γ-Secretase plays a pivotal role in the production of neurotoxic amyloid β-peptide (Aβ), the principal component of amyloid plaques present in Alzheimer’s disease. It consists of a core complex of presenilin (PS), nicastrin, anterior pharynx-defective 1 (Aph-1), and presenilin enhancer 2 (Pen-2) proteins. PS harbors the catalytic aspartates required for regulated intramembrane proteolysis and the paralogs (PS1 and PS2) contribute to the assembly of distinct subpopulations of γ-secretases that may fulfill distinct roles. To characterize the molecular environments of distinct γ-secretases complexes in-depth quantitative comparisons were performed on 1) wild-type PS1 and its derivative carrying point mutations known to cause heritable early-onset AD in mice, and 2) PS1- or PS2-containing γ-secretase complexes equipped with N-terminal tandem-affinity purification (TAP) tags on PS paralogs in HEK293 cells. Isobaric labeling of co-purifying peptides for quantitative mass spectrometry revealed that γ-secretase complexes interact with other protein networks, including the cellular catenin-cadherin network, the molecular machinery that targets and fuses synaptic vesicles to cellular membranes, and the H+-transporting lysosomal ATPase macro-complex. The study revealed mature γ-secretase complexes containing PS1 or mutant PS1 to be indistinguishable in their protein composition, confirmed several previously proposed γ-secretase interactors, identified many novel interactors and uncovered a subset of proteins which can engage in robust interactions with γ-secretase complexes in individual cell types but may escape detection when whole brains are used as biological source materials. Interestingly, signal peptide peptidase (SPP), a Type II TM cleaving aspartyl protease, was pre-dominantly found to co-purify with PS2-containing γ-secretase complexes and could be shown not to influence their maturation but to affect cleavage or release of cellular Aβ. A model emerged from this work that suggests PS1 and PS2 paralogs may divide up the task of handling a broad range of membrane stubs at least in part by associating with different molecular environments.

Increased amyloid-β (Aβ) load in the brain, neurite degeneration, neuronal loss, and decreased levels of several neurotrophins are among the characteristics of Alzheimer’s disease (AD). Generation of Aβ occurs when the amyloid precursor protein (APP) is proteolytically processed by β- and γ-secretases in the amyloidogenic pathway. However, Aβ formation is prevented if APP is cleaved by α- and γ- secretases in the non-amyloidogenic pathway. The normal function of APP is still not fully known. It seems clear that the different fragments that are produced during proteolytic processing have different bioactive properties. APP and its metabolites have been implicated in neurite outgrowth, synaptogenesis, cell adhesion, neuroprotection and apoptosis. The aim of this thesis was to investigate how neurotrophic factors affect the synthesis and processing of APP and its two mammalian paralogues the APP-like protein-1 and-2 (APLP1 and APLP2). We also wanted to determine how the expression levels of α- and β- secretases were affected in response to these factors. In addition, we wanted to analyze if the levels and function of the most well characterized APP adaptor protein, Fe65, was regulated during neuronal differentiation. Our results show that retinoic acid (RA), insulin-like growth factor-1 (IGF-1), and brain derived neurotrophic factor (BDNF) all regulate expression levels and processing of the APP protein family. Interestingly, the increased processing of the APP family involves different signaling pathways. The PI3-K/Akt pathway is involved in IGF-1-induced APP and APLP1, but not APLP2, processing. In addition, RA-induced expression of the α-secretase, a disintegrin and metalloproteinase (ADAM) 10 is dependent on PI3-K, whereas PKC is involved in RA-induced expression of another α-secretase, ADAM17/TACE. Furthermore, we present evidence that maturation of the adaptor protein Fe65, as well as its docking to APP, increases concomitant with neuronal differentiation. / At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 4: Manuscript.

