Protective Roles Of Nicotinamide Riboside On Hippocampus-associated Cognitive Impairments In Mice After Ischemia And The Underlying Mechanism

Objective: To observe the hippocampus injury after middle cerebral artery occlusion model(MCAO)in mice and study the role of NR in ischemic hippocampus and the associated cognitive functions.Methods:MCAO was employed to induce acute cerebral ischemia in mice.Mice were randomly divided into Sham,NS and NR groups.Those in NR group were treated with NR(400mg/kg)by intraperitoneal injection 20 min after the reperfusion of MCAO.CBF was monitored in the territory of MCA by laser-Doppler flowmetry during the procedures.Three days after ischemia,the hippocampus infarction was assessed by TTC staining,and ratio of hippocampus infarction was calculated.NISSL staining was used to observe morphological changes of hippocampal neurons.Neuronal apoptosis were labeled by TUNEL and immunofluorescence staining.The Morris water maze test(MWM)was applied to analyze the cognitive function of mice at 28 days after ischemia.The content of NAD and ATP in ischemic hippocampus was determined by reversed-phase high performance liquid chromatography(RP-HPLC)in a time-matched manner.Western Blot was employed to analyze the expression of inflammatory factor in hippocampus.Results:By TTC staining,it showed that NR acute treatment reduced the ratio of hippocampal infarction from 89.2% of the Sham group to 15.4% of the NR group.Morphological changes from NISSL staining demonstrated that incomplete structure,loosen cell arrangements,irregular layers and condensed nuclear chromatin of CA1 neurons appeared after ischemia,whereas these neuronal injuries were ameliorated by NR treatment.Compared with that in NS group,there were more surviving cells in the NR group(p<0.05).By TUNEL and Neu N double staining,it demonstrated that the apoptotic index of neurons in CA1 hippocampal area of NS group was(46.6±12.95)%,while it was(26.2±9.85)% in the NR group,which showed a significant reduction.The MWM test showed that there was no significant difference between groups in the swimming speed during the navigation test;mice in the NR group required shorter escape latency on day 3 and 4,compared with the time matched values of the NS group.In the spatial probe trial,mice of the NR group had increased target zone entries and target quadrant time spent,relative to that of the NS group.Results from RP-HPLC displayed that the decline of ATP content in hippocampus appeared immediately after ischemia;from 6h on,the content of ATP was elevated by NR treatment,as comparing with the time-matched values in the NS group;The NAD content in hippocampus started to decline from 3h after ischemia,comparing with that of Sham group;but from 6h after NR treatment,it showed evident recovery.By Western Blot,it showed that the expressions of TNFα and Pro-IL1β in hippocampus were significantly decreased by NR treatment.Conclusion : NR treatment after acute cerebral ischemia declined the hippocampus infarction and attenuated the relevant cognitive impairments.Based on the current results,it suggested that NR can restore the consumption of NAD and ATP in hippocampus,enhance the energy supply and ameliorate the neuroinflammation,protect the hippocampus,and finally benefit the recovery of cognitive deficits after acute ischemia.