Alzheimer's Disease Mutations Research Articles

Rab5 Mediates an Amyloid Precursor Protein Signaling Pathway That Leads to Apoptosis

Alzheimer's disease (AD) involves activation of apoptotic pathways that may be regulated through signaling cascades initiated by the amyloid precursor protein (APP). Enlarged endosomes have been observed in postmortem AD brains at very early stages of the disease. We show here that exogenous expression of a familial AD (FAD) mutant of APP or of the APP binding protein APP-BP1 in neurons causes enlargement of early endosomes, increased receptor-mediated endocytosis via a pathway dependent on APP-BP1 binding to APP, and apoptosis. Levels of both APP-BP1 and Rab5 are elevated in early endosomes in cortical embryonic neurons expressing APP(V642I) or APP-BP1, in cultured skin fibroblast cells from Down syndrome subjects, and in postmortem hippocampal tissue of individuals with AD. Indeed, Rab5 was found to bind specifically to APP-BP1, between amino acids 443 and 479. Inhibition of Rab5 or dynamin activity, but not of Eps15 (epidermal growth factor receptor pathway substrate 15) activity, rescued neurons from apoptosis induced by either APP(V642I) or APP-BP1, without affecting levels of intracellular or secreted amyloid-beta (Abeta). Induction of Rab5 activity via expression of a constitutively active mutant led to an increase in neuronal apoptosis more than twice that attributable to induction of endosome enlargement via a Rab5-independent mechanism, regardless of Abeta production. Together, these findings suggest that Rab5 activation via an APP/APP-BP1-initiated signaling pathway mediates neuronal apoptosis caused by FAD mutants of APP and that, within this pathway, Rab5 has a specific role in signaling that is distinct from, although not independent of, its role in trafficking.

Altered levels and distribution of IGF-II/M6P receptor and lysosomal enzymes in mutant APP and APP + PS1 transgenic mouse brains

The insulin-like growth factor-II/mannose-6-phosphate (IGF-II/M6P) receptor participates in the trafficking of lysosomal enzymes from the trans-Golgi network or the cell surface to lysosomes. In Alzheimer's disease (AD) brains, marked up-regulation of the lysosomal system in vulnerable neuronal populations has been correlated with altered metabolic functions. To establish whether IGF-II/M6P receptors and lysosomal enzymes are altered in the brain of transgenic mice harboring different familial AD mutations, we measured the levels and distribution of the receptor and lysosomal enzymes cathepsins B and D in select brain regions of transgenic mice overexpressing either mutant presenilin 1 (PS1; PS1 M146L+L286V), amyloid precursor protein (APP; APP KM670/671NL+V717F) or APP + PS1 (APP KM670/671NL+V717F + PS1 M146L+L286V) transgenes. Our results revealed that levels and expression of the IGF-II/M6P receptor and lysosomal enzymes are increased in the hippocampus and frontal cortex of APP and APP + PS1, but not in PS1, transgenic mouse brains compared with wild-type controls. The changes were more prominent in APP + PS1 than in APP single transgenic mice. Additionally, all β-amyloid-containing neuritic plaques in the hippocampal and cortical regions of APP and APP + PS1 transgenic mice were immunopositive for both lysosomal enzymes, whereas only a subset of the plaques displayed IGF-II/M6P receptor immunoreactivity. These results suggest that up-regulation of the IGF-II/M6P receptor and lysosomal enzymes in neurons located in vulnerable regions reflects an altered functioning of the endosomal–lysosomal system which may be associated with the increased intracellular and/or extracellular Aβ deposits observed in APP and APP + PS1 transgenic mouse brains.

Ligand Binding and Calcium Influx Induce Distinct Ectodomain/γ-Secretase-processing Pathways of EphB2 Receptor

