BACE1 Deficiency Rescues Memory Deficits and Cholinergic Dysfunction in a Mouse Model of Alzheimer's Disease

Revisiting the Amyloid Cascade Hypothesis: From Anti-Aβ Therapeutics to Auspicious New Ways for Alzheimer's Disease

Alzheimer’s disease (AD) is the most prevalent neurodegenerative disorder related to age, characterized by the cerebral deposition of fibrils, which are made from the amyloid-β (Aβ), a peptide of 40–42 amino acids. The conversion of Aβ into neurotoxic oligomeric, fibrillar, and protofibrillar assemblies is supposed to be the main pathological event in AD. After Aβ accumulation, the clinical symptoms fall out predominantly due to the deficient brain clearance of the peptide. For several years, researchers have attempted to decline the Aβ monomer, oligomer, and aggregate levels, as well as plaques, employing agents that facilitate the reduction of Aβ and antagonize Aβ aggregation, or raise Aβ clearance from brain. Unluckily, broad clinical trials with mild to moderate AD participants have shown that these approaches were unsuccessful. Several clinical trials are running involving patients whose disease is at an early stage, but the preliminary outcomes are not clinically impressive. Many studies have been conducted against oligomers of Aβ which are the utmost neurotoxic molecular species. Trials with monoclonal antibodies directed against Aβ oligomers have exhibited exciting findings. Nevertheless, Aβ oligomers maintain equivalent states in both monomeric and aggregation forms; so, previously administered drugs that precisely decrease Aβ monomer or Aβ plaques ought to have displayed valuable clinical benefits. In this article, Aβ-based therapeutic strategies are discussed and several promising new ways to fight against AD are appraised.

Urolithin A suppresses high glucose-induced neuronal amyloidogenesis by modulating TGM2-dependent ER-mitochondria contacts and calcium homeostasis

Hyperglycemia in diabetes mellitus (DM) patients is a causative factor for amyloidogenesis and induces neuropathological changes, such as impaired neuronal integrity, neurodegeneration, and cognitive impairment. Regulation of mitochondrial calcium influx from the endoplasmic reticulum (ER) is considered a promising strategy for the prevention of mitochondrial ROS (mtROS) accumulation that occurs in the Alzheimer's disease (AD)-associated pathogenesis in DM patients. Among the metabolites of ellagitannins that are produced in the gut microbiome, urolithin A has received an increasing amount of attention as a novel candidate with anti-oxidative and neuroprotective effects in AD. Here, we investigated the effect of urolithin A on high glucose-induced amyloidogenesis caused by mitochondrial calcium dysregulation and mtROS accumulation resulting in neuronal degeneration. We also identified the mechanism related to mitochondria-associated ER membrane (MAM) formation. We found that urolithin A-lowered mitochondrial calcium influx significantly alleviated high glucose-induced mtROS accumulation and expression of amyloid beta (Aβ)-producing enzymes, such as amyloid precursor protein (APP) and β-secretase-1 (BACE1), as well as Aβ production. Urolithin A injections in a streptozotocin (STZ)-induced diabetic mouse model alleviated APP and BACE1 expressions, Tau phosphorylation, Aβ deposition, and cognitive impairment. In addition, high glucose stimulated MAM formation and transglutaminase type 2 (TGM2) expression. We first discovered that urolithin A significantly reduced high glucose-induced TGM2 expression. In addition, disruption of the AIP-AhR complex was involved in urolithin A-mediated suppression of high glucose-induced TGM2 expression. Markedly, TGM2 silencing inhibited inositol 1, 4, 5-trisphosphate receptor type 1 (IP3R1)-voltage-dependent anion-selective channel protein 1 (VDAC1) interactions and prevented high glucose-induced mitochondrial calcium influx and mtROS accumulation. We also found that urolithin A or TGM2 silencing prevented Aβ-induced mitochondrial calcium influx, mtROS accumulation, Tau phosphorylation, and cell death in neuronal cells. In conclusion, we suggest that urolithin A is a promising candidate for the development of therapies to prevent DM-associated AD pathogenesis by reducing TGM2-dependent MAM formation and maintaining mitochondrial calcium and ROS homeostasis.

Trans-Cinnamaldehyde Alleviates Amyloid-Beta Pathogenesis via the SIRT1-PGC1α-PPARγ Pathway in 5XFAD Transgenic Mice

Abnormal amyloid-β (Aβ) accumulation is the most significant feature of Alzheimer’s disease (AD). Among the several secretases involved in the generation of Aβ, β-secretase (BACE1) is the first rate-limiting enzyme in Aβ production that can be utilized to prevent the development of Aβ-related pathologies. Cinnamon extract, used in traditional medicine, was shown to inhibit the aggregation of tau protein and Aβ aggregation. However, the effect of trans-cinnamaldehyde (TCA), the main component of cinnamon, on Aβ deposition is unknown. Five-month-old 5XFAD mice were treated with TCA for eight weeks. Seven-month-old 5XFAD mice were evaluated for cognitive and spatial memory function. Brain samples collected at the conclusion of the treatment were assessed by immunofluorescence and biochemical analyses. Additional in vivo experiments were conducted to elucidate the mechanisms underlying the effect of TCA in the role of Aβ deposition. TCA treatment led to improvements in cognitive impairment and reduced Aβ deposition in the brains of 5XFAD mice. Interestingly, the levels of BACE1 were decreased, whereas the mRNA and protein levels of three well-known regulators of BACE1, silent information regulator 1 (SIRT1), peroxisome proliferator-activated receptor γ (PPARγ) coactivator 1α (PGC1α), and PPARγ, were increased in TCA-treated 5XFAD mice. TCA led to an improvement in AD pathology by reducing BACE1 levels through the activation of the SIRT1-PGC1α-PPARγ pathway, suggesting that TCA might be a useful therapeutic approach in AD.

SPON1 Can Reduce Amyloid Beta and Reverse Cognitive Impairment and Memory Dysfunction in Alzheimer's Disease Mouse Model

Alzheimer’s disease (AD) is a complex, age-related neurodegenerative disease that is the most common form of dementia. However, the cure for AD has not yet been founded. The accumulation of amyloid beta (Aβ) is considered to be a hallmark of AD. Beta-site amyloid precursor protein cleaving enzyme 1 (BACE1), also known as beta secretase is the initiating enzyme in the amyloidogenic pathway. Blocking BACE1 could reduce the amount of Aβ, but this would also prohibit the other functions of BACE1 in brain physiological activity. SPONDIN1 (SPON1) is known to bind to the BACE1 binding site of the amyloid precursor protein (APP) and blocks the initiating amyloidogenesis. Here, we show the effect of SPON1 in Aβ reduction in vitro in neural cells and in an in vivo AD mouse model. We engineered mouse induced neural stem cells (iNSCs) to express Spon1. iNSCs harboring mouse Spon1 secreted SPON1 protein and reduced the quantity of Aβ when co-cultured with Aβ-secreting Neuro 2a cells. The human SPON1 gene itself also reduced Aβ in HEK 293T cells expressing the human APP transgene with AD-linked mutations through lentiviral-mediated delivery. We also demonstrated that injecting SPON1 reduced the amount of Aβ and ameliorated cognitive dysfunction and memory impairment in 5xFAD mice expressing human APP and PSEN1 transgenes with five AD-linked mutations.

Nanocurcumin: A Promising Candidate for Therapeutic Applications

Curcuma longa is an important medicinal plant and a spice in Asia. Curcumin (diferuloylmethane) is a hydrophobic bioactive ingredient found in a rhizome of the C. longa. It has drawn immense attention in recent years for its variety of biological and pharmacological action. However, its low water solubility, poor bioavailability, and rapid metabolism represent major drawbacks for its successful therapeutic applications. Hence, researchers have attempted to enhance the biological and pharmacological activity of curcumin and overcome its drawbacks by efficient delivery systems, particularly nanoencapsulation. Research efforts so far and data from the available literature have shown a satisfactory potential of nanorange formulations of curcumin (Nanocurcumin), it increases all the biological and pharmacological benefits of curcumin, which was not significantly possible earlier. For the synthesis of nanocurcumin, an array of techniques has been developed and each technique has its own advantages and individual characteristics. The two most popular and effective techniques are ionic gelation and antisolvent precipitation. So far, many curcumin nanoformulations have been developed to enhance curcumin delivery, thereby overcoming the low therapeutic effects. However, most of the nanoformulation of curcumin remained at the concept level evidence, thus, several questions and challenges still exist to recommend the nanocurcumin as a promising candidate for therapeutic applications. In this review, we discuss the different curcumin nanoformulation and nanocurcumin implications for different therapeutic applications as well as the status of ongoing clinical trials and patents. We also discuss the research gap and future research directions needed to propose curcumin as a promising therapeutic candidate.

