β-Secretase: its biology as a therapeutic target in diseases

Recent advances in Alzheimer's disease therapy: clinical trials and literature review of novel enzyme inhibitors targeting amyloid precursor protein

INTRODUCTION

Amyloid precursor protein (APP) plays a central role in the pathophysiology of Alzheimer's disease (AD). The accumulation of beta-amyloid protein is believed to be a crucial step in the development of AD. Therefore, understanding the complex biology of APP and its various cleavage products may be useful for developing effective therapeutic strategies for AD.

AREAS COVERED

The amyloidogenic pathway of APP processing involves proteolytic cleavage by two prominent secretases, γ-Secretase and β-secretase. In the late 2000s, multiple pharmaceutical drugs that inhibited γ-Secretase and β-Secretase were synthesized, some of which advanced to human clinical trials. Unfortunately, neither γ-Secretase nor β-secretase inhibitors have been approved by the FDA due to both lack of efficacy and concerns for serious side effects.

EXPERT OPINION

While targeting of Aβ accumulation through secretase inhibitors was halted due to severe side effects, γ-Secretase modulators (GSMs) have arisen as a potential alternative approach. First-generation GSMs could modulate γ-secretase activity without affecting Notch cleavage. However, to improve potency and brain penetration, second-generation GSMs were developed to reduce levels of the amylogenic form of Aβ, Aβ42, without affecting the NOTCH signaling pathway. Several of these drugs have progressed to clinical trials, although with mixed results. The development of GSM's continues to serve as a potentially safer approach to modulating Aβ production in AD treatment.

Evaluation of Selected Plant Phenolics via Beta-Secretase-1 Inhibition, Molecular Docking, and Gene Expression Related to Alzheimer's Disease

Background: The goal of the current study was to investigate the inhibitory activity of six phenolic compounds, i.e., rosmarinic acid, gallic acid, oleuropein, epigallocatechin gallate (EGCG), 3-hydroxytyrosol, and quercetin, against β-site amyloid precursor protein cleaving enzyme-1 (BACE1), also known as β-secretase or memapsin 2, which is implicated in the pathogenesis of Alzheimer's disease (AD). Methods and Results: The inhibitory potential against BACE1, molecular docking simulations, as well as neurotoxicity and the effect on the AD-related gene expression of the selected phenolics were tested. BACE1 inhibitory activity was carried out using the ELISA microplate assay via fluorescence resonance energy transfer (FRET) technology. Molecular docking experiments were performed in the human BACE1 active site (PDB code: 2WJO). Neurotoxicity of the compounds was carried out in SH-SY5Y, a human neuroblastoma cell line, by the Alamar Blue method. A gene expression analysis of the compounds on fourteen genes linked to AD was conducted using the real-time polymerase chain reaction (RT-PCR) method. Rosmarinic acid, EGCG, oleuropein, and quercetin (also used as the reference) were able to inhibit BACE1 with their respective IC50 values 4.06 ± 0.68, 1.62 ± 0.12, 9.87 ± 1.01, and 3.16 ± 0.30 mM. The inhibitory compounds were observed to occupy the non-catalytic site of the BACE1. However, hydrogen bonds were found to be present between rosmarinic acid and EGCG and aspartic amino acid D228 in the catalytic site. Oleuropein and quercetin effectively suppressed the expression of PSEN, APOE, and CLU, which are recognized to be linked to the pathogenesis of AD. Conclusions: The outcomes of the work bring quercetin, EGCG, and rosmarinic acid to the forefront as promising BACE1 inhibitors.

Navigating the Maze of Alzheimer's disease by exploring BACE1: Discovery, current scenario, and future prospects

Alzheimer's disease (AD) is a chronic neurological condition that has become a leading cause of cognitive decline in elder individuals. Hardly any effective medication has been developed to halt the progression of AD due to the disease's complexity. Several theories have been put forward to clarify the mechanisms underlying AD etiology. The identification of amyloid plaques as a hallmark of AD has sparked the development of numerous drugs targeting the players involved in the amyloidogenic pathway, such as the β-site of amyloid precursor protein cleavage enzyme 1 (BACE1) blockers. Over the last ten years, preclinical and early experimental research has led several pharmaceutical companies to prioritize producing BACE1 inhibitors. Despite all these efforts, earlier discovered inhibitors were discontinued in consideration of another second-generation small molecules and recent BACE1 antagonists failed in the final stages of clinical trials because of the complications associated either with toxicity or effectiveness. In addition to discussing the difficulties associated with development of BACE1 inhibitors, this review aims to provide an overview of BACE1 and offer perspectives on the causes behind the failure of five recent BACE1 inhibitors, that would be beneficial for choosing effective treatment approaches in the future.

Beta-Secretase 1 Recruits Amyloid-Beta Precursor Protein to ROCK2 Kinase, Resulting in Erroneous Phosphorylation and Beta-Amyloid Plaque Formation

The amyloidogenic processing of APP depends on two events: its phosphorylation by ROCK2 (at Thr654) and the phosphorylation of the APP-cleaving enzyme BACE1 (at Ser498). However, the mechanisms and structural details of APP-ROCK2 and BACE1-ROCK2 binding are unknown. Using direct physical methods in combination with an in silico approach, we found that BACE1 binds into the substrate-binding groove of ROCK2 with a low affinity (K_d = 18 µM), while no binding of APP to ROCK2 alone could be detected. On the other hand, a strong association (K_d = 3.5 nM) of APP to the weak ROCK2-BACE1 complex was observed, although no stable ternary complex was detected, i.e., BACE1 was displaced by APP. We constructed a sequential functional model: (1) BACE1 weakly binds to ROCK2 and induces an allosteric conformational change in ROCK2; (2) APP strongly binds to the ROCK2-BACE1 complex, and BACE1 is released; and (3) ROCK2 phosphorylates APP at Thr654 (leading to a longer stay in the early endosome during APP processing). Direct fluorescence titration experiments showed that the APP_646-664 or APP_665-695 fragments did not bind separately to the ROCK2-BACE1 complex. Based on these observations, we conclude that two binding sites are involved in the ROCK2-APP interaction: (1) the substrate-binding groove, where the APP_646-664 sequence containing Thr654 sits and (2) the allosteric binding site, where the APP_665-695 sequence binds. These results open the way to attack the allosteric site to prevent APP phosphorylation at Thr654 by ROCK2 without inhibiting the activity of ROCK2 towards its other substrates.

New Insights into Alzheimer’s Disease: Novel Pathogenesis, Drug Target and Delivery

Alzheimer’s disease (AD), the most common type of dementia, is characterized by senile plaques composed of amyloid β protein (Aβ) and neurofilament tangles derived from the hyperphosphorylation of tau protein. However, the developed medicines targeting Aβ and tau have not obtained ideal clinical efficacy, which raises a challenge to the hypothesis that AD is Aβ cascade-induced. A critical problem of AD pathogenesis is which endogenous factor induces Aβ aggregation and tau phosphorylation. Recently, age-associated endogenous formaldehyde has been suggested to be a direct trigger for Aβ- and tau-related pathology. Another key issue is whether or not AD drugs are successfully delivered to the damaged neurons. Both the blood–brain barrier (BBB) and extracellular space (ECS) are the barriers for drug delivery. Unexpectedly, Aβ-related SP deposition in ECS slows down or stops interstitial fluid drainage in AD, which is the direct reason for drug delivery failure. Here, we propose a new pathogenesis and perspectives on the direction of AD drug development and drug delivery: (1) aging-related formaldehyde is a direct trigger for Aβ assembly and tau hyperphosphorylation, and the new target for AD therapy is formaldehyde; (2) nano-packaging and physical therapy may be the promising strategy for increasing BBB permeability and accelerating interstitial fluid drainage.

