contrast, mice that received GABA immediately after MHV-1 inoculation became only mildly ill and all of them recovered. When GABA treatment was initiated after the appearance of illness (3 days post-MHV-1 infection), we again observed that GABA treatment significantly reduced the severity of illness and greatly increased the frequency of recovery. Therefore, the engagement of GABA receptors (GABA-Rs) prevented the MHV-1 infection-induced severe pneumonitis and death in mice. Given that GABA-R agonists, like GABA and homotaurine, are safe for human consumption, stable, inexpensive, and available worldwide, they are promising candidates to help prevent severe illness stemming from SARS-CoV-2 infection and other coronavirus strains.

Pulmonary Neuroendocrine Cells Secrete γ-Aminobutyric Acid to Induce Goblet Cell Hyperplasia in Primate Models

Mucus overproduction is a major contributor to morbidity and mortality in asthma. Mucus overproduction is induced by orchestrated actions of multiple factors that include inflammatory cytokines and γ-aminobutyric acid (GABA). GABA is produced only by pulmonary neuroendocrine cells (PNECs) in the mouse lung. Recent studies in a neonatal mouse model of allergic inflammation have shown that PNECs play an essential role in mucus overproduction by GABA hypersecretion. Whether PNECs mediate dysregulated GABA signaling for mucus overproduction in asthma is unknown. In this study, we characterized the cellular source of GABA in the lungs of nonhuman primates and humans and assessed GABA secretion and signaling in primate disease models. We found that like in mice, PNECs were the major source of GABA in primate lungs. In addition, an infant nonhuman primate model of asthma exhibited an increase in GABA secretion. Furthermore, subjects with asthma had elevated levels of expression of a subset of GABA type α (GABAα) and type β (GABAβ) receptors in airway epithelium compared with those of healthy control subjects. Last, employing a normal human bronchial epithelial cell model of preinduced mucus overproduction, we showed pharmaceutical blockade of GABAα and GABAβ receptor signaling reversed the effect of IL-13 on MUC5AC gene expression and goblet cell proliferation. Together, our data demonstrate an evolutionarily conserved intraepithelial GABA signaling that, in concert with IL-13, plays an essential role in mucus overproduction. Our findings may offer new strategies to ameliorate mucus overproduction in patients with asthma by targeting PNEC secretion and GABA signaling.

Propofol reduces acute lung injury by up-regulating gamma-aminobutyric acid type a receptors

BACKGROUND

We used a two-hit lung injury rat model that involves mechanical ventilation (MV) following lipopolysaccharide exposure to investigate the effects of propofol on the expression of GABA_A receptors (GABA_AR) and cytokine responses, and we then determined the specific effects of GABA on cytokine responses in vitro in alveolar epithelial cells (AECs).

METHODS

Forty-eight adult male Wister rats were equally and randomly divided into the following 4 groups (n = 12) using a random number table: sham group, sham+propofol group, lipopolysaccharide (LPS) + VILI group, and LPS + VILI + propofol group. All animals were anesthetized, and the animals received a 3.75 mg/kg intratracheal instillation of endotoxins or phosphate-buffered saline (PBS) as the control, as described previously. After 30 min, rats were ventilated for 5 h in a volume-controlled ventilation mode. In the LPS + VILI group, animals were ventilated with a tidal volume (Vt) of 22 ml/kg and zero positive end-expiratory pressure (PEEP) at a respiratory rate of 16-18 breaths/min, whereas control (sham) rats were ventilated with a Vt of 6 ml/kg and PEEP of 5 cmH₂O at a rate of 45-55 breaths/min. The FiO₂ remained constant as 0.4, propofol was administered intravenously in the LPS + VILI + propofol and sham + propofol groups at a rate of 10 mg·kg^-1·h^-1 while normal saline at the same rate was intravenously administered in the LPS + VILI and sham groups during the entire mechanical ventilation period. Five hours after mechanical ventilation, the rats were killed. Survival rates, histopathology, concentrations of inflammatory mediators in bronchoalveolar lavage fluid (BALF), wet weight/dry weight (W/D) ratio of the lung, myeloperoxidase (MPO) activity in lung tissues, and expression of GAD and GABA_AR by immunohistochemical detection and Western blotting were assessed. Then, human type II-like alveolar epithelial cells (A549 cells) were cultured to full confluence and incubated with GABA (100 nM) alone, picrotoxin alone, a GABA_AR antagonist (PTX, 50 nM), or GABA + PTX for 10 min, followed by stimulation with LPS (control) at 100 ng/ml for 4 h. The concentrations of IL-1β, IL-2, IL-8, and IL-10 were then measured.

