ADAM-10 over-expression increases cortical synaptogenesis

Alpha-lipoic acid alleviates cognitive deficits in transgenic APP23/PS45 mice through a mitophagy-mediated increase in ADAM10 α-secretase cleavage of APP

BACKGROUND

Alpha-lipoic acid (ALA) has a neuroprotective effect on neurodegenerative diseases. In the clinic, ALA can improve cognitive impairments in patients with Alzheimer's disease (AD) and other dementias. Animal studies have confirmed the anti-amyloidosis effect of ALA, but its underlying mechanism remains unclear. In particular, the role of ALA in amyloid-β precursor protein (APP) metabolism has not been fully elucidated.

OBJECTIVE

To investigate whether ALA can reduce the amyloidogenic effect of APP in a transgenic mouse model of AD, and to study the mechanism underlying this effect.

METHODS

ALA was infused into 2-month-old APP23/PS45 transgenic mice for 4 consecutive months and their cognitive function and AD-like pathology were then evaluated. An ALA drug concentration gradient was applied to 20E2 cells in vitro to evaluate its effect on the expression of APP proteolytic enzymes and metabolites. The mechanism by which ALA affects APP processing was studied using GI254023X, an inhibitor of A Disintegrin and Metalloproteinase 10 (ADAM10), as well as the mitochondrial toxic drug carbonyl cyanide m-chlorophenylhydrazone (CCCP).

RESULTS

Administration of ALA ameliorated amyloid plaque neuropathology in the brain tissue of APP23/PS45 mice and reduced learning and memory impairment. ALA also increased the expression of ADAM10 in 20E2 cells and the non-amyloidogenic processing of APP to produce the 83 amino acid C-terminal fragment (C83). In addition to activating autophagy, ALA also significantly promoted mitophagy. BNIP3L-knockdown reduced the mat/pro ratio of ADAM10. By using CCCP, ALA was found to regulate BNIP3L-mediated mitophagy, thereby promoting the α-cleavage of APP.

CONCLUSIONS

The enhanced α-secretase cleavage of APP by ADAM10 is the primary mechanism through which ALA ameliorates the cognitive deficits in APP23/PS45 transgenic mice. BNIP3L-mediated mitophagy contributes to the anti-amyloid properties of ALA by facilitating the maturation of ADAM10. This study provides novel experimental evidence for the treatment of AD with ALA.

Early treatment with an M1 and sigma-1 receptor agonist prevents cognitive decline in a transgenic rat model displaying Alzheimer-like amyloid pathology

The application of the selective allosteric M1 muscarinic and sigma-1 receptor agonist, AF710B (aka ANAVEX3-71), has shown to attenuate Alzheimer's disease-like hallmarks in McGill-R-Thy1-APP transgenic rats when administered at advanced pathological stages. It remains unknown whether preventive treatment strategies applying this compound may be equally effective. We tested whether daily oral administration of AF710B (10 µg/kg) in 7-month-old, preplaque, McGill-R-Thy1-APP rats for 7 months, followed by a 4-week washout period, could prevent Alzheimer's disease-like pathological hallmarks. Long-term AF710B treatment prevented the cognitive impairment of McGill-R-Thy1-APP rats. The effect was accompanied by a reduction in the number of amyloid plaques in the hippocampus and the levels of Aβ42 and Aβ40 peptides in the cerebral cortex. AF710B treatment also reduced microglia and astrocyte recruitment toward CA1 hippocampal Aβ-burdened neurons compared to vehicle-treated McGill-R-Thy1-APP rats, also altering the inflammatory cytokines profile. Lastly, AF710B treatment rescued the conversion of brain-derived neurotrophic factor precursor to its mature and biologically active form. Overall, these results suggest preventive and disease-modifying properties of the compound.

The US9-Derived Protein gPTB9TM Modulates APP Processing Without Targeting Secretase Activities

Alteration of neuronal protein processing is often associated with neurological disorders and is highly dependent on cellular protein trafficking. A prime example is the amyloidogenic processing of amyloid precursor protein (APP) in intracellular vesicles, which plays a key role in age-related cognitive impairment. Most approaches to correct this altered processing aim to limit enzymatic activities that lead to toxic products, such as protein cleavage by β-secretase and the resulting amyloid β production. A viable alternative is to direct APP to cellular compartments where non-amyloidogenic mechanisms are favored. To this end, we exploited the molecular properties of the herpes simplex virus 1 (HSV-1) transport protein US9 to guide APP interaction with preferred endogenous targets. Specifically, we generated a US9 chimeric construct that facilitates APP processing through the non-amyloidogenic pathway and tested it in primary cortical neurons. In addition to reducing amyloid β production, our approach controls other APP-dependent biochemical steps that lead to neuronal deficits, including phosphorylation of APP and tau proteins. Notably, it also promotes the release of neuroprotective soluble αAPP. In contrast to other neuroprotective strategies, these US9-driven effects rely on the activity of endogenous neuronal proteins, which lends itself well to the study of fundamental mechanisms of APP processing/trafficking. Overall, this work introduces a new method to limit APP misprocessing and its cellular consequences without directly targeting secretase activity, offering a novel tool to reduce cognitive decline in pathologies such as Alzheimer's disease and HIV-associated neurocognitive disorders.

QTC-4-MeOBnE Ameliorated Depressive-Like Behavior and Memory Impairment in 3xTg Mice

Growing evidence has associated major depressive disorder (MDD) as a risk factor or prodromal syndrome for the occurrence of Alzheimer's disease (AD). Although this dilemma remains open, it is widely shown that a lifetime history of MDD is correlated with faster progression of AD pathology. Therefore, antidepressant drugs with neuroprotective effects could be an interesting therapeutic conception to target this issue simultaneously. In this sense, 1-(7-chloroquinolin-4-yl)-N-(4-methoxybenzyl)-5-methyl-1H-1,2,3-triazole-4- carboxamide (QTC-4-MeOBnE) was initially conceived as a multi-target ligand with affinity to β-secretase (BACE), glycogen synthase kinase 3β (GSK3β), and acetylcholinesterase but has also shown secondary effects on pathways involved in neuroinflammation and neurogenesis in preclinical models of AD. Herein, we investigated the effect of QTC-4-MeOBnE (1 mg/kg) administration for 45 days on depressive-like behavior and memory impairment in 3xTg mice, before the pathology is completely established. The treatment with QTC-4-MeOBnE prevented memory impairment and depressive-like behavior assessed by the Y-Maze task and forced swimming test. This effect was associated with the modulation of plural pathways involved in the onset and progression of AD, in cerebral structures of the cortex and hippocampus. Among them, the reduction of amyloid beta (Aβ) production mediated by changes in amyloid precursor protein metabolism and hippocampal tau phosphorylation through the inhibition of kinases. Additionally, QTC-4-MeOBnE also exerted beneficial effects on neuroinflammation and synaptic integrity. Overall, our studies suggest that QTC-4-MeOBnE has a moderate effect in a transgenic model of AD, indicating that perhaps studies regarding the neuropsychiatric effects as a neuroprotective molecule are more prone to be feasible.

Marine Natural Products from the Russian Pacific as Sources of Drugs for Neurodegenerative Diseases

Neurodegenerative diseases are growing to become one of humanity's biggest health problems, given the number of individuals affected by them. They cause enough mortalities and severe economic impact to rival cancers and infections. With the current diversity of pathophysiological mechanisms involved in neurodegenerative diseases, on the one hand, and scarcity of efficient prevention and treatment strategies, on the other, all possible sources for novel drug discovery must be employed. Marine pharmacology represents a relatively uncharted territory to seek promising compounds, despite the enormous chemodiversity it offers. The current work discusses one vast marine region-the Northwestern or Russian Pacific-as the treasure chest for marine-based drug discovery targeting neurodegenerative diseases. We overview the natural products of neurological properties already discovered from its waters and survey the existing molecular and cellular targets for pharmacological modulation of the disease. We further provide a general assessment of the drug discovery potential of the Russian Pacific in case of its systematic development to tackle neurodegenerative diseases.

