Fragment Of Amyloid Precursor Protein Research Articles

Norepinephrine Drives Sleep Fragmentation Activation of Asparagine Endopeptidase, Locus Ceruleus Degeneration, and Hippocampal Amyloid-β42 Accumulation.

Chronic sleep disruption (CSD), from insufficient or fragmented sleep and is an important risk factor for Alzheimer's disease (AD). Underlying mechanisms are not understood. CSD in mice results in degeneration of locus ceruleus neurons (LCn) and CA1 hippocampal neurons and increases hippocampal amyloid-β42 (Aβ42), entorhinal cortex (EC) tau phosphorylation (p-tau), and glial reactivity. LCn injury is increasingly implicated in AD pathogenesis. CSD increases NE turnover in LCn, and LCn norepinephrine (NE) metabolism activates asparagine endopeptidase (AEP), an enzyme known to cleave amyloid precursor protein (APP) and tau into neurotoxic fragments. We hypothesized that CSD would activate LCn AEP in an NE-dependent manner to induce LCn and hippocampal injury. Here, we studied LCn, hippocampal, and EC responses to CSD in mice deficient in NE [dopamine β-hydroxylase (Dbh)-/-] and control male and female mice, using a model of chronic fragmentation of sleep (CFS). Sleep was equally fragmented in Dbh -/- and control male and female mice, yet only Dbh -/- mice conferred resistance to CFS loss of LCn, LCn p-tau, and LCn AEP upregulation and activation as evidenced by an increase in AEP-cleaved APP and tau fragments. Absence of NE also prevented a CFS increase in hippocampal AEP-APP and Aβ42 but did not prevent CFS-increased AEP-tau and p-tau in the EC. Collectively, this work demonstrates AEP activation by CFS, establishes key roles for NE in both CFS degeneration of LCn neurons and CFS promotion of forebrain Aβ accumulation, and, thereby, identifies a key molecular link between CSD and specific AD neural injuries.

Cellular depletion of major cathepsin proteases reveals their concerted activities for lysosomal proteolysis

Proteins delivered by endocytosis or autophagy to lysosomes are degraded by exo- and endoproteases. In humans 15 lysosomal cathepsins (CTS) act as important physiological regulators. The cysteine proteases CTSB and CTSL and the aspartic protease CTSD are the most abundant and functional important lysosomal proteinases. Whereas their general functions in proteolysis in the lysosome, their individual substrate, cleavage specificity, and their possible sequential action on substrate proteins have been previously studied, their functional redundancy is still poorly understood. To address a possible common role of highly expressed and functional important CTS proteases, we generated CTSB-, CTSD-, CTSL-, and CTSBDL-triple deficient (KO) human neuroblastoma-derived SH-SY5Y cells and CTSB-, CTSD-, CTSL-, CTSZ and CTSBDLZ-quadruple deficient (KO) HeLa cells. These cells with a combined cathepsin deficiency exhibited enlarged lysosomes and accumulated lipofuscin-like storage material. The lack of the three (SH-SY5Y) or four (HeLa) major CTSs caused an impaired autophagic flux and reduced degradation of endocytosed albumin. Proteome analyses of parental and CTS-depleted cells revealed an enrichment of cleaved peptides, lysosome/autophagy-associated proteins, and potentially endocytosed membrane proteins like the amyloid precursor protein (APP), which can be subject to endocytic degradation. Amino- and carboxyterminal APP fragments accumulated in the multiple CTS-deficient cells, suggesting that multiple CTS-mediated cleavage events regularly process APP. In summary, our analyses support the idea that different lysosomal cathepsins act in concert, have at least partially and functionally redundant substrates, regulate protein degradation in autophagy, and control cellular proteostasis, as exemplified by their involvement in the degradation of APP fragments.

