Treadmill exercise decreases amyloid-β burden possibly via activation of SIRT-1 signaling in a mouse model of Alzheimer's disease

Accumulation of amyloid-β (Aβ) correlates significantly with progressive cognitive deficits, a main symptom of Alzheimer's disease (AD). Although treadmill exercise reduces Aβ levels, the molecular mechanisms underlying the effects are not fully understood. We hypothesize that treadmill exercise decreases Aβ production and alleviates cognitive deficits by activating the non-amyloidogenic pathway via SIRT-1 signaling. Treadmill exercise improved cognitive deficits and alleviated neurotoxicity. Most importantly, treadmill exercise increased SIRT-1 level, which subsequently resulted in increased ADAM-10 level by down-regulation of ROCK-1 and upregulation of RARβ, ultimately facilitating the non-amyloidogenic pathway. Treadmill exercise-induced activation in SIRT-1 level also elevated PGC-1α level and reduced BACE-1 and C-99 level, resulting in inhibition of the amyloidogenic pathway. Treadmill exercise may thus inhibit Aβ production via upregulation of SIRT-1, which biases amyloid precursor protein processing toward the non-amyloidogenic pathway. This study provides novel and valuable insight into the molecular mechanisms possibly by which treadmill exercise reduces Aβ production.

Increase of α-Secretase ADAM10 in Platelets Along Cognitively Healthy Aging

ADAM10 is one of the key players in ectodomain-shedding of the amyloid-β protein precursor (AβPP). Previous research with postmortem tissue has shown reduced expression and activity of ADAM10 within the central nervous system (CNS) of Alzheimer's disease (AD) patients. Determination of cerebral ADAM10 in living humans is hampered by its transmembrane property; only the physiological AβPP cleavage product generated by ADAM10, sAβPPα, can be assessed in cerebrospinal fluid. Establishment of surrogate markers in easily accessible material therefore is crucial. It has been demonstrated that ADAM10 is expressed in platelets and that platelet amount is decreased in AD patients. Just recently it has been shown that platelet ADAM10 and cognitive performance of AD patients positively correlate. In contrast to AD patients, to our knowledge almost no information has been published regarding ADAM10 expression during normal aging. We investigated ADAM10 amount and activity in platelets of cognitively healthy individuals from three different age groups ranging from 22-85 years. Interestingly, we observed an age-dependent increase in ADAM10 levels and activity in platelets.

Oxytocin, a main breastfeeding hormone, prevents hypertension acquired in utero: A therapeutics preview

Hypertension is a major risk factor for ischemic heart disease and stroke, leading causes of morbidity and death worldwide. Intrauterine growth restriction (IUGR), caused by an excess of glucocorticoid exposure to the fetus, produces an imbalance in oxidative stress altering many biochemical and epigenetic gene transcription processes exposing the fetus and neonate to the 'thrifty' phenotype and pervasive polymorphisms appearance damaging health, cognitive, and behavioral processes in later life. OT is a major regulator of oxidative stress radicals that plays a major role in neonatal maturation of the central nervous system and many peripheral tissues expressing oxytocin/oxytocin-receptor (OT/OTR) system in the early postnatal period. OT and OTR are damaged by IUGR and early stress. This review highlights the fact that hypertension is likely to be a legacy of preterm birth due to IUGR and failure to meet nutritional needs in early infancy when fed formula instead of breastfeeding or human milk.

A Greek Tragedy: The Growing Complexity of Alzheimer Amyloid Precursor Protein Proteolysis

Proteolysis of the amyloid precursor protein (APP) liberates various fragments including the proposed initiator of Alzheimer disease-associated dysfunctions, amyloid-β. However, recent evidence suggests that the accepted view of APP proteolysis by the canonical α-, β-, and γ-secretases is simplistic, with the discovery of a number of novel APP secretases (including δ- and η-secretases, alternative β-secretases) and additional metabolites, some of which may also cause synaptic dysfunction. Furthermore, various proteins have been identified that interact with APP and modulate its cleavage by the secretases. Here, we give an overview of the increasingly complex picture of APP proteolysis.

A Systems View of the Differences between APOE ε4 Carriers and Non-carriers in Alzheimer's Disease

APOE ε4 is the strongest genetic risk factor for late-onset Alzheimer's disease (AD) and accounts for 50-65% of late-onset AD. Late-onset AD patients carrying or not carrying APOE ε4 manifest many clinico-pathological distinctions. Thus, we applied a weighted gene co-expression network analysis to identify specific co-expression modules in AD based on APOE ε4 stratification. Two specific modules were identified in AD APOE ε4 carriers and one module was identified in non-carriers. The hub genes of one module of AD APOE ε4 carriers were ISOC1, ENO3, GDF10, GNB3, XPO4, ACLY and MATN2. The other module of AD APOE ε4 carriers consisted of 10 hub genes including ANO3, ARPP21, HPCA, RASD2, PCP4 and ADORA2A. The module of AD APOE ε4 non-carriers consisted of 16 hub genes including DUSP5, TNFRSF18, ZNF331, DNAJB5 and RIN1. The module of AD APOE ε4 carriers including ISOC1 and ENO3 and the module of non-carriers contained the most highly connected hub gene clusters. mRNA expression of the genes in the cluster of the ISOC1 and ENO3 module of carriers was shown to be correlated in a time-dependent manner under APOE ε4 treatment but not under APOE ε3 treatment. In contrast, mRNA expression of the genes in the cluster of non-carriers' module was correlated under APOE ε3 treatment but not under APOE ε4 treatment. The modules of carriers demonstrated genetic bases and were mainly enriched in hereditary disorders and neurological diseases, energy metabolism-associated signaling and G protein-coupled receptor-associated pathways. The module including ISOC1 and ENO3 harbored two conserved promoter motifs in its hub gene cluster that could be regulated by common transcription factors and miRNAs. The module of non-carriers was mainly enriched in neurological, immunological and cardiovascular diseases and was correlated with Parkinson's disease. These data demonstrate that AD in APOE ε4 carriers involves more genetic factors and particular biological processes, whereas AD in APOE ε4 non-carriers shares more common pathways with other types of diseases. The study reveals differential genetic bases and pathogenic and pathological processes between carriers and non-carriers, providing new insight into the mechanisms of the differences between APOE ε4 carriers and non-carriers in AD.

Regulation of the α-secretase ADAM10 at transcriptional, translational and post-translational levels

A tremendous gain of interest in the biology of ADAM10 emerged during the past 15 years when it has first been shown that this protease was able to target the α-site of the β-amyloid precursor protein (βAPP) and later confirmed as the main physiological α-secretase activity. However, beside its well-established implication in the so-called non-amyloidogenic processing of βAPP and its probable protective role against Alzheimer's disease (AD), this metalloprotease also cleaves many other substrates, thereby being implicated in various physiological as well as pathological processes such as cancer and inflammation. Thus, in view of possible effective therapeutic interventions, a full comprehension of how ADAM10 is up and down regulated is required. This review discusses our current knowledge concerning the implication of this enzyme in AD as well as its more recently established roles in other brain disorders and provides a detailed up-date on its various transcriptional, translational and post-translational modulations.

