Neurological dysfunctions associated with altered BACE1-dependent Neuregulin-1 signaling

Effects of Anti-Seizure Medication on Neuregulin-1 Gene and Protein in Patients with First-Episode Focal Epilepsy

Introduction

Neuregulin-1 (NRG-1) appears to play a role in the pathogenesis of several neuropsychiatric disorders, including epilepsy. We conducted a study to investigate the effect of anti-seizure medication on NRG-1 mRNA and NRG-1 protein levels in patients with first-episode focal epilepsy.

Methods

The levels of NRG-1 mRNA isoforms (type I, II, III, and IV) in peripheral blood mononuclear cells (PBMCs) of 39 healthy controls, 39 first-episode focal epilepsy patients before anti-seizure medication (ASM) therapy and four weeks after administration of ASM were measured by RT-qPCR, and the levels of NRG-1 protein in the serum of samples of each group were determined using ELISA. In addition the relationship between efficacy, NRG-1 mRNA expression, and NRG-1 protein expression was analyzed.

Results

The levels of NRG-1 mRNA progressively increased in patients with first-episode focal epilepsy treated with ASM and were distinctly different from those before medication, but remained lower than in healthy controls (all P < 0.001). Before and after drug administration, NRG-1 protein levels were substantially higher in epileptic patients than in healthy controls, and no significant changes were detected with prolonged follow-up (P < 0.001). Patients with epilepsy who utilized ASM were able to control seizures with an overall efficacy of 97.4%. There was a negative correlation between NRG-1 mRNA levels and efficacy: as NRG-1 mRNA levels increased, seizures reduced (all P < 0.05).

Conclusion

Our research indicated that NRG-1 may play a role in the pathophysiology of epilepsy. NRG-1 mRNA may provide ideas for the discovery of novel epilepsy therapeutic markers and therapeutic targets for novel ASM.

BACE1-dependent metabolism of neuregulin 1: Bridging the gap in explaining the occurrence of schizophrenia-like symptoms in Alzheimer's disease with psychosis?

Alzheimer's disease is a neurodegenerative disease mainly characterized by cortico-neuronal atrophy, impaired memory and other cognitive declines. On the other hand, schizophrenia is a neuro-developmental disorder with an overtly active central nervous system pruning system resulting into abrupt connections with common symptoms including disorganised thoughts, hallucination and delusion. Nevertheless, the fronto-temporal anomaly presents itself as a common denominator for the two pathologies. There is even a strong presumption of increased risk of developing co-morbid dementia for schizophrenic individuals and psychosis for Alzheimer's disease patients, overall leading to a further deteriorated quality of life. However, convincing proofs of how these two disorders, although very distant from each other when considering their aetiology, develop coexisting symptoms is yet to be resolved. At the molecular level, the two primarily neuronal proteins β-amyloid precursor protein and neuregulin 1 have been considered in this relevant context, although the conclusions are for the moment only hypotheses. In order to propose a model for explaining the psychotic schizophrenia-like symptoms that sometimes accompany AD-associated dementia, this review projects out on the similar sensitivity shared by these two proteins regarding their metabolism by the β-site APP cleaving enzyme 1.

Insights into the Pathophysiology of Alzheimer's Disease and Potential Therapeutic Targets: A Current Perspective

The aging population increases steadily because of a healthy lifestyle and medical advancements in healthcare. However, Alzheimer's disease (AD) is becoming more common and problematic among older adults. AD-related cases show an increasing trend annually, and the younger age population may also be at risk of developing this disorder. AD constitutes a primary form of dementia, an irreversible and progressive brain disorder that steadily damages cognitive functions and the ability to perform daily tasks. Later in life, AD leads to death as a result of the degeneration of specific brain areas. Currently, the cause of AD is poorly understood, and there is no safe and effective therapeutic agent to cure or slow down its progression. The condition is entirely preventable, and no study has yet demonstrated encouraging findings in terms of treatment. Identifying this disease's pathophysiology can help researchers develop safe and efficient therapeutic strategies to treat this ailment. This review outlines and discusses the pathophysiology that resulted in the development of AD including amyloid-β plaques, tau neurofibrillary tangles, neuroinflammation, oxidative stress, cholinergic dysfunction, glutamate excitotoxicity, and changes in neurotrophins level may sound better based on the literature search from Scopus, PubMed, ScienceDirect, and Google Scholar. Potential therapeutic strategies are discussed to provide more insights into AD mechanisms by developing some possible pharmacological agents for its treatment.

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.

Key brain cell interactions and contributions to the pathogenesis of Alzheimer's disease

Alzheimer's disease (AD) is the most common neurodegenerative disease worldwide, with the two major hallmarks being the deposition of extracellular β-amyloid (Aβ) plaques and of intracellular neurofibrillary tangles (NFTs). Additionally, early pathological events such as cerebrovascular alterations, a compromised blood-brain barrier (BBB) integrity, neuroinflammation and synaptic dysfunction, culminate in neuron loss and cognitive deficits. AD symptoms reflect a loss of neuronal circuit integrity in the brain; however, neurons do not operate in isolation. An exclusively neurocentric approach is insufficient to understand this disease, and the contribution of other brain cells including astrocytes, microglia, and vascular cells must be integrated in the context. The delicate balance of interactions between these cells, required for healthy brain function, is disrupted during disease. To design successful therapies, it is critical to understand the complex brain cellular connections in AD and the temporal sequence of their disturbance. In this review, we discuss the interactions between different brain cells, from physiological conditions to their pathological reactions in AD, and how this basic knowledge can be crucial for developing new therapeutic strategies.

