Role of the ACTH/MC2R System in the Hair Cycle in Mice

Adrenocorticotropin hormone (ACTH), which is secreted in response to psychological stress, plays an important role in the hair cycle. This study examined the mechanism by which ACTH affects the hair cycle using mice deficient in melanocortin receptor-2(MC2R-/-), which is a main receptor for ACTH. We observed the hair cycle using female MC2R-/- mice at 15 weeks old and five days old to determine whether there were any age-dependent differences. The 15-week-old MC2R-/- mice showed the anagen phase for all mice. On the other hand, all of the MC2R+/+ mice showed the telogen phase at the same age. Moreover, in the five-day-old mice, the hair growth of the MC2R-/- mice occurred earlier than in the MC2R+/+ mice. Both the 15-week-old and five-day-old MC2R-/- mice had higher levels of ACTH and alpha-melanocyte stimulating hormone in the blood than did the MC2R+/+ mice. In addition, in the 15-week-old MC2R-/- mice, the hair cycle shifted to the telogen phase following the administration of a cyclic guanosine monophosphate (cGMP) inhibitor and MC1R/MC5R inhibitor. In the five-day-old MC2R-/- mice, the hair growth was slowed by the administration of corticosterone. These results suggest that the ACTH/MC2R system has an important role in the hair cycle.