Telmisartan downregulates angiotensin II type 1 receptor through activation of peroxisome proliferator-activated receptor γ

Objective: Telmisartan, an angiotensin II type 1 receptor (AT1R) antagonist, was found to have a unique property: it is a partial agonist of peroxisome proliferator-activated receptorgamma (PPAR gamma). Since previous studies have demonstrated that PPAR gamma activators suppressed AT1R expression, we examined whether telmisartan affects AT1R expression in vascular smooth muscle cells. Methods: Vascular smooth muscle cells were derived from the thoracic aorta of Wistar-Kyoto rat. Northern and Western blotting analysis were used to examine AT1R mRNA and protein expression, respectively. The DEAE-dextran method was used for transfection, and the promoter activity of AT1R was examined by luciferase assay. Results: Telmisartan decreased the expression of AT1R at the mRNA and protein levels in a dose- and time-dependent manner. Decreased AT1R promoter activity with unchanged mRNA stability suggested that telmisartan suppressed ATIR gene expression at the transcriptional level. However, the expression of AT1R was not suppressed by other AT1R antagonists such as candesartan or olmesartan. Since the suppression of AT1R expression was prevented by pretreatment with GW9662, a PPAR gamma antagonist, PPAk-y should have participated in the process. The deletion and mutation analysis of the AT1R gene promoter indicated that a GC box located in the proximal promoter region is responsible for the telmisartan-induced downregulation. Conclusion: Our data provides a novel insight into an effect of telmisartan: telmisartan inhibits AT1R gene expression through PPAR gamma activation. The dual inhibition of angiotensin II function by telmisartan - ATIR blockade and downregulation - would contribute to more complete inhibition of the renin-angiotensin system. (c) 2006 European Society of Cardiology. Published by Elsevier B.V. All rights reserved.