The Effect Of Apolipoprotein E On Endoplasmic Reticulum Stress Induced By Traumatic Brain Injury

ApoE(Apolipoprotein E, ApoE=prtein, APOE=gene) is the primaryapolipoprotein found in the central nervous system. Besides serves as animportant mediator of cholesterol and lipid transport in the brain, ApoE hasimportant neurobiology functions. Studies of APOE-/-mice have beenshown to have increase vulnerability to brain injury compare toWT(Wild-Type)mice, suggest that ApoE affords neuroprotection followingbrain injury. However, the intact ApoE holoprotein does not cross theblood-brain-barrier(BBB)due to its size which limits its its therapeuticapplication as exogenous drugs. as a treatment.COG1410is a smallApoE-mimetic peptide derived from its receptor-binding region, and retainthe neurobiology effects of the native protein yet cross the BBB. Studies ofCOG1410show that administration of COG1410can reduce neuronal lossand impove functional outcome follow brain injury, thus provide theneuroprotection of ApoE in another viewpoint. However, the mechanism ofthe neuroprotection of ApoE on brain injury was still unclear.Recently, another apoptosis pathway induced by ER stress has been receiving attention besides the two most well-studied pathways, the cellsurface death receptor pathway and the mitochondria-regulatory pathway. Inthe case of mild ER stress, cells develop a self-protective signal transductionpathway termed the unfolded protein response (UPR), and induct ofmolecular chaperones in the ER, thus relieving cells from the stress.However, if the damage is too severe to repair, the UPR ultimately initiatesthe apoptotic pathway. ER stress has been shown to be involved in variousneuronal diseases, such as Parkinson’s disease, Alzheimer’s disease, sleepapnea syndrome, and so on, and its association with brain injury is providedon animal model or in vitro experiment. However, in TBI patients whetherERS plays a role in brain injury is still unkown.Moreover, Osada[14]et al reported that the ERS in the APOE-/-mice wasmore severe as compared to WT mice which could led to an increasingneuronal loss in area CA1-CA3of the hippocampus. However, how ApoEaffect the process of ERS caused by TBI, or whether an ApoE-mimeticpeptide could affect the process of ERS thus to exert its neuroprotectionproperties is still uncleared.Therefore, we used immunohistochemistry to detect the expression ofCHOP in peripheral tissues of TBI patients with TBI, and analyze itsassociation with GCS score and apoptosis; and further detection the changesof ERS in APOE-/-mice or WT mice at different time points after TBI,and observe whether C0G1410can affect the process of ERS after TBI, cell apoptosis detected by TUNEL, with the aim of explore the effect andsignificance of ApoE on the ERS following TBI, which provideexperimental data for elucidating the neuroprotection of ApoE.Part1. Expression and significance of CHOP in TBI brain tissueObject To investigate the expression of CHOP and its significance inTBI brain tissue. Methods The periphery of contusive and lacerated braintissues of patients with TBI(n=41) and controls(n=16) from autopsy werecollected. Injury severity was determined by GCS and divided into severetype (GCS3-5) and most severe type (GCS6-8). The expression of CHOPwas detected by immunohistochemistry method. The TUNEL technique wasused to estimate the apoptotic rate, and the correlation between the level ofCHOP and the apoptotic rate was analyzed. Results Compared with thecontrol group, the expression of CHOP in TBI group was increased(P<0.05).Compared with the patients with GCS6-8, the patients with GCS3-5hadhigher level of CHOP (P<0.05). The TBI group had higher apoptotic ratethan the control group(P<0.05), and the correlation analysis showed theexpression of CHOP was positive correlated with the apoptotic rate(r=0.72,P<0.05). Conclusion The expression of CHOP is upregulated after TBIand closely related to the severity of brain injury or the apoptotic rate.，suggests that ER stress-induced apoptosis is involved in the pathogenesis ofTBI。 Part2Experimental TBI: Controlled cortical impact (CCI)Object To develop a reliable,stable,and easily to repeated brain injurymodel. Method: Brain injury model was set up by the method of controlcortical impact. Neurobiology score and morphological change wereobserved after injury, to determine whether the brain injury model issuccessfully established. Results Compared with the mice of sham groupand control group, the mice of injury group had higher neurobiologyscore;As morphological observation shown,the neuronal loss,brainedema,and infiltration of inflammatory cells was more severe in the the miceof injury group compared with the mice of sham group and control group.Conclusion: Brain injury model by CCI was successful established. and theneurological function score and morphological observation further showedthat thie brain injury model was accords with the experimental requirements,to provide guarantee for the next step of the research model.Part3The effect of apolipoprotein E on endoplasmic reticulum stressinduced by traumatic brain injuryObjective To investigate the change of the effect of ApoE on ERstress(ERS) induced by traumatic brain injury(TBI). Methods ApoE-/-mice(n=72) and WT mice(n=72) were randomized into sham operationgroup(n=24)，TBI group(n=24),and COG1410group respectively. Each group was divided into3subgroups(n=8) according to the time of removal ofthe brain tissues from sacrificed animals post-TBI:1d,3d,7d. The expressionsof GRP78and CHOP were examined with Western blot and Real-time PCR.The TUNEL technique was used to evaluate the apoptotic rate. Another27WT mice and27APOE-/-mice were randomly divided into sham operationgroup, TBI group and COG1410group. The neurologic function score wasevaluated using the Modified Neurological Severity Score (mNSS). Results1.Compared with the WT mice of sham operation group, the expression ofGRP78and CHOP was increased in WT mice of TBI group after braininjury(P<0.05). The levels of GRP78and were maximum at1d, While thelevel of CHOP was reached peak at3d.The apoptotic rate was considerableelevated, and the score of mNSS was increased at all time points.2.Compared with WT mice of TBI group, ApoE-/-mice of TBI group had ahigher level of GRP78、CHOP and (P<0.05), and a significant increase of theapoptotic rate and the score of mNSS was observed in ApoE-/-mice of TBIgroup compared with the WT mice of TBI group (P<0.05).3. Administrationof COG14010reduced the expression of GRP78and CHOP,improveneurobiology function outcome,decreased TUNNEL(+)cell in bothAPOE-/-mice and WT mice compared to the respective genotype mice ofTBI group. Conclusion APOE-/-mice are more vulnerable to ERS after TBI,and have a higher level of the apoptotic rate and more severe score of mNSS,while administration of COG14010can suppress ERS, decrease the apoptotic rate and improve neurobiology function outcome.These resultssuggest that ApoE may affect the process of endoplasmic reticulum stressand probably have a neuroprotective effects following TBI.