Calcitonin gene-related peptide and pulmonary hypertension in experimental hypoxia

The pulmonary neuroepithelial body microenvironment represents an underestimated multimodal component in airway sensory pathways

Exciting new imaging and molecular tools, combined with state-of-the-art genetically modified mouse models, have recently boosted interest in pulmonary (vagal) sensory pathway investigations. In addition to the identification of diverse sensory neuronal subtypes, visualization of intrapulmonary projection patterns attracted renewed attention on morphologically identified sensory receptor end-organs, such as the pulmonary neuroepithelial bodies (NEBs) that have been our area of expertise for the past four decades. The current review aims at providing an overview of the cellular and neuronal components of the pulmonary NEB microenvironment (NEB ME) in mice, underpinning the role of these complexly organized structures in the mechano- and chemosensory potential of airways and lungs. Interestingly, the pulmonary NEB ME additionally harbors different types of stem cells, and emerging evidence suggests that the signal transduction pathways that are active in the NEB ME during lung development and repair also determine the origin of small cell lung carcinoma. Although documented for many years that NEBs appear to be affected in several pulmonary diseases, the current intriguing knowledge on the NEB ME seems to encourage researchers that are new to the field to explore the possibility that these versatile sensor-effector units may be involved in lung pathogenesis or pathobiology.

Engineering ex vivo-expanded marrow stromal cells to secrete calcitonin gene-related peptide using adenoviral vector

Calcitonin gene-related peptide (CGRP) is a target for cardiovascular gene therapy. Marrow stromal cells (MSCs) hold promise for use in adult stem cell-based cell and gene therapy. To determine the feasibility of adenoviral-mediated CGRP gene transfer into ex vivo-expanded MSCs, rat MSCs were isolated, ex vivo expanded, and transduced with adenoviruses. Adprepro-CGRP and AdntlacZ, adenoviral vectors containing prepro-CGRP or nuclear-targeted beta-galactosidase reporter gene ntlacZ under the control of Rous sarcoma virus promoter, were used. In this study, it can be shown that transduction efficiency of adenoviral-mediated gene transfer into ex vivo-expanded MSCs is dose dependent, transgene expression persists for more than 21 days in culture, and adenoviral transduction does not alter the proliferation or viability of MSCs. Transduced MSCs retain multipotentiality and transgene expression after cell differentiation. The expression and secretion of CGRP by Adprepro- CGRP-transduced MSCs was confirmed by Western blot analysis and enzyme immunoassay. The secretion of CGRP by Adprepro-CGRP-transduced MSCs is dose dependent, and the transduced cells release as much as 9.5 +/- 0.4 pmol CGRP/1 x 10(6) cells/48 hours (mean +/- standard error of mean, n = 3) into culture medium at a multiplicity of infection of 300. Furthermore, culture supernatant from Adprepro-CGRP-transduced MSCs increases intracellular cyclic AMP levels in pulmonary artery smooth muscle cells in culture. These findings suggest that replication-deficient recombinant adenovirus can be used to gene engineer ex vivo-expanded MSCs and that high-level secretion of biologically active CGRP can be achieved, underscoring the clinical potential of using this novel adult stem cell-based cell and gene therapy strategy for the treatment of cardiovascular diseases.

Long-term induction of beta-CGRP mRNA in rat lungs by allergic inflammation

Calcitonin gene-related peptide (CGRP) is one of the major neuropeptides released from sensory nerve endings and neuroendocrine cells of the lung. Two CGRP isoforms, alpha-and beta-CGRP, have been identified in rats and humans, but no studies have attempted to reveal direct evidence of differences in action or location of these isoforms in allergic inflammation (AI). We investigated mRNA expressions of alpha-and beta-CGRP in lungs, nodose ganglia (NG), and dorsal root ganglia (DRG) of an animal model for AI of the airways, utilizing a model created by sensitizing Brown Norway (BN) rats with ovalbumin (OVA). By semiquantitative RT-PCR analysis, long-lasting enhanced expression of the beta-CGRP mRNA was shown in the lungs of the AI rats (14.5-fold enhancement at 6 hr, 8.1-fold at 24 hr, and 3.7-fold at 120 hr after OVA-challenge compared to the level in the lungs of phosphate-buffered saline (PBS)-challenged control rats). In contrast, the mRNA expression of the alpha-CGRP in AI lungs showed only a transient increase after OVA-challenge (2.7-fold at 6 hr) followed by a lower level of expression (0.5-fold at 48 hr and 0.6-fold at 120 hr). The mRNA expressions of both isoforms in NG, but not in DRG, were transiently up-regulated at 6 hr after antigen challenge. In situ RT-PCR in combination with immunohistochemical analysis revealed that beta-CGRP was expressed in neuroendocrine cells in clusters (termed neuroepithelial bodies [NEBs]) in AI lungs. These results indicate that the long-term induction of beta-CGRP in NEBs may play an important role in pulmonary AI such as bronchial asthma.

