Is M129V of PRNP gene associated with Alzheimer's disease? A case-control study and a meta-analysis

Genetic and pathological features encipher the phenotypic heterogeneity of Gerstmann-Sträussler-Scheinker disease

OBJECTIVES

To elucidate and compare the genetic, clinical, ancillary diagnostic, and pathological characteristics across different Gerstmann-Sträussler-Scheinker disease (GSS) phenotypes and explore the underlying causes of the phenotypic heterogeneities.

METHODS

The genetic, clinical, ancillary diagnostic, and pathological profiles of GSS patients reported in the literature were obtained and analyzed. Additionally, 3 patients with genetically confirmed GSS from our unit were included. Based on clinical presentation, patients were classified into typical GSS, Creutzfeldt-Jakob disease (CJD)-like GSS, GSS with dementia, and other categories.

RESULTS

A total of 329 GSS cases were included with a 1.13:1 female-to-male ratio, median onset age 44, and median duration 4 years. Of the 294 categorized patients, 50.7% had typical GSS, 24.8% showed CJD-like GSS, and 16.3% presented with GSS with dementia. Clinical classification varied significantly based on genotype, with P102L more common in typical GSS and A117V prevalent in CJD-like GSS. Polymorphism at codon 129 has no effect on GSS phenotype, but the 129 M allele acts as a protective factor in GSS patients in Asia and North America. Moderate to severe spongiform degeneration and the presence of PK-resistant small fragments migrating at <11 kDa on electrophoretic gels along with PrP27-30 fragments were more prevalent in CJD-like GSS phenotype, while hyperphosphorylated tau protein co-deposition tends to be characteristic of typical GSS and GSS with dementia.

CONCLUSION

This study reveals GSS's intricate nature, showing significant variations in clinical presentations, diagnostic findings, and pathological features. Mutation sites and pathological changes play crucial roles in determining the GSS clinical heterogeneity.

Roles of astrocytes and prions in Alzheimer's disease: insights from mathematical modeling

We present a mathematical model that explores the progression of Alzheimer's disease, with a particular focus on the involvement of disease-related proteins and astrocytes. Our model consists of a coupled system of differential equations that delineates the dynamics of amyloid beta plaques, amyloid beta protein, tau protein, and astrocytes. Amyloid beta plaques can be considered fibrils that depend on both the plaque size and time. We change our mathematical model to a temporal system by applying an integration operation with respect to the plaque size. Theoretical analysis including existence, uniqueness, positivity, and boundedness is performed in our model. We extend our mathematical model by adding two populations, namely prion protein and amyloid beta-prion complex. We characterize the system dynamics by locating biologically feasible steady states and their local stability analysis for both models. The characterization of the proposed model can help inform in advancing our understanding of the development of Alzheimer's disease as well as its complicated dynamics. We investigate the global stability analysis around the interior equilibrium point by constructing a suitable Lyapunov function. We validate our theoretical analysis with the aid of extensive numerical illustrations.

Predicting disease-gene associations through self-supervised mutual infomax graph convolution network

Illuminating associations between diseases and genes can help reveal the pathogenesis of syndromes and contribute to treatments, but a large number of associations remained unexplored. To identify novel disease-gene associations, many computational methods have been developed using disease and gene-related prior knowledge. However, these methods remain of relatively inferior performance due to the limited external data sources and the inevitable noise among the prior knowledge. In this study, we have developed a new method, Self-Supervised Mutual Infomax Graph Convolution Network (MiGCN), to predict disease-gene associations under the guidance of external disease-disease and gene-gene collaborative graphs. The noises within the collaborative graphs were eliminated by maximizing the mutual information between nodes and neighbors through a graphical mutual infomax layer. In parallel, the node interactions were strengthened by a novel informative message passing layer to improve the learning ability of graph neural network. The extensive experiments showed that our model achieved performance improvement over the state-of-art method by more than 8 % on AUC. The datasets, source codes and trained models of MiGCN are available at https://github.com/biomed-AI/MiGCN.

Genetic prion diseases presenting as frontotemporal dementia: clinical features and diagnostic challenge

Background

To elucidate the clinical and ancillary features of genetic prion diseases (gPrDs) presenting with frontotemporal dementia (FTD) to aid early identification.

Methods

Global data of gPrDs presenting with FTD caused by prion protein gene mutations were collected from literature review and our records. Fifty-one cases of typical FTD and 136 cases of prion diseases admitted to our institution were included as controls. Clinical and ancillary data of the different groups were compared.

Results

Forty-nine cases of gPrDs presenting with FTD were identified. Compared to FTD or prion diseases, gPrDs presenting with FTD were characterized by earlier onset age (median 45 vs. 61/60 years, P < 0.001, P < 0.001) and higher incidence of positive family history (81.6% vs. 27.5/13.2%, P < 0.001, P < 0.001). Furthermore, GPrDs presenting with FTD exhibited shorter duration (median 5 vs. 8 years) and a higher rate of parkinsonism (63.7% vs. 9.8%, P < 0.001), pyramidal signs (39.1% vs. 7.8%, P = 0.001), mutism (35.9% vs. 0%, P < 0.001), seizures (25.8% vs. 0%, P < 0.001), myoclonus (22.5% vs. 0%, P < 0.001), and hyperintensity on MRI (25.0% vs. 0, P < 0.001) compared to FTD. Compared to prion diseases, gPrDs presenting with FTD had a longer duration of symptoms (median 5 vs. 1.1 years, P < 0.001), higher rates of frontotemporal atrophy (89.7% vs. 3.3%, P < 0.001), lower rates of periodic short-wave complexes on EEG (0% vs. 30.3%, P = 0.001), and hyperintensity on MRI (25.0% vs. 83.0%, P < 0.001). The frequency of codon 129 Val allele in gPrDs presenting with FTD was significantly higher than that reported in the literature for gPrDs in the Caucasian and East Asian populations (33.3% vs. 19.2%/8.0%, P = 0.005, P < 0.001).

