Case-control study and meta-analysis of low density lipoprotein receptor-related protein gene exon 3 polymorphism in Alzheimer's disease

Association of Low-Density Lipoprotein Receptor-Related Protein 1 and Its rs1799986 Polymorphism With Mild Cognitive Impairment in Chinese Patients With Type 2 Diabetes

Background

Low-density lipoprotein receptor-related protein 1 (LRP1) is involved in cerebral glucose metabolism and amyloid-β clearance. This study aimed to investigate the pathogenetic roles of LRP1 and its rs1799986 polymorphism in mild cognitive impairment (MCI) among patients with type 2 diabetes mellitus (T2DM).

Methods

A total of 166 Chinese patients with T2DM were enrolled and divided into two groups according to Montreal Cognitive Assessment (MoCA) scores. Neuropsychological tests were performed. Soluble LRP1 (sLRP1) levels were assessed using enzyme-linked immunosorbent assay, and the genotype of LRP1 rs1799986 was detected using the Sequenom method.

Results

Diabetic patients with MCI (n = 60) exhibited significantly lower plasma sLRP1 levels (p = 0.033) and worse glucose control (p = 0.009) than the healthy cognition controls (n = 106). Multivariate regression analysis revealed plasma sLRP1 levels [odds ratio (OR) = 0.971, p = 0.005] and HbA1c (OR = 1.298, p = 0.003) as a risk factor for MCI in diabetic patients, in addition to insulin use and hypertension. However, there was no association between plasma sLRP1 levels and HbA1c. After adjusting for age, sex, and education level, plasma sLRP1 levels in the MCI group were negatively correlated with Stroop Color Word Test B number (r = −0.335, p = 0.011), which represents selective attention, cognitive flexibility, and processing speed. Additionally, patients with T2DM carrying the T allele of LRP1 rs1799986 showed higher Auditory Verbal Learning Test (AVLT) delayed recall scores (p = 0.025).

Conclusion

Decreased plasma sLRP1 levels are associated with MCI, particularly with attention dysfunction, in patients with T2DM. Moreover, the T allele of LRP1 rs1799986 may decrease susceptibility to MCI. Further studies with large cohorts should be designed to elucidate the roles of LRP1 in hyperglycemia-induced cognitive decline.

Alzheimer's amyloid-β and tau protein accumulation is associated with decreased expression of the LDL receptor-associated protein in human brain tissue

INTRODUCTION

One of the major neuropathological features of Alzheimer's disease (AD) is the accumulation of amyloid-β (Aβ) protein in the brain. Evidence suggests that the low-density lipoprotein receptor-associated protein (RAP) binds strongly to Aβ and enhances its cellular uptake and that decreased RAP expression correlates with increased Aβ production in animal models of AD.

METHODS

The current study examined whether RAP levels change in AD human brain tissue and whether they are related to the amount of AD pathology. RAP and NeuN levels were determined by Western blot, while low-density lipoprotein receptor-related protein 1 (LRP1), tau and Aβ levels were determined by ELISA in the temporal cortex of 17 AD and 16 control cases.

RESULTS

An increase in total Aβ and insoluble and soluble tau protein was observed in AD brain tissue. In contrast, RAP levels were significantly decreased in AD brain tissue compared to controls. Correlation analysis revealed that levels of RAP correlated with both total Aβ and soluble and insoluble tau levels. Neither LRP1 nor NeuN levels were significantly altered in AD brain tissue homogenates and did not correlate with Aβ or tau protein levels.

CONCLUSION

Reduction in RAP may contribute to the accumulation and aggregation of Aβ in the AD brain.

Association between LRP1 C766T polymorphism and Alzheimer's disease susceptibility: a meta-analysis

Low density lipoprotein receptor-related protein 1 (LRP1) C766T polymorphism (rs1799986) has been extensively investigated for Alzheimer’s disease (AD) susceptibility. However, results in different studies have been contradictory. Therefore, we conducted a meta-analysis containing 6455 AD cases and 6304 controls from 26 independent case–control studies to determine whether there was an association between the LRP1 C766T polymorphism and AD susceptibility. The combined analysis showed that there was no significant association between LRP1 C766T polymorphism and AD susceptibility (TT + CT versus CC: OR = 0.920, 95% CI = 0.817–1.037, P = 0.172). In subgroup analysis, significant decreased AD susceptibility was found among Asian population in allele model (T versus C: OR = 0.786, 95% CI = 0.635–0.974, P = 0.028) and dominant model (TT + CT versus CC: OR = 0.800, 95% CI = 0.647–0.990, P = 0.040). Moreover, T allele of LRP1 C766T was statistically associated with late onset of AD (LOAD) (T versus C: OR = 0.858, 95% CI = 0.748–0.985, P = 0.029; TT + CT versus CC: OR = 0.871, 95% CI = 0.763–0.994, P = 0.040). In conclusion, our meta-analysis suggested that LRP1 C766T polymorphism was associated with lower risk of AD in Asian, and could reduce LOAD risk especially. Considering some limitations of our meta-analysis, further large-scale studies should be done to reach a more comprehensive understanding.

