Paracrine regulation of melanogenesis

Summary

Melanocytes are generally characterized by the basic ability of melanin synthesis and transfer to adjacent keratinocytes to constitute individual skin phenotype and provide epidermal protection from various stimuli, such as ultraviolet (UV) irradiation, through a complex process called melanogenesis, which can be regulated by autocrine or paracrine factors. Recent evidences have revealed the paracrine effects of keratinocytes on melanogenesis by secreting cytokines, including alpha-melanocyte stimulating hormone (α-MSH) and endothelin-1. In addition to keratinocytes, there are other types of cells in the skin, such as fibroblasts and immune cells that are also actively involved in the regulation of melanocyte behavior through the production of paracrine factors. In addition, extracellular matrix (ECM) proteins, which are mainly secreted by skin resident cells, not only play direct roles in regulating melanocyte morphology and functions but also provide structural support between the epidermis and dermis to control the distribution of various secreted cytokines from keratinocytes and/or fibroblasts, which are potentially involved in the regulation of melanogenesis. Moreover, with respect to the origin of melanocytes (neural crest cells) and the presence of nerve endings in the epidermis, it is considerable to reveal the intimate contact between melanocytes and cutaneous specific nervous system-proteins. Melanocytes are associated with all these networks with corresponding receptors expressed on the cell surface. In this review, we provide an overview of recent advances in the intimate relationships between melanocytes and their surrounding elements, which provide insights into the complex nature of the regulation of melanogenesis.

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