RESULTS

Administration of propofol in a two-hit lung injury rat model can increase survival rates and the expression of GAD and GABA_AR (P < .05). The administration of propofol can attenuate the release of pro-inflammatory cytokines both in vivo and in vitro, and the administration of propofol can attenuate histopathological changes, the W/D ratio, and MPO activity (P < .05).

CONCLUSIONS

In this study, we found that the administration of propofol improved lung function, alleviated lung injury, and up-regulated the GAD and GABA_AR expressions in a two-hit model of acute lung injury (ALI) characterized by intratracheal instillation of an endotoxin and prolonged MV. Therefore, the protective effects of propofol may be associated with the up-regulation of GABA_A receptors in AECs.

Jejunal Metabolic Responses to Escherichia coli Infection in Piglets

This study aimed to investigate the jejunal metabolic variations in enterotoxigenic Escherichia coli (ETEC)-infected piglets. Piglets were infected with 1 × 10¹⁰ CFUs (colony-forming units) of ETEC W25K and assigned into diarrheal, recovered, control, and resistant groups. Jejunal samples were harvested at day 6 and metabolic profiles were analyzed via gas chromatography coupled to time-of-flight mass spectrometry (GC/TOFMS). The results showed that 33 metabolites in the jejunum were identified in ETEC-induced diarrhea, including amino acids, fatty acids, sugars, and organic acids. Compared with the control, resistant, and recovered piglets, diarrheal piglets showed higher concentrations of 4-aminobutyric acid (GABA) and glycine in the jejunum. Compared with the control and resistant piglets, six metabolites were markedly decreased in diarrheal piglets, including ornithine, asparagine, glutamine, citric acid, citrulline, and lysine. Collectively, this study provides insights into jejunal metabolic response to ETEC infection and ETEC induced diarrhea in piglets.

Ion channels of the lung and their role in disease pathogenesis

Maintenance of normal epithelial ion and water transport in the lungs includes providing a thin layer of surface liquid that coats the conducting airways. This airway surface liquid is critical for normal lung function in a number of ways but, perhaps most importantly, is required for normal mucociliary clearance and bacterial removal. Preservation of the appropriate level of hydration, pH, and viscosity for the airway surface liquid requires the proper regulation and function of a battery of different types of ion channels and transporters. Here we discuss how alterations in ion channel/transporter function often lead to lung pathologies.

DNA methylation profiling in peripheral lung tissues of smokers and patients with COPD

BACKGROUND

Epigenetics changes have been shown to be affected by cigarette smoking. Cigarette smoke (CS)-mediated DNA methylation can potentially affect several cellular and pathophysiological processes, acute exacerbations, and comorbidity in the lungs of patients with chronic obstructive pulmonary disease (COPD). We sought to determine whether genome-wide lung DNA methylation profiles of smokers and patients with COPD were significantly different from non-smokers. We isolated DNA from parenchymal lung tissues of patients including eight lifelong non-smokers, eight current smokers, and eight patients with COPD and analyzed the samples using Illumina's Infinium HumanMethylation450 BeadChip.

RESULTS

Our data revealed that the differentially methylated genes were related to top canonical pathways (e.g., G beta gamma signaling, mechanisms of cancer, and nNOS signaling in neurons), disease and disorders (organismal injury and abnormalities, cancer, and respiratory disease), and molecular and cellular functions (cell death and survival, cellular assembly and organization, cellular function and maintenance) in patients with COPD. The genome-wide DNA methylation analysis identified suggestive genes, such as NOS1AP, TNFAIP2, BID, GABRB1, ATXN7, and THOC7 with DNA methylation changes in COPD lung tissues that were further validated by pyrosequencing. Pyrosequencing validation confirmed hyper-methylation in smokers and patients with COPD as compared to non-smokers. However, we did not detect significant differences in DNA methylation for TNFAIP2, ATXN7, and THOC7 genes in smokers and COPD groups despite the changes observed in the genome-wide analysis.

