Gastroenterology

Gastroenterology

Volume 139, Issue 5, November 2010, Pages 1665-1676.e10
Gastroenterology

Basic—Alimentary Tract
Loss of Indian Hedgehog Activates Multiple Aspects of a Wound Healing Response in the Mouse Intestine

https://doi.org/10.1053/j.gastro.2010.07.045Get rights and content

Background & Aims

Indian Hedgehog (Ihh) is expressed by the differentiated epithelial cells of the small intestine and signals to the mesenchyme where it induces unidentified factors that negatively regulate intestinal epithelial precursor cell fate. Recently, genetic variants in the Hh pathway have been linked to the development of inflammatory bowel disease.

Methods

We deleted Ihh from the small intestinal epithelium in adult mice using Cyp1a1-CreIhhfl/fl conditional Ihh mutant mice. Intestines were examined by immunohistochemistry, in situ hybridization, and real-time polymerase chain reaction.

Results

Deletion of Ihh from the intestinal epithelium initially resulted in a proliferative response of the intestinal epithelium with lengthening and fissioning of crypts and increased Wnt signaling. The epithelial proliferative response was associated with loss of bone morphogenetic protein and Activin signaling from the epithelium of the villus and crypts, respectively. At the same stage we observed a substantial influx of fibroblasts and macrophages into the villus core with increased mesenchymal transforming growth factor-β signaling and deposition of extracellular matrix proteins. Prolonged loss of Ihh resulted in progressive leukocyte infiltration of the crypt area, blunting and loss of villi, and the development of intestinal fibrosis.

Conclusions

Loss of Ihh initiates several events that are characteristic of an intestinal wound repair response. Prolonged loss resulted in progressive inflammation, mucosal damage, and the development of intestinal fibrosis. Ihh is a signal derived from the superficial epithelial cells that may act as a critical indicator of epithelial integrity.

Section snippets

Materials and Methods

See the Supplementary Materials and Methods section for details.

Loss of Ihh Signaling in Adult β-Naphthoflavone–Injected Cyp1a1Cre-Ihhfl/fl Mice

We examined expression of Ihh messenger RNA (mRNA) (Figure 1A) and protein (Figure 1B) in the small intestine of the mouse. Both Ihh protein and mRNA were expressed exclusively by the differentiated epithelial cells on the villi. To examine the role of Ihh signaling in the adult small intestinal mucosa we injected adult Cyp1a1-Ihhfl/fl mice and Ihhfl/fl control mice with β-naphthoflavone. This resulted in substantially reduced expression of Ihh protein (Figure1B, right panel). Quantitative

Discussion

We find that loss of Ihh results in an epithelial response that is characteristic of epithelial wound repair and is associated with loss of both Bmp and Activin signaling in the epithelial cells. In addition to the epithelial remodeling we observed substantial recruitment of macrophages and fibroblasts, 2 critical mesenchymal cell types involved in wound repair, into the villus core. Unresolved loss of Ihh ultimately results in loss of smooth muscle cells, the establishment of a pericryptal

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    Conflicts of interest The authors disclose no conflicts.

    Funding The research leading to these results has received funding from the European Research Council under the European Community's Seventh Framework Program (FP7/2007-2013)/European Research Council grant agreement number 241344 and by a grant from the Dutch Digestive Foundation. Generation of floxed Ihh mice was funded by the National Institutes of Health (AR050560 to B.L.).

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