Isolated Mouse Lungs Research Articles

Endothelial RSPO3 mediates pulmonary endothelial regeneration by LGR4-dependent activation of β-catenin and ILK signaling pathways after inflammatory vascular injury

Endothelial repair is essential for restoring tissue fluid homeostasis following lung injury. R-spondin3 (RSPO3), a secreted protein mainly produced by endothelial cells (ECs), has shown its protective effect on endothelium. However, the specific mechanisms remain unknown. To explore whether and how RSPO3 regulates endothelial regeneration after inflammatory vascular injury, the role of RSPO3 in sepsis-induced pulmonary endothelial injury was investigated in EC-specific RSPO3 knockdown, inducible EC-specific RSPO3 deletion mice, EC-specific RSPO3 overexpression mice, systemic RSPO3-administration mice, in isolated mouse lung vascular endothelial cells (MLVECs), and in plasma from septic patients. Here we show that plasma RSPO3 levels are decreased in septic patients and correlated with endothelial injury markers and PaO2/FiO2 index. Both pulmonary EC-specific knockdown of RSPO3 and inducible EC-specific RSPO3 deletion inhibit pulmonary ECs proliferation and exacerbate ECs injury, whereas intra-pulmonary EC-specific RSPO3 overexpression promotes endothelial recovery and attenuates ECs injury during endotoxemia. We show that RSPO3 mediates pulmonary endothelial regeneration by a LGR4-dependent manner. Except for β-catenin, integrin-linked kinase (ILK)/Akt is also identified as a novel downstream effector of RSPO3/LGR4 signaling. These results conclude that EC-derived RSPO3 mediates pulmonary endothelial regeneration by LGR4-dependent activation of β-catenin and ILK signaling pathways after inflammatory vascular injury.

Budesonide/glycopyrronium/formoterol fumarate triple therapy prevents pulmonary hypertension in a COPD mouse model via NFκB inactivation

BackgroundChronic obstructive pulmonary disease (COPD) is a health problem that results in death, commonly due to the development of pulmonary hypertension (PH). Here, by utilizing a mouse model of intratracheal elastase-induced emphysema that presents three different phases of COPD, we sought to observe whether budesonide/glycopyrronium/formoterol fumarate (BGF) triple therapy could prevent COPD-PH in addition to ameliorating COPD progression.MethodsWe utilized intratracheal elastase-induced emphysema mouse model and performed experiments in three phases illustrating COPD progression: inflammatory (1 day post-elastase), emphysema (3 weeks post-elastase) and PH (4 weeks post-elastase), while treatments of BGF and controls (vehicle, one-drug, and two-drug combinations) were started in prior to elastase instillation (inflammatory phase), at day 7 (emphysema), or at day 14 (PH phase). Phenotype analyses were performed in each phase. In vitro, A549 cells or isolated mouse lung endothelial cells (MLEC) were treated with TNFα with/without BGF treatment to analyze NFκB signaling and cytokine expression changes.ResultsWe observed significant reductions in the proinflammatory phenotype observed in the lungs and bronchoalveolar lavage fluid (BALF) 1 day after elastase administration in mice treated with BGF compared with that in mice administered elastase alone (BALF neutrophil percentage, p = 0.0011 for PBS/Vehicle vs. PBS/Elastase, p = 0.0161 for PBS/Elastase vs. BGF). In contrast, only BGF treatment significantly ameliorated the elastase-induced emphysematous lung structure and desaturation after three weeks of elastase instillation (mean linear intercept, p = 0.0156 for PBS/Vehicle vs. PBS/Elastase, p = 0.0274 for PBS/Elastase vs. BGF). Furthermore, BGF treatment prevented COPD-PH development, as shown by improvements in the hemodynamic and histological phenotypes four weeks after elastase treatment (right ventricular systolic pressure, p = 0.0062 for PBS/Vehicle vs. PBS/Elastase, p = 0.027 for PBS/Elastase vs. BGF). Molecularly, BGF acts by inhibiting NFκB-p65 phosphorylation and subsequently decreasing the mRNA expression of proinflammatory cytokines in both alveolar epithelial and pulmonary endothelial cells.ConclusionOur results collectively showed that BGF treatment could prevent PH in addition to ameliorating COPD progression via the inhibition of inflammatory NFκB signaling.