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.

Effects of antidiabetic agents on Alzheimer's disease biomarkers in experimentally induced hyperglycemic rat model by streptozocin

BACKGROUND

Alzheimer's disease is the most common cause of dementia in the elderly population. It is characterized by the accumulation of amyloid β and intraneuronal neurofibrillary tangles in the brain. Increasing evidence shows that the disturbance of insulin signalling in the brain may contribute to the pathophysiology of Alzheimer's disease. In type 1 diabetes, these disruptions are caused by hypoinsulinemia, but in type 2 diabetes, they are caused by insulin resistance and decreased insulin secretion. Multiple studies have shown that diabetes is connected with an increased risk of acquiring Alzheimer's disease. The aim of this study was to investigate the impact of anti-diabetic agents on Alzheimer's disease progression and the levels of Alzheimer's biomarkers in a hyperglycaemic rat model, which was induced by intraperitoneal injection of streptozocin to produce insulin-deficient diabetes.

METHOD

Thirty-six male Wistar albino rats were allocated into six groups of six rats each. Group I was the negative control group. Intraperitoneal injections of streptozocin (42mg/kg) were used once for the five experimental groups. Group II served as the positive control group. The rats in Groups III, IV, V, and VI received metformin (300mg/kg), donepezil (10mg/kg), insulin glargine (3 unit/animal), and glibenclamide (10mg/kg), respectively, for 21 days.

RESULTS

Inducing hyperglycaemia in rats significantly increased the levels of serum glucose, haemoglobin A1c, total cholesterol, triglycerides, high-density lipoprotein, interleukin 6, tumour necrosis factor alpha, amyloid β 42, total plasma tau, and neurofilament light. A significant increase was also found in brain amyloid β 42, nitric oxide, acetylcholinesterase, malondialdehyde, β secretase, and phosphorylated microtubule-associated protein tau. The greatest statistically significant reductions in serum glucose, haemoglobin A1c, triglycerides, amyloid β 42, total plasma tau, brain amyloid β 42, acetylcholinesterase, and malondialdehyde were observed in rats treated with metformin. In contrast, rats treated with donepezil demonstrated the greatest statistically significant reduction in serum tumour necrosis factor alpha, brain nitric oxide, and β secretase. The levels of neurofilament light and phosphorylated microtubule-associated protein tau in the brains of rats treated with insulin glargine were significantly lower than the other treatment groups. The total cholesterol and low-density lipoprotein levels in rats treated with glibenclamide exhibited the most statistically significant reductions of all the treatment groups.

CONCLUSIONS

Metformin and donepezil, when administered at appropriate doses, were shown to successfully lower most plasma and brain biomarkers, including glucose, triglycerides, tumour necrosis factor alpha, amyloid β 42, nitric oxide, acetylcholinesterase, malondialdehyde, and β secretase in rats suffering from Diabetes Mellitus. As a result of this research, we suggest that metformin, either alone or in conjunction with donepezil, might be an excellent drug of choice for neuro-regeneration and risk reduction in Alzheimer's like disease.

BACE1: More than just a β-secretase

β-site amyloid precursor protein cleaving enzyme-1 (BACE1) research has historically focused on its actions as the β-secretase responsible for the production of β-amyloid beta, observed in Alzheimer's disease. Although the greatest expression of BACE1 is found in the brain, BACE1 mRNA and protein is also found in many cell types including pancreatic β-cells, adipocytes, hepatocytes, and vascular cells. Pathologically elevated BACE1 expression in these cells has been implicated in the development of metabolic diseases, including type 2 diabetes, obesity, and cardiovascular disease. In this review, we examine key questions surrounding the BACE1 literature, including how is BACE1 regulated and how dysregulation may occur in disease, and understand how BACE1 regulates metabolism via cleavage of a myriad of substrates. The phenotype of the BACE1 knockout mice models, including reduced weight gain, increased energy expenditure, and enhanced leptin signaling, proposes a physiological role of BACE1 in regulating energy metabolism and homeostasis. Taken together with the weight loss observed with BACE1 inhibitors in clinical trials, these data highlight a novel role for BACE1 in regulation of metabolic physiology. Finally, this review aims to examine the possibility that BACE1 inhibitors could provide a innovative treatment for obesity and its comorbidities.

Attachment Style Moderates Polygenic Risk for Incident Posttraumatic Stress in U.S. Military Veterans: A 7-Year, Nationally Representative, Prospective Cohort Study

BACKGROUND

Posttraumatic stress disorder (PTSD) develops consequent to complex gene-by-environment interactions beyond the precipitating trauma. To date, however, no known study has used a prospective design to examine how polygenic risk scores (PRSs) interact with social-environmental factors such as attachment style to predict PTSD development.

METHODS

PRSs were derived from a genome-wide association study of PTSD symptoms (N = 186,689; Million Veteran Program cohort). We evaluated combined effects of PRS and attachment style in predicting incident PTSD in a 7-year, nationally representative cohort of trauma-exposed, European-American U.S. military veterans without PTSD (N = 1083). We also conducted multivariate gene-by-environment interaction and drug repositioning analyses to identify loci that interact with multiple environmental factors and potential pharmacotherapies that may be repurposed for this disorder.

RESULTS

Veterans with higher PTSD PRS were more likely to have an incident-positive screen for PTSD over 7 years. A gene-by-environment interaction was also observed, such that higher PRS only predicted incident PTSD in veterans with an insecure attachment style and not those with a secure attachment style. At an individual locus level, the strongest gene-by-environment interaction was observed for the rs4702 variant of the FURIN gene with cumulative lifetime trauma burden. Drug repositioning revealed that genes implicated in PRS are perturbated by the drug doxylamine.

CONCLUSIONS

Attachment style moderates polygenic risk for the development of PTSD in European-American veterans. These findings may inform PTSD prevention and treatment for veterans with high polygenic risk for PTSD and suggest a potential pharmacotherapeutic target for risk genes moderated by social-environmental factors.

Safflower leaf ameliorates cognitive impairment through moderating excessive astrocyte activation in APP/PS1 mice

In addition to beta-amyloid (Aβ) plaques and neurofibrillary tangles, Alzheimer's disease (AD) is typically triggered or accompanied by abnormal inflammation, oxidative stress and astrocyte activation. Safflower (Carthamus tinctorius L.) leaf, featuring functional ingredients, is a commonly consumed leafy vegetable. Whether and how dietary safflower leaf powder (SLP) ameliorates cognitive function in an AD mouse model has remained minimally explored. Therefore, we orally administered SLP to APP/PS1 transgenic mice to explore the neuroprotective effects of SLP in preventing AD progression. We found that SLP markedly improved cognitive impairment in APP/PS1 mice, as indicated by the water maze test. We further demonstrated that SLP treatment ameliorated inflammation, oxidative stress and excessive astrocyte activation. Further investigation indicated that SLP decreased the Aβ burden in APP/PS1 mice by mediating excessive astrocyte activation. Our study suggests that safflower leaf is possibly a promising, cognitively beneficial food for preventing and alleviating AD-related dementia.

