Is a rare CXCL8 gene variant a new possible cause or course factor of inflammatory bowel disease?

Abstract

Introduction: The pathogenesis of inflammatory bowel diseases (IBD) involves genetic, environmental, immunological, and microbial factors; however, it remains unclear. Pro-inflammatory interleukin 8 (IL-8), encoded by the CXCL8 gene, assumes a crucial chemotactic role in leukocyte migration.

Methods: This study aimed to investigate whether an association exists between IBD and two CXCL8 variants, namely, c.-251A>T (rs4073) and c.91G>T (rs188378669), and IL-8 concentration. We analyzed the distribution of both variants among 353 Polish IBD patients and 200 population subjects using pyrosequencing, competitive allele-specific PCR and Sanger sequencing.

Results: The c.91T stop-gained allele was significantly more frequent in IBD patients (2.12%) than in controls (0.25%) (p = 0.0121), while the c.-251T allele frequencies were similar (54% vs. 51.5%, p = 0.4955). Serum IL-8 concentrations, measured using ELISA, were higher in IBD patients with the c.91 GG genotype compared to healthy controls (mean, 70.02 vs. 51.5 pg/ml, p<0.01) and patients with c.91 GT (mean, 61.73 pg/ml). Moreover, clinical data indicated that carriers of the c.91T variant need more often corticosteroids and surgical treatment of the disease than GG homozygous IBD patients.

Conclusion: This suggest that the CXCL8 c.91T allele may influence IBD manifestation and the course of the disorders in Polish patients, potentially serving as a novel target for future studies and therapeutic approaches.

Keywords: CXCL8 gene; Crohn’s disease; colitis ulcerosa; genetic variants; inflammation; inflammatory bowel disease (IBD); interleukin 8.

Figure 1

Linkage disequilibrium between analyzed variants in the CXCL8 gene. Haplotype diagram was prepared with Haploview v.4.2 and show calculated and graphically displayed the absolute value of Lewontin’s measure of linkage disequilibrium, D’ among both studied variants. The intensity of the filled-in box corresponds to the total linkage disequilibrium.

Figure 2

Effect of CXCL8 gene c.91 genotypes on (A) CD and CU location; L1, terminal ileum; L2, colon; L3, ileocolon; E1, ulcerative proctitis, involvement limited to rectum; E2, left-sided ulcerative colitis, involvement limited to a portion of colorectum distal to splenic flexure; E3, extensive ulcerative colitis: involvement extends proximal to splenic flexure. (B) GI tract surgical treatment; GI, gastrointestinal, p-value calculated using the Fisher’s exact test before correction, adjusted p-value using Bonferroni correction are included in Table 3 ; (C) serum IL-8 concentration, median with Q1–Q3, and min.–max. value (whiskers); each point represents a single concentration measurement, p-value calculated by non-parametric Mann–Whitney before correction, adjusted p-value using Bonferroni correction are included in Table 3 .

Figure 3

Network analysis of CXCL8 gene associations. Graph prepared based on BIOGRID database using GeneMANIA tool (44). CXCL8, C-X-C motif chemokine ligand 8 (interleukin 8); CCL8, C-C motif chemokine ligand 8; CCL2, C-C motif chemokine ligand 2; ACKR1, atypical chemokine receptor 1; PF4, platelet factor 4; CXCR1, C-X-C motif chemokine receptor 1; CXCR2, C-X-C motif chemokine receptor 2; CXCL3, C-X-C motif chemokine ligand 3; CXCL1, C-X-C motif chemokine ligand 1; CXCL2, C-X-C motif chemokine ligand 2; IL6, interleukin 6; GNA15, G protein subunit alpha 15; GNA14, G protein subunit alpha 14; ICAM1, intercellular adhesion molecule 1; IL1B, interleukin 1 beta; MMP13, matrix metallopeptidase 13; MACROH2A1, macroH2A.1 histone; CCL20, C-C motif chemokine ligand 20; CXCL10, C-X-C motif chemokine ligand 10; PLAUR, plasminogen activator, urokinase receptor; HBEGF, heparin binding EGF-like growth factor.