Spatial resolution of calpain-catalyzed proteolysis in focal cerebral ischemia

Transient forebrain ischemia induces calpain-mediated degradation of the neuronal cytoskeleton, α-fodrin, and this results in ischemic neuronal death. In this study, we investigated the spatial distribution and temporal changes of calpain-catalyzed α-fodrin proteolysis in focal cerebral ischemia and examined the effects of a calpain inhibitor. Ischemia was induced in gerbils by 3-h middle cerebral artery occlusion followed by reperfusion. Animals were divided into four groups: a sham-operated group, an ischemic group, a vehicle-treated group, and a calpain inhibitor-treated group. Intravenous injections of vehicle or calpain inhibitor I were administered 30 min before ischemia. Infarct volumes were measured 1 day after reperfusion and the spatial distribution of calpain-catalyzed α-fodrin proteolysis was investigated by immunohistochemistry 15 min, 1 h, 4 h, and 1 day after reperfusion. Infarct volume (mean ± SD) in the ischemic group and the vehicle-treated group was 204.6 ± 19.1 mm3 and 212.4 ± 16.3 mm3, respectively, and the calpain inhibitor I reduced the infarct volume [149.4 ± 25.2 mm3 (P < 0.05)]. Immunoblot analysis demonstrated that calpain inhibitor reduced proteolysis. Ischemia induced fodrin proteolysis in the ischemic core and the peri-infarct zone within 15 min after reperfusion, with proteolysis developing quickly in the ischemic core and more slowly in the peri-infarct zone. Proteolysis preceded neuronal death in the peri-infarct zone. Calpain inhibitor I ameliorated neuronal death in the peri-infarct zone but not in the ischemic core. Thus, calpain plays a pivotal role on focal ischemia as well as in global ischemia.