Conclusions

GPrDs presenting with FTD are characterized by early-onset, high incidence of positive family history, high frequency of the Val allele at codon 129, overlapping symptoms with prion disease and FTD, and ancillary features closer to FTD. PRNP mutations may be a rare cause in the FTD spectrum, and PRNP genotyping should be considered in patients with these features.

Prion protein codon 129 polymorphism in mild cognitive impairment and dementia: the Rotterdam Study

Creutzfeldt–Jakob disease is a rare, fatal, neurodegenerative disease caused by the accumulation of abnormally folded prion proteins. The common polymorphism at codon 129 (methionine/valine) in the prion protein (PRNP) gene is the most important determinant of genetic susceptibility. Homozygotes of either allele have a higher risk of sporadic Creutzfeldt–Jakob disease. Various studies suggest that this polymorphism is also involved in other forms of dementia. We studied the association between the codon 129 polymorphism of the PRNP gene and mild cognitive impairment in 3605 participants from the Rotterdam Study using logistic regression analyses. Subsequently, we studied the association between this polymorphism and incident dementia, including Alzheimer’s disease, in 11 070 participants using Cox proportional hazard models. Analyses were adjusted for age and sex. We found the prevalence of mild cognitive impairment to be higher for carriers of the methionine/methionine genotype (odds ratio, 1.40; 95% confidence interval, 1.11–1.78; P = 0.005) as well as for carriers of the valine/valine genotype (odds ratio, 1.37; 95% confidence interval, 0.96–1.97; P = 0.08). The codon 129 polymorphism was not associated with the risk of incident dementia or Alzheimer’s disease. In conclusion, we found a statistically significant higher prevalence of mild cognitive impairment in carriers of the methionine/methionine genotype in the codon 129 polymorphism of the PRNP gene within this population-based study. No associations were found between the codon 129 polymorphism and dementia or Alzheimer’s disease in the general population.

Hsp90 and Its Co-Chaperones in Neurodegenerative Diseases

Proper folding is crucial for proteins to achieve functional activity in the cell. However, it often occurs that proteins are improperly folded (misfolded) and form aggregates, which are the main hallmark of many diseases including cancers, neurodegenerative diseases and many others. Proteins that assist other proteins in proper folding into three-dimensional structures are chaperones and co-chaperones. The key role of chaperones/co-chaperones is to prevent protein aggregation, especially under stress. An imbalance between chaperone/co-chaperone levels has been documented in neurons, and suggested to contribute to protein misfolding. An essential protein and a major regulator of protein folding in all eukaryotic cells is the heat shock protein 90 (Hsp90). The function of Hsp90 is tightly regulated by many factors, including co-chaperones. In this review we summarize results regarding the role of Hsp90 and its co-chaperones in neurodegenerative disorders such as Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), and prionopathies.

The characterization of AD/PART co-pathology in CJD suggests independent pathogenic mechanisms and no cross-seeding between misfolded Aβ and prion proteins

Current evidence indicating a role of the human prion protein (PrP) in amyloid-beta (Aβ) formation or a synergistic effect between Aβ and prion pathology remains controversial. Conflicting results also concern the frequency of the association between the two protein misfolding disorders and the issue of whether the apolipoprotein E gene (APOE) and the prion protein gene (PRNP), the major modifiers of Aβ- and PrP-related pathologies, also have a pathogenic role in other proteinopathies, including tau neurofibrillary degeneration. Here, we thoroughly characterized the Alzheimer's disease/primary age-related tauopathy (AD/PART) spectrum in a series of 450 cases with definite sporadic or genetic Creutzfeldt-Jakob disease (CJD). Moreover, we analyzed: (i) the effect of variables known to affect CJD pathogenesis and the co-occurring Aβ- and tau-related pathologies; (II) the influence of APOE genotype on CJD pathology, and (III) the effect of AD/PART co-pathology on the clinical CJD phenotype. AD/PART characterized 74% of CJD brains, with 53.3% and 8.2% showing low or intermediate-high levels of AD pathology, and 12.4 and 11.8% definite or possible PART. There was no significant correlation between variables affecting CJD (i.e., disease subtype, prion strain, PRNP genotype) and those defining the AD/PART spectrum (i.e., ABC score, Thal phase, prevalence of CAA and Braak stage), and no difference in the distribution of APOE ε4 and ε2 genotypes among CJD subtypes. Moreover, AD/PART co-pathology did not significantly affect the clinical presentation of typical CJD, except for a tendency to increase the frequency of cognitive symptoms. Altogether, the present results seem to exclude an increased prevalence AD/PART co-pathology in sporadic and genetic CJD, and indicate that largely independent pathogenic mechanisms drive AD/PART and CJD pathology even when they coexist in the same brain.

Regional vulnerability in Alzheimer's disease: The role of cell-autonomous and transneuronal processes

INTRODUCTION

The stereotypical progression of Alzheimer's disease (AD) pathology is not fully understood. The selective impact of AD on distinct regions has led the field to question if innate vulnerability exists. This study aims to determine if the causative factors of regional vulnerability are dependent on cell-autonomous or transneuronal (non-cell autonomous) processes.

METHODS

Using mathematical and statistical models, we analyzed the contribution of cell-autonomous and non-cell autonomous factors to predictive linear models of AD pathology.

RESULTS

Results indicate gene expression as a weak contributor to predictive linear models of AD. Instead, the network diffusion model acts as a strong predictor of observed AD atrophy and hypometabolism.

DISCUSSION

We propose a convenient methodology for identifying genes and their role in determining AD topography, in comparison with network spread. Results reinforce the role of transneuronal network spread on disease progression and suggest that innate gene expression plays a secondary role in seeding and subsequent disease progression.

Prion Protein PRNP: A New Player in Innate Immunity? The Aβ Connection

The prion protein PRNP has been centrally implicated in the transmissible spongiform encephalopathies (TSEs), but its normal physiological role remains obscure. We highlight emerging evidence that PRNP displays antimicrobial activity, inhibiting the replication of multiple viruses, and also interacts directly with Alzheimer's disease (AD) amyloid-β (Aβ) peptide whose own antimicrobial role is now increasingly secure. PRNP and Aβ share share membrane-penetrating, nucleic acid binding, and antiviral properties with classical antimicrobial peptides such as LL-37. We discuss findings that binding of abnormal nucleic acids to PRNP leads to oligomerization of the protein, and suggest that this may be an entrapment and sequestration process that contributes to its antimicrobial activity. Some antimicrobial peptides are known to be exploited by infectious agents, and we cover evidence that PRNP is usurped by herpes simplex virus (HSV-1) that has evolved a virus-encoded 'anti-PRNP'.unction. These findings suggest that PRNP, like LL-37 and Aβ, is likely to be a component of the innate immune system, with implications for the pathoetiology of both AD and TSE.

