Rapamycin increased eNOS expression by 1.8-fold in low shear regions but dose-dependently reduced maximal eNOS expression at high shear stress levels (>5 Pa).
Does rapamycin modulate eNOS responsiveness to shear stress in normocholesteraemic and hypercholesteraemic mice?
Rapamycin increases eNOS in low shear (atherogenic) regions, potentially offering protection against atherosclerosis, while reducing eNOS at high shear stress, affecting vasomotion.
AIMS: Studies in animals and patients indicate that rapamycin affects vasodilatation differently in outer and inner curvatures of blood vessels. We evaluated in this study whether rapamycin affects endothelial nitric oxide synthase (eNOS) responsiveness to shear stress under normo- and hypercholesteraemic conditions to explain these findings. METHODS AND RESULTS: Shear stress levels were varied over a large range of values in carotid arteries of transgenic mice expressing human eNOS fused to enhanced green fluorescence protein. The mice were divided into control, low-dose rapamycin (3 microg/kg/day), and high-dose rapamycin (3 mg/kg/day) groups and into normocholesteraemic and hypercholesteraemic (ApoE-/- on high cholesterol diet for 3-4 weeks) groups. The effect of rapamycin treatment on eNOS was evaluated by quantification of eNOS expression and of intracellular protein levels by en face confocal microscopy. A sigmoid curve fit was used to described these data. The efficacy of treatment was confirmed by measurement of rapamycin serum levels (2.0 +/- 0.5 ng/mL), and of p27kip1 expression in vascular tissue (increased by 2.4 +/- 0.5-fold). In control carotid arteries, eNOS expression increased by 1.8 +/- 0.3-fold in response to rapamycin. In the treated vessels, rapamycin reduced maximal eNOS expression at high shear stress levels (>5 Pa) in a dose-dependent way and shifted the sigmoid curve to the right. Hypercholesteraemia had a tendency to increase the leftward shift and the reduction in maximal eNOS expression (P = 0.07). CONCLUSION: Rapamycin is associated with high eNOS in low shear regions, i.e. in atherogenic regions, protecting these regions against atherosclerosis, and is associated with a reduction of eNOS at high shear stress affecting vasomotion in these regions.
Cheng et al. (Thu,) conducted a other in Normo- and hypercholesteraemia (atherosclerosis model). Rapamycin vs. Control was evaluated on eNOS expression and intracellular protein levels in response to shear stress. Rapamycin increased eNOS expression by 1.8-fold in low shear regions but dose-dependently reduced maximal eNOS expression at high shear stress levels (>5 Pa).