Ngn2 and Isl1-mediated astrocyte-to-neuron conversion in vivo promotes functional recovery after spinal cord injury.

Adult neurogenesis plays a crucial role in maintaining brain homeostasis and can respond to neurogenic injuries. However, the adult mammalian spinal cord has extremely limited intrinsic neurogenic ability. Here, we show that in vivo astrocyte-to-neuron conversion can regenerate functional neurons after spinal cord injury (SCI) through CRISPRa-mediated activation of endogenous transcription factors Ngn2 and Isl1. Lineage tracing confirms that the origin of these induced neurons is reactive astrocytes, rather than endogenous neurons. Furthermore, these induced neurons express specific markers of motor neurons and glutamatergic neurons and form synaptic connections with ascending and descending spinal pathways. Importantly, astrocyte-to-neuron conversion promotes propriospinal axon regeneration, improves the neuromuscular junction (NMJ) morphology and function of muscle, and finally promotes motor functional recovery after SCI. In summary, our results would contribute to resolving the controversy surrounding lineage reprogramming and demonstrate that in vivo cell conversion may be a potential therapeutic strategy for treating SCI.