Abstract: Dorsal root ganglia neurons gradually lose their axonal regeneration ability during development and aging. To explore molecules that enhance axonal regeneration, we screened growth factors with differential gene expression patterns in the dorsal root ganglias of young adult and aged animals following sciatic nerve injury. In young adult animals, two transforming growth factor beta-related factors, activin A and angiopoietin 2, were found to be upregulated post nerve injury. Treatment of isolated dorsal root ganglia explants and cultured dorsal root ganglia neurons of neonatal and young adult rats with recombinant activin A or angiopoietin 2 protein stimulated neurite outgrowth and axonal elongation. The administration of recombinant activin A or angiopoietin 2 protein to sciatic nerve crush-injured dorsal root ganglias also supported the growth of sensory neurons and facilitated nerve regeneration in both young adult and aged rats. Using RNA sequencing, we characterized genetic changes in dorsal root ganglia neurons following recombinant activin A or angiopoietin 2 treatment, revealing the unique mechanisms of these transforming growth factor beta–related factors. Recombinant activin A elicited changes in the gene expression of cytoskeleton-related Gper1 and activated extracellular signal-regulated kinase signaling, while angiopoietin 2 increased the expression of the transcription factor gene E2f2. Our identification of activin A and angiopoietin 2 as crucial promotional factors of axonal regeneration may guide future therapeutic strategies for the treatment of nerve injury.

Key words: activin A, angiopoietin 2, axon elongation, axonal regeneration, dorsal root ganglion, E2f2, Gper1, growth factor, neurite outgrowth, neuron