Long-term nucleus basalis cholinergic depletion induces attentional deficits and impacts cortical neurons and BDNF levels without affecting the NGF synthesis

Basal forebrain cholinergic neurons (BFCNs) represent the main source of cholinergic innervation to the cortex and hippocampus and degenerate early in Alzheimer's disease (AD) progression. Phenotypic maintenance of BFCNs depends on levels of mature nerve growth factor (mNGF) and mature brain-derived neurotrophic factor (mBDNF), produced by target neurons and retrogradely transported to the cell body. Whether a reciprocal interaction where BFCN inputs impact neurotrophin availability and affect cortical neuronal markers is unknown. To address our hypothesis, we immunolesioned the nucleus basalis (nb), a basal forebrain cholinergic nuclei projecting mainly to the cortex, by bilateral stereotaxic injection of 192-IgG-Saporin (the cytotoxin Saporin binds p75ntr receptors expressed exclusively by BFCNs) in 2.5-month-old Wistar rats. At six months post-lesion, Saporin-injected rats (SAP) showed an impairment in a modified version of the 5-Choice Serial Reaction Time Task (5-choice task). Post-mortem analyses of the brain revealed a reduction of Choline Acetyltransferase-immunoreactive neurons compared to wild-type controls. A diminished number of cortical vesicular acetylcholine transporter-immunoreactive boutons was accompanied by a reduction in BDNF mRNA, mBDNF protein levels, markers of glutamatergic (vGluT1) and GABAergic (GAD65) neurons in the SAP-group compared to the controls. NGF mRNA, NGF precursor and mNGF protein levels were not affected. Additionally, cholinergic markers correlated with the attentional deficit and BDNF levels. Our findings demonstrate that while cholinergic nb loss impairs cognition and reduces cortical neuron markers, it produces differential effects on neurotrophin availability, affecting BDNF but not NGF levels.

Endoglycan (PODXL2) is proteolytically processed by ADAM10 (a disintegrin and metalloprotease 10) and controls neurite branching in primary neurons

Cell adhesion is tightly controlled in multicellular organisms, for example, through proteolytic ectodomain shedding of the adhesion-mediating cell surface transmembrane proteins. In the brain, shedding of cell adhesion proteins is required for nervous system development and function, but the shedding of only a few adhesion proteins has been studied in detail in the mammalian brain. One such adhesion protein is the transmembrane protein endoglycan (PODXL2), which belongs to the CD34-family of highly glycosylated sialomucins. Here, we demonstrate that endoglycan is broadly expressed in the developing mouse brains and is proteolytically shed in vitro in mouse neurons and in vivo in mouse brains. Endoglycan shedding in primary neurons was mediated by the transmembrane protease a disintegrin and metalloprotease 10 (ADAM10), but not by its homolog ADAM17. Functionally, endoglycan deficiency reduced the branching of neurites extending from primary neurons in vitro, whereas deletion of ADAM10 had the opposite effect and increased neurite branching. Taken together, our study discovers a function for endoglycan in neurite branching, establishes endoglycan as an ADAM10 substrate and suggests that ADAM10 cleavage of endoglycan may contribute to neurite branching.

ADAM10 suppresses demyelination and reduces seizure susceptibility in cuprizone-induced demyelination model

The metalloproteinase ADAM10 is the most important amyloid precursor protein (APP) α-secretase, preventing the deposit of neurotoxic amyloid β (Aβ) peptide and generating a soluble APP fragment (sAPP_α) with neurotrophic functions. Recent studies have suggested that ADAM10 also play a role in the pathogenesis of inflammatory CNS diseases, such as multiple sclerosis (MS). Demyelination is the hallmarks of MS but the mechanisms involved remain unclear. Here in this study, we examined the role that ADAM10 might play in the cuprizone-induced demyelination model. Our results demonstrated that ADAM10 expression and sAPP_α production were significantly reduced in the corpus callosum in response to cuprizone treatment. Overexpression of ADAM10 increased sAPP_α production and suppressed demyelination as well as neuroinflammation and oxidative stress in cuprizone-induced demyelination model. Pharmacological inhibition of ADAM10 activity, however, abrogates the protective effect of ADAM10 against demyelination, neuroinflammation and oxidative stress. It has been reported that CNS demyelination may induce seizure activity. Here, we found that overexpression of ADAM10 reduced seizure susceptibility in cuprizone-induced demyelination model, suggesting that ADAM10-derived sAPP_α suppresses demyelination and reduces seizure susceptibility via ameliorating neuroinflammation and oxidative stress in cuprizone-induced demyelination model.

Dangerous Liaisons: Tau Interaction with Muscarinic Receptors

The molecular processes underlying neurodegenerative diseases (such as Alzheimer's Disease - AD) remain poorly understood. There is also an imperative need for disease-modifying therapies in AD since the present treatments, acetylcholinesterase inhibitors and NMDA antagonists, do not halt its progression. AD and other dementias present unique pathological features such as that of microtubule associated protein tau metabolic regulation. Tau has numerous binding partners, including signaling molecules, cytoskeletal elements and lipids, which suggests that it is a multifunctional protein. AD has also been associated with severe loss of cholinergic markers in the brain and such loss may be due to the toxic interaction of tau with cholinergic muscarinic receptors. By using specific antagonists of muscarinic receptors it was found in vitro that extracellular tau binds to M1 and M3 receptors and which the increase of intracellular calcium found in neuronal cells upon tau-binding. However, so far, the significance of tau signaling through muscarinic receptor in vivo in tauopathic models remains uncertain. The data reviewed in the present paper highlight the significant effect of M1 receptor/tau interaction in exacerbating tauopathy related pathological features and suggest that selective M1 agonists may serve as a prototype for future therapeutic development toward modification of currently intractable neurodegenerative diseases, such as tauopathies.

Effect of Lentivirus-Mediated miR-499a-3p on Human Umbilical Vein Endothelial Cells

Objective

To explore the possible role of miR-499a-3p in the function of primary human umbilical vein endothelial cells (HUVECs) and the expression of ADAM10 in primary HUVEC.

Method

miR-499a-3p was first transfected into primary HUVECs via lentivirus vector. The viability, proliferation, and migration of stable transfected primary HUVEC were then determined by flow cytometry, CCK8 assays, scratch tests, and Transwell tests. The transcription of miR-499a-3p and ADAM10 was examined by reverse transcription-polymerase chain reaction (RT-PCR), and the expression of ADAM10 was examined by Western blot (WB).

Results

After transfection, miR-499a-3p transcription was significantly increased (P < 0.01), compared to the blank and nonspecific control (NC) groups, while both ADAM10 transcription and expression were significantly decreased (P < 0.05). In contrast, in the inhibitors group, miR-499a-3p transcription was significantly reduced (P < 0.05) whereas both ADAM10 transcription and expression were significantly increased (P < 0.05). The viability, proliferation, and migration of primary HUVECs were significantly impaired (P < 0.05) by the transfection of miR-499a-3p but enhanced by miR-499a-3p inhibitors (P < 0.05).

Conclusions

Upregulation of miR-499a-3p transcription will inhibit the expression of ADAM10 in HUVECs; cell migration and proliferation, however, promote apoptosis. And reverse effects were established by downregulation of miR-499a-3p transcription. All these effects may be achieved by regulating the transcription and expression of ADAM10. These results combined suggested that miR-499a-3p may affect the proliferation, migration, and apoptosis of endothelial cells and regulate AS by regulating ADAM10. miR-499a-3p may become a candidate biomarker for the diagnosis of unstable angina pectoris (UA).

Revisiting the Amyloid Cascade Hypothesis: From Anti-Aβ Therapeutics to Auspicious New Ways for Alzheimer's Disease

Alzheimer’s disease (AD) is the most prevalent neurodegenerative disorder related to age, characterized by the cerebral deposition of fibrils, which are made from the amyloid-β (Aβ), a peptide of 40–42 amino acids. The conversion of Aβ into neurotoxic oligomeric, fibrillar, and protofibrillar assemblies is supposed to be the main pathological event in AD. After Aβ accumulation, the clinical symptoms fall out predominantly due to the deficient brain clearance of the peptide. For several years, researchers have attempted to decline the Aβ monomer, oligomer, and aggregate levels, as well as plaques, employing agents that facilitate the reduction of Aβ and antagonize Aβ aggregation, or raise Aβ clearance from brain. Unluckily, broad clinical trials with mild to moderate AD participants have shown that these approaches were unsuccessful. Several clinical trials are running involving patients whose disease is at an early stage, but the preliminary outcomes are not clinically impressive. Many studies have been conducted against oligomers of Aβ which are the utmost neurotoxic molecular species. Trials with monoclonal antibodies directed against Aβ oligomers have exhibited exciting findings. Nevertheless, Aβ oligomers maintain equivalent states in both monomeric and aggregation forms; so, previously administered drugs that precisely decrease Aβ monomer or Aβ plaques ought to have displayed valuable clinical benefits. In this article, Aβ-based therapeutic strategies are discussed and several promising new ways to fight against AD are appraised.

