Changes in Cerebral Arteries and Parenchymal Arterioles With Aging: Role of Rho Kinase 2 and Impact of Genetic Background

Abstract

Vascular aging fundamentally contributes to large and small vessel disease. Despite the importance of such changes for brain function, mechanisms that mediate such changes are poorly defined. We explored mechanisms that underlie changes with age, testing the hypothesis that ROCK (Rho kinase) plays an important role. In C57BL/6 mice, baseline diameters of isolated pressurized parenchymal arterioles were similar in adult (4-5 month) and old mice (22±1 month; ≈15±1 µm). Endothelium-dependent dilation was impaired in old mice compared with adults in a pathway-specific manner. Vasodilation to NS-309 (which activates small- and intermediate-conductance Ca²⁺ activated K⁺ channels in endothelial cells) was intact while endothelial nitric oxide synthase-mediated vasodilation was reduced by ≥60%, depending on the concentration (P<0.05). A similar reduction was present in basilar arteries. Inhibiting both ROCK isoforms with Y-27632 restored the majority of endothelial function in old mice. Because genetic background is a determinant of vascular disease, we performed similar studies using FVB/N mice. Endothelial dysfunction was seen with aging in both FVB/N and C57BL/6 mice although the magnitude was increased ≈2-fold in the latter strain (P<0.05). In both strains of mice, age-induced endothelial dysfunction was reversed by inhibition of ROCK2 with SLX-2119. Thus, aging impairs endothelial function in both cerebral arteries and parenchymal arterioles, predominantly via effects on endothelial nitric oxide synthase-dependent regulation of vascular tone. The magnitude of these changes was influenced by genetic background and mediated by ROCK2.

Keywords: endothelium; genetic background; nitric oxide; rho-associated kinases; vascular diseases.

Figure 1

Active (A) and passive (B) diameter, myogenic tone (C), (A–C: young, n=15 arterioles from 15 mice; old, n=22 arterioles from 17 mice), responses to acetylcholine (Ach)(D, n=7–10), NS-309 (E, n=5–7) and nitroprusside (F, n=5) in adult and old mice. All data are mean±SE. * p<0.05 vs adult.

Figure 2

Dilation of the basilar artery to acetylcholine in adult (5.6±0.4 mo of age, n=5) and old mice (21.2±0.2 mo, n=7) in the absence or presence of Y-27632 (n=7) or Y-27632 plus L-NNA (n=5). * p<0.05 vs adult; ** p<0.05 vs old; # p<0.05 vs old plus Y-27632.

Figure 3

Baseline diameter of the basilar artery (A), responses to KCl (B), acetylcholine (Ach)(C) and papaverine (D) in adult (4.3±0.3 mo, n=5) and old (23.2±1.3 mo, n=7) C57BL/6 mice.

Figure 4

Baseline diameter of the basilar artery (A), responses to KCl (B), acetylcholine (Ach)(C) and papaverine (D) in adult (4.2±0.3 mo, n=8) and old (22.3±0.1 mo, n=10) FVB/N mice.

Figure 5

Responses of the basilar artery to acetylcholine in adult and old C57BL/6 and FVB/N mice. Ages and animal numbers of mice are provided in Figure 4.