<p>Alzheimer Disease (AD) is the most common neurodegenerative disorder in the world. One of the neuropathological hallmarks of AD is the senile plaques in the brain. The plaques are mainly composed of the amyloid β (Aβ) peptide. Aβ is generated from the amyloid precursor protein, APP, when it is first cleaved by the β-secretase and subsequently the γ-secretase complex. The γ-secretase complex cleaves at different sites, called γ and ε, where the γ-cleavage site generates Aβ peptides of different lengths and ε-cleavage generates the APP intracellular domain (AICD). The two major forms of Aβ is 40 and 42 amino acids long peptides, where the latter is more prone to aggregate and is the main component in senile plaques. The γ-secretase complex is composed of four proteins; Pen-2, Aph-1, nicastrin and presenilin (PS). The PS protein harbours the catalytic site of the complex, where two aspartate residues in position 257 and 385 (Presenilin 1 numbering) are situated. Most Familial AD (FAD) mutations in the PS gene cause a change in the γ-cleavage site, leading to a shift from producing Aβ40 to the longer more toxic variant Aβ42. Frequently, this often leads to impairments of the AICD production. Another substrate for the γ-secretase complex is Notch. It is important to maintain the Notch signaling since an intracellular domain (NICD) is formed after cleavage by the γ-secretase complex in the membrane (S3-site) and this domain is involved in transcription of genes important for cell fate decisions.</p><p>It has been reported that certain APP luminal juxtamembrane mutations could drastically alter Aβ secretion, however their effect on AICD production remains unknown. In this study we want to analyse wether the juxtamembrane region is important for the AICD production. To gain more insight into the luminal juxtamembrane function for γ-secretase-dependent proteolysis, we have made a juxtamembrane chimeric construct. A four-residue sequence preceding the transmembrane domain (TMD) of APP (GSNK), was replaced by its topological counterpart from the human Notch1 receptor (PPAQ). The resulting chimeric vector C99GVP-PPAQ and the wildtype counterpart were expressed in cells lacking PS1 and PS2 (BD8) together with PS1wt. We observed that the chimeric construct did not alter production of AICD when using a cell based luciferase reporter gene assay monitoring AICD production. We also introduced a PS1 variant lacking a big portion of the large hydrophilic loop, PS1∆exon10, since our group has previously observed that this region affect Aβ production¹⁴³. We found that the absence of the large hydrophilic loop in PS1 gave a 2-fold decrease in AICD-GVP formation from C99GVPwt compared to PS1wt.  The activity of PS1wt and PS1Δexon10 using C99GVP-PPAQ as a substrate gave similar result as the C99GVPwt substrate, i.e. a 2-fold decrease in AICD-GVP formation when comparing PS1Δexon10 with PS1wt. From this data we therefore suggest that the four residues in the juxtramembrane domain (JMD) (GSNK) is not altering ε-cleavage of APP when changed to Notch1 counterpart, PPAQ. Furthermore, we also show that the 2-fold decrease in AICD-production by the PS1Δexon10 molecule is not changed between the two substrates C99GVPwt and C99GVP-PPAQ. This indicates that the luminal region of APP is not directly involved in the ε-site processing. If the luminal region is affecting processing in the γ-cleavage sites, remains however to be investigated.</p>

Alzheimer Disease (AD) is the most common neurodegenerative disorder in the world. One of the neuropathological hallmarks of AD is the senile plaques in the brain. The plaques are mainly composed of the amyloid β (Aβ) peptide. Aβ is generated from the amyloid precursor protein, APP, when it is first cleaved by the β-secretase and subsequently the γ-secretase complex. The γ-secretase complex cleaves at different sites, called γ and ε, where the γ-cleavage site generates Aβ peptides of different lengths and ε-cleavage generates the APP intracellular domain (AICD). The two major forms of Aβ is 40 and 42 amino acids long peptides, where the latter is more prone to aggregate and is the main component in senile plaques. The γ-secretase complex is composed of four proteins; Pen-2, Aph-1, nicastrin and presenilin (PS). The PS protein harbours the catalytic site of the complex, where two aspartate residues in position 257 and 385 (Presenilin 1 numbering) are situated. Most Familial AD (FAD) mutations in the PS gene cause a change in the γ-cleavage site, leading to a shift from producing Aβ40 to the longer more toxic variant Aβ42. Frequently, this often leads to impairments of the AICD production. Another substrate for the γ-secretase complex is Notch. It is important to maintain the Notch signaling since an intracellular domain (NICD) is formed after cleavage by the γ-secretase complex in the membrane (S3-site) and this domain is involved in transcription of genes important