BACE1 Transcription Research Articles

Nicotinic acetylcholine receptor activation induces BACE1 transcription via the phosphorylation and stabilization of nuclear SP1

Epidemiological studies have shown that cigarette smoking increases the risk of Alzheimer disease. However, inconsistent results have been reported regarding the effects of smoking or nicotine on brain amyloid β (Aβ) deposition. In this study, we found that stimulation of the nicotinic acetylcholine receptor (nAChR) increased Aβ production in mouse brains and cultured neuronal cells. nAChR activation triggered the MEK/ERK pathway, which then phosphorylated and stabilized nuclear SP1. Upregulated SP1 acted on two recognition motifs in the BACE1 gene to induce its transcription, resulting in enhanced Aβ production. Mouse brain microdialysis revealed that nAChR agonists increased Aβ levels in the interstitial fluid of the cerebral cortex but caused no delay of Aβ clearance. In vitro assays indicated that nicotine inhibited Aβ aggregation. We also found that nicotine modified the immunoreactivity of anti-Aβ antibodies, possibly through competitive inhibition and Aβ conformation changes. Using anti-Aβ antibody that was carefully selected to avoid these effects, we found that chronic nicotine treatment in Aβ precursor protein knockin mice increased the Aβ content but did not visibly change the aggregated Aβ deposition in the brain. Thus, nicotine influences brain Aβ deposition in the opposite direction, thereby increasing Aβ production and inhibiting Aβ aggregation.

B lymphocytes ameliorate Alzheimer’s disease-like neuropathology via interleukin-35

Increasing evidence supports the involvement of the peripheral immune system in the pathogenesis of Alzheimer's disease (AD). In the present study, we found that B lymphocytes could mitigate beta-Amyloid (Aβ) pathology and memory impairments in a transgenic AD mouse model. Specifically, in young 5 × FAD mice, we evidenced increased B cells in the frontal cortex and meningeal tissues; depletion of mature B cells aggravated these mice’s Aβ load and memory deficits. The increased B cells produced more interleukin-35 (IL-35) in the front cortex. We further found IL-35 neutralization exacerbated Aβ pathology, while injecting IL-35 mitigated Aβ load and cognitive dysfunction in 5 × FAD mice with or without mature B cell deficiency. Mechanistically, IL-35 inhibited neuronal BACE1 transcription through modulating the SOCS1/STAT1 pathway, and reduced Aβ production accordingly. Reanalysis of the single-cell RNA sequencing data from blood samples of AD patients suggested an increased population of IL-35-producing B cells. Together, the present study revealed a novel effect of B lymphocyte-derived IL-35 on inhibiting Aβ production in the frontal cortex, which may serve as a potential target for future AD treatment.

Therapeutic effects of total saikosaponins from Radix bupleuri against Alzheimer's disease.

Alzheimer’s disease (AD) is a neurodegenerative disease characterized by memory loss and cognitive dysfunction in the elderly, with amyloid-beta (Aβ) deposition and hyperphosphorylation of tau protein as the main pathological feature. Nuclear factor 2 (Nrf2) is a transcription factor that primarily exists in the cytosol of hippocampal neurons, and it is considered as an important regulator of autophagy, oxidative stress, and inflammation. Total saikosaponins (TS) is the main bioactive component of Radix bupleuri (Chaihu). In this study, it was found that TS could ameliorate cognitive dysfunction in APP/PS1 transgenic mice and reduce Aβ generation and senile plaque deposition via activating Nrf2 and downregulating the expression of β-secretase 1 (BACE1). In addition, TS can enhance autophagy by promoting the expression of Beclin-1 and LC3-II, increasing the degradation of p62 and NDP52 and the clearance of phosphorylated tau (p-tau), and reducing the expression of p-tau. It can also downregulate the expression of nuclear factor-κB (NF-κB) to inhibit the activation of glial cells and reduce the release of inflammatory factors. In vitro experiments using PC12 cells induced by Aβ, TS could significantly inhibit the aggregation of Aβ and reduce cytotoxicity. It was found that Nrf2 knock-out weakened the inhibitory effect of TS on BACE1 and NF-κB transcription in PC12 cells. Moreover, the inhibitory effect of TS on BACE1 transcription was achieved by promoting the binding of Nrf2 and the promoter of BACE1 ARE1. Results showed that TS downregulated the expression of BACE1 and NF-κB through Nrf2, thereby reducing the generation of Aβ and inhibiting neuroinflammation. Furthermore, TS can ameliorate synaptic loss and alleviate oxidative stress. In gut microbiota analysis, dysbiosis was demonstrated in APP/PS1 transgenic mice, indicating a potential link between gut microbiota and AD. Furthermore, TS treatment reverses the gut microbiota disorder in APP/PS1 mice, suggesting a therapeutic strategy by remodeling the gut microbe. Collectively, these data shows that TS may serve as a potential approach for AD treatment. Further investigation is needed to clarify the detailed mechanisms underlying TS regulating gut microbiota and oxidative stress.

