Phenotypic and biochemical analyses of BACE1- and BACE2-deficient mice

Serum Beta-Secretase 1 Activity Is a Potential Marker for the Differential Diagnosis between Alzheimer's Disease and Frontotemporal Dementia: A Pilot Study

Alzheimer's disease (AD) and frontotemporal dementia (FTD) are the two major neurodegenerative diseases causing dementia. Due to similar clinical phenotypes, differential diagnosis is challenging without specific biomarkers. Beta-site Amyloid Precursor Protein cleaving enzyme 1 (BACE1) is a β-secretase pivotal in AD pathogenesis. In AD and mild cognitive impairment subjects, BACE1 activity is increased in brain/cerebrospinal fluid, and plasma levels appear to reflect those in the brain. In this study, we aim to evaluate serum BACE1 activity in FTD, since, to date, there is no evidence about its role. The serum of 30 FTD patients and 30 controls was analyzed to evaluate (i) BACE1 activity, using a fluorescent assay, and (ii) Glial Fibrillary Acid Protein (GFAP) and Neurofilament Light chain (NfL) levels, using a Simoa kit. As expected, a significant increase in GFAP and NfL levels was observed in FTD patients compared to controls. Serum BACE1 activity was not altered in FTD patients. A significant increase in serum BACE1 activity was shown in AD vs. FTD and controls. Our results support the hypothesis that serum BACE1 activity is a potential biomarker for the differential diagnosis between AD and FTD.

Multicolor, Cell-Impermeable, and High Affinity BACE1 Inhibitor Probes Enable Superior Endogenous Staining and Imaging of Single Molecules

The prevailing but not undisputed amyloid cascade hypothesis places the β-site of APP cleaving enzyme 1 (BACE1) center stage in Alzheimer's Disease pathogenesis. Here, we investigated functional properties of BACE1 with novel tag- and antibody-free labeling tools, which are conjugates of the BACE1-inhibitor IV (also referred to as C3) linked to different impermeable Alexa Fluor dyes. We show that these fluorescent small molecules bind specifically to BACE1, with a 1:1 labeling stoichiometry at their orthosteric site. This is a crucial property especially for single-molecule and super-resolution microscopy approaches, allowing characterization of the dyes' labeling capabilities in overexpressing cell systems and in native neuronal tissue. With multiple colors at hand, we evaluated BACE1-multimerization by Förster resonance energy transfer (FRET) acceptor-photobleaching and single-particle imaging of native BACE1. In summary, our novel fluorescent inhibitors, termed Alexa-C3, offer unprecedented insights into protein-protein interactions and diffusion behavior of BACE1 down to the single molecule level.

Electrochemiluminescence and electrochemical dual-mode detection of BACE1 activity based on the assembly of peptide and luminol co-functionalized silver nanoparticles induced by cucurbit[8]uril

A novel electrochemiluminescence (ECL) and electrochemical dual-mode sensor was developed for detecting the activity of beta-site amyloid precursor protein cleaving enzyme 1 (BACE1) and screening its inhibitor. Specifically, the adamantane (ADA)-functionalized peptide (P1), a designed substrate peptide for BACE1, was immobilized on the electrode surface via host-guest interaction between β-cyclodextrin (β-CD) and ADA. The aggregation of the peptide (P2) and luminol co-functionalized silver nanoparticles could be induced by cucurbit [8]uril (CB[8] due to the ability of CB[8] to accommodate two aromatic residues simultaneously. The obtained (CB[8]-P2-AgNPs-luminol)n aggregates with both ECL and electrochemical activity, used as the dual-mode signal probe, could be captured to the N-terminal of P1 through CB[8]. Once the substrate P1 was cleaved by BACE1, the probe-binding polypeptide fragment detached from the electrode surface, resulting in a remarkable decrease in the ECL and electrochemical signals. Taking advantage of the signal amplification function of the signal probe, the sensitive dual-mode assay for BACE1 activity can be achieved with the low detection limits of 33.11 pM for ECL and 53.19 pM for electrochemical mode. The superior analytical performance of this novel dual-mode sensor toward BACE1 activity suggested the promising application in early diagnosis of Alzheimer's disease (AD).

BACE1 in PV interneuron tunes hippocampal CA1 local circuits and resets priming of fear memory extinction

BACE1 is the rate-limiting enzyme for β-amyloid (Aβ) production and therefore is considered a prime drug target for treating Alzheimer's disease (AD). Nevertheless, the BACE1 inhibitors failed in clinical trials, even exhibiting cognitive worsening, implying that BACE1 may function in regulating cognition-relevant neural circuits. Here, we found that parvalbumin-positive inhibitory interneurons (PV INs) in hippocampal CA1 express BACE1 at a high level. We designed and developed a mouse strain with conditional knockout of BACE1 in PV neurons. The CA1 fast-spiking PV INs with BACE1 deletion exhibited an enhanced response of postsynaptic N-methyl-D-aspartate (NMDA) receptors to local stimulation on CA1 oriens, with average intrinsic electrical properties and fidelity in synaptic integration. Intriguingly, the BACE1 deletion reorganized the CA1 recurrent inhibitory motif assembled by the heterogeneous pyramidal neurons (PNs) and the adjacent fast-spiking PV INs from the superficial to the deep layer. Moreover, the conditional BACE1 deletion impaired the AMPARs-mediated excitatory transmission of deep CA1 PNs. Further rescue experiments confirmed that these phenotypes require the enzymatic activity of BACE1. Above all, the BACE1 deletion resets the priming of the fear memory extinction. Our findings suggest a neuron-specific working model of BACE1 in regulating learning and memory circuits. The study may provide a potential path of targeting BACE1 and NMDAR together to circumvent cognitive worsening due to a single application of BACE1 inhibitor in AD patients.

Preliminary In Vitro and In Vivo Insights of In Silico Candidate Repurposed Drugs for Alzheimer's Disease

Alzheimer's disease (AD) is a progressive neurodegenerative disease and is the most common type of dementia. Although a considerably large amount of money has been invested in drug development for AD, no disease modifying treatment has been detected so far. In our previous work, we developed a computational method to highlight stage-specific candidate repurposed drugs against AD. In this study, we tested the effect of the top 13 candidate repurposed drugs that we proposed in our previous work in a severity stage-specific manner using an in vitro BACE1 assay and the effect of a top-ranked drug from the list of our previous work, tetrabenazine (TBZ), in the 5XFAD as an AD mouse model. From our in vitro screening, we detected 2 compounds (clomiphene citrate and Pik-90) that showed statistically significant inhibition against the activity of the BACE1 enzyme. The administration of TBZ at the selected dose and therapeutic regimen in 5XFAD in male and female mice showed no significant effect in behavioral tests using the Y-maze and the ELISA immunoassay of Aβ40. To our knowledge, this is the first time the drug tetrabenazine has been tested in the 5XFAD mouse model of AD in a sex-stratified manner. Our results highlight 2 drugs (clomiphene citrate and Pik-90) from our previous computational work for further investigation.

The Alzheimer's disease-linked protease BACE1 modulates neuronal IL-6 signaling through shedding of the receptor gp130

BACKGROUND

The protease BACE1 is a major drug target for Alzheimer's disease, but chronic BACE1 inhibition is associated with non-progressive cognitive worsening that may be caused by modulation of unknown physiological BACE1 substrates.

METHODS

To identify in vivo-relevant BACE1 substrates, we applied pharmacoproteomics to non-human-primate cerebrospinal fluid (CSF) after acute treatment with BACE inhibitors.

RESULTS

Besides SEZ6, the strongest, dose-dependent reduction was observed for the pro-inflammatory cytokine receptor gp130/IL6ST, which we establish as an in vivo BACE1 substrate. Gp130 was also reduced in human CSF from a clinical trial with a BACE inhibitor and in plasma of BACE1-deficient mice. Mechanistically, we demonstrate that BACE1 directly cleaves gp130, thereby attenuating membrane-bound gp130 and increasing soluble gp130 abundance and controlling gp130 function in neuronal IL-6 signaling and neuronal survival upon growth-factor withdrawal.

CONCLUSION

BACE1 is a new modulator of gp130 function. The BACE1-cleaved, soluble gp130 may serve as a pharmacodynamic BACE1 activity marker to reduce the occurrence of side effects of chronic BACE1 inhibition in humans.

