Exposure to gamma-rays at the telogen phase of the hair cycle inhibits hair follicle regeneration at the anagen phase in mice

Life of the B10 Mouse: A View from the Hair Follicles and Tissue Stem Cells

In our series of studies, the changes in the skin characteristics of mice caused by aging were investigated in correlation with the stem cells for keratinocytes and melanocytes in the natural hair cycle until middle age. The aim of the present review was to investigate these characteristics of hair follicles (HFs) at older age and complete the analysis of these changes as a study throughout the mouse lifetime. In addition, stem cells for keratinocytes and melanocytes were evaluated for changes in skin characteristics caused by aging. Postnatal day 200 (P200) appears to be the age of complete maturation of skin and the onset of aging with regard to HFs. Keratin 15-positive keratinocyte stem cells complete their localization as a quantitatively sufficient amount of progenitor in the hair bulge region and orchestrate the regeneration of hairs in every anagen phase thereafter. Although their frequency is low, an unusual structure of HFs, curved HFs, appear for the first time at P200. Thereafter, abnormal hair curvature continues to increase throughout life. In contrast, HF characteristics derived from melanocytes begin to show a high frequency of hypopigmented hair bulbs at P200 and appear to lead to a significant increase in the number of white hairs. Curved HFs and white hairs were considered biomarkers of aging in mice. The number of tyrosinase-related protein 2-positive melanocyte stem cells in the hair bulge is extremely low and may be one cause underlying not only the induction of melanocyte-derived characteristics by aging but possibly also that of keratinocyte-derived characteristics. These results provide insight into the mechanisms of the actions of stem cells on hair regeneration through the aging process.

Potential of Colostrum-Derived Exosomes for Promoting Hair Regeneration Through the Transition From Telogen to Anagen Phase

Human hair dermal papillary (DP) cells comprising mesenchymal stem cells in hair follicles contribute critically to hair growth and cycle regulation. The transition of hair follicles from telogen to anagen phase is the key to regulating hair growth, which relies heavily on the activation of DP cells. In this paper, we suggested exosomes derived from bovine colostrum (milk exosomes, Milk-exo) as a new effective non-surgical therapy for hair loss. Results showed that Milk-exo promoted the proliferation of hair DP cells and rescued dihydrotestosterone (DHT, androgen hormones)-induced arrest of follicle development. Milk-exo also induced dorsal hair re-growth in mice at the level comparable to minoxidil treatment, without associated adverse effects such as skin rashes. Our data demonstrated that Milk-exo accelerated the hair cycle transition from telogen to anagen phase by activating the Wnt/β-catenin pathway. Interestingly, Milk-exo has been found to stably retain its original properties and efficacy for hair regeneration after freeze-drying and resuspension, which is considered critical to use it as a raw material applied in different types of alopecia medicines and treatments. Overall, this study highlights a great potential of an exosome from colostrum as a therapeutic modality for hair loss.

Changes in characteristics of murine hair follicles and tissue stem cells by aging

The aging process is closely related to the organization of stem cells, and skin is thought to be one of the suitable models for its investigation. We have focused on the murine hair follicle to verify this idea because it shows typical aging phenotypes and is a self-renewing structure reconstituted by its own stem cells. However, how changes in the characteristics of the hair follicle and in the behavior of tissue stem cells in the natural hair cycle occur are not fully understood. We investigated the number, morphology and pigmentation of hair follicles in anagen phases during the aging process. In addition, stem cells for keratinocytes and melanocytes were examined to evaluate the correlation between changes in skin characteristics and the stem cells. The remarkable changes caused by aging appeared to be the significant increase in qualitative phenotypes such as curved hair follicles and white hair. A significant difference between the number of keratinocyte and melanocyte stem cells in the hair bulge region is likely to be involved in these changes. Our findings may be important for understanding the mechanisms of the actions of stem cells on hair regeneration and for clarifying the mechanisms of age-related phenotypes.

Effects of gamma rays on the regeneration of murine hair follicles in the natural hair cycle

PURPOSE

This review evaluates the effects of γ-rays on the regeneration of murine hair follicles in the natural hair cycle. A series of studies were performed to investigate this issue, in which the whole bodies of C57BL/10JHir mice in the 1st telogen phase of the hair cycle were irradiated with γ-rays.

RESULTS

The dermis of the irradiated skin showed a decrease in hair follicle density and induction of curved hair follicles along with the presence of white hairs and hypopigmented hair bulbs in the 2nd and 3rd anagen phases. An increased frequency of hypopigmented hair bulbs was still observed in the later hair cycle at postnatal day 200. There was no significant difference in the number of stem cells in the hair bulge region between control and irradiated skin.

CONCLUSIONS

These results show that the effects of γ-rays on the pigmentation of murine hair follicles are persistently carried over to later hair cycles, although those on the number and structure of hair follicles appear to be hidden by the effects of aging. Our findings may be important for understanding the mechanisms of the actions of stem cells on hair regeneration in connection with age-related phenotypes.