Bombesin increases fetal lung growth and maturation in utero and in organ culture

Novel insight on GRP/GRPR axis in diseases

The gastrin-releasing peptide receptor (GRPR), a member of the G protein-coupled receptors (GPCRs), binds to ligands such as gastrin-releasing peptide (GRP) and plays a variety of biological roles. GRP/GRPR signalling is involved in the pathophysiological processes of many diseases, including inflammatory diseases, cardiovascular diseases, neurological diseases, and various cancers. In the immune system, the unique function of GRP/GRPR in neutrophil chemotaxis suggests that GRPR can be directly stimulated through GRP-mediated neutrophils to activate selective signalling pathways, such as PI3K, PKC, and MAPK, and participate in the occurrence and development of inflammation-related diseases. In the cardiovascular system, GRP increases intercellular adhesion molecule 1 (ICAM-1) and induces vascular cell adhesion molecule-1 (VCAM-1). GRP activates ERK1/2, MAPK, and AKT, leading to cardiovascular diseases, including myocardial infarction. Central nervous system signal transduction mediated by the GRP/GRPR axis plays a vital role in emotional responses, social interaction, and memory. The GRP/GRPR axis is elevated in various cancers, including lung, cervical, colorectal, renal cell, and head and neck squamous cell carcinomas. GRP is a mitogen in a variety of tumour cell lines. Its precursor, pro-gastrin-releasing peptide (ProGRP), may play an important role as an emerging tumour marker in early tumour diagnosis. GPCRs serve as therapeutic targets for drug development, but their function in each disease remains unclear, and their involvement in disease progression has not been well explored or summarised. This review lays out the above mentioned pathophysiological processes based on previous research conclusions. The GRP/GRPR axis may be a potential target for treating multiple diseases, and the study of this signalling axis is particularly important.

Intraluminal chloride regulates lung branching morphogenesis: involvement of PIEZO1/PIEZO2

BACKGROUND

Clinical and experimental evidence shows lung fluid volume as a modulator of fetal lung growth with important value in treating fetal lung hypoplasia. Thus, understanding the mechanisms underlying these morphological dynamics has been the topic of multiple investigations with, however, limited results, partially due to the difficulty of capturing or recapitulating these movements in the lab. In this sense, this study aims to establish an ex vivo model allowing the study of lung fluid function in branching morphogenesis and identify the subsequent molecular/ cellular mechanisms.

METHODS

Ex vivo lung explant culture was selected as a model to study branching morphogenesis, and intraluminal injections were performed to change the composition of lung fluid. Distinct chloride (Cl^-) concentrations (5.8, 29, 143, and 715 mM) or Cl^- channels inhibitors [antracene-9-carboxylic acid (A9C), cystic fibrosis transmembrane conductance regulator inhibitor172 (CFTRinh), and calcium-dependent Cl^- channel inhibitorA01 (CaCCinh)] were injected into lung lumen at two timepoints, day0 (D0) and D2. At D4, morphological and molecular analyses were performed in terms of branching morphogenesis, spatial distribution (immunofluorescence), and protein quantification (western blot) of mechanoreceptors (PIEZO1 and PIEZO2), neuroendocrine (bombesin, ghrelin, and PGP9.5) and smooth muscle [alpha-smooth muscle actin (α-SMA) and myosin light chain 2 (MLC2)] markers.

RESULTS

For the first time, we described effective intraluminal injections at D0 and D2 and demonstrated intraluminal movements at D4 in ex vivo lung explant cultures. Through immunofluorescence assay in in vivo and ex vivo branching morphogenesis, we show that PGP9.5 colocalizes with PIEZO1 and PIEZO2 receptors. Fetal lung growth is increased at higher [Cl^-], 715 mM Cl^-, through the overexpression of PIEZO1, PIEZO2, ghrelin, bombesin, MLC2, and α-SMA. In contrast, intraluminal injection of CFTRinh or CaCCinh decreases fetal lung growth and the expression of PIEZO1, PIEZO2, ghrelin, bombesin, MLC2, and α-SMA. Finally, the inhibition of PIEZO1/PIEZO2 by GsMTx4 decreases branching morphogenesis and ghrelin, bombesin, MLC2, and α-SMA expression in an intraluminal injection-independent manner.

CONCLUSIONS

Our results identify PIEZO1/PIEZO2 expressed in neuroendocrine cells as a regulator of fetal lung growth induced by lung fluid.

PET Probes for Preclinical Imaging of GRPR-Positive Prostate Cancer: Comparative Preclinical Study of [68Ga]Ga-NODAGA-AMBA and [44Sc]Sc-NODAGA-AMBA

Gastrin-releasing peptide receptors (GRPR) are overexpressed in prostate cancer (PCa). Since bombesin analogue aminobenzoic-acid (AMBA) binds to GRPR with high affinity, scandium-44 conjugated AMBA is a promising radiotracer in the PET diagnostics of GRPR positive tumors. Herein, the GRPR specificity of the newly synthetized [⁴⁴Sc]Sc-NODAGA-AMBA was investigated in vitro and in vivo applying PCa PC-3 xenograft. After the in-vitro assessment of receptor binding, PC-3 tumor-bearing mice were injected with [⁴⁴Sc]Sc/[⁶⁸Ga]Ga-NODAGA-AMBA (in blocking studies with bombesin) and in-vivo PET examinations were performed to determine the radiotracer uptake in standardized uptake values (SUV). ⁴⁴Sc/⁶⁸Ga-labelled NODAGA-AMBA was produced with high molar activity (approx. 20 GBq/µmoL) and excellent radiochemical purity. The in-vitro accumulation of [⁴⁴Sc]Sc-NODAGA-AMBA in PC-3 cells was approximately 25-fold higher than that of the control HaCaT cells. Relatively higher uptake was found in vitro, ex vivo, and in vivo in the same tumor with the ⁴⁴Sc-labelled probe compared to [⁶⁸Ga]Ga-NODAGA-AMBA. The GRPR specificity of [⁴⁴Sc]Sc-NODAGA-AMBA was confirmed by significantly (p ≤ 0.01) decreased %ID and SUV values in PC-3 tumors after bombesin pretreatment. The outstanding binding properties of the novel [⁴⁴Sc]Sc-NODAGA-AMBA to GRPR outlines its potential to be a valuable radiotracer in the imaging of GRPR-positive PCa.

Distinct Epithelial Cell Profiles in Normal Versus Induced-Congenital Diaphragmatic Hernia Fetal Lungs

BACKGROUND

Recent studies identified a great diversity of cell types in precise number and position to create the architectural features of the lung that ventilation and respiration at birth depend on. With damaged respiratory function at birth, congenital diaphragmatic hernia (CDH) is one of the more severe causes of fetal lung hypoplasia with unspecified cellular dynamics.

OBJECTIVES

 To characterize the epithelial cell tissue in hypoplastic lungs, a careful analysis regarding pulmonary morphology and epithelial cell profile was conducted from pseudoglandular-to-saccular phases in normal versus nitrofen-induced CDH rat lungs.

DESIGN

Our analysis comprises three experimental groups, control, nitrofen (NF) and CDH, in which the relative expression levels (western blot) by group and developmental stage were analyzed in whole lung. Spatiotemporal distribution (immunohistochemistry) was revealed by pulmonary structure during normal and hypoplastic fetal lung development. Surfactant protein-C (SP-C), calcitonin gene-related peptide (CGRP), clara cell secretory protein (CCSP), and forkhead box J1 (FOXJ1) were the used molecular markers for alveolar epithelial cell type 2 (AEC2), pulmonary neuroendocrine, clara, and ciliated cell profiles, respectively.

RESULTS

Generally, we identified an aberrant expression of SP-C, CGRP, CCSP, and FOXJ1 in nitrofen-exposed lungs. For instance, the overexpression of FOXJ1 and CGRP in primordia of bronchiole defined the pseudoglandular stage in CDH lungs, whereas the increased expression of CGRP in bronchi; FOXJ1 and CGRP in terminal bronchiole; and SP-C in BADJ classified the canalicular and saccular stages in hypoplastic lungs. We also described higher expression levels in NF than CDH or control groups for both FOXJ1 in bronchi, terminal bronchiole and BADJ at canalicular stage, and SP-C in bronchi and terminal bronchiole at canalicular and saccular stages. Finally, we report an unexpected expression of FOXJ1 in BADJ at canalicular and saccular stages, whereas the multi cilia observed in bronchi were notably absent at embryonic day 21.5 in induced-CDH lungs.

