Search

Multiple sclerosis is a chronic neuroinflammatory disorder characterized by demyelination, oligodendrocyte damage/loss and neuroaxonal injury in the context of immune cell infiltration in the CNS. No neuroprotective therapy is available to promote the survival of oligodendrocytes and protect their myelin processes in immune-mediated demyelinating diseases. Pro-inflammatory CD4 Th17 cells can interact with oligodendrocytes in multiple sclerosis and its animal model, causing injury to myelinating processes and cell death through direct contact. However, the molecular mechanisms underlying the close contact and subsequent detrimental interaction of Th17 cells with oligodendrocytes remain unclear. In this study we used single cell RNA sequencing, flow cytometry and immunofluorescence studies on CNS tissue from multiple sclerosis subjects, its animal model and controls to characterize the expression of cell adhesion molecules by mature oligodendrocytes. We found that a significant proportion of human and murine mature oligodendrocytes express melanoma cell adhesion molecule (MCAM) and activated leukocyte cell adhesion molecule (ALCAM) in multiple sclerosis, in experimental autoimmune encephalomyelitis and in controls, although their regulation differs between human and mouse. We observed that exposure to pro-inflammatory cytokines or to human activated T cells are associated with a marked downregulation of the expression of MCAM but not of ALCAM at the surface of human primary oligodendrocytes. Furthermore, we used in vitro live imaging, immunofluorescence and flow cytometry to determine the contribution of these molecules to Th17-polarized cell adhesion and cytotoxicity towards human oligodendrocytes. Silencing and blocking ALCAM but not MCAM limited prolonged interactions between human primary oligodendrocytes and Th17-polarized cells, resulting in decreased adhesion of Th17-polarized cells to oligodendrocytes and conferring significant protection of oligodendrocytic processes. In conclusion, we showed that human oligodendrocytes express MCAM and ALCAM, which are differently modulated by inflammation and T cell contact. We found that ALCAM is a ligand for Th17-polarized cells, contributing to their capacity to adhere and induce damage to human oligodendrocytes, and therefore could represent a relevant target for neuroprotection in multiple sclerosis. [ABSTRACT FROM AUTHOR]

The trafficking of autoreactive leukocytes across the blood-brain barrier (BBB) endothelium is a hallmark of multiple sclerosis (MS) pathogenesis. Although the BBB endothelium represents one of the main central nervous system (CNS) borders to interact with the infiltrating leukocytes, its exact contribution to neuroinflammation remains understudied. Here, we show that Mcam identifies inflammatory brain endothelial cells (ECs) with pro-migratory transcriptomic signature during experimental autoimmune encephalomyelitis (EAE). In addition, MCAM was preferentially upregulated on BBB ECs in MS lesions in situ and at EAE disease onset by molecular magnetic resonance imaging. In vitro and in vivo, we demonstrate that MCAM on BBB ECs contributes to EAE development by promoting the cellular trafficking of TH1 and TH17 lymphocytes across the BBB. Lastly, we showcase ST14 as an immune ligand to brain endothelial MCAM, enriched on CD4+ T lymphocytes that cross the BBB in vitro, in vivo and in MS lesions as detected by flow cytometry on rapid autopsy derived brain tissue from MS patients. Collectively, our findings reveal that MCAM is at the center of a pathological pathway used by brain ECs to recruit pathogenic CD4+ T lymphocyte from circulation early during neuroinflammation. The therapeutic targeting of this mechanism is a promising avenue to treat MS. [ABSTRACT FROM AUTHOR]

Granulocyte–macrophage colony‐stimulating factor (GM‐CSF) has been implicated in numerous chronic inflammatory diseases, including multiple sclerosis (MS). GM‐CSF impacts multiple properties and functions of myeloid cells via species‐specific mechanisms. Therefore, we assessed the effect of GM‐CSF on different human myeloid cell populations found in MS lesions: monocyte‐derived macrophages (MDMs) and microglia. We previously reported a greater number of interleukin (IL)‐15+ myeloid cells in the brain of patients with MS than in controls. Therefore, we investigated whether GM‐CSF exerts its deleterious effects in MS by increasing IL‐15 expression on myeloid cells. We found that GM‐CSF increased the proportion of IL‐15+ cells and/or IL‐15 levels on nonpolarized, M1‐polarized and M2‐polarized MDMs from healthy donors and patients with MS. GM‐CSF also increased IL‐15 levels on human adult microglia. When cocultured with GM‐CSF–stimulated MDMs, activated autologous CD8+ T lymphocytes secreted and expressed significantly higher levels of effector molecules (e.g. interferon‐γ and GM‐CSF) compared with cocultures with unstimulated MDMs. However, neutralizing IL‐15 did not attenuate enhanced effector molecule expression on CD8+ T lymphocytes triggered by GM‐CSF–stimulated MDMs. We showed that GM‐CSF stimulation of MDMs increased their expression of CD80 and ICAM‐1 and their secretion of IL‐6, IL‐27 and tumor necrosis factor. These molecules could participate in boosting the effector properties of CD8+ T lymphocytes independently of IL‐15. By contrast, GM‐CSF did not alter CD80, IL‐27, tumor necrosis factor and chemokine (C–X–C motif) ligand 10 expression/secretion by human microglia. Therefore, our results underline the distinct impact of GM‐CSF on human myeloid cells abundantly present in MS lesions. [ABSTRACT FROM AUTHOR]

Background and Objectives: Multiple sclerosis (MS) is a neuroinflammatory and neurodegenerative disease characterized by infiltration of immune cells in multifocal areas of the CNS. The specific molecular processes allowing autoreactive immune cells to enter the CNS compartment through the blood-brain barrier remain elusive., Methods: Using endothelial cell (EC) enrichment and single-cell RNA sequencing, we characterized the cells implicated in the neuroinflammatory processes in experimental autoimmune encephalomyelitis, an animal model of MS. Validations on human MS brain sections of the most differentially expressed genes in venous ECs were performed using immunohistochemistry and confocal microscopy., Results: We found an upregulation of genes associated with antigen presentation and interferon in most populations of CNS-resident cells, including ECs. Interestingly, instead of transcriptionally distinct profiles, a continuous gradient of gene expression separated the arteriovenous zonation of the brain vasculature. However, differential gene expression analysis presented more transcriptomic alterations on the venous side of the axis, suggesting a prominent role of venous ECs in neuroinflammation. Furthermore, analysis of ligand-receptor interactions identified important potential molecular communications between venous ECs and infiltrated immune populations. To confirm the relevance of our observation in the context of human disease, we validated the protein expression of the most upregulated genes ( Ackr1 and Lcn2 ) in MS lesions., Discussion: In this study, we provide a landscape of the cellular heterogeneity associated with neuroinflammation. We also present important molecular insights for further exploration of specific cell processes that promote infiltration of immune cells inside the brain of experimental autoimmune encephalomyelitis mice., (Copyright © 2022 The Author(s). Published by Wolters Kluwer Health, Inc. on behalf of the American Academy of Neurology.)