Distal Airway Cells Research Articles

GAA deficiency disrupts distal airway cells in Pompe disease.

Pompe disease is an autosomal recessive glycogen storage disease caused by mutations in the gene that encodes acid alpha-glucosidase (GAA)-an enzyme responsible for hydrolyzing lysosomal glycogen. GAA deficiency results in systemic lysosomal glycogen accumulation and cellular disruption. Glycogen accumulation in skeletal muscles, motor neurons, and airway smooth muscle cells is known to contribute to respiratory insufficiency in Pompe disease. However, the impact of GAA deficiency on the distal alveolar type 1 and type 2 cells (AT1 and AT2) has not been evaluated. AT1 cells rely on lysosomes for cellular homeostasis so that they can maintain a thin barrier for gas exchange, whereas AT2 cells depend on lysosome-like structures (lamellar bodies) for surfactant production. Using a mouse model of Pompe disease, the Gaa-/- mouse, we investigated the consequences of GAA deficiency on AT1 and AT2 cells using histology, pulmonary function and mechanics, and transcriptional analysis. Histological analysis revealed increased accumulation of lysosomal-associated membrane protein 1 (LAMP1) in the Gaa-/- mice lungs. Furthermore, ultrastructural examination showed extensive intracytoplasmic vacuoles enlargement and lamellar body engorgement. Respiratory dysfunction was confirmed using whole body plethysmography and forced oscillometry. Finally, transcriptomic analysis demonstrated dysregulation of surfactant proteins in AT2 cells, specifically reduced levels of surfactant protein D in the Gaa-/- mice. We conclude that GAA enzyme deficiency leads to glycogen accumulation in the distal airway cells that disrupts surfactant homeostasis and contributes to respiratory impairments in Pompe disease.NEW & NOTEWORTHY This research highlights the impact of Pompe disease on distal airway cells. Prior to this work, respiratory insufficiency in Pompe disease was classically attributed to pathology in respiratory muscles and motor neurons. Using the Pompe mouse model, we note significant pathology in alveolar type 1 and 2 cells with reductions in surfactant protein D and disrupted surfactant homeostasis. These novel findings highlight the potential contributions of alveolar pathology to respiratory insufficiency in Pompe disease.

Population-wide gene disruption in the murine lung epithelium via AAV-mediated delivery of CRISPR-Cas9 components

With the aim of expediting drug target discovery and validation for respiratory diseases, we developed an optimized method for in situ somatic gene disruption in murine lung epithelial cells via AAV6-mediated CRISPR-Cas9 delivery. Efficient gene editing was observed in lung type II alveolar epithelial cells and distal airway cells following assessment of single- or dual-guide AAV vector formats, Cas9 variants, and a sequential dosing strategy with combinatorial guide RNA expression cassettes. In particular, we were able to demonstrate population-wide gene disruption within distinct epithelial cell types for separate targets in Cas9 transgenic animals, with minimal to no associated inflammation. We also observed and characterized AAV vector integration events that occurred within directed double-stranded DNA break sites in lung cells, highlighting a complicating factor with AAV-mediated delivery of DNA nucleases. Taken together, we demonstrate a uniquely effective approach for somatic engineering of the murine lung, which will greatly facilitate the modeling of disease and therapeutic intervention.

