Knockdown of arginase I restores NO signaling in the vasculature of old rats

Arginase, expressed in endothelial cells and upregulated in aging blood vessels, competes with NO synthase ( NOS) for L-arginine, thus modulating vasoreactivity and attenuating NO signaling. Moreover, arginase inhibition restores endothelial NOS signaling and L-arginine responsiveness in old rat aorta. The arginase isoform responsible for modulating NOS, however, remains unknown. Because isoform-specific arginase inhibitors are unavailable, we used an antisense ( AS) oligonucleotide approach to knockdown arginase I (Arg I). Western blot and quantitative PCR confirmed that Arg I is the predominant isoform expressed in endothelialized aortic rings and is upregulated in old rats compared with young. Aortic rings from 22-month-old rats were incubated for 24 hours with sense ( S), AS oligonucleotides, or medium alone ( C). Immunohistochemistry, immunoblotting, and enzyme assay confirmed a significant knockdown of Arg I protein and arginase activity in AS but not S or C rings. Conversely, calcium-dependent NOS activity and vascular metabolites of NO was increased in AS versus S or C rings. Acetylcholine (endothelial-dependent) vasorelaxant responses were enhanced in AS versus S or C treated rings. In addition, 1H-oxadiazolo quinoxalin-1-one ( 10 mu mol/L), a soluble guanylyl cyclase inhibitor, increased the phenylephrine response in AS compared with S and C rings suggesting increased NO bioavailability. Finally, L-arginine (0.1 mmol/L)-induced relaxation was increased in AS versus C rings. These data support our hypothesis that Arg I plays a critical role in the pathobiology of age-related endothelial dysfunction. AS oligonucleotides may, therefore, represent a novel therapeutic strategy against age-related vascular endothelial dysfunction.