Background: Crohn's disease (CD) is a chronic inflammatory disorder characterized by a transmural granulomatous inflammation. The prevalence of CD is increasing worldwide and arises as a complex interplay between genetic and environmental components. CD can affect any part of the gastrointestinal tract, especially the ileum and/or colon. Besides, an increased mesenteric adipose tissue (MAT) is observed near the affected intestinal area named creeping fat, suggested to be the hallmark of the disease. Recent evidences suggest a link between CD and the endoplasmic reticulum (ER) stress. ER organelle is crucial for synthesis, folding and processing of secreted and membrane proteins and lipid. The accumulation of unfolded proteins in the ER lumen activates the unfolded protein response (UPR), which resolves the protein-folding defect and restores ER homeostasis. Here we tested the hypothesis that ER stress plays a role in the pathophysiology of CD and investigated the activation of this pro-inflammatory pathway in intestinal mucosa and MAT of CD patients.
Methods: To test this, intestinal and MAT biopsies were collected from CD patients (CD group) and from patients with no endoscopic alterations (CTR group).
Results: We first evaluated the IRE1/sXBP1 pathway. Our results show an increased expression of sXBP1 in the intestinal mucosa of CD patients compared to controls (p=0.018). The second ER stress signaling investigated was PERK/EIF2alpha pathway. Here we show an increased expression of PERK gene in intestinal mucosa of CD patients (p=0.025), as well as EIF2alpha protein expression (p=0.0031) and pEIF2alpha/EIF2alpha ratio. However, no differences in gene and protein expression were observed in MAT tissue. By qPCR we observed an increase in the cleaved/activated form of ATF6 protein in the intestinal mucosa of CD patients (p=0.0327), however, this increase does not translate in protein content augmentation. Also, no differences were observed in ATF6 gene expression in MAT. Additionally, we observed an increased expression of genes related to ER stress activation in intestinal mucosa of CD patients, like ATF3 (p=0.0226), DNAJC3 (p=0.044), CALR (p=0.0021), STC2 (p=0.0027) and the chaperones GRP94 (p=0.0277) and GRP78 (p=0.082). No differences were observed in ATF3, DNAJC3, CALR and STC2 genes in MAT, however, we found an increased gene expression of GRP94 (p=0.0087) and a decrease in the chaperone GRP78 (p=0.0017) in MAT of CD patients.
Conclusions: Our results demonstrate the activation of the three branches of ER stress in the intestinal mucosa of CD patients, while no activation in MAT. Thus, ER stress is an important pro-inflammatory mechanism of CD, specifically in intestinal mucosa, and may be an attractive therapeutic target.