PROJECT SUMMARY Microglia and astrocytes have long been suspected of participating in the pathogenesis of Alzheimer’s disease (AD). However, it is not clear how these cells orchestrate their reactions in AD and whether they play protective or deleterious roles that can be targeted therapeutically. We recently discovered a potentially neuroprotective function that we termed the “microglia barrier”. We found that the robust encapsulation of Aβ deposits by microglia processes cause Aβ aggregates to become compact, less toxic and insulated from adjacent neurites, thereby reducing the formation of dystrophic axons. This neuroprotective function was severely disrupted in mice lacking Trem2 or Dap12, which have defects in microglia polarization towards plaques, leading to a more diffuse plaque conformation and worsening of axonal dystrophy. In this proposal, we aim to explore the possibility that in addition to microglia, the astrocytic reaction to early amyloid aggregates and the coordinated reaction between these two cell types is critical for the overall glial protective function. We will utilize sophisticated super-resolution imaging of mouse and human brain, intravital optical imaging and in vivo single cell manipulations to investigate the cellular and molecular basis of astrocyte and microglia orchestrated interactions and polarization towards amyloid deposits. We will also explore signaling pathways that can be targeted to enhance this neuroprotective glial barrier and reduce AD-associated axonal pathology.