292 Deletion of RNA-Binding Protein HuR in Intestinal Epithelial Cells Delays Mucosal Repair After Ischemia/Reperfusion-Induced Injury

Abstract

Acute gut mucosal injury occurs commonly during critical pathological conditions, leading to mucosal hemorrhage, epithelial barrier dysfunction, and the translocation of luminal toxic substances and bacteria to the blood stream, but the exact mechanism underlying mucosal injury/repair are still obscure. RNA-binding proteins (RBPs) posttranscriptionally regulate gene expression and are implicated in many aspects of pathophysiology. HuR is among the most prominent sequence-specific RBP and has emerged as a master regulator of the maintenance of the homeostasis of gut mucosa. Our previous studies show that HuR regulates intestinal epithelial cell proliferation and apoptosis, but the exact role of HuR in gut mucosal repair after injury remains unknown. This study tested the hypothesis that HuR plays a role in intestinal mucosal repair after ischemia/reperfusion (I/R)-induced Injury.Methods: Studies were conducted in our recently generating intestinal epithelial tissue-specific HuR knockout (IE-HuR-/-) mice and wild-type littermates. Mucosal injury was induced by exposed to 30min of mesenteric ischemia, followed by 2-h reperfusion. Barrier function was detected by paracellular tracer flux assay using FITC-dextran. Results: The mucosa of the animals subjected to mesenteric I/R displayed signs of remarkable damage. Macroscopically, the intestines of the animals exposed to I/R exhibited swollen and edematous with areas of red streaks in both littermates and IE-HuR-/animals. Microscopic analysis showed that there were severed damages in the small intestinal mucosa as indicated by sloughed cells, denuded villi with dilated capillaries, and frank hemorrhage. Although there were no significant differences in the injury scores between littermates and IE-HuR-/mice when measured immediately after I/R, HuR deletion delayed the process of early mucosal repair after I/Rinduced injury. The mucosal surface remained discontinuous, showing sloughed cells and debris in IE-HuR-/mice (injury score: 3.3 ± 0.12) 6 h after I/R, whereas the mucosa in littermates was almost completely recovered (0.2 ± 0.03). Both littermate and IE-HuR-/mice exhibited significant gut barrier dysfunction after I/R-induced injury, but increased levels of gut permeability in IE-HuR-/mice were much greater than those observed in littermates. The recovery of gut barrier function after I/R was also inhibited by HuR deletion. Moreover, expression of the Wnt co-receptor LRP6 and ARP2 in the intestinal mucosa of HuR-/mice decreased dramatically, which are necessary for normal mucosal repair after injury. Conclusions: These results indicate that 1) HuR is crucial for maintenance of normal gut mucosal epithelial integrity and 2) HuR deletion in intestinal epithelial cells delays mucosal repair and represses the recovery of gut barrier function after I/R-induced mucosal injury.