No synergistic effect between -850 tumor necrosis factor-alpha promoter polymorphism and apolipoprotein E epsilon 4 allele in Alzheimer's disease

Polymorphisms of Proinflammatory Cytokines in Relation to APOE Epsilon 4 and Risk of Alzheimer's Disease in the Lithuanian Population

Background and objective: Neuroinflammation is one of the pathological pathways of Alzheimer's disease (AD), mediating the progression of neurodegeneration. Polymorphisms of proinflammatory cytokines have been linked to increased AD risk. Identification of certain combinations of polymorphisms could help predict disease in its preclinical stage. The aim of the study was to evaluate differences in the prevalence of TNFα -850T (rs1799724), IL1A -889T (rs1800587), and IL6 -174C (rs1800795, Intron type) polymorphisms between AD patients and healthy controls (HC) and determine the impact of these SNPs in combination with the APOEε4 allele on AD risk. Materials and Methods: The study population is comprised of 107 patients with sporadic AD (AD group) and age- and gender-matched 110 persons without impaired cognitive functions (control group). TNFα -850C > T polymorphism was revealed by a PCR and restriction fragment length polymorphism (RFLP) method. Real time PCR was used for IL1A and IL6 SNP genotyping. APOEε genotyping was done via hybridization method. Results: The frequencies of TNFα -850T, IL1A -889T, IL6 -174C allele and genotype did not differ between the AD and HC groups (p > 0.05). IL6 -174C was not in HWE, and it was not analysed further. APOEε4 allele (p = 0.001) and 3/4 and 4/4 genotypes (p = 0.005) were more prevalent in AD patients. APOEε4 carriage increased the risk of AD (OR 2.65, p = 0.001), while TNFα -850T and IL1A -889T polymorphisms were not found as significant independent risk factors for AD. The presence of at least one IL1A -889T allele in combination with APOEε4+ was associated with a lower risk of AD (OR 2.24, p = 0.047) than the carriage of APOEε4+ alone (OR 2.70, p = 0.015). Conclusions: No significant differences of TNFα -850, IL1A -889, and IL6 -174 polymorphisms frequencies were found between AD and control groups. In APOEε4 carriers IL1A -889T polymorphism was found to reduce the AD risk determined by APOEε4 alone.

Non-apolipoprotein E and apolipoprotein E genetics of sporadic Alzheimer's disease

The genetic epidemiology of sporadic Alzheimer's disease (SAD) remains a very active area of research,making it one of the most prolifically published areas in medicine and biology. Numerous putative candidate genes have been proposed. However, with the exception of apolipoprotein E (APOE), the only confirmed genetic risk factor for SAD, all the other data appear to be not consistent. Nevertheless, the genetic risk for SAD attributable to the APOE gene in the general population is 20-0%, providing a strong evidence for the existence of additional genetic risk factors. The first part of the present article was dedicated to non-APOE genetics of SAD, reviewing chromosomes-by-chromosomes the available data concerning the major candidate genes. The second part of this article focused on some recently discovered aspects of the APOE polymorphism and their implications for SAD. An attempt to identify the future directions for non-APOE genetic research in SAD was also discussed.

Systematic review by meta-analyses on the possible role of TNF-alpha polymorphisms in association with Alzheimer's disease

It has been hypothesized that polymorphisms of Tumor Necrosis Factor (TNF)-alpha gene affect the risk of developing Alzheimer's disease (AD). However, results of different studies are often inconsistent. Our aim was to investigate by meta-analysis the association of the common polymorphisms comprehensively defining the genetic variability of the TNF-alpha gene with AD risk. Hence, the results being stated are of a meta-analysis across studies, and that this meta-analysis does not invalidate the results of the individual studies previously performed. Seventeen studies that investigated the association between 5 TNF-alpha polymorphisms (-850, -308, -863, -238, and -1031) and AD were retrieved and analyzed. The model-free approach was applied to meta-analyze these case-control genetic association studies. Available data suggested a significant association between -850 polymorphism and AD risk (TT vs. TC+CC: pooled odds ratio [OR], 1.61; 95% confidence interval [CI], 1.08-2.29; p=0.02) with no evidence of between-study heterogeneity (chi(2), p>0.1). Subgroup analysis suggested that the possession of T allele significantly increased the risk of AD associated with carriage of the apolipoprotein E epsilon 4 allele in Caucasian Australians and Northern Europeans (TT+TC vs. CC: OR, 1.95; 95% CI, 1.45-2.62; p=0.00001; p>0.1; chi(2) for heterogeneity, p>0.1). No significant difference in genotype distribution of -308 polymorphism in AD was found, with a high degree of between-study heterogeneity. For the -863 and -1031 polymorphisms we did not find an association with AD, but significant between-study heterogeneity discouraged genotype data pooling. Only four studies investigated the -238 variant and the results were not significant. Current findings support an association between -850 C>T polymorphism and the risk of developing AD; hence, they strengthen the suggestion of a potential role for anti-TNF therapy to maintain physiologic levels of TNF-alpha.

