OTUD1 regulates cytokine expression and related pathways in goose fatty liver by promoting deubiquitination of its target proteins

Goose fatty liver (or foie gras) does not develop inflammation even in severe steatosis, which is different from human nonalcoholic fatty liver disease (NAFLD), and it is considered as a unique model for NAFLD study. The deubiquitinating enzyme, Ovarian Tumor (OTU)-Deubiquitinase 1 (OTUD1), is involved in various cell biological processes by regulating the expression of cytokines. Its role and mechanism in the formation of goose fatty liver however are not clear yet. This study determined the expression of OTUD1 in goose fatty liver versus normal liver and OTUD1 expression in goose primary liver treated with glucose, fatty acids and insulin using qPCR and immunoblotting assays. OTUD1 gene overexpression and subsequent transcriptome sequencing analysis were performed to identify the differentially expressed genes (DEG) and the pathways where the DEGs are enriched. Immunoprecipitation and protein mass spectrometry were employed to screen the interacting proteins of OTUD1. The results showed that both the mRNA and protein abundances of OTUD1 in goose fatty liver were higher than those of normal liver. In goose primary hepatocytes, palmitic acid and oleic acid both increased the protein levels of OTUD1, while glucose and insulin inhibited the expression of the protein. Overexpression of OTUD1 significantly affected the expression of genes and pathways related to inflammatory/immune responses and cell growth/death. The interacting proteins of OTUD1 are mainly related to membrane transport, immune/inflammatory response, ubiquitination and signaling pathways. The interaction between OTUD1 and AP1G1 was validated by co-immunoprecipitation and immunoblotting assays. Consistently, the relative ubiquitination level of AP1G1 in goose fatty liver was lower than that of normal liver, which is correlated with increased protein abundance of AP1G1 and OTUD1 in goose fatty liver. In conclusion, the increased protein abundance of OTUD1 in goose fatty liver can regulate the expression of cytokines and related pathways during the formation of goose fatty liver by promoting the deubiquitination of the interacting proteins of OTUD1, including AP1G1.