Skin pigmentation is a complex process; melanocytes produce melanin and package it into melanosomes that are in turn exocytosed into the surrounding extracellular matrix and adjacent cells. Numerous genes play a role in controlling pigmentation at various levels of melanin production. Mutations in these genes are characteristic of multiple skin disorders, including hyperpigmentation, hypopigmentation, and mixed hyper/hypopigmentation. Additionally, extrinsic factors secreted by the surrounding resident cell types also regulate the melanin expression in adult melanocytes. Human primary cells can be a useful model for elucidating melanocyte biology. However, primary cells have their limitations such as donor variability, a limited lifespan and loss of melanin. Therefore, there is a need for a more robust human cell model system for studying skin pigmentation.
In this study, we immortalized primary dermal melanocytes by expressing human telomerase reverse transcriptase (hTERT) in cells that were isolated from an adult donor. The immortalized primary melanocytes were cultured continuously for more than 40 population doublings without any signs of replicative senescence, yet retaining melanin production. The immortalized primary melanocytes maintained a consistent expression of the melanocyte-specific marker TYRP-1, and lacked expression of the fibroblast-specific marker TE7. In addition, we demonstrate the ability to modulate melanogenesis with specific stimulators and inhibitors and the capacity of immortalized melanocytes to incorporate into a functional 3D organotypic skin culture. Taken together, the hTERT-immortalized primary melanocytes described here provide a versatile in vitro cell model for studying melanin production and melanocyte:keratinocyte interactions in the dermal environment.