CONCLUSION

The recognized alterations in the epithelial cell profile contribute to a better understanding of neonatal respiratory insufficiency in induced-CDH lungs and indicate a problem in the epithelial cell differentiation in hypoplastic lungs.

The Use of Infant Pulmonary Function Tests in the Diagnosis of Neuroendocrine Cell Hyperplasia of Infancy

BACKGROUND

Infant pulmonary function tests (iPFTs) in subjects with neuroendocrine cell hyperplasia of infancy (NEHI) have demonstrated significant expiratory airflow obstruction and air trapping.

RESEARCH QUESTION

Can indexes from iPFTs be used in the diagnosis of NEHI?

STUDY DESIGN AND METHODS

This is an observational case-control study evaluating iPFT results from a registry of patients assessed at the Hadassah Hebrew University Medical Center between 2008 and 2018. We used the Kruskal-Wallis H test to compare iPFT results in infants with NEHI with those in two infants in a disease control group (infants evaluated for recurrent wheezing and infants evaluated owing to prematurity) and those in a spirometry control group of infants with normal expiratory airflow. Receiver operating characteristic (ROC) curves were used to assess the diagnostic accuracy of the iPFT indexes.

RESULTS

We evaluated iPFT data in 481 infants (15, NEHI; 292, wheezing; 128, premature; and 46, control group). Infants with NEHI had significantly increased trapped air volumes (median functional residual capacity measured with baby-body plethysmograph [FRC_pleth] was 199% predicted; median ratio of residual volume to total lung capacity was 59% predicted) when compared with results in all evaluated groups of infants (P < .001), including multiple pairwise comparisons. Airflow limitation was demonstrated in infants with NEHI when compared with the infants in the spirometry control group but was similar to that in the two infants in the disease control group. FRC_pleth had the best discriminatory ability for NEHI diagnosis, with an FRC_pleth ≥ 150% predicted demonstrating a ROC of 0.91 (95% CI, 0.82-1.00), sensitivity of 86.7% (95% CI, 59.5%-98.3%), and specificity of 95.5% (95% CI, 93.2%-97.3%).

INTERPRETATION

Findings on iPFTs of markedly increased air trapping, out of proportion to the degree of airflow limitation, are characteristic of infants with NEHI. iPFT results demonstrating an FRC_pleth ≥ 150% predicted are highly specific for NEHI and may aid in early diagnosis. Further research is required to confirm these findings in a prospective cohort and to understand the pathophysiologic explanation for these findings.

Variation in the bombesin staining of pulmonary neuroendocrine cells in pediatric pulmonary disorders-A useful marker for airway maturity

OBJECTIVES

Pulmonary neuroendocrine cells (NEC) increase with age due to pulmonary maturity. The aim of this study was to determine whether open lung biopsies from patients with interstitial lung diseases have increased pulmonary NEC compared with neuroendocrine cell hyperplasia of infancy (NEHI). Our second aim was to assess pulmonary NECs in the lung autopsy of children without lung disease who died from different causes.

METHODS

Lung tissue of 5 infants with NEHI; 21 patients with pediatric interstitial lung disease (chILD); 17 lung autopsies of infants at varying age without lung disease were included. The percentage of the airways containing neuroendocrine cells, the average percentage of neuroendocrine cells (NECs) per airway, and the number of neuroendocrine bodies (NEBs) in each case were analyzed.

RESULTS

The mean percentage of the airways containing neuroendocrine cells were 95% in the NEHI group, 30% in the chILD group, 89% under Intrauterine 37 weeks, 70% between intrauterine 37 to 40 weeks, 52% at postnatal 4 days to 6 months of autopsy ages. In the NEHI group, diffuse NE cell distribution and large NEBs were noticed in the lung biopsy. In the chILD group, neuroendocrine cells were dispersed, did not form clusters and NE cells showed solitary distribution. In the lung autopsy group, linear NE cells were detected at younger aged fetuses and solitary distribution of NE cells was detected with the older increasing age.

CONCLUSIONS

Our findings confirm that NECs are seen in many other childhood interstitial lung diseases; NE cell hyperplasia may be a marker of decreased pulmonary development and NE cells decrease with the increasing age of the fetus during Intrauterine life.

Early onset children's interstitial lung diseases: Discrete entities or manifestations of pulmonary dysmaturity?

Interstitial lung diseases in children (chILD) are rare and diverse. The current classifications include a group of early onset chILD specific to infancy, namely neuro-endocrine cell hyperplasia of infancy (NEHI), pulmonary interstitial glycogenosis (PIG) and the alveolar capillary-congenital acinar dysplasia (ACD-CAD) spectrum, as well as alveolar growth disorders. NEHI and PIG cells are seen in the normal developing foetal lung. We hypothesise that these conditions are in fact overlapping manifestations of pulmonary dysmaturity, respectively of airway, mesenchymal and vascular elements, rather than discrete clinical conditions in their own right. Clinically, these present as respiratory distress in early life. Mild cases rightly never undergo lung biopsy, and for these the clinical description 'persistent tachypnoea of infancy' has been proposed. In terms of pathology, we reviewed current literature, which showed that NEHI cells decline with age, and are not specific to NEHI, which we confirmed by unpublished re-analysis of a second dataset. Furthermore, specific genetic disorders which affect pulmonary maturation lead to a histological picture indistinguishable from NEHI. PIG and ACD-CAD are also associated with pulmonary growth disorders, and manifestations of PIG and NEHI may be present in the same child. We conclude that, contrary to current classifications, NEHI, PIG, and ACD-CAD should be considered as overlapping manifestations of pulmonary dysmaturation, frequently associated with disorders of alveolar growth, rather than as separate conditions. Identification of one of these patterns should be the start, not the end of the diagnostic journey, and underlying in particular genetic causes should be sought.

Explant Culture for Studying Lung Development

Lung development is a complex process that requires the input of various signaling pathways to coordinate the specification and differentiation of multiple cell types. Ex vivo culture of the lung is a very useful technique that represents an attractive model for investigating many different processes critical to lung development, function, and disease pathology. Ex vivo cultured lungs remain comparable to the in vivo lung both in structure and function, which makes them more suitable than cell cultures for physiological studies. Lung explant cultures offer several significant advantages for studies of morphogenetic events that guide lung development including budding, branching, and fusion. It also maintains the native physiological interactions between cells in the developing lung, enabling investigations of the direct and indirect signaling taking place between tissues and cells throughout the developmental process. Studying temporal and spatial control of gene expression by transcriptional factors using different reporters to understand their regulatory function at different moments of development is another valuable advantage of lung explants culture.

Consider the lung as a sensory organ: A tip from pulmonary neuroendocrine cells

While the lung is commonly known for its gas exchange function, it is exposed to signals in the inhaled air and responds to them by collaborating with other systems including immune cells and the neural circuit. This important aspect of lung physiology led us to consider the lung as a sensory organ. Among different cell types within the lung that mediate this role, several recent studies have renewed attention on pulmonary neuroendocrine cells (PNECs). PNECs are a rare, innervated airway epithelial cell type that accounts for <1% of the lung epithelium population. They are enriched at airway branch points. Classical in vitro studies have shown that PNECs can respond to an array of aerosol stimuli such as hypoxia, hypercapnia and nicotine. Recent in vivo evidence suggests an essential role of PNECs at neuroimmunomodulatory sites of action, releasing neuropeptides, neurotransmitters and facilitating asthmatic responses to allergen. In addition, evidence supports that PNECs can function both as progenitor cells and progenitor niches following airway epithelial injury. Increases in PNECs have been documented in a large array of chronic lung diseases. They are also the cells-of-origin for small cell lung cancer. A better understanding of the specificity of their responses to distinct insults, their impact on normal lung function and their roles in the pathogenesis of pulmonary ailments will be the next challenge toward designing therapeutics targeting the neuroendocrine system in lung.

