Abstract
Objectives
Non-alcoholic fatty liver disease (NAFLD) is characterized by the accumulation of lipid in hepatocytes. In spite of the growing number of NAFLD patients with the increased prevalence of obesity, the pathogenesis of NAFLD remains to be fully elucidated. Prohibitin1 (Phb1) is an evolutionarily conserved protein, which is expressed predominantly on the inner mitochondrial membrane. Several studies have provided evidences that the Phb1 plays a crucial role not only in proliferation of hepatocytes, but also in lipid metabolism in adipocytes. Since the liver is the major site for lipid metabolism, this study was aimed to understand the lipid metabolism regulated by Phb1 in hepatocytes.
Methods
Normal murine hepatocyte cell line, AML12 was used in this study and Phb1 was disrupted by small interfering RNA (siRNA). These siRNA transfected cells were further treated with saturated fatty acids (SFAs), palmitic acid (PA) for 24 hours. Then the cell viability and the mRNA expression level of key enzymes involved in lipid metabolism were determined.
Results
Approximately 20% cell viability decreased when Phb1 was silenced and the cell viability diminished dramatically after PA treatment in both control and Phb1 deficiency groups. Without excessive fatty acids (FAs) inside the cells, Phb1 deficiency led to significant mRNA expression of stearoyl-CoA desaturase-1 (Scd1) to generate triglycerides (TG) and activated the endoplasmic reticulum (ER) stress response by upregulating the mRNA expression level of C/EBP homologous protein (Chop). The elevated expression of peroxisome proliferator activated receptor gamma (PPARγ), which was reported to be upregulated in the livers of NAFLD patients, was also found in this study. When intracellular FAs were surplus, the catabolism of FAs was inhibited by downregulation of carnitine palmitoyltransferase 1a (Ctp1a), while the synthesis of TG was further promoted by significantly increased mRNA expression level of Scd1. The elevated mRNA expression level of Chop and Pparγ induced by Phb1 disruption were further elevated.
Conclusions
This study, Phb1 deficiency led to altered lipid metabolism, resulting in the of lipid accumulation inside the cells and ER stress, and these cytotoxic effects were further deteriorated upon the excessive PA treatment.
Funding Sources
National Research Foundation of Korea, 2-1604-001.
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