Conventional and novel stem cell based therapies for androgenic alopecia

Abstract

The prevalence of androgenic alopecia (AGA) increases with age and it affects both men and women. Patients diagnosed with AGA may experience decreased quality of life, depression, and feel self-conscious. There are a variety of therapeutic options ranging from prescription drugs to non-prescription medications. Currently, AGA involves an annual global market revenue of US$4 billion and a growth rate of 1.8%, indicating a growing consumer market. Although natural and synthetic ingredients can promote hair growth and, therefore, be useful to treat AGA, some of them have important adverse effects and unknown mechanisms of action that limit their use and benefits. Biologic factors that include signaling from stem cells, dermal papilla cells, and platelet-rich plasma are some of the current therapeutic agents being studied for hair restoration with milder side effects. However, most of the mechanisms exerted by these factors in hair restoration are still being researched. In this review, we analyze the therapeutic agents that have been used for AGA and emphasize the potential of new therapies based on advances in stem cell technologies and regenerative medicine.

Keywords: androgenic alopecia; dermal papilla; hair follicle; hair regeneration; laser; stem cell therapies; stem cells.

Figure 1

Diagram of the HF and factors involved in hair regeneration. Notes: The HF is composed of different cell types including HFSCs, DPCs, and ECs, among others. HFSCs migrate from the bulge area after activation by growth factors released by DPCs. However, BMP6 and FGF18 from the bulge cells exert autocrine inhibitory effects in HFSC proliferation. Once the HFSCs are closer to DPCs and ECs, they differentiate and proliferate during anagen phase, forming new hair. Activation of Wnt signaling is essential for DPCs to release the factors that promote differentiation and proliferation of HFSCs. DHT interferes with this Wnt signaling and, in this way, inhibits hair growth and promotes hair miniaturization. Effective cell–cell interactions between HFSCs, DPCs, and ECs are essential for hair growth. Abbreviations: BMP6, bone morphogenetic protein 6; DHT, dihydrotestosterone; DP, dermal papilla; DPCs, dermal papilla cells; ECs, endothelial cells; FGF18, fibroblast growth factor 18; HF, hair follicle; HFSCs, hair follicle stem cells.