Variations in the APP gene promoter region and risk of Alzheimer disease

Therapeutic modulation of JAK-STAT, mTOR, and PPAR-γ signaling in neurological dysfunctions

The cytokine-activated Janus kinase (JAK)-signal transducer and activator of transcription (STAT) cascade is a pleiotropic pathway that involves receptor subunit multimerization. The mammalian target of rapamycin (mTOR) is a ubiquitously expressed serine-threonine kinase that perceives and integrates a variety of intracellular and environmental stimuli to regulate essential activities such as cell development and metabolism. Peroxisome proliferator-activated receptor-gamma (PPARγ) is a prototypical metabolic nuclear receptor involved in neural differentiation and axon polarity. The JAK-STAT, mTOR, and PPARγ signaling pathways serve as a highly conserved signaling hub that coordinates neuronal activity and brain development. Additionally, overactivation of JAK/STAT, mTOR, and inhibition of PPARγ signaling have been linked to various neurocomplications, including neuroinflammation, apoptosis, and oxidative stress. Emerging research suggests that even minor disruptions in these cellular and molecular processes can have significant consequences manifested as neurological and neuropsychiatric diseases. Of interest, target modulators have been proven to alleviate neuronal complications associated with acute and chronic neurological deficits. This research-based review explores the therapeutic role of JAK-STAT, mTOR, and PPARγ signaling modulators in preventing neuronal dysfunctions in preclinical and clinical investigations.

Transcriptional and Post-Transcriptional Regulations of Amyloid-β Precursor Protein (APP) mRNA

Alzheimer’s disease (AD) is an age-associated neurodegenerative disorder characterized by progressive impairment of memory, thinking, behavior, and dementia. Based on ample evidence showing neurotoxicity of amyloid-β (Aβ) aggregates in AD, proteolytically derived from amyloid precursor protein (APP), it has been assumed that misfolding of Aβ plays a crucial role in the AD pathogenesis. Additionally, extra copies of the APP gene caused by chromosomal duplication in patients with Down syndrome can promote AD pathogenesis, indicating the pathological involvement of the APP gene dose in AD. Furthermore, increased APP expression due to locus duplication and promoter mutation of APP has been found in familial AD. Given this background, we aimed to summarize the mechanism underlying the upregulation of APP expression levels from a cutting-edge perspective. We first reviewed the literature relevant to this issue, specifically focusing on the transcriptional regulation of APP by transcription factors that bind to the promoter/enhancer regions. APP expression is also regulated by growth factors, cytokines, and hormone, such as androgen. We further evaluated the possible involvement of post-transcriptional regulators of APP in AD pathogenesis, such as RNA splicing factors. Indeed, alternative splicing isoforms of APP are proposed to be involved in the increased production of Aβ. Moreover, non-coding RNAs, including microRNAs, post-transcriptionally regulate the APP expression. Collectively, elucidation of the novel mechanisms underlying the upregulation of APP would lead to the development of clinical diagnosis and treatment of AD.

Rethinking IRPs/IRE system in neurodegenerative disorders: Looking beyond iron metabolism

Iron regulatory proteins (IRPs) and iron regulatory element (IRE) systems are well known in the progression of neurodegenerative disorders by regulating iron related proteins. IRPs are also regulated by iron homeostasis. However, an increasing number of studies have suggested a close relationship between the IRPs/IRE system and non-iron-related neurodegenerative disorders. In this paper, we reviewed that the IRPs/IRE system is not only controlled by iron ions, but also regulated by such factors as post-translational modification, oxygen, nitric oxide (NO), heme, interleukin-1 (IL-1), and metal ions. In addition, by regulating the transcription of non-iron related proteins, the IRPs/IRE system functioned in oxidative metabolism, cell cycle regulation, abnormal proteins aggregation, and neuroinflammation. Finally, by emphasizing the multiple regulations of IRPs/IRE system and its potential relationship with non-iron metabolic neurodegenerative disorders, we provided new strategies for disease treatment targeting IRPs/IRE system.

Innate Immune System Activation and Neuroinflammation in Down Syndrome and Neurodegeneration: Therapeutic Targets or Partners?

Innate immune system activation and inflammation are associated with and may contribute to clinical outcomes in people with Down syndrome (DS), neurodegenerative diseases such as Alzheimer's disease (AD), and normal aging. In addition to serving as potential diagnostic biomarkers, innate immune system activation and inflammation may play a contributing or causal role in these conditions, leading to the hypothesis that effective therapies should seek to dampen their effects. However, recent intervention studies with the innate immune system activator granulocyte-macrophage colony-stimulating factor (GM-CSF) in animal models of DS, AD, and normal aging, and in an AD clinical trial suggest that activating the innate immune system and inflammation may instead be therapeutic. We consider evidence that DS, AD, and normal aging are accompanied by innate immune system activation and inflammation and discuss whether and when during the disease process it may be therapeutically beneficial to suppress or promote such activation.

Structural Analysis of the Simultaneous Activation and Inhibition of γ-Secretase Activity in the Development of Drugs for Alzheimer's Disease

Significance: The majority of the drugs which target membrane-embedded protease γ-secretase show an unusual biphasic activation–inhibition dose-response in cells, model animals, and humans. Semagacestat and avagacestat are two biphasic drugs that can facilitate cognitive decline in patients with Alzheimer’s disease. Initial mechanistic studies showed that the biphasic drugs, and pathogenic mutations, can produce the same type of changes in γ-secretase activity. Results: DAPT, semagacestat LY-411,575, and avagacestat are four drugs that show different binding constants, and a biphasic activation–inhibition dose-response for amyloid-β-40 products in SH-SY5 cells. Multiscale molecular dynamics studies have shown that all four drugs bind to the most mobile parts in the presenilin structure, at different ends of the 29 Å long active site tunnel. The biphasic dose-response assays are a result of the modulation of γ-secretase activity by the concurrent binding of multiple drug molecules at each end of the active site tunnel. The drugs activate γ-secretase by facilitating the opening of the active site tunnel, when the rate-limiting step is the tunnel opening, and the formation of the enzyme–substrate complex. The drugs inhibit γ-secretase as uncompetitive inhibitors by binding next to the substrate, to dynamic enzyme structures which regulate processive catalysis. The drugs can modulate the production of different amyloid-β catalytic intermediates by penetration into the active site tunnel, to different depths, with different flexibility and different binding affinity. Conclusions: Biphasic drugs and pathogenic mutations can affect the same dynamic protein structures that control processive catalysis. Successful drug-design strategies must incorporate transient changes in the γ-secretase structure in the development of specific modulators of its catalytic activity.

Could Alzheimer's Disease Originate in the Periphery and If So How So?