BACE2: A Promising Neuroprotective Candidate for Alzheimer's Disease

Alzheimer's disease (AD) is the most common cause of dementia that affects millions of predominantly elderly individuals worldwide. Despite intensive research over several decades, controversies still surround the etiology of AD and the disease remains incurable. Meanwhile, new molecular players of the central amyloid cascade hypothesis have emerged and among these is a protease known as β-site APP cleavage enzyme 2 (BACE2). Unlike BACE1, BACE2 cleaves the amyloid-β protein precursor within the Aβ domain that accordingly prevents the generation of Aβ42 peptides, the aggregation of which is commonly regarded as the toxic entity that drives neurodegeneration in AD. Given this non-amyloidogenic role of BACE2, it is attractive to position BACE2 as a therapeutic target for AD. Indeed, several groups including ours have demonstrated a neuroprotective role for BACE2 in AD. In this review, we discuss emerging evidence supporting the ability of BACE2 in mitigating AD-associated pathology in various experimental systems including human pluripotent stem cell-derived cerebral organoid disease models. Alongside this, we also provide an update on the identification of single nucleotide polymorphisms occurring in the BACE2 gene that are linked to increased risk and earlier disease onset in the general population. In particular, we highlight a recently identified point mutation on BACE2 that apparently leads to sporadic early-onset AD. We believe that a better understanding of the role of BACE2 in AD would provide new insights for the development of viable therapeutic strategies for individuals with dementia.

Biological Mechanism-based Neurology and Psychiatry: A BACE1/2 and Downstream Pathway Model

In oncology, comprehensive omics and functional enrichment studies have led to an extensive profiling of (epi)genetic and neurobiological alterations that can be mapped onto a single tumor's clinical phenotype and divergent clinical phenotypes expressing common pathophysiological pathways. Consequently, molecular pathway-based therapeutic interventions for different cancer typologies, namely tumor type- and site-agnostic treatments, have been developed, encouraging the real-world implementation of a paradigm shift in medicine. Given the breakthrough nature of the new-generation translational research and drug development in oncology, there is an increasing rationale to transfertilize this blueprint to other medical fields, including psychiatry and neurology. In order to illustrate the emerging paradigm shift in neuroscience, we provide a state-of-the-art review of translational studies on the β-site amyloid precursor protein cleaving enzyme (BACE) and its most studied downstream effector, neuregulin, which are molecular orchestrators of distinct biological pathways involved in several neurological and psychiatric diseases. This body of data aligns with the evidence of a shared genetic/biological architecture among Alzheimer's disease, schizoaffective disorder, and autism spectrum disorders. To facilitate a forward-looking discussion about a potential first step towards the adoption of biological pathway-based, clinical symptom-agnostic, categorization models in clinical neurology and psychiatry for precision medicine solutions, we engage in a speculative intellectual exercise gravitating around BACE-related science, which is used as a paradigmatic case here. We draw a perspective whereby pathway-based therapeutic strategies could be catalyzed by highthroughput techniques embedded in systems-scaled biology, neuroscience, and pharmacology approaches that will help overcome the constraints of traditional descriptive clinical symptom and syndrome-focused constructs in neurology and psychiatry.

Bilateral Hippocampal Volume Mediated the Relationship Between Plasma BACE1 Concentration and Memory Function in the Early Stage of Alzheimer's Disease: A Cross-Sectional Study

BACKGROUND

β-site amyloid precursor protein cleaving enzyme 1 (BACE1) is a key enzyme in the formation of amyloid-β (Aβ) protein. Increasing evidence suggests that BACE1 concentration is a potential biomarker for Alzheimer's disease (AD).

OBJECTIVE

To evaluate the correlations between plasma BACE1 concentration, cognition, and hippocampal volume at different stages of the AD continuum.

METHODS

Plasma BACE1 concentrations were measured in 32 patients with probable dementia due to AD (ADD), 48 patients with mild cognitive impairment (MCI) due to AD, and 40 cognitively unimpaired (CU) individuals. Memory function was evaluated using the auditory verbal learning test (AVLT), and voxel-based morphometry was used to analyze bilateral hippocampal volumes. Correlation and mediation analyses were performed to investigate the associations between plasma BACE1 concentration, cognition, and hippocampal atrophy.

RESULTS

The MCI and ADD groups exhibited elevated BACE1 concentrations compared with the CU group after adjusting for age, sex, and apolipoprotein E (APOE) genotype. Increased BACE1 concentration was found in AD continuum patients who were APOE ɛ4 carriers (p < 0.05). BACE1 concentration was negatively associated with the scores of the subitems of the AVLT and hippocampal volume (p < 0.05, false discovery rate correction) in the MCI group. Moreover, bilateral hippocampal volume mediated the relationship between BACE1 concentration and recognition in the MCI group.

CONCLUSION

BACE1 expression increased in the AD continuum, and bilateral hippocampal volume mediated the effect of BACE1 concentration on memory function in patients with MCI. Research has indicated that the plasma BACE1 concentration might be a biomarker at the early stage of AD.

Amyloid-ß plaque formation and BACE1 accumulation in the brains of a 5xFAD Alzheimer's disease mouse model is associated with altered distribution and not proteolysis of BACE1 substrates Sez6 and Sez6L

The formation of amyloid-ß peptides (Aß), that accumulate in Alzheimer's disease (AD) brains, involves proteolytic processing of the amyloid precursor protein (APP) firstly by ß-secretase (BACE1). Since BACE1 cleaves a plethora of other substrates, in this work we investigated whether the proteolysis and/or distribution of other BACE1 substrates, such as seizure protein 6 (Sez6) and seizure 6-like protein (Sez6L), is altered in AD. To test this we used 5xFAD mouse model brains that show an early accumulation of Aß plaques already at 2-months of age. Here we show for the first time that accumulation of BACE1 in peri-plaque regions and its enhanced levels in AD brains does not affect proteolysis of BACE1 substrates other than APP, such as Sez6 and Sez6L. We observed altered distribution of Sez6 and Sez6L in the area of Aß plaques in 5xFAD brains which is distinct to that of APP, BACE1 and/or LAMP1, suggesting different localization and/or function of these BACE1 substrates. While it is necessary to further elucidate the potential role that this may play in the course of AD, it is likely that Aß-targeted therapies may have beneficial effects against accumulation and/or altered distribution of BACE1 and its substrates, in addition to APP.

Amylin and Secretases in the Pathology and Treatment of Alzheimer's Disease

Alzheimer’s disease remains a prevailing neurodegenerative condition which has an array physical, emotional, and financial consequences to patients and society. In the past decade, there has been a greater degree of investigation on therapeutic small peptides. This group of biomolecules have a profile of fundamentally sound characteristics which make them an intriguing area for drug development. Among these biomolecules, there are four modulatory mechanisms of interest in this review: alpha-, beta-, gamma-secretases, and amylin. These protease-based biomolecules all have a contributory role in the amyloid cascade hypothesis. Moreover, the involvement of various biochemical pathways intertwines these peptides to have shared regulators (i.e., retinoids). Further clinical and translational investigation must occur to gain a greater understanding of its potential application in patient care. The aim of this narrative review is to evaluate the contemporary literature on these protease biomolecule modulators and determine its utility in the treatment of Alzheimer’s disease.

Antimicrobial Peptides (AMPs) in the Pathogenesis of Alzheimer’s Disease: Implications for Diagnosis and Treatment

Alzheimer’s disease (AD) represents the most frequent type of dementia in elderly people. There are two major forms of the disease: sporadic (SAD)—whose causes are not completely understood—and familial (FAD)—with clear autosomal dominant inheritance. The two main hallmarks of AD are extracellular deposits of amyloid-beta (Aβ) peptide and intracellular deposits of the hyperphosphorylated form of the tau protein (P-tau). An ever-growing body of research supports the infectious hypothesis of sporadic forms of AD. Indeed, it has been documented that some pathogens, such as herpesviruses and certain bacterial species, are commonly present in AD patients, prompting recent clinical research to focus on the characterization of antimicrobial peptides (AMPs) in this pathology. The literature also demonstrates that Aβ can be considered itself as an AMP; thus, representing a type of innate immune defense peptide that protects the host against a variety of pathogens. Beyond Aβ, other proteins with antimicrobial activity, such as lactoferrin, defensins, cystatins, thymosin β4, LL37, histatin 1, and statherin have been shown to be involved in AD. Here, we summarized and discussed these findings and explored the diagnostic and therapeutic potential of AMPs in AD.

