Loss of blood‐brain barrier properties in association with endoplasmic reticulum stress in vascular cells from in vivo and in vitro models of Alzheimer’s disease

Background Alzheimer’s disease (AD) is the leading cause of dementia. Among other histopathological hallmarks, it is characterized by the abnormal accumulation of Amyloid-β (Aβ) peptides. Vascular alterations and blood-brain barrier (BBB) disruption are also evidenced in AD patients, in close association with perivascular amyloid deposits, which are composed mainly of Aβ 1-40. Aβ was linked to endoplasmic reticulum stress (ERS) induction in brain cells. In this study we characterized the progression of vascular alterations in the hippocampus of PDAPP-J20 mice, a validated transgenic model for AD. Method Brain sections from young and old PDAPP-J20 mice were processed for immunohistochemistry against occludin or stained with fluorescent tomato lectin -a vascular marker-. Some mice were previously injected with Evans blue or sodium fluorescein in order to evidence BBB disruption. Also, cerebral microvascular fractions were obtained from old PDAPP-J20 mice and the proteins from these samples were analyzed by mass spectrometry and proteomics analysis. For in vitro assays, human brain microvascular endothelial cells were exposed to fibrillar Aβ1-40. Markers for BBB and ERS were evaluated in these conditions. Result We found a significant increment in morphological alterations in vessels from AD mice compared to age-matched controls, mainly in those surrounded by Aβ deposits. In old AD mice, we found an increased BBB permeability, in association with a low signal for the endothelial tight junction protein occludin. Then, we obtained cerebral vascular fractions from AD and control mice and measured the levels of vascular proteins through mass spectrometry and proteomics analysis. We identified 82 proteins whose levels were decreased in AD mice. The enrichment analysis showed that the most represented cellular processes in this sample were translation and protein synthesis. Human brain microvascular endothelial cells exposed to Aβ1-40 showed not only a decrease in the occludin detection with a concomitant reduced transendothelial electrical resistance but an increment in BIP and IRE-1α expression, confirming that Aβ promotes ERS with disruption of the BBB in this model. Conclusion Our results suggest that ERS, downregulation of translation and loss of proteostasis in brain vascular cells emerge as mediators for Aβ-induced endothelial alterations during the progression of AD.