Deciphering the Glycan Code in Human Alzheimer's Disease Brain

Abstract: Alzheimer’s disease (AD) is a devastating diagnosis and there is a critical need to understand the fundamental molecular pathogenesis of AD to design effective therapies. In addition to the well-known AD pathologies, perturbed glucose metabolism is also a clinical feature of AD. Glycogen and N-linked glycans are two critically important but understudied facets of glucose metabolism. Both glycogen and N-linked glycans are complex carbohydrates that play vital roles in brain physiology such as cognition, memory formation, and life span. Despite the importance of these pathways in normal brain function, whether complex carbohydrate metabolism are perturbed during AD disease progression remains a critical knowledge gap in neurobiology. In exciting preliminary data, we discovered profound glycogen accumulation and protein hyperglycosylation in the prefrontal cortex of both mouse models of AD and human AD specimens. Further, we found a positive correlation between increased glycogen and Braak staging in an analysis of a 97-patient cohort. Finally, oral glucosamine supplement, a precursor to UDP-N-acetylglucosamine biosynthesis, building block of N-linked glycans further exacerbated hyperglycosylation and led to poorer cognitive performance in the 5xFAD mouse model of AD. Based on these preliminary data, we hypothesize that aberrant complex carbohydrate metabolism are pathogenic processes during AD disease progression. The major objective of this study is to systematically resolve cellular and extracellular origins of perturbed complex carbohydrate metabolism using state-of-the-art single cell technologies. We will achieve this through synergistic integration of multi-parameter single-cell mass spectrometry imaging methodologies. First, we will define complex carbohydrates with clinical course and disease progression in patient samples (Aim 1). Then, we will interrogate cellular and extra-cellular architecture in normal and AD patient samples (Aim 2). Finally, we will apply multimodal integration to track cellular and extracellular origins of complex carbohydrate perturbation in AD (Aim 3). This study will provide critical new information regarding ideal cell-, region- and temporally-specific opportunities for therapeutic modulation of AD. Collectively, we believe the resultant findings from this proposal will be highly salient for multiple related fields of Alzheimer’s disease and other neurodegenerative disorders.