Pharmacological ablation of astrocytes reduces Aβ degradation and synaptic connectivity in an ex vivo model of Alzheimer’s disease

Abstract

Background Astrocytes provide a vital support to neurons in normal and pathological conditions. In Alzheimer’s disease (AD) brains, reactive astrocytes have been found surrounding amyloid plaques, forming an astrocytic scar. However, their role and potential mechanisms whereby they affect neuroinflammation, amyloid pathology, and synaptic density in AD remain unclear. Methods To explore the role of astrocytes on Aβ pathology and neuroinflammatory markers, we pharmacologically ablated them in organotypic brain culture slices (OBCSs) from 5XFAD mouse model of AD and wild-type (WT) littermates with the selective astrocytic toxin L-alpha-aminoadipate (L-AAA). To examine the effects on synaptic circuitry, we measured dendritic spine number and size in OBCSs from Thy-1-GFP transgenic mice incubated with synthetic Aβ42 or double transgenics Thy-1-GFP/5XFAD mice treated with LAAA or vehicle for 24 h. Results Treatment of OBCSs with L-AAA resulted in an increased expression of pro-inflammatory cytokine IL-6 in conditioned media of WTs and 5XFAD slices, associated with changes in microglia morphology but not in density. The profile of inflammatory markers following astrocytic loss was different in WT and transgenic cultures, showing reductions in inflammatory mediators produced in astrocytes only in WT sections. In addition, pharmacological ablation of astrocytes led to an increase in Aβ levels in homogenates of OBCS from 5XFAD mice compared with vehicle controls, with reduced enzymatic degradation of Aβ due to lower neprilysin and insulin-degrading enzyme (IDE) expression. Furthermore, OBSCs from wild-type mice treated with L-AAA and synthetic amyloid presented 56% higher levels of Aβ in culture media compared to sections treated with Aβ alone, concomitant with reduced expression of IDE in culture medium, suggesting that astrocytes contribute to Aβ clearance and degradation. Quantification of hippocampal dendritic spines revealed a reduction in their density following L-AAA treatment in all groups analyzed. In addition, pharmacological ablation of astrocytes resulted in a decrease in spine size in 5XFAD OBCSs but not in OBCSs from WT treated with synthetic Aβ compared to vehicle control. Conclusions Astrocytes play a protective role in AD by aiding Aβ clearance and supporting synaptic plasticity.

High, in Contrast to Low Levels of Acute Stress Induce Depressive-like Behavior by Involving Astrocytic, in Addition to Microglial P2X7 Receptors in the Rodent Hippocampus

“…Based on the electrophysiological and behavioral experiments, and on the immunohistochemistry results, it is concluded that relatively mild stress may cause MDD-like behavior in rodents by activating microglial P2X7Rs, while in the case of more pronounced stress, astrocytic P2X7Rs also become involved. This was directly confirmed-in agree-ment with the electrophysiology data-by the use of mice pretreated with the selective astrocytic toxin L-α-aminoadipate [69,70] or with minocycline [71], a selective inhibitor of microglial activation.…”

The Role of Astrocytes in Synapse Loss in Alzheimer's Disease: A Systematic Review

“…Although this might suggest that the presence of astrocytes in AD is harmful and that removing them could have therapeutic effects, we have to be careful. For example, when pharmacologically ablating astrocytes in organotypic brain slices from 5xFAD mice, Aβ levels increased and spine density and size were reduced (Davis et al, 2021 ). A better treatment option might be to specifically target reactive astrocytes.…”

Infection and Immunometabolism in the Central Nervous System: A Possible Mechanistic Link Between Metabolic Imbalance and Dementia

“…In addition, crosstalk between astrocytes and microglia in the hippocampus is responsible for sensitivity to insults ( Lana et al, 2020 ), pointing to the importance of communication between astroglia and brain-resident macrophages in cognitive dysfunctions ( Liddelow et al, 2017 ; Linnerbauer et al, 2020 ). Furthermore, astrocytes and microglia participate in Aβ clearance and protection of synaptic connectivity in AD models, suggesting highly context-dependent immunological roles of these glial cell populations against AD development ( Davis et al, 2021 ).…”