Polymorphisms of CR1, CLU and PICALM confer susceptibility of Alzheimer's disease in a southern Chinese population

Investigating CR1 as an indicated Gene for mild cognitive impairment in type 2 diabetes mellitus

OBJECTIVE

Type 2 diabetes mellitus (T2DM) has beenis known as an important risk factor for cognitive impairment. Meanwhile, the liver plays a central role in the development of T2DM and insulin resistance. The present study attempted to identify and validate marker genes for mild cognitive impairment (MCI) in patients with T2DM.

METHODS

In this study, insulin resistance-related differentially expressed genes were identified from the liver tissues of individuals with T2DM and those with normal glucose tolerance using the Gene Expression Omnibus database and MCI-associated genes were identified using the GeneCards database. Next, enrichment analysis was performed with overlapping T2DM and MCI genes, followed by the identification of specific genes using the LASSO logistic regression and SVM-RFE algorithms. An important experiment involved the implementation of clinical and in vitro validation using real-time quantitative polymerase chain reaction (RT-qPCR). Finally, multiple linear regression, binary logistic regression, and receiver operating characteristic curve analyses were performed to investigate the relationship between the key gene and cognitive function in these patients.

RESULT

The present study identified 40 overlapping genes between MCI and T2DM, with subsequent enrichment analysis revealing their significant association with the roles of neuronal and glial projections. The marker gene complement receptor 1(CR1) was identified for both diseases using two regression algorithms. Based on RT-qPCR validation in 65 T2DM patients with MCI (MCI group) and 65 T2DM patients without MCI (NC group), a significant upregulation of CR1 mRNA in peripheral blood mononuclear cells was observed in the MCI group (P < 0.001). Furthermore, the CR1 gene level was significantly negatively associated with MoCA and MMSE scores, which reflect the overall cognitive function, and positively correlated with TMTB scores, which indicate the executive function. Finally, elevated CR1 mRNA levels were identified as an independent risk factor for MCI (OR = 1.481, P < 0.001).

CONCLUSION

These findings suggest that CR1 is an important predictor of MCI in patients with T2DM. Thus, CR1 has potential clinical significance, which may offer new ideas and directions for the management and treatment of T2DM. The identification and clinical validation of dysregulated marker genes in both T2DM and MCI can offer valuable insights into the intrinsic association between these two conditions. The current study insights may inspire the development of novel strategies for addressing the complicated issues related to cognitive impairment associated with diabetes.

Knowledge domains and emerging trends of Genome-wide association studies in Alzheimer's disease: A bibliometric analysis and visualization study from 2002 to 2022

OBJECTIVES

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by a progressive decline in cognitive and behavioral function. Studies have shown that genetic factors are one of the main causes of AD risk. genome-wide association study (GWAS), as a novel and effective tool for studying the genetic risk of diseases, has attracted attention from researchers in recent years and a large number of studies have been conducted. This study aims to summarize the literature on GWAS in AD by bibliometric methods, analyze the current status, research hotspots and future trends in this field.

METHODS

We retrieved articles on GWAS in AD published between 2002 and 2022 from Web of Science. CiteSpace and VOSviewer software were applied to analyze the articles for the number of articles published, countries/regions and institutions of publication, authors and cited authors, highly cited literature, and research hotspots.

RESULTS

We retrieved a total of 2,751 articles. The United States had the highest number of publications in this field, and Columbia University was the institution with the most published articles. The identification of AD-related susceptibility genes and their effects on AD is one of the current research hotspots. Numerous risk genes have been identified, among which APOE, CLU, CD2AP, CD33, EPHA1, PICALM, CR1, ABCA7 and TREM2 are the current genes of interest. In addition, risk prediction for AD and research on other related diseases are also popular research directions in this field.

CONCLUSION

This study conducted a comprehensive analysis of GWAS in AD and identified the current research hotspots and research trends. In addition, we also pointed out the shortcomings of current research and suggested future research directions. This study can provide researchers with information about the knowledge structure and emerging trends in the field of GWAS in AD and provide guidance for future research.

Influence of clusterin genetic variants on IOP elevation in pseudoexfoliation syndrome and pseudoexfoliative glaucoma in Turkish population

PURPOSE

Pseudoexfoliation syndrome (PEX) is distinguished by the deposition of fibrillary material within the aqueous humor and, in most cases, causes pseudoexfoliative glaucoma (PEG). The pathophysiologies of PEX and PEG are not completely explained. Therefore, this study aimed to assess the potential relationship between single nucleotide polymorphisms (SNPs) in the 3' untranslated region or introns of the clusterin gene (CLU) and the susceptibility to developing PEG or PEX.

METHODS

Two hundred and forty patients with PEX, 239 patients with PEG, and 240 control subjects were included. Genotyping was carried out using real-time PCR (rs2279590 C/T and rs1532278 C/T) or PCR followed by restriction endonuclease digestion (rs11136000 C/T and rs3087554 T/C).

RESULTS

The minor alleles or genotypes of CLU SNPs were not significantly associated with PEX or PEG. IOP values of patients with PEX carrying the homozygote polymorphic TT genotype were significantly elevated compared with PEX cases with the CT or CC genotypes for rs2279590, rs11136000 and rs1532278 (P = .009, P = .007, P = .010, respectively).

CONCLUSION

We present the first evidence that three SNPs in CLU gene (rs2279590, rs11136000 and rs1532278) might induce a rise in IOP in patients with PEX, conferring susceptibility to develop PEG.

Link of BIN1, CLU and IDE gene polymorphisms with the susceptibility of Alzheimer's disease: evidence from a meta-analysis

BACKGROUND

Alzheimer's disease (AD) is the most common form of neurodegenerative disorder. The association of BIN1, CLU and IDE genetic polymorphisms with AD risk have been evaluated overtimes that produced conflicting outcomes.

OBJECTIVE

We performed this meta-analysis to investigate the contribution of BIN1 (rs744373 and rs7561528), CLU (rs11136000 and rs9331888), and IDE (rs1887922) polymorphisms to AD risk.

METHODS

From a systemic literature search up to July 15, 2021, we included 25 studies with rs744373, 16 studies with rs7561528, 37 studies with rs11136000, 16 studies with rs9331888, and 4 studies with rs1887922. To analyze the correlation, we constructed seven genetic models that used odds ratio and 95% confidence intervals. We used RevMan 5.4 for meta-analysis.

RESULTS

Our study suggests that BIN1 rs744373 is associated with a significantly increased risk of AD in five genetic models (OR>1). Again, CLU rs11136000 showed reduced association in all genetic models (OR<1). CLU rs9331888 revealed an increased association in two models (OR>1). The IDE rs1887922 showed significantly increased risk in four models (OR>1). From subgroup analysis, a significantly increased risk of AD was observed in Caucasians and Asians for BIN1 rs744373. Again, BIN1 rs7561528 showed a significantly enhanced risk of AD only in Caucasians. CLU rs11136000 showed significantly reduced risk in Caucasians but rs9331888 showed increased risk in the same ethnicity.

CONCLUSION

Our meta-analysis confirms the association of BIN1 rs744373, CLU rs9331888 and IDE rs1887922 polymorphisms with an increased risk of AD, especially in Caucasians. Again, CLU rs11136000 is associated with reduced AD risk in the overall population and Caucasians.