Contribution of proteases to the hallmarks of aging and to age-related neurodegeneration

Protein quality control ensures the degradation of damaged and misfolded proteins. Derangement of proteostasis is a primary cause of aging and age-associated diseases. The ubiquitin-proteasome and autophagy-lysosome play key roles in proteostasis but, in addition to these systems, the human genome encodes for ~600 proteases, also known as peptidases. Here, we examine the role of proteases in aging and age-related neurodegeneration. Proteases are present across cell compartments, including the extracellular space, and their substrates encompass cellular constituents, proteins with signaling functions, and misfolded proteins. Proteolytic processing by proteases can lead to changes in the activity and localization of substrates or to their degradation. Proteases cooperate with the autophagy-lysosome and ubiquitin-proteasome systems but also have independent proteolytic roles that impact all hallmarks of cellular aging. Specifically, proteases regulate mitochondrial function, DNA damage repair, cellular senescence, nutrient sensing, stem cell properties and regeneration, protein quality control and stress responses, and intercellular signaling. The capacity of proteases to regulate cellular functions translates into important roles in preserving tissue homeostasis during aging. Consequently, proteases influence the onset and progression of age-related pathologies and are important determinants of health span. Specifically, we examine how certain proteases promote the progression of Alzheimer's, Huntington's, and/or Parkinson's disease whereas other proteases protect from neurodegeneration. Mechanistically, cleavage by proteases can lead to the degradation of a pathogenic protein and hence impede disease pathogenesis. Alternatively, proteases can generate substrate byproducts with increased toxicity, which promote disease progression. Altogether, these studies indicate the importance of proteases in aging and age-related neurodegeneration.

Physical Exercise, a Potential Non-Pharmacological Intervention for Attenuating Neuroinflammation and Cognitive Decline in Alzheimer's Disease Patients

This narrative review summarises the evidence for considering physical exercise (PE) as a non-pharmacological intervention for delaying cognitive decline in patients with Alzheimer’s disease (AD) not only by improving cardiovascular fitness but also by attenuating neuroinflammation. Ageing is the most important risk factor for AD. A hallmark of the ageing process is a systemic low-grade chronic inflammation that also contributes to neuroinflammation. Neuroinflammation is associated with AD, Parkinson’s disease, late-onset epilepsy, amyotrophic lateral sclerosis and anxiety disorders. Pharmacological treatment of AD is currently limited to mitigating the symptoms and attenuating progression of the disease. AD animal model studies and human studies on patients with a clinical diagnosis of different stages of AD have concluded that PE attenuates cognitive decline not only by improving cardiovascular fitness but possibly also by attenuating neuroinflammation. Therefore, low-grade chronic inflammation and neuroinflammation should be considered potential modifiable risk factors for AD that can be attenuated by PE. This opens the possibility for personalised attenuation of neuroinflammation that could also have important health benefits for patients with other inflammation associated brain disorders (i.e., Parkinson’s disease, late-onset epilepsy, amyotrophic lateral sclerosis and anxiety disorders). In summary, life-long, regular, structured PE should be considered as a supplemental intervention for attenuating the progression of AD in human. Further studies in human are necessary to develop optimal, personalised protocols, adapted to the progression of AD and the individual’s mental and physical limitations, to take full advantage of the beneficial effects of PE that include improved cardiovascular fitness, attenuated systemic inflammation and neuroinflammation, stimulated brain Aβ peptides brain catabolism and brain clearance.

Meprin β knockout reduces brain Aβ levels and rescues learning and memory impairments in the APP/lon mouse model for Alzheimer's disease

β-Site amyloid precursor protein (APP) cleaving enzyme-1 (BACE1) is the major described β-secretase to generate Aβ peptides in Alzheimer's disease (AD). However, all therapeutic attempts to block BACE1 activity and to improve AD symptoms have so far failed. A potential candidate for alternative Aβ peptides generation is the metalloproteinase meprin β, which cleaves APP predominantly at alanine in p2 and in this study we can detect an increased meprin β expression in AD brain. Here, we report the generation of the transgenic APP/lon mouse model of AD lacking the functional Mep1b gene (APP/lon × Mep1b-/-). We examined levels of canonical and truncated Aβ species using urea-SDS-PAGE, ELISA and immunohistochemistry in brains of APP/lon mouse × Mep1b-/-. Additionally, we investigated the cognitive abilities of these mice during the Morris water maze task. Aβ1-40 and 1-42 levels are reduced in APP/lon mice when meprin β is absent. Immunohistochemical staining of mouse brain sections revealed that N-terminally truncated Aβ2-x peptide deposition is decreased in APP/lon × Mep1b-/- mice. Importantly, loss of meprin β improved cognitive abilities and rescued learning behavior impairments in APP/lon mice. These observations indicate an important role of meprin β within the amyloidogenic pathway and Aβ production in vivo.

BACE2 variant identified from HSCR patient causes AD-like phenotypes in hPSC-derived brain organoids

β-site APP-cleaving enzyme 2 (BACE2) is a homolog of BACE1, which is considered as the most promising therapeutic target for Alzheimer's disease (AD). However, the expression and functional role of BACE2 in central nervous system (CNS) remain obscured. Previously, we identified several BACE2 rare variants in Hirschsprung disease (HSCR) patients and proved that BACE2-mediated APP cleavage might represent a novel HSCR pathogenesis mechanism in enteric nervous system. Here, we validated that these HSCR-associated BACE2 variants were loss-of-function mutations. Using the human pluripotent stem cell (hPSC)-derived brain organoids (BOs), we further demonstrated that BACE2 was mainly expressed in the ventricular zone and cortical plate of BOs, and its expression level was gradually increased along with the BO maturation. Functionally, we found that the BOs carrying the BACE2 loss-of-function mutation (BACE2^G446R) showed greater apoptosis and increased levels of Aβ oligomers compared to the control BOs, resembling with the AD-associated phenotypes. All these phenotypes could be rescued via the removal of APP protein in BACE2^G446R BOs. Furthermore, rather than BACE2^G446R, BACE2^WT overexpression in BOs carrying the APP Swedish/Indiana mutations attenuated the AD-associated phenotypes, including Aβ accumulation and neuronal cell death. Taken together, our results unravel that BACE2 can protect the neuronal cell from apoptosis caused by Aβ accumulation, and the deficiency of BACE2-mediated APP cleavage may represent a common pathological mechanism for both HSCR and AD.

Revisiting APP secretases: an overview on the holistic effects of retinoic acid receptor stimulation in APP processing

Alzheimer's disease (AD) is the leading cause of dementia worldwide and is characterized by the accumulation of the β-amyloid peptide (Aβ) in the brain, along with profound alterations in phosphorylation-related events and regulatory pathways. The production of the neurotoxic Aβ peptide via amyloid precursor protein (APP) proteolysis is a crucial step in AD development. APP is highly expressed in the brain and is complexly metabolized by a series of sequential secretases, commonly denoted the α-, β-, and γ-cleavages. The toxicity of resulting fragments is a direct consequence of the first cleaving event. β-secretase (BACE1) induces amyloidogenic cleavages, while α-secretases (ADAM10 and ADAM17) result in less pathological peptides. Hence this first cleavage event is a prime therapeutic target for preventing or reverting initial biochemical events involved in AD. The subsequent cleavage by γ-secretase has a reduced impact on Aβ formation but affects the peptides' aggregating capacity. An array of therapeutic strategies are being explored, among them targeting Retinoic Acid (RA) signalling, which has long been associated with neuronal health. Additionally, several studies have described altered RA levels in AD patients, reinforcing RA Receptor (RAR) signalling as a promising therapeutic strategy. In this review we provide a holistic approach focussing on the effects of isoform-specific RAR modulation with respect to APP secretases and discuss its advantages and drawbacks in subcellular AD related events.