Lipid metabolism and glial lipoproteins in the central nervous system

Lipoproteins in the central nervous system (CNS) are not incorporated from the blood but are formed mainly by glial cells within the CNS. In addition, cholesterol in the CNS is synthesized endogenously because the blood-brain barrier segregates the CNS from the peripheral circulation. Apolipoprotein (apo) E is a major apo in the CNS. In normal condition, apo E is secreted from glia, mainly from astrocytes, and forms cholesterol-rich lipoproteins by ATP-binding cassette transporters. Subsequently, apo E-containing glial lipoproteins supply cholesterol and other components to neurons via a receptor-mediated process. Recent findings demonstrated that receptors of the low density lipoprotein (LDL) receptor family not only internalize lipoproteins into the cells but also, like signaling receptors, transduce signals upon binding the ligands. In this review, the regulation of lipid homeostasis will be discussed as well as roles of lipoproteins and functions of receptors of LDL receptor family in the CNS. Furthermore, the relation between lipid metabolism and Alzheimer's disease (AD) is discussed.

A pilot study of gene/gene and gene/environment interactions in Alzheimer disease

BACKGROUND

Although some genes associated with increased risk of Alzheimer Disease (AD) have been identified, few data exist related to gene/gene and gene/environment risk of AD. The purpose of this pilot study was to explore gene/gene and gene/environment associations in AD and to obtain data for sample size estimates for larger, more definitive studies of AD.

METHODS

The effect of gene/gene and gene/environment interaction related to late onset Alzheimer Disease (LOAD) was investigated in 153 subjects with LOAD and 302 gender matched controls enrolled in the Personalized Medicine Research Project, a population-based bio-repository. Genetic risk factors examined included APOE, ACE, OLR1,and CYP46 genes, and environmental factors included smoking, total cholesterol, LDL, HDL, triglycerides, C-reactive protein, blood pressure, statin use, and body mass index.

RESULTS

The mean age of the cases was 78.2 years and the mean age of the controls was 87.2 years. APOE4 was significantly associated with LOAD (OR=3.55, 95%CL=1.70, 7.45). Cases were significantly more likely to have ever smoked cigarettes during their life (49.3% versus 38.4%, p=0.03). The highest recorded blood pressure and pulse pressure measurements were significantly higher in the controls than the cases (all P<0.005). Although not statistically significant in this pilot study, the relationship of the following factors was associated in opposite directions with LOAD based on the presence of an APOE4 allele: obesity at the age of 50, ACE, OLR1, and CYP46.

CONCLUSIONS

These pilot data suggest that gene/gene and gene/environment interactions may be important in LOAD, with APOE, a known risk factor for LOAD, affecting the relationship of ACE and OLR1 to LOAD. Replication with a larger sample size and in other racial/ethnic groups is warranted and the allele and risk factor frequencies will assist in choosing an appropriate sample size for a definitive study.

LDL receptor-related protein 1: unique tissue-specific functions revealed by selective gene knockout studies

The LDL receptor-related protein (originally called LRP, but now referred to as LRP1) is a large endocytic receptor that is widely expressed in several tissues. LRP1 is a member of the LDL receptor family that plays diverse roles in various biological processes including lipoprotein metabolism, degradation of proteases, activation of lysosomal enzymes, and cellular entry of bacterial toxins and viruses. Deletion of the LRP1 gene leads to lethality in mice, revealing a critical, but as of yet, undefined role in development. Tissue-specific gene deletion studies reveal an important contribution of LRP1 in the vasculature, central nervous system, macrophages, and adipocytes. Three important properties of LRP1 dictate its diverse role in physiology: 1) its ability to recognize more than 30 distinct ligands, 2) its ability to bind a large number of cytoplasmic adaptor proteins via determinants located on its cytoplasmic domain in a phosphorylation-specific manner, and 3) its ability to associate with and modulate the activity of other transmembrane receptors such as integrins and receptor tyrosine kinases.

