Phospholipid transfer protein (PLTP) deficiency accelerates memory dysfunction through altering amyloid precursor protein (APP) processing in a mouse model of Alzheimer's disease.

Phospholipid transfer protein (PLTP) is a widely expressed lipid transfer protein participating in the transport of cholesterol and other lipids in the plasma and peripheral tissues. Recently, elevated amyloid ß (Aß) in young and aged PLTP-deficient brains had been reported. However, the role of PLTP in amyloid precursor protein (APP) processing and Alzheimer's disease (AD) pathology remains elusive. Here we first found that deficiency of PLTP accelerated memory dysfunction in APP/PS1ΔE9 AD model mice at the age of 3 months. Further characterization showed that PLTP deficiency increased soluble Aß peptides, and intracellular accumulation of Aß was illustrated, which might be due to disrupted APP turnover and the enhanced amyloidogenic pathway. Besides, reduced brain-derived neurotrophic factor (BDNF) was found in PLTP-deficient APP/PS1ΔE9 mice, and the BDNF level was negatively correlated with Aß42 content, instead of Aß40 content. In addition, autophagic dysfunction was found in the PLTP-deficient APP/PS1ΔE9 mice. Our data presented a novel model to link phospholipid metabolism to APP processing and also suggested that PLTP played an important role in Aß metabolism and would be useful to further elucidate functions of PLTP in AD susceptibility.

Polymorphisms in the aldehyde dehydrogenase 2 and dopamine ß hydroxylase genes are not associated with Alzheimer's disease.

Since ethanol and its metabolite, acetaldehyde, are directly neurotoxic, alcohol intake could affect the development of Alzheimer's disease (AD). Mitochondrial aldehyde dehydrogenase 2 (ALDH2) metabolizes acetaldehyde into acetate and also protects against oxidative stress, playing an important role in the development of AD. The activity of dopamine ß hydroxylase (DBH) is reduced in the hippocampus and neocortex in the AD brain. DBH is also involved in the pathophysiology of alcoholism. The aim of this study was to investigate whether polymorphisms of both ALDH2 and DBH genes were associated with AD. ALDH2*2 and two functional single nucleotide polymorphisms (SNPs) of the DBH gene were analyzed using a case-control study design. Our case-control data set consisted of 201 AD patients and 130 age-matched controls. We also analyzed stratifying by alcohol consumption and apolipoprotein E (APOE) genotypes. There were no associations between the SNPs studied here and the onset of AD. No synergetic associations were found among the SNPs, APOE and the risk for AD. Although high alcohol consumption AD (HAC-AD) patients were analyzed in detail, the current three SNPs were not related with HAC-AD. ALDH2*2 and functional SNPs of the DBH gene did not modify the risk for AD. Since our data set was constructed only with AD in a Japanese population, further detailed genetic analyses with other ethnic groups would be needed.

Genetic association between APOA1 and APOD polymorphisms and Alzheimer's disease in a Japanese population.

Alterations in lipoproteins are involved in the pathophysiology of Alzheimer's disease (AD). For sporadic AD, the Apolipoprotein E (APOE) is recognized as a sole genetic risk factor. Apolipoprotein A1 (APOA1) has been suggested to bind amyloid ß and promoter polymorphisms of the APOA1 gene were likely to affect the onset of the disease. Apolipoprotein D (APOD) expression is upregulating in AD brain and evidences showed APOD polymorphisms affect the risk for AD. The aim of this study was to investigate whether polymorphisms of both APOA1 and APOD genes are associated with early-onset AD (EOAD) and late-onset AD (LOAD). Common single nucleotide polymorphisms (SNPs) of the two genes were analyzed using a case-control study design. There were no associations between the two SNPs of the APOA1 gene and the onset of AD. No synergetic associations were found among the APOA1 SNPs, APOE and the risk for AD. Rs7659, 3' UTR polymorphism of the APOD gene was associated with EOAD in APOEε4 (-) subgroup. We were unable to show any impact of the other two SNPs of the APOD gene on the risk for AD. Our results suggest that the variation of the APOD gene modifies the risk for AD. Further association studies for APOD 3' UTR polymorphisms with other ethnic groups would be needed.

Lack of genetic association of the UCHL1 gene with Alzheimer's disease and Parkinson's disease with dementia.

