Butyrate Enhances Intestinal Epithelial Barrier Function via Up-Regulation of Tight Junction Protein Claudin-1 Transcription
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Barrier function is essential for the maintenance of normal intestinal function. Dysregulation of the intestinal barrier underlies a wide range of disorders.
Previously, we found that sodium butyrate (NaB) decreased the molecular permeability of intestinal barrier in vivo model, but the mechanism by which NaB facilitated the tightness of tight junctions (TJs) in small intestinal epithelium needed further studies.
In vitro culture of the cdx2-IEC monolayer was used to mimic barrier function. The TJs were assessed by transepithelial electrical resistance (TEER) and paracellular flux of fluorescein isothiocyanate-conjugated dextran 40,000 (FD-40), Western blot, Q-RT-PCR, and immunofluorescence. Promoter and chromatin immunoprecipitation (ChIP) assays were also done to analyze the Claudin-1 gene.
NaB decreased FD-40 flux, increased TEER and TJ protein Claudin-1 expression, induced ZO-1 and Occludin redistribution in cellular membrane, and reversed the damage effect after calcium (Ca2+) switch assay. Silencing Claudin-1 prevented protective function of NaB from enhancing intestinal barrier integrity. Further studies demonstrated that NaB increased Claudin-1 transcription by facilitating the interaction between transcription factor SP1 and a specific motif within the promoter region of Claudin-1. This SP1 binding motif was located upstream of the coding region (−138 to −76 bp) and indispensable for the transcription of Claudin-1 following NaB treatment. ChIP assay confirmed the association between SP1 and Claudin-1 promoter, and the elimination of the SP1 binding site by point mutation resulted in a significant loss of Claudin-1 transcription after NaB dealing.
NaB enhanced intestinal barrier function through increasing Claudin-1 transcription via facilitating the association between SP1 and Claudin-1 promoter.
KeywordsIntestinal epithelium Tight junction Butyrate Claudin-1 Transcription
The authors thank Professor Xian Wang and Associate Professor Ming-Jiang Xu for offering laboratory and technical assistance on several assays, Min-ji Wei for HPLC assay, Professor Qiang Zhang for detection of TEER, and Elizabeth T. Chang for the language assistance. This work was funded by National natural science foundation of China, Number 31040041.
Conflict of interest
No conflicts of interest, financial or otherwise, are declared by the author.
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