Hedgehog Signaling Maintains Hair Follicle Stem Cell Phenotype in Young and Aged Human Skin

The study, involving scalp biopsies from 15 young individuals (below 40 years) and 13 aged individuals (above 70 years), examined the effects of aging on hair follicle stem cells (HFSCs) in human skin. Researchers found no significant differences in hair follicle density, bulge cell numbers, or the expression of HFSC markers such as KRT15, KRT19, and various others between young and aged individuals. Additionally, the study demonstrated that Hedgehog (Hh) signaling, which was activated in human bulge cells and down-regulated in differentiated hair follicle keratinocytes, plays a role in maintaining the bulge cell phenotype in both young and aged skin. Activation of Hh signaling through overexpression of the transcription factor Gli1 induced the transcription of HFSC markers in cultured keratinocytes, suggesting that Hh signaling is crucial for maintaining HFSC characteristics regardless of age.