SUMMARY Inflammatory cytokines have been proposed to regulate epithelial homeostasis during intestinal inflammation. We report here that interferon-γ (IFN-γ) regulates the crucial homeostatic functions of cell proliferation and apoptosis through serine-threonine protein kinase AKT-β-catenin and Wingless-Int (Wnt)-β-catenin signaling pathways. Short-term exposure of intestinal epithelial cells to IFN-γ resulted in activation of β-catenin through AKT, followed by induction of the secreted Wnt inhibitor Dkk1. Consequently, we observed an increase in Dkk1-mediated apoptosis upon extended IFN-γ treatment, and reduced proliferation through depletion of the Wnt co-receptor LRP6. These effects were enhanced by tumor necrosis factor-α (TNF)-α, suggesting synergism between the two cytokines. Consistent with these results, colitis in vivo was associated with decreased β-catenin-T-cell factor (TCF) signaling, loss of plasma membrane-associated LRP6, and reduced epithelial cell proliferation. Proliferation was partially restored in IFN-γ - deficient mice. Thus, we propose that IFN-γ regulates intestinal epithelial homeostasis by sequential regulation of converging β-catenin signaling pathways.

Recent evidence has linked intestinal permeability to mucosal inflammation, but molecular studies are lacking. Candidate regulatory molecules localized within the tight junction (TJ) include Junctional Adhesion Molecule (JAM-A), which has been implicated in the regulation of barrier function and leukocyte migration. Thus, we analyzed the intestinal mucosa of JAM-A–deficient (JAM-A−/−) mice for evidence of enhanced permeability and inflammation. Colonic mucosa from JAM-A−/− mice had normal epithelial architecture but increased polymorphonuclear leukocyte infiltration and large lymphoid aggregates not seen in wild-type controls. Barrier function experiments revealed increased mucosal permeability, as indicated by enhanced dextran flux, and decreased transepithelial electrical resistance in JAM-A−/− mice. The in vivo observations were epithelial specific, because monolayers of JAM-A−/− epithelial cells also demonstrated increased permeability. Analyses of other TJ components revealed increased expression of claudin-10 and -15 in the colonic mucosa of JAM-A−/− mice and in JAM-A small interfering RNA–treated epithelial cells. Given the observed increase in colonic inflammation and permeability, we assessed the susceptibility of JAM-A−/− mice to the induction of colitis with dextran sulfate sodium (DSS). Although DSS-treated JAM-A−/− animals had increased clinical disease compared with controls, colonic mucosa showed less injury and increased epithelial proliferation. These findings demonstrate a complex role of JAM-A in intestinal homeostasis by regulating epithelial permeability, inflammation, and proliferation.

A critical function of the intestinal mucosa is to form a barrier that separates luminal contents from the interstitium. The single layer of intestinal epithelial cells (IECs) serves as a dynamic interface between the host and its environment. Cell polarity and structural properties of the epithelium is complex and is important in the development of epithelial barrier function. Epithelial cells associate with each other via a series of intercellular junctions. The apical most intercellular junctional complex referred to as the Apical Junction Complex (AJC) is important in not only cell-cell recognition, but also in the regulation of paracellular movement of fluid and solutes. Defects in the intestinal epithelial barrier function have been observed in a number of intestinal disorders such as inflammatory bowel disease (IBD). It is now becoming evident that an aberrant epithelial barrier function plays a central role in the pathophysiology of IBD. Thus, a better understanding of the intestinal epithelial barrier structure and function in healthy and disease states such as IBD will foster new ideas for the development of therapies for such chronic disorders.

Esophageal wall defects of different etiology in the upper gastrointestinal tract can be treated successfully with EVT, considering that indication for EVT should be weighed carefully. EVT can be regarded as a novel life-saving therapeutic tool.

The epithelial apical junctional complex is important in determining epithelial barrier properties. Recent studies have highlighted contribution of proinflammatory cytokines and endocytosis of apical junctional complex proteins to the epithelial barrier defect. Continued advances in understanding of this field will yield new therapeutic targets for intestinal disorders.

Endoscopic vacuum therapy might be more effective than endoscopic stent placement in the management of esophageal anastomotic leaks.

Intestinal epithelial intercellular junctions regulate barrier properties, and they have been linked to epithelial differentiation and programmed cell death (apoptosis). However, mechanisms regulating these processes are poorly defined. Desmosomes are critical elements of intercellular junctions; they are punctate structures made up of transmembrane desmosomal cadherins termed desmoglein-2 (Dsg2) and desmocollin-2 (Dsc2) that affiliate with the underlying intermediate filaments via linker proteins to provide mechanical strength to epithelia. In the present study, we generated an antibody, AH12.2, that recognizes Dsg2. We show that Dsg2 but not another desmosomal cadherin, Dsc2, is cleaved by cysteine proteases during the onset of intestinal epithelial cell (IEC) apoptosis. Small interfering RNA-mediated downregulation of Dsg2 protected epithelial cells from apoptosis. Moreover, we report that a C-terminal fragment of Dsg2 regulates apoptosis and Dsg2 protein levels. Our studies highlight a novel mechanism by which Dsg2 regulates IEC apoptosis driven by cysteine proteases during physiological differentiation and inflammation. INTRODUCTIONMucosal epithelial barriers are dependent upon the association of neighboring cells with each other through adhesive multiprotein complexes at sites of cell-cell contacts. Simple epithelial cells (such as those lining the intestine, lungs, and kidneys) associate through a series of intercellular junctions that maintain epithelial integrity, regulate paracellular movement of solutes, and restrict access of luminal antigens/pathogens from underlying tissue compartments. Intercellular junctions include tight junctions (TJs), adherens junctions (AJs), desmosomes (DMs), and in some epithelia gap junctions (Cereijido et al., 1978;Gonzalez-Mariscal et al., 2003). DMs have been visualized as punctuate "spot welds" that hold cells together and provide mechanical strength to epithelial tissues by forming stable cell-cell contacts that are anchored to the keratin intermediate filaments (Getsios et al., 2004b). Transmembrane proteins in DMs include the cadherin superfamily members desmoglein (Dsg 1-4) and desmocollin (Dsc 1-3) (Getsios et al., 2004b;Kottke et al., 2006) that mediate calcium-dependent cell-cell adhesion. Simple epithelia such as in the intestine, express Dsg2 and Dsc2, which affiliate with underlying keratin intermediate filaments via the armadillo family of proteins and desmoplakin (DSP) (Bornslaeger et al., 1996;Hatzfeld, 1999;Jonkman et al., 2005).Epithelial cells differentiate as they migrate toward the lumen along the intestinal crypt villus axis where they detach from the basement membrane and undergo apoptosis (Dufour et al., 2004). This cycle of progenitor crypt cell proliferation, migration, differentiation, and apoptosis is vital for maintaining integrity of the epithelium and therefore mucosal barrier function. The survival of most normal intestinal epithelial cells (IECs) requires cell-cell and cellmatrix adhesion, and loss of such cell adhesion induces epithelial...

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