Role of Neuron and Glia in Alzheimer's Disease and Associated Vascular Dysfunction

Amyloidogenicity and vascular dysfunction are the key players in the pathogenesis of Alzheimer’s disease (AD), involving dysregulated cellular interactions. An intricate balance between neurons, astrocytes, microglia, oligodendrocytes and vascular cells sustains the normal neuronal circuits. Conversely, cerebrovascular diseases overlap neuropathologically with AD, and glial dyshomeostasis promotes AD-associated neurodegenerative cascade. While pathological hallmarks of AD primarily include amyloid-β (Aβ) plaques and neurofibrillary tangles, microvascular disorders, altered cerebral blood flow (CBF), and blood-brain barrier (BBB) permeability induce neuronal loss and synaptic atrophy. Accordingly, microglia-mediated inflammation and astrogliosis disrupt the homeostasis of the neuro-vascular unit and stimulate infiltration of circulating leukocytes into the brain. Large-scale genetic and epidemiological studies demonstrate a critical role of cellular crosstalk for altered immune response, metabolism, and vasculature in AD. The glia associated genetic risk factors include APOE, TREM2, CD33, PGRN, CR1, and NLRP3, which correlate with the deposition and altered phagocytosis of Aβ. Moreover, aging-dependent downregulation of astrocyte and microglial Aβ-degrading enzymes limits the neurotrophic and neurogenic role of glial cells and inhibits lysosomal degradation and clearance of Aβ. Microglial cells secrete IGF-1, and neurons show a reduced responsiveness to the neurotrophic IGF-1R/IRS-2/PI3K signaling pathway, generating amyloidogenic and vascular dyshomeostasis in AD. Glial signals connect to neural stem cells, and a shift in glial phenotype over the AD trajectory even affects adult neurogenesis and the neurovascular niche. Overall, the current review informs about the interaction of neuronal and glial cell types in AD pathogenesis and its critical association with cerebrovascular dysfunction.

The protective mutation A673T in amyloid precursor protein gene decreases Aβ peptides production for 14 forms of Familial Alzheimer's Disease in SH-SY5Y cells

The deposition of Aβ plaques in the brain leads to the onset and development of Alzheimer’s disease. The Amyloid precursor protein (APP) is cleaved by α-secretase (non-amyloidogenic processing of APP), however increased cleavage by β-secretase (BACE1) leads to the accumulation of Aβ peptides, which forms plaques. APP mutations mapping to exons 16 and 17 favor plaque accumulation and cause Familial Alzheimer Disease (FAD). However, a variant of the APP gene (A673T) originally found in an Icelandic population reduces BACE1 cleavage by 40%. A series of plasmids containing the APP gene, each with one of 29 different FAD mutations mapping to exon 16 and exon 17 was created. These plasmids were then replicated with the addition of the A673T mutation. Combined these formed the library of plasmids that was used in this study. The plasmids were transfected in neuroblastomas to assess the effect of this mutation on Aβ peptide production. The production of Aβ peptides was decreased for some FAD mutations due to the presence of the co-dominant A673T mutation. The reduction of Aβ peptide concentrations for the London mutation (V717I) even reached the same level as for A673T control in SH-SY5Y cells. These preliminary results suggest that the insertion of A673T in APP genes containing FAD mutations might confer a clinical benefit in preventing or delaying the onset of some FADs.

Using machine intelligence to uncover Alzheimer’s disease progression heterogeneity

Aim: Research suggests that Alzheimer’s disease (AD) is heterogeneous with numerous subtypes. Through a proprietary interactive ML system, several underlying biological mechanisms associated with AD pathology were uncovered. This paper is an introduction to emerging analytic efforts that can more precisely elucidate the heterogeneity of AD. Methods: A public AD data set (GSE84422) consisting of transcriptomic data of postmortem brain samples from healthy controls (n = 121) and AD (n = 380) subjects was analyzed. Data were processed by an artificial intelligence platform designed to discover potential drug repurposing candidates, followed by an interactive augmented intelligence program. Results: Using perspective analytics, six perspective classes were identified: Class I is defined by TUBB1, ASB4, and PDE5A; Class II by NRG2 and ZNF3; Class III by IGF1, ASB4, and GTSE1; Class IV is defined by cDNA FLJ39269, ITGA1, and CPM; Class V is defined by PDE5A, PSEN1, and NDUFS8; and Class VI is defined by DCAF17, cDNA FLJ75819, and SLC33A1. It is hypothesized that these classes represent biological mechanisms that may act alone or in any combination to manifest an Alzheimer’s pathology. Conclusions: Using a limited transcriptomic public database, six different classes that drive AD were uncovered, supporting the premise that AD is a heterogeneously complex disorder. The perspective classes highlighted genetic pathways associated with vasculogenesis, cellular signaling and differentiation, metabolic function, mitochondrial function, nitric oxide, and metal ion metabolism. The interplay among these genetic factors reveals a more profound underlying complexity of AD that may be responsible for the confluence of several biological factors. These results are not exhaustive; instead, they demonstrate that even within a relatively small study sample, next-generation machine intelligence can uncover multiple genetically driven subtypes. The models and the underlying hypotheses generated using novel analytic methods may translate into potential treatment pathways.

