ATF3 promotes regeneration of the central axon branch of sensory neurons but the addition of Smad1, c-Jun and STAT3 does not exert synergistic effects

ATF3 promotes regeneration of the central axon branch of sensory neurons but the addition of Smad1, c-Jun and STAT3 does not exert synergistic effects Abstract Successful axon regeneration after nerve injury is accompanied by the upregulation of hundreds of regeneration-associated genes (RAGs), including a number of transcription factors (TFs) which may be key regulators of the RAG program. We aimed to stimulate the RAG program in rat dorsal root ganglion (DRG) neurons by adeno-associated viral (AAV) vector-mediated expression of TFs, in the absence of a peripheral nerve lesion. Of the known RAG TFs, ATF3, Smad1, STAT3 and c-Jun have been functionally linked to successful axonal regeneration in the peripheral nervous system, and are known to interact functionally and physically. We hypothesised that TF expression would promote regeneration of the central axon branch of DRG neurons and that simultaneous overexpression of multiple regeneration-associated TFs would lead to greater effects than delivery of a single TF. We overexpressed either the combination of ATF3, Smad1, STAT3 and c-Jun with farnesylated enhanced green fluorescent protein (eGFPf), ATF3 only with eGFPf or eGFPf only in DRG neurons and assessed axonal regeneration after dorsal root transection or dorsal column injury and functional improvement after dorsal root injury. Histological analysis shows that both ATF3 alone and the combination of TFs promoted faster regeneration in the injured dorsal root. Surprisingly, however, the combination did not perform better than ATF3 alone. Neither treatment was able to induce functional improvement on sensory tests after dorsal root injury. Neither ATF3 nor the combination of factors promoted sprouting or regeneration in a dorsal column injury model. In conclusion, overexpression of the regeneration-associated TF ATF3 in DRG neurons promotes regeneration of injured dorsal root axons in the absence of a conditioning lesion, but a combination of four TFs, including ATF3, used here did not result in synergistic effects.