Effect of bowel resection on TLR signaling during intestinal adaptation in a rat model

Bacterial overgrowth is common complication of short bowel syndrome (SBS) and is a result of an impaired gut barrier function. Toll-like receptor 4 (TLR4) is crucial in maintaining intestinal epithelial homeostasis, participates in a vigorous signaling process and heightens inflammatory cytokine output. The objective of this study was to determine the effects of bowel resection on TLR4 signaling in intestinal mucosa in a rat model. Male Sprague-Dawley rats were randomly assigned to one of the two experimental groups of eight rats each: Sham rats underwent bowel transection and re-anastomosis and SBS rats underwent 75 % small bowel resection. Rats were killed on day 14. Bacterial translocation (BT) to mesenteric lymph nodes, liver, portal blood and peripheral blood was determined at the kill. The expression of TLR4, MyD88 and TRAF6 in the intestinal mucosa was determined using real-time PCR, Western blot and immunohistochemistry. SBS rats demonstrated a 100 % BT to lymph nodes and to liver (Level I), 80 % translocation to portal blood (Level II) and 60 % translocation to peripheral blood (Level III) at day 7 as well as a 100 % BT to lymph nodes and liver, and 40 % translocation to peripheral blood at day 14. Microarray expression profiling demonstrated that most of the TLR signaling-related genes were up-regulated in resected rats compared to control animals. SBS rats showed a significant increase in TLR4 and TRAF6 mRNA in jejunum and ileum, TLR4 and MyD88 protein expression in jejunum and ileum, and a significant increase in the number of TLR4 and TRAF6 positive cells (immunohistochemistry) compared to sham animals. In a rat model of SBS, elevated intestinal BT is associated with a stimulated TLR4 signaling.