The classical amyloid cascade model for Alzheimer's disease (AD) has been challenged by several findings. Here, an alternative molecular neurobiological model is proposed. It is shown that the presence of the APOE ε4 allele, altered miRNA expression and epigenetic dysregulation in the promoter region and exon 1 of TREM2, as well as ANK1 hypermethylation and altered levels of histone post-translational methylation leading to increased transcription of TNFA, could variously explain increased levels of peripheral and central inflammation found in AD. In particular, as a result of increased activity of triggering receptor expressed on myeloid cells 2 (TREM-2), the presence of the apolipoprotein E4 (ApoE4) isoform, and changes in ANK1 expression, with subsequent changes in miR-486 leading to altered levels of protein kinase B (Akt), mechanistic (previously mammalian) target of rapamycin (mTOR) and signal transducer and activator of transcription 3 (STAT3), all of which play major roles in microglial activation, proliferation and survival, there is activation of microglia, leading to the subsequent (further) production of cytokines, chemokines, nitric oxide, prostaglandins, reactive oxygen species, inducible nitric oxide synthase and cyclooxygenase-2, and other mediators of inflammation and neurotoxicity. These changes are associated with the development of amyloid and tau pathology, mitochondrial dysfunction (including impaired activity of the electron transport chain, depleted basal mitochondrial potential and oxidative damage to key tricarboxylic acid enzymes), synaptic dysfunction, altered glycogen synthase kinase-3 (GSK-3) activity, mTOR activation, impairment of autophagy, compromised ubiquitin-proteasome system, iron dyshomeostasis, changes in APP translation, amyloid plaque formation, tau hyperphosphorylation and neurofibrillary tangle formation.

Excess Synaptojanin 1 Contributes to Place Cell Dysfunction and Memory Deficits in the Aging Hippocampus in Three Types of Alzheimer's Disease

The phosphoinositide phosphatase synaptojanin 1 (SYNJ1) is a key regulator of synaptic function. We first tested whether SYNJ1 contributes to phenotypic variations in familial Alzheimer's disease (FAD) and show that SYNJ1 polymorphisms are associated with age of onset in both early- and late-onset human FAD cohorts. We then interrogated whether SYNJ1 levels could directly affect memory. We show that increased SYNJ1 levels in autopsy brains from adults with Down syndrome (DS/AD) are inversely correlated with synaptophysin levels, a direct readout of synaptic integrity. We further report age-dependent cognitive decline in a mouse model overexpressing murine Synj1 to the levels observed in human sporadic AD, triggered through hippocampal hyperexcitability and defects in the spatial reproducibility of place fields. Taken together, our findings suggest that SYNJ1 contributes to memory deficits in the aging hippocampus in all forms of AD.

Iron regulatory protein (IRP)-iron responsive element (IRE) signaling pathway in human neurodegenerative diseases

The homeostasis of iron is vital to human health, and iron dyshomeostasis can lead to various disorders. Iron homeostasis is maintained by iron regulatory proteins (IRP1 and IRP2) and the iron-responsive element (IRE) signaling pathway. IRPs can bind to RNA stem-loops containing an IRE in the untranslated region (UTR) to manipulate translation of target mRNA. However, iron can bind to IRPs, leading to the dissociation of IRPs from the IRE and altered translation of target transcripts. Recently an IRE is found in the 5′-UTR of amyloid precursor protein (APP) and α-synuclein (α-Syn) transcripts. The levels of α-Syn, APP and amyloid β-peptide (Aβ) as well as protein aggregation can be down-regulated by IRPs but are up-regulated in the presence of iron accumulation. Therefore, inhibition of the IRE-modulated expression of APP and α-Syn or chelation of iron in patient’s brains has therapeutic significance to human neurodegenerative diseases. Currently, new pre-drug IRE inhibitors with therapeutic effects have been identified and are at different stages of clinical trials for human neurodegenerative diseases. Although some promising drug candidates of chemical IRE inhibitors and iron-chelating agents have been identified and are being validated in clinical trials for neurodegenerative diseases, future studies are expected to further establish the clinical efficacy and safety of IRE inhibitors and iron-chelating agents in patients with neurodegenerative diseases.

Candidate gene analysis for Alzheimer's disease in adults with Down syndrome

Individuals with Down syndrome (DS) overexpress many genes on chromosome 21 due to trisomy and have high risk of dementia due to the Alzheimer's disease (AD) neuropathology. However, there is a wide range of phenotypic differences (e.g., age at onset of AD, amyloid β levels) among adults with DS, suggesting the importance of factors that modify risk within this particularly vulnerable population, including genotypic variability. Previous genetic studies in the general population have identified multiple genes that are associated with AD. This study examined the contribution of polymorphisms in these genes to the risk of AD in adults with DS ranging from 30 to 78 years of age at study entry (N = 320). We used multiple logistic regressions to estimate the likelihood of AD using single-nucleotide polymorphisms (SNPs) in candidate genes, adjusting for age, sex, race/ethnicity, level of intellectual disability and APOE genotype. This study identified multiple SNPs in APP and CST3 that were associated with AD at a gene-wise level empirical p-value of 0.05, with odds ratios in the range of 1.5-2. SNPs in MARK4 were marginally associated with AD. CST3 and MARK4 may contribute to our understanding of potential mechanisms where CST3 may contribute to the amyloid pathway by inhibiting plaque formation, and MARK4 may contribute to the regulation of the transition between stable and dynamic microtubules.

Decrease in catalytic capacity of γ-secretase can facilitate pathogenesis in sporadic and Familial Alzheimer's disease

BACKGROUND

Alzheimer's disease can be a result of an age-induced disparity between increase in cellular metabolism of Aβ peptides and decrease in maximal activity of a membrane-embedded protease γ-secretase.

RESULTS

We compared activity of WT γ-secretase with the activity of 6 FAD mutants in its presenilin-1 component and 5 FAD mutants in Aβ-part of its APP substrate (Familial Alzheimer's disease). All 11 FAD mutations show linear correlation between the decrease in maximal activity and the clinically observed age-of-onset and age-of-death. Biphasic-inhibitors showed that a higher ratio between physiological Aβ-production and the maximal activity of γ-secretase can be observed in cells that can facilitate pathogenic changes in Aβ-products. For example, Aβ production in cells with WT γ-secretase is at 11% of its maximal activity, with delta-exon-9 mutant at 26%, while with M139V mutant is at 28% of the maximal activity. In the same conditions, G384A mutant is fully saturated and at its maximal activity. Similarly, Aβ production in cells with γ-secretase complex carrying Aph1AL component is 12% of its maximal activity, while in cells with Aph1B complex is 26% of its maximal activity. Similar to the cell-based studies, clinical studies of biphasic dose-response in plasma samples of 54 healthy individuals showed variable ratios between physiological Aβ production and the maximal activity of γ-secretase.

CONCLUSIONS

The increase in the ratio between physiological Aβ production and maximal activity of γ-secretase can be an early sign of pathogenic processes in enzyme-based, cell-based, and clinical studies of sporadic and Familiar Alzheimer's disease.