Binding of EphB receptors to ephrinB ligands on the surface of adjacent cells initiates signaling cascades that regulate angiogenesis, axonal guidance, and neuronal plasticity. These functions require processing of EphB receptors and removal of EphB-ephrinB complexes from the cell surface, but the mechanisms involved are poorly understood. Here we show that the ectodomain of EphB2 receptor is released to extracellular space following cleavage after EphB2 residue 543. The remaining membrane-associated fragment is cleaved by the presenilin-dependent gamma-secretase activity after EphB2 residue 569 releasing an intracellular peptide that contains the cytoplasmic domain of EphB2. This cleavage is inhibited by presenilin 1 familial Alzheimer disease mutations. Processing of EphB2 receptor depends on specific treatments: ephrinB ligand-induced processing requires endocytosis, and the ectodomain cleavage is sensitive to peptide inhibitor N-benzyloxycarbonyl-Val-Leu-leucinal but insensitive to metalloproteinase inhibitor GM6001. The ligand-induced processing takes place in endosomes and involves the rapid degradation of the extracellular EphB2. EphrinB ligand stimulates ubiquitination of EphB2 receptor. Calcium influx- and N-methyl-d-aspartic acid-induced processing of EphB2 is inhibited by GM6001 and ADAM10 inhibitors but not by N-benzyloxycarbonyl-Val-Leu-leucinal. This processing requires no endocytosis and promotes rapid shedding of extracellular EphB2, indicating that it takes place at the plasma membrane. Our data identify novel cleavages and modifications of EphB2 receptor and indicate that specific conditions determine the proteolytic systems and subcellular sites involved in the processing of this receptor.

Diffusion tensor imaging in preclinical and presymptomatic carriers of familial Alzheimer's disease mutations

Measures are needed that identify persons that will develop Alzheimer's disease in order to target them for preventative interventions. There is evidence from animal, pathological and imaging studies that disruption of white matter occurs in the course of Alzheimer's disease and may be an early event. Prior studies have suggested that late-myelinating regions or white matter connecting limbic structures are particularly susceptible to degradation. Persons destined to develop the disease by virtue of fully penetrant genetic alterations (familial Alzheimer's disease or FAD) provide a model in which early and even presymptomatic changes of the disease may be identified. In this study we performed diffusion tensor imaging (DTI) on 2 demented and 21 subjects at-risk for inheriting an FAD mutation. We compared global and localized fractional anisotropy (FA) measures in white matter between FAD mutation carriers and non-carriers in the preclinical (clinical dementia rating <1, n = 20) and presymptomatic (clinical dementia rating = 0, n = 15) stages of the disease. There were no significant differences between mutation carriers and non-carriers with regard to absolute age, age relative to the typical age of disease diagnosis in their family, gender or Mini-Mental Status Examination Score. Among preclinical FAD mutation carriers (n = 12), mean whole brain white-matter FA (P = 0.045), FA of the columns of the fornix (P = 0.012), area of the perforant pathways bilaterally (right side: P = 0.028, left side: P = 0.027) and left orbitofrontal lobe (P = 0.024) were decreased relative to that of non-carriers (n = 8). We also found that FA in the columns of the fornix (P = 0.008) and left orbitofrontal lobe white matter (P = 0.045) were decreased in the eight presymptomatic mutation carriers compared to seven non-carriers. Logistic regression demonstrated that FA of the columns of the fornix was a better predictor of mutation status than was cross-sectional area of the fornix, global mean white-matter FA and left frontal lobe white-matter FA. In a linear regression analysis, white-matter volume (P = 0.002), hippocampal volume (P = 0.023) and mutation status (P = 0.032) significantly predicted fornix FA. We conclude that FA is decreased in the white matter in preclinical and even presymptomatic FAD mutation carriers, particularly in the late-myelinating tracts connecting limbic structures. Decreased FA in of the columns of the fornix is particularly robust in early FAD and may provide a biomarker for early disease in sporadic Alzheimer's disease.

A transgenic rat expressing human APP with the Swedish Alzheimer’s disease mutation

In recent years, transgenic mice have become valuable tools for studying mechanisms of Alzheimer’s disease (AD). With the aim of developing an animal model better for memory and neurobehavioural testing, we have generated a transgenic rat model of AD. These animals express human amyloid precursor protein (APP) containing the Swedish AD mutation. The highest level of expression in the brain is found in the cortex, hippocampus, and cerebellum. Starting after the age of 15 months, the rats show increased tau phosphorylation and extracellular Aβ staining. The Aβ is found predominantly in cerebrovascular blood vessels with very rare diffuse plaques. We believe that crossing these animals with mutant PS1 transgenic rats will result in accelerated plaque formation similar to that seen in transgenic mice.

