Microglia contribute to the propagation of Abeta pathology into healthy brain tissue

The extracellular accumulation of amyloid-beta (A) peptides is a major hallmark of Alzheimer’s disease (AD). It is widely accepted that microglia associate with A plaques and appear morphologically activated especially in their immediate vicinity. Whether microglia play a role in A plaque formation and contribute to the propagation of A pathology remains however unknown. We therefore investigated the characteristics of microglia during neural transplantation experiments where wild-type neurons are grafted into the cortex of AD mouse models. Here, we demonstrate that A from the transgenic host tissue is able to enter and deposit within wild-type (WT) grafts, a process that is accompanied by massive microglia infiltration. Notably, manipulation of microglia function or microglia elimination significantly reduced A deposition within the grafts. Similarly, time-lapse in vivo two-photon imaging revealed that microglia transport A to the site of injury thereby identifying microglia as cellular carrier of A that propagate A pathology in previously unaffected CNS tissue. Our data thus argue for a hitherto unexplored mechanism of A propagation. examination of gene profile of microglia isolated from cortical grafts and non-grafted tissue