GAA Deficiency Disrupts Distal Airway Cells in Pompe Disease

Pompe disease is an autosomal recessive glycogen storage disease caused by mutations in alpha‐glucosidase (GAA) ‐ an enzyme responsible of hydrolyzing lysosomal glycogen. GAA deficiency results in systemic lysosomal glycogen accumulation and cellular disruption. Skeletal muscle, motor neuron pathology and airway smooth muscle cells are known to contribute to respiratory insufficiency in Pompe disease, but the role of distal airway cells including alveolar type 1 and type 2 cells (AT1 and AT2, respectively) has not been evaluated. AT1 cells depend on lysosomes for cellular homeostasis to maintain a thin barrier for gas exchange whereas AT2 cells depend on lysosomal structures for surfactant production. Using an established mouse model of Pompe disease, the Gaa−/− mouse, we compared lung histology using Periodic acid‐Schiff staining, quantification of immunohistochemistry staining and electron microscopy, and pulmonary mechanics using forced oscillometry FlexiVent system, between Gaa−/− and age‐matched wild‐type (WT) mice. We also perfomed single cell‐RNA seq (scRNA‐seq) on the distal airways of Gaa‐/‐ mice. Lysosomal glycogen accumulation and engorged lamellar bodies were observed in the AT2 cells in Gaa−/− but not WT mice. Furthermore, AT2 positive surfactant protein‐C (SPC) staining and lysosomal positive lysosomal associated membrane protein 1 (LAMP1) staining is more evident with increased colocalization of LAMP1 with the type 2 cell marker after quantification of each marker in Gaa−/− airway cells. The Gaa−/− mice exhibited a significant decrease in total and central airway resistance (Rrs and Rn, respectively), as well as a significant increase in lung compliance (Crs) versus WT mice. Moreover, in the dimensionless and volume‐independent shape constant k that describes the curvature of the upper portion of the deflation limb of the Pressure‐Volume curves, a statistically significant change was observed in Gaa−/− mice. This indicates a change in the intrinsic elastic properties of the respiratory system in Pompe disease. Finally, a robust transcriptomic dysregulation in AT1 and AT2 cells was detected scRNA‐seq in Gaa‐/‐mice relative to WT mice. We conclude that GAA enzyme deficiency leads to glycogen accumulation in the distal airway stem cells that may contribute to respiratory impairments in Pompe disease. Our findings will inform the clinical care of patients with Pompe disease and will provide essential information for the development of novel therapies in Pompe disease that will address this airway pathology.

Chorioamnionitis induces changes in ovine pulmonary endogenous epithelial stem/progenitor cells in utero.

Chorioamnionitis, an intrauterine infection of the placenta and fetal membranes, is a common risk factor for adverse pulmonary outcomes in premature infants including BPD, which is characterized by an arrest in alveolar development. As endogenous epithelial stem/progenitor cells are crucial for organogenesis and tissue repair, we examined whether intrauterine inflammation negatively affects these essential progenitor pools. In an ovine chorioamnionitis model, fetuses were intra-amniotically exposed to LPS, 2d or 7d (acute inflammation) before preterm delivery at 125d of gestation, or to intra-amniotic Ureaplasma parvum for 42d (chronic inflammation). Lung function, pulmonary endogenous epithelial stem/progenitor pools, and downstream functional markers were studied. Lung function was improved in the 7d LPS and 42d Ureaplasma groups. However, intrauterine inflammation caused a loss of P63+ basal cells in proximal airways and reduced SOX-9 expression and TTF-1+ Club cells in distal airways. Attenuated type-2 cell numbers were associated with lower proliferation and reduced type-1 cell marker Aqp5 expression, indicative for impaired progenitor function. Chronic Ureaplasma infection only affected distal airways, whereas acute inflammation affected stem/progenitor populations throughout the lungs. Acute and chronic prenatal inflammation improve lung function at the expense of stem/progenitor alterations that potentially disrupt normal lung development, thereby predisposing to adverse postnatal outcomes. In this study, prenatal inflammation improved lung function at the expense of stem/progenitor alterations that potentially disrupt normal lung development, thereby predisposing to adverse postnatal outcomes. Importantly, we demonstrate that these essential alterations can already be initiated before birth. So far, stem/progenitor dysfunction has only been shown postnatally. This study indicates that clinical protocols to target the consequences of perinatal inflammatory stress for the immature lungs should be initiated as early as possible and ideally in utero. Within this context, our data suggest that interventions, which promote function or repair of endogenous stem cells in the lungs, hold great promise.

ADAMTS18 Deficiency Leads to Pulmonary Hypoplasia and Bronchial Microfibril Accumulation.

