Mechanism Of Lipid Metabolism Affecting Brain Networks Across The Alzheimer’s Disease Spectrum And Intervention Effect Study Of Transcranial Magnetic Stimulation

Part Ⅰ Effect of LRP1 Polymorphism on the Default Mode Network and Modulation of APOE on the Relationship between LRP1 and Cognition across the Alzheimer’s Disease SpectrumBackground:The low-density lipoprotein receptor-related protein 1(LRP1)is involved in the pathological process of β-amyloid protein(Aβ)and Tau protein in Alzheimer’s disease(AD).The apolipoprotein E(APOE)is the ligand of LRP1 and relies on LRP1 to mediate Aβ pathological process.However,the effect of LRP1 gene rs 1799986 polymorphism on the default mode network(DMN)across the AD spectrum is unclear,and whether APOE ε4 genotype modulates LRP1 T genotype’s effect on cognitive function is also unclear.Methods:A total of 168 subjects were incorporated in this study,including 55 normal cognitive(CN),45 subjective cognitive decline(SCD),42 mild cognitive impairment(MCI),and 26 mild AD subjects,with genotyping data,neuropsychological assessment and resting-state functional magnetic resonance imaging(rs-fMRI)scans at baseline obtained.Group-level independent component analysis(ICA)was used to select the optimal component of DMN.Multivariable linear regression analysis was adopted to investigate the main effects and interaction of LRP1 T genotype and disease status on the DMN.Linear regression analysis was also applied to study the relationship between functional connectivity(FC)within DMN and behavioral performance.In addition,moderating effect model was used to investigate whether the APOE ε4 genotype modulates the relationship between LRP1 T genotype and cognitive performance.A support vector machine(SVM)model was used to classify AD spectrum population with altered FC as an objective diagnostic biomarker.Results:The main effects and interaction of LRP1 T genotype and disease were mainly focused on the core hubs of frontal-parietal network.In the LRP1 T carriers,the altered FCs in the left middle frontal gyrus(LMFG),right posterior cortex(RPCC)and left inferior parietal cortex(LIPC)were associated with cognitive scores.In the AD spectrum,APOE ε4+and LRP1 T+could increase each other’s negative effects on glabal cognitive function.More importantly,only in the LRP1 T carriers,the FC of LMFG,RPCC,and LIPC could distinguish different stages of the AD spectrum.Conclusions:In the AD spectrum,APOE ε4+ synergizing with LRP1 T+could aggravate cognitive impairment.LRP1 T risk allele combined with altered DMN FCs provided potential as a neuroimaging marker to classify AD spectrum populations.Part Ⅱ Polygenic Effects of Lipid Metabolism on the Default Mode Network Trajectory across the Alzheimer’s Disease SpectrumBackground:Hyperlipidemia is a high-risk factor for AD.Previous studies showed that a variety of lipid metabolic abnormalities regulated Aβ,Tau pathology and synaptic dysfunction.Disturbance of lipid metabolism may accelerate the pathological damage to the brain.However,the polygenic effect of lipid metabolic pathway on the DMN subsystems across the AD spectrum is not clear.Methods:A total of 113 subjects were incorporated in this study,including 20 SCD,24 early amnestic MCI(EMCI),23 late MCI(LMCI),21 AD patients,and 25 CN subjects.They completed measurements for lipid metabolism-related genes,blood lipids and CSF core biomarkers,neuropsychological assessments,and structural magnetic resonance imaging(sMRI),rs-fMRI scans.Polygenic scores(PGS),including genetic protective score(GPS),genetic risk score(GRS)and relative risk score(RRS),were constructed according to the odds ratio(OR)and the number of alleles in each locus.The group-level ICA was used to select the optimal component of the anterior DMN(aDMN)and posterior DMN(pDMN).Linear and binomial regression analysis was applied to explore the pairwise relationship among PGS,lipids,CSF core biomarkers and cognitive function.Multivariable linear regression model was utilized to investigate the main effect of PGS and its interaction with disease status on the DMN subsystems.Results:The GPS was correlated with Aβ level(p=0.043),GRS correlated with total tau level(p=0.005),RRS correlated with Aβ,total tau and ptau levels(p<0.05).Serum total cholesterol,cholesterol ester and sphingomyelins were correlated with t-tau levels(p<0.05).The levels of free cholesterol,total cholesterol,cholesterol esters,phosphatidylcholine,sphingomyelins and total choline,as well as the levels of CSF core biomarkers could significantly impact cognitive performance in a nonlinear manner.The interactive effect of PGS and disease influenced FC of multiple brain regions within DMN,mainly in the frontal-temporal-occipital-subcortical regions.The FC of aDMN and pDMN exhibited different changing trajectories across the AD spectrum.Brain regions of the above six lipid metabolites associated with DMN consisted of sensorimotor network and occipital lobe.Conclusions:The polygenic effects of lipid metabolism affected DMN across the AD spectrum.This study deepens our understanding of the effect of lipid metabolism on the brain networks in the AD spectrum populations and provides several measurable lipid markers that enable the impairments of lipid metabolism on the brain to be monitored.Part Ⅲ Dynamic functional network connectivity and its association with lipid metabolism in Alzheimer’s disease spectrumBackground:Dynamic functional network connectivity(dFNC)has provided more potential to characterize different connectivity states of intrinsic networks in brain than static functional network connectivity(sFNC)and is emerging as a novel biomarker of disease.However,the mechanism of lipid metabolism-related factors impacting the dFNC across the AD spectrum remains unclear.Methods:This study incorporated 242 subjects,including 50 subjects with SCD,75 subjects with EMCI,35 subjects with LMCI,21 subjects with AD,and 61 