Alzheimer's Disease Pathophysiology and Novel Treatment: An Update

Alzheimer’s disease, a progressive and irreversible brain disorder predominantly affecting the elderly, is influenced by age, smoking, and head trauma. It disrupts memory, cognition, motor skills, speech, and more. Alzheimer’s disease pathophysiology is caused by two main processes: the formation of misfolded amyloid-beta plaques and misfolded tau tangles. While tau is a naturally occurring, microtubule-associated protein, amyloid-beta peptides are cleaved fragments of the transmembrane amyloid precursor protein. Accumulation of these plaques and tangles result in various negative mechanisms. Regarding the relationship between the two proteins, evidence suggests that amyloid beta induces the conversion of tau from a normal to toxic state, but they ultimately work together to contribute to Alzheimer’s disease pathogenesis. As of currently, there is still no cure for the disease, and patients rely on treatment methods that solely alleviate symptoms or benefit early stages to halt the disease’s progression. The main medications for Alzheimer’s disease are cholinesterase inhibitors such as Donepezil and Galantamine, but novel pharmacological and non-pharmacological treatments are being utilized as well, such as β-secretase inhibitors and deep brain stimulation respectively. This review investigates peer-reviewed publications on pathophysiology and treatment of Alzheimer’s disease, with a focus on novel approaches for treatment and intervention.

SIL1 improves cognitive impairment in APP23/PS45 mice by regulating amyloid precursor protein processing and Aβ generation.

SIL1, an endoplasmic reticulum (ER)-resident protein, is reported to play a protective role in Alzheimer's disease (AD). However, the effect of SIL1 on amyloid precursor protein (APP) processing remains unclear. In this study, the role of SIL1 in APP processing was explored both in vitro and in vivo. In the in vitro experiment, SIL1 was either overexpressed or knocked down in cells stably expressing the human Swedish mutant APP695. In the in vivo experiment, AAV-SIL1-EGFP or AAV-EGFP was microinjected into APP23/PS45 mice and their wild-type littermates. Western blotting (WB), immunohistochemistry, RNA sequencing (RNA-seq), and behavioral experiments were performed to evaluate the relevant parameters. Results indicated that SIL1 expression decreased in APP23/PS45 mice. Overexpression of SIL1 significantly decreased the protein levels of APP, presenilin-1 (PS1), and C-terminal fragments (CTFs) of APP in vivo and in vitro. Conversely, knockdown of SIL1 increased the protein levels of APP, β-site APP cleavage enzyme 1 (BACE1), PS1, and CTFs, as well as APP mRNA expression in 2EB2 cells. Furthermore, SIL1 overexpression reduced the number of senile plaques in APP23/PS45 mice. Importantly, Y-maze and Morris Water maze tests demonstrated that SIL1 overexpression improved cognitive impairment in APP23/PS45 mice. These findings indicate that SIL1 improves cognitive impairment in APP23/PS45 mice by inhibiting APP amyloidogenic processing and suggest that SIL1 is a potential therapeutic target for AD by modulating APP processing.

Fragments of Amyloid Precursor Protein in Urine Are Novel and Practical Biomarkers for Early Screening of Dementia

AbstractBackgroundIt has been shown that Aß is a normal component in urine (Ghiso et al, FEBS Lett, 1997) and may change with disease status (Takata et al, Neurosci Lett, 2008), however, research on amyloid in urine has been neglected for long time.MethodWe examined β amyloid proteins in urine from cognitive normal and dementia patients including Alzheimer’s disease (AD) and frontotemporal dementia (FTD) using Western blotting.ResultSeveral protein fragments were identified including the 12KD and 14KD bands recognized by the anti‐APP C‐termini antibody (Ab369), 14KD and 28KD bands by W0‐2 (Figure 1), and 28KD, 56KD and 68KD bands by Aducanumab (Figure 2) and anti‐APP N‐termini antibody (22C11). Further analysis with immunoprecipitation and mass spectrometry confirmed the presence of various APP fragments and Aß in urine. One type of peptide was found to have high affinity to Aß and APP fragments using microscale thermophoresis and circular dichroism spectroscopy. With the assistance from AIBL, we further invented a lateral flow immunoassay device with colloidal gold nanoparticles coated with anti‐APP/Aß antibodies. In the early clinical trials with aged people and children, 95% of dementia patients, 90% of MCI, 85% of SMC showed positivity while 90% of healthy children were negative. The second quality examination was performed in Oriental (Dongfeng) Hospital (Pudong, Shanghai) in Mar‐June 2022. The examination of detection limit, critical threshold, repeatability, tolerance to interferences (creatinine, protein, glucose, nitrites, pH) was performed and all passed. Furthermore, 43 of 49 cases showed positive (87.7%) while only 1 out of 30 controls was positive (3.3%). Since then, the device has been tested in a dozen of large hospitals and pathology laboratories in China, all provided positive feedback. The preliminary results from 175 AIBL participants showed overall 83.8% positivity to clinically diagnosed MCI (n = 37), while for those Aβ PET scan negative MCI (n = 17), positivity was 94.1% (Figure 3).ConclusionOur results indicates the high accuracy of this device, which has high potential to be used as an early screening tool for MCI and dementia. The longitudinal studies are currently undergoing in China (Xiangya Hospital) and in Australia (AIBL).

