Multiple Sclerosis (MS) is an autoimmune disease of the central nervous system (CNS) that is characterized by widespread focal areas of inflammation and demyelination. Although the exact cause of the disease is still not known, myelin-reactive T cells that enter the CNS trigger the disease and lead to the recruitment and activation of macrophages and other immune cells. One set of candidates that could serve to mediate these CNS changes is the family of phospholipase A2 (PLA2) enzymes, which consist of secreted (sPLA2) and cytosolic (cPLA2) forms. These enzymes hydrolyze membrane phospholipids to release free fatty acids (arachidonic acid) that can stimulate complex inflammatory cascades, and lysophospholipids that can induce myelin breakdown and demyelination, the two pathological hallmarks of MS. / For my Ph.D. research I studied the expression and role of different members of the PLA2 family in 'experimental autoimmune encephalomyelitis' (EAE), a widely used animal model of MS. I first generated a relapsing-remitting form of EAE in the C57BL/6 mouse strain that lacks a major form of sPLA2. I showed that cPLA2 is expressed by immune cells in the EAE lesions in the CNS. Furthermore blocking the activity of cPLA2 with a broad-spectrum chemical inhibitor starting at the time of EAE induction reduced the incidence and severity of disease, reduced lesion burden as well as reduced the expression of a number of chemokines and cytokines. Treating mice in the remission phase also prevented further clinical episodes. This showed that some or all members of the cPLA2 family play an important role in the onset and progression of EAE in a strain of mice lacking sPLA2. / I next carried out studies to assess the expression of all 14 members of the sPLA2 and cPLA2 families at the onset, peak and remission stages of EAE in the SJL/J mouse strain that expresses all forms of PLA2. The mRNA expression of only 4 of these PLA2s was increased. These include sPLA2 (groups IIA and V) and cPLA 2 (groups IVA and VIA). The expression of these PLA2s in the CNS was also characterized by double-immunofluorescence. The role of these PLA2s was assessed using selective inhibitors and analysed by monitoring the clinical disability scores, chemokine/cytokine protein arrays, lipomics lipid profiling, and histological analysis. Surprisingly, the sPLA2 inhibitor prevented disease remission and worsened the clinical outcome. This was accompanied by an increase in several pro-inflammatory chemokines. Selective inhibitors of cPLA2 group IVA and the calcium independent foam group VIA (iPLA2) reduced severity of EAE when given starting before onset of disease. The cPLA2 inhibitor treatment was effective only while administered, while iPLA2 inhibitor treatment was effective even after treatment was stopped. Furthermore, only delayed treatment with the iPLA2 inhibitor was effective, suggesting that cPLA2 group IVA only plays a role in the initiation of disease, while iPLA 2 plays a role in both disease onset and progression. These effects were also associated with concomitant reduction in chemokine/cytokine expression, reduction of inflammatory lipid mediators, and increase in protective lipids e.g., omega 3 fatty acids. / This work has allowed us to dissect out the expression and role of different members of the PLA2 family and has revealed the importance of selectively inhibiting some but not others in EAE. These findings may therefore have important implications for the treatment of MS.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.111895 |
| Date | January 2007 |
| Creators | Kalyvas, Athena. |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Division of Neuroscience.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 002698536, proquestno: AAINR50839, Theses scanned by UMI/ProQuest. |
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