Prenatal administration of neuropeptide bombesin promotes lung development in a rat model of nitrofen-induced congenital diaphragmatic hernia

BACKGROUND/PURPOSE

Fetal medical treatment to improve lung hypoplasia in congenital diaphragmatic hernia (CDH) has yet to be established. The neuropeptide bombesin (BBS) might play an important role in lung development. The present study aims to determine whether prenatally administered BBS could be useful to promote fetal lung development in a rat model of nitrofen-induced CDH.

METHODS

Pregnant rats were administered with nitrofen (100mg) on gestation day 9.5 (E9.5). BBS (50mg/kg/day) was then daily infused intraperitoneally from E14, and fetal lungs were harvested on E21. The expression of PCNA was assessed by both immunohistochemical staining and RT-PCR to determine the amount of cell proliferation. Lung maturity was assessed as the expression of TTF-1, a marker of alveolar epithelial cell type II.

RESULTS

The lung-body-weight ratio was significantly increased in CDH/BBS(+) compared with CDH/BBS(-) (p<0.05). The number of cells stained positive for PCNA and TTF-1 was significantly decreased in CDH/BBS(+) compared with CDH/BBS(-) (p<0.01). The TTF-1 mRNA expression levels were significantly decreased in CDH/BBS(+) compared with CDH/BBS(-) (p<0.05).

CONCLUSIONS

Prenatally administered BBS promotes lung development in a rat model of nitrofen-induced CDH. Neuropeptide BBS could help to rescue lung hypoplasia in fetal CDH.

The distribution and frequency of pulmonary neuroendocrine cells in Down syndrome fetal lungs

The pulmonary neuroendocrine cells (PNEC) are located in the epithelial lining of the airways and consist of solitary neuroendocrine cells (NEC) and NEC clusters, the neuroepithelial bodies (NEB). During fetal life, PNEC are the first to differentiate within the primitive airway epithelium, and bombesin expression favors branching of the respiratory tree. We investigated PNEC in Down syndrome (DS), where the lungs often show enlarged and reduced number of alveoli. Immunohistochemistry for bombesin and synaptophysin, PNEC markers, was evaluated in fetal lungs from 15 cases of DS and 11 age-matched controls from the 17th to 23rd week of gestation. Morphometric analysis assessed PNEC in the mucosal lining of each lung, expressed as number/mm. Nonparametric Mann-Whitney U test showed no statistical difference in frequency of PNEC in DS and controls. Our findings suggest that, at least in late second trimester, the distribution and frequency of PNEC in DS fetuses is not altered.

Oxygen, gastrin-releasing Peptide, and pediatric lung disease: life in the balance

Excessive oxygen (O2) can cause tissue injury, scarring, aging, and even death. Our laboratory is studying O2-sensing pulmonary neuroendocrine cells (PNECs) and the PNEC-derived product gastrin-releasing peptide (GRP). Reactive oxygen species (ROS) generated from exposure to hyperoxia, ozone, or ionizing radiation (RT) can induce PNEC degranulation and GRP secretion. PNEC degranulation is also induced by hypoxia, and effects of hypoxia are mediated by free radicals. We have determined that excessive GRP leads to lung injury with acute and chronic inflammation, leading to pulmonary fibrosis (PF), triggered via ROS exposure or by directly treating mice with exogenous GRP. In animal models, GRP-blockade abrogates lung injury, inflammation, and fibrosis. The optimal time frame for GRP-blockade and the key target cell types remain to be determined. The concept of GRP as a mediator of ROS-induced tissue damage represents a paradigm shift about how O2 can cause injury, inflammation, and fibrosis. The host PNEC response in vivo may depend on individual ROS sensing mechanisms and subsequent GRP secretion. Ongoing scientific and clinical investigations promise to further clarify the molecular pathways and clinical relevance of GRP in the pathogenesis of diverse pediatric lung diseases.

Extraintestinal roles of bombesin-like peptides and their receptors: lung

PURPOSE OF REVIEW

Description of the recent findings of the biological roles of bombesin-like peptides and their receptors in lungs.

RECENT FINDINGS

Gastrin-releasing peptide (GRP) was involved in the airway inflammation in murine models of airway hyperreactivity. The circulating proGRP could serve as a valuable tumor marker for small-cell lung cancers, and the plasma level of proGRP is more stable compared with that of serum proGRP. Recent studies also shed light on the intracellular signaling pathways of bombesin receptor subtype-3 (BRS-3) activation in cultured human lung cancer cells.

SUMMARY

The relevant biology of BLPs and their receptors in lung cancers and other lung diseases still remains largely unknown. With the development of several highly specific BRS-3 agonists, recent studies provided some insights into the biological effects of BRS-3 in lungs.

Gastrin-releasing peptide receptor expression in non-cancerous bronchial epithelia is associated with lung cancer: a case-control study

BACKGROUND

Normal bronchial tissue expression of GRPR, which encodes the gastrin-releasing peptide receptor, has been previously reported by us to be associated with lung cancer risk in 78 subjects, especially in females. We sought to define the contribution of GRPR expression in bronchial epithelia to lung cancer risk in a larger case-control study where adjustments could be made for tobacco exposure and sex.

METHODS

We evaluated GRPR mRNA levels in histologically normal bronchial epithelial cells from 224 lung cancer patients and 107 surgical cancer-free controls. Associations with lung cancer were tested using logistic regression models.

RESULTS

Bronchial GRPR expression was significantly associated with lung cancer (OR = 4.76; 95% CI = 2.32-9.77) in a multivariable logistic regression (MLR) model adjusted for age, sex, smoking status and pulmonary function. MLR analysis stratified by smoking status indicated that ORs were higher in never and former smokers (OR = 7.74; 95% CI = 2.96-20.25) compared to active smokers (OR = 1.69; 95% CI = 0.46-6.33). GRPR expression did not differ by subject sex, and lung cancer risk associated with GRPR expression was not modified by sex.

CONCLUSIONS

GRPR expression in non-cancerous bronchial epithelium was significantly associated with the presence of lung cancer in never and former smokers. The association in never and former smokers was found in males and females. Association with lung cancer did not differ by sex in any smoking group.

Defective pulmonary innervation and autonomic imbalance in congenital diaphragmatic hernia

Congenital diaphragmatic hernia (CDH) is associated with significant mortality due to lung hypoplasia and pulmonary hypertension. The role of embryonic pulmonary innervation in normal lung development and lung maldevelopment in CDH has not been defined. We hypothesize that developmental defects of intrapulmonary innervation, in particular autonomic innervation, occur in CDH. This abnormal embryonic pulmonary innervation may contribute to lung developmental defects and postnatal physiological derangement in CDH. To define patterns of pulmonary innervation in CDH, human CDH and control lung autopsy specimens were stained with the pan-neural marker S-100. To further characterize patterns of overall and autonomic pulmonary innervation during lung development in CDH, the murine nitrofen model of CDH was utilized. Immunostaining for protein gene product 9.5 (a pan-neuronal marker), tyrosine hydroxylase (a sympathetic marker), vesicular acetylcholine transporter (a parasympathetic marker), or VIP (a parasympathetic marker) was performed on lung whole mounts and analyzed via confocal microscopy and three-dimensional reconstruction. Peribronchial and perivascular neuronal staining pattern is less complex in human CDH than control lung. In mice, protein gene product 9.5 staining reveals less complex neuronal branching and decreased neural tissue in nitrofen-treated lungs from embryonic day 12.5 to 16.5 compared with controls. Furthermore, nitrofen-treated embryonic lungs exhibited altered autonomic innervation, with a relative increase in sympathetic nerve staining and a decrease in parasympathetic nerve staining compared with controls. These results suggest a primary defect in pulmonary neural developmental in CDH, resulting in less complex neural innervation and autonomic imbalance. Defective embryonic pulmonary innervation may contribute to lung developmental defects and postnatal physiological derangement in CDH.

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.

Neuroendocrine cell distribution and frequency distinguish neuroendocrine cell hyperplasia of infancy from other pulmonary disorders

BACKGROUND

The diagnostic gold standard for neuroendocrine cell hyperplasia of infancy (NEHI) is demonstration of increased numbers of neuroendocrine cells (NECs) amid otherwise near-normal lung histology. Typical clinical and radiographic features often are present. However, NECs are also increased after lung injury and in other disorders, which can complicate biopsy specimen interpretation and diagnosis of suspected NEHI. Our objective was to determine whether NEC prominence is specific for the diagnosis of NEHI.

