RNA-binding protein IMP1/ZBP1 directs local translation in microglial processes to regulate motility and phagocytosis during inflammation

Polarized cells in the brain, such as neurons and glia, rely on the asymmetric distribution of their proteins compartmentalizing the function of dendrites, axons, glial projections, and endfeet. Subcellular proteomes can be assembled either by the transport of proteins synthesized in the cell soma or by the delivery of mRNAs to target compartments where they are locally translated into proteins. This latter mechanism is known as local protein synthesis or local translation, and it has been best studied in neurons. Increasing evidence suggests it is also required to maintain local protein homeostasis in glial cells; however, in microglia, local translation remains largely unexplored. Given the scant evidence, we aimed at exploring the existence of local translation in peripheral microglial processes (PeMPs) and unraveling its functional significance. We report that local translation indeed happens in PeMPs, and it is enhanced by triggering a microglial inflammatory response with bacterial lipopolysaccharides (LPS) suggesting a functional relevance of this molecular mechanism in response to inflammation. We found that Actb mRNA polarizes to PeMPs and is locally translated upon LPS exposure. Interestingly, downregulation of the Actb-binding protein IMP1/ZBP1 impaired Actb mRNA polarization and its localized translation, and led to defects in filopodia distribution, PeMP motility, lamellar directed migration, and phagocytosis in microglia. Thus, our work contributes to recent findings that mRNA localization and localized translation occur in microglia and gives a mechanistic insight into the relevance of this molecular mechanism in fundamental microglial functions in response to inflammation.