The Role Of Autophagy In The Neuron Damage Correlated With Cognitive Impairment In The Rat Model Of Chronic Cerebral Hypoperfusion

BACKGROUND Chronic cerebral hypoperfusion(CCH)is considered as a high risk for cognitive decline in elder people.Permanent occlusion of bilateral common carotid arteries(BCCAO)is widely used in basic researches to replicate vascular dementia(Va D)and Alzheimer’s disease(AD).Neuron damage as well as the related mechanisms in CCH models has been widely reported.However,the dynamic variation of the cerebral blood flows(CBF)after BCCAO,the pathological and autophagic changes are largely unknown.AIM By detecting the changes of cerebral blood flow,spatial learning and memory,grey matter,white matter morphology,and Aβ accumulation at different time points after BCCAO,we explore the related autophagy mechanism.METHODS 1 CCH model was replicated by a modified two-step BCCAO using 54 Sprague Dawley(SD)rats.49 of them were divided into 7 groups,including sham-operated,BCCAO 2-,4-,8-,12-,16-,20-week groups(n=7).2 Monitor CBF at different time points before and after occlusion,using laser speckle contrast imaging(LSCI).3 The spatial learning and memory ability was assessed by Morris water maze(MWM)in all groups.4 Hematoxylineosin staining(HE)and Klüver– Barrera(KB)staining were respectively used to test histological changes of grey matter and white matter.5 Immunohistochemistry staining was used to analyze expression of intracellular Aβ positive cells and extracellular Aβ plaque burden.6 Expression of autophagic related proteins(Beclin-1、LC3B、P62)in hippocampus and cortex were analyzed with Western blot and immunohistochemistry staining.Transmission electron microscope(TEM)was used to detect autophagic vesicles in CA1 region and cortex.RESULTS 1 Spatial learning and memory ability was significantly declined in BCCAO 8~20 week groups.2 Compared to pre-occlusion level,CBF decreased immediately after BCCAO,which gradually recovered in later stages and approximated to pre-occlusion level since 8 weeks after BCCAO.3 Neuron survival rates significantly decreased since 8 weeks in hippocampal CA1 region and since 4 weeks in cortex detecting by HE staining.4 White mater was damaged since 2 to 20 weeks after BCCAO.5 Intracellular Aβ accumulation was preceded than extracellular plaque formation.Furthermore,compared with cortex,Aβ plaque accumulated earlier in hippocampus.6 The expression of Beclin-1、LC3B and P62 which represents autophagic degrading ability were elevated in the cortex of all BCCAO groups and in the hippocampus of BCCAO 4~20-week groups.It indicated that autophagy was activated but the ability of substrate degradation might be impaired.7 The results of TEM showed that autophagic vesicles in all BCCAO groups were significantly increased.CONCLUSION 1 CCH rats after two-step BCCAO,cognitive ability impaired gradually.Pathological injury deteriorated along with prolonged time.2 Autophagic mechanism played an important role in the neuron injury in the hippocampus and cortex.The abnormal protein degradation abilities might contribute to the intracellular Aβ aggregation,which closely correlated with cognitive decline in the rat model of CCH.