Targeting the γ-Aminobutyric Acid A Receptor α4 Subunit in Airway Smooth Muscle to Alleviate Bronchoconstriction. Am J Respir Cell Mol Biol 2016 Apr;54(4):546-53
Date
09/26/2015Pubmed ID
26405827Pubmed Central ID
PMC4821055DOI
10.1165/rcmb.2015-0176OCScopus ID
2-s2.0-84963730425 (requires institutional sign-in at Scopus site) 21 CitationsAbstract
We previously demonstrated that airway smooth muscle (ASM) cells express γ-aminobutyric acid A receptors (GABA(A)Rs), and that GABA(A)R agonists acutely relax ASM. Among the GABA(A)R α subunits, human ASM cells express only α4 and α5, providing the opportunity for selective pharmacologic targeting. Novel GABA(A)R-positive allosteric modulators designed for enhanced α4/α6 subunit selectivity were synthesized using iterative computational analyses (CMD-45 and XHe-III-74). Studies using oocyte heterologous expression systems confirmed that CMD-45 and XHe-III-74 led to significantly greater augmentation of currents induced by a 3% maximal effective concentration (EC3) of GABA [EC3]-induced currents in oocytes expressing α4 or α6 subunits (along with β3 and γ2) compared with other α subunits. CMD-45 and XHe-III-74 also led to greater ex vivo relaxation of contracted wild-type mouse tracheal rings compared with tracheal rings from GABA(A)R α4 subunit (Gabra4) knockout mice. Furthermore, CMD-45 and XHe-III-74 significantly relaxed precontracted human ASM ex vivo, and, at a low concentration, both ligands led to a significant leftward shift in albuterol-mediated ASM relaxation. In vivo, inhaled XHe-III-74 reduced respiratory system resistance in an asthmatic mouse model. Pretreatment of human ASM cells with CMD-45 and XHe-III-74 inhibited histamine-induced increases in intracellular calcium concentrations in vitro, an effect that was lost when calcium was omitted from the extracellular buffer, suggesting that inhibition of calcium influx due to alterations in plasma membrane potential may play a role in the mechanism of ASM relaxation. Selective targeting of the GABA(A)R α4 subunit with inhaled ligands may be a novel therapeutic pathway to treat bronchoconstriction, while avoiding sedative central nervous system effects, which are largely mediated by α1-3 subunit-containing GABA(A)Rs in the brain.
Author List
Yocum GT, Gallos G, Zhang Y, Jahan R, Stephen MR, Varagic Z, Puthenkalam R, Ernst M, Cook JM, Emala CWAuthor
James M. Cook PhD University Distinguished Professor in the Chemistry and Biochemistry department at University of Wisconsin - MilwaukeeMESH terms used to index this publication - Major topics in bold
AnimalsAsthma
Bronchoconstriction
Calcium
Humans
In Vitro Techniques
Male
Mice
Mice, Knockout
Muscle, Smooth
Receptors, GABA-A
Trachea
Xenopus laevis