Mossy cell synaptic dysfunction causes memory imprecision via miR-128 inhibition of STIM2 in Alzheimer's disease mouse model

Recently, we have reported that dentate mossy cells (MCs) control memory precision via directly and functionally innervating local somatostatin (SST) inhibitory interneurons. Here, we report a discovery that dysfunction of synaptic transmission between MCs and SST cells causes memory imprecision in a mouse model of early Alzheimer's disease (AD). Single-cell RNA sequencing reveals that miR-128 that binds to a 3'UTR of STIM2 and inhibits STIM2 translation is increasingly expressed in MCs from AD mice. Silencing miR-128 or disrupting miR-128 binding to STIM2 evokes STIM2 expression, restores synaptic function, and rescues memory imprecision in AD mice. Comparable findings are achieved by directly engineering MCs with the expression of STIM2. This study unveils a key synaptic and molecular mechanism that dictates how memory maintains or losses its details and warrants a promising target for therapeutic intervention of memory decays in the early stage of AD.

Mouse brain proteomics establishes MDGA1 and CACHD1 as in vivo substrates of the Alzheimer protease BACE1

The protease beta-site APP cleaving enzyme 1 (BACE1) has fundamental functions in the nervous system. Its inhibition is a major therapeutic approach in Alzheimer's disease, because BACE1 cleaves the amyloid precursor protein (APP), thereby catalyzing the first step in the generation of the pathogenic amyloid beta (Aβ) peptide. Yet, BACE1 cleaves numerous additional membrane proteins besides APP. Most of these substrates have been identified in vitro, but only few were further validated or characterized in vivo. To identify BACE1 substrates with in vivo relevance, we used isotope label-based quantitative proteomics of wild type and BACE1-deficient (BACE1 KO) mouse brains. This approach identified known BACE1 substrates, including Close homolog of L1 and contactin-2, which were found to be enriched in the membrane fraction of BACE1 KO brains. VWFA and cache domain-containing protein 1 (CACHD)1 and MAM domain-containing glycosylphosphatidylinositol anchor protein 1 (MDGA1), which have functions in synaptic transmission, were identified and validated as new BACE1 substrates in vivo by immunoblots using primary neurons and mouse brains. Inhibition or deletion of BACE1 from primary neurons resulted in a pronounced inhibition of substrate cleavage and a concomitant increase in full-length protein levels of CACHD1 and MDGA1. The BACE1 cleavage site in both proteins was determined to be located within the juxtamembrane domain. In summary, this study identifies and validates CACHD1 and MDGA1 as novel in vivo substrates for BACE1, suggesting that cleavage of both proteins may contribute to the numerous functions of BACE1 in the nervous system.

BACE1 partial deletion induces synaptic plasticity deficit in adult mice

BACE1 is the first enzyme involved in APP processing, thus it is a strong therapeutic target candidate for Alzheimer's disease. The observation of deleterious phenotypes in BACE1 Knock-out (KO) mouse models (germline and conditional) raised some concerns on the safety and tolerability of BACE1 inhibition. Here, we have employed a tamoxifen inducible BACE1 conditional Knock-out (cKO) mouse model to achieve a controlled partial depletion of BACE1 in adult mice. Biochemical and behavioural characterization was performed at two time points: 4-5 months (young mice) and 12-13 months (aged mice). A ~50% to ~70% BACE1 protein reduction in hippocampus and cortex, respectively, induced a significant reduction of BACE1 substrates processing and decrease of Aβx-40 levels at both ages. Hippocampal axonal guidance and peripheral nerve myelination were not affected. Aged mice displayed a CA1 long-term potentiation (LTP) deficit that was not associated with memory impairment. Our findings indicate that numerous phenotypes observed in germline BACE1 KO reflect a fundamental role of BACE1 during development while other phenotypes, observed in adult cKO, may be absent when partially rather than completely deleting BACE1. However, we demonstrated that partial depletion of BACE1 still induces CA1 LTP impairment, supporting a role of BACE1 in synaptic plasticity in adulthood.

Amyloid, APP, and Electrical Activity of the Brain

The Amyloid Precursor Protein (APP) is infamous for its proposed pivotal role in the pathogenesis of Alzheimer’s disease (AD). Much research on APP focusses on potential contributions to neurodegeneration, mostly based on mouse models with altered expression or mutated forms of APP. However, cumulative evidence from recent years indicates the indispensability of APP and its metabolites for normal brain physiology. APP contributes to the regulation of synaptic transmission, plasticity, and calcium homeostasis. It plays an important role during development and it exerts neuroprotective effects. Of particular importance is the soluble secreted fragment APPsα which mediates many of its physiological actions, often counteracting the effects of the small APP-derived peptide Aβ. Understanding the contribution of APP for normal functions of the nervous system is of high importance, both from a basic science perspective and also as a basis for generating new pathophysiological concepts and therapeutic approaches in AD. In this article, we review the physiological functions of APP and its metabolites, focusing on synaptic transmission, plasticity, calcium signaling, and neuronal network activity.

Bazhu Decoction, a Traditional Chinese Medical Formula, Ameliorates Cognitive Deficits in the 5xFAD Mouse Model of Alzheimer's Disease

Alzheimer’s disease (AD) is the most common neurodegenerative disorder associated with aging. There are currently no effective treatments for AD. Bazhu decoction (BZD), a traditional Chinese medicine (TCM) formula, has been employed clinically to alleviate AD. However, the underlying molecular mechanisms are still unclear. Here we found that middle- and high-doses of BZD ameliorated the behavioral aspects of 5xFAD transgenic mice in elevated plus maze, Y maze and Morris water maze tests. Moreover, BZD reduced the protein levels of BACE1 and PS1, resulting in a reduction of Aβ plaques. We also identified a beneficial effect of BZD on oxidative stress by attenuating MDA levels and SOD activity in the brains of 5xFAD mice. Together, these results indicate that BZD produces a dose-dependent positive effect on 5xFAD transgenic mouse model by decreasing APP processing and Aβ plaques, and by ameliorating oxidative damage. BZD may play a protective role in the cognitive and anxiety impairments and may be a complementary therapeutic option for AD.

Berberine Ameliorates Spatial Learning Memory Impairment and Modulates Cholinergic Anti-Inflammatory Pathway in Diabetic Rats

Background: Cognitive impairment caused by diabetes has been recognized. Berberine is well known for its resistance to peripheral lesions, but it is rarely used for the treatment of spatial learning and memory caused by diabetes. This study explored the mechanism of berberine to alleviate cognitive impairment via the cholinergic anti-inflammatory and insulin signaling pathways.

Methods: Morris water maze was used to appraise spatial learning and memory. Positron-emission tomography (PET) imaging was adopted to detect the transport of glucose, and blood/cerebrospinal fluid (CSF) glucose was checked using commercial blood glucose meter. Insulin level was measured by ELISA kit and β-Amyloid (Aβ) formation was observed by Congo red staining. Western-blot was performed to appraise protein expression.

Results: We found that berberine rectified some aberrant changes in signal molecules concerning inflammation, and cholinergic and insulin signaling pathways in the hippocampus. Furthermore, CSF/blood glucose, inflammatory response or acetyl cholinesterase enzyme (AChE) activity were reduced by berberine. Additionally, acetylcholine levels were enhanced after berberine treatment in diabetic rats. Finally, Aβ formation in diabetic hippocampus was inhibited and spatial learning memory was ameliorated by berberine.