METHODS

Bombesin immunoreactivity was quantified in lung biopsy specimens from 13 children with characteristic clinical presentation and imaging appearance of NEHI. The primary comparison group was 13 age-matched patients selected from children with lung disorders that are known to be associated with NEC prominence.

RESULTS

Bombesin-immunopositive epithelial area was significantly increased in NEHI compared with other diseases. Patchy bronchiolar inflammation or fibrosis was frequently observed in NEHI, with no direct association between airway histopathology and bombesin-immunopositive area. NEC prominence correlated with severity of small airway obstruction demonstrated on infant pulmonary function testing. Immunohistochemical colocalization of bombesin with Ki67 did not reveal active NEC proliferation. There was wide intra- and intersubject variability in NEC number, which did not relate to radiographic appearance of the region biopsied.

CONCLUSIONS

Our findings demonstrate that NEC prominence is a distinguishing feature of NEHI independent of airway injury. The extent of intrasubject variability and potential for overlap with control subjects suggest that clinical-radiologic-pathologic correlation is required for diagnosis and that the abundance of NECs may not fully explain the disease pathogenesis.

Gastrin-releasing peptide, immune responses, and lung disease

Gastrin-releasing peptide (GRP) is produced by pulmonary neuroendocrine cells (PNECs), with highest numbers of GRP-positive cells present in fetal lung. Normally GRP-positive PNECs are relatively infrequent after birth, but PNEC hyperplasia is frequently associated with chronic lung diseases. To address the hypothesis that GRP mediates chronic lung injury, we present the cumulative evidence implicating GRP in bronchopulmonary dysplasia (BPD), the chronic lung disease of premature infants who survive acute respiratory distress syndrome. The availability of well-characterized animal models of BPD was a critical tool for demonstrating that GRP plays a direct role in the early pathogenesis of this disease. Potential mechanisms by which GRP contributes to injury are analyzed, with the main focus on innate immunity. Autoreactive T cells may contribute to lung injury late in the course of disease. A working model is proposed with GRP triggering multiple cell types in both the innate and adaptive immune systems, promoting cascades culminating in chronic lung disease. These observations represent a paradigm shift in the understanding of the early pathogenesis of BPD, and suggest that GRP blockade could be a novel treatment to prevent this lung disease in premature infants.

Targeted disruption of NeuroD, a proneural basic helix-loop-helix factor, impairs distal lung formation and neuroendocrine morphology in the neonatal lung

Despite the importance of airspace integrity in vertebrate gas exchange, the molecular pathways that instruct distal lung formation are poorly understood. Recently, we found that fibrillin-1 deficiency in mice impairs alveolar formation and recapitulates the pulmonary features of human Marfan syndrome. To further elucidate effectors involved in distal lung formation, we performed expression profiling analysis comparing the fibrillin-1-deficient and wild-type developing lung. NeuroD, a basic helix-loop-helix transcription factor, fulfilled the expression criteria for a candidate mediator of distal lung development. We investigated its role in murine lung development using genetically targeted NeuroD-deficient mice. We found that NeuroD deficiency results in both impaired alveolar septation and altered morphology of the pulmonary neuroendocrine cells. NeuroD-deficient mice had enlarged alveoli associated with reduced epithelial proliferation in the airway and airspace compartments during development. Additionally, the neuroendocrine compartment in these mice manifested an increased number of neuroepithelial bodies but a reduced number of solitary pulmonary neuroendocrine cells in the neonatal lung. Overexpression of NeuroD in a murine lung epithelial cell line conferred a neuroendocrine phenotype characterized by the induction of neuroendocrine markers as well as increased proliferation. These results support an unanticipated role for NeuroD in the regulation of pulmonary neuroendocrine and alveolar morphogenesis and suggest an intimate connection between the neuroendocrine compartment and distal lung development.

Ontogeny of the eotaxins in human lung

The ontogeny of the C-C chemokines eotaxin-1, eotaxin-2, and eotaxin-3 has not been fully elucidated in human lung. We explored a possible role for eotaxin in developing lung by determining the ontogeny of eotaxin-1 (CCL11), eotaxin-2 (CCL24), eotaxin-3 (CCL26), and the eotaxin receptor, CCR3. We tested discarded surgical samples of developing human lung tissue using quantitative RT-PCR (QRT-PCR) and immunostaining for expression of CCL11, CCL24, CCL26, and CCR3. We assessed possible functionality of the eotaxin-CCR3 system by treating lung explant cultures with exogenous CCL11 and analyzing the cultures for evidence of changes in proliferation and activation of ERK1/2, a signaling pathway associated with CCR3. QRT-PCR analyses of 22 developing lung tissue samples with gestational ages 10-23 wk demonstrated that eotaxin-1 mRNA is most abundant in developing lung, whereas mRNAs for eotaxin-2 and eotaxin-3 are minimally detectable. CCL11 mRNA levels correlated with gestational age (P < 0.05), and immunoreactivity was localized predominantly to airway epithelial cells. QRT-PCR analysis detected CCR3 expression in 16 of 19 developing lung samples. Supporting functional capacity in the immature lung, CCL11 treatment of lung explant cultures resulted in significantly increased (P < 0.05) cell proliferation and activation of the ERK signaling pathway, which is downstream from CCR3, suggesting that proliferation was due to activation of CCR3 receptors by CCL11. We conclude that developing lung expresses the eotaxins and functional CCR3 receptor. CCL11 may promote airway epithelial proliferation in the developing lung.

Notch-1 regulates pulmonary neuroendocrine cell differentiation in cell lines and in transgenic mice

The notch gene family encodes transmembrane receptors that regulate cell differentiation by interacting with surface ligands on adjacent cells. Previously, we demonstrated that tumor necrosis factor-alpha (TNF) induces neuroendocrine (NE) cell differentiation in H82, but not H526, undifferentiated small cell lung carcinoma lines. We now test the hypothesis that TNF mediates NE cell differentiation in part by altering Notch gene expression. First, using RT-PCR, we determined that TNF treatment of H82, but not H526, transiently decreases notch-1 mRNA in parallel with induction of gene expression for the NE-specific marker DOPA decarboxylase (DDC). Second, we treated H82 and H526 with notch-1 antisense vs. sense oligodeoxynucleotides. Using quantitative RT-PCR and Western analyses we demonstrate that DDC mRNA and protein are increased in H82 by notch-1 antisense, whereas notch-1 mRNA and activated Notch-1 protein are decreased. mRNA for Hes1, a transcription factor downstream from activated Notch, is also decreased by Notch-1 antisense in H82 but not H526. After 7 days of Notch-1 antisense treatment, neural cell adhesion molecule (NCAM) immunoreactivity is induced in H82 but not H526. Third, we generated transgenic mice bearing notch-1 driven by the neural/NE-specific calcitonin promoter, which express activated Notch-1 in developing lung epithelium. Newborn NotchCal mouse lungs have high levels of hes1 mRNA, reflecting increased activated Notch, compared with wild-type. NotchCal lungs have decreased CGRP-positive NE cells, decreased protein gene product 9.5 (PGP9.5)-positive NE cells, and decreased gastrin-releasing peptide (GRP), CGRP, and DDC mRNA levels compared with normal littermates. Cumulatively, these observations provide further support for a role for Notch-1 signaling in regulating pulmonary NE cell differentiation.

Functional facets of the pulmonary neuroendocrine system

Pulmonary neuroendocrine cells (PNECs) have been around for 60 years in the scientific literature, although phylogenetically they are ancient. Their traditionally ascribed functions include chemoreception and regulation of lung maturation and growth. There is recent evidence that neuroendocrine (NE) differentiation in the lung is regulated by genes and pathways that are conserved in the development of the nervous system from Drosophila to humans (such as achaete-scute homolog-1), or implicated in the carcinogenesis of the nervous or NE system (such as the retinoblastoma tumor suppressor gene). In addition, complex neural networks are in place to regulate chemosensory and other functions. Even solitary PNECs appear to be innervated. For the first time ever, we have mouse models for lung NE carcinomas, including the most common and virulent small cell lung carcinoma. Moreover, PNECs may be important for inflammatory responses, and pivotal for lung stem cell niches. These discoveries signify an exciting new era for PNECs and are likely to have therapeutic and diagnostic applications.

