Vascular senescence and leak are features of the early breakdown of the blood-brain barrier in Alzheimer's disease models.
Alzheimer's disease (AD) is an age-related disease, with loss of integrity of the blood-brain barrier (BBB) being an early feature.  Cellular senescence is one of the reported nine hallmarks of aging. Here we show for the first time the presence of senescent cells in the vasculature in AD patients and mouse models of AD.  Senescent endothelial cells and pericytes are present in APP/PS1 transgenic mice but not in wild-type littermates at the time of amyloid deposition. In vitro, senescent endothelial cells display altered VE-cadherin expression and loss of cell junction formation and increased permeability. Consistent with this, senescent endothelial cells in APP/PS1 mice are present at areas of vascular leak that have decreased claudin-5 and VE-cadherin expression confirming BBB breakdown. Further, single cell sequencing of endothelial cells from APP/PS1 transgenic mice confirms that adhesion molecule pathways are among the most highly altered pathways in these cells. At the pre-plaque stage the vasculature shows significant signs of breakdown, with a general loss of VE-cadherin, leakage within the microcirculation, and obvious pericyte perturbation. Although senescent vascular cells were not directly observed at sites of vascular leak, senescent cells were close to the leak area. Thus, we would suggest in AD there is a progressive induction of senescence in constituents of the neurovascular unit contributing to an increasing loss of vascular integrity. Targeting the vasculature early in AD, either with senolytics or with drugs that improve the integrity of the BBB maybe valid therapeutic strategies. Overall design: Endothelial cells were isolated from the brain of WT and APP/PS1 mice using the Miltenyi Biotec reagents and protocol for "Isolation and cultivation of endothelial cells from adult mouse brain". The cells were then analysed using scRNA-seq.