Role of Estrogen Receptors α and β in a Murine Model of Asthma: Exacerbated Airway Hyperresponsiveness and Remodeling in ERβ Knockout Mice

Epidemiological data suggests increased prevalence of asthma in females than males, suggesting a plausible role for sex-steroids, especially estrogen in the lungs. Estrogen primarily acts through estrogen-receptors (ER alpha and ER beta), which play a differential role in asthma. Our previous studies demonstrated increased expression of ER beta in asthmatic human airway smooth muscle (ASM) cells and its activation diminished ASM proliferation in vitro and airway hyperresponsiveness (AHR) in vivo in a mouse (wild-type, WT) model of asthma. In this study, we evaluated the receptor specific effect of circulating endogenous estrogen in regulating AHR and remodeling using ER alpha and ER beta knockout (KO) mice. C57BL/6J WT, ER alpha KO, and ER beta KO mice were challenged intranasally with a mixed-allergen (MA) or PBS. Lung function was measured using flexiVent followed by collection of broncho-alveolar lavage fluid for differential leukocyte count (DLC), histology using hematoxylin and eosin (H&E) and Sirius red-fast green (SRFG) and detecting alpha smooth muscle actin (alpha-SMA), fibronectin and vimentin expression using immunofluorescence (IF). Resistance (Rrs), elastance (Ers), tissue-damping (G) and tissue-elasticity (H) were significantly increased, whereas compliance (Crs) was significantly decreased in WT, ER alpha KO, and ER beta KO mice (males and females) challenged with MA compared to PBS. Interestingly, ER beta KO mice showed declined lung function compared to ER alpha KO and WT mice at baseline. MA induced AHR, remodeling and immune-cell infiltration was more prominent in females compared to males across all populations, while ER beta KO females showed maximum AHR and DLC, except for neutrophil count. Histology using H&E suggests increased smooth muscle mass in airways with recruitment of inflammatory cells, while SRFG staining showed increased collagen deposition in MA challenged ER beta KO mice compared to ER alpha KO and WT mice (males and females), with pronounced effects in ER beta KO females. Furthermore, IF studies showed increased expression of alpha-SMA, fibronectin and vimentin in MA challenged populations compared to PBS, with prominent changes in ER beta KO females. This novel study indicates ER beta plays a pivotal role in airway remodeling and AHR and understanding the mechanisms involved might help to surface it out as a potential target to treat asthma.