Morphological and histochemical study of human submucosal laryngeal glands

High-Resolution Profiling of Human Vocal Fold Cellular Landscapes With Single-Nuclei RNA Sequencing

INTRODUCTION

The function of the vocal folds (VFs) is determined by the phenotype, abundance, and distribution of differentiated cells within specific microenvironments. Identifying this histologic framework is crucial in understanding laryngeal disease. A paucity of studies investigating VF cellular heterogeneity has been undertaken. Here, we examined the cellular landscape of human VFs by utilizing single-nuclei RNA-sequencing.

METHODS

Normal true VF tissue was excised from five patients undergoing pitch elevation surgery. Tissue was snap frozen in liquid nitrogen and subjected to cellular digestion and nuclear extraction. Nuclei were processed for single-nucleus sequencing using the 10X Genomics Chromium platform. Sequencing reads were assembled using cellranger and analyzed with the scanpy package in python.

RESULTS

RNA sequencing revealed 18 global cell clusters. While many were of epithelial origin, expected cell types, such as fibroblasts, immune cells, muscle cells, and endothelial cells were present. Subcluster analysis defined unique epithelial, immune, and fibroblast subpopulations.

CONCLUSION

This study evaluated the cellular heterogeneity of normal human VFs by utilizing single-nuclei RNA-sequencing. With further confirmation through additional spatial sequencing and microscopic imaging, a novel cellular map of the VFs may provide insight into new cellular targets for VF disease.

LEVEL OF EVIDENCE

NA Laryngoscope, 134:3193-3200, 2024.

Early studies of airway submucosal glands

This historical article provides a comprehensive review of early research on the structure and function of airway submucosal glands. The literature before 1950 or so, is virtually unknown, but in addition to being of historical interest it contains much of relevance to current research. Airway glands were first mentioned in 1602. The first description of their general form, size, and distribution was in 1712. Gland morphology was determined in 1827 by injecting mercury into their openings. Wax was later used. Detailed comparative information for all regions of the tracheobronchial tree was provided by Frankenhauser in 1879 (Untersuchungen uber den bau der Tracheo-Bronchial-Schleimhaut). Histological studies began in 1870, and by the end of the 19th century, all the major histological features had been described. The first physiological studies on airway mucous secretion were published in 1892. Kokin, in 1896 (Archiv für die gesamte Physiologie des Menschen und der Tiere 63: 622-630), was the first to measure secretion from individual glands. It was not, however, until 1933 that gland secretion was quantified. This early literature raises important questions as to the role of the collecting duct epithelium in modifying primary secretions. It also provides perhaps the most accurate measure of basal gland secretion in vivo.

Glycoconjugate Expression in Normal Human Inferior Turbinate Mucosa: A Lectin Histochemical Study

Background

Further study on the composition and concentration of normal nasal mucosal glycoconjugates is needed.

Methods

A battery often lectins was used to stain six carbohydrates residing in the inferior turbinate mucosa of 21 healthy individuals.

Results

The concentrations of glycoconjugates of the glycocalyx exceeded that of epithelial goblet, ciliated, and basal cells, and also of mucous, serous, and mixed submucosal glands. Epithelial goblet cells and submucosal mucous glands contained relatively high concentrations of glycoconjugates, whereas in epithelial ciliated and basal cells, similar to serous and mixed submucosal glands, concentrations were scanty. The concentrations of N-acetylgalactosamine and galactose were higher in goblet cells than in mucous glands (p = 0.006, and p = 0.056, respectively). Differences in the concentrations of N-acetylglucosamine, fucose, mannose, and sialic acid were insignificant.

Conclusions

The findings provide a baseline for comparison of the composition and concentration of carbohydrates of the normal and pathologic inferior turbinate mucosa.

The Use of Lectin Histochemistry for Detecting Apoptotic Cells in the Seminiferous Epithelium

Lectin histochemistry is commonly used to characterize the pattern of glycoconjugates in cells and tissues. Recent studies show that alterations in these glycoconjugates are associated with the entry of cells into apoptosis. A widely used technique for the detection of apoptotic cell death is TUNEL. In this chapter, we study the sensitivity of both techniques to identify apoptotic cells in the testis of photo-inhibited Syrian hamster.

The H+/K+-ATPase (proton) pump is expressed in human laryngeal submucosal glands

OBJECTIVES/HYPOTHESIS

Diagnosis and treatment of gastroesophageal and laryngopharyngeal reflux disease has significantly increased over recent years. The larynx is highly sensitive to the effects of LPRD and is similarly responsive to proton pump inhibitor pharmacotherapy. The hypothesis of the study was that proton pump activity exists in the human larynx and plays a functional role in normal and/or pathological laryngeal tissue.

STUDY DESIGN

Pathological investigation.

METHODS

Two fresh human cadaveric larynges (one male and one female larynx) were obtained as part of an exempt protocol from the Human Subjects Committee and were formalin fixed and paraffin embedded. Banked human stomach tissue was also obtained for use as comparative positive and negative control specimens. Sections were immunostained with monoclonal antibodies reactive with both alpha and beta subunits of the H+/K+-ATPase (proton) pump. Specimens were reviewed for staining pattern and intensity.