Deciphering the neuroprotective and neurogenic potential of soluble amyloid precursor protein alpha (sAPPα)

Amyloid precursor protein (APP) is a transmembrane protein expressed largely within the central nervous system. Upon cleavage, it does not produce the toxic amyloid peptide (Aβ) only, which is involved in neurodegenerative progressions but via a non-amyloidogenic pathway it is metabolized to produce a soluble fragment (sAPPα) through α-secretase. While a lot of studies are focusing on the role played by APP in the pathogenesis of Alzheimer's disease, sAPPα is reported to have numerous neuroprotective effects and it is being suggested as a candidate with possible therapeutic potential against Alzheimer's disease. However, the mechanisms through which sAPPα precisely works remain elusive. We have presented a comprehensive review of how sAPPα is regulating the neuroprotective effects in different biological models. Moreover, we have focused on the role of sAPPα during different developmental stages of the brain, neurogenic microenvironment in the brain and how this metabolite of APP is regulating the neurogenesis which is regarded as a compelling approach to ameliorate the impaired learning and memory deficits in dementia and diseases like Alzheimer's disease. sAPPα exerts beneficial physiological, biochemical and behavioral effects mitigating the detrimental effects of neurotoxic compounds. It has shown to increase the proliferation rate of numerous cell types and promised the synaptogenesis, neurite outgrowth, cell survival and cell adhesion. Taken together, we believe that further studies are warranted to investigate the exact mechanism of action so that sAPPα could be developed as a novel therapeutic target against neuronal deficits.

Rivastigmine modifies the α-secretase pathway and potentially early Alzheimer's disease

Rivastigmine (or Exelon) is a cholinesterase inhibitor, currently used as a symptomatic treatment for mild-to-moderate Alzheimer's disease (AD). Amyloid-β peptide (Aβ) generated from its precursor protein (APP) by β-secretase (or BACE1) and γ-secretase endoproteolysis. Alternative APP cleavage by α-secretase (a family of membrane-bound metalloproteases- Adamalysins) precludes the generation of toxic Aβ and yields a neuroprotective and neurotrophic secreted sAPPα fragment. Several signal transduction pathways, including protein kinase C and MAP kinase, stimulate α-secretase. We present data to suggest that rivastigmine, in addition to anticholinesterase activity, directs APP processing away from BACE1 and towards α-secretases. We treated rat neuronal PC12 cells and primary human brain (PHB) cultures with rivastigmine and the α-secretase inhibitor TAPI and assayed for levels of APP processing products and α-secretases. We subsequently treated 3×Tg (transgenic) mice with rivastigmine and harvested hippocampi to assay for levels of APP processing products. We also assayed postmortem human control, AD, and AD brains from subjects treated with rivastigmine for levels of APP metabolites. Rivastigmine dose-dependently promoted α-secretase activity by upregulating levels of ADAM-9, -10, and -17 α-secretases in PHB cultures. Co-treatment with TAPI eliminated rivastigmine-induced sAPPα elevation. Rivastigmine treatment elevated levels of sAPPα in 3×Tg mice. Consistent with these results, we also found elevated sAPPα in postmortem brain samples from AD patients treated with rivastigmine. Rivastigmine can modify the levels of several shedding proteins and directs APP processing toward the non-amyloidogenic pathway. This novel property of rivastigmine can be therapeutically exploited for disease-modifying intervention that goes beyond symptomatic treatment for AD.

O-GlcNAcylation as a Therapeutic Target for Alzheimer's Disease

Alzheimer's disease (AD) is the most common cause of dementia and the number of elderly patients suffering from AD has been steadily increasing. Despite worldwide efforts to cope with this disease, little progress has been achieved with regard to identification of effective therapeutics. Thus, active research focusing on identification of new therapeutic targets of AD is ongoing. Among the new targets, post-translational modifications which modify the properties of mature proteins have gained attention. O-GlcNAcylation, a type of PTM that attaches O-linked β-N-acetylglucosamine (O-GlcNAc) to a protein, is being sought as a new target to treat AD pathologies. O-GlcNAcylation has been known to modify the two important components of AD pathological hallmarks, amyloid precursor protein, and tau protein. In addition, elevating O-GlcNAcylation levels in AD animal models has been shown to be effective in alleviating AD-associated pathology. Although studies investigating the precise mechanism of reversal of AD pathologies by targeting O-GlcNAcylation are not yet complete, it is clearly important to examine O-GlcNAcylation regulation as a target of AD therapeutics. This review highlights the mechanisms of O-GlcNAcylation and its role as a potential therapeutic target under physiological and pathological AD conditions.

New Alzheimer's disease model mouse specialized for analyzing the function and toxicity of intraneuronal Amyloid β oligomers

Oligomers of intracellular amyloid β protein (Aβ) are strongly cytotoxic and play crucial roles in synaptic transmission and cognitive function in Alzheimer’s disease (AD). However, there is currently no AD model mouse in which to specifically analyze the function of Aβ oligomers only. We have now developed a novel AD model mouse, an Aβ-GFP transgenic mouse (Aβ-GFP Tg), that expresses the GFP-fused human Aβ_1-42 protein, which forms only Aβ oligomers within neurons throughout their life. The fusion proteins are expressed mainly in the hippocampal CA1-CA2 region and cerebral cortex, and are not secreted extracellularly. The Aβ-GFP Tg mice exhibit increased tau phosphorylation, altered spine morphology, decreased expressions of the GluN2B receptor and neuroligin in synaptic regions, attenuated hippocampal long-term potentiation, and impaired object recognition memory compared with non-Tg littermates. Interestingly, these dysfunctions have already appeared in 2–3-months-old animals. The Aβ-GFP fusion protein is bioactive and highly toxic, and induces the similar synaptic dysfunctions as the naturally generated Aβ oligomer derived from postmortem AD patient brains and synthetic Aβ oligomers. Thus, Aβ-GFP Tg mouse is a new tool specialized to analyze the function of Aβ oligomers in vivo and to find subtle changes in synapses in early symptoms of AD.

Functions of 'A disintegrin and metalloproteases (ADAMs)' in the mammalian nervous system

'A disintegrin and metalloproteases' (ADAMs) are a family of transmembrane proteins with diverse functions in multicellular organisms. About half of the ADAMs are active metalloproteases and cleave numerous cell surface proteins, including growth factors, receptors, cytokines and cell adhesion proteins. The other ADAMs have no catalytic activity and function as adhesion proteins or receptors. Some ADAMs are ubiquitously expressed, others are expressed tissue specifically. This review highlights functions of ADAMs in the mammalian nervous system, including their links to diseases. The non-proteolytic ADAM11, ADAM22 and ADAM23 have key functions in neural development, myelination and synaptic transmission and are linked to epilepsy. Among the proteolytic ADAMs, ADAM10 is the best characterized one due to its substrates Notch and amyloid precursor protein, where cleavage is required for nervous system development or linked to Alzheimer's disease (AD), respectively. Recent work demonstrates that ADAM10 has additional substrates and functions in the nervous system and its substrate selectivity may be regulated by tetraspanins. New roles for other proteolytic ADAMs in the nervous system are also emerging. For example, ADAM8 and ADAM17 are involved in neuroinflammation. ADAM17 additionally regulates neurite outgrowth and myelination and its activity is controlled by iRhoms. ADAM19 and ADAM21 function in regenerative processes upon neuronal injury. Several ADAMs, including ADAM9, ADAM10, ADAM15 and ADAM30, are potential drug targets for AD. Taken together, this review summarizes recent progress concerning substrates and functions of ADAMs in the nervous system and their use as drug targets for neurological and psychiatric diseases.

The amyloid precursor protein (APP) processing as a biological link between Alzheimer's disease and cancer

Aging is a risk factor for several illnesses, such as Alzheimer's Disease and various cancers. However, an inverse correlation between malignancies and Alzheimer's Disease has been suggested. This review addressed the potential role of non-amyloidogenic and amyloidogenic pathways of amyloid precursor protein processing as a relevant biochemical mechanism to clarify this association. Amyloidogenic and non-amyloidogenic pathways have been related to Alzheimer's Disease and certain malignancies, respectively. Several known molecules involved in APP processing, including its regulation and final products, were summarized. Among them some candidate mechanisms emerged, such as extracellular-regulated kinase (Erk) and protein kinase C (PKC). Therefore, the imbalance of APP processing may be involved with the negative correlation between cancer and Alzheimer Disease.

