Role of Ube3A-mediated p18 regulation in synaptogenesis and synaptic plasticity

This work investigates how Ube3a, an E3 ubiquitin ligase whose deficiency causes Angelman syndrome (AS), regulates synaptic development and plasticity through control of p18 (LAMTOR1) and mTORC1 signaling. The study identifies p18, a subunit of the lysosomal Ragulator complex required for mTORC1 recruitment and activation, as a direct substrate of Ube3a-mediated ubiquitination and proteasomal degradation. In healthy neurons, Ube3a interacts with p18 and ubiquitinates it, limiting p18 abundance at lysosomal membranes and thereby constraining mTORC1 activity. When Ube3a is deficient, as in AS model mice, p18 accumulates, increasing lysosomal localization of Ragulator-Rag components and driving elevated mTORC1 signaling.

The investigators connect these molecular changes to structural and functional synaptic deficits: Ube3a deficiency leads to abnormal dendritic spine morphology, impaired long-term potentiation (LTP), and deficits in learning and memory. Using cell culture, biochemical assays, and in vivo manipulations in hippocampal CA1 neurons of AS mice, the authors demonstrate that knockdown of p18 reduces elevated mTORC1 activity and rescues several synaptic phenotypes. Specifically, p18 knockdown improves dendritic spine maturation, restores LTP, and ameliorates learning performance in AS mice. The manuscript situates these findings within current understanding of mTOR signaling, highlighting that amino-acid–dependent lysosomal recruitment of mTORC1 via Ragulator-Rag complexes is essential for full mTORC1 activation and that acylation-dependent membrane anchoring of p18 regulates this process. Prior evidence had identified ubiquitination sites on p18 but had not established the responsible E3 ligase or the physiological consequences in the central nervous system.

The present study fills that gap by showing Ube3a’s direct biochemical interaction with p18 and by demonstrating functional consequences on mTORC1 signaling and synaptic plasticity. Beyond mechanistic insights, the work underscores therapeutic potential: because excessive mTORC1 activity appears to underlie synaptic abnormalities in AS, targeting p18 levels or mTORC1 hyperactivation may be promising strategies to restore synaptic function and improve cognitive outcomes. The authors also connect these findings to broader observations that imbalanced mTOR signaling in AS involves increased mTORC1 and decreased mTORC2 activity, and that normalization of mTORC1 (for example by rapamycin in prior studies) can rebalance mTOR signaling pathways.

Overall, Xiaoning Bi et al. reveal a previously unrecognized regulatory mechanism whereby Ube3a controls p18 proteostasis to tune mTORC1 activity, with significant implications for dendritic spine development, synaptic plasticity, and learning and memory. The study provides a molecular link between Ube3a deficiency and mTORC1 over-activation in the brain, and identifies p18 modulation as a potential target for interventions in cognitive disorders associated with dysregulated mTORC1 signaling.