Deregulation of neuronal polarization promotes axonal growth after spinal cord injury

The developmental maturation of a neuron requires the completion of neuronal polarization preceding the formation of a synapse. Whether neuronal polarization marks the decline in growth competence in the injured mammalian adult nervous system remains elusive. Here we show that gene expression and epigenetic signatures associated with the regenerative growth ability of dorsal root ganglia (DRG) sensory neurons are lost during the transition from a non-polarized to a polarized state. The transcriptional co-factor Cited2 was found to be epigenetically upregulated in immature DRG and following a regenerative injury, but it remained unchanged by a non-regenerative spinal cord injury (SCI). Next, Cited2 was overexpressed in DRG neurons in a model of SCI in mice where it promoted sensory axon growth and reversed the gene expression signatures associated with neuronal maturation. Importantly, Cited2 expression stirred the maturation of DRG neurons towards a non-polarized state. Together, these data suggest that the transition from a non-polarized to a polarized state marks the reversible loss of the regenerative ability of a neuron, thus paving the way to targeted repair strategies relying on neuronal de-maturation. AAV-GFP or AAV-Cited2 was injected bilaterally into the sciatic nerve 4 weeks prior to a dorsal column axotomy. 24 hours post-injury, DRG were extracted and a neruonal enriched population processed for RNA-seq