Melanocyte distribution and function in human skin effects of ultraviolet radiation

Abstract

Catalytic entities involved in melanin synthesis (including tyrosinase [TYR], tyrosinase-related protein 1 [TYRP1], and dopachrome tautomerase [DCT]) and structural proteins important to the integrity of melanosomes (including GP100/Pmel17) play active roles in the maintenance of the function and structure of those organelles produced by melanocytes. Constitutive skin pigmentation is regulated by a number of distinct factors (including melanocyte dendricity, transport of melanosomes to dendrites, and transfer of melanosomes to keratinocytes and their subsequent distribution) and can be affected by paracrine factors (from neighboring keratinocytes and fibroblasts) and the environment, including ultraviolet (UV) radiation, that regulate melanocyte proliferation and function. Because UV is inherently associated with photocarcinogenesis in the skin, including melanoma, we discuss melanocyte density and function, melanin content and distribution, DNA damage (measured by 6,4-phytoproducts [64PP] and cyclobutane pyrimidine dimers [CPD]) and apoptosis (measured by terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling [TUNEL] staining) in response to UV in three different types of skin. In sum, UV-induced DNA damage in the lower epidermis is not effectively prevented in light/fair skin and UV-induced apoptosis is not seen in light skin after low doses of UV. These observations suggest that the combination of decreased DNA damage and more efficient removal of UV-damaged cells plays an important role in the decreased photocarcinogenesis seen in darker skin. © 2006 Humana Press Inc.