Deciphering the molecular morphology of the human hair cycle: Wnt signalling during the telogen–anagen transformation

Summary Background The signals that induce anagen (growth) in ‘quiescent’ human telogen hair follicles (HFs) are as yet unknown. Their identification promises better targeted therapeutic hair growth interventions. Objectives Recognizing the central role of Wnt signalling in hair biology, the aim was to delineate the differential expression of key agonists, antagonists and target genes of this pathway during the telogen‐to‐anagen transformation of human scalp HFs. Methods This differential expression was studied by in situ hybridization in human telogen and early‐anagen scalp HF sections. Results On anagen induction, gene expression of the Wnt ligands WNT3, WNT4 and WNT10B, the Wnt ligand secretion regulator WLS, and the Wnt target genes AXIN2 and LEF1, is significantly increased within the secondary hair germ and the dermal papilla. Conversely, expression of the secreted Wnt inhibitor SFRP1 (secreted frizzled‐related protein 1) is reduced. Human epithelial HF stem cells upregulate WNT4 and WNT10A expression, suggesting that these Wnt agonists are important for stem cell activation. Conclusions We provide the first evidence that key changes in Wnt signalling that drive murine anagen induction also occur in human scalp HFs, yet with notable differences. This provides a rational basis for Wnt‐targeting therapeutic interventions to manipulate human hair growth disorders. What's already known about this topic? Upregulation of Wnt agonists and downregulation of Wnt antagonists in the secondary hair germ and/or dermal papilla drives hair growth (anagen) induction in mice. Autocrine Wnt signalling in murine epithelial hair follicle stem cells is required to maintain their stem cell function. Reduction of Wnt ligands or increased expression of Wnt antagonists induces dysregulation of the murine hair follicle cycle and causes alopecia. What does this study add? This study demonstrates for the first time that key Wnt pathway regulatory agonists, antagonists and target genes, are expressed in the human telogen‐to‐early‐anagen transformation. On human anagen induction the Wnt ligands WNT3, WNT4 and WNT10B are increased in the regenerating epithelium, whereas the Wnt antagonist, SFRP1 (secreted frizzled‐related protein 1), is reduced. Human anagen induction has fundamental differences in the expression of Wnt ligands compared with the murine system. What is the translational message? Regulation of these Wnt ligands permits targeted therapeutic interventions in human hai