Structural Covariance Network as an Endophenotype in Alzheimer's Disease-Susceptible Single-Nucleotide Polymorphisms and the Correlations With Cognitive Outcomes

The cognitive manifestations of Alzheimer’s disease (AD) are related to brain network degeneration, and genetic differences may mediate network degeneration. Several AD-susceptible loci have been reported to involve amyloid or tau cascades; however, their relationships with gray matter (GM) volume and cognitive outcomes have yet to be established. We hypothesized that single-nucleotide polymorphism genotype groups may interact with apolipoprotein E4 (ApoE4) status or independently exert an effect on cognitive outcomes. We also hypothesized that GM structural covariance networks (SCNs) may serve as an endophenotype of the genetic effect, which, in turn, may be related to neurobehavior test scores. Gray matter SCNs were constructed in 324 patients with AD using T1 magnetic resonance imaging with independent component analysis (ICA). We assessed the effects of 15 genetic loci (rs9349407, rs3865444, rs670139, rs744373, rs3851179, rs11136000, rs3764650, rs610932, rs6887649, rs7849530, rs4866650, rs3765728, rs34011, rs6656401, and rs597668) using additive, recessive, and dominant models on cognitive outcomes. Statistical analysis was performed to explore the independent role of each locus, interactions with ApoE4 status, and relationships to GM ICA network intensity score. For outcome measures, we used the Mini-Mental State Examination (MMSE), Cognitive Abilities Screening Instrument (CASI) total score, and short-term memory (STM) subscores, adjusted for the covariates of education, disease duration, and age. Clinically, the CD2AP G allele showed a protective role in MMSE, CASI total, and CASI-STM scores independently or via interactions with non-ApoE4 status, while the CR1 A genotype group was associated with lower STM subscores independent of ApoE4 status. Three loci showed synergic interactions with ApoE4: BIN 1, MS4A6A, and FTMT. Of the 15 meaningful ICA components, 5 SCNs (anterior and posterior hippocampus, right temporal, left thalamus, default mode network) showed relationships with general cognitive performance, in which only the ApoE4 and MS4A6A genotype groups were independently related to the hippocampus network. The genetic loci MS4A6A, BIN1, CLU, CR1, BIN1, PICALM, and FGF1 influenced the networks independently or in synergy. This study suggests that AD-susceptible loci may each exert clinical significance independently through interactions with ApoE4 status or through SCNs as an endophenotype and that this effect is associated with the cognitive outcomes.

Explore the role of CR1 genetic variants in late-onset Alzheimer's disease susceptibility

BACKGROUND

Complement component (3b/4b) receptor 1 (CR1) is an interesting candidate gene which has a close connection with Alzheimer's disease, and its polymorphisms have been reported to link to the late-onset Alzheimer's disease (LOAD) susceptibility. However, the findings of these related studies are inconsistent. Objective To explore the effect of CR1 genetic variants in LOAD susceptibility. MethodsWe searched relevant studies for the period up to 1 November 2020. And odds ratios (ORs) and their 95% confidence intervals (CIs) were utilized to assess the strength of the association. In addition, we carried out a case-control association study to assess their genetic association.

RESULTS

Finally, a total of 30 articles with 30108 LOAD cases and 37895 controls were included. Significant allele frequency between LOAD patients and controls was observed in rs3818361 and rs6656401 (rs3818361, T vs. C: OR,1.18; 95% CI, 1.13-1.23; rs6656401, A vs. G: OR, 1.23; 95% CI, 1.10-1.36). Moreover, these results remain significant in subgroup of rs3818361 in Asia or America (OR,1.26; 95% CI,1.06-1.45; OR, 1.18; 95% CI, 1.13-1.24, respectively) and rs6656401 in Europe (OR = 1.26; 95% CI, 1.09-1.42). In addition, the two single nucleotide polymorphisms were proved to significantly increase LOAD risk in the overall population under the dominant model (OR = 1.12; 95% CI, 1.02-1.21; OR = 1.18, 95% CI, 1.15-1.22, respectively). Our case-control study showed that the distribution of rs6656401 genotype was significant (P = 0.000; OR, 6.889; 95% CI, 2.709-17.520), suggesting the A allele of rs6656401 is the risk allele.

CONCLUSION

These available data indicate that rs6656401 in CR1 is significant to increase LOAD risk.

Associations between CLU polymorphisms and memory performance: The role of serum lipids in Alzheimer's disease

CLU encoding clusterin, has been reported to associate with Alzherimer's disease (AD) by genome-wide association studies (GWAS) based on Caucasian populations. Our previous case-control study has independently confirmed the disease association of CLU in Chinese population. Since little is known about the underlying mechanism of CLU in AD, we have conducted this study to investigate whether the genetic impact of CLU polymorphisms on cognitive functioning is via serum lipid's dysfunction. Three GWAS previously published CLU polymorphisms including rs2279590, rs11136000 and rs9331888, were genotyped in 689 subjects. Serum levels of triglyceride (TG), high-density lipoprotein cholesterol (HDL-C), and low-density lipoprotein cholesterol (LDL-C) were measured and tested as mediators. Delayed Word Recall Test (DWRT) was used to evaluate subjects' memory performance. Multiple mediation analysis, a nonparametric procedure to create confidence interval, was performed according to Preacher and Hayes's Bootstrapping method. Our findings suggested significant correlation between CLU polymorphism and DWRT scores for rs11136000 (p = 0.045) after adjustment for age, gender, body mass index, and APOEε4 status, with borderline significant correlation for rs2279590 (p = 0.058). Both T allele of rs11136000 and A allele of rs2279590 were negatively correlated with serum TG levels (p = 0.003; p = 0.001, separately). Moreover, A allele of rs2279590 was positively correlated with serum HDL-C levels (p = 0.015). Consistent with our hypotheses, the genetic impact of CLU polymorphisms on memory performance were partially mediated through TG (rs11136000 95% CI [-0.099,-0.003] and rs2279590 95% CI [-0.104, -0.004]), but not through HDL-C and LDL-C. Our findings indicate CLU polymorphisms may modify AD susceptibility through lipid metabolic pathway.

Apolipoprotein E ε4 Allele is Associated With Plasma Amyloid Beta and Amyloid Beta Transporter Levels: A Cross-sectional Study in a Rural Area of Xi'an, China

OBJECTIVE

The effects of the Apolipoprotein E (ApoE) genotype on peripheral amyloid beta (Aβ) and Aβ transporter levels are still unclear. Soluble low-density lipoprotein receptor-related protein-1 (sLRP1) and soluble receptor of advanced glycation end products (sRAGE) are the major transporter for Aβ, which can prevent plasma Aβ from flowing into brain. The aim of this study was to investigate the relationships between the ApoE genotype and plasma Aβ, sLRP1, sRAGE levels.

DESIGN

Cross-sectional study.

SETTING

The committee office of the village.

PARTICIPANTS

Residents lived in the village for more than 3 years, aged 40-85 years (n = 1,119, 63.5% women).

MEASUREMENTS

Plasma biomarkers include ApoE genotype, Aβ, sLRP1, sRAGE, fasting blood-glucose, and blood lipids. General information, medical history, living habits, and cognitive status (cognitive impairment or not) were also collected.

RESULTS

After controlling for all possible covariates, multiple linear regression analysis showed that the plasma level of Aβ₄₂ was higher and log-transformed sLRP1 was lower in ApoE ε4 carriers than that in noncarriers (β_Aβ42 = 1.214, 95% confidence interval: 0.105-2.316, p_Aβ42 = 0.031; β_sLRP1 = -0.075, 95% confidence interval: -0.129 to -0.021, p_sLRP1 = 0.006, respectively). Partial correlation analysis showed that plasma Aβ₄₀ was positively correlated with log-transformed sLRP1 and log-transformed sRAGE (r_sLRP1 = 0.116, p_sLRP1 <0.001; r_sRAGE = 0.078, p_sLRP1 = 0.009, respectively). Plasma Aβ₄₂ was positively correlated with log-transformed sRAGE (r = 0.072, p = 0.017).

CONCLUSION

ApoE ε4 carriers had higher plasma Aβ₄₂ levels and lower sLRP1 levels. These data indicated that the ApoE ε4 allele may also contribute to the pathogenesis of Alzheimer's disease through its effects on peripheral Aβ₄₂ and sLRP1 levels, but it needs to be further elucidated.

Clusterin in Alzheimer's Disease: Mechanisms, Genetics, and Lessons From Other Pathologies

Clusterin (CLU) or APOJ is a multifunctional glycoprotein that has been implicated in several physiological and pathological states, including Alzheimer's disease (AD). With a prominent extracellular chaperone function, additional roles have been discussed for clusterin, including lipid transport and immune modulation, and it is involved in pathways common to several diseases such as cell death and survival, oxidative stress, and proteotoxic stress. Although clusterin is normally a secreted protein, it has also been found intracellularly under certain stress conditions. Multiple hypotheses have been proposed regarding the origin of intracellular clusterin, including specific biogenic processes leading to alternative transcripts and protein isoforms, but these lines of research are incomplete and contradictory. Current consensus is that intracellular clusterin is most likely to have exited the secretory pathway at some point or to have re-entered the cell after secretion. Clusterin's relationship with amyloid beta (Aβ) has been of great interest to the AD field, including clusterin's apparent role in altering Aβ aggregation and/or clearance. Additionally, clusterin has been more recently identified as a mediator of Aβ toxicity, as evidenced by the neuroprotective effect of CLU knockdown and knockout in rodent and human iPSC-derived neurons. CLU is also the third most significant genetic risk factor for late onset AD and several variants have been identified in CLU. Although the exact contribution of these variants to altered AD risk is unclear, some have been linked to altered CLU expression at both mRNA and protein levels, altered cognitive and memory function, and altered brain structure. The apparent complexity of clusterin's biogenesis, the lack of clarity over the origin of the intracellular clusterin species, and the number of pathophysiological functions attributed to clusterin have all contributed to the challenge of understanding the role of clusterin in AD pathophysiology. Here, we highlight clusterin's relevance to AD by discussing the evidence linking clusterin to AD, as well as drawing parallels on how the role of clusterin in other diseases and pathways may help us understand its biological function(s) in association with AD.

