O-GLCNAC HOMEOSTASIS REGULATES MITOCHONDRIAL FUNCTION IN ALZHEIMER'S DISEASE

University Of Kansas Medical Center, Kansas City KS

Investigators

Abstract

Project Summary: Currently, 6.9 million Americans are suffering from Alzheimer's disease (AD), which is the only major disease lacking good prevention methods, treatments, or a cure. Our objective is to determine the mechanisms as to how nutrient sensing as interpreted by O-GlcNAcylation, a dynamic single sugar modification, influences mitochondrial function in Alzheimer's disease (AD). O-GlcNAc is categorized by the addition of a single O- linked β-N-acetyl-D-glucosamine moiety to serine/threonine amino acids of nuclear and cytoplasmic proteins. This modification is responsive to extracellular signals such hormones, nutrients, and environmental cues and is involved in regulating numerous cellular functions such as the cell cycle, stress response, transcription, and translation. The enzymes responsible for processing the modification are O-GlcNAc transferase (OGT), which adds the modification, and O-GlcNAcase (OGA), which removes the modification. Importantly, changes in O- GlcNAcylation alter mitochondrial function. Cells actively maintain homeostatic levels in O-GlcNAc, and cells will alter the expression of OGT and OGA to modulate O-GlcNAcylation due to changes in the environment. We hypothesize that the loss of O-GlcNAc homeostasis causes mitochondrial dysfunction promoting the onset and progression of AD. Supporting this hypothesis, we recently demonstrated that O-GlcNAc regulates mitochondrial respiration, mitophagy, and mitochondrial retrograde signaling; thus, we generated two specific aims to test this hypothesis, and we have developed several O-GlcNAc related tools to accomplish our goals. In aim 1, we will elucidate O-GlcNAc mechanistic control of mitochondrial function by identifying the OGT and OGA mitochondrial interactome in control and AD mitochondria and test how these interactions impact mitochondrial function; identify electron transport proteins that prefer to interact with O-GlcNAcylated proteins and how these interactions affect energetics; elucidate the function of O-GlcNAc on PINK1 (PTEN Induced Kinase 1), which is key regulator of mitophagy, and lastly explore sex-specific effects of OGA inhibition (a potential AD therapeutic) on mitochondrial function. These data will provide novel mechanistic information on how O-GlcNAc and the functions of OGT and OGA contribute to mitochondrial function and AD development. In our second aim, we will ascertain how altered O-GlcNAc nutrient sensing affects mitochondrial retrograde signaling to the nucleus. We identified that the function of retrograde signaling transcription factors ATF4 (Activating Transcription Factor 4) and NRF2 (Nuclear Factor erythroid 2) are modulated by O-GlcNAc. We will employ a novel CRISPR based targeting of OGT and OGA to ATF4 and NRF2 target gene promoters to determine how O-GlcNAcylation organizes cis-regulatory elements at these promoters. Next, we will identify how O-GlcNAc on NRF2 affects NRF2 function. Together, these data will demonstrate the role of O-GlcNAc homeostasis in regulating nuclear mitochondrial gene expression through mitochondria retrograde signaling. Collectively, these results will provide new mechanistic pathways in our understanding of AD.