Discussion: In conclusion, berberine clears Aβ deposit and consequently ameliorates spatial learning memory impairment via the activation of the cholinergic anti-inflammatory and insulin signaling pathways in diabetic rats.

MMP13 inhibition rescues cognitive decline in Alzheimer transgenic mice via BACE1 regulation

MMP13 (matrix metallopeptidase 13) plays a key role in bone metabolism and cancer development, but has no known functions in Alzheimer's disease. In this study, we used high-throughput small molecule screening in SH-SY5Y cells that stably expressed a luciferase reporter gene driven by the BACE1 (β-site amyloid precursor protein cleaving enzyme 1) promoter, which included a portion of the 5' untranslated region (5'UTR). We identified that CL82198, a selective inhibitor of MMP13, decreased BACE1 protein levels in cultured neuronal cells. This effect was dependent on PI3K (phosphatidylinositide 3-kinase) signalling, and was unrelated to BACE1 gene transcription and protein degradation. Further, we found that eukaryotic translation initiation factor 4B (eIF4B) played a key role, as the mutation of eIF4B at serine 422 (S422R) or deletion of the BACE1 5'UTR attenuated MMP13-mediated BACE1 regulation. In APPswe/PS1E9 mice, an animal model of Alzheimer's disease, hippocampal Mmp13 knockdown or intraperitoneal CL82198 administration reduced BACE1 protein levels and the related amyloid-β precursor protein processing, amyloid-β load and eIF4B phosphorylation, whereas spatial and associative learning and memory performances were improved. Collectively, MMP13 inhibition/CL82198 treatment exhibited therapeutic potential for Alzheimer's disease, via the translational regulation of BACE1.

Therapeutic Potential of Multifunctional Tacrine Analogues

Abstract: Tacrine is a potent inhibitor of cholinesterases (acetylcholinesterase and butyrylcholinesterase) that shows limiting clinical application by liver toxicity. In spite of this, analogues of tacrine are considered as a model inhibitor of cholinesterases in the therapy of Alzheimer’s disease. The interest in these compounds is mainly related to a high variety of their structure and biological properties. In the present review, we have described the role of cholinergic transmission and treatment strategies in Alzheimer’s disease as well as the synthesis and biological activity of several recently developed classes of multifunctional tacrine analogues and hybrids, which consist of a new paradigm to treat Alzheimer’s disease. We have also reported potential of these analogues in the treatment of Alzheimer’s diseases in various experimental systems.

Multiple BACE1 inhibitors abnormally increase the BACE1 protein level in neurons by prolonging its half-life

INTRODUCTION

There is keen interest in elucidating the biological mechanisms underlying recent failures of β-site amyloid precursor protein-cleaving enzyme-1 (BACE1) inhibitors in Alzheimer's disease trials.

METHODS

We developed a highly sensitive and specific immunoassay for BACE1 in cell lines and iPSC-derived human neurons to systematically analyze the effects of eight clinically relevant BACE1 inhibitors.

RESULTS

Seven of 8 inhibitors elevated BACE1 protein levels. Among protease inhibitors tested, the elevation was specific to BACE1 inhibitors. The inhibitors did not increase BACE1 transcription but extended the protein's half-life. BACE1 became elevated at concentrations below the IC₅₀ for amyloid β (Aβ).

DISCUSSION

Elevation of BACE1 by 7 of 8 BACE1 inhibitors raises new concerns about advancing such β-secretase inhibitors for AD. Chronic elevation could lead to intermittently uninhibited BACE1 when orally dosed inhibitors reach trough levels, abnormally increasing substrate processing. Compounds such as roburic acid that lower Aβ by dissociating β/γ secretase complexes are better candidates because they neither inhibit β- and γ-secretase nor increase BACE1 levels.

Regulation of the alternative β-secretase meprin β by ADAM-mediated shedding

Alzheimer's Disease (AD) is the sixth-leading cause of death in industrialized countries. Neurotoxic amyloid-β (Aβ) plaques are one of the pathological hallmarks in AD patient brains. Aβ accumulates in the brain upon sequential, proteolytic processing of the amyloid precursor protein (APP) by β- and γ-secretases. However, so far disease-modifying drugs targeting β- and γ-secretase pathways seeking a decrease in the production of toxic Aβ peptides have failed in clinics. It has been demonstrated that the metalloproteinase meprin β acts as an alternative β-secretase, capable of generating truncated Aβ2-x peptides that have been described to be increased in AD patients. This indicates an important β-site cleaving enzyme 1 (BACE-1)-independent contribution of the metalloprotease meprin β within the amyloidogenic pathway and may lead to novel drug targeting avenues. However, meprin β itself is embedded in a complex regulatory network. Remarkably, the anti-amyloidogenic α-secretase a disintegrin and metalloproteinase domain-containing protein 10 (ADAM10) is a direct competitor for APP at the cell surface, but also a sheddase of inactive pro-meprin β. Overall, we highlight the current cellular, molecular and structural understanding of meprin β as alternative β-secretase within the complex protease web, regulating APP processing in health and disease.

Trafficking and proteolytic processing of amyloid precursor protein and secretases in Alzheimer's disease development: An up-to-date review

Alzheimer's disease (AD), which is predicted to affect 1 in 85 persons worldwide by 2050, results in progressive loss of neuronal functions, leading to impairments in memory and cognitive abilities. As being one of the major neuropathological hallmarks of AD, senile plaques mainly consist of amyloid-β (Aβ) peptides, which are derived from amyloid precursor protein (APP) via the sequential cleavage by β- and γ-secretases. Although the overproduction and accumulation of Aβ peptides are at the center of AD research, the new discoveries point out to the complexity of the disease development. In this respect, it is crucial to understand the processing and the trafficking of APP, the enzymes involved in its processing, the cleavage products and their therapeutic potentials. This review summarizes the salient features of APP processing focusing on APP, the canonical secretases as well as the novel secretases and the cleavage products with an update of the recent developments. We also discussed the intracellular trafficking of APP and secretases in addition to their potential in AD therapy.

A Glycosaminoglycan Extract from Portunus pelagicus Inhibits BACE1, the β Secretase Implicated in Alzheimer's Disease

Therapeutic options for Alzheimer's disease, the most common form of dementia, are currently restricted to palliative treatments. The glycosaminoglycan heparin, widely used as a clinical anticoagulant, has previously been shown to inhibit the Alzheimer's disease-relevant β-secretase 1 (BACE1). Despite this, the deployment of pharmaceutical heparin for the treatment of Alzheimer's disease is largely precluded by its potent anticoagulant activity. Furthermore, ongoing concerns regarding the use of mammalian-sourced heparins, primarily due to prion diseases and religious beliefs hinder the deployment of alternative heparin-based therapeutics. A marine-derived, heparan sulphate-containing glycosaminoglycan extract, isolated from the crab Portunus pelagicus, was identified to inhibit human BACE1 with comparable bioactivity to that of mammalian heparin (IC50 = 1.85 μg mL-1 (R2 = 0.94) and 2.43 μg mL-1 (R2 = 0.93), respectively), while possessing highly attenuated anticoagulant activities. The results from several structural techniques suggest that the interactions between BACE1 and the extract from P. pelagicus are complex and distinct from those of heparin.

