εPKC may contribute to the protective effect of hypothermia in a rat focal cerebral ischemia model

Background and Purpose-Protein kinase C epsilon (epsilon PKC) has been implicated as a neuroprotectant in vitro. We studied epsilon PKC activation (by its localization and proteolysis) in a rodent stroke model and correlated the effects of hypothermia with epsilon PKC activity after cerebral ischemia. Methods-Rats were subjected to permanent distal middle cerebral artery occlusion plus 1 hour of bilateral common carotid artery occlusion. Body temperatures were maintained at 37 degrees C or 30 degrees C during common carotid artery occlusion. Brains were harvested at 10 minutes, 4 hours, and 24 hours after common carotid artery release, and the cortex corresponding to the ischemic core and penumbra was dissected. epsilon PKC localization after stroke was assessed by Western blot and immunofluorescence microscopy. A caspase-3 inhibitor was used to test whether epsilon PKC cleavage is caspase dependent. Results-epsilon PKC in the membrane fraction and whole-protein homogenates decreased moderately in the penumbra but decreased markedly in the ischemic core. Hypothermia blocked this decrease in both the ischemic core and penumbra. Confocal microscopy confirmed that neuronal epsilon PKC expression decreased in the ischemic core at 4 hours after reperfusion, and this loss was prevented by hypothermia. Two carboxyl-terminal cleavage products of epsilon PKC with molecular masses of 43 and 35 kDa were detected. Although the protein band of 43 kDa decreased after stroke, the 35-kDa band increased. Such changes were not dependent on caspase-3. However, hypothermia blocked changes in the cleavage form of 35 kDa but not 43 kDa after stroke. Conclusions-Moderate hypothermia preserves epsilon PKC activity after stroke. (Stroke. 2007;38: 375-380.)