Abstract: Objective To investigate the effect of protein phosphate 4 ( PP4) activation on hepatocyte lipoapoptosis. Methods HepG2 cells were treated with 400 μmol / L palmitic acid (PA) for 24 hours to establish hepatocyte lipoapoptosis model. C57BL / 6J mice were fed with Western diet for 16 weeks to establish non-alcoholic steatohepatitis (NASH) model. The PP4 dominant negative mutant adenovirus vector AD-PP4RL was constructed. HepG2 cells were transfected with AD-PP4RL adenovirus to inhibit the activity of PP4 in hepatocytes. Mice were intravenously injected through the tail vein with AD-PP4RL adenovirus to inhibit the activity of PP4 in the liver. HepG2 cells were transfected with RAC1 lentivirus to inhibit the expression of RAC1. The lipid accumulation was detected by BoDIPY staining in cells and tissues. The levels of apoptosis were detected by TUNEL staining. The activity of PP4 was determined by immunoprecipitation combined with serine-threonine phosphatase activity assay kit. The activity of RAC1 was detected by GTPase activity assay kit. The expression levels of lipid metabolism and lipid apoptosis related proteins were detected by Western blotting. Results ① The activity of PP4 was increased in HepG2 cells treated with PA and in the livers of NASH mice induced by Western diet. ② The overexpression of dominant negative mutant adenovirus vector AD-PP4RL inhibited the activity of PP4 effectively. ③ Inhibition of PP4 activity decreased the level of lipoapoptosis in PA-treated HepG2 cells and livers of NASH mice, as well as the expression levels of lipoapoptosis related genes such as PUMA, Bim and c-caspase3. ④ RAC1 mediates the role of PP4 in hepatocyte lipoapoptosis. Conclusion Inhibition of PP4 activity alleviates hepatocyte lipoapoptosis by inhibiting the RAC1-mediated JNK activation and lipoapoptosis signaling pathway. 

Key words: non-alcoholic steatohepatitis, protein phosphatase 4, dominant negative mutant PP4RL, lipoapoptosis