Efficacy and Safety of Lanabecestat for Treatment of Early and Mild Alzheimer Disease: The AMARANTH and DAYBREAK-ALZ Randomized Clinical Trials

Importance

Alzheimer disease (AD) is a neurodegenerative disorder characterized by cognitive deterioration and impaired activities of daily living. Current treatments provide only minor symptomatic improvements with limited benefit duration. Lanabecestat, a brain-permeable inhibitor of human beta-site amyloid precursor protein-cleaving enzyme 1 (BACE1/β-secretase), was developed to modify the clinical course of AD by slowing disease progression.

Objective

To assess whether lanabecestat slows the progression of AD compared with placebo in patients with early AD (mild cognitive impairment) and mild AD dementia.

Design, Setting, and Participants

AMARANTH (first patient visit on September 30, 2014; last patient visit on October 4, 2018) and DAYBREAK-ALZ (first patient visit on July 1, 2016; last patient visit on September 28, 2018) were randomized, placebo-controlled, phase 2/3 and phase 3 clinical trials lasting 104 weeks and 78 weeks, respectively. AMARANTH and DAYBREAK-ALZ were multicenter, global, double-blind studies conducted at 257 and 251 centers, respectively, located in 15 and 18 countries or territories, respectively. A population-based sample of men and women aged 55 to 85 years who met National Institute on Aging-Alzheimer's Association criteria for early AD or mild AD dementia was screened using cognitive assessments, and the presence of amyloid was confirmed. Patients were excluded for unstable medical conditions or medication use, significant cerebrovascular pathologic findings, or a history of vitiligo and/or current evidence of postinflammatory hypopigmentation. AMARANTH screened 6871 patients; 2218 (32.3%) were randomized, and 539 patients completed the study. DAYBREAK-ALZ screened 5706 patients; 1722 (30.2%) were randomized, and 76 patients completed the study.

Interventions

Patients were randomized (1:1:1) to once-daily oral doses of lanabecestat (20 mg), lanabecestat (50 mg), or placebo.

Main Outcomes and Measures

The primary outcome measure was change from baseline on the 13-item Alzheimer Disease Assessment Scale-cognitive subscale. Secondary outcomes included Alzheimer's Disease Cooperative Study-Instrumental Activities of Daily Living Inventory, Clinical Dementia Rating, Functional Activities Questionnaire, Mini-Mental State Examination, and Neuropsychiatric Inventory. Efficacy analyses were conducted on the intent-to-treat population.

Results

Among 2218 AMARANTH patients, the mean (SD) age was 71.3 (7.1) years, and 1177 of 2218 (53.1%) were women. Among 1722 DAYBREAK-ALZ patients, the mean (SD) age was 72.3 (7.0) years, and 1023 of 1722 (59.4%) were women. Both studies were terminated early after futility analysis. There were no consistent, reproducible dose-related findings on primary or secondary efficacy measures. Psychiatric adverse events, weight loss, and hair color changes were reported in a higher percentage of patients receiving lanabecestat than placebo.

Conclusions and Relevance

Treatment with lanabecestat was well tolerated and did not slow cognitive or functional decline.

Trial Registration

ClinicalTrials.gov identifiers: NCT02245737 and NCT02783573.

Increased Levels of Serum Neuregulin 1 Associated with Cognitive Impairment in Vascular Dementia

Objective

Neuregulin 1 (NRG 1) is a member of the epidermal growth factor (EGF) family and is believed to play an important role in neuroplasticity. However, the relationship between NRG 1 and vascular dementia (VaD) is poorly understood. The purpose of this study is to explore the correlation between neuregulin 1 and VaD. Patients and Methods. From October 2018 to September 2020, 93 VaD patients and 79 control populations who attended Liaocheng People's Hospital were included in the study. Baseline characteristics including age, gender, years of education, HDL, LDL, FBG, SBP, and DBP are collected. At the same time, peripheral blood was collected, and the concentration of serum NRG 1 was detected by enzyme-linked immunosorbent assay (ELISA). All research subjects received professional cognitive function assessment.

Results

A total of 93 VaD patients and 79 controls were enrolled. There was no significant difference in age, gender, years of education, HDL, LDL, FBG, SBP, and DBP between the two groups (p > 0.05). However, compared with the control group, VaD patients have lower MoCA and higher serum NRG 1 levels, and the difference is statistically significant (p < 0.001). The correlation analysis of MoCA and baseline characteristics showed that the MoCA score in VaD was significantly negatively correlated with serum NRG 1 (r = −0.374, p = 0.036). The results of multivariate regression showed that the MoCA score of VaD patients was only associated with NRG 1 (β = 0.258, p = 0.012).

Conclusions

The concentration of serum NRG 1 in VaD patients is significantly increased, which may be an independent risk factor for cognitive impairment in VaD patients.