Ligustilide Ameliorates Memory Deficiency in APP/PS1 Transgenic Mice via Restoring Mitochondrial Dysfunction

Ligustilide, the main lipophilic component of Radix angelicae sinensis, has been shown to ameliorate cognitive dysfunction in a few Alzheimer's disease mouse models, but its mechanism is not fully understood. In this study, we employed 7-month-old APP/PS1 mice to explore whether LIG is able to protect against Alzheimer's disease progression. The Morris water maze and Y-maze test results showed that eight weeks of intragastric administration of LIG (10 mg/kg, 40 mg/kg) every day improved memory deficit in APP/PS1 mice. The thioflavin-S staining and Western blot results (Aβ_1-42 monomer/oligomer, APP, ADAM10, SAPPα, and PreP) showed that LIG reduced Aβ levels in the brain of APP/PS1 mice. Transmission electron microscopy analysis showed that LIG reduced the mitochondria number and increased the mitochondrial length in the hippocampal CA1 area of APP/PS1 mice. A reduced level of Drp1 (fission) and increased levels of Mfn1, Mfn2, and Opa1 (fusion) were found in APP/PS1 mice treated with LIG. An increased ATP level in the brain and increased activities of cytochrome c oxidase (CCO) and succinate dehydrogenase (SDH) in mitochondrion separated from the hippocampus and cortex revealed that LIG alleviated mitochondrial dysfunction. LIG exerts an antioxidation effect via reducing the levels of malondialdehyde (MDA) and reactive oxygen species (ROS) and increasing the activity of Mn-SOD in the brain. Elevated levels of PSD-95, synaptophysin, and synapsin 1 in both the hippocampus and cortex indicated that LIG provided synaptic protection. These findings show that treatment with LIG ameliorates mitochondrial dynamics and morphology issues, improves mitochondrial function, reduces Aβ levels in the brain, restores the synaptic structure, and ameliorates memory deficit in APP/PS1 mice. These results imply that LIG may serve as a potential antidementia drug.

AF710B, an M1/sigma-1 receptor agonist with long-lasting disease-modifying properties in a transgenic rat model of Alzheimer's disease

INTRODUCTION

AF710B (aka ANAVEX 3-71) is a novel selective allosteric M1 muscarinic and sigma-1 receptor agonist. In 3×Tg-AD mice, AF710B attenuates cognitive deficits and decreases Alzheimer-like hallmarks. We now report on the long-lasting disease-modifying properties of AF710B in McGill-R-Thy1-APP transgenic (Tg) rats.

METHODS

Chronic treatment with AF710B (10 μg/kg) was initiated in postplaque 13-month-old Tg rats. Drug or vehicle was administered orally daily for 4.5 months and interrupted 5 weeks before behavioral testing.

RESULTS

AF710B long-term treatment reverted the cognitive deficits associated with advanced Alzheimer-like amyloid neuropathology in Tg rats. These effects were accompanied by reductions in amyloid pathology and markers of neuroinflammation and increases in amyloid cerebrospinal fluid clearance and levels of a synaptic marker. Importantly, these effects were maintained following a 5-week interruption of the treatment.

DISCUSSION

With M1/sigma-1 activity and long-lasting disease-modifying properties at low dose, AF710B is a promising novel therapeutic agent for treating Alzheimer's disease.

Apolipoprotein E-mediated Modulation of ADAM10 in Alzheimer's Disease

BACKGROUND

The APOE4 allele is the strongest genetic risk factor for Alzheimer's disease (AD). It has been associated with an accumulation of amyloid-β (Aβ) in the brain, which is produced through the sequential cleavage of the amyloid-β precursor protein (AβPP) by β - and γ-secretases. Alternatively, AβPP is also cleaved by α -secretases such as A Disintegrin and Metalloproteinase Domain-containing Protein 10 (ADAM10).

OBJECTIVE

While several studies have investigated the impact of apoE on β- and γ-secretase, interactions between apoE and α-secretases have not been fully examined. We investigated the effect of each apoE isoform on ADAM10 in vitro and in human cortex samples.

METHOD

ADAM10 activity and kinetics was assessed in cell-free assays and the biological activity of ADAM10 further investigated in 7WCHO cells over-expressing wild type AβPP through ELISA. Finally, ADAM10 expression and activity was observed in the soluble fraction of both control and Alzheimer's Disease human cortex samples through ELISA.

RESULTS

In a cell free assay, ADAM10 activity was found to be significantly lower in apoE4 samples compared to apoE2. 7WCHO cells over expressing wild type AβPP exposed to apoE4 demonstrated reduced formation of sAβPPα compared to other apoE isoforms. We also identified APOE and AD dependent changes in ADAM10 activity and expression in the soluble brain fraction of human brain cortex.

CONCLUSION

Overall, our data demonstrates an apoE isoform-dependent effect on ADAM10 function and AβPP processing which may describe the elevated amyloid levels in the brains of AD subjects carrying the APOE4 allele.

The Role of ADAM10 in Alzheimer's Disease

As a member of the A Disintegrin And Metalloproteinase (ADAM) family, ADAM10 has been identified as the constitutive α-secretase in the process of amyloid-β protein precursor (AβPP) cleavage and plays a critical role in reducing the generation of the amyloid-β (Aβ) peptides. Recent studies have demonstrated its beneficial role in alleviating the pathologic impairment in Alzheimer's disease (AD) both in vitro and in vivo. However, the role of ADAM10 in AD and the underlying molecular mechanisms are still not well established. Increasing evidence indicates that ADAM10 not only reduces the generation of Aβ but may also affect the pathology of AD through potential mechanisms including reducing tau pathology, maintaining normal synaptic functions, and promoting hippocampal neurogenesis and the homeostasis of neuronal networks. Mechanistically, ADAM10 regulates these functions by interacting with postsynaptic substrates in brain, especially synaptic cell receptors and adhesion molecules. Furthermore, ADAM10 protein in platelets seems to be a promising biomarker for AD diagnosis. This review will summarize the role of ADAM10 in AD and highlight its functions besides its role as the α-secretase in AβPP cleavage. Meanwhile, we will discuss the therapeutic potential of ADAM10 in treating AD.

sAPPβ and sAPPα increase structural complexity and E/I input ratio in primary hippocampal neurons and alter Ca2+ homeostasis and CREB1-signaling

One major pathophysiological hallmark of Alzheimer's disease (AD) is senile plaques composed of amyloid β (Aβ). In the amyloidogenic pathway, cleavage of the amyloid precursor protein (APP) is shifted towards Aβ production and soluble APPβ (sAPPβ) levels. Aβ is known to impair synaptic function; however, much less is known about the physiological functions of sAPPβ. The neurotrophic properties of sAPPα, derived from the non-amyloidogenic pathway of APP cleavage, are well-established, whereas only a few, conflicting studies on sAPPβ exist. The intracellular pathways of sAPPβ are largely unknown. Since sAPPβ is generated alongside Aβ by β-secretase (BACE1) cleavage, we tested the hypothesis that sAPPβ effects differ from sAPPα effects as a neurotrophic factor. We therefore performed a head-to-head comparison of both mammalian recombinant peptides in developing primary hippocampal neurons (PHN). We found that sAPPα significantly increases axon length (p = 0.0002) and that both sAPPα and sAPPβ increase neurite number (p < 0.0001) of PHN at 7 days in culture (DIV7) but not at DIV4. Moreover, both sAPPα- and sAPPβ-treated neurons showed a higher neuritic complexity in Sholl analysis. The number of glutamatergic synapses (p < 0.0001), as well as layer thickness of postsynaptic densities (PSDs), were significantly increased, and GABAergic synapses decreased upon sAPP overexpression in PHN. Furthermore, we showed that sAPPα enhances ERK and CREB1 phosphorylation upon glutamate stimulation at DIV7, but not DIV4 or DIV14. These neurotrophic effects are further associated with increased glutamate sensitivity and CREB1-signaling. Finally, we found that sAPPα levels are significantly reduced in brain homogenates of AD patients compared to control subjects. Taken together, our data indicate critical stage-dependent roles of sAPPs in the developing glutamatergic system in vitro, which might help to understand deleterious consequences of altered APP shedding in AD patients, beyond Aβ pathophysiology.