Genetic association between low-density lipoprotein receptor-related protein gene polymorphisms and Alzheimer's disease in Chinese Han population

Alzheimer's disease (AD) is the most common neurodegenerative disorders in the elderly. Low-density lipoprotein receptor-related protein (LRP), as a receptor of apolipoprotein E (APOE), APP, and alpha2 macroglobulin (alpha2-M), keeps the balance between degeneration and production of beta-amyloid protein (Abeta) clearance. Its gene had been defined as a candidate gene for AD, but the results were not universal. Total 496 AD patients and 478 controls were recruited in Chinese Han population and real-time PCR was used to detect the polymorphism of LRP C766T. Multiple logistic regression, Chi-square test and survival analysis were performed to explore the association. The distribution of LRP genotypes and alleles was significantly different between cases and controls, and T allele could reduce the risk for developing AD (OR of CT genotype: 0.57; 95% CI: 0.38-0.85, rho=0.003; OR of T allele: 0.57; 95% CI: 0.39-0.83, rho=0.003). TT genotype carriers had 5 years later for developing AD compared with CC genotype carriers, but survival analysis did not conform this (LRP TT vs. CT and CC log rank chi(2)=2.71, rho=0.26). The distribution of LRP C766T genotypes and alleles was different among different severity stratified by MMSE yet (rho=0.26). Our data suggested that the polymorphism of LRP C766T was strongly associated with AD and T allele might be a protective factor for AD in Chinese Han population.

Fatty acids, lipid metabolism and Alzheimer pathology

Alzheimer's disease is the most common form of dementia in the elderly. The cause of Alzheimer's disease is still unknown and there is no cure for the disease yet despite 100 years of extensive research. Cardiovascular risk factors such as high serum cholesterol, presence of the Apolipoprotein epsilon4 (APOE epsilon4) allele and hypertension, play important roles in the development of Alzheimer's disease. We postulate that a combination of diet, lifestyle, vascular, genetic, and amyloid related factors, which enhance each other's contribution in the onset and course of Alzheimer's disease, will be more likely the cause of the disease instead of one sole mechanism. The possibility that the risk for Alzheimer's disease can be reduced by diet or lifestyle is of great importance and suggests a preventative treatment in Alzheimer's disease. Because of the great importance of lipid diets and metabolism in preventative treatment against both Alzheimer's disease and cardiovascular disease, long-chain polyunsaturated fatty acids from fish oil, ApoE genotype and cholesterol metabolism in correlation with Alzheimer's disease will be reviewed.

Cholesterol in Alzheimer's disease

Alzheimer's disease (AD) is the most common form of neurodegenerative dementia and affects up to 15 million people worldwide. Although no single cause of AD has been identified, recent research has suggested that several pathogenetic factors influence risk and expression. A growing amount of evidence underscores a mechanistic link between cholesterol metabolism in the brain and the formation of amyloid plaques. Excess brain cholesterol has been associated with increased formation and deposition of amyloid-beta peptide from amyloid precursor protein. Cholesterol-lowering statins have become a focus of research in AD. Genetic polymorphisms associated with pivotal points in cholesterol metabolism in brain tissues may contribute to the risk and pathogenesis of AD. In this review, we summarise current knowledge of the role of cholesterol metabolism in the pathogenesis of AD and examine the potential of statins in the prevention and treatment of AD.

Longitudinal memory performance during normal aging: twin association models of APOE and other Alzheimer candidate genes

The APOE gene (apolipoprotein E) is a major risk factor for Alzheimer's Disease (AD) but has been inconsistently associated with memory in nondemented adults. Two other genes with mixed support as genetic risk factors for AD, A2M (alpha-2-macroglobulin) and LRP (low-density lipoprotein receptor-related protein), have not been studied in relation to memory among nondemented adults. The present study examined these three genes and latent growth parameters estimated from memory performance spanning 13 years in 478 twins from the Swedish Adoption/Twin Study of Aging (SATSA). APOE was associated with working and recall memory ability levels and working memory rate of change, with e4 homozygotes exhibiting the worst performance at all ages. Homozygotes for the rare A2M insertion/deletion variant exhibited accelerating decline on delayed figural recognition. There were no significant findings for LRP. Dominance, often untested in previous studies, was important in the current study's findings.

Candidate genes for late-onset Alzheimer's disease: Focus on chromosome 12

In recent years, there was an increasing interest on candidate genes may play an important role in the development of Alzheimer's disease (AD). Several genome wide screens have undertaken so far or expanded recently, and suggested a number of genomic areas that may contain novel susceptibility genes for AD, in particular most compelling have been the findings on chromosome 12. Polymorphisms in different susceptibility genes on chromosome 12 (A2M, LRP1, CP2 and OLR1) are now being suggested as possible genetic markers for increased risk of developing AD. However, many of these studies are controversial and have shown conflicting results. Thus far, the search for the chromosome 12 Alzheimer's gene must continue and there are several other genes in this region that we are looking at. In this article, we focused on the current knowledge of the genetics of familial late-onset and sporadic AD linked to the chromosome 12, and the future search for other candidate genes.

