Tet-mediated Epigenetic Regulation in Alzheimer's Disease

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PROJECT SUMMARY AD is caused by the progressive decay of neuronal connections ultimately leading to neuronal death. Loss of homeostatic neuronal function leads to severe cognitive decline in patients, inhibiting their ability to function in day-to-day life without extensive help from healthcare providers. The causes of AD are largely unknown; however, our current understanding recognizes that genetic, epigenetic, and environmental factors play a role in the disease. As epigenetic modifications are influenced by environmental factors and influence gene expression, they serve as a mediator between an individual’s genetic composition and phenotypic characteristics. Thus, epigenetic modifications hold promise to explain a significant portion of the missing heritability of AD, and several links between the epigenome, TET2, and AD have already been uncovered. Here we aim to identify novel TET2 variants associated with AD, and examine both how these variants and a reduction in abundance of TET2 lead to dysregulation of the methylome and how these alterations contribute to AD pathogenesis. Through examining the influence of TET on AD, we will advance our understanding on the role DNA hydroxymethylation plays in the brain regions most adversely affected by AD and how these changes influence gene expression, AD pathology, and learning and memory. Previously, our lab shed light on the role 5mC and 5hmC modifications play in neurodevelopment and several neurological disorders. Additionally, our lab identified differentially hydroxymethylated sites enriched in AD patients relative to controls and characterized the global 5hmC prevalence in an AD mouse model. More recently, we produced preliminary data to show enrichment of TET2 loss of function variants in individuals with early onset Alzheimer’s disease (~1.4% cases versus 0.12% controls). Building upon these previous findings, we will manipulate 5hmC modification profiles in an Alzheimer’s disease mouse model to investigate how dysregulation of TET enzymes contributes to AD pathogenesis. In conjunction with characterization of the methylome (measured via 5hmC Capture), we will analyze gene expression (measured via RNA-seq) and AD progression (measured via behavioral assays, and immunohistochemistry of Aβ plaques and neuronal populations) in wildtype and 5XFAD, a beta-amyloid plaque AD mouse model. These assays will be performed on tissues collected from the cortex and hippocampus. Our long-term goal is to identify novel AD associated TET2 mutations and how mutations in TET enzymes disrupt the balance of 5hmC signatures. Our findings may provide greater insight on genomic variants that contribute to AD risk, specific 5hmC profiles with the potential to be used as biomarkers for AD as well as variations in 5hmC profiles which confer AD pathogenicity or protection.