Rare mutations in AβPP, PSEN1, and PSEN2 cause uncommon early onset forms of Alzheimer’s disease (AD), and common variants in MAPT are associated with risk of other neurodegenerative disorders. We sought to establish whether common genetic variation in these genes confer risk to the common form of AD which occurs later in life (>65 years). We therefore tested single-nucleotide polymorphisms at these loci for association with late-onset AD (LOAD) in a large case-control sample consisting of 3,940 cases and 13,373 controls. Single-marker analysis did not identify any variants that reached genome-wide significance, a result which is supported by other recent genome-wide association studies. However, we did observe a significant association at the MAPT locus using a gene-wide approach (p = 0.009). We also observed suggestive association between AD and the marker rs9468, which defines the H1 haplotype, an extended haplotype that spans the MAPT gene and has previously been implicated in other neurodegenerative disorders including Parkinson’s disease, progressive supranuclear palsy, and corticobasal degeneration. In summary common variants at AβPP, PSEN1, and PSEN2 and MAPT are unlikely to make strong contributions to susceptibility for LOAD. However, the gene-wide effect observed at MAPT indicates a possible contribution to disease risk which requires further study.
Alzheimer’s disease; amyloid-β protein precursor; genetics; human; MAPT protein; PSEN1 protein; PSEN2 protein
Lower angiotensin-converting enzyme (ACE) activity could increase the risk of Alzheimer’s disease (AD) as ACE functions to degrade amyloid-β (Aβ). Therefore, we investigated whether ACE protein and activity levels in cerebrospinal fluid (CSF) and serum were associated with CSF Aβ, total tau (tau) and tau phosphorylated at threonine 181 (ptau).
We included 118 subjects from our memory clinic-based Amsterdam Dementia Cohort (mean age 66 ± 8 years) with subjective memory complaints (n = 40) or AD (n = 78), who did not use antihypertensive drugs. We measured ACE protein levels (ng/ml) and activity (RFU) in CSF and serum, and amyloid β1–42, tau and ptau (pg/ml) in CSF.
Cross-sectional regression analyses showed that ACE protein level and activity in CSF and serum were lower in patients with AD compared to controls. Lower CSF ACE protein level, and to a lesser extent serum ACE protein level and CSF ACE activity, were associated with lower CSF Aβ, indicating more brain Aβ pathology; adjusted regression coefficients (B) (95% CI) per SD increase were 0.09 (0.04; 0.15), 0.06 (0.00; 0.12) and 0.05 (0.00; 0.11), respectively. Further, lower CSF ACE protein level was associated with lower CSF tau and ptau levels; adjusted B’s (95% CI) per SD increase were 0.15 (0.06; 0.25) and 0.17 (0.10; 0.25), respectively.
These results strengthen the hypothesis that ACE degrades Aβ. This could suggest that lowering ACE levels by for example ACE-inhibitors might have adverse consequences for patients with, or at risk for AD.
Midlife elevated blood pressure and hypertension contribute to the development of Alzheimer's disease (AD) and overall dementia. We sought to estimate whether angiotensin-converting enzyme inhibitors (ACE-Is) reduced the risk of developing mild cognitive impairment (MCI) in cognitively normal individuals. In the Italian Longitudinal Study on Aging, we evaluated 1,445 cognitively normal individuals treated for hypertension but without congestive heart failure from a population-based sample from eight Italian municipalities with a 3.5-year follow-up. MCI was diagnosed with current clinical criteria. Dementia, AD, and vascular dementia were diagnosed based on DSM-IIIR criteria, NINCDS–ADRDA criteria, and ICD-10 codes. Among 873 hypertension-treated cognitively normal subjects, there was no significant association between continuous exposure to all ACE-Is and risk of incident MCI compared with other antihypertensive drugs [hazard ratio (HR), 0.45, 95% confidence interval (CI), 0.16–1.28]. Captopril exposure alone did not significantly modify the risk of incident MCI (HR, 1.80, 95% CI, 0.39–8.37). However, the enalapril sub-group alone (HR, 0.17, 95% CI, 0.04 –0.84) or combined with the lisinopril sub-group (HR, 0.27, 95% CI, 0.08–0.96), another ACE-I structurally related to enalapril and with similar potency, were associated with a reduced risk of incident MCI. Study duration exposure to ACE-Is as a “class” was not associated with incident MCI in older hypertensive adults. However, within-class differences linked to different chemical structures and/or drug potencies may exist, with a possible effect of the enalapril and lisinopril sub-groups in reducing the risk of incident MCI.
