Abstract:

Objective To analyze the relationship of melanocyte ultrastructure and expression of microphthalmia-associated transcription factor （MITF） as well as tyrosinase-related proteins （TRP） transcriptionally modulated by MITF to clinical types and duration of vitiligo. Methods Epidermal sheets were taken by suction blisters respectively from lesional, perilesional, and normal skin of 12 patients with vitiligo vulgaris （VV） and 8 with segmental vitiligo （SV）. The duration of vitiligo varied from 3 to 300 months in these patients. Transmission electron microscopy was performed in 10 patients with vitiligo, including 6 cases of VV and 4 cases of SV. Epidermal melanocytes from normal skin of 20 patients were subjected to culture followed by Western blot to detect the expression level of MITF and some molecules transcriptionally modulated by MITF, including tyrosinase （TYR）, TYR-related protein-1 （TYRP1）, and TYR-related protein-2 （TYRP2） in cultured melanocytes. Results Epidermal melanocytes were absent in lesional skin of 7 out of 10 patients observed for ultrastructural alterations, whereas melanocytes with reduced or absent melanin （melanosome） could accidently be seen in lesional skin of 1 patient with short-standing vitiligo and 2 patients with long-standing vitiligo. In perilesional skin, abnormal ultrastructure of melanocytes was found in 3 with a duration of vitiligo less than 15 months among 6 patients with VV, and in 1 out of 4 patients with SV. The down-regulated expression of MITF was consistent with that of TYR, TYRP1 and TYRP2 in cultured epidermal melanocytes from normal skin of patients with VV; in those from patients with SV, the down-regulated expression was observed only in MITF, while the expressions of TYR, TYRP1 and TYRP2 were nearly normal. Conclusion Differences may exist between VV and SV in the ultrastructure as well as mechanisms of transcriptional modulation by MITF in epidermal melanocytes.

Key words: vitiligo, melanocytes, melanosome, microphthalmia-associated transcription factor