Contribution of hypocretin neuron activity to Alzheimer's related sleep disturbances

PROJECT SUMMARY Sleep is a very well conserved behavioral state across all animals. Though the exact function of sleep remains unknown, it is widely appreciated that good sleep quality is a cornerstone for any healthy organism. Indeed, several neurological disorders are co-morbid with sleep disturbances. Furthermore, altered sleep as observed in sleep apnea, insomnia or sleep deprivation show impairments in memory consolidation and increased risk for depression, cancer, Alzheimer’s disease (AD), and other neuropsychiatric disorders. AD patients have been shown to display altered sleep architecture. Sleep plays a role in clearance of beta-amyloid (Aβ) in interstitial space. Excessive accumulation of Aβ, a prominent feature of AD, has been shown to alter sleep. Recent work in our lab has demonstrated that hyperexcitability of wake-promoting hypocretin (Hcrt) neurons of the lateral hypothalamus (LH), resulting from natural aging, may underlie increased sleep fragmentation during aging. It is likely that these same neurons may have altered excitability in AD, exacerbated by the presence of Aβ accumulation, and may drive sleep fragmentation and sleep disturbances observed in AD patients. The overarching aim of this proposal is to understand how Aβ accumulation impacts hypocretin neuron activity leading to altered homeostatic sleep pressure and subsequent disrupted sleep architecture observed in Alzheimer’s disease. The central hypothesis is that accumulation of Aβ accelerates natural Hcrt neuron death leading to hyperexcitability of surviving Hcrt neurons and disrupted sleep pressure and architecture. This proposal focuses on Hcrt neurons as they have been suggested to be an integration hub which consolidates several streams of input and sends signals to downstream arousal-promoting regions. To understand this interaction, I will first need to demonstrate altered Hcrt neuron activity in the presence of Aβ accumulation, its impact on sleep (Aim 1), and demonstrate changes to the intrinsic and synaptic excitability of Hcrt neurons (Aim 2). Finally, I will consolidate the findings into a biophysically realistic computational network model with sleep-wake transitions to make viable predictions about the relative contributions of various ionic / synaptic currents to changes in intrinsic Hcrt neuron activity and its impact on overall sleep structure. These predictions will then be experimentally tested using CRISPR-SaCas9 technologies in vivo, the results of which will then further inform/refine the computational model (Aim 3). The end goal being a detailed theory / biophysical explanation for the impact of Aβ accumulation on Hcrt neuron activity and their role in sleep architecture.