The Hippo Pathway Effectors YAP/TAZ Are Essential for Mineralized Tissue Homeostasis in the Alveolar Bone/Periodontal Complex.

YAP and TAZ are essential transcriptional co-activators and downstream effectors of the Hippo pathway, regulating cell proliferation, organ growth, and tissue homeostasis. To ask how the Hippo pathway affects mineralized tissue homeostasis in a tissue that is highly reliant on a tight homeostatic control of mineralized deposition and resorption, we determined the effects of YAP/TAZ dysregulation on the periodontal tissues alveolar bone, root cementum, and periodontal ligament. Loss of YAP/TAZ was associated with a reduction of mineralized tissue density in cellular cementum and alveolar bone, a downregulation in collagen I, alkaline phosphatase, and RUNX2 gene expression, an increase in the resorption markers TRAP and cathepsin K, and elevated numbers of TRAP-stained osteoclasts. Cyclic strain applied to periodontal ligament cells resulted in YAP nuclear localization, an effect that was abolished after blocking YAP. The rescue of YAP signaling with the heparan sulfate proteoglycan agrin resulted in a return of the nuclear YAP signal. Illustrating the key role of YAP on mineralization gene expression, the YAP inhibition-related downregulation of mineralization-associated genes was reversed by the extracellular matrix YAP activator agrin. Application of the unopposed mouse molar model to transform the periodontal ligament into an unloaded state and facilitate the distal drift of teeth resulted in an overall increase in mineralization-associated gene expression, an effect that was 10-20% diminished in Wnt1Cre/YAP/TAZ mutant mice. The unloaded state of the unopposed molar model in Wnt1Cre/YAP/TAZ mutant mice also caused a significant three-fold increase in osteoclast numbers, a substantial increase in bone/cementum resorption, pronounced periodontal ligament hyalinization, and thickened periodontal fiber bundles. Together, these data demonstrated that YAP/TAZ signaling is essential for the microarchitectural integrity of the periodontium by regulating mineralization gene expression and preventing excessive resorption during bodily movement of the dentoalveolar complex.

The Glycoprotein/Cytokine Erythropoietin Promotes Rapid Alveolar Ridge Regeneration In Vivo by Promoting New Bone Extracellular Matrix Deposition in Conjunction with Coupled Angiogenesis/Osteogenesis.

The loss of bone following tooth extraction poses a significant clinical problem for maxillofacial esthetics, function, and future implant placement. In the present study, the efficacy of an erythropoietin-impregnated collagen scaffold as an alveolar ridge augmentation material versus a conventional collagen scaffold and a BioOss inorganic bovine bone xenograft was examined. The collagen/Erythropoietin (EPO) scaffold exhibited significantly more rapid and complete osseous regeneration of the alveolar defect when compared to bone xenograft and the collagen membrane alone. The new EPO induced extracellular matrix was rich in Collagen I, Collagen III, Fibronectin (Fn) and E-cadherin, and featured significantly increased levels of the osteogenic transcription factors Runt-related transcription factor 2 (Runx2) and Osterix (Osx). Histomorphometric evaluation revealed a significant two-fold increase in the number of capillaries between the EPO and the BioOss group. Moreover, there was a highly significant 3.5-fold higher level of vascular endothelial growth factor (VEGF) in the collagen/EPO-treated group compared to controls. The significant effect of EPO on VEGF, FN, and RUNX2 upregulation was confirmed in vitro, and VEGF pathway analysis using VEGF inhibitors confirmed that EPO modulated extracellular matrix protein expression through VEGF even in the absence of blood vessels. Together, these data demonstrate the effectiveness of an EPO-impregnated collagen scaffold for bone regeneration as it induces rapid matrix production and osseoinduction adjacent to new capillaries via VEGF.

Meal patterns in female rats during and after intermittent nicotine administration.

Previously we observed in male rats that intermittent administration of nicotine (NIC) during the dark phase reduces food intake (FI) by initially decreasing only dark phase meal size. This was followed several days later by an increase in dark phase meal frequency such that FI returned to normal, while body weight remained suppressed. Termination of NIC treatment resulted in a modest dark phase hyperphagia. Since some human females use NIC as a weight control drug, the present study investigated changes in FI and body weight regulation in adult female rats treated for five estrous cycles with saline or a 1.40 mg/kg/day (free base) dose of NIC, which was given in four equal i.p. doses during the dark phase. The rats were followed for 15 days after cessation of NIC. Initially both dark and light phase FI were reduced and this was caused by an immediate decrease in dark and light phase meal size; the attenuation of meal size continued after cessation of NIC. On day 7 of NIC, the rats compensated by significantly increasing the number of dark, but not light, phase meals they took. This resulted in a normal 24-h FI, which was caused by a dark phase increase in FI coupled with a continued decrease in light phase FI. Importantly, these changes in meal patterns persisted for some time after termination of NIC. Upon NIC cessation, the NIC group showed no hyperphagia even though their body weight was significantly decreased. These results document that administration of NIC during the dark phase resulted in a reorganization of the microstructure of FI in females rats that resembles, but does not exactly duplicate, that observed in male rats. Like males, long lasting alterations in the microstructure of FI (e.g., meal size and meal number), were noted in female rats for up to 2 weeks after cessation of NIC. These results differ from studies in which NIC was given continuously 24-h per day and indicate that dark phase NIC administration in rats may represent an appropriate model to study the impact of NIC on meal patterns.