Inhibit Gamma-secretase Activity Research Articles

Inhibition of gamma secretase blocks HPV infection

Human papillomaviruses (HPV) are common sexually transmitted pathogens that predispose women to cervical and other anogenital cancers. HPV vaccines can prevent infection by some but not other sexually transmitted HPVs but are too costly for use in much of the world at greatest risk to HPV-associated cancers. Microbicides provide an inexpensive alternative to vaccines. In a high throughput screen, drugs that inhibit the cellular protein complex known as gamma secretase were identified as potential HPV microbicides. gamma Secretase inhibitors (GSIs) inhibited the infectivity of HPV pseudoviruses both in human keratinocytes and in mouse cells, with IC50 values in the picomolar to the nanomolar range. Using a mouse model, we observed that a GSI could inhibit HPV infection to the same degree as its effectiveness in inhibiting gamma secretase activity in vivo. We conclude that gamma secretase activity is required for HPV infection and that GSIs are effective microbicides against anogenital HPVs.

Huntingtin cleavage product A forms in neurons and is reduced by gamma-secretase inhibitors

BackgroundThe mutation in Huntington's disease is a polyglutamine expansion near the N-terminus of huntingtin. Huntingtin expressed in immortalized neurons is cleaved near the N-terminus to form N-terminal polypeptides known as cleavage products A and B (cpA and cpB). CpA and cpB with polyglutamine expansion form inclusions in the nucleus and cytoplasm, respectively. The formation of cpA and cpB in primary neurons has not been established and the proteases involved in the formation of these fragments are unknown.ResultsDelivery of htt cDNA into the mouse striatum using adeno-associated virus or into primary cortical neurons using lentivirus generated cpA and cpB, indicating that neurons in brain and in vitro can form these fragments. A screen of small molecule protease inhibitors introduced to clonal striatal X57 cells and HeLa cells identified compounds that reduced levels of cpA and are inhibitors of the aspartyl proteases cathepsin D and cathepsin E. The most effective compound, P1-N031, is a transition state mimetic for aspartyl proteases. By western blot analysis, cathepsin D was easily detected in clonal striatal X57 cells, mouse brain and primary neurons, whereas cathepsin E was only detectible in clonal striatal X57 cells. In primary neurons, levels of cleavage product A were not changed by the same compounds that were effective in clonal striatal cells or by mRNA silencing to partially reduce levels of cathepsin D. Instead, treating primary neurons with compounds that are known to inhibit gamma secretase activity either indirectly (Imatinib mesylate, Gleevec) or selectively (LY-411,575 or DAPT) reduced levels of cpA. LY-411,575 or DAPT also increased survival of primary neurons expressing endogenous full-length mutant huntingtin.ConclusionWe show that cpA and cpB are produced from a larger huntingtin fragment in vivo in mouse brain and in primary neuron cultures. The aspartyl protease involved in forming cpA has cathepsin-D like properties in immortalized neurons and gamma secretase-like properties in primary neurons, suggesting that cell type may be a critical factor that specifies the aspartyl protease responsible for cpA. Since gamma secretase inhibitors were also protective in primary neurons, further study of the role of gamma-secretase activity in HD neurons is justified.

Bisphenol A Disrupts Notch Signaling by Inhibiting Gamma-Secretase Activity and Causes Eye Dysplasia of Xenopus laevis

Bisphenol A (BPA) is being recognized as an endocrine-disrupting chemical (EDC). Recently, several reports indicated that BPA affects the central nervous system (CNS) during embryonic development. However, the molecular mechanism of BPA in the CNS is not well known. Here, we show that BPA affected Notch signaling by inhibiting the activity of the Notch intracellular domain (NICD) cleavage-related enzyme, gamma-secretase (gamma-secretase), at the neurula stage of the Xenopus laevis. BPA caused various morphologic aberrations including scoliosis, eye dysplasia, and loss of pigments in the X. laevis tadpole. These abnormalities were seen whenever BPA was used at the neurula stage. In addition, the expression levels of several marker mRNAs at the neurula stage were investigated by RT-PCR, and we found that the mRNAs expression of ectodermal marker, Pax6, CNS marker, Sox2, and neural crest marker, FoxD3, were decreased by treatment with BPA. These genes contribute to the neural differentiation at the neurula stage, and also the downstream factors of Notch signaling. Injection of NICD but not a Notch ligand, delta 1, rescued the abnormalities caused by BPA. We subsequently assayed the inhibition of the activities of NICD cleavage-related enzymes, tumor necrosis factor alpha converting enzyme, and gamma-secretase, by BPA and found that BPA inhibited the gamma-secretase activity. Furthermore, we expressed presenilin, a main component of gamma-secretase, in Escherichia coli and found the direct binding of BPA with presenilin. These results suggest that BPA affected the neural differentiation by inhibiting gamma-secretase activity, leading to neurodevelopmental abnormalities.

