Amyloid Precursor Protein Production Research Articles

Dysregulation of Amyloid Precursor Protein Impairs Adipose Tissue Mitochondrial Function and Promotes Obesity.

Mitochondrial function in white adipose tissue (WAT) is an important yet understudied aspect in adipocyte biology. Here, we report a role for amyloid precursor protein (APP) in compromising WAT mitochondrial function through a high-fat diet (HFD)-induced, unconventional mis-localization to mitochondria that further promotes obesity. In humans and mice, obese conditions significantly induce APP production in WAT and its enrichment in mitochondria. Mechanistically, a HFD-induced dysregulation of signal recognition particle subunit 54c is responsible for the mis-targeting of APP to adipocyte mitochondria. Mis-localized APP blocks the protein import machinery, leading to mitochondrial dysfunction in WAT. Adipocyte-specific and mitochondria-targeted APP overexpressing mice display increased body mass and reduced insulin sensitivity, along with dysfunctional WAT due to a dramatic hypertrophic program in adipocytes. Elimination of adipocyte APP rescues HFD-impaired mitochondrial function with significant protection from weight gain and systemic metabolic deficiency. Our data highlights an important role of APP in modulating WAT mitochondrial function and obesity-associated metabolic dysfunction.

Amyloid precursor protein, an androgen-regulated gene, is targeted by RNA-binding protein PSF/SFPQ in neuronal cells.

Amyloid precursor protein (APP) is a representative gene related to Alzheimer's disease (AD). Androgens function by binding to the androgen receptor (AR). Both androgen and RNA-binding protein PSF play a role in the pathology of AD. However, the involvement of AR and PSF in APP regulation in neuron has not been investigated. Here, we explored the regulatory mechanism of APP expression by AR and PSF using neuron-derived cells. We demonstrated that androgen up-regulates the production of APP at the mRNA and protein levels. This induction is enhanced by AR over-expression and inhibited by its silencing. One candidate AR-binding region was identified in the intron region of APP and validated its activity as AR-dependent enhancer by the luciferase assay. Furthermore, the public transcriptome data of brain tissues of mice indicated that APP is regulated by PSF post-transcriptionally. We observed a decreased expression of APP after PSF knockdown and interaction of PSF with the APP transcript. Moreover, we revealed that silencing of PSF inhibited the stability of the APP mRNA. Thus, these results presented a new regulatory mechanism of APP expression by androgen through AR-mediated transcription and PSF at the post-transcriptional level that might be associated with the occurrence of AD.

Pioglitazone Reduces β Amyloid Levels via Inhibition of PPARγ Phosphorylation in a Neuronal Model of Alzheimer's Disease.

It has been demonstrated that peroxisome proliferator-activated receptor γ (PPARγ) can regulate the transcription of its target gene, insulin-degrading enzyme (IDE), and thus enhance the expression of the IDE protein. The protein can degrade β amyloid (Aβ), a core pathological product of Alzheimer’s disease (AD). PPARγ can also regulate the transcription of other target gene, β-amyloid cleavage enzyme 1 (BACE1), and thus inhibit the expression of the BACE1 protein. BACE1 can hydrolyze amyloid precursor protein (APP), the precursor of Aβ. In adipose tissue, PPARγ agonists can inhibit the phosphorylation of PPARγ by inhibiting cyclin-dependent kinase 5 (CDK5), which in turn affects the expression of target genes regulated by PPARγ. PPARγ agonists may also exert inhibitory effects on the phosphorylation of PPARγ in the brain, thereby affecting the expression of the aforementioned PPARγ target genes and reducing Aβ levels. The present study confirmed this hypothesis by showing that PPARγ agonist pioglitazone attenuated the neuronal apoptosis of primary rat hippocampal neurons induced by Aβ1–42, downregulated CDK5 expression, weakened the binding of CDK5 to PPARγ, reduced PPARγ phosphorylation, increased the expression of PPARγ and IDE, decreased the expression of BACE1, reduced APP production, and downregulated intraneuronal Aβ1–42 levels. These effects were inhibited by the PPARγ antagonist GW9662. After CDK5 silencing with CDK5 shRNA, the above effect of pioglitazone was not observed, except when upregulating the expression of PPARγ in Aβ1–42 treated neurons. In conclusion, this study demonstrated that pioglitazone could inhibit the phosphorylation of PPARγ in vitro by inhibiting CDK5 expression, which in turn affected the expression of PPARγ target genes Ide and Bace1, thereby promoting Aβ degradation and reducing Aβ production. This reduced Aβ levels in the brain, thereby exerting neuroprotective effects in an AD model.