Reducing Nav1.6 expression attenuates the pathogenesis of Alzheimer's disease by suppressing BACE1 transcription.

Aberrant increases in neuronal network excitability may contribute to cognitive deficits in Alzheimer's disease (AD). However, the mechanisms underlying hyperexcitability of neurons are not fully understood. Voltage‐gated sodium channels (VGSC or Nav), which are involved in the formation of excitable cell's action potential and can directly influence the excitability of neural networks, have been implicated in AD‐related abnormal neuronal hyperactivity and higher incidence of spontaneous non‐convulsive seizures. Here, we have shown that the reduction of VGSC α‐subunit Nav1.6 (by injecting adeno‐associated virus (AAV) with short hairpin RNA (shRNA) into the hippocampus) rescues cognitive impairments and attenuates synaptic deficits in APP/PS1 transgenic mice. Concurrently, amyloid plaques in the hippocampus and levels of soluble Aβ are significantly reduced. Interfering with Nav1.6 reduces the transcription level of β‐site APP‐cleaving enzyme 1 (BACE1), which is Aβ‐dependent. In the presence of Aβ oligomers, knockdown of Nav1.6 reduces intracellular calcium overload by suppressing reverse sodium–calcium exchange channel, consequently increasing inactive NFAT1 (the nuclear factor of activated T cells) levels and thus reducing BACE1 transcription. This mechanism leads to a reduction in the levels of Aβ in APP/PS1 transgenic mice, alleviates synaptic loss, improves learning and memory disorders in APP/PS1 mice after downregulating Nav1.6 in the hippocampus. Our study offers a new potential therapeutic strategy to counteract hippocampal hyperexcitability and subsequently rescue cognitive deficits in AD by selective blockade of Nav1.6 overexpression and/or hyperactivity.

Sex-Specific Regulation of β-Secretase: A Novel Estrogen Response Element (ERE)-Dependent Mechanism in Alzheimer's Disease.

Women have a higher prevalence and incidence of Alzheimer's disease (AD) than age-matched men, and loss of estrogen might be partially responsible for the higher risk of AD in aged women. While β-secretase (BACE1) plays an important role in AD pathogenesis, whether BACE1 involved the sex difference in AD pathology remains unclear. This study investigated the hypothesis that estrogen regulates BACE1 transcription via the estrogen response element (ERE) and designated pathways. Using estrogen receptor (ER) knock-out mice and mutagenesis of EREs in HEK293 cells, we demonstrated sex-specific inhibition of BACE1 transcription by estrogen via direct binding to ERE sites and ERα. We also used a repressor of estrogen receptor activity (REA) and showed that an REA-ERE complex downregulated BACE1. A chromatin immunoprecipitation assay analysis determined that all three EREs at the BACE1 promoter were required for estradiol-mediated downregulation of BACE1 transcription in mice. Last, we confirmed the impairment of the REA pathway in the cortex of female AD patients. Our study identified an estrogen-specific BACE1 transcriptional regulation pathway from cell and animal models to AD patients.SIGNIFICANCE STATEMENT With the increase in the aging population and Alzheimer's disease worldwide, an urgent need to find effective approaches to treat or prevent AD. Women have a higher prevalence and incidence of AD than men. Identification of the sex-specific risk for AD may be valuable for disease prevention. This study evaluated several estrogen response element (ERE) sites on the promoter of β-secretase (BACE1), a key enzyme for AD pathology. We demonstrated that estrogen downregulated BACE1 transcription through direct binding and complex formation with ERE and cofactors. Our novel findings provide evidence that an estrogen supplement may decrease the risk of AD in menopausal and postmenopausal women. Furthermore, this study demonstrates the "sex-specific" mechanisms of BACE1 as a role in AD pathogenesis.

