Nitric oxide and butyrate affect HIF-1 activity and modulate function of tight junction in intestinal epithelial cell monolayers

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Background : Interaction between the product of the bacteria reside in the intestine and the intestinal epithelial cells under hypoxic conditions is not yet to be fully understood. Hypoxia inducible factor-1 (HIF-1) is one of the pivotal transcriptional factor by which cells may adapt to hypoxic conditions. We investigated the effect of intestinal bacterial product, butyrate on HIF-1 transcriptional activity and transcription of several genes mediated by HIF-1, as well as the barrier function of epithelial cells. Methods : We used the Caco-2 cells as a model of human intestinal epithelial cells. For hypoxic experiments, we put the Caco-2 cells into a chamber with 5%CO2, 1%O2 and N2 balance. For luciferase assay, we constructed the reporter plasmid pHREpgk1-Luc which has hypoxia response element (HRE) from 5'-flanking region of phosphoglycerate kinase-1 (PGK-1) at just upstream of minimum SV40 promoter. Reverse transcription analysis was performed about PGK-1, iNOS, or GAPDH with ubiquitous protocols. To study the barrier functions of Caco-2 cells, Transepithelial electronic resistance (TEER) was measured. Results : Butyrate reduced HIF-1 transcriptional activity. The transcription of several HIF-1 mediated genes was inhibited in Caco-2 cells. Butyrate also reduced TEER under the hypoxic condition. Discussion : As HIF-1 is regarded to be critical transcriptional factor for cellular adaptation to hypoxia, the inhibition of the activity as well as transcription of the related genes might suggest the deleterious effect of butyrate on intestinal epithelium under hypoxia. The loss of the barrier function might be associated with butyrate-induced epithelial perturbation under hypoxia.