Abstract
BackgroundSevere burn injury results in the loss of intestinal barrier function, however, the underlying mechanism remains unclear. Myosin light chain (MLC) phosphorylation mediated by MLC kinase (MLCK) is critical to the pathophysiological regulation of intestinal barrier function. We hypothesized that the MLCK-dependent MLC phosphorylation mediates the regulation of intestinal barrier function following burn injury, and that MLCK inhibition attenuates the burn-induced intestinal barrier disfunction.Methodology/Principal FindingsMale balb/c mice were assigned randomly to either sham burn (control) or 30% total body surface area (TBSA) full thickness burn without or with intraperitoneal injection of ML-9 (2 mg/kg), an MLCK inhibitor. In vivo intestinal permeability to fluorescein isothiocyanate (FITC)-dextran was measured. Intestinal mucosa injury was assessed histologically. Tight junction proteins ZO-1, occludin and claudin-1 was analyzed by immunofluorescent assay. Expression of MLCK and phosphorylated MLC in ileal mucosa was assessed by Western blot. Intestinal permeability was increased significantly after burn injury, which was accompanied by mucosa injury, tight junction protein alterations, and increase of both MLCK and MLC phosphorylation. Treatment with ML-9 attenuated the burn-caused increase of intestinal permeability, mucosa injury, tight junction protein alterations, and decreased MLC phosphorylation, but not MLCK expression.Conclusions/SignificanceThe MLCK-dependent MLC phosphorylation mediates intestinal epithelial barrier dysfunction after severe burn injury. It is suggested that MLCK-dependent MLC phosphorylation may be a critical target for the therapeutic treatment of intestinal epithelial barrier disruption after severe burn injury.
Highlights
It is well known that the intestinal epithelial mucosa plays a pivotal role in the host’s protection against luminal pathogens and antigenic molecules, providing a barrier function to protect against the invasion of intraluminal microorganisms and endotoxin through the intestinal wall into the blood or lymph
Based on the above data showing that the postburn intestinal permeability increased significantly and peaked at 6 h, we asked whether in vivo inhibiting Myosin light chain (MLC) phosphorylation with ML-9, an MLC kinase (MLCK) inhibitor, could ameliorate the increased intestinal permeability induced by severe burn injury, and selected postburn 6 h as the time point for further studies
To more precisely understand the intestinal barrier defect induced by burn injury, we evaluated the morphological changes of zonula occludens-1 (ZO-1), a member of tight junction proteins, by immunofluorescent antibody labeling assay
Summary
It is well known that the intestinal epithelial mucosa plays a pivotal role in the host’s protection against luminal pathogens and antigenic molecules, providing a barrier function to protect against the invasion of intraluminal microorganisms and endotoxin through the intestinal wall into the blood or lymph. It is well documented that the intestinal epithelial barrier function is often disrupted in many surgical diseases, including trauma, shock, burn injury, and the other surgically critical illness, resulting in the increased intestinal permeability and subsequent translocation of bacteria or/and endotoxin from gastrointestinal tract [1,2]. The tight junction, composed of multiple proteins including transmembrane proteins such as zonula occludens (ZO), occludin, claudins and junctional adhesion molecule, is a complex that forms a selectively permeable seal between adjacent epithelial cells [5,6]. The MLCK-dependent MLC phosphorylation pathway appears to be critical to the pathophysiologically disrupted intestinal barrier both in vitro and in vivo. Myosin light chain (MLC) phosphorylation mediated by MLC kinase (MLCK) is critical to the pathophysiological regulation of intestinal barrier function. We hypothesized that the MLCK-dependent MLC phosphorylation mediates the regulation of intestinal barrier function following burn injury, and that MLCK inhibition attenuates the burn-induced intestinal barrier disfunction
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