SummaryADAMTSs (a disintegrin and metalloproteinase with thrombospondin motifs) are secreted metalloproteinases that play a major role in the assembly and degradation of the extracellular matrix (ECM). In this study, we show that ADAMTS18, produced by the epithelial cells of distal airways and mesenchymal cells in lung apex at early embryonic stages, serves as a morphogen in lung development. ADAMTS18 deficiency leads to reduced number and length of bronchi, tipped lung apexes, and dilated alveoli. These developmental defects worsen lipopolysaccharide-induced acute lung injury and bleomycin-induced lung fibrosis in adult Adamts18-deficient mice. ADAMTS18 deficiency also causes increased levels of fibrillin1 and fibrillin2, bronchial microfibril accumulation, decreased focal adhesion kinase signaling, and disruption of F-actin organization. Our findings indicate that ECM homeostasis mediated by ADAMTS18 is pivotal in airway branching morphogenesis.

Aberrant Epithelial Cell Proliferation in Peripheral Airways in Bronchiectasis.

Dilation of bronchi and bronchioles caused by destruction and excessive epithelial remodeling is a characteristic feature of bronchiectasis. It is not known how epithelial progenitor cells contribute to these pathologic conditions in peripheral airways (bronchioles) in bronchiectasis. We aimed to explore the expression levels of signature airway progenitor cells in the dilated bronchioles in patients with bronchiectasis. We obtained the surgically resected peripheral lung tissues from 43 patients with bronchiectasis and 33 control subjects. Immunostaining was performed to determine the expression patterns of thyroid transcription factor-1 (TTF-1, for labeling progenitor cells in distal airways), P63 (basal cells), club cell 10 kDa protein (CC10, club cells), and surfactant protein C (SPC, alveolar type II epithelial cells) in epithelium or sub-epithelium. Here, we reported significantly lower percentage of TTF-1+ cells and CC10+ cells, and higher percentage of P63+ cells within the epithelium of dilated bronchioles compared with control bronchioles. In airway sub-epithelium of the dilated bronchioles, epithelial hyperplasia with disarrangement of TTF-1+ cells yielded cuboidal (100%) and columnar (93.0%) type among bronchiectasis patients. Most progenitor cell markers co-localized with TTF-1. The median (the 1st, 3rd quartile) percentage of P63+TTF-1+, CC10+TTF-1+, and SPC+TTF-1+ cells was 16.0% (8.9, 24.0%), 14.5% (7.1, 20.8%), and 52% (40.3, 64.4%), respectively. For cuboidal epithelial hyperplasia, 91.0% (86.5, 94.0%) of areas co-stained with SPC and TTF-1. Columnar epithelial hyperplasia was characterized by TTF-1 co-staining with P63+TTF-1+ and CC10+TTF-1+ cells. Taken together, aberrant proliferation of airway progenitor cells in both epithelium and sub-epithelium are implicated in bronchiectasis.

