The Role Of NLRP3 Inflammasome Activation In Learning And Memory Impairment Induced By Increased Blood Pressure Variability In Rats And The Intervention Of Atenolol

BackgroundClinical studies have shown that increased blood pressure variability can lead to learning and memory impairment,but the mechanism is not clear.Based on previous studies,target organ damage caused by increased blood pressure variability is closely related to inflammation,and learning and memory impairment is also closely related to inflammation and NLRP3 inflammasome activation.Therefore,we hypothesize that the learning and memory impairment caused by increased blood pressure variability is related to the activation of NLRP3 inflammasome,and antihypertensive drug atenolol has an intervention effect.AimsTo study the activation mechanism of NLRP3 inflammasome in rats with learning and memory impairment caused by increased blood pressure variability,and to observe the intervention effect of atenolol.MethodSD rats underwent sinoaortic denervation(SAD)to establish a simple model of increased blood pressure variability.The control group was Sham group.The experiment was carried out at the 2nd,4th,8th and 16 th weeks after operation in SD rats.After the femoral artery and femoral vein intubation,the hemodynamic changes of the rats in conscious and free movement state were detected to confirm the success of SAD model establishment.The systolic blood pressure(SBP),diastolic blood pressure(DBP),mean blood pressure(MBP),systolic blood pressure variability(SBPV)and diastolic blood pressure variability(DBPV),mean pressure fluctuation(MBPV),baroreceptor reflex sensitivity(BRS)were compared between the two groups,and heart rate changes after administration of the pressor drug New Folin.At the 2nd,4th,8th and 16 th week after operation,the behavioral changes related to learning and memory in rats were detected,including Morris Water Maze(MWM),Novel Object Recognition Trial(NORT),and Passive Avoidance Trial(PAT).The expression of NLRP3,ASC,Pro-caspase1,Caspase-1P20,Pro-IL-1beta,Pro-IL-18,mature-IL-1beta and mature-IL-18 proteins in the hippocampus of rats were detected at the four time points of 2,4,8 and 16 weeks after operation.The expression of NLRP3 in the hippocampus was analyzed by immunofluorescence staining of NLRP3 and microglia.The intervention experiment of atenolol was divided into Sham group,SAD group and SAD+atenolol group(Atenolol group).In the Atenolol group,20 mg/kg of atenolol was administered orally from 2 weeks after SAD operation,while in the other groups,the same volume of solvent was given orally once a day for 30 days.Then,hemodynamic changes were detected by intubation,learning and memory were detected by behavioral experiments,protein changes in the hippocampus were detected by Western blot,NLRP3 and microglia were stained by immunofluorescence,and the expression of NLRP3 fluorescence intensity in the hippocampus of three groups of rats was analyzed.Results1 Effects of increased blood pressure variability on learning and memory in rats1.1 Hemodynamic changes in SAD ratsCompared with Sham group,blood pressure including systolic blood pressure(SBP),diastolic blood pressure(DBP)and mean blood pressure(MBP)did not change significantly at 2,4,8 and 16 weeks after SAD operation.Blood pressure variability including systolic blood pressure variability(SBPV),diastolic blood pressure variability(DBPV),mean blood pressure variability(MBPV)increased significantly,and baroreceptor reflex sensitivity(BRS)decreased significantly;When blood pressure increased by 50 mm Hg,heart rate decreased less than 20 times per minute.1.2 Behavioral changes in SAD rats1.2.1MWM experiment results Compared with Sham group rats,there was no significant difference in the escape latency and the number of times of platform crossing at the 2nd week after SAD operation;there was no significant difference in the escape latency at the 4th week after SAD operation,but the number of times of platform crossing decreased significantly;at the 8th and 16 th weeks after SAD operation,the escape latency increased significantly and the number of times of platform crossing decreased significantly.1.2.2 NORT experimental results Compared with Sham group,there were no statistical changes in the two object recognition indices at the learning and memory stages at2,4 and 8 weeks after SAD operation.At the 16 th week,there was no difference between the two object recognition indices at the learning stage,but the new object recognition index decreased significantly at the memory stage.1.2.3 PAT experimental results Compared with Sham group,there were no significant differences in escape latency,time spent in the dark box,and number of errors at2,4,8 and 16 weeks