Lung endocrine cell markers, peptides, and amines

The melatonergic pathway and its interactions in modulating respiratory system disorders

Melatonin is a key intracellular neuroimmune-endocrine regulator and coordinator of multiple complex and interrelated biological processes. The main functions of melatonin include the regulation of neuroendocrine and antioxidant system activity, blood pressure, rhythms of the sleep-wake cycle, the retardation of ageing processes, as well as reseting and optimizing mitochondria and thereby the cells of the immune system. Melatonin and its agonists have therefore been mooted as a treatment option across a wide array of medical disorders. This article reviews the role of melatonin in the regulation of respiratory system functions under normal and pathological conditions. Melatonin can normalize the structural and functional organization of damaged lung tissues, by a number of mechanisms, including the regulation of signaling molecules, oxidant status, lipid raft function, optimized mitochondrial function and reseting of the immune response over the circadian rhythm. Consequently, melatonin has potential clinical utility for bronchial asthma, chronic obstructive pulmonary disease, lung cancer, lung vascular diseases, as well as pulmonary and viral infections. The integration of melatonin's effects with the alpha 7 nicotinic receptor and the aryl hydrocarbon receptor in the regulation of mitochondrial function are proposed as a wider framework for understanding the role of melatonin across a wide array of diverse pulmonary disorders.

Immediate Release of Gastrin-Releasing Peptide Mediates Delayed Radiation-Induced Pulmonary Fibrosis

Radiation-induced pulmonary fibrosis (RTPF) is a progressive, serious condition in many subjects treated for thoracic malignancies or after accidental nuclear exposure. No biomarker exists for identifying the irradiated subjects most susceptible to pulmonary fibrosis (PF). Previously, we determined that gastrin-releasing peptide (GRP) was elevated within days after birth in newborns exposed to hyperoxia who later developed chronic lung disease. The goal of the current study was to test whether radiation (RT) exposure triggers GRP release in mice and whether this contributes to RTPF in vivo. We determined urine GRP levels and lung GRP immunostaining in mice 0 to 24 after post-thoracic RT (15 Gy). Urine GRP levels were significantly elevated between 24 hours post-RT; GRP-blocking monoclonal antibody 2A11, given minutes post-RT, abrogated urine GRP levels by 6 to 12 hours and also altered phosphoprotein signaling pathways at 24 hours post-RT. Strong extracellular GRP immunostaining was observed in lung at 6 hours post-RT. Mice given one dose of GRP monoclonal antibody 2A11 24 hours post-RT had significantly reduced myofibroblast accumulation and collagen deposition 15 weeks later, indicating protection against lung fibrosis. Therefore, elevation of urine GRP could be predictive of RTPF development. In addition, transient GRP blockade could mitigate PF in normal lung after therapeutic or accidental RT exposure.

Novel role of gastrin releasing peptide-mediated signaling in the host response to influenza infection

Gastrin-releasing peptide (GRP) is an evolutionarily well-conserved neuropeptide that was originally recognized for its ability to mediate gastric acid secretion in the gut. More recently, however, GRP has been implicated in pulmonary lung inflammatory diseases including bronchopulmonary dysplasia, chronic obstructive pulmonary disease, emphysema, and others. Antagonizing GRP or its receptor mitigated lethality associated with the onset of viral pneumonia in a well-characterized mouse model of influenza. In mice treated therapeutically with the small-molecule GRP inhibitor, NSC77427, increased survival was accompanied by decreased numbers of GRP-producing pulmonary neuroendocrine cells, improved lung histopathology, and suppressed cytokine gene expression. In addition, in vitro studies in macrophages indicate that GRP synergizes with the prototype TLR4 agonist, lipopolysaccharide, to induce cytokine gene expression. Thus, these findings reveal that GRP is a previously unidentified mediator of influenza-induced inflammatory disease that is a potentially novel target for therapeutic intervention.

Formation of a Neurosensory Organ by Epithelial Cell Slithering

Epithelial cells are normally stably anchored, maintaining their relative positions and association with the basement membrane. Developmental rearrangements occur through cell intercalation, and cells can delaminate during epithelial-mesenchymal transitions and metastasis. We mapped the formation of lung neuroepithelial bodies (NEBs), innervated clusters of neuroendocrine/neurosensory cells within the bronchial epithelium, revealing a targeted mode of cell migration that we named "slithering," in which cells transiently lose epithelial character but remain associated with the membrane while traversing neighboring epithelial cells to reach cluster sites. Immunostaining, lineage tracing, clonal analysis, and live imaging showed that NEB progenitors, initially distributed randomly, downregulate adhesion and polarity proteins, crawling over and between neighboring cells to converge at diametrically opposed positions at bronchial branchpoints, where they reestablish epithelial structure and express neuroendocrine genes. There is little accompanying progenitor proliferation or apoptosis. Activation of the slithering program may explain why lung cancers arising from neuroendocrine cells are highly metastatic.

