Epithelial hedgehog signals pattern the intestinal crypt-villus axis.

Area of Science:

• Developmental biology
• Gastroenterology
• Molecular biology

Background:

• Small intestinal development involves complex epithelial and mesenchymal interactions.
• Hedgehog (Hh) signaling pathways, including Sonic (Shh) and Indian (Ihh) hedgehog, play roles in intestinal morphogenesis.
• The precise role of combined Hh signaling in neonatal intestinal development requires further elucidation.

Purpose of the Study:

• To investigate the combined function of Sonic (Shh) and Indian (Ihh) hedgehog signaling in small intestinal morphogenesis.
• To determine the impact of inhibiting hedgehog (Hh) signaling on epithelial remodeling and villus formation.
• To explore the consequences of altered Hh signaling on mesenchymal cell populations and their influence on epithelial patterning.

Main Methods:

• Generation of transgenic mice expressing the pan-hedgehog inhibitor, hedgehog interacting protein (Hhip), in the intestinal epithelium.
• Analysis of intestinal morphology, villus formation, and crypt-villus axis development in Hhip-expressing mice.
• Assessment of mesenchymal cell populations, including subepithelial myofibroblasts (ISEMFs) and smooth muscle cells (SMCs), and their spatial organization.
• Evaluation of epithelial cell proliferation and gene expression patterns, specifically Tcf4/beta-catenin target genes.

Main Results:

• Epithelial hedgehog (Hh) signaling is paracrine, acting from the epithelium onto subepithelial myofibroblasts (ISEMFs) and smooth muscle cells (SMCs).
• Strong inhibition of Hh signaling severely compromises epithelial remodeling and villus formation.
• Even modest attenuation of Hh signaling leads to aberrant villus patterning, with expanded desmin-positive smooth muscle progenitors and mislocalized ISEMFs.
• Mesenchymal alterations secondary to Hh attenuation result in enhanced Tcf4/beta-catenin activity, increased proliferation, and ectopic precrypt formation on villus tips.

Conclusions:

• The epithelium utilizes a combined hedgehog (Hh) signal to pattern the crypt-villus axis by influencing underlying ISEMFs.
• This Hh-mediated crosstalk is essential for regulating the size and precise location of the developing precrypt compartment.
• Proper Hh signaling is critical for coordinating mesenchymal and epithelial development to ensure normal small intestinal morphogenesis.