Rheumatoid arthritis-associated polymorphisms are not protective against Alzheimer\u27s disease

BACKGROUND: Rheumatoid arthritis (RA) and Alzheimer\u27s disease (AD) are inversely associated. To test the hypothesis that genetic elements associated with increased RA risk are associated with decreased AD risk, we evaluated RA genetic risk factors recently identified in genome-wide association studies (GWAS) for their association with AD in a two-stage, case-control analysis. RESULTS: In our Stage 1 analysis of ~800 AD and ~1,200 non-AD individuals, three of seventeen RA-associated SNPs were nominally associated with AD (p \u3c 0.05) with one SNP, rs2837960, retaining significance after correction for multiple testing (p = 0.03). The rs2837960_G (minor) allele, which is associated with increased RA risk, was associated with increased AD risk. Analysis of these three SNPs in a Stage 2 population, consisting of ~1,100 AD and ~2,600 non-AD individuals, did not confirm their association with AD. Analysis of Stage 1 and 2 combined suggested that rs2837960 shows a trend for association with AD. When the Stage 2 population was age-matched for the Stage 1 population, rs2837960 exhibited a non-significant trend with AD. Combined analysis of Stage 1 and the age-matched Stage 2 subset showed a significant association of rs2837960 with AD (p = 0.002, OR 1.24) that retained significance following correction for age, sex and APOE (p = 0.02, OR = 1.20). Rs2837960 is near BACE2, which encodes an aspartic protease capable of processing the AD-associated amyloid precursor protein. Testing for an association between rs2837960 and the expression of BACE2 isoforms in human brain, we observed a trend between rs2837960 and the total expression of BACE2 and the expression of a BACE2 transcript lacking exon 7 (p = 0.07 and 0.10, respectively). CONCLUSIONS: RA-associated SNPs are generally not associated with AD. Moreover, rs2837960_G is associated with increased risk of both RA and, in individuals less than 80 years of age, with AD. Overall, these results contest the hypothesis that genetic variants associated with RA confer protection against AD. Further investigation of rs2837960 is necessary to elucidate the mechanism by which rs2837960 contributes to both AD and RA risk, likely via modulation of BACE2 expression

Evaluation of the global association between cholesterol-associated polymorphisms and Alzheimer's disease suggests a role for rs3846662 and HMGCR splicing in disease risk

<p>Abstract</p> <p>Background</p> <p>Recent genome-wide association studies (GWAS) have identified single nucleotide polymorphisms (SNP)s that are essentially unequivocally associated with peripheral cholesterol. Since the alleles of the <it>APOE </it>gene, which modulate peripheral cholesterol metabolism, and midlife plasma cholesterol are both associated with Alzheimer's disease (AD) risk, we have evaluated the hypothesis that SNPs associated with plasma cholesterol are also associated with AD.</p> <p>Results</p> <p>Seventeen non-<it>APOE </it>SNPs reproducibly associated with cholesterol per GWAS were tested for association with AD in ~2,000 AD and ~4,000 non-AD subjects. As a group, these SNPs are associated with AD. Two SNPs in particular, rs3846662 and rs1532085, are associated with AD risk and age-of-onset. Additionally, rs3846662 was associated with <it>HMGCR </it>exon 13 splicing in human liver but not brain, possibly obscured by CNS cell-type heterogeneity. However, rs3846662 was associated with <it>HMGCR </it>exon 13 splicing in liver- and brain-derived cell lines.</p> <p>Conclusions</p> <p>Cholesterol-associated SNPs outside of <it>APOE </it>confer a global risk for AD. Rs3846662 and rs1532085 are associated with both AD risk and age-of-onset. Rs3846662 is associated with <it>HMGCR </it>exon 13 inclusion. Since rs3846662 affects AD risk and age-of-onset as well as statin responsiveness, this SNP may confound clinical trials evaluating the protective effects of statins on AD.</p

Evaluation of the global association between cholesterol-associated polymorphisms and Alzheimer\u27s disease suggests a role for rs3846662 and \u3cem\u3eHMGCR\u3c/em\u3e splicing in disease risk

