PPARα activation is essential for HCV core protein–induced hepatic steatosis and hepatocellular carcinoma in mice
Naoki Tanaka, Kyoji Moriya, Kendo Kiyosawa, Kazuhiko Koike, Frank J. Gonzalez, Toshifumi Aoyama
Naoki Tanaka, Kyoji Moriya, Kendo Kiyosawa, Kazuhiko Koike, Frank J. Gonzalez, Toshifumi Aoyama
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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 3

Analyses of mitochondrial abnormalities.

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Analyses of mitochondrial abnormalities. (A) Lignoceric and palmitic aci...
(A) Lignoceric and palmitic acid β-oxidation activities in 9-month-old mice. Results are expressed as the mean ± SD (n = 6/group). *P < 0.05 compared with Ppara+/+ nontransgenic mice; **P < 0.05 compared with Ppara+/–:HCVcpTg mice; #P < 0.05 compared with Ppara–/–:HCVcpTg mice. (B) Electron microscopic features of hepatic mitochondria of 9-month-old HCVcpTg mice. Upper and lower rows show a lower and higher magnification, respectively. In Ppara+/+:HCVcpTg mice, some mitochondria showing discontinuance of outer membranes (arrows) and amorphous inner structures were observed. In Ppara+/–:HCVcpTg and Ppara–/–:HCVcpTg mice, mitochondria appeared normal; the scale bars represent 200 nm (top) and 30 nm (bottom), respectively. (C) Immunoblot analysis of cytochrome c in 9-month-old mice. Whole-liver lysate, mitochondrial fraction, or cytosolic fraction (50 μg protein) was loaded in each well. Results are representative of 4 independent experiments. (D) Immunoblot analysis of representative mitochondrial β-oxidation enzymes using a mitochondrial fraction prepared from 9-month-old mouse livers. The mitochondrial fraction (20 μg protein) was loaded in each well. Results are representative of 4 independent experiments. The band intensity was quantified densitometrically and normalized by that in Ppara+/+ nontransgenic mouse. The mean value of the fold changes is shown under the representative band. LACS, long-chain acyl-CoA synthase; CPT, carnitine palmitoyl-CoA transferase.