Alterations of synapses and neuronal cell bodies in APPxPS1-KI mice and Alzheimer’s Disease

La Maladie d’Alzheimer (MA) se caractérise par une perte progressive de synapses et de neurones. La perte de synapses est un marqueur précoce corrélant de façon significative avec le déclin cognitif des patients. Comment le peptide amyloïde Abeta issu du clivage de la protéine précurseur de l’amyloïde (APP) peut induire ces pertes est toujours sujet à débat. Nous avons étudié ce mécanisme dans les souris APPxPresenilin1 knock-in (APPxPS1-KI) qui développent une perte de neurones dans le champ CA1 de l’hippocampe. Nous avons observé que cette perte de neurones est précédée d’une perte de synapses dans la stratum radiatum du CA1. Nous avons montré que ces pertes ne sont pas induites par un stress du réticulum endoplasmique et n’avons pas observé de dépression de l’activité synaptique ou d’augmentation de la dépression à long terme. Des altérations de la morphologie des épines dendritiques sont observées avant la perte de synapses et de neurones associées à un déficit de potentialisation à long terme et des troubles de la mémoire spatiale. Des altérations similaires de la forme des épines sont observées dans les biopsies de patients atteints de MA. Dans les souris ces altérations modifient la compartimentalisation électrique et biochimique de l’épine potentiellement impliquée dans la potentialisation à long terme. Dans les corps cellulaires des souris APPxPS1-KI, une accumulation d’Abeta est observée dans les lysosomes. Une modification du système lysosomal est également observée dans les biopsies de patients. Les altérations du système lysosomal sont spécifiquement observées dans les souris APPxPS1-KI et pourraient être impliquées dans les pertes de synapses et de neurones.Alzheimer’s Disease (AD) is characterized by a progressive loss of synapses and neurons. The loss of synapses is an early marker significantly correlating with cognitive decline in patients. How the Amyloid Precursor Protein (APP) cleavage product Amyloid Beta (Abeta) can trigger synapse and neuron loss remains debated. We investigated this mechanism in APPxPresenilin1 knock-in (APPxPS1-KI) mice that were previously shown to present with a loss of pyramidal neurons in the CA1 hippocampus. We observed that this loss of neurons was preceded by a loss of synapses in the stratum radiatum of CA1. We showed that these losses were not induced by an endoplasmic reticulum stress and we did not observe depression of synaptic activity or increase of long-term depression. Alterations of dendritic spine morphology were observed before the loss of synapses and neurons along with a deficit of long-term potentiation and spatial memory troubles. Similar dendritic spines morphological alterations were observed in cortical biopsies from AD patients. In mice, these alterations changed electrical and biochemical compartmentalization of the spines, potentially implicated in long-term potentiation. In APPxPS1-KI neuronal cell bodies, an accumulation of Abeta was observed in the lysosomes. A modification of the lysosomal system was also observed in biopsies from patients. The alterations of the lysosomal system were specifically observed in APPxPS1-KI mice and could be implicated in the loss of synapses and neurons

Altérations des synapses et des corps cellulaires neuronaux chez les souris APPxPS1-KI et dans la Maladie d'Alzheimer

Alzheimer’s Disease (AD) is characterized by a progressive loss of synapses and neurons. The loss of synapses is an early marker significantly correlating with cognitive decline in patients. How the Amyloid Precursor Protein (APP) cleavage product Amyloid Beta (Abeta) can trigger synapse and neuron loss remains debated. We investigated this mechanism in APPxPresenilin1 knock-in (APPxPS1-KI) mice that were previously shown to present with a loss of pyramidal neurons in the CA1 hippocampus. We observed that this loss of neurons was preceded by a loss of synapses in the stratum radiatum of CA1. We showed that these losses were not induced by an endoplasmic reticulum stress and we did not observe depression of synaptic activity or increase of long-term depression. Alterations of dendritic spine morphology were observed before the loss of synapses and neurons along with a deficit of long-term potentiation and spatial memory troubles. Similar dendritic spines morphological alterations were observed in cortical biopsies from AD patients. In mice, these alterations changed electrical and biochemical compartmentalization of the spines, potentially implicated in long-term potentiation. In APPxPS1-KI neuronal cell bodies, an accumulation of Abeta was observed in the lysosomes. A modification of the lysosomal system was also observed in biopsies from patients. The alterations of the lysosomal system were specifically observed in APPxPS1-KI mice and could be implicated in the loss of synapses and neurons.La Maladie d’Alzheimer (MA) se caractérise par une perte progressive de synapses et de neurones. La perte de synapses est un marqueur précoce corrélant de façon significative avec le déclin cognitif des patients. Comment le peptide amyloïde Abeta issu du clivage de la protéine précurseur de l’amyloïde (APP) peut induire ces pertes est toujours sujet à débat. Nous avons étudié ce mécanisme dans les souris APPxPresenilin1 knock-in (APPxPS1-KI) qui développent une perte de neurones dans le champ CA1 de l’hippocampe. Nous avons observé que cette perte de neurones est précédée d’une perte de synapses dans la stratum radiatum du CA1. Nous avons montré que ces pertes ne sont pas induites par un stress du réticulum endoplasmique et n’avons pas observé de dépression de l’activité synaptique ou d’augmentation de la dépression à long terme. Des altérations de la morphologie des épines dendritiques sont observées avant la perte de synapses et de neurones associées à un déficit de potentialisation à long terme et des troubles de la mémoire spatiale. Des altérations similaires de la forme des épines sont observées dans les biopsies de patients atteints de MA. Dans les souris ces altérations modifient la compartimentalisation électrique et biochimique de l’épine potentiellement impliquée dans la potentialisation à long terme. Dans les corps cellulaires des souris APPxPS1-KI, une accumulation d’Abeta est observée dans les lysosomes. Une modification du système lysosomal est également observée dans les biopsies de patients. Les altérations du système lysosomal sont spécifiquement observées dans les souris APPxPS1-KI et pourraient être impliquées dans les pertes de synapses et de neurones

