Endothelial TLR4 signaling drives tissue inflammation, Claudin-5 internalization, and vascular barrier breakdown in a mouse model of neonatal meningitis

Neonatal bacterial meningitis is a leading cause of infant morbidity and mortality, yet the molecular and cellular basis of the leptomeningeal response to infection remains poorly defined. Here, we study a mouse model of neonatal E. coli meningitis, combining cell-type specific gene knockouts, leptomeningeal single-nucleus RNA sequencing, and endothelial cell culture to explore the role of Toll-like receptor 4 (TLR4) signaling in the host response to infection. Endothelial-specific deletion of Tlr4 dramatically reduced the inflammatory response in all leptomeningeal cell types and abrogated the infection-associated increase in vascular permeability. In a brain endothelial cell line (bEnd.3 cells), exposure to E. coli triggered TLR4-dependent NF-{kappa}B activation, selective internalization of Claudin-5, and increased monolayer permeability, responses that were eliminated by Tlr4 knockout. RNA-seq showed that endothelial TLR4 controls an NF-{kappa}B-driven transcriptional program that orchestrates the leptomeningeal response to infection. These findings reframe the host response in neonatal Gram-negative bacterial meningitis as an endothelial-centric process.