Expression analysis of BDNF, BACE1 and their antisense transcripts in inflammatory demyelinating polyradiculoneuropathy

Acute and chronic inflammatory demyelinating polyradiculoneuropathies (AIDP and CIDP) are two immune-related conditions in the peripheral nervous system. In the current study, we assessed expression levels of Beta-secretase (BACE1), brain-derived neurotrophic factor (BDNF) and their antisense transcripts in the peripheral blood of AIDP and CIDP patients compared with age- and sex-matched controls to assess their potential as biomarkers for these conditions. Expressions of BACE1 and BACE1-AS were down-regulated in CIDP cases compared with controls (Ratios of mean expressions=0.01 and 0.03; P values= 1.07E-08, respectively). On the other hand, expressions of BDNF and BDNF-AS were up-regulated in CIDP cases compared with controls (Ratios of mean expressions=4.78 and 25.71; P values= 7.84E-03 and 2.66E-07, respectively). Expressions of BACE1 and BACE1-AS were lower in AIDP cases compared with controls (Ratios of mean expressions=0.00; P values= 6.92E-10 and 8.04E-10, respectively). While expression of BDNF was not different between AIDP cases and controls, expression of its antisense transcript was higher in total AIDP cases compared with total controls (Ratio of mean expression= 8.61, P value=3.69E-04). Expressions of BACE1-AS, BDNF and BDNF-AS were significantly higher in CIDP cases compared with AIDP cases (Ratios of mean expression=1.98, 3.49 and 2.99; P values=4.67E-02, 4.67E-04 and 8.94E-03 respectively). Expression levels of BACE1, BACE1-AS and BDNF-AS could distinguish AIDP and CIDP cases from healthy subjects. BACE1 had the best diagnostic values in differentiation of CIDP and AIDP cases from controls (AUC values=0.88 and 0.91, respectively). Combination of all genes enhanced the diagnostic power to 0.96, 0.97 and 0.97 for differentiation between CIDP/controls, AIDP/controls and all patients/controls, respectively. Taken together, these genes might be implicated in the pathogenesis of AIDP and CIDP and can be suggested as putative markers for these conditions.

Brain region-specific lipid alterations in the PLB4 hBACE1 knock-in mouse model of Alzheimer's disease

BACKGROUND

Lipid dysregulation is associated with several key characteristics of Alzheimer's disease (AD), including amyloid-β and tau neuropathology, neurodegeneration, glucose hypometabolism, as well as synaptic and mitochondrial dysfunction. The β-site amyloid precursor protein cleavage enzyme 1 (BACE1) is associated with increased amyloidogenesis, and has been affiliated with diabetes via its role in metabolic regulation.

METHODS

The research presented herein investigates the role of hBACE1 in lipid metabolism and whether specific brain regions show increased vulnerability to lipid dysregulation. By utilising advanced mass spectrometry techniques, a comprehensive, quantitative lipidomics analysis was performed to investigate the phospholipid, sterol, and fatty acid profiles of the brain from the well-known PLB4 hBACE1 knock-in mouse model of AD, which also shows a diabetic phenotype, to provide insight into regional alterations in lipid metabolism.

RESULTS

Results show extensive region - specific lipid alterations in the PLB4 brain compared to the wild-type, with decreases in the phosphatidylethanolamine content of the cortex and triacylglycerol content of the hippocampus and hypothalamus, but increases in the phosphatidylcholine, phosphatidylinositol, and diacylglycerol content of the hippocampus. Several sterol and fatty acids were also specifically decreased in the PLB4 hippocampus.

CONCLUSION

Collectively, the lipid alterations observed in the PLB4 hBACE1 knock-in AD mouse model highlights the regional vulnerability of the brain, in particular the hippocampus and hypothalamus, to lipid dysregulation, hence supports the premise that metabolic abnormalities have a central role in both AD and diabetes.

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.

CSF levels of the BACE1 substrate NRG1 correlate with cognition in Alzheimer's disease

Background

The presynaptic protein neuregulin1 (NRG1) is cleaved by beta-site APP cleaving enzyme 1 (BACE1) in a similar way as amyloid precursor protein (APP) NRG1 can activate post-synaptic receptor tyrosine-protein kinase erbB4 (ErbB4) and was linked to schizophrenia. The NRG1/ErbB4 complex is neuroprotective, can trigger synaptogenesis and plasticity, increases the expression of NMDA and GABA receptors, and can induce neuroinflammation. This complex can reduce memory formation. In Alzheimer’s disease (AD) brains, NRG1 accumulates in neuritic plaques. It is difficult to determine if NRG1 has beneficial and/or detrimental effects in AD. BACE1 levels are increased in AD brains and cerebrospinal fluid (CSF) and may lead to enhanced NRG1 secretion, but no study has assessed CSF NRG1 levels in AD and mild cognitive impairment (MCI) patients.

Methods

This retrospective study included 162 patients suffering from AD dementia (54), MCI with progression to AD dementia (MCI-AD) (27), non-AD MCI (30), non-AD dementias (30), and neurological controls (27). All patients had neurological examinations, brain MRI, and neuropsychological evaluations. After written informed consent and using enzyme-linked immunosorbent assays (ELISAs), CSF samples were evaluated for Aβ1–42, Aβ1–40, total tau (T-tau), phosphorylated tau on threonine 181 (P-tau), BACE1, growth-associated protein 43 (GAP 43), neurogranin (Ng), and NRG1.

