Estrogen signaling in chronic asthma

About This Grant

Project Summary Epidemiological data show increased incidence and severity of asthma in women, which likely reflects both inherent sex differences and importantly the effects of sex steroids, especially estrogens. Our previous studies show upregulation of estrogen receptors (ERs), ERα and ERβ in human airway smooth muscle (ASM) with differential ERα vs. ERβ signaling in regulating ASM [Ca2+]i/remodeling and airway hyperresponsiveness (AHR). However, it is unclear whether it is estrogen that is responsible or its metabolites, locally produced in ASM. Data from other systems suggest differential physiological effects of cytochromeP450 (CYP’s) mediated estrogen metabolites, particularly 16αHE2 (via CYP3A4), promoting inflammation and remodeling. In this regard, some unresolved questions are A) What are the expression profiles and activities of ASM CYP’s and how do they influence local estrogen metabolism in asthma? B) What roles do specific estrogen metabolites play in regulating AHR and/or remodeling? Preliminary studies show: 1) Functional CYP’s are expressed in human ASM with higher CYP3A4 expression and activity in female asthmatics; 2) E2 with CYP3A4 inhibition showed reduced [Ca2+]i in asthmatic ASM; 3) Inhibition of CYP3A4 decreases E2 mediated effect on ASM proliferation and ECM deposition; and 4) In a mixed allergen (MA) mouse model of asthma, 16αHE2 exacerbates AHR and remodeling while 2-HE is alleviating. Thus, our overall hypothesis is that the differential role of estrogen- metabolizing enzymes (particularly CYP3A4 and its product 16αHE2) contributes to detrimental estrogen effects on airway contractility and remodeling in asthma. This will be tested via the following Specific Aims 1. To determine the expression and function of estrogen-metabolizing enzymes and their influence on [Ca2+]i and contractility in non-asthmatic vs. asthmatic human ASM. 2. To identify mechanisms by which estrogen metabolites influence remodeling in non-asthmatic vs. asthmatic human ASM. 3. To establish the effects of estrogen metabolites on AHR and remodeling in a mouse model of asthma. Using human ASM from non- asthmatic vs. asthmatic, females and males, Aim 1 explores the effect of inflammation and asthma on the expression and activity of CYPs relevant to functional estrogen metabolites and their effects on ASM [Ca2+]i/contractility. Aim 2 explores the role of estrogen metabolites in ASM proliferation, remodeling and downstream signaling intermediates. Aim 3 explores how estrogen metabolites affect airway structure (histology, laser capture microdissection) and function (flexiVent) in vivo. Endogenous hormone effects will be assessed using ovariectomy (OVX), and the role of ASM per se using smooth muscle-specific ERαfl/fl/smMHCCre/0 and ERβfl/fl/smMHCCre/0 knockout mice. Clinical significance lies in understanding the contribution of estrogen and its metabolites on ASM structure and function in chronic asthma in women. This will provide us with the basic fundamental knowledge to understand the greater prevalence of asthma in women and will help to develop a novel therapeutic approach targeting estrogen derivatives vs. estrogen signaling pathways.