ETA and ETB receptors are expressed in vascular adventitial fibroblasts

Abstract

The adventitia has been recognized to play important roles in vascular oxidative stress, remodeling, and contraction. We recently demonstrated that adventitial fibroblasts are able to express endothelin (ET)-1 in response to ANG II. However, it is unclear whether ET-1 receptors are expressed in the adventitia. We therefore investigated the expression and roles of both ETA and ETB receptors in collagen synthesis and ET-1 clearance in adventitial fibroblasts. Adventitial fibroblasts were isolated and cultured from the mouse thoracic aorta by the explant method. Cultured cells were treated with ANG II (100 nmol/l) or ET-1 (10 pM) in the presence or absence of the ANG II type 1 receptor antagonist losartan (100 μM), the ET-1 receptor antagonists BQ-123 (ETA receptor, 1 μM) and BQ-788 (ETB receptor, 1 μM), and the ETB receptor agonist sarafotoxin 6C (100 nM). ET-1 peptide levels were determined by ELISA, whereas ETA, ETB, and collagen levels were determined by Western blot analysis. ANG II increased ET-1 peptide levels in a time-dependent manner. ANG II increased ETA and ETB receptor protein levels as well as collagen in a similar fashion. ANG II-induced collagen was reduced while in the presence of BQ-123, suggesting a role for the ETA receptor in the regulation of the extracellular matrix. ANG II treatment in the presence of BQ-788 significantly increased ET-1 peptide levels. Conversely, the ETB receptor agonist sarafotoxin 6C significantly decreased ET-1 peptide levels. These data implicate a role for the ETB receptor in the clearance of the ET-1 peptide. In conclusion, both ETA and ETB receptors are expressed in adventitial fibroblasts, which paves the ground for the biological significance of adventitial ET-1. The ETA receptor subtype mediates collagen I expression, whereas the ETB receptor subtype may play a protective role through increasing the clearance of the ET-1 peptide.