Identification of disulfiram as a secretase-modulating compound with beneficial effects on Alzheimer's disease hallmarks

ADAM10 is a metalloproteinase acting on the amyloid precursor protein (APP) as an alpha-secretase in neurons. Its enzymatic activity results in secretion of a neuroprotective APP cleavage product (sAPP-alpha) and prevents formation of the amyloidogenic A-beta peptides, major hallmarks of Alzheimer’s disease (AD). Elevated ADAM10 levels appeared to contribute to attenuation of A-beta-plaque formation and learning and memory deficits in AD mouse models. Therefore, it has been assumed that ADAM10 might represent a valuable target in AD therapy. Here we screened a FDA-approved drug library and identified disulfiram as a novel ADAM10 gene expression enhancer. Disulfiram increased ADAM10 production as well as sAPP-alpha in SH-SY5Y human neuronal cells and additionally prevented A-beta aggregation in an in vitro assay in a dose-dependent fashion. In addition, acute disulfiram treatment of Alzheimer model mice induced ADAM10 expression in peripheral blood cells, reduced plaque-burden in the dentate gyrus and ameliorated behavioral deficits. Alcohol-dependent patients are subjected to disulfiram-treatment to discourage alcohol-consumption. In such patients, enhancement of ADAM10 by disulfiram-treatment was demonstrated in peripheral blood cells. Our data suggest that disulfiram could be repurposed as an ADAM10 enhancer and AD therapeutic. However, efficacy and safety has to be analyzed in Alzheimer patients in the future.

Regulation of ADAM10 by miR-140-5p and potential relevance for Alzheimer's disease

Recent reports in Alzheimer's disease (AD) research suggest that alterations in microRNA (miRNA) expression are associated with disease pathology. Our previous studies suggest that A Disintegrin and Metalloproteinase 10 (ADAM10) expression is important in AD and could be modulated by an extended regulatory region that includes the 3' untranslated region. In this study, we have investigated the role of trans-acting factors in ADAM10 gene regulation. Our study shows that miRNA-140-5p has enhanced expression in the AD postmortem brain hippocampus using high-throughput miRNA arrays and quantitative real-time polymerase chain reaction. Interestingly, we have also seen that miRNA-140-5p seed sequence is present on 3' untranslated region of both ADAM10 and its transcription factor SOX2. The specific interaction of miRNA-140-5p with both ADAM10 and SOX2 signifies high regulatory importance of this miRNA in controlling ADAM10 expression. Thus, this investigation unravels mechanisms underlying ADAM10 downregulation by miR-140-5p and suggests that dysfunctional regulation of ADAM10 expression is exacerbated by AD-related neurotoxic effects. These findings underscore the importance of understanding the impact of trans-acting factors in the modulation of AD pathophysiology.

The lipid raft-dwelling protein US9 can be manipulated to target APP compartmentalization, APP processing, and neurodegenerative disease pathogenesis

The trafficking behavior of the lipid raft-dwelling US9 protein from Herpes Simplex Virus strikingly overlaps with that of the amyloid precursor protein (APP). Both US9 and APP processing machinery rely on their ability to shuttle between endosomes and plasma membranes, as well as on their lateral accumulation in lipid rafts. Therefore, repurposing US9 to track/modify these molecular events represents a valid approach to investigate pathological states including Alzheimer's disease and HIV-associated neurocognitive disorders where APP misprocessing to amyloid beta formation has been observed. Accordingly, we investigated the cellular localization of US9-driven cargo in neurons and created a US9-driven functional assay based on the exogenous enzymatic activity of Tobacco Etch Virus Protease. Our results demonstrate that US9 can direct and control cleavage of recombinant proteins exposed on the luminal leaflet of transport vesicles. Furthermore, we confirmed that US9 is associated with lipid-rafts and can target functional enzymes to membrane microdomains where pathologic APP-processing is thought to occur. Overall, our results suggest strongly that US9 can serve as a molecular driver that targets functional cargos to the APP machinery and can be used as a tool to study the contribution of lipid rafts to neurodegenerative disease conditions where amyloidogenesis has been implicated.

ADAM10 as a therapeutic target for brain diseases: from developmental disorders to Alzheimer's disease

INTRODUCTION

In the central nervous system a disintegrin and metalloproteinase 10 (ADAM10) controls several functions such as neurodevelopment, synaptic plasticity and dendritic spine morphology thanks to its activity towards a high number of substrates, including the synaptic cell adhesion molecules as the Amyloid Precursor Protein, N-cadherin, Notch and Ephrins. In particular, ADAM10 plays a key role in the modulation of the molecular mechanisms responsible for dendritic spine formation, maturation and stabilization and in the regulation of the molecular organization of the glutamatergic synapse. Consequently, an alteration of ADAM10 activity is strictly correlated to the onset of different types of synaptopathies, ranging from neurodevelopmental disorders, i.e. autism spectrum disorders, to neurodegenerative diseases, i.e. Alzheimer's Disease. Areas covered: We describe the most recent discoveries in understanding of the role of ADAM10 activity at the glutamatergic excitatory synapse and its involvement in the onset of neurodevelopmental and neurodegenerative disorders. Expert opinion: A progress in the understanding of the molecular mechanisms driving ADAM10 activity at synapses and its alterations in brain disorders is the first step before designing a specific drug able to modulate ADAM10 activity.

Multifaceted Roles of Metzincins in CNS Physiology and Pathology: From Synaptic Plasticity and Cognition to Neurodegenerative Disorders

The extracellular matrix (ECM) and membrane proteolysis play a key role in structural and functional synaptic plasticity associated with development and learning. A growing body of evidence underscores the multifaceted role of members of the metzincin superfamily, including metalloproteinases (MMPs), A Disintegrin and Metalloproteinases (ADAMs), A Disintegrin and Metalloproteinase with Thrombospondin Motifs (ADAMTSs) and astacins in physiological and pathological processes in the central nervous system (CNS). The expression and activity of metzincins are strictly controlled at different levels (e.g., through the regulation of translation, limited activation in the extracellular space, the binding of endogenous inhibitors and interactions with other proteins). Thus, unsurprising is that the dysregulation of proteolytic activity, especially the greater expression and activation of metzincins, is associated with neurodegenerative disorders that are considered synaptopathies, especially Alzheimer's disease (AD). We review current knowledge of the functions of metzincins in the development of AD, mainly the proteolytic processing of amyloid precursor protein, the degradation of amyloid β (Aβ) peptide and several pathways for Aβ clearance across brain barriers (i.e., blood-brain barrier (BBB) and blood-cerebrospinal fluid barrier (BCSFB)) that contain specific receptors that mediate the uptake of Aβ peptide. Controlling the proteolytic activity of metzincins in Aβ-induced pathological changes in AD patients' brains may be a promising therapeutic strategy.

Hippocampal Proteomic Analysis Reveals Distinct Pathway Deregulation Profiles at Early and Late Stages in a Rat Model of Alzheimer's-Like Amyloid Pathology

The cerebral accumulation and cytotoxicity of amyloid beta (Aβ) is central to Alzheimer's pathogenesis. However, little is known about how the amyloid pathology affects the global expression of brain proteins at different disease stages. In order to identify genotype and time-dependent significant changes in protein expression, we employed quantitative proteomics analysis of hippocampal tissue from the McGill-R-Thy1-APP rat model of Alzheimer-like amyloid pathology. McGill transgenic rats were compared to wild-type rats at early and late pathology stages, i.e., when intraneuronal Aβ amyloid burden is conspicuous and when extracellular amyloid plaques are abundant with more pronounced cognitive deficits. After correction for multiple testing, the expression levels of 64 proteins were found to be considerably different in transgenic versus wild-type rats at the pre-plaque stage (3 months), and 86 proteins in the post-plaque group (12 months), with only 9 differentially regulated proteins common to the 2 time-points. This minimal overlap supports the hypothesis that different molecular pathways are affected in the hippocampus at early and late stages of the amyloid pathology throughout its continuum. At early stages, disturbances in pathways related to cellular responses to stress, protein homeostasis, and neuronal structure are predominant, while disturbances in metabolic energy generation dominate at later stages. These results shed new light on the molecular pathways affected by the early accumulation of Aβ and how the evolving amyloid pathology impacts other complex metabolic pathways.