for cell fate decisions. It has been reported that certain APP luminal juxtamembrane mutations could drastically alter Aβ secretion, however their effect on AICD production remains unknown. In this study we want to analyse wether the juxtamembrane region is important for the AICD production. To gain more insight into the luminal juxtamembrane function for γ-secretase-dependent proteolysis, we have made a juxtamembrane chimeric construct. A four-residue sequence preceding the transmembrane domain (TMD) of APP (GSNK), was replaced by its topological counterpart from the human Notch1 receptor (PPAQ). The resulting chimeric vector C99GVP-PPAQ and the wildtype counterpart were expressed in cells lacking PS1 and PS2 (BD8) together with PS1wt. We observed that the chimeric construct did not alter production of AICD when using a cell based luciferase reporter gene assay monitoring AICD production. We also introduced a PS1 variant lacking a big portion of the large hydrophilic loop, PS1∆exon10, since our group has previously observed that this region affect Aβ production143. We found that the absence of the large hydrophilic loop in PS1 gave a 2-fold decrease in AICD-GVP formation from C99GVPwt compared to PS1wt.  The activity of PS1wt and PS1Δexon10 using C99GVP-PPAQ as a substrate gave similar result as the C99GVPwt substrate, i.e. a 2-fold decrease in AICD-GVP formation when comparing PS1Δexon10 with PS1wt. From this data we therefore suggest that the four residues in the juxtramembrane domain (JMD) (GSNK) is not altering ε-cleavage of APP when changed to Notch1 counterpart, PPAQ. Furthermore, we also show that the 2-fold decrease in AICD-production by the PS1Δexon10 molecule is not changed between the two substrates C99GVPwt and C99GVP-PPAQ. This indicates that the luminal region of APP is not directly involved in the ε-site processing. If the luminal region is affecting processing in the γ-cleavage sites, remains however to be investigated.

L’importance des activités protéolytiques associées à la membrane plasmique dans divers processus biologiques fondamentaux est de mieux en mieux définie. Les protéases de la famille ADAM (A Disintegrin and Metalloprotease), et ADAM10 en particulier, ont suscité un intérêt tout particulier du fait de l’importance de leurs substrats (récepteur de l’EGF, TNFα, Notch, APP…). Néanmoins, peu d’études se sont intéressées aux mécanismes régulant le trafic d’ADAM10.Les tétraspanines sont une super-famille de protéines de surface impliquées dans de nombreux processus biologiques fondamentaux parmi lesquels la migration, les interactions intercellulaires, la réponse immunitaire, la fusion des gamètes… L’une des caractéristiques majeure des tétraspanines est leur capacité à organiser un réseau d’interactions moléculaires appelé le « tetraspanin web ». De précédentes études menées dans le laboratoire ont montré qu’ADAM10 est associé au « tetraspanin web ». Néanmoins, la tétraspanine en interaction directe avec ADAM10 permettant son association au réseau n’est pas encore connue. Dans cette étude nous nous sommes intéressés à la régulation d’ADAM10 par les tétraspanines. Nous avons ainsi pu identifier une sous-famille de tétraspanines à 8 cystéines, les TspanC8 (Tspan5, Tspan10, Tspan14, Tspan15, Tspan17 et Tspan33), comme étant capables d’interagir directement avec ADAM10 et de réguler sa sortie du réticulum endoplasmique. Nous avons montré que Tspan5, Tspan14, Tspan15 et Tspan33 sont capables de réguler l’expression de surface d’ADAM10 et que Tspan10 et Tspan17 entrainent l’accumulation d’ADAM10 dans un compartiment endosomal tardif. Les TspanC8 pourraient également contribuer à la régulation de la spécificité de substrat d’ADAM10 puisque nous avons montré que l’expression des TspanC8 humaines Tspan5 et Tspan14 augmente l’activation de la voie Notch alors que Tspan15 n’a pas d’effet. Par ailleurs, les TspanC8 de Drosophile sont capables d’interagir directement avec Kuzbanian (l’orthologue d’ADAM10), permettent son accumulation à la surface cellulaire et régulent l’activation de la voie Notch dans différents contextes développementaux. Nous proposons que les TspanC8 soient une nouvelle famille de protéines ayant une fonction très conservée dans la régulation de l’activité et du trafic d’ADAM10, capables de réguler l’activation de la voie Notch. / Increasing evidence suggests a critical implication of membrane-associated protease activities in numerous biological processes. ADAM (A Disintegrin and Metalloprotease) proteases, and especially ADAM10, are of particular interest because of the importance of their substrates (EGF receptor, TNF α, Notch, APP…). However, few studies focus on the mechanisms of ADAM10 trafficking. Tetraspanins are a super-family of proteins implicated in numerous biological processes including migration, intercellular interactions, immune response, gamete fusion… One of the most striking features of tetraspanins is their ability