Ethnic-specific Effects of Mitochondrial DNA Variants and Environmental Factors on Cognitive Functioning and Dementia

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Among U.S race/ethnic groups over 75 years of age, African Americans exhibit the highest cognitive impairment prevalence (32%) followed by Hispanics (23%) and Non-Hispanic Whites (10%). Our proposal implements multiple novel genomic tools designed to capture ethnic-specific targets of Alzheimer's disease (AD) and related dementias (ADRD) within the mitochondrial DNA. A novel aspect of our proposal is that we can rapidly translate human mitochondrial genetic associations into cellular and animal experimental paradigms and infer whether these mtSNPs modify mitochondrial-derived peptides (MDPs), which are a group of micro-peptides that display profound effects on metabolic and neurodegenerative disease processes. We provide evidence in this proposal that we have already identified three mtSNPs in Non-Hispanic Whites, African Americans, and Hispanics that associate with AD phenotypes in an ethnic-specific fashion through MDPs. In this proposal, we will conduct several novel genetic analyses: (1) Mitochondrial Genome Wide Association Studies (MiWAS), (2) Mitochondrial Genome Wide GxE and GxG Interaction Studies (MiWIS), and (3) mitochondria RNASeq differential expression analysis (mito-transcriptomics), in three large, longitudinal multi-ethnic cohorts with comparable repeated measures of cognitive decline as well as lifestyle and metabolic factors (e.g., body mass index, diabetes, and physical activity). Using the Health and Retirement Study (HRS) and REasons for Geographic And Racial Differences in Stroke (REGARDS) cohorts, we will conduct discovery MiWAS and MiWIS for Non-Hispanic Whites (n~14,300), African Americans (n~13,400), and Hispanics (n~2,420). We will test replication of findings from HRS and REGARDS on cognitive decline and diagnosis of clinical AD using the diverse Rush Alzheimer's Disease Center (RADC) cohorts (n~4,500). We will conduct mito-transcriptomics for all ethnic groups in HRS (n~4,000; white blood cells) and in RADC (n~640; brain prefrontal cortex). Our central hypothesis is that specific mtSNPs and mitochondrial gene expression will predict clinical AD diagnosis and cognitive decline differently by ethnicity. For this project, we have assembled an interdisciplinary team to: 1) Identify ethnic-specific mtSNPs that predict cognitive decline, ADRD, and AD. 2) Identify ethnic-specific mtSNPs that interact with lifestyle factors or nuclear SNPs to affect cognitive decline, ADRD, and AD. 3) Investigate whether genes that encode mitochondrial-derived peptides are differentially expressed relative to AD or ADRD status in different ethnicities. This project permits discovery of mitochondrial genetic targets that can be explored as precision-based, ethnic-specific, potential ADRD treatment targets, in the form of micro-peptides derived from the mitochondria. Findings from this proposal will be instrumental to AD therapeutic discovery because the makeup of the national population is becoming more ethnically diverse.