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  Materials and Methods: We evaluated the morphology of lymphatic vessels in dural whole mounts of age-matched wild type, APOE3, and APOE4, female and male mice. We investigated the main cellular source of Apoe mRNA transcripts in the murine meninges using RNAscope. The levels of apoE in the meningeal dura were also assessed by western blot in mice fed a control or PLX5622 diet for 4 weeks. Single-cell RNA sequencing is being used to explore the transcriptomic signatures of meningeal dural cells from mice of different groups.
Results: Lymphatic vessel length and diameter are increased in 10-month-old APOE4 male mice, when compared to their APOE3 counterparts. This is not detected in female mice. Dural Itgam+ myeloid cells are the main source of Apoe mRNA transcripts, and a major source of local apoE protein. We show that APOE4 expression and age markedly affect the transcriptional signature of meningeal myeloid cells, leading to an up-regulation of genes linked to increased cell activation, lysosomal function, and antigen presentation.
Discussion: We describe a sex-dependent effect of APOE4 expression on the meningeal lymphatic system. We also show that myeloid cells contribute to the pool of meningeal apoE protein and the levels of Apoe expression by these cells remains high regardless of age and sex. Finally, we identify APOE isoform-, sex-, and age-specific meningeal transcriptional signatures, especially in myeloid cells, accompanying the remodeling of the brain-draining lymphatic system.
Conclusion: ApoE4 leads to an exacerbated meningeal myeloid cell activation and aberrant meningeal lymphatic morphology in male mice.
Background: Carrying the ε4 allele of the apolipoprotein E (APOE) gene is the strongest risk factor for Alzheimer’s disease (AD) besides age itself. Having one copy of APOE4 triples the risk for AD, whereas being homozygous for APOE4 increases the risk by greater than 12-fold [1]. As one potential mechanism, apoE, and especially apoE4, binds to amyloid-β (Aβ) with high affinity and acts as a catalyst to accelerate Aβ oligomer and fibril formation [2-5], increase their stability [6, 7], and promote their neurotoxicity [8-10]. Thus, inhibiting this early step in the amyloid cascade may thereby reduce or prevent neurodegeneration and AD.
Methods: We developed a high-throughput screening assay to identify inhibitors of the apoE4-Aβ interaction and used it to screen more than 3,000 compounds from small molecule drug repurposing libraries. Changes in cognition (MMSE scores) and clinical diagnoses of National Alzheimer’s Coordinating Center (NACC) participants were modeled using time slopes and Cox proportional hazards, respectively, adjusted for age and sex.
Results: We identified two FDA-approved drugs, imipramine and olanzapine, as novel inhibitors of the apoE4-Aβ interaction [11]. We confirmed that both drugs exhibited low neurotoxicity and blocked apoE-induced intracellular Aβ aggregation, tau hyperphosphorylation, and apoptosis in primary neuronal cultures. When taken by AD patients for their normal clinical indications, imipramine or olanzapine use was associated with improved cognition and increased incidence of receiving a better clinical diagnosis, especially among APOE4 carriers, relative to all other antidepressant or antipsychotic medications. Conclusions: The critical test of any proposed AD mechanism is whether it leads to effective treatments. Our screening approach identified imipramine and olanzapine, which have no structural, functional, or clinical similarities other than their shared ability to inhibit the apoE4-Aβ interaction, both of which showed evidence of improving AD cognition. These findings validate an apoE-centric approach to developing new AD therapeutics.
Frontotemporal dementia related to chromosome 3 (FTD3) is a rare sub- form of FTD, caused by a point mutation in the Charged Multivesicular Body Protein 2B (CHMP2B). This mutation causes neuronal phenotypes, such as mitochondrial deficiencies, accompanied by metabolic changes and interrupted endosomal-lysosomal fusion. However, the contribution of glial cells to FTD3 pathogenesis has until recently been rather unexplored. Since gliosis has been observed in FTD3 patient brains we sought out to investigate the role of microglia in FTD3, implementing human induced pluripotent stem cells (hiPSC) with either a heterozygous or homozygous CHMP2B mutation, introduced
Glial and vascular contributions to neurodegenerative diseases
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FDA-approved small molecule drugs inhibit the interaction of apolipoprotein E with amyloid-β and show evidence of improving cognition in Alzheimer’s disease patients Noah Johnson1, Athena Ching Jung Wang1, Christina Coughlan1, Stefan Sillau1, Esteban Lucero1, Lisa Viltz1, Neil Markham1, Cody Allen1, A. Ranjitha Dhanasekaran1, Heidi Chial1, Huntington Potter1
1Department of Neurology, University of Colorado Alzheimer’s and Cognition Center, and the Linda Crnic Institute for Down Syndrome, University of Colorado, Anschutz Medical Campus., USA
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LRP1 is a neuronal receptor for α-synuclein uptake and spread
Na Zhao1, Kai Chen1, Yuka Martens1, Axel Meneses1, Daniel Ryu2, Wenyan Lu1, Ana Caroline Raulin1, Fuyao Li1, Jing Zhao1, Yixing Chen1, Cynthia Linares1, Marshall Goodwin2, Yonghe Li1, Chia-Chen Liu1, Takahisa Kanekiyo1, David Holtzman3, Todd Golde2, Guojun Bu1
1Mayo Clinic, Jacksonville, USA, 2University of Florida, Gainesville, USA, 3Washington University School of Medicine, St. Louis, USA
 The aggregation and spread of α-synuclein (α-Syn) protein and related neuronal toxicity are the key pathological features of Parkinson’s disease (PD) and Lewy body dementia (LBD). Studies have shown that pathological species of α-Syn and tau can spread in a prion-like manner between neurons, although these two proteins have distinct pathological roles and contribute to different neurodegenerative diseases. It is reported that the low-density lipoprotein receptor-related protein 1 (LRP1) regulates the spread of tau proteins; however, the molecular regulatory mechanisms of α-Syn uptake and spread, and whether it is also regulated by LRP1, remain poorly understood. Here we established LRP1 knockout (LRP1-KO) human induced pluripotent stem cells (iPSCs) isogenic lines using a CRISPR/Cas9 strategy and generated iPSC-derived neurons (iPSNs) to test the role of LRP1 in α-Syn uptake. We found that the uptake of both monomeric and oligomeric α-Syn was significantly reduced in iPSNs with LRP1-KO compared with the WT controls. The uptake of pre-formed fibrils (PFFs) α-Syn was also inhibited in LRP1-KO iPSNs, albeit to a much lesser extent compared to α-Syn monomers and oligomers. The blocking of lysine residues on α-Syn effectively decreased the uptake of α-Syn in iPSNs and the N-terminus of α-Syn was critical for LRP1-mediated α-Syn uptake. Lastly, we constructed an adeno-associated viruses (AAV) to express human α-Syn in neurons and visualize the α-Syn spread in mouse brains. We found that the spreading of α-Syn was reduced in mouse brain with neuronal Lrp1 deletion. Altogether, we identified LRP1 as a key regulator of α-Syn neuronal uptake, as well as an important mediator of α-Syn spread in the brain. Our study provides new knowledge on the physiological and pathological role of LRP1 in α-Syn trafficking and pathology, offering insight for the treatment of synucleinopathies.
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Neurotoxicity in Frontotemporal Dementia 3 is caused by Altered Microglia Metabolism and Inflammatory Profile
Henriette Haukedal, Signe Lorenzen, Kristine Freude1
1University of Copenhagen, Frederiksberg, Denmark
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