Mosaic deletion of claudin-5 reveals rapid non-cell-autonomous consequences of blood-brain barrier leakage
Claudin-5 (CLDN5) is an endothelial tight junction protein essential for blood-brain barrier (BBB) formation. Abnormal CLDN5 expression is common in brain disease, and knockdown of Cldn5 at the BBB has been proposed to facilitate drug delivery to the brain. To study the consequences of CLDN5 loss in the mature brain, we induced mosaic endothelial-specific Cldn5 gene ablation in adult mice (Cldn5iECKO). These mice displayed increased BBB permeability to tracers up to 10 kDa in size from 7 days post induction (dpi) and ensuing lethality from 11 dpi. Single-cell RNA sequencing at 12 dpi revealed profound transcriptomic differences in brain endothelial cells regardless of their Cldn5 status in mosaic mice, suggesting major non-cell-autonomous responses. Reactive microglia and astrocytes suggested rapid cellular responses to BBB leakage. Our study demonstrates a critical role for CLDN5 in the adult BBB and provides molecular insight into the consequences and risks associated with CLDN5 inhibition. Overall design: The samples are mouse brain vasculature, freshly isolated and digested into single cell suspensions. These were subjected to the 10x Genomics Gene expression v3.1 chemistry and sequenced on a NextSeq platform as per manufacturers' recommendations.