This supplement responds to NOT-AG-20-034: Notice of Special Interest: Alzheimer's-focused administrative supplements for NIH grants that are not focused on Alzheimer's disease. Alzheimer's disease (AD) remains a looming public health crisis, despite intensive research and pharmaceutical efforts. No effective treatment option is currently available that can halt the disease process. The recent failures of several high-profile clinical trials targeting the amyloid plaques and neurofibrillary tangles, the pathological hallmarks of AD identified by Dr. Alois Alzheimer more than a century ago, suggest that new ideas and new directions in delineating the pathogenic mechanisms of AD should be pursued before effective treatment of the disease can be developed. In the parent grant, we propose to elucidate fundamental mechanisms governing neuronal maintenance by mechanistic target of rapamycin (mTOR) signaling. We identified co-translational quality control of mitochondrial outer membrane-associated translation as a key event in mitochondrial protection under stress, and showed that it is regulated by the conserved PINK1-mTOR signaling pathway implicated in Parkinson's disease (PD). In the process, we found that this quality control pathway is also involved in other neurodegenerative disease settings, including AD. In this Supplement Project, we will test the hypothesis that the biogenesis of APP requires adequate co-translational quality control activity, the insufficient supply of which due to aging or metabolic stress can result in perturbed proteostasis that contributes to or initiates AD. To enhance the disease relevance of this project, we propose to use AD mouse model and patient-derived cellular models to test this hypothesis. Two Specific Aims are proposed: Aim 1: Using AD patient fibroblasts and induced pluripotent stem cell (iPSC)-derived neurons to test the roles of co-translational quality control in proteostasis. Aim 2: Using the 5xFAD mouse model to test the effect of genetic manipulation of co-translational quality control activity on amyloid plaque formation and behavior. It is anticipated that at the end of this Supplement Project, we will have obtained concrete evidence of the involvement of co-translational quality control in the biogenesis of APP, establishing defective co- translational quality control as potentially one of the earliest pathogenic events of AD. This may profoundly impact our understanding of AD pathogenesis and stimulate novel and rational therapeutic strategies for the treatment and prevention of AD as well as other devastating neurodegenerative diseases in which impaired co- translational quality control has been implicated.