Neurons derived from NeuroD1-expressing astrocytes transition through transit-amplifying intermediates but lack functional maturity
Fangbing Chen, Xi Liu, Xiaowen Zhong, Xiaoqing Chen, Eva Nicholson, Kaiyi Liu, Huiyao Chen, Yifeng Lin, Yousheng Shu, Wenhao Zhou, Carol Schuurmans, Q. Richard Lu
Abstract
In vivo conversion of nonneuronal cells into neurons is a proposed strategy to replace neurons lost to CNS injury or disease. Glia-to-neuron trans-differentiation by viral vector–mediated GFAP mini-promoter–driven NeuroD1 remains hotly debated. Developing inducible, lineage-traceable transgenic mice, we find that astrocyte-to-neuron conversion is restricted to a specific time window within the lesion core of injured spinal cord and brain. Spatiotemporal lineage-mapping combined with single-cell transcriptomics reveals that ectopic NeuroD1 induces astrocyte-to-neuron conversion specifically in lesion cores via transit-amplifying OLIG2 + progenitors during early injury phase, but not in late phases or in nonreactive astrocytes. Neither a loss-of-function NeuroD1 mutant nor stemness-reprogramming factor SOX2 induces astrocyte-to-neuron conversion. However, contrary to previous reports, the neuronal-like cells generated by NeuroD1 lack mature neuroelectrical properties, limiting their functional integration into neural circuits. Together, our findings establish a spatiotemporal framework for NeuroD1-driven glia-to-neuron conversion, revealing a mechanistic shift from direct astrocyte conversion toward transit-amplifying intermediates and highlighting the functional immaturity of NeuroD1-converted neurons.