Concanavalin A hepatotoxicity in mice: Tumor necrosis factor–mediated organ failure independent of caspase-3–like protease activation

✍ Scribed by Gerald Künstle; Hannes Hentze; Paul-Georg Germann; Gisa Tiegs; Thomas Meergans; Dr. Albrecht Wendel

• Book ID: 102240466
• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 445 KB
• Volume: 30
• Category: Article
• ISSN: 0270-9139
• DOI: 10.1002/hep.510300517

✦ Synopsis

Several models of tumor necrosis factor (TNF)/TNFreceptor 1 (TNF-R1)-dependent liver injury in mice were investigated with respect to caspase-3-like protease activation representing a pivotal mechanism of apoptotic cell death. Injection of TNF or T-cell-activating agents (i.e., agonistic anti-CD3 antibody or staphylococcal enterotoxin B [SEB]) into galactosamine (GalN)-sensitized mice caused TNF/TNF-R1-dependent liver injury. Intravenous concanavalin A (Con A) alone induced TNF-mediated hepatotoxicity dependent on both TNF-R1 and TNF-R2. Hepatic caspase-3like proteases were activated in GalN/TNF, GalN/anti-CD3, or GalN/SEB-treated mice, but not in Con A-treated mice.

Consistently, the broad-spectrum caspase inhibitor, benzoyloxycarbonyl-val-ala-asp-fluoromethylketone (zVADfmk), prevented TNF-mediated hepatotoxicity in all GalNdependent models, but failed to protect against Con A. Under transcriptional arrest, however, Con A induced TNF-R1-dependent, but not TNF-R2-dependent, activation of caspase-3-like proteases, and zVADfmk prevented animals from Con A-mediated liver injury under this condition. Histological analysis revealed distinct differences between Con A-and GalN/Con A-induced liver injury regarding apoptotic morphology of hepatocytes. We conclude that impaired transcription induces a switch of Con A hepatotoxicity toward a caspase-3-like protease-dependent pathway. The observation that the functional state of the transcriptional machinery decides whether TNF-driven hepatocyte apoptosis involves activation of caspase-3-like proteases or alternative signaling pathways in vivo might be of relevance for the immunopathology of the liver. (HEPATOL-OGY 1999;30:1241-1251.)

Activation of T lymphocytes appears to be the initial event in the pathophysiology of a variety of autoimmune liver diseases (e.g., chronic active hepatitis) or viral hepatitis. 1 This lymphocyte activation and the ensuing interactions of these cells with macrophages leads to a systemic cytokine response. The continuous release of proinflammatory cytokines such as tumor necrosis factor (TNF) or interferon gamma (IFN-␥) into the circulation is currently held responsible for the onset of pathological symptoms and the clinical manifestation of a variety of immunologically mediated liver diseases. [2][3][4][5] Several animal models of cytokine-dependent liver tissue destruction allow the study of mechanisms of T-lymphocyte activation in relation to the extent and time course of subsequent hepatic injury. In two commonly used models, D-galactosamine (GalN)-sensitized mice are injected with T-cell-activating anti-CD3 monoclonal antibodies, 6 or with the superantigen, staphylococcal enterotoxin B (SEB). 7 These treatment regimens both result in severe liver injury 8,9 characterized by histological features of apoptosis as well as internucleosomal DNA fragmentation. 9 In contrast to these GalN models, naive mice, when injected with the T-cell mitogen, concanavalin A (Con A), develop an acute, partly apoptotic, hepatic injury that is subsequently overlaid by massive necrosis. 10,11 All three models mentioned are characterized by the production and systemic release of TNF, IFN-␥, and other cytokines. 9,11 The importance of TNF as a distal mediator in these models is substantiated by the observation that passive immunization against TNF protected mice from liver injury induced by GalN/anti-CD3, by GalN/SEB, or by Con A. 9,11,12 Apoptotic liver cell death after injection of recombinant murine TNF (rmuTNF) is only observed under the condition of impaired transcription. 13 However, the mechanism of Con A-induced liver injury requires a different explanation, because this lectin failed to arrest hepatic transcription. 14 TNF is known to transmit its cytotoxic actions via two different transmembrane receptors, i.e., the 55-kd TNF-R1 and the 75-kd TNF-R2. Under conditions of transcriptional arrest, TNF-R1 alone was shown to be responsible for the apoptotic signal transduction upon TNF binding. 15,16 This concept has been corroborated in vivo using the model of TNF-induced liver injury in GalN-sensitized mice. 13,17 The binding of TNF to TNF-R1 is followed by intracellular interactions between the death domain of the receptor and several adapter proteins that finally led to activation of apoptosis-transducing caspases, a family of cysteine proteases. [18][19][20] Previously, we and others reported that inhibition of caspases prevented TNF-induced hepatocyte apoptosis as