Homeostasis of Glial Cells in the Mammalian Gut

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The gastrointestinal tract is a vital organ that converts our diet into useful digestible nutrients, contributes to the maintenance of water balance and protects our body from pathogenic microorganisms that are present within the lumen of the gut, along with large numbers of beneficial bacteria. In order for the gut to carry out its essential functions, it contains exquisitely specialised cells, including epithelial cells, immune cells, nerve cells and muscle cells. Intestinal epithelial cells are tightly connected to each other to form a sophisticated gatekeeping system that allows the selective transport of nutrients and water but keeps away harmful toxins or pathogenic bacteria. Immune cells constantly monitor the lumen and the wall of the gut and respond in case the essential intestinal barrier is breached. Finally, complex networks of nerve cells within the gut wall are responsible for generating intestinal movements that are essential for proper digestive function by activating the musculature of the gut wall. Since the intestinal epithelium is constantly exposed to harmful substances and pathogenic microorganisms, it is quite vulnerable and is often damaged. Normally this does not have detrimental consequences for an organism since all cells of the intestinal epithelium are continuously replenished by stem cells that are dedicated to producing constantly fresh epithelial cells. Although the continuous regeneration of the intestinal epithelium is essential for maintaining it in good working order, other cell types play a major role in keeping them healthy. In particular, glial cells, which normally accompany and support nerve cells in all parts of the nervous system, are also found in the vicinity of intestinal epithelial cells and release substances that are essential for maintaining the intestinal epithelial barrier; if these enteric glial cells are eliminated in experimental conditions, the barrier breaks down and animals die from acute inflammation of the small intestine. In addition, several studies have suggested that the inflammation that accompanies common gut diseases, such as Crohn's disease or ulcerative colitis, may also involve the abnormal interaction of glial cells with intestinal epithelial cells and immune cells. These observations support the idea that despite their specialised functions, the different cell types that make up the gut wall (and indeed any organ) need to work in concert in order to support its physiological roles.Despite the important roles of the intestinal glial cells in supporting the critical functions of the nerve cells and the epithelium of the gut, very little is known about their biology in healthy individuals and in disease situations. In this proposal we will aim at filling this knowledge gap by building on some of our own recent observations. In particular, we will identify and characterise the properties of the gliogenic stem cells which generate new glial cells throughout life. We will also identify conditions and signals that modulate the behaviour of intestinal glial cells. Finally, we plan to characterise molecules which are located within the nucleus and are important for these cells to maintain their properties and continue to generate new glial cells throughout adult life.Normal digestive function depends on the fine balance between the loss of old and the production of new cells in the different gut tissues and the optimal cross talk between the different cell types. Breakdown of such an equilibrium results in uncontrolled growth of cells (cancer), severe inflammation of the gut wall (inflammatory bowel disease-IBD) or inability of the gut wall to protect the internal environment of an organisms from toxic substances or pathogenic bacteria. Understanding how local glial cells contribute to the integrity and normal function of gut tissues, we can ultimately use these cells as a means to alter the course of common debilitating gastrointestinal disorders.