Investigation of the molecular signature of greying hair shafts

Abstract

Objective Hair greying (i.e. canitie) is a physiological process occurring with the loss of melanin production and deposition within the hair shafts. Many studies reported the oxidation as the main biological process underlying this defect of pigmentation. Even though the overall appearance and biomechanical properties of hairs are reported to be altered with greying, there is a lack of information about molecular modifications occurring in grey hair shafts. The aim of this study was thus to investigate the molecular signature and associated changes occurring in greying hair shafts by confocal Raman microspectroscopy. Methods This study was conducted on pigmented, intermediate (i.e. grey) and unpigmented hairs taken from 29 volunteers. Confocal Raman microspectroscopy measurements were acquired directly on hair shafts. Results Automatic classification of Raman spectra revealed 5 groups displaying significant differences. Hence, the analysis of the molecular signature highlighted the existence of 3 sub‐groups within grey hair: light, medium and dark intermediate. Among molecular markers altered in the course of greying, this study identified for the first time a gradual modification of lipid conformation (trans/gauche ratio) and protein secondary structure (α‐helix/β‐sheet ratio), referring respectively to an alteration of barrier function and biomechanical properties of greying hair. Conclusion This study thus reports for the first time a highly specific molecular signature as well as molecular modifications within grey hair shaft.

The Role of Lipids in the Process of Hair Ageing

“…The µ-FTIR analyses of the lipid peaks inside the fibre confirmed a higher frequency value in the white hair, especially in the cuticle and cortex, indicating greater lipid disorder in these regions of the white hair. This is consistent with the higher diffusion results for the grey hair fibre, according to a reported gradual modification of the lipid conformation trans/gauche in greying [29]. Moreover, the peak amplitude was always lower in the white fibres in all three regions, with the difference being much more marked in the medulla.…”

“…Lipids in the hair follicle root differed between brown and white hair with a reduction in their content [27]; similar results were obtained in the different hair shaft sections: the cuticle, cortex and medulla [11]. In addition, a gradual modification of lipid conformation (trans/gauche ratio) was associated with changes in grey hair shafts related to the alteration of barrier function in greying hair [29]. Therefore, this work focused on the role of exogenous and endogenous lipids in brown and white Caucasian hairs to determine their influence on several physico-chemical properties.…”

“…This indicates a greater lipid disorder in these regions of white hair and is consistent with the higher diffusion results for grey hair fibres. A recent confocal Raman microspectroscopy study identified a gradual modification of lipid conformation trans/gauche in greying hair for the first time [29]. The increase in the gauche conformers obtained on unpigmented hairs supports the increase in lipid fluidity, as demonstrated by the peak frequency increase in the white hairs.…”

“…The reduced lipid content of all hair shaft sections-the cuticle, cortex, and medulla-occurs with advancing age and affects the clinical properties of grey hair [11]. The lipid order structure was also found to be modified in greying hair [28], and a gradual modification of lipid conformations (trans/gauche ratio) was associated with changes in grey hair shafts related to the alteration of the barrier function [29].…”

Quantitative mapping of human hair greying and reversal in relation to life stress

“…Our findings demonstrating an upregulation of the fatty acid synthesis and metabolism machinery resonate particularly strongly with recent work demonstrating that fatty acid synthesis by FASN ( Fafián-Labora et al, 2019 ) and transport by CPT1a ( Seok et al, 2020 ) are sufficient drivers of cell senescence, and that fatty acid metabolism regulates melanocyte aging biology ( Tang et al, 2019 ). Approaches combining both high molecular and spatial resolution may be particularly informative ( Vyumvuhore et al, 2021 ). Causally linking these putative metabolic changes to canonical aging and/or senescence markers in human hair shafts and among specific HF cell populations will be an important challenge for the field.…”