Therapeutic Strategies Targeting Amyloid-β in Alzheimer's Disease.

Alzheimer's disease (AD) is a neurodegenerative disorder linked to protein misfolding and aggregation. AD is pathologically characterized by senile plaques formed by extracellular Amyloid-β (Aβ) peptide and Intracellular Neurofibrillary Tangles (NFT) formed by hyperphosphorylated tau protein. Extensive synaptic loss and neuronal degeneration are responsible for memory impairment, cognitive decline and behavioral dysfunctions typical of AD. Amyloidosis has been implicated in the depression of acetylcholine synthesis and release, overactivation of N-methyl-D-aspartate (NMDA) receptors and increased intracellular calcium levels that result in excitotoxic neuronal degeneration. Current drugs used in AD treatment are either cholinesterase inhibitors or NMDA receptor antagonists; however, they provide only symptomatic relief and do not alter the progression of the disease. Aβ is the product of Amyloid Precursor Protein (APP) processing after successive cleavage by β- and γ-secretases while APP proteolysis by α-secretase results in non-amyloidogenic products. According to the amyloid cascade hypothesis, Aβ dyshomeostasis results in the accumulation and aggregation of Aβ into soluble oligomers and insoluble fibrils. The former are synaptotoxic and can induce tau hyperphosphorylation while the latter deposit in senile plaques and elicit proinflammatory responses, contributing to oxidative stress, neuronal degeneration and neuroinflammation. Aβ-protein-targeted therapeutic strategies are thus a promising disease-modifying approach for the treatment and prevention of AD. This review summarizes recent findings on Aβ-protein targeted AD drugs, including β-secretase inhibitors, γ-secretase inhibitors and modulators, α-secretase activators, direct inhibitors of Aβ aggregation and immunotherapy targeting Aβ, focusing mainly on those currently under clinical trials.

The cyanobacterial neurotoxin β-N-methylamino-l-alanine prevents addition of heparan sulfate to glypican-1 and increases processing of amyloid precursor protein in dividing neuronal cells

The neurotoxin β-N-methylamino-l-alanine replaces l-serine in proteins and produces Alzheimer-like pathology. In proteoglycans, e.g. glypican-1, this should preclude substitution with heparan sulfate chains. Reduced release of heparan sulfate should increase β-secretase activity and processing of amyloid precursor protein. Cultured cells were treated with β-N-methylamino-l-alanine during the growth-phase and the effect on heparan sulfate substitution and amyloid precursor protein processing was evaluated using antibodies specific for heparan sulfate, the N- and C-termini of the C-terminal fragment of β-cleaved amyloid precursor protein, and amyloid beta followed by immunofluorescence microscopy, flow cytometry or SDS-PAGE. Mouse fibroblasts, N2a neuroblastoma cells and human neural stem cells released less heparan sulfate when grown in the presence of β-N-methylamino-l-alanine. Cells expressing a recombinant, anchor-less glypican-1 secreted heparan sulfate-deficient glypican-1. There was increased processing of amyloid precursor protein in N2a cells when grown in the presence of the neurotoxin. The degradation products accumulated in cytoplasmic clusters. Secretion of amyloid beta increased approx. 3-fold. Human neural stem cells also developed cytoplasmic clusters containing degradation products of amyloid precursor protein. When non-dividing mouse N2a cells or cortical neurons were exposed to β-N-methylamino-l-alanine there was no effect on heparan sulfate substitution in glypican-1 or on amyloid precursor protein processing.

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.

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.