Infectious Agents as Potential Drivers of α-Synucleinopathies

α-synucleinopathies, encompassing Parkinson's disease, dementia with Lewy bodies, and multiple system atrophy, are devastating neurodegenerative diseases for which available therapeutic options are scarce, mostly because of our limited understanding of their pathophysiology. Although these pathologies are attributed to an intracellular accumulation of the α-synuclein protein in the nervous system with subsequent neuronal loss, the trigger(s) of this accumulation is/are not clearly identified. Among the existing hypotheses, interest in the hypothesis advocating the involvement of infectious agents in the onset of these diseases is renewed. In this article, we aimed to review the ongoing relevant factors favoring and opposing this hypothesis, focusing on (1) the potential antimicrobial role of α-synuclein, (2) potential entry points of pathogens in regard to early symptoms of diverse α-synucleinopathies, (3) pre-existing literature reviews assessing potential associations between infectious agents and Parkinson's disease, (4) original studies assessing these associations for dementia with Lewy bodies and multiple system atrophy (identified through a systematic literature review), and finally (5) potential susceptibility factors modulating the effects of infectious agents on the nervous system. © 2022 International Parkinson and Movement Disorder Society.

BACE2 suppression in mice aggravates the adverse metabolic consequences of an obesogenic diet

OBJECTIVE

Pancreatic β-cell dysfunction is a central feature in the pathogenesis of type 2 diabetes (T2D). Accumulating evidence indicates that β-site APP-cleaving enzyme 2 (BACE2) inhibition exerts a beneficial effect on β-cells in different models of T2D. Thus, targeting BACE2 may represent a potential therapeutic strategy for the treatment of this disease. Here, we aimed to investigate the effects of BACE2 suppression on glucose homeostasis in a model of diet-induced obesity.

METHODS

BACE2 knock-out (BKO) and wild-type (WT) mice were fed with a high-fat diet (HFD) for 2 or 16 weeks. Body weight, food intake, respiratory exchange ratio, locomotor activity, and energy expenditure were determined. Glucose homeostasis was evaluated by glucose and insulin tolerance tests. β-cell proliferation was assessed by Ki67-positive nuclei, and β-cell function was determined by measuring glucose-stimulated insulin secretion. Leptin sensitivity was evaluated by quantifying food intake and body weight after an intraperitoneal leptin injection. Neuropeptide gene expression and insulin signaling in the mediobasal hypothalamus were determined by qPCR and Akt phosphorylation, respectively.

RESULTS

After 16 weeks of HFD feeding, BKO mice exhibited an exacerbated body weight gain and hyperphagia, in comparison to WT littermates. Glucose tolerance was similar in both groups, whereas HFD-induced hyperinsulinemia, insulin resistance, and β-cell expansion were more pronounced in BKO mice. In turn, leptin-induced food intake inhibition and hypothalamic insulin signaling were impaired in BKO mice, regardless of the diet, in accordance with deregulation of the expression of hypothalamic neuropeptide genes. Importantly, BKO mice already showed increased β-cell proliferation and glucose-stimulated insulin secretion with respect to WT littermates after two weeks of HFD feeding, before the onset of obesity.

CONCLUSIONS

Collectively, these results reveal that BACE2 suppression in an obesogenic setting leads to exacerbated body weight gain, hyperinsulinemia, and insulin resistance. Thus, we conclude that inhibition of BACE2 may aggravate the adverse metabolic effects associated with obesity.

The case for low-level BACE1 inhibition for the prevention of Alzheimer disease

Alzheimer disease (AD) is the most common cause of dementia in older individuals (>65 years) and has a long presymptomatic phase. Preventive therapies for AD are not yet available, and potential disease-modifying therapies targeting amyloid-β plaques in symptomatic stages of AD have only just been approved in the United States. Small-molecule inhibitors of β-site amyloid precursor protein (APP)-cleaving enzyme 1 (BACE1; also known as β-secretase 1) reduce the production of amyloid-β peptide and are among the most advanced drug candidates for AD. However, to date all phase II and phase III clinical trials of BACE inhibitors were either concluded without benefit or discontinued owing to futility or the occurrence of adverse effects. Adverse effects included early, mild cognitive impairment that was associated with all but one inhibitor; preliminary results suggest that the cognitive effects are non-progressive and reversible. These discontinuations have raised questions regarding the suitability of BACE1 as a drug target for AD. In this Perspective, we discuss the status of BACE inhibitors and suggest ways in which the results of the discontinued trials can inform the development of future clinical trials of BACE inhibitors and related secretase modulators as preventative therapies. We also propose a series of experiments that should be performed to inform 'go-no-go' decisions in future trials with BACE inhibitors and consider the possibility that low levels of BACE1 inhibition could avoid adverse effects while achieving efficacy for AD prevention.

Patient-specific Alzheimer-like pathology in trisomy 21 cerebral organoids reveals BACE2 as a gene dose-sensitive AD suppressor in human brain

A population of more than six million people worldwide at high risk of Alzheimer's disease (AD) are those with Down Syndrome (DS, caused by trisomy 21 (T21)), 70% of whom develop dementia during lifetime, caused by an extra copy of β-amyloid-(Aβ)-precursor-protein gene. We report AD-like pathology in cerebral organoids grown in vitro from non-invasively sampled strands of hair from 71% of DS donors. The pathology consisted of extracellular diffuse and fibrillar Aβ deposits, hyperphosphorylated/pathologically conformed Tau, and premature neuronal loss. Presence/absence of AD-like pathology was donor-specific (reproducible between individual organoids/iPSC lines/experiments). Pathology could be triggered in pathology-negative T21 organoids by CRISPR/Cas9-mediated elimination of the third copy of chromosome 21 gene BACE2, but prevented by combined chemical β and γ-secretase inhibition. We found that T21 organoids secrete increased proportions of Aβ-preventing (Aβ1-19) and Aβ-degradation products (Aβ1-20 and Aβ1-34). We show these profiles mirror in cerebrospinal fluid of people with DS. We demonstrate that this protective mechanism is mediated by BACE2-trisomy and cross-inhibited by clinically trialled BACE1 inhibitors. Combined, our data prove the physiological role of BACE2 as a dose-sensitive AD-suppressor gene, potentially explaining the dementia delay in ~30% of people with DS. We also show that DS cerebral organoids could be explored as pre-morbid AD-risk population detector and a system for hypothesis-free drug screens as well as identification of natural suppressor genes for neurodegenerative diseases.

In Silico Inhibition of BACE-1 by Selective Phytochemicals as Novel Potential Inhibitors: Molecular Docking and DFT Studies

BACKGROUND

Alzheimer's Disease (AD) has become the most common age-dependent disease of dementia. The trademark pathologies of AD are the presence of amyloid aggregates in neurofibrils. Recently phytochemicals being considered as potential inhibitors against various neurodegenerative, antifungal, antibacterial and antiviral diseases in human beings.

OBJECTIVE

This study targets the inhibition of BACE-1 by phytochemicals using in silico drug discovery analysis.

METHODS

A total of 3150 phytochemicals were collected from almost 25 different plants through literature assessment. The ADMET studies, molecular docking and density functional theory (DFT) based analysis were performed to analyze the potential inhibitory properties of these phytochemicals.

RESULTS

The ADMET and docking results exposed seven compounds that have high potential as an inhibitory agent against BACE-1 and show binding affinity >8.0 kcal/mol against BACE-1. They show binding affinity greater than those of various previously reported inhibitors of BACE-1. Furthermore, DFT based analysis has shown high reactivity for these seven phytochemicals in the binding pocket of BACE- 1, based on ELUMO, EHOMO and Kohn-Sham energy gap. All seven phytochemicals were testified (as compared to experimental ones) as novel inhibitors against BACE-1.

CONCLUSION

Out of seven phytochemicals, four were obtained from plant Glycyrrhiza glabra i.e. Shinflavanone, Glabrolide, Glabrol and PrenyllicoflavoneA, one from Huperzia serrate i.e. Macleanine, one from Uncaria rhynchophylla i.e. 3a-dihydro-cadambine and another one was from VolvalerelactoneB from plant Valeriana-officinalis. It is concluded that these phytochemicals are suitable candidates for drug/inhibitor against BACE-1, and can be administered to humans after experimental validation through in vitro and in vivo trials.

