Neuronal Autophagy Failure Drives α-Synuclein Transfer to Microglia to Outsource Aggregate Clearance

Tunneling nanotubes (TNTs) play a crucial role in intercellular communication, enabling a dynamic network for the transfer of molecular cargo over long distances between connected cells. Previous studies have demonstrated efficient, directional transfer of -Synuclein (-Syn) aggregates from neurons to microglia, with endosomal trafficking and lysosomal processing identified as the primary events following -Syn internalization. Using human neuronal and microglial cell lines, we found that microglia exhibit higher lysosomal turnover, particularly through lysophagy, whereas neuronal lysosomes display compromised degradative capacity and impaired autophagic flux. This deficiency results in less efficient degradation of aggregates in neurons. Moreover, perturbation of autophagy enhances TNT-mediated transfer of aggregate from neuronal cells to microglia. In contrast, microglia co-cultured with -Syn-containing neurons upregulate autophagy flux, enabling efficient degradation of the transferred aggregates. These findings were further validated using human induced pluripotent stem cells (hiPSC)-derived neurons and microglia. Overall, our study highlights the distinct responses of neurons and microglia to -Syn aggregates and identifies dysfunctional autophagy in neurons as a key driver of the preferential and directional transfer of aggregates to microglia.