Mice deficient in BACE1, the Alzheimer's beta-secretase, have normal phenotype and abolished beta-amyloid generation

Cholinergic Surveillance over Hippocampal RNA Metabolism and Alzheimer's-Like Pathology

The relationship between long-term cholinergic dysfunction and risk of developing dementia is poorly understood. Here we used mice with deletion of the vesicular acetylcholine transporter (VAChT) in the forebrain to model cholinergic abnormalities observed in dementia. Whole-genome RNA sequencing of hippocampal samples revealed that cholinergic failure causes changes in RNA metabolism. Remarkably, key transcripts related to Alzheimer's disease are affected. BACE1, for instance, shows abnormal splicing caused by decreased expression of the splicing regulator hnRNPA2/B1. Resulting BACE1 overexpression leads to increased APP processing and accumulation of soluble Aβ1-42. This is accompanied by age-related increases in GSK3 activation, tau hyperphosphorylation, caspase-3 activation, decreased synaptic markers, increased neuronal death, and deteriorating cognition. Pharmacological inhibition of GSK3 hyperactivation reversed deficits in synaptic markers and tau hyperphosphorylation induced by cholinergic dysfunction, indicating a key role for GSK3 in some of these pathological changes. Interestingly, in human brains there was a high correlation between decreased levels of VAChT and hnRNPA2/B1 levels with increased tau hyperphosphorylation. These results suggest that changes in RNA processing caused by cholinergic loss can facilitate Alzheimer's-like pathology in mice, providing a mechanism by which decreased cholinergic tone may increase risk of dementia.

BACE1 Deficiency Causes Abnormal Neuronal Clustering in the Dentate Gyrus

BACE1 is validated as Alzheimer's β-secretase and a therapeutic target for Alzheimer's disease. In examining BACE1-null mice, we discovered that BACE1 deficiency develops abnormal clusters of immature neurons, forming doublecortin-positive neuroblasts, in the developing dentate gyrus, mainly in the subpial zone (SPZ). Such clusters were rarely observed in wild-type SPZ and not reported in other mouse models. To understand their origins and fates, we examined how neuroblasts in BACE1-null SPZ mature and migrate during early postnatal development. We show that such neuroblasts are destined to form Prox1-positive granule cells in the dentate granule cell layer, and mainly mature to form excitatory neurons, but not inhibitory neurons. Mechanistically, higher levels of reelin potentially contribute to abnormal neurogenesis and timely migration in BACE1-null SPZ. Altogether, we demonstrate that BACE1 is a critical regulator in forming the dentate granule cell layer through timely maturation and migration of SPZ neuroblasts.

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BACE1 deficiency causes abnormal neuronal clusters retained in the mouse SPZ

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Mis-migrated neural progenitor cells in the SPZ are destined to form granule cells

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Such neural progenitor cells form excitatory neurons but not inhibitor neurons

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Elevated levels of reelin contribute to abnormal neuronal maturation and migration

Full-length cellular β-secretase has a trimeric subunit stoichiometry, and its sulfur-rich transmembrane interaction site modulates cytosolic copper compartmentalization

The β-secretase (BACE1) initiates processing of the amyloid precursor protein (APP) into Aβ peptides, which have been implicated as central players in the pathology of Alzheimer disease. BACE1 has been described as a copper-binding protein and its oligomeric state as being monomeric, dimeric, and/or multimeric, but the native cellular stoichiometry has remained elusive. Here, by using single-molecule fluorescence and in vitro cross-linking experiments with photo-activatable unnatural amino acids, we show that full-length BACE1, independently of its subcellular localization, exists as trimers in human cells. We found that trimerization requires the BACE1 transmembrane sequences (TMSs) and cytoplasmic domains, with residues Ala⁴⁶³ and Cys⁴⁶⁶ buried within the trimer interface of the sulfur-rich core of the TMSs. Our 3D model predicts that the sulfur-rich core of the trimeric BACE1 TMS is accessible to metal ions, but copper ions did not trigger trimerization. The results of functional assays of endogenous BACE1 suggest that it has a role in intracellular copper compartmentalization by transferring cytosolic copper to intracellular compartments, while leaving the overall cellular copper concentration unaltered. Adding to existing physiological models, our results provide novel insight into the atypical interactions between copper and BACE1 and into its non-enzymatic activities. In conclusion, therapeutic Alzheimer disease prevention strategies aimed at decreasing BACE1 protein levels should be regarded with caution, because adverse effects in copper homeostasis may occur.

Inhibition of Early Growth Response 1 in the Hippocampus Alleviates Neuropathology and Improves Cognition in an Alzheimer Model with Plaques and Tangles

A sporadic form of Alzheimer disease (AD) and vascular dementia share many risk factors, and their pathogenic mechanisms are suggested to be related. Transcription factor early growth response 1 (Egr-1) regulates various vascular pathologies and is up-regulated in both AD brains and AD mouse models; however, its role in AD pathogenesis is unclear. Herein, we report that silencing of Egr-1 in the hippocampus by shRNA reduces tau phosphorylation, lowers amyloid-β (Aβ) pathology, and improves cognition in the 3xTg-AD mouse model. Egr-1 silencing does not affect levels of cyclin-dependent protein kinase 5 (Cdk5), glycogen synthase kinase 3β, protein phosphatase 1, or protein phosphatase 2A, but reduces p35 subunit of Cdk5. Egr-1 silencing also reduces levels of β-secretase 1 (BACE-1) and BACE-1-cleaved amyloid precursor protein (APP) metabolites (secreted APPβ, C99, Aβ40, and Aβ42) but has no effect on presenilin 1 and presenilin 2. In hippocampal primary neurons, Egr-1 binds to BACE-1 and p35 promoters, enhances tau phosphorylation, activates Cdk5 and BACE-1, and accelerates amyloidogenic APP processing. Blocking Cdk5 action blocks Egr-1-induced tau phosphorylation but has no effect on BACE-1 activation and amyloidogenic APP processing. Blocking BACE-1 action, on the other hand, blocks Egr-1-induced amyloidogenic APP processing but does not affect tau phosphorylation. Egr-1 regulates tau phosphorylation and Aβ synthesis in the brain by respectively controlling activities of Cdk5 and BACE-1, suggesting that Egr-1 is a potential therapeutic candidate for the treatment of AD.

