Hypothalamic orexin and mechanistic target of rapamycin activation mediate sleep dysfunction in a mouse model of tuberous sclerosis complex

Tuberous sclerosis complex (TSC) is a genetic disease related to hyperactivation of the mechanistic target of rapamycin (mTOR) pathway and manifested by neurological symptoms, such as epilepsy and sleep disorders. The pathophysiology of sleep dysfunction is poorly understood and is likely multifactorial, but may involve intrinsic biological regulators in the brain. Here, we characterized a mouse model of sleep disorders in TSC and investigated mechanisms of sleep dysfunction in this conditional knockout model involving inactivation of the Tsc1 gene in neurons and astrocytes (Tsc1CKO mice). Sleep studies utilizing EEG, EMG, and behavioral analysis found that Tsc1CKO mice have decreased REM sleep and impaired sleep-wake differentiation between light and dark phases. mTOR activity and orexin expression were increased in hypothalamic sections and cultured hypothalamic neurons from Tsc1CKO mice. Both the sleep abnormalities and increased orexin expression in Tsc1CKO mice were reversed by rapamycin treatment, indicating their dependence on mTOR activation. An orexin antagonist, suvorexant, also restored normal REM levels in Tsc1CKO mice. These results identify a novel mechanistic link between mTOR and orexin in the hypothalamus related to sleep dysfunction and suggest a targeted therapeutic approach to sleep disorders in TSC.