Increased expression of macrophage receptor with collagenous structure (MARCO) in mouse cortex following middle cerebral artery occlusion

Ischaemia induces activation of resident microglia and infiltration of peripheral monocyte/macrophage cells into the central nervous system. The role of scavenger receptors, receptors critical to the recognition and clearance of cell debris, has not been investigated during cerebral ischaemia. MARCO is an inducible member of the scavenger receptor family unique to cells of monocytic lineage and is a cell surface marker that plays a critical role in the differentiation of monocytes to dendritic cells. To understand the role of MARCO in cerebral ischaemia, we investigated its expression in mice following middle cerebral artery (MCA) occlusion. No MARCO mRNA expression was observed in naïve mouse brain. There was no significant increase in expression of MARCO mRNA following transient occlusion (60 min) of the MCA at any time point up to 24 h. However, a significant, marked increase in MARCO mRNA expression was observed at 24 h in the cortex of mouse brains after a permanent occlusion of the MCA. The increased expression of MARCO mRNA at 24 h after prolonged ischaemia is consistent with its putative role in the clearance of debris and/or degenerating cells after severe ischaemia and supports previous publications showing the presence of dendritic cells around permanently occluded lesions.