Characterization of the adult murine meningeal : cortical brain interface at homeostasis and following an acute local injury

The meninges are an essential structure that surrounds the CNS and the periphery. They are integral to development, waste clearance, immune:CNS interactions, and injury response. The cells comprising the meninges were relatively unknown, and how they interacted with the cells in the adult brain was also understudied, despite their essential task of providing a barrier for solutes, cells, and other pathogens from entering the brain. In this thesis, I describe the cell types that comprise the interface between the brain and the meninges and how they respond to acute stab injury. I used single-cell RNA sequencing (scRNA-seq) and single-cell spatial transcriptomics together with morphological lineage tracing and immunostaining to elucidate the cell types present in the murine cortical meninges, as well as the underlying layer 1 cortex. I also described a putative ligand-receptor interaction model based on specific and localized mRNAs expressed in border macrophages, border astrocytes, and leptomeningeal mesenchymal cells. Overall, I created a molecular/cellular resource to describe the meningeal:cortical interface and cellular interactions at this interface, enabling future work to investigate how this cellular compartment regulates the CNS in adulthood. I also used a cortical stab wound model, immunostaining, and single cell spatial transcriptomics to begin to elucidate how these cells at the interface respond to injury. I discovered that at 3 days post injury there is a defined core of injury associated mesenchymal cells, OPCs, and macrophages that exist within a lesion mass that extends from the skull to the brain surface, punctuated with laminin and newly forming vessels. I describe the other environments within the injury area, including the microglia rich penumbra with a distinct injury responsive microglial cell state, surrounded by the glial limitans perilesionalis, comprised of injury associated astrocytes. I also provide data that will help characterize how the structure of the injury at the brain surface and within the meninges changes at 7- and 14-days post injury.