Hypoxia and reoxygenation increased BACE1 mRNA and protein levels in human neuroblastoma SH-SY5Y cells

Thiamine insufficiency induces Hypoxia Inducible Factor-1α as an upstream mediator for neurotoxicity and AD-like pathology

Insufficiencies of the micronutrient thiamine (Vitamin B1) have been associated with inducing Alzheimer's disease (AD)-like neuropathology. The hypometabolic state associated with chronic thiamine insufficiency (TI) has been demonstrated to be a contributor towards the development of amyloid plaque deposition and neurotoxicity. However, the molecular mechanism underlying TI induced AD pathology is still unresolved. Previously, we have established that TI stabilizes the metabolic stress transcriptional factor, Hypoxia Inducible Factor-1α (HIF1α). Utilizing neuronal hippocampal cells (HT22), TI-induced HIF1α activation triggered the amyloidogenic cascade through transcriptional expression and increased activity of β-secretase (BACE1). Knockdown and pharmacological inhibition of HIF1α during TI significantly reduced BACE1 and C-terminal Fragment of 99 amino acids (C99) formation. TI also increased the expression of the HIF1α regulated pro-apoptotic protein, BCL2/adenovirus E1B 19 kDa protein-interacting protein (BNIP3). Correspondingly, cell toxicity during TI conditions was significantly reduced with HIF1α and BNIP3 knockdown. The role of BNIP3 in TI-mediated toxicity was further highlighted by localization of dimeric BNIP3 into the mitochondria and nuclear accumulation of Endonuclease G. Subsequently, TI decreased mitochondrial membrane potential and enhanced chromatin fragmentation. However, cell toxicity via the HIF1α/BNIP3 cascade required TI induced oxidative stress. HIF1α, BACE1 and BNIP3 expression was induced in 3xTg-AD mice after TI and administration with the HIF1α inhibitor YC1 significantly attenuated HIF1α and target genes levels in vivo. Overall, these findings demonstrate a critical stress response during TI involving the induction of HIF1α transcriptional activity that directly promotes neurotoxicity and AD-like pathology.

Melatonin regulates Aβ production/clearance balance and Aβ neurotoxicity: A potential therapeutic molecule for Alzheimer's disease

Alzheimer's disease (AD) is an age-related neurodegenerative disease with multiple predisposing factors and complicated pathogenesis. Aβ peptide is one of the most important pathogenic factors in the etiology of AD. Accumulating evidence indicates that the imbalance of Aβ production and Aβ clearance in the brain of AD patients leads to Aβ deposition and neurotoxic Aβ oligomer formation. Melatonin shows a potent neuroprotective effect and can prevent or slow down the progression of AD, supporting the view that melatonin is a potential therapeutic molecule for AD. Melatonin modulates the regulatory network of secretase expression and affects the function of secretase, thereby inhibiting amyloidogenic APP processing and Aβ production. Additionally, melatonin ameliorates Aβ-induced neurotoxicity and probably promotes Aβ clearance through glymphatic-lymphatic drainage, BBB transportation and degradation pathways. In this review, we summarize and discuss the role of melatonin against Aβ-dependent AD pathogenesis. We explore the potential cellular and molecular mechanisms of melatonin on Aβ production and assembly, Aβ clearance, Aβ neurotoxicity and circadian cycle disruption. We summarize multiple clinical trials of melatonin treatment in AD patients, showing that melatonin has a promising effect on improving sleep quality and cognitive function. This review aims to stimulate further research on melatonin as a potential therapeutic agent for AD.

Temporal Proteomic Profiling of SH-SY5Y Differentiation with Retinoic Acid Using FAIMS and Real-Time Searching

The SH-SY5Y cell line is often used as a surrogate for neurons in cell-based studies. This cell line is frequently differentiated with all-trans retinoic acid (ATRA) over a 7-day period, which confers neuron-like properties to the cells. However, no analysis of proteome remodeling has followed the progress of this transition. Here, we quantitatively profiled over 9400 proteins across a 7-day treatment with retinoic acid using state-of-the-art mass spectrometry-based proteomics technologies, including FAIMS, real-time database searching, and TMTpro16 sample multiplexing. Gene ontology analysis revealed that categories with the highest increases in protein abundance were related to the plasma membrane/extracellular space. To showcase our data set, we surveyed the protein abundance profiles linked to neurofilament bundle assembly, neuron projections, and neuronal cell body formation. These proteins exhibited increases in abundance level, yet we observed multiple patterns among the queried proteins. The data presented represent a rich resource for investigating temporal protein abundance changes in SH-SY5Y cells differentiated with retinoic acid. Moreover, the sample preparation and data acquisition strategies used here can be readily applied to any analogous cell line differentiation analysis.