Elevated β-secretase 1 expression mediates CD4+ T cell dysfunction via PGE2 signalling in Alzheimer's disease

Circulating CD4⁺ T cells are dysfunctional in Alzheimer's disease (AD), however, the underlying molecular mechanisms are not clear. In this study, we demonstrate that CD4⁺ T cells from AD patients and 5xFAD transgenic mice exhibit elevated levels of β-secretase 1 (BACE1). Overexpression of BACE1 in CD4⁺ T cells potentiated CD4⁺ T-cell activation and T-cell-dependent immune responses. Mechanistically, BACE1 modulates prostaglandin E2 (PGE2) synthetase-microsomal prostaglandin E synthase 2 (mPGES2)-to promote mPGES2 maturation and PGE2 production, which increases T-cell receptor (TCR) signalling. Moreover, administration of peripheral PGE2 signalling antagonists partially ameliorates CD4⁺ T cell overactivation and AD pathology in 5xFAD mice. Overall, our results reveal a potential role for BACE1 in mediating CD4⁺ T-cell dysfunction in AD.

Therapeutic Strategies Targeting Amyloid-β Receptors and Transporters in Alzheimer's Disease

Alzheimer's disease (AD) is a chronic neurodegenerative disease that has been recognized as one of the most intractable medical problems with heavy social and economic costs. Amyloid-β (Aβ) has been identified as a major factor that participates in AD progression through its neurotoxic effects. The major mechanism of Aβ-induced neurotoxicity is by interacting with membrane receptors and subsequent triggering of aberrant cellular signaling. Besides, Aβ transporters also plays an important role by affecting Aβ homeostasis. Thus, these Aβ receptors and transporters are potential targets for the development of AD therapies. Here, we summarize the reported therapeutic strategies targeting Aβ receptors and transporters to provide a molecular basis for future rational design of anti-AD agents.

The β-Secretase Enzyme BACE1: A Biochemical Enigma for Alzheimer's Disease

Beta site amyloid precursor protein cleaving enzyme 1 (BACE1) is a rational target in Alzheimer's Disease (AD) drug development due to its role in amyloidogenic cleavage of Amyloid Precursor Protein (APP) in generating Amyloid β (Aβ). This β-secretase cleaves not only Amyloid Precursor Protein (APP) and its homologues, but also small series of substrates including neuregulin and β subunit of voltage-gated sodium channel that play a very important role in the development and normal function of the brain. Moreover, BACE1 is modulated at the post-translational level by several factors that are associated with both physiological and pathological functions. Since the discovery of BACE1 over a decade ago, medicinal chemistry and pharmacokinetics of BACE1 small molecule inhibitors have proven challenging for the treatment of Alzheimer's disease.

Neuroactive venom compounds obtained from Phlogiellus bundokalbo as potential leads for neurodegenerative diseases: insights on their acetylcholinesterase and beta-secretase inhibitory activities in vitro

Background

Spider venom is a rich cocktail of neuroactive compounds designed to prey capture and defense against predators that act on neuronal membrane proteins, in particular, acetylcholinesterases (AChE) that regulate synaptic transmission through acetylcholine (ACh) hydrolysis - an excitatory neurotransmitter - and beta-secretases (BACE) that primarily cleave amyloid precursor proteins (APP), which are, in turn, relevant in the structural integrity of neurons. The present study provides preliminary evidence on the therapeutic potential of Phlogiellus bundokalbo venom against neurodegenerative diseases.

Methods

Spider venom was extracted by electrostimulation and fractionated by reverse-phase high-performance liquid chromatography (RP-HPLC) and characterized by matrix-assisted laser desorption ionization-time flight mass spectrometry (MALDI-TOF-MS). Neuroactivity of the whole venom was observed by a neurobehavioral response from Terebrio molitor larvae in vivo and fractions were screened for their inhibitory activities against AChE and BACE in vitro.

Results

The whole venom from P. bundokalbo demonstrated neuroactivity by inducing excitatory movements from T. molitor for 15 min. Sixteen fractions collected produced diverse mass fragments from MALDI-TOF-MS ranging from 900-4500 Da. Eleven of sixteen fractions demonstrated AChE inhibitory activities with 14.34% (± 2.60e-4) to 62.05% (± 6.40e-5) compared with donepezil which has 86.34% (± 3.90e-5) inhibition (p > 0.05), while none of the fractions were observed to exhibit BACE inhibition. Furthermore, three potent fractions against AChE, F1, F3, and F16 displayed competitive and uncompetitive inhibitions compared to donepezil as the positive control.

Conclusion

The venom of P. bundokalbo contains compounds that demonstrate neuroactivity and anti-AChE activities in vitro, which could comprise possible therapeutic leads for the development of cholinergic compounds against neurological diseases.

Potent In Vitro α-Glucosidase and β-Secretase Inhibition of Amyrin-Type Triterpenoid Isolated from Datura metel Linnaeus (Angel's Trumpet) Fruits

This study deals with α-glucosidase and β-secretase inhibitory screening of extract/fractions and isolated daturaolone (1), namely, 3-oxo-6-β-hydroxy-β-amyrin (daturaolone) from chloroform fraction of Datura metel L. Among entire fractions, the chloroform soluble fraction showed excellent activity against α-glucosidase with % inhibition 90.8 with IC₅₀160.2 ± 1.85 μg and daturaolone (1) with 98.7% inhibition with IC₅₀840.4 ± 1.74 μM, respectively. Similarly, extract and daturaolone (1) also exhibited significant activity against the β-secretase enzyme (BACE1) with % activities 88.27 and 95.19 and with IC₅₀ values 304.21 ± 2.98 μg and 260.70 ± 1.87 μM, respectively, as compared to the standard inhibitor (Ans670, Sta671, Val672)-amyloid-β/A4 precursor protein 770 fragments 662-675) with % activity 94.21 and IC₅₀ value 289.24 ± 1.60 μM. This finding encourages and opens a new window for further detail phytochemical investigation on D. metel in order to isolate novel compounds with promising enzyme inhibitory potential.

Environmental exposures and the etiopathogenesis of Alzheimer's disease: The potential role of BACE1 as a critical neurotoxic target

Alzheimer's disease (AD) is a major public health crisis due to devastating cognitive symptoms, a lack of curative treatments, and increasing prevalence. Most cases are sporadic (>95% of cases) after the age of 65 years, implicating an important role of environmental factors in disease pathogenesis. Environmental neurotoxicants have been implicated in neurodegenerative disorders including Parkinson's Disease and AD. Animal models of AD and in vitro studies have shed light on potential neuropathological mechanisms, yet the biochemical and molecular underpinnings of AD-relevant environmental neurotoxicity remain poorly understood. Beta-site amyloid precursor protein cleaving enzyme 1 (BACE1) is a potentially critical pathogenic target of environmentally induced neurotoxicity. BACE1 clearly has a critical role in AD pathophysiology: It is required for amyloid beta production and expression and activity of BACE1 are increased in the AD brain. Though the literature on BACE1 in response to environmental insults is limited, current studies, along with extensive AD neurobiology literature suggest that BACE1 deserves attention as an important neurotoxic target. Here, we critically review research on environmental neurotoxicants such as metals, pesticides, herbicides, fungicides, polyfluoroalkyl substances, heterocyclic aromatic amines, advanced glycation end products, and acrolein that modulate BACE1 and potential mechanisms of action. Though more research is needed to clearly understand whether BACE1 is a critical mediator of AD-relevant neurotoxicity, available reports provide convincing evidence that BACE1 is altered by environmental risk factors associated with AD pathology, implying that BACE1 inhibition and its use as a biomarker should be considered in AD management and research.