Multipotent capacity of immortalized human bronchial epithelial cells

While the adult murine lung utilizes multiple compartmentally restricted progenitor cells during homeostasis and repair, much less is known about the progenitor cells from the human lung. Translating the murine stem cell model to humans is hindered by anatomical differences between species. Here we show that human bronchial epithelial cells (HBECs) display characteristics of multipotent stem cells of the lung. These HBECs express markers indicative of several epithelial types of the adult lung when experimentally tested in cell culture. When cultured in three different three-dimensional (3D) systems, subtle changes in the microenvironment result in unique responses including the ability of HBECs to differentiate into multiple central and peripheral lung cell types. These new findings indicate that the adult human lung contains a multipotent progenitor cell whose differentiation potential is primarily dictated by the microenvironment. The HBEC system is not only important in understanding mechanisms for specific cell lineage differentiation, but also for examining changes that correlate with human lung diseases including lung cancer.

Gastrin-releasing peptide blockade as a broad-spectrum anti-inflammatory therapy for asthma

Gastrin-releasing peptide (GRP) is synthesized by pulmonary neuroendocrine cells in inflammatory lung diseases, such as bronchopulmonary dysplasia (BPD). Many BPD infants develop asthma, a serious disorder of intermittent airway obstruction. Despite extensive research, early mechanisms of asthma remain controversial. The incidence of asthma is growing, now affecting >300 million people worldwide. To test the hypothesis that GRP mediates asthma, we used two murine models: ozone exposure for air pollution-induced airway hyperreactivity (AHR), and ovalbumin (OVA)-induced allergic airway disease. BALB/c mice were given small molecule GRP blocking agent 77427, or GRP blocking antibody 2A11, before exposure to ozone or OVA challenge. In both models, GRP blockade abrogated AHR and bronchoalveolar lavage (BAL) macrophages and granulocytes, and decreased BAL cytokines implicated in asthma, including those typically derived from Th1 (e.g., IL-2, TNFα), Th2 (e.g., IL-5, IL-13), Th17 (IL-17), macrophages (e.g., MCP-1, IL-1), and neutrophils (KC = IL-8). Dexamethasone generally had smaller effects on all parameters. Macrophages, T cells, and neutrophils express GRP receptor (GRPR). GRP blockade diminished serine phosphorylation of GRPR with ozone or OVA. Thus, GRP mediates AHR and airway inflammation in mice, suggesting that GRP blockade is promising as a broad-spectrum therapeutic approach to treat and/or prevent asthma in humans.

Expression of GABAergic system in pulmonary neuroendocrine cells and airway epithelial cells in GAD67-GFP knock-in mice

Gamma-aminobutyric acid (GABA), a major inhibitory neurotransmitter in the brain, is also located in many peripheral nonneuronal tissues. The glutamate decarboxylase 67-green fluorescent protein (GAD67-GFP) knock-in mouse is a useful model for studying the distribution of GABAergic cells in many tissues and organs. The lungs of these mice contain cells with an intense GFP signal exclusively in the airway epithelium. We aimed to characterize the GFP-positive cells and to clarify their relationship with the GABAergic system. We identified the GFP-positive cells as pulmonary neuroendocrine cells (PNECs) by immunohistochemistry for the protein gene product 9.5 and calcitonin gene-related peptide and by ultrastructural analysis. Immunohistochemistry for GADs and GABA revealed GAD65/67 and GABA in GFP-positive PNECs. Reverse transcription-polymerase chain reaction analyses revealed mRNAs encoding the GABA(B) receptor subunits necessary for the assembly of functional receptors, R1 and R2, in the lung. GABA(B) receptor subunit R1 and R2 proteins were expressed in many airway epithelial cells including alveolar epithelial cells other than GFP-positive PNECs. The present findings demonstrated that PNECs in the airway epithelium have a GABA production system and indicated that GABA plays functional roles in airway epithelial cells through GABA(B) receptors.

Bombesin-like peptides modulate alveolarization and angiogenesis in bronchopulmonary dysplasia

RATIONALE

The incidence of bronchopulmonary dysplasia (BPD), a chronic lung disease of newborns, is paradoxically rising despite medical advances. We demonstrated elevated bombesin-like peptide levels in infants that later developed BPD. In the 140-day hyperoxic baboon model of BPD, anti-bombesin antibody 2A11 abrogated lung injury.

OBJECTIVES

To test the hypothesis that bombesin-like peptides mediate BPD in extremely premature baboons (born at Gestational Day 125 and given oxygen pro re nata [PRN], called the 125-day PRN model), similar to "modern-day BPD."

METHODS

The 125-day animals were treated with 2A11 on Postnatal Day 1 (P1), P3, and P6. On P14 and P21, lungs were inflation-fixed for histopathologic analyses of alveolarization. Regulation of angiogenesis by bombesin was evaluated using cultured pulmonary microvascular endothelial cells.

MEASUREMENTS AND MAIN RESULTS

In 125-day PRN animals, urine bombesin-like peptide levels at P2-3 are directly correlated with impaired lung function at P14. Gastrin-releasing peptide (the major pulmonary bombesin-like peptide) mRNA was elevated eightfold at P1 and remained high thereafter. At P14, 2A11 reduced alveolar wall thickness and increased the percentage of secondary septa containing endothelial cells. At P21, 2A11-treated 125-day PRN animals had improved alveolarization according to mean linear intercepts and number of branch points per millimeter squared. Bombesin promoted tubulogenesis of cultured pulmonary microvascular endothelial cells, but cocultured fetal lung mesenchymal cells abrogated this effect.

CONCLUSIONS

Early bombesin-like peptide overproduction in 125-day PRN animals predicted alveolarization defects weeks later. Bombesin-like peptide blockade improved septation, with the greatest effects at P21. This could have implications for preventing BPD in premature infants.

