Melanocyte stem cells (McSCs) are localized in the bulge region of hair follicles and supply melanocytes, which determine hair color by synthesizing melanin. Ectopic differentiation of McSCs, which are usually undifferentiated in the bulge region, causes depletion of McSCs and results in hair graying. Therefore, to prevent hair graying, it is essential to maintain McSCs in the bulge region, but the mechanism of McSC maintenance remains unclear. To address this issue, we investigated the role of CXCL12, a chemokine which was previously suggested to induce migration of melanocyte lineage cells, as a niche component of McSCs. Immunohistological analysis revealed that CXCL12 was highly expressed in the bulge region of human hair follicles. CXCL12 mRNA expression level was significantly lower in white hairs plucked from human scalps than in black hairs. CXCL12 attracted the migration of early-passage normal human epidermal melanocytes (eNHEMs), an in vitro model of McSCs, which had characteristics of immature melanocyte precursors. We also found that CXCL12 suppressed their differentiation. These results suggest that CXCL12 regulates differentiation of McSCs as well as their proper localization, and maintaining McSCs by regulating CXCL12 expression level in the bulge region may be a key to preventing hair graying.
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