Inhibition of Wnt signaling induces amyloidogenic processing of amyloid precursor protein and the production and aggregation of Amyloid-β (Aβ)42 peptides

Alzheimer's disease (AD) is the most common neurodegenerative disorder and the most frequent cause of dementia in the aged population. According to the amyloid hypothesis, the amyloid-β (Aβ) peptide plays a key role in the pathogenesis of AD. Aβ is generated from the amyloidogenic processing of amyloid precursor protein and can aggregate to form oligomers, which have been described as a major synaptotoxic agent in neurons. Dysfunction of Wnt signaling has been linked to increased Aβ formation; however, several other studies have argued against this possibility. Herein, we use multiple experimental approaches to confirm that the inhibition of Wnt signaling promoted the amyloidogenic proteolytic processing of amyloid precursor protein. We also demonstrate that inhibiting Wnt signaling increases the production of the Aβ₄₂ peptide, the Aβ₄₂ /Aβ₄₀ ratio, and the levels of Aβ oligomers such as trimers and tetramers. Moreover, we show that activating Wnt signaling reduces the levels of Aβ₄₂ and its aggregates, increases Aβ₄₀ levels, and reduces the Aβ₄₂ /Aβ₄₀ ratio. Finally, we show that the protective effects observed in response to activation of the Wnt pathway rely on β-catenin-dependent transcription, which is demonstrated experimentally via the expression of various 'mutant forms of β-catenin'. Together, our findings indicate that loss of the Wnt signaling pathway may contribute to the pathogenesis of AD.

Design, synthesis, and X-ray structural studies of BACE-1 inhibitors containing substituted 2-oxopiperazines as P1'-P2' ligands

We report the design and synthesis of a series of BACE1 inhibitors incorporating mono- and bicyclic 6-substituted 2-oxopiperazines as novel P1' and P2' ligands and isophthalamide derivative as P2-P3 ligands. Among mono-substituted 2-oxopiperazines, inhibitor 5a with N-benzyl-2-oxopiperazine and isophthalamide showed potent BACE1 inhibitory activity (Ki=2nM). Inhibitor 5g, with N-benzyl-2-oxopiperazine and substituted indole-derived P2-ligand showed a reduction in potency. The X-ray crystal structure of 5g-bound BACE1 was determined and used to design a set of disubstituted 2-oxopiperazines and bicyclic derivatives that were subsequently investigated. Inhibitor 6j with an oxazolidinone derivative showed a BACE1 inhibitory activity of 23nM and cellular EC50 of 80nM.

Design and synthesis of bicyclic acetals as Beta Secretase (BACE1) inhibitors

Taking advantage of the structural similarity between aspartic proteases, small-molecule peptidomimetic inhibitors that already showed activity towards Secreted Aspartic Protease 2 as anti-Candida agents and HIV protease inhibitors were exploited as potential BACE1 inhibitors. A focused library of 6,8-dioxa-3-azabicyclo[3.2.1]-octane peptidomimetic scaffolds was synthesized and assayed towards BACE1 enzyme, resulting in the identification of a thiolactam-containing hit compound possessing IC₅₀ in the low micromolar range, and confirming the bicyclic acetal portion as a potential transition state analogue in the interaction with catalytic aspartic acid residues.

BACE1 across species: a comparison of the in vivo consequences of BACE1 deletion in mice and rats

Assessing BACE1 (β-site APP cleaving enzyme 1) knockout mice for general health and neurological function may be useful in predicting risks associated with prolonged pharmacological BACE1 inhibition, a treatment approach currently being developed for Alzheimer’s disease. To determine whether BACE1 deletion-associated effects in mice generalize to another species, we developed a novel Bace1^−/− rat line using zinc-finger nuclease technology and compared Bace1^−/− mice and rats with their Bace1^+/+ counterparts. Lack of BACE1 was confirmed in Bace1^−/− animals from both species. Removal of BACE1 affected startle magnitude, balance beam performance, pain response, and nerve myelination in both species. While both mice and rats lacking BACE1 have shown increased mortality, the increase was smaller and restricted to early developmental stages for rats. Bace1^−/− mice and rats further differed in body weight, spontaneous locomotor activity, and prepulse inhibition of startle. While the effects of species and genetic background on these phenotypes remain difficult to distinguish, our findings suggest that BACE1’s role in myelination and some sensorimotor functions is consistent between mice and rats and may be conserved in other species. Other phenotypes differ between these models, suggesting that some effects of BACE1 inhibition vary with the biological context (e.g. species or background strain).

Chronic Sleep Restriction Induces Cognitive Deficits and Cortical Beta-Amyloid Deposition in Mice via BACE1-Antisense Activation

AIMS

To clarify the correlation between chronic sleep restriction (CSR) and sporadic Alzheimer disease (AD), we determined in wild-type mice the impact of CSR, on cognitive performance, beta-amyloid (Aβ) peptides, and its feed-forward regulators regarding AD pathogenesis.

METHODS

Sixteen nine-month-old C57BL/6 male mice were equally divided into the CSR and control groups. CSR was achieved by application of a slowly rotating drum for 2 months. The Morris water maze test was used to assess cognitive impairment. The concentrations of Aβ peptides, amyloid precursor protein (APP) and β-secretase 1 (BACE1), and the mRNA levels of BACE1 and BACE1-antisense (BACE1-AS) were measured.

RESULTS

Following CSR, impairments of spatial learning and memory consolidation were observed in the mice, accompanied by Aβ plaque deposition and an increased Aβ concentration in the prefrontal and temporal lobe cortex. CSR also upregulated the β-secretase-induced cleavage of APP by increasing the protein and mRNA levels of BACE1, particularly the BACE1-AS.

CONCLUSIONS

This study shows that a CSR accelerates AD pathogenesis in wild-type mice. An upregulation of the BACE1 pathway appears to participate in both cortical Aβ plaque deposition and memory impairment caused by CSR. BACE1-AS is likely activated to initiate a cascade of events that lead to AD pathogenesis. Our study provides, therefore, a molecular mechanism that links CSR to sporadic AD.

Future Therapeutics in Alzheimer's Disease: Development Status of BACE Inhibitors

Alzheimer's disease (AD) is the primary cause of dementia in the elderly. It remains incurable and poses a huge socio-economic challenge for developed countries with an aging population. AD manifests by progressive decline in cognitive functions and alterations in behaviour, which are the result of the extensive degeneration of brain neurons. The AD pathogenic mechanism involves the accumulation of amyloid beta peptide (Aβ), an aggregating protein fragment that self-associates to form neurotoxic fibrils that trigger a cascade of cellular events leading to neuronal injury and death. Researchers from academia and the pharmaceutical industry have pursued a rational approach to AD drug discovery and targeted the amyloid cascade. Schemes have been devised to prevent the overproduction and accumulation of Aβ in the brain. The extensive efforts of the past 20 years have been translated into bringing new drugs to advanced clinical trials. The most progressed mechanism-based therapies to date consist of immunological interventions to clear Aβ oligomers, and pharmacological drugs to inhibit the secretase enzymes that produce Aβ, namely β-site amyloid precursor-cleaving enzyme (BACE) and γ-secretase. After giving an update on the development and current status of new AD therapeutics, this review will focus on BACE inhibitors and, in particular, will discuss the prospects of verubecestat (MK-8931), which has reached phase III clinical trials.