Association study of polymorphisms in LRP1, tau and 5-HTT genes and Alzheimer’s disease in a sample of Colombian patients

Analysis of genetic susceptibility factors for Alzheimer's disease (AD) in populations with different genetic and environmental background may be useful to understand AD etiology. There are few genetic association studies of AD in Latin America. In the present work, we analyzed polymorphisms in 3 candidate genes; the LDL receptor related protein-1, the microtubule-associated protein Tau and the serotonin transporter genes in a sample of 106 Colombian AD patients and 97 control subjects. We did not find a significant allelic or genotypic association with any of the three polymorphisms analyzed using different statistical analysis, including a neural network model or different sample stratifications. To date, APOE polymorphisms are the only genetic risk factors identified for AD in the Colombian population. It may be factible that future combination of high-throughput genotyping platforms and multivariate analysis models may lead to the identification of other genetic susceptibility factors for AD in the Colombian population.

Current knowledge of chromosome 12 susceptibility genes for late-onset Alzheimer's disease

In the last decade, it has become more apparent the important role genes play in the development of late-onset Alzheimer's disease (AD). Great efforts, involving human genome scans and candidate gene studies, have been given towards identifying susceptibility genes for AD. A number of regions on different chromosomes have been reported to demonstrate linkage for AD. Of these, findings on chromosome 12 are some of the most compelling. Worldwide genetic association studies pre-dating and subsequent to recent linkage studies have identified and focused upon a number of genes that map to the areas of reported linkage on chromosome 12, however, analyses of those genes studied to date, on the whole, remain inconclusive and ambiguous. This paper reviews studies that have provided evidence of linkage for AD on chromosome 12 and in turn discusses the work conducted to date on candidate genes that have been identified and map to the chromosome 12 regions of interest.

Low-density lipoprotein receptor-related protein polymorphisms in patients with elevated factor VIII coagulant activity and venous thrombosis

Elevated factor VIII coagulant activity (FVIII:C) levels (>150 IU/dl) represent a prevalent independent risk factor for venous thromboembolism (VTE). Low-density lipoprotein receptor-related protein (LRP) is involved in factor VIII clearance in vivo, and elevated FVIII:C was a feature of the LRP knockout mouse model. Three coding polymorphisms of LRP1 (exon 3, C766T; exon 14, A217V; and exon 39, D2080N), together with an insertion/deletion polymorphism within the first intron of lipoprotein receptor-associated protein (LRPAP1), have been identified. In addition, LRP1 2080D was recently reported to be associated with increased plasma FVIII:C levels in normal individuals. In this study, we investigated the role of these four polymorphisms in patients with objectively confirmed VTE and elevated FVIII:C levels. In our control group, genotype distributions were consistent with previous reports. Neither the allele frequencies nor genotype distributions at LRP1 A217V, LRP1 D2080N and LRPAP1 intron 1 were significantly different between the elevated FVIII:C and control groups. In contrast to previous reports, we found no effect of LRP1 D2080N genotype on plasma FVIII:C levels in normal individuals. More importantly, prevalence of the LRP1 2080D allele was not increased in the group of patients with high FVIII:C and VTE. We conclude that LRP1 and LRPAP1 polymorphisms are not responsible for high FVIII:C levels in patients with VTE.

Genomic regulation after CD40 stimulation in microglia: Relevance to Alzheimer's disease

Key pathological processes in Alzheimer's disease (AD) include the accumulation of amyloid beta peptide (Abeta) which, in excess, triggers pathological cascades including widespread inflammation, partly reflected by chronic microglial activation. It has previously been suggested that CD40/CD40L interaction promotes AD like pathology in transgenic mice. Thus, amyloid burden, gliosis and hyperphosphorylation of tau are all reduced in transgenic models of AD lacking functional CD40L. We therefore hypothesized that cellular events leading to altered APP metabolism, inflammation and increased tau phosphorylation underlying these observations would be regulated at the genomic level. In the present report, we used the Affymetrix (GeneChip) oligonucleotide microarray U133A to gain insight into the global and simultaneous transcriptomic changes in response to microglia activation after CD40/CD40L ligation. As expected, regulation of elements of the NF-kappaB signaling, chemokine and B cell signaling pathways was observed. Taken together, our data also suggest that CD40 ligation in human microglia specifically perturbs many genes associated with APP processing.

Cholesteryl ester transfer protein (CETP) polymorphism modifies the Alzheimer's disease risk associated with APOE ε4 allele

Cholesterol regulates the production of amyloid beta (Abeta), which is central to the pathogenesis of Alzheimer's disease (AD), with high cellular cholesterol promoting and low cellular cholesterol reducing Abeta in vitro and in vivo. High density lipoprotein (HDL) plays a central role in the removal of excess cholesterol from cells, and cholesteryl ester transfer protein (CETP) is a crucial protein involved in the regulation of HDL levels. Two common polymorphisms in the promoter region (C-629A) and exon 14 I405V of the CETP gene are associated with CETP activity and HDL levels. To investigate if these sequence variants in CETP might be of importance in mediating susceptibility to AD, independently or in concert with apolipoprotein E (APOE) epsilon4 allele, we studied a sample of 286 Spanish AD patients and 315 healthy controls. In APOE epsilon4 carriers, homozygous for the CETP (-629) A allele had approximately a three times lower risk of developing AD (odds ratio 2.33, 95% CI 1.01-5.37), than homozygous and heterozygous carriers of the CETP (-629) C allele (odds ratio 7.12, 95% CI 4.51-11.24, P for APOE epsilon4/CETP (-629) AA genotype interaction < 0.001). Our data suggest that CETP behaves as a modifier gene of the AD risk associated with the APOE epsilon4 allele, possibly through modulation of brain cholesterol metabolism.

