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  MATERIALS AND METHODS: In this work we use state-of-the-art clinical neuroproteomics and systems biology to define at proteome-wide level the compositions of brain extracellular vesicles (EVs), obtained by PROSPR [2], from post-mortem brain tissues (brain regions from each subject: prefrontal cortex, caudate and hippocampus) of subjects with Schizophrenia (SCHZ) and matched controls (n=30). The obtained proteomics data, from each experimental group and brain region, were analyzed by one-way ANOVA. Significance was established at p<0.05 after Bonferroni correction.
RESULTS AND DISCUSSION: Our data indicate presence of specific molecular mechanisms of neuroinflammation in brain EVs of these subjects previously linked by us to neurodegeneration and dementia [3]. These common abnormally regulated specific molecules in SCHZ- brain-EVs include DPYSL2, GFAP and MBP to mention just a few of the most significantly altered (p<0.001) and relevant.
CONCLUSIONS: Identification of common molecular mechanisms of neuronal insult linked to neuroinflammation in neurodegenerative dementias and in SCHZ, as reported here in brain EVs, may help to identify novel therapeutic targets for these events in both brain diseases and help to prevent or ameliorate neurodegeneration in SCHZ patients. ACKNOWLEGMENTS: The research has been funded by Miguel Servet tenure track program (CP21/00096) of the Instituto de Salud Carlos III (ISCIII, Spain) awarded to X.G.-P. under the 2021 ISCIII-Health Strategy Action [This grant is co-funded by European Union Funds (Fondo Social Europeo Plus, FSE+)]. IRBLLEIDA and X.G.-P. are co-funded by CERCA Program/Generalitat de Catalunya.
Background: Homozygosity for the rare APOE3-Christchurch (APOE3Ch) variant, encoding for apoE3-R136S (apoE3-Ch), was linked to resistance against an aggressive form of familial AD. Carrying two copies of APOE3Ch was sufficient to delay autosomal AD onset by 30 years1. This remarkable protective effect makes it a strong candidate for uncovering new therapies against AD. Thus, we aim to explore the protective mechanisms of APOE3Ch against AD onset, to inform therapy. Methods: We used both amyloid mouse models and human induced- pluripotent stem cells (iPSC) models to address this hypothesis. We examined whether astrocytic expression of apoE3-Ch through an AAV- mediated approach can mitigate AD-related pathology and toxicity in 8 months 5xFAD mice. We have also established various iPSC-derived models using the iNDI line series, which is an iPSC series isogenic for APOE derived from the well-characterized KOL2.1J APOE3 parental line2. In parallel, we have also generated additional isogenic iPSC lines carrying the APOE3Ch variant from APOE3 and APOE4 parental lines by using CRISPR/Cas9 technology. Biochemical and biophysical properties of native apoE3-Ch lipoprotein particles secreted by iPSC- derived astrocytes have been investigated using heparin affinity chromatography and size-exclusion chromatography.
Results: We report initial results on the impact of astrocytic apoE3-Ch on amyloid pathology and toxicity in 8 months 5xFAD mice. Our data shows successful AAV-mediated overexpression of apoE in astrocytes and suggests apoE3-Ch specific changes in protein levels and solubility. We also report early evidence of altered biochemical properties of apoE3-Ch produced in HEK cells, showing decreased heparin binding. Finally, we present the establishment and early characterization of APOE3Ch iPSC-derived cell models, including iPSC-derived astrocytes, neurons, and cerebral organoids.
Conclusions: The proposed work and the developed methods to study apoE3-Ch promises to provide new insights into the possible roles of this rare, mutated protein in protecting against AD, offering new therapeutic avenues for AD treatment.
