Apoptosis and expression of p53 response proteins and cyclin D1 after cortical impact in rat brain

Abstract

We measured the temporal profile and cellular identification of apoptosis in rat brain after cortical contusion injury. Double staining immunohistochemistry was also used to investigate the relationship between apoptotic cell death and selective protein expression associated with DNA damage and repair (p53, Bax, MDM2, WAF1, Gadd45, PCNA) and cell cycle protein, Cyclin D1, in male Wistar rats 48 h after injury. Cortical contusion was induced in male Wistar rats with a pneumatic impactor device. The animals were sacrificed at different times after trauma (1, 2, and 14 h and 1, 2, 4, 7 and 14 days; n=4 per time point). Sham-operated rats ( n=4) and normal rats not subjected to any surgical procedure ( n=4) were used as controls for temporal profile determination. Additional 11 rats were used for study of protein expression. Coronal brain sections were analyzed using an in situ terminal deoxynucleotdyl transferase-mediated biotinylated deoxyuridine triphosphate nick end labeling (TUNEL), hematoxylin, and immunohistochemical double staining methods. Apoptotic cells were observed as early as 2 h after the impact. Apoptotic cell death peaked at 2 days, gradually tapering off afterward, although scattered apoptotic cells were detected at 2 weeks after the impact. The number of apoptotic cells at 2 days far exceeded their number at other times ( p=0.009). Apoptotic cells were observed primarily in the cortex adjacent to the site of injury. In addition, apoptotic cells in conjunction with few injured cells were present in the ipsilateral hippocampus and localized to the granule layer of dentate gyrus. Our data indicate that DNA fragmentation is present in nearly all neurons subacutely after cortical contusion and persists for at least 2 weeks thereafter. Apoptosis is also present in neurons localized to the hilus of the dentate gyrus at a site remote from the area of injury suggesting a selective role for apoptosis in promoting secondary brain damage and dysfunction after traumatic brain injury. Using double staining, we were able to show that a great majority of apoptotic cells (>95%) were neurons and the rest were astrocytes and endothelial cells. Proteins associated with DNA damage and repair (p53, Bax, MDM2, WAF1, Gadd 45, PCNA) were expressed in the cytoplasm of normal cells of naive and sham rats. These proteins were translocated to the nuclei of apoptotic and injured cells at 48 h after cortical contusion. Cyclin D1 was not present in apoptotic cells. The differential expression of proteins associated with DNA damage, repair and the cell cycle protein Cyclin D1 in the contused brain suggest a potential role for these proteins in cell survival and apoptosis after cortical contusion.