mTOR-driven brain vascular dysfunction in Alzheimer's disease

Short-term mTOR attenuation reverses neurovascular coupling (NVC) impairments in symptomatic hAPP(J20) mice modeling Alzheimer's disease.

(A-C) Fold change in cerebral blood flow are means ±SEM of n=4-5/group during whisker pad stimulation (30 sec, bold black line), stimulations conducted sequentially in the presence of (A) aCSF (vehicle), (B) 200 nM L-NPA to inhibit nNOS specifically and (C) 200 nM L-NPA+ 10 μM L-NAME to inhibit all NOS, thus defining the contribution of the non-nNOS-dependent, L-NAME sensitive eNOS.

(D) NVC responses during 30-s whisker stimulations. Area under the curve was calculated as an increase relative to baseline (i.e. only upward peaks). Baseline NVC impairments in hAPP(J20) mice relative to WT (q(33)=12.81, ****p<0.0001) are reversed by 2 months of rapamycin (q(33)=26.01, ****p<0.0001), with enhancement of NVC in rapamycin-treated hAPP(J20) mice as compared to WT (q(33)=13.93, ****p<0.0001). L-NPA superfusion significantly reduces NVC in WT mice [q(33)=5.25, *p=0.02], but not in Tg hAPP(J20) mice (q(33)=0.22, p>0.99), suggesting a preexisting nNOS deficit in this group that is restored by rapamycin treatment in the hAPP(J20)+Rapa group, indicated by a significant inhibition of NVC in the presence of 200 nM L-NPA (q(33)=12.28 vs baseline, ****p<0.0001). The remaining NVC response in the presence of L-NPA+L-NAME (inhibiting all remaining NOS activity, i.e. eNOS) was not significantly different vs L-NPA alone in WT (q(33)=1.05, p=0.99), hAPP(J20) (q(33)=0.09, p>0.99), nor in hAPP(J20)+Rapa (q(33)=3.60, p=0.24).

(E) Contributions of nNOS, eNOS and non-NOS components to total NVC. Deficits in nNOS-dependent NVC in hAPP(J20) mice (q(33)=4.47, **p=0.009 vs WT) are negated by mTOR inhibition in rapamycin-treatedhAPP(J20) mice (q(33)=11.31, ****p<0.0001 vs hAPP) and nNOS-dependent NVC is enhanced over WT (q(33)=7.10, ++++p<0.0001). Additionally, rapamycin enhances L-NAME sensitive activities (eNOS) in hAPP(J20) mice relative to vehicle-treated hAPP(J20) mice (q(33)=3.93, *p=0.02). Deficits in the remaining non-NO mediated NVC response in hAPP(J20) mice (q(33)=6.06, ***p=0.0004 vs WT) are negated in rapamycin-treated hAPP(J20) mice(q(33)=7.87, ****p<0.0001 vs vehicle-treated hAPP).

(F) Hippocampal-dependent contextual memory impairment in 12-month-old hAPP(J20) mice (hAPP(J20) vs WT, q(16)=4.19, *p=0.024) is negated by 2 months of rapamycin treatment (q(16)=3.93, *p=0.034, hAPP(J20) vs hAPP(J20)+Rapa).

(G) Baseline NVC response is correlated with contextual memory performance (r=0.668, p=0.009). Behavioral studies used n=6-7 mice per group. All post hoc analyses are Tukey’s multiple comparison tests. Unless otherwise indicated, asterisks (*) in the figure represent a significant difference relative to hAPP+Veh and pluses (+) represent a significant difference relative to WT+Veh.