A confocal microscopic study of solitary pulmonary neuroendocrine cells in human airway epithelium

BACKGROUND

Pulmonary neuroendocrine cells (PNEC) are specialized epithelial cells that are thought to play important roles in lung development and airway function. PNEC occur either singly or in clusters called neuroepithelial bodies. Our aim was to characterize the three dimensional morphology of PNEC, their distribution, and their relationship to the epithelial nerves in whole mounts of adult human bronchi using confocal microscopy.

METHODS

Bronchi were resected from non-diseased portions of a lobe of human lung obtained from 8 thoracotomy patients (Table 1) undergoing surgery for the removal of lung tumors. Whole mounts were stained with antibodies to reveal all nerves (PGP 9.5), sensory nerves (calcitonin gene related peptide, CGRP), and PNEC (PGP 9.5, CGRP and gastrin releasing peptide, GRP). The analysis and rendition of the resulting three-dimensional data sets, including side-projections, was performed using NIH-Image software. Images were colorized and super-imposed using Adobe Photoshop.

RESULTS

PNEC were abundant but not homogenously distributed within the epithelium, with densities ranging from 65/mm2 to denser patches of 250/mm2, depending on the individual wholemount. Rotation of 3-D images revealed a complex morphology; flask-like with the cell body near the basement membrane and a thick stem extending to the lumen. Long processes issued laterally from its base, some lumenal and others with feet-like processes. Calcitonin gene-related peptide (CGRP) was present in about 20% of PNEC, mainly in the processes. CGRP-positive nerves were sparse, with some associated with the apical part of the PNEC.

CONCLUSION

Our 3D-data demonstrates that PNEC are numerous and exhibit a heterogeneous peptide content suggesting an active and diverse PNEC population.

Functional morphology of pulmonary neuroepithelial bodies: extremely complex airway receptors

Innervated groups of neuroendocrine cells, called neuroepithelial bodies (NEBs), are diffusely spread in the epithelium of intrapulmonary airways in many species. Our present understanding of the morphology of NEBs in mammalian lungs is comprehensive, but none of the proposed functional hypotheses have been proven conclusively. In recent reviews on airway innervation, NEBs have been added to the list of presumed physiological lung receptors. Microscopic data on the innervation of NEBs, however, have given rise to conflicting interpretations. Using neuronal tracing, denervation, and immunostaining, we recently demonstrated that the innervation of NEBs is much more complex than the almost unique vagal nodose sensory innervation suggested by other authors. The aim of the present work is to summarize our present understanding about the origin and chemical coding of the profuse nerve terminals that selectively contact pulmonary NEBs. A thorough knowledge of the complex interactions between the neuroendocrine cells and at least five different nerve fiber populations is essential for defining the position(s) of NEBs among the many pulmonary receptors characterized by lung physiologists.

Immunohistochemical mapping of endothelin in the developing and adult mouse lung

Endothelins (ET) are a family of regulatory peptides displaying, among other abilities, potent constrictor actions. We studied the perinatal time course expression and distribution of ET in the mouse airway epithelium. In fetal mouse, ET-immunoreactivity (IR) appeared earlier (gestational Day 18) in the epithelium of upper (bronchi and large bronchioles) than in lower airways, being scarce and mainly located in the apical cytoplasm. As the lung developed, ET-IR became gradually stronger and extended throughout the cell in both bronchi and bronchioles. ET-IR was found in most airway epithelial cells. Clara cells were positive for ET, whereas ciliated and endocrine cells were not. In adult lungs, part of the myocytes and parenchymal cells also showed ET-IR. In both developing and adult mouse lungs, the cell distribution of ET-IR in the epithelium is compatible with apical and/or basal secretion. The presence of ET in mouse airway epithelium during the perinatal period may indicate a role for ET as a growth factor in lung development and its involvement in control of lung ventilation at birth.

Neuroepithelial bodies in mammalian lung express functional serotonin type 3 receptor

Serotonin (5-HT) type 3 receptor (5-HT(3)-R) is a ligand-gated ion channel found primarily in the central and peripheral nervous system. We report expression and functional characterization of 5-HT(3)-R in pulmonary neuroepithelial body (NEB) cells. Using nonisotopic in situ hybridization, we demonstrate expression of 5-HT(3)-R mRNA in NEB cells in the lungs of different mammals (hamster, rabbit, mouse, and human). Dual immunocytochemistry (for 5-HT and 5-HT(3)-R) and confocal microscopy localized 5-HT(3)-R on NEB cell plasma membrane from rabbit. The electrophysiological characteristics of 5-HT(3)-R in NEB cells were studied in fresh slices of neonatal hamster lung using the whole cell patch-clamp technique. Application of the 5-HT (5-150 microM) and 5-HT(3)-R agonist 2-methyl-5-HT (5-150 microM) induced inward currents in a concentration-dependent manner. The 5-HT-induced current was blocked (76.5 +/- 5.9%) by the specific 5-HT(3)-R antagonist ICS-205-930 (50 microM), whereas katanserin and p-4-iodo-N-(2-[4-(methoxyphenyl)-1-piperazinyl]ethyl)-N-2-pyridinylbenzamide had minimal effects. Forskolin had no effect on desensitization and amplitude of the 5-HT-induced current. The reduction of Ca(2+) and Mg(2+) in the extracellular solution enhanced the amplitude of the 5-HT-induced current because of slower desensitization. Our studies suggest that 5-HT(3)-R in NEB cells may function as an autoreceptor and may potentially be involved in modulation of hypoxia signaling.

