Functional and Transcriptional Profiling of Monocytes in Alzheimer's Disease

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Alzheimer’s disease (AD) is the most common age-related dementia, for which there is currently no disease modifying therapy. We submit our revised proposal in which we now provide a detailed description of the design, analysis and interpretation of the single-cell (sc)RNAseq pipeline we will follow to comprehensively profile the transcriptome of AD monocytes in collaboration with Dr. Martin Hemberg, a faculty member at our Center with extensive experience in scRNAseq. Also, we describe alternative functional assays we will perform using Protollin-treated AD monocytes that will be isolated from the newly identified clusters of the scRNAseq analysis. Phagocytic innate immune cells, including CNS-resident microglia and infiltrating peripheral monocytes/macrophages, lose their ability to restrict Aβ accumulation and contribute to the disease. It has been shown that AD monocytes have impaired uptake and degradation of Aβ, though investigations in this area are limited and published studies are only at the level of total blood monocyte. We applied single cell RNA-seq to perform unbiased transcriptional analysis of peripheral CD14+ monocytes from two early symptomatic AD patients and two sex, age-matched healthy individuals. We found that monocyte subsets from AD patients acquire unique transcriptional signatures compared to healthy donors. The differentially expressed genes we identified are involved in the interferon, antigen presentation, phagosome and chemotaxis pathways and indicate that AD peripheral monocyte subsets acquire transcriptional signatures that may lead to altered immune properties that contribute to the disease. Furthermore, we have previously shown that Protollin, a proteosome- based adjuvant ameliorates disease in AD mouse models by clearing brain amyloid and in new preliminary data we have found that in vitro treatment of human monocytes with Protollin induces increased soluble Aβ uptake. We hypothesize that peripheral monocytes from AD patients undergo changes at the transcriptional and functional level which impair their homeostatic properties and promotes disease development and that in vitro stimulation of AD monocyte subsets with Protollin can modulate their endogenous AD signature and promote a beneficial functional phenotype. We will address our hypothesis in the following specific aims. Aim 1: Transcriptional and functional profiling of monocyte subsets from AD patients. Aim 2: Modulation of AD monocyte subsets by stimulation with Protollin. Our studies will for the first time define a unique AD transcriptional signature and altered functional characteristics of AD monocytes. We will investigate an immune modulating treatment that could ultimately be tested in patients.