Mucosal Mast Cell Proteases Are Involved in Colonic Permeability Alterations and Subsequent Bacterial Translocation in Endotoxemic Rats

Abstract

LPS-induced endotoxemia is associated with gut immune stimulation, mucosal inflammation, colonic paracellular permeability (CPP) alteration, and it promotes bacterial translocation (BT). Gut permeability increase linked to LPS promotes mucosal barrier dysfunction resulting to BT. However, the mechanisms involved in these alterations remain unknown. We aimed to evaluate the role of colonic mucosal mast cells and luminal serine protease activity (PA) in the alterations of CPP and BT induced by LPS. Rats receiving doxantrazole, a mast cell stabilizer, combined or not with LPS from Escherichia coli and CPP as well as BT were evaluated after each treatment. Mucosal mast cell activation was assessed by histological methods and by rat mast cell protease 2 level measurement in colonic content. Colonic luminal PA and mucosal inflammation (myeloperoxidase activity) were biochemically determined. In addition, the ability of luminal contents to act on CPP was evaluated in vitro in Ussing chambers. Peripheral administration of LPS promoted mast cell degranulation and increased CPP, BT, mucosal myeloperoxidase activity as well as rat mast cell protease 2 levels, and PA in colonic content. LPS-induced CPP increase and BT were prevented by doxantrazole. In vitro, exposure of the apical side of colonic tissues with supernatants from colonic contents of LPS-treated rats increased CPP. This effect was blocked by the serine protease inhibitor soybean trypsin inhibitor. Our data bring evidence of a key role of mucosal mast cells in LPS-induced increase of CPP and BT through the release of serine proteases into the colonic lumen.

Intestinal Epithelial Barrier Dysfunction in Disease and Possible Therapeutical Interventions

“…Occludin and claudin displacement from lipid rafts to detergent soluble membrane microdomains explained disruption of the TJ structure and increased intestinal permeability. LPS themselves increased the colonic paracellular permeability, promoting bacterial translocation and neutrophils recruitment in the colonic tissues [114]. Moreover, LPS enhanced the luminal content in serine protease activity that also demonstrated the capacity to impair barrier integrity.…”

“…Proteases are involved in LPS-induced increase in colonic paracellular permeability and inflammation in rat colon [114]. Indeed, LPS administration was associated with enhanced luminal serine protease activity that displayed a permeability-enhancing effect when applied to rat proximal colon in vitro.…”

Lipopolysaccharides Facilitate Colonic Motor Alterations Associated to the Sensitization to a Luminal Antigen in Rats

“…38 Here, although not directly assessed, it is feasible to assume the presence of an altered barrier function as the doses and pattern of administration of LPS were similar to other studies demonstrating an increased epithelial permeability. 39,40 In addition, adherence of Clostridium spp. to the colonic epithelium, favored by LPS, could be a contributing factor in the alteration of the barrier function and the subsequent sensitization to OVA.…”

Mast cells regulate homeostatic intestinal epithelial migration and barrier function by a chymase/Mcpt4-dependent mechanism

“…Studies in endotoxemic rats showed that mast cell proteases increased colonic permeability and that this effect was dependent on chymase activity (14). We hypothesized that mast cells regulate homeostatic intestinal epithelial permeability through their expression of chymase/Mcpt4.…”