Decreased production of neuronal NOS-derived hydrogen peroxide contributes to endothelial dysfunction in atherosclerosis

BACKGROUND AND PURPOSE

Reduced NO availability has been described as a key mechanism responsible for endothelial dysfunction in atherosclerosis. We previously reported that neuronal NOS (nNOS)-derived H₂O₂ is an important endothelium-derived relaxant factor in the mouse aorta. The role of H₂O₂ and nNOS in endothelial dysfunction in atherosclerosis remains undetermined. We hypothesized that a decrease in nNOS-derived H₂O₂ contributes to the impaired vasodilatation in apolipoprotein E-deficient mice (ApoE^?/?).

EXPERIMENTAL APPROACH

Changes in isometric tension were recorded on a myograph; simultaneously, NO and H₂O₂ were measured using carbon microsensors. Antisense oligodeoxynucleotides were used to knockdown eNOS and nNOS in vivo. Western blot and confocal microscopy were used to analyse the expression and localization of NOS isoforms.

KEY RESULTS

Aortas from ApoE^?/? mice showed impaired vasodilatation paralleled by decreased NO and H₂O₂ production. Inhibition of nNOS with L-Arg^NO2-L-Dbu, knockdown of nNOS and catalase, which decomposes H₂O₂ into oxygen and water, decreased ACh-induced relaxation by half, produced a small diminution of NO production and abolished H₂O₂ in wild-type animals, but had no effect in ApoE^?/? mice. Confocal microscopy showed increased nNOS immunostaining in endothelial cells of ApoE^?/? mice. However, ACh stimulation of vessels resulted in less phosphorylation on Ser852 in ApoE^?/? mice.

CONCLUSIONS AND IMPLICATIONS

Our data show that endothelial nNOS-derived H₂O₂ production is impaired and contributes to endothelial dysfunction in ApoE^?/? aorta. The present study provides a new mechanism for endothelial dysfunction in atherosclerosis and may represent a novel target to elaborate the therapeutic strategy for vascular atherosclerosis.