Targeting the Amyloid Precursor Protein (APP) to Mitochondria of White Adipose Tissues Triggers Mitochondrial Dysfunction and Obesity

The role of mitochondrial dysfunction in white adipose tissues (WAT) under different metabolic conditions is not well understood. Here, we report that under high fat diet (HFD) conditions, endogenous production of APP is significantly induced and, instead of being secreted, the protein is highly enriched in WAT mitochondria. To better understand the role of APP, we established an inducible model by directing the full-length APP with a mitochondrial targeting presequence quantitatively to mitochondria, selectively in adipocytes. We validated that APP mRNA and protein levels were significantly elevated in subcutaneous WAT, and the protein was markedly accumulated in isolated mitochondria from sWAT. EM imaging suggested widespread loss of mitochondrial cristae. Respiratory measurements on a Seahorse instrument revealed a rapid impairment in mitochondrial functions in sWAT, concomitant with an increase in adipocyte size within a few days. APP transgenic mice displayed significantly enhanced fat mass, along with impaired glucose tolerance and reduced insulin sensitivity under a long term HFD challenge. By H and E staining, we observed widespread inflammatory cell infiltration in WAT, and consistent with the adipose tissue dysfunction, we also noticed massive hepatic steatosis. Adiponectin levels in plasma and sWAT were significantly reduced. We specifically eliminated endogenous APP in WAT through a conditioned knock-out mouse model (Appflox/flox) to demonstrate that adipocyte-specific deletion of APP can ameliorate high fat diet-induced mitochondrial dysfunction. In summary, accumulated APP in WAT mitochondria significantly induces mitochondrial dysfunction in adipocytes, leading to unhealthy adipose tissue expansion and eventually resulting in obesity and systemic insulin resistance. Disclosure Y.A. An: None. P.E. Scherer: None.

Early striatal amyloid deposition distinguishes Down syndrome and autosomal dominant Alzheimer's disease from late-onset amyloid deposition

IntroductionThe objective of this study was to evaluate amyloid β (Aβ) deposition patterns in different groups of cerebral β amyloidosis: (1) nondemented with amyloid precursor protein overproduction (Down syndrome); (2) nondemented with abnormal processing of amyloid precursor protein (preclinical autosomal dominant Alzheimer disease); (3) presumed alteration in Aβ clearance with clinical symptoms (late-onset AD); and (4) presumed alterations in Aβ clearance (preclinical AD). MethodsWe performed whole-brain voxelwise comparison of cerebral Aβ between 23 Down syndrome, 10 preclinical autosomal dominant Alzheimer disease, 17 late-onset AD, and 16 preclinical AD subjects, using Pittsburgh Compound B–positron emission tomography. ResultsWe found both Down syndrome and preclinical autosomal dominant Alzheimer disease shared a distinct pattern of increased bilateral striatal and thalamic Aβ deposition compared to late-onset AD and preclinical AD. ConclusionDisorders associated with early-life alterations in amyloid precursor protein production or processing are associated with a distinct pattern of early striatal fibrillary Aβ deposition before significant cognitive impairment. A better understanding of this unique pattern could identify important mechanisms of Aβ deposition and possibly important targets for early intervention.

Lentivirus-mediated expression of human secreted amyloid precursor protein-alpha prevents development of memory and plasticity deficits in a mouse model of Alzheimer's disease

Alzheimer’s disease (AD) is a neurodegenerative disease driven in large part by accumulated deposits in the brain of the amyloid precursor protein (APP) cleavage product amyloid-β peptide (Aβ). However, AD is also characterised by reductions in secreted amyloid precursor protein-alpha (sAPPα), an alternative cleavage product of APP. In contrast to the neurotoxicity of accumulated Αβ, sAPPα has many neuroprotective and neurotrophic properties. Increasing sAPPα levels has the potential to serve as a therapeutic treatment that mitigates the effects of Aβ and rescue cognitive function. Here we tested the hypothesis that lentivirus-mediated expression of a human sAPPα construct in a mouse model of AD (APPswe/PS1dE9), begun before the onset of plaque pathology, could prevent later behavioural and electrophysiological deficits. Male mice were given bilateral intra-hippocampal injections at 4 months of age and tested 8–10 months later. Transgenic mice expressing sAPPα performed significantly better than untreated littermates in all aspects of the spatial water maze task. Expression of sAPPα also resulted in partial rescue of long-term potentiation (LTP), tested in vitro. These improvements occurred in the absence of changes in amyloid pathology. Supporting these findings on LTP, lentiviral-mediated expression of sAPPα for 3 months from 10 months of age, or acute sAPPα treatment in hippocampal slices from 18 to 20 months old transgenic mice, completely reversed the deficits in LTP. Together these findings suggest that sAPPα has wide potential to act as either a preventative or restorative therapeutic treatment in AD by mitigating the effects of Aβ toxicity and enhancing cognitive reserve.