Zebrafish as a preclinical model for Extracellular Vesicle-based therapeutic development

International audienceExtracellular Vesicles (EVs) are released during various pathophysiological processes and reflect the state of their cell of origin. Once released, they can propagate through biological fluids, target cells, deliver their content and elicit functional responses. These specific features would allow their harnessing as biomarkers, drug nano-vehicles and therapeutic intrinsic modulators. However, the further development of their potential therapeutic application is hampered by the lack of knowledge about how EVs behave in vivo. Recent advances in the field of imaging EVs in vivo now allow live-tracking of endogenous and exogenous EV in various model organisms at high spatiotemporal resolution to define their distribution, half-life and fate. This review highlights current imaging tools available to image EVs in vivo and how live imaging especially in the zebrafish embryo can bring further insights into the characterization of EVs dynamics, biodistribution and functions to potentiate their development for therapeutic applications

Zebrafish as a preclinical model for Extracellular Vesicle-based therapeutic development

Extracellular Vesicles (EVs) are released during various pathophysiological processes and reflect the state of their cell of origin. Once released, they can propagate through biological fluids, target cells, deliver their content and elicit functional responses. These specific features would allow their harnessing as biomarkers, drug nano-vehicles and therapeutic intrinsic modulators. However, the further development of their potential therapeutic application is hampered by the lack of knowledge about how EVs behave in vivo. Recent advances in the field of imaging EVs in vivo now allow live-tracking of endogenous and exogenous EV in various model organisms at high spatiotemporal resolution to define their distribution, half-life and fate. This review highlights current imaging tools available to image EVs in vivo and how live imaging especially in the zebrafish embryo can bring further insights into the characterization of EVs dynamics, biodistribution and functions to potentiate their development for therapeutic applications

Activity-induced MEMRI cannot detect functional brain anomalies in the APPxPS1-Ki mouse model of Alzheimer’s disease

International audienceAlzheimer’s disease (AD) is the most common cause of dementia. Aside neuropathological lesions, abnormal neuronal activity and brain metabolism are part of the core symptoms of the disease. Activity-induced Manganese-Enhanced Magnetic Resonance Imaging (MEMRI) has been proposed as a powerful approach to visualize evoked brain activity in rodents. Here, we evaluated the relevance of MEMRI in measuring neuronal (dys-)function in the APPxPS1 knocked-in (KI) mouse model of AD. Brain anomalies were firstly demonstrated in APPxPS1-Ki mice using cognitive testing (memory impairment) and histological mapping of immediate early gene products (decreased density of fos-positive neurons). Paradoxically, MEMRI analyses were not able to confirm the occurrence of neuronal hypoactivities in vivo. We then performed a neuropathological analysis that highlighted an abnormal increased permeability of the blood-brain barrier (BBB) in APPxPS1-Ki mice. We hypothesized that diffuse weakening of the BBB results in an uncontrolled diffusion of the MR contrast agent and a lack of correlation between manganese accumulation and neuronal activity. These results bring to light a limitation of the activity-induced MEMRI approach when applied to the APPxPS1-Ki mouse model as well as other mouse models harboring a compromised BBB

