Pigmentation is an important process in skin physiology and skin diseases and presumably also plays a role in Parkinson's disease (PD). In PD, alpha-Synuclein (aSyn) has been shown to be involved in the pigmentation of neurons. The presynaptic protein is intensively investigated for its pathological role in PD, but its physiological function remains unknown. We hypothesized that aSyn is both involved in melanocytic differentiation and melanosome trafficking processes. We detected a strong expression of aSyn in human epidermal melanocytes (NHEMs) and observed its regulation in melanocytic differentiation via the microphthalmia-associated transcription factor (MITF), a central regulator of differentiation. Moreover, we investigated its role in pigmentation by performing siRNA experiments but found no effect on the total melanin content. We discovered a localization of aSyn to melanosomes, and further analysis of aSyn knockdown revealed an important role in melanocytic morphology and a reduction in melanosome release. Additionally, we found a reduction of transferred melanosomes in co-culture experiments of melanocytes and keratinocytes but no complete inhibition of melanosome transmission. In summary, this study highlights a novel physiological role of aSyn in melanocytic morphology and its so far unknown function in the pigment secretion in melanocytes.
Keywords: alpha-Synuclein; melanocytes; melanosomes; pigment transport; pigmentation.