Synaptic Cell Adhesion Molecules in Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative brain disorder associated with the loss of synapses between neurons in the brain. Synaptic cell adhesion molecules are cell surface glycoproteins which are expressed at the synaptic plasma membranes of neurons. These proteins play key roles in formation and maintenance of synapses and regulation of synaptic plasticity. Genetic studies and biochemical analysis of the human brain tissue, cerebrospinal fluid, and sera from AD patients indicate that levels and function of synaptic cell adhesion molecules are affected in AD. Synaptic cell adhesion molecules interact with Aβ, a peptide accumulating in AD brains, which affects their expression and synaptic localization. Synaptic cell adhesion molecules also regulate the production of Aβ via interaction with the key enzymes involved in Aβ formation. Aβ-dependent changes in synaptic adhesion affect the function and integrity of synapses suggesting that alterations in synaptic adhesion play key roles in the disruption of neuronal networks in AD.

Epidemiological genetics and meta-analysis of a polymorphism at codon 129 of the PRNP gene in Alzheimer's disease in Brazil

The polymorphism at codon 129 of the prion protein gene (PRNP) is a major risk factor for Creutzfeldt-Jakob disease (CJD). Several authors reported neuropathological and clinical overlapping between CJD and Alzheimer's disease (AD), with a few association studies generating conflicting results. To investigate the distribution of this polymorphism in AD, we selected 58 patients with probable AD and 73 controls from a Brazilian population. There was no association between the PRNP polymorphism at codon 129 and AD. Our meta-analysis (performed using Alzgene; http://www.alzgene.org) along with previous studies conducted in Brazil demonstrated a negative association.

Codon 129 polymorphism of prion protein gene in is not a risk factor for Alzheimer's disease

Interaction of prion protein and amyloid-b oligomers has been demonstrated recently. Homozygosity at prion protein gene (PRNP) codon 129 is associated with higher risk for Creutzfeldt-Jakob disease. This polymorphism has been addressed as a possible risk factor in Alzheimer disease (AD).ObjectiveTo describe the association between codon 129 polymorphisms and AD.MethodsWe investigated the association of codon 129 polymorphism of PRNP in 99 AD patients and 111 controls, and the association between this polymorphism and cognitive performance. Other polymorphisms of PRNP and additive effect of apolipoprotein E gene (ApoE) were evaluated.ResultsCodon 129 genotype distribution in AD 45.5% methionine (MM), 42.2% methionine valine (MV), 12.1% valine (VV); and 39.6% MM, 50.5% MV, 9.9% VV among controls (p>0.05). There were no differences of cognitive performance concerning codon 129. Stratification according to ApoE genotype did not reveal difference between groups.ConclusionCodon 129 polymorphism is not a risk factor for AD in Brazilian patients.

Alzheimer's disease and prion protein

Alzheimer's disease (AD) is a devastating neurodegenerative disease with progressive loss of memory and cognitive function, pathologically hallmarked by aggregates of the amyloid-beta (Aβ) peptide and hyperphosphorylated tau in the brain. Aggregation of Aβ under the form of amyloid fibrils has long been considered central to the pathogenesis of AD. However, recent evidence has indicated that soluble Aβ oligomers, rather than insoluble fibrils, are the main neurotoxic species in AD. The cellular prion protein (PrP(C)) has newly been identified as a cell surface receptor for Aβ oligomers. PrP(C) is a cell surface glycoprotein that plays a key role in the propagation of prions, proteinaceous infectious agents that replicate by imposing their abnormal conformation to PrP(C) molecules. In AD, PrP(C) acts to transduce the neurotoxic signals arising from Aβ oligomers, leading to synaptic failure and cognitive impairment. Interestingly, accumulating evidence has also shown that aggregated Aβ or tau possesses prion-like activity, a property that would allow them to spread throughout the brain. In this article, we review recent findings regarding the function of PrP(C) and its role in AD, and discuss potential therapeutic implications of PrP(C)-based approaches in the treatment of AD.

The association between the methionine/valine (M/V) polymorphism (rs1799990) in the PRNP gene and the risk of Alzheimer disease: an update by meta-analysis

BACKGROUND

The M/V polymorphism in the PRNP gene has been extensively examined for the association to the risk of Alzheimer disease (AD); however, results from different studies have been inconsistent. The aim of this study is to evaluate the association between the M/V polymorphism in the PRNP gene and the risk of AD.

METHODS

A meta-analysis was carried out to analyze the association between the M/V polymorphism in the PRNP gene and the risk of AD.

RESULTS

A total of 4228 cases and 4324 controls in 16 case-control studies were included in the meta-analysis. The results indicated that the variant V allele carriers (VV+MV) had a 13% decreased risk of AD, when compared with the homozygote MM (VV+MV vs. MM: OR=0.87, 95% CI=0.79-0.96, P=0.004). In the subgroup analysis by ethnicity, significant decreased risks of AD were found in the Caucasian V allele carriers (OR=0.85, 95% CI=0.77-0.94, P=0.002), but not in Asian V allele carriers (OR=1.11, 95% CI=0.78-1.57, P=0.57). In the subgroup analysis by age of onset, significant decreased risks of AD were associated with V allele carriers in late-onset Alzheimer disease (OR=0.76, 95% CI=0.62-0.93, P=0.007) but not in early-onset Alzheimer disease (OR=0.86, 95% CI=0.70-1.06, P=0.17).

CONCLUSIONS

Our results suggest that the M/V polymorphism in the PRNP gene contributes to the susceptibility of Alzheimer disease.

Can infections cause Alzheimer's disease?

