Hypoxia Inducible Factor-1α Monocarboxylate Transporter-1 Is Involved In The Protective Effect Of Short-chain Fatty Acids In The Ischemic Intestine

Objective:Intestinal ischemia reperfusion（I/R）injury is a common pathophysiological process due to hemorrhagic shock and intestinal torsion.Intestinal barrier injury is the core link of intestinal I/R injury.In this paper,hypoxia-inducing factor 1α（HIF-1α）regulates the expression of monocarboxylic acid transporter 1（MCT-1）in intestinal epithelial cells under hypoxia conditions through clinical sample experiments,animal models and cell experiments,and initially explores the protective effect of short-chain fatty acids（SCFAs）on intestinal barrier under hypoxia conditions.Methods:First,to study the changes of intestinal SCFAs after intestinal ischemia-necrosis,a mouse model of intestinal ischemia-reperfusion injury was established,and the content of intestinal SCFAs in mice with intestinal ischemia-reperfusion injury model and control mice was detected by HPLC.Secondly,to study the changes of MCT-1 in intestinal cavity after intestinal ischemia-necrosis,we collected ileal tissues of non-ischemic dead and patients with intestinal ischemia-necrosis for immunohistochemical staining to detect the expression of MCT-1 in intestinal epithelium.At the same time,immunohistochemical staining was used to detect the changes of MCT-1 in ileal tissue of mice with intestinal ischemia-reperfusion injury and mice in the control group to further verify our conjecture.We then constructed intestinal epithelial specific HIF-1αknockout mice(HIF-1α^ΔIEC)and control mice(HIF-1α^flox/flox)models,and immunohistochemical staining was performed to detect the changes of MCT-1 in ileal tissues of the two groups of mice.Then intestinal epithelial cell line Caco-2 cells were cultured to establish hypoxia model and si HIF-1αmodel to further verify the relationship between HIF-1αand MCT-1.In addition,intestinal epithelial specific HIF-1αknockout rats(HIF-1α^ΔIEC)and control mice(HIF-1α^flox/flox)were selected to construct a ischemia reperfusion（I/R）injury model,which was randomly divided into the I/R group or the I/R+butyric acid group.Immunohistochemical staining and transmission electron microscopy were used to observe the ultrastructure changes of the ileum in each group.Finally,intestinal epithelial cell line Caco-2 was cultured to establish an anoxic model,and the expression of MCT-1 and Occludin in the control group,anoxic group,butyric acid+anoxic group,si MCT-1+butyric acid+anoxic group were detected by Western blot,respectively.Transepithelial resistance（TER）was measured in each group to assess changes in intestinal epithelial barrier function.Results:Compared with sham operation group,there was no significant change in intestinal SCFAs in I/R group.In addition,both human and animal experiments showed that intestinal ischemia and hypoxia could induce high expression of MCT-1 in intestinal epithelial cells.After intestinal ischemia and hypoxia,HIF-1α^ΔIECmice had lower expression of MCT-1 and were more sensitive to I/R injury than control mice.Cell experiments further confirmed that HIF-1αcan regulate MCT-1 expression in intestinal epithelium.In addition,we found that butyric acid can relieve intestinal damage caused by ischemia and hypoxia.In order to further study the relationship between butyric acid,HIF-1αand MCT-1,we found in experimental cell experiments that butyric acid can effectively increase the expression of intestinal tight junction protein when HIF-1αand MCT-1 are normally expressed.When MCT-1 is absent in cells,the regulation effect of butyric acid on intestinal compact junction protein expression is significantly decreased.Conclusion:HIF-1αcan be activated under the condition of intestinal ischemia and hypoxia,which can induce the expression of MCT-1 in intestinal epithelial cells,and the expression of MCT-1ensures the protection of intestinal barrier by SCFAs.This also suggests that if the intestinal SCFAs content can be maintained during intestinal ischemia and hypoxia,the hypoxia response initiated by the intestine itself can help alleviate intestinal damage caused by ischemia and hypoxia.