Mutation in the 3'untranslated region of APP as a genetic determinant of cerebral amyloid angiopathy

Aβ-related cerebral amyloid angiopathy (CAA) is a major cause of primary non-traumatic brain hemorrhage. In families with an early onset of the disease, CAA can be due to amyloid precursor protein (APP) pathogenic variants or duplications. APP duplications lead to a ~1.5-fold increased APP expression, resulting in Aβ overproduction and deposition in the walls of leptomeningeal vessels. We hypothesized that rare variants in the 3'untranslated region (UTR) of APP might lead to APP overexpression in patients with CAA and no APP pathogenic variant or duplication. We performed direct sequencing of the whole APP 3'UTR in 90 patients with CAA and explored the functional consequences of one previously unreported variant. We identified three sequence variants in four patients, of which a two-base pair deletion (c.*331_*332del) was previously unannotated and absent from 175 controls of same ethnicity. This latter variant was associated with increased APP expression in vivo and in vitro. Bioinformatics and functional assays showed that the APP c.*331_*332del variant affected APP messenger RNA (mRNA) structure and binding of two microRNAs (miR-582-3p and miR-892b), providing a mechanism for the observed effects on APP expression. These results identify APP 3'UTR sequence variants as genetic determinants of Aβ-CAA.

Cerebrospinal fluid Aβ42 levels and APP processing pathway genes in Parkinson's disease

BACKGROUND

Of recent interest is the finding that certain cerebrospinal fluid (CSF) biomarkers traditionally linked to Alzheimer's disease (AD), specifically amyloid beta protein (Aβ), are abnormal in PD CSF. The aim of this exploratory investigation was to determine whether genetic variation within the amyloid precursor protein (APP) processing pathway genes correlates with CSF Aβ42 levels in Parkinson's disease (PD).

METHODS

Parkinson's disease (n = 86) and control (n = 161) DNA were genotyped for 19 regulatory region tagging single-nucleotide polymorphisms (SNPs) within nine genes (APP, ADAM10, BACE1, BACE2, PSEN1, PSEN2, PEN2, NCSTN, and APH1B) involved in the cleavage of APP. The SNP genotypes were tested for their association with CSF biomarkers and PD risk while adjusting for age, sex, and APOE ɛ4 status.

RESULTS

Significant correlation with CSF Aβ42 levels in PD was observed for two SNPs, (APP rs466448 and APH1B rs2068143). Conversely, significant correlation with CSF Aβ42 levels in controls was observed for three SNPs (APP rs214484, rs2040273, and PSEN1 rs362344).

CONCLUSIONS

In addition, results of this exploratory investigation suggest that an APP SNP and an APH1B SNP are marginally associated with PD CSF Aβ42 levels in APOE ɛ4 noncarriers. Further hypotheses generated include that decreased CSF Aβ42 levels are in part driven by genetic variation in APP processing genes. Additional investigation into the relationship between these findings and clinical characteristics of PD, including cognitive impairment, compared with other neurodegenerative diseases, such as AD, are warranted. © 2015 International Parkinson and Movement Disorder Society.

Genetic variants associated with development of TMD and its intermediate phenotypes: the genetic architecture of TMD in the OPPERA prospective cohort study

Genetic risk factors are believed to combine with environmental exposures and contribute to the risk of developing temporomandibular disorder (TMD). In this prospective cohort study, 2,737 people without TMD were assessed for common genetic variation in 358 genes known to contribute to nociceptive pathways, inflammation, and affective distress. During a median follow-up period of 2.8 years, 260 people developed first-onset TMD. Hazard ratios were computed as measures of association between 2,924 single-nucleotide polymorphisms and TMD incidence. After correction for multiple testing, no single single-nucleotide polymorphism was significantly associated with risk of onset TMD. However, several single-nucleotide polymorphisms exceeded Bonferroni correction for multiple comparison or false discovery rate thresholds (.05, .1, or .2) for association with intermediate phenotypes shown to be predictive of TMD onset. Nonspecific orofacial symptoms were associated with voltage-gated sodium channel, type I, alpha subunit (SCN1A, rs6432860, P = 2.77 × 10(-5)) and angiotensin I-converting enzyme 2 (ACE2, rs1514280, P = 4.86 × 10(-5)); global psychological symptoms with prostaglandin-endoperoxide synthase 1 (PTGS1, rs3842803, P = 2.79 × 10(-6)); stress and negative affectivity with amyloid-β (A4) precursor protein (APP, rs466448, P = 4.29 × 10(-5)); and heat pain temporal summation with multiple PDZ domain protein (MPDZ, rs10809907, P = 3.05 × 10(-5)). The use of intermediate phenotypes for complex pain diseases revealed new genetic pathways influencing risk of TMD.

PERSPECTIVE

This article reports the findings of a large candidate gene association study of first-onset TMD and related intermediate phenotypes in the OPPERA Study. Although no genetic markers predicted TMD onset, several genetic risk factors for clinical, psychological, and sensory phenotypes associated with TMD onset were observed.

Alzheimer's disease therapeutics targeted to the control of amyloid precursor protein translation: maintenance of brain iron homeostasis

The neurotoxicity of amyloid beta (Aβ), a major cleavage product of the amyloid precursor protein (APP), is enhanced by iron, as found in the amyloid plaques of Alzheimer's disease (AD) patients. By contrast, the long-known neuroprotective activity of APP is evident after α-secretase cleavage of the precursor to release sAPPα, and depends on the iron export actions of APP itself. The latter underlie its neurotrophic and protective effects in facilitating the homeostatic actions of ferroportin mediated-iron export. Thus APP-dependent iron export may alleviate oxidative stress by minimizing labile iron thus protecting neurons from iron overload during stroke and hemorrhage. Consistent with this, altered phosphorylation of iron-regulatory protein-1 (IRP1) and its signaling processes play a critical role in modulating APP translation via the 5' untranslated region (5'UTR) of its transcript. The APP 5'UTR region encodes a functional iron-responsive element (IRE) RNA stem loop that represents a potential target for modulating APP production. Targeted regulation of APP gene expression via the modulation of 5'UTR sequence function represents a novel approach for the potential treatment of AD since altering APP translation can be used to improve both the protective brain iron balance and provide anti-amyloid efficacy. Approved drugs including paroxetine and desferrioxamine and several novel compounds have been identified that suppress abnormal metal-promoted Aβ accumulation with a subset of these acting via APP 5'UTR-dependent mechanisms to modulate APP translation and cleavage to generate the non-toxic sAPPα.

