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No description available.

Presenilin-1 (PS-1) is the catalytic core of the ã-secretase complex, which is best known for its role in the generation of the Alzheimer disease (AD)-related â-amyloid peptide. Mutated forms of PS-1 are known to be associated with particularly aggressive forms of AD. Changes in monoaminergic neurotransmitter systems, including the serotonin and norepinephrine systems, have long been associated with some of the earliest events in AD, whereas changes in the availability of these same monoamines have historically been associated with clinical depression. Therefore, it is not surprising that depression has now been proposed as a risk factor for developing AD and that pre-demented carriers of mutated forms of PS-1 are more prone to developing depression. MAO-A is historically associated with depression and is also a known risk factor for AD. Given this, I hypothesized that MAO-A represents a neurochemical link between depression and AD, and I chose to examine the influence of PS-1 mutations on MAO-A function in vivo/ex vivo and in vitro.<p> I first focused on the PS-1(M146V) knock-in mouse model of AD-related PS-1/ã-secretase function. I used a radioenzymatic assay to estimate MAO-A catalytic activity and western blot analysis to determine MAO-A protein expression, and found that MAO-A activity does not correlate with MAO-A expression in the cortex and cerebellum of the PS-1(M146V) mice. Furthermore, the potency of the MAO-A inhibitor clorgyline (CLG) is greater in both the cortex and cerebellum of the PS-1(M146V) mice compared to the potency of CLG in wildtype littermates. CLG dose-response curves suggest that there might be a change in cooperativity in the MAO-A protein from PS-1(M146V) cortex (which would suggest a change in conformation and/or access of the substrate to the catalytic pocket in MAO-A). High-pressure liquid chromatography was used to analyze monoamine levels in these same regions. The levels of monoamines (i.e. serotonin, dopamine and norepinephrine) suggest that PS-1 (M146V) inhibits MAO-A function in the cortex, but not in the cerebellum. Furthermore, CLG has no significant effect on amine levels in cortex, but tends to increase their accumulation in cerebellum.<p> The overexpression of PS-1 (M146V) in neuronal cultures reveals that this protein affects MAO-A activity and, more importantly, the PS-1(M146V) protein co-precipitates with MAO-A, thus suggesting a possibility for a direct protein-protein interaction. This is supported by the observation that MAO-A activity is increased in cell extracts incubated with the PS-1 substrate-competitor, N-[N-(3,5-difluorophenacetyl)-L-alanyl]-S-phenylglycine t-butyl ester (DAPT). Preliminary studies have been undertaken to determine the motif in MAO-A that could be acting as a binding site/target site for PS-1.<p> These combined results support the hypothesis that PS-1 proteins can influence MAO-A function and, furthermore, that MAO-A is a novel interactor for PS-1/ã-secretase. This could well explain some of the ambiguous literature associated with both of these proteins in disorders as diverse as depression and AD.

The enzyme monoamine oxidase (MAO) is linked to mental disorders such as depression and neurodegenerative diseases. Our laboratory has recently demonstrated that increases in calcium (Ca2+) can enhance MAO activity and that this might contribute to Alzheimer disease (AD). AD has been linked to gain-of-function mutations in the presenilin-1 (PS-1) protein that not only promote the generation of the toxic amyloid-â peptide, but that also alter intracellular Ca2+ availability. <p>Radioenzymatic MAO assays were used to demonstrate that over-expression of different AD-related PS-1 mutant proteins, i.e. Y115H, ÄEx9 and M146V, in hippocampal-derived HT-22 cells alter either basal and/or Ca2+-sensitive MAO-A activity. The effects of PS-1 mutant proteins on the availability of intracellular Ca2+ are not consistent suggesting that this may not be the primary means of regulating MAO activity. The sensitivity of MAO to Ca2+ was also demonstrated in cortical (both MAO-A and MAO-B responded to Ca2+) and cerebellar (only MAO-A responded to Ca2+) samples from transgenic mice overexpressing the PS-1 (M146V) mutation. These changes in MAO coincided with changes in the availability of the neurotransmitters dopamine, noradrenaline and serotonin in the cerebellum, but not in the cortex, and reflect the known regional differences in neurotransmitter regulation. Immunoprecipitation studies and the observed increase in MAO-A activity following in vitro chemical inhibition of the ã-secretase complex (comprising several proteins including PS-1) support the notion that PS-1 constitutively associates with MAO-A. These effects on Ca2+-sensitive MAO function could contribute to AD-related pathology and could also contribute to the depression often associated with AD.

