Increasing H2B Monoubiquitination Improves the Transcriptome and Memory in the Aged Hippocampus

Abstract

A decline in cognitive abilities is associated with the aging process, affecting nearly 33% of US adults over the age of 70, and is a risk factor for the development of dementia and Alzheimer's disease. Several studies have reported age-related alterations in the transcriptome in the hippocampus, a major site of memory storage that is among the first regions impacted with age, dementia, and Alzheimer's disease. However, much remains unknown about why these transcriptional changes exist in the aged hippocampus and how this impacts memory late in life. Here, we show that monoubiquitination of histone H2B (H2Bubi), an epigenetic mechanism recently reported to be major regulator of the epigenome and transcriptome during memory formation in the young adult brain, decreases with age in the hippocampus of male rats. In vivo CRISPR-dCas9-mediated upregulation of Rnf20, the only ubiquitin E3 ligase for H2B, in the hippocampus significantly improved memory retention in aged rats. Remarkably, RNA-seq analysis revealed that in addition to the 18 genes typically upregulated in the aged rat hippocampus following contextual fear conditioning, Rnf20 upregulation caused learning-related increases and decreases in 40 and 11 unique genes, respectively, suggesting that these 51 genes may be among those most critical for improving memory in advanced age. Together, these data suggest that H2B monoubiquitination is a significant regulator of age-related dysregulation of the transcriptome and impairments in memory.