Stromal Indian Hedgehog Signaling Is Required for Intestinal Adenoma Formation in Mice.

Background & Aims Indian hedgehog (IHH) is an epithelial-derived signal in the intestinal stroma, inducing factors that restrict epithelial proliferation and suppress activation of the immune system. In addition to these rapid effects of IHH signaling, IHH is required to maintain a stromal phenotype in which myofibroblasts and smooth muscle cells predominate. We investigated the role of IHH signaling during development of intestinal neoplasia in mice. Methods Glioma-associated oncogene ( Gli1 ) -CreERT2 and Patched ( Ptch )- lacZ reporter mice were crossed with Apc Min mice to generate Gli1CreERT2-Rosa26-ZSGreen-Apc Min and Ptch-lacZ-Apc Min mice, which were used to identify hedgehog-responsive cells. Cyp1a1Cre-Apc ( Apc HET ) mice, which develop adenomas after administration of β-naphthoflavone, were crossed with mice with conditional disruption of Ihh in the small intestine epithelium. Apc Min mice were crossed with mice in which sonic hedgehog (SHH) was overexpressed specifically in the intestinal epithelium. Intestinal tissues were collected and analyzed histologically and by immunohistochemistry and quantitative reverse-transcription polymerase chain reaction. We also analyzed levels of IHH messenger RNA and expression of IHH gene targets in intestinal tissues from patients with familial adenomatous polyposis (n = 18) or sessile serrated adenomas (n = 15) and normal colonic tissue from control patients (n = 12). Results Expression of IHH messenger RNA and its targets were increased in intestinal adenomas from patients and mice compared with control colon tissues. In mice, IHH signaling was exclusively paracrine, from the epithelium to the stroma. Loss of IHH from Apc HET mice almost completely blocked adenoma development, and overexpression of SHH increased the number and size of adenomas that developed. Loss of IHH from Apc HET mice changed the composition of the adenoma stroma; cells that expressed α-smooth muscle actin or desmin were lost, along with expression of cyclooxygenase-2, and the number of vimentin-positive cells increased. Conclusions Apc mutant epithelial cells secrete IHH to maintain an intestinal stromal phenotype that is required for adenoma development in mice. [ABSTRACT FROM AUTHOR]