Polymorphisms in the Hsp70 gene locus are genetically associated with systemic lupus erythematosus

Abstract

Background: Heat shock proteins (Hsps) play a role in the delivery and presentation of antigenic peptides and are thought to be involved in the pathogenesis of multifactorial diseases.

Objective: To investigate genes encoding cytosolic Hsp70 proteins for associations of allelic variants with systemic lupus erythematosus (SLE).

Methods: Case-control studies of two independent Caucasian SLE cohorts were performed. In a haplotype-tagging single-nucleotide polymorphism approach, common variants of HspA1L, HspA1A and HspA1B were genotyped and principal component analyses were performed for the cohort from the Oklahoma Medical Research Foundation (OMRF). Relative quantification of mRNA was carried out for each Hsp70 gene in healthy controls. Conditional regression analysis was performed to determine if allelic variants in Hsp70 act independently of HLA-DR3.

Results: On analysis of common genetic variants of HspA1L, HspA1A and HspA1B, a haplotype significantly associated with SLE in the Erlangen-SLE cohort was identified, which was confirmed in the OMRF cohort. Depending on the cohorts, OR ranging from 1.43 to 1.88 and 2.64 to 3.16 was observed for individuals heterozygous and homozygous for the associated haplotype, respectively. Patients carrying the risk haplotype or the risk allele more often displayed autoantibodies to Ro and La in both cohorts. In healthy controls bearing this haplotype, the amount of HspA1A mRNA was significantly increased, whereas total Hsp70 protein concentration was not altered.

Conclusions: Allelic variants of the Hsp70 genes are significantly associated with SLE in Caucasians, independently of HLA-DR3, and correlate with the presence of autoantibodies to Ro and La. Hence, the Hsp70 gene locus appears to be involved in SLE pathogenesis.

Figure 1

Overview and linkage disequilibrium (LD) of the human genomic locus containing three Hsp70 genes on chromosome 6. (A) The human susceptibility locus for systemic lupus erythematosus on chromosome 6p21.33 covers a cluster of three Hsp70 genes: HspA1L, HspA1A and HspA1B. (B) On the basis of LD, five haplotype-tagging single-nucleotide polymorphisms (SNPs) were selected to identify the major haplotypes (>1% frequency). (C) LD prime charts generated using Haploview V3.32 software summarise LD patterns in Caucasians (Centre d'Etude du Polymorphisme Humaine). Dark red boxes represent regions of high pairwise r², whereas bright red boxes show lower pairwise r². The numbers in the boxes depict pairwise r² values, with empty cells representing pairwise r²=1.

Figure 2

Influence of Hsp70 polymorphisms on Hsp70 mRNA and protein expression. Primary human peripheral blood mononuclear cells (PBMCs) from donors with defined genotypes were analysed for relative expression of HspA1L, HspA1A and HspA1B mRNA under physiological conditions (A) or after heat shock (B). Data in (A) and (B) are expressed in arbitrary units that represent one out of three independent experiments. Statistical analyses were performed using the Mann–Whitney U test. p Values <0.05 were considered significant. (C) Primary human PBMCs with or without heat shock treatment were analysed for total Hsp72 protein expression. The integrated intensity of the bands for Hsp72 and β-actin were quantified. Data represent the mean result of three independent experiments.