C. M. Courtney1,2, L. K. Barron1,2, E. J. Onufer1,2, J. Guo1, B. W. Warner1,2 1Washington University,Pediatric Surgery,St. Louis, MO, USA 2St Louis Children’s Hospital,Pediatric Surgery,St Louis, MO, USA
Introduction: Toll-like receptor 4 (TLR4) signaling plays a crucial role in inflammatory cytokine responses and the metabolic consequences of massive small bowel resection (SBR). Our laboratory has pioneered a murine model that demonstrates altered body composition, impaired glucose tolerance, and hepatic steatosis after 50% SBR. Interestingly global TLR-4 knockout mice do not develop this metabolic phenotype after SBR. While the role of hepatic TLR4 has been studied in unoperated mice with similar phenotypes, the role of intestinal epithelial TLR4 is presently unknown. Our aim was to determine if a direct relationship exists between intestinal TLR4 expression and the novel resection associated metabolic phenotype.
Methods: Wild type (WT) and intestinal TLR4 knock out (iTLR4-KO) mice underwent 50% proximal small bowel resection and were maintained on standard liquid diet for 10 weeks. Weights were obtained weekly. At 10 weeks, mice were fasted overnight and glucose tolerance testing (GTT) was performed. Body composition was analyzed via echo magnetic resonance. At the time of sacrifice, liver was fixed in formalin, embedded paraffin and stained with hematoxylin and eosin. Slides were analyzed at 40x magnification (5 random fields/animal) using NIS Elements V4.3 software. Lipid area was calculated as measured lipid/ total parenchymal area. Body weights and glucose tolerance were compared using 2-way repeated measures ANOVA. Fasting blood glucose, body composition, and hepatic steatosis were compared using student’s t-test.
Results: When compared to wild type (WT) mice, iTLR4-KO mice demonstrated similar weight loss and recovery after SBR. Body composition between the groups was also similar at 10 weeks after operation with WT mice demonstrating 15% ± 0.02 fat mass and 84% ± 0.02 lean mass and iTLR4-KO mice with 17% ± 0.002 fat mass and 82% ± 0.002 lean mass (n=4 WT, n=8 iTLR4-KO). When comparing fasting blood glucose (FBG), the groups are not significantly different with WT FBG measuring 121.8 ± 9.077 (n=4) and iTLR4-KO FBG measuring 108.1 ± 5.894 (n=7). After 2mg/g intraperitoneal glucose load, iTLR4-KO glucose tolerance was not significantly different from WT mice (Figure 1A). Additionally, hepatic steatosis was not significantly different between the groups at 10 weeks post operatively (Figure 1B).
Conclusion: Specifically knocking out intestinal TLR 4 does not appear to alter the metabolic phenotype follow SBR. Future studies isolating other locations of TLR4 signaling are needed to help gain an understanding of the link between massive loss of small bowel and the resulting metabolic syndrome.
