New assays reveal opposing effects of 17b‐estradiol in the presence and absence of ovaries on the cardiac network of calmodulin‐binding proteins

Abstract

Reduced estrogen concentrations following menopause are associated with increases in the incidence of cardiovascular disease. Calmodulin (CaM) is required for the activities of numerous cardiac proteins yet is not sufficiently expressed for its binding targets. We have begun to examine the effects of 17b‐estradiol (E2) on the cardiac network of CaM‐binding proteins. Female rats received sham surgery or ovariectomy, followed by treatment with vehicle or E2 for 2 weeks. E2 treatment in sham animals increases the interaction between endogenous CaM and the cardiac α adrenergic receptor type 1A. Surprisingly, ovariectomy substantially increases this interaction, while E2 replacement now reduces it. To examine the effects of these treatments on the population of cardiac CaM‐binding sites that are unsaturated by endogenous CaM, lysate from left ventricle was subjected to saturating Ca2+ concentration and processed through a CaM sepharose column. Flow through contained CaM‐binding sites saturated by endogenous CaM, while sepharose‐bound fraction represented endogenously unsaturated CaM‐binding sites. The fractions eluted from the CaM sepharose were subsequently used in competitive binding assays using purified CaM and a CaM biosensor. E2 treatment in sham animals increases the number of unsaturated CaM‐binding sites. Ovariectomy further increases this number, while E2 treatment now reduces it. The data indicate that E2 treatment exerts opposing effects in the presence and absence of ovaries on specific endogenous CaM‐target associations and the number of endogenously unsaturable Ca2+‐dependent CaM‐binding sites in the heart. These results suggest that estrogen replacement may have unpredictable functional outcomes.Support or Funding InformationSupported by NIH Grant HL112184 to Quang‐Kim Tran and Grants from the Iowa Osteopathic and Educational Research Funds to Sarah Clayton and Quang‐Kim Tran.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.