ABSTRACT Effects of mRNA m6A methylation and its YTHDF reader proteins on human AD mRNA homeostasis Alzheimer’s disease (AD) is the leading cause of dementia in the United States but has no disease-modifying treatments. Epigenetic regulation has been shown to play pivotal roles in neurodevelopment and neurodegenerative disorders. In addition to DNA and histone modifications, more than 150 post-transcriptionally modified ribonucleosides have been identified in various types of RNA. Studies in the past decade suggest that post-transcriptional mRNA modifications can notably affect gene expression. For example, about 0.4-0.6% of all adenosines in mammalian mRNA are N6-methyladenosine (m6A) methylated. Lack of m6A methylation is lethal in mammals. We have shown that mRNA m6A methylation is critical to neuronal functions and enriched in AD- related transcripts. This methylation can be recognized by reader proteins such as YTHDF1, YTHDF2 and YTHDF3. The mRNA m6A methylation and its binding by different reader proteins play critical roles in cellular RNP granule dynamics, which dramatically affect mRNA metabolism and translation. We have observed notable changes of YTHDF proteins in AD brain tissues versus normal controls. In this Supplement, we hypothesize that aberrant YTHDF levels affect both methylation-dependent and methylation- independent stabilization of human mRNAs. This effect may also alter cellular RNP granule dynamics, leading to aberrant mRNA metabolism and translation in AD brains. To test this hypothesis, we will conduct a quantitative genome-wide brain m6A mapping using a newly developed m6A-SAC-seq protocol to identify m6A alterations associated with AD. We will also map precise RNA binding sites of all three YTHDF proteins in AD samples and controls. By integrating RNA-seq data, m6A map and YTHDF binding results we will evaluate effects of YTHDF downregulation on mRNA stability and cellular RNP granule changes. These changes may underline AD pathogenesis in patients and may suggest new intervention strategies.