A cross-species spatiotemporal proteomic analysis identifies UBE3A-dependent signaling pathways and targets

Angelman syndrome (AS) is a severe neurodevelopmental disorder caused by the loss of neuronal E3 ligase UBE3A. Restoring UBE3A levels is a potential disease-modifying therapy for AS and has recently entered clinical trials. There is paucity of data regarding the molecular changes downstream of UBE3A hampering elucidation of disease therapeutics and biomarkers. Notably, UBE3A plays an important role in the nucleus but its targets have yet to be elucidated. Using proteomics, we assessed changes during postnatal cortical development in an AS mouse model. Pathway analysis revealed dysregulation of proteasomal and tRNA synthetase pathways at all postnatal brain developmental stages, while synaptic proteins were altered in adults. We confirmed pathway alterations in an adult AS rat model across multiple brain regions and highlighted region-specific differences. UBE3A reinstatement in AS model mice resulted in near complete and partial rescue of the proteome alterations in adolescence and adults, respectively, supporting the notion that restoration of UBE3A expression provides a promising therapeutic option. We show that the nuclear enriched transketolase (TKT), one of the most abundantly altered proteins, is a novel direct UBE3A substrate and is elevated in the neuronal nucleus of rat brains and human iPSC-derived neurons. Taken together, our study provides a comprehensive map of UBE3A-driven proteome remodeling in AS across development and species, and corroborates an early UBE3A reinstatement as a viable therapeutic option. To support future disease and biomarker research, we present an accessible large-scale multi-species proteomic resource for the AS community (https://www.angelman-proteome-project.org/)

Rôle de la neuroinflammation et du récepteur microglial TREM2 dans la progression de deux modèles de tauopathie

Neuroinflammation processes appear to play a major role in Alzheimer's disease (AD). Recent genetic studies support this correlation between neuroinflammation and AD and include a gene, TREM2, expressed on microglial surface. Tauopathy is a characteristic lesion of AD. It results in hyperphosphorylation and intraneuronal aggregation of Tau protein. In the literature, only few articles describe the role of TREM2 in the development of Tau pathology, and they report contradictory results. We therefore do not know for sure whether a deficiency in TREM2 has a deleterious effect or not on tauopathy. Thus, the goal of my thesis is to study the role of neuroinflammation and TREM2 in the progression of tauopathy, in two different models. The first is obtained by stereotaxic injection of AAV vectors into the CA1 layer of the hippocampus of TREM2-deficient or non-deficient mice. These vectors lead to the overexpression of different forms of the human tau protein, thus making it possible to recapitulate the different tauopathy stages.In parallel, we used a more progressive trangenic model of tauopathy, the THY-Tau22 mouse, to study the influence of TREM2 deficiency at different stage of the pathology. Our study demonstrated the toxicity of Tau soluble forms in the AAV model compared to its aggregated forms. The THY-Tau22 transgenic model allowed us to demonstrate an increase in tauopathic lesions in TREM2 deficient mice compared to wild type mice, at late stage only. This suggests that, similar to amyloid models, the effect of TREM2 deficiency on the course of tauopathy is influenced by the stage of the disease.Les processus de neuro-inflammation jouent un rôle majeur dans la maladie d'Alzheimer (MA). Des études génétiques récentes démontrent cette association entre neuro-inflammation et MA et impliquent notamment un gène, TREM2, qui code pour un récepteur exprimé à la surface de la microglie. La tauopathie est une lésion caractéristique de la MA. Elle se traduit par l’hyperphosphorylation et l’agrégation intraneuronale de la protéine Tau. Les travaux sur le rôle de TREM2 dans le développement de la pathologie Tau sont peu nombreux et donnent des résultats contradictoiresAinsi, l’objectif de ma thèse est d’étudier le rôle de la neuroinflammation et de TREM2 dans la progression de la tauopathie, dans deux modèles différents. Le premier est obtenu par injection stéréotaxique de vecteurs AAV dans la couche CA1 de l’hippocampe de souris déficientes ou non en TREM2. Ces vecteurs entrainent la surexpression de différentes formes de la protéine Tau humaine et permettent de récapituler les différents stades de la tauopathie.Nous avons en parallèle utilisé un modèle transgénique plus progressif de tauopathie, la souris THY-Tau22, afin d’étudier l’influence du stade de la pathologie dans l’effet provoqué par une déficience en TREM2 sur l’évolution de la pathologie. Notre étude a mis en évidence la toxicité des formes solubles de Tau dans le modèle AAV par rapport à ses formes agrégées. Le modèle transgénique THY-Tau22 nous a permis de mettre en évidence une augmentation des lésions tauopathiques dans les souris déficientes en TREM2 par rapport aux souris qui ne le sont pas, uniquement à un stade avancé. Cela suggère que, à l’instar des modèles amyloïdes, l’effet de la déficience en TREM2 sur le décours de la tauopathie est différent en fonction du stade considéré

Role of Neuroinflammation and the TREM2 Microglial Receptor in the Progression of two Models of Tauopathy