Monocular denervation of visual nuclei modulates APP processing and sAPPα production: A possible role on neural plasticity

Amyloid precursor protein (APP) is essential to physiological processes such as synapse formation and neural plasticity. Sequential proteolysis of APP by beta- and gamma-secretases generates amyloid-beta peptide (Aβ), the main component of senile plaques in Alzheimer Disease. Alternative APP cleavage by alpha-secretase occurs within Aβ domain, releasing soluble α-APP (sAPPα), a neurotrophic fragment. Among other functions, sAPPα is important to synaptogenesis, neural survival and axonal growth. APP and sAPPα levels are increased in models of neuroplasticity, which suggests an important role for APP and its metabolites, especially sAPPα, in the rearranging brain. In this work we analyzed the effects of monocular enucleation (ME), a classical model of lesion-induced plasticity, upon APP content, processing and also in secretases levels. Besides, we addressed whether α-secretase activity is crucial for retinotectal remodeling after ME. Our results showed that ME induced a transient reduction in total APP content. We also detected an increase in α-secretase expression and in sAPP production concomitant with a reduction in Aβ and β-secretase contents. These data suggest that ME facilitates APP processing by the non-amyloidogenic pathway, increasing sAPPα levels. Indeed, the pharmacological inhibition of α-secretase activity reduced the axonal sprouting of ipsilateral retinocollicular projections from the intact eye after ME, suggesting that sAPPα is necessary for synaptic structural rearrangement. Understanding how APP processing is regulated under lesion conditions may provide new insights into APP physiological role on neural plasticity.

Therapeutic Potential of Secreted Amyloid Precursor Protein APPsα

Cleavage of the amyloid precursor protein (APP) by α-secretase generates an extracellularly released fragment termed secreted APP-alpha (APPsα). Not only is this process of interest due to the cleavage of APP within the amyloid-beta sequence, but APPsα itself has many physiological properties that suggest its great potential as a therapeutic target. For example, APPsα is neurotrophic, neuroprotective, neurogenic, a stimulator of protein synthesis and gene expression, and enhances long-term potentiation (LTP) and memory. While most early studies have been conducted in vitro, effectiveness in animal models is now being confirmed. These studies have revealed that either upregulating α-secretase activity, acutely administering APPsα or chronic delivery of APPsα via a gene therapy approach can effectively treat mouse models of Alzheimer's disease (AD) and other disorders such as traumatic head injury. Together these findings suggest the need for intensifying research efforts to harness the therapeutic potential of this multifunctional protein.

APP as a Protective Factor in Acute Neuronal Insults

Despite its key role in the molecular pathology of Alzheimer’s disease (AD), the physiological function of amyloid precursor protein (APP) is unknown. Increasing evidence, however, points towards a neuroprotective role of this membrane protein in situations of metabolic stress. A key observation is the up-regulation of APP following acute (stroke, cardiac arrest) or chronic (cerebrovascular disease) hypoxic-ischemic conditions. While this mechanism may increase the risk or severity of AD, APP by itself or its soluble extracellular fragment APPsα can promote neuronal survival. Indeed, different animal models of acute hypoxia-ischemia, traumatic brain injury (TBI) and excitotoxicity have revealed protective effects of APP or APPsα. The underlying mechanisms involve APP-mediated regulation of calcium homeostasis via NMDA receptors (NMDAR), voltage-gated calcium channels (VGCC) or internal calcium stores. In addition, APP affects the expression of survival- or apoptosis-related genes as well as neurotrophic factors. In this review, we summarize the current understanding of the neuroprotective role of APP and APPsα and possible implications for future research and new therapeutic strategies.

Structure and Synaptic Function of Metal Binding to the Amyloid Precursor Protein and its Proteolytic Fragments

Alzheimer’s disease (AD) is ultimately linked to the amyloid precursor protein (APP). However, current research reveals an important synaptic function of APP and APP-like proteins (APLP1 and 2). In this context various neurotrophic and neuroprotective functions have been reported for the APP proteolytic fragments sAPPα, sAPPβ and the monomeric amyloid-beta peptide (Aβ). APP is a metalloprotein and binds copper and zinc ions. Synaptic activity correlates with a release of these ions into the synaptic cleft and dysregulation of their homeostasis is linked to different neurodegenerative diseases. Metal binding to APP or its fragments affects its structure and its proteolytic cleavage and therefore its physiological function at the synapse. Here, we summarize the current data supporting this hypothesis and provide a model of how these different mechanisms might be intertwined with each other.

Amyloid precursor protein maintains constitutive and adaptive plasticity of dendritic spines in adult brain by regulating D-serine homeostasis

Dynamic synapses facilitate activity-dependent remodeling of neural circuits, thereby providing the structural substrate for adaptive behaviors. However, the mechanisms governing dynamic synapses in adult brain are still largely unknown. Here, we demonstrate that in the cortex of adult amyloid precursor protein knockout (APP-KO) mice, spine formation and elimination were both reduced while overall spine density remained unaltered. When housed under environmental enrichment, APP-KO mice failed to respond with an increase in spine density. Spine morphology was also altered in the absence of APP The underlying mechanism of these spine abnormalities in APP-KO mice was ascribed to an impairment in D-serine homeostasis. Extracellular D-serine concentration was significantly reduced in APP-KO mice, coupled with an increase of total D-serine. Strikingly, chronic treatment with exogenous D-serine normalized D-serine homeostasis and restored the deficits of spine dynamics, adaptive plasticity, and morphology in APP-KO mice. The cognitive deficit observed in APP-KO mice was also rescued by D-serine treatment. These data suggest that APP regulates homeostasis of D-serine, thereby maintaining the constitutive and adaptive plasticity of dendritic spines in adult brain.

Genetical Genomics of Behavior: A Novel Chicken Genomic Model for Anxiety Behavior

The identification of genetic variants responsible for behavioral variation is an enduring goal in biology, with wide-scale ramifications, ranging from medical research to evolutionary theory on personality syndromes. Here, we use for the first time a large-scale genetical genomics analysis in the brains of chickens to identify genes affecting anxiety as measured by an open field test. We combine quantitative trait locus (QTL) analysis in 572 individuals and expression QTL (eQTL) analysis in 129 individuals from an advanced intercross between domestic chickens and Red Junglefowl. We identify 10 putative quantitative trait genes affecting anxiety behavior. These genes were tested for an association in the mouse Heterogeneous Stock anxiety (open field) data set and human GWAS data sets for bipolar disorder, major depressive disorder, and schizophrenia. Although comparisons between species are complex, associations were observed for four of the candidate genes in mice and three of the candidate genes in humans. Using a multimodel approach we have therefore identified a number of putative quantitative trait genes affecting anxiety behavior, principally in chickens but also with some potentially translational effects as well. This study demonstrates that chickens are an excellent model organism for the genetic dissection of behavior.

Cinnamon Converts Poor Learning Mice to Good Learners: Implications for Memory Improvement

This study underlines the importance of cinnamon, a commonly used natural spice and flavoring material, and its metabolite sodium benzoate (NaB) in converting poor learning mice to good learning ones. NaB, but not sodium formate, was found to upregulate plasticity-related molecules, stimulate NMDA- and AMPA-sensitive calcium influx and increase of spine density in cultured hippocampal neurons. NaB induced the activation of CREB in hippocampal neurons via protein kinase A (PKA), which was responsible for the upregulation of plasticity-related molecules. Finally, spatial memory consolidation-induced activation of CREB and expression of different plasticity-related molecules were less in the hippocampus of poor learning mice as compared to good learning ones. However, oral treatment of cinnamon and NaB increased spatial memory consolidation-induced activation of CREB and expression of plasticity-related molecules in the hippocampus of poor-learning mice and converted poor learners into good learners. These results describe a novel property of cinnamon in switching poor learners to good learners via stimulating hippocampal plasticity.