Calcium Oscillation Frequency Is a Potential Functional Complex Physiological Relevance Indicator for a Neuroblastoma-Based 3D Culture Model

In vitro screening for drugs that affect neural function in vivo is still primitive. It primarily relies on single cellular responses from 2D monolayer cultures that have been shown to be exaggerations of the in vivo response. For the 3D model to be physiologically relevant, it should express characteristics that not only differentiate it from 2D but also closely emulate those seen in vivo. These complex physiologically relevant (CPR) outcomes can serve as a standard for determining how close a 3D culture is to its native tissue or which out of a given number of 3D platforms is better suited for a given application. In this study, Fluo-4-based calcium fluorescence imaging was performed followed by automated image data processing to quantify the calcium oscillation frequency of SHSY5Y cells cultured in 2D and 3D formats. It was found that the calcium oscillation frequency is upregulated in traditional 2D cultures while it was comparable to in vivo in spheroid and microporous polymer scaffold-based 3D models, suggesting calcium oscillation frequency as a potential functional CPR indicator for neural cultures.

Protective effects of perilla oil and alpha linolenic acid on SH-SY5Y neuronal cell death induced by hydrogen peroxide

BACKGROUND/OBJECTIVE

Oxidative stress plays a key role in neuronal cell damage, which is associated with neurodegenerative disease. The aim of present study was to investigate the neuroprotective effects of perilla oil (PO) and its active component, alpha-linolenic acid (ALA), against hydrogen peroxide (H₂O₂)-induced oxidative stress in SH-SY5Y neuronal cells.

MATERIALS/METHODS

The SH-SY5Y human neuroblastoma cells exposed to 250 µM H₂O₂ for 24 h were treated with different concentrations of PO (25, 125, 250 and 500 µg/mL) and its major fatty acid, ALA (1, 2.5, 5 and 25 µ/mL). We examined the effects of PO and ALA on H₂O₂-induced cell viability, lactate dehydrogenase (LDH) release, and nuclear condensation. Moreover, we determined whether PO and ALA regulated the apoptosis-related protein expressions, such as cleaved-poly ADP ribose polymerase (PARP), cleaved caspase-9 and -3, BCL-2 and BAX.

RESULTS

Treatment of H₂O₂ resulted in decreased cell viability, increased LDH release, and increase in the nuclei condensation as indicated by Hoechst 33342 staining. However, PO and ALA treatment significantly attenuated the neuronal cell death, indicating that PO and ALA potently blocked the H₂O₂-induced neuronal apoptosis. Furthermore, cleaved-PARP, cleaved caspase-9 and -3 activations were significantly decreased in the presence of PO and ALA, and the H₂O₂-mediated up-regulated BAX/BCL-2 ratio was blocked after treatment with PO and ALA.

CONCLUSIONS

PO and its main fatty acid, ALA, exerted the protective activity from neuronal oxidative stress induced by H₂O₂. They regulated apoptotic pathway in neuronal cell death by alleviation of BAX/BCL-2 ratio, and down-regulation of cleaved-PARP and cleaved caspase-9 and -3. Although further studies are required to verify the protective mechanisms of PO and ALA from neuronal damage, PO and ALA are the promising agent against oxidative stress-induced apoptotic neuronal cell death.

Zinc oxide nanoparticles induce toxic responses in human neuroblastoma SHSY5Y cells in a size-dependent manner

Due to the widespread applications of zinc oxide nanoparticles (ZnO NPs), the potential exposure of workers, consumers, and scientists to these particles has increased. This potential for exposure has attracted extensive attention in the science community. Many studies have examined the toxicological profile of ZnO NPs in the immune system, digestive system, however, information regarding the toxicity of ZnO NPs in the nervous system is scarce. In this study, we detected the cytotoxicity of two types of ZnO NPs of various sizes - ZnOa NPs and ZnOb NPs - and we characterized the shedding ability of zinc ions within culture medium and the cytoplasm. We found that reactive oxygen species played a crucial role in ZnO NP-induced cytotoxicity, likely because zinc ions were leached from ZnO NPs. Apoptosis and cytoskeleton changes were also toxic responses induced by the ZnO NPs, and ZnOb NPs induced more significant toxic responses than ZnOa NPs in SHSY5Y cells. In conclusion, ZnO NPs induced toxic responses in SHSY5Y cells in a size-dependent manner, which can probably be attributed to their ion-shedding ability.

