Upregulating Nrf2-ARE Pathway Promotes Neurological Function Recovery After Traumatic Brain Injury Via Inhibiting ERK Activation

Objective: Traumatic brain injury(TBI)is an acquired brain tissue injury caused by sharp instruments or sudden violence on the head.TBI includes the primary and secondary injuries and the secondary injury occurred immediately after the primary injury.It is the secondary injury that causes the TBI difficult to be repaired.Nrf2 is neuroprotective in many neurodegenerative diseases.Previous studies have shown that inhibiting ERK signaling pathway can improve neural function,but there has been no in-depth report on the correlation between Nrf2-ARE signaling pathway and ERK signaling pathway.Therefore,we made a TBI model by damagingthe nigrostriatal pathway andhypothesized that inhibiting ERK can activate Nrf2 signaling pathway to inhibit oxidative stress,thus promoting the recovery of nerve function after the TBI.Method: Male Kunming mice were randomly selected and divided into sham group,nigrostriatal pathway injury group(TBI),TBI+sulforaphane(SFN)group,and TBI+U0126(ERK inhibitor)group.The striatum pathway was damaged by sharp cuttingto make the TBI model.Immediately after the injury,the mice were given intraperitoneal injection of SFN(5mg/kg),andthe ERK signaling pathway inhibitor U0126(3?g/?L)was immediately administered in situto prevent secondary brain injury.Western blot was used to detect the expression of Nf2 in the cytoplasm and nucleus of the injured surrounding tissues,as well as the protein expression of HO-1,NQO1,p-ERK,and GFAP before and after the injury and after the drugs administration.Immunofluorescence assay was used to detect the activation and expression of GFAP and Nrf2 in injured peripheral astrocytes.SOD Kit was used to detect oxidative stress before and after the injury and after the drugs administration.The grip test and neurological score were used to measure the effect of SFN and U0126 on the neurological function recovery after the injury.Results: 1.GFAP expression was peaked at 4 day after the damage and the astrocytes showed hypertrophic cellular body with shortened and thickened processes at 4 day after the injury.2.We observed that in the sham operation group,Nrf2 expression was little and only existed in the cytoplasm.After the injury,the nuclear expression ofNrf2 was increased,but the cytoplasmic expression was decreased.After the SFN treatment,the nuclear entry was increased,and the cytoplasmic expression was decreased significantly.3.After the administration of U0126,the nuclear Nrf2 expression was slightly higher than that of the injury group,and the cytoplasmic expression was slightly lower than that of the injury group,indicating that U0126 had a promoting effect on the nucleation of Nrf2.4.The expression of HO-1 and NQO1 were slightly increased after the injury,and the expression were significantly increased after the SFN administration.The expression of HO-1 and NQO1 were also higher after U0126 administration than that in the injury group.5.The expression of p-ERK was significantly increased after the injury,decreased after SFN administration,and significantly inhibited after the U0126 administration.6.SOD expression wasdecreased significantly after the injury,and SFN and U0126 expression were increased significantly after the drug administration.7.Behavioral results showed thatthe administration of SFN and U0126 promoted the long-term neurobehavioral functionrecovery.Conclusions: ERK inhibition can reduces the reactive activation of glial cell proliferation and enhance the Nrf2 signaling pathway activation to increase the expression of detoxifying enzymes HO-1,NQO1 and SOD,which effectively blockthe oxidative stress and promot the neural functional recovery.