Dual Deletion of Keap1 and Rbpjκ Genes in Liver Leads to Hepatomegaly and Hypercholesterolemia.

The hepatic deletion of Rbpjκ ( Rbpj ^F/F ::AlbCre ) in the mouse leads to exhibition of the Alagille syndrome phenotype during early postnatal liver development with hyperlipidemia and cholestasis due to attenuated disruption of NOTCH signaling. Given the roles of NRF2 signaling in the regulation of lipid metabolism and bile ductal formation, it was anticipated that these symptoms could be alleviated by enhancing NRF2 signaling in the Rbpj ^F/F ::AlbCre mouse by hepatic deletion of Keap1 in compound Keap1 ^F/F ::Rbpj ^F/F ::AlbCre mice. Unexpectedly, these mice developed higher hepatic and plasma cholesterol levels with more severe cholestatic liver damage during the pre-weaning period than in the Rbpj ^F/F ::AlbCre mice. In addition, hypercholesterolemia and hepatic damage were sustained throughout the growth period unlike in the Rbpj ^F/F ::AlbCre mouse. These enhanced abnormalities in lipid metabolism appear to be due to NRF2-dependent changes in gene expression related to cholesterol synthetic and subsequent bile acid production pathways. Notably, the hepatic expression of Cyp1A7 and Abcb11 genes involved in bile acid homeostasis was significantly reduced in Keap1 ^F/F ::Rbpj ^F/F ::AlbCre compared to Rbpj ^F/F ::AlbCre mice. The accumulation of liver cholesterol and the weakened capacity for bile excretion during the 3 pre-weaning weeks in the Keap1 ^F/F ::Rbpj ^F/F ::AlbCre mice may aggravate hepatocellular damage level caused by both excessive cholesterol and residual bile acid toxicity in hepatocytes. These results indicate that a tuned balance of NOTCH and NRF2 signaling is of biological importance for early liver development after birth.