The Vitamin A Derivative All-Trans Retinoic Acid Repairs Amyloid-β-Induced Double-Strand Breaks in Neural Cells and in the Murine Neocortex

The amyloid-β peptide or Aβ is the key player in the amyloid-cascade hypothesis of Alzheimer's disease. Aβ appears to trigger cell death but also production of double-strand breaks (DSBs) in aging and Alzheimer's disease. All-trans retinoic acid (RA), a derivative of vitamin A, was already known for its neuroprotective effects against the amyloid cascade. It diminishes, for instance, the production of Aβ peptides and their oligomerisation. In the present work we investigated the possible implication of RA receptor (RAR) in repair of Aβ-induced DSBs. We demonstrated that RA, as well as RAR agonist Am80, but not AGN 193109 antagonist, repair Aβ-induced DSBs in SH-SY5Y cells and an astrocytic cell line as well as in the murine cortical tissue of young and aged mice. The nonhomologous end joining pathway and the Ataxia Telangiectasia Mutated kinase were shown to be involved in RA-mediated DSBs repair in the SH-SY5Y cells. Our data suggest that RA, besides increasing cell viability in the cortex of young and even of aged mice, might also result in targeted DNA repair of genes important for cell or synaptic maintenance. This phenomenon would remain functional up to a point when Aβ increase and RA decrease probably lead to a pathological state.

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.

Extract of Caragana sinica as a potential therapeutic option for increasing alpha-secretase gene expression

BACKGROUND

Alzheimer's disease represents one of the main neurological disorders in the aging population. Treatment options so far are only of symptomatic nature and efforts in developing disease modifying drugs by targeting amyloid beta peptide-generating enzymes remain fruitless in the majority of human studies. During the last years, an alternative approach emerged to target the physiological alpha-secretase ADAM10, which is not only able to prevent formation of toxic amyloid beta peptides but also provides a neuroprotective fragment of the amyloid precursor protein - sAPPalpha.

PURPOSE

To identify novel alpha-secretase enhancers from a library of 313 extracts of medicinal plants indigenous to Korea, a screening approach was used and hits were further evaluated for their therapeutic value.

METHODS

The extract library was screened for selective enhancers of ADAM10 gene expression using a luciferase-based promoter reporter gene assay in the human neuroblastoma cell line SH-SY5Y. Candidate extracts were then tested in wild type mice for acute behavioral effects using an open field paradigm. Brain and liver tissue from treated mice was biochemically analyzed for ADAM10 gene expression in vivo. An in vitro blood-brain barrier model and an in vitro ATPase assay were used to unravel transport properties of bioactive compounds from extract candidates. Finally, fractionation of the most promising extract was performed to identify biologically active components.

RESULTS

The extract of Caragana sinica (Buc'hoz) Rehder was identified as the best candidate from our screening approach. We were able to demonstrate that the extract is acutely applicable in mice without obvious side effects and induces ADAM10 gene expression in peripheral tissue. A hindered passage across the blood-brain barrier was detected explaining lack of cerebral induction of ADAM10 gene expression in treated mice. By fractionating C. sinica extract we identified alpha-viniferin as one of the biologically active components.

CONCLUSION

The extract of C. sinica and alpha-viniferin as one of its bioactive constituents might serve as novel therapeutic options for treating Alzheimer's disease by increasing ADAM10 gene expression. The identification of alpha-viniferin represents a promising starting point to achieve blood-brain barrier penetrance in the future.

Activity dependent CAM cleavage and neurotransmission

Spatially localized proteolysis represents an elegant means by which neuronal activity dependent changes in synaptic structure, and thus experience dependent learning and memory, can be achieved. In vitro and in vivo studies suggest that matrix metalloproteinase and adamalysin activity is concentrated at the cell surface, and emerging evidence suggests that increased peri-synaptic expression, release and/or activation of these proteinases occurs with enhanced excitatory neurotransmission. Synaptically expressed cell adhesion molecules (CAMs) could therefore represent important targets for neuronal activity-dependent proteolysis. Several CAM subtypes are expressed at the synapse, and their cleavage can influence the efficacy of synaptic transmission through a variety of non-mutually exclusive mechanisms. In the following review, we discuss mechanisms that regulate neuronal activity-dependent synaptic CAM shedding, including those that may be calcium dependent. We also highlight CAM targets of activity-dependent proteolysis including neuroligin and intercellular adhesion molecule-5 (ICAM-5). We include discussion focused on potential consequences of synaptic CAM shedding, with an emphasis on interactions between soluble CAM cleavage products and specific pre- and post-synaptic receptors.

All-trans-retinoic acid reduces BACE1 expression under inflammatory conditions via modulation of nuclear factor κB (NFκB) signaling

Insulin resistance and neuroinflammation have emerged as two likely key contributors in the pathogenesis of Alzheimer disease (AD), especially in those sporadic AD cases compromised by diabetes or cardiovascular disease. Amyloid-β (Aβ) deposition and its associated inflammatory response are hallmarks in sporadic AD brains. Elevated expression and activity of β-secretase 1 (BACE1), the rate-limiting enzyme responsible for the β-cleavage of amyloid precursor proteins to Aβ peptides, are also observed in sporadic AD brains. Previous studies have suggested that there is therapeutic potential for retinoic acid in treating neurodegeneration based on decreased Aβ. Here we discovered that BACE1 expression is elevated in the brains of both Tg2576 transgenic mice and mice on high fat diets. These conditions are associated with a neuroinflammatory response. We found that administration of all-trans-retinoic acid (atRA) down-regulated the expression of BACE1 in the brains of Tg2576 mice and in mice fed a high fat diet. Moreover, in LPS-treated mice and cultured neurons, BACE1 expression was repressed by the addition of atRA, correlating with the anti-inflammatory efficacy of atRA. Mutations of the NFκB binding site in BACE1 promoter abolished the suppressive effect of atRA. Furthermore, atRA disrupted LPS-induced nuclear translocation of NFκB and its binding to BACE1 promoter as well as promoting the recruitment of the corepressor NCoR. Our findings indicate that atRA represses BACE1 gene expression under inflammatory conditions via the modulation of NFκB signaling.

All-Trans Retinoic Acid Ameliorates Myocardial Ischemia/Reperfusion Injury by Reducing Cardiomyocyte Apoptosis

Myocardial ischemia/reperfusion (I/R) injury interferes with the restoration of blood flow to ischemic myocardium. Oxidative stress-elicited apoptosis has been reported to contribute to I/R injury. All-trans retinoic acid (ATRA) has anti-apoptotic activity as previously reported. Here, we investigated the effects and the mechanism of action of ATRA on myocardial I/R injury both in vivo and in vitro. In vivo, ATRA reduced the size of the infarcted area (17.81±1.05% vs. 24.41±1.03%, P<0.05) and rescued cardiac function loss (ejection fraction 46.42±6.76% vs. 37.18±4.63%, P<0.05) after I/R injury. Flow-cytometric analysis and TUNEL assay demonstrated that the protective role of ATRA on myocardial I/R injury was related to its anti-apoptotic effects. The anti-apoptotic effects of ATRA were associated with partial inhibition of reactive oxygen species (ROS) production and significantly less phosphorylation of mitogen-activated protein kinases (MAPKs) including p38, JNK, and ERK. Western blot analysis also revealed that ATRA pre-treatment increased a disintegrin and metalloproteinase domain-containing protein 10 (ADAM10) expression (0.65 ± 0.20 vs. 0.41±0.02 in vivo) and reduced the level of receptor for advanced glycation end-products (RAGE) (0.38 ± 0.17 vs. 0.52 ± 0.11 in vivo). Concomitantly, the protective role of ATRA on I/R injury was not observed in RAGE-KO mice. The current results indicated that ATRA could prevent myocardial injury and reduced cardiomyocyte apoptosis after I/R effectively. One possible mechanism underlying these effects is that ATRA could increase ADAM10 expression and thus cleave RAGE, which is the main receptor up-stream of MAPKs in myocardial I/R injury, resulting in the down-regulation of MAPK signaling and protective role on myocardial I/R injury.

