Abstract 13801: The p.Leu167del Mutation in APOE Gene causes Autosomal Dominant Hypercholesterolemia by Down-Regulation of LDL Receptor Expression in Hepatocytes
Introduction: The p.Leu167del mutation in APOE gene has been associated to different hyperlipidemias. However, the frequency of this mutation in autosomal dominant hypercholesterolemia and the mechanism of this association is not known.
Objectives: To establish the frequency of p.Leu167del mutation in APOE gene in subjects with clinical diagnosis of Autosomal Dominant Hypercholesterolemia (ADH) non-dependent of LDLR, APOB nor PCSK9 genes, and to investigate the mechanism by which this mutation associates to ADH.
Methods: We selected 288 unrelated subjects with ADH non-dependent of LDLR, APOB nor PCSK9 genes, and 220 unrelated normolipidemic subjects (control group). All available family members of mutation carrier subjects were also studied. Exon 4 of APOE gene was sequenced in all subjects.
VLDL and LDL were isolated from p.Leu167del carriers and E3/E3 control subjects by ultracentrifugation. Quantification of lipoprotein uptake in HepG2 and THP-1 cells and LDL receptor membrane-expression in HepG2 cells were carried out by flow cytometry.
Results: In the ADH group, 9 unrelated subjects (3.1%) were carriers of the p.Leu167del mutation in APOE gene and none in the control group. Eleven family members were carriers of the mutation, 7 with isolated hypercholesterolemia and 4 with mixed hyperlipidemia. A clear co-segregation of p.Leu167del mutation with elevated plasma cholesterol levels in the families was found.
VLDL isolated from p.Leu167del mutation carriers had a significantly higher uptake by HepG2 and THP-1 cells compared to VLDL isolated from E3/E3 subjects (p<0.01). When increasing incubation times of HepG2 cells with VLDL from p.Leu167del carriers, the LDL receptor expression in surface membrane diminished, in contrast with the VLDL from E3/E3 subjects. When pre-incubating HepG2 cells with VLDL from p.Leu167del mutation carriers, the percentage of LDL internalisation was significantly lower than when incubating with VLDL from E3/E3 subject (p<0.01).
Conclusion: The p.Leu167del mutation in APOE gene is associated to ADH in 3.1% of studied subjects. The mechanism of this association is higher uptake of VLDL, down regulation of the LDLR expression and decrease of LDL internalisation in hepatocytes.
Author Disclosures: A. Cenarro: None. C. Martín: None. M. Stef: None. I. de Castro-Orós: None. A. Etxebarria: None. L. Palacios: None. R. Mateo-Gallego: None. H. Ostolaza: None. T. Tejedor: None. F. Civeira: None.
- © 2014 by American Heart Association, Inc.