3055 Reconstruction of Patient-specific Distal Airway Regeneration Patterns in COPD

OBJECTIVES/SPECIFIC AIMS: The objective of this study was to reconstruct patient-specific distal airway patterns at the tissue- and single-cell resolution and develop personalized distal airway models based on utilization of patient-derived DABCs and autologous region-specific stromal cells. METHODS/STUDY POPULATION: Patient-specific distal airway units, containing parental small bronchiole (<2 mm in diameter, >12th generation) and daughter airway branches, including pre-terminal/terminal bronchioles, leading to alveoli (3-7 units/lung), were dissected. Epithelial and stromal cells were isolated from these units and processed for ddSeq single-cell RNA-sequencing (n=6 samples). Autologous DABCs and stromal cells were isolated, propagated, biobanked, and used for establishment of patient-specific distal airway models (3D-organoids and air-liquid interface-based airway wall model; n=10 samples). Region-specific tissue patterns were evaluated using immunofluorescence and laser-capture microdissection (LCM; n=6 samples). RESULTS/ANTICIPATED RESULTS: Single-cell-based human distal airway transcriptome map (constructed based on the analysis of >6,500 distal airway cells obtained from 6 subjects) identified physiological and COPD-relevant distal airway differentiation patterns, including distal airway-specific secretory phenotype (DASP) characterized with high expression of secretoglobins 3A2 and 3A1, surfactant proteins SFTPB and SFTPA2, and mucin 1, unique signatures of DABCs, and stromal (fibroblasts, smooth muscle, endothelial cell subpopulations) and immune (macrophage, T cells, B cell, mast cells). Immunofluorescence analysis and LCM confirmed distribution of cell type-specific markers with differential expression patterns of DABC and DASP signatures. Patient-derived DABC-stromal co-culture models reproduced 3 regenerative patterns: 1) physiological (high DABC-clonogenic potency, establishment of polarized differentiated organoids and DASP-expressing epithelia); 2) hypo-regenerative (failure of DABCs to form clones, spheres and mechanically stable differentiated epithelial barrier); and 3) hyperplastic (generation of DABC hyperplasia accompanied in some COPD samples by mucous-cell hyperplasia mimicking in vivo remodeling patterns). DISCUSSION/SIGNIFICANCE OF IMPACT: Patient-specific maps and models of distal airway regeneration patterns have been established in this study, which can be used to identify candidate pathways that mediate disease-relevant airway remodeling and potentially utilized as pre-clinical platforms for developing personalized therapeutic approaches to suppress the progression of distal airway remodeling in chronic lung diseases, including COPD.

Comparison of inducible nitric oxide synthase mRNA expression in different airway portions and association with nitric oxide parameters from patients with asthma.

BackgroundFractional exhaled nitric oxide concentration (FeNO) is widely used to support diagnosis and monitoring of bronchial asthma (BA). Tsoukias and George proposed a two‐compartment model (2CM) for assessing the alveolar concentration of NO, referred to as CANO(2CM), while Condorelli et al proposed a model based on the trumpet shape of the airway tree and axial diffusion (TMAD), referred to as CANO(TMAD). In addition, Högman et al proposed non‐linear model, referred to as CANO(non‐linear).ObjectiveWe examined associations between the expression of inducible nitric oxide synthase (iNOS) mRNA in airway cells (ACs) by bronchoscopy and NO‐parameters calculated by the three methods and identified which of them accurately reflected expression of iNOS mRNA from different airway portions.MethodsWe retrospectively analysed data of 18 patients with stable, mild‐moderate asthma, including 10 steroid‐naïve BA (snBA) patients. Samples were obtained from airway brushings and bronchoalveolar lavage (BAL). Expressions of iNOS protein in tissue samples were evaluated by immunostaining. The iNOS mRNA in ACs was measured by qPCR. NO‐parameters calculated by the three methods above and evaluated whether they were associated with iNOS mRNA in ACs derived from proximal (2nd carina), distal (10‐15th) airways and alveolar regions.ResultsImmunostaining revealed expression of iNOS proteins mainly in epithelial cells in the airways, while it was mainly expressed in macrophages in the alveolar region in the snBA group. The iNOS mRNA expression was increased in both proximal and distal ACs in the snBA group compared with steroid‐treated BA group (stBA). CANO(2CM) negatively associated with FEV 1 (%predicted) and also associated with iNOS mRNA in distal ACs significantly. However, CANO(TMAD) and CANO(non‐linear) showed no correlation with lung function nor iNOS mRNA expression in any portions of ACs.ConclusionsThese results suggested that CANO(2CM) reflected distal airway inflammation in steroid‐naïve asthma.

Long-Term Culture of Distal Airway Epithelial Cells Allows Differentiation Towards Alveolar Epithelial Cells Suited for Influenza Virus Studies

As the target organ for numerous pathogens, the lung epithelium exerts critical functions in health and disease. However, research in this area has been hampered by the quiescence of the alveolar epithelium under standard culture conditions. Here, we used human distal airway epithelial cells (DAECs) to generate alveolar epithelial cells. Long-term, robust growth of human DAECs was achieved using co-culture with feeder cells and supplementation with epidermal growth factor (EGF), Rho-associated protein kinase inhibitor Y27632, and the Notch pathway inhibitor dibenzazepine (DBZ). Removal of feeders and priming with DBZ and a cocktail of lung maturation factors prevented the spontaneous differentiation into airway club cells and instead induced differentiation to alveolar epithelial cells. We successfully transferred this approach to chicken distal airway cells, thus generating a zoonotic infection model that enables studies on influenza A virus replication. These cells are also amenable for gene knockdown using RNAi technology, indicating the suitability of the model for mechanistic studies into lung function and disease.