Lack of association between TNF-alpha polymorphisms and Alzheimer's disease in an Italian cohort

Tumor necrosis factor-alpha (TNF-alpha) is a pro-inflammatory cytokine that plays an important role in the inflammatory process that can be observed in Alzheimer's disease (AD) brain. Different functional promoter polymorphisms within genes modulating inflammation have been demonstrated to elevate the AD risk; thus, we studied five common variations within the promoter region of the TNF-alpha gene in 609 subjects (253 AD patients and 356 controls). No positive associations were found, confirming the greater part of previous studies. Moreover, we also investigated the combined haplotypes of the five different polymorphisms without finding a positive association. Thus, the present investigation does not support the proposal that common nucleotide variations in the TNF-alpha gene can influence the development of AD at least in Italian population.

Association of alleles carried at TNFA -850 and BAT1 -22 with Alzheimer's disease

Background

Inflammatory changes are a prominent feature of brains affected by Alzheimer's disease (AD). Activated glial cells release inflammatory cytokines which modulate the neurodegenerative process. These cytokines are encoded by genes representing several interleukins and TNFA, which are associated with AD. The gene coding for HLA-B associated transcript 1 (BAT1) lies adjacent to TNFA in the central major histocompatibility complex (MHC). BAT1, a member of the DEAD-box family of RNA helicases, appears to regulate the production of inflammatory cytokines associated with AD pathology. In the current study TNFA and BAT1 promoter polymorphisms were analysed in AD and control cases and BAT1 mRNA levels were investigated in brain tissue from AD and control cases.

Methods

Genotyping was performed for polymorphisms at positions -850 and -308 in the proximal promoter of TNFA and position -22 in the promoter of BAT1. These were investigated singly or in haplotypic association in a cohort of Australian AD patients with AD stratified on the basis of their APOE ε4 genotype. Semi-quantitative RT-PCR was also performed for BAT1 from RNA isolated from brain tissue from AD and control cases.

Results

APOE ε4 was associated with an independent increase in risk for AD in individuals with TNFA -850*2, while carriage of BAT1 -22*2 reduced the risk for AD, independent of APOE ε4 genotype. Semi-quantitative mRNA analysis in human brain tissue showed elevated levels of BAT1 mRNA in frontal cortex of AD cases.

Conclusion

These findings lend support to the application of TNFA and BAT1 polymorphisms in early diagnosis or risk assessment strategies for AD and suggest a potential role for BAT1 in the regulation of inflammatory reactions in AD pathology.

Inflammation, Depression and Dementia: Are they Connected?

Chronic inflammation is now considered to be central to the pathogenesis not only of such medical disorders as cardiovascular disease, multiple sclerosis, diabetes and cancer but also of major depression. If chronic inflammatory changes are a common feature of depression, this could predispose depressed patients to neurodegenerative changes in later life. Indeed there is now clinical evidence that depression is a common antecedent of Alzheimer's disease and may be an early manifestation of dementia before the cognitive declines becomes apparent. This review summarises the evidence that links chronic low grade inflammation with changes in brain structure that could precipitate neurodegenerative changes associated with Alzheimer's disease and other dementias. For example, neuronal loss is a common feature of major depression and dementia. It is hypothesised that the progress from depression to dementia could result from the activation of macrophages in the blood, and microglia in the brain, that release pro-inflammatory cytokines. Such cytokines stimulate a cascade of inflammatory changes (such as an increase in prostaglandin E2, nitric oxide in addition to more pro-inflammatory cytokines) and a hypersecretion of cortisol. The latter steroid inhibits protein synthesis thereby reducing the synthesis of neurotrophic factors and preventing reairto damages neuronal networks. In addition, neurotoxic end products of the tryptophan-kynurenine pathway, such as quinolinic acid, accumulate in astrocytes and neurons in both depression and dementia. Thus increased neurodegeneration, reduced neuroprotection and neuronal repair are common pathological features of major depression and dementia. Such changes may help to explain why major depression is a frequent prelude to dementia in later life.

