Topical RT1640 treatment effectively reverses gray hair and stem cell loss in a mouse model of radiation‐induced canities

Quiescence and aging of melanocyte stem cells and a novel association with programmed death-ligand 1

Cellular quiescence is a reversible and tightly regulated stem cell function essential for healthy aging. However, the elements that control quiescence during aging remain poorly defined. Using melanocyte stem cells (McSCs), we find that stem cell quiescence is neither passive nor static. For example, gene expression profiling of the transition from proliferating melanoblasts to quiescent melanocyte stem cells reveals tissue-specific regulation of the immune checkpoint protein PD-L1. In vitro, quiescence assays demonstrate that PD-L1 expression is a physiological attribute of quiescence in this cell lineage and reinforces this cell state. In vivo, a subset of quiescent McSCs is marked by PD-L1. While the overall number of McSCs decreases with age, PD-L1+ McSCs appear resistant to depletion. This phenomenon coincides with an aged McSC pool that exhibits a deeper transcriptomic quiescence. We predict that quiescent PD-L1+ stem cells retained with age may serve as cellular targets for reactivation.

Premature Graying of Hair: A Comprehensive Review and Recent Insights

Background

Hair symbolizes well-being and self-expression, with graying occurring naturally among different racial groups at varying ages. Premature graying has psychological and societal impacts, influencing self-esteem and quality of life. Gray hair usually advances gradually and is permanent, with occasional reports of natural repigmentation. Premature graying of hair (PMGH) results from a complex interplay of genetic, environmental, and cellular factors.

Materials and Methods

Studies exploring links between gray hair and conditions such as osteopenia, hearing loss, smoking, obesity, dyslipidemia, and cardiovascular disease have yielded mixed results. Despite continuous research into the causes of gray hair, effective, evidence-based treatments are lacking and still need to be improved.

Conclusion

Herein, we reviewed the causes, mechanisms, risk factors, psychosocial effects, and emerging therapies for PMGH.

Irradiation-induced hair graying in mice: an experimental model to evaluate the effectiveness of interventions targeting oxidative stress, DNA damage prevention, and cellular senescence

Hair graying, also known as canities or achromotrichia, is a natural phenomenon associated with aging and is influenced by external factors such as stress, environmental toxicants, and radiation exposure. Understanding the mechanisms underlying hair graying is an ideal approach for developing interventions to prevent or reverse age-related changes in regenerative tissues. Hair graying induced by ionizing radiation (γ-rays or X-rays) has emerged as a valuable experimental model to investigate the molecular pathways involved in this process. In this review, we examine the existing evidence on radiation-induced hair graying, with a particular focus on the potential role of radiation-induced cellular senescence. We explore the current understanding of hair graying in aging, delve into the underlying mechanisms, and highlight the unique advantages of using ionizing-irradiation-induced hair graying as a research model. By elucidating the molecular pathways involved, we aim to deepen our understanding of hair graying and potentially identify novel therapeutic targets to address this age-related phenotypic change.

Clinical Pathobiology of Radiotherapy-Induced Alopecia: A Guide toward More Effective Prevention and Hair Follicle Repair

Because hair follicles (HFs) are highly sensitive to ionizing radiation, radiotherapy-induced alopecia (RIA) is a core adverse effect of oncological radiotherapy. Yet, effective RIA-preventive therapy is unavailable because the underlying pathobiology remains underinvestigated. Aiming to revitalize interest in pathomechanism-tailored RIA management, we describe the clinical RIA spectrum (transient, persistent, progressive alopecia) and our current understanding of RIA pathobiology as an excellent model for studying principles of human organ and stem cell repair, regeneration, and loss. We explain that HFs respond to radiotherapy through two distinct pathways (dystrophic anagen or catagen) and why this makes RIA management so challenging. We discuss the responses of different HF cell populations and extrafollicular cells to radiation, their roles in HF repair and regeneration, and how they might contribute to HF miniaturization or even loss in persistent RIA. Finally, we highlight the potential of targeting p53-, Wnt-, mTOR-, prostaglandin E2-, FGF7-, peroxisome proliferator-activated receptor-γ-, and melatonin-associated pathways in future RIA management.

Protective effect of hydroxygenkwanin against hair graying induced by X-ray irradiation and repetitive plucking

Hair graying in mice is caused by various injuries such as X-ray radiation and repeated plucking that ultimately damage melanocytes and their stem cells (melanocyte stem cells). In X-ray‒induced hair graying, injuries first manifest as a loss-of-niche function of hair follicular keratinocyte stem cells to maintain melanocyte stem cells. Thus, we hypothesized that hair follicular keratinocyte stem cells could be a practical target to prevent hair graying. In this study, we investigated the in vivo effect of the flavonoid hydroxygenkwanin, which has been shown to exert the best protection on human epidermal keratinocytes against in vitro X-ray‒induced cytological effects, using X-ray‒induced and repeated hair plucking‒induced hair graying mice models. We found that hydroxygenkwanin exerted a remarkable effect in preventing hair graying; however, when receptor Y kinase Kit-mutant mice were used, no prevention effect was observed. Therefore, we propose that Kit signaling might be involved in the hydroxygenkwanin-induced protective effect against hair graying.

A novel mouse model to evaluate neuropeptide Y-mediated melanocyte pathology

Vitiligo is an autoimmune disease characterized by depigmented patches of skin due to loss of the pigment-producing melanocytes. No cure exists for vitiligo. The available treatments are inefficient for many patients, suggesting that universal treatment approaches may be inappropriate. Deeper understanding of the mechanistic basis for variability in vitiligo aetiologies is necessary. Genetic mutations in neuropeptide Y (NPY), a widely distributed protein, are associated with increased NPY expression and increased susceptibility for vitiligo. NPY is also upregulated in the circulation and lesional skin of some vitiligo patients. However, the contributions of NPY to melanocyte pathology are not understood, and presently there are no models with which to investigate this possibility. In this study, we employed NPY-overexpressing mice to explore the role of NPY in melanocyte dysfunction. Our results show that NPY overexpression induces progressive hair greying (depigmentation) due to premature depletion of follicular melanocyte stem cells. Additionally, NPY transcripts and protein are elevated in the skin and melanocytes of these mice, respectively, suggesting that these effects may be mediated locally. Together, these results suggest that supraphysiological levels of NPY in the skin can induce melanocyte dysfunction, thus identifying this mouse line as a novel model to study NPY-mediated melanocyte pathology.