The Non-genomic Signaling Pathways Mediated By G-protein Coupled Estrogen Receptor 1 (GPER) In Coronary Arteries
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Coronary heart disease (CHD) remains the leading cause of death throughout the world, and postmenopausal women are at particularly high risk for CHD. A promising new avenue of study is the novel G protein-coupled estrogen receptor (GPER) which mediates estrogen action. The major purpose of my studies in this dissertation is to investigate the role of GPER in porcine coronary artery tone regulation. In a series of studies, we tested four hypotheses: 1) activation of GPER regulates coronary artery tone by paradoxically inducing relaxation and potentiating contraction; 2) activation of GPER induces coronary artery relaxation by Gs/cAMP-dependent pathway(s); 3) activation of GPER induces coronary artery relaxation via inhibition of RhoA/Rho kinase pathway by cAMP downstream targets: the exchange proteins directly activated by cAMP (Epac) as well as PKA; and 4) activation of GPER potentiates coronary artery contraction by a G??/EGFR-dependent pathway. Isometric tension studies were performed on endothelium-denuded porcine coronary arteries to test the function role of GPER and its signaling pathways. RT-PCR, Western blots, patch-clamp experiments and kinase activity assays also were employed in these studies to confirm the expression and phosphorylation of subjective proteins, channel activities and kinase activities in porcine and human coronary artery smooth muscle cells (SMCs) and coronary artery tissues. Results from these studies suggest: 1) GPER is expressed in porcine and human coronary artery SMCs; 2) GPER mediated coronary artery relaxation is NO-independent and involves BKCa channel activity; 3) activation of GPER stimulates the production of cAMP, thus activates its downstream targets PKA and Epac; 4) GPER mediates coronary relaxation through activation of MLCP via inhibition of RhoA activity by both PKA and Epac; 5) the interaction between AKAP and PKA is involved in the cAMP/PKA signaling mediated by GPER in coronary artery; and 6) GPER potentiates coronary artery contraction via G?? signaling to stimulate transactivation of EGFR and activation of ERK1/2. These findings provided evidence of the dual effects of GPER in coronary regulation, which may help reveal the controversial actions of estrogen and provide a molecular basis for developing new compounds that better target estrogen signaling for a variety of clinical applications.