3 DISTINCT PHASES OF FODRIN PROTEOLYSIS INDUCED IN POSTISCHEMIC HIPPOCAMPUS - INVOLVEMENT OF CALPAIN AND UNIDENTIFIED PROTEASE

Background and Purpose Fodrin, a neuronal cytoskeleton protein. is pro teolyzed by calpain after ischemic insult. We examined proteolysis of fodrin induced by global forebrain ischemia in gerbil hippocampus in s patial terms by using the antibody specific to the calpain-proteolyzed form of fodrin. Methods In gerbils, a 10-minute forebrain ischemia wa s produced by occlusion of both carotid arteries. After recirculation, the hippocampus was processed for immunohistochemical and immunoblot study with the antibody against the calpain-proteolyzed form of fodrin . Additionally, short-term ischemia was studied to find the threshold of fodrin proteolysis. Results Three phases of fodrin proteolysis dist inct in chronology and distribution arose: (1) an early predegeneratio n phase in the molecular layer and stratum oriens of the CA1 and CA3 s ectors within the first 15 minutes, which lasted up to 4 hours; (2) a late predegeneration phase in the whole CA1 sector, except for the pyr amidal cells, between 12 hours and 2 days; and (3) a postdegeneration phase in the cytoplasm of the CA1 neurons, which arose in 3 to 7 days. A 4-minute (not a 3-minute) forebrain ischemia induced the late prede generation phase of fodrin proteolysis and delayed neuronal death in C A1. Immunoblotting showed that the primary product of calpain action w as further proteolyzed by an unidentified protease. Conclusions Calpai n induced proteolysis of fodrin ischemic mic hippocampus, and the tate predegeneration phase of the proteolysis was closely associated with the delayed neuronal death in the CA1 sector. Calpain and another prot ease may play a role in the development of neuronal death after transi ent forebrain ischemia.