Cell type specific expression of Follistatin-like 1 (Fstl1) in mouse embryonic lung development.

Follistatin like-1 (Fstl1) is a secreted glycoprotein and can be up-regulated by TGF-β1. To better study the function of Fstl1 in lung development, we examined Fstl1 expression in the developing lung, in a cell type specific manner, using a tamoxifen inducible Fstl1-reporter mouse strain. Our results show that Fstl1 is ubiquitously expressed at saccular stage in the developing lung. At E18.5, Fstl1 expression is robust in most type of mesenchymal cells, including airway smooth muscle cells surrounding airways, vascular smooth muscle cells, endothelial cells, and vascular pericytes from blood vessel, but not PDGFRα+ fibroblasts in the distal alveolar sacs. Meanwhile, relative weak and sporadic signals of Fstl1 expression are observed in epithelium, including a subgroup of club cells in proximal airways and a few type II alveolar epithelial cells in distal airways. Our data help to understand the critical role of Fstl1 in lung development and lung disease pathogenesis.

Demonstration of the contributions of pulmonary CYPs to naphthalene‐induced airway toxicity using lung‐Cpr‐null mice

Naphthalene (NA) is an omnipresent air pollutant and respiratory toxicant. NA induces cytotoxicity in airways following bioactivation by CYP (P450) enzymes. Previous studies suggested that liver and lung are both capable of bioactivating NA in vitro and in vivo. However, direct evidence for a specific role of pulmonary P450 enzymes in mediating NA‐induced airway toxicity, particularly upon exposure to NA via the systemic route, is still lacking.The aim of this study was to examine the specific contribution of pulmonary CYPs to airway toxicity of NA using a lung‐Cpr‐null mouse. We predicted that lung epithelial cells that lack Cpr expression, which would have little microsomal P450 activity, would be resistant to NA‐induced cytotoxicity. Cre‐mediated deletion of Cpr in the lung‐Cpr‐null mouse occurred in a substantial proportion of the Club cells, which, before undergoing Cpr deletion, had high ability to bioactivate NA. Under the conditions used, doxycycline‐induced deletion of Cpr occurred in 66% of Club cells in proximal airways and 86% of Club cells in distal airways, based on the results of a dual immunofluorescence study. Levels of NA and NA‐GSH (a biomarker of NA bioactivation) were similar in the plasma of lung‐Cpr‐null mice and their control littermates after administration of a single bolus dose of NA (200 mg/kg). Histological examination of airways revealed that NA‐induced damage of epithelial cells is focal and mild in lung‐Cpr‐null mice compared to severe exfoliation of epithelial cells in most airways in NA‐treated control mice. Moreover, the number of proliferating (BrdU‐positive) airway epithelial cells was 4‐fold lower in NA‐treated lung‐Cpr‐null mice than in NA‐treated control littermates.These results confirm that CYPs in the lung can mediate NA‐induced airway epithelial damage in vivo.Support or Funding Informationsupported in part by NIH grant ES020867This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Time- and concentration-dependent genomic responses of the rat airway to inhaled nickel sulfate.