BACKGROUND: Recent genome-wide association studies (GWAS) have identified single nucleotide polymorphisms (SNP)s that are essentially unequivocally associated with peripheral cholesterol. Since the alleles of the APOE gene, which modulate peripheral cholesterol metabolism, and midlife plasma cholesterol are both associated with Alzheimer\u27s disease (AD) risk, we have evaluated the hypothesis that SNPs associated with plasma cholesterol are also associated with AD. RESULTS: Seventeen non-APOE SNPs reproducibly associated with cholesterol per GWAS were tested for association with AD in ~2,000 AD and ~4,000 non-AD subjects. As a group, these SNPs are associated with AD. Two SNPs in particular, rs3846662 and rs1532085, are associated with AD risk and age-of-onset. Additionally, rs3846662 was associated with HMGCR exon 13 splicing in human liver but not brain, possibly obscured by CNS cell-type heterogeneity. However, rs3846662 was associated with HMGCR exon 13 splicing in liver- and brain-derived cell lines. CONCLUSIONS: Cholesterol-associated SNPs outside of APOE confer a global risk for AD. Rs3846662 and rs1532085 are associated with both AD risk and age-of-onset. Rs3846662 is associated with HMGCR exon 13 inclusion. Since rs3846662 affects AD risk and age-of-onset as well as statin responsiveness, this SNP may confound clinical trials evaluating the protective effects of statins on AD

Rheumatoid arthritis-associated polymorphisms are not protective against Alzheimer's disease

<p>Abstract</p> <p>Background</p> <p>Rheumatoid arthritis (RA) and Alzheimer's disease (AD) are inversely associated. To test the hypothesis that genetic elements associated with increased RA risk are associated with decreased AD risk, we evaluated RA genetic risk factors recently identified in genome-wide association studies (GWAS) for their association with AD in a two-stage, case-control analysis.</p> <p>Results</p> <p>In our Stage 1 analysis of ~800 AD and ~1,200 non-AD individuals, three of seventeen RA-associated SNPs were nominally associated with AD (p < 0.05) with one SNP, rs2837960, retaining significance after correction for multiple testing (p = 0.03). The rs2837960_G (minor) allele, which is associated with increased RA risk, was associated with increased AD risk. Analysis of these three SNPs in a Stage 2 population, consisting of ~1,100 AD and ~2,600 non-AD individuals, did not confirm their association with AD. Analysis of Stage 1 and 2 combined suggested that rs2837960 shows a trend for association with AD. When the Stage 2 population was age-matched for the Stage 1 population, rs2837960 exhibited a non-significant trend with AD. Combined analysis of Stage 1 and the age-matched Stage 2 subset showed a significant association of rs2837960 with AD (p = 0.002, OR 1.24) that retained significance following correction for age, sex and APOE (p = 0.02, OR = 1.20). Rs2837960 is near <it>BACE2</it>, which encodes an aspartic protease capable of processing the AD-associated amyloid precursor protein. Testing for an association between rs2837960 and the expression of <it>BACE2 </it>isoforms in human brain, we observed a trend between rs2837960 and the total expression of <it>BACE2 </it>and the expression of a <it>BACE2 </it>transcript lacking exon 7 (p = 0.07 and 0.10, respectively).</p> <p>Conclusions</p> <p>RA-associated SNPs are generally not associated with AD. Moreover, rs2837960_G is associated with increased risk of both RA and, in individuals less than 80 years of age, with AD. Overall, these results contest the hypothesis that genetic variants associated with RA confer protection against AD. Further investigation of rs2837960 is necessary to elucidate the mechanism by which rs2837960 contributes to both AD and RA risk, likely via modulation of <it>BACE2 </it>expression.</p

Rodent Aβ Modulates the Solubility and Distribution of Amyloid Deposits in Transgenic Mice

