PNA5 Restores BK Channel Function in Cerebral Arteries of Female 5x-FAD Mice

Abstract

Few therapeutic options exist for treatment of Alzheimer’s disease (AD), the most prevalent type of dementia, particularly therapies focusing on cerebral microvascular function. AD is associated with impaired neurovascular coupling (NVC) in the brain, a process that ensures blood flow to regions of increased neuronal activity through functional cerebral microvascular dilation. This dilation involves opening of large conductance, Ca2+-activated K+ channels (BKCa), a channel known to be a target for oxidative modulation in the early-onset 5x-FAD model of AD. PNA5, an agonist of the vasculo-protective Mas receptor, prevents heart failure-induced dementia partially by antioxidant mechanisms, but its effects on AD remain undetermined. Thus, we hypothesized that PNA5 improves cerebral microvascular BKCa function in 5x-FAD mice. Five-month-old female 5x-FAD mice were treated with PNA5 (100 µg/kg/day, s.c.) or saline (vehicle) for 1 month. We measured Ca2+ sparks by spinning-disk confocal microscopy, BKCa-dependent vasoreactivity by pressure myography and NVC by laser speckle contrast imaging. Data are means ± SEM, WT vs 5x-FAD or 5x-FAD + saline vs. 5x-FAD + PNA5. We observed a significant increase in Ca2+ spark frequency in 5x-FAD compared to WT mice (0.5905 ± 0.08609 vs. 1.346 ± 0.1459, n=15, p = 0.0001, Student’s t-test) with no significant differences in Ca2+ spark frequency between vehicle and PNA5-treated 5x-FAD (1.236 ± 0.1367 vs. 1.188 ± 0.1226, n = 15, p = 0.7979, Student’s t-test). We also observed that 5x-FAD + PNA5 restored BKCa vasoreactivity, seen as a larger constriction after BKCa inhibition with iberiotoxin (30 nM, Vasoconstriction (%): 6.074 ± 0.3481 vs 14.65 ± 3.174, N = 3, p = 0.0129, Student’s t-test), without additive effects of the reducing agent dithiothreitol (DTT, 10 μM) in 5x-FAD + PNA5 (Vasoconstriction (%): 15.92 ± 3.442 vs. 11.80 ± 2.292, N = 3, p = 0.133, unpaired two-tailed Student’s t-test). Further, we observed an increase in cerebral functional hyperemia in 5x-FAD + PNA5 when compared to 5x-FAD + vehicle (Increase in perfusion (%): 3.596 ± 0.6964 vs. 8.614 ± 0.6589, N = 4 / 6, p = 0.0014, Student’s test). In conclusion, these data suggest that PNA5 improves BKCa activity and neurovascular function in 5x-FAD. Ongoing studies will expand on these findings to further investigate mechanisms that underlie the effects of PNA5 and how it may serve as a potential therapeutic drug for AD.