CONCLUSIONS

Our study suggests that DNA methylation in suggestive genes, such as NOS1AP, BID, and GABRB1 may be used as epigenetic signatures in smokers and patients with COPD if the same is validated in a larger cohort. Future studies are required to correlate DNA methylation status with transcriptomics of selective genes identified in this study and elucidate their role and involvement in the progression of COPD and its exacerbations.

Differential DNA methylation marks and gene comethylation of COPD in African-Americans with COPD exacerbations

BACKGROUND

Chronic obstructive pulmonary disease (COPD) is the third-leading cause of death worldwide. Identifying COPD-associated DNA methylation marks in African-Americans may contribute to our understanding of racial disparities in COPD susceptibility. We determined differentially methylated genes and co-methylation network modules associated with COPD in African-Americans recruited during exacerbations of COPD and smoking controls from the Pennsylvania Study of Chronic Obstructive Pulmonary Exacerbations (PA-SCOPE) cohort.

METHODS

We assessed DNA methylation from whole blood samples in 362 African-American smokers in the PA-SCOPE cohort using the Illumina Infinium HumanMethylation27 BeadChip Array. Final analysis included 19302 CpG probes annotated to the nearest gene transcript after quality control. We tested methylation associations with COPD case-control status using mixed linear models. Weighted gene comethylation networks were constructed using weighted gene coexpression network analysis (WGCNA) and network modules were analyzed for association with COPD.

RESULTS

There were five differentially methylated CpG probes significantly associated with COPD among African-Americans at an FDR less than 5 %, and seven additional probes that approached significance at an FDR less than 10 %. The top ranked gene association was MAML1, which has been shown to affect NOTCH-dependent angiogenesis in murine lung. Network modeling yielded the "yellow" and "blue" comethylation modules which were significantly associated with COPD (p-value 4 × 10-10 and 4 × 10-9, respectively). The yellow module was enriched for gene sets related to inflammatory pathways known to be relevant to COPD. The blue module contained the top ranked genes in the concurrent differential methylation analysis (FXYD1/LGI4, gene significance p-value 1.2 × 10-26; MAML1, p-value 2.0 × 10-26; CD72, p-value 2.1 × 10-25; and LPO, p-value 7.2 × 10-25), and was significantly associated with lung development processes in Gene Ontology gene-set enrichment analysis.

CONCLUSION

We identified 12 differentially methylated CpG sites associated with COPD that mapped to biologically plausible genes. Network module comethylation patterns have identified candidate genes that may be contributing to racial differences in COPD susceptibility and severity. COPD-associated comethylation modules contained genes previously associated with lung disease and inflammation and recapitulated known COPD-associated genes. The genes implicated by differential methylation and WGCNA analysis may provide mechanistic targets contributing to COPD susceptibility, exacerbations, and outcomes among African-Americans.

TRIAL REGISTRATION

Trial Registration: NCT00774176 , Registry: ClinicalTrials.gov, URL: www.clinicaltrials.gov , Date of Enrollment of First Participant: June 2004, Date Registered: 04 January 2008 (retrospectively registered).

Luteolin Attenuates Airway Mucus Overproduction via Inhibition of the GABAergic System

Airway mucus overproduction is one of the most common symptoms of asthma that causes severe clinical outcomes in patients. Despite the effectiveness of general asthma therapies, specific treatments that prevent mucus overproduction in asthma patients remain lacking. Recent studies have found that activation of GABAA receptors (GABAAR) is important for promoting mucus oversecretion in lung airway epithelia. Here, we report that luteolin, a natural flavonoid compound, suppresses mucus overproduction by functionally inhibiting the GABAergic system. This hypothesis was investigated by testing the effects of luteolin on goblet cell hyperplasia, excessive mucus secretion, and GABAergic transmission using histological and electrophysiological approaches. Our results showed that 10 mg/kg luteolin significantly decreased the number of goblet cells in the lung tissue and inhibited mucus overproduction in an in vivo asthma model induced by ovalbumin (OVA) in mice. Patch-clamp recordings showed that luteolin inhibited GABAAR-mediated currents in A549 cells. Furthermore, the inhibitory effects of luteolin on OVA-induced goblet cell hyperplasia and mucus overproduction were occluded by the GABAAR antagonist picrotoxin. In conclusion, our observations indicate that luteolin effectively attenuates mucus overproduction at least partially by inhibiting GABAARs, suggesting the potential for therapeutic administration of luteolin in the treatment of mucus overproduction in asthma patients.

