Abstract Body (Do not enter title and authors here): Background: The recently identified globin Cytoglobin (Cygb), in the presence of cellular reductases, has potent nitric oxide (NO) dioxygenase (NOD) activity and serves as the major pathway of O₂-dependent NO metabolism in vascular smooth muscle. While genetic deletion of Cygb greatly decreases vascular NO metabolism, vessel tone and blood pressure (BP), the effects of increasing or partially decreasing Cygb expression are unknown.
Objective: Therefore, we investigate how upregulating or downregulating Cygb expression affects NO metabolism, vessel relaxation and BP.
Methods: Wild-type (WT), Cygb^-/+ (HET), Cygb^-/- knockout (KO), and Cygb overexpressing (OE) mice were used to determine the effect of Cygb expression levels on NO metabolism and vascular function. Cygb levels were assayed by quantitative immunoblotting. NO diffusion across the aortic wall was measured by electrode. BP was measured by tail-cuff, and endothelial-dependent vasorelaxation by the concentration-dependent acetylecholine (Ach) response in phenylephrine-preconstricted aortic rings using a strain gauge myograph.
Results: In HET mice Cygb levels were 50% of WT and in OE 500% of WT. NO diffusion flux across the aortic wall was greatly increased by the decrease/abolition of Cygb expression in HET and KO mice with 2.8 and 5.1-fold increase from WT, respectively (n= 5-7/grp, p<0.01 and p<0.001, respectively) (Fig. 1 A & B). However, in OE mice NO flux was 2.2-fold decreased (n=5-7/grp, p=0.05). Mean BP (MBP) was 29% decreased in KO and 22% in HET (n= 21/grp, p<0.01). In OE mice, MBP was 9% increased, compared to WT, p<0.05 (Fig. 1 C). In aortic vessels of Cygb KO and HET, there was a marked shift to the left in the Ach relaxation-response curve, with 50% relaxation seen at 0.34 nM or 8.6 nM Ach, respectively, compared to 154 nM in WT (n= 6/grp, p<0.0001). In contrast, a rightward shift was seen in Cygb OE vessels with 50% relaxation at 930 nM, p<0.0001).
Conclusion: Changing Cygb expression levels alters NO diffusion through the vessel wall in turn modulating vascular tone and BP. Therefore, modulation of Cygb expression could serve as a novel approach for the regulation of vascular tone in the treatment of cardiovascular disease.