Phenotypic Epithelial Changes in Laryngotracheal Stenosis

Characterizing the Cellular Constituents of Proximal Airway Disease in Granulomatosis With Polyangiitis

OBJECTIVE

Granulomatosis with polyangiitis (GPA) is a rare multisystem autoimmune vasculitis. 10-20% of patients suffer life-threatening obstruction of their proximal airways. Although progress has been made in the treatment of systemic disease, ameliorating airway disease in GPA remains an unmet need arising from limited understanding of disease pathogenesis. We sought to characterize the cellular constituents of the affected proximal airway mucosa in GPA airway scar.

STUDY DESIGN

Basic/translational study.

SETTING

Single tertiary care center.

METHODS

Using single-cell RNA sequencing, we profiled the cellular constituents of proximal airway samples from GPA and disease comparators (GPA; n = 9, idiopathic subglottic stenosis: iSGS; n = 7, post-intubation proximal stenosis: PIPS; n = 5, and control; n = 10). We report transcriptomes for subglottic epithelial, immune, endothelial, and stromal cell types and map expression of GPA risk genes to tissue types present in the proximal airway. We compared differential gene expression across immune cell populations and performed pseudotime analysis using Monocle 3.

RESULTS

Similar to iSGS and PIPS, the subglottic mucosa of GPA patients demonstrated an abundant immune infiltrate. 71% of the established GPA risk genes (10 of 14) localized to T cells and macrophages. Differential gene expression and pseudotime analysis revealed a sub-population of CD4-/CD8- inflammatory T cells that only originated from GPA.

CONCLUSION

We characterized the cellular composition of GPA airway disease and demonstrated that the expression of GPA risk alleles is predominantly localized to immune cell populations. We also identified a subset of inflammatory T cells that is unique to GPA.

Localized Knockout of E-Cadherin in Subglottic Mucosa Increases Fibrosis

OBJECTIVE

To assess the effects of localized subglottic knockout of E-cadherin (CDH1-/-) on survival, tracheal luminal thickness, and fibrotic gene expression in a mouse model of subglottic stenosis.

STUDY DESIGN

Case-control in vivo mouse study.

SETTING

Tertiary care academic hospital.

METHODS

Mice with loxP sites flanking E-cadherin underwent extratracheal placement of a fibrin-plasmin gel embedded with either CRE-expressing or control adenovirus. Mice then underwent chemomechanical injury to induce laryngotracheal stenosis, with harvest of subglottis/tracheas 21 days later. Immunofluorescence and Western blotting were used to confirm E-cadherin knockout. Outcomes of interest included Kaplan-Meier survival curves (n = 40), lamina propria thickness on hematoxylin-eosin (H&E) histology (n = 8), and fibrotic gene expression (n = 3).

RESULTS

Immunofluorescence and Western blotting confirmed decreased E-cadherin expression in CDH1-/-. On H&E, lamina propria thickness was greater in CDH1-/- mice (mean difference [95% CI] in μm, 107.2 [74.8-139.7], P < .001). Survival was significantly shorter for knockout mice relative to control (median survival in days, 5.0 vs 8.5; P = .007). Further, fibrotic gene expression of COL1 (mean difference [95% CI] in log-fold change, 11.5 [1.9-21.0]; P = .03), COL3 (31.0 [11.5-50.5]; P = .01), COL5 (6.8 [3.1-10.4]; P = .007), and FN1 (6.9 [1.3-12.6]; P = .03) was significantly greater relative to control.

CONCLUSION

CDH1-/- results in greater fibrosis and increased mortality, further supporting the role of epithelial barrier dysfunction in the pathogenesis of subglottic stenosis. Therapies that restore epithelial integrity may therefore represent a rational pharmacologic target.

Transcriptomic Features of Recurrence Rates in Idiopathic Subglottic Stenosis

OBJECTIVE

Idiopathic subglottic stenosis (iSGS) is a rare disease characterized by narrowing of the upper airway and affects near-exclusively females. Patients often experience recurrent disease and require repeated surgical dilations. The pathophysiology underlying the broad spectrum of disease severity within iSGS remains unknown. In the current study, we sought to identify transcriptomic differences between iSGS patients with markedly different recurrence rates.

METHODS

Prospectively collected clinical and bulk RNA sequencing data from subglottic tissues of 56 female iSGS patients with 1-4 years of follow-up were analyzed. DESeq2 was used to perform differential expression analysis, comparing samples from the highest (1.19-1.87 dilations/year) versus the lowest (0.30-0.65 dilations/year) quartile of surgical dilation rate (i.e., high vs. low recurrence groups).