TNF polymorphisms in Alzheimer disease and functional implications on CSF beta-amyloid levels

Alzheimer disease (AD), vascular dementia, and stroke are all associated with inflammation though their respective initiating factors differ. Recently a polymorphism in the proinflammatory cytokine tumor necrosis factor (TNF), in association with apolipoprotein E (APOE), was reported to increase AD risk. Two SNPs, rs1799724 (-850C>T; NT_007592.14:g.22400733C>T) and rs1800629 (-308G>A; [NT_007592.14:g.22401282G>A]), and the APOE polymorphism were genotyped in 506 patients with sporadic AD and in 277 cognitively healthy controls. In a subset of 90 individuals we also investigated whether these SNPs exerted any functional effects on cerebrospinal fluid (CSF) beta-amyloid (Abeta) levels. The frequency of the rs1799724 genotypes and the rs1799724-T allele were significantly different in AD individuals (P=0.009; odds ratio [OR], 1.63; 95% confidence interval [CI], 1.13-2.34), while the rs1800629 SNP was not associated with AD. Significant interaction was observed between the rs1799724-T and APOE epsilon4 alleles in that the rs1799724-T allele significantly modified risk associated with possession of the epsilon4 allele only (epsilon4 in absence of rs1799724-T: OR, 2.92; 95% CI, 2.00-4.27; epsilon4 in presence of rs1799724-T: OR, 6.65; 95% CI, 3.26-13.55; P=0.03). Haplotyping analysis revealed a significant overrepresentation of an rs1799724-T/rs1800629-G haplotype in AD (P=0.012; OR, 1.60; 95% CI, 1.11-2.29), although to a lesser degree than rs1799724-T alone. Further, the rs1799724-T allele was found to be associated with lower levels of CSF Abeta42 (P=0.023), thus corroborating the genetic findings. Inheritance of the rs1799724-T allele appears to synergistically increase the risk of AD in APOEepsilon4 carriers and is associated with altered CSF Abeta42 levels. Further investigations are warranted to assess the significance of these novel findings.

Association study of the vascular endothelial growth factor gene with the risk of developing Alzheimer's disease

Numerous observations indicate that cerebrovascular dysfunction contributes to cognitive decline and neurodegeneration in AD. Converging evidence points to a pivotal role for vascular endothelial growth factor (VEGF) in neuronal protection, and the lack of activity of this in neurodegenerative disorders. The VEGF gene is located at 6p21.3, a site several studies have shown to have significant linkage with AD, and a functional polymorphism within the VEGF promoter may alter the risk of developing AD. We assessed the potential impact of this polymorphism on the risk of developing AD in a large French case-control population, and investigated its association with the severity of brain vascular lesions (arteriosclerosis, white matter loss and cerebral amyloid angiopathy) in several brain regions (frontal, temporal, parietal and occipital cortex) in AD. No association of the VEGF promoter polymorphism with the risk of developing AD was observed. No relationship between this polymorphism and vascular pathological changes in AD was detected. Our data indicate that although this polymorphism is functional, it does not confer greater risk for AD, nor modulate the extent of vascular pathology.

CD14 receptor polymorphism and Alzheimer's disease risk

Activation of microglial cells is involved in the inflammatory component of Alzheimer's disease (AD), and it may be triggered by infectious pathogens. CD14, a receptor upregulated in activated microglia, plays a central role in innate immunity through recognition of bacterial lipopolysaccharide and initiation of inflammatory response. A polymorphism in the promoter region (-260) of the CD14 receptor has been found to be related to increased risk of bacterial infections and inflammatory diseases such as atherosclerosis. In a case-control study utilizing a clinically well-defined group of 310 sporadic AD patients and 310 control subjects, we investigated whether the CD14 (-260) polymorphism might be responsible for susceptibility to AD, and we also examined the combined gene effects between CD14 and APOE and several other proinflammatory cytokine genes. The current study does not demonstrate an association between CD14 (-260) polymorphism and AD, neither through an independent effect nor through interaction with APOE epsilon4 allele or interleukin (IL)-1A, IL-6, IL-8, tumor necrosis factor (TNF)-alpha, and intercellular adhesion molecule-1 polymorphisms.

