A genetic variant in the LDLR promoter is responsible for part of the LDL-cholesterol variability in primary hypercholesterolemia.
BACKGROUND
GWAS have consistently revealed that LDLR locus variability influences LDL-cholesterol in general population. Severe LDLR mutations are responsible for familial hypercholesterolemia (FH). However, most primary hypercholesterolemias are polygenic diseases. Although Cis-regulatory regions might be the cause of LDL-cholesterol variability; an extensive analysis of the LDLR distal promoter has not yet been performed. We hypothesized that genetic variants in this region are responsible for the LDLR association with LDL-cholesterol found in GWAS.


METHODS
Four-hundred seventy-seven unrelated subjects with polygenic hypercholesterolemia (PH) and without causative FH-mutations and 525 normolipemic subjects were selected. A 3103 pb from LDLR (-625 to +2468) was sequenced in 125 subjects with PH. All subjects were genotyped for 4 SNPs (rs17242346, rs17242739, rs17248720 and rs17249120) predicted to be potentially involved in transcription regulation by in silico analysis. EMSA and luciferase assays were carried out for the rs17248720 variant. Multivariable linear regression analysis using LDL-cholesterol levels as the dependent variable were done in order to find out the variables that were independently associated with LDL-cholesterol.


RESULTS
The sequencing of the 125 PH subjects did not show variants with minor allele frequency ≥ 10%. The T-allele from g.3131C > T (rs17248720) had frequencies of 9% (PH) and 16.4% (normolipemic), p < 0.00001. Studies of this variant with EMSA and luciferase assays showed a higher affinity for transcription factors and an increase of 2.5 times in LDLR transcriptional activity (T-allele vs C-allele). At multivariate analysis, this polymorphism with the lipoprotein(a) and age explained ≈ 10% of LDL-cholesterol variability.


CONCLUSIONS
Our results suggest that the T-allele at the g.3131 T > C SNP is associated with LDL-cholesterol levels, and explains part of the LDL-cholesterol variability. As a plausible cause, the T-allele produces an increase in LDLR transcriptional activity and lower LDL-cholesterol levels.
Departamento de Bioquímica y Biología Molecular y Celular, Universidad de Zaragoza, C, Pedro Cerbuna 12, 50009 Zaragoza, Spain. idecastro.iacs@aragon.es.
Isabel
I
De Castro-Orós
Javier
J
Pérez-López
Rocio
R
Mateo-Gallego
Soraya
S
Rebollar
Marta
M
Ledesma
Montserrat
M
León
Montserrat
M
Cofán
Jose A
JA
Casasnovas
Emilio
E
Ros
Jose C
JC
Rodríguez-Rey
Fernando
F
Civeira
Miguel
M
Pocoví
D000328:Adult; D016022:Case-Control Studies; D008078:Cholesterol, LDL / Q000235:genetics*; D005260:Female; D005787:Gene Frequency / Q000235:genetics; D020022:Genetic Predisposition to Disease; D056945:Hep G2 Cells; D006801:Humans; D006937:Hypercholesterolemia / Q000235:genetics*; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D020641:Polymorphism, Single Nucleotide / Q000235:genetics*; D011401:Promoter Regions, Genetic; D011973:Receptors, LDL / Q000235:genetics*
D008078:Cholesterol, LDL; C573412:LDLR protein, human; D011973:Receptors, LDL