Mediator1: An Important Intermediary of Vitamin D Receptor-Regulated Epidermal Function and Hair Follicle Biology

The document explored the roles of the vitamin D receptor (VDR) and its coactivator, mediator 1 (MED1), in skin and hair follicle biology. Research using transgenic mice and cultured keratinocytes showed that both VDR and MED1 were essential for keratinocyte differentiation and hair growth. VDR-null mice experienced hair loss and reduced keratinocyte differentiation, which dietary calcium could not prevent but was reversed by keratinocyte-targeted VDR expression. The study found that VDR's effects on hair follicles were largely independent of its ligand. MED1 ablation in mice also resulted in hair loss and increased keratinocyte proliferation, indicating its specific role in the vitamin D pathway. The findings suggested that defects in MED1 might contribute to human alopecia, and VDR might have a tumor suppressor function in the skin.