The normal and pathologic roles of the Alzheimer's β-secretase, BACE1

Adult neurogenesis in Alzheimer's disease

Alzheimer's disease (AD) is the most common form of age-related dementia, characterized by progressive memory loss and cognitive disturbances. The hippocampus, where adult hippocampal neurogenesis (AHN), a relatively novel form of brain plasticity that refers to the birth of new neurons, occurs, is one of the first brain regions to be affected in AD patients. Recent studies showed that AHN persists throughout life in humans, but it drops sharply in AD patients. Next questions to consider would be whether AHN impairment is a contributing factor to learning and memory impairment in AD and whether restoring AHN could ameliorate or delay cognitive dysfunction. Here, we outline and discuss the current knowledge about the state of AHN in AD patients, AHN impairment as a potentially relevant mechanism underlying memory deficits in AD, therapeutic potential of activating AHN in AD, and the mechanisms of AHN impairment in AD.

A Polyaminobiaryl-Based β-secretase Modulator Alleviates Cognitive Impairments, Amyloid Load, Astrogliosis, and Neuroinflammation in APPSwe/PSEN1ΔE9 Mice Model of Amyloid Pathology

The progress in Alzheimer’s disease (AD) treatment suggests a combined therapeutic approach targeting the two lesional processes of AD, which include amyloid plaques made of toxic Aβ species and neurofibrillary tangles formed of aggregates of abnormally modified Tau proteins. A pharmacophoric design, novel drug synthesis, and structure-activity relationship enabled the selection of a polyamino biaryl PEL24-199 compound. The pharmacologic activity consists of a non-competitive β-secretase (BACE1) modulatory activity in cells. Curative treatment of the Thy-Tau22 model of Tau pathology restores short-term spatial memory, decreases neurofibrillary degeneration, and alleviates astrogliosis and neuroinflammatory reactions. Modulatory effects of PEL24-199 towards APP catalytic byproducts are described in vitro, but whether PEL24-199 can alleviate the Aβ plaque load and associated inflammatory counterparts in vivo remains to be elucidated. We investigated short- and long-term spatial memory, Aβ plaque load, and inflammatory processes in APPSwe/PSEN1ΔE9 PEL24-199 treated transgenic model of amyloid pathology to achieve this objective. PEL24-199 curative treatment induced the recovery of spatial memory and decreased the amyloid plaque load in association with decreased astrogliosis and neuroinflammation. The present results underline the synthesis and selection of a promising polyaminobiaryl-based drug that modulates both Tau and, in this case, APP pathology in vivo via a neuroinflammatory-dependent process.

Isoniazid improves cognitive performance, clears Aβ plaques, and protects dendritic synapses in APP/PS1 transgenic mice

Background and objective

Alzheimer's disease (AD) is characterized by amyloid β (Aβ) aggregation and neuroinflammation. This study aimed to investigate the therapeutic effect of isoniazid (INH) against AD.

Methods

The APP/PS1 transgenic mouse model of AD was adopted. The APP/PS1 mice received oral INH (45 mg/kg/d) for 14 days. The cognitive capability was assessed by the Morris Water Maze test. Amyloid plaques and Aβ levels were determined by immunohistochemistry and ELISA assay. The dendritic spines were analyzed by DiOlistic labeling. Immunofluorescence staining was used to observe the microglia and astrocytes.

Results

The Morris Water Maze test suggested that INH administration can effectively attenuate the reference memory deficit and improve the working memory of the APP/PS1 mice compared to the untreated mice (all p < 0.001). INH significantly decreased the Aβ plaques in the hippocampus and cortex and reduced the levels of Aβ_1-40 and Aβ_1-42 in the brain homogenates, cerebrospinal fluid, and serum (all p < 0.001). INH also inhibited enzyme activities of β-site amyloid precursor protein cleaving enzyme 1 (BACE1, p < 0.05) and monoamine oxidase B (Mao-b, p < 0.01). INH significantly increased the protrusion density in the hippocampus (p < 0.01). Immunofluorescence staining revealed that INH significantly reduced the number of activated microglia and astrocytes around the Aβ plaques (both p < 0.01).

Conclusion

Isoniazid administration effectively improved cognitive performance, cleared Aβ plaques, protected dendritic synapses, and reduced innate immune cells around the Aβ plaques, suggesting that INH could be a potential drug for AD treatment.