Mechanism of action of novel lung edema therapeutic AP301 by activation of the epithelial sodium channel

AP301 [Cyclo(CGQRETPEGAEAKPWYC)], a cyclic peptide comprising the human tumor necrosis factor lectin-like domain (TIP domain) sequence, is currently being developed as a treatment for lung edema and has been shown to reduce extravascular lung water and improve lung function in mouse, rat, and pig models. The current paradigm for liquid homeostasis in the adult mammalian lung is that passive apical uptake of sodium via the amiloride-sensitive epithelial Na⁺ channel (ENaC) and nonselective cyclic-nucleotide-gated cation channels creates the major driving force for reabsorption of water through the alveolar epithelium in addition to other ion channels such as potassium and chloride channels. AP301 can increase amiloride-sensitive current in A549 cells as well as in freshly isolated type II alveolar epithelial cells from different species. ENaC is expressed endogenously in all of these cell types. Consequently, this study was undertaken to determine whether ENaC is the specific target of AP301. The effect of AP301 in A549 cells as well as in human embryonic kidney cells and Chinese hamster ovary cells heterologously expressing human ENaC subunits (α, β, γ, and δ) was measured in patch clamp experiments. The congener TIP peptide AP318 [Cyclo(4-aminobutanoic acid-GQRETPEGAEAKPWYD)] activated ENaC by increasing single-channel open probability. AP301 increased current in proteolytically activated (cleaved) but not near-silent (uncleaved) ENaC in a reversible manner. αβγ- or δβγ-ENaC coexpression was required for maximal activity. No increase in current was observed after deglycosylation of extracellular domains of ENaC. Thus, our data suggest that the specific interaction of AP301 with both endogenously and heterologously expressed ENaC requires precedent binding to glycosylated extracellular loop(s).

Isoflurane regulates atypical type-A γ-aminobutyric acid receptors in alveolar type II epithelial cells

BACKGROUND

Volatile anesthetics act primarily through upregulating the activity of γ-aminobutyric acid type A (GABAA) receptors. They also exhibit antiinflammatory actions in the lung. Rodent alveolar type II (ATII) epithelial cells express GABAA receptors and the inflammatory factor cyclooxygenase-2 (COX-2). The goal of this study was to determine whether human ATII cells also express GABAA receptors and whether volatile anesthetics upregulate GABAA receptor activity, thereby reducing the expression of COX-2 in ATII cells.

METHODS

The expression of GABAA receptor subunits and COX-2 in ATII cells of human lung tissue and in the human ATII cell line A549 was studied with immunostaining and immunoblot analyses. Patch clamp recordings were used to study the functional and pharmacological properties of GABAA receptors in cultured A549 cells.

RESULTS

ATII cells in human lungs and cultured A549 cells expressed GABAA receptor subunits and COX-2. GABA induced currents in A549 cells, with half-maximal effective concentration of 2.5 µM. Isoflurane (0.1-250 µM) enhanced the GABA currents, which were partially inhibited by bicuculline. Treating A549 cells with muscimol or with isoflurane (250 µM) reduced the expression of COX-2, an effect that was attenuated by cotreatment with bicuculline.

CONCLUSIONS

GABAA receptors expressed by human ATII cells differ pharmacologically from those in neurons, exhibiting a higher affinity for GABA and lower sensitivity to bicuculline. Clinically relevant concentrations of isoflurane increased the activity of GABAA receptors and reduced the expression of COX-2 in ATII cells. These findings reveal a novel mechanism that could contribute to the antiinflammatory effect of isoflurane in the human lung.

