Isolation and Characterization of Human Adult Epithelial Stem Cells from the Periodontal Ligament

Advances in tooth agenesis and tooth regeneration

The lack of treatment options for congenital (0.1%) and partial (10%) tooth anomalies highlights the need to develop innovative strategies. Over two decades of dedicated research have led to breakthroughs in the treatment of congenital and acquired tooth loss. We revealed that by inactivating USAG-1, congenital tooth agenesis can be successfully ameliorated during early tooth development and that the inactivation promotes late-stage tooth morphogenesis in double knockout mice. Furthermore, Anti- USAG-1 antibody treatment in mice is effective in tooth regeneration and can be a breakthrough in treating tooth anomalies in humans. With approximately 0.1% of the population suffering from congenital tooth agenesis and 10% of children worldwide suffering from partial tooth loss, early diagnosis will improve outcomes and the quality of life of patients. Understanding the role of pathogenic USAG-1 variants, their interacting gene partners, and their protein functions will help develop critical biomarkers. Advances in next-generation sequencing, mass spectrometry, and imaging technologies will assist in developing companion and predictive biomarkers to help identify patients who will benefit from tooth regeneration.

Bioprinting of alginate-carboxymethyl chitosan scaffolds for enamel tissue engineeringin vitro

Tissue engineering offers a great potential in regenerative dentistry and to this end, three dimensional (3D) bioprinting has been emerging nowadays to enable the incorporation of living cells into the biomaterials (such a mixture is referred as a bioink in the literature) to create scaffolds. However, the bioinks available for scaffold bioprinting are limited, particularly for dental tissue engineering, due to the complicated, yet compromised, printability, mechanical and biological properties simultaneously imposed on the bioinks. This paper presents our study on the development of a novel bioink from carboxymethyl chitosan (CMC) and alginate (Alg) for bioprinting scaffolds for enamel tissue regeneration. CMC was used due to its antibacterial ability and superior cell interaction properties, while Alg was added to enhance the printability and mechanical properties as well as to regulate the degradation rate. The bioinks with three mixture ratios of Alg and CMC (2-4, 3-3 and 4-2) were prepared, and then printed into the calcium chloride crosslinker solution (100 mM) to form a 3D structure of scaffolds. The printed scaffolds were characterized in terms of structural, swelling, degradation, and mechanical properties, followed by theirin vitrocharacterization for enamel tissue regeneration. The results showed that the bioinks with higher concentrations of Alg were more viscous and needed higher pressure for printing; while the printed scaffolds were highly porous and showed a high degree of printability and structural integrity. The hydrogels with higher CMC ratios had higher swelling ratios, faster degradation rates, and lower compressive modulus. Dental epithelial cell line, HAT-7, could maintain high viability in the printed constructs after 1, 7 and 14 d of culture. HAT-7 cells were also able to maintain their morphology and secrete alkaline phosphatase after 14 d of culture in the 3D printed scaffolds, suggesting the capacity of these cells for mineral deposition and enamel-like tissue formation. Among all combinations Alg4%-CMC2% and in a less degree 2%Alg-4%CMC showed the higher potential to promote ameloblast differentiation, Ca and P deposition and matrix mineralizationin vitro. Taken together, Alg-CMC has been illustrated to be suitable to print scaffolds with dental epithelial cells for enamel tissue regeneration.

LGR5 regulates osteogenic differentiation of human thoracic ligamentum flavum cells by Wnt signalling pathway

Thoracic ossification of the ligamentum flavum (TOLF) is ectopic ossification of the spinal ligaments. Histologically, the development of TOLF can be described as the process of endochondral ossification. However, the underlying aetiology has not been completely clarified. In this investigation, the gene expression profile associated with leucine‐rich repeat‐containing G‐protein‐coupled receptors (LGR) and Wnt signalling pathway in the thoracic ligamentum flavum cells (TLFCs) of different ossification stages was analysed via RNA sequencing. We further confirmed the significant differences in the related gene expression profile by Gene Ontology (GO) enrichment analysis. LGR5 was first identified in primary human TLFCs during osteogenic differentiation. To evaluate the effect of LGR5 on osteogenic differentiation, LGR5 has been knocked down and overexpressed in human TLFCs. We observed that the knockdown of LGR5 inhibited the activity of Wnt signalling and attenuated the potential osteogenic differentiation of TLFCs, while overexpression of LGR5 activated the Wnt signalling pathway and increased osteogenic differentiation. Our results provide important evidence for the potent positive mediatory effects of LGR5 on osteogenesis by enhancing the Wnt signalling pathway in TOLF.