Reelin induces a radial glial phenotype in human neural progenitor cells by activation of Notch-1

BackgroundReelin and Notch-1 signaling pathways have been recently found to be necessary to induce the expression of brain lipid binding protein (BLBP) and to promote the process extension and the maturation of the neuronal progenitors, the radial glial cells. In this study, we report the cross talk between these two pathways.ResultsBoth in vitro Reelin treatment and overexpression of Notch-1 intracellular domain (NICD) induced BLBP expression and a radial glial phenotype in an immortalized human neural progenitor (HNP) cell line, isolated from the cortex of 14 weeks old fetus. Reelin treatment increased the level of NICD, indicating that Reelin signaling directly activates Notch-1. In addition, reducing NICD release, by inhibiting γ-secretase activity, inhibited the Reelin-induced radial glial phenotype in human neural progenitor cells. Furthermore, we found that Dab-1, an adaptor protein downstream of Reelin, was co-immunoprecipitated with Notch-1 and NICD.ConclusionThese data indicate that Reelin signaling induces BLBP expression and a radial glial phenotype in human neural progenitor cells via the activation of Notch-1. This study suggest that Reelin signaling may act to fine tune Notch-1 activation to favor the induction of a radial glial phenotype prenataly and would thus offer an insight into how Notch-1 signaling leads to different cellular fates at different developmental stages.

Phosphoinositides Suppress γ-Secretase in Both the Detergent-soluble and -insoluble States

gamma-Secretase is an aspartic protease that hydrolyzes type I membrane proteins within the hydrophobic environment of the lipid bilayer. Using the CHAPSO-solubilized gamma-secretase assay system, we previously found that gamma-secretase activity was sensitive to the concentrations of detergent and phosphatidylcholine. This strongly suggests that the composition of the lipid bilayer has a significant impact on the activity of gamma-secretase. Recently, level of secreted beta-amyloid protein was reported to be attenuated by increasing levels of phosphatidylinositol 4,5-diphosphate (PI(4,5)P2) in cultured cells. However, it is not clear whether PI(4,5)P2 has a direct effect on gamma-secretase activity. In this study, we found that phosphoinositides directly inhibited CHAPSO-solubilized gamma-secretase activity. Interestingly, neither phosphatidylinositol nor inositol triphosphate altered gamma-secretase activity. PI(4,5)P2 was also found to inhibit gamma-secretase activity in CHAPSO-insoluble membrane microdomains (rafts). Kinetic analysis of beta-amyloid protein production in the presence of PI(4,5)P2 suggested a competitive inhibition. Even though phosphoinositides are minor phospholipids of the membrane, the concentration of PI(4,5)P2 within the intact membrane has been reported to be in the range of 4-8 mm. The presence of PI(4,5)P2-rich rafts in the membrane has been reported in a range of cell types. Furthermore, gamma-secretase is enriched in rafts. Taking these data together, we propose that phosphoinositides potentially regulate gamma-secretase activity by suppressing its association with the substrate.

Unnatural Amino Acid-Substituted (Hydroxyethyl)urea Peptidomimetics Inhibit γ-Secretase and Promote the Neuronal Differentiation of Neuroblastoma Cells

Gamma-secretase, exhibiting characteristics of aspartyl protease, mediates the intramembranous proteolysis of beta-amyloid precursor protein (APP) and Notch, and it is considered to be a prime pharmacological target in the development of therapeutics for Alzheimer's disease (AD). To identify compounds that block gamma-secretase-mediated proteolysis, we used a highly sensitive cell-based reporter gene assay for gamma-secretase in which Gal4/VP16-tagged C99-APP was expressed as the immediate substrate of gamma-secretase, and Gal4/VP16-tagged APP intracellular domain released by the gamma-secretase cleavage then activated the expression of the Gal4-driven luciferase reporter gene. Using this reporter assay, we demonstrated that the newly synthesized (hydroxyethyl)urea peptidomimetics, which contain unnatural amino acid moieties at positions P1' and/or P3', can effectively inhibit gamma-secretase activity and significantly reduce Abeta production. The gamma-secretase-dependent S3 cleavage of Notch was also consistently blocked by these (hydroxyethyl)ureas as evidenced by the decreased generation of the Notch intracellular domain, a prerequisite for the activation of Notch signaling. The inhibition of Notch signaling by active Jia compounds efficiently promotes the neuronal differentiation of neuroblastoma cells, intervening in tumorigenesis and the malignancy of neuroblastomas. Our results suggest that (hydroxyethyl)urea peptidomimetics containing unnatural amino acid substitutions could represent a novel class of gamma-secretase inhibitors with enhanced stability, providing the basis for the further development of effective therapeutics for AD and neuroblastomas.

