Association Of Caspase-1 Genetic Polymorphism With Alzheimer’s Disease Biomarkers And The Study On Its Mechanism

Background:Alzheimer’s disease（AD）is an incurable progressive neurodegenerative disease.In recent years,increased levels of inflammatory markers in AD patients,as well as the discovery of AD-related risk genes associated with the innate immune system,imply that immune-mediated neuroinflammation plays a critical role in the pathogenesis of AD.Inflammasome,as an indispensable part of the innate immune system,which activates downstream inflammatory cytokines by Caspase-1,plays a significant role in AD pathogenesis.Genetic variations in Caspase-1 have been shown associated with cognitive function in elderly individuals and in predisposition to AD,the detailed mechanism by which Caspase-1-dependent inflammation leads to cognitive decline before the typical AD onset was still unclear.Our study aims to explore the association of Caspase-1 genetic polymorphism with biomarkers of AD and the mechanism.Methods:First of all,we selected non-demented elderly individuals from the Alzheimer’s Disease Neuroimaging Initiative（ADNI）database as study population to test the impact of Caspase-1 common variant rs554344,rs580235 on the pathological processes of brain amyloidosis,tauopathy,and neurodegeneration.In order to avoid the effect of population stratification which can lead to spurious findings,we selected only non-Hispanic white individuals.Given that Caspase-1 rs554344 and rs580253 were in linkage disequilibrium,a total of 698 non-Hispanic white individuals had Caspase-1rs554344 genotype information were finally included in our study,including 256 normal cognition（NC）and 442 mild cognitive impairment（MCI）.We examined the relationship between Caspase-1 rs554344 allele carrier status with AD?related cerebrospinal fluid（CSF）and imaging biomarkers at baseline by using a multiple linear regression model in all samples and subgroups.We also analyzed the longitudinal effects of the variant on the CSF and imaging biomarkers by using a mixed effect model.Causal mediation analyses with 10,000 bootstrapped iterations were conducted to explore the mediation effects between AD pathologies.In all of the above analyses,age,gender,education years and APOEε4 status were taken as covariates for test.And then,we selected SAMP8 mice to further investigate the specific mechanism of Caspase-1 affecting the AD neuropathology.Firstly,we detected the levels of Caspase-1 in brains of 3-,7-,and 11-month-old mice in order to evaluate the activation of Caspase-1 during aging.Then,VX-765,a selective inhibitor of Caspase-1,was used to observe the effect of Caspase-1 on the neuropathology of AD in SAMP8 mice and its specific mechanism.The data were shown as mean±standard deviation（SD）,and the difference between mean values was evaluated by one-way analysis of variance（ANOVA）followed by Tukey’s post hoc test.Statistical analyses were carried out through R 4.02,SPSS 17.0 and PLINK 1.07.If p<0.05,we considered the result was statistically significant.Results:In the analysis of ADNI all subjects and MCI subgroup,we found that Caspase-1 variant was significantly associated with CSF t?tau levels（All subjects:p=0.043;MCI:p=0.021）and FDG PET levels（All subjects:p=0.013;MCI:p=0.009）at baseline in total non?demented elderly group and MCI subgroup.In addition,this variant was also detected associated with CSF p?tau levels（p=0.049）in MCI subgroup.The mediation analysis showed that CSF p?tau partially mediated the association between Caspase-1 variant and CSF t?tau levels,accounting for 80%of the total effect.In subsequent animal experiments,we firstly verified that the level of Caspase-1 was significantly increased during aging in SAMP8 mice（p<0.05）;after injection of VX-765,the levels of Caspase-1 were notably decreased by 46%（p<0.05）in the SAMP8 mice brains at the age of 7-month and compared with the vehicle-treated SAMP8 mice,the levels of activated IL-1βin VX-765-treated SAMP8 mice were 41%lower（p<0.05）.What’s more,in the brain of SAMP8 mice,inhibition of Caspase-1 by VX-765 reduced the ratio of tau hyperphosphorylated at Ser³⁹⁶and Ser²⁰²/Thr²⁰⁵（p<0.05）.And the ratio of p-GSK3β（Ser⁹）/total GSK3βin SAMP8 mice was upregulated by34%（p<0.05）in VX-765-treated SAMP8 mice.This reduction was also checked by a commercial kit for GSK3βactivity（lower by 41%,p<0.05）.Conclusions:Our study indicated that Caspase-1-dependent inflammation may affect cognitive function by acting on tau kinase to alter tau pathology.Modulating the activation of Caspase-1 may be a potential therapeutic strategy for AD and other tau-related pathologic diseases.