Fetal alveolar epithelial cells contain [D-Ala(2)]-deltorphin I-like immunoreactivity: delta- and mu-opiate receptors mediate opposite effects in developing lung

Opiate-like peptides can regulate many cellular functions. We now map [D-Ala(2)]deltorphin I (DADTI)-like immunoreactivity (DADTI-LI) in developing mouse lung and analyze potential functional roles. Most DADTI-LI-positive cells were alveolar cells negative for prosurfactant protein (proSP)-C immunoreactivity. Peak numbers of DADTI-LI-positive cells occurred on embryonic Day 18, decreasing postnatally. To analyze developmental effects of DADTI, e17-18 lung explants were treated with [D-Ala(2)]deltorphin II (DADTII, soluble DADTI analogue, delta-receptor-specific) versus dermorphin (mu-receptor-specific). Type II pneumocyte differentiation, assessed by [(3)H]choline incorporation into saturated phosphatidylcholine and proSP-C immunostaining, was inhibited by DADTII but stimulated by dermorphin. Cell proliferation, measured as [(3)H]-thymidine incorporation and proliferating cell nuclear antigen immunostaining, was stimulated by DADTII and inhibited by dermorphin. All effects were dose-dependent. DADTII-inhibited choline incorporation was reversed by the delta-blocker, naltrindole. Unexpectedly, DADTII-stimulated thymidine incorporation was augmented by naltrindole and reversed by naloxone (mu-blocker). Although dermorphin-stimulated choline incorporation was appropriately blocked by binaltorphimine, dermorphin-inhibited thymidine incorporation was reversed by delta, kappa-, or mu-blockers. The delta- and mu-receptor messenger RNAs occurred pre- and postnatally, whereas kappa-receptor transcripts occurred mainly prenatally. All three receptor proteins were present in epithelial and mesenchymal cells in e18 lung. Thus, DADTI-LI from proSP-C-immunonegative alveolar cells could regulate development via both direct and indirect effects involving multiple opiate receptors.

Differentiation and proliferation of pulmonary neuroendocrine cells

In this review article the morphological profiles of pulmonary neuroendocrine cells (PNEC) in experimental animals and humans are described. Although the mechanisms of differentiation and proliferation of neuroendocrine cells in the airway epithelium remain to be solved, several experimental studies using explant culture and cell culture systems of fetal animal lungs have been performed to clarify fundamental phenomena associated with neuroendocrine differentiation and proliferation. Experimental animal studies using chronic hypoxia, toxic substances and carcinogens have succeeded in inducing alterations in PNEC systems, and these studies have elucidated the reactions of PNEC in cell injury and inflammation, and functional aspects of PNEC in disease conditions. Human pulmonary neuroendocrine tumors include various histological subtypes, and show divergent morphological and biological varieties. Molecular abnormalities of small cell carcinoma, the most aggressive subtype of pulmonary neuroendocrine tumors, have been extensively studied, but the mechanism of neuroendocrine differentiation of this tumor is still largely unknown. PNEC share common phenotypes with neuronal cells, and developmental studies have begun contributed evidence that similar transcriptional networks, including active and repressive basic helix-loop-helix (bHLH) factors, function in the differentiation of both PNEC and neuronal cells. Such a bHLH network may also play a central role in determining cell differentiation in lung carcinomas. Further studies of the neuronal bHLH network, its regulatory system and related signal transduction pathways, will be required for understanding the mechanisms of neuroendocrine differentiation and proliferation in normal and pathological lung conditions.

Differential distribution of the neuron-associated class III beta-tubulin in neuroendocrine lung tumors

OBJECTIVE

To study the immunoreactivity profile of the neuron-associated class III beta-tubulin isotype (beta III) in epithelial lung tumors.

DESIGN

One hundred four formalin-fixed, paraffin-embedded primary and metastatic lung cancer specimens were immunostained with an anti-beta III mouse monoclonal antibody (TuJ1) and an anti-beta III affinity-purified rabbit antiserum. Paraffin sections from fetal, infantile, and adult nonneoplastic lung tissues were also examined.

RESULTS

In the fetal airway epithelium, beta III staining is detected transiently in rare Kulchitsky-like cells from lung tissues corresponding to the pseudoglandular and canalicular but not the saccular or alveolar stages of development. beta III is absent in healthy, hyperplastic, metaplastic, and dysplastic airway epithelium of the adult lung. In contrast, beta III is highly expressed in small cell lung cancer, large cell neuroendocrine carcinoma, and in some non-small cell lung cancers, particularly adenocarcinomas. There is no correlation between expression of beta III and generic neuroendocrine markers, such as chromogranin A and/or synaptophysin, in pulmonary adenocarcinomas. Also, focal beta III staining is present in primary and metastatic adenocarcinomas (to the lung) originating in the colon, prostate, and ovary. beta III is expressed to a much lesser extent in atypical carcinoids and is rarely detectable in typical carcinoids and squamous cell carcinomas of the lung. The distribution of beta III in small cell lung cancer and adenocarcinoma metastases to regional lymph nodes and brain approaches 100% of tumor cells, which is substantially greater than in the primary tumors.

