Uncoupling Protein 2 Regulates Palmitic Acid-Induced Hepatoma Cell Autophagy

Mitochondrial uncoupling protein 2 (UCP2) is suggested to have a role in the development of nonalcoholic steatohepatitis (NASH). However, the mechanism remains unclear. Autophagy is an important mediator of many pathological responses. This study aims to investigate the relationship between UCP2 and hepatoma cells autophagy in palmitic acid- (PA-) induced lipotoxicity. H4IIE cells were treated with palmitic acid (PA), and cell autophagy and apoptosis were examined. UCP2 expression, in association with LC3-II and caspase-3, which are indicators of cell autophagy and apoptosis, respectively,was measured. Results demonstrated that UCP2 was associated with autophagy during PA-induced hepatic carcinoma cells injury. Tests on reactive oxygen species (ROS) showed that UCP2 overexpression strongly decreases PA-induced ROS production and apoptosis. Conversely, UCP2 inhibition by genipin or UCP2 mRNA silencing enhances PA-induced ROS production and apoptosis. Autophagy partially participates in this progress. Moreover, UCP2 was associated with ATP synthesis during PA-induced autophagy. In conclusion, increasing UCP2 expression in hepatoma cells may contribute to cell autophagy and antiapoptotic as result of fatty acid injury. Our results may bring new insights for potential NASH therapies.

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Mitochondrial uncoupling protein-2 deficiency protects steatotic mouse hepatocytes from hypoxia/reoxygenation

AJP Gastrointestinal and Liver Physiology ◽

10.1152/ajpgi.00049.2011 ◽

2012 ◽

Vol 302 (3) ◽

pp. G336-G342 ◽

Cited By ~ 10

Author(s):

Zachary P. Evans ◽

Arun P. Palanisamy ◽

Alton G. Sutter ◽

Justin D. Ellett ◽

Venkat K. Ramshesh ◽

...

Keyword(s):

Lipid Peroxidation ◽

Uncoupling Protein ◽

Thiobarbituric Acid ◽

Atp Depletion ◽

Uncoupling Protein 2 ◽

Mitochondrial Uncoupling ◽

Mitochondrial Uncoupling Protein ◽

Ucp2 Expression ◽

Hypoxia Reoxygenation

Steatotic livers are sensitive to ischemic events and associated ATP depletion. Hepatocellular necrosis following these events may result from mitochondrial uncoupling protein-2 (UCP2) expression. To test this hypothesis, we developed a model of in vitro steatosis using primary hepatocytes from wild-type (WT) and UCP2 knockout (KO) mice and subjected them to hypoxia/reoxygenation (H/R). Using cultured hepatocytes treated with emulsified fatty acids for 24 h, generating a steatotic phenotype (i.e., microvesicular and broad-spectrum fatty acid accumulation), we found that the phenotype of the WT and UCP2 KO were the same; however, cellular viability was increased in the steatotic KO hepatocytes following 4 h of hypoxia and 24 h of reoxygenation; Hepatocellular ATP levels decreased during hypoxia and recovered after reoxygenation in the control and UCP2 KO steatotic hepatocytes but not in the WT steatotic hepatocytes; mitochondrial membrane potential in WT and UCP2 KO steatotic groups was less than control groups but higher than UCP2 KO hepatocytes. Following reoxygenation, lipid peroxidation, as measured by thiobarbituric acid reactive substances, increased in all groups but to a greater extent in the steatotic hepatocytes, regardless of UCP2 expression. These results demonstrate that UCP2 sensitizes steatotic hepatocytes to H/R through mitochondrial depolarization and ATP depletion but not lipid peroxidation.

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