Saturated free fatty acid sodium palmitate-induced lipoapoptosis by targeting glycogen synthase kinase-3ß activation in human liver cells.

BACKGROUND: Elevated serum saturated fatty acid levels and hepatocyte lipoapoptosis are features of nonalcoholic fatty liver disease (NAFLD). AIM: The purpose of this study was to investigate saturated fatty acid induction of lipoapoptosis in human liver cells and the underlying mechanisms. METHODS: Human liver L02 and HepG2 cells were treated with sodium palmitate, a saturated fatty acid, for up to 48 h with or without lithium chloride, a glycogen synthase kinase-3ß (GSK-3ß) inhibitor, or GSK-3ß shRNA transfection. Transmission electron microscopy was used to detect morphological changes, flow cytometry was used to detect apoptosis, a colorimetric assay was used to detect caspase-3 activity, and western blot analysis was used to detect protein expression. RESULTS: The data showed that sodium palmitate was able to induce lipoapoptosis in L02 and HepG2 cells. Western blot analysis showed that sodium palmitate activated GSK-3ß protein, which was indicated by dephosphorylation of GSK-3ß at Ser-9. However, inhibition of GSK-3ß activity with lithium chloride treatment or knockdown of GSK-3ß expression with shRNA suppressed sodium palmitate-induced lipoapoptosis in L02 and HepG2 cells. On a molecular level, inhibition of GSK-3ß expression or activity suppressed sodium palmitate-induced c-Jun-N-terminal kinase (JNK) phosphorylation and Bax upregulation, whereas GSK-3ß inhibition did not affect endoplasmic reticulum stress-induced activation of unfolded protein response. CONCLUSIONS: The present data demonstrated that saturated fatty acid sodium palmitate-induced lipoapoptosis in human liver L02 and HepG2 cells was regulated by GSK-3ß activation, which led to JNK activation and Bax upregulation. This finding indicates that GSK-3ß inhibition may be a potential therapeutic target to control NAFLD.

Endoplasmic reticulum stress leads to lipid accumulation through upregulation of SREBP-1c in normal hepatic and hepatoma cells.

Endoplasmic reticulum stress (ERS) has been found in non-alcoholic fatty liver disease. The study was to further explore the mechanistic relationship between ERS and lipid accumulation. To induce ERS, the hepatoblastoma cell line HepG2 and the normal human L02 cell line were exposed to Tg for 48 h. RT-PCR and Western blot were performed to evaluate glucose-regulated protein (GRP-78) expression as a marker of ERS. ER ultrastructure was assessed by electron microscopy. Triglyceride content was examined by Oil Red O staining and quantitative intracellular triglyceride assay. The hepatic nuclear sterol regulatory element-binding protein (SREBP-1c), liver X receptor (LXRs), fatty acid synthase (FAS), and acetyl-coA carboxylase (ACC1) expressions were examined by real-time PCR and Western blot. 4-(2-aminoethyl) benzenesulfonyl fluoride (AEBSF) was used to inhibit S1P serine protease inhibitor, and SREBP-1c cleavage was evaluated under ERS. SREBP-1c was knockdown and its effect on lipid metabolism was observed. Tg treatment upregulated GRP-78 expression and severely damaged the ER structure in L02 and HepG2 cells. ERS increased triglyceride deposition and enhanced the expression of SREBP-1c, FAS, and ACC1, but have no influence on LXR. AEBSF pretreatment abolished Tg-induced SREBP-1c cleavage. Moreover, SREBP-1c silencing reduced triglycerides and downregulated FAS expression. Pharmacological ERS induced by Tg leads to lipid accumulation through upregulation of SREBP-1c in L02 and HepG2 cells.

[Retracted] Hypoxia­induced mitochondrial translocation of DNM1L increases mitochondrial fission and triggers mPTP opening in HCC cells via activation of HK2.

Subsequently to the publication of the above paper, the authors have retrospectively realized that they used the human normal liver cell, line L­02, for the experiments reported in this study instead of the intended hepatocellular cell line, Huh­7. Consequently, the results and conclusions reported in this article must be considered to lack reliability. Therefore, the authors have requested that the article be retracted from the publication. The authors apologize to the Editor and to the readership for any inconvenience caused. [the original article was published in Oncology Reports 42: 1125­1132, 2019; DOI: 10.3892/or.2019.7213].

Hypoxia­induced mitochondrial translocation of DNM1L increases mitochondrial fission and triggers mPTP opening in HCC cells via activation of HK2.

Disturbed mitochondrial dynamics are closely associated with the progression of different types of cancer including hepatocellular carcinoma (HCC). However, the manner in which mitochondrial dynamics are regulated in HCC remains largely unclear. In the present study, via immunofluorescence, real­time PCR and western blot analysis, the effects of dynamin­1­like (DNM1L) on mitochondrial translocation and the mitochondrial permeability transition pore (mPTP) were investigated in HCC cells under hypoxic conditions, and the underlying molecular mechanisms were explored. Our data revealed that hypoxic treatment decreased the mitochondrial membrane potential, elevated generation of reactive oxygen species, and promoted mitochondrial fission in a DNM1L­dependent manner. Instead of changing the levels of DNMlL, hypoxia increased the translocation of DNM1L to mitochondria, leading to excessive mitochondrial fission and decreased the viability of HCC cells. In addition to the effects on mitochondrial dynamics, DNM1L also regulated mPTP opening in HCC. IP analysis revealed that DNM1L interacted with the enzyme hexokinase 2 (HK2), and was involved in its phosphorylation, resulting in HK2 detachment from the mitochondria and consequently mPTP opening.

Protective effect of apoptosis signal-regulating kinase 1 inhibitor against mice liver injury.

OBJECTIVE: To explore the protective effect and its molecular mechanism of apoptosis signal-regulating kinase 1 (ASK1) inhibitor (GS-459679) on acetaminophen-induced liver injury in mice. METHODS: The model of liver injury was established by administration of acetaminophen (APAP) (300 mg/kg, i.p.) on C57BL/6 mice. Forty-eight male C57BL/6 mice were randomly divided into four groups, consisting of control group, GS group (GS-459679, 30 mg/kg, i.p.), APAP-induced group, and GS combined with APAP-induced group. For GS combined with APAP-induced group, mice were treated with GS 30 min prior to administration of APAP. After mice were euthanized at 6 h or 12 h, respectively, serum levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) were analyzed, and mRNA levels of TNF-α, IL-6 and IL-1ß were tested. The activity of glutathione (GSH), oxidized GSH (GSSG) and malondialdehyde were quantified. In addition, ASK1, P-ASK1, JNK and P-JNK protein levels were tested in all groups. RESULTS: The ASK1 and P-ASK1 levels were up-regulated in APAP-induced group. Compared to the control group, serum levels of ALT and AST, and mRNA levels of TNF-α, IL-6 and IL-1ß were increased in APAP-induced group. Meanwhile, the levels of MAD and GSSG, and the ratio of GSSG/GSH were higher and the JNK was activatedin APAP-induced group compared with that in control group. However, compared to APAP-induced group, GS combined with APAP-induced group displayed a decrease of protein expression levels of ASK1, P-ASK1 and P-JNK, a reduction of serum levels of ALT and AST, a decrease in TNF-α, IL-6 and IL-1ß mRNA levels, and a low ration of GSSG/GSH. CONCLUSIONS: GS-459679 treatment effectively down-regulates ASK1 and P-ASK1 expression. Addition of GS-459679 decreases the generation of liver metabolites and inflammatory factors, reduces oxidative stress reaction, inhibits JNK activation, and then protects the responsiveness to APAP-induced liver injury.