While insoluble nickel subsulfide (Ni3S2) was carcinogenic in the lung in a 2‐year rat bioassay, soluble nickel sulfate hexahydrate (NiSO4*6H2O) was not. To investigate whether differences in the cellular responses to these two nickel compounds could underlie their differential activities, we conducted parallel studies to determine the gene expression changes in micro‐dissected lung distal airway cells from Fischer 344 rats following inhalation of the two compounds for one and four weeks (6 hr per day, 5 days per week). The results of the Ni3S2 study have been reported previously; this paper reports the results for NiSO4 and provides a comparative analysis. The cellular responses to NiSO4 were highly similar to those previously reported for Ni3S2, and a set of genes was identified whose expression could be used as biomarkers for comparing cellular nickel effects from in vitro or in vivo studies with soluble NiSO4 and particulate Ni3S2. Evaluation of the genomic concentration‐responses for the two compounds suggests that the highest inhaled concentration in the tumor bioassay for NiSO4, which was limited by toxicity, may not have achieved the Ni concentrations at which tumors were observed in the Ni3S2 bioassay. However, several key differences in the immune responses to NiSO4 and Ni3S2 were identified that may result from the differential intracellular disposition of Ni from NiSO4 entering the cell as an ion rather than as a slowly soluble Ni3S2 particle. These differences may also contribute to the observation of tumors in the bioassay for Ni3S2 but not NiSO4. Environ. Mol. Mutagen. 58:607–618, 2017. © 2017 The Authors Environmental and Molecular Mutagenesis published by Wiley Periodicals, Inc. on behalf of Environmental Mutagen Society

Postnatal development of the bronchiolar club cells of distal airways in the mouse lung: stereological and molecular biological studies.

Club (Clara) cells are nonciliated secretory epithelial cells present in bronchioles of distal pulmonary airways. So far, no information is available on the postnatal differentiation of club cells by a combination of molecular biological, biochemical, and stereological approaches in the murine lung. Therefore, the present study was designed to investigate the changes in the club cell secretory proteins (CC10, surfactant proteins A, B and D) and club cell abundance within the epithelium of bronchioles of distal airways during the postnatal development of the mouse lung. Perfusion-fixed murine lungs of three developmental stages (newborn, 15-day-old and adult) were used. Frozen, unfixed lungs were used for cryosectioning and subsequent laser-assisted microdissection of bronchiolar epithelial cells and RT-PCR analyses. High resolution analyses of the three-dimensional structures and composition of lung airways were obtained by scanning electron microscopy. Finally, using design-based stereology, the total and average club cell volume and the volume of secretory granules were quantified by light and transmission electron microscopy. Our results reveal that murine club cells are immature at birth and differentiate postnatally. Further, increase of the club cell volume and number of intracellular granules are closely correlated to the total lung volume enlargement. However, secretory granule density was only increased within the first 15days of postnatal development. The differentiation is accompanied by a decrease in glycogen content, and a close positive relationship between CC10 expression and secretory granule abundance. Taken together, our data are consistent with the concept that the morphological and functional differentiation of club cells is a postnatal phenomenon.

Erratum: Non-small-cell lung cancers: a heterogeneous set of diseases

Nature Reviews Cancer 14, 535–546 (2014) In the original version of this article, the word 'proximal' was incorrectly used twice instead of 'distal' in two sentences in the legend for Figure 2. The sentences should have stated “ADCs can be modelled by KrasG12D expression (long latency), KrasG12D expression and Trp53-null, and epidermal growth factor receptor (EGFR)T790M/L858R, among other genetic models, and they are thought to arise from more distal airway cells.

Downregulation of p300 gene expression in airway mesenchyme of nitrofen-induced hypoplastic lungs

Congenital diaphragmatic hernia (CDH) is a relatively common developmental abnormality causing life-threatening respiratory distress at birth. The nitrofen model has been widely used to investigate the pathogenesis of hypoplastic lungs associated with CDH. Embryos lacking p300 and CBP genes are significantly smaller in lung formation. We hypothesized that pulmonary gene expression of p300 and CBP is downregulated during late gestation in the nitrofen-induced CDH model. Time-pregnant rats were treated with either nitrofen or vehicle on gestational day 9 (D9). Fetal lungs were harvested on D18 and D21 (n = 8 at each time point). Pulmonary gene expression of p300 and CBP was analyzed by quantitative real-time PCR. Immunohistochemistry was performed to investigate expression and localization of pulmonary p300 and CBP proteins. Relative mRNA expression levels of p300 were significantly decreased in nitrofen-induced hypoplastic lungs on D18 compared to controls (3.00 ± 0.20 vs. 3.76 ± 0.14; p = 0.0039), while CBP levels were not altered. p300 immunoreactivity was markedly diminished in surrounding mesenchymal compartments and nuclei of proximal and distal airway cells, while CBP expression was not altered. Downregulation of p300 gene expression during the early canalicular stage may disrupt epithelial-mesenchymal signaling interactions, contributing to the development of hypoplastic lungs in the nitrofen-induced CDH model.