Progranulin Administration Attenuates β-Amyloid Deposition in the Hippocampus of 5xFAD Mice Through Modulating BACE1 Expression and Microglial Phagocytosis

Loss of function mutations in the progranulin (PGRN) gene is a risk factor for Alzheimer’s disease (AD). Previous works reported that the deficiency of PGRN accelerates β-amyloid (Aβ) accumulation in AD transgenic mouse brains while overexpression of PGRN could restrain disease progression. However, mechanisms of PGRN in protecting against Aβ deposition remains unclear. Here, using the 5xFAD AD mouse model, we show that intrahippocampal injection of PGRN protein leads to a reduction of Aβ plaques, downregulation of beta-secretase 1 (BACE1), and enhanced microglia Aβ phagocytosis in the mouse hippocampus. Furthermore, PGRN treatment inhibited BACE1 expression in N2a cells and primary culture neurons and improved the phagocytic capacity of microglia isolated from 5xFAD mouse brains. Collectively, our results provide further evidence that enhancing progranulin could be a promising option for AD therapy.

The Ups and Downs of BACE1: Walking a Fine Line between Neurocognitive and Other Psychiatric Symptoms of Alzheimer's Disease

Although neurocognitive deficit is the best-recognized indicator of Alzheimer's disease (AD), psychotic and other noncognitive symptoms are the prime cause of institutionalization. BACE1 is the rate-limiting enzyme in the production of Aβ of AD, and one of the promising therapeutic targets in countering cognitive decline and amyloid pathology. Changes in BACE1 activity have also emerged to cause significant noncognitive neuropsychiatric symptoms and impairments of circadian rhythms, as evident from clinical trials and reports in transgenic models. In this study, we consider key characteristics of BACE1 with its contribution to neurocognitive deficit and other psychiatric symptoms of AD. We argue that a growing list of noncognitive mental impairments related to pharmacological modulation of BACE1 might present a major obstacle in clinical translation of emerging therapeutic leads targeting this protease. The adverse effects of BACE1 inhibition on mental health call for a revision of treatment strategies that assume indiscriminate inhibition of this key protease, and stress the need for further mechanistic and translational studies.

A Novel Compound YS-5-23 Exhibits Neuroprotective Effect by Reducing β-Site Amyloid Precursor Protein Cleaving Enzyme 1's Expression and H2O2-Induced Cytotoxicity in SH-SY5Y Cells

The abnormally accumulated amyloid-β (Aβ) and oxidative stress contribute to the initiation and progression of Alzheimer's disease (AD). β-site amyloid precursor protein cleaving enzyme 1 (BACE1) is the rate-limiting enzyme for the production of Aβ. Furthermore, Aβ was reported to increase oxidative stress; then the overproduced oxidative stress continues to increase the expression and activity of BACE1. Consequently, inhibition of both BACE1 and oxidative stress is a better strategy for AD therapy compared with those one-target treatment methods. In the present study, our novel small molecule YS-5-23 was proved to possess both of the activities. Specifically, we found that YS-5-23 reduces BACE1's expression in both SH-SY5Y and Swedish mutated amyloid precursor protein (APP) overexpressed HEK293 cells, and it can also suppress BACE1's expression induced by H₂O₂. Moreover, YS-5-23 decreases H₂O₂-induced cytotoxicity including alleviating H₂O₂-induced apoptosis and loss of mitochondria membrane potential (MMP) because it attenuates the reactive oxygen species (ROS) level elevated by H₂O₂. Meanwhile, PI3K/Akt signaling pathway is involved in the anti-H₂O₂ and BACE1 inhibition effect of YS-5-23. Our findings indicate that YS-5-23 may develop as a drug candidate in the prevention and treatment of AD.

Trehalose against Alzheimer's Disease: Insights into a Potential Therapy

Trehalose is a natural disaccharide with a remarkable ability to stabilize biomolecules. In recent years, trehalose has received growing attention as a neuroprotective molecule and has been tested in experimental models for different neurodegenerative diseases. Although the underlying neuroprotective mechanism of trehalose's action is unclear, one of the most important hypotheses is autophagy induction. The chaperone-like activity of trehalose and the ability to modulate inflammatory responses has also been reported. There is compelling evidence that the dysfunction of autophagy and aggregation of misfolded proteins contribute to the pathogenesis of Alzheimer's disease (AD) and other neurodegenerative disorders. Therefore, given the linking between trehalose and autophagy induction, it appears to be a promising therapy for AD. Herein, the published studies concerning the use of trehalose as a potential therapy for AD are summarized, providing a rationale for applying trehalose to reduce Alzheimer's pathology.

Phytol loaded PLGA nanoparticles ameliorate scopolamine-induced cognitive dysfunction by attenuating cholinesterase activity, oxidative stress and apoptosis in Wistar rat

OBJECTIVE

Alzheimer's disease (AD) is an acquired neurological disorder of cognitive and behavioral impairments, with a long and progressive route. Currently, efforts are being made to develop potent drugs that target multiple pathological mechanisms that drive the successful treatment of AD in human beings. The development of nano-drug delivery systems has recently emerged as an effective strategy to treat AD.

METHODS

In the present study, the protective effect of Phytol and Phytol loaded Poly Lactic-co-Glycolic Acid nanoparticles (Phytol-PLGANPs) were evaluated in Wistar rat scopolamine model of AD.

RESULTS AND DISCUSSION

The consumption of Phytol and Phytol-PLGANPs significantly ameliorated the cognitive deficits caused by scopolamine on spatial and short term memory. Phytol and Phytol-PLGANPs significantly enhanced the cholinergic effect by inhibiting both acetylcholinesterase and butyrylcholinesterase (AChE & BuChE), β-secretase 1 (BACE1) activity, attenuating macromolecular damage, reducing reactive oxygen species (ROS) and reactive nitrogen species (RNS) level by activating antioxidative defense system (Superoxide dismutase and catalase) and restoring glutathione metabolizing enzyme systems (Glutathione S-transferase) and also regulating the apoptotic mediated cell death. Moreover, in vivo toxicity study suggests that Phytol and Phytol-PLGANPs did not cause any adverse pathological alteration in rats treated with a higher concentration of Phytol-PLGANPs (200 mg/kg). Pharmacokinetic study revealed that Phytol-PLGANPs enhanced the biodistribution and sustained the release profile of phytol in the brain and plasma.

CONCLUSION

Overall, the outcome of the study suggests that Phytol and Phytol-PLGANPs act as a potent candidate with better anti-amnesic effects and multi-faceted neuroprotective potential against scopolamine-induced memory dysfunction in Wistar rats.

Neuropathological Mechanisms Associated with Pesticides in Alzheimer's Disease

Environmental toxicants have been implicated in neurodegenerative diseases, and pesticide exposure is a suspected environmental risk factor for Alzheimer’s disease (AD). Several epidemiological analyses have affirmed a link between pesticides and incidence of sporadic AD. Meanwhile, in vitro and animal models of AD have shed light on potential neuropathological mechanisms. In this paper, a perspective on neuropathological mechanisms underlying pesticides’ induction of AD is provided. Proposed mechanisms range from generic oxidative stress induction in neurons to more AD-specific processes involving amyloid-beta (Aβ) and hyperphosphorylated tau (p-tau). Mechanisms that are more speculative or indirect in nature, including somatic mutation, epigenetic modulation, impairment of adult neurogenesis, and microbiota dysbiosis, are also discussed. Chronic toxicity mechanisms of environmental pesticide exposure crosstalks in complex ways and could potentially be mutually enhancing, thus making the deciphering of simplistic causal relationships difficult.

