The role of inflammatory cytokines in the development of idiopathic subglottic stenosis

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.

Does Idiopathic Subglottic Stenosis Length and Location Change with Serial Endoscopic Interventions?

OBJECTIVES/HYPOTHESIS

The aim was to assess changes in physical parameters of subglottic stenosis (SGS) following serial endoscopic surgical intervention.

STUDY DESIGN

This was a retrospective chart review.

METHODS

A retrospective review of 52 idiopathic subglottic stenosis (iSGS) patients undergoing multiple endoscopic (excision/dilation) procedures between 2014 and 2022 was completed. Parameters including proximal stenosis distance from the vocal process and total stenosis length collected intraoperatively were compared over serial treatments. Differences between patient variables affecting distances from the vocal process and mean stenosis length were statistically analyzed utilizing nonparametric estimators including the Mann Whitney U, Fisher exact, and linear regression models.

RESULTS

For the cohort of iSGS patients (N = 52), the mean age was 55.1 (±15.1). The patients were predominantly female (96.2%) and Caucasian (84.6%). Patients underwent an average of 3.4 (±1.3) endoscopic procedures for long-term treatment of iSGS (range: 1 to 5 procedures). Patients undergoing a total of two (2) total procedures within the data collection window demonstrated a statistically significant decrease in mean stenosis length between the first and second procedures (p = 0.014). Changes in distance of the stenosis from the glottis was not found to be statistically significant (p = 0.833). There was a statistically significant decrease in mean length of stenosis from the 1st to the 2nd procedure by approximately 0.11 cm (p = 0.0003). No additional statistically significant differences in stenosis length or location were detected.

CONCLUSIONS

Serial endoscopic excision/dilation procedures (the mainstay of iSGS surgical management) do not appear to significantly lengthen intraluminal stenosis nor change the distance of the stenosis from the glottis.

LEVEL OF EVIDENCE

4 Laryngoscope, 134:1769-1772, 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.

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.

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.

Laryngotracheal stenosis: Mechanistic review

Background

The purpose of this review article is to summarize the existing literature surrounding wound healing mechanisms in laryngotracheal stenosis.

Methods

A review of general wound healing pathophysiology, followed by a focused review of iatrogenic laryngotracheal stenosis (iLTS) and idiopathic subglottic stenosis (iSGS) as conditions of aberrant wound healing.

Results

iLTS is the scarring of the laryngotracheal complex, coming secondary to injury from prolonged intubation. iSGS is a chronic fibroinflammatory scarring and narrowing of the subglottic airway in the absence of any obvious preceding injury or trauma. They are both thought to result from a prolonged and dysregulated wound healing response that promotes the deposition of pathologic scar in the airway.

Conclusions

Understanding the mechanisms that underlie wound healing will help identify and intervene on the process early in its development and discover future therapies that target individual wound healing mechanisms limiting the incidence of this recalcitrant disease process.

Clinical Significance of Mast Cells in the Supraglottic Larynx of Children With Aerodigestive Disease

OBJECTIVE

To analyze the association of mast cells found on supraglottic biopsy of pediatric patients with common aerodigestive diseases.

STUDY DESIGN

Cross-sectional study.

SETTING

Tertiary care children's hospital.

METHODS

A total of 461 pediatric patients undergoing otolaryngology aerodigestive procedures provided consent between 2014 and 2019, and biopsies of the supraglottic larynx were collected at the time of their surgery. Pathologists reviewed biopsies for the presence and number of mast cells per high-power field. The patients' electronic health records were reviewed for relevant demographic data and clinical diagnoses present at the time of biopsy. Multivariate logistic regression was used to assess the relationship of mast cells with odds of aerodigestive disease.

RESULTS

Patients with mast cells in their biopsy had significantly higher odds of asthma (odds ratio [OR], 2.02; 95% CI, 1.17-3.46), gastroesophageal reflux disease (OR, 2.36; 95% CI, 1.47-3.77), laryngomalacia (OR, 2.98; 95% CI, 1.80-4.94), laryngeal anomalies (OR, 2.32; 95% CI, 1.52-3.55), and obstructive sleep apnea (OR, 2.16; 95% CI, 1.35-3.45). When mast cells were evaluated as a continuous variable, there was a nonlinear relationship between increasing mast cell count and odds of disease.

CONCLUSIONS

Mast cells are known to be associated with inflammatory conditions, though little is known about their presence in laryngeal inflammation. Results from our study demonstrate an association between mast cells in the pediatric larynx and asthma, gastroesophageal reflux disease, laryngomalacia, laryngeal anomalies, and obstructive sleep apnea. Our study also showed a nonlinear relationship between number of mast cells and odds of disease diagnosis.