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

Introduction

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

Methods

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

Results

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

Conclusions

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

Determination of GABA(Aα1) and GABA (B1) receptor subunits expression in tissues of gilts during the late gestation

GABA(Aα1) and GABA(B1) receptor subunits are responsible for most behavioral, physiological and pharmacological effects of GABA receptors. We investigated the expression of GABA(Aα1) and GABA(B1) receptor subunits in different tissues of gilts during late pregnancy in hot summer. The mRNA abundance of GABA(Aα1) receptor subunit in different tissues of gilts at d 90 and d 110 of gestation was as follows: d 90: brain > lung > liver > ovary > spleen > kidney > heart; d 110: brain > lung > spleen > liver > ovary > kidney > heart. And, the mRNA abundance of GABA(B1) receptor subunit was as follows: d 90: spleen > lung > brain > kidney > ovary > liver > heart; d 110: spleen > lung > kidney > brain > ovary > liver > heart. The results in this trial indicated that the GABA(Aα1) receptor subunit was abundantly expressed in brain, while GABA(B1) receptor subunit was abundant in spleen and lung of gilts during late gestation. There were no gestation stage-dependent effects on GABA(Aα1) and GABA(B1) receptor subunits expression in all tissues.

A novel role of intestine epithelial GABAergic signaling in regulating intestinal fluid secretion

γ-Aminobutyric acid (GABA) is the primary inhibitory neurotransmitter in the central nervous system, and it is produced via the enzymatic activity of glutamic acid decarboxylase (GAD). GABA generates fast biological signaling through type A receptors (GABA(A)R), an anionic channel. Intriguingly, GABA is found in the jejunum epithelium of rats. The present study intended to determine whether a functional GABA signaling system exists in the intestinal epithelium and if so whether the GABA signaling regulates intestinal epithelial functions. RT-PCR, Western blot, and immunohistochemical assays of small intestinal tissues of various species were performed to determine the expression of GABA-signaling proteins in intestinal epithelial cells. Perforated patch-clamp recording was used to measure GABA-induced transmembrane current in the small intestine epithelial cell line IEC-18. The fluid weight-to-intestine length ratio was measured in mice that were treated with GABA(A)R agonist and antagonist. The effect of GABA(A)R antagonist on allergic diarrhea was examined using a mouse model. GABA, GAD, and GABA(A)R subunits were identified in small intestine epithelial cells of mice, rats, pigs, and humans. GABA(A)R agonist induced an inward current and depolarized IEC-18. Both GABA and the GABA(A)R agonist muscimol increased intestinal fluid secretion of rats. The increased intestinal secretion was largely decreased by the GABA(A)R antagonist picrotoxin or gabazine, but not by tetrodotoxin. The expression levels of GABA-signaling proteins were increased in the intestinal epithelium of mice that were sensitized and challenged with ovalbumin (OVA). The OVA-treated mice exhibited diarrhea, which was alleviated by oral administration of gabazine or picrotoxin. An endogenous autocrine GABAergic signaling exists in the mammalian intestinal epithelium, which upregulates intestinal fluid secretion. The intestinal GABAergic signaling becomes intensified in allergic diarrhea, and inhibition of this GABA-signal system alleviates the allergic diarrhea.

The role of Cl- in the regulation of ion and liquid transport in the intact alveolus during β-adrenergic stimulation

The epithelium of the developing lung displays an evolving liquid transport phenotype, in which Cl(-) secretion during fetal life is rapidly switched to Na(+) absorption perinatally. However, the mechanisms underlying the homeostasis of the thin layer of liquid lining the postnatal pulmonary epithelium remain elusive. In particular, it remains unclear whether the stimulated clearance of excess alveolar liquid is mediated via transepithelial Cl(-) transport. Our study is a pharmacological analysis with the aim of addressing this issue, which is of major physiological significance in cases of pulmonary oedema from any cause. We measured the rate of transepithelial liquid movement (J(v)) with (125)I-albumin, in the in situ perfused adult rat lung. Transepithelial Cl(-) transport was studied with the use of the Cl(-) channel inhibitor NPPB in the resting state and during stimulation with the β(2)-adrenergic agonist terbutaline. The study of J(v) in these conditions revealed the following findings: (1) there is net absorption of excess of alveolar liquid in the resting, unstimulated state, which is predominantly amiloride sensitive; (2) inhibition of Cl(-) transport with NPPB in the resting state results in a 1.6-fold increase in net absorption of alveolar liquid; and (3) the terbutaline-stimulated net absorption of the excess liquid is enhanced by 2.8-fold in the presence of NPPB. Our results are suggestive of the functional presence of secretory, but not absorptive, Cl(-) mechanisms and show that transepithelial Cl(-) transport is not part of the mechanism underlying lung liquid clearance in response to β-adrenergic stimulation.

