The Hair Cycle and Vitamin D Receptor

The study highlighted the critical role of the Vitamin D receptor (VDR) in maintaining hair follicle function, particularly in keratinocyte stem cells located in the bulge region of the hair follicle. While calcium could compensate for the absence of VDR in epidermal keratinocyte differentiation, it could not prevent the hair follicle defects caused by VDR ablation. These defects were independent of 1,25-dihydroxyvitamin D, indicating that VDR's role in hair follicle cycling did not rely on this form of vitamin D. The absence of a functional VDR led to defects in stem cell self-renewal and lineage progression, resulting in the absence of post-morphogenic hair cycles. The specific molecular partners and target genes of VDR in these stem cells were not identified at the time.