A Network of Genetic Effects on Non-Demented Cognitive Aging: Alzheimer's Genetic Risk (CLU + CR1 + PICALM) Intensifies Cognitive Aging Genetic Risk (COMT + BDNF) Selectively for APOEɛ4 Carriers

BACKGROUND

Trajectories of complex neurocognitive phenotypes in preclinical aging may be produced differentially through selective and interactive combinations of genetic risk.

OBJECTIVE

We organize three possible combinations into a "network" of genetic risk indices derived from polymorphisms associated with normal and impaired cognitive aging, as well as Alzheimer's disease (AD). Specifically, we assemble and examine three genetic clusters relevant to non-demented cognitive trajectories: 1) Apolipoprotein E (APOE), 2) a Cognitive Aging Genetic Risk Score (CA-GRS; Catechol-O-methyltransferase + Brain-derived neurotrophic factor), and 3) an AD-Genetic Risk Score (AD-GRS; Clusterin + Complement receptor 1 + Phosphatidylinositol-binding clathrin assembly protein).

METHOD

We use an accelerated longitudinal design (n = 634; age range = 55-95 years) to test whether AD-GRS (low versus high) moderates the effect of increasing CA-GRS risk on executive function (EF) performance and change as stratified by APOE status (ɛ4+ versus ɛ4-).

RESULTS

APOEɛ4 carriers with high AD-GRS had poorer EF performance at the centering age (75 years) and steeper 9-year decline with increasing CA-GRS but this association was not present in APOEɛ4 carriers with low AD-GRS.

CONCLUSIONS

APOEɛ4 carriers with high AD-GRS are at elevated risk of cognitive decline when they also possess higher CA-GRS risk. Genetic risk from both common cognitive aging and AD-related indices may interact in intensification networks to differentially predict (1) level and trajectories of EF decline and (2) potential selective vulnerability for transitions into impairment and dementia.

Correlation of PICALM polymorphism rs3851179 with Alzheimer's disease among Caucasian and Chinese populations: a meta-analysis and systematic review

The rs3851179 which located at upstream of PICALM was reported to be associated with Alzheimer's disease (AD); however, the relationship is still undefined. To gain a more precise understanding of the association, we conducted a meta-analysis: a comprehensive survey of 16 case-control studies that evaluated the role of rs3851179 gene variants in AD patients. The overall analysis revealed a significant association between the polymorphism and AD in the allelic, homozygote, heterozygote, dominant, and recessive models (p < 0.05). When stratified by ethnicity, a significant association was observed between AD development in Caucasian populations and the five-genetic models; Asian populations, however, featured a significant association in only the allelic, homozygote, and recessive models. We did not observe any influence of APOE ε4 carrier status on the incidence of AD and rs3851179 (p > 0.05). Our meta-analysis thus suggested that the PICALM rs3851179 polymorphism was associated with AD; the APOE ε4 status did not influence the relationship. Nevertheless, considering the limitations of our meta-analysis, further large-scale studies should be conducted to gain a more comprehensive understanding.

Neurocognitive Function after Cardiac Surgery: From Phenotypes to Mechanisms

For half a century, it has been known that some patients experience neurocognitive dysfunction after cardiac surgery; however, defining its incidence, course, and causes remains challenging and controversial. Various terms have been used to describe neurocognitive dysfunction at different times after cardiac surgery, ranging from "postoperative delirium" to "postoperative cognitive dysfunction or decline." Delirium is a clinical diagnosis included in the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5). Postoperative cognitive dysfunction is not included in the DSM-5 and has been heterogeneously defined, though a recent international nomenclature effort has proposed standardized definitions for it. Here, the authors discuss pathophysiologic mechanisms that may underlie these complications, review the literature on methods to prevent them, and discuss novel approaches to understand their etiology that may lead to novel treatment strategies. Future studies should measure both delirium and postoperative cognitive dysfunction to help clarify the relationship between these important postoperative complications.

A Robust Reduced Rank Graph Regression Method for Neuroimaging Genetic Analysis

To characterize associations between genetic and neuroimaging data, a variety of analytic methods have been proposed in neuroimaging genetic studies. These methods have achieved promising performance by taking into account inherent correlation in either the neuroimaging data or the genetic data alone. In this study, we propose a novel robust reduced rank graph regression based method in a linear regression framework by considering correlations inherent in neuroimaging data and genetic data jointly. Particularly, we model the association analysis problem in a reduced rank regression framework with the genetic data as a feature matrix and the neuroimaging data as a response matrix by jointly considering correlations among the neuroimaging data as well as correlations between the genetic data and the neuroimaging data. A new graph representation of genetic data is adopted to exploit their inherent correlations, in addition to robust loss functions for both the regression and the data representation tasks, and a square-root-operator applied to the robust loss functions for achieving adaptive sample weighting. The resulting optimization problem is solved using an iterative optimization method whose convergence has been theoretically proved. Experimental results on the Alzheimer's Disease Neuroimaging Initiative (ADNI) dataset have demonstrated that our method could achieve competitive performance in terms of regression performance between brain structural measures and the Single Nucleotide Polymorphisms (SNPs), compared with state-of-the-art alternative methods.

Analyzing 74,248 Samples Confirms the Association Between CLU rs11136000 Polymorphism and Alzheimer's Disease in Caucasian But Not Chinese population

Clusterin (CLU) is considered one of the most important roles for pathogenesis of Alzheimer's Disease (AD). The early genome-wide association studies (GWAS) identified the CLU rs11136000 polymorphism is significantly associated with AD in Caucasian. However, the subsequent studies are unable to replicate these findings in different populations. Although two independent meta-analyses show evidence to support significant association in Asian and Caucasian populations by integrating the data from 18 and 25 related GWAS studies, respectively, many of the following 18 studies also reported the inconsistent results. Moreover, there are six missed and a misclassified GWAS studies in the two meta-analyses. Therefore, we suspected that the small-scale and incompletion or heterogeneity of the samples maybe lead to different results of these studies. In this study, large-scale samples from 50 related GWAS studies (28,464 AD cases and 45,784 controls) were selected afresh from seven authoritative sources to reevaluate the effect of rs11136000 polymorphism to AD risk. Similarly, we identified that the minor allele variant of rs11136000 significantly decrease AD risk in Caucasian ethnicity using the allele, dominant and recessive model. Different from the results of the previous studies, however, the results showed a negligible or no association in Asian and Chinese populations. Collectively, our analysis suggests that, for Asian and Chinese populations, the variant of rs11136000 may be irrelevant to AD risk. We believe that these findings can help to improve the understanding of the AD's pathogenesis.

Association between CLU gene rs11136000 polymorphism and Alzheimer's disease: an updated meta-analysis

Large-scale genome-wide association studies (GWAS) identified that the single nucleotide polymorphism rs11136000 in Clusterin (CLU) gene was associated with risk of Alzheimer's disease (AD) in Caucasian ancestry. However, recent studies reported either a weak association or no association between rs11136000 polymorphism and AD in Asian populations. Therefore, we performed a meta-analysis to explore whether rs11136000 polymorphism is associated with susceptibility to AD in Asian populations. A total of 17 articles including 26 studies with 19,829 cases and 30,900 controls, which were identified by searching PubMed, MEDLINE, and AlzGene up to Nov 2016, were collected for this meta-analysis. The significant association between rs11136000 and AD in the pooled population was found under all the models. In subgroup analysis, we identified significant association in Asian population under the additive mode (OR = 0.90, 95% CI = 0.85-0.96) but not in the recessive model (OR = 0.80, 95% CI = 0.53-1.21) and the dominant model (OR = 0.94, 95% CI = 0.86-1.03). Our analysis further supports previous findings that the rs11136000 polymorphism C allele is associated with AD susceptibility. To our knowledge, this is the new largest meta-analysis to access to the association of CLU rs11136000 polymorphism with AD risk.