RESULTS

In total, 220 genes were significantly differentially expressed between the high and low recurrence groups (adjusted p < 0.1 and log2 fold change > |1|). Pathway enrichment analyses showed that the high recurrence group had significantly increased expression of genes involved in adaptive immune responses (e.g., immunoglobulin subunit genes) and extracellular matrix organization (e.g., COMP, NID2) (adjusted p < 0.1). In contrast, the low recurrence group had significantly increased expression of genes involved in cilia structure and function (e.g., CFAP43, DNAI2) (adjusted p < 0.1), suggesting a relatively increased abundance of respiratory cilia.

CONCLUSION

Transcriptomic profiling suggests that lower recurrence rates in iSGS are associated with retention of respiratory cilia, while adaptive immune responses and increased extracellular matrix deposition are present in those with higher recurrence rates. These results hold promise for the development of prognostic markers and identification of therapeutic targets for iSGS.

Cohort-level clinical trajectory and molecular landscape of idiopathic subglottic stenosis for precision laryngology-a study of the Canadian Airways Research (CARE) group

BACKGROUND

First described in 1972, idiopathic subglottic stenosis (iSGS) is a serious chronic orphan disease characterised by recurrent scarring of the subglottis. Although the cause is unknown, iSGS is almost exclusively restricted to Caucasian females typically in their fourth to sixth decade. However, given its rare incidence (1:400,000), understanding the clinical trajectory and molecular factors associated with iSGS disease development and prognosis has been difficult. In the current study we sought to unravel the pathogenesis of iSGS at the clinical, transcriptional, and genetic level in a prospective cohort.

METHODS

We prospectively enrolled 126 patients with iSGS, 104 controls, and 13 patients with traumatic SGS. Within this cohort, we profiled 114 human epiglottis and 121 human subglottis biopsies across three different conditions: control, iSGS, and intubation-related traumatic stenosis using bulk and single nucleus RNA-sequencing. Whole exome sequencing for germline variants was performed for 70 controls and 75 patients with iSGS.

FINDINGS

Patients with iSGS received a median number of five (range 0-18) surgical dilations at a rate of 1.031 dilations (range: 0.12-6.2) per year. Older age at diagnosis and higher Cotton-Myers grade were associated with increased number of surgical dilations over time. Cohort-level bulk transcriptomics found that iSGS pathology was restricted within the subglottis and did not affect anatomically adjacent epiglottis, opposite to previous hypotheses. We further identified cellular subsets associated with iSGS prognosis and severity. Finally, patients with iSGS exhibit lower testosterone predicted using a polygenic score.

INTERPRETATION

Together, our data refines our understanding of laryngeal biology and provides insights into the clinical trajectory of subglottic stenoses. Future research should explore the role of testosterone in the development of iSGS.

FUNDING

This study was funded by a grant from the American Laryngology Association (#1082), an Academic Medical Organization of Southwestern Ontario innovation fund grant (INN21-016), grant support from the Departments of Otolaryngology-Head and Neck Surgery at University of Toronto and Western University. ACN was supported by the Wolfe Surgical Research Professorship in the Biology of Head and Neck Cancers Fund. PYFZ was supported by a Vanier Canada Graduate Scholarship and PSI foundation fellowship.

Third Proceedings of The North American Airway Collaborative (NoAAC): Consensus Statement on Trial Design for Airway Stenosis

Importance

Airway stenosis is a rare but debilitating disorder that significantly degrades the quality of life in affected patients. Treatments are primarily surgical, and disease management lacks established medical therapies. The North American Airway Collaborative held its third symposium at The Johns Hopkins Hospital in Baltimore, Maryland, on April 15, 2024, focused on strategies to advance the care of these patients. The proceedings summarize the discussion of trial design in airway stenosis and the resulting North American Airway Collaborative consensus regarding clinical end points for rigorous study of novel therapies.

Observations

The lectures and panels centered on the translation of a growing body of preclinical data into therapeutic targets. Additionally, detailed discussion explored design of clinical trials to evaluate safety and efficacy of novel therapeutics. The need for a consensus regarding clinically meaningful end points in airway stenosis was identified to facilitate the comparison of outcomes across institutions and future multi-institutional trials.

Conclusions and Relevance

The group achieved consensus regarding change in peak expiratory flow as the primary clinical end point in airway stenosis. Additional clinical measures, such as disease recurrence (identified as time to recurrent intervention), anatomical characterization of subglottic scar via axial computed tomography imaging, and patient-reported outcome measures (Clinical COPD Questionnaire [CCQ], Voice Handicap Index-10 [VHI-10], Eating Assessment Tool-10 [EAT-10], and 12-Item Short-Form Health Survey, version 2 [SF-12]) were identified as essential secondary outcomes.

