PPARα activation is essential for HCV core protein–induced hepatic steatosis and hepatocellular carcinoma in mice
Naoki Tanaka, … , Frank J. Gonzalez, Toshifumi Aoyama
Naoki Tanaka, … , Frank J. Gonzalez, Toshifumi Aoyama
Published January 10, 2008
Citation Information: J Clin Invest. 2008;118(2):683-694. https://doi.org/10.1172/JCI33594.
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Research Article Hepatology

PPARα activation is essential for HCV core protein–induced hepatic steatosis and hepatocellular carcinoma in mice

Abstract

Transgenic mice expressing HCV core protein develop hepatic steatosis and hepatocellular carcinoma (HCC), but the mechanism underlying this process remains unclear. Because PPARα is a central regulator of triglyceride homeostasis and mediates hepatocarcinogenesis in rodents, we determined whether PPARα contributes to HCV core protein–induced diseases. We generated PPARα-homozygous, -heterozygous, and -null mice with liver-specific transgenic expression of the core protein gene (Ppara+/+:HCVcpTg, Ppara+/–:HCVcpTg, and Ppara–/–:HCVcpTg mice. Severe steatosis was unexpectedly observed only in Ppara+/+:HCVcpTg mice, which resulted from enhanced fatty acid uptake and decreased mitochondrial β-oxidation due to breakdown of mitochondrial outer membranes. Interestingly, HCC developed in approximately 35% of 24-month-old Ppara+/+:HCVcpTg mice, but tumors were not observed in the other genotypes. These phenomena were found to be closely associated with sustained PPARα activation. In Ppara+/–:HCVcpTg mice, PPARα activation and the related changes did not occur despite the presence of a functional Ppara allele. However, long-term treatment of these mice with clofibrate, a PPARα activator, induced HCC with mitochondrial abnormalities and hepatic steatosis. Thus, our results indicate that persistent activation of PPARα is essential for the pathogenesis of hepatic steatosis and HCC induced by HCV infection.

Authors

Naoki Tanaka, Kyoji Moriya, Kendo Kiyosawa, Kazuhiko Koike, Frank J. Gonzalez, Toshifumi Aoyama

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Figure 7

Development of hepatic steatosis by long-term treatment of clofibrate in Ppara+/–:HCVcpTg mice.

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Development of hepatic steatosis by long-term treatment of clofibrate in...
(A) Histological examination of Ppara+/– and Ppara+/–:HCVcpTg mice treated with diet containing 0.05% (w/w) clofibrate for 24 months (CF). Top: Histological appearance of H&E-stained liver sections. Magnification, ×40. Microvesicular and macrovesicular steatosis were detected only in clofibrate-treated Ppara+/–:HCVcpTg mice. Middle and bottom: Electron microscopic features of hepatic mitochondria. Some C-shaped mitochondria showing discontinuance of outer membranes (arrows) were found in clofibrate-treated Ppara+/–:HCVcpTg mice. Scale bars: 400 nm (middle), 30 nm (bottom). (B and C) Content of liver triglycerides and lignoceric and palmitic acid β-oxidation activities. (D) MCAD mRNA levels. mRNA levels were normalized to those of GAPDH and subsequently normalized to those in Ppara+/+ nontransgenic mice. (E) Immunoblot analysis of AOX and CYP4A1. Whole-liver lysate (20 μg protein) was loaded in each lane. Actin was used as a loading control. Results are representative of 6 independent experiments. (F) PPARα mRNA levels and nuclear PPARα contents. Left: PPARα mRNA levels. The same samples used in D were adopted. Right: Immunoblot analysis of nuclear PPARα. Nuclear fraction obtained from each mouse (100 μg protein) was loaded in each well. Histone H1 was used as a loading control. In E and F, the mean value of the fold changes is shown under each band. Results are representative of 6 independent experiments. Band intensity was quantified densitometrically, normalized to that of the loading control, and subsequently normalized to that in Ppara+/+ nontransgenic mice. *P < 0.05 compared with untreated mice of the same genotype; **P < 0.05 compared with clofibrate-treated Ppara+/– mice without core protein gene. Results are expressed as mean ± SD (n = 6/group).