Late-onset Alzheimer's disease (AD) is the most prevalent cause of dementia among older adults, yet more than a century of research has not determined why this disease develops. One prevailing hypothesis is that late-onset AD is caused by infectious pathogens, an idea widely studied in both humans and experimental animal models. This review examines the infectious AD etiology hypothesis and summarizes existing evidence associating infectious agents with AD in humans. The various mechanisms through which different clinical and subclinical infections could cause or promote the progression of AD are considered, as is the concordance between putative infectious agents and the epidemiology of AD. We searched the PubMed, Web of Science, and EBSCO databases for research articles pertaining to infections and AD and systematically reviewed the evidence linking specific infectious pathogens to AD. The evidence compiled from the literature linking AD to an infectious cause is inconclusive, but the amount of evidence suggestive of an association is too substantial to ignore. Epidemiologic, clinical, and basic science studies that could improve on current understanding of the associations between AD and infections and possibly uncover ways to control this highly prevalent and debilitating disease are suggested.

Therapeutic effect of CHF5074, a new γ-secretase modulator, in a mouse model of scrapie

In Transmissible Spongiform Encephalopathies (TSEs) and Alzheimer disease (AD) both misfolding and aggregation of specific proteins represent key features. Recently, it was observed that PrP (c) is a mediator of a synaptic dysfunction induced by Aβ oligomers. We tested a novel γ secretase modulator (CHF5074) in a murine model of prion disease. Groups of female mice were intracerebrally or intraperitoneally infected with the mouse-adapted Rocky Mountain Laboratory prions. Two weeks prior infection, the animals were provided with a CHF5074-medicated diet (375 ppm) or a standard diet (vehicle) until they showed neurological signs and eventually died. In intracerebrally infected mice, oral administration of CHF5074 did not prolong survival of the animals. In intraperitoneally-infected mice, CHF5074-treated animals showed a median survival time of 21 days longer than vehicle-treated mice (p < 0.001). In these animals, immunohistochemistry analyses showed that deposition of PrP (Sc) in the cerebellum, hippocampus and parietal cortex in CHF5074-treated mice was significantly lower than in vehicle-treated animals. Immunostaining of glial fibrillary acidic protein (GFAP) in parietal cortex revealed a significantly higher reactive gliosis in CHF5074-treated mice compared to the control group of infected animals. Although the mechanism underlying the beneficial effects of CHF5074 in this murine model of human prion disease is unclear, it could be hypothesized that the drug counteracts PrP (Sc ) toxicity through astrocyte-mediated neuroprotection. CHF5074 shows a pharmacological potential in murine models of both AD and TSEs thus suggesting a link between these degenerative pathologies.

PRND 3'UTR polymorphism may be associated with behavioral disturbances in Alzheimer disease

The etiology of behavioral and psychological symptoms of dementia (BPSD) is complex, including putative biological, psychological, social and environmental factors. Recent years have witnessed accumulation of data on the association between genetic factors and behavioral abnormalities in Alzheimer disease (AD). In this research paper, our aim is to evaluate the association between the APOE, CYP46, PRNP and PRND genes and the profile of neuropsychiatric symptoms in Polish subjects with AD and mild cognitive impairment (MCI). We studied 99 patients with AD and 48 subjects with MCI. The presence and profile of BPSD were evaluated at baseline and prospectively with the Neuropsychiatric Inventory (NPI). Patients were dichotomized into those having ever experienced a particular symptom and those who did not over the whole disease period. Genotyping was performed using previously described standard protocols. The prevalence of comorbid behavioral symptoms and the overall level of behavioral burden were significantly greater in AD compared with the MCI group. In AD patients, carrier status of the T allele of the 3'UTR (untranslated region) PRND polymorphism was associated with an increased cumulative behavioral load and an elevated risk for delusions, anxiety, agitation/aggression, apathy and irritability/emotional ability. Among MCI subjects, APOE ε4 carriers demonstrated a reduced risk for nighttime behavior change. No other statistically significant genotype-phenotype correlations were observed, including the APOE, CYP46 and PRNP genes. A precise estimation of the exact significance of particular polymorphisms in BPSD etiology requires future studies on large populations.

Regulation of amyloid-β production by the prion protein

Alzheimer disease (AD) is characterized by the amyloidogenic processing of the amyloid precursor protein (APP), culminating in the accumulation of amyloid-β peptides in the brain. The enzymatic action of the β-secretase, BACE1 is the rate-limiting step in this amyloidogenic processing of APP. BACE1 cleavage of wild-type APP (APPWT) is inhibited by the cellular prion protein (PrP (C) ). Our recent study has revealed the molecular and cellular mechanisms behind this observation by showing that PrP (C) directly interacts with the pro-domain of BACE1 in the trans-Golgi network (TGN), decreasing the amount of BACE1 at the cell surface and in endosomes where it cleaves APPWT, while increasing BACE1 in the TGN where it preferentially cleaves APP with the Swedish mutation (APPSwe). PrP (C) deletion in transgenic mice expressing the Swedish and Indiana familial mutations (APPSwe,Ind) failed to affect amyloid-β accumulation, which is explained by the differential subcellular sites of action of BACE1 toward APPWT and APPSwe. This, together with our observation that PrP (C) is reduced in sporadic but not familial AD brain, suggests that PrP (C) plays a key protective role against sporadic AD. It also highlights the need for an APPWT transgenic mouse model to understand the molecular and cellular mechanisms underlying sporadic AD.