Presenilin-1 (PS-1) is the catalytic core of the ã-secretase complex, which is best known for its role in the generation of the Alzheimer disease (AD)-related â-amyloid peptide. Mutated forms of PS-1 are known to be associated with particularly aggressive forms of AD. Changes in monoaminergic neurotransmitter systems, including the serotonin and norepinephrine systems, have long been associated with some of the earliest events in AD, whereas changes in the availability of these same monoamines have historically been associated with clinical depression. Therefore, it is not surprising that depression has now been proposed as a risk factor for developing AD and that pre-demented carriers of mutated forms of PS-1 are more prone to developing depression. MAO-A is historically associated with depression and is also a known risk factor for AD. Given this, I hypothesized that MAO-A represents a neurochemical link between depression and AD, and I chose to examine the influence of PS-1 mutations on MAO-A function in vivo/ex vivo and in vitro.<p> I first focused on the PS-1(M146V) knock-in mouse model of AD-related PS-1/ã-secretase function. I used a radioenzymatic assay to estimate MAO-A catalytic activity and western blot analysis to determine MAO-A protein expression, and found that MAO-A activity does not correlate with MAO-A expression in the cortex and cerebellum of the PS-1(M146V) mice. Furthermore, the potency of the MAO-A inhibitor clorgyline (CLG) is greater in both the cortex and cerebellum of the PS-1(M146V) mice compared to the potency of CLG in wildtype littermates. CLG dose-response curves suggest that there might be a change in cooperativity in the MAO-A protein from PS-1(M146V) cortex (which would suggest a change in conformation and/or access of the substrate to the catalytic pocket in MAO-A). High-pressure liquid chromatography was used to analyze monoamine levels in these same regions. The levels of monoamines (i.e. serotonin, dopamine and norepinephrine) suggest that PS-1 (M146V) inhibits MAO-A function in the cortex, but not in the cerebellum. Furthermore, CLG has no significant effect on amine levels in cortex, but tends to increase their accumulation in cerebellum.<p> The overexpression of PS-1 (M146V) in neuronal cultures reveals that this protein affects MAO-A activity and, more importantly, the PS-1(M146V) protein co-precipitates with MAO-A, thus suggesting a possibility for a direct protein-protein interaction. This is supported by the observation that MAO-A activity is increased in cell extracts incubated with the PS-1 substrate-competitor, N-[N-(3,5-difluorophenacetyl)-L-alanyl]-S-phenylglycine t-butyl ester (DAPT). Preliminary studies have been undertaken to determine the motif in MAO-A that could be acting as a binding site/target site for PS-1.<p> These combined results support the hypothesis that PS-1 proteins can influence MAO-A function and, furthermore, that MAO-A is a novel interactor for PS-1/ã-secretase. This could well explain some of the ambiguous literature associated with both of these proteins in disorders as diverse as depression and AD.

The enzyme monoamine oxidase (MAO) is linked to mental disorders such as depression and neurodegenerative diseases. Our laboratory has recently demonstrated that increases in calcium (Ca2+) can enhance MAO activity and that this might contribute to Alzheimer disease (AD). AD has been linked to gain-of-function mutations in the presenilin-1 (PS-1) protein that not only promote the generation of the toxic amyloid-â peptide, but that also alter intracellular Ca2+ availability. <p>Radioenzymatic MAO assays were used to demonstrate that over-expression of different AD-related PS-1 mutant proteins, i.e. Y115H, ÄEx9 and M146V, in hippocampal-derived HT-22 cells alter either basal and/or Ca2+-sensitive MAO-A activity. The effects of PS-1 mutant proteins on the availability of intracellular Ca2+ are not consistent suggesting that this may not be the primary means of regulating MAO activity. The sensitivity of MAO to Ca2+ was also demonstrated in cortical (both MAO-A and MAO-B responded to Ca2+) and cerebellar (only MAO-A responded to Ca2+) samples from transgenic mice overexpressing the PS-1 (M146V) mutation. These changes in MAO coincided with changes in the availability of the neurotransmitters dopamine, noradrenaline and serotonin in the cerebellum, but not in the cortex, and reflect the known regional differences in neurotransmitter regulation. Immunoprecipitation studies and the observed increase in MAO-A activity following in vitro chemical inhibition of the ã-secretase complex (comprising several proteins including PS-1) support the notion that PS-1 constitutively associates with MAO-A. These effects on Ca2+-sensitive MAO function could contribute to AD-related pathology and could also contribute to the depression often associated with AD.

