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

The study investigated the changes in skin characteristics of mice due to aging, focusing on the stem cells for keratinocytes and melanocytes in the hair follicles (HFs). It was found that by postnatal day 200 (P200), the skin reaches full maturation and begins to show signs of aging. Keratin 15-positive keratinocyte stem cells complete their localization in the hair bulge region by P200, facilitating hair regeneration in every subsequent anagen phase. Unusual structures of HFs, known as curved HFs, begin to appear at P200 and continue to increase throughout life. Similarly, melanocyte-derived characteristics, such as hypopigmented hair bulbs, also start to appear at P200, leading to an increase in white hairs. These curved HFs and white hairs are considered biomarkers of aging in mice. The study also found that the number of tyrosinase-related protein 2-positive melanocyte stem cells in the hair bulge is extremely low, which may contribute to the aging characteristics of both melanocytes and keratinocytes.