Klotho Gene in Human Salt-Sensitive Hypertension

Abstract

Background and objectives: Hypertension is a common aging-related disorder. Salt intake is one of the main environmental factors contributing to the development of hypertension. Transgenic mice with one-half Klotho deficiency displayed a spontaneous BP increase and salt-sensitive hypertension in response to high sodium intake. Usually circulating levels of α-Klotho decrease with age, and this reduction may be stronger in patients with several aging-related diseases. This study aimed at exploring the association of Klotho with salt sensitivity in humans.

Design, setting, participants, & measurements: The role of Klotho polymorphisms and α-Klotho serum levels was evaluated in patients with hypertension who were treatment naive and underwent an acute salt-sensitivity test (discovery n=673, intravenous 2 L of 0.9% saline in 2 hours). Salt sensitivity was defined as a mean BP increase of >4 mm Hg at the end of the infusion. A total of 32 single nucleotide polymorphisms in the Klotho gene (KL), previously identified with a genome-wide association study, were used in the genetic analysis and studied for a pressure-natriuresis relationship.

Results: Of the patients with hypertension, 35% were classified as salt sensitive. The most relevant polymorphism associated with pressure natriuresis was the common missense single nucleotide polymorphism rs9536314, and the GG and GT genotypes were more represented among patients who were salt sensitive (P=0.001). Those carrying the G allele showed a less steep pressure-natriuresis relationship, meaning that a significant increase in mean BP was needed to excrete the same quantity of salt compared with patients who were salt resistant. KL rs9536314 also replicated the pressure-natriuresis association in an independent replication cohort (n=193) and in the combined analysis (n=866). There was an inverse relationship between circulating Klotho and mean BP changes after the saline infusion (r=-0.14, P=0.03). Moreover, circulating α-Klotho was directly related to kidney function at baseline eGFR (r=0.22, P<0.001).

Conclusions: KL rs9536314 is associated with salt-sensitive hypertension in patients with hypertension who are treatment naive. Moreover, circulating α-Klotho levels were mainly related to diastolic BP changes at the end of a salt load and to eGFR as an expression of kidney aging.

Keywords: alleles; animals; blood pressure; cohort studies; dietary sodium chloride; genetics and development; genome-wide association study; genotype; humans; hypertension; kidney; mice; natriuresis; saline solution; single nucleotide polymorphism; sodium chloride; transgenic mice.

Copyright © 2020 by the American Society of Nephrology.

Figures

Graphical abstract

Figure 1.

Inverse correlation between circulating α-Klotho and mean BP changes. ΔMBP, mean BP variation. r=−0.14; P=0.03, unadjusted; r=−0.15; P=0.02, adjusted for age, sex, and BMI.

Figure 2.

Association with pressure natriuresis of single nucleotide polymorphisms (SNPs) in KL region. (A) Tag SNPs covering the entire gene with extension to the 5′ and 3′ flanking regions and regional plot for association with pressure natriuresis at time 120 minutes. (B) Linkage disequilibrium (LD) map for the KL SNPs around exons 2–3. Numeric values represent pairwise LD as measured by r2. SNPs in high LD are represented by darker squares (r2>0.80). Chr13, chromosome 13; pter, p terminal; E2/3, exon 2/3.

Figure 3.

Pressure-natriuresis relationship variation according to KL rs9536314 genotypes during acute salt load in the combined cohort. Urinary sodium excretion (UNa+) as a function of mean BP (MBP), at basal level (t 0) and after salt load (t 120). The pressure-natriuresis curve is drawn according to the KL rs9536314 polymorphism (carriers of the nonrisk genotype TT, gray curve; carriers of the risk allele G, black dashed curve). The significantly less-steep slope of the black dashed curve compared with the gray curve indicates the need for an increase in mean BP to excrete the salt load in carriers of the G allele. Horizontal whiskers refer to mean SEM for BP, vertical whiskers refer to SEM for urinary sodium excretion. BMI, body mass index.