Prader Willi locus Snord116 RNA regulates hypothalamic functions: sleep and temperature

Sleep is a complex behavior and it is hierarchically regulated involving several brain regions, neurotransmitters, and genes that co-operate in building modulatory mechanisms aimed at controlling and maintaining sleep. Specifically, this thesis attempts to address/understand how genomic imprinting, which affect a subset of genes in mammals resulting in a monoallelic expression, may regulate sleep. One of the main brain regions involved in sleep regulation is the hypothalamus. Within the hypothalamic region imprinted genes are highly expressed. Interestingly, it has been described that hypothalamic insufficiency caused by lack of paternal expression of chromosome 15q11- q13, leads to Prader-Willi syndrome (PWS). Specifically, the microdeletion of the small nuclear ribonucleic acid (RNA)-116 (SNORD116) cluster within the PWS locus plays a major role in developing the main endophenotypes that characterize this syndrome (i.e. REM sleep dysfunction, hyperphagia and temperature instability). However, what could be the role of the paternally imprinted gene Snord116 in the hypothalamic function is unknown. Additionally, is still unclear the specific contribution of the Snord116 gene in developing the PWS symptoms. Since these unresolved points my research has been split into three parts: In the first part of this research, it has been shown that the paternally imprinted gene Snord116 plays a crucial role in the formation and organization of the orexin (OX) and melanin concentrating hormone (MCH) systems, the two main neuro-modulatory systems within the lateral hypothalamus (LH). Moreover, a compromised neuronal dynamic in the LH and a sleep- wake regulation of mice with paternal deletion of Snord116 (PWScrm+/p-) is observed. This abnormal neuronal dynamic is accompanied by a significant reduction in OX neurons in the LH of mutant mice. For this reason, it is proposed that the dysregulation of rapid eye movement (REM) sleep, food intake and temperature control observed in PWS mice are potentially due to this imbalance between OX- and MCH-expressing neurons in the LH as observed in mutant mice. In the second part of this research, it has been investigated the microstructural electrophysiological components of sleep, such as REM sleep features and sleep spindles during non-REM sleep. Indeed, REM sleep is thought to contribute to neuronal network formation early in brain development, while spindles are markers of thalamocortical processes. In neurodevelopmental disorders both sleep structures (REM and sleep spindles) are often compromised and this influence functional properties of cortical neurons. These results indicate 1 that REM sleep properties and its occurrence (REM sleep episodes classified as short-and long REM sleep episode) throughout the sleep-wake cycles are selectively influenced by the Snord116 gene in mice. Moreover, the specific abnormalities in sleep spindles in PWS model systems, indicate that these sleep features may be translated as potential biomarkers in human PWS sufferers. In the third part of this research, it has been proposed a new therapeutic approach for PWS patients aiming to ameliorate the sleep phenotypes that significantly compromise the quality of life of these patients. Pitolisant (a wake-promoting drug) was orally administrated in mice carrying the paternal deletion of the Snord116 gene that are affected by REM sleep alteration coupled with a reduction of the OX neurons. Overall the results of this research show that Pitolisant ameliorates the REM sleep alteration in these mice, although other studies are needed to clarify whether this drug may be easily translated/used in clinics. In conclusion, this thesis provides support for the important role of Snord116 in the regulation of REM sleep and its propensity and its regulatory mechanisms in the hypothalamus. Finally, a new pharmacological approach for PWS by using Pitolisant has been proposed to ameliorate the sleep alteration that significantly affects the PWS patients.