Airway stenosis: classification, pathogenesis, and clinical management

Airway stenosis (AS) is a fibroinflammatory disease characterized by abnormal activation of fibroblasts and excessive synthesis of extracellular matrix, which has puzzled many doctors despite its relatively low prevalence. Traditional treatment such as endoscopic surgery, open surgery, and adjuvant therapy have many disadvantages and are limited in the treatment of patients with recurrent AS. Therefore, it is urgent to reveal the pathogenesis of AS and accelerate its clinical transformation. Based on the discovered pathogenesis, including fibrosis, inflammation, epithelial-mesenchymal transition, metabolic reprogramming, microbiome, genetic susceptibility, and other mechanisms, researchers have developed a series of treatments, such as drug therapy, gene therapy, stem cell therapy, growth factor therapy, protein therapy, and photodynamic therapy. This review introduces the classification of AS, explores the existing pathogenesis and preclinical treatments developed based on the pathogenesis, and finally summarizes the current clinical management. In addition, the prospect of exploring the interaction between different types of cells and between microorganisms and cells to identify the intersection of multiple mechanisms based on single-cell RNA sequencing, 16S rRNA gene sequencing and shotgun metagenomic sequencing is worth looking forward to.

Microbiome and Communication Disorders: A Tutorial for Clinicians

PURPOSE

Emerging research in the field of microbiology has indicated that host-microbiota interactions play a significant role in regulating health and disease. Whereas the gut microbiome has received the most attention, distinct microbiota in other organs (mouth, larynx, and trachea) may undergo microbial shifts that impact disease states. A comprehensive understanding of microbial mechanisms and their role in communication and swallowing deficits may have downstream diagnostic and therapeutic implications.

METHOD

A literature review was completed to provide a broad overview of the microbiome, including differentiation of commensal versus pathogenic bacteria; cellular mechanisms by which bacteria interact with human cells; site-specific microbial compositional shifts in certain organs; and available reports of oral, laryngeal, and tracheal microbial dysbiosis in conditions that are associated with communication and swallowing deficits.

RESULTS/CONCLUSIONS

This review article is a valuable tutorial for clinicians, specifically introducing them to the concept of dysbiosis, with potential contributions to communication and swallowing deficits. Future research should delineate the role of specific pathogenic bacteria in disease pathogenesis to identify therapeutic targets.

The dragonfly technique for trachea closure in temporary tracheostomies. Surgical steps and clinical results

PURPOSE

To assess the effectiveness of a new suturing technique called Dragonfly for the closure of temporary tracheotomies. This technique involves placing two sutures during the tracheotomy procedure and leaving them loose and unknotted until the day of skin closure.

METHODS

Retrospective case control study. Monocentric study at a department of Otolaryngology and head and neck surgery at a tertiary centre in Italy. A total of 50 patients who underwent temporary tracheotomy between January 2017 and December 2021. Patients were divided into two groups based on the trachea closure method: traditional closure with sutures placed during the skin closure procedure (Group A) and the Dragonfly technique (Group B). The incidence of tracheal stenosis by Computed Tomography (CT), granulation tissue formation, bleeding, procedure duration, patient discomfort were evaluated.

RESULTS

The incidence of tracheal complications and tracheal stenosis was reduced in Group B (6%) compared to Group A (24%). Procedure times (3 min vs. 6 min) durations was significantly shorter. No patients had symptoms of tracheal stenosis at the end of the procedures.

CONCLUSION

The Dragonfly suturing technique is effective and safe for tracheotomy closure, reducing the incidence of tracheal stenosis and shortening hospitalization duration compared to the traditional method.

A Comprehensive Flow Cytometry Panel for Analysis of Idiopathic Subglottic Stenosis

OBJECTIVE

To present a comprehensive flow cytometry panel for idiopathic subglottic stenosis (iSGS).

STUDY DESIGN

Controlled ex vivo cohort study.

SETTING

Tertiary care academic hospital in a metropolitan area.

METHODS

Flow cytometry and single-cell RNA sequencing were performed on 9 paired normal and scar tissue samples from iSGS patients. Flow cytometry was used to assess the presence of myeloid (CD11b, CD14, CD15, Siglec8), lymphoid (CD3, CD4, CD8, gamma delta [γδ], FOXP3), endothelial (CD31), fibroblast (CD90, SMA), and epithelial (CD326, CK5) markers.

RESULTS

On flow cytometry, iSGS scar is characterized by an increased presence of myeloid, lymphoid, endothelial, and fibroblast cell types, but a decreased presence of epithelial cells. In the myeloid lineage, iSGS scar samples demonstrated increased CD11b+ monocytes (P < .001), Siglec8+ eosinophils (P = .03), and CD14+ monocytes (P = .02). In the lymphoid lineage, iSGS scar demonstrated increased CD3+ T-cells (P < .001), CD4+ helper T-cells (P < .001), γδ+ T-cells (P < .001), and FOXP3+ regulatory T-cells (P = .002). iSGS scar exhibited specific increases in CD90+ (P = .04) and SMA+ (P < .001) fibroblasts but decreased CD326+ (E-cadherin) epithelial cells (P = .01) relative to normal samples.