Synthesis, characterization, molecular docking evaluation, antidepressant, and anti-Alzheimer effects of dibenzylidene ketone derivatives

Novel bioactive compounds as synthetic analogs of the potent herbal medicines can be optimized as potential drug candidates for various neurologic disorders. This study was performed to investigate the newly synthesized dibenzylidene ketone derivatives: (2E,6E)-2,6-dibenzylidene cyclohexanone (A1K1) and (1E,4E)-5-(2,3-dichlorophenyl)-1-(4-methoxyphenyl)-2-methylpenta-1,4-diene-3-one (A2K2) and evaluate its potential anti-Alzheimer's and anti-depressant properties. Both the derivatives are chemically characterized by using HNMR and CNMR techniques. Auto Dock Vina program was used to investigate ligand-protein affinity. Forced swim test, tail suspension test, open field test, Y-maze test, and Morris water maze test (MWM) models were employed to evaluate anti-depressant and anti-Alzheimer's activity of dibenzylidene ketone derivatives in mice. Both A1K1 and A2K2 showed high binding affinities against various proteins involved in depression and Alzheimer's mechanisms like monoamine oxidase B, acetylcholinesterase, norepinephrine transporter 2, serotonin transporter, dopamine receptor, serotonin receptor modulator, and beta-amyloid targets. A1K1 and A2K2 dose-dependently (0.1-1 mg/kg) decreased immobility time, while increased swimming and climbing time of mice in forced swim test (FST). A1K1 and A2K2 decreased animal immobility time in TST. In the open field test, both A1K1 and A2K2 increased the number of ambulations and rearings. A1K1 and A2K2 dose-dependently (0.5-1.0 mg/kg) increased spontaneous alternation behavior (%) and the number of entries of mice in Y-maze test. In the MWM test, A1K1 and A2K2 decreased escape latency time. Overall, both in-silico and in-vivo investigations of A1K1 and A2K2, report their therapeutic potential for antidepressant and anti-Alzheimer properties. Hence, these compounds possess potent neuroprotective properties and may be further evaluated for their therapeutic potential in various neurological disorders.

Dietary Sargassum fusiforme improves memory and reduces amyloid plaque load in an Alzheimer's disease mouse model

Activation of liver X receptors (LXRs) by synthetic agonists was found to improve cognition in Alzheimer's disease (AD) mice. However, these LXR agonists induce hypertriglyceridemia and hepatic steatosis, hampering their use in the clinic. We hypothesized that phytosterols as LXR agonists enhance cognition in AD without affecting plasma and hepatic triglycerides. Phytosterols previously reported to activate LXRs were tested in a luciferase-based LXR reporter assay. Using this assay, we found that phytosterols commonly present in a Western type diet in physiological concentrations do not activate LXRs. However, a lipid extract of the 24(S)-Saringosterol-containing seaweed Sargassum fusiforme did potently activate LXRβ. Dietary supplementation of crude Sargassum fusiforme or a Sargassum fusiforme-derived lipid extract to AD mice significantly improved short-term memory and reduced hippocampal Aβ plaque load by 81%. Notably, none of the side effects typically induced by full synthetic LXR agonists were observed. In contrast, administration of the synthetic LXRα activator, AZ876, did not improve cognition and resulted in the accumulation of lipid droplets in the liver. Administration of Sargassum fusiforme-derived 24(S)-Saringosterol to cultured neurons reduced the secretion of Aβ₄₂. Moreover, conditioned medium from 24(S)-Saringosterol-treated astrocytes added to microglia increased phagocytosis of Aβ. Our data show that Sargassum fusiforme improves cognition and alleviates AD pathology. This may be explained at least partly by 24(S)-Saringosterol-mediated LXRβ activation.

The β-secretase (BACE) inhibitor NB-360 in preclinical models: From amyloid-β reduction to downstream disease-relevant effects

Inhibition of β-secretase 1 (BACE-1; also known as β-site amyloid precursor protein-cleaving enzyme-1) is a current approach to fight the amyloid-β (Aβ) deposition in the brains of patients with Alzheimer's disease, and a number of BACE-1 inhibitors are being tested in clinical trials. The BACE-1 inhibitor NB-360, although not a clinical compound, turned out to be a valuable pharmacological tool to investigate the effects of BACE-1 inhibition on the deposition of different Aβ species in amyloid precursor protein (APP) transgenic mice. Furthermore, chronic animal studies with NB-360 revealed relationships between BACE-1 inhibition, Aβ deposition, and Aβ-related downstream effects on neuroinflammation, neuronal function, and markers of neurodegeneration. NB-360 effects on the processing of physiological BACE-1 substrates as well as on nonenzymatic BACE-1 functions have been investigated, complementing studies in BACE-1 knockout mice. Because NB-360 is also an inhibitor for BACE-2, nonclinical studies in adult animals revealed physiological effects of BACE-2 inhibition. LINKED ARTICLES: This article is part of a themed section on Therapeutics for Dementia and Alzheimer's Disease: New Directions for Precision Medicine. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.18/issuetoc.

Effects of the dual orexin receptor antagonist DORA-22 on sleep in 5XFAD mice

Introduction

Sleep disruption is a characteristic of Alzheimer's disease (AD) that may exacerbate disease progression. This study tested whether a dual orexin receptor antagonist (DORA) would enhance sleep and attenuate neuropathology, neuroinflammation, and cognitive deficits in an AD-relevant mouse model, 5XFAD.

Methods

Wild-type (C57Bl6/SJL) and 5XFAD mice received chronic treatment with vehicle or DORA-22. Piezoelectric recordings monitored sleep and spatial memory was assessed via spontaneous Y-maze alternations. Aβ plaques, Aβ levels, and neuroinflammatory markers were measured by immunohistochemistry, enzyme-linked immunosorbent assay, and real-time polymerase chain reaction, respectively.

Results

In 5XFAD mice, DORA-22 significantly increased light-phase sleep without reducing Aβ levels, plaque density, or neuroinflammation. Effects of DORA-22 on cognitive deficits could not be determined because the 5XFAD mice did not exhibit deficits.

Discussion

These findings suggest that DORAs may improve sleep in AD patients. Further investigations should optimize the dose and duration of DORA-22 treatment and explore additional AD-relevant animal models and cognitive tests.

Assessing Spatial Working Memory Using the Spontaneous Alternation Y-maze Test in Aged Male Mice

The global population is aging and the prevalence of age-related diseases, such as Alzheimer's disease and vascular dementia is increasing. Understanding functional impairments and disease processes is of vital importance in order to develop effective therapeutics. Using the natural exploratory behavior of mice, the spontaneous alternation y-maze can assess short-term spatial working memory. The protocol for y-maze testing is straightforward and requires minimal resources, as well as animal training and output. Therefore, it can be broadly applied to study short-term memory in aged rodent models.

Carbon monoxide attenuates amyloidogenesis via down-regulation of NF-κB-mediated BACE1 gene expression

Amyloid-β (Aβ) peptides, the major constituent of plaques, are generated by sequential proteolytic cleavage of the amyloid precursor protein (APP) via β-secretase (BACE1) and the γ-secretase complex. It has been proposed that the abnormal secretion and accumulation of Aβ are the initial causative events in the development of Alzheimer's disease (AD). Drugs modulating this pathway could be used for AD treatment. Previous studies indicated that carbon monoxide (CO), a product of heme oxygenase (HO)-1, protects against Aβ-induced toxicity and promotes neuroprotection. However, the mechanism underlying the mitigative effect of CO on Aβ levels and BACE1 expression is unclear. Here, we show that CO modulates cleavage of APP and Aβ production by decreasing BACE1 expression in vivo and in vitro. CO reduces Aβ levels and improves memory deficits in AD transgenic mice. The regulation of BACE1 expression by CO is dependent on nuclear factor-kappa B (NF-κB). Consistent with the negative role of SIRT1 in the NF-κB activity, CO fails to evoke significant decrease in BACE1 expression in the presence of the SIRT1 inhibitor. Furthermore, CO attenuates elevation of BACE1 level in brains of 3xTg-AD mouse model as well as mice fed high-fat, high-cholesterol diets. CO reduces the NF-κB-mediated transcription of BACE1 induced by the cholesterol oxidation product 27-hydroxycholesterol or hydrogen peroxide. These data suggest that CO reduces the NF-κB-mediated BACE1 transcription and consequently decreases Aβ production. Our study provides novel mechanisms by which CO reduces BACE1 expression and Aβ production and may be an effective agent for AD treatment.

