Melanocytes are rare cells in the skin that produce pigment, giving skin and hair their colour. Dysfunction of melanocytes causes common and serious disorders such as vitiligo and melanoma. As it is proposed that such pathological states arise from distinct melanocyte sub-populations, elucidating cell hierarchies and regulatory mechanisms in melanocytes is a key to prevent and treat melanocytic diseases.
Towards this, we developed a flow cytometry (FACS)-based method for prospective isolation of highly purified CKIT+ melanocytes and performed scRNAseq on them. One cell cluster displayed increased expression of NTRK2, which is linked to neural progenitor function and oncogenesis. The gene expression profile of NTRK2-expressing cells had progenitor cell characteristics including signatures linked to ribosome biogenesis. Further, splicing isoform analysis and western blot revealed that the isoform of NTRK2 expressed in human melanocytes is the short-truncated form, TrkB.T1.
NTRK2+ melanocytes were detected in the epidermis and hair follicles of human and mouse skin by immunohistochemistry. Nucleolin (NCL), a regulator of ribosome biogenesis, proliferation and cell survival, was co-expressed with NTRK2 in melanocytes during mitosis. When NTRK2 was suppressed in melanocytes with siNTRK2s, expression of NCL and Internally Transcribed Spacer 2 (ITS2) of human 47S pre-rRNA were suppressed. Further, survival of siNTRK2-treated melanocytes after UVB-irradiation was inhibited in vitro, suggesting upstream regulation by NTRK2 of resistance to UV-stress via NCL. Similarly knock-out of NTRK2 in mouse melanocytes resulted in depletion of NCL in vivo, and NTRK2+ melanocytes were increased after UVB-irradiation in human and mouse skin, and downregulated in vitiliginous human skin.
These data implicate NTRK2+ melanocytes as intermediate melanocyte progenitors involved in the development of melanoma and vitiligo.