Session Information
Session Type: Abstract Submissions (ACR)
Background/Purpose:
Endoplasmic reticulum aminopeptidase 1 (ERAP1) exerts a central role in antigen presentation making it an attractive candidate gene for inflammatory diseases. Several polymorphisms in this gene have been associated with ankylosing spondylitis and then with the whole SpA group. A specific ERAP1 haplotype, rs17482078/rs10050860/rs30187-CCT, is strongly associated with increased risk of SpA, whereas the -TTC haplotype is associated with reduced risk. Because the linkage disequilibrium in the region is extensive, the causative polymorphism still remains to be determined. It has been suggested that rs30187, one of the polymorphisms of this haplotype may affect ERAP1 enzymatic activity. However, there is currently little data regarding the consequences of SpA-associated polymorphisms on gene expression level.
The aim of the present work was to determine whether SpA-associated ERAP1 polymorphisms might modify gene expression, protein level and enzymatic activity.
Methods:
The discovery cohort included 9 HLA-B27+ SpA patients and 10 healthy controls. The replication cohort consisted of 13 SpA-discordant HLA-B27 positive sib-pairs and 18 additional independent controls (11 HLA-B27+ and 7 HLA-B27-). In both cohorts, we derived dendritic cells from monocytes (MD-DCs) and stimulated them or not with lipopolysaccharide (LPS). We also used Epstein-Barr virus (EBV) immortalized lymphoblastoid cell lines from HLA-B27+ individuals homozygous for risk, neutral or protective ERAP1 haplotype (7 patients, 1 control). In all the studied populations, we investigated the relation between ERAP1 haplotype and mRNA expression level (assessed by RT-PCR in the discovery cohort and in EBV cell lines and by microarray in the replication cohort) with a likelihood ratio test in Unphased software. Additionally, the relative protein expression of ERAP1 was measured in EBV cell lines by Western-blot and enzymatic activity was determined using a fluorogenic assay.
Results:
In MD-DCs, there was a strong association between ERAP1 mRNA expression level and both rs30187 genotype and ERAP1 haplotype, at every time-point (table 1). This association was independent of the disease or HLA-B27 status. A similar trend was observed in EBV cell lines. Western-blot showed that ERAP1 protein level in cell lines harboring the risk haplotype was 2- and 1.5-fold higher than in those harboring the protective and the neutral ones, respectively. Moreover, ERAP1 enzymatic activity was higher in cell lines harboring increased risk haplotype, than in those harboring reduced risk haplotype.
|
Stimulation time-point |
Discovery |
Replication |
Pooled results |
|
H0 |
0.04 |
4.56 x 10-5 |
7.9 x 10-7 |
|
H6 |
0.04 |
1.6 x 10-4 |
1.2 x 10-6 |
|
H24 |
0.09 |
9 x 10-4 |
4.3 x 10-6 |
Table 1 – P-values of association tests between ERAP1 haplotype and mRNA expression
Conclusion:
Overall, these data provide strong evidence that SpA-associated ERAP1 polymorphisms affect the level of gene expression, protein production and aminopeptidase activity. How an increased production/activity of ERAP1 influences susceptibility to SpA remains to be determined.
Disclosure:
F. Costantino,
None;
A. Talpin,
None;
I. Evnouchidou,
None;
A. Kadi,
None;
R. Said-Nahal,
None;
A. Leboime,
None;
N. Bonilla,
None;
F. Letourneur,
None;
T. Leturcq,
None;
Z. Ka,
None;
P. van Endert,
None;
H. J. Garchon,
None;
G. Chiocchia,
None;
M. A. Breban,
None.
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ACR Meeting Abstracts - https://acrabstracts.org/abstract/spondyloarthritis-associated-polymorphisms-of-erap1-are-correlated-with-gene-expression-protein-level-and-enzymatic-activity-of-the-amino-peptidase/