Pannexin 1 – a novel regulator of hypoxic pulmonary vasoconstriction

Hypoxic pulmonary vasoconstriction (HPV) is a physiological response to alveolar hypoxia by which pulmonary blood flow is redirected from poorly ventilated areas to better aerated lung regions. Sustained HPV plays a critical role in the development of pulmonary hypertension (PH) but the exact signaling pathways underlying HPV remain incompletely defined. Recently, ATP release via Pannexin 1 (Panx1) and subsequent purinergic signaling have been linked to transient receptor potential vanlloid 4 (TRPV4) channel mediated Ca2+ signaling in systemic vasoconstriction. Here, we probed for a similar role of Panx1 in HPV and the development of PH.To test the role of Panx1, we measured HPV as increase in pulmonary artery pressure (PAP) in response to hypoxia in lungs of endothelial cell (Cdh5-CreERT2/Panx1fl/fl) and smooth muscle cell specific (SMMHC-CreERT2/Panx1fl/fl) Panx1-KO mice. Isolated perfused lungs (IPL) of C57Bl6/J and Panx1-deficient mice were ventilated with normoxic (20% O2; 5% CO2, 75% N2) or hypoxic gas (1% O2; 5% CO2, 94% N2) and PAP was recorded via a pulmonary artery catheter. To elucidate the role of Panx1 in the development of PH, C57Bl6/J as well as Panx1-KO mice were kept under hypoxic conditions (10% O2) for 5 weeks followed by measurement of right ventricular systolic pressure, echocardiography and histology.Panx1 protein was expressed in human pulmonary artery endothelial cells as well as in human pulmonary artery smooth muscle cells (hPASMCs). Genetic deletion of Panx1 in smooth muscle cells, yet not in endothelial cells reduced the HPV response in isolated mouse lungs. In lungs of C57Bl6/J mice, Panx1-inhibition by the non-specific Panx1 inhibitors spironolactone or probenecid and the Panx1 specific inhibitory peptide (10Panx1) effectively attenuated HPV. Yet, genetic deletion of Panx1 in either endothelial or smooth muscle cells did not prevent the development of PH in mice. Interestingly, ATP release in response to hypoxia was not detectable in PASMC, and ATP degradation as well as inhibition of purinergic receptors failed to affect HPV. Rather, TRPV4 antagonism and Panx1 inhibition inhibited the hypoxia-induced increase of intracellular Ca2+ concentration ([Ca2+]i) in PASMC in an additive manner, suggesting that Panx1 regulates [Ca2+]i independently of the ATP-P2Y-TRPV4 signaling axis. In line with this notion, Panx1 overexpression increased the [Ca2+]i response to hypoxia in HeLa cells. Here we identify Panx1 as novel regulator of HPV. The role of Panx1 in HPV was, however, not attributable to ATP release and downstream purinergic receptor signaling or TRPV4 activation, but may involve a direct role of Panx1 as Ca2+ channel. In contrast to its role in HPV, Panx1 does not seem to contribute to chronic hypoxic PH.

Catenin α 1 mutations cause familial exudative vitreoretinopathy by overactivating Norrin/β-catenin signaling.

Familial exudative vitreoretinopathy (FEVR) is a severe retinal vascular disease that causes blindness. FEVR has been linked to mutations in several genes associated with inactivation of the Norrin/β-catenin signaling pathway, but these account for only approximately 50% of cases. We report that mutations in α-catenin (CTNNA1) cause FEVR by overactivating the β-catenin pathway and disrupting cell adherens junctions. We identified 3 heterozygous mutations in CTNNA1 (p.F72S, p.R376Cfs*27, and p.P893L) by exome sequencing and further demonstrated that FEVR-associated mutations led to overactivation of Norrin/β-catenin signaling as a result of impaired protein interactions within the cadherin-catenin complex. The clinical features of FEVR were reproduced in mice lacking Ctnna1 in vascular endothelial cells (ECs) or with overactivated β-catenin signaling by an EC-specific gain-of-function allele of Ctnnb1. In isolated mouse lung ECs, both CTNNA1-P893L and F72S mutants failed to rescue either the disrupted F-actin arrangement or the VE-cadherin and CTNNB1 distribution. Moreover, we discovered that compound heterozygous Ctnna1 F72S and a deletion allele could cause a similar phenotype. Furthermore, in a FEVR family, we identified a mutation of LRP5, which activates Norrin/β-catenin signaling, and the corresponding knockin mice exhibited a partial FEVR-like phenotype. Our study demonstrates that the precise regulation of β-catenin activation is critical for retinal vascular development and provides new insights into the pathogenesis of FEVR.

