Impaired neuromodulator crosstalk delays vigilance-dependent astroglia Ca2+ activation in mouse models of Alzheimer's disease

Degeneration in neuronal nuclei producing the neuromodulators acetylcholine and norepinephrine is a hallmark of Alzheimers disease (AD). Therapeutic interventions that increase acetylcholine in brain ameliorate AD symptoms in human patients, and augmenting norepinephrine restores cognitive function in mouse models of AD as well as Down Syndrome, the most frequent cause of early onset AD. A prominent cellular target of noradrenergic and potentially cholinergic signaling during states of heightened vigilance are astroglia and recent studies indicate that astroglia Ca2+ dynamics in awake mice contribute to optimal cognitive performance. Here we tested the hypothesis that vigilance-dependent Ca2+ signaling in mouse primary visual cortex astrocytes is altered in mouse models of AD and provide mechanistic insight into upstream neuromodulator signaling that shapes astrocyte Ca2+ dynamics in healthy and AD conditions. In two mouse models of AD (APPswe/PSEN1dE9 and AppNL-F KI), we consistently observed delayed and less coordinated astrocyte Ca2+ elevations in response to locomotion, a well-controlled behavioral paradigm triggering widespread Ca2+ activation in astroglia throughout the brain. Combining pharmacological and genetic manipulations, we found that noradrenergic signaling to astrocytes was facilitated by cholinergic signaling, but this neuromodulator crosstalk was impaired in AppNL-F mice. Pharmacological facilitation of norepinephrine release rescued delayed and less coordinated astrocyte Ca2+ activation in AppNL-F mice and suggests that astrocytes preserve a functional reserve that can be recruited even during late-stage disease. Our findings of delayed and less coordinated astroglia Ca2+ activation predict impaired noradrenergic signaling and may contribute to the cognitive decline in AD.