BMP: bone morphogenetic protein DMEM: Dulbecco's modified Eagle's medium ELISA: enzyme-linked immunosorbent assay ENA: epithelial cell-derived neutrophil-activating peptide FGF: fibroblast growth factor GMB: gelatin hydrogel microsphere bead GRO: growth-related oncogene HB-EGF: heparin-binding EGF-like growth factor

Dermal papilla cells (DPCs) in the mammalian hair follicle have been shown to develop hair follicles through epithelial-mesenchymal interactions. A cell therapy to regenerate human hair is theoretically possible by expanding autologous human DPCs and transplanting them into bald skin, though much remains to be overcome before clinical success. In this study, we compared gene signatures of human DPCs at different passages and human dermal fibroblasts, and found TGF-β2 to be highly expressed in cultured human DPCs. Keratinocyte conditioned medium, which is known to help preserve the hair inducing capacity of hDPCs, upregulated TGF-β2 expression of human DPCs and also enhanced their alkaline phosphatase activity, a known index for hair inductive capacity. Through screening of components secreted from keratinocytes, the vitamin D3 analogue was found to promote TGF-β2 expression and alkaline phosphatase activity of human DPCs. In animal hair folliculogenesis models using rat epidermis and expanded human DPCs, inhibition of TGF-β2 signaling at the ligand or receptor level significantly impaired hair folliculogenesis and maturation. These results suggest an important role for TGF-β2 in hair follicle morphogenesis and provide insights into the establishment of future cell therapies for hair regrowth by transplanting expanded DPCs.