Exercise training ameliorates cerebrovascular dysfunction in a murine model of Alzheimer's disease: role of the P2Y2 receptor and endoplasmic reticulum stress.

Cerebrovascular dysfunction is a critical risk factor for the pathogenesis of Alzheimer's disease (AD). The purinergic P2Y2 receptor and endoplasmic reticulum (ER) stress are tightly associated with vascular dysfunction and the pathogenesis of AD. However, the protective effects of exercise training on P2Y2 receptor- and ER stress-associated cerebrovascular dysfunction in AD are mostly unknown. Control (C57BL/6, CON) and AD (APP/PS1dE9, AD) mice underwent treadmill exercise training (EX). 2-MeS-ATP-induced dose-dependent vasoreactivity was determined by using a pressurized posterior cerebral artery (PCA) from 10-12-mo-old mice. Human brain microvascular endothelial cells (HBMECs) were exposed to laminar shear stress (LSS) at 20 dyn/cm2 for 30 min, 2 h, and 24 h. The expression of P2Y2 receptors, endothelial nitric oxide synthase (eNOS), and ER stress signaling were quantified by Western blot analysis. Notably, exercise converted ATP-induced vasoconstriction in the PCA from AD mice to vasodilation in AD+EX mice to a degree commensurate to the vascular reactivity observed in CON mice. Exercise reduced the expression of amyloid peptide precursor (APP) and increased the P2Y2 receptor and Akt/eNOS expression in AD mice brain. Mechanistically, LSS increased the expression of both P2Y2 receptor and eNOS protein in HBMECs, but these increases were blunted by a P2Y2 receptor antagonist in HBMECs. Exercise also reduced the expression of aberrant ER stress markers p-IRE1, p/t-eIF2α, and CHOP, as well as Bax/Bcl-2, in AD mice brain. Collectively, our results demonstrate for the first time that exercise mitigates cerebrovascular dysfunction in AD through modulating P2Y2 receptor- and ER stress-dependent endothelial dysfunction.NEW & NOTEWORTHY A limited study has investigated whether exercise training can improve cerebrovascular function in Alzheimer's disease. The novel findings of the study are that exercise training improves cerebrovascular dysfunction through enhancing P2Y2 receptor-mediated eNOS signaling and reducing ER stress-associated pathways in AD. These data suggest that exercise training, which regulates P2Y2 receptor and ER stress in AD brain, is a potential therapeutic strategy for Alzheimer's disease.

A chronic physical activity treatment in obese rats normalizes the contributions of ET-1 and NO to insulin-mediated posterior cerebral artery vasodilation.

This study tested the hypotheses that obesity-induced decrements in insulin-stimulated cerebrovascular vasodilation would be normalized with acute endothelin-1a receptor antagonism and that treatment with a physical activity intervention restores vasoreactivity to insulin through augmented nitric oxide synthase (NOS)-dependent dilation. Otsuka Long-Evans Tokushima Fatty rats were divided into the following groups: 20 wk old food controlled (CON-20); 20 wk old free food access (model of obesity, OB-20); 40 wk old food controlled (CON-40); 40 wk old free food access (OB-40); and 40 wk old free food access+RUN (RUN-40; wheel-running access from 20 to 40 wk). Rats underwent Barnes maze testing and a euglycemic hyperinsulinemic clamp (EHC). In the 40-wk cohort, cerebellum and hippocampus blood flow (BF) were examined (microsphere infusion). Vasomotor responses (pressurized myography) to insulin were assessed in untreated, endothelin-1a receptor antagonism, and NOS inhibition conditions in posterior cerebral arteries. Insulin-stimulated vasodilation was attenuated in the OB vs. CON and RUN groups (P ≤ 0.04). Dilation to insulin was normalized with endothelin-1a receptor antagonism in the OB groups (between groups, P ≥ 0.56), and insulin-stimulated NOS-mediated dilation was greater in the RUN-40 vs. OB-40 group (P < 0.01). At 40 wk of age, cerebellum BF decreased during EHC in the OB-40 group (P = 0.02) but not CON or RUN groups (P ≥ 0.36). Barnes maze testing revealed increased entry errors and latencies in the RUN-40 vs. CON and OB groups (P < 0.01). These findings indicate that obesity-induced impairments in vasoreactivity to insulin involve increased endothelin-1 and decreased nitric oxide signaling. Chronic spontaneous physical activity, initiated after disease onset, reversed impaired vasodilation to insulin and decreased Barnes maze performance, possibly because of increased exploratory behavior.NEW & NOTEWORTHY The new and noteworthy findings are that 1) in rodents, obesity-related deficits in insulin-mediated vasodilation are associated with increased influence of insulin-stimulated ET-1 and depressed influence of insulin-stimulated NOS and 2) a physical activity intervention, initiated after the onset of disease, restores insulin-mediated vasodilation, likely by normalizing insulin-stimulated ET-1 and NOS balance. These data demonstrate that the treatment effects of chronic exercise on insulin-mediated vasodilation extend beyond active skeletal muscle vasculature and include the cerebrovasculature.

Coupling of Ca(2+) to CREB activation and gene expression in intact cerebral arteries from mouse : roles of ryanodine receptors and voltage-dependent Ca(2+) channels.

Pathological changes of the vasculature are characterized by changes in Ca(2+) handling and alterations in gene expression. In neurons and other cell types, [Ca(2+)](i) often drives changes in gene expression. However, the relationship between Ca(2+) signaling and gene expression in vascular smooth muscle is not well understood. This study examines the ability of Ca(2+) influx through voltage-dependent, L-type Ca(2+) channels (VDCCs) and Ca(2+) release through ryanodine receptors (RyRs) to activate the transcription factor, cAMP-responsive element binding protein (CREB), and increase c-fos levels in intact cerebral arteries. Membrane depolarization increased the fraction of nuclei staining for phosphorylated CREB (P-CREB) and levels of c-fos mRNA in intact mouse cerebral arteries. Ryanodine, which inhibits RyRs, increased P-CREB staining and c-fos levels. Forskolin, an activator of adenylyl cyclase, and sodium nitroprusside, an NO donor, increased P-CREB and c-fos levels. Nisoldipine, an inhibitor of VDCCs, reversed the effects of depolarization and ryanodine on P-CREB and c-fos levels, but not the effects of forskolin or sodium nitroprusside. Inhibition of Ca(2+)/calmodulin-dependent protein kinase (CaM kinase) blocked increases in P-CREB and c-fos levels seen with membrane depolarization, suggesting that CaM kinase has an important role in the pathway leading from Ca(2+) influx to CREB-mediated changes in c-fos levels. Our data suggest that membrane depolarization increases [Ca(2+)](i) through activation of VDCCs, leading to increased P-CREB and c-fos, and that RyRs have a profound effect on this pathway by indirectly regulating Ca(2+) entry through VDCCs. These results provide the first evidence of Ca(2+) regulation of CREB and c-fos in arterial smooth muscle.