Angiotensin-converting enzyme inhibitors; Mild cognitive impairment; Dementia; Antihypertensive drugs
Neprilysin (NEP), also known as membrane metalloendopeptidase (MME), is considered amongst the most important β-amyloid (Aβ)-degrading enzymes with regard to prevention of Alzheimer’s disease (AD) pathology. Variation in the NEP gene (MME) has been suggested as a risk factor for AD. We conducted a genetic association study of 7MME SNPs – rs1836914, rs989692, rs9827586, rs6797911, rs61760379, rs3736187, rs701109 - with respect to AD risk in a cohort of 1057 probable and confirmed AD cases and 424 age-matched non-demented controls from the United Kingdom, Italy and Sweden. We also examined the association of these MME SNPs with NEP protein level and enzyme activity, and on biochemical measures of Aβ accumulation in frontal cortex – levels of total soluble Aβ, oligomeric Aβ1-42, and guanidine-extractable (insoluble) Aβ – in a sub-group of AD and control cases with post-mortem brain tissue. On multivariate logistic regression analysis one of the MME variants (rs6797911) was associated with AD risk (P = 0.00052, Odds Ratio (O.R. = 1.40, 95% confidence interval (1.16-1.70)). None of the SNPs had any association with Aβ levels; however, rs9827586 was significantly associated with NEP protein level (p=0.014) and enzyme activity (p=0.006). Association was also found between rs701109 and NEP protein level (p=0.026) and a marginally non-significant association was found for rs989692 (p=0.055). These data suggest that MME variation may be associated with AD risk but we have not found evidence that this is mediated through modification of NEP protein level or activity.
Neprilysin; MME; gene; association; β-Amyloid; alzheimer disease; polymorphism
The pathophysiology of white matter hypoperfusion is poorly understood. Barker et al. quantify ante-mortem hypoperfusion by measuring myelin proteins differentially susceptible to ischaemia, and assess the extent to which vasoregulatory factors protect from or contribute to ischaemic white matter injury in Alzheimer’s disease and vascular dementia.
Little is known about the contributors and physiological responses to white matter hypoperfusion in the human brain. We previously showed the ratio of myelin-associated glycoprotein to proteolipid protein 1 in post-mortem human brain tissue correlates with the degree of ante-mortem ischaemia. In age-matched post-mortem cohorts of Alzheimer’s disease (n = 49), vascular dementia (n = 17) and control brains (n = 33) from the South West Dementia Brain Bank (Bristol), we have now examined the relationship between the ratio of myelin-associated glycoprotein to proteolipid protein 1 and several other proteins involved in regulating white matter vascularity and blood flow. Across the three cohorts, white matter perfusion, indicated by the ratio of myelin-associated glycoprotein to proteolipid protein 1, correlated positively with the concentration of the vasoconstrictor, endothelin 1 (P = 0.0005), and negatively with the concentration of the pro-angiogenic protein, vascular endothelial growth factor (P = 0.0015). The activity of angiotensin-converting enzyme, which catalyses production of the vasoconstrictor angiotensin II was not altered. In samples of frontal white matter from an independent (Oxford, UK) cohort of post-mortem brains (n = 74), we confirmed the significant correlations between the ratio of myelin-associated glycoprotein to proteolipid protein 1 and both endothelin 1 and vascular endothelial growth factor. We also assessed microvessel density in the Bristol (UK) samples, by measurement of factor VIII-related antigen, which we showed to correlate with immunohistochemical measurements of vessel density, and found factor VIII-related antigen levels to correlate with the level of vascular endothelial growth factor (P = 0.0487), suggesting that upregulation of vascular endothelial growth factor tends to increase vessel density in the white matter. We propose that downregulation of endothelin 1 and upregulation of vascular endothelial growth factor in the context of reduced ratio of myelin-associated glycoprotein to proteolipid protein 1 are likely to be protective physiological responses to reduced white matter perfusion. Further analysis of the Bristol cohort showed that endothelin 1 was reduced in the white matter in Alzheimer’s disease (P < 0.05) compared with control subjects, but not in vascular dementia, in which endothelin 1 tended to be elevated, perhaps reflecting abnormal regulation of white matter perfusion in vascular dementia. Our findings demonstrate the potential of post-mortem measurement of myelin proteins and mediators of vascular function, to assess physiological and pathological processes involved in the regulation of cerebral perfusion in Alzheimer’s disease and vascular dementia.