Activation of peroxisome proliferator-activated receptor α stimulates ADAM10-mediated proteolysis of APP

Amyloid precursor protein (APP) derivative β-amyloid (Aβ) plays an important role in the pathogenesis of Alzheimer's disease (AD). Sequential proteolysis of APP by β-secretase and γ-secretase generates Aβ. Conversely, the α-secretase "a disintegrin and metalloproteinase" 10 (ADAM10) cleaves APP within the eventual Aβ sequence and precludes Aβ generation. Therefore, up-regulation of ADAM10 represents a plausible therapeutic strategy to combat overproduction of neurotoxic Aβ. Peroxisome proliferator-activated receptor α (PPARα) is a transcription factor that regulates genes involved in fatty acid metabolism. Here, we determined that the Adam10 promoter harbors PPAR response elements; that knockdown of PPARα, but not PPARβ or PPARγ, decreases the expression of Adam10; and that lentiviral overexpression of PPARα restored ADAM10 expression in Ppara(-/-) neurons. Gemfibrozil, an agonist of PPARα, induced the recruitment of PPARα:retinoid x receptor α, but not PPARγ coactivator 1α (PGC1α), to the Adam10 promoter in wild-type mouse hippocampal neurons and shifted APP processing toward the α-secretase, as determined by augmented soluble APPα and decreased Aβ production. Accordingly, Ppara(-/-) mice displayed elevated SDS-stable, endogenous Aβ and Aβ1-42 relative to wild-type littermates, whereas 5XFAD mice null for PPARα (5X/α(-/-)) exhibited greater cerebral Aβ load relative to 5XFAD littermates. These results identify PPARα as an important factor regulating neuronal ADAM10 expression and, thus, α-secretase proteolysis of APP.

Discovery of Small Molecules for Up-Regulating the Translation of Antiamyloidogenic Secretase, a Disintegrin and Metalloproteinase 10 (ADAM10), by Binding to the G-Quadruplex-Forming Sequence in the 5' Untranslated Region (UTR) of Its mRNA

Up-regulation of a disintegrin and metalloproteinase 10 (ADAM10) to prevent the formation of β-amyloid (Aβ) peptides might be a promising strategy to treat Alzheimer's disease (AD). RNA G-quadruplex motif within the 5'-UTR of the ADAM10 mRNA is an inhibitory element for ADAM10 translation. Thus, mitigation of the suppressive effect of this motif using an RNA G-quadruplex-forming G-rich sequence (QGRS) binder might be a new approach for AD therapy. Herein, a series of new methylquinolinium derivatives were synthesized and screened by surface plasmon resonance (SPR) and the dual-luciferase reporter assay. Among them, compound 24 showed selective affinity for the QGRS of ADAM10 and could strongly up-regulate the translation of it. Moreover, treatment with 24 led to a significant increase of the secretion of sAPPα, consequently decreasing the Aβ40 in cellular. These results illustrate that the interaction between the RNA QGRS and a small molecule may be a new molecular strategy to modulate the translation of ADAM10.

Diet, nutrients and metabolism: cogs in the wheel driving Alzheimer's disease pathology?

Alzheimer's disease (AD), the most common form of dementia, is a chronic, progressive neurodegenerative disease that manifests clinically as a slow global decline in cognitive function, including deterioration of memory, reasoning, abstraction, language and emotional stability, culminating in a patient with end-stage disease, totally dependent on custodial care. With a global ageing population, it is predicted that there will be a marked increase in the number of people diagnosed with AD in the coming decades, making this a significant challenge to socio-economic policy and aged care. Global estimates put a direct cost for treating and caring for people with dementia at $US604 billion, an estimate that is expected to increase markedly. According to recent global statistics, there are 35.6 million dementia sufferers, the number of which is predicted to double every 20 years, unless strategies are implemented to reduce this burden. Currently, there is no cure for AD; while current therapies may temporarily ameliorate symptoms, death usually occurs approximately 8 years after diagnosis. A greater understanding of AD pathophysiology is paramount, and attention is now being directed to the discovery of biomarkers that may not only facilitate pre-symptomatic diagnosis, but also provide an insight into aberrant biochemical pathways that may reveal potential therapeutic targets, including nutritional ones. AD pathogenesis develops over many years before clinical symptoms appear, providing the opportunity to develop therapy that could slow or stop disease progression well before any clinical manifestation develops.

MicroRNA-138 promotes tau phosphorylation by targeting retinoic acid receptor alpha

Alzheimer's disease (AD) is a progressive neurodegenerative dementia characterized by Aβ deposition and neurofibrillary tangles (NFTs) composed of hyperphosphorylated tau. Emerging evidence shows that microRNAs (miRNAs) contribute to the pathogenesis of AD. Herein, we investigated the role of miR-138, a brain enriched miRNA, which is increased in AD patients. We found that miR-138 is increased in AD models, including N2a/APP and HEK293/tau cell lines. Overexpression of miR-138 activates glycogen synthase kinase-3β (GSK-3β), and increases tau phosphorylation in HEK293/tau cells. Furthermore, we confirm that retinoic acid receptor alpha (RARA) is a direct target of miR-138, and supplement of RARA substantially suppresses GSK-3β activity, and reduces tau phosphorylation induced by miR-138. In conclusion, our data suggest that miR-138 promotes tau phosphorylation by targeting the RARA/GSK-3β pathway.

