TLR2 activation causes tachyphylaxis to ß2-agonists in vitro and ex vivo: modelling bacterial exacerbation

Publisher:
Wiley
Publication Type:
Journal Article
Citation:
Allergy, 2014, 69 (9), pp. 1215 - 1222
Issue Date:
2014-08-08
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Background Asthma is a widespread chronic health problem exacerbated by common viral and bacterial infections. Further research is required to understand how infection worsens asthma control in order to advance therapeutic options in the future. Recent research has revealed that ß2-adrenergic receptor (ß2-AR) agonists lose bronchodilatory efficacy because the receptor-mediated molecular pathways responsible for their beneficial actions are desensitized by infection. To date, most studies have focussed on viral infection, leaving the impact of bacterial infection on ß2-AR desensitization relatively under-investigated. We address this in this study. Methods and Results Utilizing an in vitro model of bacterial exacerbation in airway smooth muscle (ASM) cells, we show that activation of toll-like receptor 2 (TLR2; mimicking bacterial infection) in the presence of an inflammatory stimulus leads to ß2-AR desensitization. This occurs via TLR2-dependent upregulation of cyclooxygenase 2 (COX-2) mRNA expression and increased secretion of PGE2. Importantly, PGE2 causes heterologous ß2-AR desensitization and reduces cAMP production in response to short-acting (salbutamol) and long-acting (formoterol) ß2-agonists. Thus, bacterial infectious stimuli act in a PGE2-dependent manner to severely curtail the beneficial actions of ß2-agonists. The impact of ß2-AR desensitization is demonstrated by reduced gene expression of the critical anti-inflammatory molecule MKP-1 in response to ß2-agonists, as well as impaired bronchodilation in a mouse lung slices. Conclusions Taken together, our results show that, like viruses, bacteria induce prostanoid-dependent ß2-AR desensitization on ASM cells. Notably, COX-2 inhibition with the specific inhibitor celecoxib represses PGE2 secretion, presenting a feasible pharmacological option for treatment of infectious exacerbation in asthma in the future.
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