Control of β-Site Amyloid Precursor Protein-Cleaving Enzyme-1 Expression by Protein Kinase C-λ/ι and Nuclear Factor κ-B.

Reportedly, acute insulin treatment in normal mice, and hyperinsulinemia in high-fat-fed (HFF) obese/diabetic mice, increase BACE1 activity and levels of Aβ-peptides and phospho- -thr-231-tau in the brain; moreover, these effects are blocked by PKC-λ/ι inhibitors. However, as chemical inhibitors may affect unsuspected targets, we presently used knockout methodology to further examine PKC-λ/ι requirements. We found that total-body heterozygous PKC-λ knockout reduced acute stimulatory effects of insulin and chronic effects of hyperinsulinemia in HFF/obese/diabetic mice, on brain PKC-λ activity and production of Aβ1-40/42 and phospho-thr-231-tau. This protection in HFF mice may reflect that hepatic PKC-λ haploinsufficiency prevents the development of glucose intolerance and hyperinsulinemia. On the other hand, heterozygous knockout of PKC-λ markedly reduced brain levels of BACE1 protein and mRNA, and this may reflect diminished activation of nuclear factor kappa-B (NFκB), which is activated by PKC-λ and increases BACE1 and proinflammatory cytokine transcription. Accordingly, whereas intravenous administration of aPKC inhibitor diminished aPKC activity and BACE1 levels by 50% in the brain and 90% in the liver, nasally-administered inhibitor reduced aPKC activity and BACE1 mRNA and protein levels by 50-70% in the brain while sparing the liver. Additionally, 24-hour insulin treatment in cultured human-derived neurons increased NFκB activity and BACE1 levels, and these effects were blocked by various PKC-λ/ι inhibitors. PKC-λ/ι controls NFκB activity and BACE1 expression; PKC-λ/ι inhibitors may be used nasally to target brain PKC-λ/ι or systemically to block both liver and brain PKC-λ/ι, to regulate NFκB-dependent BACE1 and proinflammatory cytokine expression.

Gallic acid is a dual α/β-secretase modulator that reverses cognitive impairment and remediates pathology in Alzheimer mice

Several plant-derived compounds have demonstrated efficacy in pre-clinical Alzheimer's disease (AD) rodent models. Each of these compounds share a gallic acid (GA) moiety, and initial assays on this isolated molecule indicated that it might be responsible for the therapeutic benefits observed. To test this hypothesis in a more physiologically relevant setting, we investigated the effect of GA in the mutant human amyloid β-protein precursor/presenilin 1 (APP/PS1) transgenic AD mouse model. Beginning at 12 months, we orally administered GA (20 mg/kg) or vehicle once daily for 6 months to APP/PS1 mice that have accelerated Alzheimer-like pathology. At 18 months of age, GA therapy reversed impaired learning and memory as compared with vehicle, and did not alter behavior in nontransgenic littermates. GA-treated APP/PS1 mice had mitigated cerebral amyloidosis, including brain parenchymal and cerebral vascular β-amyloid deposits, and decreased cerebral amyloid β-proteins. Beneficial effects co-occurred with reduced amyloidogenic and elevated nonamyloidogenic APP processing. Furthermore, brain inflammation, gliosis, and oxidative stress were alleviated. We show that GA simultaneously elevates α- and reduces β-secretase activity, inhibits neuroinflammation, and stabilizes brain oxidative stress in a pre-clinical mouse model of AD. We further demonstrate that GA increases abundance of a disintegrin and metalloproteinase domain-containing protein 10 (ADAM10, Adam10) proprotein convertase furin and activates ADAM10, directly inhibits β-site APP cleaving enzyme 1 (BACE1, Bace1) activity but does not alter Adam10 or Bace1 transcription. Thus, our data reveal novel post-translational mechanisms for GA. We suggest further examination of GA supplementation in humans will shed light on the exciting therapeutic potential of this molecule.

Amyloid Beta-Peptide Increases BACE1 Translation through the Phosphorylation of the Eukaryotic Initiation Factor-2α.