Quantification of apolipoprotein E receptors in human brain-derived cell lines by real-time polymerase chain reaction

Apolipoprotein (apo) E4 is a risk factor for Alzheimer's disease (AD) and other neurodegenerative diseases, compared to wild-type apoE3. The mechanism(s) is unknown. One possibility, demonstrated in peripheral tissue cell lines, is that apoE stimulates nitric oxide synthase (NOS) via a receptor-dependent signalling pathway and that apoE4 generates inappropriate amounts of nitric oxide (NO) compared to apoE3. Prior to biochemical investigations, we have quantified the expression of several candidate receptor genes, including low-density lipoprotein-receptor (LDL-r) family members and scavenger receptor class B, types I and II (SR-BI/II), as well as the three NOS isoenzymes and protein kinase B (Akt), in 38 human cell lines, of which 12 derive from brain. Expression of apoE receptor 2 (apoER2), a known signalling receptor in brain, was readily detected in SH-SY-5Y and CCF-STTG1 cells, common models of neurons and astrocytes, respectively, and was highest in H4 neuroglioma, NT-2 precursor cells and IMR-32 neuroblastoma cells. Transcripts of the other lipoprotein receptors were widely, but variably, distributed across the different cell types. Of particular note was the predominant expression of SR-BII over SR-BI in many of the brain-derived cells. As the C-terminus of SR-BII, like apoER2, contains potential SH3 signalling motifs, we suggest that in brain SR-BII functions as a signal transducer receptor.

Association study and meta-analysis of low-density lipoprotein receptor related protein in Alzheimer's disease

Genome scans in sporadic Alzheimer's disease (AD) have revealed a possible susceptibility locus on chromosome 12. The low density lipoprotein receptor related protein (LRP1) gene lies within this area of linkage. Eighteen previous AD case-control studies have investigated the C766T polymorphism in LRP1 with conflicting results, including a protective effect on AD of the T allele, an increased susceptibility towards AD with both the C and T alleles, or no association at all. We have now performed a case-control study based on a large UK cohort of 477 AD patients and 466 matched controls, and have included these data, with those drawn from the 18 previous studies, into in a meta-analysis of 4668 AD patients and 4473 controls. We find no evidence for influence on the risk for AD in either our own present cohort or in the combined data set. Furthermore, we investigated whether the C766T polymorphism might modify the clinical and pathological phenotype in our cohort. We found no association with AD when the cohort was stratified into those with early (<65 years) or late (>65 years) onset, or when split into Apolipoprotein E (APOE) epsilon4 bearers and epsilon4 non-bearers. In addition, the C766T polymorphism was shown not to influence the age onset of AD. In a separate autopsy-confirmed cohort of 130 AD cases, no association with genotype or allele was observed for tissue levels of beta-amyloid 40, beta-amyloid 42, total beta-amyloid, pathological tau proteins, microglial cells or extent of astrocytic activity. Therefore, in this present study, we find no evidence for the involvement of this polymorphism either in increasing the susceptibility to AD, or by acting as a phenotypic modifier.

Cholesterol homeostasis in neurons and glial cells

Cholesterol is highly enriched in the brain compared to other tissues. Essentially all cholesterol in the brain is synthesized endogenously since plasma lipoproteins are unable to cross the blood-brain barrier. Cholesterol is transported within the central nervous system in the form of apolipoprotein E-containing lipoprotein particles that are secreted mainly by glial cells. Cholesterol is excreted from the brain in the form of 24-hydroxycholesterol. Apolipoprotein E and cholesterol have been implicated in the formation of amyloid plaques in Alzheimer's disease. In addition, the progressive neurodegenerative disorder Niemann-Pick C disease is characterized by defects in intracellular trafficking of cholesterol.

