Chronic overexpression of PNPLA3I148M in mouse liver causes hepatic steatosis
John Zhong Li, … , Jonathan C. Cohen, Helen H. Hobbs
John Zhong Li, … , Jonathan C. Cohen, Helen H. Hobbs
Published October 1, 2012
Citation Information: J Clin Invest. 2012;122(11):4130-4144. https://doi.org/10.1172/JCI65179.
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Research Article Hepatology

Chronic overexpression of PNPLA3I148M in mouse liver causes hepatic steatosis

Abstract

A genetic variant in PNPLA3 (PNPLA3I148M), a triacylglycerol (TAG) hydrolase, is a major risk factor for nonalcoholic fatty liver disease (NAFLD); however, the mechanism underlying this association is not known. To develop an animal model of PNPLA3-induced fatty liver disease, we generated transgenic mice that overexpress similar amounts of wild-type PNPLA3 (PNPLA3WT) or mutant PNPLA3 (PNPLA3I148M) either in liver or adipose tissue. Overexpression of the transgenes in adipose tissue did not affect liver fat content. Expression of PNPLA3I148M, but not PNPLA3WT, in liver recapitulated the fatty liver phenotype as well as other metabolic features associated with this allele in humans. Metabolic studies provided evidence for 3 distinct alterations in hepatic TAG metabolism in PNPLA3I148M transgenic mice: increased formation of fatty acids and TAG, impaired hydrolysis of TAG, and relative depletion of TAG long-chain polyunsaturated fatty acids. These findings suggest that PNPLA3 plays a role in remodeling TAG in lipid droplets, as they accumulate in response to food intake, and that the increase in hepatic TAG levels associated with the I148M substitution results from multiple changes in hepatic TAG metabolism. The development of an animal model that recapitulates the metabolic phenotype of the allele in humans provides a new platform in which to elucidate the role of PNLPA3I148M in NAFLD.

Authors

John Zhong Li, Yongcheng Huang, Ruchan Karaman, Pavlina T. Ivanova, H. Alex Brown, Thomas Roddy, Jose Castro-Perez, Jonathan C. Cohen, Helen H. Hobbs

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Figure 1

Tissue distribution of PNPLA3 mRNA in transgenic mice expressing human PNPLA3 predominantly (A) in the liver or (B) in adipose tissue.

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Tissue distribution of PNPLA3 mRNA in transgenic mice expressing human P...
(A) Schematic diagram of the PNPLA3 transgene, which is under control of a liver-specific enhancer/promoter element (30). Total mRNA was isolated from tissues of C57BL/6J mice expressing wild-type (L-PNPLA3WT) or mutant (L-PNPLA3I148M) human PNPLA3 (n = 4/group). Tissue levels of PNPLA3 mRNA were determined using real-time PCR, as described in the Methods. The cycle threshold (Ct) value in the liver is provided. Each value in the nonhepatic tissues represents the mRNA level relative to the value in liver. Immunoblot analysis was performed on lipid droplets isolated from the livers (22). A total of 1% of the volume of each fraction was size fractionated on an 8% SDS-PAGE gel and probed using a polyclonal anti-human PNPLA3 antibody (22). PLIN2, a lipid droplet protein, was used as a loading control. (B) Schematic diagram of the constructs used to make the A-PNPLA3WT and A-PNPLA3I148M mice (31). Tissue levels of PNPLA3 mRNA were measured by real-time PCR and expressed relative to the level in BAT. Immunoblot analysis of PNPLA3 in lipid droplets isolated from BAT and WAT was performed as described in A. UTR, untranslated region; hAPOE, human APOE; mAP2, mouse AP2; hGH, human GH.