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 5

The rate of VLDL-TAG secretion in vivo and TAG hydrolysis and fatty acid oxidation in primary hepatocytes.

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The rate of VLDL-TAG secretion in vivo and TAG hydrolysis and fatty acid...
(A) Chow-fed male mice (10–12 weeks old) of the indicated genotypes (n = 5/group) were fasted for 6 hours and injected with Triton WR-1339 (500 mg/kg) to inhibit lipolysis. Blood samples were obtained from the retro-orbital plexus at the times indicated, and plasma TAG levels were measured. Values are mean ± SEM. (B) Glycerol release in primary hepatocytes from nontransgenic and transgenic mice. Primary hepatocytes were isolated and plated as described in the legend to Figure 4. Cells were incubated with 1.5 mM 14C-glycerol for 4 hours, washed with ice-cold PBS, and then treated with Triacsin C (5 μM). At the indicated times, medium was removed, and lipids were extracted using the Folch method (58). Radioactivity of 14C-glycerol released from cells into the aqueous phase was quantified. (C) Cellular O2 consumption was measured in primary hepatocytes using the Seahorse XF-24 analyzer. Cells treated with etomoxir (300 mM), an inhibitor of carnitine palmitoyltransferase 1, served as a positive control. Values represent mean ± SEM of triplicate samples. *P < 0.05, **P < 0.01.