Treatment with D3 removes amyloid deposits, reduces inflammation, and improves cognition in aged AβPP/PS1 double transgenic mice

One of the characteristic pathological hallmarks of Alzheimer's disease (AD) is neuritic plaques. The sequence of events leading to deposition of amyloid-β (Aβ) peptides in plaques is not clear. Here we investigate the effects of D3, an Aβ oligomer directed D-enantiomeric peptide that was obtained from a mirror image phage display selection against monomeric or small oligomeric forms of Aβ42, on Aβ deposition in aged AβPP/PS1 double transgenic AD-model mice. Using Alzet minipumps, we infused the brains of these AD model mice for 8 weeks with FITC-labeled D3, and examined the subsequent changes in pathology and cognitive deficits. Initial cognitive deficits are similar comparing control and D3-FITC-treated mice, but the treated mice show a significant improvement on the last day of testing. Further, we show that there is a substantial reduction in the amount of amyloid deposits in the animals treated with D3-FITC, compared to the control mice. Finally, the amount of activated microglia and astrocytes surrounding Aβ deposits is dramatically reduced in the D3-FITC-treated mice. Our findings demonstrate that treatments with the high affinity Aβ42 oligomer binding D-enantiomeric peptide D3 significantly decrease Aβ deposits and the associated inflammatory response, and improve cognition even when applied only at late stages and high age. Together, this suggests that the treatment reduces the level of Aβ peptide in the brains of AβPP/PS1 mice, possibly by increasing Aβ outflow from the brain. In conclusion, treatments with this D-peptide have great potential to be successful in AD patients.

Genetic susceptibility for Alzheimer disease neuritic plaque pathology

IMPORTANCE

While numerous genetic susceptibility loci have been identified for clinical Alzheimer disease (AD), it is important to establish whether these variants are risk factors for the underlying disease pathology, including neuritic plaques.

OBJECTIVES

To investigate whether AD susceptibility loci from genome-wide association studies affect neuritic plaque pathology and to additionally identify novel risk loci for this trait.

DESIGN, SETTING, AND PARTICIPANTS

Candidate analysis of single-nucleotide polymorphisms and genome-wide association study in a joint clinicopathologic cohort, including 725 deceased subjects from the Religious Orders Study and the Rush Memory and Aging Project (2 prospective, community-based studies), followed by targeted validation in an independent neuroimaging cohort, including 114 subjects from multiple clinical and research centers.

MAIN OUTCOMES AND MEASURES

A quantitative measure of neuritic plaque pathologic burden, based on assessments of silver-stained tissue averaged from multiple brain regions. Validation based on β-amyloid load by immunocytochemistry, and replication with fibrillar β-amyloid positron emission tomographic imaging with Pittsburgh Compound B or florbetapir.

RESULTS

Besides the previously reported APOE and CR1 loci, we found that the ABCA7 (rs3764650; P = .02) and CD2AP (rs9349407; P = .03) AD susceptibility loci are associated with neuritic plaque burden. In addition, among the top results of our genome-wide association study, we discovered a novel variant near the amyloid precursor protein gene (APP, rs2829887) that is associated with neuritic plaques (P = 3.3 × 10-6). This polymorphism was associated with postmortem β-amyloid load as well as fibrillar β-amyloid in 2 independent cohorts of adults with normal cognition.

CONCLUSIONS AND RELEVANCE

These findings enhance understanding of AD risk factors by relating validated susceptibility alleles to increased neuritic plaque pathology and implicate common genetic variation at the APP locus in the earliest, presymptomatic stages of AD.

A genome-wide study shows a limited contribution of rare copy number variants to Alzheimer's disease risk

We assessed the role of rare copy number variants (CNVs) in Alzheimer's disease (AD) using intensity data from 3260 AD cases and 1290 age-matched controls from the genome-wide association study (GWAS) conducted by the Genetic and Environmental Risk for Alzheimer's disease Consortium (GERAD). We did not observe a significant excess of rare CNVs in cases, although we did identify duplications overlapping APP and CR1 which may be pathogenic. We looked for an excess of CNVs in loci which have been highlighted in previous AD CNV studies, but did not replicate previous findings. Through pathway analyses, we observed suggestive evidence for biological overlap between single nucleotide polymorphisms and CNVs in AD susceptibility. We also identified that our sample of elderly controls harbours significantly fewer deletions >1 Mb than younger control sets in previous CNV studies on schizophrenia and bipolar disorder (P = 8.9 × 10(-4) and 0.024, respectively), raising the possibility that healthy elderly individuals have a reduced rate of large deletions. Thus, in contrast to diseases such as schizophrenia, autism and attention deficit/hyperactivity disorder, CNVs do not appear to make a significant contribution to the development of AD.

PuF, an antimetastatic and developmental signaling protein, interacts with the Alzheimer's amyloid-β precursor protein via a tissue-specific proximal regulatory element (PRE)

BACKGROUND

Alzheimer's disease (AD) is intimately tied to amyloid-β (Aβ) peptide. Extraneuronal brain plaques consisting primarily of Aβ aggregates are a hallmark of AD. Intraneuronal Aβ subunits are strongly implicated in disease progression. Protein sequence mutations of the Aβ precursor protein (APP) account for a small proportion of AD cases, suggesting that regulation of the associated gene (APP) may play a more important role in AD etiology. The APP promoter possesses a novel 30 nucleotide sequence, or "proximal regulatory element" (PRE), at -76/-47, from the +1 transcription start site that confers cell type specificity. This PRE contains sequences that make it vulnerable to epigenetic modification and may present a viable target for drug studies. We examined PRE-nuclear protein interaction by gel electrophoretic mobility shift assay (EMSA) and PRE mutant EMSA. This was followed by functional studies of PRE mutant/reporter gene fusion clones.

RESULTS

EMSA probed with the PRE showed DNA-protein interaction in multiple nuclear extracts and in human brain tissue nuclear extract in a tissue-type specific manner. We identified transcription factors that are likely to bind the PRE, using competition gel shift and gel supershift: Activator protein 2 (AP2), nm23 nucleoside diphosphate kinase/metastatic inhibitory protein (PuF), and specificity protein 1 (SP1). These sites crossed a known single nucleotide polymorphism (SNP). EMSA with PRE mutants and promoter/reporter clone transfection analysis further implicated PuF in cells and extracts. Functional assays of mutant/reporter clone transfections were evaluated by ELISA of reporter protein levels. EMSA and ELISA results correlated by meta-analysis.

CONCLUSIONS

We propose that PuF may regulate the APP gene promoter and that AD risk may be increased by interference with PuF regulation at the PRE. PuF is targeted by calcium/calmodulin-dependent protein kinase II inhibitor 1, which also interacts with the integrins. These proteins are connected to vital cellular and neurological functions. In addition, the transcription factor PuF is a known inhibitor of metastasis and regulates cell growth during development. Given that APP is a known cell adhesion protein and ferroxidase, this suggests biochemical links among cell signaling, the cell cycle, iron metabolism in cancer, and AD in the context of overall aging.