Bombesin inhibits alveolarization and promotes pulmonary fibrosis in newborn mice

RATIONALE

Bombesin-like peptides promote fetal lung development. Normally, levels of mammalian bombesin (gastrin-releasing peptide [GRP]) drop postnatally, but these levels are elevated in newborns that develop bronchopulmonary dysplasia (BPD), a chronic lung disease characterized by arrested alveolarization. In premature baboons with BPD, antibombesin antibodies reduce lung injury and promote alveolarization.

OBJECTIVES

The present study tests whether exogenous bombesin or GRP given perinatally alters alveolar development in newborn mice.

METHODS

Mice were given peptides intraperitoneally twice daily on Postnatal Days 1-3. On Day 14 lungs were inflation-fixed for histopathologic analyses of alveolarization.

MEASUREMENTS AND MAIN RESULTS

Bombesin had multiple effects on Day 14 lung, when alveolarization was about half complete. First, bombesin induced alveolar myofibroblast proliferation and increased alveolar wall thickness compared with saline-treated control animals. Second, bombesin diminished alveolarization in C57BL/6 (but not Swiss-Webster) mice. We used receptor-null mice to explore which receptors might mediate these effects. Compared with wild-type littermates, bombesin-treated GRP receptor (GRPR)-null mice had increased interstitial fibrosis but reduced defects in alveolarization. Neuromedin B (NMB) receptor-null and bombesin receptor subtype 3-null mice had the same responses as their wild-type littermates. GRP had the same effects as bombesin, whereas neither NMB nor a synthetic bombesin receptor type 3 ligand had any effect. All effects of GRP were abrogated in GRPR-null mice.

CONCLUSIONS

Bombesin/GRP can induce features of BPD, including interstitial fibrosis and diminished alveolarization. GRPR appears to mediate all effects of GRP, but only part of the bombesin effect on alveolarization, suggesting that novel receptors may mediate some effects of bombesin in newborn lung.

Growth factors in lung development

Organized and coordinated lung development follows transcriptional regulation of a complex set of cell-cell and cell-matrix interactions resulting in a blood-gas interface ready for physiologic gas exchange at birth. Transcription factors, growth factors, and various other signaling molecules regulate epithelial-mesenchymal interactions by paracrine and autocrine mechanisms. Transcriptional control at the earliest stages of lung development results in cell differentiation and cell commitment in the primitive lung bud, in essence setting up a framework for pattern formation and branching morphogenesis. Branching morphogenesis results in the formation of the conductive airway system, which is critical for alveolization. Lung development is influenced at all stages by spatial and temporal distribution of various signaling molecules and their receptors and also by the positive and negative control of signaling by paracrine, autocrine, and endocrine mechanisms. Lung bud formation, cell differentiation, and its interaction with the splanchnic mesoderm are regulated by HNF-3beta, Shh, Nkx2.1, HNF-3/Forkhead homolog-8 (HFH-8), Gli, and GATA transcription factors. HNF-3beta regulates Nkx2.1, a transcription factor critical to the formation of distal pulmonary structures. Nkx2.1 regulates surfactant protein genes that are important for the development of alveolar stability at birth. Shh, produced by the foregut endoderm, regulates lung morphogenesis signaling through Gli genes expressed in the mesenchyme. FGF10, produced by the mesoderm, regulates branching morphogenesis via its receptors on the lung epithelium. Alveolization and formation of the capillary network are influenced by various factors that include PDGF, vascular endothelial growth factor (VEGF), and retinoic acid. Epithelial-endothelial interactions during lung development are important in establishing a functional blood-gas interface. The effects of various growth factors on lung development have been demonstrated by gain- or loss-of-function studies in null mutant and transgenic mice models. Understanding the role of growth factors and various other signaling molecules and their cellular interactions in lung development will provide us with new insights into the pathogenesis of bronchopulmonary dysplasia and disorders of lung morphogenesis.

Overexpression of gastrin-releasing peptide receptor induced layer disorganization in brain

Gastrin-releasing peptide-preferring and neuromedin B-preferring receptors, members of the bombesin-like peptide receptor subfamily, are reported to regulate proliferation, migration and differentiation. Since they are expressed in developing brain, we postulated that the gastrin-releasing peptide-preferring and neuromedin B-preferring receptors might be involved in normal brain development. Here we examined the effects of the overexpressions of the gastrin-releasing peptide-preferring and neuromedin B-preferring receptors on chick brain development in vivo using a retrovirus. In the overexpressed exogenous gastrin-releasing peptide-preferring receptor brain, we found laminar disorganization in the telencephalon, tectum and particularly in the cerebellum with severe atrophy. Processes of the radial glial cells in the telencephalon and optic tectum, as well as the projections of the Bergmann glia in the cerebellum were distorted, which might disturb normal cell migration. Despite the atrophy of the cerebellum, densely-stained proliferating cell nuclear antigen- and phospho-histone H3-positive cells increased in number. Terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling-positive cells also increased in the cerebellum, suggesting that the ectopically proliferating cells were subjected to apoptosis. Glial fibrillary acidic protein-positive cells also increased in the hyperpallium accessorium and in the outer layers of the tectum. We also found smaller and spindle-shaped cells which resembled undifferentiated embryonic tumor cells. On the other hand, the layer structures of the neuromedin B-preferring receptors overexpressed brain were well organized and developed, and the size of brain was generally enlarged. These results indicated that although the gastrin-releasing peptide-preferring and neuromedin B-preferring receptors are involved in normal brain development, both receptors contribute and exert their effects differently.

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.

Endo/exo-proteolysis in neoplastic progression and metastasis

Biological control of individual cells, organs, and organisms is achieved through interplay of a host of specific interactions that involve various peptidic molecules as modulators or effectors. In tumor cells, these processes may result in uncontrolled growth as a consequence of autocrine and/or paracrine actions. In recent years, growing evidence has accumulated for the important role of proprotein convertases (PCs) and peptide alpha-amidation enzymes in these processes. The widespread belief that these enzymes are involved in the major features of tumor progression, namely, invasiveness and metastasis, has taken place because of their capacity to process and activate many protein precursors involved in the neoplastic progression and metastasis. This includes degrading extracellular matrix proteases, growth promoting factors, and adhesion molecules. Usually, when the processing of these precursor proteins is achieved by one or more of the known PC family members within the general motif (K/R)-(X)n-(K/R) downward arrow, where n=0, 2, 4, or 6, and X, any amino acid except Cys, the accomplishment of the maturation of these molecules is attained by various posttranslational modifications, including the carboxy-terminal alpha-amidation. This review article summarizes recent findings on the role of these enzymatic systems in multiple cellular functions that impact on the invasive/metastatic potential of cancer cells and highlight the potential use of their inhibitors in the treatment of multiple cancers.

Surfactant phospholipids and proteins are increased in fetal sheep with pulmonary hypertension secondary to fetal systemic arteriovenous fistula

To determine whether prenatal surfactant storage was altered in a model of systemic arteriovenous fistula (SAVF) with pulmonary hypertension, a fistula was created between the internal jugular vein and the carotid artery in 120-day fetal lambs, and surfactant material was explored at 134 days. Total phospholipids (TPL) and disaturated phosphatidylcholine (DSPC) were increased in whole lung tissue. Phospholipid analysis of isolated lamellar body fraction evidenced a specific increase of surfactant pool size: TPL and DSPC in this fraction were enhanced 1.9 and 2.9 times, respectively, when referred to DNA. Although the steady-state level of transcripts of surfactant protein (SP)-A and SP-B was not found to be changed at the time of death, semiquantitative Western blot analysis revealed elevated SP-A and SP-B protein contents three- and twofold, respectively. These findings indicate markedly enhanced accumulation of surfactant material in the presence of surgically induced prenatal pulmonary hypertension. Although total lung cell number was increased by 26%, SP-B immunolabeling indicated that increased surfactant amount did not result from an increased alveolar type II cell proportion, but rather from an increased rate of storage. Whether similar changes in surfactant are encountered in human neonates with persistent pulmonary hypertension is worthy of investigation.