Results

Levels of NRG1 were significantly increased in the CSF of AD (+ 36%) and MCI-AD (+ 28%) patients compared to neurological controls and also non-AD MCI and non-AD dementias. In addition, in AD and MCI-AD patients, NRG1 levels positively correlated with Aβ1–42 but not with T-tau, P-tau, and BACE1 levels and negatively correlated with MMSE scores. A longitudinal follow-up study of AD patients revealed a trend (p = 0.08) between CSF NRG1 levels and cognitive decline. In the overall population, NRG1 correlated with MMSE and the synaptic biomarkers GAP 43 and neurogranin.

Conclusions

Our results showed that CSF NRG1 levels are increased in AD and MCI-AD as compared to controls and other dementias. CSF NRG1 levels are associated with cognitive evolution, and a major outcome of our findings is that synaptic NRG1 could be involved in the pathophysiology of AD. Modulating brain NRG1 activity may represent a new therapeutic target in AD.

A systematic review of the association of neuregulin 4, a brown fat-enriched secreted factor, with obesity and related metabolic disturbances

Neuregulin 4 (Nrg4), a novel brown fat-enriched hormone, plays a key role in the modulation of glucose and lipid metabolism and energy balance. Recent data have demonstrated that the expression of Nrg4 is substantially down-regulated in mouse and human obesity, making its regulatory aspect intriguing. Because of the close relationship between Nrg4, obesity, and associated metabolic diseases, this systematic review aimed to assess the association of Nrg4 with obesity and related metabolic disturbances, emphasizing its possible mechanisms of action in these disorders. We searched PubMed/Medline, ScienceDirect, Scopus, EMBASE, ProQuest, and Google Scholar up until June 2019. The evidence reviewed here indicates that Nrg4 may contribute to the prevention of obesity and related metabolic complications by elevating brown adipose tissue activity, increasing the expression of thermogenic markers, decreasing the expression of lipogenic/adipogenic genes, exacerbating white adipose tissue browning, increasing the number of brite/beige adipocytes, promoting hepatic fat oxidation and ketogenesis, inducing neurite outgrowth, enhancing blood vessels in adipose tissue, increasing the circulatory levels of healthy adipokines, and improving glucose homeostasis. Thus, Nrg4 appears to be a novel therapeutic strategy for the treatment of obesity and associated metabolic complications. However, prospective cohort studies are warranted to confirm these outcomes.

Investigational BACE inhibitors for the treatment of Alzheimer's disease

Introduction: The amyloid hypothesis of Alzheimer's disease (AD) states that brain accumulation of amyloid-β (Aβ) oligomers and soluble aggregates represents the major causal event of the disease. Several small organic molecules have been synthesized and developed to inhibit the enzyme (β-site amyloid precursor protein cleaving enzyme-1 or BACE1) whose action represents the rate-limiting step in Aβ production.Areas covered: We reviewed the pharmacology and clinical trials of major BACE1 inhibitors.Expert opinion: In transgenic mouse models of AD, BACE1 inhibitors dose-dependently lower Aβ levels in brain and cerebrospinal fluid (CSF) but the evidence for attenuation or reversal cognitive or behavioral deficits is very scanty. In AD patients, BACE1 inhibitors robustly lower plasma and CSF Aβ levels and reduce brain plaques but without cognitive, clinical, or functional benefit. To date, seventeen BACE1 inhibitors have failed in double-blind, placebo-controlled clinical trials in patients with mild-to-moderate or prodromal AD, or in cognitively normal subjects at risk of developing AD. Several of these studies were prematurely interrupted due to toxicity or cognitive and behavioral worsening compared to placebo-treated patients. Elenbecestat, the last BACE1 inhibitor remaining in late clinical testing for AD, was recently discontinued due to safety concerns.

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.

Impaired social discrimination behavior despite normal social approach by kallikrein-related peptidase 8 knockout mouse

For social mammals, recognition of conspecifics and discrimination of each other (social memory) is crucial to living in a stable colony. Here, we investigated whether kallikrein-related peptidase 8 (KLK8)-neuregulin 1 (NRG1)-ErbB signaling is crucial for social discrimination behavior using the social discrimination three chamber behavioral test. Klk8 knockout mice (NRG1-deactivated mice) exhibited normal social approach but impaired social discrimination. Intraventricular injection of recombinant NRG1_177-246 into Klk8 knockout mice reversed this impaired social discrimination. This study reveals that KLK8 is a key regulator of NRG1-ErbB signaling, which contributes to social discrimination behavior.

