Molecular mechanisms of interleukin-38 inhibiting inflammatory bowel disease in children by regulating nuclear factor-κB and signal transduction and activator of transcription 3 pathway

Objective To explore the role of interleukin (IL)-38 in inhibiting inflammatory bowel disease (IBD) in children and to investigate the potential molecular mechanisms. Methods From January 2014 to October 2017, 67 patients with ulcerative colitis (UC) and 115 patients with Crohn′s disease (CD) admitted to Wuhan Children′s Hospital were recruited, and 40 individuals with normal endoscopic findings were selected as control. Serum levels of IL-38 of IBD patients and healthy control were determined by enzyme-linked immunosorbent assay (ELISA). Immunohistochemical staining (IHC) was used to detect the expression level of IL-38, nuclear factor κB (NF-κB), phosphorylated signal transduction and activator of transcription 3 (p-STAT3), C-reaction protein (CRP) and erythrocyte sedimentation rate (ESR) in the intestinal mucosa of IBD patients and healthy controls. The extent of disease, therapeutic agents and disease activity scores (Mayo score system for UC patients, Crohn′s disease activity index (CDAI) for CD patients) were evaluated. IL-38-C57BL/6 transgenic mice model was established, and dextran sulfate sodium was used to induce IBD mice model. The intestinal inflammation levels were compared between the wild type IBD mice and IL-38 transgenic IBD mice. The levels of IL-38, NF-κB and p-STAT3 in intestinal mucosa of mice of different groups were determined by IHC. The ratio of CD4+ IL-17+ T helper (Th) 17 cells in peripheral blood of mice of different groups was detected by flow cytometry. Independent sample t test, chi square test and Pearson correlation were performed for statistical analysis. Results The results of ELISA showed that the serum levels of IL-38 of UC and CD patients were (6.1±1.9) ng/L and (9.8±2.1) ng/L, respectively, which both were lower than that of healthy controls ((16.4±2.7) ng/L), and the differences were statistically significant (t=23.107 and 15.853, both P<0.05). The results of IHC indicated that the levels of IL-38 in the intestinal mucosal tissues of UC and CD patients were 0.04±0.01 and 0.03±0.01, respectively, which were both lower than that of healthy controls (0.18±0.02), and the differences were statistically significant (t=48.186 and 69.443, both P<0.05). The levels of NF-κB and p-STAT3 of UC and CD patients were 0.150±0.030, 0.160±0.040 and 0.130±0.030, 0.110±0.010, which were all higher than those of healthy controls (0.020±0.003 and 0.010±0.002), and the differences were statistically significant (tUC=27.273 and 23.078, tCD=23.657 and 62.684; all P<0.05). The number of patients with disease at active phase, CRP level, ESR and disease activity scores of UC and CD patients with low IL-38 expression were all significantly higher than those of patients with high IL-38 expression (χUC2=11.552, tUC=7.118, 8.991 and 7.086; χCD2=5.675, tCD=9.559, 9.358 and 11.268; all P<0.05). The results of Pearson correlation analysis demonstrated that the level of IL-38 in the intestinal mucosal tissue of UC patients was negatively correlated with CRP, ESR and Mayo scores (r=-0.291, -0.672 and -0.639; all P<0.05). And the level of IL-38 in the intestinal mucosal tissue of CD patients was negatively correlated with CRP, ESR and CDAI (r=-0.559, -0.471 and -0.353; all P<0.05). The IHC results showed that the levels of NF-κB and p-STAT3 of IL-38 transgenic IBD mice were lower than those of wild type IBD mice (0.14±0.02 vs. 0.32±0.06, 0.12±0.02 vs. 0.44±0.07), and the differences were statistically significant (t=6.971 and 10.767, both P<0.05). The results of flow cytometry showed that the ratio of CD4+ IL-17+ Th17 cells in the peripheral blood of IL-38 transgenic IBD mice was lower than that of wild type IBD mice (0.030±0.006 vs. 0.280±0.050), and the difference was statistically significant (t=12.160, P<0.05). Conclusions The expression level of IL-38 significantly decreases in the intestinal mucosal tissues of IBD patients, while the level of NF-κB and p-STAT3 significantly increases. IL-38 may inhibit IBD by regulating NF-κB and p-STAT3 signaling pathway to alleviate intestinal immune reaction. Key words: Inflammatory bowel diseases; NF-kappa B; interleukin-38; STAT3