Modulators of γ-secretase activity can facilitate the toxic side-effects and pathogenesis of Alzheimer's disease

Background

Selective modulation of different Aβ products of an intramembrane protease γ-secretase, could be the most promising strategy for development of effective therapies for Alzheimer's disease. We describe how different drug-candidates can modulate γ-secretase activity in cells, by studying how DAPT affects changes in γ-secretase activity caused by gradual increase in Aβ metabolism.

Results

Aβ 1–40 secretion in the presence of DAPT shows biphasic activation-inhibition dose-response curves. The biphasic mechanism is a result of modulation of γ-secretase activity by multiple substrate and inhibitor molecules that can bind to the enzyme simultaneously. The activation is due to an increase in γ-secretase's kinetic affinity for its substrate, which can make the enzyme increasingly more saturated with otherwise sub-saturating substrate. The noncompetitive inhibition that prevails at the saturating substrate can decrease the maximal activity. The synergistic activation-inhibition effects can drastically reduce γ-secretase's capacity to process its physiological substrates. This reduction makes the biphasic inhibitors exceptionally prone to the toxic side-effects and potentially pathogenic. Without the modulation, γ-secretase activity on it physiological substrate in cells is only 14% of its maximal activity, and far below the saturation.

Significance

Presented mechanism can explain why moderate inhibition of γ-secretase cannot lead to effective therapies, the pharmacodynamics of Aβ-rebound phenomenon, and recent failures of the major drug-candidates such as semagacestat. Novel improved drug-candidates can be prepared from competitive inhibitors that can bind to different sites on γ-secretase simultaneously. Our quantitative analysis of the catalytic capacity can facilitate the future studies of the therapeutic potential of γ-secretase and the pathogenic changes in Aβ metabolism.

The calcium-sensing receptor: a novel Alzheimer's disease crucial target?

Alzheimer's disease (AD) is the most common human neurodegenerative ailment, the most prevalent (>95%) late-onset type of which has a still uncertain etiology. The progressive decline of cognitive functions, dementia, and physical disabilities of AD is caused by synaptic losses that progressively disconnect key neuronal networks in crucial brain areas, like the hippocampus and temporoparietal cortex, and critically impair language, sensory processing, memory, and conscious thought. AD's two main hallmarks are fibrillar amyloid-β (fAβ) plaques in extracellular spaces and intracellular accumulation of fAβ peptides and neurofibrillary tangles (NFTs). It is still undecided whether either or both these AD hallmarks cause or result from the disease. Recently, the dysregulation of calcium homeostasis has been advanced as a novel cause of AD. In this case, a suitable candidate of AD driver would be the Aβ peptides-binding/activated calcium-sensing receptor (CaSR), whose intracellular signalling is triggered by Aβ peptides. In this review, we briefly discuss CaSR's roles in normal adult human astrocytes (NAHAs) and their possible impacts on AD.

The role of variation at AβPP, PSEN1, PSEN2, and MAPT in late onset Alzheimer's disease

Rare mutations in AβPP, PSEN1, and PSEN2 cause uncommon early onset forms of Alzheimer's disease (AD), and common variants in MAPT are associated with risk of other neurodegenerative disorders. We sought to establish whether common genetic variation in these genes confer risk to the common form of AD which occurs later in life (>65 years). We therefore tested single-nucleotide polymorphisms at these loci for association with late-onset AD (LOAD) in a large case-control sample consisting of 3,940 cases and 13,373 controls. Single-marker analysis did not identify any variants that reached genome-wide significance, a result which is supported by other recent genome-wide association studies. However, we did observe a significant association at the MAPT locus using a gene-wide approach (p = 0.009). We also observed suggestive association between AD and the marker rs9468, which defines the H1 haplotype, an extended haplotype that spans the MAPT gene and has previously been implicated in other neurodegenerative disorders including Parkinson's disease, progressive supranuclear palsy, and corticobasal degeneration. In summary common variants at AβPP, PSEN1, and PSEN2 and MAPT are unlikely to make strong contributions to susceptibility for LOAD. However, the gene-wide effect observed at MAPT indicates a possible contribution to disease risk which requires further study.

Role of common and rare APP DNA sequence variants in Alzheimer disease

OBJECTIVES

More than 30 different rare mutations, including copy number variants (CNVs), in the amyloid precursor protein gene (APP) cause early-onset familial Alzheimer disease (EOFAD), whereas the contribution of common APP variants to disease risk remains controversial. In this study we systematically assessed the role of both rare and common APP DNA variants in Alzheimer disease (AD) families.

METHODS

Families with EOFAD genetically linked to the APP region were screened for missense mutations and locus duplications of APP. Further, using genome-wide DNA microarray data, we examined the APP locus for CNVs in a total of 797 additional early- and late-onset AD pedigrees. Finally, 423 single nucleotide polymorphisms (SNPs) in the APP locus, including 2 promoter polymorphisms previously associated with AD risk, were tested in up to 4,200 individuals from multiplex AD families.

RESULTS

Analyses of 8 21q21-linked families revealed one family carrying a nonsynonymous mutation in exon 17 (Val717Leu) and another family with a partially penetrant 3.5-Mb locus duplication encompassing APP. CNV analysis in the APP locus revealed an additional family carrying a fully penetrant 380-kb duplication, merely spanning APP. Last, contrary to previous reports, association analyses of more than 400 different SNPs in or near APP failed to show significant effects on AD risk.

CONCLUSION

Our study shows that APP mutations and locus duplications are a very rare cause of EOFAD and that the contribution of common APP variants to AD susceptibility is insignificant. Furthermore, duplications of APP may not be fully penetrant, possibly indicating the existence of hitherto unknown protective genetic factors.

Modulation of γ-secretase activity by multiple enzyme-substrate interactions: implications in pathogenesis of Alzheimer's disease

Background

We describe molecular processes that can facilitate pathogenesis of Alzheimer's disease (AD) by analyzing the catalytic cycle of a membrane-imbedded protease γ-secretase, from the initial interaction with its C99 substrate to the final release of toxic Aβ peptides.

Results

The C-terminal AICD fragment is cleaved first in a pre-steady-state burst. The lowest Aβ42/Aβ40 ratio is observed in pre-steady-state when Aβ40 is the dominant product. Aβ42 is produced after Aβ40, and therefore Aβ42 is not a precursor for Aβ40. The longer more hydrophobic Aβ products gradually accumulate with multiple catalytic turnovers as a result of interrupted catalytic cycles. Saturation of γ-secretase with its C99 substrate leads to 30% decrease in Aβ40 with concomitant increase in the longer Aβ products and Aβ42/Aβ40 ratio. To different degree the same changes in Aβ products can be observed with two mutations that lead to an early onset of AD, ΔE9 and G384A. Four different lines of evidence show that γ-secretase can bind and cleave multiple substrate molecules in one catalytic turnover. Consequently depending on its concentration, NotchΔE substrate can activate or inhibit γ-secretase activity on C99 substrate. Multiple C99 molecules bound to γ-secretase can affect processive cleavages of the nascent Aβ catalytic intermediates and facilitate their premature release as the toxic membrane-imbedded Aβ-bundles.

