Multiregional blood-brain barrier phenotyping identifies the prefrontal cortex as the most vulnerable region to ageing in mice.

Age-associated vascular alterations make the brain more vulnerable to neuropathologies. Research in humans and rodents has demonstrated structural, molecular, and functional alterations of the aged brain vasculature that suggest blood-brain barrier dysfunction. However, these studies focused on particular features of the blood-brain barrier and specific brain regions. Thus, it remains unclear if and which blood-brain barrier age-associated phenotypes are conserved across brain areas. Moreover, there is very limited information about how blood-brain barrier dysfunction and cell-specific phenotypes relate to each other. In this manuscript, we use immunofluorescence, transmission electron microscopy, and permeability assays to assess how age-associated blood-brain barrier molecular, structural, and functional phenotypes correlate between the blood-brain barrier cell types at three brain regions (prefrontal cortex, hippocampus, and corpus callosum) during mouse early ageing. We discovered that at 18-20 months of age, changes to the mouse blood-brain barrier are subtle. The prefrontal cortex blood-brain barrier is the most affected by age, with alterations in brain endothelial cell protein expression, blood-brain barrier permeability, basement membrane thickness, and astrocyte endfoot size when compared with young mice. Here, we deliver a detailed multicellular characterization of region-dependent blood-brain barrier changes at early stages of ageing. Our data paves the way for future studies to investigate how region-specific blood-brain barrier dysfunction may contribute to disease-associated regional vulnerability.