The investigation of intrinsic abnormalities in the airway smooth muscle cells in asthma

Rationale: Airway smooth muscle dysfunction is a cardinal feature of asthma that is believed to contribute to the symptoms and recurrent exacerbations. However, the mechanisms driving this dysfunction are not fully understood. Hypothesis: Intrinsic abnormalities of the ASM from asthma exist and contribute to the functional differences in vitro which correlate with clinical characteristics Methods: Primary airway smooth muscle cells from healthy control subjects and asthmatics were used. Baseline protein and gene expression studies were assessed by mass spectrometry and microarrays. Functional differences were assessed, such as survival, proliferation, migration, wound healing and contraction. Oxidative stress DNA damage was assessed by immunohistology and comet assay, reactive oxygen species (ROS) quantification, and the role of NADPH oxidase (NOX4) and superoxide dismutase (SOD2) were assessed by quantitative gene expression and pharmacological inhibitors, mimetic and gene silencing. Results: In ex vivo airway smooth muscle cultures, asthmatic smooth muscle dysfunction persisted, indicating exaggerated contractility and pro-inflammatory mediator release compared to ASM from healthy controls. The oxidative burden and damage in asthmatic ASM was increased with increased expression of NOX4 which negatively correlated to the airflow obstruction. Agonist induced hyper-contractile response was abrogated by using pharmacological inhibition or by silencing the mRNA. Summary: Intrinsic abnormalities of the airway smooth muscle exist in asthma. Asthmatic ASM cells possess intrinsic abnormalities in gene and protein expression, synthetic mediator production and exaggerated agonist induced contraction. Increased expression of NOX4 in asthmatic ASM promotes the susceptibility of a hyper-contractile response, implicating NOX4 as a potential therapeutic target for the treatment of asthma.