Fibrillar Aβ triggers microglial proteome alterations and dysfunction in Alzheimer mouse models

Microglial dysfunction is a key pathological feature of Alzheimer´s disease (AD), but little is known about proteome-wide changes in microglia during the course of AD pathogenesis and their consequences for microglial function. Here, we performed an in-depth proteomic characterization of microglia in two AD mouse models, the overexpression APPPS1 and the knock-in AppNL-G-F (APP-KI) model. Proteome changes were followed from pre-deposition to early, middle and advanced stages of amyloid plaque pathology, revealing a large panel of Microglial Amyloid Response Proteins (MARPs) that reflect a heterogeneity of microglial alterations triggered by Aβdeposition. We demonstrate that the occurrence of MARPs coincided with the deposition of fibrillar Aβ, recruitment of microglia to amyloid plaques and phagocytic dysfunction. While the proteomic and functional microglial changes were already markedly seen in 3 months old APPPS1 mice, they were delayed in the APP-KI model that generates substantially less fibrillar Aβ. The identified microglial proteomic fingerprints of AD provide a valuable resource for functional studies of novel molecular targets and potential biomarkers for monitoring AD progression or therapeutic efficacy.