Divergent Associations of Slow-Wave Sleep versus Rapid Eye Movement Sleep with Plasma Amyloid-Beta.

OBJECTIVE: Recent evidence shows that during slow-wave sleep (SWS), the brain is cleared from potentially toxic metabolites, such as the amyloid-beta protein. Poor sleep or elevated cortisol levels can worsen amyloid-beta clearance, potentially leading to the formation of amyloid plaques, a neuropathological hallmark of Alzheimer disease. Here, we explored how nocturnal neural and endocrine activity affects amyloid-beta fluctuations in the peripheral blood. METHODS: We acquired simultaneous polysomnography and all-night blood sampling in 60 healthy volunteers aged 20-68 years. Nocturnal plasma concentrations of amyloid-beta-40, amyloid-beta-42, cortisol, and growth hormone were assessed every 20 minutes. Amyloid-beta fluctuations were modeled with sleep stages, (non)oscillatory power, and hormones as predictors while controlling for age and participant-specific random effects. RESULTS: Amyloid-beta-40 and amyloid-beta-42 levels correlated positively with growth hormone concentrations, SWS proportion, and slow-wave (0.3-4Hz) oscillatory and high-band (30-48Hz) nonoscillatory power, but negatively with cortisol concentrations and rapid eye movement sleep (REM) proportion measured 40-100 minutes previously (all t values > |3|, p values < 0.003). Older participants showed higher amyloid-beta-40 levels. INTERPRETATION: Slow-wave oscillations are associated with higher plasma amyloid-beta levels, whereas REM sleep is related to decreased amyloid-beta plasma levels, possibly representing changes in central amyloid-beta production or clearance. Strong associations between cortisol, growth hormone, and amyloid-beta presumably reflect the sleep-regulating role of the corresponding releasing hormones. A positive association between age and amyloid-beta-40 may indicate that peripheral clearance becomes less efficient with age. ANN NEUROL 2024;96:46-60.

Functional Inhibition of Katanin Affects Synaptic Plasticity.

Dynamic microtubules critically regulate synaptic functions, but the role of microtubule severing in these processes is barely understood. Katanin is a neuronally expressed microtubule-severing complex regulating microtubule number and length in cell division or neurogenesis; however, its potential role in synaptic functions has remained unknown. Studying mice from both sexes, we found that katanin is abundant in neuronal dendrites and can be detected at individual excitatory spine synapses. Overexpression of a dominant-negative ATPase-deficient katanin subunit to functionally inhibit severing alters the growth of microtubules in dendrites, specifically at premature but not mature neuronal stages without affecting spine density. Notably, interference with katanin function prevented structural spine remodeling following single synapse glutamate uncaging and significantly affected the potentiation of AMPA-receptor-mediated excitatory currents after chemical induction of long-term potentiation. Furthermore, katanin inhibition reduced the invasion of microtubules into fully developed spines. Our data demonstrate that katanin-mediated microtubule severing regulates structural and functional plasticity at synaptic sites.

Aß/Amyloid Precursor Protein-Induced Hyperexcitability and Dysregulation of Homeostatic Synaptic Plasticity in Neuron Models of Alzheimer's Disease.

Alzheimer's disease (AD) is increasingly seen as a disease of synapses and diverse evidence has implicated the amyloid-ß peptide (Aß) in synapse damage. The molecular and cellular mechanism(s) by which Aß and/or its precursor protein, the amyloid precursor protein (APP) can affect synapses remains unclear. Interestingly, early hyperexcitability has been described in human AD and mouse models of AD, which precedes later hypoactivity. Here we show that neurons in culture with either elevated levels of Aß or with human APP mutated to prevent Aß generation can both induce hyperactivity as detected by elevated calcium transient frequency and amplitude. Since homeostatic synaptic plasticity (HSP) mechanisms normally maintain a setpoint of activity, we examined whether HSP was altered in AD transgenic neurons. Using methods known to induce HSP, we demonstrate that APP protein levels are regulated by chronic modulation of activity and that AD transgenic neurons have an impaired adaptation of calcium transients to global changes in activity. Further, AD transgenic compared to WT neurons failed to adjust the length of their axon initial segments (AIS), an adaptation known to alter excitability. Thus, we show that both APP and Aß influence neuronal activity and that mechanisms of HSP are disrupted in primary neuron models of AD.