Current pharmacotherapy and putative disease-modifying therapy for Alzheimer's disease

Alzheimer's disease (AD) is an age-related neurodegenerative disease of the central nervous system correlated with the progressive loss of cognition and memory. β-Amyloid plaques, neurofibrillary tangles and the deficiency in cholinergic neurotransmission constitute the major hallmarks of the AD. Two major hypotheses have been implicated in the pathogenesis of AD namely the cholinergic hypothesis which ascribed the clinical features of dementia to the deficit cholinergic neurotransmission and the amyloid cascade hypothesis which emphasized on the deposition of insoluble peptides formed due to the faulty cleavage of the amyloid precursor protein. Current pharmacotherapy includes mainly the acetylcholinesterase inhibitors and N-methyl-D-aspartate receptor agonist which offer symptomatic therapy and does not address the underlying cause of the disease. The disease-modifying therapy has garnered a lot of research interest for the development of effective pharmacotherapy for AD. β and γ-Secretase constitute attractive targets that are focussed in the disease-modifying approach. Potentiation of α-secretase also seems to be a promising approach towards the development of an effective anti-Alzheimer therapy. Additionally, the ameliorative agents that prevent aggregation of amyloid peptide and also the ones that modulate inflammation and oxidative damage associated with the disease are focussed upon. Development in the area of the vaccines is in progress to combat the characteristic hallmarks of the disease. Use of cholesterol-lowering agents also is a fruitful strategy for the alleviation of the disease as a close association between the cholesterol and AD has been cited. The present review underlines the major therapeutic strategies for AD with focus on the new developments that are on their way to amend the current therapeutic scenario of the disease.

The APP Intracellular Domain Is Required for Normal Synaptic Morphology, Synaptic Plasticity, and Hippocampus-Dependent Behavior

The amyloid precursor protein family (APP/APLPs) has essential roles for neuromuscular synapse development and for the formation and plasticity of synapses within the CNS. Despite this, it has remained unclear whether APP mediates its functions primarily as a cell surface adhesion and signaling molecule or via its numerous proteolytic cleavage products. To address these questions, we followed a genetic approach and used APPΔCT15 knockin mice lacking the last 15 amino acids of APP, including the highly conserved YENPTY protein interaction motif. To circumvent functional compensation by the closely related APLP2, these mice were bred to an APLP2-KO background to generate APPΔCT15-DM double mutants. These APPΔCT15-DM mice were partially viable and displayed defects in neuromuscular synapse morphology and function with impairments in the ability to sustain transmitter release that resulted in muscular weakness. In the CNS, we demonstrate pronounced synaptic deficits including impairments in LTP that were associated with deficits in spatial learning and memory. Thus, the APP-CT15 domain provides essential physiological functions, likely via recruitment of specific interactors. Together with the well-established role of APPsα for synaptic plasticity, this shows that multiple domains of APP, including the conserved C-terminus, mediate signals required for normal PNS and CNS physiology. In addition, we demonstrate that lack of the APP-CT15 domain strongly impairs Aβ generation in vivo, establishing the APP C-terminus as a target for Aβ-lowering strategies.

SIGNIFICANCE STATEMENT

Synaptic dysfunction and cognitive decline are early hallmark features of Alzheimer's disease. Thus, it is essential to elucidate the in vivo function(s) of APP at the synapse. At present, it is unknown whether APP family proteins function as cell surface receptors, or mainly via shedding of their secreted ectodomains, such as neurotrophic APPsα. Here, to dissect APP functional domains, we used APP mutant mice lacking the last 15 amino acids that were crossed onto an APLP2-KO background. These APPΔCT15-DM mice showed defects in neuromuscular morphology and function. Synaptic deficits in the CNS included impairments of synaptic plasticity, spatial learning, and memory. Collectively, this indicates that multiple APP domains, including the C-terminus, are required for normal nervous system function.

The Neuroprotective Properties of the Amyloid Precursor Protein Following Traumatic Brain Injury

Despite the significant health and economic burden that traumatic brain injury (TBI) places on society, the development of successful therapeutic agents have to date not translated into efficacious therapies in human clinical trials. Injury to the brain is ongoing after TBI, through a complex cascade of primary and secondary injury events, providing a valuable window of opportunity to help limit and prevent some of the severe consequences with a timely treatment. Of note, it has been suggested that novel treatments for TBI should be multifactorial in nature, mimicking the body's own endogenous repair response. Whilst research has historically focused on the role of the amyloid precursor protein (APP) in the pathogenesis of Alzheimer's disease, recent advances in trauma research have demonstrated that APP offers considerable neuroprotective properties following TBI, suggesting that APP is an ideal therapeutic candidate. Its acute upregulation following TBI has been shown to serve a beneficial role following trauma and has lead to significant advances in understanding the neuroprotective and neurotrophic functions of APP and its metabolites. Research has focused predominantly on the APP derivative sAPPα, which has consistently demonstrated neuroprotective and neurotrophic functions both in vitro and in vivo following various traumatic insults. Its neuroprotective activity has been narrowed down to a 15 amino acid sequence, and this region is linked to both heparan binding and growth-factor-like properties. It has been proposed that APP binds to heparan sulfate proteoglycans to exert its neuroprotective action. APP presents us with a novel therapeutic compound that could overcome many of the challenges that have stalled development of efficacious TBI treatments previously.

Viral gene transfer of APPsα rescues synaptic failure in an Alzheimer's disease mouse model

Alzheimer's disease (AD) is characterized by synaptic failure, dendritic and axonal atrophy, neuronal death and progressive loss of cognitive functions. It is commonly assumed that these deficits arise due to β-amyloid accumulation and plaque deposition. However, increasing evidence indicates that loss of physiological APP functions mediated predominantly by neurotrophic APPsα produced in the non-amyloidogenic α-secretase pathway may contribute to AD pathogenesis. Upregulation of APPsα production via induction of α-secretase might, however, be problematic as this may also affect substrates implicated in tumorigenesis. Here, we used a gene therapy approach to directly overexpress APPsα in the brain using AAV-mediated gene transfer and explored its potential to rescue structural, electrophysiological and behavioral deficits in APP/PS1∆E9 AD model mice. Sustained APPsα overexpression in aged mice with already preexisting pathology and amyloidosis restored synaptic plasticity and partially rescued spine density deficits. Importantly, AAV-APPsα treatment also resulted in a functional rescue of spatial reference memory in the Morris water maze. Moreover, we demonstrate a significant reduction of soluble Aβ species and plaque load. In addition, APPsα induced the recruitment of microglia with a ramified morphology into the vicinity of plaques and upregulated IDE and TREM2 expression suggesting enhanced plaque clearance. Collectively, these data indicate that APPsα can mitigate synaptic and cognitive deficits, despite established pathology. Increasing APPsα may therefore be of therapeutic relevance for AD.

[Signaling molecules in the brain and epigenetic factors in neurodegenerative and mental disorders]

The literature on a role of signaling molecules in the organization of memory and cognitive functions is analyzed basing on mechanisms of memory physiology determined by a complex of biochemical processes initiated by the transmission of the signal to the synapse and completed by the synthesis of functionally significant molecules in the neuronal genetic apparatus. The center of these processes is a coordinated system of signal transduction, transcription, epigenetic and neurotrophic molecules. The dissonance of signal mechanisms is a prime cause of memory impairment and cognitive dysfunction as social maladaptation factors. The results of experimental and clinical studies of a role of the multilevel signaling system in age-related, neurodegenerative (Alzheimer’s disease) and mental (depression) disorders are discussed. At the same time, signaling molecules may be considered as particular targets for new therapeutic approaches.

The alpha secretase ADAM10: A metalloprotease with multiple functions in the brain

Proteins belonging to the 'A Disintegrin And Metalloproteinase' (ADAM) family are membrane-anchored proteases that are able to cleave the extracellular domains of several membrane-bound proteins in a process known as 'ectodomain shedding'. In the central nervous system, ADAM10 has attracted the most attention, since it was described as the amyloid precursor protein α-secretase over ten years ago. Despite the excitement over the potential of ADAM10 as a novel drug target in Alzheimer disease, the physiological functions of ADAM10 in the brain are not yet well understood. This is largely because of the embryonic lethality of ADAM10-deficient mice, which results from the loss of cleavage and signaling of the Notch receptor, another ADAM10 substrate. However, the recent generation of conditional ADAM10-deficient mice and the identification of further ADAM10 substrates in the brain has revealed surprisingly numerous and fundamental functions of ADAM10 in the development of the embryonic brain and also in the homeostasis of adult neuronal networks. Mechanistically, ADAM10 controls these functions by utilizing unique postsynaptic substrates in the central nervous system, in particular synaptic cell adhesion molecules, such as neuroligin-1, N-cadherin, NCAM, Ephrin A2 and A5. Consequently, a dysregulation of ADAM10 activity is linked to psychiatric and neurological diseases, such as epilepsy, fragile X syndrome and Huntington disease. This review highlights the recent progress in understanding the substrates and function as well as the regulation and cell biology of ADAM10 in the central nervous system and discusses the value of ADAM10 as a drug target in brain diseases.

