Ankylosing Spondylitis (AS) is a form of arthritis that primarily affects the spine, although other joints can become involved. It causes inflammation of the spinal joints that can lead to severe, chronic pain and discomfort. The disease pathogenesis, although not completely understood, has a strong genetic basis. The gene that confers the higher risk is HLA-B27, present in over 85% of patients. There are more than 170 recognized HLA-B27 alleles but the majority of them is not sufficiently represented for genetic association studies. So far only two alleles, the HLA-B*2706 in Asia and the HLA-B*2709 in Sardinia, have not been found to be associated with AS. Since AS is a complex disease, other genes have been found to contribute to its genetic basis. Among these, the aminopeptidases of the ER (ERAP1 and ERAP2) which contribute to the shaping of the peptide repertoire of the HLA-B27 molecules. Therefore understanding the correlation between the two ERAPs and the two HLA-B27 molecules, B*2705 and B*2709, and the effect of ERAP polymorphisms, is likely to give insights into the disease pathogenesis. This project is aimed to investigate these aspects.
The project will include the following tasks:
TASK 1. Dissecting the involvement of ER aminopeptidases in AS through genetic and functional studies
a) Assessment of the association of the newly discovered ERAP1 SNP rs758626299 with AS in Sardinia.
b) Analysis of the functional mechanism through which SNP rs758626299 controls the transcriptional levels of ERAP1 and ERAP2.
c) Correlation of the ERAP1/ERAP2 transcript and protein levels with the magnitude of HLA-B27-restricted CD8+ T cell responses to viral peptides.
d) Analysis of the relative ERAP1/2 expression in polarized M1 and M2 macrophages
Quantitative trait loci variations in gene expression (eQTL) is an important albeit disregarded aspect in pathology. This is due to several reasons among which the difficulties to identify the causes of such behavior which can go from epigenetic controls to tissue and cell specific variations. Our identification of a Single Nucleotide Polymorphism that simultaneously regulates the expression of two contiguous genes is a relevant finding. Since the two genes which are affected are two amino peptidases of the ER which shape the antigenic repertoire of the HLA molecules, makes particularly interesting this aspect. In particular, it will be interesting to understand whether this is due to a transcriptional competition or to indirect effects. Moreover, the consequences of this modulation on specific disease such as Ankylosing Spondylitis appears as particularly attractive since both ERAP genes have been found associated with the disease. In particular ERAP1 works epistatically with the HLA-B27, which is the HLA allele that contributes more to the genetic basis of Ankylosing Spondylitis. This disease is in the spotlight since many decades but its pathogenesis has not been completely elucidated. Therefore, to understand how this quantitative variations influence the HLA-B27 repertoire will be particularly interesting. Moreover, it must be considered that ERAP2 has been found involved in other pathologies which are not defined as Immune Mediated Diseases (IMD) such as pre-eclampsia suggesting more than one role for this enzyme.