Gli1+ Periodontal Mesenchymal Stem Cells in Periodontitis

Periodontal mesenchymal stem cells (MSCs) play a crucial role in maintaining periodontium homeostasis and in tissue repair. However, little is known about how periodontal MSCs in vivo respond under periodontal disease conditions, posing a challenge for periodontium tissue regeneration. In this study, Gli1 was used as a periodontal MSC marker and combined with a Gli1-cre ERT2 mouse model for lineage tracing to investigate periodontal MSC fate in an induced periodontitis model. Our findings show significant changes in the number and contribution of Gli1+ MSCs within the inflamed periodontium. The number of Gli1+ MSCs that contributed to periodontal ligament homeostasis decreased in the periodontitis-induced teeth. While the proliferation of Gli1+ MSCs had no significant difference between the periodontitis and the control groups, more Gli1+ MSCs underwent apoptosis in diseased teeth. In addition, the number of Gli1+ MSCs for osteogenic differentiation decreased during the progression of periodontitis. Following tooth extraction, the contribution of Gli1+ MSCs to the tooth socket repair was significantly reduced in the periodontitis-induced teeth. Collectively, these findings indicate that the function of Gli1+ MSCs in periodontitis was compromised, including reduced contribution to periodontium homeostasis and impaired injury response.

Dental Pulp Stem Cell Polarization: Effects of Biophysical Factors

Dental pulp stem cells (DPSCs) have the potential to polarize, differentiate, and form tubular dentin under certain conditions. However, the factors that initiate and regulate DPSC polarization and its underlying mechanism remain unclear. Identification of the factors that control DPSC polarization is a prerequisite for tubular dentin regeneration. We recently developed a unique bioinspired 3-dimensional platform that is capable of deciphering the factors that initiate and modulate cell polarization. The bioinspired platform has a simple background and confines a single cell on each microisland of the platform; therefore, it is an effective tool to study DPSC polarization at the single-cell level. In this work, we explored the effects of biophysical factors (surface topography, microisland area, geometry, tubular size, and gravity) on single DPSC polarization. Our results demonstrated that nanofibrous architecture, microisland area, tubular size, and gravity participated in regulating DPSC polarization by influencing the formation of the DPSC process and relocation of the Golgi apparatus. Among these factors, nanofibrous architecture, tubular size, and appropriate microisland area were indispensable for initiating DPSC polarization, whereas gravity served as an auxiliary factor to the process of DPSC polarization. Meanwhile, microisland geometry had a limited effect on DPSC polarization. Collectively, this work provides information on DPSC polarization and paves the way for the development of new biomaterials for tubular dentin regeneration.

Oral Sciences PhD Program Enrollment, Graduates, and Placement: 1994 to 2016

For decades, dental schools in the United States have endured a significant faculty shortage. Studies have determined that the top 2 sources of dental faculty are advanced education programs and private practice. Those who have completed both DDS and PhD training are considered prime candidates for dental faculty positions. However, there is no national database to track those trainees and no evidence to indicate that they entered academia upon graduation. The objective of this study was to assess outcomes of dental school-affiliated oral sciences PhD program enrollment, graduates, and placement between 1994 and 2016. Using the American Dental Association annual survey of advanced dental education programs not accredited by the Commission on Dental Accreditation and data obtained from 22 oral sciences PhD programs, we assessed student demographics, enrollment, graduation, and placement. Based on the data provided by program directors, the average new enrollment was 33, and graduation was 26 per year. A total of 605 graduated; 39 did not complete; and 168 were still in training. Among those 605 graduates, 211 were faculty in U.S. academic institutions, and 77 were faculty in foreign institutions. Given that vacant budgeted full-time faculty positions averaged 257 per year during this period, graduates from those oral sciences PhD programs who entered academia in the United States would have filled 9 (3.6%) vacant faculty positions per year. Therefore, PhD programs have consistently generated only a small pipeline of dental school faculty. Better mentoring to retain talent in academia is necessary. Stronger support and creative funding plans are essential to sustain the PhD program. Furthermore, the oral sciences PhD program database should be established and maintained by dental professional organizations to allow assessments of training models, trends of enrollment, graduation, and placement outcomes.

Biglycan and Decorin Expression and Distribution in Palatal Adhesion

Previous studies demonstrated that chondroitin sulfate proteoglycans (CSPGs) on apical surfaces of palatal medial edge epithelial (MEE) cells were necessary for palatal adhesion. In this study, we identified 2 proteoglycans, biglycan and decorin, that were expressed in the palatal shelves prior to adhesion. In addition, we established that these proteoglycans were dependent on transforming growth factor β (TGFβ) signaling. Laser capture microdissection was used to collect selected palatal epithelial cells from embryonic mouse embryos at various palate development stages. The expression of specific messenger RNA (mRNA) for biglycan and decorin was determined with quantitative real-time polymerase chain reaction. The TGFβrI kinase inhibitor (SB431542) was used in palatal organ cultures to determine if blocking TFGβ signaling changed biglycan and decorin distribution. Immunohistochemistry of both biglycan and decorin revealed expression on the apical and lateral surfaces of MEE cells. Biglycan protein and mRNA levels peaked as the palatal shelves adhered. Decorin was less abundant on the apical epithelial surface and also had reduced mRNA levels compared to biglycan. Their proteins were not expressed on MEE cells of palates treated with SB431542, an inhibitor of TGFβ signaling. The temporal expression of biglycan and decorin on the apical surface of MEE, combined with the evidence that these proteins were regulated through the TGFβ pathway, indicated that they may be important for adhesion.

Epithelial-mesenchymal transformation during craniofacial development

Epithelial to mesenchymal phenotype transition is a common phenomenon during embryonic development, wound healing, and tumor metastasis. This transition involves cellular changes in cytoskeleton architecture and protein expression. Specifically, this highly regulated biological event plays several important roles during craniofacial development. This review focuses on the regulation of epithelial-mesenchymal transformation (EMT) during neural crest cell migration, and fusion of the secondary palate and the upper lip.

Nicotine inhibits palatal fusion and modulates nicotinic receptors and the PI-3 kinase pathway in medial edge epithelia

OBJECTIVES

To analyze the effects of nicotine on palatal fusion inhibition in vitro and determine if nicotine modulated transforming growth factor beta3 or phosphatidylinositol-3 kinase signaling. A second objective was to determine the localization and regulation of nicotinic receptors in the medial edge epithelia (MEE) during palatal fusion.

DESIGN

Palatal shelves from embryonic day (E) 13.5 mice were cultured in serum free media and treated with 0, 0.06, 0.6, or 6 mM nicotine, nicotinic receptor antagonist alpha-bungarotoxin, or the combination of nicotine and alpha-bungarotoxin. Tissues harvested at 72 h were analyzed for epithelial-mesenchymal transformation (EMT) and fusion. MEE samples collected at 20 h were analyzed for phosphorylated Akt-Ser473, phosphorylated Smad2, and nicotinic receptors.

RESULTS

Nicotine inhibited palatal fusion in vitro in a dose dependent manner. Activated Akt-Ser473 was greater in control MEE than in nicotine treated tissues; while there was no difference in activated Smad2 between groups. The alpha7 subunit of nicotinic receptor was expressed in MEE during palate fusion and increased in nicotine treated tissues. Alpha-bungarotoxin did not rescue the nicotine treated palates.

CONCLUSION

Nicotine treatment had no effect on Smad2, but caused a down regulation of the PI-3 kinase pathway that may have contributed to inhibiting palatal fusion in vitro.