An efficient, non-invasive approach for in-vivo sampling of hair follicles: design and applications in monitoring DNA damage and aging

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.

Evaluation of short-term hair follicle storage conditions for maintenance of RNA integrity

Hair follicles provide an easily accessible tissue for interrogating gene expression for multiple purposes in mammals. RNAlater® is a liquid storage solution that stabilises and preserves cellular RNA, eliminating the need to immediately process or freeze tissue specimens. The manufacturer advises storage of samples at 2-8°C overnight before transfer to -20°C. This study aimed to evaluate RNA integrity in hair follicle samples collected from horses, stabilized in RNAlater®, and stored under three short-term storage conditions. Mane hair samples complete with follicles were collected from four horses at a single time point. Approximately 15 hairs were placed in each of three 2 mL tubes containing 0.75ml RNAlater® solution. Test group A was stored at 4°C for 24-h, then decanted and stored at -20°C. Test groups B and C were stored at 4°C and 19°C (room temperature) respectively for 7 days, then decanted and stored at -20°C. RNA was isolated from all samples and RNA quantity and quality were measured. One-way ANOVA revealed no difference in RNA concentration (A:516 +/-125 ng/ml, B:273+/-93 ng/ml, C:476+/-176 ng/ml;P = 0.2) or quality (A:9.5 +/-0.19, B:9.8+/-0.09, C:9.2+/-0.35 RIN; P = 0.46) between the test groups. There were no group differences in mean Cycle Threshold values from qPCR validation assays confirming high-quality template cDNA. The results suggest that storage of hair follicles for one week in RNAlater® at cool or room temperature conditions will not compromise RNA integrity and will permit extended transport times from remote sampling locations without the need for freezing.

Melanocyte stem cells in the skin: Origin, biological characteristics, homeostatic maintenance and therapeutic potential

Melanocyte stem cells (MSCs), melanocyte lineage-specific skin stem cells derived from the neural crest, are observed in the mammalian hair follicle, the epidermis or the sweat gland. MSCs differentiate into mature melanin-producing melanocytes, which confer skin and hair pigmentation and uphold vital skin functions. In controlling and coordinating the homeostasis, repair and regeneration of skin tissue, MSCs play a vital role. Decreased numbers or impaired functions of MSCs are closely associated with the development and therapy of many skin conditions, such as hair graying, vitiligo, wound healing and melanoma. With the advancement of stem cell technology, the relevant features of MSCs have been further elaborated. In this review, we provide an exhaustive overview of cutaneous MSCs and highlight the latest advances in MSC research. A better understanding of the biological characteristics and micro-environmental regulatory mechanisms of MSCs will help to improve clinical applications in regenerative medicine, skin pigmentation disorders and cancer therapy. KEY POINTS: This review provides a concise summary of the origin, biological characteristics, homeostatic maintenance and therapeutic potential of cutaneous MSCs. The role and potential application value of MSCs in skin pigmentation disorders are discussed. The significance of single-cell RNA sequencing, CRISPR-Cas9 technology and practical models in MSCs research is highlighted.

Follicular DNA Damage and Pesticide Exposure Among Latinx Children in Rural and Urban Communities

The intersectional risks of children in United States immigrant communities include environmental exposures. Pesticide exposures and their biological outcomes are not well characterized in this population group. We assessed pesticide exposure and related these exposures to DNA double-strand breaks (DSBs) in Latinx children from rural, farmworker families (FW; N = 30) and from urban, non-farmworker families (NFW; N = 15) living in North Carolina. DSBs were quantified in hair follicular cells by immunostaining of 53BP1, and exposure to 72 pesticides and pesticide degradation products were determined using silicone wristbands. Cholinesterase activity was measured in blood samples. DSB frequencies were higher in FW compared to NFW children. Seasonal effects were detected in the FW group, with highest DNA damage levels in April-June and lowest levels in October-November. Acetylcholinesterase depression had the same seasonality and correlated with follicular DNA damage. Organophosphate pesticides were more frequently detected in FW than in NFW children. Participants with organophosphate detections had increased follicular DNA damage compared to participants without organophosphate detection. Follicular DNA damage did not correlate with organochlorine or pyrethroid detections and was not associated with the total number of pesticides detected in the wristbands. These results point to rural disparities in pesticide exposures and their outcomes in children from vulnerable immigrant communities. They suggest that among the different classes of pesticides, organophosphates have the strongest genotoxic effects. Assessing pesticide exposures and their consequences at the individual level is key to environmental surveillance programs. To this end, the minimally invasive combined approach used here is particularly well suited for children.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12403-023-00609-1.

