Hepatocyte-specific NEMO deletion promotes NK/NKT cell- and TRAIL-dependent liver damage.

Nuclear factor kappaB (NF-kappaB) is one of the main transcription factors involved in regulating apoptosis, inflammation, chronic liver disease, and cancer progression. The IKK complex mediates NF-kappaB activation and deletion of its regulatory subunit NEMO in hepatocytes (NEMO(Delta hepa)) triggers chronic inflammation and spontaneous hepatocellular carcinoma development. We show that NEMO(Delta hepa) mice were resistant to Fas-mediated apoptosis but hypersensitive to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) as the result of a strong up-regulation of its receptor DR5 on hepatocytes. Additionally, natural killer (NK) cells, the main source of TRAIL, were activated in NEMO(Delta hepa) livers. Interestingly, depletion of the NK1.1(+) cells promoted a significant reduction of liver inflammation and an improvement of liver histology in NEMO(Delta hepa) mice. Furthermore, hepatocyte-specific NEMO deletion strongly sensitized the liver to concanavalin A (ConA)-mediated injury. The critical role of the NK cell/TRAIL axis in NEMO(Delta hepa) livers during ConA hepatitis was further confirmed by selective NK cell depletion and adoptive transfer of TRAIL-deficient(-/-) mononuclear cells. Our results uncover an essential mechanism of NEMO-mediated protection of the liver by preventing NK cell tissue damage via TRAIL/DR5 signaling. As this mechanism is important in human liver diseases, NEMO(Delta hepa) mice are an interesting tool to give insight into liver pathophysiology and to develop future therapeutic strategies.