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
View: Text | PDF
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

×

Figure 5

Cholesterol homeostasis and liver phenotype in E2F1–/– mice fed a high-cholesterol diet (HCD).

Options: View larger image (or click on image) Download as PowerPoint
Cholesterol homeostasis and liver phenotype in E2F1–/– mice fed a high-c...
(A) Plasma cholesterol profiles of E2f1+/+ and E2f1–/– mice before and after 5 weeks of being fed an HCD (1.25% cholesterol). n = 3–6 mice per group. (B and C) Plasma HDL and LDL-cholesterol levels after the 5 weeks of the HCD. n = 8–9 mice per group. (D) H&E and Oil Red O staining of E2f1+/+ and E2f1–/– liver sections. Original magnification, ×100. (E) Total lipid (triglycerides + cholesterol) and free cholesterol quantification in livers of E2f1+/+ and E2f1–/– mice. n = 5–6 mice per group. (F) Relative expression of Pcsk9 mRNA in livers from E2f1+/+ and E2f1–/– mice that were fed chow or HCD for 5 weeks. n = 6–9 mice per group. Differences were determined by 2-way ANOVA. *P < 0.05,**P < 0.01. (G) Western blot of PCSK9 in the liver tissues of E2f1+/+ and E2f1–/– mice that were fed an HCD for 5 weeks. Tubulin was used as a loading control. Normalization of the quantified values is represented. (H) Representative immunostaining of LDLR in the livers of E2f1+/+ and E2f1–/– mice that were fed an HCD. Scale bars: 100 μm. Quantification of LDLR staining is represented. Fluorescence intensity was normalized to the number of cells. (I) Western blot of LDLR in the liver tissues of E2f1+/+ and E2f1–/– mice that were fed an HCD for 5 weeks. Actin was used as a loading control. Normalization of the quantified values is represented. (J) Cd36 gene expression in livers of E2f1+/+ and E2f1–/– mice after 5 weeks of HCD. n = 5 mice per group. All data are presented as the mean ± SEM from a minimum of 5 mice per group. Differences between E2f1+/+ and E2f1–/– were determined by 2-tailed unpaired t test, unless indicated otherwise. *P < 0.05,**P < 0.005.