GPR30 Attenuates Myocardial Fibrosis in Diabetic Ovariectomized Female Rats: Role of iNOS Signaling

Premenopausal women have a reduced risk for cardiovascular disease. Estrogen deficiency augments cardiac inflammation and oxidative stress and, thereby, aggravates myocardial fibrosis (MF) and diastolic dysfunction in hypertensive female rats. However, estrogen replacement therapy has no effect on myocardial infarction and cardiac fibrosis in postmenopausal women. Further clinical studies showed that high blood glucose levels in patients with diabetes is an important cause of MF, but the underlying mechanism is unclear. To experimentally address this issue, diabetes mellitus (DM) was induced by injecting streptozotocin and administering a high-fat diet in ovariectomized (OVX) rats. High degrees of fibrosis and apoptosis were detected in the cardiac tissue of these rats, together with increased expression of iNOS. Further treatment with the G protein-coupled estrogen receptor 30 (GPR30) agonist G1 decreased iNOS expression and the apoptosis rate in cardiac tissue significantly and inhibited cardiac fibroblast (CF) proliferation. Similar trends were observed in cultured CFs treated with high concentrations of fat and glucose. In addition, treatment with the iNOS-specific inhibitor W1400 attenuated iNOS and vimentin expression, which is associated with a marked reduction in MF. These results suggest that GPR30 activation inhibits MF in diabetic OVX female rats by suppressing cardiac iNOS activity and consequently NO levels. Thus, GPR30 activation may provide novel cardioprotection strategies for postmenopausal women, especially those with DM.