Expression of MCP-1 and fractalkine on endothelial cells and astrocytes may contribute to the invasion and migration of brain macrophages in ischemic rat brain lesions

Some macrophages expressing NG2 chondroitin sulfate proteoglycan (NG2) and the macrophage marker Iba1 accumulate in the ischemic core of a rat brain subjected to transient middle cerebral artery occlusion (MCAO) for 90 min. These cells are termed BINCs (for brain Iba1+/NG2+ cells) and may play a neuroprotective role. Because BINCs are bone marrow-derived cells, they are able to invade ischemic tissue after the onset of an ischemic insult. In this study, chemokine-based mechanisms underlying the invasion of BINCs or their progenitor cells were investigated. We found that isolated BINCs expressed mRNA encoding CCR2 and CX3CR1 at high levels. Cultured astrocytes expressed mRNA encoding their ligands, MCP-1 and fractalkine. Recombinant MCP-1 and/or fractalkine, as well as astrocytes, induced the migration of BINCs in vitro. mRNA for MCP-1, fractalkine, CCR2, and CX3CR1 was expressed in the ischemic core during the acute phase of the ischemic event. Immunohistochemical studies revealed that vascular endothelial cells and astrocytic endfeet expressed MCP-1 and fractalkine, respectively, in the ischemic core during the acute phase. CCR2+/Iba1+ monocytes attached to the inside of the vascular wall at 1 day postreperfusion (dpr), and there were CCR2+/CX3CR1+ macrophage-like cells in the parenchyma in the ischemic lesion core at 2 dpr, which may be the progenitors for BINCs. These results suggest that CCR2+ monocytes are first attracted to the ischemic lesion by MCP-1+ endothelial cells and migrate toward fractalkine+ astrocytic endfeet through the disrupted bloodbrain barrier. Thus, chemokines may play a critical role in the accumulation of neuroprotective BINCs. (c) 2013 Wiley Periodicals, Inc.