Dipeptidyl peptidase 9 (DPP9) depletion from hepatocytes in experimental primary liver cancer

Dipeptidyl peptidase 9 (DPP9) is an indispensable intracellular protease. Among its many molecular functions is suppression of the NLRP1 inflammasome. Inhibitors targeting all four proteases of the DPP4 family, including DPP9, can reduce tumour burden, including in mouse liver. To explore hepatocyte DPP9 in experimental hepatocellular carcinoma (HCC), we generated hepatocyte-specific DPP9-KO mice by crossing albumin-Cre mice with DPP9 floxed mice and treated sequentially with diethylnitrosamine, then with thioacetamide combined with an atherogenic high-fat diet until 28 weeks of age. DPP9-KO mice had less body, liver and subcutaneous adipose tissue mass, lower fasting plasma glucose and fewer small macroscopic liver nodules compared to DPP9-WT control mice. However, there were no differences in the total number of macroscopic liver nodules, or of microscopic tumour burden, inflammation, fibrosis or steatosis. Consistent with the known function of DPP9 to suppress NLRP1 activation, activated caspase-1 protein and inflammation markers Nfkbib, Cxcl10 and Ccl5 were elevated in DPP9-KO liver. The tumour suppressor protein p53 was increased and the autophagy proteins beclin1, LC3B and p62 were altered. In conclusion, hepatocyte-specific DPP9 gene deletion in experimental primary liver cancer improved energy metabolism and may reduce liver cancer initiation, via mechanisms that may include increased autophagy and tumour suppression.