cognitively normal subjects.The data of lipid metabolism-related genes,serum lipid metabolites,CSF core biomarkers,structural magnetic resonance imaging(sMRI),rs-fMRI and cognitive assessment were obtained for all subjects.The sliding-window method and k-means algorithm were used to obtain the dFNC matrix of all subjects and cluster analysis was conducted.Spearman correlation analysis was employed to analyze the associations of dFNC temporal properties to CSF core biomarkers,cognitive scores and lipid metabolites.PGS were constructed based on the OR value of each gene locus,and the lipid composite score was constructed based on the significant correlative lipid components.The dynamic network difference and dFNC associations with CSF and behavioral phenotyping in lipid-related subgroups were also tested.To explore the casual relationship among lipid-related indicators,dFNC,CSF core biomarkers and behavioral phenotype,the mediation effect analysis were applied.Finally,the abnormal dFNC was used as an objective diagnostic biomarker to classify the AD spectrum populations by S VM model.Results:Two stable reoccurring connectivity states were identified after k-means clustering:frequent but weak-connected state Ⅰ,and less frequent but strong-connected state Ⅱ.The AD patients showed strong connectivity strength in both states.They represented significantly differential connectivity and temporal properties compared to non-AD participants in each state.Interestingly,they tended to dwell longer in the densely connectivity state Ⅱ,whereas the non-AD populations were prone to reside in the sparsely state I.Then,the temporal properties of two states,including fractional windows(FW)and mean dwell time(DT),were anti-correlated with CSF core biomarkers,cognitive scores,and lipid metabolites.More importantly,lipid-related subgroup analysis found that the effect of lipid composite score over dynamic connectivity differences was mainly in state Ⅰ,whereas APOE ε4 showed a wide effect on state Ⅱ network differences.The effects of PGS on the two states were not significantly different,but when APOE was removed,the effect of polygenes on state Ⅰ network differences were more involved in within-network connectivity.In addition,the state Ⅱ differential connections between APOE ε4 genotype subgroups mediates the effects of APOE genotype on CSF and cognitive phenotypes.The SVM analysis showed that the dFNC could distinguish AD from non-AD populations,especially the dFNC of state Ⅰ were better in differentiating AD from EMCI and LMCI than dFNC of state Ⅱ,but the ability to recognize the preclinical stages was still insufficient.Conclusions:This study showed the whole brain dFNC changes across the AD spectrum,and revealed different effect of lipid metabolites,APOE-4,and lipid-related polygenes over the dynamic brain networks.And dFNC could better classify AD spectrum populations than sFNC.Part Ⅳ Static and dynamic functional network connectivity changes and correlations with serum lipids:12-week rTMS targeted on the left dorsolateral prefrontal cortex in MCI patientsBackground:Repetitive transcranial magnetic stimulation(rTMS)is a promising technique in treatment of neurodegenerative disease.However,few researches perform long-term consecutive protocols,and no study inspects rTMS neuromodulation at large-scale networks levels.Methods:Seventeen MCI subjects and 20 age-,sex-and education-matched CN subjects were enrolled in this study with target on the left dorsolateral prefrontal cortex(DLPFC),at 10Hz and 80%resting exercise threshold intensity,20 minutes treatment every time and 5 times a week for 12 weeks.The MCI patients before and after rTMS and CN subjects received a battery of neuropsychological assessment,blood sampling,sMRI and rs-fMRI scanning.Linear regression model was applied to analyze the relationship between blood lipids and cognitive performance.The dFNC cluster analysis of CN subjects,MCI patients at baseline and after rTMS treatment were performed by sliding-window method and k-means algorithm.Spearman correlation analyses were used to analyze the correlations of the mean dFNC,temporal properties of each state,and serum lipids levels,cognitive domains scores.The mediation effect model was used to analyze the casual relationship among blood lipids,network connectivity and cognition.Results:The lipid levels and cognitive ability showed no significant group difference after rTMS,but individualized lipids levels declined,and cognitive performance except for episodic memory was improved in most MCI patients.Higher baseline total cholesterol was predictive of diminished visuospatial function after rTMS,and augmented body mass index predictive of worsened executive function.After cluster analysis,two stable dynamic connectivity states were identified across all groups:less frequently occurred but strong-connected state Ⅰ,and frequently occurred but weak-connected state Ⅱ.Dorsal attention network,executive control network(ECN),visual network(VIN),and cerebellum network represented significant static and dynamic differences after rTMS,and the cognitive-related sensorimotor network and VIN were reestablished after rTMS.The MCI patients dwelt longer in state Ⅱ with reduced transitions between states and upregulated variance of global efficiency after rTMS.There were numerous associations between lipids and static,dynamic connectivity,and temporal properties.Besides,the differential functional connectivity between ECN and visual,auditory networks,and visual within-network connectivity mediated the relationships between lipids and cognition.Conclusions:The long-term high-frequency rTMS over left DLPFC may modulate brain network changes to mediate the associations between lipid levels and cognitive function.These results exerted important implications for neural network reorganization and cortical plasticity and provide new research directions for early intervention of MCI.