Characterization of the role of dendritic cells in prion transfer to primary neurons.

Transmissible spongiform encephalopathies (TSEs) are neurodegenerative diseases caused by pathogenic isoforms (PrPSc) of the host-encoded cellular prion protein (PrPc). After consumption of contaminated food, PrPSc deposits rapidly accumulate in lymphoid tissues before invasion of the central nervous system (CNS). However the mechanisms of prion spreading from the periphery to the nervous system are still unclear. In this study, we investigated the role of dendritic cells (DCs) in the spreading of prion infection to neuronal cells. First, we determined that bone-marrow derived dendritic cells (BMDCs) rapidly uptake PrPSc after exposure to infected brain homogenate. Next, we observed a progressive catabolism of the internalized prion aggregates. Similar experiments performed with BMDCs isolated from knock-out (KO) or mice over-expressing PrP (tga20) indicate that both PrPSc uptake and catabolism are independent of PrPc expression in these cells. Finally, using co-cultures of prion-loaded BMDCs and cerebellar neurons, we characterized the transfer of the prion protein and the resulting infection of the neuronal cultures. Interestingly, the transfer of PrPSc was triggered by direct cell-to-cell contact. As a consequence, BMDCs kept the prion protein when cultured alone and no transfer to the recipient neurons was observed when a filter separated the two cultures or when neurons were exposed to the BMDCs conditioned media. Additionally, fixed BMDCs also failed to transfer prion infectivity to neurons suggesting an active transport of prion aggregates, in accordance with a role of tunnelling nanotubes (TNTs) observed in the co-cultures.