BACKGROUND/AIMS: Several candidate genes were suggested to modify the susceptibility to both Alzheimer's disease (AD) and Parkinson's disease (PD). Symptoms of dementia are found in approximately 30% of PD patients. Both apolipoprotein E (APO E) and ubiquitin carboxyl-terminal esterase L1 (UCHL1) are neuropathogenic proteins for both diseases. The aim of this study was to investigate whether polymorphisms of both genes are associated with AD and PD with dementia (PDD). METHODS: The APO E polymorphism and 5 common single-nucleotide polymorphisms (SNPs) of the UCHL1 gene were analyzed using a case-control study design. RESULTS: Although APO E4 affected the onset of AD, the 5 SNPs of the UCHL1 gene were not associated with risk for AD. Linkage disequilibrium (LD) analysis of our Japanese data set showed that the SNPs of the UCHL1 gene are part of one LD block. Although one SNP, rs4861387, of the UCHL1 gene showed marginal association with PDD, we did not detect any association between the other SNPs and PDD. CONCLUSION: The common SNPs of UCHL1 are not major risk factors for AD. Since our analyses on PDD are preliminary, further genetic studies on APO E, UCHL1 and PD with and without dementia are needed.

Genetic association between ghrelin polymorphisms and Alzheimer's disease in a Japanese population.

BACKGROUND/AIMS: Ghrelin has been reported to enter the hippocampus and to bind to the neurons of the hippocampal formation. This peptide also affects neuronal glucose uptake and decreases tau hyperphosphorylation. There is increasing evidence suggesting an association between ghrelin and Alzheimer's disease (AD) pathology. The aim of this study was to investigate whether single nucleotide polymorphisms (SNPs) of the ghrelin gene are associated with AD. METHODS: The SNPs were genotyped using TaqMan technology and were analyzed using a case-control study design. Our case-control dataset consisted of 182 AD patients and 143 age-matched controls. RESULTS: Hardy-Weinberg equilibrium and linkage disequilibrium analyses suggest that the region in and around the gene is highly polymorphic. One SNP, rs4684677 (Leu90Gln), showed a marginal association with age of AD onset. We did not detect any association between the other SNPs of the ghrelin gene and AD. CONCLUSION: There have been few genetic studies on the relationship between circulating ghrelin and functional SNPs. Further multifactorial studies are needed to clarify the relationship between ghrelin and AD.

Genetic association between clusterin polymorphisms and Alzheimer's disease in a Japanese population.

BACKGROUND: Previous papers have reported that clusterin (CLU, also called apolipoprotein J) maintains amyloid ß-peptide (Aß) solubility and protects against Aß neurotoxicity. Recently, two large genome-wide association studies (GWAS) identified that a specific single nucleotide polymorphism (SNP) on the gene has been reported to modify the risk for Alzheimer's disease (AD). The present study aimed to investigate whether common single nucleotide polymorphisms (SNP) of the CLU gene are associated with AD. METHODS: Six SNP, genotyped using TaqMan technology, were analyzed using a case-control study design. Furthermore, an analysis of the cases divided according to apolipoprotein E (APO E) status was also carried out. Our case-control dataset consisted of 180 AD patients and 130 age-matched controls. RESULTS: The present study failed to detect any association between the SNP of the CLU gene and AD. Although rs7982 and rs1532277 showed marginal association in the APO E4 negative group, the linkage disequilibrium analysis results suggest this to be a false positive. CONCLUSION: The negative associations were mainly the result of our small sample size. Larger genetic studies in different ethnics and future meta-analysis are needed to clarify the relationship between the CLU gene and AD.

Genetic association between PLTP gene polymorphisms and Alzheimer's disease in a Japanese population.

BACKGROUND/AIMS: A recent paper reported that the phospholipid transfer protein (PLTP) reduces phosphorylation of tau in human neuronal cells. In addition, patients with Alzheimer's disease (AD) have significantly higher levels of PLTP in brain tissue and significantly lower PLTP-mediated phospholipid transfer activity in cerebrospinal fluid. PLTP also affects apolipoprotein E (APOE) secretion from glial cells. This study aimed to investigate whether single nucleotide polymorphisms (SNPs) of the PLTP gene are associated with AD. METHODS: Five SNPs, genotyped using TaqMan technology, were analyzed using a case-control study design. Furthermore, we also checked for a synergetic association between the PLTP gene, APOE and AD. Our case-control dataset consisted of 180 AD patients and 130 age-matched controls. RESULTS: None of the SNPs showed a statistically significant association. We could not confirm any synergetic association between the SNPs and APOE in our AD patients. CONCLUSION: Our results indicate that there is no genetic association between PLTP and AD. Due to the relatively small sample size and the incomplete coverage of the region surrounding the PLTP gene of this study, larger genetic studies covering the entire PLTP gene region are needed.

Association between DNA Methylation of the BDNF Promoter Region and Clinical Presentation in Alzheimer's Disease.

