Introduction: The angiotensin II type 1 receptor (AT1R) and the peroxisome proliferator-activated receptor γ (PPARγ) have been implicated in the pathogenesis of atherosclerosis. A number of studies have reported that AT1R inhibition or genetic AT1R disruption and PPARγ activation inhibit vascular inflammation and improve glucose and lipid metabolism, underscoring a molecular interaction of AT1R and PPARγ. We here analyzed the hypothesis that vasculoprotective anti-inflammatory and metabolic effects of AT1R inhibition are mediated by PPARγ.
Material and methods: Female ApoE^–/–/AT1R^–/– mice were fedwith a high-fat and cholesterol-rich diet and received continuous treatment with the selective PPARγ antagonist GW9662 or vehicle at a rate of 700 ng/kg/min for 4 weeks using subcutaneously implanted osmotic mini-pumps. Additionally, one group of female ApoE^–/– mice served as a control group. After treatment for 4 weeks mice were sacrificed and read-outs (plaque development, vascular inflammation and insulinsensitivity) were performed.
Results: Using AT1R deficient ApoE^–/– mice (ApoE^–/–/AT1R^–/– mice) we found decreased cholesterol-induced endothelial dysfunction and atherogenesis compared to ApoE^–/– mice. Inhibition of PPARγ by application of the specific PPARγ antagonist GW9662 significantly abolished the anti-atherogenic effects of AT1R deficiency in ApoE^–/–/AT1R^–/– mice (plaque area as % of control: ApoE^–/–: 39 ±5%; ApoE^–/–/AT1R^–/–: 17 ±7%, p = 0.044 vs. ApoE^–/–; ApoE^–/–/AT1R^–/– + GW9662: 31 ±8%, p = 0.047 vs. ApoE^–/–/AT1R^–/–). Focusing on IL6 as a pro-inflammatory humoral marker we detected significantly increased IL-6 levels in GW9662-treated animals (IL-6 in pg/ml: ApoE^–/–: 230 ±16; ApoE^–/–/AT1R^–/–: 117 ±20, p = 0.01 vs. ApoE^–/–; ApoE^–/–/AT1R^–/– + GW9662: 199 ±20, p = 0.01 vs. ApoE^–/–/AT1R^–/–), while the anti-inflammatory marker IL-10 was significantly reduced after PPARγ inhibition in GW9662 animals (IL-10 in pg/ml: ApoE^–/–: 18 ±4; ApoE^–/–/AT1R^–/–: 55 ±12, p = 0.03 vs. ApoE^–/–; ApoE^–/–/AT1R^–/– + GW9662: 19 ±4, p = 0.03 vs. ApoE^–/–/AT1R^–/–). Metabolic parameters of glucose homeostasis (glucose and insulin tolerance test) were significantly deteriorated in ApoE^–/–/AT1R^–/– mice treated with GW9662 as compared to vehicle-treated ApoE^–/–/AT1R^–/– mice. Systolic blood pressure and plasma cholesterol levels were similar in all groups.
Conclusions: Genetic disruption of the AT1R attenuates atherosclerosis and improves endothelial function in an ApoE^–/– mouse model of hypercholesterolemia-induced atherosclerosis via PPARγ, indicating a significant role of PPARγ in reduced vascular inflammation, improvement of insulin sensitivity and atheroprotection of AT1R deficiency.