Expression Profiles of Long Noncoding RNAs in Intranasal LPS-Mediated Alzheimer's Disease Model in Mice

Alzheimer's disease (AD), characterized by memory loss, cognitive decline, and dementia, is a progressive neurodegenerative disease. Although the long noncoding RNAs (lncRNAs) have recently been identified to play a role in the pathogenesis of AD, the specific effects of lncRNAs in AD remain unclear. In present study, we have investigated the expression profiles of lncRNAs in hippocampal of intranasal LPS-mediated Alzheimer's disease models in mice by microarray method. A total of 395 lncRNAs and 123 mRNAs was detected to express differently in AD models and controls (>2.0 folds, p<0.05). The microarray expression was validated by Quantitative Real-Time-PCR (qRT-PCR). The pathway analysis showed the mRNAs that correlated with lncRNAs were involved in inflammation, apoptosis, and nervous system related pathways. The lncRNA-TFs network analysis suggested the lncRNAs were mostly regulated by HMGA2, ONECUT2, FOXO1, and CDC5L. Additionally, lncRNA-target-TFs network analysis indicated the FOXL1, CDC5L, ONECUT2, and CDX1 to be the TFs most likely to regulate the production of these lncRNAs. This is the first study to investigate lncRNAs expression pattern in intranasal LPS-mediated Alzheimer's disease model in mice. And these results may facilitate the understanding of the pathogenesis of AD targeting lncRNAs.

Cognitive decline in Tg2576 mice shows sex-specific differences and correlates with cerebral amyloid-beta

Patients suffering from Alzheimer's disease show a sex-dependent decline of cognitive function. The aim of this investigation was to show these differences in an animal model for Alzheimer's disease and to determine whether this effect is correlated to amyloid-beta-induced pathophysiological changes. Therefore, we assessed cognitive performance with the modified hole-board test in female and male Tg2576 and wild type mice at the age of 6, 8, 10, 12, 14, and 16 months and correlated these findings to the total amount of soluble amyloid-beta and insoluble amyloid deposits in the brain. Tg2576 mice perform worse than wild types. Female Tg2576 mice develop an accentuated cognitive impairment (wrong choice total) beginning at the age of 12 months compared to their male littermates. Alterations in the mice's behaviour do not show interference with these deficits. Cognitive impairment is correlated to the amount of soluble amyloid-beta and insoluble amyloid deposits in the brain in a sex-dependent manner.

Consequences of Pharmacological BACE Inhibition on Synaptic Structure and Function

Alzheimer's disease is the most prevalent neurodegenerative disorder among elderly persons. Overt accumulation and aggregation of the amyloid-β peptide (Aβ) is thought to be the initial causative factor for Alzheimer's disease. Aβ is produced by sequential proteolytic cleavage of the amyloid precursor protein. Beta-site amyloid precursor protein cleaving enzyme 1 (BACE1) is the initial and rate-limiting protease for the generation of Aβ. Therefore, inhibiting BACE1 is considered one of the most promising therapeutic approaches for potential treatment of Alzheimer's disease. Currently, several drugs blocking this enzyme (BACE inhibitors) are being evaluated in clinical trials. However, high-dosage BACE-inhibitor treatment interferes with structural and functional synaptic plasticity in mice. These adverse side effects may mask the therapeutic benefit of lowering the Aβ concentration. In this review, we focus on the consequences of BACE inhibition-mediated synaptic deficits and the potential clinical implications.

Trimethylamine-N-oxide promotes brain aging and cognitive impairment in mice

Gut microbiota can influence the aging process and may modulate aging‐related changes in cognitive function. Trimethylamine‐N‐oxide (TMAO), a metabolite of intestinal flora, has been shown to be closely associated with cardiovascular disease and other diseases. However, the relationship between TMAO and aging, especially brain aging, has not been fully elucidated. To explore the relationship between TMAO and brain aging, we analysed the plasma levels of TMAO in both humans and mice and administered exogenous TMAO to 24‐week‐old senescence‐accelerated prone mouse strain 8 (SAMP8) and age‐matched senescence‐accelerated mouse resistant 1 (SAMR1) mice for 16 weeks. We found that the plasma levels of TMAO increased in both the elderly and the aged mice. Compared with SAMR1‐control mice, SAMP8‐control mice exhibited a brain aging phenotype characterized by more senescent cells in the hippocampal CA3 region and cognitive dysfunction. Surprisingly, TMAO treatment increased the number of senescent cells, which were primarily neurons, and enhanced the mitochondrial impairments and superoxide production. Moreover, we observed that TMAO treatment increased synaptic damage and reduced the expression levels of synaptic plasticity‐related proteins by inhibiting the mTOR signalling pathway, which induces and aggravates aging‐related cognitive dysfunction in SAMR1 and SAMP8 mice, respectively. Our findings suggested that TMAO could induce brain aging and age‐related cognitive dysfunction in SAMR1 mice and aggravate the cerebral aging process of SAMP8 mice, which might provide new insight into the effects of intestinal microbiota on the brain aging process and help to delay senescence by regulating intestinal flora metabolites.

BACE1-cleavage of Sez6 and Sez6L is elevated in Niemann-Pick type C disease mouse brains

It is intriguing that a rare, inherited lysosomal storage disorder Niemann-Pick type C (NPC) shares similarities with Alzheimer’s disease (AD). We have previously reported an enhanced processing of β-amyloid precursor protein (APP) by β-secretase (BACE1), a key enzyme in the pathogenesis of AD, in NPC1-null cells. In this work, we characterized regional and temporal expression and processing of the recently identified BACE1 substrates seizure protein 6 (Sez6) and seizure 6-like protein (Sez6L), and APP, in NPC1^-/- (NPC1) and NPC1^+/+ (wt) mouse brains. We analysed 4-weeks old brains to detect the earliest changes associated with NPC, and 10-weeks of age to identify changes at terminal disease stage. Sez6 and Sez6L were selected due to their predominant cleavage by BACE1, and their potential role in synaptic function that may contribute to presentation of seizures and/or motor impairments in NPC patients. While an enhanced BACE1-cleavage of all three substrates was detected in NPC1 vs. wt-mouse brains at 4-weeks of age, at 10-weeks increased proteolysis by BACE1 was observed for Sez6L in the cortex, hippocampus and cerebellum of NPC1-mice. Interestingly, both APP and Sez6L were found to be expressed in Purkinje neurons and their immunostaining was lost upon Purkinje cell neurodegeneration in 10-weeks old NPC1 mice. Furthermore, in NPC1- vs. wt-mouse primary cortical neurons, both Sez6 and Sez6L showed increased punctuate staining within the endolysosomal pathway as well as increased Sez6L and BACE1-positive puncta. This indicates that a trafficking defect within the endolysosomal pathway may play a key role in enhanced BACE1-proteolysis in NPC disease. Overall, our findings suggest that enhanced proteolysis by BACE1 could be a part of NPC disease pathogenesis. Understanding the basic biology of BACE1 and the functional impact of cleavage of its substrates is important to better evaluate the therapeutic potential of BACE1 against AD and, possibly, NPC disease.

Review: Neuropathology and behavioural features of transgenic murine models of Alzheimer's disease

Our understanding of the underlying biology of Alzheimer's disease (AD) has been steadily progressing; however, this is yet to translate into a successful treatment in humans. The use of transgenic mouse models has helped to develop our understanding of AD, not only in terms of disease pathology, but also with the associated cognitive impairments typical of AD. Plaques and neurofibrillary tangles are often among the last pathological changes in AD mouse models, after neuronal loss and gliosis. There is a general consensus that successful treatments need to be applied before the onset of these pathologies and associated cognitive symptoms. This review discusses the different types of AD mouse models in terms of the temporal progression of the disease, how well they replicate the pathological changes seen in human AD and their cognitive defects. We provide a critical assessment of the behavioural tests used with AD mice to assess cognitive changes and decline, and discuss how successfully they correlate with cognitive impairments in humans with AD. This information is an important tool for AD researchers when deciding on appropriate mouse models, and when selecting measures to assess behavioural and cognitive change.

