Amplification of the Hazelnut-Induced Epigenetic Modulation of LDLR Gene Expression in THLE-2 Human Primary Hepatocytes Compared to HepG2 Hepatocarcinoma Cells

Abstract

Dietary supplementation with tree nuts, including hazelnuts, has been associated with reduced cardiovascular disease risk factors, due to improved blood lipid profile. In the attempt to identify the molecular mechanism(s) underlying such beneficial effect, we here characterized the response of the human primary hepatocytes (THLE-2 cells) to the administration of an ethanolic extract of hazelnut (Corylus avellana L., cultivar Tonda Gentile Romana) in terms of regulation of the Low-Density Lipoprotein Receptor (LDLR), a major blood cholesterol carrier that positively correlates with improved blood lipids level. We demonstrated that hazelnut (0.004-0.4 mg/ml) does not alter viability and growth of primary liver cells, but significantly stimulates (P<0.05) the LDLR mRNA and membrane protein expression. We also proved that LDLR increase is driven by an epigenetic-based mechanism, as hazelnut treatments trigger a strong DNA hypo-methylation of two CpG-rich regions in the LDLR gene promoter, mapping at -739/-548 and -221/+174 position. The hazelnutmediated hypo-methylation is much stronger and extensive in THLE-2 than in HepG2 human hepatocarcinoma cells, supporting the significance of the liver context for performing studies on dietary supplementation. As overall, our findings demonstrate that hazelnut triggers an epigenetic-dependent regulation of LDLR expression in human primary liver cells in vitro, thus identifying in the LDLR stimulation a molecular mechanism contributing to the health promoting functions of hazelnuts.