Effects of anesthetic regimes on inflammatory responses in a rat model of acute lung injury

PURPOSE

Gamma-aminobutyric acid (GABA) is the major inhibitory neurotransmitter through activation of GABA receptors. Volatile anesthetics activate type-A (GABA(A)) receptors resulting in inhibition of synaptic transmission. Lung epithelial cells have been recently found to express GABA(A) receptors that exert anti-inflammatory properties. We hypothesized that the volatile anesthetic sevoflurane (SEVO) attenuates lung inflammation through activation of lung epithelial GABA(A) receptors.

METHODS

Sprague-Dawley rats were anesthetized with SEVO or ketamine/xylazine (KX). Acute lung inflammation was induced by intratracheal instillation of endotoxin, followed by mechanical ventilation for 4 h at a tidal volume of 15 mL/kg without positive end-expiratory pressure (two-hit lung injury model). To examine the specific effects of GABA, healthy human lung epithelial cells (BEAS-2B) were challenged with endotoxin in the presence and absence of GABA with and without addition of the GABA(A) receptor antagonist picrotoxin.

RESULTS

Anesthesia with SEVO improved oxygenation and reduced pulmonary cytokine responses compared to KX. This phenomenon was associated with increased expression of the π subunit of GABA(A) receptors and glutamic acid decarboxylase (GAD). The endotoxin-induced cytokine release from BEAS-2B cells was attenuated by the treatment with GABA, which was reversed by the administration of picrotoxin.

CONCLUSION

Anesthesia with SEVO suppresses pulmonary inflammation and thus protects the lung from the two-hit injury. The anti-inflammatory effect of SEVO is likely due to activation of pulmonary GABA(A) signaling pathways.

Computational prediction of MicroRNAs targeting GABA receptors and experimental verification of miR-181, miR-216 and miR-203 targets in GABA-A receptor

BACKGROUND

GABA receptors are well known as the inhibitory receptors in the central nervous system and are also found in peripheral tissues. We have previously shown that GABA receptors are involved in lung development and fluid homeostasis. However, the microRNAs that regulate GABA receptors have not yet been identified.

RESULTS

In this study, we used the online software, TargetScan and miRanda, to query the microRNAs that directly target GABA receptors and then selected some of them to verify experimentally using 3'-UTR reporter assays. Computational approaches predict many microRNA binding sites on the 3'-UTR of GABAA receptors, but not on GABAC receptors. 3'-UTR reporter assays only verified miR-181, miR-216, and miR-203 as the microRNAs that target GABA receptor α1-subunit among 10 microRNAs tested.

CONCLUSIONS

Our studies reinforce that microRNA target prediction needs to be verified experimentally. The identification of microRNAs that target GABA receptors provides a basis for further studies of post-transcriptional regulation of GABA receptors.

Ion transport by pulmonary epithelia

The lung surface of air-breathing vertebrates is formed by a continuous epithelium that is covered by a fluid layer. In the airways, this epithelium is largely pseudostratified consisting of diverse cell types such as ciliated cells, goblet cells, and undifferentiated basal cells, whereas the alveolar epithelium consists of alveolar type I and alveolar type II cells. Regulation and maintenance of the volume and viscosity of the fluid layer covering the epithelium is one of the most important functions of the epithelial barrier that forms the outer surface area of the lungs. Therefore, the epithelial cells are equipped with a wide variety of ion transport proteins, among which Na⁺, Cl⁻, and K⁺ channels have been identified to play a role in the regulation of the fluid layer. Malfunctions of pulmonary epithelial ion transport processes and, thus, impairment of the liquid balance in our lungs is associated with severe diseases, such as cystic fibrosis and pulmonary oedema. Due to the important role of pulmonary epithelial ion transport processes for proper lung function, the present paper summarizes the recent findings about composition, function, and ion transport properties of the airway epithelium as well as of the alveolar epithelium.