Store depletion-induced h-channel plasticity rescues a channelopathy linked to Alzheimer's disease

Voltage-gated ion channels are critical for neuronal integration. Some of these channels, however, are misregulated in several neurological disorders, causing both gain- and loss-of-function channelopathies in neurons. Using several transgenic mouse models of Alzheimer's disease (AD), we find that sub-threshold voltage signals strongly influenced by hyperpolarization-activated, cyclic nucleotide-gated (HCN) channels progressively deteriorate over chronological aging in hippocampal CA1 pyramidal neurons. The degraded signaling via HCN channels in the transgenic mice is accompanied by an age-related global loss of their non-uniform dendritic expression. Both the aberrant signaling via HCN channels and their mislocalization could be restored using a variety of pharmacological agents that target the endoplasmic reticulum (ER). Our rescue of the HCN channelopathy helps provide molecular details into the favorable outcomes of ER-targeting drugs on the pathogenesis and synaptic/cognitive deficits in AD mouse models, and implies that they might have beneficial effects on neurological disorders linked to HCN channelopathies.

Transplantation of Human Menstrual Blood-Derived Mesenchymal Stem Cells Alleviates Alzheimer's Disease-Like Pathology in APP/PS1 Transgenic Mice

Extracellular β-amyloid (Aβ) plaques and neurofibrillary tangles (NFTs) are the pathological hallmarks of Alzheimer’s disease (AD). Mesenchymal stem cells (MSCs) have shown therapeutic efficacy in many neurodegenerative diseases, including AD. Human menstrual blood-derived stem cells (MenSCs) are a novel source of MSCs advantageous for their higher proliferation rate and because they are easy to obtain without ethical concerns. Although MenSCs have exhibited therapeutic efficacy in some diseases, their effects on AD remain elusive. In the present study, we showed that intracerebral transplantation of MenSCs dramatically improved the spatial learning and memory of APP/PS1 mice. In addition, MenSCs significantly ameliorated amyloid plaques and reduced tau hyperphosphorylation in APP/PS1 mice. Remarkably, we also found that intracerebral transplantation of MenSCs markedly increased several Aβ degrading enzymes and modulated a panel of proinflammatory cytokines associated with an altered microglial phenotype, suggesting an Aβ degrading and anti-inflammatory impact of MenSCs in the brains of APP/PS1 mice. In conclusion, these findings suggest that MenSCs are a promising therapeutic candidate for AD.

BACE1 Mediates HIV-Associated and Excitotoxic Neuronal Damage Through an APP-Dependent Mechanism

HIV-associated neurocognitive disorders (HANDs) share common symptoms with Alzheimer's disease (AD), which is characterized by amyloid-β (Aβ) plaques. Plaques are formed by aggregation of Aβ oligomers, which may be the toxic species in AD pathogenesis, and oligomers are generated by cleavage of amyloid precursor protein (APP) by β-site amyloid precursor protein cleaving enzyme 1 (BACE1). BACE1 inhibitors reverse neuronal loss and cognitive decline in animal models of AD. Although studies have also found evidence of altered APP processing in HIV⁺ patients, it is unknown whether increased BACE1 expression or Aβ oligomer production is a common neuropathological feature of HAND. Moreover, it is unknown whether BACE1 or APP is involved in the excitotoxic, NMDAR-dependent component of HIV-associated neurotoxicity in vitro Herein, we hypothesize that HIV-associated neurotoxicity is mediated by NMDAR-dependent elevation of BACE1 and subsequent altered processing of APP. Supporting this, we observed elevated levels of BACE1 and Aβ oligomers in CNS of male and female HIV⁺ patients. In a model of HIV-associated neurotoxicity in which rat neurons are treated with supernatants from HIV-infected human monocyte-derived macrophages, we observed NMDAR-dependent elevation of BACE1 protein. NMDA treatment also increased BACE1 and both pharmacological BACE1 inhibition and genetic loss of APP were partially neuroprotective. Moreover, in APP knock-out (APP^-/-) mouse neurons, NMDA-induced toxicity was BACE1 independent, indicating that cytotoxicity of BACE1 is dependent upon APP cleavage. Our findings suggest that increased BACE1 and the resultant Aβ oligomer production may contribute to HIV-associated neuropathogenesis and inhibition of BACE1 could have therapeutic potential in HANDs.SIGNIFICANCE STATEMENT HIV-associated neurocognitive disorders (HANDs) represent a range of cognitive impairments affecting ∼50% of HIV⁺ individuals. The specific causes of HAND are unknown, but evidence suggests that HIV-infected macrophage infiltration into the brain may cause neuronal damage. Herein, we show that neurons treated with conditioned media from HIV-infected macrophages have increased expression of β-site amyloid precursor protein cleaving enzyme 1 (BACE1), a protein implicated in Alzheimer's disease pathogenesis. Moreover, inhibition of BACE1 prevented neuronal loss after conditioned media exposure, but had no effect on HIV-associated neurotoxicity in neurons lacking its cleavage target amyloid precursor protein. We also observed increased BACE1 expression in HIV⁺ patient brain tissue, confirming the potential relevance of BACE1 as a therapeutic target in HANDs.

BACE1 SUMOylation increases its stability and escalates the protease activity in Alzheimer's disease

BACE1 is a rate-limiting enzyme for amyloid beta polypeptide production, which plays a crucial role in Alzheimer’s disease (AD) pathogenesis. However, how this essential protease is posttranslationally regulated remains incompletely understood. In the current study, we show that K501 residue on BACE1, a ubiquitin modification site, is also competitively SUMOylated. We discovered that SUMOylation of BACE1 augments its stability and enzymatic activity, resulting in senile plaque formation and cognitive defect. Identification of the posttranslational modification on BACE1 provides insight into the molecular mechanism in AD.

Amyloid beta (Aβ) is a major pathological marker in Alzheimer’s disease (AD), which is principally regulated by the rate-limiting β-secretase (i.e., BACE1) cleavage of amyloid precursor protein (APP). However, how BACE1 activity is posttranslationally regulated remains incompletely understood. Here, we show that BACE1 is predominantly SUMOylated at K501 residue, which escalates its protease activity and stability and subsequently increases Aβ production, leading to cognitive defect seen in the AD mouse model. Compared with a non-SUMOylated K501R mutant, injection of wild-type BACE1 significantly increases Aβ production and triggers cognitive dysfunction. Furthermore, overexpression of wild-type BACE1, but not non-SUMOylated K501R mutant, facilitates senile plaque formation and aggravates the cognitive deficit seen in the APP/PS1 AD mouse model. Together, our data strongly suggest that K501 SUMOylation on BACE1 plays a critical role in mediating its stability and enzymatic activity.

Premature hippocampus-dependent memory decline in middle-aged females of a genetic rat model of depression

Aging and major depressive disorder are risk factors for dementia, including Alzheimer's Disease (AD), but the mechanism(s) linking depression and dementia are not known. Both AD and depression show greater prevalence in women. We began to investigate this connection using females of the genetic model of depression, the inbred Wistar Kyoto More Immobile (WMI) rat. These rats consistently display depression-like behavior compared to the genetically close control, the Wistar Kyoto Less Immobile (WLI) strain. Hippocampus-dependent contextual fear memory did not differ between young WLI and WMI females, but, by middle-age, female WMIs showed memory deficits compared to same age WLIs. This deficit, measured as duration of freezing in the fear provoking-context was not related to activity differences between the strains prior to fear conditioning. Hippocampal expression of AD-related genes, such as amyloid precursor protein, amyloid beta 42, beta secretase, synucleins, total and dephosphorylated tau, and synaptophysin, did not differ between WLIs and WMIs in either age group. However, hippocampal transcript levels of catalase (Cat) and hippocampal and frontal cortex expression of insulin-like growth factor 2 (Igf2) and Igf2 receptor (Igf2r) paralleled fear memory differences between middle-aged WLIs and WMIs. This data suggests that chronic depression-like behavior that is present in this genetic model is a risk factor for early spatial memory decline in females. The molecular mechanisms of this early memory decline likely involve the interaction of aging processes with the genetic components responsible for the depression-like behavior in this model.

Protein Expression of BACE1 is Downregulated by Donepezil in Alzheimer's Disease Platelets

BACKGROUND

Abnormal amyloid-β protein precursor (AβPP) metabolism is a key feature of Alzheimer's disease (AD). Platelets contain most of the enzymatic machinery required for AβPP processing, and correlates of intracerebral abnormalities have been demonstrated in platelets of patients with AD. Thus, AβPP-related molecules in platelets may be regarded as peripheral markers of AD.

