ABSTRACT: Transcriptome profiling reveals different expression pattern in baseline group(after isolated hair follicles---HFs,collect samples immediately), 0G group(sham irradiation, collect organ-cultured HFs for 3 days),and 5G group(5G dose irradiation, collect organ-cultured HFs for 3 days) in ex vivo organ-cultured HFs. Hair greying or canities is one of the earliest phenomena in aging. A worldwide survey based on a large sample of human subjects showed that men grey faster than women, but in distinct scalp regions, and the populations of Asian and African descent had less grey hair than those of the same age of Caucasian descent. The average grey hair age of whites is 34 ± 9.6 years in Caucasians, while 43.9 ± 10.3 years in African. And then clinical observation demonstrates that by the age of 50 in 50% of all men in senile canities, 50% of all hair follicles (HFs) have lost their pigment. In addition, an increasing number of studies found that hair greying acts as an important predictor of aging-associated pathology, including Alzheimer’s disease, Parkinson’s disease and cardiovascular disease, etc. Grey hair is both visible and non-lethal, and it makes this phenotype a unique model system for investigating mechanisms that contribute to tissue aging and therapeutic strategies to combat this process. In humans and mice, age-related grey hair is attributed to the loss of melanocyte stem cells (MeSCs), precursor cells, and melanocytes, or their reduced or restricted functions, which is induced by a multitude of exogenous and endogenous challenges, such as radiation, inflammation, psycho-emotional stress, or gene mutation (BCL-2 deficiency), etc. Of which, ionizing radiation (IR) produces multiple clusters of double-strand breaks that mediate cell cycle arrest, apoptosis, and DNA repair, and successfully induces grey hair in mice. The accelerating process of aging by IR may provide an avenue to create a grey hair model. Although there is a mouse model of grey hair, the existence of species differences also limits the translational potential of the mice HF models for human applications. Recently, Rachmin et al demonstrated that IR could result to ectopically pigmented melanocytes (EPM) in outer root sheath (ORS) followed hair greying and speculated that this may provide a tool to prevent or reverse hair greying in humans. They proved that different genotoxicity can induce premature differentiation of MeSCs and/or amelanotic cells. However, they didn’t determine the appropriate dose of irradiation for creating the hair grey model and not discuss the mechanisms of forming the model. Hence, this study focuses on establishing a suitable ex vivo human grey HF model by IR, demonstrating the series change of grey hair and exploring the possible mechanisms of the model. In our study, parameters about senescence and melanotic features in our model are almost in line with essential traits of human grey hair in previous studies. In addition,to explore the profound mechanism of the irradiated model, we performed transcriptome analysis for baseline, 0G and 5G groups. Then, three pairwise comparisons were established---0G vs 5G, baseline vs 5G and baseline vs 0G. This profiling results be used to understand the different molecular mechanism of creating ex vivo grey HFs model,and those provided a possibility for anti-aging treatment.In summary, our results indicate that the ex vivo grey HFs by irradiation can perfectly replace elderly grey hair and establish a potential preclinical aging model for pharmacological and mechanism studies.
