Summary Molecular mechanisms underpinning nonalcoholic fatty liver disease (NAFLD) are not well understood. The earliest step of NAFLD is hepatic steatosis, which is one of the main characteristics of aging liver. Here we present a molecular scenario of age-related liver steatosis. We show that C/EBPα-S193D knock-in mice have age-associated epigenetic changes and develop hepatic steatosis at 2 months of age. The underlying mechanism of the hepatic steatosis in old wild-type (WT) mice and in young S193D mice includes increased amounts of tripartite p300-C/EBPα/β complexes that activate promoters of five genes that drive triglyceride synthesis. Knock-down of p300 in old WT mice inhibits hepatic steatosis. Indeed, transgenic mice expressing dominant-negative p300 have fewer C/EBPα/β-p300 complexes and do not develop age-dependent hepatic steatosis. Notably, p300-C/EBPα/β pathway is activated in livers of patients with NAFLD. Thus, our results show that p300 and C/EBP proteins are essential participants in hepatic steatosis.

Liver cancer is the fifth most common cancer. A highly invasive surgical resection of the liver tumor is the main approach utilized to eliminate the tumor. Mechanisms that terminate liver regeneration when the liver reaches the original size are not known. The aims of this work were to generate the animal model which fails to stop liver regeneration after surgical resections and elucidate mechanisms which are involved in termination of liver regeneration. Because epigenetic control of liver functions has been previously implicated in the regulation of liver proliferation, we have generated C/EBPα-S193A knockin mice, which have alterations in formation of complexes of C/EBP family proteins with chromatin remodeling proteins. The C/EBPα-S193A mice have altered liver morphology and altered liver functions leading to changes of glucose metabolism and blood parameters. Examination of proliferative capacity of C/EBPα-S193A livers showed that livers of S193A mice have a higher rate of proliferation after birth, but stop proliferation at the age of 2 months. These animals have increased liver proliferation in response to liver surgery as well as CCl4-mediated injury. Importantly, livers of C/EBPα-S193A mice fail to stop liver regeneration after surgery when livers reach the original, pre-resection, size. The failure of S193A livers to stop regeneration correlates with the epigenetic repression of key regulators of liver proliferation C/EBPα, p53, FXR, SIRT1, PGC1± and TERT by C/EBPβ-HDAC1 complexes. The C/EBPβ-HDAC1 complexes also repress promoters of enzymes of glucose synthesis PEPCK and G6Pase. Conclusions Our data demonstrate that a proper co-operation of C/EBP and chromatin remodeling proteins is essential for the termination of liver regeneration after surgery and for maintenance of liver functions.

Background: Older patients are more sensitive to drug-mediated development of liver disorders. Results: Age and CCl 4 treatments change expression of C/EBP proteins leading to repression of key regulators of liver biology. Conclusion:The age-associated alterations of C/EBP proteins cause severe liver injury after CCl 4 treatments. Significance: Understanding of mechanisms of age-associated severe liver injury is important for development of therapeutic approaches.

SummaryNonalcoholic fatty liver disease (NAFLD) is the most common liver disease worldwide. NAFLD usually begins as low‐grade hepatic steatosis which further progresses in an age‐dependent manner to nonalcoholic steatohepatitis (NASH), fibrosis, cirrhosis, and hepatocellular carcinoma in some patients. Ghrelin is a hormone known to promote adiposity in rodents and humans, but its potential role in hepatic steatosis is unknown. We hypothesized that genetic ghrelin deletion will protect against the development of age‐related hepatic steatosis. To examine this hypothesis, we utilized ghrelin knockout (KO) mice. Although no different in young animals (3 months old), we found that at 20 months of age, ghrelin KO mice have significantly reduced hepatic steatosis compared to aged‐matched wild‐type (WT) mice. Examination of molecular pathways by which deletion of ghrelin reduces steatosis showed that the increase in expression of diacylglycerol O‐acyltransferase‐1 (DGAT1), one of the key enzymes of triglyceride (TG) synthesis, seen with age in WT mice, is not present in KO mice. This was due to the lack of activation of CCAAT/enhancer binding protein‐alpha (C/EBPα) protein and subsequent reduction of C/EBPα‐p300 complexes. These complexes were abundant in livers of old WT mice and were bound to and activated the DGAT1 promoter. However, the C/EBPα‐p300 complexes were not detected on the DGAT1 promoter in livers of old KO mice resulting in lower levels of the enzyme. In conclusion, these studies demonstrate the mechanism by which ghrelin deletion prevents age‐associated hepatic steatosis and suggest that targeting this pathway may offer therapeutic benefit for NAFLD.

Background: Development of liver cancer involves alterations of multiple pathways of gene expression. Results: Translational activation of C/EBP␤-HDAC1 complexes represses p53, SIRT1, and PGC1␣, leading to liver cancer. Conclusion: Modulation of levels of C/EBP␤-HDAC1 complexes at different stages of cancer is involved in liver cancer. Significance: Understanding the mechanisms of liver cancer is a critical step for the development of therapeutic approaches for cancer.