Neuroprotective Effect of β-secretase Inhibitory Peptide from Pacific Hake (Merluccius productus) Fish Protein Hydrolysate

BACKGROUND

Various methodologies have been employed for the therapeutic interpolation of the progressive brain disorder Alzheimer's disease. Thus, β-secretase inhibition is significant to prevent disease progression in the early stages.

OBJECTIVE

This study seeks to purify and characterize a novel β-secretase inhibitory peptide from Pacific hake enzymatic hydrolysate.

METHODS

A potent β-secretase inhibitory peptide was isolated by sequential purifications using Sephadex G-25 column chromatography and octadecylsilane (ODS) C18 reversed-phase HPLC. A total of seven peptides were synthesized using the isolated peptide sequences. SH-SY5Y cells stably transfected with the human ''Swedish'' amyloid precursor protein (APP) mutation APP695 (SH-SY5YAPP695swe) were used as an in-vitro model system to investigate the effect of Leu-Asn peptide on APP processing.

RESULTS

The β-secretase inhibitory activity (IC50) of the purified peptide (Ser-Leu-Ala-Phe-Val-Asp- Asp-Val-Leu-Asn) from fish protein hydrolysate was 18.65 μM and dipeptide Leu-Asn was the most potent β-secretase inhibitor (IC50 value = 8.82 µM). When comparing all the seven peptides, the inhibition pattern of Leu-Asn dipeptide was found to be competitive by Lineweaver-Burk plot and Dixon plot (Ki value = 4.24 µM). The 24 h treatment with Leu-Asn peptide in SH-SY5Y cells resulted in reducing the β-amyloid (Aβ) production in a dose-dependent manner.

CONCLUSION

Therefore, the results of this study suggest that β-secretase inhibitory peptides derived from marine organisms could be potential candidates to develop nutraceuticals or pharmaceuticals as antidementia agents.

Furin substrate as a novel cell-penetrating peptide: combining a delivery vector and an inducer of cargo release

We have developed a new cell-penetrating peptide (CPP) using a repeated protease (furin) substrate. This CPP can not only deliver cargo into cells but can also be cleaved by furin in cells and release the cargo. Cell-impermeable antitumor pro-apoptotic peptide KLAKLAKKLAKLAK (KLA) and chemotherapy drug chlorambucil were chosen to be delivered by the CPP into live cancer cells and their cytotoxicity was greatly enhanced for in vivo cancer treatment.

Influence of functional moiety in lupane-type triterpenoids in BACE1 inhibition

Lupane-type triterpenoids have shown a potential effect against neurodegenerative disorders. Alzheimer's disease, one of the common neurodegenerative disease, is evident by the accumulation of amyloid-beta (Aβ) plaque in the extracellular regions of the brain. β-site amyloid precursor protein cleaving enzyme 1 (BACE1) is a key enzyme for the Aβ formation viathe cleavage of amyloid precursor protein (APP). Therefore, to find the potent BACE1 inhibitors and furthermore to explore the role of the functional group responsible for the strong BACE1 inhibitory activity, we synthesized a series of triterpenoids with lupane skeleton starting from the natural compounds calenduladiol and lupeol. Compound 1 revealed a potent competitive BACE1 inhibitory activity (IC₅₀ = 16.77 ± 1.16 μM; K_i = 19.38). Furthermore, the molecular docking simulation revealed the importance of Tyr198 residue along with the other hydrophobic interactions for the strong affinity of 1‒BACE1 complex. To sum up, our results demonstrated the importance of carbonyl moiety at 3 and 16 position of lupane-type triterpenoid over the hydroxyl group at the same position.

Alzheimer's disease: Key developments support promising perspectives for therapy

Alzheimer's is the neurodegenerative disease affecting the largest number of patients in the world. In spite of the intense research of the last decades, progress about its knowledge and therapy was limited. In particular, various cytotoxic processes remained debated, while the few drugs approved for therapy were of only marginal relevance. Recent studies have identified key aspects of the disease, such as the mechanisms governing the development of pathology. In order to operate the Aβ peptide, known as the key factor, requires a complex assembled by its high affinity binding to PrP^c, a cell surface prion protein, and mGluR5, a metabotropic glutamate receptor. Aβ and its associates bind also phosphorylated tau transferred to the extracellular space, with final activation of intracellular cytotoxic signals. Pathology is further affected by factors (including genes, receptors and their agonists) and by glial cells governing (via vesicles, cytokines and enzymes) cell immunology, inflammation and oxidative stress. Concomitant to pathology studies, strong attempts have been made for the development of new, effective therapies. Critical for this are biomarkers, by which Alzheimer's patients are recognized even before appearance of their symptoms. The question was whether patients take advantage from drugs not yet approved. The latter, first identified in mice, were found effective also in men, however only before appearance or at early stage of the disease. In other words, the drugs not yet approved induce effective protection of patients still healthy or in a preliminary stage of the disease. In contrast, developed Alzheimer's disease is practically irreversible.

Elevated cleavage of neuregulin-1 by beta-secretase 1 in plasma of schizophrenia patients

Neuregulin 1 (NRG1) is a key candidate susceptibility gene for schizophrenia. It is reported that the function of NRG1 can be regulated by cleavage via the β-Secretase (BACE1), particularly during early development. While current knowledge suggested that schizophrenia might have different phenotypes, it is unknown whether BACE1-cleaved-NRG1 (BACE1-NRG1) activity is related to clinical phenotypes of schizophrenia. In the current study, we used a newly developed enzymatic assay to detect BACE1-NRG1 activity in the human plasma and investigated the levels of cleavage of NRG1 by BACE1 in the plasma from schizophrenia patients. Our results are the first to demonstrate that the level of plasma BACE1-NRG1 activity was significantly increased in subjects affected with schizophrenia compared with healthy controls. Interestingly, the elevated BACE1-NRG1 activity was correlated with the disease severity and duration of schizophrenia, such as patients suffering from shorter-term course and worse disease status expressed higher BACE1-NRG1 activity levels compared to whom with longer duration and less severity of the disease. Furthermore, this is also the first report that the alternation of BACE1-NRG1 activity was a substrate -specific event in schizophrenia. Together, our findings suggested that the plasma BACE1-NRG1 activity can be a potential biomarker for the early diagnosis of schizophrenia.

Current Screening Methodologies in Drug Discovery for Selected Human Diseases

The increase of many deadly diseases like infections by multidrug-resistant bacteria implies re-inventing the wheel on drug discovery. A better comprehension of the metabolisms and regulation of diseases, the increase in knowledge based on the study of disease-born microorganisms’ genomes, the development of more representative disease models and improvement of techniques, technologies, and computation applied to biology are advances that will foster drug discovery in upcoming years. In this paper, several aspects of current methodologies for drug discovery of antibacterial and antifungals, anti-tropical diseases, antibiofilm and antiquorum sensing, anticancer and neuroprotectors are considered. For drug discovery, two different complementary approaches can be applied: classical pharmacology, also known as phenotypic drug discovery, which is the historical basis of drug discovery, and reverse pharmacology, also designated target-based drug discovery. Screening methods based on phenotypic drug discovery have been used to discover new natural products mainly from terrestrial origin. Examples of the discovery of marine natural products are provided. A section on future trends provides a comprehensive overview on recent advances that will foster the pharmaceutical industry.

