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Both Epidermal Growth Factor and Insulin-like Growth Factor Receptors Are Dispensable for Structural Adaptation after Massive Small Bowel Resection

Saturday, October 11, 2014: 7:45 AM
Marriott Hall 3 (San Diego Marriott Marquis )
Raphael C. Sun, MD, Jose L. Diaz-Miron, MD, Pamela Choi, MD, Joshua Sommovilla, MD, Jun Guo, PhD, Christopher R. Erwin, PhD and Brad W. Warner, MD, Washington University School of Medicine, St. Louis Children's Hospital, St. Louis, MO

Purpose

Intestinal adaptation represents structural increases in crypt depth and villus height resulting in increased mucosal surface area in response to massive small bowel resection (SBR).  Epidermal growth factor (EGF) and insulin-like growth factor 2 (IGF2) are regarded to be intestinotrophic and function through EGFR and IGF1R receptors, respectively.  Previously, we found that neither EGFR nor IGF1R were individually required for normal adaptation.  Since the effects of missing one receptor may be overcome by compensatory function of the other, we sought to determine the effect of deleting both EGFR and IGF1R on adaptive responses to massive SBR.

Methods

 

Intestine specific EGFR and IGF1R double knockout mice (EGFR-IKO and IGF1R-IKO) (n=6) were generated by using a tamoxifen inducible Villin-Cre (VC-ER) system.  Both VC-ER (+)and VC-ER(-); EGFR (flox/flox); IGF1R (flox/flox) mice were injected with tamoxifen for 3 days.  VC-ER(-); EGFR(flox/flox); IGF1R (flox/flox) mice were used as the wild-type (WT) control group (n=7).  Both groups underwent 50% proximal SBR. On post-operative day 7, structural adaptation was scored by measuring crypt depth and villus height.  Post-operative rates of enterocyte proliferation were measured as # of p-histone 3 stained crypt cells per 20 crypts.  Post-operative apoptosis index was scored by counting the number of apoptotic bodies per 50 crypts.  Post-operative angiogenesis was calculated by counting CD31 stained vessels per high power field within the submucosa.  Student's t-test was used for statistical comparisons between groups with p<0.05 defined as significant. <> 

Results

 

Successful deletion of EGFR and IGF1R protein in enterocytes was confirmed by Western blotting.  Baseline crypt depth (p-value=0.737) and villus height (p-value 0.912) were not affected by double deletion of EGFR and IGF1R. After 50% SBR, normal adaptation occurred in both WT and double knockout (KO) mice based on percent increases in crypt depth and villus height (Figure 1).  Similarly, rates of proliferation and apoptosis were no different between WT and KO mice (Table 1). However, adaptive angiogenesis after SBR was significantly less in the KO mice with p<0.05. (Table 1)

 

Conclusion

 

Disrupted expression of EGFR and IGF1R in the intestine does not affect resection-induced structural adaptation after SBR but may affect angiogenesis.  These findings suggest that villus growth is driven by receptors and pathways that occur outside the epithelial cell component in the small bowel while angiogenesis may involve epithelial-endothelial crosstalk.

Figure 1. Percent increase of crypt depth and villus height in both WT and KO group showed no significant differences. 

 

Wild type

KO

p-value

Rate of proliferation

0.154

 

0.161

 

0.492

Apoptosis index

0.034

0.03

0.590

Angiogenesis

9.06

 

7.42

0.0001

Table 1: EGFR and IGF1R do not affect enterocyte proliferation and apoptosis in adaptationPost-operative angiogenesis was significantly less in the KO mice.

 

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