CONCLUSION

We present a comprehensive flow cytometry panel for iSGS. This flow panel may serve as a common platform among airway scientists to elucidate the cellular mechanisms underpinning iSGS and other upper airway pathologies. Scar iSGS samples demonstrate a distinct cellular profile relative to normal iSGS specimens, exhibiting increased fibroblast, endothelial, and inflammatory cell types but decreased epithelium.

Idiopathic Subglottic Stenosis in Non-Caucasian Women

Objective

To characterize presentation, disease course, and treatment of idiopathic subglottic stenosis (iSGS) in non-Caucasian women and compare this cohort to the predominantly female, Caucasian patient cohorts identified in the literature.

Study Design

Retrospective review. Results are compared to systematic review of demographics.

Setting

Multiple California institutions from 2008 to 2021.

Methods

Patients with intubation within 2 years of disease or who met exclusion criteria listed in prior publications were excluded. A systematic review of iSGS patient demographics was also completed for comparison.

Results

Of 421 patients with iSGS, 58 self-identified as non-Caucasian women, with 50 ultimately included. Mean age of onset was 45.1 years old (95% confidence interval [CI], 41.5-48.8), and mean age at diagnosis was 47.2 years (95% CI, 43.6-50.7). Mean Charlson comorbidity index was 1.06 (n = 49, 95% CI, 0.69-1.44). At diagnosis, Cotton-Meyer severity scores (documented in n = 45) were Cotton-Myer (CM) I (28.9%), CM II (40%), and CM III (31.1%). Mean age at first endoscopic surgery was 47.7 (95% CI, 44.2-51.3) years. 64% experienced disease recurrence with a median of 11 months between their first and second surgery. Our systematic review identified 60 studies that reported demographic features in patients with iSGS. 95% of pooled patients were Caucasian, while other demographic features were similar to the current cohort.

Conclusion

The non-Caucasian population, almost 14% of this Californian cohort, does not differ from the majority Caucasian population detailed in contemporary literature. This cohort supports the presence of some racial and ethnic heterogeneity in this disease population.

Characterizing the T Cell Repertoire in the Proximal Airway in Health and Disease

OBJECTIVES

Recent translational scientific efforts in subglottic stenosis (SGS) support a disease model where epithelial alterations facilitate microbiome displacement, dysregulated immune activation, and localized fibrosis. Given the observed immune cell infiltrate in SGS, we sought to test the hypothesis that SGS cases possessed a low diversity (highly clonal) adaptive immune response when compared with healthy controls.

METHODS

Single cell RNA sequencing (scRNA-seq) of subglottic mucosal scar in iSGS (n = 24), iLTS (n = 8), and healthy controls (n = 7) was performed. T cell receptor (TCR) sequences were extracted, analyzed, and used to construct repertoire structure, compare diversity, interrogate overlap, and define antigenic targets using the Immunarch bioinformatics pipeline.

RESULTS

The proximal airway mucosa in health and disease are equally diverse via Hill framework quantitation (iSGS vs. iLTS vs. Control, p > 0.05). Repertoires do not significantly overlap between individuals (Morisita <0.02). Among iSGS patients, clonality of the TCR repertoire is driven by CD8+ T cells, and iSGS patients possess numerous TCRs targeting viral and intercellular pathogens. High frequency clonotypes do not map to known targets in public datasets.

CONCLUSION

SGS cases do not possess a lower diversity adaptive immune infiltrate when compared with healthy controls. Interestingly, the TCR repertoire in both health and disease contains a restricted number of high frequency clonotypes that do not significantly overlap between individuals. The target of the high frequency clonotypes in health and disease remain unresolved.

LEVEL OF EVIDENCE

NA Laryngoscope, 134:1757-1764, 2024.

Idiopathic Subglottic Stenosis Is Associated With More Frequent and Abnormal Squamous Metaplasia

OBJECTIVES

Gain insights into the pathophysiology of idiopathic subglottic stenosis (iSGS) by investigating differences in transcriptome of subglottic mucosal tissue between patients with iSGS and controls, and between tracheal and subglottic tissue within patients.

METHODS

RNA sequencing was conducted on biopsied mucosal samples collected from subglottic and tracheal (in-patient control) regions in iSGS patients, and from subglottis in controls. The gene expression differences were validated on a protein level by (1) staining the tissue samples obtained from a second cohort of patients and controls; and (2) in vitro functional assays using primary subglottic epithelial cells from both iSGS patients and healthy donors.