Aberrant proteolytic processing and therapeutic strategies in Alzheimer disease

Amyloid-β peptide (Aβ) and tau are major components of senile plaques and neurofibrillary tangles, respectively, deposited in the brains of Alzheimer disease (AD) patients. Aβ is derived from amyloid-β precursor protein that is sequentially cleaved by two aspartate proteases, β- and γ-secretases. Secreted Aβ is then catabolized by several proteases. Several lines of evidence suggest that accumulation of Aβ by increased production or decreased degradation induces the tau-mediated neuronal toxicity and symptomatic manifestations of AD. Thus, the dynamics of cerebral Aβ, called as "Aβ economy", would be the mechanistic basis of AD pathogenesis. Partial loss of γ-secretase activity leads to the increased generation of toxic Aβ isoforms, indicating that activation of γ-secretase would provide a beneficial effect for AD. After extensive discovery and development efforts, BACE1, which is a β-secretase enzyme, has emerged as a prime drug target for lowering brain Aβ levels. Recent studies revealed the decreased clearance of Aβ in sporadic AD patients, suggesting the importance of the catabolic mechanism in the pathogenesis of AD. I will discuss with these proteolytic mechanisms involved in the regulation of Aβ economy, and development of effective treatment and diagnostics for AD.

The Metalloprotease Meprin β Is an Alternative β-Secretase of APP

The membrane bound metalloprotease meprin β is important for collagen fibril assembly in connective tissue formation and for the detachment of the intestinal mucus layer for proper barrier function. Recent proteomic studies revealed dozens of putative new substrates of meprin β, including the amyloid precursor protein (APP). It was shown that APP is cleaved by meprin β in distinct ways, either at the β-secretase site resulting in increased levels of Aβ peptides, or at the N-terminus releasing 11 kDa, and 20 kDa peptide fragments. The latter event was discussed to be rather neuroprotective, whereas the ectodomain shedding of APP by meprin β reminiscent to BACE-1 is in line with the amyloid hypothesis of Alzheimer's disease, promoting neurodegeneration. The N-terminal 11 kDa and 20 kDa peptide fragments represent physiological cleavage products, since they are found in human brains under different diseased or non-diseased states, whereas these fragments are completely missing in brains of meprin β knock-out animals. Meprin β is not only a sheddase of adhesion molecules, such as APP, but was additionally demonstrated to cleave within the prodomain of ADAM10. Activated ADAM10, the α-secretase of APP, is then able to shed meprin β from the cell surface thereby abolishing the β-secretase activity. All together meprin β seems to be a novel player in APP processing events, even influencing other enzymes involved in APP cleavage.

Multiple Mechanisms Linking Type 2 Diabetes and Alzheimer's Disease: Testosterone as a Modifier

Evidence in support of links between type-2 diabetes mellitus (T2DM) and Alzheimer's disease (AD) has increased considerably in recent years. AD pathological hallmarks include the accumulation of extracellular amyloid-β (Aβ) and intracellular hyperphosphorylated tau in the brain, which are hypothesized to promote inflammation, oxidative stress, and neuronal loss. T2DM exhibits many AD pathological features, including reduced brain insulin uptake, lipid dysregulation, inflammation, oxidative stress, and depression; T2DM has also been shown to increase AD risk, and with increasing age, the prevalence of both conditions increases. In addition, amylin deposition in the pancreas is more common in AD than in normal aging, and although there is no significant increase in cerebral Aβ deposition in T2DM, the extent of Aβ accumulation in AD correlates with T2DM duration. Given these similarities and correlations, there may be common underlying mechanism(s) that predispose to both T2DM and AD. In other studies, an age-related gradual loss of testosterone and an increase in testosterone resistance has been shown in men; low testosterone levels can also occur in women. In this review, we focus on the evidence for low testosterone levels contributing to an increased risk of T2DM and AD, and the potential of testosterone treatment in reducing this risk in both men and women. However, such testosterone treatment may need to be long-term, and would need regular monitoring to maintain testosterone at physiological levels. It is possible that a combination of testosterone therapy together with a healthy lifestyle approach, including improved diet and exercise, may significantly reduce AD risk.

ER Stress and Neurodegenerative Disease: A Cause or Effect Relationship?

The accumulation of protein aggregates has a fundamental role in the patophysiology of distinct neurodegenerative diseases. This phenomenon may have a common origin, where disruption of intracellular mechanisms related to protein homeostasis (here termed proteostasis) control during aging may result in abnormal protein aggregation. The unfolded protein response (UPR) embodies a major element of the proteostasis network triggered by endoplasmic reticulum (ER) stress. Chronic ER stress may operate as possible mechanism of neurodegenerative and synaptic dysfunction, and in addition contribute to the abnormal aggregation of key disease-related proteins. In this article we overview the most recent findings suggesting a causal role of ER stress in neurodegenerative diseases.

Mechanisms of Melatonin in Alleviating Alzheimer's Disease

Alzheimer's disease (AD) is a chronic, progressive and prevalent neurodegenerative disease characterized by the loss of higher cognitive functions and an associated loss of memory. The thus far "incurable" stigma for AD prevails because of variations in the success rates of different treatment protocols in animal and human studies. Among the classical hypotheses explaining AD pathogenesis, the amyloid hypothesis is currently being targeted for drug development. The underlying concept is to prevent the formation of these neurotoxic peptides which play a central role in AD pathology and trigger a multispectral cascade of neurodegenerative processes post-aggregation. This could possibly be achieved by pharmacological inhibition of β- or γ-secretase or stimulating the nonamyloidogenic α-secretase. Melatonin the pineal hormone is a multifunctioning indoleamine. Production of this amphiphilic molecule diminishes with advancing age and this decrease runs parallel with the progression of AD which itself explains the potential benefits of melatonin in line of development and devastating consequences of the disease progression. Our recent studies have revealed a novel mechanism by which melatonin stimulates the nonamyloidogenic processing and inhibits the amyloidogenic processing of β-amyloid precursor protein (βAPP) by stimulating α -secretases and consequently down regulating both β- and γ-secretases at the transcriptional level. In this review, we discuss and evaluate the neuroprotective functions of melatonin in AD pathogenesis, including its role in the classical hypotheses in cellular and animal models and clinical interventions in AD patients, and suggest that with early detection, melatonin treatment is qualified to be an anti-AD therapy.

