Bone Morphogenetic Protein Signaling Inhibits Hair Follicle Anagen Induction by Restricting Epithelial Stem/Progenitor Cell Activation and Expansion

The study demonstrated that Bone Morphogenetic Protein (BMP) signaling inhibited the induction of the anagen phase in hair follicles by restricting the activation and expansion of epithelial stem cells (EP-SCs) in the bulge region. The expression of Noggin, a BMP antagonist, was shown to release EP-SCs from this restriction, allowing for their activation and the initiation of the anagen phase. Conditional inactivation of the BMP type IA receptor (Bmpr1a) in EP-SCs led to an overproduction of hair follicle stem/progenitor cells and the formation of matricomas. This manipulation also unexpectedly activated beta-catenin, a key component of Wnt signaling. The study proposed that BMP activity controlled the hair follicle cycle by antagonizing Wnt/beta-catenin activity, partly through BMP-mediated enhancement of PTEN function, which inhibited beta-catenin activity via the phosphatidyl inositol 3-kinase-Akt pathway.