Increased proteasome-mediated degradation of occludin in irritable bowel syndrome.
OBJECTIVE
Proteasome-mediated protein degradation may contribute to the regulation of intestinal inflammation. At the same time, low-grade inflammation and increased intestinal permeability seem to be involved in the pathophysiology of irritable bowel syndrome (IBS). Thus, we aimed to evaluate proteasome composition and activities in colonic mucosa of IBS patients and its putative pathogenic role.


METHODS
Proteasome activities and proteasome subunit expression were measured in colonic mucosa of IBS, Crohn's disease (CD), and control patients by fluorometric assays and western blot, respectively. Expression of inhibitor of kappa B factor (IkappaB alpha) and occludin, a tight junction protein, was also evaluated in colonic biopsies. The degradation of recombinant occludin incubated with protein extracts from colonic mucosa was evaluated in the presence or absence of proteasome inhibitor, MG132.


RESULTS
Proteasome trypsin-like activity was increased in IBS patients compared with CD and controls, whereas chymotrypsin-like activity was upregulated in CD patients only. Caspase-like activity was reduced both in IBS and CD patients. IkappaB alpha expression was similar between IBS and controls. In contrast, occludin expression was lower in IBS than in controls, but occludin mRNA level was similar. Protein extracts from IBS patients but not from controls degraded recombinant occludin (20% over 160 min), which was blocked by MG132. Although mast cell number was increased in IBS patients, no correlation was found between this number and proteasome alterations.


CONCLUSIONS
Our study shows that proteasome alterations are present in the colonic mucosa of IBS patients and may contribute to the pathophysiology of IBS by increasing occludin degradation.
Coëffier
Moïse
M
Nutrition Unit, Rouen University Hospital, Rouen, France. moise.coeffier@univ-rouen.fr
Gloro
Romain
R
Boukhettala
Nabile
N
Aziz
Moutaz
M
Lecleire
Stéphane
S
Vandaele
Nathalie
N
Antonietti
Michel
M
Savoye
Guillaume
G
Bôle-Feysot
Christine
C
Déchelotte
Pierre
P
Reimund
Jean Marie
JM
Ducrotté
Philippe
P
D000328:Adult; D000704:Analysis of Variance; D001707:Biopsy, Needle; D015153:Blotting, Western; D016022:Case-Control Studies; D002463:Cell Membrane Permeability / Q000502:physiology; D003424:Crohn Disease / Q000378:metabolism / Q000473:pathology; D016207:Cytokines / Q000378:metabolism; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D007413:Intestinal Mucosa / Q000378:metabolism* / Q000473:pathology; D043183:Irritable Bowel Syndrome / Q000378:metabolism* / Q000473:pathology; D008297:Male; D008407:Mast Cells / Q000166:cytology / Q000502:physiology; D008565:Membrane Proteins / Q000378:metabolism*; D008875:Middle Aged; D062793:Occludin; D011336:Probability; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D012016:Reference Values; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012680:Sensitivity and Specificity; D012720:Severity of Illness Index; D018709:Statistics, Nonparametric; D055815:Young Adult
D016207:Cytokines; D008565:Membrane Proteins; C568985:OCLN protein, human; D062793:Occludin; D046988:Proteasome Endopeptidase Complex