Wnt signaling influences the development of murine epidermal Langerhans cells

Langerhans cells (LCs) are distinct dendritic cells (DCs) that populate stratified squamous epithelia. Despite extensive studies, our understanding of LC development is incomplete. Transforming growth factor β1 (TGFβ1) is required for LC development, but other epidermis-derived influences may also be important. Recently, EpCAM (CD326) has been identified as a cell surface protein discriminating LCs from Langerin(+) dermal DCs and other DCs in the skin. EpCAM is a known transcriptional target of the Wnt signaling pathway. We hypothesized that intraepidermal Wnt signaling might influence LC development. Addition of Wnt3A into cultures of bone-marrow-derived cells in combination with TGFβ1, GM-CSF, and M-CSF resulted in increased (33%; P<0.05) accumulation of EpCAM(+) DCs. In contrast, addition of the Wnt antagonist dickkopf-related protein 1 (Dkk1) decreased the number of EpCAM(+) DCs (21%; P<0.05). We used K14-KRM1; K5-rtTA; tetO-Dkk1 triple-transgenic and K5-rtTA; tetO-Dkk1 double-transgenic mice to test the in vivo relevance of our in vitro findings. Feeding doxycycline to nursing mothers induced expression of Dkk1 in the skin of transgenic pups, causing an obvious hair phenotype. Expression of Dkk1 reduced LC proliferation (40%; P<0.01) on P7, decreased LC densities (26%; P<0.05) on P14, and decreased EpCAM expression intensities on LCs as well (33%). In aggregate, these data suggest that Wnt signaling in skin influences LC development.