Cathepsin B knockout mice are resistant to tumor necrosis factor-alpha-mediated hepatocyte apoptosis and liver injury - Implications for therapeutic applications

Tumor necrosis factor-alpha (TNF-alpha) contributes to liver injury by indu cing hepatocyte apoptosis. Recent evidence suggests that cathepsin B (cat B ) contributes to TNF-alpha -induced apoptosis in vitro. The aim of the pres ent study was to determine whether cat B contributes to TNF-alpha -induced hepatocyte apoptosis and liver injury in vivo. Cat B knockout (catB(-/-)) a nd wild-type (catB(+/+)) mice were first Infected with the adenovirus Ad5I kappaB expressing the I kappaB superrepressor to inhibit nuclear factor-kap paB-induced survival signals and then treated with murine recombinant TNF-a lpha. Massive hepatocyte apoptosis with mitochondrial release of cytochrome c and activation of caspases 9 and 3 was detected in catB(+/+) mice 2 hour s after the injection of TNF-alpha. In contrast, significantly less hepatoc yte apoptosis and no detectable release of cytochrome c or caspase activati on occurred in the livers of catB(-/-) mice. By 4 hours after TNF-alpha inj ection, only 20% of the catB(+/+) mice were alive as compared to 85% of cat B(-/-) mice. Pharmacological inhibition of cat B in catB(+/+) mice with L-3 -trans-(propylcarbamoyl)oxirane-2-carbonyl-L-isoleucyl-L-proline (CA-074 Me ) also reduced TNF-alpha -nduced liver damage. The present data demonstrate that a cat B-mitochondrial apoptotic pathway plays a pivotal role in TNF-a lpha -induced hepatocyte apoptosis and liver injury.