Published online Jul 14, 2018. doi: 10.3748/wjg.v24.i26.2867
Peer-review started: March 30, 2018
First decision: May 17, 2018
Revised: May 25, 2018
Accepted: June 9, 2018
Article in press: June 9, 2018
Published online: July 14, 2018
To explore the protective effects and underlying mechanisms of total polysaccharides of the Sijunzi decoction (TPSJ) on the epithelial barriers in vitro.
Caco-2 cell monolayers were treated with or without TPSJ in the presence or absence of TNF-α, and paracellular permeability and transepithelial electrical resistance (TEER) were measured to evaluate the epithelial barrier function. Immunofluorescence and western blotting were respectively used to evaluate the distribution and expression of the tight junction proteins claudin 1, claudin 2, zo3, and occludin in Caco-2 cells. Western blotting was also used to evaluate the cellular expression of myosin light chain (MLC), phosphorylated MLC (pMLC), MLC kinase (MLCK), and nuclear factor (NF)-κB p65.
TPSJ promoted the proliferation of Caco-2 cells and inhibited TNF-α-induced secretion of pro-inflammatory cytokines. Furthermore, TPSJ significantly ameliorated both the reduction of TEER and the increased paracellular permeability observed in tumor necrosis factor (TNF)-α-damaged Caco-2 monolayers. Furthermore, TPSJ remarkably attenuated TNF-α-induced morphological changes, downregulated the expression of claudin 1, claudin 2, zo3, and occludin, and markedly suppressed TNF-α-mediated upregulation of p-MLC and MLCK expression. Finally, TPSJ inhibited the activation and expression of NF-κB p65.
Our results demonstrate that TPSJ alleviates the TNF-α-induced impairment of the intestinal epithelial cell barrier function by suppressing NF-κB p65-mediated phosphorylation of MLCK and MLC.
Core tip: Total polysaccharides of the Sijunzi decoction (TPSJ) comprise the active ingredient of Sijunzi decoction, which has long been used to treat gastrointestinal tract disorders. However, the mechanisms by which TPSJ affects the intestinal epithelial barrier remain unclear. Our study results demonstrated that TPSJ attenuated tumor necrosis factor (TNF)-α-induced intestinal barrier dysfunction in a Caco-2 cell monolayer. Furthermore, TPSJ inhibited TNF-α-induced upregulation of myosin light chain (MLC) phosphorylation, which is mediated by MLC kinase and NF-κB, suggesting that this mechanism might underlie the protective effects of TPSJ against intestinal epithelial barrier dysfunction triggered by proinflammatory cytokines.