ABCC1 mediates b2AR effects on excitation-contraction (E-C) coupling of human airway smooth muscle

Project Abstract: Selective β2 adrenergic agonists remain a cornerstone of asthma therapy in preventing or reversing bronchoconstriction and shortening airway smooth muscle in patients with asthma. Canonically, activation of β2AR (a G protein-coupled receptor [GPCR]) induces Gαs-dependent increases in intracellular cAMP [cAMP]i, activates protein kinase A, and inhibits contractile signaling pathways to relax human airway smooth muscle (HASM). cAMP-dependent signaling is thought to be regulated by the inhibitory effect of phosphodiesterases, which degrade cAMP to AMP and Pi. Challenging this paradigm, we recently discovered that activation of the β2AR evokes [cAMP]i egress via ABCC1 (ATP-binding cassette subfamily C 1). We found that blockade of ABCC1 increases [cAMP]i, decreasing basal HASM tone and increasing β2-agonist-mediated HASM relaxation. Our preliminary data suggest that casein kinase II (CK2) and mitogen-activated protein kinase (MAPK) modulate ABCC1 function. These findings identify a novel role for ABCC1 in the homeostatic regulation of [cAMP]i that may be generalizable to other Gαs-coupled G protein-coupled receptors (GPCRs). Our central hypothesis states that ABCC1 modulates intracellular cAMP induced by Gαs-GPCRs in a CK2- and MAPK-dependent manner and plays a pivotal role in altering HASM responsiveness to β2-agonists in asthma. To test this hypothesis, we propose two aims. Aim 1 will address whether ABCC1 activation increases Gαs-GPCR-induced HASM relaxation through a CK2- and MAPK-dependent manner, providing nodal points in signaling proximal to the β2AR and ABCC1 to reverse HASM shortening and amplify β2-agonist-induced bronchodilation in the presence and absence of β2AR desensitization. Aim 2 will identify how airway inflammation, viral infections, or how inherent endotypes of Gαs-GPCR insensitivity in HASM derived from asthma donors alter ABCC1-dependent egress of [cAMP]i to decrease β-agonist mediated HASM relaxation. Project 2 has identified a potential therapeutic target, ABCC1, to enhance β-agonist-induced HASM cell relaxation, and understanding the molecular mechanisms regulating ABCC1 function to enhance HASM relaxation may improve asthma outcomes.