Instituto de Investigación Sanitaria del Hospital Clínico San Carlos, IdISSC
Genetics and molecular basis of complex diseases

Author Of 1 Presentation

Genetics and Epigenetics Oral Presentation

PS08.05 - Functional changes associated to the Multiple Sclerosis risk polymorphism in the HHEX gene

Speakers
Presentation Number
PS08.05
Presentation Topic
Genetics and Epigenetics
Lecture Time
13:39 - 13:51

Abstract

Background

Genome-wide association studies (GWAS) identified 233 SNPs (Single Nucleotide Polymorphisms) increasing multiple sclerosis (MS) susceptibility, with a main involvement of immune peripheral cells and microglia. One of these variants, rs7923837, described as eQTL in healthy individuals, is located near the HHEX (Hematopoietically Expressed Homeobox) gene, which encodes a key transcription factor in lymphopoiesis and contributes to metabolism-related traits and diseases.

Objectives

We aimed at understanding the impact of rs7923837 polymorphism located in the 3'UTR (Untranslated Region) of the HHEX gene on MS risk

Methods

The study included 154 MS patients and 117 healthy controls. The SNP rs7923837 was genotyped by TaqMan technology. Levels of expression of the HHEX gene were ascertained by real time PCR and normalized to the GUS housekeeping gene. HHEX nuclear translocation was analyzed by confocal microscopy. Extracellular acidification (ECAR) and oxygen consumption rate (OCR) were measured in peripheral blood mononuclear cells (PBMCs) with and without phytohemagglutinin (PHA) stimulation, in a Seahorse XFp Extracellular Flux Analyzer (Agilent). Mitochondrial mass was measured by FACS in PBMCs with mitotracker florescence probe.

Results

Lower levels of expression of the HHEX gene were detected in MS patients compared to controls (p=0.037). As previously described in whole blood of healthy controls, the risk polymorphism acts as eQTL in PBMCs of MS patients. The AA genotype not only showed reduced levels of mRNA expression in MS patients, but also an increased nuclear localization, in contrast to the lower nuclear localization found in controls with this genotype. In addition, PHA stimulation in PBMCs of AA-homozygotes significantly increased mitochondrial mass in controls compared with MS patients (p=0.009). The influence of genotypes in rs7923837 on the values of ECAR and OCR, indicative of glycolysis and oxidative phosphorylation respectively, were analyzed. Significant differences in ECAR were evidenced by comparison of either homozygous genotype between MS patients and controls. In basal conditions, a consistent trend to higher OCR was observed for MS patients compared with healthy controls. After PHA stimulation, AA-homozygous individuals presented increased mitochondrial maximal respiration and spare respiratory capacity, and AA-homozygous patients showed higher no mitochondrial oxygen consumption.

Conclusions

In MS patients, the homozygous AA genotype of rs7923837 in HHEX determines low levels of mRNA expression and increased nuclear location, presumably altering its function as a transcription factor. Moreover, MS patients display higher values than healthy controls in some parameters of mitochondrial respiration. Those differences are increased in minor allele homozygotes for rs7923837, and reflect a differential coupling between minor and major homozygous genotypes in MS patients.

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