Low-grade fibrosis and dyslipidemia in c-Jun~Fra-2hep livers
Fibrosis and steatosis are often associated with HCC. At 2 months, Trichrome staining of liver sections (Figure 3A), qRT-PCR (Figure 3B) and WebGestalt (41) overrepresentation of matrix/collagen-related Reactome and Gene Ontology terms (Figure 3C), as well as enrichment in MSigDB C8 hepatic stellate cell signatures (Suppl. Figure 2H), supported the occurrence of fibrotic events in Jun~Fra-2hep mutant livers. Increased TGFβ signalling was also apparent at 9 months with increasedtgfb2/tgfbR2 mRNA expression (Suppl. Figure 3A) and relative Smad2 phosphorylation (Figure 3D). On the other hand, while the epithelial-to-mesenchymal transition MSigDB hallmark gene set was enriched in mutant datasets, lipid/peroxisome metabolism-related hallmarks had negative enrichment scores (Suppl. Figure 3B), consistent with decreased Oil Red O staining and Pparγ positivity in liver sections (Figure 3E). This is in line with the suppression of Pparγ signalling and high fat diet-induced NAFLD in c-Jun~Fra-2hep mice (22). Decreased protein and mRNA expression of Pparγ and Pparγ targets were apparent at 2 and 9 months (Figure 3F, Suppl. Figure 3C-D). LXR and LXR signalling, driving early pre-neoplastic events in Fos-expressing mice (19), were not consistently affected in c-Jun~Fra-2hep mice (Suppl. Figure 3E). Liver triglycerides (Figure 3G), serum triglycerides and cholesterol (Suppl. Figure 3F) were also decreased in mutant mice at 9 months, similar to what was observed after high fat diet (22). These data indicate that while low-grade fibrosis might contribute to liver cancer development in Jun~Fra-2hepmice, tumors occur in a dyslipidemic context with decreased hepatic lipids.