PROJECT SUMMARY While amyloid plaques and neurofibrillary tangles are Alzheimer's disease (AD) defining features, Alzheimer himself originally identified a third pathology? inflammation of the brain's glial support cells. Neuroinflammation in AD is characterized by reactive astrocytes and microglia that surround amyloid plaques and chronically secrete inflammatory innate immune cytokines. The dominant view for decades has been that all forms of inflammation damage the AD brain. Yet, non-steroidal anti-inflammatory drugs failed to produce a positive signal for AD primary prevention. This raises a fundamental question: should we be blocking or possibly even promoting inflammation as an AD therapeutic? While the focus has mainly been on pro-inflammatory cerebral innate immunity, little attention has been paid to factors that curtail peripheral innate immune responses. The unifying theme of our work is that `rebalancing' peripheral innate immunity to homeostasis by releasing immunosuppression will limit AD progression. Strikingly, our focus on innate immunity in AD has just recently been validated by genome-wide association studies. These results have taken the field by storm; identifying clusters of AD risk alleles in core peripheral macrophage pathways. As a key cytokine suppressor of innate immunity and inflammation, transforming growth factor-beta (TGF-?) mRNA abundance is increased in AD patient brains. We hypothesize that the AD brain over- compensates to pro-inflammatory signals by producing these abnormally high levels of TGF-?. Paradoxically, this sets up early, low-level and chronic neuroinflammation that fails to support amyloid-? (A?) clearance. I and my team have shown in published and preliminary data that genetic or pharmacologic blockade of TGF-?- Smad 2/3 signaling in peripheral macrophages leads to brain entry of these cells and A? phagocytosis; sparing neurons from injury and restoring learning and memory. To further explore this theme, we have now generated the TgF344-AD rat that recapitulates cognitive impairment and the full array of human AD pathological features: neuroinflammation, plaques, tangles, and frank neuronal loss. In AIM 1, we will use non-invasive longitudinal imaging approaches to determine whether early neuroinflammation preempts later cognitive impairment, A? deposition, structural connectivity changes and neuronal death in TgF344-AD rats. AIM 2 is designed to longitudinally evaluate if blocking peripheral innate immune TGF-? signaling licenses A? phagocytosis and mitigates AD-like changes by delivering cutting- edge nanoparticles containing small molecule TGF-?-Smad 2/3 signaling inhibitor payload to hematogenous macrophages. Finally, we will pharmacologically delete peripheral macrophages to definitively establish if they are responsible for the beneficial effects of TGF-? signaling inhibition. While AD animal model studies are typically limited by cross-sectional designs, this project will break this barrier by coupling the most advanced multimodal, longitudinal brain imaging with peripheral TGF-? signaling inhibition in the TgF344-AD rat.