BACKGROUND/AIMS: In the present study, we examined whether DNA methylation of the brain-derived neurotrophic factor (BDNF) promoter is associated with the manifestation and clinical presentation of Alzheimer's disease (AD). METHODS: Of 20 patients with AD and 20 age-matched normal controls (NCs), the DNA methylation of the BDNF promoter (measured using peripheral blood samples) was completely analyzed in 12 patients with AD and 6 NCs. The resulting methylation levels were compared statistically. Next, we investigated the correlation between the DNA methylation levels and the clinical presentation of AD. RESULTS: The total methylation ratio (in %) of the 20 CpG sites was significantly higher in the AD patients (5.08 ± 5.52%) than in the NCs (2.09 ± 0.81%; p < 0.05). Of the 20 CpG sites, the methylation level at the CpG4 site was significantly higher in the AD subjects than in the NCs (p < 0.05). Moreover, the methylation level was significantly and negatively correlated with some neuropsychological test subscores (registration, recall, and prehension behavior scores; p < 0.05). CONCLUSION: These results suggest that the DNA methylation of the BDNF promoter may significantly influence the manifestation of AD and might be associated with its neurocognitive presentation.

Duration-dependent regulation of autophagy by isoflurane exposure in aged rats.

Current evidence suggests a central role for autophagy in many inflammatory brain disorders, including Alzheimer's disease (AD). Furthermore, it is also well accepted that some inhalation anesthetics, such as isoflurane, may cause AD-like neuropathogenesis and resultant postoperative cognitive dysfunction, especially in the elderly population. However, the impact of inhalation anesthetics on autophagic components in the brain remains to be documented. Hence, our objective was to investigate the effects of different durations of isoflurane exposure on hippocampus-dependent learning and hippocampal autophagy in aged rats. Aged Sprague-Dawley rats (20 months old) were randomly exposed to 1.5% isoflurane or 100% oxygen for 1 or 4 h. Animals were then trained in the Morris water maze (4 trials/day for 5 consecutive days). Hippocampal phagophore formation markers, beclin 1 and protein microtubule-associated protein 1 light chain-3B (LC3B), as well as p62, an indicator of autophagic flux, were quantified by western blotting. There was no significant difference in the escape latencies and time spent in the target quadrant, as well as hippocampal expression of beclin 1, LC3B-II, and p62 at 24 h post-anesthesia between the 1-h isoflurane-exposed rats and their controls (P >0.05). Four-hour exposure to isoflurane resulted in spatial learning and memory deficits, as evidenced by prolonged escape latencies on days 4 and 5 post-anesthesia and less time spent in the target quadrant than sham-exposed animals (P <0.05). These events were accompanied by a decline in hippocampal expression of LC3B-I, LC3B-II, and beclin 1 24 h after isoflurane (P <0.01 and P <0.05). Nevertheless, no significant change in p62 expression was found. Further kinetics study of autophagic changes induced by 4 h of isoflurane showed a transient upregulation of LC3B-I, LC3B-II, and beclin 1 at the end of exposure and a subsequent striking decrease within 12-24 h post-anesthesia (P <0.05). Hippocampal p62 peaked at 6 h but subsequently resolved. These results from our pilot in vivo study support a duration-dependent relationship between 1.5% isoflurane exposure, and spatial cognitive function as well as hippocampal phagophore formation.

Autophagy is involved in oral rAAV/Aß vaccine-induced Aß clearance in APP/PS1 transgenic mice.

The imbalance between ß-amyloid (Aß) generation and clearance plays a fundamental role in the pathogenesis of Alzheimer's disease (AD). The sporadic form of AD is characterized by an overall impairment in Aß clearance. Immunotherapy targeting Aß clearance is believed to be a promising approach and is under active clinical investigation. Autophagy is a conserved pathway for degrading abnormal protein aggregates and is crucial for Aß clearance. We previously reported that oral vaccination with a recombinant AAV/Aß vaccine increased the clearance of Aß from the brain and improved cognitive ability in AD animal models, while the underlying mechanisms were not well understood. In this study, we first demonstrated that oral vaccination with rAAV/Aß decreased the p62 level and up-regulated the LC3B-II/LC3B-I ratio in APP/PS1 mouse brain, suggesting enhanced autophagy. Further, inhibition of the Akt/mTOR pathway may account for autophagy enhancement. We also found increased anti-Aß antibodies in the sera of APP/PS1 mice with oral vaccination, accompanied by elevation of complement factors C1q and C3 levels in the brain. Our results indicate that autophagy is closely involved in oral vaccination-induced Aß clearance, and modulating the autophagy pathway may be an important strategy for AD prevention and intervention.

Age-Related Association between Apolipoprotein E ε4 and Cognitive Function in Japanese Patients with Alzheimer's Disease.