Regulation of presynaptic Ca2+, synaptic plasticity and contextual fear conditioning by a N-terminal β-amyloid fragment

Soluble β-amyloid has been shown to regulate presynaptic Ca(2+) and synaptic plasticity. In particular, picomolar β-amyloid was found to have an agonist-like action on presynaptic nicotinic receptors and to augment long-term potentiation (LTP) in a manner dependent upon nicotinic receptors. Here, we report that a functional N-terminal domain exists within β-amyloid for its agonist-like activity. This sequence corresponds to a N-terminal fragment generated by the combined action of α- and β-secretases, and resident carboxypeptidase. The N-terminal β-amyloid fragment is present in the brains and CSF of healthy adults as well as in Alzheimer's patients. Unlike full-length β-amyloid, the N-terminal β-amyloid fragment is monomeric and nontoxic. In Ca(2+) imaging studies using a model reconstituted rodent neuroblastoma cell line and isolated mouse nerve terminals, the N-terminal β-amyloid fragment proved to be highly potent and more effective than full-length β-amyloid in its agonist-like action on nicotinic receptors. In addition, the N-terminal β-amyloid fragment augmented theta burst-induced post-tetanic potentiation and LTP in mouse hippocampal slices. The N-terminal fragment also rescued LTP inhibited by elevated levels of full-length β-amyloid. Contextual fear conditioning was also strongly augmented following bilateral injection of N-terminal β-amyloid fragment into the dorsal hippocampi of intact mice. The fragment-induced augmentation of fear conditioning was attenuated by coadministration of nicotinic antagonist. The activity of the N-terminal β-amyloid fragment appears to reside largely in a sequence surrounding a putative metal binding site, YEVHHQ. These findings suggest that the N-terminal β-amyloid fragment may serve as a potent and effective endogenous neuromodulator.

Cilostazol suppresses β-amyloid production by activating a disintegrin and metalloproteinase 10 via the upregulation of SIRT1-coupled retinoic acid receptor-β

The accumulation of plaques of β-amyloid (Aβ) peptides, a hallmark of Alzheimer's disease, results from the sequential cleavage of amyloid precursor protein (APP) by activation of β- and γ-secretases. However, the production of Aβ can be avoided by alternate cleavage of APP by α-and γ-secretases. We hypothesized that cilostazol attenuates Aβ production by increasing a disintegrin and metalloproteinase 10 (ADAM10)/α-secretase activity via SIRT1-coupled retinoic acid receptor-β (RARβ) activation in N2a cells expressing human APP Swedish mutation (N2aSwe). To evoke endogenous Aβ overproduction, the culture medium was switched from medium containing 10% fetal bovine serum (FBS) to medium containing 1% FBS, and cells were cultured for 3∼24 hr. After depletion of FBS in media, N2aSwe cells showed increased accumulations of full-length APP (FL-APP) and Aβ in a time-dependent manner (3-24 hr) in association with decreased ADAM10 protein expression. When pretreated with cilostazol (10-30 μM), FL-APP and Aβ levels were significantly reduced, and ADAM10 and α-secretase activities were restored. Furthermore, the effect of cilostazol on ADAM10 expression was antagonized by pretreating Rp-cAMPS and sirtinol and by SIRT1-gene silencing. In the N2aSwe cells overexpressing the SIRT1 gene, ADAM10, and sAPPα levels were significantly elevated. In addition, like all-trans retinoic acid, cilostazol enhanced the protein expressions of RARβ and ADAM10, and the cilostazol-stimulated ADAM10 elevation was significantly attenuated by LE135 (a RARβ inhibitor), sirtinol, and RARβ-gene silencing. In conclusion, cilostazol suppresses the accumulations of FL-APP and Aβ by activating ADAM10 via the upregulation of SIRT1-coupled RARβ.

Pharmacogenetics of topical and systemic treatment of psoriasis

Psoriasis is a chronic inflammatory skin disease. The cause of psoriasis is unknown, although genetics may play a key role in its development. Treatment of the disease varies with severity. Topical drugs, such as corticosteroids, coal tar, retinoids and vitamin D analogs, are commonly used to treat mild psoriasis. Phototherapy and systemic drugs, such as calcineurin inhibitors, methotrexate, acitretin and biological drugs, are usually used to treat moderate-to-severe psoriasis. Not all patients respond well to treatment, and some can develop severe adverse effects. Interindividual differences in several genes may explain this variation in response to treatment. Pharmacogenetics and pharmacogenomics can facilitate more personalized medicine and prevent the adverse effects associated with treatment.

A novel blood-brain barrier co-culture system for drug targeting of Alzheimer's disease: establishment by using acitretin as a model drug

In the pathogenesis of Alzheimer’s disease (AD) the homeostasis of amyloid precursor protein (APP) processing in the brain is impaired. The expression of the competing proteases ADAM10 (a disintegrin and metalloproteinase 10) and BACE-1 (beta site APP cleaving enzyme 1) is shifted in favor of the A-beta generating enzyme BACE-1. Acitretin–a synthetic retinoid–e.g., has been shown to increase ADAM10 gene expression, resulting in a decreased level of A-beta peptides within the brain of AD model mice and thus is of possible value for AD therapy. A striking challenge in evaluating novel therapeutically applicable drugs is the analysis of their potential to overcome the blood-brain barrier (BBB) for central nervous system targeting. In this study, we established a novel cell-based bio-assay model to test ADAM10-inducing drugs for their ability to cross the BBB. We therefore used primary porcine brain endothelial cells (PBECs) and human neuroblastoma cells (SH-SY5Y) transfected with an ADAM10-promoter luciferase reporter vector in an indirect co-culture system. Acitretin served as a model substance that crosses the BBB and induces ADAM10 expression. We ensured that ADAM10-dependent constitutive APP metabolism in the neuronal cells was unaffected under co-cultivation conditions. Barrier properties established by PBECs were augmented by co-cultivation with SH-SY5Y cells and they remained stable during the treatment with acitretin as demonstrated by electrical resistance measurement and permeability-coefficient determination. As a consequence of transcellular acitretin transport measured by HPLC, the activity of the ADAM10-promoter reporter gene was significantly increased in co-cultured neuronal cells as compared to vehicle-treated controls. In the present study, we provide a new bio-assay system relevant for the study of drug targeting of AD. This bio-assay can easily be adapted to analyze other Alzheimer- or CNS disease-relevant targets in neuronal cells, as their therapeutical potential also depends on the ability to penetrate the BBB.

Unfolded protein response signaling by transcription factor XBP-1 regulates ADAM10 and is affected in Alzheimer's disease

In Alzheimer's disease (AD), disturbed homeostasis of the proteases competing for amyloid precursor protein processing has been reported: a disintegrin and metalloproteinase 10 (ADAM10), the physiological α-secretase, is decreased in favor of the amyloid-β-generating enzyme BACE-1. To identify transcription factors that modulate the expression of either protease, we performed a screening approach: 48 transcription factors significantly interfered with ADAM10/BACE-1-promoter activity. One selective inducer of ADAM10 gene expression is the X-box binding protein-1 (XBP-1). This protein regulates the unfolded protein-response pathway. We demonstrate that particularly the spliced XBP-1 variant dose dependently regulates ADAM10 expression, which can be synergistically enhanced by 100 nM insulin. Analysis of 2 different transgenic mouse models (APP/PS1 and 5xFAD) revealed that at early time points in pathology XBP-1 metabolism is induced. This is accompanied by a 2-fold augmented ADAM10 amount as compared with nontransgenic littermates (P=0.011). Along with aging of the mice, the system is counterregulated, and XBP-1 together with ADAM10 expression level decreased to ∼50% as compared with control animals. Analyses of expression levels in human AD brains showed that ADAM10 mRNA correlated with active XBP-1 (r=0.3120), but expression did not reach levels of healthy age-matched controls, suggesting deregulation of XBP-1 signaling. Our results demonstrate that XBP-1 is a driver of ADAM10 gene expression and that disturbance of this pathway might contribute to development or progression of AD.

