After massive small bowel resection (SBR), the remaining intestine compensates by a critical process termed adaptation, which includes increases in enterocyte proliferation, villus height, bowel caliber and length. Perhaps to counterbalance this mitogenic response, increased rates of enterocyte apoptosis are also observed. Preliminary studies suggest that increased expression of the pro-apoptosis factor bax and reduced expression of the prosurvival factor bcl-w are involved in the regulation of postresection apoptosis. Epidermal growth factor (EGF) enhances adaptation by increasing enterocyte proliferation. While its significance is not known, EGF also inhibits postresection enterocyte apoptosis. This project will test that overall hypothesis that EGF enhances intestinal adaptation after massive small bowel resection by inhibiting enterocyte apoptosis. The long-term goal of this project is to optimize therapy for patients with the short bowel syndrome by delineating the significance of enterocyte apoptosis during intestinal adaptation.
Our specific aims are: 1) Determine the effect of EGF receptor stimulation and inhibition on bax and bcl-w gene expression and apoptosis during adaptation. To test the hypothesis that EGF receptor signaling regulates the expression of bax and bcl-w to direct enterocyte apoptosis during adaptation, laser capture microdissection (LCM) microscopy will be used to establish a temporal and regional, enterocyte-specific expression of bax and bcl-w mRNA and protein along the crypt- villus axis after SBR. The expression of bax and bcl-w in enterocytes will then be determined in LCM extracted enterocytes after SBR during conditions of EGF receptor stimulation and inhibition. 2) Determine the mechanism for reduced enterocyte apoptosis by EGF. To test the hypothesis that bax and bcl-w are required for the regulation of postresection apoptosis by EGF, SBR or sham operations will be performed in bax and bcl-w knockout mice. Crossbreeding experiments will permit direct testing of the effect of absent bax or bcl-w expression during conditions of EGF receptor-directed amplified or impaired adaptation. 3) Determine the mechanism for Bax and Bcl-w expression by EGFR signal transduction. We will develop an in vitro model system using intestinal epithelial cells to test relevant EGFR signal transduction pathways for the activation of bax and bcl-w expression. These studies will substantially contribute toward an enhanced understanding of the genetic regulation of adaptation and the relevance of apoptosis to this process. This information is vital for the future development of safe and effective clinical therapy designed to amplify this important compensatory response in patients suffering massive intestinal loss.
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