Alterations of neuronal lysosomes in Alzheimer's disease and in APPxPS1-KI mice

International audienceBackground: The cellular and molecular alterations associated with synapse and neuron loss in Alzheimer's disease (AD) remain unclear. In transgenic mouse models that express mutations responsible for familial AD, neuronal and synaptic losses occur in populations that accumulate fibrillar amyloid-β 42 (Aβ42) intracellularly.Objective: We aimed to study the subcellular localization of these fibrillar accumulations and whether such intraneuronal assemblies could be observed in the human pathology.Methods: We used immunolabeling and various electron microscopy techniques on APP x presenilin1 - knock-in mice and on human cortical biopsies and postmortem samples.Results: We found an accumulation of Aβ fibrils in lipofuscin granule-like organelles in APP x presenilin1 - knock-in mice. Electron microscopy of human cortical biopsies also showed an accumulation of undigested material in enlarged lipofuscin granules in neurons from AD compared to age-matched non-AD patients. However, in those biopsies or in postmortem samples we could not detect intraneuronal accumulations of Aβ fibrils, neither in the lipofuscin granules nor in other intraneuronal compartments.Conclusion: The intralysosomal accumulation of Aβ fibrils in specific neuronal populations in APPxPS1-KI mice likely results from a high concentration of Aβ42 in the endosome-lysosome system due to the high expression of the transgene in these neurons

Evidence for altered dendritic spine compartmentalization in Alzheimer’s disease and functional effects in a mouse model

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Golgi localization of SARS-CoV-2 spike protein and interaction with furin in cerebral COVID-19 microangiopathy: a clue to the central nervous system involvement?

International audienceIn a neuropathological series of 20 COVID-19 cases, we analyzed six cases (three biopsies and three autopsies) with multiple foci predominantly affecting the white matter as shown by MRI. The cases presented with microhemorrhages evocative of small artery diseases. This COVID-19 associated cerebral microangiopathy (CCM) was characterized by perivascular changes: arterioles were surrounded by vacuolized tissue, clustered macrophages, large axonal swellings and a crown arrangement of aquaporin-4 immunoreactivity. There was evidence of bloodbrain-barrier leakage. Fibrinoid necrosis, vascular occlusion, perivascular cuffing and demyelination were absent. While no viral particle or viral RNA was found in the brain, the SARS-CoV-2 spike protein was detected in the Golgi apparatus of brain endothelial cells where it closely associated with furin, a host protease known to play a key role in virus replication. Endothelial cells in culture were not permissive to SARS-CoV-2 replication. The distribution of the spike protein in brain endothelial cells differed from that observed in pneumocytes. In the latter, the diffuse cytoplasmic labeling suggested a complete replication cycle with viral release, notably through the lysosomal pathway. In contrast, in cerebral endothelial cells the excretion cycle was blocked in the Golgi apparatus. Interruption of the excretion cycle could explain the difficulty of SARS-CoV-2 to infect endothelial cells in vitro and to produce viral RNA in the brain. Specific metabolism of the virus in brain endothelial cells could weaken the cell walls and eventually lead to the characteristic lesions of COVID-19 associated cerebral microangiopathy. Furin as a modulator of vascular permeability could provide some clues for the control of late effects of microangiopathy

Golgi localization of SARS-CoV-2 spike protein and interaction with furin in cerebral COVID-19 microangiopathy: a clue to the central nervous system involvement?

International audienceIn a neuropathological series of 20 COVID-19 cases, we analyzed six cases (three biopsies and three autopsies) with multiple foci predominantly affecting the white matter as shown by MRI. The cases presented with microhemorrhages evocative of small artery diseases. This COVID-19 associated cerebral microangiopathy (CCM) was characterized by perivascular changes: arterioles were surrounded by vacuolized tissue, clustered macrophages, large axonal swellings and a crown arrangement of aquaporin-4 immunoreactivity. There was evidence of bloodbrain-barrier leakage. Fibrinoid necrosis, vascular occlusion, perivascular cuffing and demyelination were absent. While no viral particle or viral RNA was found in the brain, the SARS-CoV-2 spike protein was detected in the Golgi apparatus of brain endothelial cells where it closely associated with furin, a host protease known to play a key role in virus replication. Endothelial cells in culture were not permissive to SARS-CoV-2 replication. The distribution of the spike protein in brain endothelial cells differed from that observed in pneumocytes. In the latter, the diffuse cytoplasmic labeling suggested a complete replication cycle with viral release, notably through the lysosomal pathway. In contrast, in cerebral endothelial cells the excretion cycle was blocked in the Golgi apparatus. Interruption of the excretion cycle could explain the difficulty of SARS-CoV-2 to infect endothelial cells in vitro and to produce viral RNA in the brain. Specific metabolism of the virus in brain endothelial cells could weaken the cell walls and eventually lead to the characteristic lesions of COVID-19 associated cerebral microangiopathy. Furin as a modulator of vascular permeability could provide some clues for the control of late effects of microangiopathy

Ustensiles et espaces culinaires de la Protohistoire au début du XXe siècle, pré-actes du colloque international Corpus, Dijon, 4-7 juin 2024

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