PPAR¿ activation improves oxidative stress and downregulates COX-2 expression in vascular cells
Introduction: The increased renin-angiotensin system (RAS) activity seems to contribute to the pathophysiology of hypertension by the increase in reactive oxygen species (ROS) levels and proinflammatory mediators. Endothelin-1 (ET-1) has been proposed to explain the cardiovascular damage induced by angiotensin II (AngII). Moreover, peroxisome proliferator activated receptor ¿ (PPAR¿) agonists have anti-inflammatory actions by interference with redox-sensitive transcription factors, such as NFkB or AP-1, involved in the transcription of proinflammatory genes including cyclooxygenase-2 (COX-2). Aim: To analyze if AngII contributes to the increased COX-2 levels in vascular smooth muscle cells (VSMC) from spontaneously hypertensive (SHR) rats by mechanisms dependent of ROS and ET-1 production and whether PPAR¿ activation regulates this effect. Methods: Aortic VSMC from SHR were stimulated with AngII in the absence and the presence of different drugs. mRNA levels were measured by qRT-PCR and protein expression by Western blot. Aortic segments from SHR and Wistar-Kyoto (WKY) rats untreated and treated with losartan (15 mg/Kg/day, 12 weeks) were also used. Results: COX-2 mRNA levels were greater in segments from SHR than WKY; the treatment with losartan reduced COX-2 levels in SHR. In VSMC from SHR, AngII (0.1 ¿M, 2 h) induced COX-2, ET-1 and NOX-1 mRNA levels; this effect was reduced by losartan (10 ¿M). AngII-induced COX-2 protein expression was also reduced by the NADPHox inhibitor apocynin (30 mM). The antagonist of the ETA receptor BQ 123 (1 ¿M), but not of the ETB receptor BQ 788 (1 ¿M), also reduced COX-2 and NOX-1 mRNA levels after AngII. The proteasome inhibitor lactacystin (20 ¿M) did not modify the ET-1 mRNA levels but inhibited those of NOX-1 and COX-2. AngII also increased c-jun expression; this expression was reduced by losartan but not by BQ 123. Moreover, the PPAR¿ activator pioglitazone (10 ¿M) decreased AngII-induced COX-2 and NOX-1 mRNA levels in VSMC from SHR. Conclusions: 1) The RAS activation contributes to the increased vascular COX-2 expression in hypertension. 2) AngII-induced COX-2 expression in VSMC is related with NOX-1 induction and NFkB and AP-1 activation. 3) AngII-induced ET-1 production and ETA activation contributes, at least partially, to the increased NOX-1 and COX-2 expression. 4) PPAR¿ activation inhibits AngII-induced COX-2 expression by reducing NOX-1 levels; we suggest that transrepression mechanisms on NFkB and/or AP-1 can play an important role in this inhibitory effect of PPAR¿ activation.