Apatite microtopographies instruct signaling tapestries for progenitor-driven new attachment of teeth

Notum suppresses the osteogenic differentiation of periodontal ligament stem cells through the Wnt/Beta catenin signaling pathway

OBJECTIVES

The aims of this study were to explore: (ⅰ) the effect of Notum on periodontitis in vivo; (ⅱ) the effect of Notum on the osteogenic differentiation of human periodontal ligament stem cells (hPDLSCs) in vitro; and (ⅲ) the potential mechanism of Notum in inhibiting the osteogenic differentiation of hPDLSCs.

DESIGN

C57BL/6J mice were randomly assigned into two groups: control group (n = 4) and periodontitis group (n = 4). Immunohistochemical staining was used to evaluate the expression of Notum. In in vitro experiments, Western blot, qRT- PCR and ELISA were used to examine the expression of Notum in a lipopolysaccharide-induced inflammation model. Alkaline phosphatase staining was used to evaluate alkaline phosphatase activity. Western blot and qRT - PCR were used to measure the expression of osteogenic-related markers after adding human recombinant Notum and Notum inhibitor ABC99. In addition, LiCl, an agonist of the Wnt/Beta-catenin signaling pathway, was added to explore using Western blot whether Notum was involved in regulating the osteogenic differentiation of human periodontal ligament stem cells through the Wnt/Beta-catenin signaling pathway.

RESULTS

Notum was highly expressed in periodontal tissues of mice and lipopolysaccharide-induced inflammation cell model. The protein and messenger ribonucleic acid levels of hPDLSCs osteogenic markers were reduced after adding human recombinant Notum. However, the inhibitory effect of Notum on the osteogenic differentiation of hPDLSCs could be significantly reversed by adding LiCl.

CONCLUSION

These results demonstrated that Notum inhibited the osteogenic differentiation of hPDLSCs probably via the Wnt/Beta-catenin the downstream signaling pathway.

Cell-Based Therapy for Tooth Replantation Following Avulsion: A Systematic Review

The management of avulsed teeth undergoing delayed replantation remains a clinical challenge as there are currently no effective interventions that can improve periodontal healing and prevent replacement root resorption. While several preclinical studies have reported varied success using cell-based tissue engineering to improve periodontal healing, a consensus is required before further clinical translation. Therefore, this systematic review seeks to evaluate the efficacy of cell-based therapy in promoting periodontal healing following delayed replantation in animal models. MEDLINE (PubMed) and Embase were searched on September 27, 2020. Ten studies involving rodent and dog models met the inclusion criteria. Cell sources included gingiva, periodontal ligament (PDL), bone marrow, and adipose tissues. Generally, cell-based therapy had increased the proportion of root surfaces displaying periodontal healing and concomitantly reduced the proportion presenting with replacement root resorption and ankylosis. The best outcomes were observed following treatment with PDL-derived cells of various potency. Future preclinical studies will benefit from adopting measures to minimize bias during the conduct of animal experiments and the standardization of the outcome measures reporting. This will facilitate future reviews with possible pooling of results in the form of meta-analyses, allowing a consensus to be obtained from the literature. In addition, further research will be required to shed light on the implications of using allogeneic cells as well as the optimization of cell delivery protocols. The findings of this systematic review demonstrated the therapeutic potential of certain cell-based therapies in promoting periodontal healing following delayed replantation, thus highlighting their prospective clinical benefits and translational value.

Surface-Dependent Osteoblasts Response to TiO2 Nanotubes of Different Crystallinity

