Thyrotropin Releasing Hormone: A New Player in Human Hair Growth Control

The study investigated the role of Thyrotropin-releasing hormone (TRH) in human hair growth control. Researchers found that the epithelium of normal human scalp hair follicles (HFs) not only has TRH receptors but also produces TRH itself. When HFs were treated with TRH, there was an increase in hair shaft elongation, an extension of the growth phase of the hair cycle, and a reduction in the termination of this phase by TGF-beta2. Additionally, TRH treatment resulted in increased proliferation and decreased apoptosis of hair matrix keratinocytes, potentially through the modulation of p53 phosphorylation via the ATM/Atr pathway. Microarray analysis identified several genes that were up- or down-regulated in response to TRH. The findings suggest that TRH is a significant stimulator of hair growth, indicating that human HFs can be used to explore nonclassical functions of TRH in human epithelial biology.