# Sleep rescues age-associated loss of glial engulfment

## TL;DR

This study shows that sleep can restore the ability of glial cells to clear damaged neurons in aging fruit flies, linking sleep loss to age-related cognitive decline.

## Contribution

The study demonstrates that sleep rescues age-related glial dysfunction and identifies molecular pathways affected by aging and sleep loss.

## Key findings

- Sleep restoration in aged flies improves glial clearance of damaged axons.
- Sleep enhances the induction of the phagocytic protein Draper in aged flies.
- Aging leads to loss of transcriptional induction of autophagy and ribosomal genes in glia after injury.

## Abstract

Neuronal injury due to trauma or neurodegeneration is a common feature of aging. The clearance of damaged neurons by glia is thought to be critical for maintenance of proper brain function. Sleep loss has been shown to inhibit the motility and function of glia that clear damaged axons while enhancement of sleep promotes clearance of damaged axons. Despite the potential role of glia in maintenance of brain function and protection against neurodegenerative disease, surprisingly little is known about how sleep loss impacts glial function in aged animals. Axotomy of the Drosophila antennae triggers Wallerian degeneration, where specialized olfactory ensheathing glia engulf damaged neurites. This glial response provides a robust model system to investigate the molecular basis for glial engulfment and neuron-glia communication. Glial engulfment is impaired in aged and sleep-deprived animals, raising the possibility that age-related sleep loss underlies deficits in glial function. To define the relationship between sleep- and age-dependent reductions in glial function, we used two complementary approaches to enhance sleep in aged animals and examined the effects on glial clearance of damaged axons. Both pharmacological and genetic induction of sleep restores clearance of damaged neurons in aged flies. Further analysis revealed that sleep restored post-injury induction of the phagocytic protein Draper to aged flies, fortifying the notion that loss of sleep contributes to reduced glial-mediated debris clearance in aged animals. To identify age-related changes in the transcriptional response to neuronal injury, we used single-nucleus RNA-seq (snRNA-seq) of the central brains from axotomized young and old flies. We identified broad transcriptional changes within the ensheathing glia of young flies, and the loss of transcriptional induction of autophagy-associated genes. We also identify age-dependent loss of transcriptional induction of 18 transcripts encoding for small and large ribosomal protein subunits following injury in old flies, suggesting dysregulation of ribosomal biogenesis contributes to loss of glial function. Together, these findings provide further support for a functional link between sleep loss, aging and Wallerian degeneration.

Aging is commonly associated with sleep disturbances and a decline in cognitive function, including impaired clearance of damaged neurites. Here, we use the fruit fly, Drosophila melanogaster, to investigate the relationship between age-related sleep loss and loss of glial capacity to remove damaged neurites. By employing both pharmacological and genetic methods to induce sleep in aged flies, we demonstrated that sleep restores glial function and enhances critical engulfment proteins in aged animals. Utilizing single-cell RNA sequencing, we identified key molecular pathways associated with age-related loss of glial function. This research paves the way for further investigations into how enhancing sleep could improve glial function and potentially mitigate age-related cognitive decline.