CONCLUSIONS

In the context of neuroendocrine lung tumors, beta III immunoreactivity is a molecular signature of high-grade malignant neoplasms (small cell lung cancer and large cell neuroendocrine carcinoma) although its importance in atypical carcinoids must be evaluated further. In addition, beta III may be a useful diagnostic marker in distinguishing between small cell lung cancers and certain non-small cell lung cancers (poorly differentiated squamous cell carcinomas), especially in small biopsy specimens. To our knowledge, beta III is the only tumor biomarker that exhibits a substantially more widespread distribution in poorly differentiated than in better differentiated pulmonary neuroendocrine tumors. However, the significance of beta III phenotypes in non-small cell lung cancer, particularly adenocarcinoma, with respect to neuroendocrine differentiation and prognostic value, requires further evaluation.

Perinatal exposure to aged and diluted sidestream cigarette smoke produces airway hyperresponsiveness in older rats

Exposing rats to aged and diluted sidestream cigarette smoke (ADSS) throughout in utero and postnatal life results in airway hyperresponsiveness and an increase in pulmonary neuroendocrine cells (PNECs) and neuroepithelial bodies (NEBs) in 7- to 10-week-old rats. Since human epidemiologic studies suggest that perinatal exposure to environmental tobacco smoke (ETS) may be detrimental to the lung function of older children, this study was designed to determine if perinatal exposure alone results in airway hyperresponsiveness and increased PNECs/NEBs later in life in rats. Pregnant Sprague-Dawley rats were exposed to filtered air (FA, n = 7) or ADSS (1 mg/m3 total suspended particulates, n = 7) for 4 to 6 h/day starting on Day 3 of gestation. Their pups continued to receive the same exposure regimen postnatally until 21 days of age. Thereafter all pups were exposed to FA until about 8 weeks of age. The airway responsiveness of one female pup from each litter was then assessed using an isolated perfused lung system whereby increasing doses of methacholine (-9.25 to -7.50 log mol) were administered into the pulmonary artery and lung resistance (Rl), dynamic compliance (Cdyn), and pulmonary pressure (Ppa) were measured. The number of PNECs/NEBs and mast cells per millimeter basal lamina were determined using immunocytochemical and histological staining and morphometric analysis. Statistics were performed using an unpaired Student's t test and repeated measures analysis of variance. Perinatal ADSS exposure enhanced methacholine-induced changes in Rl (p = 0.02), Cdyn (p = 0.004), and Ppa (p = 0.007). At the highest dose of methacholine, Rl in the ADSS-exposed lungs was threefold that in FA-exposed lungs. Although total PNEC number increased approximately twofold in the ADSS-exposed animals, this change was not found to be statistically significant. Mast cell number also was not different between groups. These data suggest that exposure to ADSS during the perinatal period followed by 5 weeks exposure to FA induces airway hyperresponsiveness in the absence of a significant change in PNECs, NEBs, or mast cells.

The pulmonary neuroendocrine system and drainage of the fetal lung: effects of serotonin

The neuroendocrine system of the lungs is maximally developed and activated at birth, but has no clear function. Here, one of its products, serotonin, was tested for an ability to stop lung fluid production or activate reabsorption. Lungs from fetal guinea pigs (61 +/- 2 days of gestation) were supported in vitro for 3 h; lung liquid production was monitored by a dye dilution method. Initial studies on 36 young fetuses (61 +/- 1 days of gestation) showed that untreated controls produced fluid at 1.17 +/- 0.23 ml.kg-1.h-1, with no significant change over 3 h (ANOVA; regression analysis); those given 10(-8) M serotonin during the middle hour showed no significant changes, but those given 5 x 10(-8), 10(-7), 10(-6), or 10(-5) M serotonin reduced production significantly (P < 0.01 to P < 0.0005). Responses were linear up to 10(-7) M (threshold, 10(-9) M) and then become maximal at 50% reduction. However, responses increased with age. Comparison of 40 fetuses divided into groups of 60-61 or 65-67 days of gestation showed a large and significant increase in responses in the older fetuses (P < 0.01), where half the preparations reabsorbed fluid. Serotonin receptors were involved, since 10(-6) M cyproheptadine abolished responses (based on 24 preparations). Amiloride-sensitive Na+ channels were involved, since 10(-6) M amiloride abolished responses (based on 24 preparations). These results, in combination with earlier results from somatostatin and dopamine, together with histochemical and clinical observations, strongly suggest that the neuroendocrine system of the lungs may find a function in clearing fluid from the lungs at time of birth.

Immunoreactivity for the alpha-subunit of the pituitary glycoprotein hormones in pulmonary neuroendocrine cells of developing human lung and various perinatal diseases

Infant lung tissue, obtained at autopsy, was studied by immunohistochemistry for the presence of pituitary glycoprotein hormones (PGHs) in the lung. The infants, born at term or preterm, died of various causes. The results provide the first immunological evidence of the presence of the common a-subunit of the pituitary glycoprotein hormones (alphaPGH) in the lung. The immunoreactivity is located in the pulmonary neuroendocrine cells and neuroepithelial bodies. In addition, the cells labelled by alphaPGH antisera (alphaPGH cells) form a subpopulation of the neuroendocrine cells detected by anti-calcitonin immunohistochemistry (CT cells). Moreover, the number of alphaPGH cells appears to increase after neonatal pneumonia or when the number of CT cells is elevated following the development of disease. Also, the weak staining of one of the monoclonal antibodies against the specific b-subunit of thyrotropin (TSH) might, in combination with the increased detectability of a-subunits, indicate that TSH can be endogenously produced in the lung.

