Repeated sleep deprivation selectively reactivates hippocampal CA1 pyramidal neurons

Sleep supports a variety of physiological processes, ranging from metabolic to immune system homeostasis, and plays a critical role in cognition and memory. A brief period of sleep loss impairs memory, particularly hippocampus-dependent memories, alters molecular signaling, and synaptic plasticity in the hippocampus. Studies have shown that sleep deprivation (SD) alters neuronal activation as indicated by broad changes in gene expression signatures and by the increased expression of c-Fos, an immediate early gene that functions as a molecular marker of neuronal activity. In the present study, we examined hippocampal subregion-specific c-Fos induction patterns via immunohistochemical staining. We found that CA1 pyramidal neurons exhibit the most robust c-Fos induction after SD. Using an activity-driven ribosomal tagging system (c-Fos-RiboTag) and a repeated SD model, we labeled sleep deprivation activated CA1 neurons and observed a population of excitatory neurons in area CA1 that are reactivated by repeated SD. Using the c-Fos-RiboTag system that enables the isolation of ribosomes with attached mRNA from labeled neurons, we performed fosTRAP-seq and identified activity-dependent gene expression changes in c-Fos+ CA1 neurons. Our results revealed that synapse organization, protein dephosphorylation, cellular response to endogenous stimulus (such as insulin) are upregulated, whereas mRNA processing and splicing are downregulated. In summary, our study provides a detailed characterization of hippocampal neuronal activation following SD and identifies a subset of CA1 pyramidal neurons that are selectively reactivated by repeated SD. This SD-sensitive neuronal population enables investigation of molecular changes in neurons specifically impacted by sleep loss and suggests a potential connection between acute and chronic sleep loss at the cellular and molecular levels.