Cathepsin B Deficiency Improves Memory Deficits and Reduces Amyloid-β in hAβPP Mouse Models Representing the Major Sporadic Alzheimer's Disease Condition

The lysosomal cysteine protease cathepsin B (CTSB) has been suggested as a biomarker for Alzheimer's disease (AD) because elevated serum CTSB in AD patients has been found to correlate with cognitive dysfunction. Furthermore, CTSB gene knockout (KO) in non-transgenic and transgenic AD animal models showed that elimination of CTSB improved memory deficits. However, conflicting CTSB KO results on amyloid-β (Aβ) pathology in transgenic AD models have been reported. The conflict is resolved here as likely being due to the different hAβPP transgenes used in the different AD mouse models. CTSB gene KO reduced wild-type (Wt) β-secretase activity, brain Aβ, pyroglutamate-Aβ, amyloid plaque, and memory deficits in models that used cDNA transgenes expressing hAβPP isoform 695. But in models that used mutated mini transgenes expressing hAβPP isoforms 751 and 770, CTSB KO had no effect on Wt β-secretase activity and slightly increased brain Aβ. All models expressed the AβPP transgenes in neurons. These conflicting results in Wt β-secretase activity models can be explained by hAβPP isoform specific cellular expression, proteolysis, and subcellular processing. CTSB KO had no effect on Swedish mutant (Swe) β-secretase activity in hAβPP695 and hAβPP751/770 models. Different proteolytic sensitivities for hAβPP with Wt versus Swe β-secretase site sequences may explain the different CTSB β-secretase effects in hAβPP695 models. But since the vast majority of sporadic AD patients have Wt β-secretase activity, the CTSB effects on Swe β-secretase activity are of little importance to the general AD population. As neurons naturally produce and process hAβPP isoform 695 and not the 751 and 770 isoforms, only the hAβPP695 Wt models mimic the natural neuronal hAβPP processing and Aβ production occurring in most AD patients. Significantly, these CTSB KO findings in the hAβPP695 Wt models demonstrate that CTSB participates in memory deficits and production of pyroglutamate-Aβ (pyroglu-Aβ), which provide rationale for future investigation of CTSB inhibitors in AD therapeutics development.

Herpes Simplex Virus Infection Increases Beta-Amyloid Production and Induces the Development of Alzheimer's Disease

Background

Alzheimer's disease, a neurodegenerative memory disease, primarily results from the formation of amyloid plaques (Aβ) that gradually inhibit neuron communications. The entire mechanism of Aβ production remains unclear to date, and it is of particular interest among scientists to find out the exact mechanism that leads to amyloid precursor protein (APP) cleavage through the amyloidogenic pathway so that effective treatments can be developed.

Method

2 sets of experiments with the use of human H4-N cell lines are proposed to fully investigate the validity of the hypothesis. All of the experiments would involve immunoblotting of Aβ using an anti-Aβ antibody, and the results would be analyzed with the assistance of an image analyzer. A significant amount of Aβ would be expected to be present in the cytoplasm of cells with herpes simplex virus (HSV-1) applied, as APP endocytosis would be induced by HSV-1, which leads to higher Aβ levels inside the cell.

Results

In this paper, a new hypothesis is presented on how HSV-1 infection initiates APP endocytosis and causes an increase in APP cleavage and Aβ production inside the cells. It is also hypothesized that increased Aβ peptides exit the cell via exocytosis, therefore, leading to the development of Alzheimer's disease. The findings will support the hypothesis if intracellular Aβ concentration is significantly higher after the introduction of dHSV-1 and subsequently if extracellular Aβ concentration becomes higher without TeNT exocytosis inhibition.

Conclusion

The results of this study would provide valuable insights into the mechanisms underlying Alzheimer's disease and open new scopes of research for its potential treatments. Further studies on virus infection and the development of memory diseases should be conducted to investigate possible correlations.

The Emerging Roles of the β-Secretase BACE1 and the Long Non-coding RNA BACE1-AS in Human Diseases: A Focus on Neurodegenerative Diseases and Cancer

The β-Secretase (BACE1) is widely studied to be particularly involved in amyloid deposition, a process known as the pathogenic pathway in neurodegenerative diseases. Therefore, BACE1 expression is frequently reported to be upregulated in brain samples of the patients with Alzheimer’s disease (AD). BACE1 expression is regulated by BACE1-AS, a long non-coding RNA (lncRNA), which is transcribed in the opposite direction to its locus. BACE1-AS positively regulates the BACE1 expression, and their expression levels are regulated in physiological processes, such as brain and vascular homeostasis, although their roles in the regulation of amyloidogenic process have been studied further. BACE1-AS dysregulation is reported consistent with BACE1 in a number of human diseases, such as AD, Parkinson’s disease (PD), heart failure (HF), and mild cognitive impairment. BACE1 or less BACE1-AS inhibition has shown therapeutic potentials particularly in decreasing manifestations of amyloid-linked neurodegenerative diseases. Here, we have reviewed the role of lncRNA BACE1 and BACE1-AS in a number of human diseases focusing on neurodegenerative disorders, particularly, AD.

