Project description:BackgroundThe three-layered meninges cover and protect the central nervous system and form the interface between cerebrospinal fluid and the brain. They are host to a lymphatic system essential for maintaining fluid dynamics inside the cerebrospinal fluid-filled subarachnoid space and across the brain parenchyma via their connection to glymphatic structures. Meningeal fibroblasts lining and traversing the subarachnoid space have direct impact on the composition of the cerebrospinal fluid through endocytotic uptake as well as extensive protein secretion. In addition, the meninges are an active site for immunological processes and act as gatekeeper for immune cells entering the brain. During aging in mice, lymphatic drainage from the brain is less efficient contributing to neurodegenerative processes. Aging also affects the immunological status of the meninges, with increasing numbers of T cells, changing B cell make-up, and altered macrophage complement.MethodsWe employed RNASeq to measure gene expression and to identify differentially expressed genes in meninges isolated from young and aged mice. Using Ingenuity pathway, GO term, and MeSH analyses, we identified regulatory pathways and cellular functions in meninges affected by aging.ResultsAging had profound impact on meningeal gene expression. Pathways related to innate as well as adaptive immunity were affected. We found evidence for increasing numbers of T and B lymphocytes and altered activity profiles for macrophages and other myeloid cells. Furthermore, expression of pro-inflammatory cytokine and chemokine genes increased with aging. Similarly, the complement system seemed to be more active in meninges of aged mice. Altered expression of solute carrier genes pointed to age-dependent changes in cerebrospinal fluid composition. In addition, gene expression for secreted proteins showed age-dependent changes, in particular, genes related to extracellular matrix composition and organization were affected.ConclusionsAging has profound effects on meningeal gene expression; thereby affecting the multifaceted functions meninges perform to maintain the homeostasis of the central nervous system. Thus, age-dependent neurodegenerative processes and cognitive decline are potentially in part driven by altered meningeal function.

Project description:Emerging evidence suggests that the meningeal compartment plays instrumental roles in various neurological disorders and can modulate neurodevelopment and behavior. While this has sparked great interest in the meninges, we still lack fundamental knowledge about meningeal biology. Here, we utilized high-throughput RNA sequencing (RNA-seq) techniques to investigate the transcriptional response of the meninges to traumatic brain injury (TBI) and aging in the sub-acute and chronic time frames. Using single-cell RNA sequencing (scRNA-seq), we first explored how mild TBI affects the cellular and transcriptional landscape in the meninges in young mice at one week post-injury. Then, using bulk RNA sequencing, we assessed the differential long-term outcomes between young and aged mice following a TBI. In our scRNA-seq studies, we found that mild head trauma leads to an activation of type I interferon (IFN) signature genes in meningeal macrophages as well as the mobilization of multiple distinct sub-populations of meningeal macrophages expressing hallmarks of either classically activated or wound healing macrophages. We also revealed that dural fibroblasts in the meningeal compartment are highly responsive to TBI, and pathway analysis identified differential expression of genes linked to various neurodegenerative diseases. For reasons that remain poorly understood, the elderly are especially vulnerable to head trauma, where even mild injuries can lead to rapid cognitive decline and devastating neuropathology. To better understand the differential outcomes between the young and the elderly following brain injury, we performed bulk RNA-seq on young and aged meninges from mice that had received a mild TBI or Sham treatment 1.5 months prior. Notably, we found that aging alone induced massive upregulation of meningeal genes involved in antibody production by B cells and type I IFN signaling. Following injury, the meningeal transcriptome had largely returned to its pre-injury signature in young mice. In stark contrast, aged TBI mice still exhibited massive upregulation of immune-related genes and markedly reduced expression of genes involved in extracellular matrix remodeling and maintenance of cellular junctions. Overall, these findings illustrate the dynamic and complex transcriptional response of the meninges to mild head trauma. Moreover, we also reveal how aging modulates the meningeal response to TBI.

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Impact of aging on meningeal gene expression

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