Novel trends, challenges and new perspectives for enamel repair and regeneration to treat dental defects

Dental enamel is the hardest tissue in the human body, providing external protection for the tooth against masticatory forces, temperature changes and chemical stimuli. Once enamel is damaged/altered by genetic defects, dental caries, trauma, and/or dental wear, it cannot repair itself due to the loss of enamel producing cells following the tooth eruption. The current restorative dental materials are unable to replicate physico-mechanical, esthetic features and crystal structures of the native enamel. Thus, development of alternative approaches to repair and regenerate enamel defects is much needed but remains challenging due to the structural and functional complexities involved. This review paper summarizes the clinical aspects to be taken into consideration for the development of optimal therapeutic approaches to tackle dental enamel defects. It also provides a comprehensive overview of the emerging acellular and cellular approaches proposed for enamel remineralization and regeneration. Acellular approaches aim to artificially synthesize or re-mineralize enamel, whereas cell-based strategies aim to mimic the natural process of enamel development given that epithelial cells can be stimulated to produce enamel postnatally during the adult life. The key issues and current challenges are also discussed here, along with new perspectives for future research to advance the field of regenerative dentistry.

Organoids from human tooth showing epithelial stemness phenotype and differentiation potential

Insight into human tooth epithelial stem cells and their biology is sparse. Tissue-derived organoid models typically replicate the tissue’s epithelial stem cell compartment. Here, we developed a first-in-time epithelial organoid model starting from human tooth. Dental follicle (DF) tissue, isolated from unerupted wisdom teeth, efficiently generated epithelial organoids that were long-term expandable. The organoids displayed a tooth epithelial stemness phenotype similar to the DF’s epithelial cell rests of Malassez (ERM), a compartment containing dental epithelial stem cells. Single-cell transcriptomics reinforced this organoid-ERM congruence, and uncovered novel, mouse-mirroring stem cell features. Exposure of the organoids to epidermal growth factor induced transient proliferation and eventual epithelial-mesenchymal transition, highly mimicking events taking place in the ERM in vivo. Moreover, the ERM stemness organoids were able to unfold an ameloblast differentiation process, further enhanced by transforming growth factor-β (TGFβ) and abrogated by TGFβ receptor inhibition, thereby reproducing TGFβ's known key position in amelogenesis. Interestingly, by creating a mesenchymal-epithelial composite organoid (assembloid) model, we demonstrated that the presence of dental mesenchymal cells (i.e. pulp stem cells) triggered ameloblast differentiation in the epithelial stem cells, thus replicating the known importance of mesenchyme-epithelium interaction in tooth development and amelogenesis. Also here, differentiation was abrogated by TGFβ receptor inhibition. Together, we developed novel organoid models empowering the exploration of human tooth epithelial stem cell biology and function as well as their interplay with dental mesenchyme, all at present only poorly defined in humans. Moreover, the new models may pave the way to future tooth-regenerative perspectives.

Isolation of dental pulp and periodontal cells from human teeth for single-cell RNA sequencing

Teeth and the surrounding periodontal tissues are affected by many pathologies that compromise their integrity and significantly affect life quality. The study of the main dental tissues, the dental pulp and periodontium, is made arduous by their close association with highly mineralized tissues (dentin, cementum, and alveolar bone). Here we describe a protocol to isolate all cells composing human dental pulp and periodontium for single-cell RNA sequencing analysis. For complete details on the use and execution of this protocol, please refer to Pagella et al. (2021).

