A dual hit of α-synuclein internalization and immune challenge leads to formation and maintenance of Lewy body-like inclusions in human dopaminergic neurons

Lewy bodies (LBs), rich in α-synuclein, are a hallmark of Parkinson′s disease (PD). Understanding their biogenesis is likely to provide insight into the pathophysiology of PD, yet a cellular model for LB formation remains elusive. The realization that immune challenge is a trigger for neurodevelopmental disease has been a breakthrough in the understanding of PD. Here, iPSC-derived human dopaminergic (DA) neurons from multiple healthy donors were found to form LB-like inclusions following treatment with α-synuclein preformed fibrils, but only when coupled to an immune challenge (interferon-gamma) or when co-cultured with activated microglia. Human cortical neurons derived from the same iPSC lines did not form LB-like inclusions. Exposure to interferon-gamma impairs autophagy in a lysosomal-specific manner in vitro similar to the disruption of proteostasis pathways that contribute to PD. We find that lysosomal membrane proteins LAMP1 and LAMP2 and transcription factors regulating lysosomal biogenesis and function are downregulated in DA but not cortical neurons. Finally, due to the excellent sample preservation afforded by cells compared to post-mortem PD brain tissue, we conclude that the LB-like inclusions in DA neurons are membrane-bound, suggesting they are not limited to the cytoplasmic compartment.