Gastroenterology

Gastroenterology

Volume 141, Issue 3, September 2011, Pages 1024-1035
Gastroenterology

Original Research
Basic and Translational—Alimentary Tract
Altered Endoplasmic Reticulum Stress Affects Translation in Inactive Colon Tissue From Patients With Ulcerative Colitis

https://doi.org/10.1053/j.gastro.2011.05.033Get rights and content

Background & Aims

Ulcerative colitis (UC) is a chronic inflammatory disorder that affects the colonic epithelium. Epidemiology studies indicate an environmental component is involved in pathogenesis, although the primary changes in the digestive epithelium that cause an uncontrolled inflammatory response are not known. Animal studies have shown that altered endoplasmic reticulum (ER) stress response initiates intestinal inflammation in epithelial tissues, but abnormalities associated with ER stress have not been identified in patients with UC.

Methods

Using immunoblotting, real-time polymerase chain reaction, immunohistochemistry, and immunofluorescence analyses, we assessed ER stress signaling in uninflammed colonic mucosa from patients with UC and controls. Genome-wide microarray analysis of actively translated polysome-bound messenger RNA was performed using samples of unaffected mucosa from patients with UC, and data were compared with those from controls.

Results

Inositol-requiring kinase and activating transcription factor signaling pathways were activated in inactive colonic epithelium from patients with UC; these mediate proinflammatory and regenerative responses. Blocking phosphorylation of the translation initiation factor 2 (eIF2α), which mediates the integrated stress response, deregulated initiation of translation and reduced the numbers of stress granules in colonic epithelial cells from patients with UC. Genome-wide microarray analysis of actively translated, polysome-bound messenger RNA from patients revealed changes in protein translation that altered colonic epithelial barrier function (levels of detoxification and antioxidant enzymes and proteins that regulate the cell cycle, cell-cell adhesion, and secretion), compared with controls.

Conclusions

Colonic mucosa samples from patients with UC have defects in the eIF2α pathway that controls protein translation and the cell stress response. This pathway might be investigated to identify new therapeutic targets for patients with UC.

Section snippets

Patients and Biopsy Specimens

All patients were followed in the Department of Gastroenterology (Beaujon's hospital). The protocol was approved by the local Ethics Committee (CPP-Ile de France IV No. 2009/17), and written informed consent was obtained from all patients before enrollment. Colonic pinch biopsy specimens were obtained during endoscopic investigations in 11 patients with UC. Surgical colon samples were collected from 15 patients with UC who underwent a colectomy (Supplementary Table 1). The diagnosis of UC was

Unaffected Colonic UC Mucosa Exhibit Extended IRE1β and ATF6α Branch Signaling

UPR activation was assessed by determining IRE1β-mediated splicing of XPB-1 in unaffected colonic mucosa from UC and healthy individuals. Spliced XBP-1 (XBP-1s) mRNA levels were significantly increased in UC mucosa and the ratio of spliced to unspliced XBP-1 (XBP-1s/XBP-1u) was 1.8 and 3.8 in controls and UC, respectively (Figure 1A). Consistent with hyperactivation of the IRE1β/XBP-1 arm, increased expression of the UPR-related target genes glucose-regulated proteins (GRP94, GRP78), and ER

Discussion

There are 3 original findings in this study. First, the coordinated expression of all 3 branches of the UPR identified in controls is impaired in unaffected UC mucosa; second, unaffected UC mucosa are prone to ER stress because of impairment of the ISR; and, third, the coordinated changes in eIF2α phosphorylation, SG formation, and translation initiation selectivity identified in unaffected UC mucosa represent new approaches to understand the pathogenesis of UC.

This study shows that the 3 known

Acknowledgments

The authors thank Drs Laurence Bougnères–Vermont and Matthieu Collin from INSERM-Transfert, Dr Renato Monteiro from INSERM U699 for helpful discussions, and Sylvie Mosnier (Beaujon Hospital) for helpful technical assistance.

Electron microscopy was performed by A. Grodet in the setting of the Atelier de Microscopie ElecTronique (AMET) IFR02/CRB3. Confocal microscopy was carried out by Samira Benadda (IFR02).

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    Xavier Tréton and Eric Pédruzzi contributed equally to this work.

    Conflicts of interest The authors disclose no conflicts.

    Funding Supported by grants from Institut National de la Santé et de la Recherche Médicale (INSERM), Association François Aupetit (AFA) (to E.O.D.), Assistance Publique-Hôpitaux de Paris (AP-HP) (to E.O.D.: Interface Fellowship), University Denis Diderot Paris 7, Société Nationale Française de Gastro-Entérologie (SNFGE), Association Française pour l'étude du foie (AFEF), Programme National de Recherche en Hépato-Gastroentérologie (PNRHGE) (to X.T. and E.O.D.), and a doctoral position from INSERM (poste d'accueil) (to X.T.).

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