MiR-16 attenuates β-amyloid-induced neurotoxicity through targeting β-site amyloid precursor protein-cleaving enzyme 1 in an Alzheimer's disease cell model

The aberrant deposition of β-amyloid (Aβ) is closely linked to the pathogenesis and development of Alzheimer's disease (AD). MiR-16 was abnormally downregulated and may be related to the development of AD. However, the functional role and molecular mechanism of miR-16 in AD pathogenesis are still not well elucidated. The expressions of miR-16 and β-site amyloid precursor protein-cleaving enzyme 1 (BACE1) mRNA and protein levels in AD brain tissues and Aβ-treated PC12 cellular AD model were examined by qRT-PCR and western blot analyses. Luciferase reporter assay was used to verify the potential target of miR-16. The cell viability, apoptosis, and caspase-3 activity in PC12 cells were determined by the MTT assay, flow cytometry analysis, and caspase-3 activity assay, respectively. Downregulation of miR-16 and upregulation of BACE1 existed in AD tissues and the cellular AD model of PC12. In addition, miR-16 directly suppressed BACE1 expression. Moreover, miR-16 overexpression and BACE1 knockdown facilitated Aβ-induced cell toxicity, apoptosis, and caspase-3 activity in N2a cells, which was partially eliminated by overexpression of BACE1. In contrast, BACE1 knockdown reversed the miR-16 inhibition-mediated inhibitory effect on Aβ-induced cell toxicity, apoptosis, and caspase-3 activity in PC12 cells. Collectively, miR-16 attenuated Aβ-induced neurotoxicity through targeting BACE1 in an Aβ insult cellular AD model, providing a potential therapeutic target for AD treatment.

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.

A Close Look at BACE1 Inhibitors for Alzheimer's Disease Treatment

Alzheimer's disease (AD), the most common cause of age-dependent dementia, is one of the most significant healthcare problems worldwide. Aggravating this situation, drugs that are currently US Food and Drug Administration (FDA)-approved for AD treatment do not prevent or delay disease progression. Therefore, developing effective therapies for AD patients is of critical urgency. Human genetic and clinical studies over the past three decades have indicated that abnormal generation or accumulation of amyloid-β (Aβ) peptides is a likely culprit in AD pathogenesis. Aβ is generated from amyloid precursor protein (APP) via proteolytic cleavage by β-site APP cleaving enzyme 1 (BACE1) (memapsin 2, β-secretase, Asp 2 protease) and γ-secretase. Mice deficient in BACE1 show abrogated production of Aβ. Therefore, pharmacological inhibition of BACE1 is being intensively pursued as a therapeutic approach to treat AD patients. Recent setbacks in clinical trials with BACE1 inhibitors have highlighted the critical importance of understanding how to properly inhibit BACE1 to treat AD patients. This review summarizes the recent studies on the role of BACE1 in synaptic functions as well as our views on BACE1 inhibition as an effective AD treatment.

iPSC-Based Compound Screening and In Vitro Trials Identify a Synergistic Anti-amyloid β Combination for Alzheimer's Disease

In the process of drug development, in vitro studies do not always adequately predict human-specific drug responsiveness in clinical trials. Here, we applied the advantage of human iPSC-derived neurons, which offer human-specific drug responsiveness, to screen and evaluate therapeutic candidates for Alzheimer's disease (AD). Using AD patient neurons with nearly 100% purity from iPSCs, we established a robust and reproducible assay for amyloid β peptide (Aβ), a pathogenic molecule in AD, and screened a pharmaceutical compound library. We acquired 27 Aβ-lowering screen hits, prioritized hits by chemical structure-based clustering, and selected 6 leading compounds. Next, to maximize the anti-Aβ effect, we selected a synergistic combination of bromocriptine, cromolyn, and topiramate as an anti-Aβ cocktail. Finally, using neurons from familial and sporadic AD patients, we found that the cocktail showed a significant and potent anti-Aβ effect on patient cells. This human iPSC-based platform promises to be useful for AD drug development.

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.

Non-cell-autonomous function of DR6 in Schwann cell proliferation

Death receptor 6 (DR6) is an orphan member of the TNF receptor superfamily and controls cell death and differentiation in a cell-autonomous manner in different cell types. Here, we report an additional non-cell-autonomous function for DR6 in the peripheral nervous system (PNS). DR6-knockout (DR6 KO) mice showed precocious myelination in the PNS Using an in vitro myelination assay, we demonstrate that neuronal DR6 acts in trans on Schwann cells (SCs) and reduces SC proliferation and myelination independently of its cytoplasmic death domain. Mechanistically, DR6 was found to be cleaved in neurons by "a disintegrin and metalloprotease 10" (ADAM10), releasing the soluble DR6 ectodomain (sDR6). Notably, in the in vitro myelination assay, sDR6 was sufficient to rescue the DR6 KO phenotype. Thus, in addition to the cell-autonomous receptor function of full-length DR6, the proteolytically released sDR6 can unexpectedly also act as a paracrine signaling factor in the PNS in a non-cell-autonomous manner during SC proliferation and myelination. This new mode of DR6 signaling will be relevant in future attempts to target DR6 in disease settings.

BACE1 deletion in the adult mouse reverses preformed amyloid deposition and improves cognitive functions

This study uses mouse models to answer how BACE1 inhibitory drugs will be beneficial to Alzheimer’s patients. Hu et al. find that sequentially increased deletion of BACE1 in one adult Alzheimer’s mouse model reverses preexisting amyloid plaques and mitigates synaptic failures.