Pulmonary epithelial stem cells

Classically, the stem/progenitor cells of the pulmonary epithelium are considered to be the basal and mucous cells of the proximal airways, Clara cells in the bronchioles and type II pneumocytes in the alveoli. Recent data suggest that there is a variant of Clara cells, lying in pulmonary neuroendocrine bodies, that meets several stem cell criteria and that type II pneumocytes exist in at least two populations, one of which is more resistant to injury. However, a complete revision of our understanding of pulmonary stem cell biology is underway as a result of the discovery of pulmonary epithelium derived from blood-borne cells. In addition, the existence in the lung of a 'universal' pluripotent cell has long been speculated upon and now some initial evidence has emerged with the identification of a spore-like cell that can differentiate in vitro to bronchiolar tissue.

Bombesin-like peptide receptor gene expression, regulation, and function in fetal murine lung

Bombesin-peptide (BLP) immunoreactivity occurs at high levels in fetal lung. Previous studies showed that bombesin promotes fetal lung development. To test the hypothesis that such effects are mediated by known mammalian bombesin receptors [gastrin-releasing peptide (GRP)/bombesin-preferring receptor (GRPR), neuromedin B (NMB) receptor (NMBR), and the orphan bombesin receptor subtype-3 (BRS-3)], we analyzed the ontogeny of GRPR, NMBR, and BRS-3 gene expression in mouse lung. We examined the regulation of these three genes by dexamethasone and bombesin, which modulate lung development. Using incorporation of [3H]thymidine and [3H]choline, we then assessed whether GRP, NMB, and Leu8-phyllolitorin modulate lung growth and maturation in fetal lung explants. GRPR gene expression was detected predominantly in utero, whereas NMBR and BRS-3 genes were expressed from embryonic days 13-16 and on multiple postnatal days. All three mRNAs are present in airway epithelium and mesenchymal cells but occur in different relative patterns. These genes were regulated differently. Dexamethasone and bombesin increased GRPR mRNA, bombesin downregulated NMBR, and neither agent affected BRS-3. GRP increased incorporation of [3H]thymidine and [3H]choline in explants, whereas NMB induced cell proliferation and Leu8-phyllolitorin yielded variable results. Cumulative data suggest the involvement of multiple BLP receptors, including novel molecules, and argue against simple functional redundancy within this gene family during lung development.

The diffuse endocrine system: from embryogenesis to carcinogenesis

In the present review we will summarise the current knowledge about the cells comprising the Diffuse Endocrine System (DES) in mammalian organs. We will describe the morphological, histochemical and functional traits of these cells in three major systems gastrointestinal, respiratory and prostatic. We will also focus on some aspects of their ontogeny and differentiation, as well as to their relevance in carcinogenesis, especially in neuroendocrine tumors. The first chapter describes the characteristics of DES cells and some of their specific biological and biochemical traits. The second chapter deals with DES in the gastrointestinal organs, with special reference to the new data on the differentiation mechanisms that leads to the appearance of endocrine cells from an undifferentiated stem cell. The third chapter is devoted to DES of the respiratory system and some aspects of its biological role, both, during development and adulthood. Neuroendocrine hyperplasia and neuroendocrine lung tumors are also addressed. Finally, the last chapter deals with the prostatic DES, discussing its probable functional role and its relevance in hormone-resistant prostatic carcinomas.

Amniotic sac infection syndrome features fetal lung neuroendocrine cell hyperfunction

Neuroendocrine cells (NEC) are abundant in fetal and neonatal lungs, but reduced in infants with hyaline membrane disease. Perinatal neuroendocrine cell hyperplasia (NCH) has been reported in the hypoplastic lung in diaphragmatic hernia, bronchopulmonary dysplasia, and Wilson-Mikity syndrome. Since we are unaware of any reports on NCH in fetal inflammatory conditions, this report addresses the NEC in fetuses with congenital pneumonia. Twenty-one fetuses/neonates with congenital pneumonia, autopsied between 1995 and 2001, were compared to 21 fetuses without a congenital infection matched for gestational age. Lung sections were immunostained for chromogranin, bombesin, calcitonin, and synaptophysin. Proportions of immunopositive cells lining 20 consecutive bronchioles calculated from digital images were significantly higher in the study than the control group for chromogranin (1.8 vs. 0.8%, P = 2.4 E-06), calcitonin (1.2 vs. 0.7%, P = 0.005), and bombesin (1.1 vs. 0.7%, P = 0.005). There was no difference in synaptophysin (11.7% vs. 12.6%, P = 0.07). The absence of significant differences in the synaptophysin ratio excludes simple NCH in the study group. The synchronous increase in three neurohormones is indicative of NEC hyperfunction, due to either altered enzymatic inactivation by neutral endopeptidase, known to be reduced in adult lung inflammation, or by an increase in expression of the neurohormone genes. These data indicate that NEC hyperfunction may be responsible for the deranged fetal/neonatal lung function and circulatory adaptation, and contribute to the lethality of the amniotic sac infection syndrome.

A catalytic antioxidant attenuates alveolar structural remodeling in bronchopulmonary dysplasia

Superoxide anion and other oxygen-free radicals have been implicated in the pathogenesis of bronchopulmonary dysplasia. We tested the hypothesis that a catalytic antioxidant metalloporphyrin AEOL 10113 can protect against hyperoxia-induced lung injury using a fetal baboon model of bronchopulmonary dysplasia. Fetal baboons were delivered by hysterotomy at 140 days of gestation (term = 185 days) and given 100% oxygen for 10 days. Morphometric analysis of alveolar structure showed that fetal baboons on 100% oxygen alone had increased parenchymal mast cells and eosinophils, increased alveolar tissue volume and septal thickness, and decreased alveolar surface area compared with animals given oxygen as needed. Treatment with AEOL 10113 (continuous intravenous infusion) during 100% oxygen exposure partially reversed these oxygen-induced changes. Hyperoxia increased the number of neuroendocrine cells in the peripheral lung, which was preceded by increased levels of urine bombesin-like peptide at 48 hours of age. AEOL 10113 inhibited the hyperoxia-induced increases in urine bombesin-like peptide and numbers of neuroendocrine cells. An increasing trend in oxygenation index over time was observed in the 100% oxygen group but not the mimetic-treated group. These results suggest that AEOL 10113 might reduce the risk of pulmonary oxygen toxicity in prematurely born infants.

Cystic fibrosis transmembrane conductance regulator modulates neurosecretory function in pulmonary neuroendocrine cell-related tumor cell line models

The pulmonary neuroendocrine cell (PNEC) system consists of solitary cells and distinctive cell clusters termed neuroepithelial bodies (NEB) localized in the airway epithelium. PNEC/NEB express a variety of bioactive substances, including amine (serotonin, 5HT) and neuropeptides. We have previously shown that NEB cells are O(2) sensors expressing nicotinamide adenine diphosphate oxidase complex and O(2) sensitive K(+) channel. Recently, we demonstrated expression of functional cystic fibrosis transmembrane conductance regulator (CFTR) and Cl(-) conductances in NEB cells of rabbit neonatal lung. Because PNEC/NEB are sparsely distributed and difficult to study in native lung, we investigated small-cell lung carcinoma (SCLC) and carcinoid tumor cell lines (tumor counterparts of normal PNEC/NEB) as models for PNEC/NEB. SCLC (H146, H345) and carcinoid (H727) cell lines express neuroendocrine cell markers, including chromogranin A, neural cell adhesion molecule (N-CAM), 5HT, and tryptophan hydroxylase. We report that H146, H345, and H727 express CFTR messenger RNA (reverse transcription polymerase chain reaction) and protein (immunoblotting) and possess functional CFTR Cl(-) conductance, demonstrated by an iodide efflux assay inhibitable by transfection with antisense CFTR. Using an immunoassay to quantitate 5HT secretion, we also show that downregulation of CFTR abolishes hypoxia-induced 5HT release, and reduces secretory response to high potassium. Our findings suggest that CFTR may modulate neurosecretory activity of PNEC/NEB possessing O(2) sensor function. We propose that these tumor cell lines may be useful models for investigating the role of CFTR in PNEC/NEB functions in health and disease.