Long Non-coding RNA: Insight Into Mechanisms of Alzheimer's Disease

Alzheimer's disease (AD), a heterogeneous neurodegenerative disorder, is the most common cause of dementia accounting for an estimated 60–80% of cases. The pathogenesis of AD remains unclear, and no curative treatment is available so far. Increasing evidence has revealed a vital role of non-coding RNAs (ncRNAs), especially long non-coding RNAs (lncRNAs), in AD. LncRNAs contribute to the pathogenesis of AD via modulating amyloid production, Tau hyperphosphorylation, mitochondrial dysfunction, oxidative stress, synaptic impairment and neuroinflammation. This review describes the biological functions and mechanisms of lncRNAs in AD, indicating that lncRNAs may provide potential therapeutic targets for the diagnosis and treatment of AD.

Relationship Between Alzheimer's Disease and Retinal Choroidal Thickness: A Cross-Sectional Study

BACKGROUND

The choroid is involved directly or indirectly in many pathological conditions such as Alzheimer's disease (AD), Parkinson's disease (PD), and multiple sclerosis (MS).

OBJECTIVE

The objective of this study was to investigate the association between retinal choroidal properties and the pathology of AD by determining choroidal thickness, hippocampus volume, cognitive functions, and plasma BACE1 activity.

METHODS

In this cross-sectional study, 37 patients with AD and 34 age-matched controls were included. Retinal choroidal thickness was measured via enhanced depth imaging optical coherence tomography. Hippocampal volume was measured via 3.0T MRI. Cognitive functions were evaluated using the Mini-Mental State Examination (MMSE) and Alzheimer's Disease Assessment Scale-cognitive subscale (ADAS-Cog). Plasma BACE1 activity was analyzed using a fluorescence substrate-based plasma assay, and regression model were to analyze the data.

RESULTS

Retinal choroidal thickness was significantly thinner in the AD group than in the control group [(114.81±81.30) μm versus (233.79±38.29) μm, p < 0.05]. Multivariable regression analysis indicated that the ADAS-cog scores (β=-0.772, p = 0.000) and age (β=-0.176, p = 0.015) were independently associated with choroidal thickness. The logistic regression model revealed that the subfoveal choroidal thickness was a significant predictor for AD (OR = 0.984, 95% CI: 0.972-0.997).

CONCLUSION

There was a general tendency of choroid thinning as the cognitive function declined. Although choroidal thickness was not a potential indicator for early stage AD, it was valuable in monitoring AD progression.

Alzheimer Disease Clinical Trials Targeting Amyloid: Lessons Learned From Success in Mice and Failure in Humans

BACKGROUND

The goal of slowing or halting the development of Alzheimer disease (AD) has resulted in the huge allocation of resources by academic institutions and pharmaceutical companies to the development of new treatments. The etiology of AD is elusive, but the aggregation of amyloid-β and tau peptide and oxidative processes are considered critical pathologic mechanisms. The failure of drugs with multiple mechanisms to meet efficacy outcomes has caused several companies to decide not to pursue further AD studies and has left the field essentially where it has been for the past 15 years. Efforts are underway to develop biomarkers for detection and monitoring of AD using genetic, imaging, and biochemical technology, but this is of minimal use if no intervention can be offered.

REVIEW SUMMARY

In this review, we consider the natural progression of AD and how it continues despite present attempts to modify the amyloid-related machinery to alter the disease trajectory. We describe the mechanisms and approaches to AD treatment targeting amyloid, including both passive and active immunotherapy as well as inhibitors of enzymes in the amyloidogenic pathway.

CONCLUSION

Lessons learned from clinical trials of amyloid reduction strategies may prove crucial for the leap forward toward novel therapeutic targets to treat AD.

