Dottorato in NEUROSCIENZE DEL COMPORTAMENTO

Titolo della tesi: BDNF-dependent cerebellar alterations are associated with neurobiological abnormalities and autistic-like traits in a mouse model of cholesterol storage disorder

Abstract Niemann–Pick type C1 (NPC1) disease is an autosomal recessive lysosomal storage disorder caused by mutations in the Npc1 gene, leading to defective intracellular cholesterol trafficking and widespread cellular dysfunction. Among the affected brain regions, the cerebellum exhibits the most pronounced pathology, characterized by progressive degeneration of Purkinje cells and ataxia. Although traditionally considered a neurodegenerative disorder, recent evidence from our group indicates that NPC1 also displays distinctive neurodevelopmental features, aligning it with the spectrum of neurodevelopmental disorders. Previous studies showed that Npc1 deficiency disrupts Sonic hedgehog signaling during early postnatal cerebellar development, impairing granule cell (GC) proliferation. Several Sonic hedgehog-dependent processes also rely on brain-derived neurotrophic factor (BDNF) activity, which is likewise dysregulated in developing Npc1nmf164 mice, resulting in defective GC migration to the internal granule layer (IGL). In the present work, we investigated whether altered neurotrophic signaling contributes to defective GC differentiation and synaptic connectivity, postnatal developmental processes that normally occur during the first weeks of life, leading to the emergence of behavioral abnormalities in adult Npc1nmf164 mice. We specifically addressed sex-related differences—an aspect previously overlooked—to delineate divergent molecular and behavioral trajectories in males and females following Npc1 loss. By integrating molecular, morphological, and behavioral approach, we demonstrate that Npc1 loss severely impairs cerebellar maturation by persistently affecting BDNF–TrkB signaling and downstream PTEN–mTOR pathway. These alterations coincide with reduced levels of key synaptic proteins (Snap25, PSD95, Shank3, and Nlgn3) crucial for pre- and postsynaptic organization, excess immature dendritic spines particularly in Npc1nmf164 male mice, and decreased IGL volume, collectively indicating impaired differentiation and connectivity. Biochemical analyses revealed unchanged cerebellar GABA levels but elevated glutamine in Npc1 mice, indicating altered glutamate–glutamine metabolism and an excitatory–inhibitory imbalance. Notably, these neurodevelopmental abnormalities manifested as sex-dependent behavioral alterations, with male Npc1nmf164 mice showing marked deficits in social interaction during adulthood, consistent with an autistic-like phenotype. Overall, our findings demonstrate that Npc1 deficiency disrupts neurotrophic signaling and GC synaptic maturation, leading to long-lasting alterations in cerebellar circuitry and social behavior. These effects exhibit a sex-dependent pattern, with males showing greater vulnerability to molecular, structural, and behavioral alterations than females. These results support the view that early cerebellar dysfunction—driven by impaired BDNF–TrkB signaling and altered synaptic organization—contributes to the emergence of autistic-like features in NPC1 disease, positioning the cerebellum as a critical hub linking lipid metabolism, neurotrophic regulation, and socio-emotional development