Alzheimer’s disease; brain ischaemia; cerebral blood flow; dementia; neuropathology
There is increasing evidence that deficient clearance of β-amyloid (Aβ) contributes to its accumulation in late-onset Alzheimer disease (AD). Several Aβ-degrading enzymes, including neprilysin (NEP), endothelin-converting enzyme (ECE), and angiotensin-converting enzyme (ACE) reduce Aβ levels and protect against cognitive impairment in mouse models of AD. In post-mortem human brain tissue we have found that the activity of these Aβ-degrading enzymes rise with age and increases still further in AD, perhaps as a physiological response that helps to minimize the build-up of Aβ. ECE-1/-2 and ACE are also rate-limiting enzymes in the production of endothelin-1 (ET-1) and angiotensin II (Ang II), two potent vasoconstrictors, increases in the levels of which are likely to contribute to reduced blood flow in AD. This review considers the possible interdependence between Aβ-degrading enzymes, ischemia and Aβ in AD: ischemia has been shown to increase Aβ production both in vitro and in vivo, whereas increased Aβ probably enhances ischemia by vasoconstriction, mediated at least in part by increased ECE and ACE activity. In contrast, NEP activity may help to maintain cerebral perfusion, by reducing the accumulation of Aβ in cerebral blood vessels and lessening its toxicity to vascular smooth muscle cells. In assessing the role of Aβ-degrading proteases in the pathogenesis of AD and, particularly, their potential as therapeutic agents, it is important to bear in mind the multifunctional nature of these enzymes and to consider their effects on other substrates and pathways.
endothelin-1; angiotensin-converting enzyme; neprilysin; cerebral hypoperfusion; cerebral amyloid angiopathy; Alzheimer's disease
Background: Reducing the excessive accumulation of amyloid β-protein (Aβ) in Alzheimer's disease (AD) is a key objective of most AD therapies. Several studies suggest that pharmacological inhibition of angiotensin-converting enzyme (ACE) or its by-product angiotensin II may delay onset or progression of dementia and it has been suggested that this occurs via regulation of Aβ. Intraneuronal oligomeric accumulation of Aβ is postulated to be one of the earliest pathological events. Thus this study investigated the effect of an ACE-inhibitor, captopril, and two angiotensin II receptor blockers (ARBs), eprosartan and valsartan, on intraneuronal Aβ pathology and oligomeric Aβ levels in a triple transgenic (3xTGAD) mouse model of AD. Methods: Male, adult (3-4 month old) 3xTgAD mice (n=39) were randomly assigned to 4 treatment groups: valsartan (0.17g/l), eprosartan (0.8g/l), captopril (5g/l) or normal drinking water and the drugs given ad libitum for 2 months. Mean arterial blood pressure (MABP) was measured at baseline, at 2 weeks and at 2 months when the mice were sacrificed and the brains hemisected for analysis. One hemisphere was processed for Aβ and amyloid precursor protein (APP) immunohistochemistry and the other for biochemical measurement of oligomeric Aβ and APP. ACE activity was measured in the brain and kidney. Results: MABP was significantly reduced at 2 weeks and 2 months in the ACE-I group (p=0.0006) but was unaltered in the ARB groups compared to vehicle. Neither ACE-I nor ARB treatment altered Aβ and APP immunolabelling or the level of Aβ or APP in brain tissue homogenates. Similarly neither ACE-I nor ARB treatment altered ACE activity in either brain or kidney compared to control tissue. Conclusions: ACE-I or ARB administration over 2 months did not affect APP levels or either intraneuronal Aβ or oligomeric Aβ levels in 3xTGAD mice. While ARBs did not alter MABP, captopril did mediate reductions in MABP in the 3xTGAD mice which appeared to be independent of ACE activity. Further studies are needed to examine the effects of these drugs over a longer term and in older mice (i.e. when AD-like changes are more pronounced).