The Interactive Effects of Age and PICALM rs541458 Polymorphism on Cognitive Performance, Brain Structure, and Function in Non-demented Elderly

The PICALM rs541458 T allele has been recognized as a risk factor for late-onset Alzheimer's disease, and age might modulate the effects that genetic factors have on cognitive functions and brain. Thus, the current study intended to examine whether the effects of rs541458 on cognitive functions, brain structure, and function were modulated by age in non-demented Chinese elderly. We enrolled 638 subjects aged 50 to 82 years and evaluated their cognitive functions through a series of neuropsychological tests. Seventy-eight of these participants also received T1-weighted structural and resting state functional magnetic resonance imaging. Dividing subjects into groups <65 and ≥65 years old, results of neuropsychological tests showed that interactive effects of rs541458 × age existed with regard to executive function and processing speed after controlling for gender, years of education and APOE ε4 status. In addition, the effects of rs541458 on resting state functional connectivity of left superior parietal gyrus within left frontal-parietal network and on gray matter volume of left middle temporal gyrus were modulated by age. Furthermore, reduction of functional connectivity of left superior parietal gyrus was closely related with better executive function in the T allele carriers <65 years old. Further, greater volume of left middle temporal gyrus was significantly related to better executive function in both CC genotype <65 years old and CC genotype ≥65 years old groups, separately. Pending further confirmation from additional studies, our results support the hypothesis that the modulation of age, with respect to the rs541458, has interactional effects on cognitive performance, brain function, and structural measurements.

Alzheimer's Disease: From Genetic Variants to the Distinct Pathological Mechanisms

Being the most common cause of dementia, AD is a polygenic and neurodegenerative disease. Complex and multiple factors have been shown to be involved in its pathogenesis, of which the genetics play an indispensable role. It is widely accepted that discovery of potential genes related to the pathogenesis of AD would be of great help for the understanding of neurodegeneration and thus further promote molecular diagnosis in clinic settings. Generally, AD could be clarified into two types according to the onset age, the early-onset AD (EOAD) and the late-onset AD (LOAD). Progresses made by genetic studies on both EOAD and LOAD are believed to be essential not only for the revolution of conventional ideas but also for the revelation of new pathological mechanisms underlying AD pathogenesis. Currently, albeit the genetics of LOAD is much less well-understood compared to EOAD due to its complicated and multifactorial essence, Genome-wide association studies (GWASs) and next generation sequencing (NGS) approaches have identified dozens of novel genes that may provide insight mechanism of LOAD. In this review, we analyze functions of the genes and summarize the distinct pathological mechanisms of how these genes would be involved in the pathogenesis of AD.

rs3851179 Polymorphism at 5' to the PICALM Gene is Associated with Alzheimer and Parkinson Diseases in Brazilian Population

Alzheimer's (AD) and Parkinson's diseases (PD) share clinical and pathological features, suggesting that they could have common pathogenic mechanisms, as well as overlapping genetic modifiers. Here, we performed a case-control study in a Brazilian population to clarify whether the risk of AD and PD might be influenced by shared polymorphisms at PICALM (rs3851179), CR1 (rs6656401) and CLU (rs11136000) genes, which were previously identified as AD risk factors by genome-wide association studies. For this purpose, 174 late-onset AD patients, 166 PD patients and 176 matched controls were genotyped using TaqMan^® assays. The results revealed that there were significant differences in genotype and allele frequencies for the SNP PICALM rs3851179 between AD/PD cases and controls, but none for CR1 rs6656401 and CLU rs11136000 intronic polymorphisms. After stratification by APOE ε4 status, the protective effect of the PICALM rs3851179 A allele in AD cases remains evident only in APOE ε4 (-) carriers, suggesting that the APOE ε4 risky allele weakens its protective effect in the APOE ε4 (+) subgroup. More genetic studies using large-sized and well-defined matched samples of AD and PD patients from mixed populations as well as functional correlation analysis are urgently needed to clarify the role of rs3851179 in the AD/PD risk. An understanding of the contribution of rs3851179 to the development of AD and PD could provide new targets for the development of novel therapies.

Effect of PICALM rs3851179 polymorphism on the default mode network function in mild cognitive impairment

Alterations in default mode network (DMN) functional connectivity (FC) might accompany the dysfunction of Alzheimer's disease (AD). Indeed, episodic memory impairment is a hallmark of AD, and mild cognitive impairment (MCI) has been associated with a high risk for AD. Phosphatidylinositol-binding clathrin assembly protein (PICALM) (rs3851179) has been associated with AD; in particular, the A allele may serve a protective role, while the G allele serves as a strong genetic risk factor. Therefore, the identification of genetic polymorphisms associated with the DMN is required in MCI subjects. In all, 32 MCI subjects and 32 healthy controls (HCs) underwent resting-state functional magnetic resonance imaging (rs-fMRI) and a genetic imaging approach. Subjects were divided into four groups according to the diagnosis (i.e., MCI and HCs) and the PICALM rs3851179 polymorphism (i.e., AA/AG genotype and GG genotype). The differences in FC within the DMN between the four subgroups were explored. Furthermore, we examined the relationship between our neuroimaging measures and cognitive performance. The regions associated with the genotype-by-disease interaction were in the left middle temporal gyrus (LMTG) and left middle frontal gyrus (LMFG). These changes in LMFG FC were generally manifested as an "inverse U-shaped curve", while a "U-shaped curve" was associated with the LMTG FC between these four subgroups (all P<0.05). Furthermore, higher FC within the LMFG was related to better episodic memory performance (i.e., AVLT 20min DR, rho=0.72, P=0.044) for the MCI subgroups with the GG genotype. The PICALM rs3851179 polymorphism significantly affects the DMN network in MCI. The LMFG and LMTG may be associated with opposite patterns. However, the altered LMFG FC in MCI patients with the GG genotype was more sensitive to episodic memory impairment, which is more likely to lead to a high risk of AD.

An Aberrant Phosphorylation of Amyloid Precursor Protein Tyrosine Regulates Its Trafficking and the Binding to the Clathrin Endocytic Complex in Neural Stem Cells of Alzheimer's Disease Patients

Alzheimer's disease (AD) is the most common cause of dementia and is likely caused by defective amyloid precursor protein (APP) trafficking and processing in neurons leading to amyloid plaques containing the amyloid-β (Aβ) APP peptide byproducts. Understanding how APP is targeted to selected destinations inside neurons and identifying the mechanisms responsible for the generation of Aβ are thus the keys for the advancement of new therapies. We previously developed a mouse model with a mutation at tyrosine (Tyr) 682 in the C-terminus of APP. This residue is needed for APP to bind to the coating protein Clathrin and to the Clathrin adaptor protein AP2 as well as for the correct APP trafficking and sorting in neurons. By extending these findings to humans, we found that APP binding to Clathrin is decreased in neural stem cells from AD sufferers. Increased APP Tyr phosphorylation alters APP trafficking in AD neurons and it is associated to Fyn Tyr kinase activation. We show that compounds affecting Tyr kinase activity and counteracting defects in AD neurons can control APP location and compartmentalization. APP Tyr phosphorylation is thus a potential therapeutic target for AD.

Association of GWAS Top Genes With Late-Onset Alzheimer's Disease in Colombian Population

OBJECTIVE

The association of variants in CLU, CR1, PICALM, BIN1, ABCA7, and CD33 genes with late-onset Alzheimer's disease (LOAD) was evaluated and confirmed through genome-wide association study. However, it is unknown whether these associations can be replicated in admixed populations.

METHODS

The association of 14 single-nucleotide polymorphisms in those genes was evaluated in 280 LOAD cases and 357 controls from the Colombian population.

RESULTS

In a multivariate analysis using age, gender, APOE∊4 status, and admixture covariates, significant associations were obtained ( P < .05) for variants in BIN1 (rs744373, odds ratio [OR]: 1.42), CLU (rs11136000, OR: 0.66), PICALM (rs541458, OR: 0.69), ABCA7 (rs3764650, OR: 1.7), and CD33 (rs3865444, OR: 1.12). Likewise, a significant interaction effect was observed between CLU and CR1 variants with APOE.

CONCLUSION

This study replicated the associations previously reported in populations of European ancestry and shows that APOE variants have a regulatory role on the effect that variants in other loci have on LOAD, reflecting the importance of gene-gene interactions in the etiology of neurodegenerative diseases.

