Airway wall extracellular matrix changes induced by bronchial thermoplasty in severe asthma

Abstract

Airway remodeling is a prominent feature of asthma, including increased airway smooth muscle (ASM) mass and altered extracellular matrix (ECM) composition. Bronchial thermoplasty (BT), a bronchoscopic treatment for severe asthma, targets this airway remodeling. To investigate the effect of BT on ECM composition and its association with clinical outcomes. This is a sub-study of the TASMA trial. Thirty severe asthma patients were BT treated, of which 13 patients prior to BT were treated by six months of standard therapy (control group). Demographic data, clinical data including pulmonary function and bronchial biopsies were collected. Biopsies at BT treated and non-treated locations were analyzed by histological and immune-histochemical staining. Associations between histology and clinical outcomes were explored. Six months after treatment, reticular basement membrane (RBM) thickness was reduced from 7.28μm to 5.74μm (21% relative reduction) and the percentage area of tissue positive for collagen increased from 26.3% to 29.8% (13% relative increase). Collagen structure analysis revealed a reduction in the curvature frequency of fibers. The percentage area positive for fibulin-1 and fibronectin increased with 2.5% and 5.9% respectively (relative increase of 124% and 15%). No changes were found for elastin. The changes in collagen and fibulin-1 negatively associated with changes in FEV1-reversibility. Next to ASM reduction, BT impacts RBM thickness and the ECM arrangement characterized by an increase in tissue area occupied by collagen with a less dense fiber organization. Both collagen and fibulin-1 are negatively associated with the change in FEV1-reversibility. BT induces ECM reorganization and airway wall stability.