E2F1 inhibits circulating cholesterol clearance by regulating Pcsk9 expression in the liver
Qiuwen Lai, … , Pierre-Damien Denechaud, Lluis Fajas
Qiuwen Lai, … , Pierre-Damien Denechaud, Lluis Fajas
Published May 18, 2017
Citation Information: JCI Insight. 2017;2(10):e89729. https://doi.org/10.1172/jci.insight.89729.
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Research Article Hepatology Metabolism

E2F1 inhibits circulating cholesterol clearance by regulating Pcsk9 expression in the liver

Abstract

Cholesterol accumulation in the liver is an early event in nonalcoholic fatty liver disease (NAFLD). Here, we demonstrate that E2F1 plays a crucial role in maintaining cellular cholesterol homeostasis by regulating cholesterol uptake via proprotein convertase subtilisin/kexin 9 (PCSK9), an enzyme that promotes low-density lipoprotein receptor (LDLR) degradation upon activation. E2f1–/– mice display reduced total plasma cholesterol levels and increased cholesterol content in the liver. In this study, we show that E2f1 deletion in cellular and mouse models leads to a marked decrease in Pcsk9 expression and an increase in LDLR expression. In addition to the upregulation of LDLR, we report that E2f1–/– hepatocytes exhibit increased LDL uptake. ChIP-Seq and PCSK9 promoter reporter experiments confirmed that E2F1 binds to and transactivates the PCSK9 promoter. Interestingly, E2f1–/– mice fed a high-cholesterol diet (HCD) display a fatty liver phenotype and liver fibrosis, which is reversed by reexpression of PCSK9 in the liver. Collectively, these data indicate that E2F1 regulates cholesterol uptake and that the loss of E2F1 leads to abnormal cholesterol accumulation in the liver and the development of fibrosis in response to an HCD.

Authors

Qiuwen Lai, Albert Giralt, Cédric Le May, Lianjun Zhang, Bertrand Cariou, Pierre-Damien Denechaud, Lluis Fajas

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Figure 4

E2F1-KO HepG2 cells show increased LDL-cholesterol (LDL-C) uptake and decreased cholesterol biosynthesis.

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E2F1-KO HepG2 cells show increased LDL-cholesterol (LDL-C) uptake and d...
(A) Relative expression of PCSK9 mRNA in HepG2 and E2F1-KO HepG2 cells. Three independent experiments in triplicate. (B) Representative images of PCSK9 Western blots from HepG2 and E2F1-KO HepG2 cells. Three independent experiments. Normalization of the quantified values is represented. (C) Representative images of LDL-C uptake in HepG2 and E2F1-KO HepG2 cells. Three independent experiments. Red fluorescence denotes LDL-C, and nuclei are stained in blue. Scale bars: 100 μm. (D) Representative images of LDLR Western blots from HepG2 and E2F1-KO HepG2 cell membranes. Three independent experiments. Ponceau staining is shown as loading control (LC). (E) Quantification of the rate of cholesterol biosynthesis in HepG2 and E2F1-KO HepG2 cells. Three independent experiments in triplicate. (F) Representative role of E2F1 in PCSK9-LDLR cholesterol uptake. All data are presented as the mean ± SEM. Differences between HepG2 and E2F1-KO HepG2 were determined by 2-tailed unpaired t test. **P < 0.01, ***P < 0.001, ****P < 0.0001.