Mechanisms and modulation of intestinal epithelial repair.

The mucosal epithelium of the alimentary tract represents a crucial barrier to a broad spectrum of noxious and immunogenic substances within the intestinal lumen. An impairment of the integrity of the mucosal epithelial barrier is observed in the course of various intestinal disorders including inflammatory bowel diseases (IBD), celiac disease, intestinal infections, and various other diseases. Furthermore, even under physiologic conditions temporary damage of the epithelial surface mucosa may be caused by proteases, residential flora, dietary compounds, or other factors. Generally, the integrity of the intestinal mucosal surface barrier is rapidly reestablished even after extensive destruction because of an enormous regenerative capability of the mucosal surface epithelium. Rapid resealing of the surface epithelium is accomplished by epithelial cell migration, also termed epithelial restitution, epithelial cell proliferation, and differentiation. Healing of the intestinal surface epithelium is regulated by a complex network of highly divergent factors, among them a broad spectrum of structurally distinct regulatory peptides that have been identified within the mucosa of the intestinal tract. These regulatory peptides, conventionally designated as growth factors and cytokines, play an essential role in regulating differential epithelial cell functions to preserve normal homeostasis and integrity of the intestinal mucosa. In addition, a number of other peptide molecules such as extracellular matrix factors and blood clotting factors, and also nonpeptide molecules including phospholipids, shortchain fatty acids, adenine nucleotides, trace elements, and pharmacological agents, have been demonstrated to modulate intestinal epithelial repair mechanisms. Some of these molecules may be released by platelets, adjacent stromal cells, inflammatory cells, or injured epithelial and nonepithelial cells and may play an important role in the modulation of intestinal injury. Repeated damage and injury of the intestinal surface are key features of various intestinal disorders including IBD and require constant repair of the epithelium. Enhancement of intestinal repair mechanisms by regulatory peptides or other modulatory factors may provide future approaches for the treatment of diseases that are characterized by injuries of the epithelial surface.