Intestinal barrier homeostasis in inflammatory bowel disease

Abstract

The single-cell thick intestinal epithelial cell (IEC) lining with its protective layer of mucus is the primary barrier protecting the organism from the harsh environment of the intestinal lumen. Today it is clear that the balancing act necessary to maintain intestinal homeostasis is dependent on the coordinated action of all cell types of the IEC, and that there are no passive bystanders to gut immunity solely acting as absorptive or regenerative cells: Mucin and antimicrobial peptides on the epithelial surface are continually being replenished by goblet and Paneth's cells. Luminal antigens are being sensed by pattern recognition receptors on the enterocytes. The enteroendocrine cells sense the environment and coordinate the intestinal function by releasing neuropeptides acting both on IEC and inflammatory cells. All this while cells are continuously and rapidly being regenerated from a limited number of stem cells close to the intestinal crypt base. This review seeks to describe the cell types and structures of the intestinal epithelial barrier supporting intestinal homeostasis, and how disturbance in these systems might relate to inflammatory bowel disease.

Altered Prostasin (CAP1/Prss8) Expression Favors Inflammation and Tissue Remodeling in DSS-induced Colitis

“…and 2), that is indicative for a dysbalance of the intestinal homeostasis. 45 Moreover, local inflammation could be observed together with mild edema, however without signs of infiltrating leucocytes or macrophages. Interestingly, the histological analysis of colonspecific prostasin knockout mice shows no colonic alterations, and the mice are indistinguishable from the control group.…”

The Potential of Gut Commensals in Reinforcing Intestinal Barrier Function and Alleviating Inflammation

“…The most prominent antimicrobial peptides include defensins, cathelicidins, and C-type lectins, which are expressed as a result of pattern recognition receptor (PRR) activation in the intestinal epithelial cells [ 15 ]. In order to sustain intestinal integrity, the epithelial cells need to be renewed constantly by continuous differentiation from stem cells to goblet cells, Paneth cells, enteroendocrine cells, or enterocytes [ 16 ]. Enterocytes form the physical barrier by linking together with different cell junctions, including desmosomes, adherens junctions, and tight junctions.…”

Extracellular Vesicles with Possible Roles in Gut Intestinal Tract Homeostasis and IBD

“…As for the intestinal defense system, it mainly consists of three parts, including the mucus layer, intestinal epithelial cells (IECs), and other immune cells, such as lymphocytes and macrophages that are associated with the innate immune system. Additionally, effective communication among these cells plays a critical role in maintaining the intestinal homeostasis, which is mainly mediated by extracellular factors and receptors, such as growth factor and its receptor tyrosine kinase [2,3]. How-ever, in recent decades, extracellular vesicles (EVs) have been recognized as a novel mediator not only for the cell-to-cell but also for the organism-to-cell interaction [4][5][6].…”