Cellular prion protein expression is not regulated by the Alzheimer's amyloid precursor protein intracellular domain

There is increasing evidence of molecular and cellular links between Alzheimer's disease (AD) and prion diseases. The cellular prion protein, PrP^C, modulates the post-translational processing of the AD amyloid precursor protein (APP), through its inhibition of the β-secretase BACE1, and oligomers of amyloid-β bind to PrP^C which may mediate amyloid-β neurotoxicity. In addition, the APP intracellular domain (AICD), which acts as a transcriptional regulator, has been reported to control the expression of PrP^C. Through the use of transgenic mice, cell culture models and manipulation of APP expression and processing, this study aimed to clarify the role of AICD in regulating PrP^C. Over-expression of the three major isoforms of human APP (APP₆₉₅, APP₇₅₁ and APP₇₇₀) in cultured neuronal and non-neuronal cells had no effect on the level of endogenous PrP^C. Furthermore, analysis of brain tissue from transgenic mice over-expressing either wild type or familial AD associated mutant human APP revealed unaltered PrP^C levels. Knockdown of endogenous APP expression in cells by siRNA or inhibition of γ-secretase activity also had no effect on PrP^C levels. Overall, we did not detect any significant difference in the expression of PrP^C in any of the cell or animal-based paradigms considered, indicating that the control of cellular PrP^C levels by AICD is not as straightforward as previously suggested.

Genetic cross-interaction between APOE and PRNP in sporadic Alzheimer's and Creutzfeldt-Jakob diseases

Alzheimer's disease (AD) and Creutzfeldt-Jakob disease (CJD) represent two distinct clinical entities belonging to a wider group, generically named as conformational disorders that share common pathophysiologic mechanisms. It is well-established that the APOE ε4 allele and homozygosity at polymorphic codon 129 in the PRNP gene are the major genetic risk factors for AD and human prion diseases, respectively. However, the roles of PRNP in AD, and APOE in CJD are controversial. In this work, we investigated for the first time, APOE and PRNP genotypes simultaneously in 474 AD and 175 sporadic CJD (sCJD) patients compared to a common control population of 335 subjects. Differences in genotype distribution between patients and control subjects were studied by logistic regression analysis using age and gender as covariates. The effect size of risk association and synergy factors were calculated using the logistic odds ratio estimates. Our data confirmed that the presence of APOE ε4 allele is associated with a higher risk of developing AD, while homozygosity at PRNP gene constitutes a risk for sCJD. Opposite, we found no association for PRNP with AD, nor for APOE with sCJD. Interestingly, when AD and sCJD patients were stratified according to their respective main risk genes (APOE for AD, and PRNP for sCJD), we found statistically significant associations for the other gene in those strata at higher previous risk. Synergy factor analysis showed a synergistic age-dependent interaction between APOE and PRNP in both AD (SF = 3.59, p = 0.027), and sCJD (SF = 7.26, p = 0.005). We propose that this statistical epistasis can partially explain divergent data from different association studies. Moreover, these results suggest that the genetic interaction between APOE and PRNP may have a biological correlate that is indicative of shared neurodegenerative pathways involved in AD and sCJD.

Unaltered prion protein expression in Alzheimer disease patients

The suggested role of cellular prion protein (PrP (C) ) in mediating the toxic effects of oligomeric amyloid β peptide (Aβ) in Alzheimer disease (AD) is controversial. To address the hypothesis that variable PrP (C)  expression is involved in AD pathogenesis, we analyzed PrPC expression in the frontal and temporal cortices and hippocampus of individuals with no cognitive impairment (NCI), amnestic mild cognitive impairment (aMCI), mild AD (mAD), and AD. We found that PrP (C)  expression in all brain regions was not significantly altered among the various patient groups. In addition, PrP (C)  levels in all groups did not correlate with expression of methionine (M) or valine (V) at codon 129 of the PrP gene, a polymorphism that has been linked in some studies to increased risk for AD, and which occurs in close proximity to the proposed binding region for the oligomeric Aβ peptide. Our results indicate that, if PrP (C)  is involved in mediating the toxic effects of the oligomeric Aβ peptide, these effects occur independently of steady state levels of PrP or the codon 129 polymorphism.

Amyloid-beta42 interacts mainly with insoluble prion protein in the Alzheimer brain

The prion protein (PrP) is best known for its association with prion diseases. However, a controversial new role for PrP in Alzheimer disease (AD) has recently emerged. In vitro studies and mouse models of AD suggest that PrP may be involved in AD pathogenesis through a highly specific interaction with amyloid-β (Aβ42) oligomers. Immobilized recombinant human PrP (huPrP) also exhibited high affinity and specificity for Aβ42 oligomers. Here we report the novel finding that aggregated forms of huPrP and Aβ42 are co-purified from AD brain extracts. Moreover, an anti-PrP antibody and an agent that specifically binds to insoluble PrP (iPrP) co-precipitate insoluble Aβ from human AD brain. Finally, using peptide membrane arrays of 99 13-mer peptides that span the entire sequence of mature huPrP, two distinct types of Aβ binding sites on huPrP are identified in vitro. One specifically binds to Aβ42 and the other binds to both Aβ42 and Aβ40. Notably, Aβ42-specific binding sites are localized predominantly in the octapeptide repeat region, whereas sites that bind both Aβ40 and Aβ42 are mainly in the extreme N-terminal or C-terminal domains of PrP. Our study suggests that iPrP is the major PrP species that interacts with insoluble Aβ42 in vivo. Although this work indicated the interaction of Aβ42 with huPrP in the AD brain, the pathophysiological relevance of the iPrP/Aβ42 interaction remains to be established.

β-amyloid oligomers and prion protein: Fatal attraction?

The relationship between Alzheimer disease (AD) and prion-related encephalopathies (TSE) has been proposed by different points of view. Recently, the scientific attention has been attracted by the results proposing the possibility that PrPc, the protein whose pathologic form is responsible of TSE, can mediated the toxic effect of β amyloid (Aβ) oligomers. The oligomers are considered the culprit of the neurodegenerative process associated to AD, although the pathogenic mechanism activated by these small aggregates remain to be elucidated. In the initial study based on the binding screening PrPc was identified as ligand /receptor of Aβ oligomers, while long term potentiation (LTP) analysis in vitro and behavioural studies in vivo, demonstrated that the absence of PrPc abolished the damage induced by Aβ oligomers. The high affinity binding Aβ oligomers-PrPc has been confirmed, whereas a functional role of this association has been excluded by three different studies. We approached this issue by the direct application of Aβ oligomers in the brain followed by the behavioural examination of memory deficits. Our data using PrP knock-out mice suggest that Aβ 1-42 oligomers are responsible for cognitive impairment in AD but PrPc is not required for their effect. Similarly, in two other studies the LTP alterations induced by Aβ 1-42 oligomers was not influenced by the absence of PrP. Possible explanations of these contradictory results are discussed.

