Live cell imaging of exogenous α-synuclein fibrils in primary microglia and neuron co-cultures.

α-synuclein (α-syn) rich Lewy bodies are a prominent pathological feature of Parkinson's disease (PD), with intra-cellular accumulation occurring in neurons and possibly microglia. Tracking α-syn movement between the two different cell types is of critical importance in determining how pathology spreads. We hypothesized that the separate pre-treatment of either primary cortical neurons or microglia with exogenous α-syn preformed fibrils (PFFs) will foster a cytotoxic environment when co-cultured with the opposite naïve cell type. To this end, using real time live cell imaging, we found an accumulation of Alexa Fluor 488 labelled α-syn PFFs in both microglia and neurons. In the co-cultures, the labelled-PFFs showed differing patterns of spread to non-seeded cells. The PFF treatment also provoked cellular loss that increased with the passage of time and induced marked vacuolation and changes in microglial morphology. Microglia appeared to accumulate PFFs from morphologically compromised neurons and shifted to a predominately dystrophic and "foamy enlarged fried egg" morphology over time and was associated with a reduction in levels of the anti-inflammatory cytokine, interleukin-4 (IL-4). We currently provide a novel in vitro co-culture model that allows for tracking α-syn spread between primary cortical microglia and neurons.