Chemoproteomic profiling reveals that cathepsin D off-target activity drives ocular toxicity of β-secretase inhibitors

Inhibition of β-secretase BACE1 is considered one of the most promising approaches for treating Alzheimer's disease. Several structurally distinct BACE1 inhibitors have been withdrawn from development after inducing ocular toxicity in animal models, but the target mediating this toxicity has not been identified. Here we use a clickable photoaffinity probe to identify cathepsin D (CatD) as a principal off-target of BACE1 inhibitors in human cells. We find that several BACE1 inhibitors blocked CatD activity in cells with much greater potency than that displayed in cell-free assays with purified protein. Through a series of exploratory toxicology studies, we show that quantifying CatD target engagement in cells with the probe is predictive of ocular toxicity in vivo. Taken together, our findings designate off-target inhibition of CatD as a principal driver of ocular toxicity for BACE1 inhibitors and more generally underscore the power of chemical proteomics for discerning mechanisms of drug action.

Several β-secretase (BACE) inhibitors exhibit unexplained ocular toxicity in preclinical studies. Here the authors generate a clickable photoaffinity probe to interrogate off-targets in cells and animals, and identify inhibition of cathepsin D as a driver of ocular toxicity.

Modulation of Kv7 channels and excitability in the brain

Neuronal Kv7 channels underlie a voltage-gated non-inactivating potassium current known as the M-current. Due to its particular characteristics, Kv7 channels show pronounced control over the excitability of neurons. We will discuss various factors that have been shown to drastically alter the activity of this channel such as protein and phospholipid interactions, phosphorylation, calcium, and numerous neurotransmitters. Kv7 channels locate to key areas for the control of action potential initiation and propagation. Moreover, we will explore the dynamic surface expression of the channel modulated by neurotransmitters and neural activity. We will also focus on known principle functions of neural Kv7 channels: control of resting membrane potential and spiking threshold, setting the firing frequency, afterhyperpolarization after burst firing, theta resonance, and transient hyperexcitability from neurotransmitter-induced suppression of the M-current. Finally, we will discuss the contribution of altered Kv7 activity to pathologies such as epilepsy and cognitive deficits.

Aβ-Degrading Proteases: Therapeutic Potential in Alzheimer Disease

The amyloid β-protein (Aβ) plays an indispensable role in the pathogenesis of Alzheimer disease (AD). Aβ is subject to proteolytic degradation by a diverse array of peptidases and proteinases, known collectively as Aβ-degrading proteases (AβDPs). A growing number of AβDPs have been identified that impact Aβ powerfully and in a surprising variety of ways. As such, AβDPs hold considerable therapeutic potential for the treatment and/or prevention of AD. Here, we critically review the relative merits of therapeutic strategies targeting AβDPs compared with current Aβ-lowering strategies focused on immunotherapies and pharmacological modulation of Aβ-producing enzymes. Several innovative advances have increased considerably the feasibility of delivering AβDPs to the brain or enhancing their activity in a non-invasive manner. We argue that therapies targeting AβDPs offer numerous potential advantages that should be explored through continued research into this promising field.

Presynaptic dystrophic neurites surrounding amyloid plaques are sites of microtubule disruption, BACE1 elevation, and increased Aβ generation in Alzheimer's disease

Alzheimer’s disease (AD) is characterized by amyloid plaques composed of the β-amyloid (Aβ) peptide surrounded by swollen presynaptic dystrophic neurites consisting of dysfunctional axons and terminals that accumulate the β-site amyloid precursor protein (APP) cleaving enzyme (BACE1) required for Aβ generation. The cellular and molecular mechanisms that govern presynaptic dystrophic neurite formation are unclear, and elucidating these processes may lead to novel AD therapeutic strategies. Previous studies suggest Aβ may disrupt microtubules, which we hypothesize have a critical role in the development of presynaptic dystrophies. To investigate this further, here we have assessed the effects of Aβ, particularly neurotoxic Aβ42, on microtubules during the formation of presynaptic dystrophic neurites in vitro and in vivo. Live-cell imaging of primary neurons revealed that exposure to Aβ42 oligomers caused varicose and beaded neurites with extensive microtubule disruption, and inhibited anterograde and retrograde trafficking. In brain sections from AD patients and the 5XFAD transgenic mouse model of amyloid pathology, dystrophic neurite halos with BACE1 elevation around amyloid plaques exhibited aberrant tubulin accumulations or voids. At the ultrastructural level, peri-plaque dystrophies were strikingly devoid of microtubules and replete with multi-lamellar vesicles resembling autophagic intermediates. Proteins of the microtubule motors, kinesin and dynein, and other neuronal proteins were aberrantly localized in peri-plaque dystrophies. Inactive pro-cathepsin D also accumulated in peri-plaque dystrophies, indicating reduced lysosomal function. Most importantly, BACE1 accumulation in peri-plaque dystrophies caused increased BACE1 cleavage of APP and Aβ generation. Our study supports the hypothesis that Aβ induces microtubule disruption in presynaptic dystrophic neurites that surround plaques, thus impairing axonal transport and leading to accumulation of BACE1 and exacerbation of amyloid pathology in AD.

Functions of the Alzheimer's Disease Protease BACE1 at the Synapse in the Central Nervous System

Inhibition of the protease β-site amyloid precursor protein-cleaving enzyme 1 (BACE1) is a promising treatment strategy for Alzheimer's disease, and a number of BACE inhibitors are currently progressing through clinical trials. The strategy aims to decrease production of amyloid-β (Aβ) peptide from the amyloid precursor protein (APP), thus reducing or preventing Aβ toxicity. Over the last decade, it has become clear that BACE1 proteolytically cleaves a number of substrates in addition to APP. These substrates are not known to be involved in the pathogenesis of Alzheimer's disease but have other roles in the developing and/or mature central nervous system. Consequently, BACE inhibition and knockout in mice results in synaptic and other neuronal dysfunctions and the key substrates responsible for these deficits are still being elucidated. Of the BACE1 substrates that have been validated to date, a number may contribute to the synaptic deficits seen with BACE blockade, including neuregulin 1, close homologue of L1 and seizure-related gene 6. It is important to understand the impact that BACE blockade may have on these substrates and other proteins detected in substrate screens and, if necessary, develop substrate-selective BACE inhibitors.