to organise multi-molecular complexes called « Tetraspanin Web ». Previous studies in the laboratory have shown that ADAM10 is associated to the « Tetraspanin Web ». Nevertheless, the tetraspanin in direct interaction with ADAM10 that drives its association to the web is not known. In this study, we focused on ADAM10 regulation by tetraspanins. We identified a subfamily of tetraspanins with 8 cysteines in their large extracellular domain that we called TspanC8 (Tspan5, Tspan10, Tspan14, Tspan15, Tspan17 and Tspan33) that can directly interact with ADAM10 and regulate its egress from the endoplasmic reticulum. We have shown that Tspan5, Tspan14, Tspan15 and Tspan33 regulate the surface expression of ADAM10 and that Tspan10 and Tspan17 accumulate ADAM10 in a late endosomal compartment. TspanC8 could also contribute to substrate specificity since Tspan5 and Tspan14 can increase Notch activation when Tspan15 cannot. Drosophila TspanC8 directly interact with the Drosophila ADAM10 ortholog Kuzbanian, increase its accumulation at the cell surface and modulate Notch activation in several developmental contexts. We propose that TspanC8 constitute a new family of Notch regulators with conserved functions in the regulation of ADAM10 trafficking and activity.

Kočová, K.: Natural compounds and their β-secretase inhibitory activity, Diploma thesis, Charles University in Prague, Faculty of Pharmacy in Hradci Králové, Department of Pharmaceutical Botany and Ecology, Hradec Králové 2015, 83 p. Data used in this Diploma Thesis have been taken from foreigner scientific literature. It provides the whole summary of natural compounds with β-secretase inhibitory activity. First chapter Alzheimer's disease briefly describes a definition, risk factors and symptomatology of the disease. Most of this chapter characterizes an etiopathology of the disease focused on amyloid theory. Finally there are also mentioned current approaches to therapy of Alzheimer's disease and those, which stay in clinical trials. Next part is dedicated to physiological functions and substrates of the β-secretase. This diploma thesis evaluates the current state of scientific research of synthetic inhibitors of β-secretase, describes the most important methods of testing inhibition and activity of β-secretase in vitro and outlines the issue of development of new inhibitors using in silico method. Main part of this work consists of the list of natural compounds with β- secretase inhibitory activity. This part is structured according to particular types of primary and secondary metabolites....

L'importance des activités protéolytiques associées à la membrane plasmique dans divers processus biologiques fondamentaux est de mieux en mieux définie. Les protéases de la famille ADAM (A Disintegrin and Metalloprotease), et ADAM10 en particulier, ont suscité un intérêt tout particulier du fait de l'importance de leurs substrats (récepteur de l'EGF, TNFα, Notch, APP...). Néanmoins, peu d'études se sont intéressées aux mécanismes régulant le trafic d'ADAM10.Les tétraspanines sont une super-famille de protéines de surface impliquées dans de nombreux processus biologiques fondamentaux parmi lesquels la migration, les interactions intercellulaires, la réponse immunitaire, la fusion des gamètes... L'une des caractéristiques majeure des tétraspanines est leur capacité à organiser un réseau d'interactions moléculaires appelé le " tetraspanin web ". De précédentes études menées dans le laboratoire ont montré qu'ADAM10 est associé au " tetraspanin web ". Néanmoins, la tétraspanine en interaction directe avec ADAM10 permettant son association au réseau n'est pas encore connue. Dans cette étude nous nous sommes intéressés à la régulation d'ADAM10 par les tétraspanines. Nous avons ainsi pu identifier une sous-famille de tétraspanines à 8 cystéines, les TspanC8 (Tspan5, Tspan10, Tspan14, Tspan15, Tspan17 et Tspan33), comme étant capables d'interagir directement avec ADAM10 et de réguler sa sortie du réticulum endoplasmique. Nous avons montré que Tspan5, Tspan14, Tspan15 et Tspan33 sont capables de réguler l'expression de surface d'ADAM10 et que Tspan10 et Tspan17 entrainent l'accumulation d'ADAM10 dans un compartiment endosomal tardif. Les TspanC8 pourraient également contribuer à la régulation de la spécificité de substrat d'ADAM10 puisque nous avons montré que l'expression des TspanC8 humaines Tspan5 et Tspan14 augmente l'activation de la voie Notch alors que Tspan15 n'a pas d'effet. Par ailleurs, les TspanC8 de Drosophile sont capables d'interagir directement avec Kuzbanian (l'orthologue d'ADAM10), permettent son accumulation à la surface cellulaire et régulent l'activation de la voie Notch dans différents contextes développementaux. Nous proposons que les TspanC8 soient une nouvelle famille de protéines ayant une fonction très conservée dans la régulation de l'activité et du trafic d'ADAM10, capables de réguler l'activation de la voie Notch.