Internalized Antibodies to the Aβ Domain of APP Reduce Neuronal Aβ and Protect against Synaptic Alterations

Immunotherapy against beta-amyloid peptide (Abeta) is a leading therapeutic direction for Alzheimer disease (AD). Experimental studies in transgenic mouse models of AD have demonstrated that Abeta immunization reduces Abeta plaque pathology and improves cognitive function. However, the biological mechanisms by which Abeta antibodies reduce amyloid accumulation in the brain remain unclear. We provide evidence that treatment of AD mutant neuroblastoma cells or primary neurons with Abeta antibodies decreases levels of intracellular Abeta. Antibody-mediated reduction in cellular Abeta appears to require that the antibody binds to the extracellular Abeta domain of the amyloid precursor protein (APP) and be internalized. In addition, treatment with Abeta antibodies protects against synaptic alterations that occur in APP mutant neurons.

Alzheimer’s presenilin 1 modulates sorting of APP and its carboxyl‐terminal fragments in cerebral neurons in vivo

Studies in continuously cultured cells have established that familial Alzheimer's disease (FAD) mutant presenilin 1 (PS1) delays exit of the amyloid precursor protein (APP) from the trans-Golgi network (TGN). Here we report the first description of PS1-regulated APP trafficking in cerebral neurons in culture and in vivo. Using neurons from transgenic mice or a cell-free APP transport vesicle biogenesis system derived from the TGN of those neurons, we demonstrated that knocking-in an FAD-associated mutant PS1 transgene was associated with delayed kinetics of APP arrival at the cell surface. Apparently, this delay was at least partially attributable to impaired exit of APP from the TGN, which was documented in the cell-free APP transport vesicle biogenesis assay. To extend the study to APP and carboxyl terminal fragment (CTF) trafficking to cerebral neurons in vivo, we performed subcellular fractionation of brains from APP transgenic mice, some of which carried a second transgene encoding an FAD-associated mutant form of PS1. The presence of the FAD mutant PS1 was associated with a slight shift in the subcellular localization of both holoAPP and APP CTFs toward iodixanol density gradient fractions that were enriched in a marker for the TGN. In a parallel set of experiments, we used an APP : furin chimeric protein strategy to test the effect of artificially forcing TGN concentration of an APP : furin chimera that could be a substrate for beta- and gamma-cleavage. This chimeric substrate generated excess Abeta42 when compared with wildtype APP. These data indicate that the presence of an FAD-associated mutant human PS1 transgene is associated with redistribution of the APP and APP CTFs in brain neurons toward TGN-enriched fractions. The chimera experiment suggests that TGN-enrichment of a beta-/gamma-secretase substrate may play an integral role in the action of mutant PS1 to elevate brain levels of Abeta42.

Putting presenilins centre stage

Genetic analysis of autosomal dominant Alzheimer disease has identified the amyloid precursor protein (APP) and the presenilins as its pathogenic loci (Rogaeva, 2002). APP is normally cleaved by γ‐secretase into the APP intracellular domain (AICD) and the 40‐residue amyloid β peptide (Aβ40) or, less frequently, the 42‐residue Aβ42. Analyses of blood plasma from mutation carriers shows that all of the pathogenic mutations cause an increase in the Aβ42/Aβ40 ratio, suggesting that they alter the position of the γ‐secretase cleavage of APP (Scheuner et al , 1996; Haass & Selkoe, 1993). Gene‐ablation studies and focused mutagenesis experiments by De Strooper, Wolfe and their colleagues (De Strooper et al , 1998; Wolfe et al , 1999) shows that the presenilins—along with other accessory proteins (Edbauer et al , 2003)—form the γ‐secretase complex. This work is a good example of how genetic analysis can give direct mechanistic insight into the pathogenesis of …

