Vesicular Rps6 Released by Astrocytes in an Experimental Model of AD Regulates Local Translation and Enhances Synaptic Integrity in Neurones.

In neurones, like in any other cell, their function often relies on the fine-tuning of their protein levels, which is achieved by the balance between protein synthesis and turnover. Defects in protein homeostasis frequently lead to neuronal dysfunction and neurological disorders. Given their extreme morphological complexity and high compartmentalization, neurones highly depend on the asymmetrical distribution of their proteome. The common belief is that proteins that sustain axonal, dendritic and synaptic functions are synthesized in the soma and then transported to distal neuronal compartments. However, there is a complementary mechanism by which the mRNAs, and not the proteins, are transported to distal subneuronal domains, and once they reach their destination, they are locally translated. Although once considered heretical, local translation (or local protein synthesis) is now widely accepted by the scientific community. Nonetheless, there is one question that remains largely unexplored in the field, and that is whether local translation in dendrites, axons and synapses is fully regulated by the neurone itself or if non-neuronal cells (e.g., glia) can modulate this mechanism in a non-cell-autonomous manner. Here, we combined primary neuronal cultures, astrocyte-derived extracellular vesicle (EVs) isolation, and proteomics to investigate whether astroglial EVs modulate local translation in axons. We show that EVs released by astrocytes exposed to amyloid-β peptide (Aβ) enhance protein synthesis specifically in distal axons and increase synaptic integrity. Proteomics analysis and western blotting identified the ribosomal protein Rps6 as an astroglial Aβ-EV cargo delivered to axons. Interestingly, genetic downregulation revealed the contribution of vesicular Rps6 to translation regulation in axons and synaptic integrity. To our knowledge, this is the first report that directly demonstrates glial control of local translation in neurones through EVs, revealing a novel glia-to-neurone communication mechanism in an experimental model of Alzheimer's disease (AD).