The Development of Pharmacological Therapies for Alzheimer's Disease

Alzheimer’s disease (AD) is a progressive neurodegenerative disorder that currently has no cure. The aged population is growing globally, creating an urgent need for more promising therapies for this debilitating disease. Much effort has been made in recent decades, and the field is highly dynamic, with numerous trials. The main focus of these trials includes disease modification and symptomatic treatment. Some have shown beneficial outcomes, while others have shown no significant benefits. Here, we cover the outcome of recently published AD clinical trials, as well as the mechanism of action of these therapeutical agents, to re-think drug development strategies and directions for future studies.

Cyclopentanone Derivative Attenuates Memory Impairment by Inhibiting Amyloid Plaques Formation in the 5xFAD Mice

Alzheimer's disease (AD) is a chronic neurodegenerative disorder. This study was designed to investigate the effects of cyclopentanone derivative i.e., 2-(hydroxyl-(3-nitrophenyl)methyl)cyclopentanone (3NCP) on behavior, amyloid β (Aβ) plaque deposition, and βAPP cleaving enzyme-1 (BACE-1) expression in the 5xFAD mouse brain. In this study, computational studies were conducted to predict the binding mode of the 3NCP with target sites of the β-secretase. In vivo studies were performed on the 5xFAD mice model of AD using different behavioral test models like light/dark box, elevated plus maze (EPM), and the Barnes maze tests for the assessment of anxiety, spatial learning and memory. The thioflavin-S staining, immunohistochemistry (IHC), and RT-PCR studies were carried out to find the effect of the 3NCP on the β-amyloid plaques formation and BACE-1 expression. The results of the computational studies showed that the 3NCP has excellent binding affinities for beta-secretase. The light/dark box study depicted that the 3NCP does not cause anxiety. The 3NCP treatment effects in the EPM and Barnes maze tests showed a significant effect on learning and memory. Furthermore, the results of the thioflavin staining and IHC revealed that the 3NCP significantly reduced the formation of the beta-amyloid plaques in brain tissues. Moreover, the RT-PCR study showed that 3NCP significantly reduced the BACE-1 expression in the brain. Conclusively, the results of the current study demonstrate that the 3NCP may be a potential candidate for AD treatment in the future.

Microbiota-gut-brain axis and Alzheimer's disease: Implications of the blood-brain barrier as an intervention target

The microbiota-gut-brain axis has emerged as a focal point of biomedical research. Alterations of gut microbiota are involved in not only various immune/inflammatory disorders but also neurological disorders including Alzheimer's disease (AD). The initial stage of the involvement of gut microbiota in the pathogenesis of AD may be the dysfunction of the blood-brain barrier (BBB). Gut microbiota-derived products in the circulation can worsen the BBB integrity, easily cross the disrupted BBB and enter the brain to promote pathological changes in AD. In this review, we first summarize the current evidence of the associations among gut microbiota, AD, and BBB integrity. We then discuss the mechanism of gut microbiota on BBB dysfunction with a focus on bacteria-derived lipopolysaccharide and exosomal high-mobility group box 1. Novel insights into the modification of the BBB as an intervention approach for AD are highlighted as well.

Gga3 deletion and a GGA3 rare variant associated with late onset Alzheimer's disease trigger BACE1 accumulation in axonal swellings

Axonal dystrophy, indicative of perturbed axonal transport, occurs early during Alzheimer's disease (AD) pathogenesis. Little is known about the mechanisms underlying this initial sign of the pathology. This study proves that Golgi-localized γ-ear-containing ARF binding protein 3 (GGA3) loss of function, due to Gga3 genetic deletion or a GGA3 rare variant that cosegregates with late-onset AD, disrupts the axonal trafficking of the β-site APP-cleaving enzyme 1 (BACE1) resulting in its accumulation in axonal swellings in cultured neurons and in vivo. We show that BACE pharmacological inhibition ameliorates BACE1 axonal trafficking and diminishes axonal dystrophies in Gga3 null neurons in vitro and in vivo. These data indicate that axonal accumulation of BACE1 engendered by GGA3 loss of function results in local toxicity leading to axonopathy. Gga3 deletion exacerbates axonal dystrophies in a mouse model of AD before β-amyloid (Aβ) deposition. Our study strongly supports a role for GGA3 in AD pathogenesis, where GGA3 loss of function triggers BACE1 axonal accumulation independently of extracellular Aβ, and initiates a cascade of events leading to the axonal damage distinctive of the early stage of AD.

An Overview of β-Amyloid Cleaving Enzyme 1 (Bace1) in Alzheimer's Disease Therapy Elucidating its Exosite-Binding Antibody and Allosteric Inhibitor

Over decades of its identification, numerous past and ongoing researches have focused on the therapeutic roles of β-amyloid cleaving enzyme 1 (BACE1) as a target in treating Alzheimer's disease (AD). Although the initial BACE1 inhibitors at phase-3 clinical trials tremendously reduced β-amyloid-associated plaques in patients with AD, the researchers eventually discontinued the tests due to the lack of potency. This discontinuation has resulted in limited drug development and discovery targeted at BACE1, despite the high demand for dementia and AD therapies. It is, therefore, imperative to describe the detailed underlying biological basis of the BACE1 therapeutic option in neurological diseases. Herein, we highlight BACE1 bioactivity, genetic properties, and role in neurodegenerative therapy. We review research contributions to BACE1 exosite-binding antibody and allosteric inhibitor development as AD therapies. The review also covers BACE1 biological function, the disease-associated mechanisms, and the enzyme conditions for amyloid precursor protein sites splitting. Based on the present review, we suggest further studies on anti-BACE1 exosite antibodies and BACE1 allosteric inhibitors. Non-active site inhibition might be the way forward to BACE1 therapy in Alzheimer's neurological disorder.

Association Analysis of Variants of DSCAM and BACE2 With Hirschsprung Disease Susceptibility in Han Chinese and Functional Evaluation in Zebrafish

Hirschsprung disease (HSCR) has a higher incidence in children with Down syndrome (DS), which makes trisomy 21 a predisposing factor to HSCR. DSCAM and BACE2 are close together on the HSCR-associated critical region of chromosome 21. Common variants of DSCAM and rare variants of BACE2 were implicated to be associated with sporadic HSCR. However, the submucosal neuron defect of DS mouse model could not be rescued by normalization of Dscam. We aimed to explore the contribution of DSCAM and BACE2 to the development of the enteric nervous system (ENS) and HSCR susceptibility. We genotyped 133 tag single-nucleotide polymorphisms (SNPs) in DSCAM and BACE2 gene region in 420 HSCR patients and 1,665 controls of Han Chinese. Expression of DSCAM and BACE2 homologs was investigated in the developing gut of zebrafish. Overexpression and knockdown of the homologs were performed in zebrafish to investigate their roles in the development of ENS. Two DSCAM SNPs, rs430255 (P_Addtive = 0.0052, OR = 1.36, 95% CI: 1.10–1.68) and rs2837756 (P_Addtive = 0.0091, OR = 1.23, 95% CI: 1.05–1.43), showed suggestive association with HSCR risk. Common variants in BACE2 were not associated with HSCR risk. We observed dscama, dscamb, and bace2 expression in the developing gut of zebrafish. Knockdown of dscama, dscamb, and bace2 caused a reduction of enteric neurons in the hindgut of zebrafish. Overexpression of DSCAM and bace2 had no effects on neuron number in the hindgut of zebrafish. Our results suggested that common variation of DSCAM contributed to HSCR risk in Han Chinese. The dysfunction of both dscams and bace2 caused defects in enteric neuron, indicating that DSCAM and BACE2 might play functional roles in the occurrence of HSCR. These novel findings might shed new light on the pathogenesis of HSCR.

Human pluripotent stem cell-derived brain organoids as in vitro models for studying neural disorders and cancer

The sheer complexities of brain and resource limitation of human brain tissue greatly hamper our understanding of the brain disorders and cancers. Recently developed three-dimensional (3D) brain organoids (BOs) are self-organized and spontaneously differentiated from human pluripotent stem cells (hPSCs) in vitro, which exhibit similar features with cell type diversity, structural organization, and functional connectivity as the developing human brain. Based on these characteristics, hPSC-derived BOs (hPDBOs) provide new opportunities to recapitulate the complicated processes during brain development, neurodegenerative disorders, and brain cancers in vitro. In this review, we will provide an overview of existing BO models and summarize the applications of this technology in modeling the neural disorders and cancers. Furthermore, we will discuss the challenges associated with their use as in vitro models for disease modeling and the potential future direction.