Genetic Polymorphisms in Estrogen Metabolic Pathway Associated with Risks of Alzheimer's Disease: Evidence from a Southern Chinese Population

OBJECTIVES

To investigate whether genetic variations on the estrogen metabolic pathway would be associated with risk of Alzheimer's disease (AD).

DESIGN

Cross-sectional study.

SETTING

Individuals were recruited at the Memory Clinic, Queen Mary Hospital, Hong Kong.

PARTICIPANTS

Chinese individuals with (n = 426) and without (n = 350) AD.

MEASUREMENTS

All subjects underwent a standardized cognitive assessment and genotyping of four candidate genes on the estrogen metabolic pathway (estrogen receptor α gene (ESR1), estrogen receptor β gene (ESR2), cytochrome P450 19A1 gene (CYP19A1), cytochrome P450 11A1 gene (CYP11A1)).

RESULTS

Apart from consistent results showing an association between apolipoprotein (APO)E and AD, strong evidence of disease associations were found for polymorphisms in ESR2 and CYP11A1 based on the entire data set. For ESR2, significant protective effects were found for A alleles of rs4986938 (permuted P = .02) and rs867443 (permuted P = .02). For CYP11A1, significant risk effects were found for G alleles of rs11638442 (permuted P = .03) and rs11632698 (permuted P = .03). Stratifying subjects according to APOE ε4 status, their genetic effects continued to be significant in the APOE ε4-negative subgroup. Associations between CYP11A1 polymorphisms (rs2279357, rs2073475) and risk of AD were detected in women but not men. Further gene-level analysis confirmed the above association between ESR2 and CYP11A1, and pathway-level analysis highlighted the genetic effect of the estrogen metabolic pathway on disease susceptibility (permuted pathway-level P = .03).

CONCLUSION

Consistent with previous biological findings for sex steroid hormones in the central nervous system, genetic alterations on the estrogen metabolic pathway were revealed in the Chinese population. Confirmation of these present findings in an independent population is warranted to elucidate disease pathogenesis and to explore the potential of hormone therapy in the treatment of AD.

Association between clusterin gene polymorphism rs11136000 and late-onset Alzheimer's disease susceptibility: A review and meta-analysis of case-control studies

The present study aimed to evaluate the association between rs11136000 in clusterin (CLU) and late-onset Alzheimer's disease (LOAD) by meta-analysis. Several databases including PubMed, EMbase, CBMdisc and CMCC were searched for relevant case-control studies based on defined selection criteria. Odds ratios (OR) and 95% confidence interval (CI) of the rs11136000 genotype and allele distribution were analyzed with RevMan and Stata software. The control population and heterogeneity between populations were examined in the selected studies using the Hardy-Weinberg equilibrium. Overall OR among the frequencies of the genotype and allele in both patients with AD and controls was estimated using fixed or random effect models. The summary of the OR and 95% CI were then analyzed to obtain the effects across the studies. Publication bias was examined using a funnel plot, Egger's test and Begg's test, and a Fail-safe Number (N_fs). A total of 20 reports were used. The summary OR for studies in the Caucasian population with a frequency of TT+TC/CC genotype and T/C allele at rs11136000 locus in CLU were 0.79 (95% CI, 0.73-0.86; P<0.00001) and 0.87 (95% CI, 0.85-0.90; P<0.00001). The summary OR for the studies conducted in the Asian population were 0.90 (95% CI, 0.81-0.99; P=0.04) and 0.87 (95% CI, 0.81-0.93; P<0.0001). The summary OR in other mixed ethnic groups with regards to the frequency of T/C allele was 0.82 (95% CI, 0.68-0.99; P=0.04). These results demonstrated the presence of a statistically significant difference in LOAD susceptibility between individuals with the T allele CLU rs11136000 polymorphism and those without. The studies conducted in populations of African descent or Hispanics showed no statistically significant difference. Negligible publication bias was present, with N_fs being 750.604. In summary, polymorphism rs11136000 in the CLU gene may contribute to susceptibility to LOAD, and the presence of the T allele may reduce the risk of LOAD in Caucasian and Asian populations. However, no definitive association was found between the presence of the CLU rs11136000 polymorphism and LOAD in populations of African or Hispanic descent.

Risk prediction for sporadic Alzheimer's disease using genetic risk score in the Han Chinese population

More than 30 independent single-nucleotide polymorphisms (SNPs) have been associated with Alzheimer's disease (AD) risk by genome-wide association studies (GWAS) in European. We aimed to confirm these SNPs in Chinese Han and investigate the utility of these genetic markers. We randomly divided 459 sporadic AD (SAD) patients and 751 cognitively normal controls into two sets (discovery and testing). Thirty-three SAD risk-associated SNPs were firstly tested in the discovery set. Significant SNPs were used to calculate genetic risk score (GRS) in the testing set. Predictive performance of GRS was evaluated using the area under the receiver operating characteristic curve (AUC). In the discovery set, 6 SNPs were confirmed (P = 7.87 × 10⁻¹¹~0.048), including rs9349407 in CD2AP, rs11218343 in SORL1, rs17125944 in FERMT2, rs6859 in PVRL2, rs157580 and rs2075650 in TOMM40. The first three SNPs were associated with SAD risk independent of APOE genotypes. GRS based on these three SNPs were significantly associated with SAD risk in the independent testing set (P = 0.002). The AUC for discriminating cases from controls was 0.58 for GRS, 0.60 for APOE, and 0.64 for GRS and APOE. Our data demonstrated that GRS based on AD risk-associated SNPs may supplement APOE for better assessing individual risk for AD in Chinese.

Plasma Clusterin and the CLU Gene rs11136000 Variant Are Associated with Mild Cognitive Impairment in Type 2 Diabetic Patients

Objective: Type 2 diabetes mellitus (T2DM) is related to an elevated risk of mild cognitive impairment (MCI). Plasma clusterin is reported associated with the early pathology of Alzheimer's disease (AD) and longitudinal brain atrophy in subjects with MCI. The rs11136000 single nucleotide polymorphism within the clusterin (CLU) gene is also associated with the risk of AD. We aimed to investigate the associations among plasma clusterin, rs11136000 genotype and T2DM-associated MCI.

Methods: A total of 231 T2DM patients, including 126 MCI and 105 cognitively healthy controls were enrolled in this study. Demographic parameters were collected and neuropsychological tests were conducted. Plasma clusterin and CLU rs11136000 genotype were examined.

Results: Plasma clusterin was significantly higher in MCI patients than in control group (p = 0.007). In subjects with MCI, plasma clusterin level was negatively correlated with Montreal cognitive assessment and auditory verbal learning test_delayed recall scores (p = 0.027 and p = 0.020, respectively). After adjustment for age, educational attainment, and gender, carriers of rs11136000 TT genotype demonstrated reduced risk for MCI compared with the CC genotype carriers (OR = 0.158, χ² = 4.113, p = 0.043). Multivariable regression model showed that educational attainment, duration of diabetes, high-density lipoprotein cholesterol (HDL-c), and plasma clusterin levels are associated with MCI in T2DM patients.

Conclusions: Plasma clusterin was associated with MCI and may reflect a protective response in T2DM patients. TT genotype exhibited a reduced risk of MCI compared to CC genotype. Further investigations should be conducted to determine the role of clusterin in cognitive decline.

Trial registration Advanced Glycation End Products Induced Cognitive Impairment in Diabetes: BDNF Signal Meditated Hippocampal Neurogenesis ChiCTR-OCC-15006060; http://www.chictr.org.cn/showproj.aspx?proj=10536

The Association Between Clusterin and APOE Polymorphisms and Late-Onset Alzheimer Disease in a Turkish Cohort

Previous studies have demonstrated that clusterin (CLU), which is also known as apolipoprotein J, is involved in the pathogenesis of Alzheimer disease (AD). In this study, we investigated the association between rs2279590, rs11136000, and rs9331888 single-nucleotide polymorphisms (SNPs) in CLU and apolipoprotein E (APOE) genotypes in a cohort of Turkish patients with late-onset AD (LOAD). There were 183 patients with LOAD and 154 healthy controls included in the study. The CLU and APOE polymorphisms were genotyped using the LightSNiP assay. The "GG" genotype of rs9331888 was significantly more frequent in patients with LOAD. The "CC" genotype of the SNP was significantly more frequent in controls. The rs9331888 "GG" genotype in patients and the "CC" genotype in controls were significantly higher in non-∊4 allele carriers of APOE The haplotype analysis showed the CLU "GCG" haplotype was a risk haplotype. Our findings indicate the rs9331888 SNP of CLU is associated with LOAD independent of APOE.

