Tribbles-1 regulates hepatic lipogenesis through posttranscriptional regulation of C/EBPα
Robert C. Bauer, … , David J. Steger, Daniel J. Rader
Robert C. Bauer, … , David J. Steger, Daniel J. Rader
Published September 8, 2015
Citation Information: J Clin Invest. 2015;125(10):3809-3818. https://doi.org/10.1172/JCI77095.
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Research Article Metabolism

Tribbles-1 regulates hepatic lipogenesis through posttranscriptional regulation of C/EBPα

Abstract

Variants near the gene TRIB1 are significantly associated with several plasma lipid traits, circulating liver enzymes, and the development of coronary artery disease in humans; however, it is not clear how its protein product tribbles-1 regulates lipid metabolism. Here, we evaluated mice harboring a liver-specific deletion of Trib1 (Trib1_LSKO) to elucidate the role of tribbles-1 in mammalian hepatic lipid metabolism. These mice exhibited increased hepatic triglyceride (TG) content, lipogenic gene transcription, and de novo lipogenesis. Microarray analysis revealed altered transcription of genes that are downstream of the transcription factor C/EBPα, and Trib1_LSKO mice had increased hepatic C/EBPα protein. Hepatic overexpression of C/EBPα in WT mice phenocopied Trib1_LSKO livers, and hepatic knockout of Cebpa in Trib1_LSKO mice revealed that C/EBPα is required for the increased lipogenesis. Using ChIP-Seq, we found that Trib1_LSKO mice had increased DNA-bound C/EBPα near lipogenic genes and the Trib1 gene, which itself was transcriptionally upregulated by C/EBPα overexpression. Together, our results reveal that tribbles-1 regulates hepatic lipogenesis through posttranscriptional regulation of C/EBPα, which in turn transcriptionally upregulates Trib1. These data suggest an important role for C/EBPα in mediating the lipogenic effects of hepatic Trib1 deletion and provide insight into the association between TRIB1 and plasma lipids, and liver traits in humans.

Authors

Robert C. Bauer, Makoto Sasaki, Daniel M. Cohen, Jian Cui, Mikhaila A. Smith, Batuhan O. Yenilmez, David J. Steger, Daniel J. Rader

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Figure 3

Trib1_LSKO mice have increased hepatic TG content, transcription of fatty acid synthetic genes, and de novo lipogenesis.

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Trib1_LSKO mice have increased hepatic TG content, transcription of fatt...
(A) Liver mass of Trib1_fl/fl and Trib1_LSKO mice (n = 5) represented as percentage of body mass. (B) Liver TG content measured by colorimetric assay using 20 mg whole liver homogenized in PBS from Trib1_fl/fl and Trib1_LSKO mice 4 weeks after injection. (C) Liver cholesterol content measured by colorimetric assay from same liver homogenates used in B. (D) H/E staining of liver sections from Trib1_fl/fl and Trib1_LSKO mice 4 weeks after injection shows increased lipid deposition and breakdown of hepatocyte organization. (E) Enlarged image of steatotic liver from Trib1_LSKO mice. The white arrowhead indicates a hypertrophic hepatocyte with microvesicular steatosis, and the black arrowhead indicates a typical Mallory body. (F) Lipogenic gene transcription in livers of Trib1_fl/fl and Trib1_LSKO mice measured by TaqMan real-time RT-PCR (n = 5). (G) De novo lipogenesis in mice (n = 6) fasted overnight, then refed and injected with 100 μCi of [3H]-Acetate for labeling of newly synthesized fatty acids. Lipids were extracted from 100 mg liver, and values are CPM/mg liver. Scale bars: 20 µm. Significance was determined by Student’s t test (*P ≤ 0.05, **P ≤ 0.01, ***P ≤ 0.001).