Role of differential estrogen receptor activation in airway hyperreactivity and remodeling in a murine model of asthma

Evidence suggests that airway hyperresponsiveness (AHR) is a characteristic feature of asthma. Epidemiological studies have confirmed that the severity of asthma is greater in women, suggesting a critical role of female sex steroid hormones (especially estrogen). Very few in vivo studies have examined the role of sex steroid hormones in asthma, and the sequence of events that occur through differential activation of estrogen receptors (ERs) remains to be determined in asthmatic airways. Our recent in vitro findings indicated that ERb had increased expression in asthmatic airway smooth muscle (ASM), and that its activation by an ERb-specific agonist downregulated airway remodeling. In this study, we translated the in vitro findings to a murine asthma model and examined the differential role of ER activation in modulating lung mechanics. C57BL/6J male, female, and ovariectomized mice were exposed to mixed allergen (MA) and subcutaneously implanted with sustained-release pellets of placebo, an ERa agonist (4,49,499-(4-propyl-[1H]-pyrazole-1,3,5-triyl)trisphenol [PPT]), and/or an ERb agonist (WAY-200070). We then evaluated the effects of these treatments on airway mechanics, biochemical, molecular, and histological parameters. Mice exposed to MA showed a significant increase in airway resistance, elastance, and tissue damping, and a decrease in compliance; pronounced effects were observed in females. Compared with PPT, WAY treatment significantly reversed the MA-induced changes. The increased mRNA/protein expression of ERa, ERb, and remodeling genes observed in MA-treated mice was significantly reversed in WAY-treated mice. This novel study indicates that activation of ERb signaling downregulates AHR and airway remodeling, and is a promising target in the development of treatments for asthma.