Adrenergic regulation of IgE involves modulation of CD23 and ADAM10 expression on exosomes

Soluble CD23 plays a role in the positive regulation of an IgE response. Engagement of the β2 adrenergic receptor (β2AR) on a B cell is known to enhance the level of both soluble CD23 and IgE, although the mechanism by which this occurs is not completely understood. In this study, we report that, in comparison with a CD40 ligand/IL-4-primed murine B cell alone, β2AR engagement on a primed B cell increased gene expression of a disintegrin and metalloproteinase (ADAM)10, which is the primary sheddase of CD23, as well as protein expression of both CD23 and ADAM10, in a protein kinase A- and p38 MAPK-dependent manner, and promoted the localization of these proteins to exosomes as early as 2 d after priming, as determined by both Western blot and flow cytometry and confirmed by electron microscopy. In comparison with isolated exosomes released from primed B cells alone, the transfer of exosomes released from β2AR agonist-exposed primed B cells to cultures of recipient primed B cells resulted in an increase in the level of IgE produced per cell, without affecting the number of cells producing IgE, as determined by ELISPOT. These effects still occurred when a β2AR antagonist was added along with the transfer to block residual agonist, and they failed to occur when exosomes were isolated from β2AR-deficient B cells. These findings suggest that the mechanism responsible for mediating the β2AR-induced increase in IgE involves a shuttling of the β2AR-induced increase in CD23 and ADAM10 proteins to exosomes that subsequently mediate an increase in IgE.

Drug repositioning: an opportunity to develop novel treatments for Alzheimer's disease

Alzheimer's Disease (AD) is the most common cause of dementia, affecting approximately two thirds of the 35 million people worldwide with the condition. Despite this, effective treatments are lacking, and there are no drugs that elicit disease modifying effects to improve outcome. There is an urgent need to develop and evaluate more effective pharmacological treatments. Drug repositioning offers an exciting opportunity to repurpose existing licensed treatments for use in AD, with the benefit of providing a far more rapid route to the clinic than through novel drug discovery approaches. This review outlines the current most promising candidates for repositioning in AD, their supporting evidence and their progress through trials to date. Furthermore, it begins to explore the potential of new transcriptomic and microarray techniques to consider the future of drug repositioning as a viable approach to drug discovery.

Retinoic acid-elicited RARα/RXRα signaling attenuates Aβ production by directly inhibiting γ-secretase-mediated cleavage of amyloid precursor protein

Retinoic acid (RA)-elicited signaling has been shown to play critical roles in development, organogenesis, and the immune response. RA regulates expression of Alzheimer's disease (AD)-related genes and attenuates amyloid pathology in a transgenic mouse model. In this study, we investigated whether RA can suppress the production of amyloid-β (Aβ) through direct inhibition of γ-secretase activity. We report that RA treatment of cells results in significant inhibition of γ-secretase-mediated processing of the amyloid precursor protein C-terminal fragment APP-C99, compared with DMSO-treated controls. RA-elicited signaling was found to significantly increase accumulation of APP-C99 and decrease production of secreted Aβ40. In addition, RA-induced inhibition of γ-secretase activity was found to be mediated through significant activation of extracellular signal-regulated kinases (ERK1/2). Treatment of cells with the specific ERK inhibitor PD98059 completely abolished RA-mediated inhibition of γ-secretase. Consistent with these findings, RA was observed to inhibit secretase-mediated proteolysis of full-length APP. Finally, we have established that RA inhibits γ-secretase through nuclear retinoic acid receptor-α (RARα) and retinoid X receptor-α (RXRα). Our findings provide a new mechanistic explanation for the neuroprotective role of RA in AD pathology and add to the previous data showing the importance of RA signaling as a target for AD therapy.

Regulation of URG4/URGCP and PPARα gene expressions after retinoic acid treatment in neuroblastoma cells

Neuroblastoma (NB), originating from neural crest cells, is the most common extracranial tumor of childhood. Retinoic acid (RA) which is the biological active form of vitamin A regulates differentiation of NB cells, and RA derivatives have been used for NB treatment. PPARα (peroxisome proliferator-activated receptor) plays an important role in the oxidation of fatty acids, carcinogenesis, and differentiation. URG4/URGCP gene is a proto-oncogene and that overexpression of URG4/URGCP is associated with metastasis and tumor recurrence in osteosarcoma. It has been known that URG4/URGCP gene is an overexpressed gene in hepatocellular carcinoma and gastric cancers. This study aims to detect gene expression patterns of PPARα and URG4/URGCP genes in SH-SY5Y NB cell line after RA treatment. Expressions levels of PPARα and URG4/URGCP genes were analyzed after RA treatment for reducing differentiation in SH-SY5Y NB cell line. To induce differentiation, the cells were treated with 10 μM RA in the dark for 3-10 days. Gene expression of URG4/URGCP and PPARα genes were presented as the yield of polymerase chain reaction (PCR) products from target genes compared with the yield of PCR products from the glyceraldehyde-3-phosphate dehydrogenase (GAPDH) gene. SH-SY5Y cells possess small processes in an undifferentiated state, and after treatment with RA, the cells developed long neurites, resembling a neuronal phenotype. PPARα gene expression increased in RA-treated groups; URG4/URGCP gene expression decreased in SH-SY5Y cells after RA treatment compared with that in the control cells. NB cell differentiation might associate with PPARα and URG4/URGCP gene expression profile after RA treatment.

The retinoic acid receptor agonist Am80 increases hippocampal ADAM10 in aged SAMP8 mice

The retinoic acid (RA, a vitamin A metabolite) receptor (RAR) is a transcription factor. Vitamin A/RA administration improves the Alzheimer's disease (AD)- and age-related attenuation of memory/learning in mouse models. Recently, a disintegrin and metalloproteinase domain-containing protein 10 (ADAM10) was identified as a key molecule in RA-mediated anti-AD mechanisms. We investigated the effect of chronic administration of the RAR agonist Am80 (tamibarotene) on ADAM10 expression in senescence-accelerated mice (SAMP8). Moreover, we estimated changes in the expression of the amyloid precursor protein (APP), amyloid beta (Aβ), and hairy/enhancer of split (Hes), which are mediated by ADAM10. Spatial working memory and the levels of a hippocampal proliferation marker (Ki67) were also assessed in these mice. ADAM10 mRNA and protein expression was significantly reduced in the hippocampus of 13-month-old SAMP8 mice; their expression improved significantly after Am80 administration. Further, after Am80 administration, the expression levels of Hes5 and Ki67 were restored and the deterioration of working memory was suppressed, whereas APP and Aβ levels remained unchanged. Our results suggest that Am80 administration effectively improves dementia by activating the hippocampal ADAM10-Notch-Hes5 proliferative pathway.

