RIPK1 and MLKL in hepatocytes do not mediate Concanavalin A (ConA)-mediated liver toxicity

Apoptosis and necrosis are distinct forms of hepatocyte death and prominent features of liver diseases. In contrast to apoptosis, which seems to be the dominant form of hepatocyte death in most models of hepatitis, ConA-injection is associated with immune cell-mediated inflammation and hepatocyte necrosis. So far it is still unclear how ConA induces liver necrosis and which molecules are involved in this process. Previous studies indicate that necroptosis, a regulated form of necrosis that involves activation and complex formation of RIPK1, RIPK3 and MLKL, occurs after ConA-application. The studies indicate that especially RIPK1 and MLKL are critical mediators of ConA-mediated liver damage, whereas RIPK3 is not involved in this process. However, the interpretation of these results is partly difficult due to poor strain-matching of control and knock-out (KO) mice, the investigation of just a single time point after Injection or potential off-target effects of inhibitors like the RIPK1 kinase inhibitor necrostatin-1 s. Therefore it is still unclear if necroptosis is involved in ConA-mediated liver toxicity.

To evaluate the role of RIPK1 and MLKL in this context in more detail we used mice with a conditional ablation of RIPK1 or MLKL in liver parenchymal cells (RIPK1^LPC-KO and MLKL^LPC-KO) and investigated the amount of necrotic damage after ConA-injection compared with the respective Wildtype (WT) litter mates.

Intravenous ConA-treatment for 7h, 24h or 48h did not reveal any differences in liver enzymes and the degree of necrotic liver damage in RIPK1^LPC-KO and MLKL^LPC-KO mice arguing against a hepatocyte-specific function of RIPK1 and MLKL in ConA toxicity. These obvious differences to previous studies emphasize the importance of the use of specific conditional KO mice and indicate that the interpretation of results generated with constitutive KO mice or by the use of systemic inhibitors must be interpreted with caution. Considering all this data it cannot be excluded that other intra- and extra-hepatic cell compartments than hepatocytes are involved in ConA-mediated liver damage. To stimulate the discussion on this topic it would be therefore helpful to analyze the effect of ConA in mice lacking RIPK1 or MLKL in other cell compartments. Taken together, our findings indicate that hepatocytic RIPK1 and MLKL do not modulate acute liver toxicity of ConA in mice. Furthermore they provide evidence for a lack of function of necroptosis in this process.