The Role of Matrix Metalloproteinases in Leukocyte Transmigration in Murine Experimental Autoimmune Encephalomyelitis

Abstract: Murine experimental autoimmune encephalomyelitis (EAE) is a commonly used model in the investigation of the human disease multiple sclerosis (MS), a debilitating inflammatory disease of the central nervous system (CNS). MS and EAE involve multiple steps, primarily, auto-antigenic leukocyte (mainly T-cells and macrophages) crossing the blood-brain barrier and later their invasion into the CNS where they degrade myelin basic protein, eventually resulting in axonal degradation and CNS inflammation. Major MS/EAE research focuses their attention on the detrimental effects of leukocytes within the CNS and the role of proteases in these inflamed areas of the CNS. Our work, in contrast focuses mainly on the first step of leukocyte migration through the blood-brain barrier. This is the rate limiting step in both EAE and MS, without which clinical symptoms of the disease do not appear. In this study we demonstrates that the gelatinases, MMP-2 and MMP-9 are the major MMPs active in EAE and localize their activity in the CNS parenchyma subjacent to the parenchymal basement membrane/astroglial border, and we identify ?-dystroglycan to be a specific substrate for the active MMPs at the level of the blood-brain barrier. This is the first identification of a gelatinase substrate at the level of the blood-brain barrier. We further identify macrophages as the major source of MMP-2 and MMP-9, and demonstrate that elimination of both MMP-2 and MMP-9 (double KO mice, and treatment with specific inhibitors) protects mice against EAE. Our date further suggest that MMP-2 and MMP-9 not only have an effect at the BBB, but also at earlier stages of EAE induction. Finally, we examine the TNF-? KO mouse, which have a characteristic delay in EAE onset with prolonged retention of leukocytes in the perivascular cuff.