Gene Prioritization for Imaging Genetics Studies Using Gene Ontology and a Stratified False Discovery Rate Approach

Imaging genetics is an emerging field in which the association between genes and neuroimaging-based quantitative phenotypes are used to explore the functional role of genes in neuroanatomy and neurophysiology in the context of healthy function and neuropsychiatric disorders. The main obstacle for researchers in the field is the high dimensionality of the data in both the imaging phenotypes and the genetic variants commonly typed. In this article, we develop a novel method that utilizes Gene Ontology, an online database, to select and prioritize certain genes, employing a stratified false discovery rate (sFDR) approach to investigate their associations with imaging phenotypes. sFDR has the potential to increase power in genome wide association studies (GWAS), and is quickly gaining traction as a method for multiple testing correction. Our novel approach addresses both the pressing need in genetic research to move beyond candidate gene studies, while not being overburdened with a loss of power due to multiple testing. As an example of our methodology, we perform a GWAS of hippocampal volume using both the Enhancing NeuroImaging Genetics through Meta-Analysis (ENIGMA2) and the Alzheimer's Disease Neuroimaging Initiative datasets. The analysis of ENIGMA2 data yielded a set of SNPs with sFDR values between 10 and 20%. Our approach demonstrates a potential method to prioritize genes based on biological systems impaired in a disease.

Differential roles of Aβ processing in hypoxia-induced axonal damage

Axonopathy is a common and early phase in neurodegenerative and traumatic CNS diseases. Recent work suggests that amyloid β (Aβ) produced from amyloid precursor protein (APP) may be a critical downstream mediator of CNS axonopathy in CNS diseases, particularly those associated with hypoxia. We critically tested this hypothesis in an adult retinal explant system that preserves the three-dimensional organization of the retina while permitting direct imaging of two cardinal features of early-stage axonopathy: axonal structural integrity and axonal transport capacity. Using this system, we found via pharmacological inhibition and genetic deletion of APP that production of Aβ is a necessary step in structural compromise of retinal ganglion cell (RGC) axons induced by the disease-relevant stressor hypoxia. However, identical blockade of Aβ production was not sufficient to protect axons from associated hypoxia-induced reduction in axonal transport. Thus, Aβ mediates distinct facets of hypoxia-induced axonopathy and may represent a functionally selective pharmacological target for therapies directed against early-stage axonopathy in CNS diseases.

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

As the most common neurodegenerative disease, therapeutic avenues for the treatment and prevention of Alzheimer's Disease are highly sought after. The aspartic protease BACE1 is the initiator enzyme for the formation of Aβ, a major constituent of amyloid plaques that represent one of the hallmark pathological features of this disorder. Thus, targeting BACE1 for disease-modifying AD therapies represents a rationale approach. The collective knowledge acquired from investigations of BACE1 deletion mutants and characterization of BACE1 substrates has downstream significance not only for the discovery of AD drug therapies but also for predicting side effects of BACE1 inhibition. Here we discuss the identification and validation of BACE1 as the β-secretase implicated in AD, in addition to information regarding BACE1 cell biology, localization, substrates and potential physiological functions derived from BACE1 knockout models.

Mild oxidative stress induces redistribution of BACE1 in non-apoptotic conditions and promotes the amyloidogenic processing of Alzheimer's disease amyloid precursor protein