Zein-Based Nanoparticles Improve the Therapeutic Efficacy of a TrkB Agonist toward Alzheimer's Disease.

The brain-derived neurotrophic factor (BDNF)/TrkB pathway plays a crucial role in neural plasticity and neuronal survival but is often deficient in neurodegenerative diseases like Alzheimer's disease (AD). CF3CN acts as a specific TrkB agonist that displays therapeutic effects in the AD mouse model, but its brain/plasma ratio (B/P ratio) distribution is not satisfactory. To increase its brain exposure, we synthesized several derivatives and employed nanoparticle (NP) formulation to optimize the most potent #2 derivative's in vivo PK profiles. We generated stable #2-loaded zein/lactoferrin composite NPs (#2/zein/LF) using the antisolvent co-precipitation method. In vivo PK studies revealed that nanoencapsulation improved #2's oral bioavailability by approximately 2-fold and significantly enhanced its plasma Cmax and t1/2, but the brain profiles were comparable. Pharmacodynamics showed that #2/zein/LF activates TrkB signaling that phosphorylates asparagine endopeptidase (AEP) T322 and decreases its enzymatic activity, resulting in reduced AEP-cleaved amyloid precursor protein and Tau fragments in the brains of AD mice, correlating with its PK profiles. After 3 months of treatment in 3xTg mice, #2/zein/LF decreased AD pathologies and alleviated cognitive dysfunction. Hence, zein/LF composite nanoencapsulation is a promising drug delivery method for improving the PK profiles of a potential preclinical candidate for treating neurodegenerative diseases.

HIV-1 promotes ubiquitination of the amyloidogenic C-terminal fragment of APP to support viral replication

HIV-1 replication in macrophages and microglia involves intracellular assembly and budding into modified subsets of multivesicular bodies (MVBs), which support both viral persistence and spread. However, the cellular factors that regulate HIV-1’s vesicular replication remain poorly understood. Recently, amyloid precursor protein (APP) was identified as an inhibitor of HIV-1 replication in macrophages and microglia via an unknown mechanism. Here, we show that entry of HIV-1 Gag into MVBs is blocked by the amyloidogenic C-terminal fragment of APP, “C99”, but not by the non-amyloidogenic product, “C83”. To counter this, Gag promotes multi-site ubiquitination of C99 which controls both exocytic sorting of MVBs and further processing of C99 into toxic amyloids. Processing of C99, entry of Gag into MVBs and release of infectious virus could be suppressed by expressing ubiquitination-defective C99 or by γ-secretase inhibitor treatment, suggesting that APP’s amyloidogenic pathway functions to sense and suppress HIV-1 replication in macrophages and microglia.