Lactacystin decreases amyloid‐β peptide production by inhibiting β‐secretase activity

The human amyloid precursor protein (APP) is processed by the nonamyloidogenic and the amyloidogenic catabolic pathways. The sequential cleavage of APP by the beta- and gamma-secretase activities, known as the amyloidogenic processing of APP, leads to the formation of the amyloid-beta peptide (Abeta). Abeta is the main constituent of the amyloid core of senile plaques, a typical hallmark of Alzheimer's disease. In addition to secretases, other cellular proteolytic activities, like the proteasome, might participate in the metabolism of APP. We investigated the consequence of proteasome inhibition on the amyloidogenic processing of human APP. CHO cells and primary cultures of rat cortical neurons expressing human APP or a protein corresponding to its beta-cleaved C-terminal fragment (C99) were treated with lactacystin, an irreversible inhibitor of the chymotrypsin-like activity of the proteasome. Lactacystin significantly decreased the level of Abeta produced from APP in both cellular models, whereas the production of Abeta from C99 was not affected. Lactacystin did not inhibit gamma-secretase activity but was found to inhibit the beta-cleavage of APP, leading to a proportional decrease in Abeta production. Although lactacystin did not inhibit the catalytic activity of recombinant BACE1, a decrease in neuronal beta-secretase activity was measured after treatment with lactacystin.

γ-Secretase as a Therapeutic Target for Treatment of Alzheimers Disease

Alzheimer's disease (AD) is the most common cause of dementia with aging, that is pathologically characterized by senile plaques that contain amyloid-beta peptides (Abeta) and neurofibrillary tangles comprised of phosphorylated tau. Genetic and biological studies provide evidence that the production and deposition of Abeta contribute to the etiology of AD. gamma-Secretase is the pivotal enzyme in generating the C terminus of Abeta, that determines its aggregability and propensity for deposition. Drugs that regulate the production of Abeta by inhibiting gamma-secretase activity could provide an effective therapeutics for AD, although recent studies suggest that gamma-secretase plays important roles in novel signaling pathways that play essential roles in embryonic development. This review focuses on recent progresses in the gamma-secretase biology that shed substantial light on the proteolytic mechanism, regulation and composition of this unusual enzyme. Moreover, we review the recent development of inhibitors and provide a direction for the effective treatment of AD through inhibition of gamma-secretase activity.

Treatment and Management of the Elderly Patients with Alzheimer's Disease

Alzheimer's disease (AD) is the most common cause of dementia in older people. Cerebral deposition of amyloid plaques containing amyloid beta-peptide (Aβ) has traditionally been considered the central feature of AD. γ-Secretase is the pivotal enzyme in generating the C terminus of Aβ, that determines its aggregability and propensity for deposition. Drugs that regulate the production of Aβ by inhibiting gamma-secretase activity could provide an effective therapeutics for AD, however we can't use these drugs clinically now. Anti-amyloid immunotherapy for AD has received considerable attention following reports that amyloid pathology was reduced in an amyloid precursor protein (APP) transgenic mouse model on vaccination with aggregated Aβ42. Clinical trials were terminated after four early reports of autoimmune meningoencephalitis, but a post-mortem study in one patient showed evidence of plaque reduction. Currently, no effective pharmacologic interventions have been researched enough to support their use in prevention of AD. Many epidemiological studies suggest that apolipoprotein E type 4 allele, diabetes, obesity, hypertension, and hyperlipidemia were associated the risk factor for late onset AD. Two key treatment approaches for AD have been driven by retrospective epidemiology: non-steroidal anti-inflammatory drugs and cholesterol-lowering statins. In both cases, the exact target in the disease cascade remains to be elucidated. In constant, only one acetylcholinesterase inhibitor, donepezil has been proven effective and used for patients with mild or moderate AD in Japan. Donepezil have demonstrated the effectiveness in stabilizing cognitive function and delaying behavioral symptoms. Given the likelihood that agents will become available that reliably delay onset and/or slow progression of AD, it will be important to detect preclinical AD as early as possible for maximal treatment effect. Cognitive function is generally examined by Mini-mental State Examination (MMSE), revised version of Hasegawa's Dementia Rating Scale (HDS-R) and Wechsler adult intelligence scale-revised (WAIS-R). The positron emission tomography or the single photon emission computed tomography were used for diagnosis of early stage AD. Caregivers should analyze behaviors and environmental factors which precede harmful abnormal conduct and try to avoid them.

