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Background and Objective In health, the periodontal ligament maintains a constant width throughout an organism’s lifetime. The molecular signals responsible for maintaining homeostatic control over the periodontal ligament are unknown. The purpose of this study was to investigate the role of Wnt signaling in this process by removing an essential chaperone protein, Wntless (Wls) from odontoblasts and cementoblasts, and observing the effects of Wnt depletion on cells of the periodontal complex. Material and Methods The Wnt responsive status of the periodontal complex was assessed using two strains of Wnt reporter mice, Axin2LacZ/+ mice and Lgr5LacZ/+. The function of this endogenous Wnt signal was evaluated by conditionally eliminating the Wntless (Wls) gene using an Osteocalcin Cre driver. The resulting OCN-Cre;Wlsfl/fl mice were examined using micro-CT and histology, immunohistochemical analyses for Osteopontin, Runx2 and Fibromodulin, in situ hybridization for Osterix, and alkaline phosphatase activity. Results The adult periodontal ligament is Wnt responsive. Elimination of Wnt signaling in the periodontal complex of OCN-Cre;Wlsfl/fl mice results in a wider periodontal ligament space. This pathologically increased periodontal width is due to a reduction in the expression of osteogenic genes and proteins, which results in thinner alveolar bone. A concomitant increase in fibrous tissue occupying the periodontal space was observed along with a disruption in the orientation of the periodontal ligament. Conclusion The periodontal ligament is a Wnt dependent tissue. Cells in the periodontal complex are Wnt responsive and eliminating an essential component of the Wnt signaling network leads to a pathological widening of the periodontal ligament space. Osteogenic stimuli are reduced and a disorganized fibrillary matrix results from depletion of Wnt signaling. Collectively, these data underscore the importance of Wnt signaling in homeostasis of the periodontal ligament.

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The therapeutic potential of Wnt proteins has long been recognized but challenges associated with in vivo stability and delivery have hindered their development as drug candidates. By exploiting the hydrophobic nature of the protein we provide evidence that exogenous Wnt3a can be delivered in vivo if it is associated with a lipid vesicle. Recombinant Wnt3a associates with the external surface of the lipid membrane; this association stabilizes the protein and leads to prolonged activation of the Wnt pathway in primary cells. We demonstrate the consequences of Wnt pathway activation in vivo using a bone marrow engraftment assay. These data provide validation for the development of WNT3A as a therapeutic protein.

Many ciliopathies have clinical features that include tooth malformations but how these defects come about is not clear. Here we show that genetic deletion of the motor protein Kif3a in dental mesenchyme results in an arrest in odontogenesis. Incisors are completely missing, and molars are enlarged in Wnt1 Cre+ Kif3a fl/fl embryos. Although amelogenesis and dentinogenesis initiate in the molar tooth bud, both processes terminate prematurely. We demonstrate that loss of Kif3a in dental mesenchyme results in loss of Hedgehog signaling and gain of Wnt signaling in this same tissue. The defective dental mesenchyme then aberrantly signals to the dental epithelia, which prompts an upregulation in the Hedgehog and Wnt responses in the epithelia and leads to multiple attempts at invagination and an expanded enamel organ. Thus, the primary cilium integrates Hedgehog and Wnt signaling between dental epithelia and mesenchyme, and this cilia-dependent integration is required for proper tooth development.