No description available.

<p>The cancer stem cell hypothesis claims that only a small subpopulation of cells within a tumor is responsible for tumor growth, recurrence after treatment and metastasis. These cells have been termed tumor-initiating cells or cancer stem cells and are functionally defined by their capacity to elicit the growth of tumors in immune-compromised animals that recapitulate the cellularity of the tumor from which they were isolated. Several reports demonstrate that tumor-initiating cells are resistant to most current treatments. Hence, novel therapies for breast cancer should be developed that specifically target these tumorigenic cells. The Notch signaling pathway is hyperactive in human breast cancer as well as in mouse mammary tumor-initiating cells. In this study, I have found that inhibitors of the pathway target breast tumor-initiating cells from various breast cancer subtypes and may provide a novel therapy for breast cancer. MRK-003, a gamma-secretase inhibitor that blocks Notch signaling, inhibited the self-renewal of breast tumor-initiating cells <em>in vitro</em> and reduced tumor growth in xenograft models. MRK-003 inhibited proliferation of tumor cells within xenografts and induced their apoptosis and differentiation towards the myoepithelial lineage. Expression of the Notch pathway antagonists led to similar outcome in human breast tumor cell lines. Notably, tumors in MRK-003 treated mice were devoid of tumor initiating cells, suggesting that inhibitors of Notch signaling may lead to durable cancer cures. These findings suggest that GSIs target breast tumor-initiating cells and may prove to be effective novel anti breast cancer drugs. <strong> </strong></p> <p><strong> </strong></p> / Doctor of Philosophy (PhD)

As enzimas, acetilcolinesterase (AChE) e ?-secretase1 (BACE1), são alvos validados para o tratamento da Doença de Alzheimer (DA) uma vez que atuam no sistema nervoso central contribuindo para o avanço da doença. Neste contexto, o interesse por inibidores destas enzimas e a busca por ensaios enzimáticos seletivos e eficazes tem importância crucial. Neste trabalho é descrito o desenvolvimento de metodologias on-line, em capilares de sílica fundida, e off-line, em esferas de agarose para triagem de ligantes envolvendo as enzimas AChE e BACE1 via imobilização e co-imobilização por ligação covalente. Nos métodos on-line, a imobilização da BACE1 e a co-imobilização das enzimas AChE e BACE1 em capilares de sílica fundida foram realizadas via ligação amino-glutaraldeído e as atividades das enzimas foram monitoradas on-line por cromatografia líquida de alta de eficiência e espectrometria de massa (CLAE-EM) através da medida das massas correspondentes aos produtos das clivagens enzimáticas. Nestes, foram possíveis se determinar os parâmetros cinéticos para as enzimas imobilizadas como; variações de pH e temperatura, as constantes cinéticas (KMap) e validação com inibidores padrão. Ressaltando também a aplicação na triagem de uma coleção de oito compostos sintéticos com identificação de dois compostos e a caracterização dos mesmos. Nos métodos off-line, a imobilização da AChE e da BACE1 em suportes de agarose foram realizadas partindo de diferentes tipos de ligação com grupos nucleófilos previamente ligados ao suporte. Os diferentes suportes de agarose com a AChE imobilizada foram estudados usando o propionato de p-nitrofenil como substrato por meio da medida da absorbância do produto formado p-nitrofenol a 348 nm. O sistema com a enzima imobilizada agarose-trietilamina-AChE (agarose-TEA-AChE) ótimo foi utilizado para validação do método para triagem de ligantes com o inibidor padrão sendo determinado os parâmetros cinéticos e termodinâmicos de inibição, tais como; potência inibitória (IC50), constante de inibição (Ki) e constante de dissociação (KD). Já para a enzima BACE1, a atividade enzimática foi monitorada por fluorescência a ?em= 495 nm (?ex= 395 nm) utilizando o substrato IV, sendo possível a seleção