RESULTS

Stomach parietal cells (known to produce gastric acid) exhibited strongly positive staining for both the alpha and beta subunits of the proton pump. There was no staining in stomach cells that were not morphologically consistent with the parietal cell. In the human larynx there were strong focal and identical staining patterns in the serous cells and ducts of the minor seromucinous glands by both alpha and beta monoclonals to the proton pump. There was variable staining in the laryngeal epithelium that was thought to be consistent with artifact staining resulting from tissue processing.

CONCLUSION

The H+/K+-ATPase (proton) pump is present in serous cells and ducts of submucosal glands in the human larynx. Proton pump inhibitor pharmacotherapy may have a site of action in seromucinous glands of the human larynx, with possible relevance for patients treated for chronic laryngitis with or without laryngopharyngeal reflux disease.

Anatomical definition of the subglottic region

BACKGROUND

Due to laryngeal neoplasia, as well as infectious and autoimmune diseases, the subglottic region is of great clinical relevance. However, descriptions of the subglottic structures are inconsistent. The aim of our study was to present a precise analysis of the subglottic region and derive functional and clinical conclusions.

METHODS

Histological, histochemical and immunohistochemical investigations as well as scanning electron microscopy were performed and combined with injection techniques applied to the subglottic region of the larynges of 33 body donors.

RESULTS

The three-dimensional extensions of the subglottic region were newly defined: the inferior arcuate line of the vocal cord was defined as the cranial border. The lower margin of the cricoid is the caudal border. Craniolaterally, the elastic cone and, further caudally, the cricoid form the border. Therefore, the definition presented comprises heretofore unnamed ventral and dorsal parts of the lower larynx. The subglottic region can be described as cylindrical, becoming smaller in the cranial direction, following the elastic cone. The ventral boundary is formed by the median part of the cricothyroid ligament (ligamentum conicum), the dorsal part by the cricoid cartilage. The walls of the subglottis are divided into three or four layers composed of collagenous and elastic fibres in which seromucous glands are embedded. Subglottic blood vessels including a tight subepithelial capillary plexus were delineated.

CONCLUSION

The new definition of the subglottic extensions presented is helpful and essential for precise laryngeal tumour classification. The results indicate that the boundaries are unlikely to counteract tumour progression in the subglottis. Furthermore, the findings suggest that these structures contribute to temperature regulation of breath, protection against inflammation as well as breath frequency and depth-dependent mucus secretion.

Parasympathetic control of airway submucosal glands: central reflexes and the airway intrinsic nervous system

Airway submucosal glands produce the mucus that lines the upper airways to protect them against insults. This review summarizes evidence for two forms of gland secretion, and hypothesizes that each is mediated by different but partially overlapping neural pathways. Airway innate defense comprises low level gland secretion, mucociliary clearance and surveillance by airway-resident phagocytes to keep the airways sterile in spite of nearly continuous inhalation of low levels of pathogens. Gland secretion serving innate defense is hypothesized to be under the control of intrinsic (peripheral) airway neurons and local reflexes, and these may depend disproportionately on non-cholinergic mechanisms, with most secretion being produced by VIP and tachykinins. In the genetic disease cystic fibrosis, airway glands no longer secrete in response to VIP alone and fail to show the synergy between VIP, tachykinins and ACh that is observed in normal glands. The consequent crippling of the submucosal gland contribution to innate defense may be one reason that cystic fibrosis airways are infected by mucus-resident bacteria and fungi that are routinely cleared from normal airways. By contrast, the acute (emergency) airway defense reflex is centrally mediated by vagal pathways, is primarily cholinergic, and stimulates copious volumes of gland mucus in response to acute, intense challenges to the airways, such as those produced by very vigorous exercise or aspiration of foreign material. In cystic fibrosis, the acute airway defense reflex can still stimulate the glands to secrete large amounts of mucus, although its properties are altered. Importantly, treatments that recruit components of the acute reflex, such as inhalation of hypertonic saline, are beneficial in treating cystic fibrosis airway disease. The situation for recipients of lung transplants is the reverse; transplanted airways retain the airway intrinsic nervous system but lose centrally mediated reflexes. The consequences of this for gland secretion and airway defense are poorly understood, but it is possible that interventions to modify submucosal gland secretion in transplanted lungs might have therapeutic consequences.

