Airway smooth muscle in contractility and remodeling of asthma: potential drug target mechanisms

Abstract

Introduction: Asthma is characterized by enhanced airway contractility and remodeling where airway smooth muscle (ASM) plays a key role, modulated by inflammation. Understanding the mechanisms by which ASM contributes to these features of asthma is essential for the development of novel asthma therapies.

Areas covered: Inflammation in asthma contributes to a multitude of changes within ASM including enhanced airway contractility, proliferation, and fibrosis. Altered intracellular calcium ([Ca²⁺]_i) regulation or Ca²⁺ sensitization contributes to airway hyperreactivity. Increased airway wall thickness from ASM proliferation and fibrosis contributes to structural changes seen with asthma.

Expert opinion: ASM plays a significant role in multiple features of asthma. Increased ASM contractility contributes to hyperresponsiveness, while altered ASM proliferation and extracellular matrix production promote airway remodeling both influenced by inflammation of asthma and conversely even influencing the local inflammatory milieu. While standard therapies such as corticosteroids or biologics target inflammation, cytokines, or their receptors to alleviate asthma symptoms, these approaches do not address the underlying contribution of ASM to hyperresponsiveness and particularly remodeling. Therefore, novel therapies for asthma need to target abnormal contractility mechanisms in ASM and/or the contribution of ASM to remodeling, particularly in asthmatics resistant to current therapies.

Keywords: Lung; airway; airway hyperreactivity; airway smooth muscle; calcium; drug targets; fibrosis; proliferation.

Figure.1:. Pathways involved in airway hypercontractility:

The figure displays key pathways upregulating intracellular Ca²⁺ homeostasis and Ca²⁺ sensitivity. Proinflammatory mediators such as TNFα, growth factors (TGFβ), IL-4, IL-13, and Alarmins (TSLP, IL-33, IL-25) and external factors such as allergens, pollutants, and cigarette smoke activate different components ( GPRC, ROC, CD38, CaSR, Orai1, SOCE, and Caveolae)) within the asthmatic airway smooth muscle cells (ASM) where it produces secondary messengers bind to its receptors (IP3R, RYR, and STIM) on the sarcoplasmic reticulum (SR) to facilitate Ca²⁺ release. The Ca²⁺ -calmodulin also stimulates myosin light-chain kinase (MLCK) to initiate muscle contraction. Created with BioRender.com.