Drug development for Alzheimer's disease: review

Alzheimer's disease (AD) is a chronic neurodegenerative disease, which is considered as one of the most intractable medical problems with heavy social and economic costs. The current drugs for AD, including acetylcholinesterase inhibitors (AChEIs) and memantine, a NMDA receptor antagonist, only temporarily ameliorate cognitive decline, but are unable to stop or reverse the progression of dementia. This paper reviewed the recent advance in AD drug development. The drug discovery programs under clinical trials targeting cholinergic system, α7 nicotinic acetylcholine receptors (nAChRs), N-methyl-d-aspartate receptor (NMDAR), β-secretase, γ-secretase modulators, tau, inflammatory mediators and glucagon-like peptide-1 (GLP-1) were discussed. Though several drug discovery programs are ongoing, the high failure rate is an outstanding issue. Novel techniques and strategies are desperately needed to significantly accelerate this process.

A gender dimorphism in up-regulation of BACE1 gene expression in schizophrenia

Schizophrenia has long been considered as a devastating brain disorder in which both genetic and environmental factors are involved. The BACE1 gene is one of the most important susceptibility genes for this disorder. However, the changes in BACE1 expression in schizophrenic patients compared with healthy subjects have not been evaluated yet. In this case-control study, we examined BACE1 expression in a group of 50 patients with schizophrenia and 50 healthy controls. The level of BACE1 gene expression was measured using Real-Time PCR. Substantial increase in gene expression was detected in the patients compared with normal individuals (P = 0.001). Furthermore, a gender dimorphism was observed in BACE1 gene expression in the patients in a way that the male patients manifested a statistically significant higher levels of BACE1 expression (P = 0.002). BACE1 might be implicated in the pathogenesis of schizophrenia. Besides, BACE1 physiology may be gender -based at some levels. Our findings warrant an investigation of BACE1 gene in a larger number of cases and controls.

Therapeutic impact of rHuEPO on abnormal platelet APP, BACE 1, presenilin 1, ADAM 10 and Aβ expressions in chronic kidney disease patients with cognitive dysfunction like Alzheimer's disease: A pilot study

BACKGROUND

Cognitive dysfunction is reported to be a major cause of morbidity in chronic kidney disease (CKD). The senile plaques (SPs) in the brain are one of the most pathophysiological characteristics of cognitive dysfunction and its major constituent amyloid β (Aβ) released from amyloid precursor protein (APP) by β (BACE1) and γ (presenilin 1) secretases . Platelets contain more than 95% of the circulating APP and implicate as a candidate biomarker for cognitive decline. Recombinant human erythropoietin (rHuEPO) is a standard therapy for anemia in CKD and also acts as a neuroprotective agent. The aim of the study is to determine the impact of rHuEPO therapy on platelet APP processing in CKD with Cognitive Dysfunction.

METHODS

A total of 60 subjects comprising of 30 CKD without cognitive dysfunction and 30 CKD with cognitive dysfunction based on neuropsychological assessment. APP, BACE1, Presenilin 1, ADAM 10 (α secretase) and Aβ expressions in platelets were determined by western blotting and lipid peroxidation (LPO) in platelet rich plasma (PRP) was done by spectrophotometrically. The parameters were statistically compared with Alzheimer's disease (AD), Normocytic normochromic anemic and healthy subjects.

RESULTS

Significantly (p < 0.05) decreased APP, ADAM 10 while increased BACE1, Presenilin 1, Aβ and LPO were observed in CKD with cognitive dysfunction like AD subjects compared to other groups. The parameters were reassessed in CKD with cognitive dysfunction subjects after rHuEPO (100 IU/ kg, weekly twice, 6 months) therapy. All the parameters were retrieved significantly (p < 0.05) along with improved neuropsychological tests scoring after rHuEPO therapy.

CONCLUSIONS

This study demonstrated that rHuEPO is an effective neuroprotective agent in the context of CKD associated cognitive dysfunction and proved its clinical usefulness.

Increased Plasma Beta-Secretase 1 May Predict Conversion to Alzheimer's Disease Dementia in Individuals With Mild Cognitive Impairment

BACKGROUND

Increased beta-secretase 1 (BACE1) activity has consistently been detected in brain tissue and cerebrospinal fluid of subjects with mild cognitive impairment (MCI) and probable Alzheimer's disease (AD) compared with control subjects. The collection of cerebrospinal fluid by lumbar puncture is invasive. We sought to identify the presence of plasma BACE1 activity and determine potential alterations in subjects with MCI with clinical follow-up examinations for 3 years using patients with diagnosed probable AD dementia compared with healthy control subjects.

METHODS

Seventy-five patients with probable AD, 96 individuals with MCI, and 53 age-matched and sex-matched healthy control subjects were recruited from three independent international academic memory clinics and AD research expert centers. Plasma BACE1 activity was measured by a synthetic fluorescence substrate enzyme-linked immunosorbent assay. BACE1 protein expression was assessed by Western blotting using three different antibodies that recognize the epitopes of the N-terminus, C-terminus, and full-length BACE1.

RESULTS

Compared with healthy control subjects, plasma BACE1 activity (V_max) significantly increased by 53.2% in subjects with MCI and by 68.9% in patients with probable AD. Subjects with MCI who converted to probable AD dementia at follow-up examinations exhibited significantly higher BACE1 activity compared with cognitively stable MCI nonconverters and showed higher levels of BACE1 activity than patients with AD.

CONCLUSIONS

Plasma BACE1 activity is significantly increased in MCI converters and patients with probable AD. The sensitivities and specificities of BACE1 activity for the patients were 84% and 88%, respectively. Our results indicate that plasma BACE1 activity may be a biomarker for AD risk and could predict progression from prodromal to probable AD dementia.

Effects of safflower yellow on beta-amyloid deposition and activation of astrocytes in the brain of APP/PS1 transgenic mice

Safflower yellow (SY), one of traditional Chinese medicine extracted from safflower, has been shown to have neuroprotective effects on animal models of vascular dementia and Alzheimer's diseases (AD), by inhibiting oxidative injury, neuronal apoptosis and tau hyperphosphorylation. In this study, we investigated whether safflower yellow (SY) can improve cognitive function, decrease Amyloid β (Aβ) accumulation and overactivation of astrocytes in AD mouse model. We found that SY treatment significantly ameliorated the learning and memory deficits of APP/PS1 mice. By hematoxylin-eosin staining, we found that the neuronal loss and death in APP/PS1 mice was decreased by SY treatment. Immunohistochemical staining showed that SY treatment dramatically down-regulated Aβ_1-42 deposition and glial fibrillary acidic protein (GFAP) level in APP/PS1 mice. Biochemical analysis also showed that SY treatment reduced soluble and insoluble Aβ_1-42 level in the cortex and soluble Aβ_1-42 level in the hippocampus of APP/PS1 mice. Moreover, we found that SY treatment decreased the expression of proteins related to generation of Aβ, and markedly increased expression of enzymes associated with clearance of Aβ in the brain of APP/PS1 mice. These results indicate that the SY can serve as a promising therapeutic approach for the treatment of AD.

