The Role Of MBL In Regulation Of Intestinal Epithelial Barrier

Background:Intestinal tract consist of a single-cell layer that constitutes the most important barrier against the external microbe invasion. It acts as a selectively permeable barrier, which permit the absorption of nutrients, and maintaining an effective defense against microbe. The permitted nutrients include include sugar, fat, protein, amino acids, vitamins and trace elements; Mechanical barriers play an important role in intestinal barrier. Inflammatory bowel disease( IBD), total parenteral nutrition( TPN), endotoxin and trauma firstly damage mechanical barrie, resulting in loss of intestinal barrier function and causing bacteria translocation.Innate immunity is an evolutionarily ancient in host defense. The major components of the innate immune system include epithelial barriers(the skin, and the mucosal epithelia of the respiratory, gastrointestinal, and reproductive tracts), soluble molecules(anti-microbial peptides, complement, cytokines, and natural antibodies), phagocytes(macrophages and neutrophils), and pattern recognition receptors(PRRs)(TLRs, NLRs, scavenger receptors, and C-type lectin receptors). Mannose binding lectin(MBL) is a Ca2+-dependent(C-type) animal lectin. As a member of innate immunity system, MBL constitutes the carbohydrate recognition domains and collagen-like regions, binding to certain carbohydrates of microorganism and activating complement pathway. In addition, MBL can also directly bind to phagocyte through its cell receptor, which reveals the functions of host defense.It has been shown that MBL was related with mucous barrier. Thought the injury and death of MBL-null mouse is elevated in actual IBD model, the barrier function of C3 deficiency mouse were protected in actual DSS model. Meanwhile, MBL may protect host intestinal mucosa by directly binding to the bacteria and reduced the secretion of IL-6.Moreover researches mainly show that MBL initiating the lectin pathway of complement activation in the gut, yet none of a research is associated with the interation of MBL with epithelium cell. In this study, we investigated the complement independent roles of MBL. This research explored the MBL directly regulate barrier function under conditions of LPS induced injury by HE stain, western blotting and PCR.Methods:1. LPS was administered intraperitoneal 6h to form the model of Intestinal Endotoxemia in C57 mice. hematoxylin-eosin(HE) stain, immunofluorescence and Ussing Chame were used to observe function of intestinal barrier include permeability and morphology.2. In LPS model, the expression of MBL was observed by immune-histochemisty, western-blotting and realtime-PCR.3. In vitro, intestinal epithelium cell(Caco-2 cells) transfected MBL-shRNA plasmid be used to study the function of intestinal barrier include Tight junction proteins and permeability.Results:1. After the treatment of LPS,we found that LPS cause the loss and shortening of villi, marked epithelial cell denudation, intestinal permeability and epithelial cell apoptosis increase in LPS model induced injury.2. The expression of MBL mRNA and protein were increased in vivo and vitro after LPS treatment.3. In vitro, we found that the expression of TJ(claudin-1 and Occludin) in MBL sh RNA cells were down-regulated, localization of TJ were disrupted and distributed in a diffuse manner. The delayed development of TER in MBL sh RNA cells was associated with disrupted localization of TJ. However, height concentration rh MBL induced epithelial cell apoptosis,light concentration MBL hardly influenced cell apoptosis.Conclusion:1. Intestinal barrier permeability was increased both in vivo and vitro study, the morphology of intestinal villus was disrupted and the apoptotic rates of epithelial cells were increased. The expression of MBL was up-regulated after LPS treatment. In addition, MBL may be directly associated with protect the function intestinal barrier.2. MBL involved in the regulation of the TJ proteins expression.