Cellular prion protein mediates the toxicity of beta-amyloid oligomers: implications for Alzheimer disease

Alzheimer disease (AD) is the most common cause of age-related dementia, affecting more than 25 million people worldwide. The accumulation of insoluble beta-amyloid (Abeta) plaques in the brain has long been considered central to the pathogenesis of AD. However, recent evidence suggests that soluble oligomeric assemblies of Abeta may be of greater importance. beta-Amyloid oligomers have been found to be potent synaptotoxins, but the mechanism by which they exert their action has remained elusive. Herein, we review the recently published finding that cellular prion protein (PrP(c)) is a high-affinity receptor for Abeta oligomers, mediating their toxic effects on synaptic plasticity. We further discuss the relationship between AD and PrP(c) and the potential clinical implications. Cellular prion protein may provide a novel target for therapeutic intervention in AD.

Prion protein and Alzheimer disease

Alzheimer and prion diseases are neurodegenerative disorders characterised by the abnormal processing of amyloid-beta (Abeta) peptide and prion protein (PrP(C)), respectively. Recent evidence indicates that PrP(C) may play a critical role in the pathogenesis of Alzheimer disease. PrP(C) interacts with and inhibits the beta-secretase BACE1, the rate-limiting enzyme in the production of Abeta. More recently PrP(C) was identified as a receptor for Abeta oligomers and the expression of PrP(C) appears to be controlled by the amyloid intracellular domain (AICD). Here we review these observations and propose a feedback loop in the normal brain where PrP(C) exerts an inhibitory effect on BACE1 to decrease both Abeta and AICD production. In turn, the AICD upregulates PrP(C) expression, thus maintaining the inhibitory effect of PrP(C) on BACE1. In Alzheimer disease, this feedback loop is disrupted, and the increased level of Abeta oligomers bind to PrP(C) and prevent it from regulating BACE1 activity.

Lack of association between PRNP 1368 polymorphism and Alzheimer's disease or vascular dementia

BACKGROUND

Polymorphisms of the prion protein gene (PRNP) at codons 129 and 219 play an important role in the susceptibility to Creutzfeldt-Jakob disease (CJD), and might be associated with other neurodegenerative disorders. Several recent reports indicate that polymorphisms outside the coding region of PRNP modulate the expression of prion protein and are associated with sporadic CJD, although other studies failed to show an association. These reports involved the polymorphism PRNP 1368 which is located upstream from PRNP exon 1. In a case-controlled protocol, we assessed the possible association between the PRNP 1368 polymorphism and either Alzheimer's disease (AD) or vascular dementia (VaD).

METHODS

To investigate whether the PRNP 1368 polymorphism is associated with the occurrence of AD or VaD in the Korean population, we compared the genotype, allele, and haplotype frequencies of the PRNP 1368 polymorphism in 152 AD patients and 192 VaD patients with frequencies in 268 healthy Koreans.

RESULTS AND CONCLUSION

Significant differences in genotype, allele and haplotype frequencies of PRNP 1368 polymorphism were not observed between AD and normal controls. There were no significant differences in the genotype and allele frequencies of the PRNP 1368 polymorphism between Korean VaD patients and normal controls. However, in the haplotype analysis, haplotype Ht5 was significantly over-represented in Korean VaD patients. This was the first genetic association study of a polymorphism outside the coding region of PRNP in relation to AD and VaD.

Increased frequency of positive family history of dementia in sporadic CJD

OBJECTIVE

To analyze whether a positive family history of dementia (PFHD) is more common in sporadic CJD (sCJD) than in healthy/population controls and to study associated risk factors.

PATIENTS/METHODS

Six hundred and eighty-five sCJD patients and 659 sex-/age-matched controls were included. A PFHD in parents/grandparents/siblings was evaluated. The PRNP M129V polymorphism and ApoE genotype in sCJD with/without PFHD were determined by PCR.

RESULTS

PFHD was found in 12.1% of sCJD patients and 5.6% of controls (p<0.001). No significant difference in M129V polymorphism was found between sCJD with and without PFHD. Thirty-six percent of sCJD patients with PFHD, 26% without PFHD and 19% of healthy controls had at least one ApoE4 allele. Compared to controls, ApoE4 allele frequency (p=0.005) and proportion of ApoE4 allele carriers (p=0.019) were significantly higher in sCJD with PFHD.

INTERPRETATION

A higher frequency of the ApoE4 allele in sCJD with a PFHD could be indicative of an additional risk factor in CJD.

Molecular pathology of human prion diseases

Prion diseases are fatal neurodegenerative conditions in humans and animals. In this review, we summarize the molecular background of phenotypic variability, relation of prion protein (PrP) to other proteins associated with neurodegenerative diseases, and pathogenesis of neuronal vulnerability. PrP exists in different forms that may be present in both diseased and non-diseased brain, however, abundant disease-associated PrP together with tissue pathology characterizes prion diseases and associates with transmissibility. Prion diseases have different etiological background with distinct pathogenesis and phenotype. Mutations of the prion protein gene are associated with genetic forms. The codon 129 polymorphism in combination with the Western blot pattern of PrP after proteinase K digestion serves as a basis for molecular subtyping of sporadic Creutzfeldt-Jakob disease. Tissue damage may result from several parallel, interacting or subsequent pathways that involve cellular systems associated with synapses, protein processing, oxidative stress, autophagy, and apoptosis.

Fluorodeoxyglucose-positron-emission tomography, single-photon emission tomography, and structural MR imaging for prediction of rapid conversion to Alzheimer disease in patients with mild cognitive impairment: a meta-analysis

BACKGROUND AND PURPOSE

Patients with mild cognitive impairment (MCI) are at risk for developing Alzheimer disease (AD). To diagnose AD at an early stage, one must develop highly specific and sensitive tools to identify it among at-risk subjects. The purpose of this study was to evaluate and compare the ability of fluorodeoxyglucose-positron-emission tomography (FDG-PET), single-photon emission tomography (SPECT), and structural MR imaging to predict conversion to AD in patients with MCI.