after SAD before electric shock.After electric shock,there was no significant difference between SAD group and control group at 2 weeks after operation;The escape latency decreased significantly at 4 weeks;the escape latency decreased significantly and dark time increased significantly at 8 weeks;The escape latency and number of errors increased significantly and the time spent in the dark box increased significantly at 16 weeks.1.3 Changes of proinflammatory factors in the hippocampus of SAD ratsCompared with Sham group,Pro-IL-18 and mature-IL-18 increased significantly at 2weeks after SAD operation,but Pro-IL-1beta and mature-IL-1beta had no significant difference;Pro-IL-1beta,mature-IL-1beta,Pro-IL-18 increased significantly at 4 weeks after SAD,and mature-IL-18 had no significant difference;Pro-IL-1beta,mature-IL-1beta,Pro-IL-18,mature-IL-1beta,Pro-IL-18 and mature-IL-18 increased significantly at 8 and 16 weeks after SAD.1.4 Changes of NLRP3 Inflammasome Proteins in the hippocampus of RatsCompared with Sham group,there were no significant differences in NLRP3Inflammasome-related proteins including NLRP3,apoptosis-related dot-like protein ASC,Pro-caspase1 and caspase-1P20 at the 2nd week after SAD operation,but there were significant increases in NLRP3 Inflammasome-related proteins at the 4th,8th and 16 th week after SAD.Compared with Sham group,there was no significant difference in NLRP3 fluorescence intensity in the hippocampus at the 2nd week after SAD,but significant increase in NLRP3 fluorescence intensity at the 4th,8th and 16 th week after SAD.2 Effects of atenolol on learning and memory and NLRP3 inflammasome in SAD rats2.1Effects on hemodynamics in SAD ratsCompared with Sham group,the blood pressure remained unchanged,the variability of blood pressure increased significantly,and the sensitivity of baroreceptor reflex decreased significantly in SAD group.Compared with SAD group,the systolic blood pressure decreased significantly,while the variability of blood pressure decreased significantly and the baroreceptor reflex sensitivity increased significantly in the Atenolol group.2.2 Effect of atenolol on behavior of SAD rats2.2.1 MWM experimental results Compared with Sham group,the escape latency of SAD rats was significantly increased and the number of times of crossing the platform was reduced significantly;compared with SAD group,the escape latency of the Atenolol group rats was significantly reduced,and the number of times of crossing the platform was significantly increased.2.2.2 NORT experimental results Compared with Sham group,there was no significant difference in the exploratory recognition index of SAD rats;compared with SAD rats,there was no significant difference in the exploratory identification index of the same object in the Atenolol group,and there was an increasing trend in the recognition of different objects,but there was no significant difference.2.2.3 PAT experimental results Compared with the Sham group,there was no significant difference in escape latency,stay time in the dark box and the number of errors in SAD rats before being shocked.The escape latency of SAD rats decreased significantly and the number of errors in the dark box increased significantly after being shocked.Compared with SAD rats,the rats in the Atenolol group escaped latency,stay time in the dark box and the number of errors has no significant difference before being shocked.The escape latency of rats increased significantly,and the time spent in the dark box and the number of errors decreased significantly after being shocked in the Atenolol group.2.3 Effects of atenolol on proinflammatory factors in the hippocampus of SAD ratsCompared with Sham group,the levels of Pro-IL-18,mature-IL-18,Pro-IL-1beta and mature-IL-1beta protein in the hippocampus of SAD rats increased significantly,while the levels of Pro-IL-18,mature-IL-18,Pro-IL-1beta and mature-IL-1beta protein in the hippocampus of the Atenolol group decreased significantly.2.4 Effects of atenolol on NLRP3 inflammasome in SAD ratsCompared with the Sham group,the levels of NLRP3,ASC,Pro-caspase1,caspase-1P20 in the hippocampus of SAD rats increased significantly,and the fluorescence intensity of NLRP3 increased significantly.Compared with SAD rats,the levels of NLRP3,ASC,Pro-caspase1 and caspase-1P20 in the hippocampus of the Atenolol group were significantly higher;The fluorescence intensity of NLRP3 protein in the hippocampus decreased significantly.Conclusions1.The mechanism of learning and memory impairment induced by increased blood pressure variability in rats may be related to the activation of NLRP3 inflammasome.2.Atenolol can improve learning and memory impairment in rats caused by increased blood pressure variability.