DRD1 downregulation contributes to mechanical stretch-induced lung endothelial barrier dysfunction

Rationale: The lung-protective effects of dopamine and its role in the pathology of ventilator-induced lung injury (VILI) are emerging. However, the underlying mechanisms are still largely unknown.Objective: To investigate the contribution of dopamine receptor dysregulation in the pathogenesis of VILI and therapeutic potential of dopamine D1 receptor (DRD1) agonist in VILI.Methods: The role of dopamine receptors in mechanical stretch-induced endothelial barrier dysfunction and lung injury was studied in DRD1 knockout mice, in isolated mouse lung vascular endothelial cells (MLVECs), and in lung samples from patients who underwent pulmonary lobectomy with mechanical ventilation for different time periods.Measurements and Main Results: DRD1 was downregulated in both surgical patients and mice exposed to mechanical ventilation. Prophylactic administration of dopamine or DRD1 agonist attenuated mechanical stretch-induced lung endothelial barrier dysfunction and lung injury. By contrast, pulmonary knockdown or global knockout of DRD1 exacerbated these effects. Prophylactic administration of dopamine attenuated mechanical stretch-induced α-tubulin deacetylation and subsequent endothelial hyperpermeability through DRD1 signaling. We identified that cyclic stretch-induced glycogen-synthase-kinase-3β activation led to phosphorylation and activation of histone deacetylase 6 (HDAC6), which resulted in deacetylation of α-tubulin. Upon activation, DRD1 signaling attenuated mechanical stretch-induced α-tubulin deacetylation and subsequent lung endothelial barrier dysfunction through cAMP/exchange protein activated by cAMP (EPAC)-mediated inactivation of HDAC6.Conclusions: This work identifies a novel protective role for DRD1 against mechanical stretch-induced lung endothelial barrier dysfunction and lung injury. Further study of the mechanisms involving DRD1 in the regulation of microtubule stability and interference with DRD1/cAMP/EPAC/HDAC6 signaling may provide insight into therapeutic approaches for VILI.

Hypoxic Pulmonary Vasoconstriction in Isolated Mouse Lungs

BackgroundHypoxic pulmonary vasoconstriction (HPV) is a physiological mechanism of lung to ensure maximal gas exchange and blood oxygenation. Persistent and global alveolar hypoxia leads to sustained vasoconstriction and vascular remodeling causing pulmonary hypertension. It has been demonstrated that acute HPV is initiated by an increase in cytosolic [Ca2+] ([Ca2+]cyt) in pulmonary arterial smooth muscle cells (PASMC) and modulated by factors released from endothelium. Acute HPV is well reserved in isolated perfused/ventilated lungs, whereas HPV in isolated pulmonary arterial rings shows different pattern in comparison to HPV in intact animals and humans. In this study, we aimed to use isolated perfused/ventilated mouse lungs to further study potential mechanisms involved in development of HPV.MethodsC57BL/6 mice (male, 8–10 weeks old) were anesthetized by pentobarbital sodium (120 mg/kg). After tracheostomy, isolated lungs were immediately ventilated with normoxic gas (21% O2/5% CO2) using a rodent ventilator (80 breaths/min with a tidal volume of 250 μl). The mice were then placed in an isolated lung system chamber with a heated water jacket at 37°C. After tracheal intubation, the chest was opened and a catheter was inserted into the main PA via the right ventricle to measure PAP. The lung vasculature was consistently superfused with physiological salt solution (PSS) via a pump while lung airway and alveoli were ventilated with normoxic or hypoxic gas. Before experimentation, the isolated lung was first superfused with the 40 mM K+‐containing PSS (40K) to stabilize the basal PAP. The lung was then repetitively challenged by ventilation of hypoxic gas (1% O2 in N2, for 4 min) to induce an increase in PAP (due to HPV). Pharmacological effects of various inhibitors on HPV were examined by superfusion of PSS containing the inhibitors while the lung was ventilated with hypoxic gas.ResultsOur results show that HPV was dependent on Ca2+ influx through a) nifedipine‐sensitive L‐type voltage‐dependent Ca2+ channels; b) SKF‐sensitive non‐selective cation channels; and c) TRP channels like TRPC6, TRPV1 and TRPP. HPV in isolated perfused lung was also significantly inhibited by blocking Ca2+‐sensing receptors (CaSR) and Notch receptors and by extracellular Mg2+ and Mn2+. Interestingly, blockade of Ca2+‐activated Cl− channels and inhibition of muscarinic receptors and endothelin receptors had little effect on HPV. Furthermore, inhibition of nitric oxide synthase (eNOS) potentiated HPV.ConclusionAn increase in [Ca2+]cyt due to Ca2+ influx through various Ca2+‐permeable cation channels in PASMC influx is required for the initiation of acute HPV. Both voltage‐gated Ca2+ channels (e.g., CaV1.2) and receptor‐operated Ca2+ channels (TRPC6/V1/P) are involved in mediating Ca2+ influx to induce HPV. G protein‐coupled receptor/CaSR‐mediated synthesis of intracellular signaling molecules (e.g., diacylglycerol and inositol 1, 4, 5‐trisphosphate) and Notch‐associated cell‐to‐cell interaction also play important roles in HPV. These data indicate that multiple mechanisms are involved in the initiation and regulation of HPV.Support or Funding InformationNIH NIHLBI HL135807

