KCNE2 is a single transmembrane modulatory ? subunit that in heterologous systems can modulate a variety of K channel pore-forming 1 subunits including Kv4.2 and Kv4.3, major components of fast transient outward K+ currents (Ito,f) in the heart. Highlighting its clinical relevance, KCNE2 inherited mutations are associated with human cardiac arrhythmogenesis and long QT syndrome. Recently Dr. Abbott in a personal communication informed me that KCNE2 knockout (KCNE2-/-) mice display a major reduction in Ito,f currents and a propensity to drug induced arrhythmogenesis. Further, we recently found that KCNE2, via a direct genomic mechanism, is activated by estrogen (E2), a well-known steroid hormone with cardioprotective properties in several species. In particular, in mouse, E2 treatment ameliorates the hypertrophic response to pressure overload by transaortic constriction (TAC). Thus, I decided to investigate whether E2- induced KCNE2 remodeling including its subcellular localization correlates with Ito,f changes and rescue from cardiac stress. Preliminary data indicates that: In non-stressed animals with high E2 cardiac KCNE2 transcript levels are dramatically upregulated. Strikingly, E2 favored KCNE2 localization in the T-tubules which should facilitate its association with T-tubular Kv a-subunits;while in TAC animals, E2 administration exerted a dramatic rescue from heart failure (HF) restoring ejection fraction and cardiac excitability together with KCNE2 transcript upregulation and protein redistribution to the T-tubular membrane. Thus, the general hypothesis postulates that: Heart E2 levels may upregulate KCNE2 transcript and protein levels, with targeting to the T-tubules favoring KCNE2 interaction with Kv4.3/Kv4.2 channels potentiating Ito,f currents. To test the overall hypothesis, a multidisciplinary approach will be used including molecular biology, biochemistry, electrophysiology and proteomics in conjunction with high-resolution confocal microscopy.
The Specific Aims are 1) To determine in normal animals the mechanism(s) of estrogen-induced changes on the expression of Ito,f and IK,slow and functional consequences: role of Kv4.3/4.2 and Kv1.5 and auxiliary subunits (KCNE2 and KChIP2);and 2) To determine the mechanism(s) of estrogen-induced rescue of TAC induced heart failure. These studies will provide new information on KCNE2 and E2 roles in cardioprotection and cardiac excitability and provide molecular mechanisms to understand gender related differences in propensity to ventricular arrhythmias.
Females during the reproductive age have low incidence to heart disease when compared with males supporting the view that female hormones (estrogen) may have a protective action. However, the role of estrogen and the mechanisms involved are little understood. The goal of this project is to gain insight in how estrogen may induce cardioprotection by regulating the activity of a gene that is exquisitely modulated by estrogen and that modifies cardiac excitability.
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