Alzheimer's disease (AD) is tightly linked to oxidative stress since amyloid beta-peptide (Aβ) aggregates generate free radicals. Moreover, the aggregation of Aβ is increased by oxidative stress, and the neurotoxicity induced by the oligomers and fibrils is in part mediated by free radicals. Interestingly, it has been reported that oxidative stress can also induce BACE1 transcription and expression. BACE1 is the key enzyme in the cleavage of the amyloid precursor protein to produce Aβ, and the expression of this enzyme has been previously shown to be enhanced in the brains of Alzheimer's patients. Here, we have found that BACE1 expression is increased in the hippocampi from AD patients at both the early (Braak stage II) and late (Braak stage VI) stages of the disease as studied by immunohistochemistry and western blot. To address the role of Aβ and oxidative stress in the regulation of BACE1 expression, we have analyzed the effect of subtoxic concentrations of Aβ oligomers (0.25 μM) and H2O2 (10 mM) on a human neuroblastoma cell line. Firstly, our results show that Aβ oligomers and H2O2 induce an increase of BACE1 mRNA as we studied by qPCR. Regarding BACE1 translation, it is dependent on the phosphorylation of the eukaryotic initiation factor 2α (eIF2α), since BACE1 mRNA bears a 5′UTR that avoids its translation under basal conditions. BACE1 5′UTR contains four upstream initiating codons (uAUGs), and its translation is activated when eIF2α is phosphorylated. Consistently, we have obtained that Aβ oligomers and H2O2 increase the levels of BACE1 and p-eIF2α assayed by western blot and confocal microscopy. Our results suggest that Aβ oligomers increase BACE1 translation by phosphorylating eIF2α in a process that involves oxidative stress and conforms a pathophysiological loop, where the Aβ once aggregated favors its own production continuously by the increase in BACE1 expression as observed in AD patients.

High-fat diet exacerbates cognitive and metabolic abnormalities in neuronal BACE1 knock-in mice – partial prevention by Fenretinide

ABSTRACT Objective: The β-site APP-cleaving enzyme 1 (BACE1) is a rate-limiting step in β-amyloid (Aβ) production in Alzheimer’s disease (AD) brains, but recent evidence suggests that BACE1 is also involved in metabolic regulation. Here, we aimed to assess the effects of highfat diet (HFD) on metabolic and cognitive phenotypes in the diabetic BACE1 knock-in mice (PLB4) and WT controls; we additionally examined whether these phenotypes can be normalized with a synthetic retinoid (Fenretinide, Fen) targeting weight loss. Methods: Five-month old male WT and PLB4 mice were fed either (1) control chow diet, (2) 45%-saturated fat diet (HFD), (3) HFD with 0.04% Fen (HFD + Fen) or (4) control chow diet with 0.04% Fen (Fen) for 10 weeks. We assessed basic metabolic parameters, circadian rhythmicity, spatial habituation (Phenotyper) and working memory (Y-maze). Hypothalami, forebrain and liver tissues were assessed using Western blots, qPCR and ELISAs. Results: HFD feeding drastically worsened metabolism and induced early mortality (−40%) in otherwise viable PLB4 mice. This was ameliorated by Fen, despite no effects on glucose intolerance. In HFD-fed WT mice, Fen reduced weight gain, glucose intolerance and hepatic steatosis. The physiological changes induced in WT and PLB4 mice by HFD (+/−Fen) were accompanied by enhanced cerebral astrogliosis, elevated PTP1B, phopsho-eIF2α and altered hypothalamic transcription of Bace1, Pomc and Mc4r. Behaviourally, HFD feeding exacerbated spatial memory deficits in PLB4 mice, which was prevented by Fen and linked with increased full-length APP, normalized brain Aβ*56 oligomerization and astrogliosis. Conclusions: HFD induces early mortality and worsened cognition in the Alzheimer’s-like BACE1 mice– partial prevention was achieved with Fenretinide, without improvements in glucose homeostasis.

Expression of BACE1 in the Rat Carotid Body.

This study explored the expression of BACE1 (β-amyloid precursor protein cleaving enzyme 1) in the rat carotid body and the effect of CIH (cyclic intermittent hypoxia) on the expression of BACE1. We found that BACE1 was expressed in the rat carotid body and located in the nerve endings and type II cells but not in type I cells. CIH reduced BACE1 level in the carotid body, and reoxygenation or ROS scavenger alleviated this reduction. Furthermore, we found that CIH augmented the mRNA level of PGC-1α but attenuated the mRNA level of BACE1 in the carotid body. Taken together, our results suggest that CIH promotes the production of ROS that upregulates the level of PGC-1α, which may in turn inhibits the transcription of BACE1, and that a reduction in the BACE1 level may be related to CIH-induced reversible and ROS-dependent carotid body plasticity. Our study provides a new candidate molecule for further study of the mechanism of carotid body plasticity.