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.

Dual sensory innervation of pulmonary neuroepithelial bodies

The characteristics of the different populations of sensory nerve terminals that selectively contact pulmonary neuroepithelial bodies (NEBs) in rat lungs were investigated after chemical denervation with capsaicin and compared with control lungs. Vagal calbindin D28k and P2X(3) purinoceptor immunoreactive (IR) afferent nerve terminals contacting NEBs appeared to have their origin in the nodose ganglion. Thick CB/P2X(3)-IR nerve fibers were seen to be myelinated and to lose their myelin sheaths just before branching and protruding intraepithelially between the NEB cells. This vagal sensory component of the innervation of NEBs was not affected by capsaicin nor expressed capsaicin receptors (vanilloid receptor subtype 1). A second sensory nerve fiber population that selectively innervates pulmonary NEBs in the rat lung consists of thin unmyelinated nonvagal substance P/calcitonin gene-related peptide IR nerve fibers, contacting mainly the basal pole of pulmonary NEBs, and having their origin in dorsal root ganglia. In concordance with vanilloid receptor 1 expression on these nerve terminals, the spinal sensory substance P/calcitionin gene-related peptide-IR component of the innervation of NEBs was depleted by systemic capsaicin treatment. The complex sensory innervation pattern of pulmonary NEBs characterized in the present study strongly suggests that, physiologically, pulmonary NEBs represent a group of intraepithelial receptors that may be able to accommodate various local and central reflex actions, in relation to both chemo- and mechanosensory stimuli.

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.

Role of calcitonin gene-related peptide (CGRP) in chronic hypoxia-induced pulmonary hypertension in the mouse. Influence of gene transfer in vivo

Calcitonin gene-related peptide (CGRP) is believed to play an important role in maintaining low pulmonary vascular resistance (PVR) and may be involved in modulating the pulmonary vascular response to chronic hypoxia. In the present study, an adenoviral vector encoding CGRP (AdRSVCGRP) was used to examine the effects of in vivo gene transfer of CGRP to the lung on increases in PVR, right ventricular mass, and pulmonary vascular remodeling that occurs in chronic hypoxia in the mouse. Following intratracheal administration of AdRSVCGRP or reporter gene mice were exposed to 16 days of chronic hypoxia (FIO(2) 0.10). The increase in pulmonary arterial pressure (PAP), PVR, right ventricular mass, and pulmonary vascular remodeling in response to chronic hypoxia was attenuated in animals overexpressing CGRP, whereas systemic arterial pressure was not altered. Following exposure to hypoxia, a subgroup of mice were treated with capsaicin, which did not significantly alter CGRP expression in the mouse lung. These data show that in vivo transfer of the CGRP gene to the lung attenuates the increase in PVR, right ventricular mass, and pulmonary vascular remodeling in chronically hypoxic mice with little effect on the systemic circulation. Moreover, these data suggest that adenoviral gene transfer of CGRP to the lung results in expression of the gene product in non-neural tissue.

Neuroepithelial bodies: a morphologic substrate for the link between neuronal nitric oxide and sensitivity to airway hypoxia?