EFFECTS OF ALVEOLAR MORPHOLOGY ON ALVEOLAR MECHANICS: AN EXPERIMENTAL STUDY OF MOUSE LUNG BASED ON TWO- AND THREE-DIMENSIONAL IMAGING METHODS

Understanding alveolar mechanics is important for preventing the possible lung injuries during mechanical ventilation. Alveolar clusters with smaller size are found having lower compliance in two-dimensional studies. But the influence of alveolar shape on compliance is unclear. In order to investigate how alveolar morphology affects their behavior, we tracked subpleural alveoli of isolated mouse lungs during quasi-static ventilation using two- and three-dimensional imaging techniques. Results showed that alveolar clusters with smaller size and more spherical shape had lower compliance. There was a better correlation of sphericity rather than circularity with alveolar compliance. The compliance of clusters with great shape change was larger than that with relatively slight shape change. These findings suggest the contribution of lung heterogeneous expansion to lung injuries associated with mechanical ventilation.

A Peptide Inhibitor of NADPH Oxidase (NOX2) Activation Markedly Decreases Mouse Lung Injury and Mortality Following Administration of Lipopolysaccharide (LPS).

We have previously derived three related peptides, based on a nine-amino acid sequence in human or rat/mouse surfactant protein A, that inhibit the phospholipase A2 activity of peroxiredoxin 6 (Prdx6) and prevent the activation of lung NADPH oxidase (type 2). The present study evaluated the effect of these Prdx6-inhibitory peptides (PIP) in a mouse (C57Bl/6) model of acute lung injury following lipopolysaccharide (LPS) administration. All three peptides (PIP-1, 2 and 3) similarly inhibited the production of reactive O2 species (ROS) in isolated mouse lungs as detected by the oxidation of Amplex red. PIP-2 inhibited both the increased phospholipase A2 activity of Prdx6 and lung reactive oxygen species (ROS) production following treatment of mice with intratracheal LPS (5 µg/g body wt.). Pre-treatment of mice with PIP-2 prevented LPS-mediated lung injury while treatment with PIP-2 at 12 or 16 h after LPS administration led to reversal of lung injury when evaluated 12 or 8 h later, respectively. With a higher dose of LPS (15 µg/g body wt.), mortality was 100% at 48 h in untreated mice but only 28% in mice that were treated at 12–24 h intervals, with PIP-2 beginning at 12 h after LPS administration. Treatment with PIP-2 also markedly decreased mortality after intraperitoneal LPS (15 µg/g body wt.), used as a model of sepsis. This study shows the dramatic effectiveness of a peptide inhibitor of Prdx6 against lung injury and mouse mortality in LPS models. We propose that the PIP nonapeptides may be a useful modality to prevent or to treat human ALI.

The effects of hydroxyethyl starch and gelatine on pulmonary cytokine production and oedema formation

Recently, side effects of plasma expanders like hydroxyethyl starch and gelatine gained considerable attention. Most studies have focused on the kidneys; lungs remain unconsidered. Isolated mouse lungs were perfused for 4 hours with buffer solutions based on hydroxyethyl starch (HES) 130/0.4, HES 200/0.5 or gelatine and ventilated with low or high pressure under physiological pH and alkalosis. Outcome parameters were cytokine levels and the wet-to-dry ratio. For cytokine release, murine and human PCLS were incubated in three different buffers and time points.In lungs perfused with the gelatine based buffer IL-6, MIP-2 and KC increased when ventilated with high pressure. Wet-to-dry ratios increased stronger in lungs perfused with gelatine - compared to HES 130/0.4. Alkalotic perfusion resulted in higher cytokine levels but normal wet-to-dry ratio. Murine PCLS supernatants showed increased IL-6 and KC when incubated in gelatine based buffer, whereas in human PCLS IL-8 was elevated. In murine IPL HES 130/0.4 has lung protective effects in comparison to gelatine based infusion solutions, especially in the presence of high-pressure ventilation. Gelatine perfusion resulted in increased cytokine production. Our findings suggest that gelatine based solutions may have side effects in patients with lung injury or lung oedema.