Overexpression of Amyloid Precursor Protein Promotes the Onset of Seborrhoeic Keratosis and is Related to Skin Ageing.

Seborrhoeic keratosis (SK) is an age-related skin disease. Amyloid precursor protein (APP) plays an important role in the pathogenesis of age-related Alzheimer's disease. The aim of this study was to elucidate the expression characteristics of APP in SK tissues (n = 50), and explore whether the production of APP is related to the onset of SK and skin ageing, including ultraviolet (UV)-induced ageing, as observed in normal skin (n = 79). The results of immunohistochemistry, Western blotting and quantitative real-time PCR showed that APP and its downstream products (i.e. amyloid-β42) were more highly expressed in SK than in paired adjacent normal skin tissues. In contrast, the expression of its key secretase (i.e. β-secretase1) was generally low. Furthermore, APP expression was higher in UV-exposed than non-exposed skin sites, and expression in the older age group (61-85 years) was greater than that in the younger age group (41-60 years) in SK tissues (p<0.05). APP expression correlated positively with age in epidermis (p<0.05), but not in dermis. These findings suggest that overexpression of APP may promote the onset of SK and is a marker of skin ageing and UV damage. Further research will elucidate whether therapeutic mitigation of increased levels of APP in the skin might delay the onset of SK and skin ageing.

Is it time to rethink the Alzheimer's disease drug development strategy by targeting its silent phase?

Is it time to rethink the Alzheimer's disease drug development strategy by targeting its silent phase?

Expression of BC1 Impairs Spatial Learning and Memory in Alzheimer's Disease Via APP Translation.

Aggregation of amyloid-β (Aβ) peptides, which are the cleavage products of amyloid precursor protein (APP), is a major pathological hallmark in the brain of Alzheimer's disease (AD). Now, we know little about the roles of APP translation in the disease progression of AD. Here, we show that BC1, a long noncoding RNA (lncRNA), is expressed in the brain of AD mice. BC1 induces APP mRNA translation via association with a fragile X syndrome protein (FMRP). Inhibition of BC1 or BC1-FMRP association in AD mice blocks aggregation of Aβ in the brain and protects against the spatial learning and memory deficits. Expression of exogenous BC1 in excitatory pyramidal neurons of mice induces Aβ peptides accumulation and the spatial learning and memory impairments. This study provides a novel mechanism underlying aggregation of Aβ peptides via BC1 induction of APP mRNA translation and hence warrants a promising target for AD therapy.

Amyloid precursor protein products concentrate in a subset of exosomes specifically endocytosed by neurons.

Amyloid beta peptide (Aβ), the main component of senile plaques of Alzheimer's disease brains, is produced by sequential cleavage of amyloid precursor protein (APP) and of its C-terminal fragments (CTFs). An unanswered question is how amyloidogenic peptides spread throughout the brain during the course of the disease. Here, we show that small lipid vesicles called exosomes, secreted in the extracellular milieu by cortical neurons, carry endogenous APP and are strikingly enriched in CTF-α and the newly characterized CTF-η. Exosomes from N2a cells expressing human APP with the autosomal dominant Swedish mutation contain Aβ peptides as well as CTF-α and CTF-η, while those from cells expressing the non-mutated form of APP only contain CTF-α and CTF-η. APP and CTFs are sorted into a subset of exosomes which lack the tetraspanin CD63 and specifically bind to dendrites of neurons, unlike exosomes carrying CD63 which bind to both neurons and glial cells. Thus, neuroblastoma cells secrete distinct populations of exosomes carrying different cargoes and targeting specific cell types. APP-carrying exosomes can be endocytosed by receiving cells, allowing the processing of APP acquired by exosomes to give rise to the APP intracellular domain (AICD). Thus, our results show for the first time that neuronal exosomes may indeed act as vehicles for the intercellular transport of APP and its catabolites.

The amyloid connection in Parkinson's

Neurodegeneration Parkinson's disease is a progressive neurodegenerative disorder that is commonly associated with activating mutations in the kinase LRRK2. The disease results in dementia owing to loss of dopaminergic neurons. Chen et al. discovered why activating LRRK2 mutations are toxic to neurons. When phosphorylated by mutant LRRK2, a cleavage product of amyloid precursor protein (APP) translocated to the nucleus and was more transcriptionally active, which killed the dopaminergic neurons. These findings connect the pathology of Parkinson's to that of Alzheimer's disease, in which dementia is associated with another APP cleavage product, β-amyloid. Sci. Signal. 10 , eaam6790 (2017).