BACE1-Dependent Neuregulin-1 Signaling: An Implication for Schizophrenia

Schizophrenia is a chronic psychiatric disorder with a lifetime prevalence of about 1% in the general population. Recent studies have shown that Neuregulin-1 (Nrg1) is a candidate gene for schizophrenia. At least 15 alternative splicing of NRG1 isoforms all contain an extracellular epidermal growth factor (EGF)-like domain, which is sufficient for Nrg1 biological activity including the formation of myelin sheaths and the regulation of synaptic plasticity. It is known that Nrg1 can be cleaved by β-secretase (BACE1) and the resulting N-terminal fragment (Nrg1-ntf) binds to receptor tyrosine kinase ErbB4, which activates Nrg1/ErbB4 signaling. While changes in Nrg1 expression levels in schizophrenia still remain controversial, understanding the BACE1-cleaved Nrg1-ntf and Nrg1/ErbB4 signaling in schizophrenia neuropathogenesis is essential and important. In this review paper, we included three major parts: (1) Nrg1 structure and cleavage pattern by BACE1; (2) BACE1-dependent Nrg1 cleavage associated with schizophrenia in human studies; and (3) Animal studies of Nrg1 and BACE1 mutations with behavioral observations. Our review will provide a better understanding of Nrg1 in schizophrenia and a potential strategy for using BACE1 cleavage of Nrg1 as a unique biomarker for diagnosis, as well as a new therapeutic target, of schizophrenia.

Amyloid precursor protein and endosomal-lysosomal dysfunction in Alzheimer's disease: inseparable partners in a multifactorial disease

Abnormalities of the endosomal-lysosomal network (ELN) are a signature feature of Alzheimer's disease (AD). These include the earliest known cytopathology that is specific to AD and that affects endosomes and induces the progressive failure of lysosomes, each of which are directly linked by distinct mechanisms to neurodegeneration. The origins of ELN dysfunction and β-amyloidogenesis closely overlap, which reflects their common genetic basis, the established early involvement of endosomes and lysosomes in amyloid precursor protein (APP) processing and clearance, and the pathologic effect of certain APP metabolites on ELN functions. Genes that promote β-amyloidogenesis in AD (APP, PSEN1/2, and APOE4) have primary effects on ELN function. The importance of primary ELN dysfunction to pathogenesis is underscored by the mutations in more than 35 ELN-related genes that, thus far, are known to cause familial neurodegenerative diseases even though different pathogenic proteins may be involved. In this article, I discuss growing evidence that implicates AD gene-driven ELN disruptions as not only the antecedent pathobiology that underlies β-amyloidogenesis but also as the essential partner with APP and its metabolites that drive the development of AD, including tauopathy, synaptic dysfunction, and neurodegeneration. The striking amelioration of diverse deficits in animal AD models by remediating ELN dysfunction further supports a need to integrate APP and ELN relationships, including the role of amyloid-β, into a broader conceptual framework of how AD arises, progresses, and may be effectively therapeutically targeted.-Nixon, R. A. Amyloid precursor protein and endosomal-lysosomal dysfunction in Alzheimer's disease: inseparable partners in a multifactorial disease.

Association of β-Secretase Functional Polymorphism with Risk of Schizophrenia

AIM

The NRG1-ERBB4 neurotransmitter signaling pathway plays a key role in the pathogenesis of schizophrenia (SZ). The intronic single-nucleotide polymorphism rs707284 in ERBB4 links to PI3K-AKT suppression in SZ. Another protein indirectly affecting NRG1-ERBB4 signaling is β-secretase, which is encoded by the BACE1 gene, and activates NRG1 by proteolytic cleavage. In this study, we aimed to investigate the association of ERBB4 rs707284 and BACE1 rs490460 with the risk of SZ in an Iranian population.

SUBJECTS AND METHODS

A total of 973 subjects, including 480 SZ patients and 493 healthy controls, matched by ethnicity, age, and gender, were recruited in a case-control study. Genomic DNA was extracted from peripheral blood of all subjects and genotyping of rs707284 and rs490460 was performed using polymerase chain reaction (PCR)-restriction fragment length polymorphism and tetra-primer amplification refractory mutation system (tetra-ARMS) PCR genotyping assays, respectively.

RESULTS

A significant association was observed between the rs490460 T allele and SZ (p = 0.0002, odds ratio 0.69, 95% confidence interval 0.57-0.84). There was no association between the risk of SZ and rs707284.

CONCLUSION

Our data indicate that rs490460 is associated with the risk of SZ. In silico analysis indicates that rs490460 may be a potential splicing site, which affects protein structure. Replication studies are needed to confirm our data.

Palmitoylated APP Forms Dimers, Cleaved by BACE1

A major rate-limiting step for Aβ generation and deposition in Alzheimer's disease brains is BACE1-mediated cleavage (β-cleavage) of the amyloid precursor protein (APP). We previously reported that APP undergoes palmitoylation at two cysteine residues (Cys186 and Cys187) in the E1-ectodomain. 8-10% of total APP is palmitoylated in vitro and in vivo. Palmitoylated APP (palAPP) shows greater preference for β-cleavage than total APP in detergent resistant lipid rafts. Protein palmitoylation is known to promote protein dimerization. Since dimerization of APP at its E1-ectodomain results in elevated BACE1-mediated cleavage of APP, we have now investigated whether palmitoylation of APP affects its dimerization and whether this leads to elevated β-cleavage of the protein. Here we report that over 90% of palAPP is dimerized while only ~20% of total APP forms dimers. PalAPP-dimers are predominantly cis-oriented while total APP dimerizes in both cis- and trans-orientation. PalAPP forms dimers 4.5-times more efficiently than total APP. Overexpression of the palmitoylating enzymes DHHC7 and DHHC21 that increase palAPP levels and Aβ release, also increased APP dimerization in cells. Conversely, inhibition of APP palmitoylation by pharmacological inhibitors reduced APP-dimerization in coimmunoprecipitation and FLIM/FRET assays. Finally, in vitro BACE1-activity assays demonstrate that palmitoylation-dependent dimerization of APP promotes β-cleavage of APP in lipid-rich detergent resistant cell membranes (DRMs), when compared to total APP. Most importantly, generation of sAPPβ-sAPPβ dimers is dependent on APP-palmitoylation while total sAPPβ generation is not. Since BACE1 shows preference for palAPP dimers over total APP, palAPP dimers may serve as novel targets for effective β-cleavage inhibitors of APP as opposed to BACE1 inhibitors.

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

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

Post-translational regulation of the β-secretase BACE1

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

Impact of physiological, pathological and environmental factors on the expression and activity of human cytochrome P450 2D6 and implications in precision medicine

With only 1.3-4.3% in total hepatic CYP content, human CYP2D6 can metabolize more than 160 drugs. It is a highly polymorphic enzyme and subject to marked inhibition by a number of drugs, causing a large interindividual variability in drug clearance and drug response and drug-drug interactions. The expression and activity of CYP2D6 are regulated by a number of physiological, pathological and environmental factors at transcriptional, post-transcriptional, translational and epigenetic levels. DNA hypermethylation and histone modifications can repress the expression of CYP2D6. Hepatocyte nuclear factor-4α binds to a directly repeated element in the promoter of CYP2D6 and thus regulates the expression of CYP2D6. Small heterodimer partner represses hepatocyte nuclear factor-4α-mediated transactivation of CYP2D6. GW4064, a farnesoid X receptor agonist, decreases hepatic CYP2D6 expression and activity while increasing small heterodimer partner expression and its recruitment to the CYP2D6 promoter. The genotypes are key determinants of interindividual variability in CYP2D6 expression and activity. Recent genome-wide association studies have identified a large number of genes that can regulate CYP2D6. Pregnancy induces CYP2D6 via unknown mechanisms. Renal or liver diseases, smoking and alcohol use have minor to moderate effects only on CYP2D6 activity. Unlike CYP1 and 3 and other CYP2 members, CYP2D6 is resistant to typical inducers such as rifampin, phenobarbital and dexamethasone. Post-translational modifications such as phosphorylation of CYP2D6 Ser135 have been observed, but the functional impact is unknown. Further functional and validation studies are needed to clarify the role of nuclear receptors, epigenetic factors and other factors in the regulation of CYP2D6.

