Impaired α -Synuclein aggregate clearance in neuronal cells drive their spread to microglia through tunneling...

Tunneling nanotubes (TNTs) play a crucial role in intercellular communication, enabling transfer of molecular cargoes over long distances between connected cells. Previous studies have demonstrated efficient, directional transfer of $\alpha$ -Synuclein ( $\alpha$ -Syn) aggregates from neurons to microglia, with endosomal trafficking and lysosomal processing identified as the primary events following $\alpha$ -Syn internalization. Using human neuronal and microglial cell lines, we show that microglia exhibit higher lysosomal turnover, particularly through lysophagy, whereas neuronal lysosomes display compromised degradative capacity and impaired autophagic flux upon $\alpha$ -Syn exposure, resulting in compromised aggregate clearance. Such a response to $\alpha$ -Syn aggregates is also conserved in human iPSC-derived neurons and microglia. Moreover, perturbing aggregate clearance via autophagy inhibition enhances TNT-mediated transfer of $\alpha$ -Syn from neuronal cells to microglia. Microglia co-cultured with $\alpha$ -Syn-containing neurons upregulate autophagy flux, enabling efficient degradation of the transferred aggregates. These results highlight dysfunctional autophagy in neurons as a key driver outsourcing $\alpha$ -Syn aggregates to microglia.