Alzheimer's disease (AD) is a neurodegenerative disease associated with progressive dementia. This mini-review focuses on how the amyloid precursor protein (APP) plays a central role in AD and Down syndrome as the regulator of the APP-BP1/hUba3 activated neddylation pathway. It is argued that the physiological function of APP is to downregulate the level of β-catenin. However, this APP function is abnormally amplified in patients with familial AD (FAD) mutations in APP and presenilins, resulting in the hyperactivation of neddylation and the decrease of β-catenin below a threshold level. Evidence in the literature is summarized to show that dysfunction of APP in downregulating β-catenin may underlie the mechanism of neuronal death in AD and Down syndrome.

Intercellular signalling is essential for multicellular organisms to coordinate growth and development, and is mediated by a huge variety of proteins. Some signalling pathways rely on the proteolytic cleavage of membrane proteins by a relatively newly discovered process of regulated intramembrane proteolysis (RIP), the cleavage of proteins within a transmembrane domain. There are four classes of intramembrane cleaving proteases (ICliPs) – Rhomboids, Site-2-proteases, Signal peptide peptidases and γ-secretase. Of all the ICliPs studied to date, γ-secretase is unique, as it is comprised of a four-protein complex, and is only found in multicellular organisms. A vast amount of research is carried out on the γ-secretase complex, not just because of its role in developmentally important pathways, such as NOTCH signalling, but also due to its role in Alzheimer’s disease. The β-amyloid precursor protein (APP) is cleaved by γ-secretase, and defects in this process result in the release of abnormal peptides that form the senile plaques in the brains of Alzheimer’s disease patients. Homologues of the four components of γ-secretase (PRESENILIN (PS), NICASTRIN (NCT), ANTERIOR PHARYNX DEFECTIVE-1 (APH-1) and PRESENILIN ENHANCER-2 (PEN-2)) are found in plants. The aim of this thesis was to characterise the potential γ-secretase components in Arabidopsis thaliana, to determine whether they form a complex, and to analyse what role, if any, they play in plant signalling. The members of the putative Arabidopsis γ-secretase complex (AtPS1 and 2, AtNCT, AtAPH1 and AtPEN2) were identified through BLAST searches, and found to be uniformly expressed. Analysis of T-DNA insertion mutants in each of these genes, and combinations there of, revealed no gross morphological differences to wild type under normal growth conditions and when subjected to a range of stresses. Protein fusions to GFP under the control of the 35S promoter were constructed and stably transformed into plants. AtPEN2:GFP is expressed throughout the plant, and accumulates in BFA sensitive Golgi bodies in roots. AtPS1:GFP, only accumulates strongly in developing seeds. Native blue PAGE was used to look for high molecular weight complexes (HMW) containing AtPEN2:GFP and AtPS1:GFP. Both fusion proteins were found in similar sized HMW complexes. A variety of methods were used to look for substrates of the iv putative γ-secretase complex in Arabidopsis, and although no specific substrates were identified, a potential role in seed development has been established.