Non-invasive assessment of hair regeneration in androgenetic alopecia mice in vivo using two-photon and second harmonic generation imaging

The identification of crucial targets for hair regrowth in androgenetic alopecia (AGA) involves determining important characteristics and different stages during the process of hair follicle regeneration. Traditional methods for assessing key features and different stages of hair follicle primarily involve taking skin tissue samples and determining them through various staining or other methods. However, non-invasive assessment methods have been long sought. Therefore, in this study, endogenous fluorescence signals from skin keratin and second harmonic signals from skin collagen fibers were utilized as probes, two-photon excited fluorescence (TPEF) and second harmonic generation (SHG) imaging techniques were employed to non-invasively assess hair shafts and collagen fibers in AGA mice in vivo. The TPEF imaging technique revealed that the alternation of new and old hair shafts and the different stages of the growth period in AGA mice were delayed. In addition, SHG imaging found testosterone reduced hair follicle area and miniaturized hair follicles. The non-invasive TPEF and SHG imaging techniques provided important methodologies for determining significant characteristics and different stages of the growth cycle in AGA mice, which will facilitate future non-invasive assessments on human scalps in vivo and reduce the use of animal testing.

Refinement in the European Union: A Systematic Review

Refining experiments and housing conditions so as to cause the minimum possible pain and distress is one of the three principles (3Rs) on which Directive 2010/63/EU is based. In this systematic review, we aimed to identify and summarize published advances in the refinement protocols made by European Union-based research groups from 2011 to 2021, and to determine whether or not said research was supported by European or national grants. We included 48 articles, the majority of which were related to improvements in experimental procedures (37/77.1%) for mice (26/54.2%) and were written by research groups belonging to universities (36/57.1%) and from the United Kingdom (21/33.9%). More than two thirds (35/72.9%) of the studies received financial support, 26 (mostly British) at a national level and 8 at a European level. Our results indicated a clear willingness among the scientific community to improve the welfare of laboratory animals, as although funding was not always available or was not specifically granted for this purpose, studies were published nonetheless. However, in addition to institutional support based on legislation, more financial support is needed. We believe that more progress would have been made in refinement during these years if there had been more specific financial support available at both the national and European Union levels since our data suggest that countries investing in refinement have the greatest productivity in successfully publishing refinements.

Modeling human gray hair by irradiation as a valuable tool to study aspects of tissue aging

As one of the earliest and most visible phenomenon of aging, gray hair makes it a unique model system for investigating the mechanism of aging. Ionizing radiation successfully induces gray hair in mice, and also provides a venue to establish an organ-cultured human gray hair model. To establish a suitable organ-cultured human gray HF model by IR, which imitates gray hair in the elderly, and to explore the mechanisms behind the model. By detecting growth parameters, melanotic and senescence markers of the model, we found that the model of 5 Gy accords best with features of elderly gray hair. Then, we investigated the formation mechanisms of the model by RNA-sequencing. We demonstrated that the model of organ-cultured gray HFs after 5 Gy irradiation is closest to the older gray HFs. Moreover, the 5 Gy inhibited the expression of TRP-1, Tyr, Pmel17, and MITF in hair bulbs/ORS of HFs. The 5 Gy also significantly induced ectopically pigmented melanocytes and increased the expression of DNA damage and senescence in HFs. Finally, RNA-seq analysis of the model suggested that IR resulted in cell DNA damage, and the accumulation of oxidative stress in the keratinocytes. Oxidative stress and DNA damage caused cell dysfunction and decreased melanin synthesis in the gray HFs. We found that HFs irradiated at 5 Gy successfully constructed an appropriate aging HF model. This may provide a useful model for cost-effective and predictable treatment strategies to human hair graying and the process of aging.

Cellular Senescence: Molecular Targets, Biomarkers, and Senolytic Drugs

Cellular senescence is defined as irreversible cell cycle arrest caused by various processes that render viable cells non-functional, hampering normal tissue homeostasis. It has many endogenous and exogenous inducers, and is closely connected with age, age-related pathologies, DNA damage, degenerative disorders, tumor suppression and activation, wound healing, and tissue repair. However, the literature is replete with contradictory findings concerning its triggering mechanisms, specific biomarkers, and detection protocols. This may be partly due to the wide range of cellular and in vivo animal or human models of accelerated aging that have been used to study senescence and test senolytic drugs. This review summarizes recent findings concerning senescence, presents some widely used cellular and animal senescence models, and briefly describes the best-known senolytic agents.