Abstract 050: Endothelin-1 Overexpression In Endothelial Cells Increases Blood Pressure In An Endothelin Type A Receptor-Dependent Manner

Abstract

Introduction: The mechanisms of blood pressure (BP) regulation by endothelin (ET)-1 produced by endothelial cells (EC) are complex and remain unclear. Transgenic mice with constitutive EC-specific human ET-1 ( EDN1 ) overexpression presented vascular injury but no change in BP, which could be due to adaptation to life-long high ET-1 exposure. We have now generated an inducible EC-restricted EDN1 overexpressing mouse (ieET-1) in order to demonstrate the effects of ET-1 on BP regulation independent of developmental effects. Method: Two transgenic mouse lines (C134 and C170) expressing chloramphenicol acetyltransferase ( cat ) and EDN1 before and after Cre-mediated excision, respectively, were crossed with mice expressing tamoxifen-inducible CreER T2 under the control of Tie2 promoter (ieCre) to generate ieET-1 mice. Mice were treated with tamoxifen (1 mg/kg/day, SC) or vehicle for 5 days and sacrificed 16 days later. Additional mice were treated with 5 or 10 mg/kg/day PO of ET type A receptor blocker, atrasentan, from day 10. BP was determined by telemetry. Plasma ET-1 levels were assessed by ELISA. ET type A and B receptors expression, Ednra and Ednrb , were evaluated in the kidney by quantitative PCR. Results: Tamoxifen increased plasma ET-1 in ieET-1 C134 and C170 (7.1±0.7 and 13.2±2 pg/mL, respectively, P <0.01), when compared to control ieET-1 C134 and C170 (0.7±0.2 and 1.0±0.3 pg/mL) and tamoxifen-treated ieCre (0.8±0.1 pg/mL). ET-1 overexpression increased night systolic BP in ieET-1 C134 and C170 (137±4 and 132±4 mmHg) compared to tamoxifen-treated ieCre (116±7 mmHg), which was reversed partially or completely with 5 or 10 mg/kg/day of atrasentan, respectively (122±3 and 115±4 mmHg, P <0.01). ET-1 overexpression in ieET-1 C134 was accompanied by increased Ednra expression in renal cortex and medulla (2.9±0.6 and 8.2±3.0 fold, P <0.05) and Ednrb levels in the renal cortex (2.0±0.3 fold, P <0.05) and a trend to increased levels in renal medulla (3.8±1.3 fold) compared to control ieET-1 C134. Conclusion: Our results demonstrate that this new inducible EC-restricted EDN1 overexpressing mouse exhibits ET-1-dependent elevated BP mediated by ET type A receptors. The increased expression of renal ET receptors could play a role in ET-1-induced BP rise.