Double-Edged Roles of Nitric Oxide Signaling on APP Processing and Amyloid-β Production In Vitro: Preliminary Evidence from Sodium Nitroprusside

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that is thought to be caused in part by the age-related accumulation of amyloid-β (Aβ) in the brain. Recent findings have revealed that nitric oxide (NO) modulates the processing of amyloid-β precursor protein (APP) and alters Aβ production; however, the previously presented data are contradictory and the underlying molecular mechanisms are still incomplete. Here, using human SH-SY5Y neuroblastoma cells stably transfected with wild-type APPwt695, we found that NO, derived from NO donor sodium nitroprusside (SNP), bi-directionally modulates APP processing in vitro. The data from ELISA and Western blot (WB) tests indicated that SNP at lower concentrations (0.01 and 0.1 μM) inhibits BACE1 expression, thus consequently suppresses APP β-cleavage and decreases Aβ production. In contrast, SNP at higher concentrations (10 and 20 μM) biases the APP processing toward the amyloidogenic pathway as evidenced by an increased BACE1 but a decreased ADAM10 expression, together with an elevated Aβ secretion. This bi-directional modulating activity of SNP on APP processing was completely blocked by specific NO scavenger c-PTIO, indicating NO-dependent mechanisms. Moreover, the anti-amyloidogenic activity of SNP is sGC/cGMP/PKG-dependent as evidenced by its reversal by sGC/PKG inhibitions, whereas the amyloidogenic activity of SNP is peroxynitrite-related and can be reversed by peroxynitrite scavenger uric acid. In summary, these present findings predict a double-edged role of NO in APP processing in vitro. Low (physiological) levels of NO inhibit the amyloidogenic processing of APP, whereas extra-high (pathological) concentrations of NO favor the amyloidogenic pathway of APP processing. This preliminary study may provide further evidence to clarify the molecular roles of NO and NO-related signaling in AD and supply potential molecular targets for AD treatment.

Activation of TRPML1 clears intraneuronal Aβ in preclinical models of HIV infection

Antiretroviral therapy extends the lifespan of human immunodeficiency virus (HIV)-infected patients, but many survivors develop premature impairments in cognition. These residual cognitive impairments may involve aberrant deposition of amyloid β-peptides (Aβ). By unknown mechanisms, Aβ accumulates in the lysosomal and autophagic compartments of neurons in the HIV-infected brain. Here we identify the molecular events evoked by the HIV coat protein gp120 that facilitate the intraneuronal accumulation of Aβ. We created a triple transgenic gp120/APP/PS1 mouse that recapitulates intraneuronal deposition of Aβ in a manner reminiscent of the HIV-infected brain. In cultured neurons, we found that the HIV coat protein gp120 increased the transcriptional expression of BACE1 through repression of PPARγ, and increased APP expression by promoting interaction of the translation-activating RBP heterogeneous nuclear ribonucleoprotein C with APP mRNA. APP and BACE1 were colocalized into stabilized membrane microdomains, where the β-cleavage of APP and Aβ formation were enhanced. Aβ-peptides became localized to lysosomes that were engorged with sphingomyelin and calcium. Stimulating calcium efflux from lysosomes with a TRPM1 agonist promoted calcium efflux, luminal acidification, and cleared both sphingomyelin and Aβ from lysosomes. These findings suggest that therapeutics targeted to reduce lysosomal pH in neurodegenerative conditions may protect neurons by facilitating the clearance of accumulated sphingolipids and Aβ-peptides.

Abnormalities in the zinc-metalloprotease-BDNF axis may contribute to megalencephaly and cortical hyperconnectivity in young autism spectrum disorder patients

Whereas aberrant brain connectivity is likely the core pathology of autism-spectrum disorder (ASD), studies do not agree as to whether hypo- or hyper-connectivity is the main underlying problem. Recent functional imaging studies have shown that, in most young ASD patients, cerebral cortical regions appear hyperconnected, and cortical thickness/brain size is increased. Collectively, these findings indicate that developing ASD brains may exist in an altered neurotrophic milieu. Consistently, some ASD patients, as well as some animal models of ASD, show increased levels of brain-derived neurotrophic factor (BDNF). However, how BDNF is upregulated in ASD is unknown. To address this question, we propose the novel hypothesis that a putative zinc-metalloprotease-BDNF (ZMB) axis in the forebrain plays a pivotal role in the development of hyperconnectivity and megalencephaly in ASD. We have previously demonstrated that extracellular zinc at micromolar concentrations can rapidly increase BDNF levels and phosphorylate the receptor tyrosine kinase TrkB via the activation of metalloproteases. The role of metalloproteases in ASD is still uncertain, but in fragile X syndrome, a monogenic disease with an autistic phenotype, the levels of MMP are increased. Early exposure to lipopolysaccharides (LPS) and other MMP activators such as organic mercurials also have been implicated in ASD pathogenesis. The resultant increases in BDNF levels at synapses, especially those involved in the zinc-containing, associative glutamatergic system may produce abnormal brain circuit development. Various genetic mutations that lead to ASD are also known to affect BDNF signaling: some down-regulate, and others up-regulate it. We hypothesize that, although both up- and down-regulation of BDNF may induce autism symptoms, only BDNF up-regulation is associated with the hyperconnectivity and large brain size observed in most young idiopathic ASD patients. To test this hypothesis, we propose to examine the ZMB axis in animal models of ASD. Synaptic zinc can be examined by fluorescence zinc staining. MMP activation can be measured by in situ zymography and Western blot analysis. Finally, regional levels of BDNF can be measured. Validating this hypothesis may shed light on the central pathogenic mechanism of ASD and aid in the identification of useful biomarkers and the development of preventive/therapeutic strategies.

Amyloid precursor protein and neural development

Interest in the amyloid precursor protein (APP) has increased in recent years due to its involvement in Alzheimer's disease. Since its molecular cloning, significant genetic and biochemical work has focused on the role of APP in the pathogenesis of this disease. Thus far, however, these studies have failed to deliver successful therapies. This suggests that understanding the basic biology of APP and its physiological role during development might be a crucial missing link for a better comprehension of Alzheimer's disease. Here, we present an overview of some of the key studies performed in various model organisms that have revealed roles for APP at different stages of neuronal development.

Enhancement of morphological plasticity in hippocampal neurons by a physically modified saline via phosphatidylinositol-3 kinase

Increase of the density of dendritic spines and enhancement of synaptic transmission through ionotropic glutamate receptors are important events, leading to synaptic plasticity and eventually hippocampus-dependent spatial learning and memory formation. Here we have undertaken an innovative approach to upregulate hippocampal plasticity. RNS60 is a 0.9% saline solution containing charge-stabilized nanobubbles that are generated by subjecting normal saline to Taylor-Couette-Poiseuille (TCP) flow under elevated oxygen pressure. RNS60, but not NS (normal saline), PNS60 (saline containing a comparable level of oxygen without the TCP modification), or RNS10.3 (TCP-modified normal saline without excess oxygen), stimulated morphological plasticity and synaptic transmission via NMDA- and AMPA-sensitive calcium influx in cultured mouse hippocampal neurons. Using mRNA-based targeted gene array, real-time PCR, immunoblot, and immunofluorescence analyses, we further demonstrate that RNS60 stimulated the expression of many plasticity-associated genes in cultured hippocampal neurons. Activation of type IA, but not type IB, phosphatidylinositol-3 (PI-3) kinase by RNS60 together with abrogation of RNS60-mediated upregulation of plasticity-related proteins (NR2A and GluR1) and increase in spine density, neuronal size, and calcium influx by LY294002, a specific inhibitor of PI-3 kinase, suggest that RNS60 upregulates hippocampal plasticity via activation of PI-3 kinase. Finally, in the 5XFAD transgenic model of Alzheimer's disease (AD), RNS60 treatment upregulated expression of plasticity-related proteins PSD95 and NR2A and increased AMPA- and NMDA-dependent hippocampal calcium influx. These results describe a novel property of RNS60 in stimulating hippocampal plasticity, which may help AD and other dementias.