The Role Of NRF2 And FGF9 In Wallerian Degeneration

Part One:Finding a reliable animal model of Wallerian degeneration.Objective:To establish a stable and repeatable animal model of Wallerian degeneration.Methods:We conducted morphalogy observation of sciatic nerves from accute sciatic nerve crush model and amyotrophic lateral sclerosis model-SOD1^G93A mice.Results:1.Degeneration was the main tune before Day 7 after injury,then regeneration became dominantly.2.Major pathological process of Wallerian degeneration（WD）was reappear in acute sciatic nerve injury,including,macrophage infiltration,the damage of blood-nerve-barrier（BNB）,and phagocytosis of myelin sheath.3.The distribution of degenerated nerve fibers from Wallerian-like degenerated nerves(SOD1^G93A mice)were clustered,the major pathological events including:axons and Schwann cells degenration,macrophage infiltraion,myelin degradation,and without obvious regenerated axons sprouts.4.The transcription factor NF-E2-related factor 2（Nrf2）and fibroblast growth factor 9（FGF9）expression were downregulated,we regulate the expression or content of NRF2 and FGF9 to observe the pathological changes in WD preocess in the Part Two and Part Three.Deepen the understanding of pathological of NRF2 and FGF9 in nerve crush.Conclusion:In conclusion,acute sciatic nerve crush was a better animal model to mimic Wallerian degeneraion process.Part Two:Schwann cell plasticity is regulated by a weakened intrinsic antioxidant defense system in acute peripheral nerve injuryObjective:To investigate the biological effects of Nrf2 in acute peripheral nervous system（PNS）injury.Methods:Analyzing the morphology and molecular changes of Nrf2knockout and Nrf2 activation experiments.Results:1.The antioxidant system was rapidly inactivated after acute PNS injury in a partly Nrf2-dependent manner,giving rise to a temporary state of oxidative stress,and then slowly and partially recovered following regeneration.2.Nrf2 knockout promoted the reprogramming and proliferation of Schwann cells and inhibited myelination,as well as the redifferentiation of repair Schwann cells.3.Dimethyl fumarate had no influence on the myelination of regenerated nerves.4.Nrf2 functional regulation was able to regulate the redox status of nerves by changing the levels of target antioxidants and reactive oxygen species（ROS）at the same time,without altering the balance between them.Conclusion:The Nrf2-antioxidant system was temporarily inactivated in injured nerves,promoting Schwann cell reprogramming and proliferation,and its functional recovery was essential for Schwann cell redifferentiation and myelination.Part Three:FGF9 Alters The Wallerian Degeneration Process by Inhibiting Schwann Cell Dedifferentiation and Accelerating Macrophage InfiltrationObjective:To understand the effects of FGF9 on WD and nerve regeneration.Methods:We employed strategies to regulate FGF9 in sciatic nerve crush by generating a mouse model,wherein Fgf9 is specifically knocked-out in Schwann cells（SCs）,and an intraneural injection of human FGF9 protein administered to overexpress FGF9 independently.Furthermore,an inhibitor of extracellular-regulated kinases 1/2（ERK1/2）,PD0325901,was used to clarify the underlying downstream mechanism of ERK1/2 activated by FGF9.Results:1.FGF9 was expressed both in axons and SCs,which was decreased during WD process.2.Fgf9 knockout in SCs impaired the debris clearance and eventually impeded the regeneration of nerve fibers after damage.3.Fgf9 knockout in SCs promoted the dedifferentiation of SCs and delayed the infiltration of macrophages by decreasing Mcp1,Tnfα,Il1βlevels and leaky blood-nerve-barrier（BNB）in WD.4.FGF9 injection preserved the nerve fibers,inhibited SCs dedifferentiation and accelerated macrophages infiltration.5.ERK1/2 phosphorylation was increased by exogenous FGF9 injection.P75,Cyclin D1,Mcp1,Tnfα,Il1β,c-Jun changes by FGF9 intraneural injection were partially reversed by the ERK1/2 inhibitor.Conclusion:FGF9 inhibited the dedifferentiation of SCs and accelerated the accumulation of macrophages in WD,and exogenous FGF9 took effects partially by ERK1/2.