Purinergic P2X7 receptor regulates lung surfactant secretion in a paracrine manner

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

Role of GABA receptors in fetal lung development in rats

Fluid accumulation is critical for lung distension and normal development. The multi-subunit γ-amino butyric acid type A receptors (GABA_A) mainly act by mediating chloride ion (Cl⁻) fluxes. Since fetal lung actively secretes Cl⁻-rich fluid, we investigated the role of GABA_A receptors in fetal lung development. The physiological ligand, GABA, and its synthesizing enzyme, glutamic acid decarboxylase, were predominantly localized to saccular epithelium. To examine the effect of activating GABA_A receptors in fetal lung development in vivo, timed-pregnant rats of day 18 gestation underwent an in utero surgery for the administration of GABA_A receptor modulators into the fetuses. The fetal lungs were isolated on day 21 of gestation and analyzed for changes in fetal lung development. Fetuses injected with GABA had a significantly higher body weight and lung weight when compared to phosphate-buffered saline (control)-injected fetuses. GABA-injected fetal lungs had a higher number of saccules than the control. GABA increased the number of alveolar epithelial type II cells as indicated by surfactant protein C-positive cells. However, GABA decreased the number of α-smooth muscle actin-positive myofibroblasts, but did not affect the number of Clara cells or alveolar type I cells. GABA-mediated effects were blocked by the GABA_A receptor antagonist, bicuculline. GABA also increased cell proliferation and Cl⁻ efflux in fetal distal lung epithelial cells. In conclusion, our results indicate that GABA_A receptors accelerate fetal lung development, likely through an enhanced cell proliferation and/or fluid secretion.

Characteristics of Cl- uptake in rat alveolar type I cells

Although Cl- transport in fetal lung is important for fluid secretion and normal lung development, the role of Cl- transport in adult lung is not well understood. In physiological studies, the cystic fibrosis transmembrane regulator (CFTR) plays a role in fluid absorption in the distal air spaces of adult lung, and alveolar type II cells cultured for 5 days have the capacity to transport Cl-. Although both alveolar type I and type II cells express CFTR, it has previously not been known whether type I cells transport Cl-. We studied Cl- uptake in isolated type I cells directly, using either radioisotopic tracers or halide-sensitive fluorescent indicators. By both methods, type I cells take up Cl-. In the presence of beta-adrenergic agonist stimulation, Cl- uptake can be inhibited by CFTR antagonists. Type I cells express both the Cl-/HCO3- anion exchanger AE2 and the voltage-gated Cl- channels CLC5 and CLC2. Inhibitors of AE2 also block Cl- uptake in type I cells. Together, these results demonstrate that type I cells are capable of Cl- uptake and suggest that the effects seen in whole lung studies establishing the importance of Cl- movement in alveolar fluid clearance may be, in part, the result of Cl- transport across type I cells.

Valproate-related peripheral oedema: a manageable but probably neglected condition

Valproate-related peripheral oedema is usually regarded as a problem occurring after long-term administration of valproate. The scarcity of reports is partially responsible for the lack of a full understanding of this condition. This report describes two patients acquiring peripheral oedema after short-term use of add-on therapy with valproate. The oedema could appear and reappear quickly. Discontinuing valproate resulted in rapid improvement of this condition, and the cause-effect relationship was supported by double challenge. We also put forward a preliminary hypothesis to explain this treatable situation.

UTP regulation of ion transport in alveolar epithelial cells involves distinct mechanisms

UTP is known to regulate alveolar fluid clearance. However, the relative contribution of alveolar type I cells and type II cells to this process is unknown. In this study, we investigated the effects of UTP on ion transport in type I-like cell (AEC I) and type II-like cell (AEC II) monolayers. Luminal treatment of cell monolayers with UTP increased short-circuit current (I(sc)) of AEC II but decreased I(sc) of AEC I. The Cl(-) channel blockers NPPB and DIDS inhibited the UTP-induced changes in I(sc) (DeltaIsc) in both types of cells. Amiloride, an inhibitor of epithelial Na(+) channels (ENaC), abolished the UTP-induced DeltaI(sc) in AEC I, but not in AEC II. The general blocker of K(+) channels, BaCl(2), eliminated the UTP-induced DeltaI(sc) in AEC II, but not in AEC I. The intermediate conductance (IK(Ca)) blocker, clofilium, also blocked the UTP effect in AEC II. The signal transduction pathways mediated by UTP were the same in AEC I and AEC II. Furthermore, UTP increased Cl(-) secretion in AEC II and Cl(-) absorption in AEC I. Our results suggest that UTP induces opposite changes in I(sc) in AEC I and AEC II, likely due to the reversed Cl(-) flux and different contributions of ENaC and IK(Ca). Our results further imply a new concept that type II cells contribute to UTP-induced fluid secretion and type I cells contribute to UTP-induced fluid absorption in alveoli.

