325 CELF2 Induced Splicing Results in Loss of the Bir Domain in Survivin: Critical Role of XIAP in Radiation Induced Mitotic Catastrophe

Abstract

ized wild-type(CVN), MyD88f/f (WT), MyD88-/and MyD88IEC-/mice (4-8/group) were subjected to ileal ischemia by obstructing the distal branches of the superior mesenteric artery for 60 minutes (ischemia) followed by 90 minutes of reperfusion. Sections of the ileum inside the ischemic region (damage) and outside (healthy) were collected and fixed in 10% formalin. Tissue damage was assessed using a histological necrosis scoring system. Expression of ileal pro-inflammatory mediators (Cxcl1, Il1b, Tnf) was evaluated using ABIPrism sequence detection system. Neutrophil infiltration wasmeasured by stainingmyeloperoxidase (MPO) using IHC. Results: Intestinal RNA showed the expected WT MyD88 product of 405 bp (MyD88f/f), whereas a fragment length of 226 bp was found in MyD88IEC-/mice. I/R-induced ileal injury was greater in GF mice vs. CVN mice (6+/-0.9vs2.8+/0.8,p<0.05). This finding suggests that bacteria play a protective role during I/R-induced injury. To link this effect to host innate signaling, we performed I/R in MyD88 deficient mice. No difference in histological damage was observed between genotypes after 60 min ischemia, but I/R-induced intestinal damage diminished in MyD88IEC-/compared to MyD88f/f control mice after 90min reperfusion (4.6+/-1.3vs10+/-1.7,p<0.05). This improvement was similar to the one observed in MyD88-/mice. Neutrophil infiltration per crypt/ villus significantly decreased in I/R-exposed MyD88IEC-/mice compared to MyD88f/f control mice (1.7+/-0.3vs4+/-0.3,p<0.05). In addition, Cxcl1 mRNA accumulation (foldincrease over healthy WT control) significantly decreased in I/R-exposed MyD88IEC-/mice compared to MyD88f/f control mice (205+/-130vs1372+/-538,p<0.05). In contrast Tnf mRNA expression was significantly upregulated in I/R-exposed MyD88IEC-/mice compared to MyD88f/f control mice (8.37+/-1.9-fold over WT,p<0.05) whereas the Il1b mRNA expression remained unchanged. Conclusion: Our data suggests that while bacteria protect against I/R-induced intestinal injury, this effect is independent of IEC-derived MyD88 signaling. In contrast, epithelial-derived MyD88 signaling contributes to intestinal damage and is associated with enhanced Cxcl1 expression and crypt neutrophil infiltration.