AbstractThe overall objectives of my PhD were to investigate the expression pattern of various TAM receptors and ligand Gas6 in different brain regions throughout development, effect of Gas6 on glial cell development, in particular oligodendrocytes, demyelination and remyelination, as well as revealing the signalling mechanisms through which Gas6 exerts it effects, by looking at alterations of genes involved in MS with Gas6 stimulation. And the last but not the least, to reveal Gas6 as a potential new therapeutic target for treatment of multiple sclerosis (MS). My main findings are as follow:
1. By analysing mRNA and protein extracts in qPCR and western blotting, we observed that the peaks of Tyro3 expression during postnatal development, overlaps with peaks of myelination periods in mice (Chapter 3).
2. Using qPCR analysis, we observed that Tyro3 mRNA was uniquely expressed in oligodendrocytes, but not in astrocytes. In contrast, the expression of Axl mRNA was higher in astrocytes compared to oligodendrocytes. Gas6 was highly expressed in astrocytes and was absent in oligodendrocytes (Chapter 3).
3. Using in vitro culture models, we obtained the functional effect of Gas6 on oligodendrogenesis and demyelination. We showed that treatment of optic nerves in culture with Gas6 for 72 hours, resulted in a significant increase in the number of oligodendrocyte precursor cells (OPCs). This suggests the involvement of Gas6 in glial cell development. We also showed that addition of Gas6 to organotypic cerebellar slice culture treated with lysolecithin, significantly attenuated the extent of demyelination in the brain sections. Although we did not observe a positive effect for Gas6 on remyelination, but this observation indicate the inhibitory role of Gas6 in a demyelination model (Chapter 4).
4. By using a mouse multiple sclerosis micro array kit, we analysed the effect of Gas6 on 84 different genes, all of which are involved in MS. We showed that Gas6 resulted in downregulation of Mmp9, Epha1 and Gfap, which suggest a positive regulatory role for Gas6 in cell development and differentiation as well as maintenance of blood brain barrier (BBB). Our analysis also showed the upregulation of Il10 gene with the effect of Gas6, which indicate Gas6 to have anti-inflammatory and immune regulatory properties (Chapter 5).
5. By using in vivo animal models, we tested the effect of acute and chronic vitamin K administration on Gas6 and protein S gene expression. We showed that treatment of mice with various concentrations of vitamin K and at different time points resulted in alteration of Gas6 and protein S gene level in brain and liver. This suggest that vitamin K can be used to induce the production endogenous Gas6 in the brain for therapeutic purposes (Chapter 6).
Taken together, these observations indicate the positive role for Gas6 in a number of cellular processes, including cell proliferation, differentiation and survival, all of which are central in the progression of MS. In addition provide evidence that shows Gas6 to be a potential immune suppressive or an immune modulator that has the ability to control the immune response in MS patients. Therefore it can be used as a therapy that can be both regenerative and immune suppressive at the same time, something that can be effective in the progressive form of MS.
|Date of Award
|Sassan Hafizi (Supervisor) & Arthur Butt (Supervisor)