Published online Mar 14, 2020. doi: 10.3748/wjg.v26.i10.1029
Peer-review started: November 21, 2019
First decision: January 7, 2020
Revised: February 15, 2020
Accepted: February 21, 2020
Article in press: February 21, 2020
Published online: March 14, 2020
Nonalcoholic fatty liver disease (NAFLD) is a global metabolism-associated liver disease. Mesencephalic astrocyte-derived neurotrophic factor (MANF) is a newly discovered secreted protein that is involved in metabolic homeostasis. However, much remains to be discovered about its function in hepatic lipid metabolism; thus, we assessed whether MANF could regulate hepatic metabolism.
To establish in vivo and in vitro NAFLD models to explore the role of MANF in hepatic lipid metabolism.
HepG2 cells treated with free fatty acids (FFAs) and ob/ob mice were used as NAFLD models. Liver tissues collected from wild type and ob/ob mice were used to detect MANF expression. Cells were treated with FFAs for different durations. Moreover, we used lentiviral constructs to establish overexpression and knockdown cell models in order to interfere with MANF expression levels and observe whether MANF influences hepatic steatosis. Western blot analysis and quantitative real-time PCR were used to detect protein and gene expression, and oil red O staining was used to visualize intracellular lipid droplets.
Hepatic MANF protein and mRNA expression in wild type mice were 10-fold and 2-fold higher, respectively, than those in ob/ob mice. The MANF protein was temporarily increased by 1.3-fold after stimulation with FFAs for 24 h and gradually decreased to 0.66-fold that of the control at the 72 h time point in HepG2 cells. MANF deficiency upregulated the expression of genes involved in fatty acid synthesis, cholesterol synthesis, and fatty acid uptake and aggravated HepG2 cell steatosis, while MANF overexpression inhibited fatty acid synthesis and uptake and cholesterol synthesis, and rescued HepG2 cells from FFAs-induced steatosis. Furthermore, a significant decrease in triglyceride levels was observed in the MANF overexpression group compared with the control group (0.4288 ± 0.0081 mmol/g vs 0.3746 ± 0.0121 mmol/g, P < 0.05) upon FFAs treatment. There was also a 17% decrease in intracellular total cholesterol levels between the MANF overexpression group and the control group (0.1301 ± 0.0059 mmol/g vs 0.1088 ± 0.0009 mmol/g, P < 0.05) upon FFAs treatment. Moreover, MANF suppressed lipid deposition in HepG2 cells.
Our findings indicate that MANF improves the phenotype of liver cell steatosis and may be a potential therapeutic target in hepatic steatosis processes.
Core tip: We first uncovered an important function of mesencephalic astrocyte-derived neurotrophic factor (MANF) in the pathogenesis of nonalcoholic fatty liver disease. We found that MANF exerts a significant effect on hepatic fatty metabolism. This study suggests for the first time that MANF expression was increased at an early stage and gradually decreased afterward under high free fatty acids stimulation in HepG2 cells. Moreover, the results from gain-and-loss functional experiments showed that loss of MANF accelerated lipogenesis and aggravated HepG2 cell steatosis, while MANF overexpression inhibited lipogenesis and rescued HepG2 cell steatosis from free fatty acids treatment.