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

Human periodontal ligament stromal/stem cells (PDLSCs) are ideal candidates for periodontal regeneration and are of significant importance in clinical practice. However, PDLSCs derived from diseased microenvironments exert impaired behavior, which leads to the failure of periodontal regeneration. The epithelial cell rests of Malassez (ERM), which are involved in periodontal homeostasis, are residual cells from Hertwig's epithelial root sheath (HERS). However, the function of ERM remains largely unknown. Therefore, the aim of this study was to evaluate the effect of ERM on the osteogenic potential of PDLSCs from an impaired microenvironment. PDLSCs from healthy donors (H-PDLSCs), periodontitis donors (P-PDLSCs) and human ERM were harvested. Osteogenic evaluation showed a lower osteogenic potential of P-PDLSCs compared to that of H-PDLSCs. Then, we co-cultured ERM with P-PDLSCs, and the data showed that ERM promoted the expression of osteogenic genes and proteins in P-PDLSCs. In addition, we collected the PDLSCs from aged donors (A-PDLSCs) and analyzed the osteogenesis capacity of the A-PDLSCs and A-PDLSCs + ERM groups, which displayed similar results to P-PDLSCs. Finally, we evaluated the Wnt pathway, which is associated with osteogenic differentiation of stromal/stem cells, in A-PDLSCs + ERM and P-PDLSCs + ERM groups, which indicated that suppression of the Wnt pathway may result in an increase in the osteogenic properties of A-PDLSCs + ERM and P-PDLSCs + ERM groups. Taken together, the above findings shed new light on the function of ERM and provide a novel therapeutic for optimizing PDLSCs-based periodontal regeneration.

Notch signaling in the dynamics of perivascular stem cells and their niches

The Notch signaling pathway is a fundamental regulator of cell fate determination in homeostasis and regeneration. In this work, we aimed to determine how Notch signaling mediates the interactions between perivascular stem cells and their niches in human dental mesenchymal tissues, both in homeostatic and regenerative conditions. By single cell RNA sequencing analysis, we showed that perivascular cells across the dental pulp and periodontal human tissues all express NOTCH3, and that these cells are important for the response to traumatic injuries in vivo in a transgenic mouse model. We further showed that the behavior of perivascular NOTCH3‐expressing stem cells could be modulated by cellular and molecular cues deriving from their microenvironments. Taken together, the present studies, reinforced by single‐cell analysis, reveal the pivotal importance of Notch signaling in the crosstalk between perivascular stem cells and their niches in tissue homeostasis and regeneration.

Isolation and immunohistochemical characterization of periodontal ligament stem cells: A preliminary study

Context:

It is a known fact that periodontal tissue regeneration can be achieved by the use of periodontal ligament stem cells (PDLSCs). Current mainstay of periodontal treatment is focusing on stem cell tissue engineering as an effective therapy, making it important to isolate PDLSCs from periodontal tissues.

Aims:

The present research endeavor was undertaken to elucidate a technique for isolating PDLSCs for in vivo reconstructing the natural PDL tissue.

Settings and Design:

The study design involves In vitro prospective study.

Materials and Methods:

Premolar teeth were extracted from 12 patients who were under orthodontic treatment. PDL cells were scraped from their roots. Using 10 ml of Dulbecco's modified Eagle's medium with pH 7.2, the specimens of the periodontal tissue were transferred to laboratory where cell culture was done. Isolated stem cells were grown on 24-well microtiter plates-containing cover slips. They were incubated overnight at approximately 37°C in 95% air and 5% humidification. Anti-CD 45, CD73, CD90, CD105, and CD146 antibodies were used. After staining, cells were observed under phase-contrast microscopy and in inverted microscope.

Results:

The cells showed a marked growth and 90% confluence at day 6. Cells presented thin and long fibroblastic spindle morphology. Isolated PDLSCs showed colony-forming ability at the 14^th day after seeding. Immunohistochemical staining of PDLSCs showed positive uptake for CD146, CD90, CD73, CD105, and negative uptake for CD45.

