Tanshinone IIA Modulates Low Density Lipoprotein Uptake via Down-Regulation of PCSK9 Gene Expression in HepG2 Cells.

Hung-Chen Chen,Jui-Hung Yen,Ming-Jiuan Wu,Mi-Hsueh Tai,Pei-Yi Chen,Maria Cristina Vinci

doi:10.1371/journal.pone.0162414

Abstract

Tanshinone IIA, one of the most pharmacologically bioactive phytochemicals isolated from Salvia miltiorrhiza Bunge, possesses several biological activities such as anti-inflammation, anti-cancer, neuroprotection and hypolipidemic activities. In this study, we aim to investigate the hypocholesterolemic effect of tanshinone IIA in hepatic cells. We demonstrated that tanshinone IIA significantly increased the amount of low-density lipoprotein receptor (LDLR) and LDL uptake activity in HepG2 cells at the post-transcriptional regulation. We further demonstrated that tanshinone IIA inhibited the expression of proprotein convertase subtilisin/kexin type 9 (PCSK9) mRNA and mature protein, which may lead to an increase the cell-surface LDLR in hepatic cells. We further identified a regulatory DNA element involved in the tanshinone IIA-mediated PCSK9 down-regulation, which is located between the -411 and -336 positions of the PCSK9 promoter. Moreover, we found that tanshinone IIA markedly increased the nuclear forkhead box O3a (FoxO3a) level, enhanced FoxO3a/PCSK9 promoter complexes formation and decreased the PCSK9 promoter binding capacity of hepatocyte nuclear factor 1α (HNF-1α), resulting in suppression of PCSK9 gene expression. Finally, we found that the statin-induced PCSK9 overexpression was attenuated and the LDLR activity was elevated in a synergic manner by combination of tanshinone IIA treatment in HepG2 cells. Overall, our results reveal that the tanshinone IIA modulates LDLR level and activity via down-regulation of PCSK9 expression in hepatic cells. Our current findings provide a molecular basis of tanshinone IIA to develop PCSK9 inhibitors for cholesterol management.

Highlights

Epidemiological studies have demonstrated that elevated circulating triglyceride-rich remnant lipoproteins and high concentrations of plasma low-density lipoprotein cholesterol (LDL-C) are directly correlated with the risk of atherosclerosis and cardiovascular disorders [1, 2]
We demonstrate that tanshinone IIA markedly down-regulates proprotein convertase subtilisin/kexin type 9 (PCSK9) gene expression, which is associated with increases in the amount of cell-surface LDL receptor (LDLR) and its LDL-uptake activity in HepG2 cells
We show that tanshinone IIA dramatically elevates the nuclear abundance of the forkhead box O3a (FoxO3a) and its interaction with PCSK9 promoter, which may result in the inhibition of hepatocyte nuclear factor 1α (HNF-1α)/PCSK9 promoter complex formation and the down-regulation of

Summary

Introduction

Epidemiological studies have demonstrated that elevated circulating triglyceride-rich remnant lipoproteins and high concentrations of plasma low-density lipoprotein cholesterol (LDL-C) are directly correlated with the risk of atherosclerosis and cardiovascular disorders [1, 2]. Tanshinone IIA Down-Regulates PCSK9 Gene Expression circulating LDL level is primarily determined by its rate of uptake through the LDL receptor (LDLR), a membrane glycoprotein in the human liver. Hepatic LDLR mediates the internalization of receptor-bound LDL particles and delivers the complex to the endosomes for degradation, and the LDLR returns to the cell membrane. The free cholesterol is further metabolized to bile acids for excretion in hepatic cells [3]. The hepatic expression of LDLR plays a critical role in removing plasma LDL and is important in modulating cholesterol homeostasis. Raising the level of the cell-surface LDLR and receptor activity to increase the cholesterol clearance is an efficient way to reduce LDL levels in the bloodstream [4]

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