Angiotensin converting enzyme inhibitor; angiotensin-II receptor blocker; triple transgenic mouse model; Alzheimer's disease; amyloid-beta (Aβ)
ACE is a candidate gene for Alzheimer's disease (AD) and associations have been reported between ACE variants and plasma ACE levels, AD risk, AD age at onset of disease and cerebrospinal fluid levels of Aβ. Despite evidence that ACE can degrade Aβ, the relationships between ACE variants and the levels of different types of Aβ in the brain are not known. We have investigated the relationship between AD-associated ACE variants, for which the associations with brain activity of ACE were previously analysed, and brain homogenate levels of soluble, insoluble and oligomeric Aβ. Reported AD risk variants in the ACE indel (rs1799752) and its ‘proxy’ rs4343 were significantly associated with soluble Aβ level in AD only (p=0.001), as was rs1800764 but less so (p=0.014). In contrast, insoluble Aβ was associated with ACE indel and rs4343 variants in controls only (p < 0.01). No associations were found for oligomeric Aβ. These data indicate a complex relationship between ACE and Aβ that differs between AD and control brains.
Alzheimer's disease; angiotensin; ACE; amyloid; neuropathology; soluble Aβ; insoluble Aβ; SNP; association; Aβ degrading enzyme; cerebral blood flow; hypertension
Bridging integrator 1 (BIN1) has been implicated in sporadic Alzheimer’s disease (AD) by a number of genome wide association studies (GWAS) in a variety of populations. Here we measured BIN1 in frontal cortex samples from 24 sporadic AD and 24 age-matched non-dementia brains and correlated the expression of this protein with markers of AD. BIN1 was reduced by 87% (p=0.007) in sporadic AD compared to non-dementia controls, but BIN1 in sporadic AD did not correlate with soluble Aβ (rs=-0.084, p=0.698), insoluble Aβ (rs=0.237, p=0.269), Aβ plaque load (rs=0.063, p=0.771) or phospho-tau load (rs=-0.160, p=0.489). In contrast to our findings in sporadic AD, BIN1 was unchanged in the hippocampus from 6 cases of familial AD compared to 6 age-matched controls (p=0.488). BIN1 declined with age in a cohort of non-dementia control cases between 25 and 88 years but the correlation was not significant (rs=-0.449, p=0.081). Although BIN1 is known to have a role in endocytosis, and the processing of the amyloid precursor protein (APP) to form amyloid-β (Aβ) peptides is dependent on endocytosis, knockdown of BIN1 by targeted siRNA or the overexpression of BIN1 in a human neuroblastoma cell line (SH-SY5Y) had no effect on APP processing. These data suggest that the alteration in BIN1 is involved in the pathogenesis of sporadic, but not familial AD and is not a consequence of AD neurodegeneration or the ageing process, a finding in keeping with the numerous GWAS that implicate BIN1 in sporadic AD. However, the mechanism of its contribution remains to be established.
Alzheimer’s disease (AD) is the most common type of dementia, and represents a vast worldwide socio-economic burden, and in the absence of a current cure, effective therapeutic strategies are still needed. Cholinergic and cerebral blood flow deficits, excessive levels of oxidative stress, neuroinflammation and glutamate excitatory mechanisms are all believed to contribute to the development and progression of the disease. Scoparia dulcis, Catharanthus roseus, Sesamum indicum, Erythrina senegalensis and Vigna unguiculata represent five plants that have been used as traditional medicines for the treatment of AD in certain cultures. Review of the scientific literature was conducted to explore the properties of these plants that might be beneficial and explain what would be perceived by many to be largely anecdotal evidence of their benefit. All plants were found to possess varying levels of anti-oxidant capability. Scoparia dulcis was also found to potentiate nerve growth factor-like effects upon cell lines. Catharanthus roseus appears to inhibit acetylcholinesterase with relatively high potency, while Sesamum indicum demonstrated the strongest antioxidant ability. Comparisons with currently used plant derived therapeutics illustrate how these plants may be likely to have some therapeutic benefits in AD. The evidence presented also highlights how appropriate dietary supplementation with some of these plants in various cultural settings might have effects analogous or complementary to the so-called protective Mediterranean diet. However, prior to embarking on making any formal recommendations to this end, further rigorous evaluation is needed to better elucidate the breadth and potential toxicological aspects of medicinal properties harboured by these plants. This would be vital to ensuring a more informed and safe delivery of preparations of these plants if they were to be considered as a form of dietary supplementation and where appropriate, how these might interact with more formally established therapies in relation to AD.
