Prostanoid-mediated contractions of the carotid artery become Nox2-independent with aging

Abstract

Aging is a major risk factor for carotid artery disease that may lead to stroke and dementia. Vascular effects associated with aging include increased vasomotor tone, as well as enhanced contractility to endothelial vasoconstrictor prostanoids and reduced nitric oxide (NO) bioactivity partly due to increased oxidative stress. We hypothesized that vascular NADPH oxidase (Nox)-derived superoxide may be involved in prostanoid- and NO-related functional aging. NO-mediated relaxations and prostanoid-mediated contractions to acetylcholine as well as phenylephrine-dependent contractions were investigated in the carotid artery from young (4 months) and aged mice (24 months). Gene expression of Nox subunits and endothelial NO synthase (eNOS) was determined in the carotid artery and aorta. In young mice, the thromboxane-prostanoid receptor antagonist SQ 29,548 fully blocked acetylcholine-induced contractions while reducing responses to phenylephrine by 75 %. The Nox2-targeted inhibitor Nox2ds-tat and the superoxide scavenger tempol reduced acetylcholine-stimulated, prostanoid-mediated contractions by 85 and 75 %, respectively, and phenylephrine-dependent contractions by 45 %. Unexpectedly, in aged mice, the substantial Nox2-dependent component of acetylcholine- and phenylephrine-induced, prostanoid-mediated contractions was abolished. In addition, endothelium-dependent, NO-mediated relaxations were impaired with aging. The expression of Nox subunits was greater in the aorta compared with the carotid artery, in which Nox1 was undetectable. eNOS gene expression was reduced in the aorta of aged compared to young mice. In conclusion, aging decreases prostanoid-mediated contractility in the carotid artery involving a loss of Nox2 activity and is associated with impaired endothelium-dependent, NO-mediated relaxation. These findings may contribute to a better understanding of the pathophysiology of carotid artery disease and the aging process.

GPER Mediates Functional Endothelial Aging in Renal Arteries

“…Indeed, many GPCRs exhibit basal or intrinsic activity sufficient to regulate cell signaling [27]. Furthermore, effects reported in the present study are independent of blood pressure, as both wild-type and GPER-deficient mice at 3 and 24 months of age, respectively, remain normotensive [12, 17]. …”

“…In contrast to the murine aorta or carotid arteries from young animals [12, 17], the endothelium-dependent, NO-mediated relaxant response induced by acetylcholine was about 20% less potent in renal arteries, and impaired to an even greater extent with age. Although this age-dependent reduction was largely reversed by inhibiting Nox, several mechanisms may also play a role.…”

“…Although this age-dependent reduction was largely reversed by inhibiting Nox, several mechanisms may also play a role. Acetylcholine-dependent generation of cyclooxygenase-derived vasoconstrictor prostanoids counteracts the vasodilatory activity of NO [18], and their formation and activity increases with aging [19], an effect that may become insensitive to Nox1/2 inhibition by gp91ds-tat [17]. Of note, compared to other arterial beds, the renal artery produces higher levels of endothelium-derived vasoconstrictor prostanoids [20], which are co-stimulated with NO in response to acetylcholine.…”

G protein-coupled estrogen receptor inhibits vascular prostanoid production and activity

“…Experiments to measure vascular reactivity of carotid arteries were performed as described (Meyer et al 2014a; Meyer et al 2015). Briefly, rings were equilibrated in warmed (37 °C) PSS bubbled with 21% O 2 , 5% CO 2 , and balanced N 2 (pH 7.4) before they were stretched step-wise to the optimal level of passive tension for force generation.…”

“…Functional integrity of the endothelium was assumed if arteries contracted with phenylephrine (1 μmol/L or 10 μmol/L) dilated >85% in response to acetylcholine (100 nmol/L). Acetylcholine initiates two distinct endothelium-dependent responses in murine carotid arteries, with NO-mediated relaxations at lower concentrations (1–100 nmol/L), followed by contractions mediated by COX-derived prostanoids at concentrations ≥ 100 nmol/L (Traupe et al 2002a; Zhou et al 2005; Meyer et al 2015). To study the full biphasic response to acetylcholine, rings in protocol 1 were contracted with phenylephrine to a stable plateau at 40% of KCl (60 mmol/L)-induced contractions, and concentration-dependent effects of acetylcholine (0.1 nmol/L – 10 μmol/L) were recorded.…”