Stepping closer to treating Alzheimer's disease patients with BACE1 inhibitor drugs

Alzheimer’s disease (AD) is the most common age-dependent neurodegenerative disease which impairs cognitive function and gradually causes patients to be unable to lead normal daily lives. While the etiology of AD remains an enigma, excessive accumulation of β-amyloid peptide (Aβ) is widely believed to induce pathological changes and cause dementia in brains of AD patients. BACE1 was discovered to initiate the cleavage of amyloid precursor protein (APP) at the β-secretase site. Only after this cleavage does γ-secretase further cleave the BACE1-cleaved C-terminal APP fragment to release Aβ. Hence, blocking BACE1 proteolytic activity will suppress Aβ generation. Due to the linkage of Aβ to the potential cause of AD, extensive discovery and development efforts have been directed towards potent BACE1 inhibitors for AD therapy. With the recent breakthrough in developing brain-penetrable BACE1 inhibitors, targeting amyloid deposition-mediated pathology for AD therapy has now become more practical. This review will summarize various strategies that have successfully led to the discovery of BACE1 drugs, such as MK8931, AZD-3293, JNJ-54861911, E2609 and CNP520. These drugs are currently in clinical trials and their updated states will be discussed. With the promise of reducing Aβ generation and deposition with no alarming safety concerns, the amyloid cascade hypothesis in AD therapy may finally become validated.

Lamotrigine Reduces β-Site AβPP-Cleaving Enzyme 1 Protein Levels Through Induction of Autophagy

Lamotrigine (LTG), a broad-spectrum anti-epileptic drug widely used in treatment for seizures, shows potential efficacy in Alzheimer's disease (AD) therapy. Chronic LTG treatment rescues the suppressed long-term potentiation, loss of spines and cognitive deficits in AβPP/PS1 mice, known to overexpress a chimeric mouse/human mutant amyloid-β protein precursor (AβPP) and a mutant human presenilin 1 (PS1). These changes are accompanied by reduction of amyloid-β (Aβ) plaques density and of levels of β-C-terminal fragment of AβPP (β-CTF), a fragment of AβPP cleaved by β-secretase. These results suggest LTG treatment reduces Aβ production, possibly through modulation of cleavage of AβPP by β-secretase. However, the underlying mechanisms still remain unclear. In this study, decreased protein levels, but not mRNA levels of β-site AβPP-cleaving enzyme 1 (BACE1), were observed in cultured HEK293 cells and the brains of AβPP/PS1 transgenic mice upon LTG treatment. Moreover, LTG treatment suppressed mammalian target of rapamycin (mTOR) signaling, while enhancing activation of cAMP response element binding protein (CREB), two signaling pathways essential for autophagy induction. LTG treatment increased the numbers of LC3-GFP + puncta and LC3-II levels in HEK293 cells, indicating an induction of autophagy. The downregulation of BACE1 by LTG treatment was prevented by the autophagy inhibitor 3-Methyladenine. Therefore, this study shows that LTG treatment reduces the protein levels of BACE1 through activation of autophagy, possibly via inhibition of mTOR signaling and activation of CREB.

Ion channel regulation by β-secretase BACE1 - enzymatic and non-enzymatic effects beyond Alzheimer's disease

β-site APP-cleaving enzyme 1 (BACE1) has become infamous for its pivotal role in the pathogenesis of Alzheimer's disease (AD). Consequently, BACE1 represents a prime target in drug development. Despite its detrimental involvement in AD, it should be quite obvious that BACE1 is not primarily present in the brain to drive mental decline. In fact, additional functions have been identified. In this review, we focus on the regulation of ion channels, specifically voltage-gated sodium and KCNQ potassium channels, by BACE1. These studies provide evidence for a highly unexpected feature in the functional repertoire of BACE1. Although capable of cleaving accessory channel subunits, BACE1 exerts many of its physiologically significant effects through direct, non-enzymatic interactions with main channel subunits. We discuss how the underlying mechanisms can be conceived and develop scenarios how the regulation of ion conductances by BACE1 might shape electric activity in the intact and diseased brain and heart.

Current pharmacotherapy and putative disease-modifying therapy for Alzheimer's disease

Alzheimer's disease (AD) is an age-related neurodegenerative disease of the central nervous system correlated with the progressive loss of cognition and memory. β-Amyloid plaques, neurofibrillary tangles and the deficiency in cholinergic neurotransmission constitute the major hallmarks of the AD. Two major hypotheses have been implicated in the pathogenesis of AD namely the cholinergic hypothesis which ascribed the clinical features of dementia to the deficit cholinergic neurotransmission and the amyloid cascade hypothesis which emphasized on the deposition of insoluble peptides formed due to the faulty cleavage of the amyloid precursor protein. Current pharmacotherapy includes mainly the acetylcholinesterase inhibitors and N-methyl-D-aspartate receptor agonist which offer symptomatic therapy and does not address the underlying cause of the disease. The disease-modifying therapy has garnered a lot of research interest for the development of effective pharmacotherapy for AD. β and γ-Secretase constitute attractive targets that are focussed in the disease-modifying approach. Potentiation of α-secretase also seems to be a promising approach towards the development of an effective anti-Alzheimer therapy. Additionally, the ameliorative agents that prevent aggregation of amyloid peptide and also the ones that modulate inflammation and oxidative damage associated with the disease are focussed upon. Development in the area of the vaccines is in progress to combat the characteristic hallmarks of the disease. Use of cholesterol-lowering agents also is a fruitful strategy for the alleviation of the disease as a close association between the cholesterol and AD has been cited. The present review underlines the major therapeutic strategies for AD with focus on the new developments that are on their way to amend the current therapeutic scenario of the disease.

Design, synthesis and in vitro evaluation studies of sulfonyl-amino-acetamides as small molecule BACE-1 inhibitors

The identification of a series of sulfonyl-amino-acetamides as BACE-1 (β-secretase) inhibitors for the treatment of Alzheimer's disease is reported. The derivatives were designed based on the docking simulation study, synthesized and assessed for BACE-1 inhibition in vitro. The designed ligands revealed desired binding interactions with the catalytic aspartate dyad and occupance of S1 and S2' active site regions. These in silico results correlated well with in vitro activity. Out of 33 compounds synthesized, 12 compounds showed significant inhibition at 10μM concentration. The most active compound 2.17S had IC50 of 7.90μM against BACE-1, which was concomitant with results of in silico docking study.