Currently, the significance of nitric oxide (NO) in the respiratory tract is a matter of great interest because NO is believed to play a major role in the physiological regulation of airway function but also in lung pathology. What is especially intriguing with respect to the present investigation, are reports that the pulmonary expression of neuronal NO synthase (nNOS) is altered as a result of airway hypoxia. We examined the possible relationship between intrapulmonary nitrergic structures and pulmonary neuroepithelial bodies (NEBs), chemoreceptor-like epithelial cell groups that are known to have all necessary components for oxygen perception. Tyramide-enhanced immunostaining for nNOS was combined with known markers for NEBs in an ontogenetic study of rat lungs. From postnatal day 2 onward, nNOS-immunoreactive (-IR) neuronal cell bodies, present mainly in the lamina propria at all levels of intrapulmonary airways, were seen to give rise to remarkable intraepithelial terminal arborizations that invariably colocalized with NEBs. nNOS immunoreactivity was absent from the vagal calbindin D28k(CB) -IR and the spinal calcitonin gene-related peptide(CGRP) -IR extrinsic sensory nerve fiber populations that our group reported earlier to selectively contact NEBs. Quantitative analysis showed that all NEBs receiving nNOS-IR terminals were also contacted by CGRP-IR nerve fibers, whereas approximately 55% were additionally contacted by CB-IR nerves. The reported nitrergic neurons did not express the cholinergic marker vesicular acetylcholine transporter and were always surrounded by a basket of CGRP-IR nerve terminals. In conclusion, part of the pulmonary NEBs selectively receive extensive nitrergic nerve terminals that originate from intrinsic neurons. Together with literature data on lung physiology and pharmacology, some interesting suggestions for the functional significance of the association between pulmonary CGRP-IR NEBs, nNOS-IR neurons, and CGRP-IR afferents described in the present study, are discussed.

In vivo gene transfer of prepro-calcitonin gene-related peptide to the lung attenuates chronic hypoxia-induced pulmonary hypertension in the mouse

BACKGROUND

Calcitonin gene-related peptide (CGRP) is believed to play an important role in maintaining low pulmonary vascular resistance (PVR) and in modulating pulmonary vascular responses to chronic hypoxia; however, the effects of adenovirally mediated gene transfer of CGRP on the response to hypoxia are unknown.

METHODS AND RESULTS

In the present study, an adenoviral vector encoding prepro-CGRP (AdRSVCGRP) was used to examine the effects of in vivo gene transfer of CGRP on increases in PVR, right ventricular mass (RVM), and pulmonary vascular remodeling that occur in chronic hypoxia in the mouse. Intratracheal administration of AdRSVCGRP, followed by 16 days of chronic hypoxia (FIO(2) 0.10), increased lung CGRP and cAMP levels. The increase in pulmonary arterial pressure (PAP), PVR, RVM, and pulmonary vascular remodeling in response to chronic hypoxia was attenuated in animals overexpressing prepro-CGRP, whereas systemic pressure was not altered while in chronically hypoxic mice, angiotensin II and endothelin-1-induced increases in PAP were reduced, whereas decreases in PAP in response to CGRP and adrenomedullin were not changed and decreases in PAP in response to a cAMP phosphodiesterase inhibitor were enhanced by AdRSVCGRP.

CONCLUSIONS

In vivo CGRP lung gene transfer attenuates the increase in PVR and RVM, pulmonary vascular remodeling, and pressor responses in chronically hypoxic mice, suggesting that CGRP gene transfer alone and with a cAMP phosphodiesterase inhibitor may be useful for the treatment of pulmonary hypertensive disorders.

[Congenital diaphragmatic hernia. I. Simple defect of the diaphragm or anomaly of the pulmonary mesenchyme?]

Described for the first time in 1848 by Bochdalek, congenital diaphragmatic hernia is still a hot topic. How can it be that a simple defect of the diaphragm still has a mortality rate reaching 50% in 1997, and this despite continuous progress in neonatal intensive care? If some problems remain unsolved, experimental studies over the past 30 years have raised some questions concerning the pathogenesis, and have shed some light into the pathophysiology of congenital diaphragmatic hernia. This article reviews the recent knowledge about the aetiology, pathogenesis and pathophysiology of this complex malformation.

