Project Summary/ Abstract Memory loss in Alzheimer's disease (AD) reflects a progressive failure of neural network function in the setting of pathology and neuroinflammation. The overall goal of this proposal is to explore a novel paradigm for the role of the REST transcription factor in the modulation of neural networks and microglial function in AD, and to advance a new therapeutic approach. We discovered that the master developmental regulator REST/NRSF is induced in the aging human brain and coordinates the expression of a gene network that protects aging neurons from neurotoxic stress and hyperexcitation. REST is downregulated in AD, beginning at the stage of mild cognitive impairment. Our preliminary studies in conditional REST-deficient mice indicate that REST protects against amyloid and tau pathology, as well as cognitive decline in AD mouse models. To begin to understand the role of REST in critical neural circuits, we will generate highly selective knockouts of REST in layer II entorhinal cortical neurons, or in CA1 or CA3 hippocampal neurons, components of the entorhinal cortex (EC)-hippocampal circuit that is affected early in AD. These novel REST knockout mice will be crossed with established AD transgenic lines to explore effects on neural network excitation, synaptic plasticity, memory and pathology. We will also extend recent preliminary studies showing that REST is lost in microglia in AD, and that REST-deficient microglia are functionally impaired. To explore the role of REST in microglia, we have generated a conditional microglial REST-knockout mouse line. This mouse model, together with primary microglial cell cultures, will be used to investigate REST-regulated immune/inflammatory signaling pathways, as well as effects on phagocytosis and Aβ clearance. RNA-seq and ChIP-seq analysis will be performed to broadly define REST-regulated gene networks and signaling pathways that affect microglial function. A central question is whether REST is a druggable target. We have identified novel REST-activating drugs that prevent memory loss and pathology in AD mouse models. Drug activity is lost in REST-deficient mice, indicating specificity for REST. Importantly, the prototype REST-activating drug does not show evidence of toxicity in mice following chronic administration for more than two years. These novel agents not only provide proof-of- principle for translation, but are also valuable tools for discovering underlying mechanisms of REST-mediated neuroprotection. One such mechanism is the unfolded protein response, which may be modulated by REST activation through target genes and signaling pathways that will be investigated. This multidisciplinary approach may provide novel insights into neuroprotective mechanisms in aging and AD, with potentially important therapeutic implications.