Single-cell RNA sequencing reveals B cell–related molecular biomarkers for Alzheimer’s disease

Abstract

In recent years, biomarkers have been integrated into the diagnostic process and have become increasingly indispensable for obtaining knowledge of the neurodegenerative processes in Alzheimer’s disease (AD). Peripheral blood mononuclear cells (PBMCs) in human blood have been reported to participate in a variety of neurodegenerative activities. Here, a single-cell RNA sequencing analysis of PBMCs from 4 AD patients (2 in the early stage, 2 in the late stage) and 2 normal controls was performed to explore the differential cell subpopulations in PBMCs of AD patients. A significant decrease in B cells was detected in the blood of AD patients. Furthermore, we further examined PBMCs from 43 AD patients and 41 normal subjects by fluorescence activated cell sorting (FACS), and combined with correlation analysis, we found that the reduction in B cells was closely correlated with the patients’ Clinical Dementia Rating (CDR) scores. To confirm the role of B cells in AD progression, functional experiments were performed in early-stage AD mice in which fibrous plaques were beginning to appear; the results demonstrated that B cell depletion in the early stage of AD markedly accelerated and aggravated cognitive dysfunction and augmented the Aβ burden in AD mice. Importantly, the experiments revealed 18 genes that were specifically upregulated and 7 genes that were specifically downregulated in B cells as the disease progressed, and several of these genes exhibited close correlation with AD. These findings identified possible B cell-based AD severity, which are anticipated to be conducive to the clinical identification of AD progression.

Alzheimer’s disease: A new biomarker for disease progression?

Molecular tests built around analyzing B cells, a specialized type of immune cell, could aid in the diagnosis of Alzheimer’s disease. Liu-Lin Xiong from the Affiliated Hospital of Zunyi Medical University, China, and coworkers used single-cell RNA sequencing to profile gene activity in individual peripheral blood mononuclear cells from people with and without Alzheimer’s disease. They discovered that people with Alzheimer’s, especially those with more advanced disease, had lower levels of circulating B cells than healthy subjects. Twenty-five specific genes in the B cells were expressed at significantly higher or lower levels as the disease progressed. The researchers found similar results regarding B cells and Alzheimer’s progression in mouse models, and showed that massive depletion of B cells in the early onset was associated with accelerated cognitive decline and increased accumulation of sticky brain plaques.