Two sides to the story

Editorial1 February 2007free access Two sides to the story Frank Gannon Frank Gannon Search for more papers by this author Frank Gannon Frank Gannon Search for more papers by this author Author Information Frank Gannon EMBO Reports (2007)8:111-111https://doi.org/10.1038/sj.embor.7400904 PDFDownload PDF of article text and main figures. ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareFacebookTwitterLinked InMendeleyWechatReddit Figures & Info Progress in science relies in part on the public presentation of results, and the discussion of their validity and meaning; but, how often have you attended a conference, heard an enlightening talk, listened to the speaker's confident explanations and then met a colleague over coffee who said, “wasn't that awful?”? Usually, this triggers a debate in which the speaker's arguments are scrutinized and their conclusions challenged. The problem, however, is that the speaker is not present and has no chance to respond. Such a one-sided debate not only is unfair, but also misses the opportunity to discuss rationally differing views on a specific topic. To create a forum for such divergent interpretations of results, EMBO reports is launching a new type of article this month—the Talking Point—that allows scientists to present different views on a given topic. In the Reviews section of this issue, Michael S. Wolfe (see ) and Bart de Strooper (see ) present their views on the role of presenilin mutations in Alzheimer disease. In the future, we will feature Talking Points not only in the Reviews section, but also in the Science & Society section. Frequently, a third party will place the two views in context and draw a conclusion from the different perspectives. We should not underestimate the need for this type of forum. Scientific research is replete with conflicting or divergent opinions, but there are few avenues available for debating these differences. Many research fields are dominated by schools of thought that can be traced back to a founding laboratory that created the original hypothesis. The prevailing theory is further confirmed and reinforced through particular methods of experimentation and analysis. ‘Outsiders’ who have developed their own ideas or methods might have a hard time publishing their ‘deviant’ data and interpretations in those journals that set the tone for the field; at conferences, they are likely to meet the fate outlined above. The fact is that publications contradicting the current orthodoxy are more likely to undergo critical review before acceptance. Of course, this varies from paper to paper, but referees might be extra careful if a paper has the potential to challenge existing paradigms, rather than merely presenting more data to support a well-established theory. But to create a fruitful debate about the merits and shortcomings of each theory or interpretation of data—which is in the interests of both scientists and science—it is necessary to provide all parties with the opportunity to present their views side-by-side. There is another aspect of this issue that is worth mentioning. Reputations can be rapidly tarnished if one person uses a closed and friendly audience to question the quality of another's work. Fairness and civility require the right to reply. Those who believe that their iconoclastic view is being kept at the periphery of debates should contact us if they want to stimulate discussion. EMBO reports welcomes correspondence and provides another forum in the form of Concept articles. This peer-reviewed format allows authors to present ideas that are based on published data but that point to a novel interpretation of a biological problem. Collectively, we hope that these features will enable more free and intellectually satisfying debates, which, of course, should be at the heart of all scientific activities. Previous ArticleNext Article Volume 8Issue 21 February 2007In this issue RelatedDetailsLoading ...

BACE1 gene deletion prevents neuron loss and memory deficits in 5XFAD APP/PS1 transgenic mice

Evidence suggests that beta-amyloid (Abeta) peptide triggers a pathogenic cascade leading to neuronal loss in Alzheimer's disease (AD). However, the causal link between Abeta and neuron death in vivo remains unclear since most animal models fail to recapitulate the dramatic cell loss observed in AD. We have recently developed transgenic mice that overexpress human APP and PS1 with five familial AD mutations (5XFAD mice) and exhibit robust neuron death. Here, we demonstrate that genetic deletion of the beta-secretase (BACE1) not only abrogates Abeta generation and blocks amyloid deposition but also prevents neuron loss found in the cerebral cortex and subiculum, brain regions manifesting the most severe amyloidosis in 5XFAD mice. Importantly, BACE1 gene deletion also rescues memory deficits in 5XFAD mice. Our findings provide strong evidence that Abeta ultimately is responsible for neuron death in AD and validate the therapeutic potential of BACE1-inhibiting approaches for the treatment of AD.

Novel numerical and graphical representation of DNA sequences and proteins

We have introduced novel numerical and graphical representations of DNA, which offer a simple and unique characterization of DNA sequences. The numerical representation of a DNA sequence is given as a sequence of real numbers derived from a unique graphical representation of the standard genetic code. There is no loss of information on the primary structure of a DNA sequence associated with this numerical representation. The novel representations are illustrated with the coding sequences of the first exon of β-globin gene of half a dozen species in addition to human. The method can be extended to proteins as is exemplified by humanin, a 24-aa peptide that has recently been identified as a specific inhibitor of neuronal cell death induced by familial Alzheimer's disease mutant genes.

