Abstract
To investigate the role of hepatic 18-carbon fatty acids (FA) accumulation in regulating CYP2A5/2A6 and the significance of Nrf2 in the process during hepatocytes steatosis, Nrf2-null, and wild type mice fed with high-fat diet (HFD), and Nrf2 silenced or over expressed HepG2 cells administered with 18-carbon FA were used. HE and Oil Red O staining were used for mice hepatic pathological examination. The mRNA and protein expressions were measured with real-time PCR and Western blot. The results showed that hepatic CYP2A5 and Nrf2 expression levels were increased in HFD fed mice accompanied with hepatic 18-carbon FA accumulation. The Nrf2 expression was increased dose-dependently in cells administered with increasing concentrations of stearic acid, oleic acid, and alpha-linolenic acid. The Nrf2 expression was dose-dependently decreased in cells treated with increasing concentrations of linoleic acid, but the Nrf2 expression level was still found higher than the control cells. The CYP2A6 expression was increased dose-dependently in increasing 18-carbon FA treated cells. The HFD-induced up-regulation of hepatic CYP2A5 in vivo and the 18-carbon FA treatment induced up-regulation of CYP2A6 in HepG2 cells were, respectively, inhibited by Nrf2 deficiency and Nrf2 silencing. While the basal expression of mouse hepatic CYP2A5 was not impeded by Nrf2 deletion. Nrf2 over expression improved the up-regulation of CYP2A6 induced by 18-carbon FA. As the classical target gene of Nrf2, GSTA1 mRNA relative expression was increased in Nrf2 over expressed cells and was decreased in Nrf2 silenced cells. In presence or absence of 18-carbon FA treatment, the change of CYP2A6 expression level was similar to GSTA1 in Nrf2 silenced or over expressed HepG2 cells. It was concluded that HFD-induced hepatic 18-carbon FA accumulation contributes to the up-regulation of CYP2A5/2A6 via activating Nrf2. However, the CYP2A5/2A6 expression does not only depend on Nrf2.
Highlights
Non-alcoholic fatty liver disease (NAFLD) is an important chronic liver disease and metabolic syndrome, correlated with diabetes, obesity, and cardiovascular diseases (Angulo, 2002; Marchesini et al, 2003; Yoneda et al, 2012)
Our objective is to investigate the relationship between hepatocellular 18-carbon fatty acids (FA) accumulation and CYP2A5/2A6 expression and the involvement of NF-E2related factor 2 (Nrf2) in the process by (i) investigating the effects of hepatic steatosis on CYP2A5 expression via Nrf2 in Nrf2-null and wild type (WT) mice fed with high-fat diet (HFD), (ii) examining the effects of 18-carbon FA [stearic acid (SA, C18:0), oleic acid (OA, C18:1), linoleic acid (LA, C18:2), and alpha-linolenic acid (ALA, C18:3)], which significantly accumulated in the HFD fed mice liver, on Nrf2 and CYP2A6 expressions in HepG2 cells, and (iii) if the effects of 18-carbon FA on CYP2A5/2A6 expression are related to Nrf2 with Nrf2 silenced or over expressed HepG2 cells
Our former researches showed that hepatic Nrf2 and CYP2A5 mRNA expressions were increased significantly in HFD fed mice (Wang C. et al, 2016) and accompanied with badly hepatic 18-carbon FA (SA, OA, LA, and α-linolenic acid (ALA)) accumulation, which is the most abundant component of liver FA (Wang X. et al, 2016)
Summary
Non-alcoholic fatty liver disease (NAFLD) is an important chronic liver disease and metabolic syndrome, correlated with diabetes, obesity, and cardiovascular diseases (Angulo, 2002; Marchesini et al, 2003; Yoneda et al, 2012). Lipid deposition in hepatocytes is considered to be the first hit, which caused by insulin resistance and lipometabolism disorder and resulted in non-alcoholic liver simple steatosis (SS). The second hit contributes to the progressive development of non-alcoholic steatohepatitis (NASH), liver fibrosis, cirrhosis, and even hepatocellular carcinoma from SS (Bugianesi et al, 2002). Excessive fatty acids (FA) deposition and its peroxidation in hepatocytes are considered to be the major factors causing cytotoxicity and exacerbated hepatopathology. CYP2A5 and Nrf expression were both induced by 18-carbon FA treatment in mouse primary hepatocytes (Cui et al, 2016). The role of 18-carbon FA in inducing CYP2A6 in human hepatoma cell line has never been reported
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