Defining a leptomeningeal blood–cerebrospinal fluid barrier as a specialized vascular interface

Central nervous system vascular barriers comprise anatomically distinct interfaces that regulate molecular exchange and immune communication between the circulation and neural tissues. Although the blood brain barrier has been extensively characterized, whether endothelial cells within the leptomeningeal vasculature represent a specialized vascular population distinct from cortical blood brain barrier endothelial cells has remained unclear. Here, we integrate cross study transcriptomic analyses, single nucleus RNA sequencing, and experimental models of neonatal meningitis to define the molecular and functional organization of leptomeningeal endothelial cells. We show that leptomeningeal endothelial cells possess a transcriptional program distinct from cortical blood brain barrier endothelial cells, characterized by enhanced extracellular matrix remodeling and immune interface programs together with reduced expression of canonical Wnt/β catenin signaling transcripts. These molecular differences coincide with a transcriptionally distinct stromal Wnt ligand environment, vascular architecture, and context-dependent remodeling during infection. Together, our findings define the leptomeningeal blood cerebrospinal fluid barrier as a specialized CNS vascular interface with distinct molecular, structural, and functional properties, expanding the current framework of CNS barrier organization.