内质网应激与肝脏疾病研究进展

Changes of TRB3 and CHOP expression in nonalcoholic fatty liver disease in rats

AIM: To investigate the changes of Tribbles related protein 3 (TRB3) and CCAAT/enhancer-binding protein homologous protein (CHOP) expression in nonalcoholic fatty liver disease (NAFLD) in rats.

METHODS: Thirty Wistar rats were randomly divided into a normal control group and an NAFLD group. The rats of the NAFLD group were given a high-fat, high-glucose diet for 16 weeks to induce NAFLD, while the normal control group was given an ordinary diet. The levels of total cholesterol (TC), triglyceride (TG), low-density lipoprotein (LDL) and high-density lipoprotein (HDL) were detected with an automatic biochemical analyzer. The expression of TRB3 and CHOP mRNAs in the liver was detected by real-time quantitative PCR. The expression of TRB3 and CHOP proteins in liver tissue was detected by immunohistochemistry. Cell apoptosis was detected by flow cytometry.

RESULTS: The levels of TC, TG, and LDL in the NAFLD group were significantly higher than those in the normal control group (P < 0.05), while the level of HDL was lower than that in the normal control group (P < 0.05). Compared with the normal group, levels of TRB3 and CHOP mRNAs and proteins in the NAFLD group were significantly increased (mRNA: P < 0.05 or P < 0.01; protein: P < 0.01). Flow cytometry analysis showed that the apoptosis in the NAFLD group was higher than that in the normal control group.

CONCLUSION: The changes of TRB3 and CHOP expression may play important roles in the development of NAFLD.

Change of protein kinase R-like endoplasmic reticulum kinase/eukaryotic translation initiator factor-2α signaling pathway in nonalcoholic fatty liver disease in rats

AIM: To observe the change of the protein kinase R-like endoplasmic reticulum kinase/eukaryotic translation initiator factor-2α (PERK/eIF-2α) signaling pathway in nonalcoholic fatty liver disease (NAFLD) and to discuss the possible clinical significance.

METHODS: Thirty Wistar rats were randomly and equally divided into two groups: a normal control group (group 1) and an NAFLD group (group 2). NAFLD was induced by feeding a high-fat, high-glucose diet for 16 wk, and group 1 was given an ordinary diet at the same time. Serum levels of total cholesterol (TC), triglyeride (TG), low-density lipoprotein (LDL) and high-density lipoprotein (HDL) were measured in all rats. The mRNA expression of PERK, eIF-2α, C/EBP homology protein (CHOP) and glucose regulated protein 78 kDa (GRP78) in the liver was detected by real-time PCR, while Western blot was used to detect the expression of p-PERK, p-eIF-2α, CHOP and GRP78 proteins. Cell apoptosis was tested by flow cytometry.

RESULTS: Levels of TC, TG, and LDL in group 1 were significantly higher than those in group 2 (P < 0.05), but the level of HDL was significantly lower in group 1 (P < 0.05). Compared with group 1, the expression of p-PERK, p-eIF-2α, CHOP and GRP78 protein in group 2 was significantly increased (P < 0.05), and the expression of PERK, eIF-2α, CHOP and GRP78 mRNAs was also significantly elevated in group 2 (P < 0.05 or P < 0.01). Flow cytometry analysis suggested that apoptosis in group 2 was increased.

CONCLUSION: The PERK/eIF-2α signaling pathway is involved in the development and progression of NAFLD, which may cause endoplasmic reticulum stress and induce apoptosis.

Protective effect of kaempferol on endoplasmic reticulum stress-induced hepatocyte apoptosis and underlying mechanism

AIM: To explore the protective effect of kaempferol on human normal hepatocyte line HL-7702 cells under the endoplasmic reticulum stress and the underlying mechanism.

METHODS: In order to develop a hepatocyte apoptosis model, endoplasmic reticulum stress inducer tunicamycin was used to induce HL-7702 cell apoptosis. After HL-7702 cells were incubated with different concentrations of kaempferol (0.01, 0.1, 1 μmol/L), cell morphological changes were observed by microscopy, cell viability was measured by MTT assay, lactate dehydrogenase (LDH) activity in cell supernatants was determined with an LDH assay kit, apoptosis was measured by flow cytometry, and the protein expression of CHOP, a special marker of apoptosis induced by endoplasmic reticulum stress, was detected by Western blot.

