Abstracts

Rationale: Sleep disorders are a common, disabling comorbidity of epilepsy and may exacerbate seizures in tuberous sclerosis complex patients (TSC), but the mechanisms of sleep dysfunction in TSC are poorly understood. Although environmental and other extrinsic factors may contribute, intrinsic dysfunction in sleep circuits and cellular physiology of the TSC brain due to TSC gene mutations may independently lead to sleep problems. However, few clinical or research studies exist that have specifically investigated fundamental biological mechanisms for sleep disorders in TSC. Development of an animal model of sleep disorders in TSC would greatly facilitate mechanistic studies of the neurological basis of sleep dysfunction in TSC, potentially leading to novel targeted therapies for sleep problems in TSC. In this study, we developed and characterized a mouse model of sleep disorders in TSC and tested the hypothesis that sleep disruption may be related to a mTOR-dependent increase in orexin expression in the hypothalamus. Methods: Four to six week-old Tsc1 ^GFAPCKO mice, with conditional inactivation of the Tsc1 gene primarily in neurons and glia, and littermate control mice received sleep studies, involving video-EEG and EMG electrodes to analyze sleep-wake states. Mice with spontaneous seizures were excluded from analysis. Immunohistochemistry and western blotting was performed for orexin and mTOR marker (P-S6) expression in hypothalamic sections or isolated hypothalamic neurons in culture. Rapamycin treatment was used to test whether sleep dysfunction and orexin-expression was mTOR-dependent. Results: Tsc1 ^GFAPCKO mice exhibited decreased REM sleep, decreased REM sleep transitions, and impaired sleep-wake differentiation between light and dark cycles, independent of seizures (n=6 mice per group, p<0.05). Orexin expression and mTOR activity were increased in hypothalamic sections and hypothalamus neurons in culture from Tsc1 ^GFAPCKO mice (n=4-6 mice per group, p<0.05). Both the sleep abnormalities and increased orexin expression were at least partially reversed by rapamycin treatment (n=6-8 mice per group, p<0.05).   Conclusions: Tsc1 ^GFAPCKO mice exhibit sleep abnormalities that mimic similar sleep disorders seen in TSC patients, suggesting an intrinsic biological basis to sleep dysfunction in TSC. These sleep abnormalities in Tsc1 ^GFAPCKO mice are independent of seizures, are dependent on mTOR, and may relate to increased orexin expression in hypothalamus. These results identify a novel mechanistic explanation and potential targeted therapeutic approaches for sleep disorders in TSC. Funding: NIH R01 NS056872First three authors were equal contributors.