Introduction:
Estrogen deficiency is linked with dyslipidemia, especially in postmenopausal women, through a poorly understood mechanism. GPER is a recently recognized GPCR which is activated by estrogens. However, the role of GPER in mediating estrogen’s effects on lipid metabolism is unknown. We recently identified a common hypofunctional missense variant of GPER, namely P16L (allele frequency ~ 20%). We studied association of this with plasma LDL cholesterol levels. Further, we studied the role of GPER in regulating expression of the LDL receptor.
Methods:
Our discovery cohort was a genetically isolated population of Northern European descent (n=415), and our validation cohort consisted of 505 normal, healthy subjects 18-56 years of age from London, Ontario. Genomic DNA was extracted from whole blood and genotyped for GPER using a dedicated TaqMan assay. Additionally we examined the role of GPER on the regulation of LDL receptor expression by treatment with the GPER agonist, G1.
Results:
In the discovery cohort, the GPER P16L genetic variant was associated with a significant gene-dosage related increase in LDL cholesterol (CC [homozygous wild type] =3.18±0.84 (mean+SD); CT [heterozygote] =3.25±0.80; and TT [homozygous variant] =4.25±0.87 mmol/L, p<0.05). Total cholesterol concentrations followed a similar gradient across genotypes. In the validation cohort, the GPER P16L genetic variant was associated with a similar significant gene-dosage related increase in LDL cholesterol (CC =2.16±0.67; CT [heterozygote] =2.29±0.67; TT =2.40±0.84 mmol/L, p<0.05). In HepG2 cells expressing GPER, G1 mediated a concentration-dependent increase in LDL receptor expression. Pre-treating the cells with the GPER antagonist G15 attenuated the effect of G1 on LDL receptor upregulation. Further, downregulation of GPER expression via infection with a shGPER construct also attenuated G1's effect on LDL receptor upregulation.
Conclusion:
GPER activation upregulates LDL receptor expression. Further, carrying the hypofunctional P16L genetic variant of GPER, increases plasma LDL cholesterol in humans. In aggregate these data suggest an important role of GPER in regulation of LDL receptor expression and consequently LDL metabolism.
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