Early synaptic gene expression downregulation in the frontal cortex distinguishes Alzheimer’s disease from normal aging in a genetically diverse mouse population

Abstract

AbstractBackgroundThe frontal cortex is critical to many cognitive processes and is vulnerable to pathology and neurodegeneration in Alzheimer’s disease. Cortical dysfunction and impaired connectivity in the frontal cortex have also been observed in “normal” age‐related cognitive decline, suggesting common mechanisms contributing to both age‐related and AD‐related cognitive decline. The divergence that may lead to AD versus normal aging, however, is unclear.MethodHere, we have used genetically diverse mouse populations modeling either AD or normal aging, the AD‐BXDs and their nontransgenic littermates (Neuner et al, Neuron, 2019). We measured cognitive function from early (6mo) to middle (14mo) adulthood to capture presymptomatic and advanced AD stages and early aging processes. We performed bulk RNAseq from the frontal cortex, followed by age‐ and AD‐related differential gene expression analysis and Weighted Gene Coexpression Network Analysis (WGCNA) to identify genes and gene networks whose expression is associated with normal and pathological aging.ResultIn both differential gene expression analysis and WGCNA, we found common mechanisms underlying normal aging and AD (e.g., upregulation of inflammation‐related gene pathways). We also found that downregulation of genes and gene networks associated with synaptic function specifically occurred in AD and not in normal aging, suggesting that early synaptic dysfunction and/or synaptic loss is a unique feature of AD that distinguishes it from normal aging processes. Based on differential gene expression, network analyses, presence of high‐impact variants across the BXD panel, and association with cognitive function, we identified one gene candidate, B230209E15Rik, a lncRNA, as a potential regulator of synaptic gene networks in the frontal cortex that promotes resilience to cognitive decline in AD.ConclusionOverall, our data indicate that cognitive aging and AD may share common neuroimmune activation and dysregulation of neuronal maintenance, but that AD, and particularly late AD, is uniquely characterized by synaptic dysfunction. We nominate an intriguing candidate, B230209E15Rik, as a potentially key driver of synaptic gene regulation in the frontal cortex. In order to elucidate the mechanism by which this gene may promote cognitive resilience in AD, we are currently validating this finding in vivo.