COCH Expression in the Hair Follicle Microenvironment Is Associated With Cortical Disulfide Bonding and Tensile Resistance in Aging Hair.

Although hair aging affects appearance and hair quality, objective biomarkers linking molecular alterations to clinically relevant mechanical properties of hair remain limited. Here, we investigated the relationships among age, hair tensile resistance, and cortical disulfide bond content. Hair shafts from healthy volunteers (20-40 years vs. > 50 years) were analysed for tensile resistance, which was measured as maximum tensile force, and disulfide bond content was assessed by Raman spectroscopy. In parallel, human scalp hair follicles were stratified according to disulfide bond content and donor age to generate transcriptomic datasets for analysis. We identified follicular gene-expression signatures associated with these parameters. Differential expression analysis revealed a shared gene set associated with reduced disulfide bond content and age, which was subsequently evaluated in ex vivo human hair follicle cultures. Among these candidates, cochlin (COCH) emerged as a prominent candidate gene associated with higher cortical disulfide bond content and enhanced tensile resistance of the hair shaft. Immunohistochemical analysis revealed that COCH predominantly localized to the hair matrix and outer root sheath, supporting a follicle-derived contribution to shaft biochemistry. Together, these findings identify COCH as a promising candidate marker linked to disulfide bond integrity and tensile properties of human hair and establish an integrative framework for connecting follicular gene expression with age-associated changes in hair shaft mechanics.