BACE1 initiates the generation of the β-amyloid peptide, which likely causes Alzheimer’s disease (AD) when accumulated abnormally. BACE1 inhibitory drugs are currently being developed to treat AD patients. To mimic BACE1 inhibition in adults, we generated BACE1 conditional knockout (BACE1^fl/fl) mice and bred BACE1^fl/fl mice with ubiquitin-Cre^ER mice to induce deletion of BACE1 after passing early developmental stages. Strikingly, sequential and increased deletion of BACE1 in an adult AD mouse model (5xFAD) was capable of completely reversing amyloid deposition. This reversal in amyloid deposition also resulted in significant improvement in gliosis and neuritic dystrophy. Moreover, synaptic functions, as determined by long-term potentiation and contextual fear conditioning experiments, were significantly improved, correlating with the reversal of amyloid plaques. Our results demonstrate that sustained and increasing BACE1 inhibition in adults can reverse amyloid deposition in an AD mouse model, and this observation will help to provide guidance for the proper use of BACE1 inhibitors in human patients.

BACE2 distribution in major brain cell types and identification of novel substrates

β-Site APP-cleaving enzyme 1 (BACE1) inhibition is considered one of the most promising therapeutic strategies for Alzheimer's disease, but current BACE1 inhibitors also block BACE2. As the localization and function of BACE2 in the brain remain unknown, it is difficult to predict whether relevant side effects can be caused by off-target inhibition of BACE2 and whether it is important to generate BACE1-specific inhibitors. Here, we show that BACE2 is expressed in discrete subsets of neurons and glia throughout the adult mouse brain. We uncover four new substrates processed by BACE2 in cultured glia: vascular cell adhesion molecule 1, delta and notch-like epidermal growth factor-related receptor, fibroblast growth factor receptor 1, and plexin domain containing 2. Although these substrates were not prominently cleaved by BACE2 in healthy adult mice, proinflammatory TNF induced a drastic increase in BACE2-mediated shedding of vascular cell adhesion molecule 1 in CSF. Thus, although under steady-state conditions the effect of BACE2 cross-inhibition by BACE1-directed inhibitors is rather subtle, it is important to consider that side effects might become apparent under physiopathological conditions that induce TNF expression.

Role of BACE1 in Alzheimer's synaptic function

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

BACE1 Deficiency Causes Abnormal Neuronal Clustering in the Dentate Gyrus

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

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BACE1 deficiency causes abnormal neuronal clusters retained in the mouse SPZ

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

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Such neural progenitor cells form excitatory neurons but not inhibitor neurons

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Elevated levels of reelin contribute to abnormal neuronal maturation and migration

BACE1 regulates the proliferation and cellular functions of Schwann cells

BACE1 is an indispensable enzyme for generating β-amyloid peptides, which are excessively accumulated in brains of Alzheimer's patients. However, BACE1 is also required for proper myelination of peripheral nerves, as BACE1-null mice display hypomyelination. To determine the precise effects of BACE1 on myelination, here we have uncovered a role of BACE1 in the control of Schwann cell proliferation during development. We demonstrate that BACE1 regulates the cleavage of Jagged-1 and Delta-1, two membrane-bound ligands of Notch. BACE1 deficiency induces elevated Jag-Notch signaling activity, which in turn facilitates proliferation of Schwann cells. This increase in proliferation leads to shortened internodes and decreased Schmidt-Lanterman incisures. Functionally, evoked compound action potentials in BACE1-null nerves were significantly smaller and slower, with a clear decrease in excitability. BACE1-null nerves failed to effectively use lactate as an alternative energy source under conditions of increased physiological activity. Correlatively, BACE1-null mice showed reduced performance on rotarod tests. Collectively, our data suggest that BACE1 deficiency enhances proliferation of Schwann cell due to the elevated Jag1/Delta1-Notch signaling, but fails to myelinate axons efficiently due to impaired the neuregulin1-ErbB signaling, which has been documented.

Physiological Functions of the β-Site Amyloid Precursor Protein Cleaving Enzyme 1 and 2

BACE1 was discovered as the β-secretase for initiating the cleavage of amyloid precursor protein (APP) at the β-secretase site, while its close homology BACE2 cleaves APP within the β-amyloid (Aβ) domain region and shows distinct cleavage preferences in vivo. Inhibition of BACE1 proteolytic activity has been confirmed to decrease Aβ generation and amyloid deposition, and thus specific inhibition of BACE1 by small molecules is a current focus for Alzheimer’s disease therapy. While BACE1 inhibitors are being tested in advanced clinical trials, knowledge regarding the properties and physiological functions of BACE is highly important and this review summarizes advancements in BACE1 research over the past several years. We and others have shown that BACE1 is not only a critical enzyme for testing the “Amyloid Hypothesis” associated with Alzheimer’s pathogenesis, but also important for various functions such as axon growth and pathfinding, astrogenesis, neurogenesis, hyperexcitation, and synaptic plasticity. BACE2 appears to play different roles such as glucose homeostasis and pigmentation. This knowledge regarding BACE1 functions is critical for monitoring the safe use of BACE1 inhibitors in humans.

BACE1-Deficient Mice Exhibit Alterations in Immune System Pathways

BACE1 encodes for the beta-site amyloid precursor protein cleaving enzyme 1 or β-secretase. Genetic deletion of Bace1 leads to behavioral alterations and affects midbrain dopaminergic signaling and memory processes. In order to further understand the role of BACE1 in brain function and behavior, we performed microarray transcriptome profiling and gene pathway analysis in the hippocampus of BACE1-deficient mice compared to wild type. We identified a total of 91 differentially expressed genes (DEGs), mostly enriched in pathways related to the immune and inflammation systems, particularly IL-9 and NF-κB activation pathways. Serum levels of IL-9 were elevated in BACE1-deficient mice. Our network analysis supports an intimate connection between immune response via NF-κB and BACE1 signaling through the NRG1/Akt1 pathway. Our findings warrant future mechanistic studies to determine if BACE1 signaling and the IL-9 pathway interact to alter behavior and brain function. This study opens new avenues in the investigation of hippocampus-related neuroimmunological and neuroinflammation-associated disorders.

