Hepatocyte-specific Keap1 deletion reduces liver steatosis but not inflammation during non-alcoholic steatohepatitis development

•We challenged hepatocyte-specific Keap1 knockout mice with two different models of non-alcoholic steatohepatitis.•Lack of Keap1 resulted in reduced liver steatosis via inhibition of lipogenesis and enhanced mitochondrial functionality.•Hepatocyte-specific Keap1 deletion significantly decreased apoptotic cell death.•Hepatocyte-specific Keap1 deletion did not attenuate hepatic inflammation and fibrosis.

Generation of reactive oxygen species (ROS) in response to fatty acids accumulation has been classically proposed as a possible “second hit” triggering progression from simple steatosis to non-alcoholic steatohepatitis (NASH). In this study we challenged hepatocyte-specific Keap1 knockout mice (Keap1Δhepa) and littermate Cre- controls (Keap1fx/fx) with two different diet models of NASH in order to evaluate the effects of the anti-oxidant transcription factor Nrf2 over-activation on hepatic metabolism and disease progression. After 4 weeks of MCD diet the liver/body weight ratio of Keap1Δhepa mice was significantly higher compared to littermate controls with no differences in total body weight. Strikingly, liver histology revealed a dramatic reduction of lipid droplets confirmed by a decreased content of intra-hepatic triglycerides in Keap1Δhepa compared to controls. In parallel to reduced expression of genes involved in lipid droplet formation, protein expression of Liver X Receptor (LXRα/β) and Peroxisome proliferator-activated receptor α (PPARα) was significantly decreased. In contrast, genes involved in mitochondrial lipid catabolism were markedly up-regulated in Keap1Δhepa livers. A similar phenotype characterized by inhibition of lipogenesis in favor of increased mitochondrial catabolic activity was also observed after 13 weeks of western diet administration. MCD-induced apoptosis was significantly dampened in Keap1Δhepa compared to Keap1fx/fx as detected by TUNEL, cleaved caspase-3 and Bcl-2 protein expression analyses. However, no differences in inflammatory F4/80- and CD11b-positive cells and pro-fibrogenic genes were detected between the two groups. Although hepatic lack of Keap1 did not ameliorate inflammation, the resulting constitutive Nrf2 over-activation in hepatocytes strongly reduced hepatic steatosis via enhanced lipid catabolism and repressed de novo lipogenesis during murine NASH development.

Graphical abstractSchematic illustration showing hypothetical cellular consequences of Keap1 hepatic deletion. Under basal condition lack of Keap1 results in a basal activation of Nrf2 which might promote improved mitochondrial functionality in parallel to an increased cell survival with activation of cluster of genes involved in cell toxicants defenses (A). Under metabolic stress characterized by increased fatty acids mobilization and a pro-oxidant environment, mitochondrial activity is further increased and uncoupling respiration might protect cell from an excess of superoxide production generating from the electron transport chain (B).Figure optionsDownload full-size imageDownload high-quality image (113 K)Download as PowerPoint slide