Dysfunction of the Autophagy System and MDM2–p53 Axis Leads to the Accumulation of Amyloidogenic Proteins in Angelman Syndrome Models

Angelman Syndrome (AS) is a neurodevelopmental disorder caused by the deficiency of the UBE3A gene that for a E3 ligase protein part of the ubiquitin-proteasome system (UPS). Autophagy and UPS systems remove abnormal proteins, but any dysfunction in these processes can affect neuronal development and wellbeing. Herein, the involvement of the UPS/autophagy system in the regulation of intracellular signaling pathways related to toxic protein accumulation was investigated in cellular/mice AS models, silenced for UB3A (UB3A^-). The main findings are as follows: (i) autophagy was upregulated in UBE3A^- cells with respect to control cells; (ii) a dysregulation of the AKT/mTOR pathway, linked to autophagy/synaptic development, was evidenced in cellular/animal models of AS with respect to controls; (iii) the ubiquitin ligase MDM2 was downregulated, and the tumor suppressor p53, normally inhibited by MDM2, enhanced its expression and transcriptional activity in UB3A^- cells with respect to controls. Finally, UB3A^- cells presented a significant alteration in the levels of β-amyloids with respect to control cells, and a reduction of α-synuclein levels, typical of neurodevelopmental disorder. Nevertheless, UB3A^- cells do not show evident morphological abnormalities. Overall, these data suggest that AS models presented an altered signaling pathway related to autophagy/UPS systems, potentially leading to the accumulation of toxic proteins affecting synaptic development.