Murine hepatocyte apoptosis induced in vitro and in vivo by TNF-alpha requires transcriptional arrest

Abstract

Freshly isolated mouse hepatocytes were essentially insensitive to TNF-alpha cytotoxicity. However, TNF-alpha induced a concentration-dependent cell death in hepatocytes that had been pretreated with the transcriptional inhibitors actinomycin D (ActD), D-galactosamine, or alpha-amanitin. Unlike RNA synthesis inhibition, a translational block in the presence of cycloheximide (CHX) or puromycin did not sensitive hepatocytes to TNF. On the contrary, these agents prevented hepatocytotoxicity induced by ActD/TNF. Pretreatment with peroxides or glutathione depletors had no significant influence on TNF cytotoxicity. In vivo treatment of mice with ActD/TNF caused hepatic failure, which was significantly reduced by co-treatment with CHX. These findings demonstrate that protein synthesis is required for this mechanism of cell death. To test whether TNF may trigger an endogenous suicide program in hepatocytes, we examined whether DNA fragmentation preceded cell death. In the culture system, hepatocellular DNA fragmentation in the presence of ActD/TNF was observed several hours before lactate dehydrogenase release and was inhibited by CHX. Similar results were obtained in vivo. Chromatin condensation and the formation of apoptotic bodies were observed in livers from mice treated with ActD/TNF and significant DNA fragmentation was detected as early as 4 h after challenge. At this time, organ total glutathione content and plasma transaminase levels were not significantly different from those of untreated controls. The findings of this study demonstrate that direct hepatotoxicity of TNF-alpha is associated with an apoptotic mechanism that becomes manifest under the metabolic condition of arrested transcription and functional translation.