Alzheimer’s disease; oxidative stress; hypertension; diabetes; neuroprotective; cholinergic; scoparia dulcis; catharanthus roseus; sesamum indicum; erythrina senegalensis; vigna unguiculata
A key pathological feature of late-onset Alzheimer’s disease (LOAD) is the abnormal extracellular accumulation of the amyloid beta (Aβ) peptide. Thus altered Aβ degradation could be a major contributor to the development of LOAD. Variants in the gene encoding the Aβ-degrading enzyme, angiotensin-1 converting enzyme (ACE) therefore represent plausible candidates for association with LOAD pathology and risk. Following Alzgene meta-analyses of all published case-control studies, the ACE variants rs4291 and rs1800764 showed significant association with LOAD risk. Furthermore ACE haplotypes are associated with both plasma ACE levels and LOAD risk. We tested three ACE variants (rs4291, rs4343 and rs1800764) for association with LOAD in ten Caucasian case-control populations (n=8,212). No association was found using multiple logistic models (all p>0.09). We found no population heterogeneity (all p>0.38) or evidence for association with LOAD risk following meta-analysis of the ten populations for rs4343 (OR=1.00), rs4291 (OR=0.97) or rs1800764 (OR=0.99). Although we found no haplotypic association in our complete dataset (p=0.51), a significant global haplotypic p-value was observed in one population (p=0.007) due to an association of the H3 haplotype (OR=0.72, p=0.02) and a trend towards an association of H4 (OR=1.38, p=0.09) and H7 (OR=2.07, p=0.08) although these did not survive Bonferroni correction. Previously reported associations of ACE variants with LOAD will be diminished following this study. At best, ACE variants have modest effect sizes, which are likely part of a complex interaction between genetic, phenotypic and pharmacological effects that would be undetected in traditional case-control studies.
Alzheimer Disease; Late Onset; Angiotensin-1 Converting Enzyme; Haplotype; Heterogeneity; Meta-Analysis
The cellular prion protein (PrPC) has been implicated in the development of Alzheimer's disease (AD). PrPC decreases amyloid-β (Aβ) production, which is involved in AD pathogenesis, by inhibiting β-secretase (BACE1) activity. Contactin 5 (CNTN5) has also been implicated in the development of AD by a genome-wide association study. Here we measured PrPC and CNTN5 in frontal cortex samples from 24 sporadic AD and 24 age-matched control brains and correlated the expression of these proteins with markers of AD. PrPC was decreased in sporadic AD compared to controls (by 49%, p = 0.014) but there was no difference in CNTN5 between sporadic AD and controls (p = 0.217). PrPC significantly inversely correlated with BACE1 activity (rs = −0.358, p = 0.006), Aβ load (rs = −0.456, p = 0.001), soluble Aβ (rs = −0.283, p = 0.026) and insoluble Aβ (rs = −0.353, p = 0.007) and PrPC also significantly inversely correlated with the stage of disease, as indicated by Braak tangle stage (rs = −0.377, p = 0.007). CNTN5 did not correlate with Aβ load (rs = 0.040, p = 0.393), soluble Aβ (rs = 0.113, p = 0.223) or insoluble Aβ (rs = 0.169, p = 0.125). PrPC was also measured in frontal cortex samples from 9 Down's syndrome (DS) and 8 age-matched control brains. In contrast to sporadic AD, there was no difference in PrPC in the DS brains compared to controls (p = 0.625). These data are consistent with a role for PrPC in regulating Aβ production and indicate that brain PrPC level may be important in influencing the onset and progression of sporadic AD.
