Enhancing microglia-dependent plaque clearance in the Alzheimer disease brain by targeting Ifi27l2a expression

摘要

Abstract Alzheimer’s disease (AD) and cerebral amyloid angiopathy (CAA) are devastating aging-associated neurodegenerative diseases which involve pathological deposition of amyloid-beta (Aβ) in the brain parenchyma and around the leptomeningeal vasculature. Aβ uptake in microglia (MG) is strikingly reduced with age, which may contribute to reduced amyloid clearance and increased plaque accumulation. Recently, a novel subset of MG with a distinct gene expression signature (“disease- associated microglia”; DAM) have emerged as a critical player in phagocytosis of Aβ in AD. Using unbiased analysis of single-cell RNA sequencing (scRNAseq), we discovered that Interferon alpha- inducible protein 27-like protein 2A (Ifi27l2a) is the most highly upregulated gene in MG following ischemic stroke, with a greater increase in aging. Using this finding as a launch point, we then examined if similar upregulation occurred in conditions of AD and CAA. We subsequently found that Ifi27l2a mRNA expression is significantly elevated in the brain of symptomatic TgSwDI mice – a mouse model which develops both vascular and parenchymal Aβ deposits. In human brain samples, we found significantly elevated Ifi27l2a protein expression in MG in sections from patients with confirmed CAA and AD pathology versus non-disease age-matched controls. We also found upregulation of Ifi27l2a in a human microglial cell line (HMC3) following inflammatory challenge. Our scRNAseq analysis of the MG population showed a positive correlation between Ifi27l2a expression and inflammatory genes and a negative correlation with phagocytic (and DAM-identifying) genes. In light of our new findings regarding the role of Ifi27l2a in MG/DAM phenotype and the known role of MG in Aβ clearance, we now propose to explore the novel role of Ifi27l2a in regulating MG phagocytic function and Aβ clearance using a mouse model which demonstrates both vascular and parenchymal amyloid plaque formation (TgSwDI). We will test our model in which elevated Ifi27l2a expression in MG promotes reduced phagocytic capacity and thus impaired clearance of Aβ. In aim 1, we will examine potential mechanisms of post-transcriptional Ifi27l2a regulation. We will use primary MG (cultured from aged mouse brain) and a human MG cell line to determine the contribution of two in silico predicted microRNAs on Ifi27l2a level and on resulting phagocytic function. In aim 2, we will demonstrate the in vivo role of Ifi27l2a in regulating MG/DAM phagocytic phenotype and determine the potential for Ifi27l2a down-regulation to promote enhanced clearance of vascular and parenchymal Aβ plaques. For these studies, we will use TgSwDI mice at a stage where Aβ vascular deposits and parenchymal plaques are evident. If successful, these studies would provide the basis for new approaches for enhancing clearance of Aβ aggregates in the brain.