Potential repurposing of oncology drugs for the treatment of Alzheimer's disease

Alzheimer's disease (AD) is the most common form of neurodegenerative dementia, affecting about 30 million people worldwide. Despite recent advances in understanding its molecular pathology, no mechanism-based drugs are currently available that can halt the progression of AD. Because amyloid-β-peptide (Aβ), a primary component of senile plaques, is thought to be a central pathogenic culprit, several disease-modifying therapies are being developed, including inhibitors of Aβ-producing proteases and immunotherapies with anti-Aβ antibodies. Drug repositioning or repurposing is regarded as a complementary and reasonable approach to identify new drug candidates for AD. This commentary will discuss the clinical relevance of an attractive candidate compound reported in a recent paper by Hayes et al. (BMC Medicine 2013) as well as perspectives regarding the possible repositioning of oncology drugs for the treatment of AD. See related research article here http://www.biomedcentral.com/1741-7015/11/81.

Seven sirtuins for seven deadly diseases of aging

Sirtuins are a class of NAD(+)-dependent deacetylases having beneficial health effects. This extensive review describes the numerous intracellular actions of the seven mammalian sirtuins, their protein targets, intracellular localization, the pathways they modulate, and their role in common diseases of aging. Selective pharmacological targeting of sirtuins is of current interest in helping to alleviate global disease burden. Since all sirtuins are activated by NAD(+), strategies that boost NAD(+) in cells are of interest. While most is known about SIRT1, the functions of the six other sirtuins are now emerging. Best known is the involvement of sirtuins in helping cells adapt energy output to match energy requirements. SIRT1 and some of the other sirtuins enhance fat metabolism and modulate mitochondrial respiration to optimize energy harvesting. The AMP kinase/SIRT1-PGC-1α-PPAR axis and mitochondrial sirtuins appear pivotal to maintaining mitochondrial function. Downregulation with aging explains much of the pathophysiology that accumulates with aging. Posttranslational modifications of sirtuins and their substrates affect specificity. Although SIRT1 activation seems not to affect life span, activation of some of the other sirtuins might. Since sirtuins are crucial to pathways that counter the decline in health that accompanies aging, pharmacological agents that boost sirtuin activity have clinical potential in treatment of diabetes, cardiovascular disease, dementia, osteoporosis, arthritis, and other conditions. In cancer, however, SIRT1 inhibitors could have therapeutic value. Nutraceuticals such as resveratrol have a multiplicity of actions besides sirtuin activation. Their net health benefit and relative safety may have originated from the ability of animals to survive environmental changes by utilizing these stress resistance chemicals in the diet during evolution. Each sirtuin forms a key hub to the intracellular pathways affected.

Amyloid β inhibits retinoic acid synthesis exacerbating Alzheimer disease pathology which can be attenuated by an retinoic acid receptor α agonist

The retinoic acid receptor (RAR) α system plays a key role in the adult brain, participating in the homeostatic control of synaptic plasticity, essential for memory function. Here we show that RARα signalling is down-regulated by amyloid beta (Aβ), which inhibits the synthesis of the endogenous ligand, retinoic acid (RA). This results in the counteraction of a variety of RARα-activated pathways that are key in the aetiopathology of Alzheimer's disease (AD) but which can be reversed by an RARα agonist. RARα signalling improves cognition in the Tg2576 mice, it has an anti-inflammatory effect and promotes Aβ clearance by increasing insulin degrading enzyme and neprilysin activity in both microglia and neurons. In addition, RARα signalling prevents tau phosphorylation. Therefore, stimulation of the RARα signalling pathway using a synthetic agonist, by both clearing Aβ and counteracting some of its toxic effects, offers therapeutic potential for the treatment of AD.

PuF, an antimetastatic and developmental signaling protein, interacts with the Alzheimer's amyloid-β precursor protein via a tissue-specific proximal regulatory element (PRE)

BACKGROUND

Alzheimer's disease (AD) is intimately tied to amyloid-β (Aβ) peptide. Extraneuronal brain plaques consisting primarily of Aβ aggregates are a hallmark of AD. Intraneuronal Aβ subunits are strongly implicated in disease progression. Protein sequence mutations of the Aβ precursor protein (APP) account for a small proportion of AD cases, suggesting that regulation of the associated gene (APP) may play a more important role in AD etiology. The APP promoter possesses a novel 30 nucleotide sequence, or "proximal regulatory element" (PRE), at -76/-47, from the +1 transcription start site that confers cell type specificity. This PRE contains sequences that make it vulnerable to epigenetic modification and may present a viable target for drug studies. We examined PRE-nuclear protein interaction by gel electrophoretic mobility shift assay (EMSA) and PRE mutant EMSA. This was followed by functional studies of PRE mutant/reporter gene fusion clones.

RESULTS

EMSA probed with the PRE showed DNA-protein interaction in multiple nuclear extracts and in human brain tissue nuclear extract in a tissue-type specific manner. We identified transcription factors that are likely to bind the PRE, using competition gel shift and gel supershift: Activator protein 2 (AP2), nm23 nucleoside diphosphate kinase/metastatic inhibitory protein (PuF), and specificity protein 1 (SP1). These sites crossed a known single nucleotide polymorphism (SNP). EMSA with PRE mutants and promoter/reporter clone transfection analysis further implicated PuF in cells and extracts. Functional assays of mutant/reporter clone transfections were evaluated by ELISA of reporter protein levels. EMSA and ELISA results correlated by meta-analysis.

CONCLUSIONS

We propose that PuF may regulate the APP gene promoter and that AD risk may be increased by interference with PuF regulation at the PRE. PuF is targeted by calcium/calmodulin-dependent protein kinase II inhibitor 1, which also interacts with the integrins. These proteins are connected to vital cellular and neurological functions. In addition, the transcription factor PuF is a known inhibitor of metastasis and regulates cell growth during development. Given that APP is a known cell adhesion protein and ferroxidase, this suggests biochemical links among cell signaling, the cell cycle, iron metabolism in cancer, and AD in the context of overall aging.

5-HT4 receptors constitutively promote the non-amyloidogenic pathway of APP cleavage and interact with ADAM10

In addition to the amyloidogenic pathway, amyloid precursor protein (APP) can be cleaved by α-secretases, producing soluble and neuroprotective APP alpha (sAPPα) (nonamyloidogenic pathway) and thus preventing the generation of pathogenic amyloid-β. However, the mechanisms regulating APP cleavage by α-secretases remain poorly understood. Here, we showed that expression of serotonin type 4 receptors (5-HT(4)Rs) constitutively (without agonist stimulation) induced APP cleavage by the α-secretase ADAM10 and the release of neuroprotective sAPPα in HEK-293 cells and cortical neurons. This effect was independent of cAMP production. Interestingly, we demonstrated that 5-HT(4) receptors physically interacted with the mature form of ADAM10. Stimulation of 5-HT(4) receptors by an agonist further increased sAPPα secretion, and this effect was mediated by cAMP/Epac signaling. These findings describe a new mechanism whereby a GPCR constitutively stimulates the cleavage of APP by α-secretase and promotes the nonamyloidogenic pathway of APP processing.