Biological and genetic factors influencing plasma factor VIII levels in a healthy family population: results from the Stanislas cohort

The mechanisms underlying the variability of factor VIII (FVIII) levels are still poorly understood. The only receptor of FVIII identified so far is the lipoprotein receptor-related protein (LRP), which is thought to be involved in FVIII degradation. We aimed to characterize biological and genetic factors related to FVIII variability, focusing on coding polymorphisms of the LRP gene and polymorphisms potentially detected by molecular screening of the LRP-binding domains of the FVIII gene. Plasma FVIII coagulant activity (FVIII:C) and von Willebrand factor (VWF:Ag) antigen levels were measured in a sample of 100 healthy nuclear families (200 parents and 224 offspring). The ABO blood group and the three coding polymorphisms of the LRP gene (A217V, D2080N and C766T) were genotyped. Lipids and anthropometric factors poorly contributed to the variability of FVIII:C (<5%). A strong effect of ABO blood groups on FVIII:C levels was observed that remained significant after adjustment for VWF:Ag levels (P = 0.02). These two factors explained more than 50% of FVIII:C variability. After adjustment for VWF:Ag and ABO blood groups, a residual resemblance for FVIII:C persisted between biological relatives (rho = 0.13 +/- 0.06 between parents and offspring, rho = 0.24 +/- 0.09 between siblings) compatible with an additional genetic influence. The N allele of the LRP/D2080N polymorphism was associated with decreased levels of FVIII:C (90.4 +/- 8.7 vs. 102.2 +/- 3.5 IU/dl, P = 0.03) and VWF:Ag levels (109.1 +/- 11.2 vs. 125.4 +/- 4.4 IU/dl, P = 0.02). No polymorphism was detected in the LRP-binding domains of the FVIII gene. This study reinforces the hypothesis of a genetic influence of FVIII levels beyond the influence of VWF:Ag and ABO blood groups. The D2080N polymorphism of the LRP gene weakly contributed to the variability of FVIII:C levels in this healthy population.

Cholesterol at the crossroads: Alzheimer's disease and lipid metabolism

Alzheimer's Disease (AD) is a devastating disease that affects millions of elderly persons. Despite years of intense investigations, genetic risk factors that affect the majority of AD cases have yet to be determined. Recent studies suggest that cholesterol metabolism has integral part in AD pathogenesis, suggesting that genes that regulate lipid metabolism may also play roles in AD. This review will first describe emerging evidence that links cholesterol to the mechanisms thought to underlie AD. Based on this rationale, candidate genes located in regions implicated in AD that have roles in lipid metabolism will then be discussed.

Meta-analysis of serotonin transporter polymorphisms and affective disorders

Polymorphisms in the promoter region (5-HTTLPR) of the serotonin transporter and a variable number of tandem repeats polymorphism in the second intron have been widely studied. However, the results of association studies examining unipolar depression (MDD) or bipolar disorder depression (BPD) have been mixed. To precisely ascertain small associations with both polymorphisms, a meta-analysis was performed involving several thousand subjects, using random-effects modeling. For MDD, the effect of the 5-HTTLPR genotype was significant (chi2=6.1, P<0.05), with 21% of MDD subjects and 17% of controls homozygous for the short (S) allele (odds ratio, 1.16). Similar findings were noted in BPD, with a higher frequency of S/S genotypes in affected patients, although the results did not reach statistical significance. Results of transmission disequilibrium tests trended in a similar direction but also did not reach statistical significance. No consistent effect of the variable number of tandem repeats polymorphism was revealed for either MDD or BPD. The results suggest that the S allele, or a neighboring allele in linkage disequilibrium, is recessive for MDD and possibly BPD. Notably, the association is very small. With these small associations, confounding issues such as population stratification require addressing. Significant heterogeneity between studies was also evident, possibly reflecting differences in diagnosis, different control populations, and different ethnic populations. These factors should Influence the interpretation of the association found in this analysis.

Genetic and functional characteristics of the human in vivo LRP1/A2MR receptor suggested as a risk marker for Alzheimer’s disease and other complex (degenerative) diseases

LDL receptor-related protein/alpha2-macroglobulin receptor (LRP1/A2MR) a multiligand receptor is considered as not only being a possible risk factor of neurodegenerative diseases like Alzheimer's disease but also as determining the progression of other complex diseases like atherosclerosis and cancer. Although a large number of in vitro studies have highlighted its functional importance, as yet not enough is known about the clinical importance of the genetic background of LRP1 in human diseases. The aim of this ex vivo/in vivo study of 448 subjects was to present data on genetic LRP1 variants of healthy European Caucasians from Central Germany. Genotype-dependent LRP1 expression was analyzed in a representative subgroup (gene expression: n = 127, protein expression: n = 44). These data were evaluated in comparison to other published clinical LRP1 studies. For 15 functionally interesting genetic variants the genotype and allele distributions of the German Caucasians were presented in relation to their in vivo LRP1 gene and protein expression. A direct influence of the LRP1 promoter polymorphism c.1-25C>G on the human in vivo LRP1 expression level was demonstrated. In an analysis of 48 further studies genomic and functional results were evaluated. The analysis especially on Alzheimers's disease partly highlighted contradictory results, but suggested that ethnic as well as genomic characteristics determine LRP1 expression and must be considered in clinical investigations on human LRP1.

