Contribution of genetic and dietary insulin resistance to Alzheimer phenotype in APP/PS1 transgenic mice.

According to epidemiological studies, type-2 diabetes increases the risk of Alzheimer's disease. Here, we induced hyperglycaemia in mice overexpressing mutant amyloid precursor protein and presenilin-1 (APdE9) either by cross-breeding them with pancreatic insulin-like growth factor 2 (IGF-2) overexpressing mice or by feeding them with high-fat diet. Glucose and insulin tolerance tests revealed significant hyperglycaemia in mice overexpressing IGF-2, which was exacerbated by high-fat diet. However, sustained hyperinsulinaemia and insulin resistance were observed only in mice co-expressing IGF-2 and APdE9 without correlation to insulin levels in brain. In behavioural tests in aged mice, APdE9 was associated with poor spatial learning and the combination of IGF-2 and high-fat diet further impaired learning. Neither high-fat diet nor IGF-2 increased ß-amyloid burden in the brain. In male mice, IGF-2 increased ß-amyloid 42/40 ratio, which correlated with poor spatial learning. In contrast, inhibitory phosphorylation of glycogen synthase kinase 3ß, which correlated with good spatial learning, was increased in APdE9 and IGF-2 female mice on standard diet, but not on high-fat diet. Interestingly, high-fat diet altered τ isoform expression and increased phosphorylation of τ at Ser202 site in female mice regardless of genotype. These findings provide evidence for new regulatory mechanisms that link type-2 diabetes and Alzheimer pathology.

Lack of genetic association between PPARG gene polymorphisms and Finnish late-onset Alzheimer's disease.

Single nucleotide polymorphisms (SNPs) in diabetes related peroxisome proliferator-activated receptor gamma (PPARG) gene were investigated with a case-control approach. To examine the genetic association of this gene with Alzheimer's disease (AD) risk, we used the TaqMan technique to genotype eight SNP sites for PPARG gene, in 538 Finnish AD cases and 672 controls and conducted a single allele and genotypic distribution comparison as well as estimated haplotype frequencies between cases and controls. No significant differences in AD risk were found in single SNP and haplotype analyses for PPARG gene between the study groups. We conclude that PPARG gene does not play a major role in the genetic predisposition to AD in the Finnish population.

Increased expression of Abeta degrading enzyme IDE in the cortex of transgenic mice with Alzheimer's disease-like neuropathology.

Expression levels of amyloid beta (Abeta)-degrading enzymes, insulin degrading enzyme (IDE) and neprilysin (NEP), were examined in transgenic mice with Alzheimer's disease-like neuropathology. After the development of first Abeta plaques in transgenic mice brain, cortical mRNA and protein levels of IDE were significantly up-regulated in the transgenic mice compared to their non-transgenic littermates. Up-regulation of IDE mRNA-levels occurred in parallel with increased Abeta40 and Abeta42 production. Additionally, a significant positive correlation was observed between protein levels of IDE and full-length amyloid precursor protein (APP) in the cerebral cortex. mRNA and protein levels of NEP were also nominally up-regulated in Tg mice compared to controls. These data may reflect up-regulation of the IDE and possibly of NEP expression in response to the Abeta accumulation.

Insulin-degrading enzyme is genetically associated with Alzheimer's disease in the Finnish population.

The gene for insulin-degrading enzyme (IDE), which is located at chromosome 10q24, has been previously proposed as a candidate gene for late-onset Alzheimer's disease (AD) based on its ability to degrade amyloid beta-protein. Genotyping of single nucleotide polymorphisms (SNPs) in the IDE gene in Finnish patients with AD and controls revealed SNPs rs4646953 and rs4646955 to be associated with AD, conferring an approximately two-fold increased risk. Single locus findings were corroborated by the results obtained from haplotype analyses. This suggests that genetic alterations in or near the IDE gene may increase the risk for developing AD.

Somatostatin genetic variants modify the risk for Alzheimer's disease among Finnish patients.

The levels of somatostatin are consistently decreased in the brain and cerebrospinal fluid of Alzheimer's disease (AD) patients. The somatostatin gene is located on chromosome 3q27.3 close to an association region identified in late-onset AD patients originating from Finland. Since somatostatin is a good candidate on both positional and functional grounds, we studied whether single nucleotide polymorphisms (SNPs) in the somatostatin gene were associated with AD in the Finnish population. We genotyped three SNPs within this gene in Finnish AD patients (n = 424) and non-demented controls (n = 466). AD patients were compared with non-demented control subjects using single-locus and haplotype approaches. In the whole study group, the age, sex and APOE adjusted OR for the risk of AD in C-allele carriers of the SNP rs4988 514 was 1.42 (p <0.05). Interestingly, in APOE epsilon4-allele carriers, the age and sex adjusted OR for the risk of AD in C-allele carriers of the rs4988 514 increased to 2.05 (p <0.01). Additionally, SNP rs4988514 may interact with the APOE epsilon4-allele to increase the risk of AD. Assessment of individual haplotype distributions revealed a 2-fold overrepresentation of the TCG haplotype of SNPs rs3864101, rs4988 514 and rs7624 906 in the AD APOE epsilon4-allele group (p <0.01). Conversely, a major haplotype TTG was significantly underrepresented among all the AD patients as well as APOE epsilon4-allele carrying AD patients. Thus the major haplotype TTG of somatostatin may have a protective effect against AD. This first genetic association study between somatostatin and AD indicates that genetic variations in the somatostatin gene may modify the risk for AD among Finnish AD subjects.