Conclusions

Gradual saturation of γ-secretase with its substrate can be the pathogenic process in different alleged causes of AD. Thus, competitive inhibitors of γ-secretase offer the best chance for a successful therapy, while the noncompetitive inhibitors could even facilitate development of the disease by inducing enzyme saturation at otherwise sub-saturating substrate. Membrane-imbedded Aβ-bundles generated by γ-secretase could be neurotoxic and thus crucial for our understanding of the amyloid hypothesis and AD pathogenesis.

APOE and AβPP gene variation in cortical and cerebrovascular amyloid-β pathology and Alzheimer's disease: a population-based analysis

Cortical and cerebrovascular amyloid-β (Aβ) deposition is a hallmark of Alzheimer's disease (AD), but also occurs in elderly people not affected by dementia. The apolipoprotein E (APOE) ε4 is a major genetic modulator of Aβ deposition and AD risk. Variants of the amyloid-β protein precursor (AβPP) gene have been reported to contribute to AD and cerebral amyloid angiopathy (CAA). We analyzed the role of APOE and AβPP variants in cortical and cerebrovascular Aβ deposition, and neuropathologically verified AD (based on modified NIA-RI criteria) in a population-based autopsy sample of Finns aged ≥ 85 years (Vantaa85 + Study; n = 282). Our updated analysis of APOE showed strong associations of the ε4 allele with cortical (p = 4.91 × 10-17) and cerebrovascular (p = 9.87 × 10-11) Aβ deposition as well as with NIA-RI AD (p = 1.62 × 10-8). We also analyzed 60 single nucleotide polymorphisms (SNPs) at the AβPP locus. In single SNP or haplotype analyses there were no statistically significant AβPP locus associations with cortical or cerebrovascular Aβ deposition or with NIA-RI AD. We sequenced the promoter of the AβPP gene in 40 subjects with very high Aβ deposition, but none of these subjects had any of the previously reported or novel AD-associated mutations. These results suggest that cortical and cerebrovascular Aβ depositions are useful quantitative traits for genetic studies, as highlighted by the strong associations with the APOE ε4 variant. Promoter mutations or common allelic variation in the AβPP gene do not have a major contribution to cortical or cerebrovascular Aβ deposition, or very late-onset AD in this Finnish population based study.

Role of mitochondrial homeostasis and dynamics in Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disease that affects a staggering percentage of the aging population and causes memory loss and cognitive decline. Mitochondrial abnormalities can be observed systemically and in brains of patients suffering from AD, and may account for part of the disease phenotype. In this review, we summarize some of the key findings that indicate mitochondrial dysfunction is present in AD-affected subjects, including cytochrome oxidase deficiency, endophenotype data, and altered mitochondrial morphology. Special attention is given to recently described perturbations in mitochondrial autophagy, fission-fusion dynamics, and biogenesis. We also briefly discuss how mitochondrial dysfunction may influence amyloidosis in Alzheimer's disease, why mitochondria are a valid therapeutic target, and strategies for addressing AD-specific mitochondrial dysfunction.

Common polymorphisms in dystonia-linked genes and susceptibility to the sporadic primary dystonias

Genes involved in familial dystonia syndromes (DYT genes) are ideal candidates for investigating whether common genetic variants influence the susceptibility to sporadic primary dystonia. To date, there have been few candidate gene studies for primary dystonia and only two DYT genes, TOR1A and THAP1, have been assessed. We therefore employed a haplotype-tagging strategy to comprehensively assess if common polymorphisms in eight DYT genes (TOR1A, TAF1, GCH1, THAP1, MR-1 (PNKD), SGCE, ATP1A3 and PRKRA) confer risk for sporadic primary dystonia. The 230 primary dystonia cases were matched for age and gender to 228 controls, recruited from movement disorder clinics in Brisbane, Australia and the Australian electoral roll. All subjects were genotyped for 56 tagging SNPs and genotype associations were investigated. Modest genotypic associations (P<0.05) were observed for three GCH1 SNPs (rs12147422, rs3759664 and rs10483639) when comparing all cases against controls. Associations were also seen when the cases were stratified based on presentation. Overall, our findings do not support the hypothesis that common TOR1A variants affect susceptibility for sporadic primary dystonia, and that it is unlikely that common variants around the DYT genes confer substantial risk for sporadic primary dystonia. Further work is warranted to follow up the GCH1 SNPs and the subgroup analyses.

Alzheimer's disease pathologic cascades: who comes first, what drives what

This review discusses known and speculated relationships between Alzheimer's disease (AD) biochemical, molecular, and histologic phenomena. In the AD brain, various pathologies including neuritic plaques, neurofibrillary tangles, synaptic loss, oxidative stress, cell cycle re-entry, and mitochondrial changes have all been described. In an attempt to explain what exactly goes wrong in the AD brain various investigators have proposed different heuristic and hierarchical schemes. It is important to accurately define the AD pathology hierarchy because treatments targeting the true apex of its pathologic cascade arguably have the best chance of preventing, mitigating, or even curing this disease.

Functional activity of the novel Alzheimer's amyloid β-peptide interacting domain (AβID) in the APP and BACE1 promoter sequences and implications in activating apoptotic genes and in amyloidogenesis

Amyloid-β peptide (Aβ) plaque in the brain is the primary (post mortem) diagnostic criterion of Alzheimer's disease (AD). The physiological role(s) of Aβ are poorly understood. We have previously determined an Aβ interacting domain (AβID) in the promoters of AD-associated genes (Maloney and Lahiri, 2011. Gene. 15,doi:10.1016/j.gene.2011.06.004. epub ahead of print.). This AβID interacts in a DNA sequence-specific manner with Aβ. We now demonstrate novel Aβ activity as a possible transcription factor. Herein, we detected Aβ-chromatin interaction in cell culture by ChIP assay. We observed that human neuroblastoma (SK-N-SH) cells treated with FITC conjugated Aβ1-40 localized Aβ to the nucleus in the presence of H2O2-mediated oxidative stress. Furthermore, primary rat fetal cerebrocortical cultures were transfected with APP and BACE1 promoter-luciferase fusions, and rat PC12 cultures were transfected with polymorphic APP promoter-CAT fusion clones. Transfected cells were treated with different Aβ peptides and/or H2O2. Aβ treatment of cell cultures produced a DNA sequence-specific response in cells transfected with polymorphic APP clones. Our results suggest the Aβ peptide may regulate its own production through feedback on its precursor protein and BACE1, leading to amyloidogenesis in AD.

