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Background: Pigmentation is controlled by complex mechanisms. Evidence suggests that miRNAs can regulate pigmentation. However, the mechanism has not been fully elucidated. Objective In this study, we revealed a novel mechanism that regulates pigmentation involving exosomes, miRNAs and the crosstalk between keratinocytes and melanocytes., Methods: The expression and localization of exosome specific marker TSG101 in keratinocytes and melanocytes; Changes of melanin content in melanocytes after co-culture of exosome and melanocytes; Expression changes of target gene TYR and its related genes and inhibitory effect of miR-330-5p on pigmentation were studied by using various molecular biological techniques., Results: In this experiment, we used miR-330-5p in keratinocytes to verify the effect of keratinocyte derived exosome on melanocyte pigmentation. First, we found that keratinocytes secrete exosomes carrying miR-330-5p; moreover, greater miR-330-5p expression was found in exosomes derived from keratinocytes that overexpressed miR-330-5p. Second, we found that exosomes derived from keratinocytes with overexpression of miR-330-5p caused a significant increase in miR-330-5p in melanocytes. Finally, exosomes derived from keratinocytes that overexpressed miR-330-5p induced a significant decrease in the production of melanin and expression of TYR in melanocytes. Meanwhile, we overexpressed miR-330-5p in melanocytes, which also proved the inhibitory effect of miR-330-5p on pigmentation., Conclusion: These findings suggest that keratinocytes crosstalk with melanocytes in the epidermal melanin unit via exosomal miRNAs. These studies reveal an important role of exosomes in melanocyte pigmentation, which opens a new pathway of melanogenesis., (Copyright © 2019 Japanese Society for Investigative Dermatology. All rights reserved.)

Fibroblast growth factor 21 (FGF21) is known as a metabolic regulator to regulate the metabolism of glucose and lipids. However, the underlying mechanism of FGF21 on melanin synthesis remains unknown. Therefore, the current study investigates the effect of FGF21 on melanogenesis in alpaca melanocytes. We transfected the FGF21 into alpaca melanocytes, then detected the melanin contents, protein and mRNA levels of pigmentation-related genes in order to determine the melanogenesis-regulating pathway of FGF21. The results showed that FGF21 overexpression suppressed melanogenesis and decreased the expression of the major target genes termed microphthalmia-associated transcription factor (MITF) and its downstream genes, including tyrosinase (TYR) and tyrosinase-related protein 2 (TRP2). However FGF21 increased the expression of phospho-extracellular signal-regulated kinase (p-Erk1/2). In contrast, FGF21-siRNA, a small interference RNA mediating FGF21 silencing, abolished the inhibition of melanogenesis. Altogether, FGF21 may decrease melanogenesis in alpaca melanocytes via ERK activation and subsequent MITF downregulation, which is then followed by the suppression of melanogenic enzymes and melanin production., (Copyright © 2017. Published by Elsevier Inc.)

MicroRNAs (miRNAs) play an essential role in the regulation of almost all the biological processes, including melanogenesis. MiR-27a-3p is nearly six times higher in white alpaca skin compared to brown skin, which indicates that miR-27a-3p may be a candidate regulator for melanogenesis. Wnt3a plays an important role in promoting melanoblasts to differentiate into melanocytes and melanogenesis. To confirm the function of miR-27a-3p to melanogenesis in mammals, miR-27a-3p mimic, inhibitor and their negative control were transfected into mouse melanocytes. As a result, miR-27a-3p inhibits melanogenesis by repressing Wnt3a at post-transcriptional level. A significant decrease in Wnt3a luciferase activity was observed in 293T cells co-transfected with the matched luciferase reporter vector and pre-miR-27a. Furthermore, the presence of exogenous miR-27a-3p significantly decreased Wnt3a protein expression rather than mRNA and reduced β-catenin mRNA levels in melanocytes. The over-expression of miR-27a-3p significantly increased the melanin content of melanocytes. However, miR-27a-3p inhibitor performs an opposite effect on melanogenesis. Wnt3a is one target of miR-27a-3p. MiR-27a-3p could inhibit Wnt3a protein amount by post-transcriptional regulation and melanogenesis in mouse melanocytes. Previous studies reported that Wnt3a promoted melanogenensis in mouse melanocytes. Thus, miR-27-3p inhibits melanogenesis by repressing Wnt3a protein expression.

Previously, we created miR-137 overexpressing transgenic mice that produced lighten color phenotypes including gray mice phenotype. However, the miR-137 functional role in coat color regulation is still not well understood. In this study, the quantity of melanin granule and the relative expression of TYRP2 in gray miR-137 overexpression transgenic mouse skin were significantly lower than that in C57BL/6J black mouse skin. The mRNA and protein expression level ofc-Kitandc-Kitdownstream geneTyrp2in miR-137 expression plasmid-transfected melanocytes were significantly down-regulated comparing with that of the control melanocytes. In melanocytes, miR-137 overexpression could decrease the enhanced expression ofc-KitandTyrp2and the increased melanin production caused by UV treatment. The target relationship of miR-137 andc-Kitwas identified by luciferase assay. The results suggest that miR-137 could inhibit melanogenesis in mouse skin melanocytes by repressing the expression ofc-KitandTyrp2inSCF/c-Kitsignaling pathway. MiR-137 inhibits melanogenesis in mouse skin melanocytes. [ABSTRACT FROM PUBLISHER]

Hepatocyte growth factor (HGF)/c-Met signaling has been considered as a key pathway in both melanocyte development and melanogenesis. To understand better the expression patterns and tissue distribution characterization of HGF and its receptor c-Met in skin of white versus brown alpaca ( Vicugna pacos ), we detected the tissue distribution of HGF and c-Met using immunohistochemistry and analyzed the expression patterns by using Western blot and quantitative real time PCR (qPCR). Immunohistochemistry analysis demonstrated that HGF staining robustly increased in the dermal papilla and mesenchymal cells of white alpaca skin compared with that of brown. However, c-Met staining showed strongly positive result, particularly inhair matrix and root sheath in brown alpaca skin. Western blot and qPCR results suggested that HGF and c-Met were expressed at significantly high levels in white and brown alpaca skins, respectively, and protein and transcripts possessed the same expression pattern in white and brown alpaca skins. The results suggested that HGF/c-Met signaling functions in alpaca coat color formation offer essential theoretical basis for further exploration of the role of HGF/c-Met signaling in pigment formation. [ABSTRACT FROM AUTHOR]