Double staining of β-galactosidase with fibrosis and cancer markers reveals the chronological appearance of senescence in liver carcinogenesis induced by diethylnitrosamine.

Cellular senescence is characterized by irreversible cell arrest and is associated with the development of chronic diseases, including cancer. Here, we investigated the induction of cellular senescence during liver carcinogenesis. Liver cancer was induced in Fischer 344 rats with a weekly intraperitoneal injection of diethylnitrosamine (50mg/kg body weight) for 16 weeks. Double-detection of β-galactosidase with Ki67 for cell proliferation; a-SMA and Pdgfrb for cell specificity; p53, p21, p16, and cyclin D1, CDK2, and CDK4 for senescence-associated molecular pathways and γ-glutamyltranspeptidase (GGT) for hepatocarcinogenesis was assessed to determine the association of these markers with cellular senescence. DNA damage was measured through senescence-associated heterochromatin foci (SAHF) detection. Progressive cellular senescence was observed in both fibrotic septa and hepatocytes from week 10 to 18. The maximum peak of positive senescent and fibrotic cells was observed at week 16 and decreased at week 18, but cell proliferation remained high. Whereas the increased p16 expression and SAHF were concomitant with that of β-galactosidase, those of p53 and p21 were barely detected. Furthermore, β-galactosidase positive myofibroblast-like cells were mainly surrounding GGT-positive tumors. Our findings showed that in hepatocarcinogenesis by diethylnitrosamine, cellular senescence is associated with p16 pathway activation and is mainly localized in myofibroblast-like cells.