RESULTS

We found 7 upregulated genes in the subglottic region of iSGS patients relative to both the tracheal mucosa and subglottic region of controls. A gene ontology enrichment analysis found that the epithelial cell differentiation and cornification pathways are significant, involving specifically 3 of the genes: involucrin (IVL), small proline rich protein 1B (SPRR1B), and keratin 16 (KRT16). Involvement of these pathways suggests squamous metaplasia of the epithelium. Histological analyses of epithelium in subglottic mucosal biopsies revealed squamous metaplasia in 41% of the samples from iSGS patients and in 25% from controls. Immunohistochemical evaluation of the samples presented with squamous epithelium revealed increased expression of the protein encoded by SPRR1B, hyperproliferative basal cells, shedding of apical layers, and accompanying lesions in iSGS compared to CTRL. Cultured primary subglottic epithelial cells from iSGS patients had higher proliferation rates compared to healthy donors and squamous metaplastic differentiation formed thinner epithelia with increased expression proteins encoded by INV, SPRR1B, and KRT16, suggesting intrinsic dysfunction of basal cells in iSGS.

CONCLUSIONS

Abnormal squamous differentiation of epithelial cells may contribute to the pathogenesis of iSGS. Patients having metaplastic epithelial phenotype may be sensitive to drugs that reverse it to a normal phenotype.

Assessment of wood smoke induced pulmonary toxicity in normal- and chronic bronchitis-like bronchial and alveolar lung mucosa models at air-liquid interface

BACKGROUND

Chronic obstructive pulmonary disease (COPD) has the highest increased risk due to household air pollution arising from biomass fuel burning. However, knowledge on COPD patho-mechanisms is mainly limited to tobacco smoke exposure. In this study, a repeated direct wood smoke (WS) exposure was performed using normal- (bro-ALI) and chronic bronchitis-like bronchial (bro-ALI-CB), and alveolar (alv-ALI) lung mucosa models at air-liquid interface (ALI) to assess broad toxicological end points.

METHODS

The bro-ALI and bro-ALI-CB models were developed using human primary bronchial epithelial cells and the alv-ALI model was developed using a representative type-II pneumocyte cell line. The lung models were exposed to WS (10 min/exposure; 5-exposures over 3-days; n = 6-7 independent experiments). Sham exposed samples served as control. WS composition was analyzed following passive sampling. Cytotoxicity, total cellular reactive oxygen species (ROS) and stress responsive NFkB were assessed by flow cytometry. WS exposure induced changes in gene expression were evaluated by RNA-seq (p ≤ 0.01) followed by pathway enrichment analysis. Secreted levels of proinflammatory cytokines were assessed in the basal media. Non-parametric statistical analysis was performed.

RESULTS

147 unique compounds were annotated in WS of which 42 compounds have inhalation toxicity (9 very high). WS exposure resulted in significantly increased ROS in bro-ALI (11.2%) and bro-ALI-CB (25.7%) along with correspondingly increased NFkB levels (bro-ALI: 35.6%; bro-ALI-CB: 18.1%). A total of 1262 (817-up and 445-down), 329 (141-up and 188-down), and 102 (33-up and 69-down) genes were differentially regulated in the WS-exposed bro-ALI, bro-ALI-CB, and alv-ALI models respectively. The enriched pathways included the terms acute phase response, mitochondrial dysfunction, inflammation, oxidative stress, NFkB, ROS, xenobiotic metabolism of AHR, and chronic respiratory disorder. The enrichment of the 'cilium' related genes was predominant in the WS-exposed bro-ALI (180-up and 7-down). The pathways primary ciliary dyskinesia, ciliopathy, and ciliary movement were enriched in both WS-exposed bro-ALI and bro-ALI-CB. Interleukin-6 and tumor necrosis factor-α were reduced (p < 0.05) in WS-exposed bro-ALI and bro-ALI-CB.

CONCLUSION

Findings of this study indicate differential response to WS-exposure in different lung regions and in chronic bronchitis, a condition commonly associated with COPD. Further, the data suggests ciliopathy as a candidate pathway in relation to WS-exposure.

Dysfunctional Epithelial Barrier Is Characterized by Reduced E-Cadherin in Idiopathic Subglottic Stenosis

OBJECTIVES

To aim of the study was to characterize the molecular profile and functional phenotype of idiopathic subglottic stenosis (iSGS)-scar epithelium.

METHODS

Human tracheal biopsies from iSGS scar (n = 6) and matched non-scar (n = 6) regions were analyzed using single-cell RNA sequencing (scRNA-seq). Separate specimens were used for epithelial cell expansion in vitro to assess average growth rate and functional capabilities using transepithelial-electrical resistance (TEER), fluorescein isothiocyanate-dextran flux permeability assay, ciliary coverage, and cilia beating frequency (CBF). Finally, epithelial tight junction protein expression of cultured cells was quantified using immunoblot assay (n = 4) and immunofluorescence (n = 6).