Impact of PICALM and CLU on hippocampal degeneration

PICALM and CLU are two major risk genes of late-onset Alzheimer's disease (LOAD), and there is strong molecular evidence suggesting their interaction on amyloid-beta deposition, hence finding functional dependency between their risk genotypes may lead to better understanding of their roles in LOAD development and greater clinical utility. In this study, we mainly investigated interaction effects of risk loci PICALM rs3581179 and CLU rs11136000 on hippocampal degeneration in both young and elderly adults in order to understand their neural mechanism on aging process, which may help identify robust biomarkers for early diagnosis and intervention. Besides volume we also assessed hippocampal shape phenotypes derived from diffeomorphic metric mapping and nonlinear dimensionality reduction. In elderly individuals (75.6 ± 6.7 years) significant interaction effects existed on hippocampal volume (P < 0.001), whereas in young healthy adults (19.4 ± 1.1 years) such effects existed on a shape phenotype (P = 0.01) indicating significant variation at hippocampal head and tail that mirror most AD vulnerable regions. Voxel-wise analysis also pointed to the same regions but lacked statistical power. In both cohorts, PICALM protective genotype AA only exhibited protective effects on hippocampal degeneration and cognitive performance when combined with CLU protective T allele, but adverse effects with CLU risk CC. This study revealed novel PICALM and CLU interaction effects on hippocampal degeneration along aging, and validated effectiveness of diffeomorphometry in imaging genetics study. Hum Brain Mapp 37:2419-2430, 2016. © 2016 Wiley Periodicals, Inc.

Effect of CLU genetic variants on cerebrospinal fluid and neuroimaging markers in healthy, mild cognitive impairment and Alzheimer's disease cohorts

The Clusterin (CLU) gene, also known as apolipoprotein J (ApoJ), is currently the third most associated late-onset Alzheimer's disease (LOAD) risk gene. However, little was known about the possible effect of CLU genetic variants on AD pathology in brain. Here, we evaluated the interaction between 7 CLU SNPs (covering 95% of genetic variations) and the role of CLU in β-amyloid (Aβ) deposition, AD-related structure atrophy, abnormal glucose metabolism on neuroimaging and CSF markers to clarify the possible approach by that CLU impacts AD. Finally, four loci (rs11136000, rs1532278, rs2279590, rs7982) showed significant associations with the Aβ deposition at the baseline level while genotypes of rs9331888 (P = 0.042) increased Aβ deposition. Besides, rs9331888 was significantly associated with baseline volume of left hippocampus (P = 0.014). We then further validated the association with Aβ deposition in the AD, mild cognitive impairment (MCI), normal control (NC) sub-groups. The results in sub-groups confirmed the association between CLU genotypes and Aβ deposition further. Our findings revealed that CLU genotypes could probably modulate the cerebral the Aβ loads on imaging and volume of hippocampus. These findings raise the possibility that the biological effects of CLU may be relatively confined to neuroimaging trait and hence may offer clues to AD.

New Insights to Clathrin and Adaptor Protein 2 for the Design and Development of Therapeutic Strategies

The Amyloid Precursor Protein (APP) has been extensively studied for its role as the precursor of the β-amyloid protein (Aβ) in Alzheimer’s disease (AD). However, our understanding of the normal function of APP is still patchy. Emerging evidence indicates that a dysfunction in APP trafficking and degradation can be responsible for neuronal deficits and progressive degeneration in humans. We recently reported that the Y₆₈₂ mutation in the ₆₈₂YENPTY₆₈₇ domain of APP affects its binding to specific adaptor proteins and leads to its anomalous trafficking, to defects in the autophagy machinery and to neuronal degeneration. In order to identify adaptors that influence APP function, we performed pull-down experiments followed by quantitative mass spectrometry (MS) on hippocampal tissue extracts of three month-old mice incubated with either the ₆₈₂YENPTY₆₈₇ peptide, its mutated form, ₆₈₂GENPTY₆₈₇ or its phosphorylated form, ₆₈₂pYENPTY₆₈₇. Our experiments resulted in the identification of two proteins involved in APP internalization and trafficking: Clathrin heavy chain (hc) and its Adaptor Protein 2 (AP-2). Overall our results consolidate and refine the importance of Y₆₈₂ in APP normal functions from an animal model of premature aging and dementia. Additionally, they open the perspective to consider Clathrin hc and AP-2 as potential targets for the design and development of new therapeutic strategies.

Meta-analysis of the Association between Alzheimer Disease and Variants in GAB2, PICALM, and SORL1

The genetic variants play a crucial role in the pathogenesis of Alzheimer's disease (AD), while the relationships of specific single nucleotide polymorphisms (SNPs) with AD are still controversial. We performed the meta-analysis to obtain a more precise estimation of whether growth factor receptor-bound protein-associated binding protein 2 (GAB2), phosphatidylinositol binding clathrin assembly protein (PICALM), and sortilin-related receptor (SORL1) variants are associated with AD. Databases including PubMed, Embase, and Cochrane Library were searched to find relevant studies. Cochran's Q-statistic and I ² were used to assess the heterogeneity among the included studies. Odds ratios (OR) and 95 % confidence intervals (95 % CIs) were conducted to evaluate the association between the SNP and the susceptibility to AD. Publication bias was estimated by funnel plots. All of the statistical analyses were implemented using R Version 3.2.1 software. A total of 35 case-control studies involving 15 SNPs were included. There was no significant association between SNPs of GAB2 rs2373115 (G > T) and PICALM rs541458 (C > T) and AD. The allele T of rs3851179 in PICALM was associated with a 13 % increase in the risk of AD. Seven SNPs on SORL1 were significantly associated with AD. Four SNPs, including rs1010159*T, rs641120*A, rs668387*T, and rs689021*A, were associated with a decreased risk of AD, while the other three SNPs, including rs12285364*T, rs2070045*G, and rs2282649*T, were all associated with an increased risk of AD. The results of the present study suggested that multiple gene variants were associated with AD. The SNP of rs3851179 (PICALM), rs12285364 (SORL1), rs2070045 (SORL1), and rs2282649 (SORL1) was associated with an increased risk of AD, whereas SORL1 rs1010159, rs641120, rs668387, and rs689021 were associated with a decreased risk of AD.

CR1 rs3818361 Polymorphism Contributes to Alzheimer's Disease Susceptibility in Chinese Population

Recent genome-wide association studies (GWAS) reported CR1 rs3818361 polymorphism to be an Alzheimer's disease (AD) susceptibility variant in European ancestry. Three independent studies investigated this association in Chinese population. However, these studies reported weak or no significant association. Here, we reinvestigated the association using all the samples from three independent studies in Chinese population (N = 4047, 1244 AD cases and 2803 controls). We also selected three independent studies in European ancestry population (N = 11787, 3939 AD cases and 7848 controls) to evaluate the effect of rs3818361 polymorphism on AD risk in different ethnic backgrounds. In Chinese population, we did not identified significant heterogeneity using additive, recessive, and dominant genetic models. Meta-analysis showed significant association between rs3818361 and AD with P = 6.00E-03 and P = 5.00E-03. We further identified no heterogeneity of rs3818361 polymorphism between Chinese and European populations. We found that rs3818361 polymorphism contributed to AD with similar genetic risk in Chinese and European populations. In summary, this is the first study to show significant association between rs3818361 polymorphism and AD in Chinese population by a meta-analysis method. Our findings indicate that the effect of CR1 rs3818361 polymorphism on AD risk in Chinese cohorts is consistent with the increased risk observed in European AD cohorts.

Impaired vascular-mediated clearance of brain amyloid beta in Alzheimer's disease: the role, regulation and restoration of LRP1

Amyloid beta (Aβ) homeostasis in the brain is governed by its production and clearance mechanisms. An imbalance in this homeostasis results in pathological accumulations of cerebral Aβ, a characteristic of Alzheimer’s disease (AD). While Aβ may be cleared by several physiological mechanisms, a major route of Aβ clearance is the vascular-mediated removal of Aβ from the brain across the blood-brain barrier (BBB). Here, we discuss the role of the predominant Aβ clearance protein—low-density lipoprotein receptor-related protein 1 (LRP1)—in the efflux of Aβ from the brain. We also outline the multiple factors that influence the function of LRP1-mediated Aβ clearance, such as its expression, shedding, structural modification and transcriptional regulation by other genes. Finally, we summarize approaches aimed at restoring LRP1-mediated Aβ clearance from the brain.