A large genetic screen in flies uncovers human modifiers of Aβ42 and tau toxicity

AbstractBackgroundAlzheimer’s disease (AD) is a multifactorial neurodegenerative disorder characterized by dementia and cognitive decline due to progressive cerebral cortical atrophy. Brains of AD patients are characterized by the accumulation of microscopic extracellular amyloid‐beta (Aβ) plaques and intracellular neurofibrillary tangles composed of hyperphosphorylated tau. The deposition of Aβ42, which is one of the fragments of amyloid precursor protein (APP), has been known to play a role in initiating the events leading to the formation of amyloid and subsequently hyperphosphorylation of tau. However, animal models expressing either Aβ42 or tau individually do not mimic the complexity of the human condition. Indeed, recent evidence suggests that Aβ42 and pathological tau interact synergistically to modulate neurotoxicity in AD.MethodTo shed light on their concerted roles in AD pathogenesis and to discover pathways mediating Aβ42 and tau interactions, we generated transgenic flies co‐expressing human Aβ42 fused to a signal peptide along with the longest wild‐type tau isoform.ResultOverexpression of Aβ42 or tau in Drosophila using the UAS‐Gal4 system causes mild to the moderate rough eye. In comparison, co‐expression of Aβ42 with tau causes severe roughening and reduction of the eye size. The level of neuronal cell death in eye tissues was also significantly enhanced in flies co‐expressing Aβ42 and tau. To identify pathways mediating Aβ42+tau interactions, we are currently using the Aβ42+tau eye phenotype as platform to screen 1,500 UAS lines expressing a variety of human genes.ConclusionWe have identified few enhancers and suppressors not previously known to be involved in AD pathogenesis, which will be helpful to uncover new molecular pathways and potential therapeutic targets. This work is supported by NIH grant R21AG069050 to DERL.

Familial Alzheimer’s Disease‐linked Swedish mutation impairs APP axonal transport

AbstractBackgroundIt is well‐established that most familial Alzheimer’s disease (AD) mutations alter processing of the amyloid precursor protein (APP) and perturb the balance between its proteolytic fragments. Considering different APP fragments play a role in its axonal transport, we here ask whether familial APP mutations impair axonal transport and homeostasis.MethodStem cells‐derived human neurons were transduced with either APPwt_GFP or APPswe_tRFP. Time‐lapse movies were analyzed using tracking algorithms to describe axonal transport parameters. Immunocytochemistry was performed to assess APP localization. To evaluate the impact of APPswe on other cargoes we also studied axonal transport of Rab5 endosomes.ResultProportions of movement, velocity, and distances of APPswe particles were decreased in anterograde direction compared to wt, while increased pauses and reversions were found. Accumulation of APP at the soma compared to neurite was found for APP mutant vs wt. Moreover, effect of APPswe resulted in the enlargement of Rab5 endosomes vs ctrl. Furthermore, to validate other effects of the APP mutant on Rab5, we studied its transport and found changes in some parameters compared with the ctrl.ConclusionThis work shows that APPswe impairs axonal transport. The change found on anterograde transport of APPswe, goes in hand with its accumulation at the soma vs neurite. Moreover, our results suggest that the Swedish mutation affects other proteins linked with APP, as described for the early‐endosome protein, Rab5. In line with many studies conducted on APP, our data suggest once more the importance of understanding as many mechanisms as possible involved in the biology of this protein.

Small Molecule Decoys of Aggregation for Elimination of Aβ-Peptide Toxicity.

Several lines of evidence suggest that a characteristic of the neuropathology of Alzheimer's disease (AD) is the aggregation of the amyloid beta peptides (Aβ), fragments of the human amyloid precursor protein (hAPP). The dominating species are the Aβ40 and Aβ42 fragments with 40 and 42 amino acids, respectively. Aβ initially forms soluble oligomers that continue to expand to protofibrils, suggestively the neurotoxic intermediates, and thereafter turn into insoluble fibrils that are markers of the disease. Using the powerful tool of pharmacophore simulation, we selected small molecules not known to possess central nervous system (CNS) activity but that might interact with Aβ aggregation, from the NCI Chemotherapeutic Agents Repository, Bethesda, MD. We assessed the activity of these compounds on Aβ aggregation using the thioflavin T fluorescence correlation spectroscopy (ThT-FCS) assay. Förster resonance energy transfer-based fluorescence correlation spectroscopy (FRET-FCS) was used to characterize the dose-dependent activity of selected compounds at an early stage of Aβ aggregation. Transmission electron microscopy (TEM) confirmed that the interfering substances block fibril formation and identified the macrostructures of Aβ aggregates formed in their presence. We first found three compounds generating protofibrils with branching and budding never observed in the control. One compound generated a two-dimensional sheet structure and another generated a double-stranded filament. Importantly, these compounds generating protofibrils with altered macrostructure protected against Aβ-induced toxicity in a cell model while showing no toxicity in a model of cognition in normal mice. The data suggest that the active compounds act as decoys turning the aggregation into nontoxic trajectories and pointing toward novel approaches to therapy.