Beta-Amyloid, Oxidative Stress and Down Syndrome

Down syndrome (DS) provides a model for studying important aspects of Alzheimer disease (AD). Chromosome 21 contains several genes that have been implicated in neurodegenerative mechanisms. These include Cu/Zn superoxide dismutase (SOD-1), Ets-2 transcription factors, Down Syndrome Critical Region 1 (DSCR1) stress-inducible factor, and the amyloid precursor protein (APP). The accumulation of Abeta plaques is progressive across the lifespan in DS. Overexpression of APP in the obligate region for DS is associated with abundant Abeta plaques and tangles consistent with Braak stage V-VI. Intraneuronal Abeta in DS appears to trigger a pathological cascade leading to oxidative stress and a neurodegeneration typical of AD. There are suggestions that an increase in subcellular processing of APP and factors related to membrane APP cleavage favor the secretion of Abeta with age in DS. A misbalance between SOD-1 and glutathione perioxidase activity in DS has been linked to free radical generation. Ets-2 and DSCR1 overexpression in DS has been linked to cell degeneration. Age-related accumulation of somatic DNA mutations in both DS and AD contribute to oxidative stress that exacerbates the imbalance in gene expression. This leads to enhanced Abeta deposition and further neuronal vulnerability. The consequence of these factors and their temporal relationships is likely to be the subject of future research. Since the pathological processes leading to AD are seen across the lifespan in DS, an opportunity is afforded for early pharmacological intervention in the disorder.

FAD mutants unable to increase neurotoxic Aβ 42 suggest that mutation effects on neurodegeneration may be independent of effects on Aβ

Strong support for a primary causative role of the Abeta peptides in the development of Alzheimer's disease (AD) neurodegeneration derives from reports that presenilin familial AD (FAD) mutants alter amyloid precursor protein processing, thus increasing production of neurotoxic Abeta 1-42 (Abeta 42). This effect of FAD mutants is also reflected in an increased ratio of peptides Abeta 42 over Abeta 1-40 (Abeta 40). In the present study, we show that several presenilin 1 FAD mutants failed to increase production of Abeta 42 or the Abeta 42/40 ratio. Our data suggest that the mechanism by which FAD mutations promote neurodegeneration and AD may be independent of their effects on Abeta production.

Intraneuronal amyloid β and reduced brain volume in a novel APP T714I mouse model for Alzheimer's disease

Transgenic mouse models of Alzheimer's disease (AD) expressing high levels of amyloid precursor protein (APP) with familial AD (FAD) mutations have proven to be extremely useful in understanding pathogenic processes of AD especially those that involve amyloidogenesis. We earlier described Austrian APP T714I pathology that leads to one of the earliest AD age-at-onsets with abundant intracellular and extracellular amyloid deposits in brain. The latter strikingly was non-fibrillar diffuse amyloid, composed of N-truncated Aβ42 in absence of Aβ40. In vitro, this mutation leads to one of the highest Aβ42/Aβ40 ratios among all FAD mutations. We generated an APP T714I transgenic mouse model that despite having 10 times lower transgene than endogenous murine APP deposited intraneuronal Aβ in brain by 6 months of age. Accumulations increased with age, and this was paralleled by decreased brain sizes on volumetric MRI, compared to age-matched and similar transgene-expressing APP wild-type mice, although, with these levels of transgenic expression we did not detect neuronal loss or significant memory impairment. Immunohistochemical studies revealed that the majority of the intraneuronal Aβ deposits colocalized with late endosomal markers, although some Aβ inclusions were also positive for lysosomal and Golgi markers. These data support earlier observations of Aβ accumulation in the endosomal–lysosomal pathway and the hypothesis that intraneuronal accumulation of Aβ could be an important factor in the AD pathogenesis.

