Key Metalloproteinases Are Expressed by Specific Cell Types in Experimental Autoimmune Encephalomyelitis

Abstract

Metalloproteinases (MPs) include matrix metalloproteinases (MMPs) and metalloproteinase-disintegrins (ADAMs). Their physiological inhibitors are tissue inhibitor of metalloproteinases (TIMPs). MPs are thought to be mediators of cellular infiltration in the pathogenesis of multiple sclerosis and its animal model, experimental autoimmune encephalomyelitis (EAE). We used real-time RT-PCR to profile the expression of all 22 known mouse MMPs, seven ADAMs, and all four known TIMPs in spinal cord from SJL/J mice and mice with adoptively transferred myelin basic protein (MBP)-specific EAE. A significant and >3-fold alteration in expression was observed for MMP-8, MMP-10, MMP-12, ADAM-12, and TIMP-1, which were up-regulated, and for MMP-15, which was down-regulated. Expression levels correlated with disease course, with all but ADAM-12 returning toward control levels in remission. To examine potential cellular sources of these strongly affected proteins in the inflamed CNS, we isolated macrophages, granulocytes, microglia, and T cells by cell sorting from the CNS of mice with EAE and analyzed their expression by real-time RT-PCR. This identified macrophages as a major source of MMP-12 and TIMP-1. Granulocytes were a major source of MMP-8. ADAM-12 was expressed primarily by T cells. Cellular localization of MMP-10, TIMP-1, and ADAM-12 in perivascular infiltrates was confirmed by immunostaining or in situ hybridization. Microglia from control mice expressed strong signal for MMP-15. Strikingly, the expression of MMP-15 by microglia was significantly down-regulated in EAE, which was confirmed by immunostaining. Our study identifies the cellular sources of key MPs in CNS inflammation.