The effect of sprouty protein on oligodendrocyte differentiation
Ekwegbalu, Ezinne C.
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Multiple sclerosis is an autoimmune disease of the CNS (central nervous system) in which the myelin sheaths are damaged, leading to demyelination and scarring. Along with the myelin sheaths of axons, oligodendrocytes, the myelin producing cells in the nervous system, are destroyed. Myelin can be regenerated in a process known as remyelination, which restores rapid salutatory conduction of action potential and maintains axonal integrity. It is unknown what regulates remyelination and human oligodendrocyte differentiation, thus preventing the development of effective treatment. Remyelination has been extensively studied in rodents, however, human and rodent glia differ in their response to environmental factors and express distinct gene expression profiles during development. We examined the expression profiles of genes involved in the negative regulation of the MAPK/ERK pathway to determine genes of interest which were most closely associated to those expressed by OPCs (oligodendrocyte progenitor cells). Through whole genome microarray and analysis, we found that Spry1 mRNA expression was conserved between species and upregulated in human and mouse OPCs, suggesting that it may act as a novel OPC regulator. In this thesis, we first characterized CD140a + and O4 + subpopulations of OPCs in the fetal human brain. We analyzed the expression of the transcription factors OLIG2 and SOX10 and the mitotic competency of OPC subpopulations using the proliferation marker, Ki67. We found that all OPC populations express OLIG2 and SOX10 and found that the cessation of CD140a was associated with the loss of OPC proliferation. We then sought identify endogenous Spry1 expression in the mouse and human brain throughout myelination. In mouse brain, in contrast to microarray data, we found that that Spry1 was not expressed by OLIG2 + oligodendrocyte lineage cells, NG2 + OPCs, CC1 + mature oligodendrocytes. In human fetal brain, we found that Spry1 was expressed in CD140a + OPCs. However, Spry1 was expressed by Nestin + neural precursor cells and CD68 + microglia. We next used Spry1 transgenic mouse model to determine the effect of Spry1 protein on oligodendrocyte differentiation. The conditional overexpression of Spry1 in mouse CNPase-expressing OLs OPCs did not grossly effect on OPC or OL differentiation in the mouse brain or spinal cord. Finally, to directly determine the role of Spry1 in human OPCs, we transplantated human CD140a + OPCs infected with a Spry1 over-expression lentivirus into homozygous shiverer/rag2 mice. Preliminary results suggests that Spry1 over-expression increased both of MBP expression myelin fibers and the proportion of CC1 + /hNA + human oligodedendrocyte cells in the corpus callosum at 8 weeks. The data suggest that Spry1 may have a species specific effect on human OPCs and acts to induce human oligodendrocyte differentiation and maturation in vivo. Thus, we anticipate that targeting Spry1 activity via pharmacologic means may be a viable approach to therapeutically influence myelin repair in the human brain.