Increased NBCn1 expression, Na+/HCO3- co-transport and intracellular pH in human vascular smooth muscle cells with a risk allele for hypertension.

Fu Liang Ng,Ebbe Boedtkjer,Shu Ye,Mark J Caulfield,Meixia Ren,Arthur Tucker,Ruoxin Zhang,Katarzyna Witkowska,Christian Aalkjær

doi:10.1093/hmg/ddx015

Abstract

Genome-wide association studies have revealed an association between variation at the SLC4A7 locus and blood pressure. SLC4A7 encodes the electroneutral Na+/ co-transporter NBCn1 which regulates intracellular pH (pHi). We conducted a functional study of variants at this locus in primary cultures of vascular smooth muscle and endothelial cells. In both cell types, we found genotype-dependent differences for rs13082711 in DNA-nuclear protein interactions, where the risk allele is associated with increased SLC4A7 expression level, NBCn1 availability and function as reflected in elevated steady-state pHi and accelerated recovery from intracellular acidosis. However, in the presence of Na+/H+ exchange activity, the SLC4A7 genotypic effect on net base uptake and steady-state pHi persisted only in vascular smooth muscle cells but not endothelial cells. We found no discernable effect of the missense polymorphism resulting in the amino acid substitution Glu326Lys. The finding of a genotypic influence on SLC4A7 expression and pHi regulation in vascular smooth muscle cells provides an insight into the molecular mechanism underlying the association of variation at the SLC4A7 locus with blood pressure.

Highlights

Hypertension is a common and major etiological factor in cardiovascular, cerebrovascular and renovascular disease, estimated to cause up to 12.8% of global mortality and 3.7% of morbidity[1], with its complications contributing to a major worldwide economic burden[2]
Allelic difference in SLC4A7 expression level The lead blood pressure (BP) genome-wide association studies (GWAS) single nucleotide polymorphism (SNP) rs13082711 is in high LD (r2≥0.8) with 92 other SNPs which together span a 134 kb genomic interval
To investigate if the BP-associated variants influence the expression of SLC4A7, NEK10 and/or EOMES, we first performed RT-PCR assays of these genes to determine if they were expressed in vascular smooth muscle cells (VSMCs) and/or vein endothelial cells (VECs)

Summary

Introduction

Hypertension is a common and major etiological factor in cardiovascular, cerebrovascular and renovascular disease, estimated to cause up to 12.8% of global mortality and 3.7% of morbidity[1], with its complications contributing to a major worldwide economic burden[2]. There is a strong contribution from genes and their interaction with the environment to blood pressure (BP) regulation and the pathogenesis of hypertension[4,5]. The study presented here attempts to translate the genetic information on a gene relevant to hypertension into a biomedical context. The identification of a path linking genetic variation to protein availability, protein activity and subsequently cellular behaviors provides further confidence in pursuing NBCn1 as a potential therapeutic target in hypertension

Methods

Results

Conclusion