Rapid Macropinocytic Transfer of Α-Synuclein to Lysosomes

The nervous system spread of alpha-synuclein fibrils is thought to cause Parkinson???s disease (PD) and other synucleinopathies; however, the mechanisms underlying internalization and cellular spread are enigmatic. Here, we use confocal and superresolution microscopy, subcellular fractionation, and electron microscopy (EM) of immunogold-labeled a-synuclein preformed fibrils (PFFs) to demonstrate that this form of the protein undergoes rapid internalization and is targeted directly to lysosomes in as little as 2 min. Uptake of PFFs is disrupted by macropinocytic inhibitors and circumvents classical endosomal pathways. Immunogold-labeled PFFs are seen at the highly curved inward edge of membrane ruffles, in newly formed macropino-somes, in multivesicular bodies and in lysosomes. While most fibrils remain in lysosomes, a portion is trans-ferred to neighboring naive cells along with markers of exosomes. These data indicate that PFFs use a unique internalization mechanism as a component of cell-to-cell propagation.