Investigating the Role of PSD-95 in Sleep in SHINE Syndrome

PROJECT SUMMARY SHINE syndrome, a rare form of monogenic autism, is named for its key symptoms: sleep problems, hypotonia, intellectual disability, neurological disorders, and epilepsy. This condition arises from an autosomal-dominant mutation in the gene discs large MAGUK scaffold protein 4 (DLG4), which encodes postsynaptic density protein 95 (PSD-95). PSD-95 is crucial for scaffolding, localizing, and stabilizing receptors on excitatory postsynaptic membranes, thereby influencing synaptic strength and plasticity. The mechanism of sleep problems in SHINE syndrome may be due to disruption of the molecular circadian clock and/or in synaptic function. Previous work in our lab demonstrated that siRNA knockdown of DLG4 in cells results in a shortened circadian period, suggesting that PSD-95 modulates circadian rhythms and contributes to the sleep issues observed in SHINE syndrome. Our team has recently generated novel SHINE syndrome mice with a patient-derived mutation, and these mice exhibit locomotor and sleep abnormalities. It remains unknown how PSD-95, either through molecular or synaptic changes, impacts sleep and circadian processes. The overarching goal of this proposed work is to elucidate the mechanisms behind sleep and circadian disturbances in SHINE syndrome. With two related but independent aims, this proposal investigates: (i) whether PSD-95 modulates circadian rhythms through tropomyosin receptor kinase B (TRKB)/mechanistic target of rapamycin (MTOR) signaling, (ii) abnormalities in receptor levels and synaptic function in the hypothalamus, and (iii) possible rescue of abnormalities with ketamine. Aim 1 proposes to determine whether there is abnormal TRKB signaling in SHINE mice–resulting in subsequent abnormal MTOR activity–affecting the cycling of the circadian clock protein BMAL1 in the hypothalamus. This will be accomplished by measuring MTOR activity and BMAL1 cycling in the hypothalamus of SHINE mice at baseline, after chronic administration of TRKB modulators (including ketamine), and following a washout period. The synchrony of molecular rhythms will also be assessed. Aim 2 will then identify impairment in receptor composition and synaptic function in the hypothalamus of SHINE mice. Sleep and epilepsy will be monitored by EEG, and levels of AMPA and NMDA receptor subunits in the hypothalamus will be measured at baseline and after ketamine administration. Collectively, the knowledge gained from this proposal has the potential to uncover disruption caused by PSD-95 mutations and inform potential interventions to restore normal sleep and synaptic function in patients with SHINE syndrome.