Proteolytic Activation of Monocyte Chemoattractant Protein-1 by Plasmin Underlies Excitotoxic Neurodegeneration in Mice

Abstract

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 effectorintheexcitotoxicpathwaytriggeredbyplasminandidentifyplasminasanextracellularchemokineactivator.Finally,ourresultsprovide a mechanism that explains the resistance of plasminogen-deficient mice to excitotoxicity.

The chemokine CCL2 activates p38 mitogen-activated protein kinase pathway in cultured rat hippocampal cells

“…Recent studies show that CCL2 and its receptor CCR2 are expressed in the normal hippocampus and that the levels of expression increase during neuroinflammatory conditions associated with CNS injury and disease (Banisadr et al, 2005a;Banisadr et al, 2005b;Galasso et al, 2000;Kalehua et al, 2004;Little et al, 2002;Sakurai-Yamashita et al, 2006;Sheehan et al, 2007;Szaflarski et al, 1998). These results implicate a role for CCL2 in the hippocampus, particularly during neuroinflammatory conditions.…”

Truncation of monocyte chemoattractant protein 1 by plasmin promotes blood–brain barrier disruption

“…However, it is not known whether plasmin-mediated cleavage of MCP1 at K104, which enhances its chemotactic activity (Sheehan et al, 2007), affects MCP1-induced BBB compromise. To address this question, we used four recombinant MCP1 proteins, full-length MCP1 (FL), plasmin-noncleavable MCP1 (K104A), constitutively cleaved MCP1 (K104Stop) and MCP1 C-terminal extension (CT), that we previously characterized (Yao and Tsirka, 2010).…”

“…By binding to their specific Gprotein-coupled receptors, chemokines induce cell-specific migration and activation of immune cells (Glabinski et al, 1996;Hulkower et al, 1993;Lahrtz et al, 1998;Miller and Meucci, 1999). Monocyte chemoattractant protein-1 (MCP1; officially known as C-C motif chemokine 2, CCL2) is one of the most highly and transiently expressed chemokines in many central nervous system (CNS) injuries, including ischemia, hemorrhage and excitotoxic injury (Capoccia et al, 2008;Dimitrijevic et al, 2006;Frangogiannis et al, 2007;Hanisch, 2002;Kim et al, 2008;Morimoto et al, 2008;Sheehan et al, 2007;Yan et al, 2007). The rodent MCP1 differs from the human protein at the C-terminus, with the rodent protein having a longer highly glycosylated Cterminus.…”

“…The rodent MCP1 differs from the human protein at the C-terminus, with the rodent protein having a longer highly glycosylated Cterminus. We have previously shown that mouse MCP1 can be cleaved by plasmin at K104, and the truncated MCP1 is more potent than the full-length MCP1 in inducing microglial migration (Sheehan et al, 2007;Yao and Tsirka, 2010) through its receptor CCR2.…”

Unveiling an exceptional zymogen: the single-chain form of tPA is a selective activator of NMDA receptor-dependent signaling and neurotoxicity

“…[11][12][13] There are also evidences that tPA mediates a number of plasminogen-independent functions on non-fibrin substrates. These substrates, binding proteins or receptors for tPA include the platelet-derived growth factor-C, 14 the low density lipoprotein receptor-related protein, 10 annexin-II, 9,15 the chemokine macrophage chemoattractant protein, macrophage chemoattractant protein-1 16 and the N-methyl-D-aspartate receptor (NMDAR). 6 It is now well established that the interaction of tPA with the NMDAR leads to an increased calcium influx, activation of Erk(½) and neuronal death.…”