Progressive mitochondrial dysfunction contributes to neuronal degeneration in age-mediated disease. An essential regulator of mitochondrial function is the deacetylase, sirtuin 3 (SIRT3). Here we investigate a role for CNS Sirt3 in mitochondrial responses to reactive oxygen species (ROS)- and Alzheimer’s disease (AD)-mediated stress. Pharmacological augmentation of mitochondrial ROS increases Sirt3 expression in primary hippocampal culture with SIRT3 over-expression being neuroprotective. Furthermore, Sirt3 expression mirrors spatiotemporal deposition of β-amyloid in an AD mouse model and is also upregulated in AD patient temporal neocortex. Thus, our data suggest a role for SIRT3 in mechanisms sensing and tackling ROS- and AD-mediated mitochondrial stress.
Although several studies have described an association between Alzheimer disease (AD) and genetic variation of mitochondrial DNA (mtDNA), each has implicated different mtDNA variants, so the role of mtDNA in the etiology of AD remains uncertain.
We tested 138 mtDNA variants for association with AD in a powerful sample of 4,133 AD case patients and 1,602 matched controls from 3 Caucasian populations. Of the total population, 3,250 case patients and 1,221 elderly controls met the quality control criteria and were included in the analysis.
In the largest study to date, we failed to replicate the published findings. Meta-analysis of the available data showed no evidence of an association with AD.
The current evidence linking common mtDNA variations with AD is not compelling.
The association between angiotensin-converting enzyme (ACE) genotypes and functional decline in older adults remains controversial. To assess if ACE gene variations influences functional abilities at older age, the present study explored the association between the common ACE insertion/deletion (I/D) polymorphism and disability measured with activities of daily living (ADL) in hospitalized older patients. We analyzed the frequency of the ACE genotypes (I/I, I/D, and D/D) in a population of 2,128 hospitalized older patients divided according to presence or absence of ADL disability. Logistic regression analysis adjusted for possible confounding factors, identified an association between the I/I genotype with ADL disability (OR = 1.54, 95% CI 1.04–2.29). This association was significant in men (OR = 2.01, 95% CI 1.07–3.78), but not in women (OR = 1.36, 95% CI 0.82–2.25). These results suggested a possible role of the ACE polymorphism as a genetic marker for ADL disability in hospitalized older patients.
Angiotensin-converting enzyme; Disability; Aging; Hospitalized patients
Reducing excessive accumulation of amyloid-β (Aβ) in Alzheimer's disease (AD) is a key objective of most AD therapies, and inhibition of angiotensin-converting enzyme (ACE) may delay onset or progression of AD. The effects of an ACE-inhibitor (ACE-I) and an angiotensin II receptor blocker (ARB) on Aβ and tau pathology in a triple transgenic (3xTGAD) mouse model of AD were investigated. 9-10month 3xTGAD mice were treated with ARB, ACE-I or vehicle for 6 months. Mean arterial blood pressure (MABP) was measured periodically and mice were assessed behaviourally. Aβ, phospho-tau, amyloid precursor protein (APP) and ACE activity were analysed. MABP was significantly reduced at 2 weeks and 3 months in the ACE-I group and at 3 months in the ARB group, compared to vehicle. Neither drug altered performance of 3xTGAD mice in Morris Water Maze or T-maze, nor were Aβ, tau immunolabelling or APP levels altered. ACE-I significantly reduced ACE activity in kidney. Prolonged treatment with ACE-I or ARB does not affect Aβ or phospho-tau accumulation in brains of aged 3xTGAD mice.
Angiotensin-converting enzyme inhibitor; angiotensin II receptor blocker; hypertension; triple transgenic mouse model; Alzheimer’s disease; amyloid-beta
Neuroinflammation contributes to the pathogenesis of sporadic Alzheimer’s disease (AD). Variations in genes relevant to inflammation may be candidate genes for AD risk. Whole-genome association studies have identified relevant new and known genes. Their combined effects do not explain 100% of the risk, genetic interactions may contribute. We investigated whether genes involved in inflammation, i.e. PPAR-α, interleukins (IL) IL- 1α, IL-1β, IL-6, and IL-10 may interact to increase AD risk.
The Epistasis Project identifies interactions that affect the risk of AD. Genotyping of single nucleotide polymorphisms (SNPs) in PPARA, IL1A, IL1B, IL6 and IL10 was performed. Possible associations were analyzed by fitting logistic regression models with AD as outcome, controlling for centre, age, sex and presence of apolipoprotein ε4 allele (APOEε4). Adjusted synergy factors were derived from interaction terms (p<0.05 two-sided).
