UC Davis

Multiple sclerosis (MS) is an autoimmune, demyelinating disease of the central nervous system. Importantly, it is an illness with unmet medical need. Although current therapeutics mitigate relapses, there is no treatment that halts the progression of MS. In order to develop improved medicines, we must better understand the disease and factors that drive it. Hence, the mouse model of MS, experimental autoimmune encephalomyelitis (EAE) has been employed in the field of neuroimmunology. In my thesis, I elucidate the roles of two myeloid cell-associated proteins in affecting EAE pathogenesis.In chapter 1, I review the current understanding of the role of myeloid cells in MS. In the healthy CNS, dendritic cells, granulocytes, tissue resident macrophages are present in small quantities. Importantly, microglia reside in the healthy CNS and continuously monitor the milieu. During inflammatory conditions, microglia become activated, and a host of other myeloid cells and lymphocytes infiltrate into the CNS and cause demyelination. Although lymphocytes are important, myeloid cells are an underappreciated component of MS disease which initiate and perpetuate the disease. Additionally, I review a few of the current MS therapeutics on the market, their targets, and their impact on myeloid cells. One target that has been studied for its therapeutic potential in MS treatment is CSF1R. PLX5622, a CSF1R antagonist, is known to deplete microglia. Microglial depletion has been previously proposed to be the cause of reduced EAE clinical symptoms that are detected in CSF1R-antagonized mice. In chapter 2, I show that PLX5622 formulated into rodent chow (PLX5622 diet; PD), in addition to ameliorating EAE clinical score, also increases infiltration into the CNS of PD mice. I determined that this was not due to changes in peripheral priming. Furthermore, although spinal cords were largely devoid of infiltration, cerebella showed increased infiltration in PD compared to CD mice. I propose that decreased incidence of ascending paralysis, a symptom associated with spinal cord demyelinating damage, is due to immune cell relocation to the cerebellum. Lastly, I explore possible mechanisms causing the observed relocation. An area of unmet therapeutic need is in developmental and adult myelination. In chapter 3, I explore the function of 5 lipoxygenase (5LO) in the healthy central nervous system (CNS). First, I show that 5LO, 5LO pathway, and 5LO’s enzymatic products, leukotrienes (LTs), are detected in development and adulthood in the CNS; this suggests that the 5LO pathway is present and active in healthy conditions. Due to the detection of the highest levels of 5LO pathway components being detected during developmental myelination, we investigate the connection between 5LO and the most dynamic cell type in the CNS, oligodendrocyte lineage cells (OLCs). Addition of leukotrienes onto differentiating oligodendrocyte progenitor cells in vitro promotes oligodendrocyte differentiation in my experiments, providing initial evidence of the link between LTs and OLCs. Next, in vivo experiments involving fate mapping of cells in the corpus callosum of 5LO global knockout mice and their littermate controls confirms that 5LO and LTs promote OLC differentiation. Lastly, pharmacological and genetic methods reveal that microglia are the primary expressors of 5LO and ostensibly, LTs.