One of the major challenges of implantology is to design nanoscale modifications of titanium implant surfaces inducing osseointegration. The aim of this study was to investigate the behavior of rat osteoblasts cultured on anodized TiO2 nanotubes of different crystallinity (amorphous and anatase phase) up to 24 days. TiO2 nanotubes were fabricated on VT1-0 titanium foil via a two-step anodization at 20 V using NH4F as an electrolyte. Anatase-phase samples were prepared by heat treatment at 500 °C for 1 h. VT1-0 samples with flat surfaces were used as controls. Primary rat osteoblasts were seeded over experimental surfaces for several incubation times. Scanning electron microscopy (SEM) was used to analyze tested surfaces and cell morphology. Cell adhesion and proliferation were investigated by cell counting. Osteogenic differentiation of cells was evaluated by qPCR of runt-related transcription factor 2 (RUNX2), osteopontin (OPN), integrin binding sialoprotein (IBSP), alkaline phosphatase (ALP) and osteocalcin (OCN). Cell adhesion and proliferation, cell morphology and the expression of osteogenic markers were affected by TiO2 nanotube layered substrates of amorphous and anatase crystallinity. In comparison with flat titanium, along with increased cell adhesion and cell growth a large portion of osteoblasts grown on the both nanostructured surfaces exhibited an osteocyte-like morphology as early as 48 h of culture. Moreover, the expression of all tested osteogenic markers in cells cultured on amorphous and anatase TiO2 nanotubes was upregulated at least at one of the analyzed time points. To summarize, we demonstrated that amorphous and anodized TiO2 layered substrates are highly biocompatible with rat osteoblasts and that the surface modification with about 1500 nm length nanotubes of 35 ± 4 (amorphous phase) and 41 ± 8 nm (anatase phase) in diameter is sufficient to induce their osteogenic differentiation. Such results are significant to the engineering of coating strategies for orthopedic implants aimed to establish a more efficient bone to implant contact and enhance bone repair.

Histone Methylation Mechanisms Modulate the Inflammatory Response of Periodontal Ligament Progenitors

Inflammatory conditions affect periodontal ligament (PDL) homeostasis and diminish its regenerative capacity. The complexity of biological activities during an inflammatory response depends on genetic and epigenetic mechanisms. To characterize the epigenetic changes in response to periodontal pathogens we have focused on histone lysine methylation as a relatively stable chromatin modification involved in the epigenetic activation and repression of transcription and a prime candidate mechanism responsible for the exacerbated and prolonged response of periodontal cells and tissues to dental plaque biofilm. To determine the effect of inflammatory conditions on histone methylation profiles, related gene expression and cellular functions of human periodontal ligament (hPDL) progenitor cells, a hPDL cell culture system was subjected to bacterial cell wall toxin exposure [lipopolysaccharide (LPS)]. Chromatin immunoprecipitation-on-chip analysis revealed that healthy PDL cells featured high enrichment levels for the active H3K4me3 mark at COL1A1, COL3, and RUNX2 gene promoters, whereas there were high occupancy levels for the repressive H3K27me3 marks at DEFA4, CCL5, and IL-1β gene promoters. In response to LPS, H3K27me3 enrichment increased on extracellular matrix and osteogenesis lineage gene promoters, whereas H3K4me3 enrichment increased on the promoters of inflammatory response genes, suggestive of an involvement of epigenetic mechanisms in periodontal lineage differentiation and in the coordination of the periodontal inflammatory response. On a gene expression level, LPS treatment downregulated COL1A1, COL3A1, and RUNX2 expression and upregulated CCL5, DEFA4, and IL-1β gene expression. LPS also greatly affected PDL progenitor function, including a reduction in proliferation and differentiation potential and an increase in cell migration capacity. Confirming the role of epigenetic mechanisms in periodontal inflammatory conditions, our studies highlight the significant role of histone methylation mechanisms and modification enzymes in the inflammatory response to LPS bacterial cell wall toxins and periodontal stem cell function.