Plasma and platelet clusterin ratio is altered in Alzheimer's disease patients with distinct neuropsychiatric symptoms: findings from a pilot study

BACKGROUND

Clusterin protein in plasma has been found to differentiate between people with and without cognitive changes. However, these findings are not conclusive, despite the clusterin gene variations repeatedly being linked to increased risk for dementia, in particular Alzheimer's disease (AD).

METHOD

We analysed the level of clusterin in platelet and plasma in 25 subjects with a clinical diagnosis of AD and 26 subjects with no cognitive impairment.

RESULTS

In the current study, we report that the levels of both plasma and platelet clusterin are similar between AD and cognitively intact individuals. Clusterin plasma and platelet levels, as well as the plasma/platelet clusterin ratio, were not affected by age, gender, cognitive impairment and/or overt behavioural symptomatology, including presence of hallucinations and delusions, as well as depression. However, the plasma/platelet clusterin ratio was positively associated in with the Neuropsychiatric Inventory measures of agitation, apathy, irritability and motor aberrant behaviour in AD subjects.

CONCLUSION

Previous inconsistencies in reported blood clusterin levels may be a result of underlying non-cognitive symptoms in people with AD. Our findings need now to be replicated in larger group of dementia subjects.

Genetic associations of CLU rs9331888 polymorphism with Alzheimer's disease: A meta-analysis

Recent studies showed the Clusterin gene (CLU) is associated with Alzheimer's disease (AD). However, studies investigating the association of CLU single-nucleotide polymorphism (SNP) rs9331888 with AD are controversial. We then performed a meta-analysis to assess the association between CLU SNP rs9331888 and AD. Computerized bibliographic searches of PUBMED and AlzGene database were conducted for the period up to July, 2014. The strength of the association between SNP rs9331888 and AD was estimated by odds ratios (ORs) and OR 95% confidence intervals (CIs). A total of 11 studies composed of 8766 AD cases and 11,366 controls were included in this study. Significant association of SNP rs9331888 with AD was found in Caucasian population among allelic model (C vs. G: OR=1.12, 95%CI=1.06-1.17, P<0.001), additive model (CC vs. GG: OR=1.25, 95%CI=1.12-1.40, P<0.001), recessive model (CC vs. CG+GG: OR=1.20, 95%CI=1.07-1.34, P=0.001), and dominant model (CC+CG vs. GG: OR=1.13, 95%CI=1.06-1.21, P<0.001). No significant association among these models was found in Asian and overall populations. Sensitivity analysis found that one study caused the distinct heterogeneity in Asian subgroup. Our analysis demonstrated that CLU SNP rs9331888 might be associated with an increased AD risk in Caucasian population, but not in Asian population.

CLU rs9331888 Polymorphism Contributes to Alzheimer's Disease Susceptibility in Caucasian But Not East Asian Populations

Large-scale genome-wide association studies (GWAS) identified three single nucleotide polymorphisms rs11136000, rs2279590, and rs9331888 in CLU gene to be significantly associated with Alzheimer's disease (AD) in Caucasian ancestry. Both rs11136000 and rs2279590 variants were successfully replicated in Asian population. However, previous studies reported either a weak association or no association between rs9331888 polymorphism and AD in Asian population. Here, we searched the PubMed, AlzGene, and Google Scholar databases. We selected 12 independent studies that evaluated the association between the rs9331888 polymorphism and AD using a case-control design. Using an additive model, we did not identify significant heterogeneity among these 12 studies. We observed significant association between rs9331888 polymorphism and AD in pooled populations (P = 2.26E - 07, odds ratio (OR) = 1.10, 95% confidence interval (CI) 1.06-1.14). In subgroup analysis, we did not identify significant heterogeneity in both Asian and Caucasian populations. We identified significant association in Caucasian population (P = 1.67E - 08, OR = 1.13, 95% CI 1.08-1.18) but not in East Asian population (P = 0.49, OR = 1.02, 95% CI 0.96-1.10).

Maternal immune activation and abnormal brain development across CNS disorders

Epidemiological studies have shown a clear association between maternal infection and schizophrenia or autism in the progeny. Animal models have revealed maternal immune activation (mIA) to be a profound risk factor for neurochemical and behavioural abnormalities in the offspring. Microglial priming has been proposed as a major consequence of mIA, and represents a critical link in a causal chain that leads to the wide spectrum of neuronal dysfunctions and behavioural phenotypes observed in the juvenile, adult or aged offspring. Such diversity of phenotypic outcomes in the mIA model are mirrored by recent clinical evidence suggesting that infectious exposure during pregnancy is also associated with epilepsy and, to a lesser extent, cerebral palsy in children. Preclinical research also suggests that mIA might precipitate the development of Alzheimer and Parkinson diseases. Here, we summarize and critically review the emerging evidence that mIA is a shared environmental risk factor across CNS disorders that varies as a function of interactions between genetic and additional environmental factors. We also review ongoing clinical trials targeting immune pathways affected by mIA that may play a part in disease manifestation. In addition, future directions and outstanding questions are discussed, including potential symptomatic, disease-modifying and preventive treatment strategies.

The Role of PICALM in Alzheimer's Disease

Alzheimer's disease (AD) is a highly heritable disease (with heritability up to 76%) with a complex genetic profile of susceptibility, among which large genome-wide association studies (GWASs) pointed to the phosphatidylinositol-binding clathrin assembly protein (PICALM) gene as a susceptibility locus for late-onset Alzheimer's disease (LOAD) incidence. Here, we summarize the known functions of PICALM and discuss its genetic polymorphisms and their potential physiological effects associated with LOAD. Compelling data indicated that PICALM affects AD risk primarily by modulating production, transportation, and clearance of β-amyloid (Aβ) peptide, but other Aβ-independent pathways are discussed, including tauopathy, synaptic dysfunction, disorganized lipid metabolism, immune disorder, and disrupted iron homeostasis. Finally, given the potential involvement of PICALM in facilitating AD occurrence in multiple ways, it might be possible that targeting PICALM might provide promising and novel avenues for AD therapy.

An intronic PICALM polymorphism, rs588076, is associated with allelic expression of a PICALM isoform

BACKGROUND

Although genome wide studies have associated single nucleotide polymorphisms (SNP)s near PICALM with Alzheimer's disease (AD), the mechanism underlying this association is unclear. PICALM is involved in clathrin-mediated endocytosis and modulates Aß clearance in vitro. Comparing allelic expression provides the means to detect cis-acting regulatory polymorphisms. Thus, we evaluated whether PICALM showed allele expression imbalance (AEI) and whether this imbalance was associated with the AD-associated polymorphism, rs3851179.

RESULTS

We measured PICALM allelic expression in 42 human brain samples by using next-generation sequencing. Overall, PICALM demonstrated equal allelic expression with no detectable influence by rs3851179. A single sample demonstrated robust global PICALM allelic expression imbalance (AEI), i.e., each of the measured isoforms showed AEI. Moreover, the PICALM isoform lacking exons 18 and 19 (D18-19 PICALM) showed significant AEI in a subset of individuals. Sequencing these individuals and subsequent genotyping revealed that rs588076, located in PICALM intron 17, was robustly associated with this imbalance in D18-19 PICALM allelic expression (p = 9.54 x 10-5). This polymorphism has been associated previously with systolic blood pressure response to calcium channel blocking agents. To evaluate whether this polymorphism was associated with AD, we genotyped 3269 individuals and found that rs588076 was modestly associated with AD. However, when both the primary AD SNP rs3851179 was added to the logistic regression model, only rs3851179 was significantly associated with AD.

CONCLUSIONS

PICALM expression shows no evidence of AEI associated with rs3851179. Robust global AEI was detected in one sample, suggesting the existence of a rare SNP that strongly modulates PICALM expression. AEI was detected for the D18-19 PICALM isoform, and rs588076 was associated with this AEI pattern. Conditional on rs3851179, rs588076 was not associated with AD risk, suggesting that D18-19 PICALM is not critical in AD. In summary, this analysis of PICALM allelic expression provides novel insights into the genetics of PICALM expression and AD risk.