RESULTS

scRNA-seq analysis revealed a decrease in goblet, ciliated, and basal epithelial cells in the scar iSGS cohort. Furthermore, mRNA expression of proteins E-cadherin, claudin-3, claudin-10, occludin, TJP1, and TJP2 was also reduced (p < 0.001) in scar epithelium. Functional assays demonstrated a decrease in TEER (paired 95% confidence interval [CI], 195.68-890.83 Ω × cm2 , p < 0.05), an increase in permeability (paired 95% CI, -6116.00 to -1401.99 RFU, p < 0.05), and reduced epithelial coverage (paired 95% CI, 0.1814-1.766, fold change p < 0.05) in iSGS-scar epithelium relative to normal controls. No difference in growth rate (p < 0.05) or CBF was found (paired 95% CI, -2.118 to 3.820 Hz, p > 0.05). Immunoblot assay (paired 95% CI, 0.0367-0.605, p < 0.05) and immunofluorescence (paired 95% CI, 13.748-59.191 mean grey value, p < 0.05) revealed E-cadherin reduction in iSGS-scar epithelium.

CONCLUSION

iSGS-scar epithelium has a dysfunctional barrier and reduced structural protein expression. These results are consistent with dysfunctional epithelium seen in other airway pathology. Further studies are warranted to delineate the causality of epithelial dysfunction on the downstream fibroinflammatory cascade in iSGS.

LEVEL OF EVIDENCE

NA Laryngoscope, 134:374-381, 2024.

Murine Model of Airway Fibrosis has Anatomic, Physiologic, and Molecular Congruency to Human iSGS

OBJECTIVE

To narrow knowledge gaps in the pathophysiology of idiopathic subglottic stenosis (iSGS) through comparison of a murine subglottic stenosis model with iSGS.

STUDY DESIGN

In vivo animal study.

SETTING

Academic institution.

METHODS

Murine samples/measurements were obtained from mice that underwent chemomechanical injury with a wire brush and bleomycin. Human samples/measurements were obtained from iSGS patients. Anatomic, physiologic, and epithelial molecular data were collected using histology, human peak expiratory flow (PEF) and murine airway conductance, gene expression analysis with quantitative polymerase chain reaction, and protein analysis with quantitative immunohistochemistry.

RESULTS

Anatomic patterns of scars at the subglottis and proximal trachea seen in the murine model are similar to iSGS patients. Subglottic stenosis (SGS) mice had a decrease (P = .0194) in airway conductance compared to healthy controls, similar to a decrease (P = .0001) in predilation PEF versus postdilation in iSGS patients. There was decreased epithelial gene expression of E-cadherin (ECAD) (P < 0.01), occludin (OCLN) (P < .01), and cytokeratin-5 (CK5) (P < .05) and protein expression of ECAD (H/M: P < .001), OCLN (H: P < 0.05, M: P < .001), and CK5 (H: P < .001, M: P < .01) in murine SGS and iSGS versus controls.

CONCLUSION

The murine SGS model shows anatomic, physiologic, and molecular congruency with human iSGS, making it a reasonable model to investigate iSGS. The molecular similarities in epithelial barrier dysfunction suggest it may best be suited to explore epithelial mechanisms of iSGS and therapies directed at epithelial reconstitution. This model provides a foundation to collect data that will improve understanding of iSGS, and, ultimately, translate into more accurate animal models for future use.

Localizing Hormone Receptor Expression to Cellular Compartments in Idiopathic Subglottic Stenosis

OBJECTIVES

Idiopathic subglottic stenosis (iSGS) is an unexplained progressive fibrosis of the upper airway. iSGS almost exclusively affects women; as a result, female hormones (estrogen and progesterone) have been proposed to participate in the pathogenesis of iSGS. Our aim was to localize cell-specific gene expression of estrogen receptors (ESR1 and ESR2) and progesterone receptor (PGR) using an established iSGS single-cell RNA sequencing (scRNAseq) cell atlas.

STUDY DESIGN

Ex vivo molecular study of airway scar and healthy mucosa from iSGS patients.

METHODS

An established scRNAseq atlas consisting of 25,974 individually sequenced cells from subglottic scar (n = 7) or matched unaffected mucosa (n = 3) in iSGS patients was interrogated for RNA expression of ESR1, ESR2, and PGR. Results were quantified and compared across cell subsets, then visualized using Uniform Manifold Approximation and Projection (UMAP). Confirmatory protein assessment of endocrine receptors in fibroblasts from iSGS patients (n = 5) was performed via flow cytometry.

RESULTS

The proximal airway mucosa in iSGS patients demonstrates differential expression of endocrine receptors (ESR1, ESR2, PGR). Within airway scar, endocrine receptors are primarily expressed by fibroblasts, immune cells, and endothelial cells. Fibroblasts show strong ESR1 and PGR expression, while immune cells possess RNA for both ESR1 and ESR2. Endothelial cells predominantly express ESR2. Epithelial cells in unaffected mucosa express all three receptors, which are all reduced in airway scar.

