ABSTRACT
Melanocytes of the hair follicle produce melanin and are essential in determining the differences in hair color. Pigment cell-specific MELanocyte Protein (PMEL17) plays a crucial role in melanogenesis. One of the critical steps is the amyloid-like functional oligomerization of PMEL17. Beta Site APP Cleaving Enzyme-2 (BACE2) and γ-secretase have been shown to be key players in generating the proteolytic fragments of PMEL17. The ß-secretase (BACE1) is responsible for the generation of amyloid-ß (Aß) fragments in the brain and is therefore proposed as a therapeutic target for Alzheimer's disease (AD). Currently BACE1 inhibitors, most of which lack selectivity over BACE2, have demonstrated efficacious reduction of amyloid-ß peptides in animals and the CSF of humans. BACE2 knock-out mice have a deficiency in PMEL17 proteolytic processing leading to impaired melanin storage and hair depigmentation. Here, we confirm BACE2-mediated inhibition of PMEL17 proteolytic processing in vitro in mouse and human melanocytes. Furthermore, we show that wildtype as well as bace2(+/-) and bace2(-/-) mice treated with a potent dual BACE1/BACE2 inhibitor NB-360 display dose-dependent appearance of irreversibly depigmented hair. Retinal pigmented epithelium showed no morphological changes. Our data demonstrates that BACE2 as well as additional BACE1 inhibition affects melanosome maturation and induces hair depigmentation in mice.
Subject(s)
Amyloid Precursor Protein Secretases/metabolism , Aspartic Acid Endopeptidases/metabolism , Hair/metabolism , gp100 Melanoma Antigen/metabolism , Amyloid Precursor Protein Secretases/antagonists & inhibitors , Amyloid Precursor Protein Secretases/genetics , Amyloid beta-Peptides/metabolism , Animals , Aspartic Acid Endopeptidases/antagonists & inhibitors , Aspartic Acid Endopeptidases/genetics , Blotting, Western , Cell Line, Tumor , Female , Hair/drug effects , Hair/pathology , Humans , Male , Melanins/metabolism , Melanocytes/cytology , Melanocytes/metabolism , Mice , Mice, Inbred C57BL , Mice, Knockout , Microscopy, Fluorescence , Peptide Fragments/metabolism , Picolinic Acids/pharmacology , Pigmentation/drug effects , Prosencephalon/metabolism , Prosencephalon/pathology , Protease Inhibitors/pharmacology , RNA, Messenger/metabolism , Real-Time Polymerase Chain Reaction , Thiazines/pharmacology , Uvea/drug effects , Uvea/metabolism , Uvea/pathology , gp100 Melanoma Antigen/antagonists & inhibitorsABSTRACT
Tyrosinase is the rate-limiting enzyme in the melanogenesis process. It remains the most efficient way to downregulate melanin production and improve unsightly pigmentary disorders. The aim of our investigations was to find a structurally characterized molecule with better efficacy than existing molecules without cell toxicity. We focused our investigations on compounds that could act as substrate-mimicking inhibitors of tyrosinase and identified N-feruloyldopamine as the best candidate. In vitro, N-feruloyldopamine inhibited human tyrosinase with higher efficacy than the reference inhibitor arbutin without cell toxicity at least up to 100 µM as measured in cultured normal human epidermal melanocytes (NHEMs). Moreover, the inhibition appeared to be specific to mammalian tyrosinases as shown by a very poor inhibition of mushroom tyrosinase, but a significant decrease of total melanin in B16-F10 cells. The antioxidant capacity assessed using DPPH (1,1-diphenyl-2-picrylhydrazyl) assay was comparable to that of vitamin C and finally, N-feruloyldopamine exerted a significant inhibition of Pmel17 gene expression when used at 100 µM on cultured NHEM. Taken together, these results suggest that N-feruloyldopamine is a serious candidate for in vivo application as complexion-brightening ingredient.
