Bronchial Asthma, Airway Remodeling and Lung Fibrosis as Successive Steps of One Process

Abstract

Bronchial asthma is a heterogeneous disease characterized by persistent respiratory system inflammation, airway hyperreactivity, and airflow obstruction. Airway remodeling, defined as changes in airway wall structure such as extensive epithelial damage, airway smooth muscle hypertrophy, collagen deposition, and subepithelial fibrosis, is a key feature of asthma. Lung fibrosis is a common occurrence in the pathogenesis of fatal and long-term asthma, and it is associated with disease severity and resistance to therapy. It can thus be regarded as an irreversible consequence of asthma-induced airway inflammation and remodeling. Asthma heterogeneity presents several diagnostic challenges, particularly in distinguishing between chronic asthma and other pulmonary diseases characterized by disruption of normal lung architecture and functions, such as chronic obstructive pulmonary disease. The search for instruments that can predict the development of irreversible structural changes in the lungs, such as chronic components of airway remodeling and fibrosis, is particularly difficult. To overcome these challenges, significant efforts are being directed toward the discovery and investigation of molecular characteristics and biomarkers capable of distinguishing between different types of asthma as well as between asthma and other pulmonary disorders with similar structural characteristics. The main features of bronchial asthma etiology, pathogenesis, and morphological characteristics as well as asthma-associated airway remodeling and lung fibrosis as successive stages of one process will be discussed in this review. The most common murine models and biomarkers of asthma progression and post-asthmatic fibrosis will also be covered. The molecular mechanisms and key cellular players of the asthmatic process described and systematized in this review are intended to help in the search for new molecular markers and promising therapeutic targets for asthma prediction and therapy.

Keywords: airway remodeling; asthma; biomarkers; in vivo models; lung fibrosis.

Figure 1

Principal pathophysiological components of airway remodeling emergence in allergic asthma. After contact with allergens, alveolar epithelial cells (AECs) initiate several processes through TGF-β, Sonic hedgehog (Shh), and Wnt pathways, such as airway smooth muscle cell proliferation, goblet cell hyperplasia, and fibroblast-to-myofibroblast transition. Together, these biological processes lead to the production and deposition of extracellular matrix (ECM) components, which, alongside ECM degradation products, lead to the emergence of subepithelial fibrosis and airway remodeling.