Increased sensitivity of melanocytes to oxidative stress and abnormal expression of tyrosinase-related protein in vitiligo

Background Vitiligo is a depigmenting disease of the skin, which may derive from programmed melanocyte death or destruction due to inherent sensitivit y to oxidative stress arising from either toxic intermediates of melanin, a melanocyte-specific protein, or other sources. Tyrosinase-related protein (TRP) -1 has been shown to be involved not only in melanin biosynthesis but also in the prevention of premature melanocyte death in animals. Objectives To clarify the biological role of human TRP-1 in melanocyte surv ival. Methods Cultured melanocyte strains from an active advancing border of viti ligo were established and studied. Results The established 'vitiligo melanocytes' showed large perikaryon and stubby dendrites. They showed early cell death when exposed to oxidative st ress (ultraviolet B) and increased and abnormal immunostaining and immunopr ecipitation by antibodies against human and mouse TRP-1, indicating an alte red synthesis and processing of TRP-1. In pulse-chase and sequential immuno precipitation experiments, vitiligo melanocytes revealed abnormal protein-p rotein interaction with calnexin, a melanogenesis-associated chaperone, sug gesting altered folding and maturation of nascent TRP-1 polypeptides. North ern blot analysis indicated a decreased expression of TRP-1 mRNA, but heter oduplex analysis and verification of the mutation at the carboxy terminus o f TRP-1 by restriction enzyme analysis did not show any abnormality. Conclusions Our study suggests that the early cell death of vitiligo melano cytes is related to their increased sensitivity to oxidative stress, which may arise from complex processes of abnormal synthesis and processing of TR P-1 and its interaction with calnexin.