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Local Translation in Perisynaptic Astrocytic Processes Is Specific and Changes after Fear Conditioning.

ABSTRACT: Local translation is a conserved mechanism conferring cells the ability to quickly respond to local stimuli. In the brain, it has been recently reported in astrocytes, whose fine processes contact blood vessels and synapses. Yet the specificity and regulation of astrocyte local translation remain unknown. We study hippocampal perisynaptic astrocytic processes (PAPs) and show that they contain the machinery for translation. Using a refined immunoprecipitation technique, we characterize the entire pool of ribosome-bound mRNAs in PAPs and compare it with the one expressed in the whole astrocyte. We find that a specific pool of mRNAs is highly polarized at the synaptic interface. These transcripts encode an unexpected molecular repertoire, composed of proteins involved in iron homeostasis, translation, cell cycle, and cytoskeleton. Remarkably, we observe alterations in global RNA distribution and ribosome-bound status of some PAP-enriched transcripts after fear conditioning, indicating the role of astrocytic local translation in memory and learning.

SUBMITTER: Mazare N

PROVIDER: S-EPMC7450274 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Local translation is a conserved molecular mechanism. It allows a cell with a complex shape to bypass somatic protein synthesis and transport, and thus to respond quickly to a local stimulus. Local translation also contributes to the establishment of molecular and functional polarity. In the brain, it has been extensively studied in neurons and has also been described more recently in astrocytes - a type of glial cell with specialized extensions that contact vessels and synapses. Here, we studied perisynaptic astrocytic processes (PAPs) in the dorsal hippocampus and showed that they contain RNAs, ribosomes, the endoplasmic reticulum-Golgi intermediate compartment, particles of the Golgi apparatus, and protein synthesis events. We used our recently refined polysome immunoprecipitation technique to characterize the pool of polysomal mRNAs in PAPs (which we refer to as the “PAPome”) from the dorsal hippocampus and compared it with the polysomal mRNAs found in the astrocyte as a whole. The polysomal transcripts that were enriched in the PAPome encoded mostly cytoplasmic proteins and defined an unexpected molecular repertoire with the most enriched transcripts coding for proteins involved in iron homeostasis, translation, cell cycle and cytoskeleton. Interestingly, among them Erz, Fth1, and Rplp1 were enriched in PAPs compared to perivascular astrocytic processes indicating that local translation differ at these two interfaces and may sustain distinct molecular properties. The PAP-enriched transcripts Flt1, Fth1, Ccnd2, Mdm2, Gnb2l1 and Eef1a1 code for proteins involved in memory and learning mechanisms. We therefore studied their local translation in the context of fear conditioning (i.e. behavior involving the dorsal hippocampus). We observed changes in the density and/or distribution of these mRNAs in astrocytes processes as well as a drop of their translation specifically in PAPs. Our results highlight unexpected molecular properties of hippocampal PAPs and suggest for the first time that local translation in this perisynaptic compartment is linked to fear-related memory.

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Local Translation in Perisynaptic Astrocytic Processes Is Specific and Changes after Fear Conditioning.

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