Differentiation of human pulmonary type II cells in vitro by glucocorticoid plus cAMP

Mature alveolar type II cells that produce pulmonary surfactant are essential for adaptation to extrauterine life and prevention of infant respiratory distress syndrome. We have developed a new in vitro model to further investigate regulation of type II cell differentiation. Epithelial cells isolated from human fetal lung were cultured in serum-free medium on plastic. Cells treated with dexamethasone + cAMP analog and isobutylmethylxanthine for 4 days exhibited increased phosphatidylcholine synthesis and content of disaturated phosphatidylcholine species, manyfold increases in all surfactant proteins with processing to mature forms, and abundant lamellar bodies. DNA microarray analysis identified approximately 3,100 expressed genes, including subsets of genes induced 2- to >100-fold (approximately 2.5%) or repressed 2- to 18-fold (approximately 1.2%) by hormone treatment. Of the highly regulated genes, most were coregulated in an additive or synergistic manner by dexamethasone and cAMP agents. Approximately 90% of the regulated genes identified by this initial microarray analysis have not been previously recognized as hormone responsive. One newly identified hormone-induced gene is Nkx2.1 (thyroid transcription factor-1), which has a critical role in surfactant protein gene expression. Our findings indicate that glucocorticoid + cAMP is sufficient and necessary for precocious induction of functional type II cells in this in vitro system and that these hormones act primarily in combination to regulate expression of a subset of specific genes.

Expression of CFTR and Cl(-) conductances in cells of pulmonary neuroepithelial bodies

The pulmonary neuroendocrine cell system comprises solitary neuroendocrine cells and clusters of innervated cells or neuroepithelial bodies (NEBs). NEBs figure prominently during the perinatal period when they are postulated to be involved in physiological adaptation to air breathing. Previous studies have documented hyperplasia of NEBs in cystic fibrosis (CF) lungs and increased neuropeptide (bombesin) content produced by these cells, possibly secondary to chronic hypoxia related to CF lung disease. However, little is known about the role of NEBs in the pathogenesis of CF lung disease. In the present study, using a panel of cystic fibrosis transmembrane conductance regulator (CFTR)-specific antibodies and confocal microscopy in combination with RT-PCR, we demonstrate expression of CFTR message and protein in NEB cells of rabbit neonatal lungs. NEB cells expressed CFTR along with neuroendocrine markers. Confocal microscopy established apical membrane localization of the CFTR protein in NEB cells. Cl(-) conductances corresponding to functional CFTR were demonstrated in NEB cells in a fresh lung slice preparation. Our findings suggest that NEBs, and related neuroendocrine mechanisms, likely play a role in the pathogenesis of CF lung disease, including the early stages before establishment of chronic infection and chronic lung disease.

Direct effects of corticotropin-releasing hormone and thyrotropin-releasing hormone on fetal lung explants

Fetal lung produces corticotropin-releasing hormone (CRH) without known direct effects. We tested the hypothesis that CRH can directly regulate lung development. In baboon fetal lung explants, CRH strongly induces surfactant phospholipid synthesis and SP-C immunostaining, plus [(3)H]thymidine incorporation. CRH receptor mRNA was detected in lung from multiple baboons at e125. Testing thyrotropin (TRH) as a specificity control, we did demonstrate different direct effects with only modest stimulation of surfactant phospholipid synthesis and strong induction of cytidylyltransferase gene expression. Therefore, CRH, similar to ACTH and glucocorticoids, is a potent inducer of cell differentiation in fetal lung.

Bombesin-like peptide and receptors in lung injury models: diverse gene expression, similar function

We previously demonstrated that bombesin-like peptide (BLP) mediates lung injury in premature infants with bronchopulmonary dysplasia (BPD). We now investigate gene expression and function of BLP (gastrin-releasing peptide, GRP) and BLP-receptors (GRP-R and BRS-3) in lung from two baboon BPD models. In the "interrupted gestation model," only GRP mRNA was up-regulated. In the "hyperoxic model," GRP-R mRNA was up-regulated. In lung explants from O2-treated animals, all BPD animals responded to 1nM bombesin, whereas non-BPD animals did not; the opposite effect was observed with a BLP blocking antibody. Cumulatively, these observations suggest that novel BLPs and/or BLP receptors are likely to be implicated in the pathogenesis of BPD.

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.

The molecular basis of lung morphogenesis

To form a diffusible interface large enough to conduct respiratory gas exchange with the circulation, the lung endoderm undergoes extensive branching morphogenesis and alveolization, coupled with angiogenesis and vasculogenesis. It is becoming clear that many of the key factors determining the process of branching morphogenesis, particularly of the respiratory organs, are highly conserved through evolution. Synthesis of information from null mutations in Drosophila and mouse indicates that members of the sonic hedgehog/patched/smoothened/Gli/FGF/FGFR/sprouty pathway are functionally conserved and extremely important in determining respiratory organogenesis through mesenchymal-epithelial inductive signaling, which induces epithelial proliferation, chemotaxis and organ-specific gene expression. Transcriptional factors including Nkx2.1, HNF family forkhead homologues, GATA family zinc finger factors, pou and hox, helix-loop-helix (HLH) factors, Id factors, glucocorticoid and retinoic acid receptors mediate and integrate the developmental genetic instruction of lung morphogenesis and cell lineage determination. Signaling by the IGF, EGF and TGF-beta/BMP pathways, extracellular matrix components and integrin signaling pathways also directs lung morphogenesis as well as proximo-distal lung epithelial cell lineage differentiation. Soluble factors secreted by lung mesenchyme comprise a 'compleat' inducer of lung morphogenesis. In general, peptide growth factors signaling through cognate receptors with tyrosine kinase intracellular signaling domains such as FGFR, EGFR, IGFR, PDGFR and c-met stimulate lung morphogenesis. On the other hand, cognate receptors with serine/threonine kinase intracellular signaling domains, such as the TGF-beta receptor family are inhibitory, although BMP4 and BMPR also play key inductive roles. Pulmonary neuroendocrine cells differentiate earliest in gestation from among multipotential lung epithelial cells. MASH1 null mutant mice do not develop PNE cells. Proximal and distal airway epithelial phenotypes differentiate under distinct transcriptional control mechanisms. It is becoming clear that angiogenesis and vasculogenesis of the pulmonary circulation and capillary network are closely linked with and may be necessary for lung epithelial morphogenesis. Like epithelial morphogenesis, pulmonary vascularization is subject to a fine balance between positive and negative factors. Angiogenic and vasculogenic factors include VEGF, which signals through cognate receptors flk and flt, while novel anti-angiogenic factors include EMAP II.

Neuroepithelial bodies of pulmonary airways serve as a reservoir of progenitor cells capable of epithelial regeneration

Remodeling of the conducting airway epithelium is a common finding in the chronically injured lung and has been associated with increased risk for developing lung cancer. Pulmonary neuroendocrine cells and clusters of these cells termed neuroepithelial bodies (NEBs) play a central role in each of these processes. We previously developed an adult mouse model of airway injury and repair in which epithelial regeneration after naphthalene-induced Clara cell ablation occurred preferentially at airway branch points and gave rise to nascent Clara cells. Continued repair was accompanied by NEB hyperplasia. We now provide the following evidence that the NEB microenvironment serves as a source of airway progenitor cells that contribute to focal regeneration of the airway epithelium: 1) nascent Clara cells and NEBs localize to the same spatial domain; 2) within NEB, both Clara cell secretory protein- and calcitonin gene-related peptide-immunopositive cells are proliferative; 3) the NEB microenvironment of both the steady-state and repairing lung includes cells that are dually immunopositive for Clara cell secretory protein and calcitonin gene-related peptide, which were previously identified only within the embryonic lung; and 4) NEBs harbor variant Clara cells deficient in cytochrome P450 2F2-immunoreactive protein. These data suggest that the NEB microenvironment is a reservoir of pollutant-resistant progenitor cells responsive to depletion of an abundant airway progenitor such as the Clara cell.

