Chronic activation of the novel
estrogen receptor GPR30 by its agonist G1 mitigates the adverse effects of
estrogen (E2) loss on cardiac structure and function. Using the ovariectomized (OVX) mRen2.Lewis rat, an E2-sensitive model of diastolic dysfunction, we found that E2 status is inversely correlated with local cardiac
angiotensin II (Ang II) levels, likely via Ang I/
chymase-mediated production. Since
chymase is released from cardiac mast cells during stress (e.g., volume/pressure overload,
inflammation), we hypothesized that GPR30-related cardioprotection after E2 loss might occur through its opposing actions on cardiac mast cell proliferation and
chymase production. Using real-time quantitative PCR, immunohistochemistry, and immunoblot analysis, we found mast cell number,
chymase expression, and cardiac Ang II levels were significantly increased in the hearts of OVX-compared to ovary-intact mRen2.Lewis rats and the
GPR30 agonist G1 (50 mg/kg/day, s.c.) administered for 2 weeks limited the adverse effects of
estrogen loss. In vitro studies revealed that GPR30 receptors are expressed in the RBL-2H3 mast cell line and G1 inhibits serum-induced cell proliferation in a dose-dependent manner, as determined by cell counting,
BrdU incorporation assay, and Ki-67 staining. Using specific antagonists to
estrogen receptors, blockage of GPR30, but not ERα or ERβ, attenuated the inhibitory effects of
estrogen on
BrdU incorporation in RBL-2H3 cells. Further study of the mechanism underlying the effect on cell proliferation showed that G1 inhibits
cyclin-dependent kinase 1 (CDK1)
mRNA and
protein expression in RBL-2H3 cells in a dose-dependent manner.