R. C. Sun1, J. Guo1, B. W. Warner1 1Washington University,Pediatric Surgery/General Surgery,St. Louis, MO, USA
Introduction: Mammalian target of rapamycin (mTOR) is a serine/threonine kinase that is important for intestinal stem cell renewal and maintaining mucosa structure. It is also essential for Wnt-driven intestinal tumor initiation and growth. Rapamycin can bind the mTORC1 complex resulting in inhibition of downstream signals and intestinal regeneration. Intestinal adaptation is a phenomenon that occurs after small bowel resection (SBR) with increased crypt depth and villus height which is believed to be driven by enhanced enterocyte proliferation. Our objective was to investigate whether mTOR signaling is necessary for small bowel adaptation after SBR.
Methods: Male C57/Bl6 mice,aged 8 weeks underwent a 50% proximal SBR. Postoperatively,mice were randomized to receive daily injections of rapamycin (n=8) or vehicle (n=7). On postoperative day 7,mice were harvested and intestine was collected for histology to measure structural adaptation by counting crypt depth and villus height. Rates of enterocyte proliferation were measured by counting the number of p-histone 3 stained cells per 20 crypts. Western blot confirmed rapamycin inhibition of mTOR signaling by probing for pS6. To see whether rapamycin affects the integrity of intestinal structure at baseline, rapamycin (n=4) and vehicle (n=5) were injected daily in two separate groups of non-operative mice. After 7 days,mice were harvested and histology and proliferation were compared. Student’s t-test was used to statistically compare groups with p<0.05 defined as significant.
Results:The degree of adaptation was diminished in the rapamycin treated group compared to controls after proximal 50% SBR (Figure). Similarly,rates of proliferation significantly dropped in rapamycin treated group compared to vehicle treated group (2.1±0.1 vs 4.5±0.3, p-value<0.01). Western blot showed a decrease in pS6 signaling which confirms mTOR signaling inhibition by rapamycin within the enterocytes. Daily injections of rapamycin in non-operated C57/Bl6 mice did not affect crypt depth (74.9±3.5µm vs 72.5±3.5µm,p-value=0.7) or villus height (219.8±9.9µm vs 215.9±8.0µm, p-value=0.8) when compared to vehicle injections.
Conclusion:mTorC1 pathway may play a critical role in intestinal adaptation post SBR. Rapamycin diminishes the degree of adaptation and enterocyte proliferation after SBR. However,rapamycin was given systemically in this study and tissue specific contribution of mTOR signaling in adaptation could not be determined. This is the first time mTor pathway has been studied in the context of resection-associated adaptation. Further studies will focus on the role of enterocyte specific mTOR signaling involved in intestinal adaptation.
