Effect and mechanism of Acyl-CoA: lysocardiolipin acyltransferase 1 knockdown on hepatocyte steatosis and oxidative stress / 中华消化杂志

ABSTRACT

Objective:To investigate the effect and mechanism of Acyl-CoA lysocardiolipin acyltransferase 1 (ALCAT1) on hepatocyte steatosis and oxidative stress in fatty liver cell model.Methods:A fatty liver cell model was established and induced by free fatty acids (FFA). The expression of ALCAT1 in fatty liver cell model was detected by quantitative real-time polymerase chain reaction (qRT-PCR) and Western blotting. The empty siRNA plasmid and ALCAT1 siRNA plasmid were constructed. For the fatty liver cell model group, human normal hepatocytes (L-02 cells) were transfected with empty siRNA plasmid for 24 hours, and then cultured with FFA for 24 hours. For the ALCAT1 interfering group, L-02 cells were transfected with ALCAT1 siRNA plasmid for 24 hours, and then cultured with FFA for 24 hours. And L-02 cells cultured in common medium were used as as blank control group. Lipid droplet deposition and mitochondrial morphology were observed under transmission electron microscopy. The expression levels of autophagy-associated proteins (microtubule-associated protein 1 light chain 3 (LC3)-Ⅱ and Beclin1) and key proteins of autophagy signal pathway (mammalian target of rapamycin (mTOR) and serine/threonine kinase (AKT)) were measured by Western blotting. The expression levels of oxidative stress products (malondialdehyde, 4-hydroxynonenal (4-HNE) and reactive oxygen species (ROS)) and inflammatory factors (interleukin-6(IL-6) and tumor necrosis factor (TNF)-α) were detected by enzyme-linked immunosorbent assay (ELISA) kits. Independent sample t test was used for statistical analysis. Results:The mRNA and protein expression levels of ALCAT1 of the fatty liver cell model group were both higher than that of negative control group (9.26±0.83 vs. 1.02±0.12, 0.35±0.02 vs. 0.17±0.01), and the differences were statistically significant ( t=9.82 and 6.83, both P<0.05). The results of electron microscopy indicated that the deposition of lipid droplets of the fatty liver cell model group and ALCAT1 interfering group were both higher than that of blank control group (17.67±3.52 and 7.67±0.33 vs. 4.33±0.33), the quantity of lipid droplets deposition of ALCAT1 interfering group was lower than that of fatty liver cell model group (7.67±0.33 vs. 17.67±3.52), and the differences were statistically significant ( t=3.76, 7.07 and 2.82, all P<0.05). The degree of mitochondria swelling of fatty liver cell model group was higher than that of blank control group and the degree of mitochondria swelling of ALCAT1 interfering group was lower than that of fatty liver cell model group. The results of Western blotting showed that the expression level of LC3-Ⅱof the fatty liver cell model group was higher than that of the blank control group (0.43±0.01 vs. 0.28±0.02), and the difference was statistically significant ( t=7.32, P<0.05). However there was no significant difference in the expression level of Beclin1 between fatty live cell model group and blank control group (0.93±0.05 vs. 0.98±0.05, P>0.05). The expression levels of LC3-Ⅱ and Beclin1 of the ALCAT1 interfering group were both higher than those of the fatty liver cell model group and blank control group (0.95±0.04 vs. 0.42±0.01 and 0.28±0.02, 2.07±0.06 vs. 0.93±0.05 and 0.98±0.05), and the differences were statistically significant ( t=13.30, 15.63, 14.05 and 13.02, all P<0.05). The expression levels of mTOR of the fatty liver cell model group and ALCAT1 interfering group were both lower than that of the blank control group (1.44±0.02 and 0.74±0.01 vs. 1.93±0.10), the expression level of mTOR of the ALCAT1 interfering group was lower than that of the fatty liver cell model group (0.74±0.01 vs. 1.44±0.02), and the differences were statistically significant ( t=4.83, 12.04 and 32.14, all P<0.05). The expression levels of phosphorylated AKT of the fatty liver cell model group and ALCAT1 interfering group were both lower than that of the blank control group (0.14±0.01 and 0.07±0.01 vs. 0.28±0.01), while the expression level of phosphorylated AKT of the ALCAT1 interfering group was lower than that of the fatty liver cell model group (0.07±0.01 vs. 0.14±0.01), and the differences were statistically significant ( t=8.59, 14.10 and 5.96, all P<0.05). The results of ELISA indicated that the expression levels of ROS, malondialdehyde, 4-HNE, IL-6 and TNF-α of the fatty liver cell model group and the ALCAT1 interfering group were all higher than those of the blank control group ((11.44±0.30) and (5.84±0.36) g/L vs. (1.72±0.38) g/L; (19.94±2.47) and (11.95±1.55) μmol/L vs. (1.47±0.18) μmol/L; (5.00±0.43) and (2.99±0.37) ng/L vs. (1.46±0.23) ng/L; (203.40±5.16) and (92.07±11.98) ng/L vs. (23.32±3.33) ng/L; (123.70±8.38) and (67.42±4.88) ng/L vs. (47.18±4.57) ng/L), and the differences were all statistically significant ( t=19.86, 7.86, 7.45, 6.74, 7.22, 3.49, 29.34, 5.53, 8.02 and 3.03, all P<0.05). While the expression levels of ROS, 4-HNE, IL-6 and TNF-α of the ALCAT1 interfering group were all lower than those of the fatty liver cell model group ((5.84±0.36) g/L vs. (11.44±0.30) g/L, (2.99±0.37) ng/L vs. (5.00±0.43) ng/L, (92.07±11.98) ng/L vs. (203.40±5.16) ng/L and (67.42±4.88) ng/L vs. (123.70±8.38) ng/L), and all the differences were statistically significant ( t=11.99, 3.51, 8.54 and 5.81, all P<0.05). There was no statistically significant difference in the expression of malondialdehyde between ALCAT1 interfering group and fatty liver cell model group ((11.95±1.55) μmol/L vs. (19.94±2.47) μmol/L, P>0.05). Conclusions:The expression of ALCAT1 is up-regulated in fatty liver cell model. Knockdown of ALCAT1 can inhibit the expression of mTOR pathway proteins, activate autophagy, alleviate hepatocyte steatosis, oxidative stress and inflammatory response.