title: Impaired shear stress-induced nitric oxide production through decreased NOS phosphorylation contributes to age-related vascular stiffness.
abstract: Endothelial dysfunction and increased arterial stiffness contribute to multiple vascular diseases and are hallmarks of cardiovascular aging. To investigate the effects of aging on shear stress-induced endothelial nitric oxide (NO) signaling and aortic stiffness, we studied young (3-4 mo) and old (22-24 mo) rats in vivo and in vitro. Old rat aorta demonstrated impaired vasorelaxation to acetylcholine and sphingosine 1-phosphate, while responses to sodium nitroprusside were similar to those in young aorta. In a customized flow chamber, aortic sections preincubated with the NO-sensitive dye, 4-amino-5-methylamino-2',7'-difluorofluorescein diacetate, were subjected to steady-state flow with shear stress increase from 0.4 to 6.4 dyn/cm(2). In young aorta, this shear step amplified 4-amino-5-methylamino-2',7'-difluorofluorescein fluorescence rate by 70.6 +/- 13.9%, while the old aorta response was significantly attenuated (23.6 +/- 11.3%, P < 0.05). Endothelial NO synthase (eNOS) inhibition, by N(G)-monomethyl-l-arginine, abolished any fluorescence rate increase. Furthermore, impaired NO production was associated with a significant reduction of the phosphorylated-Akt-to-total-Akt ratio in aged aorta (P < 0.05). Correspondingly, the phosphorylated-to-total-eNOS ratio in aged aortic endothelium was markedly lower than in young endothelium (P < 0.001). Lastly, pulse wave velocity, an in vivo measure of vascular stiffness, in old rats (5.99 +/- 0.191 m/s) and in N(omega)-nitro-l-arginine methyl ester-treated rats (4.96 +/- 0.118 m/s) was significantly greater than that in young rats (3.64 +/- 0.068 m/s, P < 0.001). Similarly, eNOS-knockout mice demonstrated higher pulse wave velocity than wild-type mice (P < 0.001). Thus impaired Akt-dependent NO synthase activation is a potential mechanism for decreased NO bioavailability and endothelial dysfunction, which likely contributes to age-associated vascular stiffness.
authors.affiliation: Department of Biomedical Engineering, Johns Hopkins Medical Institutions, Baltimore, Maryland 21287, USA.
authors.forename: Kevin G
authors.initials: KG
authors.lastname: Soucy
authors.forename: Sungwoo
authors.initials: S
authors.lastname: Ryoo
authors.forename: Alexandre
authors.initials: A
authors.lastname: Benjo
authors.forename: Hyun Kyo
authors.initials: HK
authors.lastname: Lim
authors.forename: Gaurav
authors.initials: G
authors.lastname: Gupta
authors.forename: Jayson S
authors.initials: JS
authors.lastname: Sohi
authors.forename: Jeremy
authors.initials: J
authors.lastname: Elser
authors.forename: Miguel A
authors.initials: MA
authors.lastname: Aon
authors.forename: Daniel
authors.initials: D
authors.lastname: Nyhan
authors.forename: Artin A
authors.initials: AA
authors.lastname: Shoukas
authors.forename: Dan E
authors.initials: DE
authors.lastname: Berkowitz
mesh_terms: D000367:Age Factors; D000375:Aging / Q000502:physiology*; D000818:Animals; D001011:Aorta / Q000502:physiology*; D004548:Elasticity; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D009569:Nitric Oxide / Q000378:metabolism*; D052250:Nitric Oxide Synthase Type III / Q000378:metabolism*; D010766:Phosphorylation; D051381:Rats; D017208:Rats, Wistar; D033081:Shear Strength; D014655:Vascular Resistance / Q000502:physiology*
chemical_list: D009569:Nitric Oxide; D052250:Nitric Oxide Synthase Type III