Promoter polymorphisms which modulate BACE1 expression are associated with sporadic Alzheimer's disease

Relationship between the polymorphism in exon 5 of BACE1 gene and Alzheimer's disease

BACKGROUND AND AIMS

The β-Site APP-cleaving enzyme 1 (BACE1) gene polymorphism (rs638405) has been extensively investigated for association to Alzheimer's disease (AD). However, results of different studies have been contradictory. The aim of this meta-analysis was to evaluate the association between BACE1 gene polymorphism (rs638405) and AD.

METHODS

All eligible studies were searched in PubMed, Cochrane Library, Embase, SinoMed, and the China Knowledge Resource Integrated Database. Pooled odds ratios (ORs) and 95 % confidence intervals (95 % CIs) were used to evaluate the strength of the association between BACE1 gene polymorphism and AD.

RESULTS

Twenty studies in 19 papers containing 4377 AD patients and 4563 controls were included for rs638405 polymorphism. The results suggested that rs638405 in BACE1 was not associated with the risk of AD. Stratification analyses indicated rs638405 decreased the risk of apolipoprotein-E ε4 (APOE4) positive AD patients. Furthermore, we found rs638405 also decreased the risk of Asian AD patients. By exclusion of three studies that did not conform to Hardy-Weinberg equilibrium (HWE), our data suggested rs638405 in BACE1 was a protective factor of AD.

CONCLUSIONS

To sum up, our data indicated that BACE1 gene polymorphism in exon 5 might decrease the risk of Asian AD and APOE4 positive patients.

Expression of β-site APP-cleaving enzyme 1 in the hippocampal tissue of an insulin-resistant rat model of Alzheimer's disease

The aim of this study was to investigate the expression of β-site APP-cleaving enzyme 1 (BACE1) in the hippocampal tissue of an insulin-resistant rat model, and thereby explore the roles of BACE1 and insulin resistance (IR) in the pathogenesis of Alzheimer's disease (AD). A total of 36 male Sprague-Dawley rats, aged 2 months, were randomly divided into three groups. These were an insulin-resistant (experimental) group, a high fat control group and a blank control group. The cognitive function and behavioral changes of the rats were tested by a Morris water maze experiment. Amyloid β (Aβ) deposition was detected by an immunohistochemical method. The expression levels of BACE1 in the rat hippocampal tissues were detected by enzyme-linked immunosorbent assay, western blotting and reverse transcription-quantitative polymerase chain reaction technology. The rats in the experimental group had evident learning and memory impairment, with significantly decreased learning memory. The modeling was successful; in the experimental group, the rats exhibited IR and their glucose metabolism was significantly abnormal. However, there was no characteristic pathology of AD. The expression of BACE1 in the brain tissue of rats in the experimental group was significantly higher than that in high fat control and blank control groups (P<0.01). In conclusion, the expression of BACE1 in the brain tissue of insulin-resistant rats increased, and IR was indicated to participate in the pathogenesis of AD.

Association of BACE1 Gene Polymorphism with Cerebellar Volume but Not Cognitive Function in Normal Individuals

Aims

β-Site amyloid precursor protein (APP)-cleaving enzyme 1 (BACE1) is a biological and positional candidate gene for Alzheimer's disease (AD). Previous studies found that BACE1-null mice had impaired performance on cognition and neurodegeneration during the aging process. Additionally, a synonymous polymorphism of BACE1 (rs638405) in exon 5 has been reported to be associated with risk for AD. We hypothesized that this BACE1 gene variant might influence regional brain volumes and cognitive tests in normal individuals.

Methods

Participants were 330 normal volunteers between 21 and 92 years of age (mean age 56.3 ± 22.0 years; 191 males, 139 females). Cognitive tests (the Mini-Mental State Examination and Digit Spans), magnetic resonance imaging, and genotyping of BACE1 rs638405 were examined for each subject. The differences in regional gray matter (GM) volumes between G homozygotes and C-allele carriers were tested using optimized voxel-based morphometry.

Results

Compared to C-allele carriers, G homozygotes exhibited significantly larger GM volumes in the left cerebellar culmen and right cerebellar lingual area, but no significant differences on cognitive function tests.

Conclusion

The findings suggest that the BACE1 rs638405 polymorphism may affect cerebellar morphology, but not cognitive function in healthy humans.

