MiR-9 promotes microglial activation by targeting MCPIP1

Microglia participate in innate inflammatory responses within the central nervous system. The highly conserved microRNA-9 (miR-9) plays critical roles in neurogenesis as well as axonal extension. Its role in microglial inflammatory responses, however, remains poorly understood. Here we identify a unique role of miR-9 in mediating the microglial inflammatory response via distinct signalling pathways. MiR-9-mediated regulation of cellular activation involved downregulated expression of the target protein, monocyte chemotactic protein-induced protein 1 (MCPIP1) that is crucial for controlling inflammation. Results indicate that miR-9-mediated cellular activation involved signalling via the NF-κB pathway, but not the β-catenin pathway. MicroRNA-9 (miR-9) is known for its function in neurogenesis and axonal extension but its role in the immune responses in the brain is not fully understood. Here, Yao et al. show that miR-9 is involved in the activation of microglia, cells of the myeloid origin that are involved in immune surveillance in the brain.