Abnormal amyloid β42 expression and increased oxidative stress in plasma of CKD patients with cognitive dysfunction: A small scale case control study comparison with Alzheimer's disease

BackgroundCognitive dysfunction has been increasingly recognized in chronic kidney disease (CKD) patients. Senile plaques are important pathophysiological characteristic of cognitive dysfunction. The major component of plaques is the amyloid β (Aβ) peptide released from proteolytic cleavage of amyloid precursor protein (APP). Plasma Aβ has been a focus of the growing literature on blood based biomarkers for cognitive dysfunction. Oxidative stress is prevalent in CKD and it plays an important role in cognitive dysfunction. Increased oxidative stress leads to cause cleavage of APP and Aβ production. The aim of this study is to assess the antioxidant status and Aβ42 levels in plasma of CKD patients with cognitive dysfunction compared to CKD without cognitive dysfunction. MethodsA total of 60 subjects divided into 30 CKD without cognitive dysfunction and 30 CKD with cognitive dysfunction based on neuropsychological assessment tests. To compare antioxidant status and Aβ42 levels in plasma, the following groups such as healthy subjects (n=30), normocytic normochromic anemia (n=30) and Alzheimer's disease (AD, n=10) patients were also maintained. Plasma Superoxide dismutase (SOD), Catalase (CAT), Glutathione peroxidase (GPx), Reduced glutathione (GSH) and lipid peroxidation (LPO) were determined by spectrophotometrically. Aβ level was determined by immunoblotting method. The parameters were statistically compared with healthy, normocytic normochromic anemia and AD subjects. ResultsLike AD subjects, significantly increased Aβ and LPO level while decreased SOD, CAT, GPx and GSH levels were observed in plasma of CKD patients with cognitive dysfunction when compared to healthy, CKD without cognitive dysfunction and normocytic normochromic anemic subjects. ConclusionResults suggest that elevated plasma oxidative stress and Aβ were seen in CKD patients with cognitive dysfunction may be attributed to pathological changes within the brain.

Functional Roles of the Interaction of APP and Lipoprotein Receptors.

The biological fates of the key initiator of Alzheimer’s disease (AD), the amyloid precursor protein (APP), and a family of lipoprotein receptors, the low-density lipoprotein (LDL) receptor-related proteins (LRPs) and their molecular roles in the neurodegenerative disease process are inseparably interwoven. Not only does APP bind tightly to the extracellular domains (ECDs) of several members of the LRP group, their intracellular portions are also connected through scaffolds like the one established by FE65 proteins and through interactions with adaptor proteins such as X11/Mint and Dab1. Moreover, the ECDs of APP and LRPs share common ligands, most notably Reelin, a regulator of neuronal migration during embryonic development and modulator of synaptic transmission in the adult brain, and Agrin, another signaling protein which is essential for the formation and maintenance of the neuromuscular junction (NMJ) and which likely also has critical, though at this time less well defined, roles for the regulation of central synapses. Furthermore, the major independent risk factors for AD, Apolipoprotein (Apo) E and ApoJ/Clusterin, are lipoprotein ligands for LRPs. Receptors and ligands mutually influence their intracellular trafficking and thereby the functions and abilities of neurons and the blood-brain-barrier to turn over and remove the pathological product of APP, the amyloid-β peptide. This article will review and summarize the molecular mechanisms that are shared by APP and LRPs and discuss their relative contributions to AD.

Intranasal Lactoferrin Enhances α-Secretase-Dependent Amyloid Precursor Protein Processing via the ERK1/2-CREB and HIF-1α Pathways in an Alzheimer's Disease Mouse Model.

