Abstract
BACKGROUND AND AIMS: The liver is frequently challenged by toxins and reactive oxygen species. Therefore, hepatocytes require cytoprotective strategies to cope with these insults. Since the transcription factors Nrf2 and NF-κB regulate the cellular antioxidant defense system and important survival pathways, we determined their individual and overlapping functions in the liver.
METHODS: We generated mice lacking Nrf2 and the NF-κB RelA/p65 subunit in hepatocytes and we analyzed their liver using histopathology, immunohistochemistry, quantitative RT-PCR, Westernblot and Oxyblot analysis. Human inflammatory hepatocellular adenomas (iHCA) were analyzed by immunohistochemistry.
RESULTS: Loss of either Nrf2 or NF-κB/RelA had only a minor effect on liver homeostasis, but the double knockout mice spontaneously developed liver inflammation and fibrosis. Upon aging, more than one third of the female double mutant mice developed tumors, which histologically resemble human iHCA, a tumor that predominantly occurs in women. The mouse tumors also recapitulated the immunohistochemical marker profile characteristic for human iHCA. Moreover, pNRF2 and NF-κB RelA/p65 was not detectable in the nuclei of iHCA tumor cells. The mouse phenotype was not due to a synergistic effect of both transcription factors on cytoprotective Nrf2 target genes. Rather, loss of Nrf2 or NF-κB/RelA altered the expression of different genes, and the combination of these alterations likely affects liver homeostasis in the double mutant mice.
CONCLUSIONS: Our results provide genetic evidence for a functional cross-talk of Nrf2 and NF-κB/RelA in hepatocytes, which protects the liver from necrosis, inflammation and fibrosis. Furthermore, the double mutant mice represent a valuable animal model for iHCA.
Köhler, Ulrike A