Intraneuronal β-Amyloid Aggregates, Neurodegeneration, and Neuron Loss in Transgenic Mice with Five Familial Alzheimer's Disease Mutations: Potential Factors in Amyloid Plaque Formation

Mutations in the genes for amyloid precursor protein (APP) and presenilins (PS1, PS2) increase production of beta-amyloid 42 (Abeta42) and cause familial Alzheimer's disease (FAD). Transgenic mice that express FAD mutant APP and PS1 overproduce Abeta42 and exhibit amyloid plaque pathology similar to that found in AD, but most transgenic models develop plaques slowly. To accelerate plaque development and investigate the effects of very high cerebral Abeta42 levels, we generated APP/PS1 double transgenic mice that coexpress five FAD mutations (5XFAD mice) and additively increase Abeta42 production. 5XFAD mice generate Abeta42 almost exclusively and rapidly accumulate massive cerebral Abeta42 levels. Amyloid deposition (and gliosis) begins at 2 months and reaches a very large burden, especially in subiculum and deep cortical layers. Intraneuronal Abeta42 accumulates in 5XFAD brain starting at 1.5 months of age (before plaques form), is aggregated (as determined by thioflavin S staining), and occurs within neuron soma and neurites. Some amyloid deposits originate within morphologically abnormal neuron soma that contain intraneuronal Abeta. Synaptic markers synaptophysin, syntaxin, and postsynaptic density-95 decrease with age in 5XFAD brain, and large pyramidal neurons in cortical layer 5 and subiculum are lost. In addition, levels of the activation subunit of cyclin-dependent kinase 5, p25, are elevated significantly at 9 months in 5XFAD brain, although an upward trend is observed by 3 months of age, before significant neurodegeneration or neuron loss. Finally, 5XFAD mice have impaired memory in the Y-maze. Thus, 5XFAD mice rapidly recapitulate major features of AD amyloid pathology and may be useful models of intraneuronal Abeta42-induced neurodegeneration and amyloid plaque formation.

MAPK-activated Protein Kinase 2 Deficiency in Microglia Inhibits Pro-inflammatory Mediator Release and Resultant Neurotoxicity: RELEVANCE TO NEUROINFLAMMATION IN A TRANSGENIC MOUSE MODEL OF ALZHEIMER DISEASE

MAPK-activated protein kinase 2 (MAPKAP K2 or MK2) is one of several kinases directly regulated by p38 MAPK. A role for p38 MAPK in the pathology of Alzheimer disease (AD) has previously been suggested. Here, we provide evidence to suggest that MK2 also plays a role in neuroinflammatory and neurodegenerative pathology of relevance to AD. MK2 activation and expression were increased in lipopolysaccharide (LPS) + interferon gamma-stimulated microglial cells, implicating a role for MK2 in eliciting a pro-inflammatory response. Microglia cultured ex vivo from MK2-deficient (MK2-/-) mice demonstrated significant inhibition in release of tumor necrosis factor alpha, KC (mouse chemokine with highest sequence identity to human GROs and interleukin-8), and macrophage inflammatory protein 1alpha on stimulation with LPS + interferon gamma or amyloid-beta peptide (1-42) compared with MK2+/+ wild-type microglia. Consistent with an inhibition in pro-inflammatory mediator release, cortical neurons co-cultured with LPS + interferon gamma-stimulated or amyloid-beta peptide (1-42)-stimulated MK2-/- microglia were protected from microglial-mediated neuronal cell toxicity. In a transgenic mouse model of AD in which amyloid precursor protein and presenilin-1 harboring familial AD mutations are overexpressed in specific regions of the brain, elevated activation and expression of MK2 correlated with beta-amyloid deposition, microglial activation, and up-regulation of tumor necrosis factor alpha, macrophage inflammatory protein 1alpha, and KC gene expression in the same brain regions. Our data propose a role for MK2 in AD brain pathology, for which neuroinflammation involving cytokines and chemokines and overt neuronal loss have been documented.

Tauroursodeoxycholic acid modulates p53‐mediated apoptosis in Alzheimer's disease mutant neuroblastoma cells