The Alzheimer's amyloid β-peptide (Aβ) binds a specific DNA Aβ-interacting domain (AβID) in the APP, BACE1, and APOE promoters in a sequence-specific manner: characterizing a new regulatory motif

Deposition of extracellular plaques, primarily consisting of amyloid β peptide (Aβ), in the brain is the confirmatory diagnostic of Alzheimer's disease (AD); however, the physiological and pathological role of Aβ is not fully understood. Herein, we demonstrate novel Aβ activity as a putative transcription factor upon AD-associated genes. We used oligomers from 5'-flanking regions of the apolipoprotein E (APOE), Aβ-precursor protein (APP) and β-amyloid site cleaving enzyme-1 (BACE1) genes for electrophoretic mobility shift assay (EMSA) with different fragments of the Aβ peptide. Our results suggest that Aβ bound to an Aβ-interacting domain (AβID) with a consensus of "KGGRKTGGGG". This peptide-DNA interaction was sequence specific, and mutation of the first "G" of the decamer's terminal "GGGG" eliminated peptide-DNA interaction. Furthermore, the cytotoxic Aβ25-35 fragment had greatest DNA affinity. Such specificity of binding suggests that the AβID is worth of further investigation as a site wherein the Aβ peptide may act as a transcription factor.

Amyloid precursor protein (APP) processing genes and cerebrospinal fluid APP cleavage product levels in Alzheimer's disease

The aim of this exploratory investigation was to determine if genetic variation within amyloid precursor protein (APP) or its processing enzymes correlates with APP cleavage product levels: APPα, APPβ or Aβ42, in cerebrospinal fluid (CSF) of cognitively normal subjects or Alzheimer's disease (AD) patients. Cognitively normal control subjects (n = 170) and AD patients (n = 92) were genotyped for 19 putative regulatory tagging SNPs within 9 genes (APP, ADAM10, BACE1, BACE2, PSEN1, PSEN2, PEN2, NCSTN and APH1B) involved in the APP processing pathway. SNP genotypes were tested for their association with CSF APPα, APPβ, and Aβ42, AD risk and age-at-onset while taking into account age, gender, race and APOE ε4. After adjusting for multiple comparisons, a significant association was found between ADAM10 SNP rs514049 and APPα levels. In controls, the rs514049 CC genotype had higher APPα levels than the CA, AA collapsed genotype, whereas the opposite effect was seen in AD patients. These results suggest that genetic variation within ADAM10, an APP processing gene, influences CSF APPα levels in an AD specific manner.

Regulation of amyloid precursor protein processing by the Beclin 1 complex

Autophagy is an intracellular degradation pathway that functions in protein and organelle turnover in response to starvation and cellular stress. Autophagy is initiated by the formation of a complex containing Beclin 1 (BECN1) and its binding partner Phosphoinositide-3-kinase, class 3 (PIK3C3). Recently, BECN1 deficiency was shown to enhance the pathology of a mouse model of Alzheimer Disease (AD). However, the mechanism by which BECN1 or autophagy mediate these effects are unknown. Here, we report that the levels of Amyloid precursor protein (APP) and its metabolites can be reduced through autophagy activation, indicating that they are a substrate for autophagy. Furthermore, we find that knockdown of Becn1 in cell culture increases the levels of APP and its metabolites. Accumulation of APP and APP C-terminal fragments (APP-CTF) are accompanied by impaired autophagosomal clearance. Pharmacological inhibition of autophagosomal-lysosomal degradation causes a comparable accumulation of APP and APP-metabolites in autophagosomes. Becn1 reduction in cell culture leads to lower levels of its binding partner Pik3c3 and increased presence of Microtubule-associated protein 1, light chain 3 (LC3). Overexpression of Becn1, on the other hand, reduces cellular APP levels. In line with these observations, we detected less BECN1 and PIK3C3 but more LC3 protein in brains of AD patients. We conclude that BECN1 regulates APP processing and turnover. BECN1 is involved in autophagy initiation and autophagosome clearance. Accordingly, BECN1 deficiency disrupts cellular autophagy and autophagosomal-lysosomal degradation and alters APP metabolism. Together, our findings suggest that autophagy and the BECN1-PIK3C3 complex regulate APP processing and play an important role in AD pathology.

Regulation of amyloid precursor protein processing by the Beclin 1 complex

Autophagy is an intracellular degradation pathway that functions in protein and organelle turnover in response to starvation and cellular stress. Autophagy is initiated by the formation of a complex containing Beclin 1 (BECN1) and its binding partner Phosphoinositide-3-kinase, class 3 (PIK3C3). Recently, BECN1 deficiency was shown to enhance the pathology of a mouse model of Alzheimer Disease (AD). However, the mechanism by which BECN1 or autophagy mediate these effects are unknown. Here, we report that the levels of Amyloid precursor protein (APP) and its metabolites can be reduced through autophagy activation, indicating that they are a substrate for autophagy. Furthermore, we find that knockdown of Becn1 in cell culture increases the levels of APP and its metabolites. Accumulation of APP and APP C-terminal fragments (APP-CTF) are accompanied by impaired autophagosomal clearance. Pharmacological inhibition of autophagosomal-lysosomal degradation causes a comparable accumulation of APP and APP-metabolites in autophagosomes. Becn1 reduction in cell culture leads to lower levels of its binding partner Pik3c3 and increased presence of Microtubule-associated protein 1, light chain 3 (LC3). Overexpression of Becn1, on the other hand, reduces cellular APP levels. In line with these observations, we detected less BECN1 and PIK3C3 but more LC3 protein in brains of AD patients. We conclude that BECN1 regulates APP processing and turnover. BECN1 is involved in autophagy initiation and autophagosome clearance. Accordingly, BECN1 deficiency disrupts cellular autophagy and autophagosomal-lysosomal degradation and alters APP metabolism. Together, our findings suggest that autophagy and the BECN1-PIK3C3 complex regulate APP processing and play an important role in AD pathology.

Current status on Alzheimer disease molecular genetics: from past, to present, to future

Linkage studies, candidate gene and whole-genome association studies have resulted in a tremendous amount of putative risk genes for Alzheimer's disease (AD). Yet, besides the three causal genes-amyloid precursor protein and presenilin 1 and 2 genes-and one risk gene apolipoprotein E (APOE), no single functional risk variant was identified. Discussing the possible involvement of rare alleles and other types of genetic variants, this review summarizes the current knowledge on the genetic spectrum of AD and integrates different approaches and recent discoveries by genome-wide association studies.