Hyperoxia-induced airway remodeling and pulmonary neuroendocrine cell hyperplasia in the weanling rat

Infants dying with bronchopulmonary dysplasia (BPD) demonstrate increased numbers of pulmonary neuroendocrine cells (PNEC). These infants also possess altered airway epithelial and smooth muscle dimensions reminiscent of oxygen-exposed animals. Because the pathogenesis of BPD involves oxygen toxicity, we hypothesized that chronic hyperoxia would induce both airway remodeling and PNEC hyperplasia. To test this theory, we compared the small airway morphology of 21-d-old rats subsequently exposed to 2 wk of > 95% O2 (Ox; n = 12) with that of normoxic controls (Con; n = 12). In paraffin-embedded sections, airways < 1500 microns cut in cross-section were analyzed using light microscopy and image analysis software. The degree of epithelial and smooth muscle hyperplasia was assessed with proliferating cell nuclear antigen (PCNA). PNEC content was assessed via immunohistochemical staining for calcitonin gene-related peptide (CGRP) and the number of solitary PNEC (PNECsol) and PNEC clusters (neuroepithelial bodies, NEB) counted per section. We found that oxygen exposure increased epithelial and smooth muscle wall thickness (epithelium: Con, 12.3 +/- 1.4 versus Ox, 14.8 +/- 1.4 microns, p < 0.05; smooth muscle: Con, 7.0 +/- 1.0 versus Ox, 10.0 +/- 1.0 microns, p < 0.05). The changes in wall dimensions were accompanied by a 20% increase in fractional PCNA labeling of the epithelium but not the smooth muscle. Both PNECsol and NEB number increased in the Ox group (PNECsol Con, 3.6 +/- 2.6 versus Ox, 6.3 +/- 3.1/100 mm epithelium, p < 0.05; NEB Con, 7.1 +/- 4.0 versus 11.9 +/- 3.6/100 mm epithelium, p < 0.05). These findings document an association between hyperoxia, airway remodeling, and PNEC hyperplasia and imply that PNEC products may contribute to the pathogenesis of oxygen-related pulmonary diseases such as BPD.

Postnatal development of the pulmonary neuroepithelial bodies in various animal species

Various aspects of the postnatal development of intrapulmonary neuroepithelial bodies (NEB) were quantified in guinea-pigs, rabbits, cats, rats and hamsters. The highest densities of NEB were found at birth, especially in species with very immature neonates. Postnatally this density decreased, most probably by lung expansion and growth. The number of corpuscular cells per NEB generally did not change during postnatal development. Likewise, the volume density of their secretory dense cored vesicles remained unchanged. On the other hand, in most species and especially in those with very immature neonates, the number of intracorpuscular NEB nerve endings increased during postnatal development. At the same time, the number of afferent nerve endings increased at the expense of the efferent ones. We argue that NEB serve a dual function: endocrine and chemoreceptor. The endocrine function, dependent on the number of cells and their content of secretory vesicles, is already well developed at birth and does not mature further. The chemoreceptor function, dependent on the innervation, shows considerable maturation in the postnatal period.

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.

Increased intracellular levels of calcitonin gene-related peptide-like immunoreactivity in pulmonary endocrine cells in an experimental model of congenital diaphragmatic hernia

A congenital diaphragmatic hernia (CDH) model was induced in pregnant rats following administration of 100 mg nitrofen. The fetuses were stored and fixed in Bouin's solution for 24 h after caesarean section at term. After fixation, the lungs were dissected out. Immunostaining of the CDH lungs and controls with rabbit anti-rat calcitonin gene-related peptide (CGRP) antibody at "optimal" and "supraoptimal" dilution levels was obtained by examining the intensity of staining with a series of dilutions of the antisera from 1: 1,000 to 1: 20,000. Supraoptimal dilution detects variations in antigen concentration that may be masked if the routine optimal dilution is used. Immunostaining of the lung by antisera to platelet-derived growth factor (PDGF) and alpha-smooth-muscle actin (ASMA) was performed to examine vascular remodelling. The number of CGRP-immunoreactive cells was significantly (P <0.001) greater in the lungs of CDH rats (n = 26) (0.74 +-0.19 NEB [neuroepithelial bodies]/mm(2); mean +- SEM) compared with controls (n = 21) (0.30+-0.16 NEB/mm(2)) seen at supraoptimal dilution (1:20,000). Since CGRP is a vasodilator, this could have important implications in the development of pulmonary hypertension. The pattern of ASMA and PDGF immunostaining was similar in CDH lungs and controls, and therefore, vascular remodelling is not a feature of CDH lungs in fetuses delivered by caesarean section and not exposed to hypoxia.