BACE1 is responsible for β-secretase cleavage of the amyloid precursor protein (APP), which represents the first step in the production of amyloid β (Aβ) peptides. Previous reports, by us and others, have indicated that the levels of BACE1 protein and activity are increased in the brain cortex of patients with Alzheimer's disease (AD). The association between oxidative stress (OS) and AD has prompted investigations that support the potentiation of BACE1 expression and enzymatic activity by OS. Here, we have established conditions to analyse the effects of mild, non-lethal OS on BACE1 in primary neuronal cultures, independently from apoptotic mechanisms that were shown to impair BACE1 turnover. Six-hour treatment of mouse primary cortical cells with 10-40 µM hydrogen peroxide did not significantly compromise cell viability but it did produce mild oxidative stress (mOS), as shown by the increased levels of reactive radical species and activation of p38 stress kinase. The endogenous levels of BACE1 mRNA and protein were not significantly altered in these conditions, whereas a toxic H2O2 concentration (100 µM) caused an increase in BACE1 protein levels. Notably, mOS conditions resulted in increased levels of the BACE1 C-terminal cleavage product of APP, β-CTF. Subcellular fractionation techniques showed that mOS caused a major rearrangement of BACE1 localization from light to denser fractions, resulting in an increased distribution of BACE1 in fractions containing APP and markers for trans-Golgi network and early endosomes. Collectively, these data demonstrate that mOS does not modify BACE1 expression but alters BACE1 subcellular compartmentalization to favour the amyloidogenic processing of APP, and thus offer new insight in the early molecular events of AD pathogenesis.

Methylparaben protects 6-hydroxydopamine-induced neurotoxicity in SH-SY5Y cells and improved behavioral impairments in mouse model of Parkinson's disease

Parkinson's disease (PD) is a progressive neurodegenerative disorder of unknown etiology. Considerable evidence suggests that free radical formation and oxidative stress might play an important role in the pathogenesis of PD. In the present investigation we evaluated the therapeutic potential of methylparaben (MP) a well known pharmaceutical preservative against 6-hydroxydopamine (6-OHDA) neurotoxicity in SH-SY5Y cells and in a mouse model of PD. At nanomolar concentrations MP (0.01, 0.1 and 1 nM) significantly attenuated the 6-OHDA- and hydrogen peroxide-induced cytotoxicity in SH-SY5Y cells. The reactive oxygen species generated by 6-OHDA in SH-SY5Y cells was also inhibited by MP in a concentration dependent fashion. Further, intranigral damage induced by stereotaxically injecting 6-OHDA in mouse brain was significantly attenuated by MP treatment. MP (1, 10 or 50 μg/kg, i.p.) prevented apomorphine-induced rotational behavior and significantly improved motor deficits in 6-OHDA-lesioned mice. The cognitive impairments as evaluated by passive avoidance and Y-maze task in mice were also attenuated by MP concentration dependently. Immunohistochemical analysis of substantia nigra in MP treated mice showed significantly higher number of surviving tyrosine hydroxylase positive cells. Furthermore, MP also suppressed the lipid peroxidation products in 6-OHDA-lesioned mouse brain tissues. Considering the results obtained, the marked neuroprotection exhibited by MP might be attributed to its potent antioxidant property. In conclusion, this study reports the neuroprotective properties of MP in experimental models of PD for the first time and can be developed as a potential therapeutic agent.

Regulation of mammalian MOR-1 gene expression after chronic treatment with morphine

Morphine is an effective analgesic that acts by binding to the µ-opioid receptor (MOR) coded in the human by the OPRM1 gene. In the present study, we investigated the regulation of µ-opioid receptor (MOR-1) mRNA levels in all-trans-retinoic acid-differentiated SH-SY5Y human neuroblastoma cells under in vitro conditions with 10 µM morphine treatment for 24 h. In addition, we measured the MOR-1 levels in recombinant Chinese hamster ovary (CHO) cells, transfected with human µ-opioid receptor gene (hMOR) with 10 µM morphine treatment for 24 h. The isolated mRNA from these cells was subjected to real-time quantitative RT-PCR analysis to determine the regulation of µ-opioid receptor gene expression. It was observed that morphine treatment did not alter MOR-1 levels in undifferentiated SH-SY5Y cells compared to undifferentiated control cells. However, the MOR-1 levels in all-trans-retinoic acid-differentiated cells were significantly higher compared to the undifferentiated cells. Morphine treatment in differentiated SH-SY5Y cells caused significant downregulation of MOR-1 expression compared to the control cells. In the morphine-treated CHO cells, the hMOR-1 mRNA levels remained the same as the untreated control. Finally, pretreatment of SH-SY5Y cells with 10 µM naloxone, the antagonist of µ-opioid receptor, for 1 h significantly blocked the downregulation of MOR-1 mRNA levels with morphine treatment. These findings suggest that regulation of MOR-1 gene expression is cell-type specific after chronic morphine treatment and provide some evidence in the understanding of morphine tolerance.

