Inhaled Corticosteroids Stimulate cAMP Production and Enhance βAR Signaling In a Non‐Genomic Fashion In Human Airway Smooth Muscle Cells

Abstract

Inhaled corticosteroids have been shown to be highly beneficial when combined with β‐adrenergic receptor (βAR) agonists in treatment of asthma. The mechanism for this synergy has never been fully clear, but corticosteroids have been shown to increase βAR expression and reverse βAR desensitization via canonical genomic actions. The current study investigated whether inhaled corticosteroids have an effect on cAMP production in both primary and immortalized human airway smooth muscle (HASM) cells. We measured real‐time cAMP dynamics in live HASM cells using the downward cAMP difference detector in situ (cADDis) cAMP sensor (Montana Molecular, Bozeman MT). Addition of various concentrations of either prednisone, fluticasone or allopregnanolone increased cAMP production over basal within 3 min without phosphodiesterase inhibitors present. We examined various passages of HASM cells and cells from different patients and found fluticasone consistently increased cAMP production at concentrations between 10 nM and 10 μM. We also examined cAMP responses to fluticasone in human embryonic kidney (HEK‐293) cells and observed no increases in cAMP production in response to fluticasone, prednisone, or progesterone. We repeated studies in the presence of glucocorticoid receptor GR‐α antagonists, RU‐486 and GSK‐9027, to understand how corticosteroids may be increasing cAMP levels. Pretreatment with either antagonist attenuated cAMP responses to all activators, including forskolin and βAR agonists, implying these drugs have considerable non‐specific effects. We also evaluated how corticosteroids would alter responses to other cAMP‐elevating agents. Fluticasone (0.1 to 1 μM) increased the potency and maximal effect of isoproterenol, PGE2 and forskolin. These findings are consistent with the idea that corticosteroids directly stimulate cAMP signaling in a non‐genomic manner and can enhance signaling by βAR and prostaglandin E receptors. Future studies will identify the molecular mechanism for this effect and determine if GR‐α is required. These findings reveal an unappreciated action of inhaled corticosteroids that may help explain how these drugs are beneficial in combination with β‐adrenergic receptor agonists for the treatment of asthma.Support or Funding InformationThis work was supported by NIH grant GM107094 (RO)This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.