Received for publication December 22, 2004.
Revised February 4, 2005.
Accepted for publication February 8, 2005.

Insulin receptor-PKC- signaling mediates inhibition of hypoxia-induced necrosis of cortical neurons

Abstract

Ischemic stress causes neuronal death and functional impairment. Previous evidence has suggested that cells in the ischemic core lose viability first due to the decline in blood flow and cellular energy metabolism, and die by necrosis. Although inhibition of necrosis could be a potent therapeutic target for brain ischemia, known neurotrophic factors are ineffective for neuronal necrosis. In a previous study, we found that insulin, but not BDNF or IGF-1, inhibited neuronal necrosis under serum-free starvation stress. Although insulin receptors are abundant in the central nervous system as well as in peripheral tissues, neurons are not dependent upon insulin for their glucose supply, indicating that insulin receptors have other roles in the central nervous system. In the present study using hypoxia- reperfusion stress, cortical neurons rapidly died by necrosis as evaluated by propidium iodide staining and transmission electron microscopic analysis. As expected, insulin treatment significantly inhibited neuronal necrosis and this effect was blocked by pretreatment with an antisense oligonucleotide for the insulin receptor. Furthermore, an inhibitor of protein kinase C (PKC) eliminated the insulin-induced anti- necrotic effect. The addition of insulin induced significant translocation of only the PKC- isoform, and antisense oligonucleotide treatment for this isoform abolished the insulin-induced inhibition of necrosis. Taken together, these results suggest that insulin mediates inhibition of neuronal necrosis through a novel mechanism involving PKC- activation.

Key words: PKC-, cortex, hypoxia-reperfusion, insulin receptor, necrosis, propidium iodide