AIMS: In the present study, we investigated whether apolipoprotein E (APOE) polymorphisms influenced the cognitive function of Japanese patients with Alzheimer's disease (AD) at certain ages. METHODS: Among 200 outpatients with dementia and amnestic mild cognitive impairment, 133 Japanese patients with AD were recruited and divided into two genotypic groups: APOE ε4 carriers and noncarriers. Then, we compared several neuropsychological test scores between the two genotypic groups for two different generations: 70s (70-79 years) and 80s (80-89 years). RESULTS: The total Mini-Mental State Examination score (p < 0.05) and one of its subtest scores, the 3-stage command score (p < 0.01), were significantly lower for the ε4 carriers than for the noncarriers among patients in their 80s, but not among those in their 70s. The duration of illness differed significantly between the ε4 carriers and the noncarriers among subjects in their 80s but was not correlated with cognitive function. CONCLUSION: The present results suggest that APOE may significantly influence comparatively simple memory processing in certain generations of Japanese patients with AD.

Genetic Association between Neurotrophin-3 Polymorphisms and Alzheimer's Disease in Japanese Patients.

BACKGROUND: Some polymorphisms of the neurotrophin family have previously been investigated as candidate genes for Alzheimer's disease (AD). In the present study, we examined whether neurotrophin-3 (NTF-3) polymorphisms are genetic risk factors in patients with AD. METHODS: From a sample of 507 subjects, we recruited 248 age-matched subjects divided into 2 groups: AD patients (n = 143) and normal controls (NCs) (n = 105). We identified 3 representative NTF-3 single nucleotide polymorphisms (SNPs): rs6332, rs6489630, and rs4930767. Next, we statistically compared the allele frequencies of each SNP between the AD and NC groups in the early-onset (<65 years) cases under a more limited age-matched condition. RESULTS: We found a significant association between rs6332 and the total group of AD patients (p = 0.013) and significant associations between both rs6332 (p = 0.033) and rs6489630 (p = 0.035) and early-onset AD patients. CONCLUSION: These results suggest that NTF-3 SNPs may not only be associated with AD itself, but also with early-onset AD in Japanese patients, assuming that the NTF-3 gene may have age-related effects on neurodegenerative diseases.

Lack of Genetic Associations of PPAR-γ and PGC-1α with Alzheimer's Disease and Parkinson's Disease with Dementia.

BACKGROUND AND AIMS: Similar clinical and pathological features have been observed in Alzheimer's disease (AD) and Parkinson's disease with dementia (PDD). Both the peroxisome proliferator-activated receptor-γ (PPAR-γ) gene and the peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) gene are candidates modifying the risk for both diseases. The aim of this study was to clarify whether common single nucleotide polymorphisms (SNPs) of the PPAR-γ gene and the PGC-1α gene affect the onset of AD and PDD genetically. METHODS: Four exonic SNPs of both genes (rs1801282 and rs3856806 of the PPAR-γ gene, rs3736265 and rs8192678 of the PGC-1α gene) were genotyped in 171 AD patients, 136 age-matched controls and 53 PDD patients. Haplotype analysis and logistic regression analysis with apolipoprotein E (APO E) status were performed for AD. RESULTS: There was no statistical difference between AD cases and controls for the 4 SNPs, nor was there any statistical difference between PDD cases and controls for the 4 SNPs. We could not find any synergetic associations between these SNPs, APO E4 and AD. CONCLUSIONS: The 4 SNPs studied here did not influence the risk for AD in a Japanese population. As the number of PDD cases was small, comprehensive genetic studies considering diabetes would be needed.

Genetic Association between Akt1 Polymorphisms and Alzheimer's Disease in a Japanese Population.

A recent paper reported that Aß oligomer causes neuronal cell death through the phosphatidylinositol-3-OH kinase (PI3K)-Akt-mTOR signaling pathway. Intraneuronal Aß, a main pathological finding of Alzheimer's disease (AD), is also known as inhibiting activation of Akt. This study aims to investigate whether single nucleotide polymorphisms (SNPs) of the Akt1 gene are associated with AD. SNPs genotyped using TaqMan technology was analyzed using a case-control study design. Our case-control dataset consisted of 180 AD patients and 130 age-matched controls. Although two SNPs showed superficial positive, Hardy-Weinberg equilibrium (HWE) tests, and linkage disequilibrium (LD) analyses suggested that genetic regions of the gene are highly polymorphic. We failed to detect any synergetic association among Akt1 polymorphisms, Apolipoprotein E (APO E), and AD. Further genetic studies are needed to clarify the relationship between the Akt1 and AD.

Genetic association between CALHM1, 2, and 3 polymorphisms and Alzheimer's disease in a Japanese population.

A recent paper reported that a variant (rs2986017) of the calcium homeostasis modulator 1 (CALHM1) gene affects risk for late-onset Alzheimer's disease (AD). This study aims to investigate whether single nucleotide polymorphisms (SNPs) of the CALHM1 gene are associated with AD. SNPs in the genes of two other CALHM subtypes, CALHM2 and CALHM3, were also studied. Our study failed to detect any association between the SNPs of the three genes and AD. Although rs729211 showed marginal association in the APOE4 negative group, the linkage disequilibrium analysis results suggest this to be a false positive.