Induction of the mitochondrial permeability transition by protease activity in rats: a mechanism of hepatocyte necrosis.

BACKGROUND & AIMS: The mitochondrial membrane permeability transition (MMPT) has been proposed as a mechanism of cell necrosis. In contrast, it has been suggested that enhanced activity of calpain-like proteases causes cell necrosis. To integrate these concepts, the hypothesis that stimulation of mitochondrial calpain-like protease activity induces the MMPT was developed.

METHODS

Calpain-like protease activity and the MMPT were measured in rat liver mitochondria. The mitochondrial membrane potential and cell necrosis were measured in rat hepatocytes.

RESULTS

The protease inhibitor Cbz-Leu-Leu-Tyr-CHN2 inhibited both calpain-like protease activity and induction of the MMPT by Ca2+ and tert-butyl hydroperoxide. This effect of Cbz-Leu-Leu-Tyr-CHN2 was specific because serine, aspartate, and metalloprotease inhibitors did not inhibit the MMPT. The protease inhibitor Cbz-Leu-Leu-Tyr-CHN2 also delayed the onset of mitochondrial depolarization and cell necrosis during treatment of rat hepatocytes with tert-butyl hydroperoxide, a model of oxidative stress relevant to human disease.

CONCLUSIONS

These data suggest a unifying hypothesis linking calpain-like protease activity to the MMPT in cell necrosis. We propose for the first time that activation of mitochondrial calpain-like protease activity can function as a cytolytic trigger initiating the MMPT in cell necrosis.