Asthma pathobiology is characterized by persistent oxidative stress in the lungs that causes oxidative damage in the cell membrane and extracellular phospholipids. This damage results in the accumulation of oxidized phosphatidylcholines (OxPC), potent mediators of oxidative stress. We recently discovered that allergen challenge causes OxPC accumulation in the lungs of human participants that correlates with airway hyperresponsiveness (AHR). OxPC also play a significant role in the pathophysiology of human airway smooth muscle (HASM) cells. The research projects outlined in this thesis aimed to elucidate the functional effects of OxPC on HASM cells, and to identify the downstream effector(s) and/or signaling pathway(s) mediating these effects. Furthermore, we investigated the potential impact of OxPC on the pathophysiologic hallmarks of allergen-induced ‘asthma’ in a murine model.

Our findings demonstrate that OxPC directly induce airway narrowing in murine thin-cut lung slices (TCLS) and activate the contractile machinery within HASM cells. OxPC mediate both transient and sustained cytosolic Ca2+ flux through two distinct pathways: intracellular ryanodine receptors and plasma membrane transient receptor potential ankyrin 1 (TRPA1) channels. These pathways are interdependently required for OxPC-induced HASM contraction and airway narrowing. Next, we demonstrated that OxPC selectively attenuate HASM relaxation in response to bronchodilators (β2-adrenergic receptor (β2AR) agonists; isoproterenol, albuterol) using both ex vivo (murine tracheal rings and TCLS) and in vivo models. These effects correlate with a diminished cyclic-adenosine-monophosphate (cAMP) signaling cascade within HASM cells. The results from this study revealed that OxPC uncouple β2AR signaling from downstream effectors via activation of protein kinase-C (PKC), a mechanism contributing to the development of bronchodilator insensitivity. Furthermore, we characterized the exacerbation of oxidative burden within the lungs of a murine model of allergic asthma, observing a concomitant increase in OxPC accumulation. In this model, we showed that immuno-pharmacological neutralization of OxPC using intranasal E06 monoclonal antibody can prevent allergen-induced airway inflammation and AHR.

Collectively, our results indicate that bioactive OxPC are pivotal mediators of oxidative stress-associated allergic lung pathophysiology. These molecules directly contribute to airway contraction and induce bronchodilator insensitivity by modulating airway smooth muscle function, an implication for the phenotype of poorly controlled asthma.