Epithelial Cell Rests of Malassez Provide a Favorable Microenvironment for Ameliorating the Impaired Osteogenic Potential of Human Periodontal Ligament Stem Cells

Effect of Porphyromonas Gingivalis Infection on Epithelial Rests of Malassez

The epithelial cell rests of Malassez (ERM) are located within the periodontal ligament. They are reportedly involved in maintaining homeostasis, particularly with regards to the thickness of the periodontal ligament. Their role in apical periodontitis lesions remains unclear, however. This study investigated the response of ERM to infection with Porphyromonas gingivalis. After being infected, the morphology of the P. gingivalis-infected cells was observed using confocal laser-scanning microscopy. The gene expression of P. gingivalis-infected and uninfected cells was investigated by RNA-sequencing analysis. Morphological observation showed the invasion and adhesion of P. gingivalis to the surface of ERM. The RNA analysis showed that the gene expression profile significantly differed between the infected and uninfected cells. At an expression level of ≥2 and false discovery rate of <0.1, the infected cells showed a decrease in 99 genes and an increase in 6 compared with in the non-infected cells. Most of the upregulated genes were unique to epithelial cells, such as endothelial cell-specific molecules and cytokeratin 5; the upregulated genes were associated with the immune response, however. These results indicate that ERM upregulate genes associated with epithelial cells and suppress those associated with the immune response following P. gingivalis infection.

A Combinatorial Approach to Regenerate the Periodontal Ligament and Cementum in a Nondental Microenvironment

While treated dentin matrix (TDM) has been used for regeneration of dental tissues, the quality and quantity of regenerated periodontal tissue structure are suboptimal. The present study was undertaken to test whether the combined use of the TDM with dental follicle cells (DFCs) and Hertwig's epithelial root sheath (HERS) cells enhances the regeneration of periodontal structures in a nondental microenvironment. TDMs were fabricated from 3-month-old Sprague-Dawley (SD) rats. DFCs and HERS cells were isolated from postnatal 7-day SD rats. Purified DFCs and HERS cells, both in combination or alone, were seeded and cultured on TDM in vitro and characterized. The cell-seeded TDMs were subsequently implanted into a 3-month-old rat greater omentum for 6 weeks, and further histological evaluation was performed. The results showed that cells grew well on the surface of TDMs, and mineralized nodules could be seen, especially in the HERS + DFCs group. After transplantation in rat omentum, periodontal ligament-like fibers and cementum-like structures were observed around the TDM in 1/3 of the samples in both the HERS group and the DFCs group and in 2/3 of the samples in the HERS + DFCs group, while almost no attached tissue formation was found in the TDM only group. The formed cementum width and the periodontal ligament length were significantly larger in the HERS + DFCs group. The periodontal ligament-like fibers in the HERS + DFCs group were orderly arranged and attached to the cementum-like tissues, which resembled the cementum-periodontal structure. Therefore, the combined use of DFCs, TDM, and HERS cells may be a promising strategy for the regeneration of the periodontal structures, especially in the nondental microenvironment.

Gold nanoparticles enhance proliferation and osteogenic differentiation of periodontal ligament stem cells by PINK1-mediated mitophagy

OBJECTIVE

Evidence suggests that gold nanoparticles (AuNPs) improve osteogenic differentiation of periodontal ligament stem cells (PDLSCs), PTEN-induced putative kinase 1 (PINK1) dependent mitophagy modulates inter-clonal communication among PDLSCs with osteogenic heterogeneity, but the mechanism remains vague. Therefore, the current research assessed the influence of AuNPs on proliferation, osteogenic differentiation and mitophagy of PDLSCs and the potential mechanism was analyzed.

METHODS

Gold nanospheres with a diameter of 5, 10, 20, 40, and 80 nm were synthesized and characterized through transmission electron microscopy, and rat PDLSCs were isolated using flow sorting. Next, PDLSCs were treated with AuNPs or PINK1 lentivirus to obtain its overexpression or suppression. Proliferation and osteogenic differentiation were evaluated by CCK-8, ALP staining, ARS staining, and immunoblotting of OCN, OPN, RUNX2, ALP, BMP2, and COL1. Mitochondrial quality, homeostasis and quantity were assessed though JC-1 staining, immunoblotting of Tom20, Tim23 and HSP60 and mitochondrial ROS detection. PINK1, Parkin, Beclin1 and LC3 expression was quantified to investigate mitophagy, using RT-qPCR and immunoblotting and the formation of RFP-GFP-LC3-labeled autophagosomes were also measured.

RESULTS

The proliferation ability of PDLSCs almost reached the maximum under 20 nm AuNPs for 24 h. AuNPs enhanced the proliferation and osteogenic differentiation of PDLSCs, improved mitochondrial quality and homeostasis as well as attenuated mitochondrial quantity. Additionally, mitophagy was enhanced by PDLSCs. Activation of PINK1 synergistically enhanced AuNPs-mediated mitophagy, mitochondrial quality, homeostasis and osteogenic differentiation in PDLSCs, obtaining opposite effects when PINK1 was suppressed.

CONCLUSION

AuNPs enhance proliferation and osteogenic differentiation of PDLSCs through PINK1-mediated mitophagy.

Strategies and Challenges in the Treatment of Dental Enamel

Enamel tissue, the hardest body tissue, which covers the outside of the tooth shields the living tissue, but it erodes and disintegrates in the acidic environment of the oral cavity. On the one hand, mature enamel is cell-free and, if damaged, does not regenerate. Tooth sensitivity and decay are caused by enamel loss. On the other hand, the tissue engineering approach is challenging because of the unique structure of tooth enamel. To develop an exemplary method for dental enamel rebuilding, accurate knowledge of the structure of tooth enamel, knowing how it is created and how proteins interact in its structure, is critical. Furthermore, novel techniques in tissue engineering for using stem cells to develop enamel must be established. This article aims to discuss current attempts to regenerate enamel using synthetic materials methods, recent advances in enamel tissue engineering, and the prospects of enamel biomimetics to find unique insights into future possibilities for repairing enamel tissue, perhaps the most fascinating of all tooth tissues.

Hypes and Hopes of Stem Cell Therapies in Dentistry: a Review

One of the most exciting advances in life science research is the development of 3D cell culture systems to obtain complex structures called organoids and spheroids. These 3D cultures closely mimic in vivo conditions, where cells can grow and interact with their surroundings. This allows us to better study the spatio-temporal dynamics of organogenesis and organ function. Furthermore, physiologically relevant organoids cultures can be used for basic research, medical research, and drug discovery. Although most of the research thus far focuses on the development of heart, liver, kidney, and brain organoids, to name a few, most recently, these structures were obtained using dental stem cells to study in vitro tooth regeneration. This review aims to present the most up-to-date research showing how dental stem cells can be grown on specific biomaterials to induce their differentiation in 3D. The possibility of combining engineering and biology principles to replicate and/or increase tissue function has been an emerging and exciting field in medicine. The use of this methodology in dentistry has already yielded many interesting results paving the way for the improvement of dental care and successful therapies.