Immortalised hippocampal astrocytes from 3xTG-AD mice fail to support BBB integrity in vitro: Role of extracellular vesicles in glial-endothelial communication

Impairments of the blood brain barrier (BBB) and vascular dysfunction contribute to Alzheimers disease (AD) from the earliest stages. However, the effects of AD-affected astrocytes on the BBB remain largely unexplored. In the present study we created an in vitro BBB using human immortalised endothelial cells in combination with immortalised astroglial cell lines from the hippocampus of 3xTG-AD and wild-type mice (3Tg-iAstro and WT-iAstro, respectively). We found that co-culturing endothelial monolayers with WT-iAstro up-regulates expression of endothelial tight junction proteins (claudin-5, occludin, ZO-1) and increases the trans-endothelial electrical resistance (TEER). In contrast, co-culturing with 3Tg-iAstro does not affect expression of tight junction proteins and does not change the TEER of endothelial monolayers. The same in vitro model has been used to evaluate the effects of extracellular vesicles (EVs) derived from the WT-iAstro and 3Tg-iAstro. The EVs derived from WT-iAstro increased TEER and up-regulated expression of tight junction proteins, whereas EVs from 3Tg-iAstro were ineffective. In conclusion, we show for the first time that immortalised hippocampal astrocytes from 3xTG-AD mice exhibit impaired capacity to support BBB integrity in vitro through paracrine mechanisms and may represent an important factor underlying vascular abnormalities during development of AD.