Soluble form of the APP fragment, sAPPβ, positively regulates tau secretion

Extracellular tau has been highlighted in the pathogenesis of Alzheimer disease (AD), which is the most common neurodegenerative disease. Pathological analyses as well as model animal studies suggest that amyloid-β peptide (Aβ) deposition facilitates the spreading of tau aggregation pathology via extracellular tau. However, the precise mechanism of tau secretion remains unknown. Here, we show that the overexpression of amyloid precursor protein (APP) enhances the secretion of tau phosphorylated at threonine 181 in mouse neuroblastoma Neuro2a cells. Moreover, we found that soluble amyloid precursor protein β (sAPPβ), which is generated by β-site APP cleaving enzyme 1 (BACE1), mediates tau secretion. Our results demonstrate that BACE1-mediated cleavage of APP plays pathological roles in AD pathogenesis by not only Aβ production, but by the spreading of tau aggregation pathology via sAPPβ in AD patients.

Soluble amyloid-β dimers are resistant to amyloid-β prion conversion in vivo suggesting antiprion properties.

According to the instructions for authors, short communications should be published without abstract.

The η-secretase-derived APP fragment ηCTF is localized in Golgi, endosomes and extracellular vesicles and contributes to Aβ production

The processing of the amyloid precursor protein (APP) is one of the key events contributing to Alzheimer’s disease (AD) etiology. Canonical cleavages by β- and γ-secretases lead to Aβ production which accumulate in amyloid plaques. Recently, the matrix metalloprotease MT5-MMP, referred to as η-secretase, has been identified as a novel APP cleaving enzyme producing a transmembrane fragment, ηCTF that undergoes subsequent cleavages by α- and β-secretases yielding the Aηα and Aηβ peptides, respectively. The functions and contributions of ηCTF and its related fragments to AD pathology are poorly understood. In this study, we designed a novel immunological probe referred to as ηCTF-NTer antibody that specifically interacts with the N-terminal part of ηCTF targeting ηCTF, Aηα, Aηβ but not C99, C83 and Aβ. We examined the fate and localization of ηCTF fragment in various cell models and in mice. We found that overexpressed ηCTF undergoes degradation in the proteasomal and autophagic pathways and accumulates mainly in the Golgi and in endosomes. Moreover, we observed the presence of ηCTF in small extracellular vesicles purified from neuroblastoma cells or from mouse brains expressing ηCTF. Importantly, the expression of ηCTF in fibroblasts devoid on APP leads to Aβ production demonstrating its contribution to the amyloidogenic pathway. Finally, we observed an ηCTF-like immunoreactivity around amyloid plaques and an age-dependent accumulation of ηCTF in the triple-transgenic mouse AD model. Thus, our study suggests that the ηCTF fragment likely contributes to AD pathology by its exosomal spreading and involvement in Aβ production.

Pharmacological Inhibition of p-21 Activated Kinase (PAK) Restores Impaired Neurite Outgrowth and Remodeling in a Cellular Model of Down Syndrome.

