Activity-dependent translation in astrocytes

Gene expression requires two steps-- transcription and translation-- which can be regulated independently to allow nuanced, localized, and rapid responses to cellular stimuli. Neurons are known to respond transcriptionally and translationally to bursts of brain activity, and a transcriptional response to this activation has also been recently characterized in astrocytes. However, the extent to which astrocytes respond translationally is unknown. We tested the hypothesis that astrocytes also have a programmed translational response by characterizing the change in transcript ribosome occupancy in astrocytes using Translating Ribosome Affinity Purification subsequent to a robust induction of neuronal activity in vivo via acute seizure. We identified a reproducible change in transcripts on astrocyte ribosomes, highlighted by a rapid decrease in housekeeping transcripts, such as ribosomal and mitochondrial components, and a rapid increase in transcripts related to cytoskeleton, motor activity, ion transport, and cell communication. This indicates a dynamic response, some of which might be secondary to activation of Receptor Tyrosine Kinase signaling. Using acute slices, we quantified the extent to which individual cues and sequela of neuronal activity can activate translation acutely in astrocytes. This identified both BDNF and KCl as contributors to translation induction, the latter with both action-potential sensitive and insensitive components. Finally, we show that this translational response requires the presence of neurons, indicating the response is acutely or chronically non-cell autonomous. Regulation of translation in astrocytes by neuronal activity suggests an additional mechanism by which astrocytes may dynamically modulate nervous system functioning.