Role of PTEN in basal cell derived lung carcinogenesis

Lung adenocarcinoma (AdC) and lung squamous cell carcinoma (SCC) are the most common non-small cell lung cancer (NSCLC) subtypes, however, most genetic mouse models of lung cancer produce predominantly, if not exclusively, AdC. Whether this is secondary to targeting mutations to the distal airway cells or to the use of activating Kras mutations that drive AdC formation is unknown. We previously showed that targeting Kras(G12D) activation and transforming growth factor β receptor type II (TGFβRII) deletion to airway basal cells via a keratin promoter induced formation of both lung AdC and SCC. In this study we assessed if targeting phosphatase and tensin homologue (PTEN) deletion to airway basal cells could initiate lung tumor formation or increase lung SCC formation. We found that PTEN deletion is capable of initiating both lung AdC and SCC formation when targeted to basal cells and although PTEN deletion is a weaker tumor initiator than Kras(G12D) with low tumor multiplicity and long latency, tumors initiated by PTEN deletion were larger and displayed more malignant conversion than Kras(G12D) initiated tumors. That PTEN deletion did not increase lung SCC formation compared to Kras(G12D) activation, suggests that the initiating genetic event does not dictate tumor histology when genetic alterations are targeted to a specific cell. These studies also confirm that basal cells of the conducting airway are capable of giving rise to multiple NSCLC tumor types.

Long-term responses of canine lungs to acidic particles

Sixteen beagle dogs were housed in four large chambers under minimum restraint. They were exposed for 16 months to clean air and individual baseline data of markers were obtained. For 13 months, eight dogs were further exposed to clean air and eight dogs for 6 h/d to 1-μm MMAD (mass median aerodynamic diameter) acidic sulfate particles carrying 25 μmol H+ m−3 into their lungs. To establish functional responses (lung function, cell and tissue integrity, redox balance, and non-specific respiratory defense capacity), each exposed animal served as its own control. To establish structural responses, the eight non-exposed animals served as controls. Acidic particles were produced by nebulization of aqueous sodium hydrogen sulfate at pH 1.5. Only subtle exposure-related changes of lung function and structure were detected. A significant increase in respiratory burst function of alveolar macrophages points to a marginal inflammatory response. This can be explained by the significant production of prostaglandin E2, activating cyclooxygenase-dependent mechanisms in epithelia and thus inhibiting lung inflammation. The non-specific defense capacity was slightly affected, giving increased tracheal mucus velocity and reduced in vivo dissolution of moderately soluble test particles. Hypertrophy and hyperplasia of bronchial epithelia were not observed, but there was an increase in volume density of bronchial glands and a shift from neutral to acidic staining of epithelial secretory cells in distal airways. The acidic exposure had thus no pathophysiological consequences. It is therefore unlikely that long-term inhalation of acidic particles is associated with a health risk.

Small Cell Lung Cancer: Significance of RB Alterations and TTF-1 Expression in its Carcinogenesis, Phenotype, and Biology

