IL-4-induced microglia-derived small extracellular vesicles promote neuronal differentiation through miR-34a-5p

Abstract Neuroinflammatory processes in the brain are mediated mainly by microglia, which are the innate immune cells of the central nervous system (CNS). In the developing brain, microglia also contribute to neurogenesis in addition to their numerous other roles in homeostasis maintenance, phagocytosis, and synaptic pruning. The anti-inflammatory phenotype of microglia has been shown to stimulate neuronal differentiation. As extracellular vesicles have emerged as a significant way of communication within the brain, we hypothesized that small extracellular vesicles (sEVs) from microglia interact with neural progenitor cells (NPCs) and we have demonstrated the uptake of PKH67-labelled sEVs by NPCs. Microglial anti-inflammatory phenotype secretes sEVs with differential content compared to control sEVs, which in turn affects the differentiation of NPCs. In the present study, we have demonstrated that sEVs from control and IL-4-induced N9 microglia have differential miRNA content. Furthermore, NPCs derived from CGR8.0 ESC line enhanced neurite outgrowth and neuronal differentiation when exposed to sEVs from IL-4-induced microglia. Since the increase in neuronal markers and neurite outgrowth in recipient cells was mitigated by the miR-34a-5p inhibitor, we have concluded that IL-4-induced sEVs promote neuronal differentiation through miR-34a-5p. Our findings offer new insights into the regulation of neuronal cell fate in expression levels by linking immune cell signaling, miRNA-mediated gene regulation and intercellular communication.