Human Female Hair Follicles Are a Direct, Nonclassical Target for Thyroid-Stimulating Hormone

The study investigated the role of thyroid-stimulating hormone (TSH) in human female hair follicles (HFs) and found that these follicles were direct, nonclassical targets for TSH. Despite the presence of TSH receptors (TSH-R) in the mesenchymal compartments of scalp HFs, TSH did not significantly affect hair growth, cycling, or pigmentation in vitro. However, TSH treatment increased cAMP secretion and altered gene expression, indicating functional TSH-R activity. The study involved approximately 30 HFs from two female donors and suggested that TSH might influence HF functions indirectly through mesenchymal signaling, affecting gene expression related to hair keratin and keratin-associated proteins. These findings highlighted the potential of HFs as a model for understanding nonclassical TSH functions beyond traditional thyroid-related activities.