ERAP1 molecular characterization: Identification of a de novo allelic variant

A First Step for the Molecular Characterization of Neurological Involvement of Behçet Syndrome: an Italian Pivotal Study

Behçet syndrome (BS) is a vasculitis characterized by several clinical manifestations including the rare neurological involvement (neuro-BS, NBS). The aim of our pivotal study was to investigate the mutational status of several inflammation-related genes in a cohort of Italian patients with and without the neurological involvement (20 NBS vs 40 no-NBS patients). The preliminary in silico single nucleotide polymorphism (SNP) selection and primer design were performed by NCBI Primer-Blast tool. Genomic DNA was isolated and amplified using PCR. PCR amplicons were sequenced and bioinformatically analysed. Twelve tagSNPs were selected and genotyped: ERAP1 rs30187, rs17482078, and rs27044; IL10 rs1800872 and rs1518111, IL12A rs17810546, IL23R rs17375018, IL23R-IL12RB2 rs924080, STAT4 rs7572482, CCR1 rs7616215, KLRC4 rs2617170, and UBAC2 rs3825427. ERAP1 and IL23R SNPs showed statistically significant higher frequencies in NBS group than no-NBS. ERAP1 rs30187 AA was more common in no-NBS patients (20.0% NBS vs 47.5% no-NBS; p < 0.05), while rs17482078 GA frequency was higher in NBS patients (55.0% NBS vs 22.5% no-NBS; p < 0.05, OR: 4.21). IL23R rs17375018 GG was more frequent in NBS group (65.0% NBS vs 40.0% no-NBS; p < 0.05), according to a previous finding. No other statistically significant differences were found. In conclusion, ERAP1 and IL23R SNPs were found associated with neurological involvement of BS. Additional and larger analyses were required to verify our preliminary findings.

From structure to function for the characterization of ERAP1 active site in Behçet syndrome. A novel polymorphism associated with known gene variations

INTRODUCTION

ERAP1 has been recently proposed as risk marker of Behçet syndrome (BS). Gene single nucleotide polymorphisms (SNPs) could affect the enzymatic activity and the conserved active site is pivotal for the aminopeptidase function. This study aims to characterize the ERAP1 active site in a cohort of BS patients vs healthy controls (HC) integrating genomics, transcriptomics and bioinformatics approach.

MATERIALS AND METHODS

We recruited 109 consecutive Italian BS patients (63M:46 F; mean age: 45.07 ± 12.28 years) and 106 matched HC (55M:51 F; mean age: 42.57 ± 12.29 years). DNA was isolated and amplified using PCR with home made-primer pairs. PCR products were directly sequenced and computational analyses were performed to search active site SNPs (NCBI-BlastN tool), to predict SNPs functional effect (PolyPhen-2 software) and to obtain protein 3D modelling (Protean3D software). In a second phase of analysis, RNA was extracted and reverse transcribed. Quantitative Real-Time PCR (qPCR) was performed to assess ERAP1 mRNA level in presence (target) and in absence (control) of gene polymorphisms. The Fold change was calculated for the relative quantification of gene expression.

RESULTS

A novel coding variation (NG_027839.1:g.25637 T > G; NP_057526.3:p.Phe360Cys, HGSV nomenclature) was found in heterozygosity state in 5/109 BS patients (4.59 % of cases) and none of HC. It was recognized in association with rs2287987, rs30187, rs17482078, and rs27044 BS-related polymorphisms for 4 out of 5 patients. All patients carrying the novel SNP were HLA-B*51-positive. The novel SNP was released in GenBank database with MK140632.1 ID. The SNP was predicted to be damaging and resides within the Zn-binding HEXXH(X)₁₈E region of the active site, changing the structurally conserved region for the amminopeptidase function. In fact, the change in energy (ΔE) score between wild-type and SNP-containing protein showed a less stable protein in presence of p.Cys360 (ΔE:3.584) (Protean3D prediction). Preliminary qPCR results underlined a significant difference in fold change value when target and control values were compared (p < 0.05), suggesting a reduced expression of ERAP1 mRNA in presence of the novel SNP.

CONCLUSIONS

Our study strengthens the association between ERAP1 and BS. The most significant point was the localization of the novel p.Phe360Cys SNP within the Zn-binding region of protein active site that was predicted to affect its function, causing protein destabilization. Our findings need to be tested in larger genetic studies.

Behçet's Disease: An Overview of Etiopathogenesis

Behçet's disease (BD) is a systemic inflammatory disease with a chronic, relapsing-remitting course of unknown etiology hallmarked predominantly by mucocutaneous lesions and ocular involvement. BD shares some common features with autoimmune and autoinflammatory diseases and spondyloarthropathies (MHC-I-opathies). It is related to more than one pathogenic pathway triggered by environmental factors such as infectious agents in genetically predisposed subjects. The interplay between genetic background and immune system is linked to the BD presentation. Genetic factors have been investigated extensively, and several recent genome-wide association studies have confirmed HLA-B ^* 51 to be the strongest genetic susceptibility factor. However, new non-HLA susceptibility genes have been identified. Genetic variations in the genes encoding the cytokines could affect their function and be associated with disease susceptibility. Infectious agents such as Streptococcus sanguinis or the differences in salivary or gut microbiome composition can be considered to trigger the innate-derived inflammation, which is, subsequently, sustained by adaptive immune responses. Altered trimming of microbial and/or endogenous peptides by endoplasmic reticulum aminopeptidase 1 (ERAP1), presented by HLA-B ^* 51, may play a key role in BD pathogenesis causing an alteration in T cell balance with downregulation of Tregs and expansion of Th1 and Th17. The activity of neutrophils is increased and there is an intense neutrophil infiltration in the early stage of inflammation in organs affected by the disease. Association with HLA-B ^* 51 and increased IL-17 response seems to have an important role in neutrophil activity. In this paper, we provide an overview of the most recent advances on BD etiopathogenesis.