Effects of keratinocyte-derived and fibroblast-derived exosomes on human epidermal melanocytes

Background: Exosomes have been demonstrated to carry proteins, membrane lipids, mRNAs and microRNAs which can be transferred to surrounding cells and regulate the functions of those recipient cells. Objectives: The objective of the study was to investigate the effects of exosomes released by keratinocytes and fibroblasts on the proliferation, tyrosinase activity and melanogenesis of melanocytes. Methods: Melanocytes, keratinocytes and fibroblasts obtained from human foreskin were cultured and exosomes secreted by keratinocytes and fibroblasts were harvested from the culture supernatants by ultracentrifugation. Each exosome fraction was divided into two parts; one part was subjected to high-throughput sequencing using an Illumina HiSeq sequencer to characterize the microRNA expression profiles, while the other part was labeled with the fluorescent dye PKH67 and was then co-cultivated with epidermal melanocytes. Results: High-throughput sequencing analysis showed 168 differentially expressed microRNA within exosomes derived from keratinocytes and from fibroblasts, 97 of those being up-regulated with the other 71 down-regulated. Gene ontology analysis showed that the target genes responsible for these differentially expressed microRNAs were mainly enriched in the protein-binding region of molecular functions. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed that target genes regulated by differentially expressed microRNA were mainly involved in mitogen-activated protein kinase (MAPK) signaling pathway, Ras signaling pathway, cAMP signaling pathway and Wnt signaling pathway. Keratinocyte-derived exosomes were taken up by melanocytes co-cultured with them and promoted the proliferation, tyrosinase activity and melanin synthesis of those melanocytes. However, fibroblast-derived exosomes had no similar effects on melanocytes. Conclusion: Keratinocyte-derived exosomes but not fibroblast-derived exosomes were taken up by melanocytes in co-culture and significantly stimulated their proliferation, tyrosinase activity and melanin synthesis. Those different effects may be mainly due to the differential expression of microRNAs in exosomes derived from the different types of cells. Limitations: Electron microscopy of the obtained exosomes and in-depth study of apparently differentially expressed microRNAs were not performed

Melanocyte spheroids are formed by repetitive long-term trypsinization

Background: Autologous melanocyte transplantation plays an important role in the treatment of vitiligo. Objective: Previous studies have indicated that, compared with melanocytes growing in monolayers, melanocyte spheroids have a better survival in growth factor- and serum-deprived conditions. Methods: Melanocyte spheroids were obtained from human epidermis by repetitive long-term trypsinization and maintained an aggregated morphology for a short period in certain conditions. Results: Melanocyte spheroids were capable of growing into normal dendritic melanocytes in monolayer when they were harvested and reinoculated in 24-well plates. Immunohistochemical analysis of the melanocyte spheroids revealed that they were positive for HMB45, a melanosome-specific marker. No melanomas occurred when melanocyte spheroids were transplanted into mice. Conclusion: Our study provides a promising approach for melanocyte transplantation to treat vitiligo.

Familial progressive hypo- and hyperpigmentation: A variant case.

Familial progressive hyper- and hypopigmentation (FPHH) is characterized by diffuse hyperpigmentation with variable intensity. Cafe'-au-lait macules and larger hypopigmented ash-leaf macules are also present. Herein, we reported a variant case of FPHH. The patient was a two-year-old Chinese girl showing diffuse hyper- and hypopigmented lesions, longitudinal melanonychia in both thumbs, and infantile seizures, without any lentigines.