Regeneration of neural circuitry in mature mammalian brain or spinal cord after injury is limited. After trauma and degeneration, astrocytes become reactive and act as a physical and biochemical barrier to neuronal regeneration that retards the repair process. Potentially, developing methods that limit gliosis and permit the reestablishment of lost neural circuitry should aid recovery.

Recent advances have shown that somatic cells can be genetically modified to alter their phenotype and emerge as potential regeneration-based therapeutics for brain repair. Here, we used astrocytes as a large, endogenous cellular pool for ‘‘on-site’’ brain repair by reprogramming them into neurons, in and around an injury site in mouse cerebral cortex. To reprogram these glia, we used adeno-associated viral vectors (AAV) that encoded either the NeuroD1 or SOX2 transcription factor (TF).

Initial in vitro studies validated the effectiveness and efficiency of both of these vectors in reprogramming astrocytes to induced functional neurons, confirmed by morphological, histochemical, and electrophysiological analyses. In vivo, after needle stick injuries made in the cortex of anaesthetised adult mice, we found that a single dose delivery of these TFs can successfully converted reactive astrocytes to neurons and replenished the injury site while reducing glial scarring. Importantly, a 3D self-assembling peptide hydrogel was also used to create microenvironments that mimic cellular compartments and facilitate cell survival and differentiation. This injectable hydrogel addresses multiple difficulties with viral vector delivery, reducing viral dosage at the target site, minimising off-target delivery, thus enhancing the vector’s targeting and reprogramming efficiency.