Down syndrome (DS) is characterized by the trisomy of chromosome 21 and by cognitive deficits that have been related to neuronal morphological alterations in humans, as well as in animal models. The gene encoding for amyloid precursor protein (APP) is present in autosome 21, and its overexpression in DS has been linked to neuronal dysfunction, cognitive deficit, and Alzheimer's disease-like dementia. In particular, the neuronal ability to extend processes and branching is affected. Current evidence suggests that APP could also regulate neurite growth through its role in the actin cytoskeleton, in part by influencing p21-activated kinase (PAK) activity. The latter effect is carried out by an increased abundance of the caspase cleavage-released carboxy-terminal C31 fragment. In this work, using a neuronal cell line named CTb, which derived from the cerebral cortex of a trisomy 16 mouse, an animal model of human DS, we observed an overexpression of APP, elevated caspase activity, augmented cleavage of the C-terminal fragment of APP, and increased PAK1 phosphorylation. Morphometric analyses showed that inhibition of PAK1 activity with FRAX486 increased the average length of the neurites, the number of crossings per Sholl ring, the formation of new processes, and stimulated the loss of processes. Considering our results, we propose that PAK hyperphosphorylation impairs neurite outgrowth and remodeling in the cellular model of DS, and therefore we suggest that PAK1 may be a potential pharmacological target.

Expression of Amyloid Precursor Protein, Caveolin-1, Alpha-, Beta-, and Gamma-Secretases in Penumbra Cells after Photothrombotic Stroke and Evaluation of Neuroprotective Effect of Secretase and Caveolin-1 Inhibitors.

Our studies reveal changes in the expression of the main participants in the processing of amyloid precursor protein (APP) in neurons and astrocytes after photothrombotic stroke (PTS). Here we show the increase in the level of N- and C-terminal fragments of APP in the cytoplasm of ischemic penumbra cells at 24 h after PTS and their co-immunoprecipitation with caveolin-1. The ADAM10 α-secretase level decreased in the rat brain cortex on the first day after PTS. Levels of γ-secretase complex proteins presenilin-1 and nicastrin were increased in astrocytes, but not in neurons, in the penumbra after PTS. Inhibitory analysis showed that these changes lead to neuronal death and activation of astrocytes in the early recovery period after PTS. The caveolin-1 inhibitor daidzein shifted APP processing towards Aβ synthesis, which caused astroglial activation. γ-secretase inhibitor DAPT down-regulated glial fibrillary acidic protein (GFAP) in astrocytes, prevented mouse cerebral cortex cells from PTS-induced apoptosis, and reduced the infarction volume. Thus, new generation γ-secretase inhibitors may be considered as potential agents for the treatment of stroke.

COOH-terminal fragment of APP interacts with p62, forms an aggregate, and induces autophagic degradation in Alzheimer's cell model.

Alzheimer's disease is an intractable disease, and the accumulation of amyloid β in the brain is thought to be involved in the onset of the disease. Additionally, abnormal protein accumulation due to autophagic deficiency may also be involved in disease progression. Autophagy involves a mechanism called selective autophagy. However, the relationship between selective autophagy and the amyloid precursor protein (APP) remains unclear. In the present study, we analyzed the interaction between p62, an adapter protein, and an APP-related molecule and found that p62 interacted with the COOH-terminal fragment of APP (C60). When C60 and p62 are overexpressed, aggregates are formed and C60 is degraded by autophagy. These aggregates cannot be easily degraded, even with a reducing agent. We also found that autophagosome- and lysosome marker-positive vesicles were formed in the C60- and p62-expressing cells. Superresolution technology also revealed that p62-C60-positive autophagosomes were formed in the cells. Overall, these results suggest that p62 may bind with C60 to form aggregates and induce autophagy in autophagosomes. These results reveal one of the mechanisms underlying the progression of Alzheimer's disease, in which selective autophagy may be involved.