The amino acid sequence of amyloid precursor protein (APP) is highly conserved, and age-related Abeta aggregates have been described in a variety of vertebrate animals, with the notable exception of mice and rats. Three amino acid substitutions distinguish mouse and human Abeta that might contribute to their differing properties in vivo. To examine the amyloidogenic potential of mouse Abeta, we studied several lines of transgenic mice overexpressing wild-type mouse amyloid precursor protein (moAPP) either alone or in conjunction with mutant PS1 (PS1dE9). Neither overexpression of moAPP alone nor co-expression with PS1dE9 caused mice to develop Alzheimer-type amyloid pathology by 24 months of age. We further tested whether mouse Abeta could accelerate the deposition of human Abeta by crossing the moAPP transgenic mice to a bigenic line expressing human APPswe with PS1dE9. The triple transgenic animals (moAPP x APPswe/PS1dE9) produced 20% more Abeta but formed amyloid deposits no faster and to no greater extent than APPswe/PS1dE9 siblings. Instead, the additional mouse Abeta increased the detergent solubility of accumulated amyloid and exacerbated amyloid deposition in the vasculature. These findings suggest that, although mouse Abeta does not influence the rate of amyloid formation, the incorporation of Abeta peptides with differing sequences alters the solubility and localization of the resulting aggregates

Biochemical detection of Aβ isoforms: implications for pathogenesis, diagnosis, and treatment of Alzheimer’s disease

AbstractPrior to the identification of the various abnormal proteins deposited as fibrillar aggregates in the Alzheimer’s disease (AD) brain, there was tremendous controversy over the importance of the various lesions with respect to primacy in the pathology of AD. Nevertheless, based on analogy to systemic amyloidosis, many investigators believed that the amyloid deposits in AD played a causal role and that characterization of these deposits would hold the key to understanding this complex disease. Indeed, in retrospect, it was the initial biochemical purifications of the ∼4 kDa amyloid β-peptide (Aβ) from amyloid deposits in the mid 1980s that launched a new era of AD research (Glenner and Wong, Biochem. Biophys. Res. Commun. 122 (1984) 1121–1135; Wong et al., Proc. Natl. Acad Sci. USA 82 (1985) 8729–8732; and Masters et al., Proc. Natl. Acad Sci. USA 82 (1985) 4245–4249). Subsequent studies of the biology of Aβ together with genetic studies of AD have all supported the hypothesis that altered Aβ metabolism leading to aggregation plays a causal role in AD. Although there remains controversy as to whether Aβ deposited as classic amyloid or a smaller, aggregated, form causes AD, the relevance of studying the amyloid deposits has certainly been proven. Despite the significant advances in our understanding of the role of Aβ in AD pathogenesis, many important aspects of Aβ biology remain a mystery. This review will highlight those aspects of Aβ biology that have led to our increased understanding of the pathogenesis of AD as well as areas which warrant additional study

BACE1 Deficiency Rescues Memory Deficits and Cholinergic Dysfunction in a Mouse Model of Alzheimer's Disease

Abstractβ-site APP cleaving enzyme 1 (BACE1) is the β-secretase enzyme required for generating pathogenic β-amyloid (Aβ) peptides in Alzheimer's disease (AD). BACE1 knockout mice lack Aβ and are phenotypically normal, suggesting that therapeutic inhibition of BACE1 may be free of mechanism-based side effects. However, direct evidence that BACE1 inhibition would improve cognition is lacking. Here we show that BACE1 null mice engineered to overexpress human APP (BACE1−/−·Tg2576+) are rescued from Aβ-dependent hippocampal memory deficits. Moreover, impaired hippocampal cholinergic regulation of neuronal excitability found in the Tg2576 AD model is ameliorated in BACE1−/−·Tg2576+ bigenic mice. The behavioral and electrophysiological rescue of deficits in BACE1−/−·Tg2576+ mice is correlated with a dramatic reduction of cerebral Aβ40 and Aβ42 levels and occurs before amyloid deposition in Tg2576 mice. Our gene-based approach demonstrates that lower Aβ levels are beneficial for AD-associated memory impairments, validating BACE1 as a therapeutic target for AD

Environmental Enrichment Mitigates Cognitive Deficits in a Mouse Model of Alzheimer's Disease