Role of alpha-synuclein in presynaptic dopamine recruitment.

Real-time monitoring of stimulated dopamine release in mice with different alpha-synuclein expression was used to study the role of alpha-synuclein in presynaptic dopamine recruitment. Repeated electrical stimulations of ascending dopaminergic pathways decreased the capacity of the readily releasable pool (RRP) and temporarily increased its refilling rate, significantly slowing the rate of dopamine decline in mice with normally expressed alpha-synuclein. Mice with alpha-synuclein null mutation demonstrated a permanent increase of the refilling rate. This increase maintained stable dopamine release during stimulation (which induced dopamine decline in other animals) and served as an adaptation to altered dopamine compartmentalization. Mice without alpha-synuclein and with overexpression of human A30P mutated alpha-synuclein had a lower capacity of the dopamine storage pool than other animals. Reducing capacity of the storage pool in transgenic A30P mice led to paradoxical effects of l-dopa, which elevated dopamine release in response to single stimulation but decreased the refilling rate of the RRP.

Genetic analysis of BDNF and TrkB gene polymorphisms in Alzheimer's disease.

According to previous biochemical and genetic findings, brain-derived neurotrophic factor (BDNF), via activation of its tyrosine kinase receptor B (TrkB), is considered as a plausible candidate for contributing to Alzheimer's disease (AD). To examine the genetic association of BDNF and TrkB genes with AD, we genotyped multiple single nucleotide polymorphisms (SNPs) within these genes among 375 Finnish AD patients and 460 control subjects. Single locus and multi-loci haplotype association analyses of BDNF and TrkB gene SNPs did not reveal significant differences between unstratified AD and control groups. In the case of BDNF SNPs, different allele and haplotype frequencies were observed when 160 sporadic AD cases were compared with 460 control subjects. However, these differences did not remain statistically significant after multiple corrections. We conclude that BDNF and TrkB genes are not contributing significant risk effect among Finnish AD patients.

The expression and promoter specificity of the birch homologs for PISTILLATA/GLOBOSA and APETALA3/DEFICIENS.

B-function genes determine the identity of petals and stamens in the flowers of model plants such as Arabidopsis and Antirrhinum. Here, we show that a putative B-function gene BpMADS2, a birch homolog for PISTILLATA, is expressed in stamens and carpels of birch inflorescences. We also present a novel birch gene BpMADS8, a homolog for APETALA3/DEFICIENS, which is expressed in stamens. Promoter-GUS analysis revealed that BpMADS2 promoter is active in the receptacle of Arabidopsis flower buds while BpMADS8 promoter is highly specific in mature stamens. BpMADS2 promoter::BARNASE construct prevented floral organ development in Arabidopsis and tobacco. In birch, inflorescences with degenerated stamens and carpels were obtained. BpMADS8::BARNASE resulted in degeneration of stamens in Arabidopsis and birch causing male sterility. In tobacco, only sepals were developed instead of normal flowers. The results show that the BpMADS2::BARNASE construct can be used to specifically disrupt floral organ development in phylogenetically distant plant species. The stamen-specific promoter of BpMADS8 is a promising tool for biotechnological applications in inducing male sterility or targeting gene expression in the late stamen development.

Genetic variation in apolipoprotein D and Alzheimer's disease.

Apolipoprotein D (apoD) is a lipoprotein-associated glycoprotein, structurally unrelated to apoE, that transports small hydrophobic ligands including cholesterol and sterols. Levels are increased in the hippocampus and CSF of Alzheimer's disease (AD) patients. We tested whether variation in the APOD gene affects AD risk. Four single nucleotide polymorphisms (SNPs) were investigated (in map order): exon 2, 15T-->C encodes an amino acid substitution Phe-->Ser at codon 15; intron 2, -352G-->A; intron 3, +45C-->T; intron 4, +718C-->T, determined by SNaPshot assay. SNP frequencies for 394 eastern Finnish AD patients were compared with those found for 470 control subjects, dividing subjects also into early-onset AD (EOAD; < or = 65 years) and late-onset AD (LOAD; >65 years) groups. The -352G allele was associated with a significant 3-fold increase in the risk of EOAD (OR: 2.7; 95% CI: 1.1-6.5). The -352G containing haplotypes were more common for EOAD cases (TGCC: 0.48 vs 0.41; TGCT: 0.08 vs 0.01 (p = 0.002). In the Grade-of-membership analysis, APOD genotype frequencies at each SNP site and disease status were used to construct two latent groups: the affected group carried -352 as GG or GA and +45 CC, was often women and enriched in APOE epsilon4. Each method suggested that the -352G allele frequency is higher for EOAD in the eastern Finnish population.

