Background and aim: Epithelial barrier function is impaired in ulcerative colitis (UC), but the pathophysiological mechanisms leading to this barrier defect are still far from clear. Because epithelial barrier function is primarily regulated by the most apical intercellular junction, referred to as the tight junction (TJ), we investigated the expression of TJ proteins on rectal epithelial mucosa in UC.
Methods: Biopsies from the rectum of patients with active UC and of controls were studied. Tight-junction proteins were dual stained using specific antibodies (claudin-1, -2, -3, -4, and -7) as primary antibodies, and Cy-3 conjugated anti-rabbit IgG and Alexa488-conjugated anti-mouse IgG as secondary antibodies. Samples were analyzed by immunofluorescence microscopy. Immunoblotting and real-time polymerase chain reaction were performed to quantify TJ proteins and mRNA, respectively.
Results: At TJ, claudin-4 and -7 staining was down-regulated in active UC, whereas claudin-2 staining was up-regulated. Claudin-4 and -7 proteins were down-regulated on immunoblotting, whereas claudin-2 protein was up-regulated in active UC. Claudin-1 and -3 expression levels were unchanged in controls and active UC. In active UC claudin-2 mRNA was increased, whereas claudin-4 and -7 mRNA were decreased.
Conclusions: Down-regulation of claudin-4 and claudin-7, and up-regulation of claudin-2, might lead to altered TJ structure and be related to the impaired epithelial function in active UC.