Small cell lung cancer (SCLC) exhibits highly aggressive behavior and has a poor prognosis. While numerous investigations have been carried out, the exact mechanism of its carcinogenesis and aggressiveness is still unclear. SCLC is categorized as a neuroendocrine neoplasia and has a genetic profile characterized by universal alterations of the RB and TP53 genes. Epidemiological studies indicate the majority of SCLCs to be caused by smoking and the TP53 mutational pattern to be consistent with that evoked by smoke carcinogens; however, there is no direct evidence that such carcinogens induce alterations to RB in SCLC. While the importance of these alterations in the carcinogenesis of SCLC is strongly suggested, the exact molecular mechanism has been only little elucidated. SCLC cells almost always express mammalian achaete-scute homolog-1 (MASH1) and thyroid transcription factor-1 (TTF-1). MASH1 plays a critical role in neuroendocrine differentiation. TTF-1 is a characteristic marker of distal airway cells and pulmonary adenocarcinomas, but is also expressed in extrapulmonary neuroendocrine cancers. Thus, TTF-1 may well play a significant role in the development of neuroendocrine cancers. Recent studies indicate that the airway stem cell is committed to the neuroendocrine lineage through MASH1 and Notch signaling and that only RB-deleted neuroendocrine cells selectively proliferate in response to E2F3, eventually undergoing transformation to neuroendocrine cancer cells, probably in concert with TP53 gene aberrations. Thus, alterations of both the RB and TP53 genes are central to the carcinogenesis of SCLC, while many other factors including MASH1 and TTF-1 contribute to the development and biological behavior of SCLC.

CHARACTERIZATION OF ALVEOLAR EPITHELIAL CELLS CULTURED IN SEMIPERMEABLE HOLLOW FIBERS

Cell culture methods commonly used to represent alveolar epithelial cells in vivo have lacked airflow, a 3-dimensional air-liquid interface, and dynamic stretching characteristics of native lung tissue—physiological parameters critical for normal phenotypic gene expression and cellular function. Here the authors report the development of a selectively semipermeable hollow fiber culture system that more accurately mimics the in vivo microenvironment experienced by mammalian distal airway cells than in conventional or standard air-liquid interface culture. Murine lung epithelial cells (MLE-15) were cultured within semipermeable polyurethane hollow fibers and introduced to controlled airflow through the microfiber interior. Under these conditions, MLE-15 cells formed confluent monolayers, demonstrated a cuboidal morphology, formed tight junctions, and produced and secreted surfactant proteins. Numerous lamellar bodies and microvilli were present in MLE-15 cells grown in hollow fiber culture. Conversely, these alveolar type II cell characteristics were reduced in MLE-15 cells cultured in conventional 2D static culture systems. These data support the hypothesis that MLE-15 cells grown within our microfiber culture system in the presence of airflow maintain the phenotypic characteristics of type II cells to a higher degree than those grown in standard in vitro cell culture models. Application of our novel model system may prove advantageous for future studies of specific gene and protein expression involving alveolar epithelial or bronchiolar epithelial cells.

Side population cells and Bcrp1 expression in lung.

Side population (SP) cells are a rare subset of cells found in various tissues that are highly enriched for stem cell activity. SP cells can be isolated by dual-wavelength flow cytometry because of their capacity to efflux Hoechst dye, a process mediated by the ATP-binding cassette transporter breast cancer resistance protein (Bcrp) 1. By performing flow cytometry of enzymedigested mouse lung stained with Hoechst dye, we found that SP cells comprise 0.03-0.07% of total lung cells and are evenly distributed in proximal and distal lung regions. By RT-PCR, we found that lung SP cells express hepatocyte nuclear factor-3beta, but not thyroid transcription factor-1. Surface marker analysis revealed lung SP cells to be stem cell antigen 1 positive, Bcrp1 positive, lineage marker negative, and heterogeneous at the CD45 locus. As expected, we did not detect lung SP cells in Bcrp1-deficient animals. We, therefore, employed nonisotopic in situ hybridization and immunostaining for Bcrp1 as a strategy to localize these cells in vivo. Expression was observed in distinct lung cell types: bronchial and vascular smooth muscle cells and round cells within the distal air space. We confirmed the expression of Bcrp1 in primary bronchial smooth muscle cell cultures (BSMC) and in lavaged distal airway cells, but neither possessed the capacity to efflux Hoechst dye. In BSMC, Bcrp1 was localized to an intracellular compartment, suggesting that the molecular site of Bcrp1 expression regulates SP phenotype.