Splicing alterations in healthy aging and disease

Alternative RNA splicing is a key step in gene expression that allows generation of numerous messenger RNA transcripts encoding proteins of varied functions from the same gene. It is thus a rich source of proteomic and functional diversity. Alterations in alternative RNA splicing are observed both during healthy aging and in a number of human diseases, several of which display premature aging phenotypes or increased incidence with age. Age-associated splicing alterations include differential splicing of genes associated with hallmarks of aging, as well as changes in the levels of core spliceosomal genes and regulatory splicing factors. Here, we review the current known links between alternative RNA splicing, its regulators, healthy biological aging, and diseases associated with aging or aging-like phenotypes. This article is categorized under: RNA in Disease and Development > RNA in Disease RNA Processing > Splicing Regulation/Alternative Splicing.

Splicing alterations in healthy aging and disease

Alternative RNA splicing is a key step in gene expression that allows generation of numerous messenger RNA transcripts encoding proteins of varied functions from the same gene. It is thus a rich source of proteomic and functional diversity. Alterations in alternative RNA splicing are observed both during healthy aging and in a number of human diseases, several of which display premature aging phenotypes or increased incidence with age. Age-associated splicing alterations include differential splicing of genes associated with hallmarks of aging, as well as changes in the levels of core spliceosomal genes and regulatory splicing factors. Here, we review the current known links between alternative RNA splicing, its regulators, healthy biological aging, and diseases associated with aging or aging-like phenotypes. This article is categorized under: RNA in Disease and Development > RNA in Disease RNA Processing > Splicing Regulation/Alternative Splicing.

MicroRNA-298 reduces levels of human amyloid-β precursor protein (APP), β-site APP-converting enzyme 1 (BACE1) and specific tau protein moieties

Alzheimer's disease (AD) is the most common age-related form of dementia, associated with deposition of intracellular neuronal tangles consisting primarily of hyperphosphorylated microtubule-associated protein tau (p-tau) and extracellular plaques primarily comprising amyloid- β (Aβ) peptide. The p-tau tangle unit is a posttranslational modification of normal tau protein. Aβ is a neurotoxic peptide excised from the amyloid-β precursor protein (APP) by β-site APP-cleaving enzyme 1 (BACE1) and the γ-secretase complex. MicroRNAs (miRNAs) are short, single-stranded RNAs that modulate protein expression as part of the RNA-induced silencing complex (RISC). We identified miR-298 as a repressor of APP, BACE1, and the two primary forms of Aβ (Aβ40 and Aβ42) in a primary human cell culture model. Further, we discovered a novel effect of miR-298 on posttranslational levels of two specific tau moieties. Notably, miR-298 significantly reduced levels of ~55 and 50 kDa forms of the tau protein without significant alterations of total tau or other forms. In vivo overexpression of human miR-298 resulted in nonsignificant reduction of APP, BACE1, and tau in mice. Moreover, we identified two miR-298 SNPs associated with higher cerebrospinal fluid (CSF) p-tau and lower CSF Aβ42 levels in a cohort of human AD patients. Finally, levels of miR-298 varied in postmortem human temporal lobe between AD patients and age-matched non-AD controls. Our results suggest that miR-298 may be a suitable target for AD therapy.

Is It the Twilight of BACE1 Inhibitors?

β-secretase (BACE1) has been regarded as a prime target for the development of amyloid beta (Aβ) lowering drugs in the therapy of Alzheimer´s disease (AD). Although the enzyme was discovered in 1991 and helped to formulate the Aβ hypothesis as one of the very important features of AD etiopathogenesis, progress in AD treatment utilizing BACE1 inhibitors has remained limited. Moreover, in the last years, major pharmaceutical companies have discontinued clinical trials of five BACE1 inhibitors that had been strongly perceived as prospective. In our review, the Aβ hypothesis, the enzyme, its functions, and selected substrates are described. BACE1 inhibitors are classified into four generations. Those that underwent clinical trials displayed adverse effects, including weight loss, skin rashes, worsening of neuropsychiatric symptoms, etc. Some inhibitors could not establish a statistically significant risk-benefit ratio, or even scored worse than placebo. We still believe that drugs targeting BACE1 may still hide some potential, but a different approach to BACE1 inhibition or a shift of focus to modulation of its trafficking and/or post-translational modification should now be followed.

The effect of BACE1-AS on β-amyloid generation by regulating BACE1 mRNA expression

Background

The BACE1 antisense transcript (BACE1-AS) is a conserved long noncoding RNA (lncRNA). The level of BACE1-AS is significantly increased and the level of the BACE1 mRNA is slightly increased in subjects with AD. BACE1-AS exerts a significant moderating effect on the expression of the BACE1 mRNA and promotes the formation of Aβ. After the administration of Aβ_1-42 to SH-SY5Y cells and C57/BL6J mice, we detected the expression of BACE1-AS, BACE1 mRNA, and BACE1 protein, as well as the concentration of Aβ_1-40. Then, we silenced the expression of BACE1-AS in SH-SY5Y and 20E2 cells using siRNAs targeting BACE1-AS and detected its effects on the levels of the BACE1 mRNA and BACE1 protein and Aβ_1-40 generation.