Conclusions:

The human PDLSCs can be clearly isolated and characterized by using CD90, CD73, CD146, and CD105 markers of stem cells.

Constitutive Hedgehog/GLI2 signaling drives extracutaneous basaloid squamous cell carcinoma development and bone remodeling

Uncontrolled activation of the Hedgehog (Hh) signaling pathway, operating through GLI transcription factors, plays a central role in the pathogenesis of cutaneous basal cell carcinoma and contributes to the development of several malignancies arising in extracutaneous sites. We now report that K5-tTA;tetO-Gli2 bitransgenic mice develop distinctive epithelial tumors within their jaws. These tumors consist of large masses of highly proliferative, monomorphous, basaloid cells with scattered foci of keratinization and central necrosis, mimicking human basaloid squamous cell carcinoma (BSCC), an aggressive upper aerodigestive tract tumor. Like human BSCC, these tumors express epidermal basal keratins, and differentiation-specific keratins within squamous foci. Mouse BSCCs express high levels of Gli2 and Hh target genes, including Gli1 and Ptch1, which we show are also upregulated in a subset of human BSCCs. Mouse BSCCs appear to arise from distinct epithelial sites, including the gingival junctional epithelium and epithelial rests of Malassez, a proposed stem cell compartment. Although Gli2 transgene expression is restricted to epithelial cells, we also detect striking alterations in bone adjacent to BSCCs, with activated osteoblasts, osteoclasts, and osteal macrophages, indicative of active bone remodeling. Gli2 transgene inactivation resulted in rapid BSCC regression and reversal of the bone remodeling phenotype. This first-reported mouse model of BSCC supports the concept that uncontrolled Hh signaling plays a central role in the pathogenesis of a subset of human BSCCs, points to Hh/GLI2 signaling as a potential therapeutic target, and provides a powerful new tool for probing the mechanistic underpinnings of tumor-associated bone remodeling.

A single-cell atlas of human teeth

Teeth exert fundamental functions related to mastication and speech. Despite their great biomedical importance, an overall picture of their cellular and molecular composition is still missing. In this study, we have mapped the transcriptional landscape of the various cell populations that compose human teeth at single-cell resolution, and we analyzed in deeper detail their stem cell populations and their microenvironment. Our study identified great cellular heterogeneity in the dental pulp and the periodontium. Unexpectedly, we found that the molecular signatures of the stem cell populations were very similar, while their respective microenvironments strongly diverged. Our findings suggest that the microenvironmental specificity is a potential source for functional differences between highly similar stem cells located in the various tooth compartments and open new perspectives toward cell-based dental therapeutic approaches.

•

Dental atlas of the pulp and periodontal tissues of human teeth

•

Identification of three common MSC subclusters between dental pulp and periodontium

•

Dental pulp and periodontal MSCs are similar, and their niches diverge

Small molecules efficiently reprogram apical papilla stem cells into neuron-like cells

Stem cell-based therapy may provide a novel approach for neural tissue regeneration. A small molecule cocktail-based culture protocol was previously shown to enhance neurogenic differentiation of stem cells from dental tissues. The present study aimed to investigate the early phase of small molecule-induced neurogenic differentiation of stem cells from the apical papilla (SCAP). SCAP were cultured in neural-induction medium or neural-induction medium with small molecules (NIMS-SCAP) and examined for their cell morphologies. Expression levels of neural progenitor cell-related markers, including Nestin, paired-box gene 6 (Pax6) and Sry-related HMG box 2 (Sox2), were examined using western blotting and immunocytofluorescence. Expression of differentiated neuron-related markers, including neurofilament protein (NFM), neuron-specific nuclear protein (NeuN) and microtubule-associated protein (MAP)-2, were also examined using western blotting, while NFM and MAP2 gene expression and cell proliferation were assessed using reverse transcription-quantitative (RT-q)PCR and Cell Counting Kit (CCK)-8 assays, respectively. SCAP morphology was affected by small molecules after as little as 30 min. Specifically, Nestin, Pax6 and Sox2 expression detected using western blotting was increased by day 3 but then decreased over the course of 7 days with neural induction, while immunocytofluorescence revealed expression of all three markers in NIMS-SCAP. The protein levels of NFM, NeuN and MAP2 on day 7 were significantly upregulated in NIMS-SCAP, as detected using western blotting, while NFM and MAP2 gene expression levels detected using RT-qPCR were significantly increased on days 5 and 7. Proliferation of NIMS-SCAP ceased after 5 days. Electrophysiological analysis showed that only SCAP cultured in NIMS had the functional activity of neuronal cells. Thus, small molecules reprogrammed SCAP into neural progenitor cells within the first 3 days, followed by further differentiation into neuron-like cells.

