804 Human hair follicles operate core elements of a functional peripheral equivalent of the central hypothalamic-pituitary-thyroid axis

This study provides the first evidence that human scalp hair follicles (HFs) operate core elements of a functional peripheral equivalent of the central hypothalamic-pituitary-thyroid (HPT) axis. Researchers used immunofluorescence microscopy and in situ hybridization to confirm the presence of all HPT axis components in HFs. When treated with thyrotrophin-releasing hormone (TRH) or thyrotropin (TSH), HFs showed increased expression of TSH, TRHR, TSHR, and THRβ proteins, indicating a positive feedback loop, which contrasts with the negative feedback observed in the brain. This suggests that HFs have an independent HPT axis, and further research is being conducted to understand its role in HF physiology.