Epidemiological studies suggest that individuals with greater education or more cognitively demanding occupations have diminished risk of developing dementia. We wanted to test whether this effect could be recapitulated in rodents using environmental enrichment, a paradigm well documented to attenuate behavioral deficits induced by various pathological insults. Here, we demonstrate that learning and memory deficits observed in a transgenic mouse model of Alzheimer's disease can be ameliorated by enrichment. Female transgenic mice overexpressing amyloid precursor protein and/or presenilin-1 and nontransgenic controls were placed into enriched or standard cages at 2 months of age and tested for cognitive behavior after 6 months of differential housing. Enrichment significantly improved performance of all genotypes in the radial water maze and in the classic and repeated-reversal versions of the Morris water maze. However, enrichment did not benefit all genotypes equally. Mice overproducing amyloid-β (Aβ), particularly those with amyloid deposits, showed weaker memory for the platform location in the classic Morris water maze and learned new platform positions in the repeated-reversals task less quickly than their nontransgenic cagemates. Nonetheless, enrichment normalized the performance of Aβ-overproducing mice to the level of standard-housed nontransgenic mice. Moreover, this functional preservation occurred despite increased neuritic plaque burden in the hippocampus of double-transgenic animals and elevated steady-state Aβ levels, because both endogenous and transgene-derived Aβ are increased in enriched animals. These results demonstrate that the generation of Aβ in vivo and its impact on the function of the nervous system can be strongly modulated by environmental factors

Blood type gene locus has no influence on ACE association with Alzheimer's disease

The ABO blood group locus was recently found to contribute independently as well as via interactions with ACE gene variation to plasma levels of angiotensin converting enzyme (ACE). Variation in ACE has also previously been implicated as conferring susceptibility for Alzheimer’s disease (AD), but has also been proposed to confer risk via interactions with other as yet unknown genes. More recently, larger studies have not supported ACE as a risk factor for AD, while the role of ACE pathway in AD has come under increased levels of scrutiny with respect to various aspects of AD pathology and possible therapies. We explored the potential combined involvement of ABO and ACE variation in the genetic susceptibility of 2067 AD cases compared to 1376 non-demented elderly. Including the effects of ABO haplotype did not provide any evidence for the genetic association of ACE with AD

Expression of SORL1 and a novel SORL1 splice variant in normal and Alzheimers disease brain

<p>Abstract</p> <p>Background</p> <p>Variations in sortilin-related receptor (SORL1) expression and function have been implicated in Alzheimers Disease (AD). Here, to gain insights into SORL1, we evaluated SORL1 expression and splicing as a function of AD and AD neuropathology, neural gene expression and a candidate single nucleotide polymorphism (SNP).</p> <p>Results</p> <p>To identify SORL1 splice variants, we scanned each of the 46 internal SORL1 exons in human brain RNA samples and readily found SORL1 isoforms that lack exon 2 or exon 19. Quantification in a case-control series of the more abundant isoform lacking exon 2 (delta-2-SORL1), as well as the "full-length" SORL1 (FL-SORL1) isoform containing exon 2 showed that expression of FL-SORL1 was reduced in AD individuals. Moreover, FL-SORL1 was reduced in cognitively intact individuals with significant AD-like neuropathology. In contrast, the expression of the delta-2-SORL1 isoform was similar in AD and non-AD brains. The expression of FL-SORL1 was significantly associated with synaptophysin expression while delta-2-SORL1 was modestly enriched in white matter. Lastly, FL-SORL1 expression was associated with rs661057, a SORL1 intron one SNP that has been associated with AD risk. A linear regression analysis found that rs661057, synaptophysin expression and AD neuropathology were each associated with FL-SORL1 expression.</p> <p>Conclusion</p> <p>These results confirm that FL-SORL1 expression declines in AD and with AD-associated neuropathology, suggest that FL-SORL1 declines in cognitively-intact individuals with AD-associated neuropathology, identify a novel SORL1 splice variant that is expressed similarly in AD and non-AD individuals, and provide evidence that an AD-associated SNP is associated with SORL1 expression. Overall, these results contribute to our understanding of SORL1 expression in the human brain.</p