Neves, Sofia Pereira das

Abstract Introduction Colony stimulating factor 1 receptor (CSF1R)-related leukoencephalopathy is an early onset neurodegenerative disease characterized by microglial deficits, abnormal glial responses, white matter pathology, and severe motor and cognitive decline. Methods At 8 months, mice lacking two copies of the Csf1r gene Fms-intronic regulatory element (FIRE) recapitulate some of the brain pathological features of CSF1R-related leukoencephalopathy, namely the deficits in microglia, astrogliosis, and demyelination. Of note, we detected deficits in lymphatic vasculature and altered macrophage activation in the meninges of Csf1rΔFIRE/ΔFIRE mice by flow, prior to the appearance of brain gliosis, neuronal dystrophy, and fine motor impairment. Results Eliminating the remainder CSF1R-expressing innate immune cells, including border-associated macrophages (BAMs), with PLX5622 at 2 months reshaped the immune crosstalk at the meningeal dura and restored lymphatic vascular expansion in Csf1rΔFIRE/ΔFIRE mice Conclusion Ongoing experiments in the lab will clarify the exact mechanisms through which dysfunctional innate immunity at the brain-meningeal interface and lack of meningeal lymphatic vasculature contribute to the development of brain pathology and impaired motor behavior in this model of CSF1R-related leukoencephalopathy. This work has unveiled novel molecular insights involving the meningeal lymphatic system that might be of therapeutic relevance to canonical central nervous system white matter diseases. Funding Source n/a Topic Categories Neuroimmunology (NEUR)

AbstractBackgroundThe meningeal layers form a unique interface between the central nervous and peripheral immune systems. The lymphatic vasculature that is present in the meningeal dura and drains cerebrospinal fluid (CSF) becomes dysregulated during aging and in models of neurodegenerative disorders such as Alzheimer’s disease (AD). Apolipoprotein E (APOE), and the isoform APOE4 in particular, increases the risk for late‐onset sporadic AD. However, it is still poorly understood whether changes in meningeal lymphatic morphology and drainage are mediating the deleterious effects of APOE4 expression. In the present study, we investigate the effects of human APOE3 or APOE4 on meningeal lymphatic function and immunity.MethodWe evaluated the morphology of lymphatic vessels in dural whole mounts of age‐matched wild type, Apoe‐KO, APOE3, and APOE4 mice at 2‐3, and 11‐12 months. This assessment was performed in both male and female mice. The drainage function of meningeal lymphatics is being assessed in the same mice by in vivo imaging of CSF‐derived fluorescent tracers into the deep cervical lymph nodes. We have also performed RNAscope and protein measurements using murine meningeal tissue to investigate the main cellular source(s) of Apoe, and single‐cell RNA sequencing to explore the cell‐specific transcriptomic signatures linked to the changes in meningeal lymphatic function.ResultLymphatic vessel length is increased in 11‐12‐month‐old APOE4 male mice, when compared to their APOE3 counterparts. Interestingly, the same was not detected in female mice. Dural myeloid cells, expressing Itgam (encoding for CD11b), are the main source of Apoe mRNA transcripts, and one of the main sources of apoE protein in the brain dura mater. APOE4 expression and age markedly alter the transcriptional profile of meningeal myeloid cells, which show overexpression of lysosomal, antigen presentation, and complement genes.ConclusionAPOE4 expression leads to a sex‐dependent meningeal lymphatic vascular remodeling, which is associated with an exacerbated activation of meningeal macrophages. In future studies, we will test whether the changes in meningeal lymphatics observed in mice expressing APOE4 are mediated by myeloid cell derived APOE.