BACE1 in Alzheimer's disease

Targeting BACE1 (β-site APP cleaving enzyme 1 or β-secretase) is the focus of Alzheimer's disease (AD) research because this aspartyl protease is involved in the abnormal production of β amyloid plaques (Aβ), the hallmark of its pathophysiology. Evidence suggests that there is a strong connection between AD and BACE1. As such, strategies to inhibit Aβ formation in the brain should prove beneficial for AD treatment. Aβ, the product of the large type1 trans-membrane protein amyloid precursor protein (APP), is produced in a two-step proteolytic process initiated by BACE1 (β-secretase) and followed by γ-secretase. Due to its apparent rate limiting function, BACE1 appears to be a prime target to prevent Aβ generation in AD. Following its discovery, the BACE1 has been cloned, its structure solved, novel physiologic substrates discovered and numerous inhibitors developed. This review focuses on elucidating the role of BACE1 to facilitate drug development in the treatment of AD.

Regulation of β-site APP-cleaving enzyme 1 gene expression and its role in Alzheimer's disease

Alzheimer's disease (AD) is the most common neurodegenerative disorder leading to dementia. Neuritic plaques are the hallmark neuropathology in AD brains. Proteolytic processing of amyloid-β precursor protein at the β site by beta-site amyloid-β precursor protein-cleaving enzyme 1 (BACE1) is essential to generate Aβ, a central component of the neuritic plaques. BACE1 is increased in some sporadic AD brains, and dysregulation of BACE1 gene expression plays an important role in AD pathogenesis. This review will focus on the regulation of BACE1 gene expression at the transcriptional, post-transcriptional, translation initiation, translational and post-translational levels, and its role in AD pathogenesis. Further studies on BACE1 gene expression regulation will greatly contribute to our understanding of AD pathogenesis and reveal potential novel approaches for AD prevention and drug development.

The potential dual effects of anesthetic isoflurane on hypoxia-induced caspase-3 activation and increases in β-site amyloid precursor protein-cleaving enzyme levels

BACKGROUND

β-Amyloid protein (Aβ) accumulation, caspase activation, apoptosis, and hypoxia-induced neurotoxicity have been suggested to be involved in Alzheimer disease neuropathogenesis. Aβ is produced from amyloid precursor protein through proteolytic processing by the aspartyl protease β-site amyloid precursor protein-cleaving enzyme (BACE) and γ-secretase. Inhaled anesthetics have long been considered to protect against neurotoxicity. However, recent studies have suggested that the inhaled anesthetic isoflurane may promote neurotoxicity by inducing caspase activation and apoptosis, and by increasing levels of BACE and Aβ. We therefore sought to determine whether isoflurane can induce concentration-dependent dual effects on hypoxia-induced caspase-3 activation and increases in BACE levels: protection versus promotion.

METHODS

H4 human neuroglioma cells were treated with hypoxia (3% O(2)) alone, different concentrations of isoflurane (0.5% and 2%), and the combination of hypoxia and 0.5% or 2% isoflurane. The levels of caspase-3 cleavage (activation), BACE, and Bcl-2 were determined by Western blot analysis.

RESULTS

We show for the first time that treatment with 0.5% isoflurane for 8 hours attenuated, whereas treatment with 2% isoflurane for 8 hours enhanced, hypoxia-induced caspase-3 activation and increases in BACE levels. The 2% isoflurane treatment also enhanced a hypoxia-induced decrease in Bcl-2 levels.

CONCLUSIONS

These results suggest a potential concept that isoflurane has dual effects (protection versus promotion) on hypoxia-induced toxicity, which may act through Bcl-2 family proteins. These findings could lead to more systematic studies to determine the potential dual effects of anesthetics on Alzheimer disease-associated neurotoxicity.

Hypothesis on the relationship between the change in intracellular pH and incidence of sporadic Alzheimer's disease or vascular dementia

In order to perform their normal physiological functions, it is important that cells maintain the intracellular pH within the physiological range. Intracellular enzyme activity, cytoskeleton component integration, and cellular growth and differentiation rates are all closely associated with the intracellular pH. It has been demonstrated that in nervous system diseases, such as ischemic stroke, traumatic brain injury, epilepsy, Parkinson's disease, and Alzheimer's disease (AD), the common characteristics are decreased pH or acidosis at both tissular and cellular levels. Particularly, some AD-associated enzymes will have altered activities under acidic conditions. We inferred that aging or ischemia may cause intracellular acidification. This acidification not only induces apoptosis but also substantially alters enzyme activities and promotes the development of AD or vascular dementia. The hypothesis of an intracellular pH role in sporadic AD or vascular dementia will be discussed in this paper. If confirmed, this hypothesis may lead to the formulation of new pathogenesis and new therapeutic approaches to AD or vascular dementia.