Results

The administration of Aβ_1-42 increased the expression of BACE1-AS, BACE1 mRNA and protein, as well as the concentration of Aβ_1-40 in SH-SY5Y cells and the brains of C57BL/6J mice. Pretreatment with the BACE1-AS siRNA inhibited the effect of Aβ_1-42 on increasing the expression of BACE1-AS and BACE1, as well as the generation of Aβ.

Conclusions

The mechanism by which exogenous Aβ_1-42 induces BACE1 expression and Aβ generation is mediated by BACE1-AS. BACE1-AS is involved in the mechanism regulating BACE1 expression and Aβ generation in APPsw transgenic cells.

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.

Neuronally derived extracellular vesicles: an emerging tool for understanding Alzheimer's disease

In order for Alzheimer’s disease (AD) to manifest, cells must communicate “pathogenic material” such as proteins, signaling molecules, or genetic material to ensue disease propagation. Small extracellular vesicles are produced via the endocytic pathways and released by nearly all cell types, including neurons. Due to their intrinsic interrelationship with endocytic processes and autophagy, there has been increased interest in studying the role of these neuronally-derived extracellular vesicles (NDEVs) in the propagation of AD. Pathologic cargo associated with AD have been found in a number of studies, and NDEVs have been shown to induce pathogenesis in vivo and in vitro. Exogenous NDEVs are also shown to reduce plaque burden in AD models. Thus, the NDEV has the potential to become a useful biomarker, a pathologic potentiator, and a therapeutic opportunity. While the field of NDEV research in AD is still in its infancy, we review the current literature supporting these three claims.

DNA Aptamers Targeting BACE1 Reduce Amyloid Levels and Rescue Neuronal Deficiency in Cultured Cells

β-amyloid (Aβ) plays an essential role in the pathogenesis of Alzheimer's disease (AD). Beta-site amyloid precursor protein cleaving enzyme 1 (BACE1) is indispensable for Aβ production, and knockout of BACE1 has no overt phenotypes in mouse. Thus, fine modulation of BACE1 may be a safe and effective treatment for AD patients. However, the large active site of BACE1 makes it challenging to target BACE1 with classical small-molecule inhibitors. DNA aptamer can have high affinity and specificity against diverse targets, and it provides an alternative strategy to target BACE1. In this study, we used a novel cell-systematic evolution of ligands by exponential enrichment (SELEX) strategy to select specific DNA aptamers optimized to target BACE1 under physiological status. After 17 rounds of selection, we identified two DNA aptamers against BACE1: BI1 and BI2. The identified aptamers interacted with BACE1 in pull-down assay, inhibited BACE1 activity in in vitro fluorescence resonance energy transfer (FRET) assay and HEK293-APP stable cell line, reduced Aβ in the culture medium of HEK293-amyloid protein precursor (APP) stable cell line and APP-PS1 primary cultured neurons, and rescued Aβ-induced neuronal deficiency in APP-PS1 primary cultured neurons. In contrast, the identified aptamers had no effect on α- or γ-secretase. In addition, cholesteryl tetraetylene glycol (TEG) modification further improved the potency of the identified aptamers. Our study suggests that it is feasible and effective to target BACE1 with DNA aptamers, and the therapeutic potential of the identified aptamers deserves further investigation.

Lack of β-amyloid cleaving enzyme-1 (BACE1) impairs long-term synaptic plasticity but enhances granule cell excitability and oscillatory activity in the dentate gyrus in vivo

BACE1 is a β-secretase involved in the cleavage of amyloid precursor protein and the pathogenesis of Alzheimer's disease (AD). The entorhinal cortex and the dentate gyrus are important for learning and memory, which are affected in the early stages of AD. Since BACE1 is a potential target for AD therapy, it is crucial to understand its physiological role in these brain regions. Here, we examined the function of BACE1 in the dentate gyrus. We show that loss of BACE1 in the dentate gyrus leads to increased granule cell excitability, indicated by enhanced efficiency of synaptic potentials to generate granule cell spikes. The increase in granule cell excitability was accompanied by prolonged paired-pulse inhibition, altered network gamma oscillations, and impaired synaptic plasticity at entorhinal-dentate synapses of the perforant path. In summary, this is the first detailed electrophysiological study of BACE1 deletion at the network level in vivo. The results suggest that BACE1 is important for normal dentate gyrus network function. This has implications for the use of BACE1 inhibitors as therapeutics for AD therapy, since BACE1 inhibition could similarly disrupt synaptic plasticity and excitability in the entorhinal-dentate circuitry.

