The overall goal of this exploratory project is to investigate how the misregulation of normal signaling by the Amyloid Precursor Protein (APP) might contribute to Alzheimer's disease (AD). APP is best known as the source of beta amyloid (Aβ) peptides that accumulate in AD, and clinical trials have focused on reducing Aβ levels in patients. Unfortunately, these trials have not substantially improved patient outcomes, and the mechanisms of Aβ toxicity are still under debate. At the same time, growing evidence has shown APP itself may serve important functions in the brain, including synaptogenesis, remodeling, and regrowth responses following injury. In addition, neurotoxic forms of Aβ can directly bind APP, suggesting that Aβ might also provoke neurodegeneration by perturbing the normal functions of APP. Although APP may interact with a variety of signaling molecules, compelling work has now shown that it can function as an atypical G protein- coupled receptor, specifically regulating the heterotrimeric G protein Goα. Studies in cell culture have shown that APP can bind and activate Goα via a conserved cytoplasmic motif, while chronic stimulation of APP-Goα signaling in transfected cells provokes Ca2+ overload and apoptosis. Mutated forms of APP linked with AD can also hyperactivate Goα, while the severity of AD symptoms in human patients corresponds with a general elevation in G protein activity. Until recently, however, authentic roles for APP-Goα signaling remained controversial. Using insect models as convenient in vivo assays, we demonstrated that APP family proteins regulate Goα-dependent neuronal guidance in the developing nervous system. Likewise, we showed that APP- Goα signaling controls the motile behavior of cultured murine hippocampal neurons. Based on these studies, we have now discovered that Aβ oligomers may cause aberrant APP-Goα signaling in cultured neurons, resulting in the loss of dendritic complexity and synaptic function. Accordingly, we will explicitly test the hypothesis that neurotoxic forms of Aβ disrupt the APP-Goα signaling pathway. In Aim 1, will first define the normal role of APP-Goα signaling in cultured mouse hippocampal neurons. We will use a combination of biochemical assays, gene knockdown and re-expression methods, and advanced imaging strategies to define how APP-Goα signaling regulates synaptic formation and function. In Aim 2, we will test how neurotoxic forms of Aβ affect aspects of synaptogenesis and function that are regulated by APP-Goα signaling, complemented by experiments using APP knockout mice and a transgenic line that overexpresses human Aβ. In Aim 3, we will use human brain samples to evaluate how APP-Goα interactions change over the course of AD, compared to healthy age-matched controls. Future studies will focus on identifying downstream effectors that provoke neurodegenerative responses when the APP-Goα pathway is misregulated. Public Heath Relevance: Defining the mechanisms by which misregu...