Growing evidence suggests that lactoferrin (Lf), an iron-binding glycoprotein, is a pleiotropic functional nutrient. In addition, Lf was recently implicated as a neuroprotective agent. These properties make Lf a valuable therapeutic candidate for the treatment of Alzheimer's disease (AD). However, the mechanisms regulating the physiological roles of Lf in the pathologic condition of AD remain unknown. In the present study, an APPswe/PS1DE9 transgenic mouse model of AD was used. We explored whether intranasal human Lf (hLf) administration could reduce β-amyloid (Aβ) deposition and ameliorate cognitive decline in this AD model. We found that hLf promoted the non-amyloidogenic metabolism of amyloid precursor protein (APP) processing through activation of α-secretase a-disintegrin and metalloprotease10 (ADAM10), resulting in enhanced cleavage of the α-COOH-terminal fragment of APP and the corresponding elevation of the NH2-terminal APP product, soluble APP-α (sAPPα), which consequently reduced Aβ generation and improved spatial cognitive learning ability in AD mice. To gain insight into the molecular mechanism by which Lf modulates APP processing, we evaluated the involvement of the critical molecules for APP cleavage and the signaling pathways in N2a cells stably transfected with Swedish mutant human APP (APPsw N2a cells). The results show that the ERK1/2-CREB and HIF-1α signaling pathways were activated by hLf treatment, which is responsible for the expression of induced ADAM10. Additional tests were performed before suggesting the potential use of hLf as an antioxidant and anti-inflammatory. These findings provide new insights into the sources and mechanisms by which hLf inhibits the cognitive decline that occurs in AD via activation of ADAM10 expression in an ERK1/2-CREB and HIF-1α-dependent manner.

Tetraspanin 3: A central endocytic membrane component regulating the expression of ADAM10, presenilin and the amyloid precursor protein

Despite existing knowledge about the role of the A Disintegrin and Metalloproteinase 10 (ADAM10) as the α-secretase involved in the non-amyloidogenic processing of the amyloid precursor protein (APP) and Notch signalling we have only limited information about its regulation. In this study, we have identified ADAM10 interactors using a split ubiquitin yeast two hybrid approach. Tetraspanin 3 (Tspan3), which is highly expressed in the murine brain and elevated in brains of Alzheimer´s disease (AD) patients, was identified and confirmed to bind ADAM10 by co-immunoprecipitation experiments in mammalian cells in complex with APP and the γ-secretase protease presenilin. Tspan3 expression increased the cell surface levels of its interacting partners and was mainly localized in early and late endosomes. In contrast to the previously described ADAM10-binding tetraspanins, Tspan3 did not affect the endoplasmic reticulum to plasma membrane transport of ADAM10. Heterologous Tspan3 expression significantly increased the appearance of carboxy-terminal cleavage products of ADAM10 and APP, whereas N-cadherin ectodomain shedding appeared unaffected. Inhibiting the endocytosis of Tspan3 by mutating a critical cytoplasmic tyrosine-based internalization motif led to increased surface expression of APP and ADAM10. After its downregulation in neuroblastoma cells and in brains of Tspan3-deficient mice, ADAM10 and APP levels appeared unaltered possibly due to a compensatory increase in the expression of Tspans 5 and 7, respectively. In conclusion, our data suggest that Tspan3 acts in concert with other tetraspanins as a stabilizing factor of active ADAM10, APP and the γ-secretase complex at the plasma membrane and within the endocytic pathway.

Curcumin attenuates paraquat-induced cell death in human neuroblastoma cells through modulating oxidative stress and autophagy

Paraquat is a neurotoxic agent, and oxidative stress plays an important role in neuronal cell death after paraquat exposure. In this study, we assessed the neuroprotective effect of curcumin against paraquat and explored the underlying mechanisms of curcumin in vitro. Curcumin treatment prevented paraquat-induced reactive oxygen species (ROS) and apoptotic cell death. Curcumin also exerted a neuroprotective effect by increasing the expression of anti-apoptotic and antioxidant genes. The pretreatment of curcumin significantly decreased gene expression and protein production of amyloid precursor protein. The activation of autophagy process was found defective in paraquat-induced cells, indicated by the accumulation and reduction of LC3I/II. Noteworthy, curcumin restored LC3I/II expression after the pretreatment. Collectively, curcumin demonstrated as a prominent suppressor of ROS, and could reverse autophagy induction in SH-SY5Y cells. The consequences of this were the reduction of APP production and prevention of SH-SY5Y cells from apoptosis. Altogether, curcumin potentially serves as a therapeutic agent of neurodegenerative diseases, associated with ROS overproduction and autophagy dysfunction.