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  Results: With GiD model, we found that mild reactive astrocytes can naturally reverse its reactivity, whereas severe reactive astrocytes can cause irreversible neurodegeneration, brain atrophy and cognitive deficits, all within 30 d. Mechanistically, excessive H2O2 originated from monoamine oxidase B in severe reactive astrocytes causes glial activation, tauopathy, neuronal death, brain atrophy, cognitive impairment and eventual death, which are significantly prevented by AAD-2004, a potent H2O2 scavenger. These H2O2-induced pathological features of AD in GiDs are consistently recapitulated in a three- dimensional culture AD model, virus-infected APP/PS1 mice and the brains of patients with AD.
Discussion: Our study indicates that severe reactive astrocytes are sufficient for neurodegeneration and proposes that there is a conserved molecular pathway in reactive astrocytes found under various toxic environments such as AD. Furthermore, our study raises profound implications for the current theory of AD pathogenesis: once the neurotoxic severe reactive astrocytes are turned on, irreversible neurodegeneration continues regardless of the presence or absence of an Aβ burden.
Conclusions: Our study identifies H2O2 from severe but not mild reactive astrocytes as a key determinant of neurodegeneration in AD.
Aims: In 2019, CD22, a canonical B-cell receptor, was discovered as a surface receptor and negative regulator of phagocytosis in microglia [1]. While CD22 levels were increased in 24 month old wild type mice, CD22’s role in the pathogenesis of Alzheimer´s disease (AD) is yet unknown. Impaired microglial phagocytosis has been linked to the accumulation of amyloid beta, one of the hallmarks of AD, and associated with microglia-mediated neuroinflammation. As microglial phagocytosis is thought to be an important process in counteracting amyloid beta deposition, we set out to investigate beneficial effects of CD22 loss on microglial phagocytosis in the context of Alzheimer-like pathology and inflammation, in vitro and in vivo.
Methods: Primary microglia were isolated from wild type and CD22- /- pups. With these cells we assessed the inflammatory response, autophagy and amyloid-beta (Abeta) phagocytosis. For in vivo aims, we crossed the APPPS1 mouse to the CD22-/- mouse and will assess Abeta pathology response at the age of 4 months.
Results: To mimic the increase of CD22 during aging, primary microglia in a mixed glia culture were aged in vitro. We could confirm the expression of CD22 in microglia as well as the deletion of CD22 on the mRNA and protein level in CD22-/- cells. At different time points, cells were stimulated with LPS/ATP and the inflammatory response was measured in the supernatant of the wild type CD22-/- microglia. To assess phagocytosis, cells were incubated with fluorescent labelled amyloid beta and the expression of different receptors associated with amyloid beta was investigated. Next, amyloid beta deposition and neuroinflammation will be analyzed in APPPS1 and APPPS1.CD22-/- microglia.
Conclusion: Taken together, our in vitro data present a model where the effect of in vitro aging and inflammation on CD22-dependent processes can be investigated and later be correlated to the in vivo data.
Glial and vascular contributions to neurodegenerative diseases
    PP14
Characterization of the Role of Microglial CD22 in Alzheimer’s Disease
Tyler Pugeda1, Marina Jendrach1, Frank Heppner1
1Department of Neuropathology, Department of Neuropathology, Charité– Universitätsmedizin Berlin, Berlin, Germany
   PP13
Conditionally knocking out the RNA-binding protein,Tia1,in microglia of a mouse model
of tauopathy reduces inflammation
Chelsea J. Webber1, Anna Cruz1, Rebecca Roberts1, Lushuang Zhang1, Estefania Obandoa1, Benjamin Wolozin1,2 1Department of Pharmacology and Experimental Therapeutics, Boston University School of
Medicine, Boston, USA, 2Department of Neurology, Boston University School of Medicine, Boston, USA
 The RNA-binding protein, T-cell antigen interacting protein 1 (Tia1), is central to the translational stress response and regulates transcription. Tia1 is directly implicated in neurodegeneration because mutations in Tia1 cause amyotrophic lateral sclerosis (ALS). Our laboratory has demonstrated that Tia1 also promotes the accumulation of toxic tau oligomers in neuronal models of Alzheimer’s disease (AD). Interestingly, ubiquitous Tia1 knockout increases peripheral inflammatory responses, such as TNFα and COX-2 transcription. This is important because chronic inflammation contributes to the pathophysiology of AD, ADRD and ALS. The ubiquitous expression of Tia1 raises the possibility that its actions on other cell types might also contribute to disease progression.
To elucidate the role of Tia1 in the immune system in the brain, we conditionally knocked out Tia1 in microglia, using a Cx3cr1 driven cre- recombinase, and then crossed this knockout to P301S tau mice, which overexpresses human 4R1N tau and develop strong tauopathy.
We found that conditional Tia1 knockout in microglia in P301S tau mice decreased microglial activation, decreased tau aggregation, and increased neuron survival. At 9 months of age, levels of interleukin- 1β (1L-1β) and TREM2 were both decreased in TIA1-/-xP301S tau mice. IL-1β was decreased 78.9% by ELISA and 62.5% by rt-qPCR and TREM2 transcript exhibited a 46.7% reduction when compared to P301S/TIA1+/+ mice. Additionally, neurons had a 42.3% reduction in C1qa transcription and a 47% increase in phosphorylated-ERK, indicating increased neuronal resilience. Conditionally knocking out Tia1 also reduced toxic oligomeric tau (tau fractionation 54.1%, MC1 immunohistochemistry 44.9%).
These results indicate that Tia1 expression contributes to activation of microglia in tauopathy mice and that selectively knocking out Tia1 reduces this activation, in turn protecting surrounding cells. This provides insight into the strong effect microglial responses exert on neurons, enhancing tau aggregation and neuronal degeneration.
Background: The cellular prion protein (PrPC) acts as a high affinity receptor for amyloid beta oligomers (AβO), a main neurotoxic species mediating Alzheimer’s disease (AD) pathology. The interaction of AβO with PrPC subsequently activates Fyn tyrosine kinase and neuroinflammation. Herein, we used our previously developed a small peptide aptamer 8 (PA8) binding to PrPC as a therapeutic to target the AβO-PrP-Fyn axis and prevent its associated pathologies.
Methods: Using in vitro experiments, we found that PA8 prevents the binding of AβO with PrPC and reduces AβO-induced neurotoxicity in mouse neuroblastoma N2a cells and primary hippocampal neurons. Next, we performed in vivo experiments using transgenic 5XFAD mouse model of AD. 5XFAD mice were treated with PA8 and scaffold protein thioredoxin A (control) at 14.4ug/day dosage for 12 weeks by intraventricular infusion using Alzet® osmotic pumps. After completion of treatment, behavioral studies were performed. Following behavioral experiments, brain tissues were processed for biochemical, single/
  PP15
Peptide aptamer (PA8) targeting Aβ-PrP-Fyn axis reduces activated gliosis and improves memory function in 5XFAD transgenic mouse model
Tahir Ali1,2, Antonia N. Klein1,2, Alex Vu1,2, Sabine Gilch1,2
1Calgary Prion Research Unit, Department of Comparative Biology & Experimental Medicine, Faculty of Veterinary Medicine, University of Calgary, Calgary, Alberta, Canada., Calgary, Canada, 2Hotchkiss Brain Institute, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada, Calgary, Canada
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