Melanosome transfer to and translocation in the keratinocyte

Abstract

Complexion coloration in humans is primarily regulated by the amount and type of melanin synthesized by the epidermal melanocyte. However, additional and equally contributing factors consist of (1) efficient transfer of melanin from the melanocytes to the neighboring keratinocytes and (2) distribution and degradation of the transferred melanosomes by the recipient keratinocytes. Once synthesized in the cell body of the epidermal melanocyte, pigmented melanosomes are translocated down the dendrites and captured at the dendritic tips via various cytoskeletal elements. Molecules recently identified that participate in this process consist of Rab27a, myosin-Va and melanophilin. Eventually, these peripherally localized melanosomes are transferred to keratinocytes by a presently undefined mechanism. The protease-activated receptor-2 (PAR-2) and unidentified surface lectins and glycoproteins facilitate this transfer process. Once incorporated into the keratinocytes, melanosomes are distributed individually or as clusters, aggregated towards the apical pole of the nucleus, and degraded as the keratinocytes undergo terminal differentiation and desquamation. Ultraviolet irradiation (UVR) can modulate the process of melanosome transfer from the melanocytes to the keratinocytes. UVR can upregulate expression of PAR-2 and lectin-binding receptors and increase phagocytic activity of cultured keratinocytes. Therefore, many cellular and molecular events that occur after melanogenesis contribute to skin color.

Fisiopatologia do melasma

“…Tem sido sugerido que o pigmento, no interior destas células atua, também, como varredor de radicais livres fotoproduzidos, sempre no sentido de proteger o DNA celular. 12,22,23 As propriedades de fotoproteção da melanina, na pele humana, têm sido bem documentadas e ocorrem pela absorção e dispersão, tanto da luz ultravioleta quanto da luz visível. Essa absorção aumenta linearmente na faixa de 720-620 nm e então, exponencialmente, através de ondas mais curtas (300-600 nm).…”

Differentiation-inducing activity of lupane triterpenes on a mouse melanoma cell line

“…In response to hormones and UV irradiation, melanin pigments are synthesized in melanosomes, which are transferred from the tips of melanocyte dendrites to the surrounding keratinocytes to protect against UV damage or carcinogenic effects (Boissy 2003;Okazaki et al 1976;Seiberg 2001). Studies have demonstrated that the dendritic outgrowth of melanocyte/melanoma cells is promoted by UV irradiation, cAMP-elevating agents and growth factors, as well as by the induction of melanogenesis; therefore, dendrites are recognized as a morphological indicator of melanocyte/melanoma cell differentiation (Hara et al 1995;Yoshida et al 2000).…”

[6]-Shogaol inhibits melanogenesis in B16 mouse melanoma cells through activation of the ERK pathway

“…Melanin is synthesized in melanosomes, and transferred from melanocytes to keratinocytes [1] . Melanin production is mainly controlled by the expression and activity of tyrosinase, which is known to be the most essential enzyme involved in melanin synthesis.…”