Mort cellulaire et maladie d'Alzheimer : mécanismes moléculaires impliqués dans l'apoptose neuronale induite par le peptide b-amyloïde (Ab) sous forme soluble et facteurs protecteurs associés

[Résumé en français] Une théorie domine l'activité de recherche liée à la maladie d'Alzheimer (MA) depuis deux décennies : l'hypothèse de la cascade amyloïde, impliquant de façon causative l'agrégation du peptide Ab dans les caractéristiques pathologiques associées à la MA. De nombreuses études dont les nôtres suggèrent que l'agrégation des peptides, en tant qu'élément causatif de la pathologie, est à reconsidérer au profit d'une implication primordiale des oligomères solubles des peptides Ab une théorie domine l'activité de recherche liée à la maladie d'Alzheimer (MA) depuis deux décennies: l'hypothèse de la cascade amyloïde, impliquant de façon causative l'agrégation du peptide Ab dans les caractéristiques pathologiques associées à la MA. De nombreuses études dont les nôtres suggèrent que l'agrégation des peptides, en tant qu'élément causatif de la pathologie, est à reconsidérer au profit d'une implication primordiale des oligomères solubles des peptides Ab. Notre projet propose d'étudier les phénomènes de neurodégénérescence impliqués dans la MA en se focalisant sur les mécanismes moléculaires et cellulaires déclenchés par les peptides Ab (1-40/42) solubles. Nous avons mis en évidence que les peptides Ab solubles possèdent des propriétés fusogènes in vitro. Ces propriétés sont responsables de la neurotoxicité des peptides, due à leur interaction spécifique avec la membrane plasmique. En modifiant la fluidité membranaire, les peptides A~ solubles entraînent une apoptose caspase-3, -9 et calpaïnes dépendante, impliquant un stress oxydant et une déstabilisation précoce du réseau de microtubules (MTs). Nous avons montré qu'un enrichissement membranaire en cholestérol module la sensibilité des neurones aux peptides Ab solubles. Parmi les cibles intracellulaires permettant d'expliquer la perturbation des MTs, nous avons démontré que les peptides Ab solubles entraînent une néosynthèse de protéine tau sous forme déphosphorylée, associée à une dégradation des protéines MAP1A, MAP1B et de trois isoformes de MAP2 (2a, 2b, 2c). Ces modifications liées aux MTs ont un impact primordial sur l'établissement du trafic vésiculaire et sur la subséquente apoptose neuronale.[Résumé en anglais] For two decades, the predominant theory in the research related to Alzheimer's Disease (AD) has consisted in the amyloid cascade hypothesis, causally linking the Ab peptide aggregation to the pathological characteristics associated to AD. Many studies, including ours, suggest that the aggregation of the peptides as a causal element of the pathology should be reconsidered in favour of a crucial role played by the soluble oligomers of Ab. The aim of this study is to analyse the neurodegenerative processes involved in AD by focusing on the molecular and cellular mechanisms triggered by the soluble oligomers of Ab(1-40/42). We highlight the in vitro fusogenic properties of the soluble Ab peptides, which are responsible for the neurotoxicity of the peptides due to their specifie interaction with the plasma membrane. By modulating the membrane fluidity, the soluble Ap peptides entail a caspase-3, -9 and calpain-dependent apoptosis, inducing an oxidative stress and an early perturbation of the microtubule network (MTs). We show that, by enriching the membrane with cholesterol, the susceptibility of the neurons to the soluble Ab peptides is inhibited. Among the intracellular targets serving as explanations for the MTs perturbation, we have proved that the soluble Ap peptides entail the overexpression of the tau protein, independently of its phosphorylation state, associated with a degradation of the MAP1A, MAP1B proteins and of the three isoforms of MAP2 (2a, 2b, 2c). These perturbations linked to the MTS have a major impact on the setting-up of the vesicular traffic and on the subsequent neuronal apoptosis.NANCY1-SCD Medecine (545472101) / SudocSudocFranceF

Heparan sulfate 3- O -sulfotransferase 2 (HS3ST2) displays an unexpected subcellular localization in the plasma membrane

Background: Heparan sulfate (HS) 3-O-sulfation can be catalysed by seven 3-O-sulfotransferases (HS3STs) in humans, still it is the rarest modification in HS and its biological function is yet misunderstood. HS3ST2 and HS3ST3B exhibit the same activity in vitro. They are however differently expressed in macrophages depending on cell environment, which suggests that they may be involved in distinct cellular processes. Here, we hypothesized that both isozymes might also display distinct subcellular localizations.Methods: The subcellular distribution of HS3ST2 and HS3ST3B was analysed by using overexpression systems in HeLa cells. The localization of endogenous HS3ST2 was confirmed by immunostaining in primary macrophages.Results: We found that HS3ST3B was only localized in the Golgi apparatus and no difference between full-length enzyme and truncated construct depleted of its catalytic domain was observed. In contrast, HS3ST2 was clearly visualized at the plasma membrane. Its truncated form remained in the Golgi apparatus, meaning that the catalytic domain might support correct addressing of HS3ST2 to cell surface. Moreover, we found a partial co-localization of HS3ST2 with syndecan-2 in HeLa cells and primary macrophages. Silencing the expression of this proteoglycan altered the localization of HS3ST2, which suggests that syndecan-2 is required to address the isozyme outside of the Golgi apparatus.Conclusions: We demonstrated that HS3ST3B is a Golgi-resident isozyme, while HS3ST2 is addressed to the plasma membrane with syndecan-2.General significance: The membrane localization of HS3ST2 suggests that this enzyme may participate in discrete processes that occur at the cell surface

The role of heparan sulfates in protein aggregation and their potential impact on neurodegeneration

Neurodegenerative disorders, such as Alzheimer´s, Parkinson´s, and prion diseases, are directly linked to the formation and accumulation of protein aggregates in the brain. These aggregates, principally made of proteins or peptides that clamp together after acquisition of β-folded structures, also contain heparan sulfates. Several lines of evidence suggest that heparan sulfates centrally participate in the protein aggregation process. In vitro, they trigger misfolding, oligomerization, and fibrillation of amyloidogenic proteins, such as Aβ, tau, α-synuclein, prion protein, etc. They participate in the stabilization of protein aggregates, protect them from proteolysis, and act as cell-surface receptors for the cellular uptake of proteopathic seeds during their spreading. This review focuses attention on the importance of heparan sulfates in protein aggregation in brain disorders including Alzheimer´s, Parkinson´s, and prion diseases. The presence of these sulfated polysaccharides in protein inclusions in vivo and their capacity to trigger protein aggregation in vitro strongly suggest that they might play critical roles in the neurodegenerative process. Further advances in glyco-neurobiology will improve our understanding of the molecular and cellular mechanisms leading to protein aggregation and neurodegeneration.Fil: Maïza, Auriane. Universite de Paris; FranciaFil: Chantepie, Sandrine. Universite de Paris; FranciaFil: Vera, Claudia Cecilia. Universite de Paris; Francia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto Superior de Investigaciones Biológicas. Universidad Nacional de Tucumán. Instituto Superior de Investigaciones Biológicas; ArgentinaFil: Fifre, Alexandre. Universite de Paris; FranciaFil: Huynh, Minh Bao. Universite de Paris; FranciaFil: Stettler, Olivier. Universite de Paris; FranciaFil: Ouidja, Mohand Ouidir. Universite de Paris; FranciaFil: Papy Garcia, Dulce. Universite de Paris; Franci

Fetal bovine serum impacts the observed N‐glycosylation defects in TMEM165 KO HEK cells

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