IGF1R Signaling Acts on the Anagen-to-Catagen Transition in the Hair Cycle

The study investigated the role of the Igf1 receptor (Igf1r) in hair follicle biology by using a conditional and inducible knockout in keratin 15-expressing bulge cells. In K15-Igf1r knockout (KO) mice, the deletion of Igf1r did not affect epidermal homeostasis or wound healing in young mice, although it resulted in a reduced number of bulge cells. These KO mice entered the anagen phase of the hair cycle earlier and experienced a delay in transitioning from anagen to catagen compared to controls. Additionally, Bmp-4 mRNA expression was inhibited, and MED1 transcription was impaired in the epidermis of K15-Igf1r KO mice. The findings suggested that Igf1r played a role in controlling the hair cycle, partly through the activation of Bmp-4.