CONCLUSIONS

scRNAseq data localized endocrine receptor expression to specific cell subsets. These results provide the foundation for future work interrogating how hormone-dependent mechanisms promote, sustain, or participate in iSGS disease pathogenesis.

LEVEL OF EVIDENCE

NA; Basic science Laryngoscope, 133:3506-3511, 2023.

Mapping Genetic Susceptibility to Stenosis in the Proximal Airway

OBJECTIVES

Recent translational scientific efforts in subglottic stenosis (SGS) support a disease model where epithelial alterations facilitate microbiome displacement, dysregulated immune activation, and localized fibrosis. Yet despite recent advances, the genetic basis of SGS remains poorly understood. We sought to identify candidate risk genes associated with an SGS phenotype, investigate their biological function, and identify the cell types enriched for their expression.

METHODS

The Online Mendelian Inheritance in Man (OMIM) database was queried for single gene variants associated with an SGS phenotype. The functional intersections and molecular roles of the identified genes were explored using pathway enrichment analysis (PEA) computational methods. Cellular localization of the candidate risk genes was measured via transcriptional quantification in an established single cell RNA sequencing (scRNA-seq) atlas of the proximal airway.

RESULTS

Twenty genes associated with SGS phenotype were identified. PEA resulted in 24 significantly enriched terms including "cellular response to TGF-β," "epithelial-to-mesenchymal transition," and "adherens junctions." Mapping the 20 candidate risk genes to the scRNA-seq atlas found 3 (15%) genes were enriched in epithelial cells, 3 (15%) in fibroblasts, and 3 (15%) in endothelial cells. 11 (55%) genes were expressed ubiquitously among tissue types. Interestingly, immune cells were not significantly enriched for candidate risk genes.

CONCLUSION

We identify and provide biologic context for 20 genes associated with fibrotic disease of the proximal airway and form the foundation for future detailed genetic study.

LEVEL OF EVIDENCE

N/A Laryngoscope, 133:3049-3056, 2023.

Human Leukocyte Antigen Genotyping of Idiopathic Subglottic Stenosis

OBJECTIVE

Despite recent scientific inquiry, idiopathic subglottic stenosis (iSGS) remains an enigmatic disease. The consistent demographics of the affected population suggest genetic factors may contribute to disease susceptibility. Given the inflammation observed in the affected proximal airway mucosa, we interrogated disease association with human leukocyte antigen (HLA) polymorphisms. Polymorphisms in the HLA locus have previously been shown to influence individuals' susceptibility to distinct inflammatory diseases.

METHODS

High-resolution HLA typing of 37 iSGS patients was compared with 1,242,890 healthy Caucasian controls of European ancestry from the USA National Marrow Donor Program and 281 patients with granulomatosis with polyangiitis (GPA).

RESULTS

Complete HLA genotyping of an iSGS population showed no significant associations when compared to a North American Caucasian control population. Unlike GPA patients, iSGS was not associated with allele DPB1*04:01 nor did allele homozygosity correlate with disease severity.

CONCLUSIONS

There was not a detectable HLA association observed in iSGS. These results support the concept that iSGS possesses a distinct genetic architecture from GPA. If genetic susceptibility exists in iSGS, it likely lies outside the HLA locus.

LEVEL OF EVIDENCE

NA, basic science Laryngoscope, 133:2533-2539, 2023.

Characterizing the Macrophage Population in Patients With Idiopathic Subglottic Stenosis

OBJECTIVES

Idiopathic subglottic stenosis (iSGS) is characterized by progressive fibrosis and subglottic luminal narrowing. Currently, immune characterization has focused on T-cells; however, macrophages remain largely unexplored. The goals of this study are to characterize the transcriptome of iSGS macrophages and the fibrogenic nature of identifed biomarkers.

STUDY DESIGN

Bioinformatics and in vitro.

METHODS

Human tracheal biopsies from iSGS scar (n = 4), and matched non-scar (n = 4) regions were analyzed using single-cell RNA-seq (scRNA-seq). Immunofluorescence (IF) was performed on rapidly processed autopsies (RPA) and iSGS tracheal resections (n = 4) to co-localize S100A8/9 and CD11b. Collagen gene/protein expression was assessed in iSGS fibroblasts (n = 4) treated with protein S100A8/9 (1000 ng/ml). Macrophages were subclustered to identify distinct subpopulations.

