Disrupted Barrier Function through Epithelial Cell Apoptosis

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Abstract
Abstract:  Epithelial barrier function is determined by trans‐ and paracellular permeabilities, the latter of which is mainly influenced by tight junctions (TJs) and apoptotic leaks within the epithelium. The present article aims to present experimental evidence for a functional role of epithelial apoptoses by means of cell culture models as well as in tissues from patients with inflammatory bowel disease. It is shown that epithelial apoptoses are sites of elevated conductance within the intestinal epithelium and that proinflammatory cytokines like TNF‐α upregulate both the apoptotic rate and single apoptotic conductivity, making cytokine‐induced apoptosis functionally far more relevant than is spontaneous apoptosis. In ulcerative colitis and Crohn's disease (CD), but not in collagenous colitis, apoptotic rates are increased to about 5%, in mild‐to‐moderately inflamed colon specimens, where as the control apoptotic rate is about 2%. Thus, epithelial apoptoses lead to a loss of ions and water into the intestinal lumen, causing leak flux diarrhea and enabling small antigens of