Pulmonary neuroendocrine cell system in pediatric and adult lung disease

In humans lungs affected by naturally occurring pulmonary disease, the pulmonary neuroendocrine cell system, which is normally arranged in a sparse but even distribution throughout the respiratory tract, increases in size. It is likely that the stimulus for this is pulmonary injury and that its purpose is the paracrine regulation of the restoration of pulmonary tissues to their normal state, an hypothesis supported by studies of animal lungs subjected to experimental injury as well as of the development of human and animal lungs in utero. Initially, this increase involves the development of interrupted rows of neuroendocrine cells. In the later stages, however, development of more disorderly intraepithelial aggregates can occur and the small, locally invasive neuroendocrine cell lesions known as tumourlets may occasionally result. Both of these latter structures often contain secretory products not found in the neuroendocrine cells of normal human lungs, probably indicating a derangement of what appears to be a fundamentally physiological response. It is likely that, in some circumstances, this disorderly change may contribute to pulmonary disease as well as being the result of it.

Comparative histology of pulmonary neuroendocrine cell system in mammalian lungs

It is increasingly recognized that neuroepithelial endocrine cells and organoid clusters of these cells termed neuroepithelial bodies are widely distributed in the respiratory tract of vertebrates. This review focuses on the neuroepithelial endocrine system in the airway epithelium of mammals according to observations made in a wide range of species, as it appears in light and electron microscopy by means of various visualization techniques under normal and experimental conditions. Because there are similarities but also marked differences between species, wherever possible studies in human airways are emphasized. Conventional histochemical and ultrastructural studies including microspectrofluorimetry have demonstrated the amine-handling properties and the presence of neurosecretory granules in neuroendocrine cells of the epithelium of all mammals studies so far. The neuroepithelial bodies are innervated by morphological afferent- and efferentlike synaptic specializations. These, together with the presence of reciprocal synapses, emphasize that these cells may be involved in dual functions of chemoreception and secretion. Light and electron microscopic immunohistochemistry has demonstrated that neuroepithelial endocrine cells may contain various biogenic agents, suggesting that the neuroendocrine system is highly heterogeneous. Neural elements may interact in a complex manner, and the activation of certain neural pathways may control the release of biogenic substances to influence physiological airway functions. They may be particularly relevant in pulmonary diseases. Consequently, the function of this system is complex and it is highly probable that many of its aspects are still not elucidated.

Molecular events in lung carcinogenesis

Genetic alterations seen in established lung cancers are also often found in premalignant respiratory epithelium. The frequency, usual order, biologic consequences, and prognostic import of the alterations are only beginning to be studied. Increased knowledge regarding pulmonary premalignancy may provide earlier, more treatable endpoints for early detection and therapy.

Ontogeny of neuroepithelial bodies: correlations with mitogenesis and innervation

This paper summarizes current knowledge and advances speculation about the formation of the neuroendocrine system of mammalian lungs (comprising uninnervated solitary and clustered small-granule cells and innervated neuroepithelial bodies). It relates the initial appearance of neuroendocrine cells to regulation of mitotic activity in the epithelium during the development of the lung and pays special attention to the later in growth of nerves that converts some of them into neuroepithelial bodies, structures considered ideally adapted to function as chemoreceptors. A few original observations from ongoing immunohistochemical, electron microscopic, and analytical studies have been included here and there to point the discussion. The neuroendocrine cells are derived from undifferentiated precursors present in the endodermal pulmonary epithelium. At an early pseudoglandular stage of lung development these precursors begin to differentiate into neuroendocrine small-granule cells, commencing in the larynx and upper trachea, and expanding centrifugally into pulmonary airways almost as rapidly as these are laid down. Subsequently many of the intrapulmonary small-granule cell clusters become innervated. This event, the delayed appearance of small-granule cells synthesizing other than the dominant peptides and amines (calcitonin gene-related peptide and serotonin in rodents, gastrin-releasing peptide and serotonin in human beings), and other regional adjustments yield the population distribution present in the lungs of adults. Neuroendocrine cell precursors normally differentiate into typical serotonin- or peptide-synthesizing small-granule cells without requiring direct contact by nerves, and dissociated cells from a previously innervated population continue to exhibit physiological characteristics of oxygen sensors despite the loss of contact with nerves. Development of the innervation occurs in stages. Small-granule cell clusters are reached first by ganglion cells derived from pulmonary neuroblasts and later on by processes of extrinsic sensory nerves. The latter not only convey information to the central nervous system but also serve in a variety of ways to extend the neuroepithelial bodies' sphere of influence within the lung itself.

