Age is a major risk factor for developing Alzheimer's disease (AD) for which the pathophysiological processes may begin more than a decade prior to the onset of symptoms. We have found that AD is associated with epigenetic biomarkers of age (epigenetic clock) based on DNA methylation levels. However, it is unknown to what extent existing and novel epigenetic biomarkers can capture the true biological age of the brain and whether epigenetic changes mediate the risk of chronological change on AD susceptibility. To address these questions, there is a critical need for a comprehensive large scale study of DNA methylation in the context of AD neuropathology both in humans and suitable mouse models of AD. The resulting data will allow us and others to characterize age-related DNA methylation changes that associate with and contribute to the pathologic changes of AD. The overarching goals of this proposal are a) to establish the role and impact of epigenetic brain aging in the development and progression of AD and b) to develop novel biomarkers or combinations of biomarkers that can be used to characterize different types of AD. Using a well-validated Infinium DNA methylation array that applies to both humans and preclinical models, this proposal will generate high-quality DNA methylation profiles from human postmortem brain tissues and murine models of AD. To develop these biomarkers, genome-wide DNA methylation data will be integrated with complementary neuropathological findings - synaptic loss, amyloid deposition, abnormally phosphorylated tau, neurofibrillary tangle formation, neuro-inflammatory markers to arrive at epigenetic biomarkers of AD neuropathology and brain aging. The investigative team has broad expertise conducting cross disciplinary research spanning Alzheimer's disease, neurobiology of aging, epigenomics, mouse models of AD, and biomarker development. By leveraging a large sample size (four brain regions from human, mouse, and rat), a battery of established measures of neuropathology, clinical history and state of the art statistical methodologies, we will develop and evaluate epigenetic biomarkers of brain aging that promise to elucidate epigenetic risk factors for AD development and progression. These findings have the potential to both further our understanding of epigenetic mechanisms underlying AD and epigenetic biomarkers for future therapeutic interventions. These investigations will result in (a) the validation and development of DNAm biomarkers for clinical and preclinical studies of Alzheimer's disease and (b) context-of-use statements that fully describe the purpose and use of each biomarker.