An association study of the tumor necrosis factor alpha C-850T polymorphism and childhood acute lymphoblastic leukemia in a population from northern Greece

Excessive production of tumor necrosis factor alpha (TNFalpha) may influence the risk and/or progression of hematologic malignancies and has been associated with febrile episodes at diagnosis. We have examined the putative association of the C-850T polymorphism of the human TNFalpha gene with childhood acute lymphoblastic leukemia (ALL) and with clinical and laboratory findings at diagnosis, in 58 childhood ALL patients from northern Greece. No statistically significant associations have emerged between this polymorphism and either the risk for childhood ALL or presence of fever, anemia, leukocytosis and leukopenia at diagnosis, in this study.

Major histocompatibility complex and sporadic Alzheimer's disease: a critical reappraisal

Epidemiological data suggest that some genetic determinants of Alzheimer's disease (AD) might reside in those polymorphisms for the immune system genes that regulate immune inflammatory responses, such as the major histocompatibility complex (MHC). Therefore, MHC polymorphisms have been the focus of a large number of AD association studies. Class Ia, Ib (hemochromatosis gene (HFE)), class II and class III (complement, tumour necrosis factor and heat shock proteins) alleles have been studied. Nearly every positive result has been followed by several studies that have failed to replicate it or that have contradicted it. Several factors, including methodological biases, might explain these discordant results. However, the discordant results obtained with the same alleles in the various populations might also indicate linkage with another nearby locus, different in the diverse populations. In fact, the non-random assortment of alleles at neighbouring loci, i.e. ancestral haplotypes (AH), has been claimed to be maintained as the result of directional selection, i.e. molecular cooperation during the immune response. Thus, AH studies might contribute to explaining why discordant results are obtained with the same alleles in different populations. Hence, it has been suggested that the overall chance of a subject to develop AD might be profoundly affected by a 'susceptibility profile' reflecting the combined influence of inheriting multiple high-risk alleles. Discordant results may be due to other genetic factors not determined in these MHC studies and multivariate analysis in large patient cohorts considering both MHC and non-MHC genes are therefore necessary.

The Tumor Necrosis Factor Alpha −308G>A Polymorphism Is Associated with Dementia in the Oldest Old

OBJECTIVES

To test the hypothesis that the tumor necrosis factor (TNF) -308 G>A promoter gene polymorphism is a risk factor in age-related dementia and longevity.

DESIGN

A cross-sectional and a longitudinal study.

SETTING

A population-based sample of Danish centenarians.

PARTICIPANTS

One hundred-year-old Danes (n=122) from "The Longitudinal Study of Danish Centenarians." Octogenarians (n=174) and healthy volunteers aged 18 to 30 (n=47) served as reference groups.

METHODS

Whether the distribution of TNF -308 GG/GA/AA genotypes were different in centenarians than in younger age groups was investigated (Fischer exact test). Furthermore, whether the TNF -308 G>A polymorphism was associated with the prevalence of dementia (logistic regression analysis), the plasma level of TNF-alpha (analysis of variance), and mortality in the following 5 years (Cox regression analysis) within the cohort of centenarians was tested.

RESULTS

The distribution of TNF -308 genotypes was not different across the three different age groups, but the GA genotype was associated with decreased prevalence of dementia in centenarians. The few centenarians with AA carrier status had higher mortality risk and tended to show higher plasma levels of TNF-alpha, but the significance was questionable due to a low number of subjects with this genotype.

CONCLUSION

It is possible that the TNF -308 A allele is maintained during aging because subjects who are heterozygous for this polymorphism possess the optimal inflammatory response with regard to protection against age-related neurodegeneration.

Exclusion of CYP46 and APOM as candidate genes for Alzheimer's disease in a French population

Alzheimer's disease (AD) is a complex, multifactorial disorder, probably resulting from an interaction between environmental and genetic factors. Increasing evidence points to a link between cholesterol turnover and AD, suggesting that genes implicated in brain cholesterol homeostasis may be potential candidate genes for AD. With this background, we tested the potential association of the CYP46, APOM and APOF genes with the risk of developing AD. CYP46 encodes the enzyme cholesterol 24-hydrolase, which plays a key role in brain cholesterol turnover, and APOF and APOM encode apolipoproteins belonging to the large lipocalin family, which also includes ApoE. In contrast to two previous reports but in accordance with one other, we were unable to detect an association between an intron 2 polymorphism of CYP46 and AD. We also searched for polymorphisms within the APOM and APOF by dHPLC. We were unable to detect any polymorphisms in the coding and exon/intron sequences of the APOF. Finally, we excluded APOM as a genetic determinant of AD in our large French case control population.

