ABSTRACT
Objective To investigate the effect of inhibition of ghrelin O-acyltransferase (GOAT) by small interfering RNA (siRNA) on hepatocyte fatty degeneration and related mechanism of action.Methods Human LO2 hepatocytes were treated with free fatty acid (FFA)to induce hepatocyte fatty degeneration.LO2 hepatocytes were treated with FFA and siRNA-GOAT alone or in combination and then divided into normal control (NC) group (treated with phosphate buffered saline alone),siRNA-GOAT group (treated with siRNA-GOAT at a final concentration of 10 nm),FFA group (treated with FFA at a final concentration of 1 mm),and FFA + siRNA-GOAT group (treated with FFA at a final concentration of 1 mm and siRNA-GOAT at a final concentration of 10 nm).Oil red O staining was performed for hepatocytes to identify lipid droplets;the triglyceride (TG) test kit was used to measure the lipid level in LO2 hepatocytes;Western blot,qRT-PCR,immunofluorescent staining,and electron microscopy were used to measure autophagy;ELISA and RT-PCR were used to measure the levels of tumor necrosis factor-α (TNFα) and interleukin-6 (IL-6);ELISA was used to measure the changes in the levels of mammalian target of rapamycin (mTOR),phosphorylated mTOR (p-mTOR),AMP-activated protein kinase (AMPK),and phosphorylated AMPK.A one-way analysis of variance was used for comparison between multiple groups,and the least significant difference t-test was used for further comparison between any two groups.Results Compared with the FFA group,the FFA + siRNA-GOAT group had a significant reduction in the formation of lipid droplets and a significantly lower TG level (P ＜0.001).Compared with the FFA group,the FFA + siRNA-GOAT group had significant reductions in the protein and mRNA expression of TNFα and IL-6 (all P ＜ 0.005).The siRNA + GOAT group had significantly higher mRNA expression of LC3-Ⅱ and Beclin-1 than the NC group (all P ＜0.001).The FFA + siRNA-GOAT group had significantly higher mRNA expression of LC3-Ⅱ and Beclin-1 than the FFA group (all P ＜0.001).The siRNA + GOAT group had significantly higher protein expression of LC3-Ⅱ and Beclin-1 than the NC group (all P ＜ 0.05).The FFA + siRNA-GOAT group had significantly higher protein expression of LC3-Ⅱ and Beclin-1 than the FFA group (all P ＜ 0.05).Immunofluorescent staining showed that compared with the FFA group and the siRNA-GOAT group,the FFA + siRNA-GOAT group had a significant increase in the expression of endogenous LC3-Ⅱ in LO2 hepatocytes.Electron microscopy showed that compared with the FFA group,the FFA + siRNA-GOAT group had a significant increase in the expression of autophagosome.After the LO2 hepatocytes were treated by autophagy inhibitors siRNA-ATG5 and 3-MA or an autophagy stimulant,rapamycin,there was a significant difference in TG level between the FFA + siRNA-ATG5 group and the FFA + siRNA-GOAT group (P ＜ 0.001),as well as between the FFA + 3-MA group and the FFA + rapamycin group (P ＜ 0.001).The FFA + siRNA-GOAT group had a significantly higher level of LC3-Ⅰ/Ⅱ than the FFA + siRNA-ATG5 group (P ＜0.05),and the FFA + rapamycin group had a significantly higher level of LC3-Ⅰ/Ⅱ than the FFA + 3-MA group (P ＜ 0.05).Compared with the FFA group,the FFA + siRNA-GOAT group had significantly higher protein expression of p-AMPK (P ＜ 0.05) and significantly lower protein expression of p-rmTOR (P ＜ 0.05).Conclusion GOAT inhibition by siRNA can upregnlate autophagy and alleviate hepatocyte fatty degeneration,possibly by regulating the AMPK/mTOR pathway.
ABSTRACT
Objective To investigate the effect of deoxyribonucleic acid (DNA) methylation on the expression of hepatocyte nuclear factor-4α (HNF4c) and its role in the expression of HNF4α regulated by transforming growth factor-β1 (TGF-β1).Methods The expression of HNF4αP1 mRNA in six human hepatoma cell lines (HepG2,Huh-7,Hep3B,SMMC-7721,BEL-7405 and FOCUS),20 hepatic carcinoma specimens and corresponding adjacent tissues was detected by real-time reverse transcription polymerse chain reaction (real-time RT-PCR).The methylation status of the promoter region of HNF4αP1 in six human hepatoma cell lines was examined by bisulfite sequencing PCR (BSP).FOCUS cells were treated with 5-aza-2'-deoxycytidine (5-AZA-CdR) and then the methylation status of the promoter region of HNF4αP1 was examined by BSP.The expression of HNF4αP1 mRNA was detected by real-time RT-PCR.The six human hepatoma cell lines were treated with TGFβ1 and the expression of HNF4αP1 mRNA was detected by real-time RT-PCR.FOCUS cells were cotreated with 5-AZA-CdR,TGF-β1 and 5-AZA-CdR.The expression of HNF4αP1 mRNA was detected by real-time RT-PCR,and t test was performed for statistical analysis.Results Among 20 human hepatic carcinoma specimens and corresponding adjacent tissues,the expression of HNF4αP1 mRNA of 13 human hepatic carcinoma specimens was lower than that of corresponding adjacent tissues (t=2.350,P＜0.05).The relative quantity of the expression of HNF4αP1 mRNA was higher in Hep3B,HepG2 and Huh-7 cells,whereas that in SMMC-7721,BEL-7405 and FOCUS cells was lower.The methylation of the promoter region of HNF4αP1 in HepG2,Huh-7 and Hep3B was lower,but that in SMMC-7721,BEL-7405 and FOCUS was higher.Along with the increasing of the concentration of 5-AZA-CdR (0,0.1,1.0 and 2.5 μmol/L),the degree of the methylation of the promoter region of HNF4αP1 in FOCUS cells gradually decreased (61％,46％,32％ and 27％),and however the relative quantity of the expression of HNF4αP1 mRNA gradually increased ((9.661 ± 0.336)×10-7,(2.001±0.432)×10-6,(3.689±0.714)×10-6and (4.732±2.451)×10-6).After stimulated with TGF-β1,the relative quantity of the expression of HNF4αP1 mRNA was downregulated in HepG2,Huh-7 and Hep3B cells in which the methylation of the promoter region was low (t=12.994,8.441,and 9.032,all P＜0.01).There was no significant difference in the relative quantity of the expression of HNF4αP1 mRNA in SMMC-7721,BEL-7405 and FOCUS cells in which the methylation of the promoter region was high (all P ＞ 0.05).The relative quantity of the expression of HNF4αP1 mRNA in 5-AZA-CdR treated FOCUS cells ((4.972±0.035) × 10-6) was higher than that of control group ((1.411 ± 0.104) × 10-6) and the difference was statistically significant (t=13.212,P＜0.01).The relative quantity of the expression of HNF4αP1 mRNA in FOCUS cells co-treated with 5-AZA-CdR and TGF-β1 was lower than that in cells treated with 5-AZA-CdR alone and the difference was statistically significant ((1.181 ± 0.132) × 10-6 vs (4.972 ± 0.035) × 10-6,t=13.873,P＜0.01).Conclusions The expression of HNF4αP1 is down-regulated in hepatic carcinoma tissues.DNA methylation may regulate the expression of HNF4αP1 in hepatoma cells.The methylation of HNF4αP1 promoter region inhibits the regulating function of TGF-β1 in the expression of HNF4αP1.