Anthocyanin-enriched bilberry and blackcurrant extracts modulate amyloid precursor protein processing and alleviate behavioral abnormalities in the APP/PS1 mouse model of Alzheimer's disease.

A growing body of epidemiological evidence suggests that fruit and vegetable juices containing various phenolic compounds can reduce the risk of Alzheimer's disease (AD). As the altered amyloid precursor protein (APP) processing leading to increased ß-amyloid (Aß) production is a key pathogenic feature of AD, we elucidated the effects of different polyphenols on neuroprotection and APP processing under different in vitro stress conditions. The effects of these compounds were also investigated in transgenic AD mice (APdE9). Free radical toxicity and apoptosis were induced in human SH-SY5Y neuroblastoma cells overexpressing APP751. Menadione-induced production of reactive oxygen species was significantly decreased upon treatment with myricetin, quercetin or anthocyanin-rich extracts in a dose-dependent manner. However, these extracts did not affect caspase-3 activation, APP processing or Aß levels upon staurosporine-induced apoptosis. APdE9 mice fed with anthocyanin-rich bilberry or blackcurrant extracts showed decreased APP C-terminal fragment levels in the cerebral cortex as compared to APdE9 mice on the control diet. Soluble Aß40 and Aß42 levels were significantly decreased in bilberry-fed mice as compared to blackcurrant-fed mice. Conversely, the ratio of insoluble Aß42/40 was significantly decreased in blackcurrant-fed mice relative to bilberry-fed mice. Both berry diets alleviated the spatial working memory deficit of aged APdE9 mice as compared to mice on the control diet. There were no changes in the expression or phosphorylation status of tau in APdE9 mice with respect to diet. These data suggest that anthocyanin-rich bilberry and blackcurrant diets favorably modulate APP processing and alleviate behavioral abnormalities in a mouse model of AD.

Genetic analysis of genes involved in amyloid-ß degradation and clearance in Alzheimer's disease.

Accumulation of amyloid ß-peptide (Aß) in the brain of Alzheimer's disease (AD) patients has been postulated to reflect defects in Aß degradation or clearance. Here, we selected 12 genes (MMEL1, ECE1, ECE2, AGER, PLG, PLAT, NR1H3, MMP3, LRP1, TTR, NR1H2, and MMP9) involved in Aß catabolism on the basis of PubMed-based literature search and elucidated their genetic role in AD among Finnish case-control cohort consisting of total ∼1,300 AD patients and control subjects. Thirty one single nucleotide polymorphisms (SNPs) were selected for genotyping. In a smaller subset of AD patients, cerebrospinal fluid (CSF) levels of Aß42 (n = 124), total-tau (n = 59), and phospho-tau (n = 54) analyses were performed with respect to SNPs. Moreover, age of onset analyses with respect to the studied SNPs were conducted among the AD patient cohort (n = 642). Association analysis of the liver X receptor α (NR1H3) gene SNPs showed a protective effect for C allele carriers of rs7120118 (OR = 0.70, 95% CI 0.53-0.93), while the total-tau and phospho-tau levels in CSF were decreased in AD patients carrying the C allele. Also, a decrease in the age of onset was observed in AD patients carrying the A allele of rs723744 and the C allele of rs3794884 in transthyretin (TTR) gene. However, after adjusting the p-values for multiple comparisons, these results were not statistically significant, suggesting that genetic variations in MMEL1, ECE1, ECE2, AGER, PLG, PLAT, NR1H3, MMP3, LRP1, TTR, NR1H2, and MMP9 genes do not play major role among the Finnish AD patient cohort.

No association between high temperature requirement 1 (HTRA1) gene polymorphisms and Alzheimer's disease.

High temperature requirement 1 (HTRA1) gene is a plausible risk factor in Alzheimer's disease (AD) as it encodes a protease known to degrade amyloid-ß peptide. Here we have studied whether single nucleotide polymorphisms (SNPs) in the HTRA1 gene or its nearby regions associated with AD in a large clinic-based case-control cohort originating from Finland. We did not observe significant association of the HTRA1 SNPs with AD among the whole case-control cohort or age-at-onset risk effect among AD patients.

The CALHM1 P86L polymorphism is a genetic modifier of age at onset in Alzheimer's disease: a meta-analysis study.

The only established genetic determinant of non-Mendelian forms of Alzheimer's disease (AD) is the ε4 allele of the apolipoprotein E gene (APOE). Recently, it has been reported that the P86L polymorphism of the calcium homeostasis modulator 1 gene (CALHM1) is associated with the risk of developing AD. In order to independently assess this association, we performed a meta-analysis of 7,873 AD cases and 13,274 controls of Caucasian origin (from a total of 24 centers in Belgium, Finland, France, Italy, Spain, Sweden, the UK, and the USA). Our results indicate that the CALHM1 P86L polymorphism is likely not a genetic determinant of AD but may modulate age of onset by interacting with the effect of the ε4 allele of the APOE gene.