The mink as an animal model for Pseudomonas aeruginosa adhesion: binding of the bacterial lectins (PA-IL and PA-IIL) to neoglycoproteins and to sections of pancreas and lung tissues from healthy mink

Lung infection with Pseudomonas aeruginosa, leading to chronic lung disease with impaired function, is the major course of morbidity and mortality among cystic fibrosis patients. The bacterium produces two lectins that bind to alpha-D-galactose (PA-IL) and L-fucose (PA-IIL), respectively, and lectin-carbohydrate interactions may be involved in microbial pathogenicity by creating bacterial adherence to epithelial and endothelial cells. An ideal animal model for P. aeruginosa infection has until now not been established, but the mink seems to be the only animal that has been reported to develop spontaneous P. aeruginosa infections in the airways. Since cystic fibrosis also severely may affect pancreatic function, we incubated sections from mink lungs and pancreas with a medium containing Pseudomonas lectins in order to detect in situ binding of the bacterial lectins. In the lungs, both lectins adhered to seromucinous glands located in the submucosa of the larger bronchi. Additionally, PA-IL reacted with the capillaries in the alveolar walls and with the small blood vessels forming the vasa vasorum around the larger vessels, while PA-IIL marked the goblet cells in the bronchial surface epithelium. In the pancreas, both lectins bound to the epithelium in the excretory ducts, and additionally, PA-IL strongly stained the pancreatic capillaries while PA-IIL staining was noticed in the apical part of acinar cells in the exocrine part of the gland while no lectin reaction could be recorded in the endocrine cells. Judging from the results in the present paper the mink should be considered a suitable model to study P. aeruginosa adherence.

[Onco-surgical significance of anatomo-morphological specificity of glottic region of the larynx]

Glottis is a medium level of the larynx, involving the vocal cords, vocal process of arytenoid cartilage, and the anterior and posterior commissures. This region of heterogeneous histomorphological structure has specific characteristics: the internal striated muscles, the outer and inner perichondrium, atypical intra-cartilaginous areas of ossification, and unusual muscular insertion to cartilage. Microtomy of 3 thick successive sections was performed at the level of the upper surface of vocal cords. Standard histological staining methods were used. Microphotographs were taken by light microscope under different magnification along with histomorphometric measurements. Cancer spread is partially restricted by anatomic barriers: vocal ligament and tendon of the anterior commissure, and subsequently by the elastic cone. Easier tumor extension may be due to absence of the internal perichondrium and ossification of thyroid cartilage. Microvascularization of the anterior commissure is significant for tumor spread in glottis and paraglottic space. The role of commissural lymph network in local spread of the cancer is completely vague. It is certain that there are causes, still unrecognized, which have an effect on the pathways and direction of malignant tumor spread.

Subglottic region: normal topography and possible clinical implications

A precise definition of clinically important laryngeal regions and compartments is still a matter of controversy. The often neglected subglottic area was reinvestigated in plastinated serial sections of 21 human adult specimens. The superior border of the subglottic region is defined by the transition of squamous stratified epithelium covering the vocal cords into the respiratory epithelium of the caudal airways. It is found at the inferior margin of the vocal fold at variable distance from the free edge of the vocal cord and bears a high risk of carcinogenesis. The anterior border of the subglottic region is the cricothyroid space between the thyroid cartilage and cricoid arch. Medially, it is bridged by the median cricothyroid ligament. Laterally, the gap between thyroid and cricoid cartilage is filled by adipose tissue in most cases. This provides a broad connection of intra- and extralaryngeal connective tissue. There, cancer may escape the larynx. The conus elasticus is often regarded as a firm fibroelastic membrane within the subglottic region, but its structure may be disturbed by piercing blood vessels or age-related changes, facilitating cancerous spread. The cricoid lamina representing the dorsal border of the subglottic space ossifies preferentially in its superior part, which is often attacked by tumor invasion. The inferior border of the subglottic region is defined at the inferior rim of the cricoid cartilage. At this level, the endocricoid submucosal tissue contains loosely arranged collagenous fibers, which probably do not act as an anatomic barrier.

Does botulinum toxin alter laryngeal secretions and mucociliary transport?

Localized botulinum toxin injection disrupts cholinergic transmission and has potential to cause focal dysautonomia. Mucociliary transport and laryngeal secretions are thought to be mediated in part by autonomic, cholinergic transmission. We questioned whether patients who receive Botox injection for adductor spasmodic dysphonia (ADSD) report postinjection symptoms possibly related to altered mucociliary clearance or laryngeal secretions. Medical histories, audiotaped interviews, and symptom ratings were retrospectively examined for 29 patients with ADSD who were followed after one or more Botox injections. Patients had received bilateral, percutaneous Botox injections of 2.5 units using an EMG-guided approach. One or more weeks after injection, four patients reported either burning, tickling, or irritation of the larynx/throat, excessive thick secretions, or dryness. Symptoms recurred with subsequent injections in two patients and were not associated with swallowing difficulty. These symptoms are consistent with, but not diagnostic of, the known effects of botulinum toxin on cholinergic, autonomic transmission.

Different glycoconjugates in the submucosal glands of the supraglottis and subglottis. Lectin histochemistry study in the hamster

A lectin histochemistry study was performed in the supraglottic and subglottic regions of 10 hamsters. The submucosal glands were observed by light microscopy. The supraglottic submucosal glands presented numerous mucous tubules but on the other hand, the subglottic submucosal glands had serous tubules which finished at the distal portion in serous acini. The results suggest that the distribution of fucosylated-mucin and serum-type glycoproteins between the supra- and subglottic submucosal glands suggest a different viscosity and function of the mucus.