The β-Secretase BACE1 in Alzheimer's Disease

BACE1 (beta-site amyloid precursor protein cleaving enzyme 1) was initially cloned and characterized in 1999. It is required for the generation of all monomeric forms of amyloid-β (Aβ), including Aβ42, which aggregates into bioactive conformational species and likely initiates toxicity in Alzheimer's disease (AD). BACE1 concentrations and rates of activity are increased in AD brains and body fluids, thereby supporting the hypothesis that BACE1 plays a critical role in AD pathophysiology. Therefore, BACE1 is a prime drug target for slowing down Aβ production in early AD. Besides the amyloidogenic pathway, BACE1 has other substrates that may be important for synaptic plasticity and synaptic homeostasis. Indeed, germline and adult conditional BACE1 knockout mice display complex neurological phenotypes. Despite BACE1 inhibitor clinical trials conducted so far being discontinued for futility or safety reasons, BACE1 remains a well-validated therapeutic target for AD. A safe and efficacious compound with high substrate selectivity as well as a more accurate dose regimen, patient population, and disease stage may yet be found. Further research should focus on the role of Aβ and BACE1 in physiological processes and key pathophysiological mechanisms of AD. The functions of BACE1 and the homologue BACE2, as well as the biology of Aβ in neurons and glia, deserve further investigation. Cellular and molecular studies of BACE1 and BACE2 knockout mice coupled with biomarker-based human research will help elucidate the biological functions of these important enzymes and identify their substrates and downstream effects. Such studies will have critical implications for BACE1 inhibition as a therapeutic approach for AD.

Neoline Improves Memory Impairment and Reduces Amyloid-β Level and Tau Phosphorylation Through AMPK Activation in the Mouse Alzheimer's Disease Model

BACKGROUND

Alzheimer's disease (AD) is the most general, chronic, and progressive neurodegenerative senile disorder characterized clinically by progressive cognitive deterioration and memory impairment. Neoline is effective against neuropathic pain models, but the effects of neoline against AD-like phenotypes have not been investigated.

OBJECTIVE

We offer the investigation of the effects of neoline in AD.

METHODS

In this study, a Tg-APPswe/PS1dE9 AD mouse model was treated orally with neoline at a concentration of 0.5 mg/kg or 0.1 mg/kg starting at 7.5 months and administered for three months, and its anti-AD effects were evaluated.

RESULTS

Neoline improved memory and cognition impairments and reduced the number of amyloid-beta plaque and the amount of amyloid-β in the brain of AD mice. Furthermore, neoline reduced the anxiety behavior in the AD mouse model. The chronic administration of neoline also induced AMPK phosphorylation and decreased tau, amyloid-β, and BACE1 expression in the hippocampus. These findings indicate that chronic administration of neoline has therapeutic effects via AMPK activation, and BACE1 downregulation resulted in a decrease in the amyloid-β levels in the brain of Tg-APPswe/PS1dE9 AD mice.

CONCLUSION

Our results suggest that neoline is a therapeutic agent for the cure of neurodegenerative diseases like AD.

A Structure-Based Discovery Platform for BACE2 and the Development of Selective BACE Inhibitors

The ability to perform routine structure-guided drug design for selective BACE inhibitors has been limited because of the lack of robust platform for BACE2 expression, purification, and crystallization. To overcome this limitation, we developed a platform that produces 2-3 mg of pure BACE2 protein per liter of E. coli culture, and we used this protein to design macrocyclic compounds that potently and selectively inhibit BACE1 over BACE2. Compound 2 was found to potently inhibit BACE 1 (K_i = 5 nM) with a selectivity of 214-fold over BACE2. The X-ray crystal structures of unbound BACE2 (2.2 Å) and BACE2 bound to compound 3 (3.0 Å and K_i = 7 nM) were determined and compared to the X-ray structures of BACE1 revealing the S1-S3 subsite as a selectivity determinant. This platform should enable a more rapid development of new and selective BACE inhibitors for the treatment of Alzheimer's disease or type II diabetes.

Identification of truncated C-terminal fragments of the Alzheimer's disease amyloid protein precursor derived from sequential proteolytic pathways

Recent evidence supports the emerging hypothesis that the amyloid-β precursor protein C-terminal fragments (APP-CTFs) and dysregulations in both their qualitative and quantitative productions may actively and directly contribute to the neuronal toxicity in early phases of Alzheimer's disease (AD). These new findings revealed the urgent needs and gaps in better understanding the metabolism and full spectrum of APP-CTFs. In this study, we characterized by mass spectrometry the full patterns of APP-CTFs in different cell types and in the brain of an AD APPPS1 mouse model. In these systems, we first discovered a series of 71-80 amino acids long N-terminally truncated APP-CTFs of unknown functions. We next demonstrated that these N-terminally truncated APP-CTFs are sequentially produced by the proteolytic processing of APP-C80, by an as yet unidentified protease. Finally, these N-terminally truncated APP-CTFs are likely protein substrates recognized and processed by the γ-secretase complex, leading to the production of N-terminally truncated Aβ peptides. Together, our findings provide new insights into the metabolism of APP and offer potential new strategies to modulate the production of toxic Aβ peptides in AD.

Bridging the Gap Between Fluid Biomarkers for Alzheimer's Disease, Model Systems, and Patients

Alzheimer’s disease (AD) is a debilitating neurodegenerative disease characterized by the accumulation of two proteins in fibrillar form: amyloid-β (Aβ) and tau. Despite decades of intensive research, we cannot yet pinpoint the exact cause of the disease or unequivocally determine the exact mechanism(s) underlying its progression. This confounds early diagnosis and treatment of the disease. Cerebrospinal fluid (CSF) biomarkers, which can reveal ongoing biochemical changes in the brain, can help monitor developing AD pathology prior to clinical diagnosis. Here we review preclinical and clinical investigations of commonly used biomarkers in animals and patients with AD, which can bridge translation from model systems into the clinic. The core AD biomarkers have been found to translate well across species, whereas biomarkers of neuroinflammation translate to a lesser extent. Nevertheless, there is no absolute equivalence between biomarkers in human AD patients and those examined in preclinical models in terms of revealing key pathological hallmarks of the disease. In this review, we provide an overview of current but also novel AD biomarkers and how they relate to key constituents of the pathological cascade, highlighting confounding factors and pitfalls in interpretation, and also provide recommendations for standardized procedures during sample collection to enhance the translational validity of preclinical AD models.

Therapeutic Strategies Targeting Amyloid-β in Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disorder linked to protein misfolding and aggregation. AD is pathologically characterized by senile plaques formed by extracellular Amyloid-β (Aβ) peptide and Intracellular Neurofibrillary Tangles (NFT) formed by hyperphosphorylated tau protein. Extensive synaptic loss and neuronal degeneration are responsible for memory impairment, cognitive decline and behavioral dysfunctions typical of AD. Amyloidosis has been implicated in the depression of acetylcholine synthesis and release, overactivation of N-methyl-D-aspartate (NMDA) receptors and increased intracellular calcium levels that result in excitotoxic neuronal degeneration. Current drugs used in AD treatment are either cholinesterase inhibitors or NMDA receptor antagonists; however, they provide only symptomatic relief and do not alter the progression of the disease. Aβ is the product of Amyloid Precursor Protein (APP) processing after successive cleavage by β- and γ-secretases while APP proteolysis by α-secretase results in non-amyloidogenic products. According to the amyloid cascade hypothesis, Aβ dyshomeostasis results in the accumulation and aggregation of Aβ into soluble oligomers and insoluble fibrils. The former are synaptotoxic and can induce tau hyperphosphorylation while the latter deposit in senile plaques and elicit proinflammatory responses, contributing to oxidative stress, neuronal degeneration and neuroinflammation. Aβ-protein-targeted therapeutic strategies are thus a promising disease-modifying approach for the treatment and prevention of AD. This review summarizes recent findings on Aβ-protein targeted AD drugs, including β-secretase inhibitors, γ-secretase inhibitors and modulators, α-secretase activators, direct inhibitors of Aβ aggregation and immunotherapy targeting Aβ, focusing mainly on those currently under clinical trials.