MicroRNAs and Periodontal Homeostasis

MicroRNAs (miRNAs) are a group of small RNAs that control gene expression in all aspects of eukaryotic life, primarily through RNA silencing mechanisms. The purpose of the present review is to introduce key miRNAs involved in periodontal homeostasis, summarize the mechanisms by which they affect downstream genes and tissues, and provide an introduction into the therapeutic potential of periodontal miRNAs. In general, miRNAs function synergistically to fine-tune the regulation of biological processes and to remove expression noise rather than by causing drastic changes in expression levels. In the periodontium, miRNAs play key roles in development and periodontal homeostasis and during the loss of periodontal tissue integrity as a result of periodontal disease. As part of the anabolic phase of periodontal homeostasis and periodontal development, miRNAs direct periodontal fibroblasts toward alveolar bone lineage differentiation and new bone formation through WNT, bone morphogenetic protein, and Notch signaling pathways. miRNAs contribute equally to the catabolic aspect of periodontal homeostasis as they affect osteoclastogenesis and osteoclast function, either by directly promoting osteoclast activity or by inhibiting osteoclast signaling intermediaries or through negative feedback loops. Their small size and ability to target multiple regulatory networks of related sets of genes have predisposed miRNAs to become ideal candidates for drug delivery and tissue regeneration. To address the immense therapeutic potential of miRNAs and their antagomirs, an ever growing number of delivery approaches toward clinical applications have been developed, including nanoparticle carriers and secondary structure interference inhibitor systems. However, only a fraction of the miRNAs involved in periodontal health and disease are known today. It is anticipated that continued research will lead to a more comprehensive understanding of the periodontal miRNA world, and a systematic effort toward harnessing the enormous therapeutic potential of these small molecules will greatly benefit the future of periodontal patient care.

Periodontal ligament stem/progenitor cells with protein-releasing scaffolds for cementum formation and integration on dentin surface

Purpose/Aim: Cementogenesis is a critical step in periodontal tissue regeneration given the essential role of cementum in anchoring teeth to the alveolar bone. This study is designed to achieve integrated cementum formation on the root surfaces of human teeth using growth factor-releasing scaffolds with periodontal ligament stem/progenitor cells (PDLSCs).

MATERIALS AND METHODS

Human PDLSCs were sorted by CD146 expression, and characterized using CFU-F assay and induced multi-lineage differentiation. Polycaprolactone scaffolds were fabricated using 3D printing, embedded with poly(lactic-co-glycolic acids) (PLGA) microspheres encapsulating connective tissue growth factor (CTGF), bone morphogenetic protein-2 (BMP-2), or bone morphogenetic protein-7 (BMP-7). After removing cementum on human tooth roots, PDLSC-seeded scaffolds were placed on the exposed dentin surface. After 6-week culture with cementogenic/osteogenic medium, cementum formation and integration were evaluated by histomorphometric analysis, immunofluorescence, and qRT-PCR.

RESULTS

Periodontal ligament (PDL) cells sorted by CD146 and single-cell clones show a superior clonogenecity and multipotency as compared with heterogeneous populations. After 6 weeks, all the growth factor-delivered groups showed resurfacing of dentin with a newly formed cementum-like layer as compared with control. BMP-2 and BMP-7 showed de novo formation of tissue layers significantly thicker than all the other groups, whereas CTGF and BMP-7 resulted in significantly improved integration on the dentin surface. The de novo mineralized tissue layer seen in BMP-7-treated samples expressed cementum matrix protein 1 (CEMP1). Consistently, BMP-7 showed a significant increase in CEMP1 mRNA expression.

CONCLUSION

Our findings represent important progress in stem cell-based cementum regeneration as an essential part of periodontium regeneration.

First-principles study of structural and surface properties of (001) and (010) surfaces of hydroxylapatite and carbonated hydroxylapatite

Since it was first discovered that the main component of the mineral phase of bone, dentine and enamel is made from non-stoichiometric hydroxylapatite [Ca10(PO4)6(OH)2; OHAp], many successful efforts have been made to characterize its structure physico-chemically and to use it as a biomaterial for tissue repair and reconstruction. For the latter, it has been suggested that the biomimetic features of OHAp can be improved by vacancies and ionic substitutions, as typically found in natural bone tissues. In the present work, this line of thought has been followed, and the structural and electrostatic potential features of the (001) and (010) surfaces of OHAp and defective typeA, typeBand typeABcarbonated hydroxylapatite (COHAp) have been studied usingab initioquantum mechanics at the DFT/B3LYP level. The results are in good agreement with previous experimental and preliminary theoretical work. They provide a deep analysis of the modulation of OHAp features caused by carbonate substitutions, and extend the current knowledge of the structural and surface properties of apatites.