The inhibitory effects of different curcuminoids on β-amyloid protein, β-amyloid precursor protein and β-site amyloid precursor protein cleaving enzyme 1 in swAPP HEK293 cells

The hallmark of Alzheimer's disease (AD) is the accumulation of β-amyloid protein (Aβ). Aβ is generated from the β-amyloid precursor protein (APP) through the proteolysis of β-site APP cleaving enzyme 1 (BACE1) and γ-secretase. Aβ(42) isoform is more easily aggregate and more toxic to neurons than any other Aβ isoforms, thus being regarded as the primary toxic specie in AD. Curcumin mix has potent anti-amyloidogenic effect and shows great promise for AD treatment and prevention. The present study was conducted to examine the effects of curcumin mix and its different curcuminoids including curcumin (Cur), demethoxycurcumin (DMC) and bisdemethoxycurcumin (BDMC) on Aβ(42), APP and BACE1. We found that Cur was the most active curcuminoid fraction in suppressing Aβ(42) production and the order of inhibitory potency of other curcuminoids was DMC>curcumin mix>BDMC. Cur, but not other curcuminoids, could reduce APP protein expression and none of curcuminoids affected APP mRNA level. BDMC could reduce BACE1 mRNA and protein levels, while DMC only affected BACE1 mRNA expression. Our data indicate that the anti-amyloidogenic effect of Cur may be mediated through the modulation of APP, while the anti-amyloidogenic effect of BDMC may be mediated through the modulation of BACE1.

Salidroside attenuates hypoxia-induced abnormal processing of amyloid precursor protein by decreasing BACE1 expression in SH-SY5Y cells

Hypoxia which is mainly mediated by hypoxia-inducible factor 1 (HIF-1), can greatly contribute to the occurrence of Alzheimer's disease (AD) by increasing beta-site APP cleaving enzyme (BACE1) gene expression, protein level and beta-secretase activity, resulting in a significant generation of amyloid-beta (Abeta). Salidroside has been reported to have great neuroprotective effects. The aim of this study was to investigate the effects of salidroside on hypoxia-induced abnormal processing of the amyloid precursor protein (APP) in SH-SY5Y cells and its possible mechanism. Western blot analysis showed that 200muM of salidroside pretreatment significantly decreased BACE1 protein level and promoted the secretion of sAPPalpha in hypoxic condition. Salidroside had no effect on the level of APP, ADAM10 and ADAM17. ELISA analysis revealed that salidroside was able to inhibit the increase of beta-secretase activity and Abeta generation induced by hypoxia, with no effect on gamma-secretase activity. Notably, under hypoxia condition, mRNA of BACE1 and protein level of HIF-1alpha were decreased by salidroside pretreatment. These results demonstrated for the first time that salidroside was able to attenuate abnormal processing of amyloid precursor protein induced by hypoxia in SH-SY5Y cells, providing a new insight into prevention and treatment of Alzheimer's disease.

Mutant presenilin 1 increases the expression and activity of BACE1

Mutations of the presenilin 1 (PS1) gene are the most common cause of early onset familial Alzheimer disease (FAD). PS1 mutations alter the activity of the gamma-secretase on the beta-amyloid precursor protein (APP), leading to selective overproduction of beta-amyloid (Abeta) 42 peptides, the species that forms oligomers that may exert toxic effects on neurons. Here we show that PS1 mutations, expressed both transiently and stably, in non-neuronal and neuronal cell lines increase the expression and the activity of the beta-secretase (BACE1), the rate-limiting step of Abeta production. Also, BACE1 expression and activity are elevated in brains of PS1 mutant knock-in mice compared with wild type littermates as well as in cerebral cortex of FAD cases bearing various PS1 mutations compared with in sporadic AD cases and controls. The up-regulation of BACE1 by PS1 mutations requires the gamma-secretase cleavage of APP and is proportional to the amount of secreted Abeta42. Abeta42, and not AICD (APP intracellular domain), is indeed the APP derivative that mediates the overexpression of BACE1. The effect of PS1 mutations on BACE1 may contribute to determine the wide clinical and pathological phenotype of early onset FAD.