Therapeutic Effects of Auditory Stimulation at 40 Hz on Sleep Disturbances in an Alzheimer`s Disease Mouse Model: Focusing on the Role of Astrocytes

Abstract

The sensory stimulation at 40 Hz showed therapeutic impacts on Alzheimer`s disease (AD). Previous studies reported that amyloid-beta (Aβ) accumulation and sleep disturbances in AD have positive feedback loop and impaired Ca2+ influx and volume transient in astrocytes. However, the role of astrocytes to sleep disturbances remains unknown. We hypothesized that 40-Hz auditory stimulation could ameliorate sleep disturbances by enhancing the astrocytic Ca2+ influx. We used 6-month-old 5xFAD as Alzheimer`s disease model. Two-hour daily 40-Hz auditory stimulation were applied for two-weeks. We recorded the 24-hour electroencephalographic (EEG) for sleep-wake analysis at pre- and post-stimulation day. Reactive astrocytes and GABA were measured using immunohistochemistry. Patch clamping recordings measured the tonic GABA currents of nNOS neurons. Using GCaMP6f and intrinsic optical singals were measured astrocytic Ca2+ and volume swelling. qRT-PCR measured the transcriptional levels. Our studiy demonstrated that repeated auditory steady state responses (rASSR) at 40 Hz mitigated Aβ pathology and sleep disturbances. We observed that astrocytic γ-aminobutyric acid (GABA) reduced inhibition on neuronal nitric oxide synthase (nNOS)-containing neurons, sleep-promoting cortical neurons, by rASSR. Additionally, rASSR enhanced neuronal activity-induced transient volume and Ca2+ influx in astrocytes, which subsequently decreased monoamine oxidase B (MAO-B) and increased nuclear factor erythroid 2-related factor 2 (Nrf2). Finally, optogenetic boosting of astrocytic Ca2+ influx using MonSTIM1 mimicked the therapeutic effects of the rASSR at 40 Hz. Our findings suggest that 40-Hz rASSR ameliorates Aβ pathology and sleep disturbances by neuron-astrocyte interaction.