Background & hypothesis: Obesity is a public health epidemic in a global scale. An array of co-morbidities associated with obesity lead to poor life quality, disability and mortality. Asthma is a chronic airway disease characterized by airway inflammation, remodeling and airway hyper-responsiveness (AHR). Obesity increase the clinical severity of asthma and reduces response to conventional asthma treatment. Airway smooth muscle (ASM) cells are the primary drivers of AHR in asthma and provide therapeutic targets for alleviating asthma symptoms. We tested the hypothesis that agonist-induced contractile response is amplified in airway smooth muscle cells obtained from obese human lung donors.

Methods: Human ASM (HASM) cells obtained from age,sex and race-matched lung donors (lean donors:  BMI 22.71±0.87, n=10 donors; obese donors: BMI 44.31±6.71, n=10 donors) were maintained in vitro and the following cellular markers of excitation-contraction (EC) coupling were measured in the presence of contractile agonists carbachol (CCh, 10 uM) or histamine (1 uM): (i) cytosolic increase in Ca²⁺ (ii) myosin light chain (MLC) phosphorylation, and (iii) Protein kinase B (Akt) phosphorylation. In parallel, agonist-induced force generation was measured in HASM cells using Fluorescently-Labeled Elastomeric Contractile Surfaces (FLECS) technique.

Results: Compared to the cells from lean donors, HASM cells obtained from obese lung donors showed significantly increased (i) CCh or histamine-induced cytosolic Ca²⁺ and (ii) CCh-induced MLC phosphorylation (Fold change over baseline: lean 1.7±0.43 Vs obese 4.5±1, p<0.05). CCh or histamine-induced HASM cell force generation was significantly increased in obese donor-derived cells compared to that of lean donors. Lean and obese donor – derived HASM cells showed comparable levels of Akt phosphorylation, both at baseline and following CCh stimulation.

Conclusions: Findings support our hypothesis that obesity amplifies agonist-induced excitation-contraction coupling in HASM cells.

Significance: Amplified EC coupling and force generation in HASM cells are likely to be the important mechanisms of obesity-associated AHR. HASM cells may provide a useful therapeutic target to prevent or control clinically severe asthma in obese patients.