HMG-CoA reductase inhibitor improves endothelial dysfunction in spontaneous hypertensive rats via down-regulation of caveolin-1 and activation of endothelial nitric oxide synthase

Abstract

Hypertension is associated with endothelial dysfunction and increased cardiovascular risk. Caveolin-1 regulates nitric oxide (NO) signaling by modulating endothelial nitric oxide synthase (eNOS). The purpose of this study was to examine whether HMG-CoA reductase inhibitor improves impaired endothelial function of the aorta in spontaneous hypertensive rat (SHR) and to determine the underlying mechanisms involved. Eight-week-old male SHR were assigned to either a control group (CON, n=11) or a rosuvastatin group (ROS, n=12), rosuvastatin (10 mg/kg/day) administered for eight weeks. Abdominal aortic rings were prepared and responses to acetylcholine (10(-9)-10(-4) M) were determined in vitro. To evaluate the potential role of NO and caveolin-1, we examined the plasma activity of NOx, eNOS, phosphorylated-eNOS and expression of caveolin-1. The relaxation in response to acetylcholine was significantly enhanced in ROS compared to CON. Expression of eNOS RNA was unchanged, whereas NOx level and phosphorylated-eNOS at serine-1177 was increased accompanied with depressed level of caveolin-1 in ROS. We conclude that 3-Hydroxy-3-methylglutaryl Coenzyme-A (HMG-CoA) reductase inhibitor can improve impaired endothelial dysfunction in SHR, and its underlying mechanisms are associated with increased NO production. Furthermore, HMG-CoA reductase inhibitor can activate the eNOS by phosphorylation related to decreased caveolin-1 abundance. These results imply the therapeutic strategies for the high blood pressure-associated endothelial dysfunction through modifying caveolin status.

Keywords: Caveolins; Hydroxymethylglutaryl-CoA Reductase Inhibitors; Nitric Oxide; Nitric Oxide Synthase Type III.

Fig. 1

Treatment of rosuvastatin (10 mg/kg/day) for 8 weeks significantly enhances endothelium-dependent vasodilatation in the aorta of SHRs. (A) Aortic rings from rosuvastatin-treated SHRs exhibit a significantly higher response to acetylcholine-induced vasorelaxation compared with control SHRs (n=8 for each group). (B) Addition of NO analog, sodium nitroprusside, to the medium induced complete vasorelaxation, indicating maintenance of proper smooth muscle cell function in SHRs. Column=mean values, error bar=standard error. ^*P<0.05 as compared to the control.

Fig. 2

Plasma nitrite and nitrate concentration is increased in rosuvastatin-treated group. NOx concentration in plasma, representing the circulating pool of bioactive nitrate and nitrite, was approximately 1.6 fold higher in rosuvastatin-treated group than control group. Column=mean values, error bar=standard error. ^*P<0.05 as compared to the control.

Fig. 3

(A) eNOS mRNA expression in aorta from rosuvastatin-treated or control SHRs. mRNA expression of eNOS was not different between two groups. (B) Protein expression of eNOS was also not different between two groups. However, phosphorylated eNOS (p-eNOS) was expressed much higher (≈2.3 fold) in rosuvastatin-treated compared with control SHRs. The expression level of p-eNOS was determined by western blot with monoclonal-anti-phospho-eNOS antibody at Ser1177. Column=mean values, error bar=standard error. ^*P<0.05 as compared to the control.

Fig. 4

Assessment of the effect of rosuvastatin on caveolin-1 protein in the aorta of rats Top: Immunoblot of caveolin-1 protein in the aorta (lane 1, 2, 3, and 4, aorta from control SHR; lane 5, 6, 7, and 8, aorta from the rosuvastatin-treated SHR). Bottom: quantified data for caveolin-1 protein in rosuvastatin-treated and control SHRs. Optical density caveolin-1 positive bands were quantified by scanning densitometry and plotted relative to the control. Column=mean values, error bar=standard error. ^*P<0.01 as compared to the control.

Fig. 5

Down-regulation of caveolin-1 by treatment of rosuvastatin in aortic endothelium of SHRs. The expression of caveolin-1 in aortic endothelium of control SHR (A), and rosuvastatin-treated SHR (B). The level of expression of caveolin-1 was determined by immunohistochemical staining with polyclonal-anti-caveolin-1 antibody. Endothelial cells of the aorta were stained and the arrow indicates caveolin-1.