Characterisation of concurrent liver injury and oncogenes in a plasmid-based mouse model of liver cancer

Abstract

Primary liver cancer is characterised by poor prognosis, growing disease burden and propensity to develop on a background of chronic liver injury. Delivery of oncogene expression plasmids by hydrodynamic tail vein injection (HTVI) is an emergent method of modelling liver cancer, but does not reproduce chronic injury and fibrosis typical in human liver cancer. Injury and fibrosis contribute to the pathogenesis of liver cancer, although this is not well characterised in plasmid-HTVI liver cancer models. Two previously published plasmid-HTVI models (SB/AKT/c-Met, SB/AKT/NRas) were combined with the hepatotoxin thioacetamide (TAA) to induce liver injury. Consistent with previous characterisation, SB/AKT/c-Met developed steatosis with hepatocellular tumours, while SB/AKT/NRas developed steatosis with both hepatocellular and cholangiocellular tumours. TAA did not increase tumour burden but altered the phenotype of surrounding tissue. TAA reduced plasmid-induced steatosis and increased inflammatory cells and fibrosis with different morphology to TAA alone. In order to find novel gene expression and pathways associated with the cancer-injury combination, liver tissue was subject to whole transcriptome sequencing. Metabolism, inflammation, cell cycling and proliferative signalling pathways were among those that differed by either cancer or injury alone. The cancer-injury combinations had gene expression profiles distinct from cancer or injury alone, with a few differentially expressed genes not explained by either cancer or injury alone. In cancer-injury combinations, some pathways were synergistically upregulated but in many cases cancer and injury were antagonistic. Lipid and xenobiotic metabolism were novel pathways uniquely activated in the cancer-injury combinations. Selected genes were validated by conventional gene expression assays and immunohistochemistry. By characterising a plasmid-HTVI model with concomitant liver injury and fibrosis, it was found that liver injury did not accelerate or increase tumorigenesis but altered the phenotype and transcriptomic profile of the cancer models. In some cases, injury and oncogenes antagonised each other with respect to cancer-associated processes such as fibrosis and steatosis. Novel genes and pathways associated with the cancer-injury combination give insight into how chronic injury interacts with liver cancer in humans.