OGR1-dependent regulation of the allergen-induced asthma phenotype

The proton-sensing receptor, ovarian cancer G protein-coupled receptor (OGR1), has been shown to be expressed in airway smooth muscle (ASM) cells and is capable of promoting ASM contraction in response to decreased extracellular pH. OGR1 knockout (OGR1KO) mice are reported to be resistant to the asthma features induced by inhaled allergen. We recently described certain benzodiazepines as OGR1 activators capable of mediating both procontractile and prorelaxant signaling in ASM cells. Here we assess the effect of treatment with the benzodiazepines lorazepam or sulazepam on the asthma phenotype in wild-type (WT) and OGR1KO mice subjected to inhaled house dust mite (HDM; Dermatophagoides pteronyssius) challenge for 3 wk. In contrast to previously published reports, both WT and OGR1KO mice developed significant allergen-induced lung inflammation and airway hyperresponsiveness (AHR). In WT mice, treatment with sulazepam (a Gs-biased OGR1 agonist), but not lorazepam (a balanced OGR1 agonist), prevented allergen-induced AHR, although neither drug inhibited lung inflammation. The protection from development of AHR conferred by sulazepam was absent in OGR1KO mice. Treatment of WT mice with sulazepam also resulted in significant inhibition of HDM-induced collagen accumulation in the lung tissue. These findings suggest that OGR1 expression is not a requirement for development of the allergen-induced asthma phenotype, but OGR1 can be targeted by the Gs-biased OGR1 agonist sulazepam (but not the balanced agonist lorazepam) to protect from allergen-induced AHR, possibly mediated via suppression of chronic bronchoconstriction and airway remodeling in the absence of effects on airway inflammation.