Inhibiting BACE1 to reverse synaptic dysfunctions in Alzheimer's disease

Over the past two decades, many studies have identified significant contributions of toxic β-amyloid peptides (Aβ) to the etiology of Alzheimer's disease (AD), which is the most common age-dependent neurodegenerative disease. AD is also recognized as a disease of synaptic failure. Aβ, generated by sequential proteolytic cleavages of amyloid precursor protein (APP) by BACE1 and γ-secretase, is one of major culprits that cause this failure. In this review, we summarize current findings on how BACE1-cleaved APP products impact learning and memory through proteins localized on glutamatergic, GABAergic, and dopaminergic synapses. Considering the broad effects of Aβ on all three types of synapses, BACE1 inhibition emerges as a practical approach for ameliorating Aβ-mediated synaptic dysfunctions. Since BACE1 inhibitory drugs are currently in clinical trials, this review also discusses potential complications arising from BACE1 inhibition. We emphasize that the benefits of BACE1 inhibitory drugs will outweigh the concerns.

The Distinct Role of ADAM17 in APP Proteolysis and Microglial Activation Related to Alzheimer's Disease

Alzheimer's disease (AD) is a progressive neurodegenerative disease with the symptom of cognitive impairment. The deposition of amyloid β (Aβ) peptide is believed to be the primary cause to neuronal dystrophy and eventually dementia. Aβ is the proteolytic product from its precursor amyloid precursor protein (APP) by β- and γ- secretase. An optional cleavage by α-secretase happens inside the Aβ domain. ADAM17 is supposed to be the regulated α-secretase of APP. Enhanced activity of ADAM17 leads to the increasing secretion of neuroprotective soluble APP α fragment and reduction of Aβ generation, which may be benefit to the disease. ADAM17 is then considered the potential therapeutic target for AD. Microglia activation and neuroinflammation is another important event in AD pathogenesis. Interestingly, ADAM17 also participates in the cleavage of many other membrane-bound proteins, especially some inflammatory factors related to microglia activation. The facilitating role of ADAM17 in inflammation and further neuronal damage has also been illustrated. In results, the activation of ADAM17 as the solution to AD may be a tricky task. The comprehensive consideration and evaluation has to be carried out carefully before the final treatment. In the present review, the distinct role of ADAM17 in AD-related APP shedding and neuroinflammatory microglial activation will be carefully discussed.

Alzheimer's therapy targeting the β-secretase enzyme BACE1: Benefits and potential limitations from the perspective of animal model studies

Accumulating evidence points to the amyloid-β (Aβ) peptide as the culprit in the pathogenesis of Alzheimer's disease (AD). β-Site amyloid precursor protein (APP)-cleaving enzyme 1 (BACE1) is a protease that is responsible for initiating Aβ production. Although precise mechanisms that trigger Aβ accumulation remain unclear, BACE1 inhibition undoubtedly represents an important intervention that may prevent and/or cure AD. Remarkably, animal model studies with knockouts, virus-delivered small interfering RNAs, immunization and bioavailable small-molecule agents that specifically inhibit BACE1 activity strongly support the idea for the therapeutic BACE1 inhibition. Meanwhile, a growing number of BACE1 substrates besides APP uncover new physiological roles of this protease, raising some concern regarding the safety of BACE1 inhibition. Here, I review recent progress in preclinical studies that have evaluated the efficacies and potential limitations of genetic/pharmacological inhibition of BACE1, with special focus on AD-associated phenotypes including synaptic dysfunction, neuron loss and memory deficits in animal models.

Post-translational regulation of the β-secretase BACE1

β-Secretase, widely known as β-site APP cleaving enzyme 1 (BACE1), is a membrane-associated protease that cleaves amyloid precursor protein (APP) to generate amyloid β-protein (Aβ). As this cleavage is a pathologically relevant event in Alzheimer's disease, BACE1 is considered a viable therapeutic target. BACE1 can be regulated at the transcriptional, post-transcriptional, translational, and post-translational levels. Elucidation of the regulatory pathways of BACE1 is critical, not only for understanding the pathological mechanisms of AD but also developing effective therapeutic strategies to inhibit activity of the protease. This mini-review focuses on the post-translational regulation of BACE1, as modulation at this level is closely associated with both physiological and pathological conditions. Current knowledge on the mechanisms underlying such BACE1 regulation and their implications for therapy are discussed.

Drug Development in Alzheimer's Disease: The Contribution of PET and SPECT

Clinical trials aiming to develop disease-altering drugs for Alzheimer’s disease (AD), a neurodegenerative disorder with devastating consequences, are failing at an alarming rate. Poorly defined inclusion-and outcome criteria, due to a limited amount of objective biomarkers, is one of the major concerns. Non-invasive molecular imaging techniques, positron emission tomography and single photon emission (computed) tomography (PET and SPE(C)T), allow visualization and quantification of a wide variety of (patho)physiological processes and allow early (differential) diagnosis in many disorders. PET and SPECT have the ability to provide biomarkers that permit spatial assessment of pathophysiological molecular changes and therefore objectively evaluate and follow up therapeutic response, especially in the brain. A number of specific PET/SPECT biomarkers used in support of emerging clinical therapies in AD are discussed in this review.

Amyloid Proteins and Their Role in Multiple Sclerosis. Considerations in the Use of Amyloid-PET Imaging

Thioflavin T derivatives are used in positron-emission tomography (PET) studies to detect amyloid protein deposits in patients with Alzheimer disease. These tracers bind extensively to white matter, which suggests that they may be useful in studies of multiple sclerosis (MS), and that proteins resulting from proteolytic processing of the amyloid precursor protein (APP) may contribute to MS. This article reviews data from both clinical and preclinical studies addressing the role of these proteins, whether they are detected in CSF studies or using PET imaging. APP is widely expressed in demyelinated axons and may have a protective effect in MS and in experimental allergic encephalomyelitis in animals. Several mechanisms associated with this increased expression may affect the degree of remyelination in MS. Amyloid-PET imaging may help determine the degree of demyelination and provide information on the molecular changes linked to APP proteolytic processing experienced by patients with MS.

miR-186 is decreased in aged brain and suppresses BACE1 expression

Accumulation of amyloid β (Aβ) in the brain is a key pathological hallmark of Alzheimer's disease (AD). Because aging is the most prominent risk factor for AD, understanding the molecular changes during aging is likely to provide critical insights into AD pathogenesis. However, studies on the role of miRNAs in aging and AD pathogenesis have only recently been initiated. Identifying miRNAs dysregulated by the aging process in the brain may lead to novel understanding of molecular mechanisms of AD pathogenesis. Here, we identified that miR-186 levels are gradually decreased in cortices of mouse brains during aging. In addition, we demonstrated that miR-186 suppresses β-site amyloid precursor protein-cleaving enzyme 1 (BACE1) expression by directly targeting the 3'UTR of Bace1 mRNA in neuronal cells. In contrast, inhibition of endogenous miR-186 significantly increased BACE1 levels in neuronal cells. Importantly, miR-186 over-expression significantly decreased Aβ level by suppressing BACE1 expression in cells expressing human pathogenic mutant amyloid precursor protein. Taken together, our data demonstrate that miR-186 is a potent negative regulator of BACE1 in neuronal cells and it may be one of the molecular links between brain aging and the increased risk for AD during aging. We identified that miR-186 levels are gradually decreased in mouse cortices during aging. Furthermore, we demonstrated that miR-186 is a novel negative regulator of beta-site amyloid precursor protein-cleaving enzyme 1 (BACE1) expression in neuronal cells. Therefore, we proposed that reduction in miR-186 levels during aging may lead to the up-regulation of BACE1 in the brain, thereby increasing a risk for Alzheimer's disease in aged individuals. Read the Editorial Highlight for this article on page 308.