BACE1 Regulates Proliferation and Neuronal Differentiation of Newborn Cells in the Adult Hippocampus in Mice

β-Site amyloid precursor protein cleaving enzyme 1 (BACE1) is required for the production of β-amyloid (Aβ), one of the major pathogenic molecules of Alzheimer's disease (AD), and is therefore being actively pursued as a drug target for AD. Adult hippocampal neurogenesis (AHN) is a lifelong process that is known to be important for learning and memory and may have the potential to regenerate damaged neural tissue. In this study, we examined whether BACE1 regulates AHN, which holds important implications for its suitability as a drug target in AD. Cohorts of 2-month-old wild-type (BACE1^+/+), heterozygous, and homozygous BACE1 knockout mice (BACE1^+/- and BACE1^-/-, respectively) were injected with 5-bromo-2'-deoxyuridine (BrdU) and sacrificed 1 day later to examine the impact of loss of BACE1 on neural precursor cell (NPC) proliferation in the adult brain. Parallel cohorts of mice were sacrificed 4 weeks after BrdU injection to determine the effects of BACE1 on survival and differentiation of newborn NPCs. We found that NPC proliferation was increased in BACE1^-/- mice compared to BACE1^+/+ mice, while no difference was observed in NPC survival across genotypes. Differentiation of NPCs to neuronal lineage was impaired in BACE1^-/- mice. However, no differences were observed in astrogenesis, the proportion of immature neurons, or the production of oligodendrocytes across genotypes. Importantly, corresponding with a decrease in neuronal differentiation in the absence of a complementary increase in an alternate cell fate, BACE1^-/- mice were found to have a pool of undifferentiated NPCs in the hippocampus compared to BACE1^+/+ and BACE1^+/- mice.

A New Fluorogenic Small-Molecule Labeling Tool for Surface Diffusion Analysis and Advanced Fluorescence Imaging of β-Site Amyloid Precursor Protein-Cleaving Enzyme 1 Based on Silicone Rhodamine: SiR-BACE1

β-site APP-cleaving enzyme 1 (BACE1) is a major player in the pathogenesis of Alzheimer's disease. Structural and functional fluorescence microscopy offers a powerful approach to learn about the physiology and pathophysiology of this protease. Up to now, however, common labeling techniques require genetic manipulation, use large antibodies, or are not compatible with live cell imaging. Fluorescent small molecules that specifically bind to the protein of interest can overcome these limitations. Herein, we introduce SiR-BACE1, a conjugate of the BACE1 inhibitor S-39 and SiR647, as a novel fluorogenic, tag-free, and antibody-free label for BACE1. We present its chemical development, characterize its photophysical and pharmacologic properties, and evaluate its behavior in solution, in overexpression systems, and in native brain tissue. We demonstrate its applicability in confocal, stimulated emission depletion and dynamic single-molecule microscopy. The first functional studies with SiR-BACE1 on the surface mobility of BACE1 revealed a markedly confined diffusion pattern.

Knockdown of BACE1-AS by siRNA improves memory and learning behaviors in Alzheimer's disease animal model

Alzheimer's disease (AD) is a devastating neurodegenerative disease that causes progressive damage to neurons. Emerging evidence has demonstrated that long non-coding RNAs (lncRNAs) serve an important role in many neurological diseases, such as AD. β-secretase 1 (BACE1)-antisense transcript (BACE1-AS) was identified as a conserved non-coding antisense BACE1. Previous reports stated that BACE1-AS positively regulated BACE1 mRNA and subsequently BACE1 protein expression in vitro and in vivo. However, whether BACE1-AS is able to regulate memory and learning behaviors remains to be elucidated. In the present study, the role of lncRNA BACE1-AS on memory and learning was investigated. It was demonstrated that lncRNA BACE1-AS expression was highly expressed in blood samples from AD patients, and also upregulated in peripheral blood samples and hippocampi from an AD animal model. Knockdown of BACE1-AS by short interfering RNA increased the primary hippocampal neurons proliferation in vitro. Knockdown of BACE1-AS mediated by lentivirus in vivo improved the memory and learning behaviors of SAMP8 mice, inhibited BACE1 and amyloid precursor protein production, and phosphorylation of tau protein in hippocampi. Therefore, the present findings suggested that BACE1-AS may be a potential target for management of memory loss related diseases, such as AD.

