PB1217 - The contribution of plasmin(ogen) receptors to neuroinflammation in a murine model of MS.

Background: Plasmin is a promiscuous protease that degrades fibrin and an array of extracellular matrix proteins. Plasmin-mediated proteolysis drives multiple facets of macrophage biology, including migration. Localization of plasmin to the macrophage cell surface is necessary to facilitate these actions, via plasminogen receptors (PlgRs). There are multiple pools of PlgRs, including intracellular proteins that are externalized upon macrophage activation and a transmembrane protein known as Plg-RKT. Externalization of the intracellular PlgRs can be blocked by inhibition of L-type calcium channels. Multiple sclerosis (MS) is an autoimmune demyelinating disease of the central nervous system. Autoreactive T-cells initiate the immune response driving macrophages-mediated destruction of myelin, with resultant neurological impairment. Macrophages that migrate into the CNS are a primary effector cell of MS. We have previously found that plasmin(ogen) deficiency delays the onset and severity of a murine model of MS, experimental autoimmune encephalomyelitis (EAE). We hypothesize that plasmin localization to the macrophage surface, via PlgRs is necessary to drive EAE disease.

Aims: We aim to define the relevant PlgRs that drive neuroinflammatory disease.

Methods: We have separately targeted the two pools of PlgRs by challenging constitutive Plg-RKT-/- mice and LysMcre/Cav1.2flox mice with EAE. Amlodipine was used to inhibit L-type calcium channels.

Results: Despite the importance of plasminogen in driving neuroinflammation in EAE, surprisingly we observed that Plg-RKT-/- did not have significant protection from EAE disease severity. Similarly, macrophage specific knockout of Cav1.2 (LysMcre+/Cav1.2flox) were not protected from the onset or severity of demyelination associated with EAE. Inhibition of Cav1.2 does not influence disease course, IBA1 expression or demyelination.

Conclusion(s): Individually, neither Plg-RKT nor externalization of intracellular PlgRs, contribute to driving EAE disease severity. This was unexpected, as elimination of either pool of PlgRs have previously been reported to interfere with macrophage migration. This suggests, in EAE, the individual pools of PlgRs function in a redundant manner.