Pulmonary neuroendocrine cells in neonatal rats with congenital diaphragmatic hernia

Lung hypoplasia and persistent pulmonary hypertension are the principal causes of high mortality and morbidity in infants with congenital diaphragmatic hernia (CDH). Amine- and peptide-producing pulmonary neuroendocrine cells (PNEC), widely distributed throughout the airway mucosa, are thought to play an important role in both pulmonary development and regulation of pulmonary vascular tone. Furthermore, recent studies show increased levels of calcitonin gene-related peptide (CGRP), a pulmonary vasodilator produced by PNEC, during chronic hypoxia. The article reports data on morphometric analysis of CGRP immunoreactive PNEC clusters (neuroepithelial bodies, NEB) in a rat model of CDH. CDH was induced in neonatal Sprague Dawley rats by oral administration of 2,4-dichloro-phenyl-p-nitrophenylether (Nitrofen; Rohm Haas, Philadelphia, PA) to the mother at 10 days of gestation. Sections of lungs from term neonatal rats with and without CDH and controls were immunostained for CGRP (marker of NEB) with specific antibody against rat CGRP. NEB size and number of NEB/area of lung were assessed using a semiautomatic image analysis system. In lungs of neonatal rats with CDH, the number of NEB per surface area of lung parenchyma was significantly increased compared with the age-matched controls. Although the mean size of NEB was larger in CDH, the differences were not significant. This is the first study of PNEC in CDH. Whether the phenomenon observed in this study results in altered NEB function including imbalance in vasoactive mediators requires further studies, especially in the human being.

Ontogeny of endocrine cells in the respiratory system of Syrian golden hamsters. II. Intrapulmonary airways and alveoli

Results of this and the preceding study reveal 3 patterns of endocrine cell development in hamster airway. The first, a prenatal wave, begins in the larynx and sweeps down the extra- and intrapulmonary conducting airway to the bronchioloalveolar portals. Cells differentiate singly and in groups (presumptive neuroepithelial bodies, pNEBs), colocalize immunoreactivity for serotonin (5-HT) and calcitonin gene-related peptide (CGRP), and persist throughout adulthood. Postnatally a few cells also express calcitonin (CT). Appearance of 5-HT and CGRP staining correlates with the onset of local, NEB-associated mitogenesis in fetal hamster airway epithelium. The second pattern begins after birth and is unique to the larynx and cartilaginous trachea. It involves differentiation of single cells which stain for CGRP but not 5-HT. Later, a proportion also stain for CT. This pattern seemingly accounts for the predominance of single cells in laryngotracheal epithelium of adult animals. In the third pattern, cells immunoreactive for peptide YY (PYY) differentiate, singly at first and later among cells of tiny pNEBs. This begins postnatally in alveoli, spreading centripetally with retrograde differentiation of alveolar epithelium back into the bronchiolar terminations. Restricted distribution and lack of immunoreactivity for 5-HT, CGRP, or CT suggest that the PYY-positive endocrine cells form a regional subset performing special roles in pulmonary homeostasis.

Calcium and ionophore A23187 lower calcitonin gene-related peptide-like immunoreactivity in endocrine cells of organ cultured fetal rat lungs

Small-granule endocrine cells differentiate in airway epithelium of intact and cultured fetal rat lungs. We noted that the cells store calcitonin gene-related peptide (CGRP) in vitro as well as in vivo and used the ionophore A23187 to test the effects of calcium on peptide secretion in this system. Lungs of 14-day and 15-day fetal rats, organ cultured for 6-9 days, were divided into groups of 5 explants each and incubated for 15 min at 37 degrees C in the basic medium containing 0 mM, 1 mM, or 10 mM CaCl2, with or without 8 microM A23187, or 10 mM EGTA. Intracellular CGRP in these explants was quantified by supraoptimal dilution peroxidase immunocytochemistry (Springall et al.: J. Pathol. 155:259-267, 1988): counts were made of endocrine cells stained with a 1/60,000 dilution of anti-CGRP and repeated on the same sections after restaining with antibody diluted at 1/1,000. Results, analyzed by Chi-square test, were expressed as % cells stained with antibody at 1/60,000 vs. those stained at 1/1,000. Immunoreactivity for CGRP was significantly reduced by A23187 in the presence of high extracellular Ca2+ (10 mM), the inference being that these cells secrete peptide hormones in response to Ca2+ influx across the plasma membrane. The organ cultures evidently can be used to assess certain physiological responses of lung endocrine cells in an accessible, relatively organotypical setting.