MATERIALS AND METHODS

Relevant studies were identified with MEDLINE from January 1990 to April 2008. Meta-analysis and meta-regression were done on the diagnostic performance data for each technique from eligible studies. We estimated and compared the weighted summary sensitivities, specificities, likelihood ratios (LRs), and summary receiver operating characteristic curves of each imaging technique.

RESULTS

Twenty-four eligible studies were included, with a total of 1112 patients. FDG-PET performed statistically better in LR+ and odds ratio (OR), whereas no statistical difference was found in pooled sensitivity, specificity, and LR- for each technique. No statistical difference was confirmed between SPECT and MR imaging. The Q* index estimates for FDG-PET, SPECT, and structural MR imaging were respectively 0.86, 0.75, and 0.76. In meta-regression, statistical significance was found only between technique and log OR, with a regression coefficient of -0.575.

CONCLUSIONS

This meta-analysis showed that FDG-PET performs slightly better than SPECT and structural MR imaging in the prediction of conversion to AD in patients with MCI; parallel performance was found between SPECT and MR imaging.

Prion infection of mice transgenic for human APPSwe: increased accumulation of cortical formic acid extractable Abeta(1-42) and rapid scrapie disease development

Neuropathological, epidemiological and experimental data indicate a potential interrelationship between Alzheimer's disease and prion diseases. Proteolytic processing of amyloid precursor protein (APP) by beta-secretase was recently suggested to be controlled by prion protein expression. Here, we characterized the prion infection of Tg2576 mice, which overexpress the human APP(Swe) protein. Prion infection of Tg2576-mice led to an early death of the animals, which was preceded by a relatively short symptomatic stage. However, disease-associated gliosis and deposition of misfolded prion protein PrP(Sc) were identical in infected Tg2576-mice and non-transgenic littermate controls. To analyze the effect of prion infection on APP processing and generation of beta-amyloid we determined cortical levels of SDS- and formic acid (FA)-extractable forms of beta-amyloid (1-40) and (1-42) by ELISA. Formic acid-extractable Abeta (1-42) levels were 10-fold higher in infected versus uninfected Tg2576 mice whereas other forms of Abeta were essentially unaffected by the prion infection. Hence, the experimental model demonstrates that a prion infection of the CNS promotes selectively formation of FA-extractable Abeta(1-42) in Tg2576 mice.

Physiology of the prion protein

Prion diseases are transmissible spongiform encephalopathies (TSEs), attributed to conformational conversion of the cellular prion protein (PrP(C)) into an abnormal conformer that accumulates in the brain. Understanding the pathogenesis of TSEs requires the identification of functional properties of PrP(C). Here we examine the physiological functions of PrP(C) at the systemic, cellular, and molecular level. Current data show that both the expression and the engagement of PrP(C) with a variety of ligands modulate the following: 1) functions of the nervous and immune systems, including memory and inflammatory reactions; 2) cell proliferation, differentiation, and sensitivity to programmed cell death both in the nervous and immune systems, as well as in various cell lines; 3) the activity of numerous signal transduction pathways, including cAMP/protein kinase A, mitogen-activated protein kinase, phosphatidylinositol 3-kinase/Akt pathways, as well as soluble non-receptor tyrosine kinases; and 4) trafficking of PrP(C) both laterally among distinct plasma membrane domains, and along endocytic pathways, on top of continuous, rapid recycling. A unified view of these functional properties indicates that the prion protein is a dynamic cell surface platform for the assembly of signaling modules, based on which selective interactions with many ligands and transmembrane signaling pathways translate into wide-range consequences upon both physiology and behavior.

Octarepeat changes of prion protein in Parkinson's disease

Polymorphism in prion protein (PrP) is related to different phenotypes of spongiform encephalopathies and some mental illnesses. The octarepeat region of PrP, encompassing the codon 51 through 91, is related to cellular anti-oxidation function and may play a role in genetic contribution of PrP polymorphism to neurodegeneration, such as Parkinson's disease (PD). We analyzed the genomic patterns of PrP gene from 528 subjects and found a predominance of Met/Met variant at codon 129 of PD subjects without significant difference (97.3%, and 96.5% in controls). But among PD subjects there were one with heterozygosity of silent nucleotide substitution (NS) on octarepeats (R1-2-3g-3-4/R1-2-2-3-4) and three with heterozygosity of single copy deletion (CD) on octarepeats (R1-2-3-4/R1-2-2-3-4). Consistent genomic DNA and cDNA sequences were found in a PD subject without any octarepeat changes and the one with NS, but R1-2-3g-3-4/R1-2-2-3-4 of cDNA pattern occurred in the one with genomic CD. This is the first report of the polymorphic PrP octarepeat change among those with parkinsonism. We proposed a hypothesis about an initial secondary hairpin structure of the template strand followed by the transcript "shift backward" due to the high homology of the sequences between R2 and R3 motifs while synthesizing RNA. This phenomenon may be a key step of neurodegeneration resulting from PrP polymorphism and require further studies.

Meta-analysis of genetic variability in the beta-amyloid production, aggregation and degradation metabolic pathways and the risk of Alzheimer's disease

BACKGROUND

Variants in genes encoding enzymes involved in production, aggregation or degradation of beta-amyloid are potential risk factors for sporadic Alzheimer's disease (AD).

METHODS

Meta-analyses on AD association with BACE1 exon 5, BACE1 intron 5, FE65 intron 13, CYP46 intron 2, alpha(1)-antichymotrypsine Ala17Thr, bleomycin hydrolase I443V, lectin-like oxidized low-density lipoprotein receptor (OLR1) 3'-UTR (+1071) and (+1073), and very-low-density lipoprotein receptor (VLDLR) 5'-UTR (CGG-repeat) polymorphisms.