Drug repositioning for Alzheimer's disease

Existing drugs for Alzheimer's disease provide symptomatic benefit for up to 12 months, but there are no approved disease-modifying therapies. Given the recent failures of various novel disease-modifying therapies in clinical trials, a complementary strategy based on repositioning drugs that are approved for other indications could be attractive. Indeed, a substantial body of preclinical work indicates that several classes of such drugs have potentially beneficial effects on Alzheimer's-like brain pathology, and for some drugs the evidence is also supported by epidemiological data or preliminary clinical trials. Here, we present a formal consensus evaluation of these opportunities, based on a systematic review of published literature. We highlight several compounds for which sufficient evidence is available to encourage further investigation to clarify an optimal dose and consider progression to clinical trials in patients with Alzheimer's disease.

Tetraspanin15 regulates cellular trafficking and activity of the ectodomain sheddase ADAM10

A disintegrin and metalloproteinase10 (ADAM10) has been implicated as a major sheddase responsible for the ectodomain shedding of a number of important surface molecules including the amyloid precursor protein and cadherins. Despite a well-documented role of ADAM10 in health and disease, little is known about the regulation of this protease. To address this issue we conducted a split-ubiquitin yeast two-hybrid screen to identify membrane proteins that interact with ADAM10. The yeast experiments and co-immunoprecipitation studies in mammalian cell lines revealed tetraspanin15 (TSPAN15) to specifically associate with ADAM10. Overexpression of TSPAN15 or RNAi-mediated knockdown of TSPAN15 led to significant changes in the maturation process and surface expression of ADAM10. Expression of an endoplasmic reticulum (ER) retention mutant of TSPAN15 demonstrated an interaction with ADAM10 already in the ER. Pulse-chase experiments confirmed that TSPAN15 accelerates the ER-exit of the ADAM10-TSPAN15 complex and stabilizes the active form of ADAM10 at the cell surface. Importantly, TSPAN15 also showed the ability to mediate the regulation of ADAM10 protease activity exemplified by an increased shedding of N-cadherin and the amyloid precursor protein. In conclusion, our data show that TSPAN15 is a central modulator of ADAM10-mediated ectodomain shedding. Therapeutic manipulation of its expression levels may be an additional approach to specifically regulate the activity of the amyloid precursor protein alpha-secretase ADAM10.

Alzheimer culprits: cellular crossroads and interplay

Alzheimer's disease (AD) is the primary cause of dementia in the elderly and one of the major health problems worldwide. Since its first description by Alois Alzheimer in 1907, noticeable but insufficient scientific comprehension of this complex pathology has been achieved. All the research that has been pursued takes origin from the identification of the pathological hallmarks in the forms of amyloid-β (Aβ) deposits (plaques), and aggregated hyperphosphorylated tau protein filaments (named neurofibrillary tangles). Since this discovery, many hypotheses have been proposed to explain the origin of the pathology. The "amyloid cascade hypothesis" is the most accredited theory. The mechanism suggested to be one of the initial causes of AD is an imbalance between the production and the clearance of Aβ peptides. Therefore, Amyloid Precursor Protein (APP) synthesis, trafficking and metabolism producing either the toxic Aβ peptide via the amyloidogenic pathway or the sAPPα fragment via the non amyloidogenic pathway have become appealing subjects of study. Being able to reduce the formation of the toxic Aβ peptides is obviously an immediate approach in the trial to prevent AD. The following review summarizes the most relevant discoveries in the field of the last decades.

ADAM10 expression and promoter haplotype in Alzheimer's disease

Alzheimer's disease is confirmed at autopsy according to the accumulation of brain neuritic plaques and neurofibrillary tangles in the brain. Neuritic plaques contain amyloid-β (Aβ) and lower levels of Aβ correspond to an increase in ADAM10 α-secretase activity. ADAM10 α-secretase activity produces a soluble amyloid precursor protein (APP) alpha (sAPPα) product and negates the pathological production of Aβ. In this investigation, it was hypothesized that genetic variation with the ADAM10 promoter is associated with ADAM10 expression levels as well as cerebrospinal fluid sAPPα levels. Results from this investigation suggest that the ADAM10 rs514049-rs653765 C-A promoter haplotype is associated with: (1) higher CSF sAPPα levels in cognitively normal controls compared with Alzheimer's disease (AD) patients, (2) higher postmortem brain hippocampus, but not cerebellum, ADAM10 protein levels in subjects with low plaque scores compared with those with high plaque scores, and (3) higher promoter activity for promoter-only reporter constructs compared with promoter 3' untranslated region (3'UTR) constructs in the human neuroblastoma SHSY5Y cell line, but not in HepG2 or U118 cell lines. Taken together, these findings suggest that ADAM10 expression is modulated according to a promoter haplotype that is influenced in a brain region- and cell type-specific manner.

Activation of NMDA receptors upregulates a disintegrin and metalloproteinase 10 via a Wnt/MAPK signaling pathway

A disintegrin and metalloproteinase 10 (ADAM10) is the constitutive α-secretase that governs the nonamyloidogenic pathway of β-amyloid precursor protein processing and is an attractive drug target for treating Alzheimer's disease. To date, little is known about the mechanism by which ADAM10 is regulated in neurons. Using mouse primary cortical neurons, we show here that NMDA receptor (NMDAR) activation led to upregulation of the genes encoding ADAM10 and β-catenin proteins. Interestingly, the ADAM10 upregulation was abolished by inhibitors of Wnt/β-catenin signaling. Conversely, activation of the Wnt/β-catenin signaling pathway by recombinant Wnt3a stimulated ADAM10 expression. We further showed that both the NMDAR- and Wnt3a-induced ADAM10 upregulation was blocked by ERK inhibitors. We suggest that the NMDARs control ADAM10 expression via a Wnt/MAPK signaling pathway.

Retinoids for treatment of Alzheimer's disease

Retinoids are Vitamin A derivatives involved in cellular regulatory processes including cell differentiation, neurite outgrowth and defense against oxidative stress. Retinoids may also influence Amyloid beta processing upregulation of alpha secretase via ADAM10. Vitamin A and other retinoids also directly inhibit formation of Amyloid fibrils in vivo. These properties of retinoids are relevant to theories of Alzheimer's disease pathogenesis. Retinoids are already used in treatment of acne vulgaris, psoriasis, neuroblastoma and acute promyelocytic leukemia. Clinical studies involving in cognitively impaired older adults with Alzheimer's disease are beginning with a variety of retinoids. These studies need to address safety issues of retinoids in older populations, and hold hope for demonstrating efficacy in translating these basic mechanisms to treatment of a widespread dementing illness.

Potential of chromatin modifying compounds for the treatment of Alzheimer's disease

Alzheimer's disease is a very common progressive neurodegenerative disorder affecting the learning and memory centers in the brain. The hallmarks of disease are the accumulation of β-amyloid neuritic plaques and neurofibrillary tangles formed by abnormally phosphorylated tau protein. Alzheimer's disease is currently incurable and there is an intense interest in the development of new potential therapies. Chromatin modifying compounds such as sirtuin modulators and histone deacetylase inhibitors have been evaluated in models of Alzheimer's disease with some promising results. For example, the natural antioxidant and sirtuin 1 activator resveratrol has been shown to have beneficial effects in animal models of disease. Similarly, numerous histone deacetylase inhibitors including Trichostatin A, suberoylanilide hydroxamic acid, valproic acid and phenylbutyrate reduction have shown promising results in models of Alzheimer's disease. These beneficial effects include a reduction of β-amyloid production and stabilization of tau protein. In this review we provide an overview of the histone deacetylase enzymes, with a focus on enzymes that have been identified to have an important role in the pathobiology of Alzheimer's disease. Further, we discuss the potential for pharmacological intervention with chromatin modifying compounds that modulate histone deacetylase enzymes.

