Induction of Heme Oxygenase-1 (HO-1) in the Contused Spinal Cord of the Rat

The induction of heme oxygenase-1 (HO-1) was studied in intact spinal cords and injured spinal cords after a moderate, thoracic contusion injury. HO-1 was immunolocalized in the normal cord and along the axis of the cord at 1, 2, 3 and 4 days after contusion. Induction of this enzyme in astrocytes and microglia/macrophages was evaluated using immunofluorescent double labeling with monoclonal antibodies to HO-1 and either glial fibrillary acidic protein or the complement C3bi receptor. HO-1 was expressed in neurons in the normal spinal cord. After contusion, HO-1 was induced in both gray and white matter at the impact site. In segments of cord that were 1 cm proximal or distal to the injury, HO-1 was primarily induced in the dorsal columns and occasionally in the lateral white matter. This pattern of induction was noted at all time points. The HO-1 was induced primarily in microglia/macrophages. The distribution of the HO-1 positive cells closely correlated with the pattern of intraparenchymal hemorrhage. These findings demonstrate acute induction of HO-1 in non-neuronal cells in the injured spinal cord. Induction of HO-1 in glia may be a consequence of multiple factors including exposure to heme proteins, hypoxia and oxidative stress.