The high prevalence of coexistent sleep and metabolic disorders suggest that these processes are integrated at the molecular level, but mechanisms of this integration are unknown. The recent finding that the AMPK family member SIK3 is a phylogenetically conserved sleep drive regulator combined with our preliminary data showing both reduced sleep and elevated energy stores in animals mutant for the C. elegans SIK homolog kin- 29, suggests that SIKs are key nodes connecting sleep and energy homeostasis. The model motivating this proposal is that SIKs are responsive to the energy level in particular neurons; low energy (i.e. low ATP levels) result in the movement of SIK into the nucleus where, via phosphorylation of a class II HDAC it de-represses genes that signal to promote sleep and energy reserve mobilization. We will test this model using the nematode Caenorhabditis elegans and with the following hypotheses: (1) Cellular energy charge is lower under conditions of increased sleep drive. (2) KIN-29/SIK signals under conditions of low energy to mobilize energy stores and restore cellular ATP levels and sleep. (3) KIN-29/SIK functions acutely in metabolically-responsive sensory neurons that regulate the sleep-inducing ALA and RIS neurons; It functions in the same neurons to regulate fat stores. (4) KIN-29/SIK sleep-promoting activity is controlled by nuclear import, which is regulated by the upstream kinases LKB1 and PKA. Finally, (5) we will pursue an exploratory aim by performing a pilot genetic screen to discover new genes that are required for the reduced sleep phenotype of kin-29 mutants. Experiments in aims 1-4 will illuminate the molecular and cellular mechanism by which SIKs function to regulate animal sleep and energetic stores.
Aim 5, in which we will identify new sleep genes, will provide a bridge into the next set of hypotheses regarding mechanisms of sleepiness. Lessons gained from the nematode can motivate focused experiments in mammals, and will inform our understanding of patients with disorders of sleep regulation.
Disorders of sleep regulation frequently occur in individuals with disorders of metabolism such as diabetes mellitus, but the relationship between the two is not understood. Our research focuses on a particular mechanism that may link sleep regulation with metabolic regulation.