Behavioral differences between donor site-matched adult and neonatal melanocytes in culture

Little is known about the biologic behaviors of cultured melanocytes in relation to donor age. To investigate age-dependent differences, neonatal and adult melanocytes were isolated from the same anatomical site, the foreskin, and cultured in the same growth medium supplemented with cAMP inducers (choleratoxin and 3-isobutyl-methylxanthine). The morphology, melanin content, pattern of melanosome distribution, and growth rate were then compared. Neonatal melanocytes were bipolar in appearance, whereas adult melanocytes were highly dendritic in appearance. Image analysis showed that adult melanocytes were larger and longer, and had a greater number of dendrites than neonatal melanocytes. When the growth medium was replaced by a medium without cAMP inducers, adult melanocytes showed a change in their morphology from dendritic to spindle-shaped, while the morphology of neonatal melanocytes remained unchanged. Melanosomes of adult melanocytes were distributed singly along the dendrites, and extracellular secretion of melanosomes was also found. In contrast, melanosomes of neonatal melanocytes were aggregated near the nuclei. No age-dependent differences in melanin content and growth rate were noted in the donor site-matched cultured melanocytes. These results suggest that donor age is one of the factors involved in determining melanocyte dendricity and melanosome distribution, and that increased dendricity of adult melanocytes is due to increased sensitivity to cAMP inducers. In addition, the adult melanocytes established in our culture system, which resembled dendritic melanocytes in vivo, could be considered a desirable model for studying the mechanisms of adult-onset hyperpigmentary disorders and melanogenesis.