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.

Cellular Trafficking of Amyloid Precursor Protein in Amyloidogenesis Physiological and Pathological Significance

The accumulation of excess intracellular or extracellular amyloid beta (Aβ) is one of the key pathological events in Alzheimer's disease (AD). Aβ is generated from the cleavage of amyloid precursor protein (APP) by beta secretase-1 (BACE1) and gamma secretase (γ-secretase) within the cells. The endocytic trafficking of APP facilitates amyloidogenesis while at the cell surface, APP is predominantly processed in a non-amyloidogenic manner. Several adaptor proteins bind to both APP and BACE1, regulating their trafficking and recycling along the secretory and endocytic pathways. The phosphorylation of APP at Thr668 and BACE1 at Ser498, also influence their trafficking. Neurotrophins and proneurotrophins also influence APP trafficking through their receptors. In this review, we describe the molecular trafficking pathways of APP and BACE1 that lead to Aβ generation, the involvement of different signaling molecules or adaptor proteins regulating APP and BACE1 subcellular localization. We have also discussed how neurotrophins could modulate amyloidogenesis through their receptors.

The emerging role of alternative splicing in senescence and aging

Deregulation of precursor mRNA splicing is associated with many illnesses and has been linked to age-related chronic diseases. Here we review recent progress documenting how defects in the machinery that performs intron removal and controls splice site selection contribute to cellular senescence and organismal aging. We discuss the functional association linking p53, IGF-1, SIRT1, and ING-1 splice variants with senescence and aging, and review a selection of splicing defects occurring in accelerated aging (progeria), vascular aging, and Alzheimer's disease. Overall, it is becoming increasingly clear that changes in the activity of splicing factors and in the production of key splice variants can impact cellular senescence and the aging phenotype.

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

INTRODUCTION

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

Cross-Sectional and Longitudinal Effects of CREB1 Genotypes on Individual Differences in Memory and Executive Function: Findings from the BLSA

Purpose: Previously, we have shown that the SNP rs10932201 genotype of the cyclic AMP responsive element binding protein 1 gene (CREB1) contributes to individual differences in executive and memory function at the neural system and behavioral levels in healthy, young adults. However, longitudinal effects of CREB1 genotypes on cognition have not yet been addressed. Furthermore we were interested in replicating associations between CREB1 genotypes and human cognition in previous cross-sectional studies and explore whether APOE𝜀4 status might modify these relations. Materials and Methods: We investigated whether common, independent tag SNPs within CREB1 (rs2253206, rs10932201, rs6785) influence individual differences in age-related longitudinal change and level of executive function and memory performance independent of baseline age, sex, APOE𝜀4 status, and education. Our analysis included data from cognitively unimpaired older adults participating in the Baltimore Longitudinal Study of Aging. Eleven measures from six cognitive tests (sample sizes range 617-786) were analyzed using linear mixed effects and generalized estimating equations models. Mean baseline age ranged from 50 to 69 years and mean time of follow-up (interval) ranged from 8 to 22 years. Results: We found significant effects of all three CREB1 SNPs on performance level and/or longitudinal change in performance based on eight measures assessing semantic memory, episodic memory, or both executive function and semantic memory. SNP rs10932201 showed the most significant and largest effect (Cohen's d = -0.70, p < 0.01) on age-related longitudinal decline of semantic memory. Additionally, we show interactions between all three CREB1 SNPs and APOE𝜀4 status on age-related longitudinal declines and levels of memory and executive function. Conclusion: Our results suggest that CREB1 genotypes independently and by interactions with APOE𝜀4 status contribute to individual differences in cognitive aging.

A hybrid siRNA delivery complex for enhanced brain penetration and precise amyloid plaque targeting in Alzheimer's disease mice

