Dual Mechanisms for the Fibrate-mediated Repression of Proprotein Convertase Subtilisin/Kexin Type 9

Yassine Zaïr,Patrick Nguyen,Michel Krempf,Anne Laure Jarnoux,Sanae Kourimate,Bertrand Cariou,Cédric Le May,Khadija Ouguerram,Cédric Langhi,Philippe Costet

doi:10.1074/jbc.m705831200

Abstract

Proprotein convertase subtilisin/kexin type 9 (PCSK9) is associated with familial autosomal dominant hypercholesterolemia and is a natural inhibitor of the LDL receptor (LDLr). PCSK9 is degraded by other proprotein convertases: PC5/6A and furin. Both PCSK9 and the LDLr are up-regulated by the hypocholesterolemic statins. Thus, inhibitors or repressors of PCSK9 should amplify their beneficial effects. In the present study, we showed that PPARalpha activation counteracts PCSK9 induction by statins by repressing PCSK9 promoter activity and by increasing PC5/6A and furin expression. Quantification of mRNA and protein levels showed that various fibrates decreased PCSK9 and increased PC5/6A and furin expression. Fenofibric acid (FA) reduced PCSK9 protein content in immortalized human hepatocytes (IHH) as well as its cellular secretion. FA suppressed PCSK9 induction by statins or by the liver X receptor agonist TO901317. PCSK9 repression is occurring at the promoter level. We showed that PC5/6A and furin fibrate-mediated up-regulation is PPARalpha-dependent. As a functional test, we observed that FA increased by 30% the effect of pravastatin on the LDLr activity in vitro. In conclusion, fibrates simultaneously decreased PCSK9 expression while increasing PC5/6A and furin expression, indicating a broad action of PPARalpha activation in proprotein convertase-mediated lipid homeostasis. Moreover, this study validates the functional relevance of a combined therapy associating PCSK9 repressors and statins.

Highlights

Tein; PC5/6A, proprotein convertase 5/6A; LDL receptor (LDLr), low density lipoprotein receptor; HDL, high density lipoprotein; HDL-C, HDL-cholesterol; LDL-C, LDL-cholesterol; IHH, immortalized human hepatocytes; LPDS, lipoprotein-deficient serum; PPAR␣, peroxisome proliferator-activated receptor ␣; CPT-1, carnitine palmitoyl transferase-1; Fenofibric acid (FA), fenofibric acid; PV, pravastatin; wt, wild type; mut, mutant; siRNA, short interfering RNA
We show that various fibrates repressed Proprotein convertase subtilisin/kexin type 9 (PCSK9) expression in immortalized human hepatocytes (IHH)
PCSK9 Expression Is Repressed by Various PPAR␣ Ligands in Human Immortalized Hepatocytes—To assess whether PCSK9 repression by fenofibrate could be extended to other PPAR␣ agonists and to the human gene, we exposed IHH cells for 24 h to Wy14643 (100 ␮M) or to 250 ␮M FA, clofibrate, and gemfibrozil (Fig. 1A)

Summary

Introduction

Tein; PC5/6A, proprotein convertase 5/6A; LDLr, low density lipoprotein receptor; HDL, high density lipoprotein; HDL-C, HDL-cholesterol; LDL-C, LDL-cholesterol; IHH, immortalized human hepatocytes; LPDS, lipoprotein-deficient serum; PPAR␣, peroxisome proliferator-activated receptor ␣; CPT-1, carnitine palmitoyl transferase-1; FA, fenofibric acid; PV, pravastatin; wt, wild type; mut, mutant; siRNA, short interfering RNA. We show that various fibrates repressed PCSK9 expression in immortalized human hepatocytes (IHH). Fenofibric acid (FA), the active form of fenofibrate, reduced the protein content of PCSK9 in IHH as well as its cellular secretion and prevented its accumulation caused by statins or the LXR agonist TO901317. These repressive effects were reproduced at the PCSK9 promoter level. To test the functional relevance of these findings, we verified that FA amplified the effect of pravastatin on LDLr activity

Methods

Results

Conclusion