The Journal of Neuroscience, February 14, 2007, 27(7):1738-1745; doi:10.1523/JNEUROSCI.4987-06.2007
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Cellular/Molecular
Proteolytic Activation of Monocyte Chemoattractant Protein-1 by Plasmin Underlies Excitotoxic Neurodegeneration in Mice
John J. Sheehan,
Chun Zhou,
Iordanis Gravanis,
Andrew D. Rogove,
Yan-Ping Wu,
Daniel F. Bogenhagen, and
Stella E. Tsirka
Department of Pharmacological Sciences and Program in Molecular and Cellular Pharmacology, Stony Brook University, Stony Brook, New York 11794-8651
Correspondence should be addressed to Stella E. Tsirka at the above address. Email: stella{at}pharm.stonybrook.edu
Exposure of neurons to high concentrations of excitatory neurotransmitters causes them to undergo excitotoxic death via multiple synergistic injury mechanisms. One of these mechanisms involves actions undertaken locally by microglia, the CNS-resident macrophages. Mice deficient in the serine protease plasmin exhibit decreased microglial migration to the site of excitatory neurotransmitter release and are resistant to excitotoxic neurodegeneration. Microglial chemotaxis can be signaled by the chemokine monocyte chemoattractant protein-1 (MCP-1)/CCL2 (CC chemokine ligand 2). We show here that mice genetically deficient for MCP-1 phenocopy plasminogen deficiency by displaying decreased microglial recruitment and resisting excitotoxic neurodegeneration. Connecting these pathways, we demonstrate that MCP-1 undergoes a proteolytic processing step mediated by plasmin. The processing, which consists of removal of the C terminus of MCP-1, enhances the potency of MCP-1 in in vitro migration assays. Finally, we show that infusion of the cleaved form of MCP-1 into the CNS restores microglial recruitment and excitotoxicity in plasminogen-deficient mice. These findings identify MCP-1 as a key downstream effector in the excitotoxic pathway triggered by plasmin and identify plasmin as an extracellular chemokine activator. Finally, our results provide a mechanism that explains the resistance of plasminogen-deficient mice to excitotoxicity.
Key words: MCP-1; plasmin; excitotoxicity; microglia; mice; neurodegeneration
Received Sept. 5, 2006;
revised Jan. 2, 2007;
accepted Jan. 2, 2007.
Correspondence should be addressed to Stella E. Tsirka at the above address. Email: stella{at}pharm.stonybrook.edu
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