Les processus de neuro-inflammation jouent un rôle majeur dans la maladie d'Alzheimer (MA). Des études génétiques récentes démontrent cette association entre neuro-inflammation et MA et impliquent notamment un gène, TREM2, qui code pour un récepteur exprimé à la surface de la microglie. La tauopathie est une lésion caractéristique de la MA. Elle se traduit par l’hyperphosphorylation et l’agrégation intraneuronale de la protéine Tau. Les travaux sur le rôle de TREM2 dans le développement de la pathologie Tau sont peu nombreux et donnent des résultats contradictoiresAinsi, l’objectif de ma thèse est d’étudier le rôle de la neuroinflammation et de TREM2 dans la progression de la tauopathie, dans deux modèles différents. Le premier est obtenu par injection stéréotaxique de vecteurs AAV dans la couche CA1 de l’hippocampe de souris déficientes ou non en TREM2. Ces vecteurs entrainent la surexpression de différentes formes de la protéine Tau humaine et permettent de récapituler les différents stades de la tauopathie.Nous avons en parallèle utilisé un modèle transgénique plus progressif de tauopathie, la souris THY-Tau22, afin d’étudier l’influence du stade de la pathologie dans l’effet provoqué par une déficience en TREM2 sur l’évolution de la pathologie. Notre étude a mis en évidence la toxicité des formes solubles de Tau dans le modèle AAV par rapport à ses formes agrégées. Le modèle transgénique THY-Tau22 nous a permis de mettre en évidence une augmentation des lésions tauopathiques dans les souris déficientes en TREM2 par rapport aux souris qui ne le sont pas, uniquement à un stade avancé. Cela suggère que, à l’instar des modèles amyloïdes, l’effet de la déficience en TREM2 sur le décours de la tauopathie est différent en fonction du stade considéré.Neuroinflammation processes appear to play a major role in Alzheimer's disease (AD). Recent genetic studies support this correlation between neuroinflammation and AD and include a gene, TREM2, expressed on microglial surface. Tauopathy is a characteristic lesion of AD. It results in hyperphosphorylation and intraneuronal aggregation of Tau protein. In the literature, only few articles describe the role of TREM2 in the development of Tau pathology, and they report contradictory results. We therefore do not know for sure whether a deficiency in TREM2 has a deleterious effect or not on tauopathy. Thus, the goal of my thesis is to study the role of neuroinflammation and TREM2 in the progression of tauopathy, in two different models. The first is obtained by stereotaxic injection of AAV vectors into the CA1 layer of the hippocampus of TREM2-deficient or non-deficient mice. These vectors lead to the overexpression of different forms of the human tau protein, thus making it possible to recapitulate the different tauopathy stages.In parallel, we used a more progressive trangenic model of tauopathy, the THY-Tau22 mouse, to study the influence of TREM2 deficiency at different stage of the pathology. Our study demonstrated the toxicity of Tau soluble forms in the AAV model compared to its aggregated forms. The THY-Tau22 transgenic model allowed us to demonstrate an increase in tauopathic lesions in TREM2 deficient mice compared to wild type mice, at late stage only. This suggests that, similar to amyloid models, the effect of TREM2 deficiency on the course of tauopathy is influenced by the stage of the disease

THY-Tau22 mouse model accumulates more tauopathy at late stage of the disease in response to microglia deactivation through TREM2 deficiency

International audienceThe role played by microglia has taken the center of the stage in the etiology of Alzheimer's disease (AD). Several genome-wide association studies carried out on large cohorts of patients have indeed revealed a large number of genetic susceptibility factors corresponding to genes involved in neuroinflammation and expressed specifically by microglia in the brain. Among these genes TREM2, a cell surface receptor expressed by microglia, arouses strong interest because its R47H variant confers a risk of developing AD comparable to the ε4 allele of the APOE gene. Since this discovery, a growing number of studies have therefore examined the role played by TREM2 in the evolution of amyloid plaques and neurofibrillary tangles, the two brain lesions characteristic of AD. Many studies report conflicting results, reflecting the complex nature of microglial activation in AD. Here, we investigated the impact of TREM2 deficiency in the THY-Tau22 transgenic line, a well-characterized model of tauopathy. Our study reports an increase in the severity of tauopathy lesions in mice deficient in TREM2 occurring at an advanced stage of the pathology. This exacerbation of pathology was associated with a reduction in microglial activation indicated by typical morphological features and altered expression of specific markers. However, it was not accompanied by any further changes in memory performance. Our longitudinal study confirms that a defect in microglial TREM2 signaling leads to an increase in neuronal tauopathy occurring only at late stages of the disease

Development of an AAV-based model of tauopathy targeting retinal ganglion cells and the mouse visual pathway to study the role of microglia in Tau pathology

Tauopathy is a typical feature of Alzheimer's disease of major importance because it strongly correlates with the severity of cognitive deficits experienced by patients. During the pathology, it follows a characteristic spatiotemporal course which takes its origin in the transentorhinal cortex, and then gradually invades the entire forebrain. To study the mechanisms of tauopathy, and test new therapeutic strategies, it is necessary to set-up relevant and versatile in vivo models allowing to recapitulate tauopathy. With this in mind, we have developed a model of tauopathy by overexpression of the human wild-type Tau protein in retinal ganglion cells in mice (RGCs). This overexpression led to the presence of hyperphosphorylated forms of the protein in the transduced cells as well as to their progressive degeneration. The application of this model to mice deficient in TREM2 (Triggering Receptor Expressed on Myeloid cells-2, an important genetic risk factor for AD) as well as to 15-month-old mice showed that microglia actively participate in the degeneration of RGCs. Surprisingly, although we were able to detect the transgenic Tau protein up to the terminal arborization of RGCs at the level of the superior colliculi, spreading of the transgenic Tau protein to post-synaptic neurons was detected only in aged animals. This suggests that there may be neuron-intrinsic- or microenvironment mediators facilitating this spreading that appear with aging