Sphingosine Kinase 1 Regulates Inflammation and Contributes to Acute Lung Injury in Pneumococcal Pneumonia via the Sphingosine-1-Phosphate Receptor 2.

Severe pneumonia may evoke acute lung injury, and sphingosine-1-phosphate is involved in the regulation of vascular permeability and immune responses. However, the role of sphingosine-1-phosphate and the sphingosine-1-phosphate producing sphingosine kinase 1 in pneumonia remains elusive. We examined the role of the sphingosine-1-phosphate system in regulating pulmonary vascular barrier function in bacterial pneumonia. Controlled, in vitro, ex vivo, and in vivo laboratory study. Female wild-type and SphK1-deficient mice, 8-10 weeks old. Human postmortem lung tissue, human blood-derived macrophages, and pulmonary microvascular endothelial cells. Wild-type and SphK1-deficient mice were infected with Streptococcus pneumoniae. Pulmonary sphingosine-1-phosphate levels, messenger RNA expression, and permeability as well as lung morphology were analyzed. Human blood-derived macrophages and human pulmonary microvascular endothelial cells were infected with S. pneumoniae. Transcellular electrical resistance of human pulmonary microvascular endothelial cell monolayers was examined. Further, permeability of murine isolated perfused lungs was determined following exposition to sphingosine-1-phosphate and pneumolysin. Following S. pneumoniae infection, murine pulmonary sphingosine-1-phosphate levels and sphingosine kinase 1 and sphingosine-1-phosphate receptor 2 expression were increased. Pneumonia-induced lung hyperpermeability was reduced in SphK1 mice compared with wild-type mice. Expression of sphingosine kinase 1 in macrophages recruited to inflamed lung areas in pneumonia was observed in murine and human lungs. S. pneumoniae induced the sphingosine kinase 1/sphingosine-1-phosphate system in blood-derived macrophages and enhanced sphingosine-1-phosphate receptor 2 expression in human pulmonary microvascular endothelial cell in vitro. In isolated mouse lungs, pneumolysin-induced hyperpermeability was dose dependently and synergistically increased by sphingosine-1-phosphate. This sphingosine-1-phosphate-induced increase was reduced by inhibition of sphingosine-1-phosphate receptor 2 or its downstream effector Rho-kinase. Our data suggest that targeting the sphingosine kinase 1-/sphingosine-1-phosphate-/sphingosine-1-phosphate receptor 2-signaling pathway in the lung may provide a novel therapeutic perspective in pneumococcal pneumonia for prevention of acute lung injury.

Measuring Innate Immune Function in Mouse Mononuclear Phagocytes.

While serving as a conduit for gas exchange, the lung continually encounters potentially harmful airborne and bloodborne substances including particulate matter, allergens, toxins, and infectious agents. Resident alveolar and interstitial macrophages coordinate with neutrophils, dendritic cells, and recruited blood-derived monocytes to provide phagocytic host defense that aids in the removal and destruction of antigenic material following this myriad of exposures. Here we describe flow cytometric methods for specifically assessing phagocytic activity ex vivo in isolated mouse lung macrophages and monocytes utilizing fluorescently labeled Streptococcus pneumoniae.

Water-soluble substituted chitosan derivatives as technology platform for inhalation delivery of siRNA

Despite research efforts full potential of siRNA-based therapeutics has not yet been fully realized due to a need for suitable, effective delivery formulations. Here, we examine a potential of a new class of water-soluble chitosans as siRNA platform for pulmonary delivery. The system is based on piperazine-substituted chitosans, a material designed to integrate established, safe application of chitosan for mucosal administration with novel properties: the piperazine-substituted chitosans are freely water-soluble at physiological pH, possess low cytotoxicity (no significant reduction in cell viability up to 0.1 mg/ml), and provide efficient incorporation of siRNA into sub-300 nm colloidal complexes (at relatively low polymer/siRNA ratio of 5:1). In vitro, the complexes achieved silencing of a model gene at a level of 40–80%, when tested in a panel of lung epithelial cells. Considering the formulation ‘developability’, there were no significant changes in the complexes’ size and integrity on aerosolisation by microsprayer (PenCentury™) device. Following intratracheal aerolisation, the complexes deposited throughout the lung, although relatively inhomogeneously, as judged from IVIS imaging of the isolated mouse lung (visualizing DY647-siRNA). In vivo data illustrate absence of adverse effects on repeated administration of complexes and significant tumor reduction in atopical lung cancer model in mice. Altogether, the data illustrates potential of substituted chitosan derivatives to be utilized as a safe system for inhalation delivery of siRNA.