Current status of cardiac regenerative medicine; An update on point of view to cell therapy application

Cardiovascular diseases (CVDs) are the leading cause of death globally. Because of the economic and social burden of acute myocardial infarction and its chronic consequences in surviving patients, understanding the pathophysiology of myocardial infarction injury is a major priority for cardiovascular research. MI is defined as cardiomyocytes death caused by an ischemic that resulted from the apoptosis, necrosis, necroptosis, and autophagy. The phases of normal repair following MI including inflammatory, proliferation, and maturation. Normal repair is slow and inefficient generally so that other treatments are required. Because of difficulties, outcomes, and backwashes of traditional therapies including coronary artery bypass grafting, balloon angioplasty, heart transplantation, and artificial heart operations, the novel strategy in the treatment of MI, cell therapy, was newly emerged. In cell therapy, a new population of cells has created that substitute with damaged cells. Different types of stem cell and progenitor cells have been shown to improve cardiac function through various mechanisms, including the formation of new myocytes, endothelial cells, and vascular smooth muscle cells. Bone marrow- and/or adipose tissue-derived mesenchymal stem cells, embryonic stem cells, autologous skeletal myoblasts, induced pluripotent stem cells, endothelial progenitor cells, cardiac progenitor cells and cardiac pericytes considered as a source for cell therapy. In this study, we focused on the point of view of the cell sources.

Effect of Aging on Homeostasis in the Soft Tissue of the Periodontium: A Narrative Review

Aging is characterized by a progressive decline or loss of physiological functions, leading to increased susceptibility to disease or death. Several aging hallmarks, including genomic instability, cellular senescence, and mitochondrial dysfunction, have been suggested, which often lead to the numerous aging disorders. The periodontium, a complex structure surrounding and supporting the teeth, is composed of the gingiva, periodontal ligament, cementum, and alveolar bone. Supportive and protective roles of the periodontium are very critical to sustain life, but the periodontium undergoes morphological and physiological changes with age. In this review, we summarize the current knowledge of molecular and cellular physiological changes in the periodontium, by focusing on soft tissues including gingiva and periodontal ligament.

Exploiting teeth as a model to study basic features of signaling pathways

Teeth constitute a classical model for the study of signaling pathways and their roles in mediating interactions between cells and tissues in organ development, homeostasis and regeneration. Rodent teeth are mostly used as experimental models. Rodent molars have proved fundamental in the study of epithelial–mesenchymal interactions and embryonic organ morphogenesis, as well as to faithfully model human diseases affecting dental tissues. The continuously growing rodent incisor is an excellent tool for the investigation of the mechanisms regulating stem cells dynamics in homeostasis and regeneration. In this review, we discuss the use of teeth as a model to investigate signaling pathways, providing an overview of the many unique experimental approaches offered by this organ. We discuss how complex networks of signaling pathways modulate the various aspects of tooth biology, and the models used to obtain this knowledge. Finally, we introduce new experimental approaches that allow the study of more complex interactions, such as the crosstalk between dental tissues, innervation and vascularization.