Role of LRP in TGF?2-mediated neuronal uptake of A? and effects on memory

There is increasing evidence that soluble amyloid-beta peptide (Abeta) uptake into neurons is an early event in the pathogenesis of Alzheimer's disease (AD). Identification of the early events leading to neuronal dysfunction is key to developing therapeutic strategies, but relative roles of receptors and factors modulating uptake are poorly understood. Studies have shown that transforming growth factor beta (TGFbeta), particularly TGFbeta2, can influence the targeting of Abeta to cells in vitro. TGFbeta2 can target Abeta to neurons in organotypic hippocampal slice cultures (OHSC). We examine a specific mechanism for TGFbeta2-mediated targeting of Abeta to neurons. The receptor-associated protein (RAP), a low-density lipoprotein receptor-related protein (LRP) antagonist, can attenuate the cellular targeting of Abeta both in vitro and in vivo and prevent Abeta/TGFbeta2-induced memory retention deficits. Using both in vitro and in vivo methods, we identify LRP as playing a role in TGFbeta2-mediated Abeta uptake, neurodegeneration, and spatial memory impairment.

Familial clustering and genetic risk for dementia in a genetically isolated Dutch population

Despite advances in elucidating the genetic epidemiology of Alzheimer's disease and frontotemporal dementia, the aetiology for most patients with dementia remains unclear. We examined the genetic epidemiology of dementia in a recent genetically isolated Dutch population founded around 1750. The series of 191 patients ascertained comprised 122 probable Alzheimer's disease patients with late onset and 17 with early onset, and 22 with possible Alzheimer's disease. It further included 10 patients with vascular dementia, nine with Lewy body dementia and six with frontotemporal dementia. All patients, except those with vascular dementia, were more closely related than healthy individuals from the same area. Clustering was strongest for patients with early-onset Alzheimer's disease or Lewy body dementia. Although 14% of late-onset Alzheimer's disease patients had evidence of autosomal dominant disease, consanguinity was found in three late-onset Alzheimer's disease patients, suggesting a recessive or polygenic model underlying the trait. We found no clustering of vascular dementia, implying a difference in genetic risk for late-onset Alzheimer's disease and vascular dementia. Mutations in known genes could not explain the occurrence of dementia, but the population attributable proportion of apolipoprotein E gene (APOE*4) was high (45%) due to a high frequency of APOE*4 carriers. Earlier identified regions on chromosomes 10 and 12, nor the effect of the alpha-2-macroglobulin (A2M) I/D polymorphism on Alzheimer's disease could be confirmed in our study. We did find evidence for association between the A2M D-allele and Lewy body dementia. Our data showed a strong familial clustering of various forms of dementia in this isolated Dutch population. A high percentage of late-onset Alzheimer's disease could be explained by APOE*4, but 55% of its origin is still unknown.

Commonalities between genetics of cardiovascular disease and neurodegenerative disorders

PURPOSE OF REVIEW

Numerous epidemiological and clinical data suggest that neurodegenerative disorders, such as Alzheimer's disease, may be related directly or indirectly to cardiovascular risk. Genetic studies have demonstrated that they share at least one common susceptibility gene, encoding apolipoprotein E, a modulator of cardiac risk and of cognitive impairment. Several studies have suggested that other genes involved in the development of cardiovascular diseases may be involved. Previous studies indicated that additional genes contribute to Alzheimer's disease, in particular to the sporadic, more common late-onset form. In this review, the authors focus on recent findings concerning the modulation of the risk of Alzheimer's disease by genes also involved in the development of cardiovascular diseases.

RECENT FINDINGS

The intensive search conducted in the past year gave rise to many publications, more than half of which were related to genes common to cardiovascular and neurodegenerative disorders. The majority of the genes studied are involved in cholesterol metabolism, hypertension, lipid oxidation and detoxication, or inflammatory processes.

SUMMARY

In the past year, approximately 100 studies concerning the genetics of Alzheimer's disease were published around the world. Results suggest that the risk of Alzheimer's disease is modulated by various genes encoding proteins involved in cholesterol metabolism, in the detoxication of lipoprotein oxidation or encoding cytokines.

