Drug-induced oxidative stress actively prevents caspase activation and hepatocyte apoptosis.

Cell death is a fundamental process in health and disease. Emerging research shows the existence of numerous distinct cell death modalities with similar and intertwined signaling pathways, but resulting in different cellular outcomes, raising the need to understand the decision-making steps during cell death signaling. Paracetamol (Acetaminophen, APAP)-induced hepatocyte death includes several apoptotic processes but eventually is executed by oncotic necrosis without any caspase activation. Here, we studied this paradoxical form of cell death and revealed that APAP not only fails to activate caspases but also strongly impedes their activation upon classical apoptosis induction, thereby shifting apoptosis to necrosis. While APAP intoxication results in massive drop in mitochondrial respiration, low cellular ATP levels could be excluded as an underlying cause of missing apoptosome formation and caspase activation. In contrast, we identified oxidative stress as a key factor in APAP-induced caspase inhibition. Importantly, caspase inhibition and the associated switch from apoptotic to necrotic cell death was reversible through the administration of antioxidants. Thus, exemplified by APAP-induced cell death, our study stresses that cellular redox status is a critical component in the decision-making between apoptotic and necrotic cell death, as it directly affects caspase activity.

Non-canonical BIM-regulated energy metabolism determines drug-induced liver necrosis.

Paracetamol (acetaminophen, APAP) overdose severely damages mitochondria and triggers several apoptotic processes in hepatocytes, but the final outcome is fulminant necrotic cell death, resulting in acute liver failure and mortality. Here, we studied this switch of cell death modes and demonstrate a non-canonical role of the apoptosis-regulating BCL-2 homolog BIM/Bcl2l11 in promoting necrosis by regulating cellular bioenergetics. BIM deficiency enhanced total ATP production and shifted the bioenergetic profile towards glycolysis, resulting in persistent protection from APAP-induced liver injury. Modulation of glucose levels and deletion of Mitofusins confirmed that severe APAP toxicity occurs only in cells dependent on oxidative phosphorylation. Glycolytic hepatocytes maintained elevated ATP levels and reduced ROS, which enabled lysosomal recycling of damaged mitochondria by mitophagy. The present study highlights how metabolism and bioenergetics affect drug-induced liver toxicity, and identifies BIM as important regulator of glycolysis, mitochondrial respiration, and oxidative stress signaling.

Liver receptor homolog-1 (NR5A2) orchestrates hepatic inflammation and TNF-induced cell death.

The nuclear receptor liver receptor homolog-1 (LRH-1) has been shown to promote apoptosis resistance in various tissues and disease contexts; however, its role in liver cell death remains unexplored. Hepatocyte-specific deletion of LRH-1 causes mild steatosis and inflammation but unexpectedly shields female mice from tumor necrosis factor (TNF)-induced hepatocyte apoptosis and associated hepatitis. LRH-1-deficient hepatocytes show markedly attenuated estrogen receptor alpha and elevated nuclear factor κB (NF-κB) activity, while LRH-1 overexpression inhibits NF-κB activity. This inhibition relies on direct physical interaction of LRH-1's ligand-binding domain and the Rel homology domain of NF-κB subunit RelA. Mechanistically, increased transcription of anti-apoptotic NF-κB target genes and the proteasomal degradation of pro-apoptotic BCL-2 interacting mediator of cell death prevent mitochondrial apoptosis and ultimately protect mice from TNF-induced liver damage. Collectively, our study emphasizes LRH-1 as a critical, sex-dependent regulator of cell death and inflammation in the healthy and diseased liver.