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Hippocampal neurons’ cytosolic and membrane-bound ribosomal transcript profiles are differentially regulated by learning and subsequent sleep

ABSTRACT: The hippocampus is essential for consolidating transient experiences into long-lasting memories. Memory consolidation is facilitated by postlearning sleep, although the underlying cellular mechanisms are largely unknown. We took an unbiased approach to this question by using a mouse model of hippocampally mediated, sleep-dependent memory consolidation (contextual fear memory). Because synaptic plasticity is associated with changes to both neuronal cell membranes (e.g., receptors) and cytosol (e.g., cytoskeletal elements), we characterized how these cell compartments are affected by learning and subsequent sleep or sleep deprivation (SD). Translating ribosome affinity purification was used to profile ribosome-associated RNAs in different subcellular compartments (cytosol and membrane) and in different cell populations (whole hippocampus, Camk2a+ neurons, or highly active neurons with phosphorylated ribosomal subunit S6 [pS6+]). We examined how transcript profiles change as a function of sleep versus SD and prior learning (contextual fear conditioning; CFC). While sleep loss altered many cytosolic ribosomal transcripts, CFC altered almost none, and CFC-driven changes were occluded by subsequent SD. In striking contrast, SD altered few transcripts on membrane-bound (MB) ribosomes, while learning altered many more (including long non-coding RNAs [lncRNAs]). The cellular pathways most affected by CFC were involved in structural remodeling. Comparisons of post-CFC MB transcript profiles between sleeping and SD mice implicated changes in cellular metabolism in Camk2a+ neurons and protein synthesis in highly active pS6+ (putative "engram") neurons as biological processes disrupted by SD. These findings provide insights into how learning affects hippocampal neurons and suggest that the effects of SD on memory consolidation are cell type and subcellular compartment specific.

ORGANISM(S): Mus musculus

PROVIDER: GSE216163 | GEO | 2022/10/25

REPOSITORIES: GEO

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Project description:Sleep has been strongly implicated in learning and especially in the reprocessing of recently acquired memory. Children with intellectual disability (ID) tend to have sleep-wake disturbances, which may contribute to the pathophysiology of the disease. As far as sleep is, in part, a circadian process, we decided to study rhythmic gene expression in hippocampus, a brain structure, which plays a key role in memory in human and rodents. By investigating the transcriptome of mouse adult hippocampus, we report here the identification of 663 circadian rhythm (CR)-regulated genes, which have been clustered in four categories, based on their temporal pattern of expression. In addition to the standard core-clock genes, enrichment analysis of the hippocampal CR-regulated genes revealed the presence of several transcription factors, underlying the existence of an inter-regulation of genes' expression between clusters. Interestingly, these hippocampal circadian rhythm-regulated genes are very enriched in sleep/wakefulness related genes. We show here that glucocorticoid signaling, already shown to be involved in memory regulation, is a circadian regulated pathway in hippocampus. Furthermore, we identified a list of 30 CR-regulated ID genes. Our results demonstrate that hippocampus can be considered as a peripheral oscillator and illustrate the link between circadian rhythm, sleep, intellectual disability and memory consolidation. In order to identify circadian rhythm-regulated genes in mouse hippocampus, we realized a study in dark-dark conditions, thus allowing to overcome the effects induced by light changes. To systematically identify genes with circadian regulated expression, RNA samples from the hippocampus of three mice at four Circadian Time (CT) points were used for expression profiling using Agilent microarray technology. The dark/dark period started at 7 p.m. The Circadian Time (CT) 18 samples were taken after 30 h of continuous dark; the other circadian times followed at 6-h intervals: CT0, CT6 and CT12 after 36, 42 and 48 h of continuous darkness, respectively.

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Hippocampal neurons’ cytosolic and membrane-bound ribosomal transcript profiles are differentially regulated by learning and subsequent sleep

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