RESULTS: Compared with the tunicamycin-induced hepatocyte apoptosis group, low concentrations of kaempferol (0.01, 0.1, 1 μmol/L) significantly inhibited endoplasmic reticulum stress-induced hepatocyte apoptosis. Kaempferol improved cell morphology, increased liver cell survival (tunicamycin model group, 80.14% ± 8.00%; 0.01 μmol/L kaempferol group, 96.16% ± 10.00%, P < 0.01; 0.1 μmol/L kaempferol, 91.43% ± 9.10%, P < 0.01; 1 μmol/L kaempferol, 87.84% ± 6.90%, P < 0.01), and reduced the levels of LDH released from HL-7702 cells (tunicamycin model group, 398.5 U ± 30.8 U; 0.01 μmol/L kaempferol, 89.9 U ± 21.4 U, P < 0.05; 0.1 μmol/L kaempferol, 95.1 U ± 8.9 U, P < 0.05; 1 μmol/L kaempferol, 120.5 U ± 24.2 U, P < 0.05), the apoptosis rates (tunicamycin model group, 4.58% ± 0.90%; 0.01 μmol/L kaempferol, 1.18% ± 0.48%, P < 0.05; 0.1 μmol/L kaempferol, 1.97% ± 0.32%, P < 0.05; 1 μmol/L kaempferol, 2.63% ± 0.16%, P < 0.05) and significantly reduced the expression of CHOP protein.

CONCLUSION: Low concentrations of kaempferol may inhibit endoplasmic reticulum stress-induced hepatocyte apoptosis by decreasing the expression of CHOP. Kaempferol may be a new drug to protect against liver injury induced by liver disease.

Endoplasmic reticulum oxidoreductin 1α mediates homocysteine-induced hepatocyte endoplasmic reticulum stress

AIM: To assess the role of endoplasmic reticulum oxidoreductin 1α (ERO1α) in homocysteine (Hcy)-induced endoplasmic reticulum stress (ERS).

METHODS: Hepatocytes were cultured in the presence or absence of Hcy (100 μmol/L), and ELISA was used to determine the concentrations of of glucose-regulated protein 78 (GRP78), X-box binding protein-1 (XBP-1), protein kinase RNA-like endoplasmic reticulum kinase (PERK) and activating transcription factor 6 (ATF6). Hepatocytes were then cultured with different concentrations of Hcy (0, 50, 100, 200, 500 μmol/L) and 100 μmol/L Hcy plus folic acid and vitamin B₁₂, and the expression of ERO1α was detected by qRT-PCR and Western blot. ERO1α recombinant plasmid and ERO1α small interfering RNAs were then used to transfect hepatocytes, and the expression of ERO1α and the concentrations of GRP78, PERK, ATF6 and XBP-1 were measured.

RESULTS: Compared with non-treated cells, the concentrations of GRP78, PERK, ATF6 and XBP-1 significantly increased in Hcy-treated cells (P < 0.01, P < 0.01, P < 0.05, P < 0.01). Hcy decreased the expression of ERO1α at mRNA and protein levels (P < 0.01) in a dose-dependent manner. Transfection with ERO1α recombinant plasmid significantly increased the expression of ERO1α (P < 0.01), while transfection with three ERO1α small interfering RNAs significantly decreased the expression of ERO1α, with siRNA2 having the most significant effect (P < 0.01). Compared with the Hcy group, the concentrations of GRP78, PERK, ATF6 and XBP-1 significantly decreased in the Hcy + pERO1α recombinant plasmid group (P < 0.05), but increased in the Hcy + siRNA2 group (P < 0.01).

CONCLUSION: ERO1α may be involved in Hcy-induced hepatocyte ERS possibly by regulation of the GRP78-XBP-1/PERK/ATF6 signal pathway.