Ionotropic GABA receptor expression in the lung during development

Cl(-) transport is essential for lung development. Because gamma-aminobutyric acid (GABA) receptors allow the flow of negatively-charged Cl(-) ions across the cell membrane, we hypothesized that the expression of ionotropic GABA receptors are regulated in the lungs during development. We identified 17 GABA receptor subunits in the lungs by real-time PCR. These subunits were categorized into four groups: Group 1 had high mRNA expression during fetal stages and low in adults; Group 2 had steady expression to adult stages with a slight up-regulation at birth; Group 3 showed an increasing expression from fetal to adult lungs; and Group 4 displayed irregular mRNA fluctuations. The protein levels of selected subunits were also determined by Western blots and some subunits had protein levels that corresponded to mRNA levels. Further studied subunits were primarily localized in epithelial cells in the developing lung with differential mRNA expression between isolated cells and whole lung tissues. Our results add to the knowledge of GABA receptor expression in the lung during development.

Novel and extensive aspects of paraquat-induced pulmonary fibrogenesis: comparative and time-course microarray analyses in fibrogenic and non-fibrogenic rats

Although paraquat (PQ) is widely known to induce pulmonary fibrosis, the molecular mechanisms are poorly understood. Therefore, to bring a new dimension to the elucidation of the mechanisms, we conducted microarray experiments to investigate the expression profiles of 1,090 genes in the lungs during the progressive phase of PQ-induced pulmonary fibrosis in rats. After several s.c. injections of PQ, rats were divided into a fibrogenic group and a non-fibrogenic group. Time-course gene expression analysis of the fibrogenic group showed altered gene regulation throughout the experimental period. The expression levels of many cell membrane channel, transporter, and receptor genes were substantially altered. These genes were classified into two categories: polyamine transporter- and electrolyte/fluid balance-related genes. Moreover, comparative analysis of the fibrogenic and the non-fibrogenic group revealed 36 genes with significantly different patterns of expression, including the pro-apoptotic gene Bad. This indicates that Bad is a key factor in apoptosis and that apoptosis provides a major turning point in PQ-induced pulmonary fibrosis. Notably, subtypes of transforming growth factor (TGF)-beta genes that are considered to play a pivotal role in fibrogenesis showed no differences in expression between the two groups, though TGF-beta3 was markedly induced in both groups. These results provide novel and extensive insights into the molecular mechanisms that lead to pulmonary fibrosis after exposure to PQ.

Chloride-dependent secretion of alveolar wall liquid determined by optical-sectioning microscopy

The liquid layer lining the pulmonary alveolar wall critically determines the lung's immune defense against inhaled pathogens, because it provides a liquid milieu in the air-filled alveolus for dispersal of immune cells and defensive surfactant proteins. However, mechanisms underlying formation of the liquid are unknown. We achieved visualization of the alveolar wall liquid (AWL) in situ in mouse lungs by means of optical-sectioning microscopy. Continuous liquid secretion was present in alveoli of wild-type (WT) mice under baseline conditions. This secretion was blocked by inhibitors of the cystic fibrosis transmembrane regulator (CFTR). The secretion was absent in Cftr(-/-) mice, and it was blocked when chloride was depleted from the perfusate of WT mice, providing the first evidence that CFTR-dependent chloride secretion causes AWL formation. Injected microparticles demonstrated flow of the AWL. The flow was blocked by CFTR inhibition and was absent in Cftr(-/-) mice. We conclude that CFTR-dependent liquid secretion is present in alveoli of the adult mouse. Defective alveolar secretion might impair alveolar immune defense and promote alveolar disease.