MicroRNAs in CNS-derived extracellular microvesicles as peripheral blood biomarkers for Alzheimer disease

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Summary In this study we propose to address several major challenges in current Alzheimer disease (AD) biomarker research, specifically: 1) limited accessibility and high expense associated with neuroimaging measurements, 2) difficulties in developing antibody-based, quantitative protein assays for most novel candidates and significant variability among existing immunoassays, 3) invasive sampling inhibiting widespread use of CSF-based biomarkers, 4) low sensitivity/specificity and/or lack of validation in relatively large cohorts for blood-based markers, and, 5) detection of AD at early or even preclinical stages. To these ends we will target microRNAs packaged in central nervous system (CNS) derived extracellular microvesicles (EMVs) in blood plasma. microRNAs are a class of small, non-coding RNAs playing important roles in many cellular processes by post- transcriptional regulation of protein levels, and aberrant microRNA expression has become an emerging theme for a wide variety of diseases including AD and other neurodegenerative disorders. microRNAs found in body fluids can be routinely and reliably measured by well- established methods (e.g., RT-PCR), and data shows EMVs transport biomolecules between the CNS and peripheral blood and their cargo proteins and nucleic acids vary by cell of origin. Measurement of cargo proteins in such EMVs has shown particular promise in identifying blood- based biomarkers for AD and mild cognitive impairment (MCI, or prodromal AD). In a pilot R21 study, we employed global profiling of microRNAs in CNS-derived, relatively neuron-specific (L1CAM-positive) EMVs in plasma and identified many microRNA and other small RNA transcripts to be differentially expressed between AD and healthy controls, between AD and Parkinson disease, or between disease stages. Here, we aim to confirm and validate the identified candidates for AD/MCI diagnosis, differential diagnosis, and disease progression in several large, well-established cohorts, including Alzheimer's Disease Research Centers (ADRCs) affiliated with the University of Washington and University of Pennsylvania, and ADNI (Alzheimer's Disease Neuroimaging Initiative), with cross- sectional and longitudinal samples collected, along with extensive clinical characterization. In parallel, we will use global profiling methods to identify additional microRNA candidates in different CNS cell type- or neuronal subpopulation- specific EMVs in plasma. Finally, to improve early or pre-clinical diagnosis, we will evaluate potential microRNA biomarkers in a very early MCI cohort, subjects at elevated risk for AD. Our project design is geared towards the production of a panel of biomarkers that is more robust, repeatable, and clinically accessible than currently available.