The neuropeptide galanin is a novel inhibitor of human hair growth

Background Galanin is a trophic factor of the central and peripheral nervous system that shows widespread distribution in human skin. However, the exact localization and the role of galanin in the hair follicle (HF) remain to be clarified. Objectives To characterize galanin expression in human scalp HFs and to examine the effects of galanin on normal human scalp HF growth in organ culture. Methods Immunohistochemistry was performed on cryosections of human female scalp skin. Anagen HFs were microdissected and cultured up to 9 days and treated with 100 nmol L-1 galanin. Staining for Ki-67, TUNEL and Masson-Fontana were used to analyse proliferation, apoptosis and hair cycle staging of the HFs. Functional effects of galanin were tested in serum-free HF organ culture. Results Galanin-like immunoreactivity was detected in the outer root sheath (ORS) and inner root sheath. Additionally, galanin mRNA was detected in ORS keratinocytes and all HF samples tested. Galanin receptor transcripts (GalR2, GalR3) were also detected in selected samples. Galanin reduced proliferation of hair matrix keratinocytes in situ compared with vehicle-treated controls, shortened the hair growth phase (anagen) in vitro and reduced hair shaft elongation. This was accompanied by the premature development of a catagen-like morphology of galanin-treated HFs. Conclusions We present the first evidence that human HFs are both a source and a functionally relevant target of galanin. Due to its hair growth-inhibitory properties in vitro, galanin application deserves further exploration as a potential new treatment strategy for unwanted hair growth (hirsutism, hypertrichosis).