Apricot carotenoids possess potent anti-amyloidogenic activity in vitro

Alzheimer's disease (AD) is the most common form of dementia and is characterized by the progressive accumulation of amyloid β protein (Aβ) in areas of the brain. There has been an increased interest in screening for food-grade anti-amyloidogenic compounds in foodstuffs. The purpose of this study was to screen and identify bioactive compounds with anti-amyloidogenicity in apricot fruits using synthetic Aβ(1-42). The anti-amyloidogenicity was investigated using thioflavin T fluorescence assay, electron microscopy, and dot blotting analysis. The carotenoid fraction from apricot showed strong inhibitory effects against oligomer and fibril formation of Aβ and fibril-destabilizing effects. Among the peaks in the HPLC chromatogram, lutein showed the strongest inhibitory effect on Aβ fibril formation. The inhibitory effect was dependent on the number and portion of hydroxyl groups on both sides of carotenoids. These findings suggest that lutein in fruits may be useful as a preventive agent for amyloid-associated diseases.

A deacetylase-deficient SIRT1 variant opposes full-length SIRT1 in regulating tumor suppressor p53 and governs expression of cancer-related genes

SIRT1 is an NAD-dependent deacetylase and epigenetic regulator essential for normal mammalian development and homeostasis. Here we describe a human SIRT1 splice variant, designated SIRT1-Δ2/9, in which the deacetylase coding sequence is lost due to splicing between exons 2 and 9. This work aimed to determine if SIRT1-Δ2/9 is a novel functional product of the SIRT1 gene. Endogenous SIRT1-Δ2/9 protein was identified in human cell lysate by immunoblotting and splice variant-specific RNA interference (RNAi). SIRT1-Δ2/9 mRNA is bound by CUGBP2, which downregulates its translation. Using pulldown assays, we demonstrate that SIRT1-Δ2/9 binds p53 protein. SIRT1-Δ2/9 maintains basal p53 protein levels and supports p53 function in response to DNA damage, as evidenced by RNAi-mediated depletion of SIRT1-Δ2/9 prior to damage. In turn, basal p53 downregulates SIRT1-Δ2/9 RNA levels, while stress-activated p53 eliminates SIRT1-Δ2/9. Loss of wild-type (wt) p53 has been correlated with overexpression of SIRT1-Δ2/9 in a range of human cancers. Exogenous SIRT1-Δ2/9 protein associates with specific promoters in chromatin and can regulate cancer-related gene expression, as evidenced by chromatin immunoprecipitation analysis and RNAi/genomic array data. SIRT1 is of major therapeutic importance, and potential therapeutic drugs are screened against SIRT1 deacetylase activity. Our discovery of SIRT1-Δ2/9 identifies a new, deacetylase-independent therapeutic target for SIRT1-related diseases, including cancer.

Activation of α-secretase cleavage

Alpha-secretase-mediated cleavage of the amyloid precursor protein (APP) releases the neuroprotective APP fragment sαAPP and prevents amyloid β peptide (Aβ) generation. Moreover, α-secretase-like cleavage of the Aβ transporter 'receptor for advanced glycation end products' counteracts the import of blood Aβ into the brain. Assuming that Aβ is responsible for the development of Alzheimer's disease (AD), activation of α-secretase should be preventive. α-Secretase-mediated APP cleavage can be activated via several G protein-coupled receptors and receptor tyrosine kinases. Protein kinase C, mitogen-activated protein kinases, phosphatidylinositol 3-kinase, cAMP and calcium are activators of receptor-induced α-secretase cleavage. Selective targeting of receptor subtypes expressed in brain regions affected by AD appears reasonable. Therefore, the PACAP receptor PAC1 and possibly the serotonin 5-HT(6) receptor subtype are promising targets. Activation of APP α-secretase cleavage also occurs upon blockade of cholesterol synthesis by statins or zaragozic acid A. Under physiological statin concentrations, the brain cholesterol content is not influenced. Statins likely inhibit Aβ production in the blood by α-secretase activation which is possibly sufficient to inhibit AD development. A disintegrin and metalloproteinase 10 (ADAM10) acts as α-secretase on APP. By targeting the nuclear retinoic acid receptor β, the expression of ADAM10 and non-amyloidogenic APP processing can be enhanced. Excessive activation of ADAM10 should be avoided because ADAM10 and also ADAM17 are not APP-specific. Both ADAM proteins cleave various substrates, and therefore have been associated with tumorigenesis and tumor progression.

Translational repression of the disintegrin and metalloprotease ADAM10 by a stable G-quadruplex secondary structure in its 5'-untranslated region

Anti-amyloidogenic processing of the amyloid precursor protein APP by α-secretase prevents formation of the amyloid-β peptide, which accumulates in senile plaques of Alzheimer disease patients. α-Secretase belongs to the family of a disintegrin and metalloproteases (ADAMs), and ADAM10 is the primary candidate for this anti-amyloidogenic activity. We recently demonstrated that ADAM10 translation is repressed by its 5'-UTR and that in particular the first half of ADAM10 5'-UTR is responsible for translational repression. Here, we asked whether specific sequence motifs exist in the ADAM10 5'-UTR that are able to form complex secondary structures and thus potentially inhibit ADAM10 translation. Using circular dichroism spectroscopy, we demonstrate that a G-rich region between nucleotides 66 and 94 of the ADAM10 5'-UTR forms a highly stable, intramolecular, parallel G-quadruplex secondary structure under physiological conditions. Mutation of guanines in this sequence abrogates the formation of the G-quadruplex structure. Although the G-quadruplex structure efficiently inhibits translation of a luciferase reporter in in vitro translation assays and in living cells, inhibition of G-quadruplex formation fails to do so. Moreover, expression of ADAM10 was similarly repressed by the G-quadruplex. Mutation of the G-quadruplex motif results in a significant increase of ADAM10 levels and consequently APPsα secretion. Thus, we identified a critical RNA secondary structure within the 5'-UTR, which contributes to the translational repression of ADAM10.

Carotenoids and Alzheimer's disease: an insight into therapeutic role of retinoids in animal models

Carotenoids play a pivotal role in prevention of many degenerative diseases mediated by oxidative stress including neurodegenerative diseases like Alzheimer's Disease (AD). The involvement of retinoids in physiology, AD pathology and their therapeutic role in vitro and in vivo has been extensively studied. This review focuses on the role of carotenoids like retinoic acid (RA), all trans retinoic acid (ATRA), lycopene and β-carotene in prevention of AD symptoms primarily through inhibition of amyloid beta (Aβ) formation, deposition and fibril formation either by reducing the levels of p35 or inhibiting corresponding enzymes. The role of antioxidant micronutrients in prevention or delaying of AD symptoms has been included. This study emphasizes the dietary supplementation of carotenoids to combat AD and warrants further studies on animal models to unravel their mechanism of neuroprotection.