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

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.

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.

Delayed effects of acute whole body lethal radiation exposure in mice pre-treated with BBT-059

The threat of nuclear exposure is heightened and it is imperative to identify potential countermeasures for acute radiation syndrome. Currently no countermeasures have been approved for prophylactic administration. Effective countermeasures should function to increase survival in the short term as well as to increase the overall prognosis of an exposed individual long term. Here we describe the use of a promising radiation countermeasure, BBT-059, and the results of a long term mouse study (up to 12 months) in the male CD2F1 strain using ⁶⁰Co gamma irradiation (~0.6 Gy/min, 7.5-12.5 Gy). We report the dose reduction factor of 1.28 for BBT-059 (0.3 mg/kg) compared to control administered 24 h prior to irradiation. In the long term study animals showed accelerated recovery in peripheral blood cell counts, bone marrow colony forming units, sternal cellularity and megakaryocyte numbers in drug treated mice compared to formulation buffer. In addition, increased senescence was observed in the kidneys of animals administered control or drug and exposed to the highest doses of radiation. Decreased levels of E-cadherin, LaminB1 and increased levels of Cyc-D and p21 in spleen lysates were observed in animals administered control. Taken together the results indicate a high level of protection following BBT-059 administration in mice exposed to lethal and supralethal doses of total body gamma-radiation.