Toward prevention of alzheimers disease – Potential nutraceutical strategies for suppressing the production of amyloid beta peptides

Alzheimers disease (AD) can be viewed as a vicious cycle in which excess production and deposition of amyloid beta (Abeta) peptides promote microglial activation, and the resultant production of inflammatory mediators further boosts Abeta production while inducing death and dysfunction of neurons. Abeta production is mediated by beta- and gamma-secretase activities; it is prevented by alpha-secretase activity, and insulin-degrading enzyme (IDE) catabolizes Abeta. High cellular cholesterol content increases Abeta synthesis by boosting beta-secretase activity; inhibition of cholesterol syntheses and/or stimulation of cholesterol export thus diminishes Abeta production. PPARgamma activity decreases Abeta production by promoting harmless catabolism of amyloid precursor protein while blocking the up-regulatory impact of cytokines on beta-secretase expression. Nitric oxide produced by the healthy cerebral microvasculature can suppress Abeta production by boosting expression of alpha-secretase while suppressing that of beta-secretase; conversely, cerebral ischemia provokes increased APP expression. Good insulin sensitivity and efficient brain insulin function protect by inhibiting gamma-secretase activity and increasing expression of IDE. The DHA provided by fish oil diminishes cerebral Abeta deposition in rodent AD models, for unclear reasons. Various measures which oppose microglial activation can inhibit up-regulation of beta-secretase and gamma-secretase by oxidants and cytokines, respectively. These considerations suggest that a number of nutraceutical or lifestyle measures may have potential for preventing or slowing AD: policosanol; 9-cis-beta-carotene; isomerized hops extract; DHA; measures which promote efficient endothelial NO generation, such as low-salt/potassium-rich diets, exercise training, high-dose folate, and flavanol-rich cocoa; chromium picolinate and cinnamon extract as aids for insulin sensitivity; and various agents which can oppose microglial activation, including vitamin D, genistein, and sesamin. The impact of these measures on Abeta production in rodent models of AD should be evaluated, with the intent of defining practical strategies for AD prevention.

The inhibition of gamma-secretase as a therapeutic approach to Alzheimer's disease.

Alzheimer's disease is a dementing neurodegenerative disorder for which there is no effective treatment at present. Genetic and biological studies provide evidence that the production and deposition of amyloid-beta peptides (Abeta contribute to the etiology of Alzheimer's disease. gamma-Secretase is the pivotal enzyme in generating the C terminus of Abeta which determines its aggregability and speed of deposition. Drugs that regulate the production of Abeta by inhibiting gamma-secretase activity could provide an effective therapy for Alzheimer's disease, although recent studies suggest that gamma-secretase plays important roles in cellular signaling. This review focuses on studies of the gamma-secretase biology and provides the direction for developing effective and selective gamma-secretase inhibitors as drugs for the treatment of Alzheimer's disease.

Continuing strategies for inhibiting Alzheimer's gamma-secretase.

Gamma-secretase processing of the amyloid-beta precursor protein (APP) releases the amyloid-beta peptide, which is widely held to be involved in the pathogenesis of Alzheimer's disease. This protease is apparently a complex of integral membrane proteins that includes the multi-pass presenilin. Transition-state analogue inhibitors of gamma-secretase are important molecular probes of the enzyme active site. We have identified new transition-state analogues, (hydroxyethy) urea peptidomimetics, that inhibit gamma-secretase activity at submicromolar concentrations in cell culture. The inhibitory activity of a family of such compounds provided further support that gamma-secretase has loose sequence specificity at the active site, and one of these compounds allowed partial purification of the protease complex. In addition, because the site of gamma-secretase cleavage of APP lies within its single transmembrane domain, we designed short peptides based on this domain which assume a helical conformation. These peptides inhibited gamma-secretase in the low micromolar range in cell culture, suggesting that they indeed mimick the APP substrate conformation.