OBJECTIVE

We sought to determine the protein expression of the AβPP secretases (ADAM10, BACE1, and PSEN1) and AβPP ratio in platelets of patients with mild or moderate AD compared to healthy controls. We further determined whether the protein expression of these markers might be modified by chronic treatment with donepezil.

METHODS

Platelet samples were obtained from patients and controls at baseline and after 3 and 6 months of continuous treatment with therapeutic doses of donepezil. The protein expression of platelet markers was determined by western blotting.

RESULTS

AD patients had a significant decrease in AβPP ratio, ADAM10, and PSEN1 compared to controls at baseline, but these differences were not modified by the treatment. Nonetheless, a significant reduction in the protein expression of BACE1 was observed in patients treated with donepezil for 6 months.

CONCLUSION

Our results corroborate previous findings from our group and others of decreased AβPP ratio and protein expression of ADAM10 in AD. We further show that PSEN1 is decreased in AD platelets, and that the protein expression of BACE1 is downregulated by chronic treatment with donepezil. This effect may be interpreted as evidence of disease modification.

Reduced cognitive function, increased blood-brain-barrier transport and inflammatory responses, and altered brain metabolites in LDLr -/-and C57BL/6 mice fed a western diet

Recent work suggests that diet affects brain metabolism thereby impacting cognitive function. Our objective was to determine if a western diet altered brain metabolism, increased blood-brain barrier (BBB) transport and inflammation, and induced cognitive impairment in C57BL/6 (WT) mice and low-density lipoprotein receptor null (LDLr -/-) mice, a model of hyperlipidemia and cognitive decline. We show that a western diet and LDLr -/- moderately influence cognitive processes as assessed by Y-maze and radial arm water maze. Also, western diet significantly increased BBB transport, as well as microvessel factor VIII in LDLr -/- and microglia IBA1 staining in WT, both indicators of activation and neuroinflammation. Interestingly, LDLr -/- mice had a significant increase in ¹⁸F- fluorodeoxyglucose uptake irrespective of diet and brain ¹H-magnetic resonance spectroscopy showed increased lactate and lipid moieties. Metabolic assessments of whole mouse brain by GC/MS and LC/MS/MS showed that a western diet altered brain TCA cycle and β-oxidation intermediates, levels of amino acids, and complex lipid levels and elevated proinflammatory lipid mediators. Our study reveals that the western diet has multiple impacts on brain metabolism, physiology, and altered cognitive function that likely manifest via multiple cellular pathways.

A Novel Small Molecule Modulator of Amyloid Pathology

Because traditional approaches to drug development for Alzheimer's disease are becoming increasingly expensive and in many cases disappointingly unsuccessful, alternative approaches are required to shift the paradigm. Following leads from investigations of dihydropyridine calcium channel blockers, we observed unique properties from a class of functionalized naphthyridines and sought to develop these as novel therapeutics that minimize amyloid pathology without the adverse effects associated with current therapeutics. Our data show methyl 2,4-dimethyl-5-oxo-5,6-dihydrobenzo[c][2,7]naphthyridine-1-carboxylate (BNC-1) significantly decreases amyloid burden in a well-established mouse model of amyloid pathology through a unique mechanism mediated by Elk-1, a transcriptional repressor of presenilin-1. Additionally, BNC-1 treatment leads to increased levels of synaptophysin and synapsin, markers of synaptic integrity, but does not adversely impact presenilin-2 or processing of Notch-1, thus avoiding negative off target effects associated with pan-gamma secretase inhibition. Overall, our data show BNC-1 significantly decreases amyloid burden and improves markers of synaptic integrity in a well-established mouse model of amyloid deposition by promoting phosphorylation and activation of Elk-1, a transcriptional repressor of presenilin-1 but not presenilin-2. These data suggest BNC-1 might be a novel, disease-modifying therapeutic that will alter the pathogenesis of Alzheimer's disease.

Impairments of spatial memory in an Alzheimer's disease model via degeneration of hippocampal cholinergic synapses

Choline acetyltransferase neurons in the vertical diagonal band of Broca (vChATs) degenerate in the early stage of Alzheimer’s disease (AD). Here, we report that vChATs directly innervate newly generated immature neurons (NGIs) in the dorsal hippocampus (dNGIs) of adult mice and regulate both the dNGIs survival and spatial pattern separation. In a mouse model that exhibits amyloid-β plaques similar to AD patients, cholinergic synaptic transmission, dNGI survival and spatial pattern separation are impaired. Activation of vChATs with theta burst stimulation (TBS) that alleviates the decay in cholinergic synaptic transmission effectively protects against spatial pattern separation impairments in the AD mice and this protection was completely abolished by inhibiting the dNGIs survival. Thus, the impairments of pattern separation-associated spatial memory in AD mice are in part caused by degeneration of cholinergic synaptic transmission that modulates the dNGIs survival.

Cholinergic neurons in the diagonal band of Broca degenerate early in Alzheimer’s disease. Here the authors show that in healthy mice, these cholinergic inputs innervate newborn neurons in the hippocampus, and that loss of this innervation in an Alzheimer’s disease model leads to impairments in spatial memory.

Comparative molecular docking studies of lupeol and lupenone isolated from Pueraria lobata that inhibits BACE1: Probable remedies for Alzheimer's disease

OBJECTIVE

To discover lead lupane triterpenoid's potential isolated from Pueraria lobata roots against β-site amyloid precursor protein cleaving enzyme 1 (BACE1), which serve as a rate limiting step in amyloid beta (Aβ) production altering the course of Alzheimer's disease. In addition, enzyme kinetics study and molecular docking were conducted to establish the inhibition type and structure activity relationship.

METHODS

A systematic study of 70% ethanolic P. lobata root extract was employed to identify its BACE1 inhibitory potential. Further, BACE1 inhibitory potential of two lupane terpenoids, yielded from ethanolic extract, was assessed. In order to determine their inhibition mode, Lineweaver-Burk plots and Michaelis-Menten model for BACE1 was performed. AutoDock 4.2 program in addition determined the molecular interaction of BACE1 with isolated terpenoids.

RESULTS

Considering the inhibitory potential of 70% ethanolic extract of P. lobata against BACE1 (IC₅₀ = 80.35 μg/mL), lupeol and lupenone were subsequently isolated and exhibited notable or moderate BACE1 inhibitory activity with IC₅₀ values of 5.12 and 62.98 μmol/L, respectively, as compared to the positive control quercetin (IC₅₀ = 21.28 μmol/L). The enzyme kinetics study enabled us to identify both compounds as competitive inhibitors, where lupeol displayed a very potent inhibition against BACE1 with low inhibition constant (K_i) value of 1.43 μmol/L, signifying greater binding affinity. In order to understand the binding mechanism and structure-activity relationship of two triterpene-based BACE1 inhibitors, we employed computer aided docking studies which evidently revealed that hydroxyl group of lupeol formed two hydrogen bonds with the ASP32 (catalytic aspartic residue) and SER35 residues of BACE1 with the binding energy of (-8.2 kcal/mol), while the ketone group of lupenone did not form any hydrogen bonds with BACE1 giving evidence for less binding affinity. These results in turn have predicted the dependence of the inhibitory activity in the presence of hydroxyl group which has provided a new basis for BACE1 blockade.

CONCLUSIONS

Our results have successfully explored the molecular mechanism of lupane triterpenoids via BACE1 inhibition, suggesting that lupeol in particular could be utilized as a useful therapeutic and preventive agent to mitigate Alzheimer's disease.

