Airway Epithelial Secretome Markers in Respiratory Disease

Abstract

The airway epithelial secretome, comprising a diverse array of proteins and signaling molecules released by respiratory epithelial cells, has emerged as a critical determinant in the pathogenesis, progression, and therapeutic monitoring of various respiratory diseases. Recent advances in omics technologies have enabled the identification of novel secretome markers that offer insights into airway inflammation, remodeling, and host-pathogen interactions. This review synthesizes current knowledge on airway epithelial secretome markers, their mechanistic roles, epidemiological significance, clinical implications, and relevance to diagnostic and therapeutic strategies in respiratory diseases such as asthma, chronic obstructive pulmonary disease (COPD), and cystic fibrosis. We integrate recent evidence, highlight emerging biomarkers, and discuss guideline-based approaches for integrating secretome profiling into clinical practice.

Introduction

The respiratory epithelium forms the primary interface between the external environment and the host's internal milieu, orchestrating defense mechanisms crucial for airway integrity and function. Beyond acting as a physical barrier, epithelial cells actively secrete a repertoire of cytokines, chemokines, growth factors, and antimicrobial peptides collectively referred to as the "secretome". Dysregulation of this secretome underlies the pathobiology of many airway diseases, influencing immune responses, tissue remodeling, and susceptibility to infection. Elucidating the patterns and functions of secretome markers holds promise for advancing disease detection, phenotyping, and personalized therapy in respiratory medicine.

Epidemiology / Disease Burden

Respiratory diseases constitute a major global health burden, with asthma affecting over 350 million people and COPD ranking as the third leading cause of death worldwide. The heterogeneous clinical presentation and variable course of these conditions are partly attributable to underlying airway epithelial dysfunction. Secretome markers not only reflect local airway pathology but also correlate with disease severity, exacerbation risk, and long-term outcomes. Large-scale cohort studies have demonstrated that altered levels of key epithelial-derived mediators, such as periostin and YKL-40, are associated with increased healthcare utilization and morbidity in patients with chronic airway diseases.

Pathophysiology

The airway epithelial secretome plays a pivotal role in orchestrating immune surveillance, mucociliary clearance, and repair processes. In response to environmental insults (e.g., allergens, pathogens, pollutants), epithelial cells release pro-inflammatory cytokines (IL-6, IL-8), alarmins (TSLP, IL-33), and growth factors (EGF, TGF-β), which modulate local and systemic inflammatory cascades. Dysregulated secretion of these mediators contributes to chronic airway inflammation, goblet cell hyperplasia, subepithelial fibrosis, and airway remodeling. Furthermore, the secretome mediates crosstalk between the epithelium, immune cells, and the underlying mesenchyme, amplifying disease processes and influencing therapeutic response.

Risk Factors

Numerous intrinsic and extrinsic factors modulate the airway epithelial secretome. Genetic predisposition, epigenetic modifications, and underlying atopic status influence baseline secretory profiles. Environmental exposures such as tobacco smoke, occupational irritants, viral and bacterial infections, and urban pollution can acutely or chronically alter secretome composition. Notably, comorbidities including obesity, gastroesophageal reflux, and metabolic syndrome have been linked to aberrant secretome patterns, further exacerbating disease risk and progression.

Clinical Features

Alterations in the airway epithelial secretome are reflected in the clinical heterogeneity observed across respiratory diseases. Patients with Th2-high asthma, for instance, exhibit elevated periostin and TSLP levels, correlating with eosinophilic inflammation, airway hyperresponsiveness, and poor response to conventional corticosteroid therapy. In COPD, increased secretion of neutrophil-attracting chemokines (e.g., CXCL8/IL-8) and matrix metalloproteinases is associated with neutrophilic airway inflammation, emphysematous changes, and accelerated lung function decline. Secretome marker profiling thus enables more precise endotyping and risk stratification.

Diagnosis

Traditional diagnostic algorithms for airway diseases rely on clinical evaluation, spirometry, and imaging, which often lack sensitivity for early or atypical disease phenotypes. Incorporating secretome marker analysis using non-invasive samples such as induced sputum, exhaled breath condensate, or nasal lavage offers an adjunctive tool for disease detection and monitoring. Biomarkers such as periostin, YKL-40, and exosomal miRNAs are under investigation for their ability to differentiate phenotypes, predict exacerbations, and guide therapeutic selection. Standardization of assay techniques and validation in diverse populations remain key challenges.

Treatment & Management

Understanding airway epithelial secretome dynamics informs individualized treatment strategies. In asthma, targeting upstream epithelial-derived cytokines (e.g., TSLP, IL-33) with biologic agents has demonstrated efficacy in reducing exacerbations and improving symptom control, particularly in steroid-resistant phenotypes. In COPD, therapies aimed at modulating neutrophilic inflammation and protease-antiprotease imbalance are under active investigation. Monitoring secretome markers offers a potential means to assess response to treatment, anticipate relapses, and tailor therapy intensity.

Recent Advances / Emerging Therapies

Recent advances in proteomics, transcriptomics, and single-cell sequencing have expanded the repertoire of putative secretome markers and elucidated novel disease mechanisms. The development of monoclonal antibodies targeting epithelial alarmins (e.g., anti-TSLP: tezepelumab) and the identification of exosomal miRNAs as minimally invasive biomarkers represent significant translational milestones. Ongoing clinical trials are evaluating the prognostic and predictive value of secretome markers in therapy selection and disease monitoring across a spectrum of respiratory conditions.

Guideline Recommendations

Contemporary clinical guidelines increasingly recognize the importance of airway epithelial biomarkers in disease management. The Global Initiative for Asthma (GINA) and Global Initiative for Chronic Obstructive Lung Disease (GOLD) recommend the integration of biomarker-based phenotyping for optimizing biologic therapy and risk stratification. However, guidelines underscore the need for robust multicenter validation, cost-effectiveness analyses, and harmonization of sampling and assay methodologies before routine clinical implementation of secretome marker profiling.

Conclusion

The airway epithelial secretome represents a dynamic and mechanistically informative source of biomarkers for respiratory diseases. Advances in marker discovery, coupled with growing clinical evidence, are reshaping approaches to diagnosis, phenotyping, and personalized therapy. Continued research into the standardization and clinical validation of secretome markers will be critical for translating these insights into improved patient outcomes and more precise management of airway diseases.