NCAM expression in the pulmonary neural and diffuse neuroendocrine cell system

Neural cell adhesion molecule (NCAM)--a membrane protein involved in cell-cell adhesion within the central and peripheral nervous systems--was demonstrated to be a sensitive and specific marker for neuroepithelial bodies (NEB) and neural tissue elements in the cat lung. Using the streptavidin-biotin immunoperoxidase method, NCAM reactive sites were investigated with monoclonal and polyclonal antibodies on serial section of Bouin fixed, paraffin embedded lung tissue. Moreover, NCAM expression was compared with that of neuron-specific enolase (NSE) on adjacent sections. The most obvious NCAM staining was obtained with the monoclonal antibody. From newborn to adult life, cell surface labeling was identified on NEB cells. In mature cat lung, they were no longer positive. Solitary neuroendocrine cells (NEC) were always negative. In contrast to the transient postnatal immunoreactivity of NEB cells, nerve fibers and ganglion cells were stained throughout all life stages and studied. The distribution of NCAM in NEB, nerve fibers and ganglion cells was similar to that NSE, except in the adult lung. This study reveals that during lung growth shared NCAM antigens exist between the pulmonary nervous and endocrine system, whereas in mature lung NCAM proteins are confined to neural tissue elements. The difference in NCAM expression between NEB and NEC might suggest an involvement of NCAM in the formation of contacts between NEB cells and nerves.

Endocrine cells in tumour-bearing lungs

BACKGROUND

When hormones are detected in the serum of patients with bronchial carcinoma they are generally considered to originate from the tumour, but this may be not the only explanation. Pulmonary endocrine cells proliferate in lungs affected by non-neoplastic disease and their products are often demonstrable in the serum. The aim of this study was to examine the pulmonary endocrine systems of a series of tumour-bearing lungs to see whether any changes in them could possibly account for raised levels of pulmonary peptides in the blood.

METHODS

The morphology, number, distribution, and content of pulmonary endocrine cells in 30 pairs of tumour-bearing lungs from patients coming to necropsy with bronchial carcinoma were examined. These features were related to the pathology of the tumour and to other pathological changes present in the lungs, and compared with pulmonary endocrine cells in 10 pairs of control lungs from patients without pulmonary disease.

RESULTS

Increased numbers of endocrine cells, often in the form of large abnormal aggregates, were present in 17 pairs of tumour-bearing lungs where they were associated not with the tumour but with non-tumoral pathology, especially inflammation and changes associated with cardiac failure. Appropriate and inappropriate peptides were identified within them.

CONCLUSION

The possibility is raised that, in some subjects with bronchial carcinoma who have raised serum hormone levels, the source of these substances might be the endocrine cells in the diseased lung around the tumour.

Pulmonary Neuroendocrine Cells and Lung Development

Pulmonary neuroendocrine cells produce bioactive peptides such as gastrin-releasing peptide (GRP) at high levels in developing fetal lung. The role of GRP and other peptides in promoting branching morphogenesis, cell proliferation, and cell differentiation during lung organogenesis is reviewed. Possible roles for bioactive peptides derived from these cells in the pathophysiology of perinatal lung disorders are discussed.

Spectrum of neuroendocrine differentiation in lung cancer cell lines featured by cytomorphology, markers, and their corresponding tumors

Lung cancer cell lines which show features of neuroendocrine (NE) differentiation can be divided into 4 types which have distinct clinicopathologic correlates: classic small cell lung cancer (SCLC), variant SCLC, pulmonary carcinoid, and non-small cell lung cancer with NE features (NSCLC-NE). These cell lines form a spectrum regarding their degree of NE differentiation which ranges from high levels seen in carcinoid cell lines to very low which is typical of the variant SCLC. A careful comparison of the properties of tumors and their cell lines and correlating these data with the clinical history of the patient has markedly enhanced the relevance of cell lines as models for NE biology and lung carcinogenesis.

Hamster pulmonary endocrine cells with neural cell adhesion molecule (NCAM) immunostaining

Pulmonary endocrine cells of Syrian golden hamster were stained for neural cell adhesion molecule (NCAM) with indirect fluorescent immunostaining and observed with a confocal laser scanning microscope equipped with an argon laser. Sections 100 microns thick of hamster lung fixed with phosphate-buffered 4% paraformaldehyde were prepared. The sections were incubated with rat monoclonal antibody against NCAM, followed by fluorescence-labeled antibody against rat immunoglobulin. Some were doubly immunostained for NCAM and one of the following endocrine markers: neuron-specific enolase, calcitonin gene-related peptide and serotonin. Expression of NCAM in the hamster airway epithelium was seen in cell nests resembling neuroepithelial bodies (NEBs). NCAM immunostaining was positive at the lateral cell borders between the cells composing the nest, but negative at the border with the adjacent, presumably non-endocrine cells. Double immunostaining confirmed that the grouped cells with NCAM immunoreactivity were of an endocrine nature, but that single endocrine cells did not show NCAM immunoreactivity. An electron microscopic study with NCAM immunostaining confirmed the light microscopic study. These suggest that NCAM expression could be important for the morphogenesis of NEBs. A confocal laser microscope was used to make three-dimensional images of NEBs after NCAM immunostaining and the spatial interaction between NEBs and the surrounding microenvironment was studied.

