E2F1 inhibits circulating cholesterol clearance by regulating Pcsk9 expression in the liver
Qiuwen Lai, Albert Giralt, Cédric Le May, Lianjun Zhang, Bertrand Cariou, Pierre-Damien Denechaud, Lluis Fajas
Qiuwen Lai, Albert Giralt, Cédric Le May, Lianjun Zhang, Bertrand Cariou, Pierre-Damien Denechaud, Lluis Fajas
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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 6

E2f1–/– mice exhibit more pronounced liver fibrosis after 5 weeks on the high-cholesterol diet (HCD).

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E2f1–/– mice exhibit more pronounced liver fibrosis after 5 weeks on th...
Expression of PCSK9 protect liver of E2f1–/– mice from liver injuries. (A) Representative images of trichrome staining and Sirius red staining of livers from the E2f1+/+ and E2f1–/– mice that were fed an HCD for 5 weeks. Blue denotes collagen staining. Scale bar: 100 μm. (B) Relative mRNA expression of fibrosis-inflammation–related genes in the liver tissues from the E2f1+/+ and E2f1–/– mice that were fed an HCD for 5 weeks. All data are presented as the mean ± SEM. n = 4–9 mice per group. Differences between E2f1+/+ and E2f1–/– were determined by 2-tailed unpaired t test. *P < 0.05, **P < 0.01. (C) Fecal total bile acid (BA) quantification of E2f1+/+ and E2f1–/– mice before and after 5 weeks of HCD (5–7 samples per group). Differences between E2f1+/+ and E2f1–/– were determined by 2-way ANOVA. **P < 0.01. (D) E2f1+/+ and E2f1–/– mice were fed 5 weeks on HCD. After 2 weeks of HCD diet, E2f1–/– mice were injected with Ad-null or Ad-PCSK9. E2f1+/+ mice injected with Ad-null are used as control. Representative images of H&E staining, Sirius red staining, and Oil Red O staining of liver sections. Original magnification, ×100. (E) Relative mRNA expression of PCSK9, fibrosis-related genes, and Cd36 in the liver tissues from the E2f1+/+ and E2f1–/– mice fed on HCD and injected with Ad-null or Ad-PCSK9 as indicated. All data are presented as the mean ± SEM. n = 4–6 mice per group. Differences between E2f1–/– Ad-null and E2f1–/– Ad-PCSK9 were determined by one-way ANOVA. *P < 0.05, **P < 0.01.