Mutations of three genes encoding amyloid precursor protein (APP), presenilin-1 (PSEN1), and presenilin-2 (PSEN2) have been shown to reliably result in familial early-onset Alzheimer's disease (FAD); a rare, but catastrophic, subtype of Alzheimer's disease (AD) marked by symptom emergence before age 65 as well as accelerated cognitive deterioration. The current study represents the first known meta-analysis on the association of APP, PSEN1 or PSEN2 on neurocognitive variables. A total of 278 FAD mutation-carriers (FAD-MC) and 284 cognitively healthy non-mutation-carriers (NC) across 10 independent investigations meeting inclusion criteria were chosen for the current meta-analysis (random effects design). Findings revealed an overarching trend of poorer performance by FAD-MC individuals compared to NC individuals across the majority of cognitive domains identified. Significant differences in effect sizes suggested FAD-MC individuals exhibited worse performance on measures of attention, explicit memory, fluency, primary memory, verbal, and visuospatial functioning. Findings indicative of differential sensitivity to cognitive domain impairments across FAD-MC and NC groups inform neuropsychological descriptions of individuals in preclinical phases of FAD.

Le réticulum endoplasmique (RE) joue un rôle majeur dans la conformation des protéines. L’accumulation de protéines non- ou mal-conformées dans le RE induit un stress qui peut être résolu par la réponse aux protéines mal-conformées (UPR). Un stress chronique du RE entraine une apoptose dépendante de l’UPR et se traduit par un déséquilibre de l’homéostasie tissulaire. Bien que l’apoptose dépendante d’un stress du RE soit observée et à l’origine d’un grand nombre de maladies humaines, les mécanismes pro-apoptotiques ainsi que ceux favorisant l’homéostasie tissulaire en réponse à un stress chronique du RE restent à ce jour méconnus. Cette thèse apporte une meilleure compréhension de ces mécanismes grâce à un nouveau modèle d’induction de stress du RE chez la drosophile basé sur la surexpression de la préséniline. L’apoptose observée dans ce modèle dépend d’une répression au moins transcriptionnelle du gène anti-apoptotique diap1 par la branche PERK/ATF4 de l’UPR, alors que les voies pro-apoptotiques classiquement impliquées dans l’apoptose en réponse à un stress du RE chez les mammifères ne semblent pas être impliquées. Par ailleurs, la branche PERK/ATF4 active la voie JNK par l’intermédiaire de la petite GTPase Rac1 et de la MAP3K Slipper qui sont activées dans les cellules apoptotiques. Cette activation aboutit à l’expression de Dilp8, un peptide ressemblant à l’insuline qui cause un retard de développement et permet ainsi de remplacer partiellement les cellules éliminées par apoptose. Dans notre modèle, les mécanismes classiquement décrits dans le maintien de l’homéostasie tissulaire chez la drosophile tels que la prolifération compensatoire ou la réparation des tissus ne semblent pas avoir de rôle majeur. Ces résultats établissent, une nouvelle voie qui participe à l’homéostasie tissulaire dans un nouveau modèle de stress chronique du RE / The Endoplasmic Reticulum (ER) plays a major role in protein folding. The accumulation of unfolded proteins in the ER induces a stress which can be resolved by the Unfolded Protein Response (UPR). The chronicity of ER-stress leads to UPR-induced apoptosis and in turn to an unbalance of tissue homeostasis. Although ER stress-dependent apoptosis is observed in a great number of devastating human diseases, how cells activate apoptosis and promote tissue homeostasis after chronic ER-stress remains poorly understood. During my thesis we have established of a novel model of chronic ER-stress using the Drosophila wing imaginal disc as a model system. We have validated that Presenilin (Psn) overexpression induces chronic ER-stress in Drosophila associated to a PERK/ATF4-dependent apoptosis requiring the down-regulation of the anti-apoptotic diap1 gene. Interestingly, the classical pro-apoptotic pathways described in mammals do not seem implicated in Psn-overexpression-dependent apoptosis. PERK/ATF4 also activated the JNK pathway through the small GTPase Rac1 and the MAP3K Slipper activation in apoptotic cells, leading to the expression of Dilp8. This insulin-like peptide caused a developmental delay, which partially allowed the replacement of apoptotic cells. The other mechanisms involved in tissue homeostasis in Drosophila, i.e. compensatory homeostasis and wound healing, do not seem to have a major role in our model. These results establish a new pathway that participates in tissue homeostasis thanks to a novel chronic Drosophila ER stress model