Loss of Ataxin-1 potentiates Alzheimer's pathogenesis by elevating cerebral BACE1 transcription

Summary Expansion of CAG trinucleotide repeats in ATXN1 causes spinocerebellar ataxia type 1 (SCA1), a neurodegenerative disease that impairs coordination and cognition. While ATXN1 is associated with increased Alzheimer’s disease (AD) risk, CAG repeat number in AD patients is not changed. Here, we investigated the consequences of ataxin-1 loss of function and discovered that knockout of Atxn1 reduced CIC-ETV4/5-mediated inhibition of Bace1 transcription, leading to increased BACE1 levels and enhanced amyloidogenic cleavage of APP, selectively in AD-vulnerable brain regions. Elevated BACE1 expression exacerbated Aβ deposition and gliosis in AD mouse models and impaired hippocampal neurogenesis and olfactory axonal targeting. In SCA1 mice, polyglutamine-expanded mutant ataxin-1 led to the increase of BACE1 post-transcriptionally, both in cerebrum and cerebellum, and caused axonal-targeting deficit and neurodegeneration in the hippocampal CA2 region. These findings suggest that loss of ataxin-1 elevates BACE1 expression and Aβ pathology, rendering it a potential contributor to AD risk and pathogenesis.

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

IntroductionThere is keen interest in elucidating the biological mechanisms underlying recent failures of β-site amyloid precursor protein–cleaving enzyme-1 (BACE1) inhibitors in Alzheimer's disease trials. MethodsWe developed a highly sensitive and specific immunoassay for BACE1 in cell lines and iPSC-derived human neurons to systematically analyze the effects of eight clinically relevant BACE1 inhibitors. ResultsSeven of 8 inhibitors elevated BACE1 protein levels. Among protease inhibitors tested, the elevation was specific to BACE1 inhibitors. The inhibitors did not increase BACE1 transcription but extended the protein's half-life. BACE1 became elevated at concentrations below the IC50 for amyloid β (Aβ). DiscussionElevation of BACE1 by 7 of 8 BACE1 inhibitors raises new concerns about advancing such β-secretase inhibitors for AD. Chronic elevation could lead to intermittently uninhibited BACE1 when orally dosed inhibitors reach trough levels, abnormally increasing substrate processing. Compounds such as roburic acid that lower Aβ by dissociating β/γ secretase complexes are better candidates because they neither inhibit β- and γ-secretase nor increase BACE1 levels.

Loss of Ataxin-1 Potentiates Alzheimer's Pathogenesis by Elevating Cerebral BACE1 Transcription.

Expansion of CAG trinucleotide repeats in ATXN1 causes spinocerebellar ataxia type 1 (SCA1), a neurodegenerative disease that impairs coordination and cognition. While ATXN1 is associated with increased Alzheimer's disease (AD) risk, CAG repeat number in AD patients is not changed. Here, we investigated the consequences of ataxin-1 loss of function and discovered that knockout of Atxn1 reduced CIC-ETV4/5-mediated inhibition of Bace1 transcription, leading to increased BACE1 levels and enhanced amyloidogenic cleavage of APP, selectively in AD-vulnerable brain regions. Elevated BACE1 expression exacerbated Aβ deposition and gliosis in AD mouse models and impaired hippocampal neurogenesis and olfactory axonal targeting. InSCA1 mice, polyglutamine-expanded mutant ataxin-1 led to the increase of BACE1 post-transcriptionally, both in cerebrum and cerebellum, and caused axonal-targeting deficit and neurodegeneration in the hippocampal CA2 region. These findings suggest that loss of ataxin-1 elevates BACE1 expression and Aβ pathology, rendering it a potential contributor to AD risk and pathogenesis.

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

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

δ-Secretase-cleaved Tau stimulates Aβ production via upregulating STAT1-BACE1 signaling in Alzheimer's disease.