Gastrodin suppresses BACE1 expression under oxidative stress condition via inhibition of the PKR/eIF2α pathway in Alzheimer's disease

The expression of β-site APP-cleaving enzyme 1 (BACE1) is increased in the brain of late-onset sporadic Alzheimer's disease (AD) and oxidative stress may be the potential cause of this event. The phenolic glucoside gastrodin (Gas), a main component of a Chinese herbal medicine Gastrodia elata Blume, has been demonstrated to display antioxidant activity and suppresses BACE1 expression. However, the mechanisms by which Gas suppresses BACE1 expression are not clear. Morris water maze test was performed to assess the effect of Gas treatment on memory impairments in Tg2576 mice. The level of oxidative stress in the brain of Tg2576 mice was determined by measuring the superoxide dismutase (SOD) activity, catalase (CAT) activity, and the levels of malondialdehyde (MDA) and ROS. In vivo and in vitro, we detected the expression levels of BACE1, pPKRThr446, PKR, pPERKThr981, PERK, peIF2αSer51, and eIF2α using western blot analysis. We found that Gas improved learning and memory abilities of Tg2576 transgenic mice and attenuated intracellular oxidative stress in hippocampi of Tg2576 mice. We discovered that the expression levels of BACE1, activated PKR (pPKRThr446) and activated eIF2α (peIF2αSer51) were elevated in the brains of Tg2576 mice and hydrogen peroxide (H2O2)-stimulated SH-SY5Y cells. Moreover, peptide PKR inhibitor (PRI) and Gas down-regulated BACE1 expression in Tg2576 mice and H2O2-stimulated SH-SY5Y cells by inhibiting activation of PKR and eIF2α. Gas alleviates memory deficits in mice and suppresses BACE1 expression by inhibiting the protein kinase/Eukaryotic initiation factor-2α (PKR/eIF2α) pathway. The research suggested that Gas may develop as an drug candidate in neurodegenerative diseases.

Acceleration of amyloidogenesis and memory impairment by estrogen deficiency through NF-κB dependent beta-secretase activation in presenilin 2 mutant mice

Nearly 7-10 million people are living with Alzheimer's disease (AD) worldwide. Senile plaques composed of β-amyloid (Aβ) are a pathological hallmark of Alzheimer's disease. Presenilin 2 (PS2) mutations increase Aβ generation in the brains of AD patients. The Aβ is generated through the sequential cleavage of amyloid precursor protein by β- and γ-secretases. Additionally, increasing evidences suggest that estrogen can reduce the development of AD via regulation of β-secretases activity and beta-site APP-cleaving enzyme (BACE1) expression. But the underlying correlation mechanism of Aβ generation by PS2 mutations and estrogen remains to be clarified. To investigate the anti-amyloidogenesis effect of estrogen in a PS2 mutative condition, we examined memory impairment in ovariectomized PS2 mutation (N141I) mice in which cognitive function was assessed by the Morris water maze test and passive avoidance test. In addition, Western blot analysis, immunostaining, immunofluorescence staining, ELISA and enzyme activity assays were used to examine the degree of Aβ deposition in the brains. In the present study, Aβ accumulated more in the ovariectomized PS2 mutant mice brain, and greatly worsened memory impairment and glial activation as well as neurogenic inflammation. In parallel with increased memory impairment, activity of β-secretase and expression of the BACE1 increased inovariectomized PS2 mutant mice. Much higher activity of NF-κB was observed by EMSA in ovariectomized PS2 mutant mice. In addition, the Aβ level was decreased by treatment of β-estradiol through inhibiting BACE1 expression in PS2 transfacted PC12 cells. These results suggest that mutation of PS2 can lead to NF-κB mediate amyloidogensis, and this effect can be amplified by the absence of estrogen.

Kinetics and molecular docking studies of fucosterol and fucoxanthin, BACE1 inhibitors from brown algae Undaria pinnatifida and Ecklonia stolonifera

Since the action of β-site amyloid precursor protein cleaving enzyme 1 (BACE1) is strongly correlated with the onset of Alzheimer's disease (AD), the development of BACE1 inhibitors as therapeutic agents is being vigorously pursued. In our ongoing research aimed at identifying anti-AD remedies derived from maritime plants, we evaluated the BACE1 inhibitory activities of fucosterol and fucoxanthin from Ecklonia stolonifera and Undaria pinnatifida. In vitro anti-AD activities were performed via BACE1 inhibition assays, as well as enzyme kinetic and molecular docking predictions. Based on enzyme-based assays, fucosterol and fucoxanthin showed noncompetitive and mixed-type inhibition, respectively, against BACE1. In addition, docking simulation results demonstrated that the Lys224 residue of BACE1 interacted with one hydroxyl group of fucosterol, while two additional BACE1 residues (Gly11 and Ala127) interacted with two hydroxyl groups of fucoxanthin. Moreover, the binding energy of fucosterol and fucoxanthin was negative (-10.1 and -7.0 kcal/mol), indicating that hydrogen bonding may stabilize the open form of the enzyme and potentiate tight binding of the active site of BACE1, resulting in more effective BACE1 inhibition. The results suggest that fucosterol and fucoxanthin may be used beneficially in the treatment of AD and provide potential guidelines for the design of new BACE1 inhibitors.

Curcumin Ameliorates Memory Decline via Inhibiting BACE1 Expression and β-Amyloid Pathology in 5×FAD Transgenic Mice

Alzheimer's disease (AD) is the most common dementia and the trigger of its pathological cascade is widely believed to be the overproduction and accumulation of β-amyloid protein (Aβ) in the affected brain. However, effective AD remedies are still anxiously awaited. Recent evidence suggests that curcumin may be a potential agent for AD treatment. In this study, we used 5×FAD transgenic mice as an AD model to investigate the effects of curcumin on AD. Our results showed that curcumin administration (150 or 300 mg/kg/day, intragastrically, for 60 days) dramatically reduced Aβ production by downregulating BACE1 expression, preventing synaptic degradation, and improving spatial learning and memory impairment of 5×FAD mice. These findings suggest that curcumin is a potential candidate for AD treatment.

