To Örebro University

Background: Ulcerative colitis (UC), a major subtype of inflammatory bowel disease, is characterized by chronic inflammation of the colon and rectum. Enteric glial cells (EGC) play a crucial role in gut barrier maintenance and may contribute to UC pathophysiology. This study aims to investigate EGC and their associated proteins in patients during clinically active disease and in clinical remission following anti-inflammatory treatment.

Methods: Colonic or rectal biopsies were obtained at baseline from both inflamed and non-inflamed segments in 14 patients with clinically active UC initiating anti-inflammatory therapy and from the same segments when the patients were in clinical and endoscopic remission during follow-up. As control groups, colonic biopsies from 16 patients with irritable bowel syndrome (IBS)-Mixed and 16 healthy controls were included. Immunofluorescence staining assessed two EGC markers: the glial fibrillary acidic protein (GFAP+) and S100 calcium-binding protein B (S100β+). Relative estimates of inflammatory proteins in biopsies were analysed using Olink technology, In vitro, the EGC cell line CRL-2690 was exposed to interleukins (IL)-4, IL-6, and IL-18 at varying concentrations and durations, with GFAP expression analysed by western blot.

Results: In patients with UC, immunofluorescence analysis revealed significantly higher GFAP+ and S100β+ EGC counts in inflamed biopsies during active disease compared to macroscopically non-inflamed biopsies obtained during clinical and endoscopic remission. Compared to baseline biopsies from macroscopically non-inflamed mucosa, GFAP expression significantly decreased during follow-up (Figure 1), while S100β levels remained unaltered. Regardless of mucosal inflammatory status, patients with UC exhibited higher EGC counts than IBS-mixed patients and healthy controls. Our findings also showed a significant upregulation of EGC-associated pro-inflammatory proteins, such as IL-6, IL-8 and TNF in inflamed biopsies from patients with clinically active UC, compared to biopsies obtained when the patients were in remission as well as to healthy controls. Notably, these protein levels decreased during inactive UC, approaching levels observed in the healthy controls. In vitro, IL-6 upregulated GFAP expression dose- and time-dependently, while IL-4 and IL-18 induced expression in a less predictable pattern.

Conclusion: Elevated EGC counts, and pro-inflammatory proteins characterise inflamed mucosa in UC during clinical active disease highlighting their potential roles in UC related inflammation. These findings may suggest that EGC could be explored as a potential therapeutic target and may contribute to the discovery of novel biomarkers for disease monitoring.