Nitrogen metabolism in sleep homeostasis and pathology

Sleep is essential for life, and chronic sleep deprivation (SD) is associated with pathology including Alzheimer's disease in humans. Urea cycle abnormalities have been observed by others in animal SD paradigms and human sleep and fatigue disorders. I found that polyamines (PAs), coupled to urea cycle by the metabolite ornithine, are elevated in Drosophila sleep mutants, especially acetylated PAs and putrescine. I hypothesize that nitrogen diversion from urea cycle to PA synthesis drives sleep when SD is acute and neurodegeneration when SD is chronic.

Mentored Aim 1 will test what mechanisms link SD to nitrogen metabolism by using sleep mutants for 13C-ornithine mass spectrometry to identify the metabolites that ornithine is channeled toward, and enzyme assays to assess what catalytic differences shape the nitrogen metabolome under chronic SD. Mass spectrometry will also be conducted under more acute SD to determine if this mirrors chronic SD in PA profile. Mentored Aim 2 will test how PA supplements, and broadly expressed RNAi that promote putrescine synthesis, both promote sleep in wild-type flies. Subpopulation RNAi sleep experiments will assess what neural circuits are involved in PA sleep responses.

Broadly expressed RNAi sleep experiments will determine whether PAs generally are required for rebound sleep following SD, and whether production of putrescine specifically is required for PA supplement sleep increases. Independent Aim 3 will test whether PA increases contribute to the well-documented worsening of Alzheimer's pathology by SD. Mass spectrometry will test whether PA increases observed in mouse Alzheimer's models by others, which are very similar to my fly sleep mutants, carry over to multiple fly Alzheimer's models. I will also test whether broad PA synthesis RNAi that blunts production of acetyl-PAs and putrescine can block the worsening effects of SD in multiple fly Alzheimer's models.

Measures of protein pathology, cell death, lethality, and memory will be used as metrics. Independent Aim 4 will test whether PA synthesis is sleep-regulated and sleep-promoting in mouse brain. Mass spectrometry under chronic environmental enrichment SD will test whether mice exhibit similar PA changes to what I observe in my fly sleep mutants. Motion-sensing and EEG sleep metrics will be used to assess whether both PA supplementation and pharmacological depletion of PAs alter sleep in mice.

Any one of these four aims has the potential to launch a long-running research project if successful, enhancing my ability to launch an independent career from this proposal. My training plan builds on my core mouse and fly skillsets, adding important complementary skills in genetic engineering, fly memory behavior, specialized mouse sleep behavior protocols, and isotopic labeling metabolomics. My training plan will also enhance my theoretical knowledge of neurodegeneration and enhance my mentorship skills. This proposal will give me the data and skills I need to succeed as an independent investigator at a research institution, building out a lab of my own focused on biochemical regulation of homeostasis, and linkages to neural pathology.

Grant Number: 5R00NS118561-05
NIH Institute/Center: NIH
Principal Investigator: JOSEPH BEDONT