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

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

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

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

Inhibiting BACE1 to reverse synaptic dysfunctions in Alzheimer's disease

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

Genetic Deletion of the Clathrin Adaptor GGA3 Reduces Anxiety and Alters GABAergic Transmission

Golgi-localized γ-ear-containing ARF binding protein 3 (GGA3) is a monomeric clathrin adaptor that has been shown to regulate the trafficking of the Beta-site APP-cleaving enzyme (BACE1), which is required for production of the Alzheimer’s disease (AD)-associated amyloid βpeptide. Our previous studies have shown that BACE1 is degraded via the lysosomal pathway and that depletion of GGA3 results in increased BACE1 levels and activity owing to impaired lysosomal trafficking and degradation. We further demonstrated the role of GGA3 in the regulation of BACE1 in vivo by showing that BACE1 levels are increased in the brain of GGA3 null mice. We report here that GGA3 deletion results in novelty-induced hyperactivity and decreased anxiety-like behaviors. Given the pivotal role of GABAergic transmission in the regulation of anxiety-like behaviors, we performed electrophysiological recordings in hippocampal slices and found increased phasic and decreased tonic inhibition in the dentate gyrus granule cells (DGGC). Moreover, we found that the number of inhibitory synapses is increased in the dentate gyrus of GGA3 null mice in further support of the electrophysiological data. Thus, the increased GABAergic transmission is a leading candidate mechanism underlying the reduced anxiety-like behaviors observed in GGA3 null mice. All together these findings suggest that GGA3 plays a key role in GABAergic transmission. Since BACE1 levels are elevated in the brain of GGA3 null mice, it is possible that at least some of these phenotypes are a consequence of increased processing of BACE1 substrates.

One for All? Hitting Multiple Alzheimer's Disease Targets with One Drug

HIGHLIGHTS Many AD target combinations are being explored for multi-target drug design.New databases and models increase the potential of computational drug designLiraglutide and other antidiabetics are strong candidates for repurposing to AD.Donecopride a dual 5-HT/AChE inhibitor shows promise in pre-clinical studies Alzheimer's Disease is a complex and multifactorial disease for which the mechanism is still not fully understood. As new insights into disease progression are discovered, new drugs must be designed to target those aspects of the disease that cause neuronal damage rather than just the symptoms currently addressed by single target drugs. It is becoming possible to target several aspects of the disease pathology at once using multi-target drugs (MTDs). Intended as an introduction for non-experts, this review describes the key MTD design approaches, namely structure-based, in silico, and data-mining, to evaluate what is preventing compounds progressing through the clinic to the market. Repurposing current drugs using their off-target effects reduces the cost of development, time to launch, and the uncertainty associated with safety and pharmacokinetics. The most promising drugs currently being investigated for repurposing to Alzheimer's Disease are rasagiline, originally developed for the treatment of Parkinson's Disease, and liraglutide, an antidiabetic. Rational drug design can combine pharmacophores of multiple drugs, systematically change functional groups, and rank them by virtual screening. Hits confirmed experimentally are rationally modified to generate an effective multi-potent lead compound. Examples from this approach are ASS234 with properties similar to rasagiline, and donecopride, a hybrid of an acetylcholinesterase inhibitor and a 5-HT4 receptor agonist with pro-cognitive effects. Exploiting these interdisciplinary approaches, public-private collaborative lead factories promise faster delivery of new drugs to the clinic.

Dysregulation of ErbB Receptor Trafficking and Signaling in Demyelinating Charcot-Marie-Tooth Disease

Charcot-Marie-Tooth (CMT) disease is the most common inherited peripheral neuropathy with the majority of cases involving demyelination of peripheral nerves. The pathogenic mechanisms of demyelinating CMT remain unclear, and no effective therapy currently exists for this disease. The discovery that mutations in different genes can cause a similar phenotype of demyelinating peripheral neuropathy raises the possibility that there may be convergent mechanisms leading to demyelinating CMT pathogenesis. Increasing evidence indicates that ErbB receptor-mediated signaling plays a major role in the control of Schwann cell-axon communication and myelination in the peripheral nervous system. Recent studies reveal that several demyelinating CMT-linked proteins are novel regulators of endocytic trafficking and/or phosphoinositide metabolism that may affect ErbB receptor signaling. Emerging data have begun to suggest that dysregulation of ErbB receptor trafficking and signaling in Schwann cells may represent a common pathogenic mechanism in multiple subtypes of demyelinating CMT. In this review, we focus on the roles of ErbB receptor trafficking and signaling in regulation of peripheral nerve myelination and discuss the emerging evidence supporting the potential involvement of altered ErbB receptor trafficking and signaling in demyelinating CMT pathogenesis and the possibility of modulating these trafficking and signaling processes for treating demyelinating peripheral neuropathy.