Single-cell transcriptomics profiling of Alzheimer’s disease pathology in asymptomatic individuals across brain and leptomeninges
Embargo Date
2027-03-25
OA Version
Citation
Abstract
Alzheimer's Disease (AD) is a neurodegenerative disorder characterized by cognitive decline and neuronal loss with no known cure. Recent attention has shifted to the roles of brain-resident immune cell types and vascular integrity in disease progression. Some individuals remain cognitively intact despite exhibiting AD pathology, termed asymptomatic Alzheimer’s disease (AsymAD), making them intriguing subjects for research into potential protective mechanisms. The complexity of AD disease requires advanced, systematic techniques like single-cell transcriptomics to decipher underlying molecular players of cognitive impairment. In this thesis, we employed single-nucleus RNA sequencing to explore transcriptional changes in AsymAD, focusing on the leptomeninges and the temporal lobe. We performed snRNA-seq of the leptomeninges, which is the area that resides above the brain, is protected by tight barriers, and contains the major blood vessels. By sequencing samples from AD, AsymAD, and control patients, we uncovered diverse cell types of human leptomeninges, including fibroblast-like, vascular, and resident immune cell types. Gene set enrichment analysis (GSEA) revealed increased cytoskeleton- and extracellular matrix-related gene sets in AD vascular cell types, indicative of vascular leakage, while AsymAD showed enrichment in IFNγ-related gene sets alongside controls. We hypothesized that increased IFNγ expression in AsymAD helps with vascular integrity. An iPSC-based blood-brain barrier (BBB) model confirmed the barrier integrity-enhancing effects of IFNγ, supporting our hypothesis. GSEA on macrophages revealed decreased antigen presentation in AD; T cells showed reduced T cell activation, suggesting immune dysregulation in AD but not in AsymAD patients.
Next, we performed snRNA-seq on the temporal lobe of AD, AsymAD, and control brains. We conducted a GSEA analysis on each cell type, and endothelial cells showed increased BBB leakage-related gene sets in AD and increased IFNγ gene sets in AsymAD, similar to the leptomeninges regions. Immunohistochemistry of the temporal lobe confirmed the increased BBB leakage in AD but not AsymAD. The GSEA analysis of brain-resident antigen-presenting cells, microglia, showed increased antigen presentation in AsymAD while it was decreased in AD, suggesting dysfunctional antigen-presentation in AD. Immunohistochemistry of microglia cells immunolabeled for MHC class II proteins showed reduced cell surface expression in AD microglia, indicating non-functional MHC presentation in AD conditions while this was preserved in AsymAD. Ligand-receptor signaling inference analysis on leptomeninges and the temporal lobe showed increased signaling in MHC class II, T cell activation co-stimulatory signals in AsymAD. Analysis of cell type-specific AD GWAS genes and SNPs revealed that disruption of processes associated with T cell activation in microglia and macrophages is likely a contributing factor to the pathogenesis of AD. Together, these findings strongly implicate defective antigen presentation as a causal component in AD disease progression, and preservation of these pathways in AsymAD might be the cause of cognitive resilience. Overall, the results herein indicate that increased IFNγ expression in AsymAD may underpin cognitive resilience by preserving the integrity of both the blood-brain barrier and immune regulation at the level of antigen presentation; each of these findings offers new therapeutic avenues for the prevention and treatment of AD.
Description
2024
License
Attribution-NonCommercial-NoDerivatives 4.0 International