RESULTS

In BACE1 exon 5, genotype CC+CT acts as a protective factor in Apolipoprotein E (ApoE) epsilon 4 carriers [odds ratio (OR) = 0.57; 95% confidence interval (CI): 0.38-0.88], and as a risk factor in ApoE epsilon 4 non-carriers (OR = 1.33; 95% CI: 1.00-1.78). OLR1 3'-UTR (+1073) allele C is associated with increased risk (OR = 1.23; 95% CI: 1.01-1.50). VLDLR 5'-UTR genotype 2 is associated with increased risk (OR = 1.70; 95% CI: 1.09-2.63) in the Asian population and is protective (OR = 0.48; 95% CI: 0.26-0.86) in the non-Asian population. Other studied polymorphisms are not associated with AD.

CONCLUSIONS

The overall impact on AD risk of the genes for which meta-analyses are now available is rather limited. Additional meta-analyses of other different genes encoding for A beta production, aggregation and degradation mediators might help in determining the risk profile for AD.

Absence of association between codon 129 and 219 polymorphisms of the prion protein gene and vascular dementia

BACKGROUND

Polymorphisms of the prion protein gene (PRNP) are known to cause a strong susceptibility to the occurrence of prion diseases, such as Creutzfeldt-Jakob disease, and might be associated with other neurodegenerative disorders. However, an association between PRNP polymorphisms and vascular dementia (VaD) has not been reported thus far.

OBJECTIVE

To investigate whether the PRNP polymorphisms are associated with an increased risk for developing VaD in the Korean population.

METHODS

We compared the genotype, allele and haplotype frequencies of PRNP polymorphisms in 160 VaD patients with those in 236 healthy Koreans.

RESULTS AND CONCLUSION

Codon 129 (M129V) and 219 (Q219K) polymorphisms in Korean VaD patients were found in the open reading frame of PRNP. Our study shows that there is no significant difference in the genotype, allele and haplotype frequencies of PRNP codon 129 and 219 polymorphisms between Korean VaD patients and normal controls. This was the first genetic association study of the polymorphisms of PRNP with VaD.

ApoE distribution and family history in genetic prion diseases in Germany

We analyzed the ApoE genotype in patients with genetic prion diseases (gPD) with respect to family history (FH) of dementia/prion disease (PD) compared to non-demented controls. Fifty-nine gPD patients and 51 sex-/age-matched controls were included. A positive FH of dementia and PD (PFH) were evaluated. The prion protein gene (PRNP) codon 129 and ApoE genotype were determined by polymerase chain reaction (PCR). The frequency of FH of neurodegenerative disorder/prion disease/dementia varied in different PRNP mutations. PFH was found in 87% of D178N patients, but was rarer in others. Although the ApoE genotype distribution was not significantly different between gPD patients and controls, the protective E2 alleles were more frequent in controls than in patients without a PFH and even less frequent in those with a PFH (18, 16, and 11%). E4 alleles as a risk factor of Alzheimer's disease were more common in controls and patients with a PFH than in those without PFH (25, 21, and 13%). No effect of the codon 129 genotype was detected. Only about two-thirds of gPD patients had PFH of PD, while in one-third, PFH of slowly progressive dementia was reported. Underreporting of PFH of gPD may play a role; however, the varying PFH frequency across various mutations is not explained by this factor only.

The prion protein knockout mouse: a phenotype under challenge

The key pathogenic event in prion disease involves misfolding and aggregation of the cellular prion protein (PrP). Beyond this fundamental observation, the mechanism by which PrP misfolding in neurons leads to injury and death remains enigmatic. Prion toxicity may come about by perverting the normal function of PrP. If so, understanding the normal function of PrP may help to elucidate the molecular mechansim of prion disease. Ablation of the Prnp gene, which encodes PrP, was instrumental for determining that the continuous production of PrP is essential for replicating prion infectivity. Since the structure of PrP has not provided any hints to its possible function, and there is no obvious phenotype in PrP KO mice, studies of PrP function have often relied on intuition and serendipity. Here, we enumerate the multitude of phenotypes described in PrP deficient mice, many of which manifest themselves only upon physiological challenge. We discuss the pleiotropic phenotypes of PrP deficient mice in relation to the possible normal function of PrP. The critical question remains open: which of these phenotypes are primary effects of PrP deletion and what do they tell us about the function of PrP?

Systematic meta-analyses of Alzheimer disease genetic association studies: the AlzGene database

The past decade has witnessed hundreds of reports declaring or refuting genetic association with putative Alzheimer disease susceptibility genes. This wealth of information has become increasingly difficult to follow, much less interpret. We have created a publicly available, continuously updated database that comprehensively catalogs all genetic association studies in the field of Alzheimer disease (http://www.alzgene.org). We performed systematic meta-analyses for each polymorphism with available genotype data in at least three case-control samples. In addition to identifying the epsilon4 allele of APOE and related effects, we pinpointed over a dozen potential Alzheimer disease susceptibility genes (ACE, CHRNB2, CST3, ESR1, GAPDHS, IDE, MTHFR, NCSTN, PRNP, PSEN1, TF, TFAM and TNF) with statistically significant allelic summary odds ratios (ranging from 1.11-1.38 for risk alleles and 0.92-0.67 for protective alleles). Our database provides a powerful tool for deciphering the genetics of Alzheimer disease, and it serves as a potential model for tracking the most viable gene candidates in other genetically complex diseases.

Prion protein gene M129 allele is a risk factor for Alzheimer's disease

Prion protein gene polymorphism M129V represents a known risk factor for Creutzfeldt-Jakob disease. Recently, the meta-analysis revealed that homozygosity at codon 129 is connected with increased risk of Alzheimer's disease (AD). To determine whether M129V polymorphism is a risk factor for AD we analyzed a group of early-onset, and late-onset Polish AD patients. We observed that in LOAD patients there is a statistically significant increase of MM (p=0.0028) and decrease of MV (p=0.0006) genotype frequency, as compared to controls. When both groups were stratified according to APOE4 status, increase of MM and decrease of MV genotype frequency were significant in the LOAD subgroup with no APOE4 (p=0.017, and p=0.018, respectively). In the subgroup with APOE4 allele, only MV genotype frequency was significantly lower, as compared to controls (p=0.035). However, no interaction was found between APOE4 status and M129V polymorphism. We conclude that MM genotype increases LOAD risk in Polish population independently from the APOE4 status.