Project Summary/Abstract We will determine the effects of APP and APP proteolytic products on mitophagy and bioenergetic function. We hypothesize that amyloid precursor protein (APP) facilitates mitophagy through direct interactions with PINK1 and p62. We further hypothesize that loss of APP expression or reduced mitochondrial localization affects mitochondrial function through inhibition of mitophagy. Metabolic deficiencies are prominent in Alzheimer’s disease (AD). A clear relationship between amyloid precursor protein (APP) and mitochondria is described in the literature but the function of APP at mitochondria is not well understood. APP and Aβ localize to mitochondria and can alter mitochondrial function. Our data show that mitochondrial membrane potential directly correlates with Aβ production and APP mitochondrial localization. Under conditions of increased mitophagy APP mitochondrial localization is increased. Our data indicate loss of APP at mitochondria or loss of APP expression, reduces mitochondrial electron transport chain (ETC) function and mitophagy. Overall, our data support a role of APP in modulating mitophagy and bioenergetic flux. A current gap in our knowledge is if these observations are attributed to full-length APP or APP processing products. We will address this knowledge gap here. A relationship between mitochondria, bioenergetics, mitophagy, and APP is evident. Our data support a relationship between APP localization at mitochondria, bioenergetic function, and mitophagy. We hypothesize that loss of APP at mitochondria alters bioenergetic flux (Aim 1) and mitochondrial localized APP facilitates mitophagy (Aim 2). The overall goal of this study is to understand the role of APP and its derivatives in mitophagy and bioenergetic flux. We will use in vivo and in vitro models across two aims. In vitro models include engineered induced pluripotent stem cells (iPSC) cells with either wild-type (WT) APP, APP knockout, or mitochondrial localization incompetent APP (3M APP) expression. Engineered iPSCs will be differentiated to neurons and astrocytes. In vivo models will include non-transgenic, transgenic WT APP mice and APP knockout mice. Use of both in vivo and in vitro models allows for elucidation of cell type specific effects (in vitro models) and sex differences (in vivo). We will measure endpoints in the models proposed under native conditions and under conditions where APP processing is inhibited or increased. We will determine the role of full-length APP versus APP processing products in mitophagy and bioenergetic flux pathways.