This study tested the hypothesis that angiotensin II (Ang II) AT1 receptor is involved in development of hypertension and cardiac fibrosis via modifying ACE2 activity, eNOS expression and CD44-hyaluronan interaction.Main methods:
Male Sprague-Dawley rats were subjected to Ang II infusion (500 ng/kg/min) using osmotic minipumps up to 4 weeks and the AT1 receptor blocker, telmisartan was administered by gastric gavage (10 mg/kg/day) during Ang II infusion.Key findings:
Our results indicated that Ang II enhances AT1 receptor, downregulates AT2 receptor, ACE2 activity and eNOS expression, and increases CD44 expression and hyaluronidase activity, an enzyme for hyaluronan degradation. Further analyses revealed that Ang II increases blood pressure and augments vascular/interstitial fibrosis. Comparison of the Ang II group, treatment with telmisartan significantly increased ACE2 activity and eNOS expression in the intracardiac vessels and intermyocardium. These changes occurred in coincidence with decreased blood pressure. Furthermore, the locally-expressed AT1 receptor was downregulated, as evidenced by an increased ratio of the AT2 over AT1 receptor (1.4 ± 0.4% vs. 0.4 ± 0.1% in Ang II group, P < 0.05). Along with these modulations, telmisartan inhibited membrane CD44 expression and hyaluronidase activity, decreased populations of macrophages and myofibroblasts, and reduced expression of TGFβ1 and Smads. Collagen I synthesis and tissue fibrosis were attenuated as demonstrated by the less extensive collagen-rich area.Significance:
These results suggest that the AT1 receptor is involved in development of hypertension and cardiac fibrosis. Selective activating ACE2/eNOS and inhibiting CD44/HA interaction might be considered as the therapeutic targets for attenuating Ang II induced deleterious cardiovascular effects.