Extracellular Vesicles From 3xTg-AD Mouse and Alzheimer’s Disease Patient Astrocytes Impair Neuroglial and Vascular Components

Abstract

Astrocytes are specialized glial cells that are essential components of the neurovascular unit (NVU) and are involved in neurodevelopment, brain maintenance and repair, and neurodegeneration. Astrocytes mediate these processes by releasing cellular mediators such as extracellular vesicles (EVs). EVs are vehicles of cell-cell communication and have been proposed as mediators of damage in AD. However, the transcellular mechanism by which Alzheimer disease (AD) astrocytes impair the function of NVU components is poorly understood. Therefore, we evaluated the effects of adult PS1-KI and 3xTg-AD astrocyte conditioned media (CM) and EVs on NVU components (neuroglia and endothelium) in vitro. Additionally, SAD and FAD astrocyte-derived EVs (A-EVs) were characterized, and we evaluated their effects on NVU in cocultured cells in vitro and on intrahippocampal CA1 cells in vivo. Surprisingly, cultured 3xTg-AD astrocytes showed increased glial fibrillary acidic protein (GFAP) reactivity compared to PS1-KI astrocytes, which denotes astrocytic hyperreactivity. CM from adult mice 3xTg-AD astrocytes increased cell-cell gaps between endothelial cells, filopodia-like dendritic protrusions in neurons and neuronal and endothelial cell death. 3xTg-AD A-EVs induced neurotoxicity and increased astrocyte GFAP reactivity. Cultured human postmortem astrocytes from AD patients also increased GFAP reactivity and EVs release. No differences in the size or number of A-EVs were detected between AD and control samples; however, both SAD and FAD A-EVs showed increased expression of the surface marker aquaporin 4. A-EVs induced cytotoxicity and astrocyte hyperactivation: specifically, FAD A-EVs induced neuroglial cytotoxicity and increased gaps between the endothelium, while SAD A-EVs mainly altered the endothelium. Similarly, both AD A-EVs increased astrocyte GS reactivity and vascular deterioration in vivo. We associated this finding with perivascular reactive astrocytes and vascular deterioration in the human AD brain. In summary, these results suggest that AD A-EVs impair neuroglial and vascular components.

Beta-Secretase 1 Underlies Reactive Astrocytes and Endothelial Disruption in Neurodegeneration

“…Although we did not observe changes between dementia cases by immunoprecipitation, it was clear by confocal microscopy that BACE1 was overregulated mainly in astrocytes on FAD and SAD groups, with a particular association with vessels in SAD. Additionally accumulated CLDN5 was found according to previous reports (Villar-Vesga et al, 2020;González-Molina et al, 2021). Such BACE1 + reactive astrocytes associated to disrupted vessels were also closer but not overlapping with PHF-tau.…”

“…Complementarily to these data, we have found differential patterns of astrocytes implication in dementia using additional markers such as AQP4, GS1, GLAST1, and for ECs such as Lectin UEA, vimentin, PECAM1 and CLDN5. However, SAD always showed more affection in relationship with disrupted vessels, less thickness, and more production of CLDN5 + extracellular vesicles (EVs) [Henao-Restrepo J et al data non published ( Villar-Vesga et al, 2020 ; González-Molina et al, 2021 )]. Furthermore, the study from Gonzalez-Molina et al suggested that EVs from astrocytes of 3xTgAD mice and AD human brain carried out messages that produced endothelial disruption and neuronal retraction ( González-Molina et al, 2021 ).…”

“…This term was defined as: disruption of endothelial cells involving extravasation ( Hirata et al, 1995 ) and inflammation more than cell death ( Israelov et al, 2020 ). To determine the number of these spaces, F-actin signals were segmented using machine learning and intensity thresholding by Otsu algorithm, to standardize the signals in all the images, a binary image of each analyzed field was generated using the “Magic Wand” tool of the Adobe Photoshop software ( González-Molina et al, 2021 ). With the images obtained, the number and area of gaps were measured using the “Count and measure objects” tool of the Image-Pro Plus software.…”

Blood–Brain Barrier Breakdown: An Emerging Biomarker of Cognitive Impairment in Normal Aging and Dementia

“…Figure 1 shows the difference between young or normal BBB and aged or dysfunctional BBB. (Bell and Zlokovic, 2009;Grinberg and Thal, 2010;Richardson et al, 2012;Rouhl et al, 2012;Sagare et al, 2012) Yes (Salmina et al, 2010;Villar-Vesga et al, 2020;Chacón-Quintero et al, 2021;González-Molina et al, 2021) Yes (Wardlaw et al, 2003;Zhang et al, 2014;Rajani et al, 2018;Wang et al, 2018;Tayler et al, 2021;Zhu et al, 2021) Extracellular components…”

High fat diet exacerbates cognitive decline in mouse models of Alzheimer’s disease and mixed dementia in a sex-dependent manner

“…Vascular abnormalities observed in humans with AD and in the 3xTg-AD mouse, such as reduced cerebrovascular volume (59), may make 3xTg-AD mice more susceptible to vascular insult. While we did not directly examine the mechanistic link between AD and vascular pathology, mechanistic possibilities include hypoxia-induced increases in BACE1 expression via Hif1-alpha (60,61), blood brain barrier breakdown (62,63), inflammation (43,64), or altered glucose uptake into the brain (65). Sex differences in the 3xTg-AD mouse have been noted, including a greater association between plaques and markers of hypoxia (50).…”