MicroRNA 302/367 Cluster Effectively Facilitates Direct Reprogramming from Human Fibroblasts into Functional Neurons

Recent studies suggest that mature somatic cells can be reprogrammed to become induced pluripotent stem cells by overexpressing specific transcription factors or microRNAs (miRNAs). Theoretically, this technique could provide a wide array of cells for therapeutics. However, the process of redifferentiation after cell reprogramming to pluripotency is inefficient and time restricted. We proposed that the differentiation of somatic cells into specific cells of another germ layer can be induced and accelerated with appropriate miRNAs and culture conditions. In human fibroblasts, we found that overexpression of pluripotency stem cell-specific miRNA-302/367 cluster, together with two other neuron-specific miRNAs (miRNA-9/9* and miRNA-124) induced fibroblasts conversion into neurons. The cells assumed neuron morphology, were positive for several neuron markers, and exhibited neuronal membrane potential feature. Moreover, concentrated expression of synaptic markers were observed in these cells in vitro and in vivo in nude mice brain, suggesting possible connectivity. To achieve efficient reprogramming, miRNA-302/367 cluster, miRNA-9/9*, and miRNA-124 were all required. The combination of the proved pluripotency-inducing miRNA-302/367 cluster and cell-specific miRNAs provides a unique strategy for one-step cellular conversion that could have important implications for studies of neuron development and neurological disease therapy.