Hormonally Induced Hepatocellular Carcinoma in Diabetic Wild Type and Carbohydrate Responsive Element Binding Protein Knockout Mice

Hepatocellular Ballooning is Due to Highly Pronounced Glycogenosis Potentially Associated with Steatosis and Metabolic Reprogramming

Background and Aims

Hepatocellular ballooning is a common finding in chronic liver disease, mainly characterized by rarefied cytoplasm that often contains Mallory-Denk bodies (MDB). Ballooning has mostly been attributed to degeneration but its striking resemblance to glycogenotic/steatotic changes characterizing preneoplastic hepatocellular lesions in animal models and chronic human liver diseases prompts the question whether ballooned hepatocytes (BH) are damaged cells on the path to death or rather viable cells, possibly involved in neoplastic development.

Methods

Using specimens from 96 cirrhotic human livers, BH characteristics were assessed for their glycogen/lipid stores, enzyme activities, and proto-oncogenic signaling cascades by enzyme- and immunohistochemical approaches with serial paraffin and cryostat sections.

Results

BH were present in 43.8% of cirrhotic livers. Particularly pronounced excess glycogen storage of (glycogenosis) and/or lipids (steatosis) were characteristic, ground glass features and MDB were often observed. Decreased glucose-6-phosphatase, increased glucose-6-phosphate dehydrogenase activity and altered immunoreactivity of enzymes involved in glycolysis, lipid metabolism, and cholesterol biosynthesis were discovered. Furthermore, components of the insulin signaling cascade were upregulated along with insulin dependent glucose transporter glucose transporter 4 and the v-akt murine thymoma viral oncogene homolog/mammalian target of rapamycin signaling pathway associated with de novo lipogenesis.

Conclusions

BH are hallmarked by particularly pronounced glycogenosis with facultative steatosis, many of their features being reminiscent of metabolic aberrations documented in preneoplastic hepatocellular lesions in experimental animals and chronic human liver diseases. Hence, BH are not damaged entities facing death but rather viable cells featuring metabolic reprogramming, indicative of a preneoplastic nature.

Glucose-induced and ChREBP: MLX-mediated lipogenic program promotes hepatocellular carcinoma development

The Carbohydrate Response Element (ChoRE) Binding Protein (ChREBP) and its binding partner Max-like protein X (MLX) mediate transcription of lipogenic genes under glucose-rich conditions. Dysregulation of glucose and lipid metabolism frequently occurs in cancers, including Hepatocellular Carcinomas (HCCs). However, it is currently unclear whether the glucose-induced lipogenic program plays a role in the development of HCCs. Here, we show that MLX expression is elevated in HCC specimens and downregulation of MLX expression inhibits proliferation of HCC cells. In mice, liver-specific knockout of Mlx results in dramatic decrease in the expression of lipogenic genes and lipid levels in circulation. Interestingly, in the absence of Mlx, the development of tumors in multiple HCC models, such as diethylnitrosamine (DEN) treatment and hydrodynamic injection of oncogenes (AKT/RAS or CTNNB1/RAS), is robustly blocked. However, a high-fat diet can partially restore tumorigenesis in Mlx-deficient livers, indicating a critical role of lipid synthesis in HCC development. In addition, liver-specific expression of a dominant negative MLX (dnMLX) via adeno-associated virus effectively blocks tumorigenesis in mice. Thus, the glucose-induced lipogenic program is required in the development of HCC, and the ChREBP: MLX transcription factors serve as a potential target for cancer therapies.