Vasculotide reduces pulmonary hyperpermeability in experimental pneumococcal pneumonia

BackgroundCommunity-acquired pneumonia (CAP) is a significant cause of morbidity and mortality worldwide. Despite effective antimicrobial therapy, CAP can induce pulmonary endothelial hyperpermeability resulting in life-threatening lung failure due to an exaggerated host-pathogen interaction. Treatment of acute lung injury is mainly supportive because key elements of inflammation-induced barrier disruption remain undetermined. Angiopoietin-1 (Ang-1)-mediated Tie2 activation reduces, and the Ang-1 antagonist Ang-2 increases, inflammation and endothelial permeability in sepsis. Vasculotide (VT) is a polyethylene glycol-clustered Tie2-binding peptide that mimics the actions of Ang-1. The aim of our study was to experimentally test whether VT is capable of diminishing pneumonia-induced lung injury.MethodsVT binding and phosphorylation of Tie2 were analyzed using tryptophan fluorescence spectroscopy and phospho-Tie-2 enzyme-linked immunosorbent assay. Human and murine lung endothelial cells were investigated by immunofluorescence staining and electric cell-substrate impedance sensing. Pulmonary hyperpermeability was quantified in VT-pretreated, isolated, perfused, and ventilated mouse lungs stimulated with the pneumococcal exotoxin pneumolysin (PLY). Furthermore, Streptococcus pneumoniae-infected mice were therapeutically treated with VT.ResultsVT showed dose-dependent binding and phosphorylation of Tie2. Pretreatment with VT protected lung endothelial cell monolayers from PLY-induced disruption. In isolated mouse lungs, VT decreased PLY-induced pulmonary permeability. Likewise, therapeutic treatment with VT of S. pneumoniae-infected mice significantly reduced pneumonia-induced hyperpermeability. However, effects by VT on the pulmonary or systemic inflammatory response were not observed.ConclusionsVT promoted pulmonary endothelial stability and reduced lung permeability in different models of pneumococcal pneumonia. Thus, VT may provide a novel therapeutic perspective for reduction of permeability in pneumococcal pneumonia-induced lung injury.

Deficiency of \u03b17 Nicotinic Acetylcholine Receptor Attenuates Bleomycin-Induced Lung Fibrosis in Mice

α7 nicotinic acetylcholine receptor (α7 nAChR, coded by Chrna7) is indispensable in dampening proinflammatory responses. However, whether α7 nAChR plays a role in regulating bleomycin (BLM)-induced lung fibrosis is less investigated. Here, we challenged wild-type and Chrna7−/− mice with BLM intratracheally to elicit lung fibrosis. Taking advantage of this model, we measured body weight loss, lung fibrogenic genes (Acta2, Col1a1, Fsp1 and Fstl1), histology, Masson’s trichrome staining, hydroxyproline levels and expression of α-SMA at protein levels in the BLM-challenged lung to evaluate the severity of lung fibrosis. We also pretreated human fibroblasts (MRC5 cell line) and isolated mouse lung fibroblasts with GTS-21 (an α7 nAChR agonist) to study its effects on TGF-β-stimulated profibrotic profiles. We found that lung Chrna7 expression and CD4+CHAT+ cells (choline acetyltransferase, an enzyme for local acetylcholine synthesis) were elevated 12-fold and 4.5-fold, respectively, in the early stage of lung fibrosis. Deletion of Chrna7 prevented body-weight loss and reduced lung fibrogenic genes (Acta2, Colla1, Fsp1 and Fstl1) and Arg 1 (coding arginase 1). Deletion of Chrna7 attenuated lung arginase 1+Ly6C+ cells, Masson’s trichrome staining, hydroxyproline levels and expression of α-SMA at protein levels in BLM-challenged mice. Mechanistically, activation of α7 nAChR in human fibroblasts increased TGF-β-induced phosphorylation of Smad2/3 and transcription of fibrogenic genes (Acta2, Colla1). In isolated mouse lung fibroblasts, activation of α7 nAChR also enhanced TGF-β-induced transcription of fibrogenic genes; however, deletion of Chrna7 diminished these effects. Taken together, deficiency of α7 nAChR could suppress the development of BLM-induced lung fibrosis. Thus, α7 nAChR might be a novel therapeutic target for treating lung fibrosis.

Identification and Validation of Larixyl Acetate as a Potent TRPC6 Inhibitor.

