Tyrosinase expression and its relationship to eumelanin and phaeomelanin synthesis in human hair follicles.

Tyrosinase expression was examined in hair follicles from twenty three red- and dark-haired individuals. Tyrosinase activity was greater in the hair follicles of red-haired subjects than in those from dark-haired subjects. Tyrosinase synthesis was also greater in the red-haired subjects and this presumably accounted for their higher levels of tyrosinase activity. The levels of tyrosinase synthesis in the red-haired subjects correlated well with the phaeomelanin content in the hair but in the dark-haired individuals a better correlation was seen with eumelanin. alpha-Melanocyte stimulating hormone failed to increase tyrosinase synthesis in the hair follicles of either group of subjects and in the follicles from the redheads actually produced a decrease. 8-Bromo-cyclic AMP, on the other hand, increased tyrosinase synthesis but only in the hair follicles from dark-haired subjects. These findings contrast with those previously reported in mice and it would appear that the control mechanisms that regulate tyrosinase in human melanocytes are different in many respects from those in mice.