Question:
Oxidative stress has been considered as a conjoint pathological mechanism, and it
contributes to initiation and progression of liver injury, fibrosis and carcinogenesis.
The KEAP1 (Kelch-like ECH-associated protein-1)/NRF2 (erythroid 2-related factor 2)
axis is a major regulator system of cellular redox balance. We investigated whether
activation of the NRF2 pathway, due to KEAP1 deletion, affects the development of
liver injury, fibrogenesis and HCC development in an inflammation driven murine HCC
model.
Methods:
Hepatocyte specific NEMO (NEMOΔhepa) knock-out mice were crossed with hepatocyte specific KEAP1 (KEAP1Δhepa) knock-out mice to generate NEMOΔhepa/KEAP1Δhepa mice. Primary hepatocytes as well as livers of all four genotypes were subjected
to microarray analysis. Furthermore, liver injury, cell death, DNA damage, proliferation
as well as liver fibrogenesis and HCC development were analyzed.
Results:
Microarray analysis of primary hepatocytes as well as livers revealed that hepatocyte
specific KEAP1 deletion increased NRF2 target genes involved in glutathione metabolism
and xenobiotic stress (e.g. HO-2, Nqo1). Furthermore the deficiency of one of the
most important antioxidants, Glutathione (GSH) in NEMOΔhepa livers could be rescued by additionally deletion of KEAP1. As a consequence the activation
of the NRF2 pathway resulted in reduced apoptosis in NEMOΔhepa/KEAP1Δhepa livers compared to NEMOΔhepa livers. Microarray analysis of primary hepatocytes further
revealed a dramatic downregulation of genes involved in cell cycle regulation and
DNA replication in NEMOΔhepa/KEAP1Δhepa compared to NEMOΔhepa primary hepatocytes. Of note, in livers of NEMOΔhepa/KEAP1Δhepa mice instead of hepatocytes,
CK19+ cells are proliferating. Further validation in in vitro and in vivo experiments confirmed that the hepatocyte specific KEAP1 deletion protects from DNA
damage. In aging mice, NEMOΔhepa/KEAP1Δhepa livers displayed decreased fibrogenesis, a lower tumor incidence, a reduced tumor
number and decreased tumor size compared to NEMOΔhepa mice.
Conclusions:
Hepatocyte specific inactivation of KEAP1 in NEMOΔhepa livers attenuated apoptosis, DNA damage and hepatic fibrosis progression. Consequently,
deletion of KEAP1 in NEMOΔhepa mice ameliorated HCC progression. Hence, KEAP1 is an attractive target to treat chronic
liver disease.