Regional European differences in allele and genotype frequencies of low density lipoprotein receptor-related protein 1 polymorphism in Alzheimer's disease

The low density lipoprotein receptor-related protein 1 (LRP1 gene) is a candidate gene for Alzheimer's disease (AD), because it is a ligand for proteins involved in AD pathogenesis, such as apolipoprotein E (APOE), alpha2-macroglobulin (A2M), amyloid precursor protein (APP), and is located on chromosome 12, within a region linked with AD. An association between a silent polymorphism (C/T) in exon 3 and late onset AD has been reported, with an increased frequency of the C allele, although with conflicting results. We examined this polymorphism in a cohort of 166 sporadic AD patients and 225 sex- and age-matched nondemented controls from Southern Italy. No statistically significant differences were found in LRP1 genotype and allele frequencies between the whole AD sample and controls, nor in early- and late-onset subsets of AD patients. No statistically significant differences in frequencies between LRP1 alleles and AD among APOE allele, age, or gender strata were found. Finally, comparing our results with the findings from other European populations, the LRP1 C allele frequency showed a statistically significant decreasing trend from Northern to Southern regions of Europe, with a concomitant increase in LRP1 T allele frequency, but in AD patients only. Finally, in the AD sample, a decreasing geographical trend from North to South of Europe was found for LRP1 CC genotype, and an inverse trend for LRP1 CT genotype frequency. We suggest that these regional variations in LRP1 genotype and allele frequencies in AD could be related to the different patterns of association between this polymorphism and the disease in various European studies.

Lack of association between the levels of the low-density lipoprotein receptor-related protein (LRP) and either Alzheimer dementia or LRP exon 3 genotype

The low-density lipoprotein receptor-related protein (LRP), which interacts with the Alzheimer disease (AD) beta-amyloid precursor protein (APP), represents an important pathway in AD pathology. LRP-mediated receptor pathways appear to regulate both the production and the clearance of amyloid beta-protein (Abeta), a principal neuropathological product in AD. Several conflicting studies have examined levels of LRP in AD brains, as well as the relationship between the LRP exon 3 (C766T) polymorphism and LRP levels and/or disease susceptibility. In order to further investigate the role of LRP in AD, we examined well-characterized brain samples collected from subjects with varying degrees of cognitive impairment for LRP protein expression levels as well as for the presence of the LRP exon 3 polymorphism. We found no correlation between LRP levels and either presence of the disease or cognitive decline. In addition, we found no correlation between the LRP exon 3 polymorphism and either AD or LRP levels.

Islet-brain1/C-Jun N-terminal kinase interacting protein-1 (IB1/JIP-1) promoter variant is associated with Alzheimer's disease

Islet-brain1 (IB1) or c-Jun NH2 terminal kinase interacting protein-1 (JIP-1), the product of the MAPK8IP1 gene, functions as a neuronal scaffold protein to allow signalling specificity. IB1/JIP-1 interacts with many cellular components including the reelin receptor ApoER2, the low-density lipoprotein receptor-related protein (LRP), kinesin and the Alzheimer's amyloid precursor protein. Coexpression of IB1/JIP-1 with other components of the c-Jun NH2 terminal-kinase (JNK) pathway activates the JNK activity; conversely, selective disruption of IB1/JIP-1 in mice reduces the stress-induced apoptosis of neuronal cells. We therefore hypothesized that IB1/JIP-1 is a risk factor for Alzheimer's disease (AD). By immunocytochemistry, we first colocalized the presence of IB1/JIP-1 with JNK and phosphorylated tau in neurofibrillary tangles. We next identified a -499A>G polymorphism in the 5' regulatory region of the MAPK8IP1 gene. In two separate French populations the -499A>G polymorphism of MAPK8IP1 was not associated with an increased risk to AD. However, when stratified on the +766C>T polymorphism of exon 3 of the LRP gene, the IB1/JIP-1 polymorphism was strongly associated with AD in subjects bearing the CC genotype in the LRP gene. The functional consequences of the -499A>G polymorphism of MAPK8IP1 was investigated in vitro. In neuronal cells, the G allele increased transcriptional activity and was associated with an enhanced binding activity. Taken together, these data indicate that the increased transcriptional activity in the presence of the G allele of MAPK8IP1 is a risk factor to the onset of in patients bearing the CC genotype of the LRP gene.

Lack of association of two lipoprotein lipase polymorphisms with Alzheimer's disease

A recent genetic study demonstrated associations between an altered risk of Alzheimer's disease (AD) and two polymorphisms in the lipoprotein lipase (LPL) gene, Asn291Ser and Ser447Ter. LPL immunostains senile plaques, and is a ligand of the low-density lipoprotein receptor-related protein (LRP), a major apolipoprotein E (apoE) receptor. LPL increases the cellular uptake of apoE via LRP, and polymorphisms in LPL alter its ability to mediate apoE-LRP interactions, with potential implications for AD pathogenesis. Here, we tested the genetic association of LPL with AD in a case-control study. For the Asn291Ser polymorphism, we analyzed 277 individuals (141 AD, 136 control) and found no significant difference in allele frequencies between the AD and control groups. For the Ser447Ter polymorphism, we analyzed 187 individuals (108 AD, 79 control) and again found no significant difference in allele frequencies between the AD and control groups. Thus, our study does not support associations between AD and two common polymorphisms in LPL.