Duarte Barral, PhD
Associate Professor Chronic Diseases Research Center (CEDOC)
NOVA Medical School
Universidade NOVA de LisboaShort CV
Skin color is determined by the pigment melanin, which protects skin cells against ultra-violet radiation (UVr). Melanin is produced and stored in specialized organelles termed melanosomes, within melanocytes and then transferred to keratinocytes, where it exerts its photoprotective effect against UVr-induced damage, photo-aging and skin cancer. Therefore, skin pigmentation relies on the crosstalk between melanocytes, the pigment producers and keratinocytes, the pigment recipients. Melanosomes share several features with lysosomes, like low pH, the presence of lysosomal membrane proteins and catalytic enzymes, and are thus considered lysosome-related organelles. Melanosome biogenesis is initiated at the perinuclear region, whereas mature melanosomes accumulate at the tips of melanocyte dendrites. Once there, melanosomes are secreted from melanocytes and transferred to keratinocytes. The evidence collected by us over recent years strongly suggests that the predominant form of melanin transfer is via coupled exo/phagocytosis, where melanocytes exocytose the melanin core, or melanocore in a process dependent on the small GTPase Rab11b and the exocyst tethering complex. Moreover, we found that melanocore internalization by keratinocytes occurs through phagocytosis in a Protease-activated receptor (PAR)-2-dependent manner. Furthermore, we and others reported that upon internalization by keratinocytes, melanocores accumulate in moderately acidic and degradative compartments, which can explain why melanin is long-lived within these cells. In this seminar, I will also present recent unpublished data on the role of lysosomes and autophagy in melanin processing within keratinocytes.