RESULTS

scRNA-seq analysis revealed S100A8/S100A9 (fold change (FC) = 4.1/1.88, p < 0.001) as top differentially expressed genes in iSGS macrophages. IF exhibited increased CD11b+/S100A8/9+ cells in tracheal samples of iSGS versus RPA (26.75% ± 7.08 vs. 0.594% ± 0.974, n = 4, p = 0.029). iSGS fibroblasts treated with S100A8/9 demonstrated increased gene expression of COL1A1 (FC = 2.30 ± 0.45, p = 0.03, n = 4) and COL3A1 (FC = 2.44 ± 0.40, p = 0.03, n = 4). COL1A1 protein assays revealed an increase in the experimental group, albeit not significant, (p = 0.12, n = 4). Finally, macrophage sub clustering revealed one subpopulation as a predominant source of S100A8/S100A9 expression (FC = 7.94/5.47, p < 0.001).

CONCLUSIONS

S100A8/9 is a key biomarker in iSGS macrophages. Although S100A8/9 demonstrates profibrotic nature in vitro, the role of S100A8/9+ macrophages in vivo warrants further investigation.

LEVEL OF EVIDENCE

NA Laryngoscope, 133:2308-2316, 2023.

Idiopathic subglottic stenosis arises at the epithelial interface of host and pathogen

Background

Idiopathic subglottic stenosis (iSGS) is a rare fibrotic disease of the proximal airway affecting adult Caucasian women nearly exclusively. Life-threatening ventilatory obstruction occurs secondary to pernicious subglottic mucosal scar. Disease rarity and wide geographic patient distribution has previously limited substantive mechanistic investigation into iSGS pathogenesis.

Result

By harnessing pathogenic mucosa from an international iSGS patient cohort and single-cell RNA sequencing, we unbiasedly characterize the cell subsets in the proximal airway scar and detail their molecular phenotypes. Results show that the airway epithelium in iSGS patients is depleted of basal progenitor cells, and the residual epithelial cells acquire a mesenchymal phenotype. Observed displacement of bacteria beneath the lamina propria provides functional support for the molecular evidence of epithelial dysfunction. Matched tissue microbiomes support displacement of the native microbiome into the lamina propria of iSGS patients rather than disrupted bacterial community structure. However, animal models confirm that bacteria are necessary for pathologic proximal airway fibrosis and suggest an equally essential role for host adaptive immunity. Human samples from iSGS airway scar demonstrate adaptive immune activation in response to the proximal airway microbiome of both matched iSGS patients and healthy controls. Clinical outcome data from iSGS patients suggests surgical extirpation of airway scar and reconstitution with unaffected tracheal mucosa halts the progressive fibrosis.

Conclusion

Our data support an iSGS disease model where epithelial alterations facilitate microbiome displacement, dysregulated immune activation, and localized fibrosis. These results refine our understanding of iSGS and implicate shared pathogenic mechanisms with distal airway fibrotic diseases.

The role of tracheal wall injury in the development of benign airway stenosis in rabbits

To investigate the role of tracheal wall injury in the development of benign airway stenosis in rabbits. Prospective study. We injured the tracheal walls of 28 New Zealand white rabbits using four different methods. Experimental group: Group A (n = 7, mild injury of tracheal mucosa by ordinary brush under bronchoscopy); Group B (n = 7, severe injury of tracheal mucosa by nylon brush under tracheotomy); Group C (n = 7, tracheal cartilage was injured by vascular clamp after tracheotomy); Group D (n = 7, the tracheal cartilage was injured with vascular forceps and the tracheal mucosa was injured with a nylon brush after tracheotomy). Bronchoscopy was performed on each experimental rabbit at 1, 2, 3 and 4 weeks after operation. High-resolution computed tomography (HRCT) and endobronchial optical coherence tomography (EB-OCT) were performed at 4 weeks, and the rabbits were sacrificed after the examination. Their gross and histological findings were comparatively determined whether the experimental rabbit stenosis was established. No airway stenosis was observed in group A. In group B, 28.57% of experimental rabbits developed tracheal stenosis (granulation tissue proliferation was observed in rabbits No. 2 and No. 6 at 1, 2 and 3 weeks after operation, and the tracheal scar contracture was observed in No.6 rabbit at 4 weeks after operation). Fourteen rabbits in group C and group D had tracheal stenosis caused by granulation tissue proliferation at 1, 2 and 3 weeks after operation. At the fourth week after operation, 71.43% of experimental rabbits had tracheal stenosis due to granulation tissue hyperplasia, 7.14% of experimental rabbits had tracheal stenosis due to scar contracture and granulation hyperplasia, and 21.43% of experimental rabbits had tracheal stenosis due to scar contracture. EB-OCT scan showed that the cartilage layer with low signal reflection band was discontinuous. The injury of cartilage is the key factor of benign airway stenosis. Acute injury of airway mucosa alone is unlikely to cause airway stenosis, but combined with cartilage injury may aggravate airway stenosis. EB-OCT can clearly identify the airway layers of rabbits, which is helpful to evaluate the damage of tracheal cartilage and mucosa. The diagnostic potential of this technique makes EB-OCT a promising approach for the study and monitoring of airway diseases.