The Use of Antimicrobial and Antiviral Drugs in Alzheimer's Disease

The aggregation and accumulation of amyloid-β plaques and tau proteins in the brain have been central characteristics in the pathophysiology of Alzheimer's disease (AD), making them the focus of most of the research exploring potential therapeutics for this neurodegenerative disease. With success in interventions aimed at depleting amyloid-β peptides being limited at best, a greater understanding of the physiological role of amyloid-β peptides is needed. The development of amyloid-β plaques has been determined to occur 10-20 years prior to AD symptom manifestation, hence earlier interventions might be necessary to address presymptomatic AD. Furthermore, recent studies have suggested that amyloid-β peptides may play a role in innate immunity as an antimicrobial peptide. These findings, coupled with the evidence of pathogens such as viruses and bacteria in AD brains, suggests that the buildup of amyloid-β plaques could be a response to the presence of viruses and bacteria. This has led to the foundation of the antimicrobial hypothesis for AD. The present review will highlight the current understanding of amyloid-β, and the role of bacteria and viruses in AD, and will also explore the therapeutic potential of antimicrobial and antiviral drugs in Alzheimer's disease.

AP-2 reduces amyloidogenesis by promoting BACE1 trafficking and degradation in neurons

Cleavage of amyloid precursor protein (APP) by BACE-1 (β-site APP cleaving enzyme 1) is the rate-limiting step in amyloid-β (Aβ) production and a neuropathological hallmark of Alzheimer's disease (AD). Despite decades of research, mechanisms of amyloidogenic APP processing remain highly controversial. Here, we show that in neurons, APP processing and Aβ production are controlled by the protein complex-2 (AP-2), an endocytic adaptor known to be required for APP endocytosis. Now, we find that AP-2 prevents amyloidogenesis by additionally functioning downstream of BACE1 endocytosis, regulating BACE1 endosomal trafficking and its delivery to lysosomes. AP-2 is decreased in iPSC-derived neurons from patients with late-onset AD, while conditional AP-2 knockout (KO) mice exhibit increased Aβ production, resulting from accumulation of BACE1 within late endosomes and autophagosomes. Deletion of BACE1 decreases amyloidogenesis and mitigates synapse loss in neurons lacking AP-2. Taken together, these data suggest a mechanism for BACE1 intracellular trafficking and degradation via an endocytosis-independent function of AP-2 and reveal a novel role for endocytic proteins in AD.

Huperzine A ameliorates obesity-related cognitive performance impairments involving neuronal insulin signaling pathway in mice

Type 2 diabetes (T2D) and Alzheimer's disease (AD) share several common pathophysiological features. Huperzine A (Hup A), a Lycopodium alkaloid extracted from the Chinese herb moss Huperzia serrata, is a specific and reversible inhibitor of acetylcholinesterase, which is clinically used for the treatment of AD. In this study, we investigated whether Hup A improved the metabolic and cognitive functions in the high fat-induced (HFD) obese mice and genetic ob/ob mice. HFD and ob/ob mice were treated with Hup A (0.1, 0.3 mg · kg-1 · d-1, ig) for 3 months. Body weight was monitored and glucose tolerance tests were performed. Novel object recognition test and Morris water maze assay were conducted to evaluate the cognitive functions. We found that the Hup A treatment had no significant effect on peripheral metabolism of obese mice, whereas Hup A (0.1, mg · kg-1 · d-1) improved both the abilities of object recognition and spatial memory in HFD-fed mice, but not in ob/ob mice. Furthermore, Hup A treatment significantly upregulated the insulin and phosphorylated Akt levels in the cortex of HFD-fed mice, but not ob/ob mice. In addition, Hup A (0.3, mg · kg-1 · d-1) significantly decreased cortical β-secretase (BACE1) expression. In conclusion, these results demonstrate that treatment with Hup A (0.1, mg · kg-1 · d-1) can effectively improve the cognitive functions, at least in diet-induced obese mice.

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.

Dreaming of a New World Where Alzheimer's Is a Treatable Disorder

Alzheimer’s disease (AD) is the most common form of dementia. It’s a chronic and untreatable neurodegenerative disease with irreversible progression and has important social and economic implications in terms of direct medical and social care costs. Despite prolonged and expensive efforts employed by the scientific community over the last few decades, no effective treatments are still available for patients, and the development of disease-modifying drugs is now a really urgent need. The recent failure of clinical trials based on the immunotherapeutic approach against amyloid-β(Aβ) protein questioned the validity of the “amyloid cascade hypothesis” as the molecular machinery causing the disease. Indeed, most attempts to design effective treatments for AD have been based until now on molecular targets suggested to be implicated in AD pathogenesis by the amyloid cascade hypothesis. However, mounting evidence from scientific literature supports the view of AD as a multifactorial disease that results from the concomitant action of multiple molecular players. This view, together with the lack of success of the disease-modifying single-target approaches, strongly suggests that AD drug design needs to be shifted towards multi-targeted compounds or drug combinations acting synergistically on the main core features of disease pathogenesis. The discovery of drug candidates targeting multiple factors involved in AD would greatly improve drug development. So, it is reasonable that upcoming strategies for the design of preventive and/or therapeutic agents for AD point to a multi-pronged approach including more than one druggable target to definitely defeat the disease.

Elucidating Critical Proteinopathic Mechanisms and Potential Drug Targets in Neurodegeneration

Neurodegeneration entails progressive loss of neuronal structure as well as function leading to cognitive failure, apathy, anxiety, irregular body movements, mood swing and ageing. Proteomic dysregulation is considered the key factor for neurodegeneration. Mechanisms involving deregulated processing of proteins such as amyloid beta (Aβ) oligomerization; tau hyperphosphorylation, prion misfolding; α-synuclein accumulation/lewy body formation, chaperone deregulation, acetylcholine depletion, adenosine 2A (A2A) receptor hyperactivation, secretase deregulation, leucine-rich repeat kinase 2 (LRRK2) mutation and mitochondrial proteinopathies have deeper implications in neurodegenerative disorders. Better understanding of such pathological mechanisms is pivotal for exploring crucial drug targets. Herein, we provide a comprehensive outlook about the diverse proteomic irregularities in Alzheimer's, Parkinson's and Creutzfeldt Jakob disease (CJD). We explicate the role of key neuroproteomic drug targets notably Aβ, tau, alpha synuclein, prions, secretases, acetylcholinesterase (AchE), LRRK2, molecular chaperones, A2A receptors, muscarinic acetylcholine receptors (mAchR), N-methyl-D-aspartate receptor (NMDAR), glial cell line-derived neurotrophic factor (GDNF) family ligands (GFLs) and mitochondrial/oxidative stress-related proteins for combating neurodegeneration and associated cognitive and motor impairment. Cross talk between amyloidopathy, synucleinopathy, tauopathy and several other proteinopathies pinpoints the need to develop safe therapeutics with ability to strike multiple targets in the aetiology of the neurodegenerative disorders. Therapeutics like microtubule stabilisers, chaperones, kinase inhibitors, anti-aggregation agents and antibodies could serve promising regimens for treating neurodegeneration. However, drugs should be target specific, safe and able to penetrate blood-brain barrier.