Conditional Depletion of Hippocampal Brain-Derived Neurotrophic Factor Exacerbates Neuropathology in a Mouse Model of Alzheimer's Disease

Damage occurring to noradrenergic neurons in the locus coeruleus (LC) contributes to the evolution of neuroinflammation and neurodegeneration in a variety of conditions and diseases. One cause of LC damage may be loss of neurotrophic support from LC target regions. We tested this hypothesis by conditional unilateral knockout of brain-derived neurotrophic factor (BDNF) in adult mice. To evaluate the consequences of BDNF loss in the context of neurodegeneration, the mice harbored familial mutations for human amyloid precursor protein and presenilin-1. In these mice, BDNF depletion reduced tyrosine hydroxylase staining, a marker of noradrenergic neurons, in the rostral LC. BDNF depletion also reduced noradrenergic innervation in the hippocampus, the frontal cortex, and molecular layer of the cerebellum, assessed by staining for dopamine beta hydroxylase. BDNF depletion led to an increase in cortical amyloid plaque numbers and size but was without effect on plaque numbers in the striatum, a site with minimal innervation from the LC. Interestingly, cortical Iba1 staining for microglia was reduced by BDNF depletion and was correlated with reduced dopamine beta hydroxylase staining. These data demonstrate that reduction of BDNF levels in an LC target region can cause retrograde damage to LC neurons, leading to exacerbation of neuropathology in distinct LC target areas. Methods to reduce BDNF loss or supplement BDNF levels may be of value to reduce neurodegenerative processes normally limited by LC noradrenergic activities.

Role of BACE1 in Alzheimer's synaptic function

Alzheimer's disease (AD) is the most common age-dependent disease of dementia, and there is currently no cure available. This hallmark pathologies of AD are the presence of amyloid plaques and neurofibrillary tangles. Although the exact etiology of AD remains a mystery, studies over the past 30 have shown that abnormal generation or accumulation of β-amyloid peptides (Aβ) is likely to be a predominant early event in AD pathological development. Aβ is generated from amyloid precursor protein (APP) via proteolytic cleavage by β-site APP cleaving enzyme 1 (BACE1). Chemical inhibition of BACE1 has been shown to reduce Aβ in animal studies and in human trials. While BACE1 inhibitors are currently being tested in clinical trials to treat AD patients, it is highly important to understand whether BACE1 inhibition will significantly impact cognitive functions in AD patients. This review summarizes the recent studies on BACE1 synaptic functions. This knowledge will help to guide the proper use of BACE1 inhibitors in AD therapy.

NF-κB-regulated microRNA-574-5p underlies synaptic and cognitive impairment in response to atmospheric PM2.5 aspiration

Background

PM_2.5 (particulate matter ≤ 2.5 μm) is one of the leading environmental risk factors for the global burden of disease. Whereas increasing evidence has linked the adverse roles of PM_2.5 with cardiovascular and respiratory diseases, limited but growing emerging evidence suggests that PM_2.5 exposure can affect the nervous system, causing neuroinflammation, synaptic dysfunction and cognitive deterioration. However, the molecular mechanisms underlying the synaptic and cognitive deficits elicited by PM_2.5 exposure are largely unknown.

Methods

C57BL/6 mice received oropharyngeal aspiration of PM_2.5 (1 and 5 mg/kg bw) every other day for 4 weeks. The mice were also stereotaxically injected with β-site amyloid precursor protein cleaving enzyme 1 (β-secretase, BACE1) shRNA or LV-miR-574-5p lentiviral constructs in the absence or presence of PM_2.5 aspiration at 5 mg/kg bw every other day for 4 weeks. Spatial learning and memory were assessed with the Morris water maze test, and synaptic function integrity was evaluated with electrophysiological recordings of long-term potentiation (LTP) and immunoblot analyses of glutamate receptor subunit expression. The expression of α-secretase (ADAM10), BACE1, and γ-secretase (nicastrin) and the synthesis and accumulation of amyloid β (Aβ) were measured by immunoblot and enzyme-linked immunosorbent assay (ELISA). MicroRNA (miRNA) expression was screened with a microRNA microarray analysis and confirmed by real-time quantitative reverse transcription PCR (qRT-PCR) analysis. Dual-luciferase reporter gene and chromatin immunoprecipitation (ChIP) analyses were used to detect the binding of miR-574-5p in the 3’UTR of BACE1 and NF-κB p65 in the promoter of miR-574-5p, respectively.

Results

PM_2.5 aspiration caused neuroinflammation and deteriorated synaptic function integrity and spatial learning and memory, and the effects were associated with the induction of BACE1. The action was mediated by NF-κB p65-regulated downregulation of miR-574-5p, which targets BACE1. Overexpression of miR-574-5p in the hippocampal region decreased BACE1 expression, restored synaptic function, and improved spatial memory and learning following PM_2.5 exposure.

Conclusions

Taken together, our findings reveal a novel molecular mechanism underlying impaired synaptic and cognitive function following exposure to PM_2.5, suggesting that miR-574-5p is a potential intervention target for the prevention and treatment of PM_2.5-induced neurological disorders.

Electronic supplementary material

The online version of this article (10.1186/s12989-017-0215-3) contains supplementary material, which is available to authorized users.

Beta-secretase inhibitors in phase I and phase II clinical trials for Alzheimer's disease

INTRODUCTION

BACE 1 is a protease that cleaves the transmembrane amyloid precursor protein and generates amyloid-β peptides that accumulate in AD brains. No known mutations are identified in the gene encoding BACE1 in AD. However, enzyme levels are elevated in AD and a single residue mutation in amyloid precursor protein protects against protein cleavage by BACE1, suggesting BACE involvement in disease pathogenesis. Drugs that can inhibit BACE1 would theoretically prevent Aβ accumulation and halt AD onset and progression. Areas covered: This review discusses clinical developments of BACE1 inhibitors and focuses on what is learned about these inhibitors as a potential treatment. Expert opinion: BACE1 inhibition as a therapeutic strategy to improve cognition in AD has been challening. Brain-penetrant BACE1 inhibitors have been developed and clinical trials are underway, both safety and efficacy are questionable. Several clinical trials suggest that BACE1 inhibition and other immunotherapies to reduce brain Aβ are insufficient to improve cognition in AD. This may be due to the emphasis on the amyloid hypothesis despite big failures. We may have to seriously consider shifting attention to therapeutic strategies other than BACE1 inhibition or reduction of Aβ alone and pay more attention to simultaneous clearance of tau and Aβ.

APP mouse models for Alzheimer's disease preclinical studies

Animal models of human diseases that accurately recapitulate clinical pathology are indispensable for understanding molecular mechanisms and advancing preclinical studies. The Alzheimer's disease (AD) research community has historically used first‐generation transgenic (Tg) mouse models that overexpress proteins linked to familial AD (FAD), mutant amyloid precursor protein (APP), or APP and presenilin (PS). These mice exhibit AD pathology, but the overexpression paradigm may cause additional phenotypes unrelated to AD. Second‐generation mouse models contain humanized sequences and clinical mutations in the endogenous mouse App gene. These mice show Aβ accumulation without phenotypes related to overexpression but are not yet a clinical recapitulation of human AD. In this review, we evaluate different APP mouse models of AD, and review recent studies using the second‐generation mice. We advise AD researchers to consider the comparative strengths and limitations of each model against the scientific and therapeutic goal of a prospective preclinical study.

Artemisia scoparia attenuates amyloid β accumulation and tau hyperphosphorylation in spontaneously hypertensive rats

The preventive effects of Artemisia scoparia extract (AS) and AS + garlic extract (ASG) on the risk of Alzheimer's disease (AD) were evaluated in spontaneously hypertensive rats. Rats were supplemented with diets containing 2% (w/w) of AS or ASG for 6 weeks. The AS group showed lower levels of amyloid β and beta-site amyloid precursor protein cleaving enzyme 1 expressions and higher expression levels of low-density lipoprotein receptor-related protein 1 than did the control group (p < 0.05). In addition, the AS showed remarkably reduced levels of phosphorylated tau proteins and suppressed expression of phosphorylated glycogen synthase kinase 3β at tyrosine 216 (active form) (p < 0.05). The ASG group also suppressed amyloid β accumulation and tau hyperphosphorylation. However, there was no synergistic effect of garlic with AS in lowering the risk of AD. These results indicate that AS could be a potential candidate to ameliorate the risk of AD.