Evidence for autocrine actions of neuromedin B and gastrin-releasing peptide in non-small cell lung cancer

Gastrin-releasing peptide (GRP), a member of the bombesin family of peptides, has been shown to have mitogenic activity in small cell lung carcinoma (SCLC), and to be produced by SCLC in an autocrine fashion. In this report, we demonstrate that both GRP and another member of the bombesin family of peptides, neuromedin B (NMB), are also autocrine growth factors for non-small cell lung carcinoma (NSCLC). Using the reverse transcription-polymerase chain reaction (RT-PCR), we have detected mRNA for the neuromedin B receptor (NMBR) in all 14 of the NSCLC cell lines examined. GRP receptor (GRPR) mRNA was also expressed in the majority of NSCLC cell lines (nine of 14). By immunoblotting using SDS-PAGE gradient gels fixed in trichloroacetic acid, GRP and NMB were found in fractions of culture medium that had been purified by high pressure liquid chromatography (HPLC) from NSCLC cell lines. NMB was detected in the conditioned medium of seven of nine cell lines and GRP in seven of nine cell lines; both peptides were produced in six cell lines. In four of the cell lines where both peptides were produced, the relative amount of NMB secreted into the medium was 7-15 times that of GRP; in the other two cases, the relative amounts of GRP and NMB were equivalent. Cultured human bronchial epithelial (HBE) cells expressed the GRPR and NMBR but did not produce either peptide. A subline of A549 cells that was adapted to grow in serum-free and growth factor-free conditions, termed A549-R(0), secreted both bombesin-like peptides (BLPs) into the culture medium. Using either a colony-forming assay or a BrDU incorporation assay, both NMB and GRP were found to be mitogens for three NSCLC cell lines that express mRNA for BLP receptors and secrete BLPs, regardless of which peptide and/or receptor subtype was detected. The monoclonal antibody 2A11, which preferentially recognizes GRP, was able to block the in vitro proliferative response to GRP in the BrDU incorporation assay, and partially blocked the response to NMB. The 2A11 antibody could only partially block the in vivo growth of cell lines that showed proliferative responses to BLPs. 2A11 antibody was more effective against the 239T cell line, which secreted a low amount of GRP into the medium (0.6 nM), compared to the 201T cell line, which secreted a higher amount of both GRP and NMB (4.2 nM and 36.6 nM, respectively). These results suggest that both NMB and GRP are autocrine growth factors for NSCLC, but that the production of NMB and expression of the NMBR may be more prominent than the production of GRP and expression of the GRP receptor. If BLP ligand-receptor systems are to be targeted therapeutically in NSCLC, it will be necessary to inhibit both NMB and GRP.

Bombesin-like peptides and receptors in normal fetal baboon lung: roles in lung growth and maturation

Previously, we have shown that bombesin-like peptide (BLP) promotes fetal lung development in rodents and humans but mediates postnatal lung injury in hyperoxic baboons. The present study analyzed the normal ontogeny of BLP and BLP receptors as well as the effects of BLP on cultured normal fetal baboon lungs. Transcripts encoding gastrin-releasing peptide (GRP), a pulmonary BLP, were detectable on gestational day 60 (ED60), peaked on approximately ED90, and then declined before term (ED180). Numbers of BLP-immunopositive neuroendocrine cells peaked from ED80 to ED125 and declined by ED160, preceding GRP-receptor mRNAs detected from ED125 until birth. BLP (0.1-10 nM) stimulated type II cell differentiation in organ cultures as assessed by [(3)H]choline incorporation into surfactant phospholipids, electron microscopy, and increased surfactant protein (SP) A- and/or SP-C-immunopositive cells and SP-A mRNA. BLP also induced neuroendocrine differentiation on ED60. Cell proliferation was induced by GRP, peaking on ED90. Similarly, blocking BLP degradation stimulated lung growth and maturation, which was completely reversed by a BLP-specific antagonist. The dissociation between GRP and GRP-receptor gene expression during ontogeny suggests that novel BLP receptors and/or peptides might be implicated in these responses.

Syntaxin 1A is transiently expressed in fetal lung mesenchymal cells: potential developmental roles

Lung development is a complex process in which epithelial-mesenchymal interactions play a key role. A conserved secretory apparatus, the soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex, is essential for exocytosis in many cell types. Syntaxins, located on the terminal plasma membrane (T-SNAREs), are a critical component of the secretosomal complex involved in vesicular docking, fusion, and exocytosis. We analyzed syntaxin 1A mRNA and protein in fetal rat lung ontogeny, demonstrating peak expression on about day 19 of embryonic development, immediately preceding type II pneumocyte differentiation. Syntaxin 1A is predominantly expressed by lipofibroblasts, which are required for bombesin-like peptide-induced surfactant phospholipid synthesis (choline uptake) by isolated type II cells. In organ cultures, anti-syntaxin 1A antibody HPC-1 blocks choline uptake both at baseline and when induced by bombesin-like peptide or dexamethasone. HPC-1 also promotes thymidine uptake in parallel in a dose-dependent fashion. These observations indicate a potential role for syntaxin 1A during fetal lung development, possibly through involvement in secretion of mesenchymal cell-derived factors that induce terminal type II cell differentiation.

CD10/neutral endopeptidase inhibition augments pulmonary neuroendocrine cell hyperplasia in hamsters treated with diethylnitrosamine and hyperoxia

In previous studies, we demonstrated that pulmonary neuroendocrine cell (PNEC) hyperplasia in hamsters treated with diethylnitrosamine (DEN) plus 65% hyperoxia (DEN/O2) reflects predominantly neuroendocrine cell differentiation. Several peptides implicated in non-neoplastic PNEC hyperplasia are hydrolyzed by CD10/neutral endopeptidase 24.11 (CD10/NEP), an enzyme known to downregulate neurogenic inflammation of the lung by modulating locally effective concentrations of multiple bioactive peptides. In fetal mice, we observed that CD10/NEP inhibition by SCH32615 potentiates cell proliferation and type II cell differentiation in the lung in utero. Further, CD10/NEP messenger RNA levels parallelled relative PNEC numbers in DEN/O2-treated hamster lung, suggesting that the enzyme might mediate spontaneous regression of PNEC hyperplasia. The goals of the present study were: (1) to determine whether CD10/NEP inhibition would alter the extent of PNEC hyperplasia occurring in these hamsters, and (2) to analyze cellular mechanisms potentially involved in altering numbers of PNECs in this model. We administered SCH32615 chronically to a subset of DEN/O2-treated hamsters. Immunostaining of lungs from the CD10/ NEP-inhibited subset demonstrated significant acceleration of the development of PNEC hyperplasia, increased PNEC proliferation, and diminished PNEC apoptosis as compared with animals receiving no SCH32615. These observations indicate that PNEC hyperplasia can occur as a result of multiple cellular processes, including increased neuroendocrine cell differentiation, proliferation, and survival. CD10/NEP modulates PNEC numbers primarily by promoting cell differentiation and proliferation during lung injury, probably via increasing the half-life of bioactive peptides in the lung.

Congenital cystic adenomatoid malformation of the lung (CCAM): evaluation of the cellular components

Congenital cystic adenomatoid malformation of the lung (CCAM) is a rare congenital lesion whose pathogenesis is not well defined. It is generally accepted that the various types of CCAMs originate at different levels of the tracheobronchial tree. To further define the pathogenesis of CCAM, we evaluated the cellular composition of different CCAM types by immunohistochemistry. Twenty-two CCAMs (17 CCAM type 1, two type 2, one type 3, and two type 4) were collected. The cellular composition was determined using immunohistochemical stains for type I cell-associated antigen (T1 cell-Ag), surfactant proteins and surfactant protein precursors (SP-A, SP-B, proSP-B, and proSP-C), neuroendocrine cells (GRP), Clara cells (UP-1), and the adhesion molecule CD44v6, a glycoprotein thought to be involved in cell-matrix and cell-cell interactions. Eleven fetal lungs also were analyzed to compare cytodifferentiation of the epithelial-lined cysts of the different types of CCAM with the stages of normal lung development. Our results indicate that CCAM is caused by an arrest in lung development, and, on the basis of cytodifferentiation, two major subtypes can be distinguished. One subtype consisting of CCAM types 1, 2, and 3 that shows a bronchiolar type of epithelium and a second subtype, consisting of CCAM type 4, that has an acinar-alveolar type of epithelium. Our findings also suggest that these two subtypes may arise at different stages of the branching of the bronchopulmonary tree, the first at the pseudoglandular stage and the second at the saccular stage.