Lyophilized platelet-rich fibrin (PRF) promotes craniofacial bone regeneration through Runx2

Freeze-drying is an effective means to control scaffold pore size and preserve its composition. The purpose of the present study was to determine the applicability of lyophilized Platelet-rich fibrin (LPRF) as a scaffold for craniofacial tissue regeneration and to compare its biological effects with commonly used fresh Platelet-rich fibrin (PRF). LPRF caused a 4.8-fold±0.4-fold elevation in Runt-related transcription factor 2 (Runx2) expression in alveolar bone cells, compared to a 3.6-fold±0.2-fold increase when using fresh PRF, and a more than 10-fold rise of alkaline phosphatase levels and mineralization markers. LPRF-induced Runx2 expression only occurred in alveolar bone and not in periodontal or dental follicle cells. LPRF also caused a 1.6-fold increase in osteoblast proliferation (p<0.001) when compared to fresh PRF. When applied in a rat craniofacial defect model for six weeks, LPRF resulted in 97% bony coverage of the defect, compared to 84% for fresh PRF, 64% for fibrin, and 16% without scaffold. Moreover, LPRF thickened the trabecular diameter by 25% when compared to fresh PRF and fibrin, and only LPRF and fresh PRF resulted in the formation of interconnected trabeculae across the defect. Together, these studies support the application of lyophilized PRF as a biomimetic scaffold for craniofacial bone regeneration and mineralized tissue engineering.

Interaction of adult human neural crest-derived stem cells with a nanoporous titanium surface is sufficient to induce their osteogenic differentiation

Osteogenic differentiation of various adult stem cell populations such as neural crest-derived stem cells is of great interest in the context of bone regeneration. Ideally, exogenous differentiation should mimic an endogenous differentiation process, which is partly mediated by topological cues. To elucidate the osteoinductive potential of porous substrates with different pore diameters (30 nm, 100 nm), human neural crest-derived stem cells isolated from the inferior nasal turbinate were cultivated on the surface of nanoporous titanium covered membranes without additional chemical or biological osteoinductive cues. As controls, flat titanium without any topological features and osteogenic medium was used. Cultivation of human neural crest-derived stem cells on 30 nm pores resulted in osteogenic differentiation as demonstrated by alkaline phosphatase activity after seven days as well as by calcium deposition after 3 weeks of cultivation. In contrast, cultivation on flat titanium and on membranes equipped with 100 nm pores was not sufficient to induce osteogenic differentiation. Moreover, we demonstrate an increase of osteogenic transcripts including Osterix, Osteocalcin and up-regulation of Integrin β1 and α2 in the 30 nm pore approach only. Thus, transplantation of stem cells pre-cultivated on nanostructured implants might improve the clinical outcome by support of the graft adherence and acceleration of the regeneration process.

SCF promotes dental pulp progenitor migration, neovascularization, and collagen remodeling - potential applications as a homing factor in dental pulp regeneration

Stem cell factor (SCF) is a powerful chemokine that binds to the c-Kit receptor CD117 and has shown promise as a homing agent capable of progenitor cell recruitment. In the present study we have documented high levels of both SCF and its receptor c-Kit in differentiating dental pulp (DP) cells and in the sub-odontoblastic layer of Höhl. In vitro studies using human DP progenitors revealed a significant increase in cell proliferation after100 nM SCF application, explained by a 2-fold upregulation in cyclin D3 and FGF2 cell cycle regulators, and a 7-fold increase in CDK4 expression. DP cell migration in the presence of SCF was up-regulated 2.7-fold after a 24 h culture period, and this effect was accompanied by cytoskeletal rearrangement, a 1.5-fold increase in polymeric F-actin over G-actin, and a 1.8-fold increase in RhoA expression. Explaining the signaling effect of SCF on DP migration, PI3K/Akt and MEK/ERK pathway inhibitors were demonstrated to significantly reduce DP cell migration, while SCF alone doubled the number of migrated cells. ERK and AKT phosphorylation were dramatically upregulated already 3-5 min after SCF addition to the culture medium and declined thereafter, classifying SCF as a fast acting chemokine. When applied as an agent to promote tissue regeneration in subcutaneously implanted collagen sponges, SCF resulted in a 7-fold increase in the cell number in the implanted tissue construct, a more than 9-fold increase in capillaries, as well as collagen sponge remodeling and collagen fiber neogenesis. Together, these studies demonstrate the suitability of SCF as a potent aid in the regeneration of dental pulp and other mesenchymal tissues, capable of inducing cell homing, angiogenesis, and tissue remodeling.