do melhor método para imobilização da BACE1. Em ambos os métodos, on-line e off-line, a imobilização foi eficiente refletindo na atividade de cada enzima após o processo. Os métodos para triagem desenvolvidos neste trabalho são inéditos para ambas as enzimas e reportam grandes avanços comparados aos ensaios já consolidados, uma vez que a co-imobilização contribuiu para a construção de um modelo de triagem inovador, sendo possível a avaliação das interações específicas de um ligante contra dois alvos biológicos em um mesmo sistema (CLAE-EM) automatizado. Ressaltando também que os métodos com a AChE e BACE1 em duas matrizes distintas forneceram modelos de ensaios com formatos diferentes que podem ser aplicados de acordo com as ferramentas analíticas disponíveis, desde as mais simples como espectrofotometria no UV-Vis, fluorescência, aos mais sofisticados e automatizados como CLAE-EM. / The enzymes, acetylcholinesterase (AChE) and ?-secretase1 (BACE1), are targets validated for the treatment of Alzheimer\'s Disease (AD) because they act in the central nervous system contributing to the disease advance. In this context, the interest in inhibitors of these enzymes and the search for selective and effective enzymatic assays is of crucial importance. This work describes the development of on-line methodologies, in fused silica capillaries, and off-line in agarose beads for screening ligands involving the AChE and BACE1 enzymes via immobilization and co-immobilization by covalent attachment. In the on-line methods the immobilization of BACE1 and co-immobilization of AChE and BACE1 enzymes in fused silica capillaries were performed via amino-glutaraldehyde bonding and the enzyme activities were monitored on-line employing high performance liquid chromatography and mass spectrometry (HPLC-MS) by measuring the masses corresponding to the products of the enzymatic cleavages. In these enabled the determination of kinetic parameters for immobilized enzymes such as; pH and temperature variations, kinetic constants (KMap) and validation with standard inhibitors. Also, the application in the screening of a collection of eight synthetic compounds with identification and characterizations of two compounds was carried out. In the off-line methods, the immobilizations of AChE and BACE1 on agarose supports were performed through different types of binding with nucleophilic groups previously attached to the support. The different active-agarose supports with immobilized AChE were studied using p-nitrophenyl propionate as substrate by measuring the absorbance of the product formed p-nitrophenol at 348 nm. The system with the immobilized enzyme optimal agarose-triethylamine-AChE (agarose-TEA-AChE) was used for validation of the method for screening ligands with the standard inhibitor being determined the kinetic and thermodynamic parameters of inhibition, such as; inhibitory power (IC50), inhibition constant (Ki) and dissociation constant (KD). For BACE1 enzyme, the enzymatic activity was monitored by fluorescence at ?em = 495 nm (?ex = 395 nm) using the substrate IV, and it was possible to select the best method for immobilization of BACE1. In both methods, both on-line and off-line, the immobilizations procedures were efficient reflecting on the activity of each enzyme after the process. The screening methods developed in this work are unprecedented for both enzymes and represent an improvement to the already consolidated screenings assays, because the co-immobilization contributed to the construction of an innovative screening model, being possible the evaluation of the specific interactions of a ligand against two biological targets in the same automated system. It is worth emphasizing that the AChE and BACE1 methods in two different matrices have provided models of assays in different format that can be applied according to the available analytical tools, from the simplest ones such as UV-Vis spectrophotometry, fluorescence, to the automated systems such as HPLC-MS.