δ-Secretase, an age-dependent asparagine protease, cleaves both amyloid precursor protein (APP) and Tau and is required for amyloid plaque and neurofibrillary tangle pathologies in Alzheimer's disease (AD). However, whether δ-secretase activation is sufficient to trigger AD pathogenesis remains unknown. Here we show that the fragments of δ-secretase-cleavage, APP (586-695) and Tau(1-368), additively drive AD pathogenesis and cognitive dysfunctions. Tau(1-368) strongly augments BACE1 expression and Aβ generation in the presence of APP. The Tau(1-368) fragment is more robust than full-length Tau in binding active STAT1, a BACE1 transcription factor, and promotes its nuclear translocation, upregulating BACE1 and Aβ production. Notably, Aβ-activated SGK1 or JAK2 kinase phosphorylates STAT1 and induces its association with Tau(1-368). Inhibition of these kinases diminishes stimulatory effect of Tau(1-368). Knockout of STAT1 abolishes AD pathologies induced by δ-secretase-generated APP and Tau fragments. Thus, we show that Tau may not only be a downstream effector of Aβ in the amyloid hypothesis, but also act as a driving force for Aβ, when cleaved by δ-secretase.

Glycyrrhiza uralensis and Semilicoisoflavone B Reduce Aβ Secretion by Increasing PPARγ Expression and Inhibiting STAT3 Phosphorylation to Inhibit BACE1 Expression.

Glycyrrhiza uralensis extract (GUE) has been reported to improve amyloid beta (Aβ)-induced cognitive deficits in mice. However, the mechanisms underlying this effect and the components involved have not been previously explored. Extracellular Aβ plaques are one of the major pathological hallmarks of Alzheimer's disease (AD). Therefore, decreasing Aβ levels is one strategy for preventing the etiology of AD. This study aims to test the effect of GUE and semilicoisoflavone B (SB) on Aβ secretion and investigates the mechanism underlying this effect. GUE and its bio-activated compound SB reduce Aβ secretion. We find that this effect contribute to the downregulation of the β-secretase-1 (BACE1) protein and mRNA. In a subsequent mechanism study, we find that GUE and SB regulate BACE1 transcription factors by inducing the expression of peroxisome proliferator activated receptor γ (PPARγ) and inhibiting the phosphorylation of signal transducer and activator of transcription 3. In addition, the effect of GUE and SB on BACE1 expression and Aβ secretion are attenuated by treatment with PPARγ-siRNA or its antagonist, GW9662. These findings indicate that GUE and SB may function as PPARγ agonists, thereby inhibiting BACE1 expression and ultimately reducing the secretion of Aβ.

BAG-1M co-activates BACE1 transcription through NF-κB and accelerates Aβ production and memory deficit in Alzheimer’s disease mouse model

Accumulation of amyloid β protein (Aβ)-containing neuritic plaques in the brain is a neuropathological feature of Alzheimer's disease (AD). The β-site APP-cleaving enzyme 1 (BACE1) is essential for Aβ generation and dysregulation of BACE1 expression may lead to AD pathogenesis. Bcl-2-associated athanogen 1M (BAG-1M), initially identified as an anti-apoptotic protein, has also been found to be highly expressed in the same neurons that contain intracellular amyloid in the hippocampus of AD patient. In this report, we found that over-expression of BAG-1M enhances BACE1-mediated cleavage of amyloid precursor protein (APP) and Aβ production by up-regulating BACE1 gene transcription. The regulation of BACE1 transcription by BAG-1M was dependent on NF-κB, as BAG-1M complexes NF-κB at the promoter of BACE1 gene and co-activates NF-κB-facilitated BACE1 transcription. Moreover, expression of BAG-1M by lentiviral vector in the hippocampus of AD transgenic model mice promotes Aβ generation and formation of neuritic plaque, and subsequently accelerates memory deficits of the mice. These results provide evidence for an emerging role of BAG-1M in the regulation of BACE1 expression and AD pathogenesis and that targeting the BAG-1M-NF-κB complex may provide a mechanism for inhibiting Aβ production and plaque formation.

Epigallocatechin Gallate Attenuates β-Amyloid Generation and Oxidative Stress Involvement of PPARγ in N2a/APP695 Cells.