We observed four significant interactions between different SNPs in PPARA and in interleukins IL1A, IL1B, IL10 that may affect AD risk. There were no significant interactions between PPARA and IL6.
In addition to an association of the PPARA L162V polymorphism with the AD risk, we observed four significant interactions between SNPs in PPARA and SNPs in IL1A, IL1B and IL10 affecting AD risk. We prove that gene-gene interactions explain part of the heritability of AD and are to be considered when assessing the genetic risk. Necessary replications will require between 1450 and 2950 of both cases and controls, depending on the prevalence of the SNP, to have 80% power to detect the observed synergy factors.
AD; genetics; epistasis; inflammation; interleukin; steroid receptors; PPAR-alpha; sporadic; genetic interaction
Pro-inflammatory cytokines, such as tumour necrosis factor-α (TNF-α), are increased in serum and CSF in Alzheimer's disease (AD). We investigated the effect of TNF-α on gene and protein expression levels of Aβ degrading enzymes (ACE, ECE-1, ECE- 2, IDE and NEP) in vitro. Differentiated (DC) and non-differentiated (NDC) neuroblastoma cells (SH-SY5Y) were exposed to TNF-α for 15 minutes and 3 hours and protein and gene expression levels measured using western blotting or sandwich ELISA (ECE-2), and real time-PCR (RT-PCR). Only ECE-2 protein levels decreased significantly in NDCs in a dose-dependent manner after 15 minutes of TNF-α exposure but reverted to basal levels after 3 hours. Basal NEP gene expression levels were higher in control DCs compared to NDCs but TNF-α treatment did not significantly alter the levels of expression of any of the Aβ degrading enzymes. In conclusion, apart from a transient reduction in ECE-2 protein levels, TNF-α had no impact in our in vitro experimental system on transcription or translation of any of our selected mediators of Aβ degradation.
Alzheimer's disease; inflammation; TNF-α; SH-SY5Y cells; RT-PCR; western blot
We sought to identify new susceptibility loci for Alzheimer’s disease (AD) through a staged association study (GERAD+) and by testing suggestive loci reported by the Alzheimer’s Disease Genetic Consortium (ADGC). First, we undertook a combined analysis of four genome-wide association datasets (Stage 1) and identified 10 novel variants with P≤1×10−5. These were tested for association in an independent sample (Stage 2). Three SNPs at two loci replicated and showed evidence for association in a further sample (Stage 3). Meta-analyses of all data provide compelling evidence that ABCA7 (meta-P 4.5×10−17; including ADGC meta-P=5.0×10−21) and the MS4A gene cluster (rs610932, meta-P=1.8×10−14; including ADGC meta-P=1.2×10−16; rs670139, meta-P=1.4×10−9; including ADGC meta-P=1.1×10−10) are novel susceptibility loci for AD. Second, we observed independent evidence for association for three suggestive loci reported by the ADGC GWAS, which when combined shows genome-wide significance: CD2AP (GERAD+ P=8.0×10−4; including ADGC meta-P=8.6×10−9), CD33 (GERAD+ P=2.2×10−4; including ADGC meta-P=1.6×10−9) and EPHA1 (GERAD+ P=3.4×10−4; including ADGC meta-P=6.0×10−10). These findings support five novel susceptibility genes for AD.
PICALM, the gene encoding phosphatidylinositol-binding clathrin assembly (picalm) protein, was recently shown to be associated with risk of Alzheimer disease (AD). Picalm is a key component of clathrin-mediated endocytosis. It recruits clathrin and adaptor protein (AP)-2 to the plasma membrane and along with AP-2 recognizes target proteins. The attached clathrin triskelions cause membrane deformation around the target proteins enclosing them within clathrin-coated vesicles to be processed in lysosomes or endosomes. We examined the distribution of picalm in control and AD brain tissue and measured levels of picalm mRNA by real-time polymerase chain reaction. Immunolabeling of brain tissue showed that picalm is predominately present in endothelial cells. This was further supported by the demonstration of picalm in human cerebral microvascular cells grown in culture. Picalm mRNA was elevated in relation to glyceraldehyde-3-phosphate dehydrogenase but not factor VIII-related antigen or CD31 mRNA in the frontal cortex in AD. No change was seen in the temporal cortex or thalamus. The transport of Aβ across vessel walls and into the bloodstream is a major pathway of Aβ removal from the brain and picalm is ideally situated within endothelial cells to participate in this process. Further research is needed to determine whether PICALM expression is influenced by Aβ levels and whether it affects Aβ uptake and transport by endothelial cells.
