Signalling by senescent melanocytes hyperactivates hair growth.

Niche signals maintain stem cells in a prolonged quiescence or transiently activate them for proper regeneration1. Altering balanced niche signalling can lead to regenerative disorders. Melanocytic skin nevi in human often display excessive hair growth, suggesting hair stem cell hyperactivity. Here, using genetic mouse models of nevi2,3, we show that dermal clusters of senescent melanocytes drive epithelial hair stem cells to exit quiescence and change their transcriptome and composition, potently enhancing hair renewal. Nevus melanocytes activate a distinct secretome, enriched for signalling factors. Osteopontin, the leading nevus signalling factor, is both necessary and sufficient to induce hair growth. Injection of osteopontin or its genetic overexpression is sufficient to induce robust hair growth in mice, whereas germline and conditional deletions of either osteopontin or CD44, its cognate receptor on epithelial hair cells, rescue enhanced hair growth induced by dermal nevus melanocytes. Osteopontin is overexpressed in human hairy nevi, and it stimulates new growth of human hair follicles. Although broad accumulation of senescent cells, such as upon ageing or genotoxic stress, is detrimental for the regenerative capacity of tissue4, we show that signalling by senescent cell clusters can potently enhance the activity of adjacent intact stem cells and stimulate tissue renewal. This finding identifies senescent cells and their secretome as an attractive therapeutic target in regenerative disorders.

Hair graying with aging in mice carrying oncogenic RET.

Hair graying is a representative sign of aging in animals and humans. However, the mechanism for hair graying with aging remains largely unknown. In this study, we found that the microscopic appearance of hair follicles without melanocyte stem cells (MSCs) and descendant melanocytes as well as macroscopic appearances of hair graying in RET-transgenic mice carrying RET oncogene (RET-mice) are in accordance with previously reported results for hair graying in humans. Therefore, RET-mice could be a novel model mouse line for age-related hair graying. We further showed hair graying with aging in RET-mice associated with RET-mediated acceleration of hair cycles, increase of senescent follicular keratinocyte stem cells (KSCs), and decreased expression levels of endothelin-1 (ET-1) in bulges, decreased endothelin receptor B (Ednrb) expression in MSCs, resulting in a decreased number of follicular MSCs. We then showed that hair graying in RET-mice was accelerated by congenitally decreased Ednrb expression in MSCs in heterozygously Ednrb-deleted RET-mice [Ednrb(+/-);RET-mice]. We finally partially confirmed common mechanisms of hair graying with aging in mice and humans. Taken together, our results suggest that age-related dysfunction between ET-1 in follicular KSCs and endothelin receptor B (Ednrb) in follicular MSCs via cumulative hair cycles is correlated with hair graying with aging.

Pigmentation of regenerated hairs after wounding.

BACKGROUND: After severe wounding, hair follicles were known to be regenerated de novo along with the re-epithelialization. However, the regenerated hairs lack pigmentation. OBJECTIVE: We aimed to find out the condition to regenerate pigmented hairs after severe wounding. METHODS: De novo hair regeneration was observed during the re-epithelialization process after the full thickness excision of dorsal skin. Hair pigmentation mechanism was assessed by the modulation of Wnt and Kit signalings. RESULTS: Stable regeneration of pigmented hairs was demonstrated when a wound was created to the mice during the anagen stage of the hair cycle. A significant increase in the number of melanocyte stem cells in the postnatal 1st anagen interfollicular skin of 5-week-old mice was observed. An increase of Wnt7a of the keratinocytes was observed in the skin at this stage, which may direct melanocyte stem cells to produce pigmented hairs in the regenerating follicles. This was supported by the finding that transgenic mice expressing the melanocyte stimulatory factor Kitl in their skin promoted the regeneration of pigmented hairs irrespective of the stage of the hair cycle. CONCLUSION: Our results provide a new insight into the intimate regulation process between two follicular stem cell systems, keratinocyte stem cells and melanocyte stem cells, during de novo hair regeneration after wounding.

Antioxidative effects of cherry leaves extract on tert-butyl hydroperoxide-mediated cytotoxicity through regulation of thioredoxin-2 protein expression levels.

Components of cherry trees have been used as traditional herbal remedies for various diseases. These components are known to possess antioxidative effects. However, the mechanisms underlying cherry tree component-mediated antioxidative effects remain largely unknown. This study focused on cherry leaves extract (CLE) and examined the mechanism underlying the effect of CLE on tert-butyl hydroperoxide (t-BOOH)-induced melanocytic cell death with DNA damage. Interestingly, CLE prevented t-BOOH-induced cell death with reduction in DNA damage, p38 kinase activation, and reactive oxygen species (ROS) production. CLE-mediated suppression of cell death with reduction of DNA damage, p38 kinase activity and ROS production was prevented by a thioredoxin (Trx) system inhibitor but not by a glutathione (GSH) system inhibitor. Finally, data showed that CLE prevented t-BOOH-induced reduction of Trx2 but not Trx1 and Trx reductases (TrxR1 and TrxR2) protein expression. Thus, our results suggest that CLE prevents t-BOOH-induced reduction in Trx2 expression, promotion of ROS production, activation of p38 kinase, and increase in DNA damage and that it protects against cell death.