Histone methyltransferase Ezh2 coordinates mammalian axon regeneration via regulation of key regenerative pathways (RRBS)

Current treatments for neurodegenerative diseases and neural injuries fall short of success. One primary reason is that neurons in the mammalian central nervous system (CNS) lose their regeneration ability as they mature. Here, we investigated the role of Ezh2, a histone methyltransferase, in regulation of mammalian axon regeneration. We found that Ezh2 declined in the mouse nervous system during maturation but was upregulated in adult dorsal root ganglion neurons to support spontaneous axon regeneration following peripheral nerve injury. In addition, overexpression of Ezh2 in retinal ganglion cells in the CNS promoted optic nerve regeneration via both histone methylation-dependent and -independent mechanisms. Further investigation revealed that Ezh2 supported axon regeneration by systematically silencing the transcription of genes regulating synaptic function and inhibiting axon regeneration, while simultaneously activating various axon regeneration promoting factors. In particular, our study demonstrated that the GABA transporter 2 encoded by the gene Slc6a13 acted downstream of Ezh2 to control axon regeneration. Our study suggested that modulating chromatin accessibility was a promising strategy to promote CNS axon regeneration. Overall design: To study how Ezh2 and its mutant form Ezh2-Y726D support axon regeneration of retinal ganglion cells, we profiled the changes in the DNA methylation landscape of retinal ganglion cells induced by Ezh2 or Ezh2-Y726D overexpression and/or optic nerve crush with reduced representation bisulfite sequencing. We intravitreally injected AAV2-GFP, AAV2-Ezh2, or AAV2-Ezh2-Y726D and crushed the optic nerve after two weeks. Uninjured groups only received AAV2 injection but did not undergo optic nerve crush. Three days after the optic nerve crush (injured groups) or 17 days after AAV2 injection (uninjured groups), retinal ganglion cells were enriched from dissociated retinal cells.