Syndecan-4 is a ubiquitously expressed heparan sulfate proteoglycan that modulates cell interactions with the extracellular matrix. It is transiently up-regulated during tissue repair by cells that mediate wound healing. Here, we report that syndecan-4 is essential for optimal fibroblast response to the three-dimensional fibrin-fibronectin provisional matrix that is deposited upon tissue injury. Interference with syndecan-4 function inhibits matrix contraction by preventing cell spreading, actin stress fiber formation, and activation of focal adhesion kinase and RhoA mediated-intracellular signaling pathways. Tenascin-C is an extracellular matrix protein that regulates cell response to fibronectin within the provisional matrix. Syndecan-4 is also required for tenascin-C action. Inhibition of syndecan-4 function suppresses tenascin-C activity and overexpression of syndecan-4 circumvents the effects of tenascin-C. In this way, tenascin-C and syndecan-4 work together to control fibroblast morphology and signaling and regulate events such as matrix contraction that are essential for efficient tissue repair. INTRODUCTIONTissue architecture is defined by the three-dimensional (3D) organization of the proteins and proteoglycans that comprise the extracellular matrix (ECM). Individual ECM components influence cell arrangements and activities through binding to transmembrane receptors, thus initiating intracellular signaling and altering gene expression and other downstream events. Tissues undergo continual maintenance and remodeling through controlled deposition and removal of specific ECM components. These changes in ECM composition and organization modulate cell behaviors and serve important roles throughout development and in the adult during both physiological and pathological processes (Lukashev and Werb, 1998).The provisional matrix that forms at sites of tissue injury undergoes extensive remodeling and turnover during wound repair. Composed predominantly of covalently cross-linked fibrin and plasma fibronectin (FN), this fibrin-FN provisional matrix coordinates the activities of cells involved in wound repair. It is remodeled over time to recapitulate normal tissue and this remodeling involves cellmediated contraction and deposition of new FN-rich matrix (Clark, 1996;Midwood et al., 2004). FN, a major component of the matrix, is a ubiquitously expressed, multifunctional extracellular glycoprotein that promotes cell adhesion. It controls many intracellular pathways and influences a wide range of cell functions (Hynes, 1990). For example, FN within a 3D fibrin-FN provisional matrix initiates signaling via focal adhesion kinase (FAK) and RhoA in order to promote fibroblast spreading, stress fiber formation, and focal adhesion assembly (Wenk et al., 2000;.The provisional matrix contacts many other ECM proteins that are induced at different stages of tissue repair, including thrombospondins, SPARC, and tenascin-C. These proteins are specifically up-regulated at wound sites where they modulate cell-ECM interactions (re...

A growing body of evidence suggests that interaction of epithelial and immune cells via neuropeptides, hormones, and cytokines participate in the pathophysiology of diarrhea and intestinal inflammation (reviewed in ref. 1). Neurotensin (NT), a bioactive peptide (2) with a primary distribution in the brain and the gastrointestinal tract, has been localized by immunohistochemistry to endocrine cells (N cells) and neurons in the intestinal mucosa, submucosa, and muscularis of animals and humans (3). A wide range of biological activities has been described for NT with actions on the cardiovascular, gastrointestinal, reproductive, and central nervous systems (3). The known intestinal effects of this peptide include trophic effects on small and large bowel, pancreas, and stomach; inhibition of small bowel and gastric motility; and stimulation of colonic motor activity (3). Studies in animals (3, 4, 5) and humans (3, 6) also demonstrate that NT may modulate fluid secretion in the intestinal tract and that its secretory effects in the ileum may be mediated through a nervous reflex in the enteric nervous system (5).Several lines of evidence indicate that NT may also participate in inflammatory reactions. Intravenous administration of NT to rats causes mast cell degranulation (7) and increases vascular permeability and levels of histamine and leukotriene C4 in the plasma (8); these effects can be inhibited by a specific NT receptor antagonist (9).NT also interacts in vitro with immune and inflammatory cells, including leukocytes (10), peritoneal mast cells (7), and macrophages (11,12). Although these studies point to a role for NT in inflammatory reactions, the possibility that this peptide participates in the pathogenesis of colonic inflammation has not been examined.NT exerts its effects by interacting with specific receptors (NTR) on cell surfaces. Two specific receptors for NT (NTR1 and NTR2), which belong to the seven transmembrane G protein-linked superfamily, have been identified and cloned (13,14). NTR1-mRNA and NT binding sites have been identified in the brain (15), small and large intestine of animals and humans (13, 15), human colonic epithelial cell lines (16,17), human blood mononuclear cells (11), and endothelial cells (18). Recently, we demonstrated the presence of NTR1 mRNA in the rat colonic mucosa, including colonic epithelial cells (19). We also showed that administration of the specific NT receptor nonpeptide antagonist SR-48,692 to rats attenuated colonic mucin secretion and mast cell activation following immobilization stress, indicating a critical role for NT in stress-related colonic responses (19).Clostridium difficile is the primary pathogenic factor of antibiotic-associated diarrhea in humans and animals The neuropeptide neurotensin mediates several intestinal functions, including chloride secretion, motility, and cellular growth. However, whether this peptide participates in intestinal inflammation is not known. Toxin A, an enterotoxin from Clostridium difficile, mediates pseudomembranous col...

Saccharomyces boulardii is a nonpathogenic yeast used in the treatment of Clostridium difficile diarrhea and colitis. We have reported that S. boulardii inhibitsC. difficile toxin A enteritis in rats by releasing a 54-kDa protease which digests the toxin A molecule and its brush border membrane (BBM) receptor (I. Castagliuolo, J. T. LaMont, S. T. Nikulasson, and C. Pothoulakis, Infect. Immun. 64:5225–5232, 1996). The aim of this study was to further evaluate the role of S. boulardii protease in preventing C. difficile toxin A enteritis in rat ileum and determine whether it protects human colonic mucosa from C. difficile toxins. A polyclonal rabbit antiserum raised against purified S. boulardii serine protease inhibited by 73% the proteolytic activity present in S. boulardii conditioned medium in vitro. The anti-protease immunoglobulin G (IgG) prevented the action of S. boulardiion toxin A-induced intestinal secretion and mucosal permeability to [3H]mannitol in rat ileal loops, while control rabbit IgG had no effect. The anti-protease IgG also prevented the effects ofS. boulardii protease on digestion of toxins A and B and on binding of [3H]toxin A and [3H]toxin B to purified human colonic BBM. Purified S. boulardii protease reversed toxin A- and toxin B-induced inhibition of protein synthesis in human colonic (HT-29) cells. Furthermore, toxin A- and B-induced drops in transepithelial resistance in human colonic mucosa mounted in Ussing chambers were reversed by 60 and 68%, respectively, by preexposing the toxins to S. boulardii protease. We conclude that the protective effects of S. boulardii onC. difficile-induced inflammatory diarrhea in humans are due, at least in part, to proteolytic digestion of toxin A and B molecules by a secreted protease.

No abstract