Alzheimer disease; β-amyloid; Clathrin-mediated endocytosis; Endothelial cells; Picalm
Micro-RNAs (miRNAs) are short non-coding RNAs capable of regulating gene expression at the translational level. A number of studies have suggested that the expression of several miRNAs is changed in AD. The pro-inflammatory cytokine tumour necrosis factor-a (TNF-α) is increased in serum and CSF in AD. We measured the expression of TNFA and several AD candidate gene-associated miRNAs (let7a/b, miR-128a/b, miR-27a/b, miR-155) in frontal and temporal neocortex from AD and control brains. The expression of these miRNAs was also measured after incubating non-differentiated (NDC) and retinoic acid -differentiated (DC) SH-SY5Y neuroblastoma cells with TNF-α. TNFA expression was similar in AD and control brains but miR-128a/b levels were significantly reduced in the temporal cortex and miR-128b in the frontal cortex in AD. MiRNA levels did not correlate with TNFA expression in brain tissue but exposure of NDC and DC SH-SY5Y cells to TNF-α caused a variable dose-dependent response in the level of some of the miRNAs studied. Our brain tissue findings argue against a role for TNF-α in influencing the expression of these miRNAs in AD.
Alzheimer's disease; Tumour necrosis factor-a; microRNA; SH-SY5Y cells
Late Onset Alzheimer's disease (LOAD) is the leading cause of dementia. Recent large genome-wide association studies (GWAS) identified the first strongly supported LOAD susceptibility genes since the discovery of the involvement of APOE in the early 1990s. We have now exploited these GWAS datasets to uncover key LOAD pathophysiological processes.
We applied a recently developed tool for mining GWAS data for biologically meaningful information to a LOAD GWAS dataset. The principal findings were then tested in an independent GWAS dataset.
We found a significant overrepresentation of association signals in pathways related to cholesterol metabolism and the immune response in both of the two largest genome-wide association studies for LOAD.
Processes related to cholesterol metabolism and the innate immune response have previously been implicated by pathological and epidemiological studies of Alzheimer's disease, but it has been unclear whether those findings reflected primary aetiological events or consequences of the disease process. Our independent evidence from two large studies now demonstrates that these processes are aetiologically relevant, and suggests that they may be suitable targets for novel and existing therapeutic approaches.
The loss of noradrenergic neurones of the locus coeruleus is a major feature of Alzheimer's disease (AD). Dopamine β-hydroxylase (DBH) catalyses the conversion of dopamine to noradrenaline. Interactions have been reported between the low-activity -1021T allele (rs1611115) of DBH and polymorphisms of the pro-inflammatory cytokine genes, IL1A and IL6, contributing to the risk of AD. We therefore examined the associations with AD of the DBH -1021T allele and of the above interactions in the Epistasis Project, with 1757 cases of AD and 6294 elderly controls.
We genotyped eight single nucleotide polymorphisms (SNPs) in the three genes, DBH, IL1A and IL6. We used logistic regression models and synergy factor analysis to examine potential interactions and associations with AD.
We found that the presence of the -1021T allele was associated with AD: odds ratio = 1.2 (95% confidence interval: 1.06-1.4, p = 0.005). This association was nearly restricted to men < 75 years old: odds ratio = 2.2 (1.4-3.3, 0.0004). We also found an interaction between the presence of DBH -1021T and the -889TT genotype (rs1800587) of IL1A: synergy factor = 1.9 (1.2-3.1, 0.005). All these results were consistent between North Europe and North Spain.
Extensive, previous evidence (reviewed here) indicates an important role for noradrenaline in the control of inflammation in the brain. Thus, the -1021T allele with presumed low activity may be associated with misregulation of inflammation, which could contribute to the onset of AD. We suggest that such misregulation is the predominant mechanism of the association we report here.