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.
Robert C. Bauer, Makoto Sasaki, Daniel M. Cohen, Jian Cui, Mikhaila A. Smith, Batuhan O. Yenilmez, David J. Steger, Daniel J. Rader
(A) Hepatic transcript levels of Trib1-3 in mice (n = 5) receiving 1.5 × 1011 gc of either AAV_Null (Trib1_fl/fl) or AAV-TBG-Cre (Trib1_LSKO) 4 weeks after injection. Transcript levels were measured by TaqMan real-time RT-PCR of cDNA made from 1 μg liver total RNA. ND, not detectable. (B) Hepatic message levels of Trib1-3 in Trib1fl/fl mice crossed onto the albumin-Cre background causing germline deletion of hepatic Trib1. Mice were all aged 8–10 weeks, n = 5. (C) Plasma ALTs in male and female Trib1_fl/fl and Trib1_LSKO mice 4 weeks after injection, as measured by Cobas-Mira autoanalyzer. (D) Plasma ALTs of Trib1fl/fl Alb-Cre – and Trib1fl/fl Alb-Cre + males and females (n = 5), aged 8–10 weeks. Significance was determined in all panels by Student’s t test (**P ≤ 0.01, ***P ≤ 0.001).