Glial and vascular contributions to neurodegenerative diseases
Protective mechanism of APOE3-Christchurch in Alzheimer’s disease
Ana-Caroline Raulin1, Cynthia Linares1, Lindsey Kuchenbecker1, Sydney V. Doss1, Maxwell Dacquel1,
Yuka A. Martens1, Chia-Chen Liu1, Guojun Bu1
1Mayo Clinic, Department of Neuroscience, Jacksonville, USA
Translocator protein (18 kDa) regulates microglial synaptic engulfment in synucleinopathy
Yuan Shi1,2,3, Mochen Cui1,2,4, Juan Zu1,2,4, Jochen Herms1,2,3 1Center for Neuropathology, Ludwig Maximilian University of Munich, Munich, Germany, 2Department of Translational Brain Research, German Center for Neurodegenerative Diseases (DZNE), Munich, Germany, 3Munich Cluster for Systems Neurology (SyNergy), Munich,
Germany, 4Munich Medical Research School, Ludwig Maximilian University of Munich, Munich, Germany
 Background: Synaptic loss does coincide with cognitive impairment in synucleinopathies, such as Parkinson’s disease dementia, or Lewy body dementia. It is frequently seen in these diseases that synaptic loss is accompanied by the elevation of translocator protein (18 kDa) (TSPO), a five-transmembrane domain protein located at the outer membrane of mitochondria. TSPO is highly expressed in activated microglia and has recently been identified as a key modulator of microglial synaptic engulfment [1]. We hypothesized that this synaptic engulfment pathway is activated early in synucleinopathies and mediates synaptic loss.
Materials and Methods: Using in vivo two-photon microscopy, we monitored dendritic spines of GFP-labelled apical dendrites of layer V pyramidal neurons in PDGF-h-α-syn mice at 3-4 months of age – a mouse model of synucleinopathy, in which human wild-type alpha- synuclein is overexpressed predominantly in neurons. We further pharmacologically inhibited TSPO activation and genetically depleted TSPO, respectively, in PDGF-h-α-syn mice of the same age to check how TSPO affects dendritic spines and microglial engulfment of synaptic material.
Results: We observed a gradual decrease of dendritic spine density in PDGF-h-α-syn mice, which is accompanied by an elevated microglial TSPO activation and increased microglial engulfment of synaptic materials. By interfering with TSPO activation using high-affinity TSPO ligand PK11195 or depleting TSPO genetically, we observed a recovered dendritic spine density with alleviated microglial TSPO and their engulfment.
Conclusions: Collectively, our findings suggest an essential role of TSPO in regulating microglial synaptic engulfment in synucleinopathy. TSPO might serve as a potential therapeutic target for synaptic loss and subsequent cognitive impairment in various synucleinopathies.
60 • ISMND 2022
Background: Triggering receptor expressed on myeloid cells 2 (TREM2) is an innate immune receptor expressed by microglia [1]. While heterozygous variants in TREM2 have been implicated in risk for late- onset Alzheimer’s disease (AD) [2,3], homozygous loss of function TREM2 variants cause a rare leukodystrophy characterized by bone cysts and early-onset dementia, Nasu-Hakola disease (NHD) [4,5]. However, despite intense investigation, the role of TREM2 in NHD pathogenesis remains poorly understood.
Defects in lysosomal function and lipid metabolism in human microglia harboring a TREM2 loss of function mutation
Fabia Filipello1, Shih Feng You1, Sidhartha Mahali1, Abhirami Kannan Iyer1, Rita Martinez1, Olena Korvatska2, Wendy H Raskind2, Bryan Bollman3, Luca De Feo3, Laura Ghezzi3, Miguel Minaya1, Anil Cashikar1, Jun-Ichi Satoh4, Beatty Wandy5, Marina Cella6, Laura Piccio3, Celeste Karch1
1Department of Psychiatry, Washington University in St Louis, St Louis, USA, 2Department of Psychiatry and Behavioral Sciences, University of Washington, Seattle, USA, 3Department of Neurology, Washington University in St Louis, St Louis, USA, 4Department of Bioinformatics and Molecular Neuropathology, Meiji Pharmaceutical University, Tokyo, Japan, 5Department of Molecular Microbiology, Washington University School of Medicine, St Louis, USA, 6Department Of Pathology and Immunology, Washington University in St Louis, St Louis, USA

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