Triptolide treatment reduces Alzheimer's disease (AD)-like pathology through inhibition of BACE1 in a transgenic mouse model of AD

The complex pathogenesis of Alzheimer’s disease (AD) involves multiple contributing factors, including amyloid β (Aβ) peptide accumulation, inflammation and oxidative stress. Effective therapeutic strategies for AD are still urgently needed. Triptolide is the major active compound extracted from Tripterygium wilfordii Hook.f., a traditional Chinese medicinal herb that is commonly used to treat inflammatory diseases. The 5-month-old 5XFAD mice, which carry five familial AD mutations in the β-amyloid precursor protein (APP) and presenilin-1 (PS1) genes, were treated with triptolide for 8 weeks. We observed enhanced spatial learning performances, and attenuated Aβ production and deposition in the brain. Triptolide also inhibited the processing of amyloidogenic APP, as well as the expression of βAPP-cleaving enzyme-1 (BACE1) both in vivo and in vitro. In addition, triptolide exerted anti-inflammatory and anti-oxidative effects on the transgenic mouse brain. Triptolide therefore confers protection against the effects of AD in our mouse model and is emerging as a promising therapeutic candidate drug for AD.

Evidence for cadherin-11 cleavage in the synovium and partial characterization of its mechanism

Introduction

Engagement of the homotypic cell-to-cell adhesion molecule cadherin-11 on rheumatoid arthritis (RA) synovial fibroblasts with a chimeric molecule containing the cadherin-11 extracellular binding domain stimulated cytokine, chemokine, and matrix metalloproteinases (MMP) release, implicating cadherin-11 signaling in RA pathogenesis. The objective of this study was to determine if cadherin-11 extracellular domain fragments are found inside the joint and if a physiologic synovial fibroblast cleavage pathway releases those fragments.

Methods

Cadherin-11 cleavage fragments were detected by western blot in cell media or lysates. Cleavage was interrupted using chemical inhibitors or short-interfering RNA (siRNA) gene silencing. The amount of cadherin-11 fragments in synovial fluid was measured by western blot and ELISA.

Results

Soluble cadherin-11 extracellular fragments were detected in human synovial fluid at significantly higher levels in RA samples compared to osteoarthritis (OA) samples. A cadherin-11 N-terminal extracellular binding domain fragment was shed from synovial fibroblasts after ionomycin stimulation, followed by presenilin 1 (PSN1)-dependent regulated intramembrane proteolysis of the retained membrane-bound C-terminal fragments. In addition to ionomycin-induced calcium flux, tumor necrosis factor (TNF)-α also stimulated cleavage in both two- and three-dimensional fibroblast cultures. Although cadherin-11 extracellular domains were shed by a disintegrin and metalloproteinase (ADAM) 10 in several cell types, a novel ADAM- and metalloproteinase-independent activity mediated shedding in primary human fibroblasts.

Conclusions

Cadherin-11 undergoes ectodomain shedding followed by regulated intramembrane proteolysis in synovial fibroblasts, triggered by a novel sheddase that generates extracelluar cadherin-11 fragments. Cadherin-11 fragments were enriched in RA synovial fluid, suggesting they may be a marker of synovial burden and may function to modify cadherin-11 interactions between synovial fibroblasts.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-015-0647-9) contains supplementary material, which is available to authorized users.

Pharmacological inhibition of BACE1 impairs synaptic plasticity and cognitive functions

BACKGROUND

BACE1 (beta site amyloid precursor protein cleaving enzyme 1) is the rate limiting protease in amyloid β production, hence a promising drug target for the treatment of Alzheimer's disease. Inhibition of BACE1, as the major β-secretase in vivo with multiple substrates, however is likely to have mechanism-based adverse effects. We explored the impact of long-term pharmacological inhibition of BACE1 on dendritic spine dynamics, synaptic functions, and cognitive performance of adult mice.

METHODS

Sandwich enzyme-linked immunosorbent assay was used to assess Aβ40 levels in brain and plasma after oral administration of BACE1 inhibitors SCH1682496 or LY2811376. In vivo two-photon microscopy of the somatosensory cortex was performed to monitor structural dynamics of dendritic spines while synaptic functions and plasticity were measured via electrophysiological recordings of excitatory postsynaptic currents and hippocampal long-term potentiation in brain slices. Finally, behavioral tests were performed to analyze the impact of pharmacological inhibition of BACE1 on cognitive performance.

RESULTS

Dose-dependent decrease of Aβ40 levels in vivo confirmed suppression of BACE1 activity by both inhibitors. Prolonged treatment caused a reduction in spine formation of layer V pyramidal neurons, which recovered after withdrawal of inhibitors. Congruently, the rate of spontaneous and miniature excitatory postsynaptic currents in pyramidal neurons and hippocampal long-term potentiation were reduced in animals treated with BACE1 inhibitors. These effects were not detected in Bace1(-/-) mice treated with SCH1682496, confirming BACE1 as the pharmacological target. Described structural and functional changes were associated with cognitive deficits as revealed in behavioral tests.

CONCLUSIONS

Our findings indicate important functions to BACE1 in structural and functional synaptic plasticity in the mature brain, with implications for cognition.

Disturbed calcium signaling in spinocerebellar ataxias and Alzheimer's disease

Neurodegenerative disorders, such as spinocerebellar ataxias (SCAs) and Alzheimer's disease (AD) represent a huge scientific and medical question, but the molecular mechanisms of these diseases are still not clear. There is increasing evidence that neuronal calcium signaling is abnormal in many neurodegenerative disorders. Abnormal neuronal calcium release from the endoplasmic reticulum may result in disturbances of cell homeostasis, synaptic dysfunction, and eventual cell death. Neuronal loss is observed in most cases of neurodegenerative diseases. Recent experimental evidence supporting the role of neuronal calcium signaling in the pathogenesis of SCAs and AD is discussed in this review.

The Roles of the Stem Cell-Controlling Sox2 Transcription Factor: from Neuroectoderm Development to Alzheimer's Disease?

Sox2 is a component of the core transcriptional regulatory network which maintains the totipotency of the cells during embryonic preimplantation period, the pluripotency of embryonic stem cells, and the multipotency of neural stem cells. This maintenance is controlled by internal loops between Sox2 and other transcription factors of the core such as Oct4, Nanog, Dax1, and Klf4, downstream proteins of extracellular ligands, epigenetic modifiers, and miRNAs. As Sox2 plays an important role in the balance between stem cells maintenance and commitment to differentiated lineages throughout the lifetime, it is supposed that Sox2 could regulate stem cells aging processes. In this review, we provide an update concerning the involvement of Sox2 in neurogenesis during normal aging and discuss its possible role in Alzheimer's disease.