Cholesterol Overloading Leads To Hepatic L02 Cell Damage Through Activation Of The Unfolded Protein Response

Reported data demonstrated that cholesterol loading in liver could cause the hepatic injury. To explore the possible mechanisms of cell damage resulted from cholesterol overloading in hepatocyte, the cell apoptosis, the unfolded protein response (UPR) and the correlation between them were tested in cholesterol-overloading human normal hepatic cell line L02. L02 cells were incubated with 200μg/ml of low density Hpoprotein (LDL) for 24h with or without 20μg/ml of 58035, an inhibitor of acyl-CoA:cholesterol acyltransferase (ACAT). In LDL+58035 group, the intracellular cholesterol level was dramatically increased, which was measured by an enzymetic combinated high performance liquid chromatography (HPLC) assay. The expression of immunoglobulin-binding protein (BiP), X-box binding protein (XBP1), activating transcription factor 6(ATF6), activating transcription factor 4(ATF4), CCAAT/enhancer-binding protein homologous protein-10 (CHOP), which were all the markers of endoplasmic reticulum (ERS)/UPR, were up-regulated by reverse transcription-polymerase chains reaction (RT-PCR) or Western Blot analysis. The rate of apoptotic cell death increased to 21.3±2.4%. Meanwhile, the active caspase-3 protein expression increased to 8.4 folds of that in the controls. Furthermore, 4-Phenylbutyric acid (PBA), an inhibitor of UPR, could partly reduce the cell apoptosis and activation of caspase-3. This study suggests that cholesterol overloading in hepatic L02 cells induced the ERS and activated UPR which partly leads to apoptotic damage of cells.