Exosomes released from neural progenitor cells and induced neural progenitor cells regulate neurogenesis through miR-21a

Neural stem/progenitor cells (NPCs) are known to have potent therapeutic effects in neurological disorders through secreting exosomes. The limited numbers of NPCs in adult brain and the decline of NPC pool in many neurological disorders restrain the further use of exosomes in treating these diseases. The direct conversion of somatic cells into induced NPCs (iNPCs) provides abundant NPC-like cells to study the therapeutic effects of NPCs-originated exosomes (EXOs). Our recent study demonstrated that iNPCs-derived exosomes (iEXOs) exhibit distinct potential in facilitating the proliferation of NPCs, compared to EXOs, indicating the importance to investigate the effects of EXOs and iEXOs on the differentiation of NPCs, which remains unknown. Here, our results suggest that EXOs, but not iEXOs, promoted neuronal differentiation and neither of them had effect on glial generation. Microarray analysis revealed different miRNA signatures in EXOs and iEXOs, in which miR-21a was highly enriched in EXOs. Perturbation of function assay demonstrated the key roles of miR-21a in the generation of neurons and mediating the neurogenic potential of exosomes. Our data suggest that EXOs and iEXOs may achieve their therapeutic effects in promoting neurogenesis through transferring key miRNAs, which sheds light on the development of highly efficient cell-free therapeutic strategies for treating neurological diseases.