Induction of apoptosis signal regulating kinase 1 (ASK1) after spinal cordinjury in rats: Possible involvement of ASK1-JNK and-p38 pathways in neuronal apoptosis

The aims of this study were to clarify the mechanism of cell death by apopt osis in the spinal cord after traumatic injury, and to examine the role of the mitogen-activated protein kinase (MAPK) pathways in the transmission of apoptosis signals. The rat spinal cord, experimentally injured by extradur al static weight-compression, was studied by hematoxylin and eosin staining , Nissl-staining, terminal deoxynucleotidyl transferase (TdT) mediated dUTP nick-end labeling (TUNEL) staining, and immunostaining using polyclonal an tibodies against Apoptosis Signal-regulating Kinase 1 (ASK1), c-Jun N-termi nal kinase (JNK), and p38 MAPK. TUNEL-positive cells were present at all st ages studied until 7 days after injury, and percentage positivity for these cells was maximal at 3 days after injury. Electron microscopic analysis re vealed the occurrence of apoptosis in both neuronal cells and glial cells. TUNEL-positive glial cells were stained by oligodendrocyte-specific maker. Expression of ASKI was maximal at 24 h after injury in the gray matter and at 3 days after injury in the white matter. Following the expression of ASK 1, activated forms of JNK and p38 were observed in apoptotic cells detected by the TUNEL method. Colocalization of ASK1 and activated JNK or activated p38 was observed in the same cell. These findings suggest the involvement of the stress-activated MAPK pathways including ASK1 in the transmission of apoptosis signals after spinal cord injury.