β2-Adrenoceptor Dysfunction in Severe Asthma

Abstract

Rationale: Accumulating evidence suggests an impaired β2-AR function in airway smooth muscle (ASM) cells as a possible mechanism for poor efficacy of β2-agonist therapy in severe asthma. We here tested this hypothesis by comparing ASM cell responsiveness to β2-agonists in both healthy and severe asthmatic subjects. Methods: ASM cell responsiveness to β2-agonists in both healthy and severe asthmatic subjects was investigated by their ability to i) inhibit chemokine production and induce STC-1 induction, ii) promote collagen gel relaxation, iii) produce cAMP accumulation, iv) induce phosphorylation of VASP, v) modulate transcriptome response using RNA-seq. Finally, we assessed whether manipulating β2-AR expression would rescue the impaired response to β2-agonists seen in ASM in severe asthma. Results: In healthy ASM cells with albuterol dose-dependently inhibited CCL5, PTX3 and CXCL-10 production induced by TNFa, reaching a maximum inhibition of 47%, 49% and 48% at 10-5M, respectively. In contrast, albuterol failed to inhibit chemokine production in severe asthma ASM cells treated with TNFa. Albuterol-induced STC-1 production was significantly reduced in ASM cells from severe asthmatics when compared to healthy ASM cells. Both albuterol and isoproterenol reduced the spontaneous contraction of healthy cell-embedded collagen gels by 50.1% and 62%, respectively, while no effect was seen in severe asthmatic cell-embedded collagen gels. In addition, β2-agonists-induced cAMP production and VASP phosphorylation at ser157 or ser239 were reduced in ASM cells from severe asthmatics when compared to cells from healthy subjects. The RNA-seq analysis uncovered a profound difference in the transcriptomic response associated with β2-AR activation in ASM cells severe asthmatic compared to healthy controls, with a number of genes and associated different pathways being absent or reduced in severe asthma. Interestingly, overexpressing β2-AR in severe asthmatic ASM cells rescued their responsiveness to β2-agonists to inhibit chemokine production and induce cAMP production.