Conditional Ablation of JAK-STAT5 Signaling Induces Anagen Hair Growth

The study investigated the role of JAK-STAT5 signaling in hair follicle stem cells (HFSCs) and its effect on hair growth. Researchers used STAT5 floxed mice with inducible CreER drivers targeting the hair follicle to conditionally ablate STAT5 expression. They found that systemic tamoxifen treatment during mid-telogen phase was sufficient to knock out STAT5 in the epidermal compartment. This led to the initiation of hair growth in the shaved telogen skin of the genetically modified mice after 3 weeks, while no such effect was observed in wild-type littermates. The new hair growth was uniform across the dorsum of the mice, contrasting with the patchy pattern seen in wild-type mice. Immunofluorescence studies showed that phosphorylated STAT5 (pSTAT5) was localized to the bulge region of the hair follicle during telogen, peaking at mid-telogen and disappearing during the transition to anagen phase. These results provide genetic evidence supporting previous work that showed induction of anagen hair growth using small molecule JAK inhibitors.