Apolipoprotein D is elevated in oligodendrocytes in the peri-infarct region after experimental stroke: influence of enriched environment

Injury to the brain (e.g., stroke) results in a disruption of neuronal connectivity and loss of fundamental sensori-motor functions. The subsequent recovery of certain functions involves structural rearrangements in areas adjacent to the infarct. This remodeling of the injured brain requires trafficking of macromolecular components including cholesterol and phospholipids, a transport carried out by apolipoproteins including apolipoprotein D (apoD). We investigated the changes in the levels of apoD mRNA and protein, and its cellular localization during a recovery period up to 30 days after experimental stroke in the rat brain. In the core of the brain infarct, apoD immunoreactivity but not mRNA increased in dying pyramidal neurons, indicative of cellular redistribution of lipids. During 2 to 7 days of recovery after stroke, the apoD levels increased in the peri-infarct and white matter areas in cells identified as mature oligodendrocytes. The apoD expressing cells were conspicuously located along the rim of the infarct, suggesting a role for apoD in tissue repair. Furthermore, housing animals in an enriched environment improved sensori-motor function and increased the apoD levels. Our data strongly suggest that apoD is involved in regenerative processes and scar formation in the peri-infarct area presumably by enhancing lipid trafficking.