Thomas S. Lisse, Vaibhav Saini, Hengguang Zhao, Hilary F. Luderer, Francesca Gori, Marie B. Demay

Alopecia (hair loss) in vitamin D receptor (VDR)-null mice is due to absence of ligand-independent actions of the VDR that are required for initiation of post-morphogenic hair cycles. Investigations were undertaken to determine if the VDR is required for induction of signaling pathways that play an important role in this process. The induction of cWnt and hedgehog target genes that characterizes early anagen was found to be dramatically attenuated in VDR(-/-) mice, relative to wild type mice. To determine if this reflects impaired responsiveness to cWnt ligands, in vitro studies were performed in primary keratinocytes. These studies demonstrated impaired induction of cWnt target genes in response to Wnt 3a in VDR(-/-) keratinocytes, relative to wild type keratinocytes. Chromatin immunoprecipitation (ChIP) analyses revealed that the VDR was recruited to the regulatory regions of cWnt and hedgehog target genes in WT keratinocytes, but not in VDR(-/-) or Lef1(-/-) keratinocytes. Lef1 was enriched on these same regulatory regions in WT keratinocytes, but not in VDR(-/-) keratinocytes. In vivo studies were performed to determine if activation of the hedgehog pathway could bypass the defect in cWnt signaling observed in the absence of the unliganded VDR. In WT, but not VDR(-/-) mice, hedgehog agonist treatment resulted in induction of cWnt and hedgehog target genes and generation of mature anagen hair follicles. Thus, these studies demonstrate that the unliganded VDR interacts with regulatory regions in cWnt and hedgehog target genes and is required for induction of these pathways during the post-natal hair cycle.