Role of an extracellular chaperone, Clusterin in the pathogenesis of Pseudoexfoliation Syndrome and Pseudoexfoliation Glaucoma

Pseudoexfoliation (PEX), an age related disorder is a prominent contributor to secondary glaucoma. Earlier studies have suggested involvement of clusterin in the development of PEX. We designed a case-control study to understand the role of clusterin single nucleotide polymorphisms (SNPs) in PEX and analyzed the role of risk alleles in the disease. Genotyping of SNPs in 136 PEX patients and 89 controls of Indian origin revealed a genetic association between rs2279590 and PEX in Indian population with a p-value of 0.004. The high risk allele "G" at rs2279590 has an effect on clusterin mRNA expression. There was a twofold higher clusterin mRNA level in "GG" genotyped individuals in comparison to "AA" genotyped individuals (p = 0.039). Western blot and immunohistochemistry studies showed an upregulation of Clusterin protein in pseudoexfoliation glaucoma (PXG) affected individuals in both aqueous humor and lens capsules respectively. Together, our results reveal that rs2279590 was found to be associated with PEX in Indian population and the risk allele mediates an allele specific upregulation of the clusterin mRNA. Moreover, upregulation of Clusterin protein in PXG individuals augments further protein deposition.

Meta-analysis of the association between CR1 polymorphisms and risk of late-onset Alzheimer's disease

CR1 polymorphisms have been reported to be associated with late-onset Alzheimer's disease (LOAD) susceptibility. The findings of these studies, however, have been inconsistent. Therefore, we performed a meta-analysis to assess the association between CR1 variants and LOAD susceptibility. We retrieved all relevant studies of the associations between CR1 polymorphisms and the susceptibility to LOAD for the period up to March 30, 2014. The strength of the association between CR1 polymorphisms and LOAD risk was estimated by odds ratios (ORs) and their 95% confidence intervals (CIs). A total of 6 articles were eventually identified with 2752 LOAD cases and 2313 controls for the rs6656401 polymorphism, and 4 studies containing 2547 LOAD cases and 2338 controls were included for the rs3818361 polymorphism. Overall, the pooled data showed that the CR1 rs6656401 polymorphism was significantly associated with LOAD risk in the overall population (A vs. G: OR=1.32, 95%CI=1.17-1.50, P=0.000; AG+AA vs. GG: OR=1.39, 95%CI=1.20-1.61, P=0.000). With respect to the CR1 rs3818361 polymorphism, a statistically significant increased LOAD risk was observed in the overall population (T vs. C: OR=1.24, 95% CI=1.13-1.37, P=0.000; TT+TC vs. CC: OR=1.30, 95% CI=1.15-1.46, P=0.000; TT vs. TC+CC: OR=1.35, 95% CI=1.06-1.71, P=0.014). This meta-analysis demonstrated significant associations of both the CR1 rs6656401 and CR1 rs3818361 polymorphisms with LOAD susceptibility.

CLU rs2279590 polymorphism contributes to Alzheimer's disease susceptibility in Caucasian and Asian populations

It is reported that CLU rs2279590 polymorphism is significantly associated with Alzheimer's disease (AD) in European ancestry. Recent studies investigated rs2279590 polymorphism in Asian population (Chinese, Japanese and Korean). Four studies showed negative association and two studies showed weak association between rs2279590 and AD. We believe that the weak association or no association may be caused by the relatively small sample size in Asian population. Here, we reinvestigated the association in Asian population. Meanwhile, to investigate the genetic heterogeneity of the rs2279590 polymorphism in Asian and Caucasian populations, we searched the PubMed and AlzGene databases and selected 11 independent studies (6 studies in Asian population and 5 studies in Caucasian population) including 20,655 individuals (8,605 cases and 12,050 controls) for meta-analysis. Our results showed significant association between rs2279590 polymorphism and AD in Asian population with P = 2.00E-04 and P = 2.00E-04 using additive and recessive models, respectively. We observed no significant heterogeneity between Asian and Caucasian populations. We believe that our results may be helpful to understand the mechanisms of CLU in AD pathogenesis and will be useful for future genetic studies in AD.

An Updated Analysis with 85,939 Samples Confirms the Association Between CR1 rs6656401 Polymorphism and Alzheimer's Disease

The complement receptor 1 (CR1) rs6656401 polymorphism was first identified to be associated with Alzheimer's disease (AD) in European ancestry. However, the following studies reported weak or no significant association in Chinese, Japanese, Korean, African-American, Polish, and Canadian populations. We think that these negative results may have been caused by either relatively small sample sizes compared with those used for the previous genome-wide association studies (GWAS) in European ancestry or the genetic heterogeneity of the rs6656401 polymorphism in different populations. Here, we reevaluated this association using the relatively large-scale samples from previous 24 studies (N = 85,939, 30,100 cases and 55,839 controls) by searching the PubMed, AlzGene, and Google Scholar databases. Using additive model, we did not identify significant heterogeneity among the 24 studies. We observed significant association between the rs6656401 polymorphism and AD in pooled populations (P = 1.82E-26, odds ratio (OR) = 1.18, 95 % confidence interval (CI) 1.15-1.22). In subgroup analysis, we identified significant results in East Asian population with P = 5.00E-04, OR = 1.31, 95 % CI 1.13-1.52. To our knowledge, this is the first meta-analysis to investigate the association between rs6656401 polymorphism and AD in East Asian, African-American, Canadian, and European populations. Our analysis further supports previous findings that the CR1 rs6656401 polymorphism contributes to AD susceptibility. We believe that our findings will be very useful for future genetic studies on AD.

Common GSAP promoter variant contributes to Alzheimer's disease liability

Toxic amyloid-β40-42 (Aβ40-42) peptide cleaved from Aβ protein precursor by β- and γ secretases plays a crucial role in the etiology of Alzheimer's disease (AD). Recently, Paul Greengard laboratory described a novel γ-secretase activating protein (gSAP) that specifically increases Aβ40-42 production without affecting the cleavage of another γ-secretase substrate, Notch. In this study, we show that expression of messenger RNA for GSAP, the gene that encodes the gSAP precursor protein, in human temporal cortex correlates with genotypes of 6 linked single-nucleotide polymorphisms (SNPs) located within the 5' region of GSAP in both Han Chinese and Caucasian populations. One of these SNPs, rs4727380, associates with AD diagnosis in a Han Chinese-based case-control study comprising 397 AD cases and 474 controls and in a Caucasian-based sample comprising 1906 cases and 1475 controls. As predicted, the high-expression allele of rs4727380 was identified as the AD risk allele in both samples. We also determined that rs4727380 correlates with AD diagnosis primarily among APOE4 noncarriers. To our knowledge, this is the first report providing genetic evidence linking GSAP to AD liability.

CR1 in Alzheimer's disease

The complement component receptor 1 gene (CR1), which encodes a type-I transmembrane glycoprotein, has recently been identified as one of the most important risk genes for late-onset Alzheimer's disease (LOAD). In this article, we reviewed the recent evidence concerning the role of CR1 in LOAD. First, we introduced the structure, localization and physiological function of CR1 in humans. Afterward, we summarized the relation of CR1 polymorphisms with LOAD risk. Finally, we discussed the possible impact of CR1 on the pathogenesis of AD including amyloid-β pathology, tauopathy, immune dysfunction and glial-mediated neuroinflammation. We hope that a more comprehensive understanding of the role that CR1 played in AD may lead to the development of novel therapeutics for the prevention and treatment of AD.

Influence of Alzheimer's disease genes on cognitive decline: the Guangzhou Biobank Cohort Study

Cognitive decline is a reduction in cognitive ability usually associated with aging, and those with more extreme cognitive decline either have or are at risk of progressing to mild cognitive impairment and dementia including Alzheimer's disease (AD). We hypothesized that genetic variants predisposing to AD should be predictive of cognitive decline in elderly individuals. We selected 1325 subjects with extreme cognitive decline and 1083 well-matched control subjects from the Guangzhou Biobank Cohort Study in which more than 30,000 southern Chinese older people have been recruited and followed up. Thirty single-nucleotide polymorphisms in 29 AD-associated genes were genotyped. No statistically significant allelic associations with cognitive decline were found by individual variant analysis. At the level of genotypic association, we confirmed that the APOE ε4 homozygote significantly accelerated cognitive decline and found that carriers of the ACE rs1800764_C allele were more likely to show cognitive decline than noncarriers, particularly in those without college education. However, these effects do not survive after multiple testing corrections, and together they only explain 1.7% of the phenotypic variance in cognitive score change. This study suggests that AD risk variants and/or genes are not powerful predictors of cognitive decline in our Chinese sample.