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Intestine-Specific Deletion of P38α Mapk Perturbs Enterocyte Kinetics Following Massive Small Bowel Resection
Derek Wakeman*, Jennifer a. Leinicke, Mark E. Mcmellen, Jun Guo, Christopher R. Erwin, Brad W. Warner
Surgery, Division of Pediatric Surgery, Washington University School of Medicine, Saint Louis, MO

Introduction: Intestinal adaptation after massive small bowel resection (SBR) is characterized by enhanced crypt cell proliferation and apoptosis. Both of these responses are modulated by epidermal growth factor receptor (EGFR) signaling. We have demonstrated in vitro that p38α MAPK is required for apoptosis mediated by EGFR inhibition. The purpose of this study was to determine the effect of in vivo deletion of p38α expression on intestinal adaptation after SBR. Specifically, we tested the hypothesis that resection-induced enterocyte apoptosis would be altered by p38α MAPK deletion.Methods: Inducible, intestine-specific p38α MAPK-null mice (Ip38-null) were created by crossing mice with a tamoxifen-inducible-Cre-fusion protein under control of the villin promoter with mice in which the floxed p38α MAPK gene had been tagged for recombination. Tamoxifen was injected intraperitoneally at a dose of 0.5mg/day for 2 days. Seven days after first injection Ip38-null mice underwent either 50% SBR (n=10) or sham operation (n=9). Wild-type littermate controls (n=7) were also injected with tamoxifen and subjected to 50% SBR. Mice were sacrificed after 3 days and the remnant bowel was harvested for analysis. Crypt depth, villus length, crypt cell proliferative and apoptotic rates were measured.Results: Western blot analysis confirmed that Ip38-null mice had a >90% reduction in p38α MAPK protein levels. After 50% SBR Ip38-null mice exhibited significant adaptive increases in crypt depth, villus length, proliferation, and apoptosis relative to shams. After SBR crypt and villus elongation in the Ip38-null mice were comparable to the adaptive changes in the wild-type controls. However, after SBR the Ip38-null mice had slightly increased rates of crypt proliferation relative to wild-type controls (17.3 +/- 0.8 vs. 15.2 +/- 0.8 BrdU labeled cells/crypt, p=.09). In addition, Ip38-null mice had lower apoptotic rates in the crypt compartment compared to wild-type controls after SBR (6.85 +/- 0.6 vs. 10.9 +/- 0.8 apoptotic bodies/100 crypts, p<.005).Conclusions: Deleting p38α MAPK in an inducible, intestine-specific manner does not impair intestinal adaptation in mice. However, loss of p38α MAPK does partially block the increase in crypt apoptosis normally seen after SBR. These findings support an important role for p38α MAPK in the kinetics of enterocyte turnover after small bowel resection.

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