PATHOLOGIC ALTERATIONS IN THE INTESTINAL EXTRACELLULAR MATRIX IN SMALL BOWEL CROHN’S DISEASE

Abstract BACKGROUND The extracellular matrix (ECM) is increasingly recognized in inflammatory bowel disease (IBD) pathogenesis. Chondroitin sulfates (CS) are important interstitial ECM components and consist of glycosaminoglycan (GAG) chains of repeating CS isomers. Certain CS isomers promote matrix stability (CS-A and CS-B), while others are implicated in inflammation and plasticity (CS-C and CS-E). Whether ileal CS-GAGs are altered in small bowel (SB) Crohn’s disease (CD) is unknown. SB CD poses a particular challenge in that some individuals develop irreversible fibrosis, a process strongly linked to ECM remodeling. We therefore hypothesized that SB CD is associated with pathologic changes in ileal CS-GAG composition characterized by reduced stabilizing CS isomers and increased inflammatory CS isomers. METHODS We quantified relative CS isomer abundance in ileal biopsy samples from 53 pediatric and young adult patients (n = 19 controls, n = 34 ileal CD; 40%(f)/60%(m); age range 6-23, age mean 13.9±4.1) using liquid chromatography-tandem mass spectrometry. For patients with ileal CD, biopsies were obtained at diagnosis (Dx) before treatment and again at follow-up on therapy during clinical remission (CR). The majority (90%) of patients were on anti-tumor necrosis factor alpha therapy. RESULTS At Dx, patients with ileal CD had significantly decreased matrix stabilizing isomers compared to controls (CS-A: 70.2% vs 75.7%, p < 0.001; CS-B: 0.9% vs 1.3%, p < 0.01) and increased pro-inflammatory isomers (CS-C: 20.0% vs 15.9%, p < 0.01; CS-E: 6.9% vs 4.6%, p < 0.0001). At follow-up in CR, this pattern was largely reversed: CS-A increased (74.1% vs 70.2%, p < 0.001), CS-B increased modestly (1.1% vs 0.9%, p < 0.05) and CS-E decreased (5.2% vs 6.9%, p < 0.0001), whereas CS-C remained elevated. This CS isomer pattern in CR closely resembled those of controls. Stabilizing CS isomers inversely correlated with the degree of histologic inflammation (CS-A: p < 0.0001, CS-B: p < 0.01), while inflammatory isomers correlated positively with histologic severity (CS-E: p < 0.0001, CS-C: p < 0.01). Immunohistochemistry localized CS-GAGs to the stroma of the ileum in proximity to fibroblasts and immune cells. CONCLUSIONS Ileal CS-GAG composition is altered in SB CD in a pattern predicted to be pathologic and that correlates with histologic IBD severity. This imbalance in CS isomers is restored in the same patients upon achieving CR at follow up. Although the causality of this association is still under investigation, these findings implicate CS-GAGs as potential contributors to IBD pathogenesis, likely via effects on fibrosis and mucosal immunity through interactions with fibroblasts and immune cells.