PROJECT SUMMARY/ABSTRACT Recent FDA approval of the anti-beta-amyloid (Ab) antibodies Aducanumab and Lecanemab as the first mechanism-based Alzheimer's disease (AD) therapies has strengthened the central role of the Ab protein in AD pathogenesis. However, these imperfect medications have only shown modest cognitive benefits, as AD clinical symptoms often occur decades after amyloid formation and deposition, and the molecular mechanisms leading to the demise of neurons in AD brains remain poorly understood. Nevertheless, the success of anti-Aβ therapeutic antibodies and identification of an APP mutation that protects against AD attest to the existence of amyloid-related molecular mechanisms that restrain Ab toxicity and confer resilience to AD. Meanwhile, cryo- electron microscopy structural studies have revealed several types of Aβ filaments isolated from AD brains, and they differ from those assembled in vitro. These observations suggest that in vivo assembly of amyloid filaments may require additional cellular factors that control progression of amyloid pathology and connect with non- amyloid AD pathways. Proteomic studies identified three prominent groups of AD pathology-associated proteins (ADPs). The current project seeks to test the hypothesis that Midkine and Netrin proteins, top-ranked human ADPs regulate Ab pathology and connect non-amyloid pathways in AD protein networks. The choice of Midkine and Netrin was informed by unbiased proteomic screening of hundreds of human brains, by validation studies that establish functional and physical links to amyloid pathology, and by their potential connections to UNC5C and ApoE/LRP pathways. The project is organized into three specific aims: 1) to determine the pathophysiological roles and AD protein networks mediated by Midkine and Pleiotrophin; 2) to map Midkine interactome and its physical interactions with Aβ filaments; 3) to elucidate the synergistic roles of Midkine, Pleiotrophin, and Netrin-1 in AD pathogenesis. These studies will reveal the impact of select AD pathology- associated proteins on disease progression, uncover non-amyloid pathways mediated by these ADPs, and elucidate the biochemical mechanisms by which Midkine and Netrin family ADPs regulate assembly of Ab filaments to potentially confer resilience to amyloid toxicity. Success of this project will inform the development of more robust experimental models and more specific and sensitive therapeutic and imaging agents for AD.