Activation of G Protein‐Coupled Estrogen Receptor (GPER) Potentiates Porcine Coronary Artery Contraction via EGFR Transactivation

Estrogen exerts protection against cardiovascular diseases in younger women, but is associated with an increased risk of both coronary heart disease and stroke in older postmenopausal women. Studies have shown that GPER activation may relax or constrict arteries. Thus, GPER mediates opposite effects on blood vessels, and we propose it is highly likely that these dual actions of GPER can contribute to the seemingly paradoxical effects of estrogen in regulating coronary artery function. While most studies have focused on the mechanism of GPER‐mediated vasorelaxation, the mechanism of vasoconstriction has been largely neglected. The objective of this study is to test the hypothesis that activation of GPER enhances vasoconstrictor‐induced porcine coronary artery contraction via epidermal growth factor receptor (EGFR) transactivation and extracellular signal‐regulated kinases (ERK1/2) signaling. Isometric tension studies and Western blot were performed to determine the functional role of GPER in vasoconstrictor‐induced coronary artery contraction. The selective GPER agonist G‐1 was used either before applying endothelin 1 (ET‐1, 0.1–30 nM) to contract the artery or after prostaglandin F2 alpha (PGF 2α , 1 μM) ‐ induced constriction reached its plateau in endothelium‐denuded coronary artery rings. Our findings demonstrated that pretreatment of coronary artery rings with G‐1 (1 μM) significantly enhanced artery contraction induced by ET‐1 (0.1–30 nM), without changing the EC50 (8.59 nM). G‐36 (10 μM), a specific GPER antagonist, blocked this G‐1‐induced enhancement of vasoconstriction. Gallein (10 μM), a Gβγ inhibitor, significantly inhibited G‐1‐enhanced vasoconstriction. On the other hand, pretreatment with gallein (10 μM) enhanced G‐1‐induced relaxation (10–3,000 nM) of coronary arteries pre‐constricted with PGF 2α . Similarly, inhibition of EGFR with AG1478 (5 μM) or inhibition of Src, the upstream activator of EGFR, with phosphatase 2 (10 μM) further increased G‐1‐induced relaxation response of PGF2α‐constricted arteries, but decreased G‐1 (1 μM) pretreatment‐induced enhancement of ET‐1‐vasoconstriction. Western blot experiments in porcine coronary artery smooth muscle cells (PCASMC) showed that G‐1 increased EGFR phosphorylation, whereas AG1478 attenuated the effect of G‐1 on phospho‐EGFR. Lastly, the role of ERK1/2 was determined by applying the MEK inhibitor, PD98059 (1 μM), in isometric tension studies and detecting phospho‐ERK1/2 in immunoblotting. PD98059 potentiated G‐1‐ induced relaxation response of PGF2α pre‐constricted artery rings, but blocked G‐1 pretreated ET‐1‐induced contraction. When the adenylyl cyclase inhibitor, SQ22536 (100 μM), was used to eliminate the effect of GPER‐mediated cAMP, G‐1 significantly increased ERK1/2 phosphorylation in PCASMC. In contrast, G‐1 treatment decreased phospho‐ERK1/2 in the absence of SQ22536. In conclusion, we revealed that the activation of GPER potentiated porcine coronary contraction by a mechanism involving transactivation of EGFR and the phosphorylation of ERK1/2 via Gβγ/src signaling. Support or Funding Information AHA # 15BGIA25060013