New pharmacological strategies for treatment of Alzheimer's disease: focus on disease modifying drugs

Current approved drug treatments for Alzheimer disease (AD) include cholinesterase inhibitors (donepezil, rivastigmine, galantamine) and the NMDA receptor antagonist memantine. These drugs provide symptomatic relief but poorly affect the progression of the disease. Drug discovery has been directed, in the last 10 years, to develop 'disease modifying drugs' hopefully able to counteract the progression of AD. Because in a chronic, slow progressing pathological process, such as AD, an early start of treatment enhances the chance of success, it is crucial to have biomarkers for early detection of AD-related brain dysfunction, usable before clinical onset. Reliable early biomarkers need therefore to be prospectively tested for predictive accuracy, with specific cut off values validated in clinical practice. Disease modifying drugs developed so far include drugs to reduce β amyloid (Aβ) production, drugs to prevent Aβ aggregation, drugs to promote Aβ clearance, drugs targeting tau phosphorylation and assembly and other approaches. Unfortunately none of these drugs has demonstrated efficacy in phase 3 studies. The failure of clinical trials with disease modifying drugs raises a number of questions, spanning from methodological flaws to fundamental understanding of AD pathophysiology and biology. Recently, new diagnostic criteria applicable to presymptomatic stages of AD have been published. These new criteria may impact on drug development, such that future trials on disease modifying drugs will include populations susceptible to AD, before clinical onset. Specific problems with completed trials and hopes with ongoing trials are discussed in this review.

Structural and functional characterization of H2 haplotype MAPT promoter: unique neurospecific domains and a hypoxia-inducible element would enhance rationally targeted tauopathy research for Alzheimer's disease

Alzheimer's disease (AD) is the leading cause of dementia in the elderly. Extraneuronal plaque comprising mostly the amyloid β peptide and intraneuronal tangles of hyperphosphorylated microtubule-associated τ protein (τ, gene MAPT) are typical of AD. Misfolded τ is also implicated in Parkinson's disease and frontotemporal dementia. We aim to understand the regulation of the human MAPT promoter by mapping its functional domains. We subcloned a 4868 base pair (bp) fragment from human BAC RPCI-11 100C5. Sequence analysis revealed an H2 haplotype MAPT promoter, 5'-UTR, and intronal fragment. Database analysis of the fragment showed 50%-75% homology with mouse and >90% with rhesus monkey. Comparison with human H1 sequences revealed differences that crossed predicted transcription factor sites. DNA-protein interaction studies by electrophoretic mobility shift assay suggested hypoxia response and an active specificity protein 1 (SP1) site in the 5'-untranslated region. Transfection of a series of MAPT promoter deletions revealed unique functional domains. The distal-most had different activities in neuronal vs. non-neuronal cells. We have cloned, sequenced, and functionally characterized a 4868bp fragment of the human MAPT 5'-flanking region, including the core promoter region (-302/+4), neurospecific domains (-4364/-1992 and +293/+504, relative to +1 TSS), and a hypoxia-inducible element (+60/+84). Our work extended functional analysis of the MAPT sequence further upstream, and explores cell-type specificity of MAPT promoter activity. Finally, we provided direct comparison of likely transcription factor binding sites, which are useful to understand differences between H1/H2 pathogenic associations.

Flavonoids lower Alzheimer's Aβ production via an NFκB dependent mechanism

Alzheimer's disease (AD) is characterized by the brain accumulation of Aβ peptides and by the presence of neurofibrillary tangles. Aβ is believed to play an important role in AD and it has been shown that certain flavonoids can affect Aβ production. Recently, it was suggested that the Aβ lowering properties of flavonoids are mediated by a direct inhibition the β-secretase (BACE-1) activity, the rate limiting enzyme responsible for the production of Aβ peptides. Westernblots and ELISAs were employed to monitor the impact of flavonoids on amyloid precursor protein processing and Aβ production. A cell free chemoluminescent assay using human recombinant BACE-1 was used to assess the effect of flavonoids on BACE-1 activity. The effect of flavonoids on NFκB activation was determined by using a stable NFκB luciferase reporter cell line. Molecular docking simulations were performed to predict the binding of flavonoids to the BACE-1 catalytic site. Real time quantitative PCR was used to determine the effect of flavonoids on BACE-1 transcription. We show in a cell free assay that flavonoids are only weak inhibitors of BACE-1 activity. Docking simulation studies with different BACE-1 structures also suggest that flavonoids are poor BACE-1 inhibitors as they appear to adopt various docking poses in the active site pocket and have weak docking scores that differ as a function of the BACE-1 structures studied. Moreover, a weak correlation was observed between the effect of flavonoids on Aβ production in vitro and their ability to lower BACE-1 activity suggesting that the Aβ lowering properties of flavonoids in whole cells are not mediated via direct inhibition of BACE-1 activity. We found however a strong correlation between the inhibition of NFκB activation by flavonoids and their Aβ lowering properties suggesting that flavonoids inhibit Aβ production in whole cells via NFκB related mechanisms. As NFκB has been shown to regulate BACE-1 expression, we show that NFκB lowering flavonoids inhibit BACE-1 transcription in human neuronal SH-SY5Y cells. Altogether, our data suggest that flavonoids inhibit Aβ and sAPPβ production by regulating BACE-1 expression and not by directly inhibiting BACE-1 activity.