Circadian and homeostatic regulation of sleep in a diurnal model of Smith-Magenis Syndrome - ABSTRACT Sleep maintains brain structure and function, but more than 1 in 4 individuals with neurodevelopmental disorders exhibit sleep disturbances. These sleep problems exacerbate difficult behavior such as aggression and self-injury and improved sleep improves them. Unfortunately, the neural mechanisms underlying such disordered sleep in neurodevelopmental disorders remain unknown. Interestingly, many genes causal for monogenic neurodevelopmental disorders encode transcriptional regulators that can influence circadian gene expression. In Smith-Magenis syndrome (SMS) in particular there are other indicators of a strong role for circadian influences on sleep/wake dysfunction: namely a reversed daily cycle of melatonin and altered function of melanopsin, the photoreceptor mediating non-visual effect of light. In this syndrome, human patients show reduced daytime wakefulness and reduced nighttime sleep, quite possibly consistent with these melatonin cycle abnormalities and/or impairment in melanopsin-mediated light response. Despite this initial suggestive evidence, it remains unclear how light or melatonin contributes to sleep/wake alterations in this condition. Using CRISPR-based gene editing in Nile grass rat, Arvicanthis niloticus, we have developed a diurnal rodent model of SMS by targeting Rai1, the casual gene for the disorder. Preliminary data in Rai1-KO grass rats showed disrupted daily rhythms and sleep disturbances, mimicking the human phenotype. The proposed study will further characterize the effects of Rai1 deficiency on sleep and neural network, and test the central hypothesis that RAI1 haploinsufficiency disrupts light and/or melatonin-based regulation of sleep rhythm and neural network function in diurnal mammals, in the following specific aims: Aim1 will determine the role of RAI1 in daily sleep/wake rhythms neural network properties. We will determine the role of RAI1 in a) daily sleep/wake rhythms using electroencephalography (EEG) and electromyography (EMG), as well as in b) daily modulation prefrontal cortical network spiking dynamics recorded with silicon probes. Aim 2 will test the hypothesis that sleep disturbances in Rai1-KO grass rats are due to impaired photic input, based on elevated daytime melatonin, excessive daytime sleepiness, and altered pupillary reflex indicating dysfunction in photoreceptor melanopsin reported in SMS individuals. To test this, we will a) house both KO and WT animals in constant darkness housing (remove photic cue), and b) maximize melanoptic stimulation using full-spectrum daylight (replenish photic input, Aim 2B). Aim 3 will test the hypothesis that sleep disturbances in Rai1-KO grass rats are due to altered melatonin rhythm. We will first remove melatonin by pinealectomy, followed by day or night melatonin infusion using a programable minipump. Sleep/wake and network electrophysiologic function will be measured to determine how light or melatonin contributes to the sleep phenotypes and network properties in SMS . This work will shed light on neural mechanisms of sleep disturbances in SMS, and lead to novel interventions to improve sleep in patients of SMS and other neurodevelopmental disorders.
