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

Abstract

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 <i>Escherichia coli</i> meningitis, combining conditional 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. Deletion of <i>Tlr4</i> in non-myeloid cells 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 <i>E. coli</i> triggered NF-κB activation, selective internalization of Claudin-5, and increased monolayer permeability, responses that were eliminated by <i>Tlr4</i> knockout. RNA-seq showed that TLR4 controls an NF-κB-driven transcriptional program that orchestrates the endothelial response to <i>E. coli</i>. These findings reveal multiple TLR4-dependent host responses to neonatal Gram-negative bacterial meningitis.