Three-dimensional printed multiphase scaffolds for regeneration of periodontium complex

Tooth-supporting periodontium forms a complex with multiple tissues, including cementum, periodontal ligament (PDL), and alveolar bone. In this study, we developed multiphase region-specific microscaffolds with spatiotemporal delivery of bioactive cues for integrated periodontium regeneration. Polycarprolactione-hydroxylapatite (90:10 wt%) scaffolds were fabricated using three-dimensional printing seamlessly in three phases: 100-μm microchannels in Phase A designed for cementum/dentin interface, 600-μm microchannels in Phase B designed for the PDL, and 300-μm microchannels in Phase C designed for alveolar bone. Recombinant human amelogenin, connective tissue growth factor, and bone morphogenetic protein-2 were spatially delivered and time-released in Phases A, B, and C, respectively. Upon 4-week in vitro incubation separately with dental pulp stem/progenitor cells (DPSCs), PDL stem/progenitor cells (PDLSCs), or alveolar bone stem/progenitor cells (ABSCs), distinctive tissue phenotypes were formed with collagen I-rich fibers especially by PDLSCs and mineralized tissues by DPSCs, PDLSCs, and ABSCs. DPSC-seeded multiphase scaffolds upon in vivo implantation yielded aligned PDL-like collagen fibers that inserted into bone sialoprotein-positive bone-like tissue and putative cementum matrix protein 1-positive/dentin sialophosphoprotein-positive dentin/cementum tissues. These findings illustrate a strategy for the regeneration of multiphase periodontal tissues by spatiotemporal delivery of multiple proteins. A single stem/progenitor cell population appears to differentiate into putative dentin/cementum, PDL, and alveolar bone complex by scaffold's biophysical properties and spatially released bioactive cues.

Successful periodontal ligament regeneration by periodontal progenitor preseeding on natural tooth root surfaces

The regeneration of lost periodontal ligament (PDL) and alveolar bone is the purpose of periodontal tissue engineering. The goal of the present study was to assess the suitability of 3 odontogenic progenitor populations from dental pulp, PDL, and dental follicle for periodontal regeneration when exposed to natural and synthetic apatite surface topographies. We demonstrated that PDL progenitors featured higher levels of periostin and scleraxis expression, increased adipogenic and osteogenic differentiation potential, and pronounced elongated cell shapes on barren root chips when compared with dental pulp and dental follicle cells. When evaluating the effect of surface characteristics on PDL progenitors, natural root surfaces resulted in elongated PDL cell shapes, whereas PDL progenitors on synthetic apatite surfaces were rounded or polygonal. In addition, surface coatings affected PDL progenitor gene expression profiles: collagen I coatings enhanced alkaline phosphatase and osteocalcin expression levels and laminin-1 coatings increased epidermal growth factor (EGF), nestin, cadherin 1, and keratin 8 expression. PDL progenitors seeded on natural tooth root surfaces in organ culture formed new periodontal fibers after 3 weeks of culture. Finally, replantation of PDL progenitor-seeded tooth roots into rat alveolar bone sockets resulted in the complete formation of a new PDL and stable reattachment of teeth over a 6-month period. Together, these findings indicate that periodontal progenitor cell type as well as mineral surface topography and molecular environment play crucial roles in the regeneration of true periodontal anchorage.