A rhesus monkey model to characterize the role of gastrin-releasing peptide (GRP) in lung development. Evidence for stimulation of airway growth

Gastrin-releasing peptide (GRP) is developmentally expressed in human fetal lung and is a growth factor for normal and neoplastic lung but its role in normal lung development has yet to be clearly defined. In this study we have characterized the expression of GRP and its receptor in fetal rhesus monkey lung and determined the effects of bombesin on fetal lung development in vitro. By RNA blot analysis, GRP mRNA was first detectable in fetal monkey lung at 63 days gestation, reached highest levels at 80 days gestation, and then declined to near adult levels by 120 days gestation; a pattern closely paralleling GRP expression in human fetal lung. As in human lung, in situ hybridization localized GRP mRNA to neuroendocrine cells though during the canalicular phase of development (between 63-80 days gestation) GRP mRNA was present not only in classic pulmonary neuroendocrine cells, but also in cells of budding airways. Immunohistochemistry showed that bombesin-like immunoreactivity was present in neuroendocrine cells, but not in budding airways, suggesting that in budding airways either the GRP mRNA is not translated, is rapidly secreted, or a related, but different RNA is present. RNase protection analysis using a probe to the monkey GRP receptor demonstrated that the time course of receptor RNA expression closely paralleled the time course of GRP RNA expression. In situ hybridization showed that GRP receptors were primarily expressed in epithelial cells of the developing airways. Thus GRP would appear to be secreted from neuroendocrine cells to act on target cells in developing airways. This hypothesis was confirmed by organ culture of fetal monkey lung in the presence of bombesin and bombesin antagonists. Bombesin treatment at 1 and 10 nM significantly increased DNA synthesis in airway epithelial cells and significantly increased the number and size of airways in cultured fetal lung. In fact, culturing 60 d fetal lung for 5 d with 10 nM bombesin increased airway size and number nearly to that observed in cultured 80 d fetal lung. The effects of bombesin could be blocked by specific GRP receptor antagonists. Thus this study demonstrates that GRP receptors are expressed on airway epithelial cells in developing fetal lung and that the interaction of GRP with the GRP receptor stimulates airway development.

Oxygen sensing in airway chemoreceptors

Pulmonary neuroepithelial bodies, composed of innervated clusters of amine- and peptide-containing cells, are widely distributed throughout the airway mucosa of human and animal lungs. Structurally, neuroepithelial bodies resemble chemoreceptors (such as carotid body, taste buds) and are thought to function as hypoxia sensitive airway sensors. Evidence for this is indirect, however, and the mechanism of oxygen sensing by these cells is unknown. Here we culture neuroepithelial bodies isolated from rabbit fetal lungs and identify voltage-activated potassium, calcium and sodium currents using the whole-cell patch clamp technique. Upon exposure to hypoxia there is a reversible reduction (25-30%) in the outward potassium current, with no change in inward currents. In addition, we demonstrate the expression of an oxygen-binding protein (b-cytochrome, NADPH oxidase) on the plasma membrane of these cells. The identification of an oxygen-sensing mechanism (namely the presence of an O2-sensitive potassium channel coupled to an O2 sensor protein) in the cells of pulmonary neuroepithelial bodies indicates that they are transducers of the hypoxia stimulus and hence may function as airway chemoreceptors in the regulation of respiration.

Development of PGP 9.5- and calcitonin gene-related peptide-like immunoreactivity in organ cultured fetal rat lungs

Knowing that small-granule endocrine cells develop in organ cultured fetal lungs, we investigated whether the cells produce regulatory peptides in vitro, and if sufficient amounts appear to permit using the cultures as an experimental system for physiological study of secretory mechanisms. The paired lungs from 14-day and 15-day fetal rats were organ cultured for 1-8 days and examined daily for development of immunoreactivity against marker proteins and regulatory peptides associated with small-granule endocrine cells and nerves. They proved reactive against protein gene product 9.5 (PGP) and calcitonin-gene related peptide (CGRP) but not against calcitonin or neurofilament protein 200 K, although positive controls were obtained for these substances in lungs from postnatal animals. Initially PGP-like immunoreactivity is associated with cell bodies and processes of neuroblasts which run medial to the bronchial axis on day 14 and are increasingly prevalent on day 15. In 15-day explants PGP becomes detectable after a day in vitro in rare "clear cell" precursors of small-granule cells located in the epithelium lining proximate parts of the lungs, although in 14-day explants comparable reactivity is not seen until the third day (14 + 3 days). In culture PGP-positive neuroblasts increase in number, and nerve processes gradually extend down the airway to encircle the sleeve of smooth muscle that develops as the bronchial tree expands. Concurrently, the initially small clusters of small-granule cells increase in size, and new ones appear in the airway lining. By 15 + 5 days they extend to the boundary between a taller, more proximal epithelium and a glycogen-rich cuboidal layer that lines one or two most-distal generations of branches. Thereafter, the trachea and central, cartilage-bound segments of the primary bronchi mainly contain solitary endocrine cells and the more peripheral lung a mixture of single cells and clusters, much as in near-term lungs in vivo. At this stage PGP-positive nerves extend as far as the entrances of the terminal sacs, and most are distributed to the airway muscle plexus. Exceptionally, they may innervate a small-granule cell cluster, converting it into a neuroepithelial body. CGRP-like immunoreactivity initially appears in small-granule cells of 15 + 2-day cultures but does not develop in ganglion cells or nerves. It localizes to endocrine cells at all conducting airway levels, increasing in staining intensity and accounting for most if not all of the PGP-positive population between 15 + 4 - 15 + 8 days.(ABSTRACT TRUNCATED AT 400 WORDS)