Classical or canonical transient receptor potential 6 (TRPC6), a nonselective and Ca(2+)-permeable cation channel, mediates pathophysiological responses within pulmonary and renal diseases that are still poorly controlled by current medication. Thus, controlling TRPC6 activity may provide a promising and challenging pharmacological approach. Recently identified chemical entities have demonstrated that TRPC6 is pharmacologically targetable. However, isotype-selectivity with regard to its closest relative, TRPC3, is difficult to achieve. Reasoning that balsams, essential oils, or incense materials that are traditionally used for inhalation may contain biologic activities to block TRPC6 activity, we embarked on a natural compound strategy to identify new TRPC6-blocking chemical entities. Within several preparations of plant extracts, a strong TRPC6-inhibitory activity was found in conifer balsams. The biologic activity was associated with nonvolatile resins, but not with essential oils. Of various conifers, the larch balsam was unique in displaying a marked TRPC6-prevalent mode of action. By testing the main constituents of larch resin, we identified larixol and larixyl acetate as blockers of Ca(2+) entry and ionic currents through diacylglycerol- or receptor-activated recombinant TRPC6 channels, exhibiting approximately 12- and 5-fold selectivity compared with its closest relatives TRPC3 and TRPC7, respectively. No significant inhibition of more distantly related TRPV or TRPM channels was seen. The potent inhibition of recombinant TRPC6 by larixyl acetate (IC50 = 0.1-0.6 µM) was confirmed for native TRPC6-like [Ca(2+)]i signals in diacylglycerol-stimulated rat pulmonary artery smooth muscle cells. In isolated mouse lungs, larix-6-yl monoacetate (CAS 4608-49-5; larixyl acetate; 5 µM) prevented acute hypoxia-induced vasoconstriction. We conclude that larch-derived labdane-type diterpenes are TRPC6-selective inhibitors and may represent a starting point for pharmacological TRPC6 modulation within experimental therapies.

Physiological parameters of the isolated perfused mouse lung and their dependency on age

BACKGROUND: The “Isolated lung perfusion system” has been established to study lung physiological parameters of mice or other small animals, but little is known about the influence of age on the lung function in mice. METHODS:We used a buffer-perfused lung system with negative-pressure ventilation to study the effect of age on physiological parameters in the isolated mouse lung. Our study included C57BL/6N mice when they were young (3 to 4 months), adult (5 to 9 months) or old (24 months). RESULTS: The ex vivo data indicated that maximal function of the lung is achieved in the early adulthood (5 to 6 months of age). In this period, lung developed highest maximal expiratory flow rate which declined steadily with increasing age. After this age (>7 months) the dynamic lung compliance increased with significant changes in the 24-month-old mice. However, mouse age had no effect on airway resistance and pulmonary artery pressure. Moreover, we did not find an influence of age on the integrity of the endothelial-epithelial barrier. CONCLUSION: Our findings indicate the importance of age, in particular on the respiratory mechanics in isolated mouse lungs, which should be considered in the pulmonary research using the “Isolated lung perfusion system”.

Carnosol Is a Potent Lung Protective Agent: Experimental Study on Mice

IntroductionOxidative stress has been implicated in various disease states and ischemia/reperfusion injury is a direct consequence of oxidative stress in lung transplantation. Because the success rate of organ transplantation in which ischemia/reperfusion is inevitable is highly influenced by oxidative stress, development of strategies to control oxidative stress would be beneficial. Here we identified natural compounds to reduce oxidative stresses in isolated mouse lungs. MethodsWe screened compounds associated with antioxidative stress in 200 plant extracts by monitoring the activities of nuclear factor erythroid 2-related factor 2 (NRF2). Compounds found to ameliorate antioxidative stress were enriched and mice were administered the extract orally every day for 1 week. Then, the lungs were isolated and cultured in the culture medium at 37°C. Lung damage was monitored by lactate dehydrogenase (LDH) released in the culture medium. Arterial (left ventricle) blood gas levels were also monitored after hilar clamping. ResultsWe found that Callicarpa longissima extract was rich in NRF2 activators. The responsible compounds were carnosic acid and its oxidative product, carnosol. Carnosol induced heme-oxygenase 1 (HO-1) expression, which is downstream of NRF2, more efficiently than carnosic acid. ConclusionsLungs from mice treated with C longissima extract were less damaged than those from control mice and accompanied by HO-1 induction. These results suggest that carnosol is a candidate compound to increase the success rate of lung transplantation.