To realize the therapeutic potential of gene drugs for Alzheimer's disease (AD), non-invasive, tissue-specific and efficient delivery technologies must be developed. Here, a hybrid system for amyloid plaques targeted siRNA delivery was formed by PEGylated Poly(2-(N,N-dimethylamino) ethyl methacrylate) (PEG-PDMAEMA) conjugated with two d-peptides, a CGN for brain penetration and a QSH for β-amyloid binding. The hybrid complex CQ/siRNA, composed of 25% MPEG-PDMAEMA, 50% CGN-PEG-PDMAEMA and 25% QSH-PEG-PDMAEMA, showed negligible cytotoxicity and could protect siRNA from enzyme degradation. Being taken up by neuron cells, the complexes could escape from lysosomes, release siRNA in the cytoplasm and thus producing effective gene silence (down-regulated protein level to 18.5%). After intravenous injection, CQ/siRNA penetrated into the brain in an intact form and located around the plaques in transgenic AD mice. The precisely amyloid plaques delivery resulted in increased therapeutic activities, which was demonstrated by the strong mRNA (36.4%) knockdown of BACE1 (a therapeutic target of AD), the less yield of enzyme-digested products sAPPβ (-42.6%), as well as the better neurons protection than the single component complexes. In conclusion, the hybrid complex could efficiently and precisely deliver an siRNA to the AD lesion and might be a potential candidate for gene therapy for AD.

STATEMENT OF SIGNIFICANCE

The gene delivery system achieving high brain penetration and lesion region accumulation was first applied to treat AD, and the preparation exhibited a significantly better neuroprotective effect than that modified with a single ligand. The intracellular process of which the complexes escape from lysosomes and release the siRNA in cytoplasm was revealed. The brain targeting and amyloid plaque binding ability of the complex were systemic evaluated, and the in vivo co-location experiments provided a direct evidence of the precise delivery of the siRNA to the amyloid plaques. One of the targeting ligands, CGN, which was a retro-inverso modified peptide to achieve better affinity to the BBB, was first applied to the brain targeting system.

BACE1 levels are increased in plasma of Alzheimer's disease patients compared with matched cognitively healthy controls

Aim: BACE1 is the secretase that acts in Aβ production in Alzheimer's disease (AD). Materials & methods: We investigated mRNA expression in total blood and the levels of plasma protein BACE1 in AD patients compared with cognitively healthy subjects. Probable AD (n = 47) and non-AD control group (n = 32) were evaluated for mRNA expression for BACE1 using reverse transcription-qPCR. A subsample of n = 21 AD and n = 20 non-AD had plasma BACE1 levels analyzed, using ELISA. Results: No differences were found on BACE1 mRNA between groups. However, higher levels of BACE1 were detected in plasma of AD patients. Discussion: Blood-based diagnostic tools are desired to improve AD diagnosis. BACE1 plasma levels could provide an additional diagnostic tool for AD in association with neuropsychological tests.

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.

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.

Role of long noncoding RNAs in malignant disease (Review)

Long noncoding RNAs (lncRNAs) are endogenous transcribed RNA molecules without protein-coding potential, ranging between 200 and 100,000 nt in length. LncRNAs regulate the expression of specific genes in several ways, including guiding chromatin-remodeling, and affecting splicing, transcription or translation. The mutations and dysregulation of lncRNAs have been found to be important in various human diseases, but particularly in human cancer. Previous studies have demonstrated that changes to lncRNAs are closely associated with tumorigenesis, metastasis, prognosis and diagnosis. The current review aims to present a brief overview of the associated reports of lncRNAs in malignant neoplasms, including breast cancer, prostate cancer and hematological malignancies. LncRNAs may be evaluated as novel markers in disease diagnosis, and as prospective therapeutic targets for the prevention and treatment of human diseases.

Amyloid accumulation is a late event in sporadic Alzheimer's disease-like pathology in nontransgenic rats

The amyloid cascade hypothesis posits that deposition of the amyloid β (Aβ) peptide in the brain is a key event in the initiation of Alzheimer's disease (AD). Nonetheless, it now seems increasingly unlikely that amyloid toxicity is the cause of sporadic AD, which leads to cognitive decline. Here, using accelerated-senescence nontransgenic OXYS rats, we confirmed that aggregation of Aβ is a later event in AD-like pathology. We showed that an age-dependent increase in the levels of Aβ_1–42 and extracellular Aβ deposits in the brain of OXYS rats occur later than do synaptic losses, neuronal cell death, mitochondrial structural abnormalities, and hyperphosphorylation of the tau protein. We identified the variants of the genes that are strongly associated with the risk of either late-onset or early-onset AD, including App, Apoe4, Bace1, Psen1, Psen2, and Picalm. We found that in OXYS rats nonsynonymous SNPs were located only in the genes Casp3 and Sorl1. Thus, we present proof that OXYS rats may be a model of sporadic AD. It is possible that multiple age-associated pathological processes may precede the toxic amyloid accumulation, which in turn triggers the final stage of the sporadic form of AD and becomes a hallmark event of the disease.