The AICD fragment of APP initiates a FoxO3a mediated response via FANCD2

The amyloid precursor protein (APP) is a cell surface protein of uncertain function that is notable for being the parent protein of beta-amyloid. Research around this protein has focussed heavily on the link to Alzheimer's disease and neurodegeneration. However, there is increasing evidence that APP may be linked to neuronal loss through mechanisms independent of beta-amyloid. FoxO3a is a transcription factor associated with neuronal longevity and apoptosis. In neurons, FoxO3a is associated with cell death through pathways that include BIM, a BCL-2 family member. In this study we have shown that APP overexpression increased the cellular levels and activity of FoxO3a. This increased expression and activity is not a result of decreased phosphorylation but is more likely a result of increased nuclear stability due to increased levels of FANCD2, a binding partner of FoxO3a. The changes caused by APP overexpression were shown to be due to the AICD fragment of APP possibly directly inducing transcription increase in FANCD2. These findings strengthen the link between APP metabolism and FoxO3a neuronal activity. This link may be crucial in better understanding the cellular role of APP and its link to neurodegeneration and aging.

Genetic Mapping of APP and Amyloid-β Biology Modulation by Trisomy 21.

Individuals who have Down syndrome (DS) frequently develop early onset Alzheimer’s disease (AD), a neurodegenerative condition caused by the build-up of aggregated amyloid-β and tau proteins in the brain. Amyloid-β is produced by amyloid precursor protein (APP), a gene located on chromosome 21. People who have Down syndrome have three copies of chromosome 21 and thus also an additional copy of APP; this genetic change drives the early development of Alzheimer’s disease in these individuals. Here we use a combination of next-generation mouse models of Down syndrome (Tc1, Dp3Tyb, Dp(10)2Yey and Dp(17)3Yey) and a knockin mouse model of amyloid-β accumulation (AppNL-F) to determine how chromosome 21 genes, other than APP, modulate APP/amyloid-β in the brain when in three copies. Using both male and female mice, we demonstrate that three copies of other chromosome 21 genes are sufficient to partially ameliorate amyloid-β accumulation in the brain. We go on to identify a subregion of chromosome 21 that contains the gene/genes causing this decrease in amyloid-β accumulation and investigate the role of two lead candidate genes Dyrk1a and Bace2. Thus an additional copy of chromosome 21 genes, other than APP, can modulate APP/amyloid-β in the brain under physiological conditions. This work provides critical mechanistic insight into the development of disease and an explanation for the typically later age of onset of dementia in people who have ADDS, compared to those who have familial AD caused by triplication of APP.

Proteasome activity modulates amyloid toxicity.

Alzheimer's disease (AD) is responsible for 60%-80% of identified cases of dementia. While the generation and accumulation of amyloid precursor protein (APP) fragments is accepted as a key step in AD pathogenesis, the precise role of these fragments remains poorly understood. To overcome this deficit, we induced the expression of the soluble C-terminal fragment of APP (C99), the rate-limiting peptide for the generation of amyloid fragments, in yeast that contain thermosensitive mutations in genes encoding proteasome subunits. Our previous work with this system demonstrated that these proteasome-deficient yeast cells, expressing C99 when proteasome activity was blunted, generated amyloid fragments similar to those observed in AD patients. We now report the phenotypic repercussions of inducing C99 expression in proteasome-deficient cells. We show increased levels of protein aggregates, cellular stress and chaperone expression, electron-dense accumulations in the nuclear envelope/ER, abnormal DNA condensation, and an induction of apoptosis. Taken together, these findings suggest that the generation of C99 and its associated fragments in yeast cells with compromised proteasomal activity results in phenotypes that may be relevant to the neuropathological processes observed in AD patients. These data also suggest that this yeast model should be useful for testing therapeutics that target AD-associated amyloid, since it allows for the assessment of the reversal of the perturbed cellular physiology observed when degradation pathways are dysfunctional.

An advanced yeast model to investigate the interplay between structure and function of human gamma-secretase and its substrates

The promiscuous nature of the Alzheimer’s disease associated gamma-secretase (gSec) amongst its substrates remains mysterious after decades of research. In contrast to most other aspartate proteases, gSec cleaves its substrates within the hydrophobic transmembrane domain (TMD), releases an intracellular domain (ICD) and further processes the remaining fragment prior release into the extracellular compartment. Aggregation of the extracellular fragment of the substrate Amyloid Precursor Protein (APP) is related to Alzheimer’s disease.