The accumulation of β-amyloid (Aβ) peptide plaques is a major pathogenic event in Alzheimer's disease (AD). Aβ is a cleaved fragment of APP via BACE1, which is the rate-limiting enzyme in APP processing and Aβ generation. Nuclear receptor peroxisome proliferator-activated receptor gamma (PPARγ) is considered to be a potential target for AD treatment, because of its potent antioxidant and inhibitory effects on Aβ production by negatively regulating BACE1. Epigallocatechin gallate (EGCG), a highly active catechin found in green tea, is known to enhance metabolic activity and cognitive ability in the mice model of AD. To investigate whether the therapeutic effect of EGCG is related to the PPARγ pathway, we analysed the alterations in the intracellular molecular expression of PPARγ after EGCG treatment in the N2a/APP695 cell line. In this study, we observed that EGCG attenuated Aβ generation in N2a/APP695 cells, such as the PPARγ agonist, pioglitazone, by suppressing the transcription and translation of BACE1 and that its effect was attenuated by the PPARγ inhibitor, GW9662. Intriguingly, EGCG significantly reinforced the activity of PPARγ by promoting its mRNA and protein expressions in N2a/APP695 cells. Moreover, EGCG also decreased the expression of pro-apoptotic proteins (Bax, caspase-3), reduced the activity of the anti-inflammatory agent NF-κB and inhibited the oxidative stress by decreasing the levels of ROS and MDA and increasing the expression of MnSOD. Co-administration of GW9662 also significantly decreased the EGCG-mediated neuroprotective effect evidenced by the increase in oxidative stress and inflammatory markers. The therapeutic efficacy of EGCG in AD may be derived from the up-regulation of PPARγ mRNA and protein expressions.

Aβ42 oligomers modulate β-secretase through an XBP-1s-dependent pathway involving HRD1.

The aspartyl protease β-site APP cleaving enzyme, BACE1, is the rate-limiting enzyme involved in the production of amyloid-β peptide, which accumulates in both sporadic and familial cases of Alzheimer’s disease and is at the center of gravity of the amyloid cascade hypothesis. In this context, unravelling the molecular mechanisms controlling BACE1 expression and activity in both physiological and pathological conditions remains of major importance. We previously demonstrated that Aβ controlled BACE1 transcription in an NFκB-dependent manner. Here, we delineate an additional cellular pathway by which natural and synthetic Aβ42 oligomers enhance active X-box binding protein XBP-1s. XBP-1s lowers BACE1 expression and activity indirectly, via the up-regulation of the ubiquitin-ligase HRD1 that acts as an endogenous down-regulator of BACE1. Thus, we delineate a novel pathway by which cells could compensate for Aβ42 oligomers production and thus, associated toxicity, by triggering a compensatory mechanism aimed at lowering BACE-1-mediated Aβ production by a molecular cascade involving XBP-1s and HRD1. It thus identifies HRD1 as a potential target for a novel Aβ-centered therapeutic strategy.

Early Growth Response 1 (Egr-1) Is a Transcriptional Activator of β-Secretase 1 (BACE-1) in the Brain

Accumulation of amyloid-β peptide (Aβ) in the brain is regarded as central to Alzheimer's disease (AD) pathogenesis. Aβ is generated by a sequential cleavage of amyloid precursor protein (APP) by β-secretase 1 (BACE-1) followed by γ-secretase. BACE-1 cleavage of APP is the committed step in Aβ synthesis. Understanding the mechanism by which BACE-1 is activated leading to Aβ synthesis in the brain can provide better understanding of AD pathology and help to develop novel therapies. In this study, we found that the levels of Aβ and BACE-1 are significantly reduced in the brains of mice lacking transcription factor early growth response 1 (Egr-1) when compared with the WT. We demonstrate that in COS-7 cells, Egr-1 binds to the BACE-1 promoter and activates BACE-1 transcription. In rat hippocampal primary neurons, overexpression of Egr-1 induces BACE-1 expression, activates BACE-1, promotes amyloidogenic APP processing, and enhances Aβ synthesis. In mouse hippocampal primary neurons, knockdown of BACE-1 almost completely blocks Egr-1-induced amyloidogenic APP processing and Aβ synthesis. Our data indicate that Egr-1 promotes Aβ synthesis via transcriptional activation of BACE-1 and suggest that Egr-1 plays role in activation of BACE-1 and acceleration of Aβ synthesis in AD brain. Egr-1 is a potential therapeutic target for AD.