Changes in Different Melanocyte Populations During Hair Follicle Involution (Catagen)

The study demonstrated that different melanocyte populations in the hair follicle exhibited distinct patterns of apoptosis and survival during the catagen phase of the hair cycle. Using Trp2-LacZ transgenic mice, it was found that melanocytes in the outer root sheath expressed Bcl-2 and were TUNEL-negative, indicating survival, while pigment-producing melanocytes above the follicular papilla expressed Fas and TUNEL, suggesting apoptosis. Some melanocytes in the follicular papilla expressed c-kit and Bcl-2, indicating survival. During late catagen, non-proliferating melanocytes expressing Bcl-2 were observed in the secondary germ, suggesting repopulation from the outer root sheath or follicular papilla. These findings provided insights into the remodeling of the follicular pigmentary unit during the hair cycle and could inform in vivo models for pharmacological modulation of melanocyte apoptosis and survival.