Inflammatory mediators in the elderly

Ageing is accompanied by 2-4-fold increases in plasma/serum levels of inflammatory mediators such as cytokines and acute phase proteins. A wide range of factors seems to contribute to this low-grade inflammation, including an increased amount of fat tissue, decreased production of sex steroids, smoking, subclinical infections (e.g. asymptomatic bacteriuria), and chronic disorders such as cardiovascular diseases and Alzheimer's disease. Furthermore, there is some evidence that ageing is associated with a dysregulated cytokine response following stimulation. Several inflammatory mediators such as tumour necrosis factor-alpha and interleukin-6 have the potential to induce/aggravate risk factors in age-associated pathology, providing a positive feedback mechanism. Thus, it is possible that inflammatory mediators constitute a link between life style factors, infections and physiological changes in the process of ageing on the one hand and risk factors for age-associated diseases on the other. Consistent with this, inflammatory mediators are strong predictors of mortality independently of other known risk factors and co-morbidity in elderly cohorts. A direct pathogenetic role of inflammatory mediators would be highly likely if longevity was shown to be associated with cytokine polymorphisms regulating cytokine production. Several studies support indeed this hypothesis but, unfortunately, findings in this area are conflicting, which probably reflects the complexity of the effect of cytokine polymorphisms and their interaction with the lifestyle and sex.

Association study of Notch 4 polymorphisms with Alzheimer's disease

BACKGROUND

The NOTCH4 gene is located at 6p21.3, a site shown in several studies to have significant linkage with Alzheimer's disease.

OBJECTIVE

To investigate the potential impact of two polymorphisms within this gene on the risk of developing Alzheimer's disease.

METHODS

Genotyping of promoter and 5'-UTR polymorphisms was done in Scottish, English, and French populations. The potential functionality of the 5'-UTR polymorphism was assessed by testing its impact on A beta load in Alzheimer brains and also by undertaking electrophoretic mobility shift assays and transfection experiments.

RESULTS

No association of the Notch4 polymorphisms alone with the disease was observed in any of the populations. However, an interaction of the 5'-UTR C/T polymorphism with the epsilon 4 allele of the APOE gene was detected in United Kingdom populations but not in the French. No relation between the 5'-UTR polymorphism and A beta loads was detected overall or in the presence or absence of the epsilon 4 allele. No DNA protein specific binding was found with proteins from neuroblastoma, glioma, or astrocytoma cells, and no allele dependent transcriptional activity was detected.

CONCLUSIONS

No association between two NOTCH4 polymorphisms alone and Alzheimer's disease was observed in the three populations, but there was evidence of an increased risk associated with the 5'-UTR CC genotype in epsilon 4 bearers in the United Kingdom. As no functionality for this polymorphism could be determined, it is likely that the interaction is spurious or results from a linkage disequilibrium of this 5'-UTR polymorphism with another marker elsewhere in the 6p21.3 locus.

The role of −850 tumor necrosis factor-α and apolipoprotein E genetic polymorphism in patients with Down's syndrome-related dementia

Down's syndrome (DS) is a disease with a complex etiology. It is likely that other factors besides genes located on chromosome 21 may play a role in clinical features of affected patients. Tumor necrosis factor-alpha (TNF-alpha) (6p21.3) and apolipoprotein E (APOE) (19q13.2) are candidate genes as they interact with the brain deposition of Abeta, one of the neuropathological hallmarks in DS. We examined 136 DS patients and 113 controls for -850 TNF-alpha and APOE polymorphisms. The -850T frequency in DS was significantly higher than in controls (P<0.005, OR 2.05, 95% CI 1.22-3.49) while the APOE E4 allele was negatively selected in patients compared to normal subjects (P<0.005, OR 0.38, 95% CI 0.20-0.71). Our findings suggest that the -850T allele, which is more common among patients at high risk of dementia such as those with DS, might eventually play a role in the development of dementia; no inference on the role of the allele APOE E4 in DS-related dementia may be derived from our results.