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

Beta-site APP-cleaving enzyme 1 (BACE1) gene has been suggested as a candidate gene for Alzheimer's disease (AD). However, little is known regarding the effects of polymorphisms in regulatory sequences of BACE1 on AD susceptibility. To evaluate the relationship between polymorphisms in the BACE1 promoter and sporadic AD (SAD) genetically and functionally, we performed a case-control study (429 cases and 346 controls of Han Chinese descent) and functional characterization of the polymorphisms in vitro using luciferase assay and electrophoretic mobility shift assay (EMSA). Two polymorphisms (-918G/A, rs4938369; -2014T/C, rs3017608) were identified in the BACE1 promoter. The results showed that the -918G/A polymorphism was associated with SAD and the -918GG carriers had a 1.67-fold higher risk for SAD than the carriers with -918AA and GA genotypes (OR = 1.667, 95% CI = 1.087-2.556, P = 0.019). The haplotype -918G/-2014T may be a possible risk factor for SAD (P = 0.016). Luciferase reporter assays showed the -918G allele and its resultant haplotype -918G/-2014T induced an increase of transcriptional activity. A more marked increase in -918G/-2014T transcriptional activity was seen when under hypoxia treatment. EMSA indicated that the -918G allele bound nuclear factors more strongly than -918A allele did. Our findings suggest that the BACE1 promoter polymorphisms which regulate BACE1 expression may contribute to SAD susceptibility. Further independent studies are required to verify our findings.

Recent insights into the molecular genetics of dementia

Our understanding of the molecular genetic basis of two common neurodegenerative dementias, Alzheimer's disease (AD) and frontotemporal lobar degeneration (FTLD), has greatly advanced in recent years. Progranulin mutations were identified as a major cause of FTLD and a potential susceptibility factor for other forms of dementia. In addition, through copy-number analyses of previously identified disease genes and the study of microRNA regulation in dementia, new evidence emerged to support the view that subtle variability in the expression of known disease proteins could increase the risk for sporadic forms of dementia. Finally, in late-onset AD populations, the first genome-wide association studies were performed and novel potential AD susceptibility genes reported. These exciting findings provide novel insights into the disease mechanisms underlying dementia and hold promise for the development of potential treatments.

Identification of the promoter region and the 5'-untranslated exons of the human voltage-gated sodium channel Nav1.1 gene (SCN1A) and enhancement of gene expression by the 5'-untranslated exons

Voltage-gated sodium channels play critical roles in the excitability of the brain. A decreased level of Na(v)1.1 has been identified as the cause of severe myoclonic epilepsy in infancy. In the present study, we identified the transcription start site and three 5'-untranslated exons of SCN1A by using 5'-full RACE. The 2.5-kb region upstream of the transcription start site was targeted as a potential location of the promoter. The 2.5-kb genomic fragment (P(2.5), from +26 to -2,500) and the 2.7-kb fragment (P(2.7), P(2.5) combined with the 227-bp 5'-untranslated exons) were cloned to produce luciferase constructs. The P(2.5) and the P(2.7) drove luciferase gene expression in the human neuroblastoma cell line SH-SY5Y but not in the human embryonic kidney cell line HEK-293. The 5'-untranslated exons could greatly enhance gene expression in SH-SY5Y cells. The P(2.7) could be used as a functional unit to study the role of SCN1A noncoding sequences in gene expression. These findings will also help in exploring the possibility of promoter mutant-induced diseases and revealing the mechanism underlying the regulation of SCN1A expression in the normal brain.

Overexpression of wild-type human APP in mice causes cognitive deficits and pathological features unrelated to Abeta levels

Transgenic mice expressing mutant human amyloid precursor protein (APP) develop an age-dependent amyloid pathology and memory deficits, but no overt neuronal loss. Here, in mice overexpressing wild-type human APP (hAPP(wt)) we found an early memory impairment, particularly in the water maze and to a lesser extent in the object recognition task, but beta-amyloid peptide (Abeta(42)) was barely detectable in the hippocampus. In these mice, hAPP processing was basically non-amyloidogenic, with high levels of APP carboxy-terminal fragments, C83 and APP intracellular domain. A tau pathology with an early increase in the levels of phosphorylated tau in the hippocampus, a likely consequence of enhanced ERK1/2 activation, was also observed. Furthermore, these mice presented a loss of synapse-associated proteins: PSD95, AMPA and NMDA receptor subunits and phosphorylated CaMKII. Importantly, signs of neurodegeneration were found in the hippocampal CA1 subfield and in the entorhinal cortex that were associated to a marked loss of MAP2 immunoreactivity. Conversely, in mice expressing mutant hAPP, high levels of Abeta(42) were found in the hippocampus, but no signs of neurodegeneration were apparent. The results support the notion of Abeta-independent pathogenic pathways in Alzheimer's disease.

Nuclear bodies in neurodegenerative disease

Neurodegenerative diseases are characterized by a relentlessly progressive loss of the functional and structural integrity of the central nervous system. In many cases, these diseases arise sporadically and the causes are unknown. The abnormal aggregation of protein within the cytoplasm or the nucleus of brain cells represents a unifying pathological feature of these diseases. There is increasing evidence for nuclear dysfunction in neurodegenerative diseases. How this relates to protein aggregation in the context of "cause and effect" remains to be determined in most cases. Co-ordinated nuclear function is predicated on the activity of distinct nuclear subdomains, or nuclear bodies, each responsible for a specific function. If nuclear dysfunction represents an important etiopathological feature in neurodegenerative disease, then this should be reflected by functional and/or morphological alterations in this nuclear compartmentalization. For most neurodegenerative diseases, evidence for nuclear dysfunction, with attendant consequences for nuclear architecture, is only beginning to emerge. In this review, I will discuss neurodegenerative diseases in the context of nuclear dysfunction and, more specifically, alterations in nuclear bodies. Although research in this field is in its infancy, identifying alterations in the nucleus in neurodegenerative disease has potentially profound implications for elucidating the pathogenesis of these disorders.

Molecular genetics of Alzheimer's disease: an update

Alzheimer's disease (AD) is a complex disorder of the central nervous system (CNS). Molecular genetic research has provided a wealth of information regarding the genetic etiology of this devastating disease. Identification and functional characterization of autosomal dominant mutations in the amyloid precursor protein gene (APP) and the presenilin genes 1 and 2 (PSEN1 and PSEN2) have contributed substantially to our understanding of the biological mechanisms leading towards CNS neurodegeneration in AD. Nonetheless, a large part of the genetic etiology remains unresolved, especially that of more common, sporadic forms of AD. While substantial efforts were invested in the identification of genetic risk factors underlying sporadic AD, using carefully designed genetic association studies in large patient-control groups, the only firmly established risk factor remains the epsilon4 allele of the apolipoprotein E gene (APOE). Nevertheless, one can expect that with the current availability of high-throughput genotyping platforms and dense maps of single-nucleotide polymorphisms (SNPs), large-scale genetic studies will eventually generate additional knowledge about the genetic risk profile for AD. This review provides an overview of the current understanding in the field of AD genetics, covering both the rare monogenic forms as well as recent developments in the search for novel AD susceptibility genes.