Critical role of peroxiredoxin 6 in the repair of peroxidized cell membranes following oxidative stress

Phospholipids are a major structural component of all cell membranes; their peroxidation represents a severe threat to cellular integrity and their repair is important to prevent cell death. Peroxiredoxin 6 (Prdx6), a protein with both GSH peroxidase and phospholipase A2 (PLA2) activity, plays a critical role in antioxidant defense of the lung and other organs. We investigated the role of Prdx6 in the repair of peroxidized cell membranes in pulmonary microvascular endothelial cells (PMVEC) and isolated mouse lungs treated with tert-butyl hydroperoxide and lungs from mice exposed to hyperoxia (100% O2). Lipid peroxidation was evaluated by measurement of thiobarbituric acid reactive substances, oxidation of diphenyl-1-pyrenylphosphine, or ferrous xylenol orange assay. The exposure dose was varied to give a similar degree of lipid peroxidation at the end of exposure in the different models. Values for lipid peroxidation returned to control levels within 2h after oxidant removal in wild-type PMVEC and perfused lungs but were unchanged in Pxdx6 null preparations. An intermediate degree of repair was observed with PMVEC and lungs that expressed only C47S or D140A mutant Prdx6; the former mutant does not have peroxidase activity, while the latter loses its PLA2 activity. Prdx6 null mice showed markedly delayed recovery from lipid peroxidation during 20h observation following exposure to hyperoxia. Thus, Prdx6 plays a critical role in the repair of peroxidized phospholipids in cell membranes and the recovery of lung cells from peroxidative stress; the peroxidase and PLA2 activity each contribute to the recovery process.

Both Peroxidase and Phospholipase A2 Activities of peroxiredoxin 6 Protect Against Oxidative Stress by Reduction of Peroxidized Cell Membranes

Peroxiredoxin 6 (Prdx6), a protein with both peroxidase and PLA2 activities, plays a critical role in antioxidant defense of lung and other organs. We investigated the relative importance of these 2 activities of Prdx6 in the “repair” of peroxidized cell membranes in pulmonary microvascular endothelial cells (PMVECs) and isolated mouse lungs. Lipid peroxidation was evaluated by measurement of thiobarbituric acid reactive substances (TBARS) or oxidation of diphenyl‐1‐pyrenylphosphine (DPPP). PMVECs were treated with tert‐butyl hydroperoxide (tBOOH, 0.2 mM) or Cu2+ /ascorbate for 4 h and then evaluated at 0,2,4 and 6 h after removal of the oxidant. Values for lipid peroxidation returned to control levels in 2 h with wild type (WT) PMVECs but were unchanged at 6 h after oxidant removal in Pxdx6 null PMVECs. An intermediate degree of repair was observed with lentivirus transfected C47S or D140A mutant Prdx6 PMVECs; the former express only PLA2 activity and the latter only peroxidase activity. Similar results were obtained with the isolated mouse lungs from WT, Prdx6 null and Prdx6‐C47S or ‐D140A “knock‐in” mice that were observed for 3 h following 60 min of perfusion with 15 mM tBOOH. These results indicate that the peroxidase and phospholipase A2 activities of Prdx6 both play a critical role in the repair of peroxidized phospholipids in cell membranes and the recovery of lung cells from peroxidative stress.

Serine 32 to threonine mutation preserves peroxiredoxin 6 structure and enzymatic function but abolishes its trafficking to lamellar bodies in vivo

Peroxiredoxin 6 (Prdx6), a bifunctional protein with lysosomal‐type phospholipase A2 (aiPLA2) and GSH peroxidase activities, protects lungs from oxidative stress and participates in lung surfactant phospholipid (PL) turnover. Prdx6 has been localized to both cytosol and acidic organelles (lamellar bodies [LB] and lysosomes) in lung epithelium and its organellar targeting sequence has been identified (31DSWGILFSHP40, Am.J.Physiol.297 : L871, 2009). Interestingly, an S32T mutation fully preserved secondary structure of recombinant protein and had no effect on either its peroxidase or aiPLA2 activity. In a “knock‐in” mouse model carrying the S32T mutation in the Prdx6 gene, Prdx6 protein and aiPLA2 activity were present in lung epithelial cells. However,the protein was absent from epithelial cell LB. Lung surfactant dipalmitoylphosphatidylcholine (DPPC) is endocytosed by alveolar epithelial cells and degraded by aiPLA2. The content of total phospholipid, PC, and disaturated phosphatidylcholine (DSPC) in bronchoalveolar lavage fluid, lung lamellar bodies, and lung homogenate was increased in S32T mutant animals and degradation of internalized [3H]DPPC in isolated mouse lungs was significantly decreased. Thus, Thr can substitute for Ser for the enzymatic activities of Prdx6 but not for its targeting to LB. These results confirm an important role for lamellar body Prdx6 in the degradation and remodeling of lung surfactant phosphatidylcholine. [HL‐019737, HL102016 and HL105509]