Thyroid-Stimulating Hormone, a Novel, Locally Produced Modulator of Human Epidermal Functions, Is Regulated by Thyrotropin-Releasing Hormone and Thyroid Hormones

The study demonstrated that normal human epidermis expressed thyroid-stimulating hormone (TSH) at both mRNA and protein levels and transcribed TSH receptors (TSH-R). It was found that intraepidermal TSH expression was up-regulated by thyrotropin-releasing hormone (TRH) and down-regulated by thyroid hormones. Although TSH-R immunoreactivity was not observed within the epidermis, it was present in the adjacent dermis. TSH treatment in organ-cultured human skin significantly increased the expression of epidermal proteins such as involucrin, loricrin, and keratins 5 and 14. This suggested that the epidermis acted as both a source and a target of TSH signaling, regulated by the same endocrine controls as the hypothalamic-pituitary-thyroid axis.