C-myc Gene Regulates Regenerative Ability Of Adult Peripheral Axon

Objective:Intrinsic axon regenerative mechanisms after peripheral nerve injury are tightly regulated by various genes.C-myc gene is a transcription factor that regulates cell growth,apoptosis and other physiological activities.Recent research suggested that overexpression of transcription factor c-myc promotes axonal regeneration of damaged optic nerve.Our study intends to investigate the role of transcription factor c-myc in axon regeneration after peripheral nerve injury.Method:1.RT-PCR and Western Blot were applied to the sciatic nerve injury model of mouse for the detection of c-myc mRNA and protein expression in 1,3 and 7 days of dorsal root ganglion(dorsal root ganglion node,DRG).2.DRG neurons of mouse were cultured after inhibition of c-myc by drugs or specific siRNA,axons are marked by immunofluorescence staining.Axon length was measured to detect whether c-myc inhibition could regulate the growth of axons.On the other hand,L4-L5 DRG neurons of adult mouse with axotomy for 7 days of were were treated with inhibitor and cultured for 20 hours,then the growth of axons was detected.3.DRG neurons of mouse were cultured in promoting substrate: laminin,or inhibiting substrate: myelin or CSPGs after overexpression of c-myc plasmid to determine whether overexpression of c-myc promotes the growth of damaged axons on different substrates.4.In vivo electroporation with solution containing siRNAs or c-myc plamid and/or GFP plasmid was performed in adult mouse L4-L5 DRGs.Three days after nerve crush on the side of the electroporated DRGs,the whole sciatic nerve were dissected out and regenerative axons were identified.Inhibitor was intraperitoneal injected in adult mouse with axotomy for 7 days once a day.L4-5 DRGs of these mouse were dissociated and cultured for 20 hours in vitro,then the growth of axons was detected.Result:1.The expression of c-myc mRNA and protein in DRG neurons increased significantly after sciatic nerve injury.2.Inhibition of c-myc gene function by drugs or siRNA significantly inhibited axonal growth of mouse DRG neurons compared with the control group.At the same time,the injection of c-myc inhibitors to sciatic nerve injury model can block the up-regulated axon regeneration ability,but c-myc inhibitors do not affect axon regeneration in DRG neurons that c-myc gene has been raised.3.Overexpression of c-myc gene by plasmid significantly increased the axonal growth ability of DRG neurons in mice,and significantly promoted axon growth of DRG neurons in vitro4.Overexpression of c-myc gene significantly increased the axonal growth of DRG neurons in vivo.C-myc inhibition with intraperitoneal injection in axotomy mice prevented axon regeneration.Conclusion:Peripheral nerve injury activates the upregulation of c-myc,thereby ensuring the translation and synthesis of proteins required during axonal outgrowth.In the process of axonal regeneration after peripheral nerve injury,transcription factor c-myc plays an important role in regulating the axon regeneration.Increasing the expression of c-myc gene can effectively promote axon regeneration of damaged peripheral neurons.