Sonic Hedgehog Signaling in the Regulation of Barrier Tissue Homeostasis and Inflammation

The document reviewed the role of Sonic Hedgehog (Shh) signalling in maintaining barrier tissue homeostasis and regulating inflammation, particularly in the skin and lungs. Shh was crucial for skin development, hair follicle formation, and dermal papilla maturation, and it maintained homeostasis in adult skin, necessary for hair growth and skin regeneration. Aberrant activation of the Hedgehog pathway could lead to skin cancer. Shh was upregulated in response to skin injury, promoting keratinocyte proliferation, wound repair, and hair regeneration by activating hair follicle stem cells. In the skin, Shh reduced atopic dermatitis by increasing regulatory T-cells and their immunosuppressive function, protecting against inflammation. In the lungs, Shh was crucial for development and repair but was associated with chronic inflammatory diseases like asthma. The study highlighted Shh's dual role in barrier tissues, emphasizing its protective effects against inflammation in the skin and its promotion of atopic disease in the lungs, suggesting further research into its tissue-dependent mechanisms.