Impaired shear stress-induced nitric oxide production through decreased NOS phosphorylation contributes to age-related vascular stiffness.
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.
Soucy
Kevin G
KG
Department of Biomedical Engineering, Johns Hopkins Medical Institutions, Baltimore, Maryland 21287, USA.
Ryoo
Sungwoo
S
Benjo
Alexandre
A
Lim
Hyun Kyo
HK
Gupta
Gaurav
G
Sohi
Jayson S
JS
Elser
Jeremy
J
Aon
Miguel A
MA
Nyhan
Daniel
D
Shoukas
Artin A
AA
Berkowitz
Dan E
DE
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*
D009569:Nitric Oxide; D052250:Nitric Oxide Synthase Type III