β-Secretase BACE1 Is Required for Normal Cochlear Function

Cleavage of amyloid precursor protein (APP) by β-secretase BACE1 initiates the production and accumulation of neurotoxic amyloid-β peptides, which is widely considered an essential pathogenic mechanism in Alzheimer's disease (AD). Here, we report that BACE1 is essential for normal auditory function. Compared with wild-type littermates, BACE1^-/- mice of either sex exhibit significant hearing deficits, as indicated by increased thresholds and reduced amplitudes in auditory brainstem responses (ABRs) and decreased distortion product otoacoustic emissions (DPOAEs). Immunohistochemistry revealed aberrant synaptic organization in the cochlea and hypomyelination of auditory nerve fibers as predominant neuropathological substrates of hearing loss in BACE1^-/- mice. In particular, we found that fibers of spiral ganglion neurons (SGN) close to the organ of Corti are disorganized and abnormally swollen. BACE1 deficiency also engenders organization defects in the postsynaptic compartment of SGN fibers with ectopic overexpression of PSD95 far outside the synaptic region. During postnatal development, auditory fiber myelination in BACE1^-/- mice lags behind dramatically and remains incomplete into adulthood. We relate the marked hypomyelination to the impaired processing of Neuregulin-1 when BACE1 is absent. To determine whether the cochlea of adult wild-type mice is susceptible to AD treatment-like suppression of BACE1, we administered the established BACE1 inhibitor NB-360 for 6 weeks. The drug suppressed BACE1 activity in the brain, but did not impair hearing performance and, upon neuropathological examination, did not produce the characteristic cochlear abnormalities of BACE1^-/- mice. Together, these data strongly suggest that the hearing loss of BACE1 knock-out mice represents a developmental phenotype.SIGNIFICANCE STATEMENT Given its crucial role in the pathogenesis of Alzheimer's disease (AD), BACE1 is a prime pharmacological target for AD prevention and therapy. However, the safe and long-term administration of BACE1-inhibitors as envisioned in AD requires a comprehensive understanding of the various physiological functions of BACE1. Here, we report that BACE1 is essential for the processing of auditory signals in the inner ear, as BACE1-deficient mice exhibit significant hearing loss. We relate this deficit to impaired myelination and aberrant synapse formation in the cochlea, which manifest during postnatal development. By contrast, prolonged pharmacological suppression of BACE1 activity in adult wild-type mice did not reproduce the hearing deficit or the cochlear abnormalities of BACE1 null mice.

Multi-target-directed-ligands acting as enzyme inhibitors and receptor ligands

In this review, we present the latest advances in the field of multi-target-directed ligand (MTDL) design for the treatment of various complex pathologies of multifactorial origin. In particular, latest findings in the field of MTDL design targeting both an enzyme and a receptor are presented for different diseases such as Alzheimer's disease (AD), depression, addiction, glaucoma, non-alcoholic steatohepatitis and pain and inflammation. The ethology of the diseases is briefly described, with special emphasis on how the MTDL can evolve into novel therapies that replace the classic pharmacological dogma "one target one disease". Considering the current needs for therapy adherence improvement, it is exposed as from the medicinal chemistry, different molecular scaffolds are studied. With the use of structure activity relationship studies and molecular optimization, new hybrid molecules are generated with improved biological properties acting at two biologically very distinct targets.

Safety, Tolerability, and Pharmacokinetics of the β-Site Amyloid Precursor Protein-Cleaving Enzyme 1 Inhibitor Verubecestat (MK-8931) in Healthy Elderly Male and Female Subjects

β‐site amyloid precursor protein‐cleaving enzyme 1 (BACE1) is required for the production of β‐amyloid peptides, which are implicated in the etiology of Alzheimer's disease. The safety and pharmacokinetics of the BACE1 inhibitor verubecestat have previously been studied in young adults aged 19–45 years. In this randomized, placebo‐controlled, phase I study (protocol MK‐8931‐006), we investigated the safety, tolerability, and pharmacokinetics of a single dose (100 mg) or multiple doses (30, 80, and 120 mg) once daily for 28 days of verubecestat in healthy elderly subjects. Safety end points were assessed at baseline and during the duration of the study period and indicated that verubecestat was generally well tolerated. Verubecestat pharmacokinetics were similar between healthy elderly male and female subjects and similar to those reported in healthy young males in previous studies. These data supported subsequent studies to assess the potential efficacy of verubecestat in subjects with Alzheimer's disease.

The BACE-1 inhibitor CNP520 for prevention trials in Alzheimer's disease

The beta‐site amyloid precursor protein cleaving enzyme‐1 (BACE‐1) initiates the generation of amyloid‐β (Aβ), and the amyloid cascade leading to amyloid plaque deposition, neurodegeneration, and dementia in Alzheimer's disease (AD). Clinical failures of anti‐Aβ therapies in dementia stages suggest that treatment has to start in the early, asymptomatic disease states. The BACE‐1 inhibitor CNP520 has a selectivity, pharmacodynamics, and distribution profile suitable for AD prevention studies. CNP520 reduced brain and cerebrospinal fluid (CSF) Aβ in rats and dogs, and Aβ plaque deposition in APP‐transgenic mice. Animal toxicology studies of CNP520 demonstrated sufficient safety margins, with no signs of hair depigmentation, retina degeneration, liver toxicity, or cardiovascular effects. In healthy adults ≥ 60 years old, treatment with CNP520 was safe and well tolerated and resulted in robust and dose‐dependent Aβ reduction in the cerebrospinal fluid. Thus, long‐term, pivotal studies with CNP520 have been initiated in the Generation Program.

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.

Aβ34 is a BACE1-derived degradation intermediate associated with amyloid clearance and Alzheimer's disease progression

The beta-site APP cleaving enzyme 1 (BACE1) is known primarily for its initial cleavage of the amyloid precursor protein (APP), which ultimately leads to the generation of Aβ peptides. Here, we provide evidence that altered BACE1 levels and activity impact the degradation of Aβ40 and Aβ42 into a common Aβ34 intermediate. Using human cerebrospinal fluid (CSF) samples from the Amsterdam Dementia Cohort, we show that Aβ34 is elevated in individuals with mild cognitive impairment who later progressed to dementia. Furthermore, Aβ34 levels correlate with the overall Aβ clearance rates in amyloid positive individuals. Using CSF samples from the PREVENT-AD cohort (cognitively normal individuals at risk for Alzheimer’s disease), we further demonstrate that the Aβ34/Aβ42 ratio, representing Aβ degradation and cortical deposition, associates with pre-clinical markers of neurodegeneration. We propose that Aβ34 represents a marker of amyloid clearance and may be helpful for the characterization of Aβ turnover in clinical samples.

Aβ34 is generated from degradation of Aβ40 and Aβ42 by β-secretase. Here, the authors show that Aβ34 is a marker for amyloid clearance and is elevated in the CSF of patients that go on to convert from mild cognitive impairment to Alzheimer’s disease, suggesting it may be a useful biomarker.

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.

Low Evolutionary Selection Pressure in Senescence Does Not Explain the Persistence of Aβ in the Vertebrate Genome

The argument is frequently made that the amyloid-β protein (Aβ) persists in the human genome because Alzheimer's disease (AD) primarily afflicts individuals over reproductive age and, therefore, there is low selective pressure for the peptide's elimination or modification. This argument is an important premise for AD amyloidosis models and therapeutic strategies that characterize Aβ as a functionless and intrinsically pathological protein. Here, we review if evolutionary theory and data on the genetics and biology of Aβ are consistent with low selective pressure for the peptide's expression in senescence. Aβ is an ancient neuropeptide expressed across vertebrates. Consistent with unusually high evolutionary selection constraint, the human Aβ sequence is shared by a majority of vertebrate species and has been conserved across at least 400 million years. Unlike humans, the overwhelming majority of vertebrate species do not cease reproduction in senescence and selection pressure is maintained into old age. Hence, low selective pressure in senescence does not explain the persistence of Aβ across the vertebrate genome. The "Grandmother hypothesis" (GMH) is the prevailing model explaining the unusual extended postfertile period of humans. In the GMH, high risk associated with birthing in old age has lead to early cessation of reproduction and a shift to intergenerational care of descendants. The rechanneling of resources to grandchildren by postreproductive individuals increases reproductive success of descendants. In the GMH model, selection pressure does not end following menopause. Thus, evolutionary models and phylogenetic data are not consistent with the absence of reproductive selection pressure for Aβ among aged vertebrates, including humans. Our analysis suggests an alternative evolutionary model for the persistence of Aβ in the vertebrate genome. Aβ has recently been identified as an antimicrobial effector molecule of innate immunity. High conservation across the Chordata phylum is consistent with strong positive selection pressure driving human Aβ's remarkable evolutionary longevity. Ancient origins and widespread conservation suggest the human Aβ sequence is highly optimized for its immune role. We detail our analysis and discuss how the emerging "Antimicrobial Protection Hypothesis" of AD may provide insights into possible evolutionary roles for Aβ in infection, aging, and disease etiology.