Generation of aggregation prone N-terminally truncated amyloid β peptides by meprin β depends on the sequence specificity at the cleavage site

BACKGROUND

The metalloprotease meprin β cleaves the Alzheimer's Disease (AD) relevant amyloid precursor protein (APP) as a β-secretase reminiscent of BACE-1, however, predominantly generating N-terminally truncated Aβ2-x variants.

RESULTS

Herein, we observed increased endogenous sAPPα levels in the brains of meprin β knock-out (ko) mice compared to wild-type controls. We further analyzed the cellular interaction of APP and meprin β and found that cleavage of APP by meprin β occurs prior to endocytosis. The N-terminally truncated Aβ2-40 variant shows increased aggregation propensity compared to Aβ1-40 and acts even as a seed for Aβ1-40 aggregation. Additionally, we observed that different APP mutants affect the catalytic properties of meprin β and that, interestingly, meprin β is unable to generate N-terminally truncated Aβ peptides from Swedish mutant APP (APPswe).

CONCLUSION

Concluding, we propose that meprin β may be involved in the generation of N-terminally truncated Aβ2-x peptides of APP, but acts independently from BACE-1.

Meta-analysis of BACE1 gene rs638405 polymorphism and the risk of Alzheimer's disease in Caucasion and Asian population

Recent studies showed the β-site amyloid precursor protein cleaving enzyme (BACE) is associated with Alzheimer's disease (AD). However, studies investigating the association of single-nucleotide polymorphism (SNP) in exon 5 of BACE1 (rs638405, C786G, Val262) with AD are controversial. Therefore we conducted this meta-analysis to clarify the association. Relevant studies were identified on PubMed, Cochrane library and CNKI from established through July 2015 according to the inclusion criteria. Odds ratios (ORs) with 95% confidence intervals (CIs) and five genetic models were applied to assess the association. A total of 13 studies composed of 2538 AD patients and 3020 controls were included in this study. Significant association of SNP rs638405 with AD was found in overall population among allelic genetic model (G vs. C: OR=1.11, 95%CI=1.02-1.20, P=0.01), codominant genetic model (GG vs. CC: OR=1.22, 95%CI=1.04-1.44, P=0.02) and recessive genetic model (GG vs. GC+ CC: OR=1.25, 95%CI=1.10-1.42, P=0.0008). Besides, subgroup analysis indicated significant association among Asian population (allelic genetic model, G vs. C, OR=1.18, 95%CI=1.04-1.34, P=0.01; codominant genetic model, GG vs. CC, OR=1.43, 95%CI=1.08-1.89, P=0.01 and recessive genetic model, GG vs. GC+ CC, OR=1.40, 95%CI=1.09-1.78, P=0.008) and Caucasion population (recessive genetic model, GG vs. GC+ CC, OR=1.20, 95%CI=1.02-1.39, P=0.02). Our analysis demonstrated that GG genotype and G allele of BACE1 gene rs638405 probably increase the risk of AD.

β-Secretase 1's Targeting Reduces Hyperphosphorilated Tau, Implying Autophagy Actors in 3xTg-AD Mice

β-site APP cleaving enzyme 1 (BACE1) initiates APP cleavage, which has been reported to be an inducer of tau pathology by altering proteasome functions in Alzheimer’s disease (AD). However, the exact relationship between BACE1 and PHF (Paired Helical Filaments) formation is not clear. In this study, we confirm that BACE1 and Hsc70 are upregulated in the brains of AD patients, and we demonstrate that both proteins show enhanced expression in lipid rafts from AD-affected triple transgenic mouse brains. BACE1 targeting increased Hsc70 levels in the membrane and cytoplasm fractions and downregulated Hsp90 and CHIP in the nucleus in the hippocampi of 3xTg-AD mice. However, these observations occurred in a proteasome-independent manner in vitro. The BACE1miR-induced reduction of soluble hyperphosphorylated tau was associated with a decrease in MAPK activity. However, the BACE1 RNAi-mediated reduction of hyperphosphorylated tau was only blocked by 3-MA (3-methyladenine) in vitro, and it resulted in the increase of Hsc70 and LAMP2 in lipid rafts from hippocampi of 3xTg-AD mice, and upregulation of survival and homeostasis signaling. In summary, our findings suggest that BACE1 silencing neuroprotects reducing soluble hyperphosphorylated tau, modulating certain autophagy-related proteins in aged 3xTg-AD mice.

Disrupted-in-Schizophrenia-1 Attenuates Amyloid-β Generation and Cognitive Deficits in APP/PS1 Transgenic Mice by Reduction of β-Site APP-Cleaving Enzyme 1 Levels

Disrupted-in-Schizophrenia-1 (DISC1) is a genetic risk factor for a wide range of major mental disorders, including schizophrenia, major depression, and bipolar disorders. Recent reports suggest a potential role of DISC1 in the pathogenesis of Alzheimer's disease (AD), by referring to an interaction between DISC1 and amyloid precursor protein (APP), and to an association of a single-nucleotide polymorphism in a DISC1 intron and late onset of AD. However, the function of DISC1 in AD remains unknown. In this study, decreased levels of DISC1 were observed in the cortex and hippocampus of 8-month-old APP/PS1 transgenic mice, an animal model of AD. Overexpression of DISC1 reduced, whereas knockdown of DISC1 increased protein levels, but not mRNA levels of β-site APP-Cleaving Enzyme 1 (BACE1), a key enzyme in amyloid-β (Aβ) generation. Reduction of BACE1 protein levels by overexpression of DISC1 was accompanied by an accelerating decline rate of BACE1, and was blocked by the lysosomal inhibitor chloroquine, rather than proteasome inhibitor MG-132. Moreover, overexpression of DISC1 in the hippocampus with an adeno-associated virus reduced the levels of BACE1, soluble Aβ40/42, amyloid plaque density, and rescued cognitive deficits of APP/PS1 transgenic mice. These results indicate that DISC1 attenuates Aβ generation and cognitive deficits of APP/PS1 transgenic mice through promoting lysosomal degradation of BACE1. Our findings provide new insights into the role of DISC1 in AD pathogenesis and link a potential function of DISC1 to the psychiatric symptoms of AD.