AbstractMultiple sclerosis (MS) is a demyelinating disease of the central nervous system (CNS) characterised by immune-mediated destruction of myelin-producing oligodendrocytes. While there is a plethora of disease-modifying therapies to reduce relapses, there are currently no available treatments to boost oligodendrocyte and myelin regeneration. Therefore, uncovering the mechanisms that regulate remyelination is an essential task to elucidate druggable targets and improve the quality of life of people living with MS or other demyelinating conditions.
Previously, we reported that regulatory T cells (Treg) are required for efficient myelin regeneration in the mouse CNS. Treg secrete cellular communication network factor 3 (CCN3), a matricellular protein that promotes oligodendrocyte progenitor cell (OPC) differentiation and myelination in murine mixed glial and brain slice cultures, respectively. In addition, previous reports demonstrated that CCN3 is expressed by CNS cells in the human and rat brain, suggesting that Treg may not be the predominant source of CCN3 in this context. Based on these findings, we hypothesised that CCN3: 1) is expressed in the adult mouse CNS, 2) is required for CNS myelination and 3) is necessary for efficient myelin regeneration. To test these hypotheses, an immunohistochemical characterisation of CCN3 expression was first performed in the mouse CNS. Furthermore, myelination and remyelination were investigated in CCN3-deficient mice and wild type (WT) controls. To interrogate the latter, two models of toxin-induced demyelination were used: cuprizone feeding and lysolecithin injection in the spinal cord ventral white matter.
We found that CCN3 is detected in specific anatomical regions of the healthy CNS, predominantly in neurons. Despite this expression, CCN3-/- mice myelinate to levels comparable to WT controls. When demyelination is induced in WT animals, CCN3 becomes transiently upregulated during demyelination and remyelination. In the brain of cuprizone-fed mice, CCN3 is detected in bulbar-like structures that co-localise with a marker of axonal damage. In spinal cord lysolecithin-induced lesions, CCN3 is briefly upregulated by oligodendrocyte lineage cells and glial fibrillary acidic protein- positive cells. However, despite this expression, CCN3 deficiency did not impair OPC differentiation during remyelination in these models.
Despite the negative functional outcomes in the models used in this study, the peculiar and dynamic expression patterns of CCN3 in the mouse CNS suggest unidentified roles in a range of neurological processes. This thesis lays a framework of reference for future studies investigating the roles of CCN3 (and other CCN proteins) in myelination, remyelination and other neurological functions.
|Date of Award||Dec 2021|
|Sponsors||Wellcome Trust & Northern Ireland Department for the Economy|
|Supervisor||Denise Fitzgerald (Supervisor) & Beckie Ingram (Supervisor)|