An immunopharmacological approach to identifying novel targets for human hair growth stimulation: From cyclosporine A to Wnt signalling

Abstract

The human hair follicle (HF) is a mini-organ that transitions between phases of growth (anagen), regression (catagen) and quiescence (telogen), collectively known as the HF cycle. While it is well appreciated that dysregulation of the HF cycle leads to hair loss, the current pharmacological treatment to prevent alopecia is unsatisfactory, with patients limited to only two FDA approved treatment options. As an innovative strategy to develop more effective hair growth promoting agents, we turned to the calcineurin inhibitor, cyclosporine A (CsA), which characteristically induces hypertrichosis in transplant patients after systemic application. The underlying molecular mechanisms of CsA-induced hair growth have been explained in part by blocking the nuclear translocation of the NFAT family of transcription factors. However, since these observations are derived entirely from murine models, it is therefore completely unknown if they translate to the human HF. Using micro-dissected, organ-cultured human scalp HFs, whose ex vivo growth characteristics mimic their in vivo behaviour, we demonstrate that CsA prolongs active hair growth (anagen) through blocking catagen. In addition, utilising qRT-PCR and immunofluorescence microscopy we provide evidence that this is independent of the NFAT pathway, suggesting that other signalling mechanisms underlie its catagen-inhibitory effect in humans. To identify how CsA prolongs anagen in humans, microarray analysis was performed on CsA treated human HFs ex vivo. This revealed that, despite the extensive CsA literature, Wnt signalling is an overlooked, non-immune inhibitory target of CsA within the HF. Specifically, we show that CsA inhibits the expression of SFRP1, a secreted Wnt inhibitor, in the mesenchymal command centre of the HF, the dermal papilla. We also identify that SFRP1 takes part in an intricate mesenchymal-epithelial interaction that regulates canonical beta-catenin activity through antagonising Wnt ligands within the epithelium. The use of a reportedly well tolerated and specific SFRP1 inhibitor, WAY-316606, enhanced hair shaft elongation and inhibited catagen, exactly replicating the desired therapeutic effect of CsA. Since CsA is known to activate epithelial hair follicle stem cells (eHFSCs) and induce anagen in murine models, the SFRP1-Wnt pathway recognised here, may provide an insight into how CsA modulates the telogen-anagen transition in humans. Taking advantage of freshly isolated telogen and early-anagen HFs, for the first time, we have mapped the molecular components of the Wnt/beta-catenin pathway within the telogen-to-anagen transition of the human HF cycle. This revealed that Wnt activity is elevated within the secondary hair germ and eHFSCs upon anagen induction, and this was accompanied by a reduction in SFRP1 protein. Collectively this suggests that SFRP1 negatively regulates Wnt/beta-catenin activity in the telogen HF and may act as a switch for anagen induction in humans. The novel pharmacological mechanism of action by WAY-316606 elucidated here, and the function of SFRP1 in telogen HFs, may serve to develop a new generation of hair growth promoters to help cure various forms of alopecia.

Date of Award	1 Aug 2018
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Ralf Paus (Supervisor) & Iain Haslam (Supervisor)