Cytoglobin (Cygb) can effectively metabolize nitric oxide (NO), a potent vasodilator, in the presence of oxygen and reductants. Cygb in the vascular wall may affect cardiovascular functions by changing the rate of NO metabolism. In this study, we directly tested the vascular role of Cygb using Cygb knockout (Cygb-/-) mice. The mean blood pressure of Cygb-/- and C57BL/6 wild type (WT) mice was 65.3 ± 1.9 mmHg and 93.7 ± 1.5 mmHg, respectively (n=10). Using echocardiography, we observed that cardiac output (CO) was increased in Cygb-/- mice compared to WT with values of 29.8 ± 3.9 vs 17.7 ± 0.9 ml/min. The systemic vascular resistance (SVR) of Cygb-/- mice was decreased by ~60% vs that of WT mice (Fig. 1). Further, the inner diameter (id) of aorta of Cygb-/- mice was dilated compared to WT with values of 2.2 ± 0.1 mm vs 1.5 ± 0.05 mm (n=5), respectively. After treatment with the NO synthase inhibitor L-NAME, no difference in the aortic id remained between Cygb-/- (1.55 ± 0.03 mm) and WT (1.49 ± 0.02 mm) mice, indicating that the NO pathway is responsible for the difference in vascular inner diameters and tone. Myograph experiments show that the aortic vasodilation response of Cygb-/- mice is much more sensitive to acetylcholine (Ach) or the NO donor nitroprusside (SNP) (EC50 shifts from 13 nM and 2.9 nM (WT mice) to 0.33 nM and 0.16 nM (Cygb-/-) for Ach and SNP, respectively). Using NO electrodes to measure the rate of NO consumption by SMCs and quantitative imunoblotting to estimate Cygb content in RSMCs-AR and Cygb knockdown RSMCs, we observed that 90% of NO consumption by RSMCs-AR is caused by the intracellular Cygb. Our results indicate that Cygb deficiency in the vascular wall of Cygb-/- mice greatly reduces the rate of NO metabolism and increases vascular NO concentration, resulting in vasodilation, increase in vessel lumen diameter, and decrease in SVR. These results demonstrate that Cygb regulates cardiac function and vessel tone by controlling the rate of vascular NO metabolism.
Nitric oxide metabolism in heart mitochondria
