Bacterial meningitis in the early postnatal mouse studied at single-cell resolution

Area of Science:

• Neuroscience
• Immunology
• Cell Biology

Background:

• Bacterial meningitis poses significant risks, particularly to vulnerable populations.
• Understanding the cellular responses within the meninges during infection is crucial for developing effective treatments.

Purpose of the Study:

• To investigate the cellular and molecular responses of meningeal cell types to early postnatal E. coli infection in mice.
• To elucidate the signaling pathways, particularly Toll-like receptor 4 (TLR4), involved in the meningeal vascular response to bacterial meningitis.

Main Methods:

• Single nucleus RNA sequencing (snRNAseq) to analyze transcriptomic changes in meningeal cells.
• Confocal imaging of leptomeninges and dura for cell quantification and morphology assessment.
• Genetic (Tlr4 knockout) and pharmacologic (liposomal clodronate) perturbations to assess immune cell and signaling roles.

Main Results:

• Distinct transcriptomic changes were observed in endothelial cells (ECs), macrophages, and fibroblasts upon infection.
• Leptomeningeal ECs showed redistribution of CLDN5 and PECAM1, with compromised blood-brain barrier integrity.
• Vascular response was largely mediated by TLR4 signaling, as evidenced by similar responses to LPS and blunted responses in Tlr4 mice.
• Depletion of macrophages or knockout of Ccr2 had minimal impact on EC responses.

Conclusions:

• Endothelial cell responses to E. coli meningitis are predominantly driven by intrinsic EC sensing of lipopolysaccharide (LPS) via TLR4.
• Macrophage activity and monocyte chemoattraction appear less critical for the early EC response in this model.