Early onset familial Alzheimer's disease (FAD) is linked to autosomal dominant mutations in the amyloid precursor protein (APP) and presenilin 1 and 2 (PS1 and PS2) genes. These are critical mediators of total amyloid beta-peptide (Abeta) production, inducing cell death through uncertain mechanisms. Tauroursodeoxycholic acid (TUDCA) modulates exogenous Abeta-induced apoptosis by interfering with E2F-1/p53/Bax. Here, we used mouse neuroblastoma cells that express either wild-type APP, APP with the Swedish mutation (APPswe), or double-mutated human APP and PS1 (APPswe/DeltaE9), all exhibiting increased Abeta production and aggregation. Cell viability was decreased in APPswe and APPswe/DeltaE9 but was partially reversed by z-VAD.fmk. Nuclear fragmentation and caspase 2, 6 and 8 activation were also readily detected. TUDCA reduced nuclear fragmentation as well as caspase 2 and 6, but not caspase 8 activities. p53 activity, and Bcl-2 and Bax changes, were also modulated by TUDCA. Overexpression of p53, but not mutant p53, in wild-type and mutant neuroblastoma cells was sufficient to induce apoptosis, which, in turn, was reduced by TUDCA. In addition, inhibition of the phosphatidylinositide 3'-OH kinase pathway reduced TUDCA protection against p53-induced apoptosis. In conclusion, FAD mutations are associated with the activation of classical apoptotic pathways. TUDCA reduces p53-induced apoptosis and modulates expression of Bcl-2 family.

Linear patterns of Alzheimer's disease mutations along α‐helices of presenilins as a tool for PS‐1 model construction

We performed an analysis of mutation patterns in all 10 hydrophobic regions (HRs) of presenilin-1 (PS-1) and PS-2 using a recent database of Alzheimer's disease (AD) mutations. The linear patterns were confirmed and extended to areas spanning as many as three faces of a given HR. The complementary areas of residues free of AD mutations were identified based on the location of non-pathogenic polymorphisms and PS-1 versus PS-2 amino acid discordances. Taking into account the location of areas of AD mutations and mutation-free areas/regions, we proposed a preliminary model of PS-1 structure using a general stick-out-mutation rule. To build a molecular structure of PS-1 and preserve features of the preliminary model, we used bacteriorhodopsin template in homology/comparative modelling. Two molecular models were built differing in the location of C-terminal fragment helices. The models properly distinguish residues belonging to AD-affected sites and non-pathogenic areas, and may be used for classification purposes. They also comply with experimental results, such as differences in accessibility of the catalytic residues in uncleaved PS-1, and binding of PEN-2 by the PS-1 NF motif.

S2-01-02: Identification of novel genes and mutations in Alzheimer disease

S2-01-02: Identification of novel genes and mutations in Alzheimer disease

O4-06-04: Intraneuronal Abeta42 aggregates seed amyloid plaques and cause neuronal loss in transgenic mice with five familial Alzheimer’s disease mutations

Amyloid plaques, composed of beta–amyloid 42 (Abeta42), are defining lesions in Alzheimer's disease (AD), yet how they form and relate to neuronal loss in AD is unknown. Familial AD mutations in amyloid precursor protein (APP) and presenilins (PS1 and PS2) cause early onset AD and increase Abeta42 production, strongly suggesting that Abeta42 promotes AD pathogenesis and plaque formation. In addition, Abeta42–elevating mutations when combined in the same molecule additively increase Abeta42 production in vitro, suggesting a novel transgenic approach for driving very high Abeta42 levels and early amyloid deposition in the brain. Here, we made transgenic mice that co–express 5 familial AD mutations (5XFAD mice) to additively drive Abeta42 overproduction for studying the effects of very high cerebral Abeta42 levels on amyloid plaque formation and neurodegeneration. Thy1 promoter–driven transgenes expressing APP K670N/M671L (Swedish) + I716V (Florida) + V717I (London) and PS1 M146L+ L286V were co–injected into single cell mouse embryos to generate co–integrated, bigenic mice that bred as single transgenics. Mice were sacrificed at different ages and analyzed for amyloid pathology, neurodegeneration, and behavior using standard methods. 5XFAD mice generate Abeta42 almost exclusively. In 5XFAD brain, we observe intraneuronal Abeta42 accumulation at 1.5 months of age, before amyloid plaques form at 2 months. Importantly, intraneuronal Abeta42 aggregates occur in neuron soma and neurites and appear to seed amyloid deposits. Moreover, 5XFAD synaptophysin levels are dramatically reduced, correlating with impaired Y–maze performance, and profound neuron loss occurs in cortical layer 5 and subiculum. These results strongly suggest that intraneuronal Abeta42 aggregates cause neurodegeneration and neuron lysis, and aggregates thus released act as seeds for plaques. This model provides a coherent explanation for both neuronal loss and plaque genesis and suggests reduction of intraneuronal Abeta should be beneficial for AD.