Impairment of Endogenous H2S Pathway due to Aging and Endothelium Denudation in Mouse Isolated Thoracic Aorta

Hydrogen sulfide (H2S) is a gas neurotransmitter that is synthesized in various mammalian tissues including vascular tissues and regulates vascular tone. The aim of this study is to investigate whether the endogenous L-cysteine/H2S pathway is impaired due to aging and endothelial denudation in mouse isolated thoracic aorta. For this purpose, young (3-4 months) and old (23-25 months) mice were used in the experiments. The effects of aging and endothelium on endogenous and exogenous H2S-induced vasorelaxation were investigated by cumulative L-cysteine-(1 microM-10 mM) and NaHS-(1 microM-3 mM) induced vasorelaxations, respectively. The L-cysteine-induced relaxations were reduced in old mice aorta compared to the young mice. Also, vasorelaxant responses to L-cysteine (1 microM-10 mM) were reduced on aorta rings with denuded-endothelium of young and old mice. However, the relaxation responses to NaHS were not altered by age or endothelium denudation. The loss of staining of CSE in the endothelial layer was observed in old thoracic aorta. Ach-induced (1-30 microM) relaxation almost abolished in endothelium-denuded rings from both mice group. Also, relaxation Ach reduced in intact endothelium tissue of old mice aorta. In conclusion, the vasorelaxant responses to L-cysteine but not NaHS decreased and the protein expression of CSE reduced in old thoracic aorta rings consistent with a decrease in H2S concentration with aging and endothelium damage, suggesting that aging may be lead to decrease in enzyme expression and H2S signaling system due to endothelium damage in mouse thoracic aorta. Key words Aging, Hydrogen sulfide, L-cysteine, Endothelium, Thoracic aorta.