Tooth-Supporting Hard Tissue Regeneration Using Biopolymeric Material Fabrication Strategies

The mineralized tissues (alveolar bone and cementum) are the major components of periodontal tissues and play a critical role to anchor periodontal ligament (PDL) to tooth-root surfaces. The integrated multiple tissues could generate biological or physiological responses to transmitted biomechanical forces by mastication or occlusion. However, due to periodontitis or traumatic injuries, affect destruction or progressive damage of periodontal hard tissues including PDL could be affected and consequently lead to tooth loss. Conventional tissue engineering approaches have been developed to regenerate or repair periodontium but, engineered periodontal tissue formation is still challenging because there are still limitations to control spatial compartmentalization for individual tissues and provide optimal 3D constructs for tooth-supporting tissue regeneration and maturation. Here, we present the recently developed strategies to induce osteogenesis and cementogenesis by the fabrication of 3D architectures or the chemical modifications of biopolymeric materials. These techniques in tooth-supporting hard tissue engineering are highly promising to promote the periodontal regeneration and advance the interfacial tissue formation for tissue integrations of PDL fibrous connective tissue bundles (alveolar bone-to-PDL or PDL-to-cementum) for functioning restorations of the periodontal complex.

LGRs in Skeletal Tissues: An Emerging Role for Wnt-Associated Adult Stem Cell Markers in Bone

Leucine-rich repeat-containing G protein-coupled receptors (LGRs) are adult stem cell markers that have been described across various stem cell niches, and expression of LGRs and their corresponding ligands (R-spondins) has now been reported in multiple bone-specific cell types. The skeleton harbors elusive somatic stem cell populations that are exceedingly compartment-specific and under tight regulation from various signaling pathways. Skeletal progenitors give rise to multiple tissues during development and during regenerative processes of bone, requiring postnatal endochondral and intramembranous ossification. The relevance of LGRs and the LGR/R-spondin ligand interaction in bone and tooth biology is becoming increasingly appreciated. LGRs may define specific stem cell and progenitor populations and their behavior during both development and regeneration, and their role as Wnt-associated receptors with specific ligands poses these proteins as unique therapeutic targets via potential R-spondin agonism. This review seeks to outline the current literature on LGRs in the context of bone and its associated tissues, and points to key future directions for studying the functional role of LGRs and ligands in skeletal biology. © 2020 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

LGR5+ epithelial tumor stem-like cells generate a 3D-organoid model for ameloblastoma

Ameloblastoma (AM) is a benign but locally aggressive tumor with high recurrences. Currently, underlying pathophysiology remains elusive, and radical surgery remains the most definitive treatment with severe morbidities. We have recently reported that AM harbors a subpopulation of tumor epithelial stem-like cells (AM-EpiSCs). Herein, we explored whether LGR5⁺ epithelial cells in AM possess stem-like cell properties and their potential contribution to pathogenesis and recurrence of AM. We found that LGR5 and stem cell-related genes were co-expressed in a subpopulation of AM epithelial cells both in vivo and in vitro, which were enriched under 3D-spheroid culture. As compared to LGR5⁻ counterparts, LGR5⁺ AM epithelial cells showed increased expression of various EMT- and stemness-related genes, and functionally, exhibited increased capacity to form 3D-spheroids and generate human tumor 3D organoids, which recapitulated the histopathologic features of distinct subtypes of solid AM, thus, contributing a useful human tumor platform for targeted therapeutic screening. Treatment with a selective BRAF^V600E inhibitor, vemurafenib, unexpectedly enriched the subpopulation of LGR5⁺ AM-EpiSCs in tumor 3D organoids, which may have explained therapeutic resistances and recurrences. These findings suggest that LGR5⁺ AM-EpiSCs play a pivotal role in pathogenesis and progression of AM and targeted inhibition of both BRAF and LGR5 potentially serves a novel nonsurgical adjuvant therapeutic approach for this aggressively benign jaw tumor.

R-spondin signaling as a pivotal regulator of tissue development and homeostasis

R-spondins (Rspos) are cysteine-rich secreted glycoproteins which control a variety of cellular functions and are essential for embryonic development and tissue homeostasis. R-spondins (Rspo1 to 4) have high structural similarity and share 60% sequence homology. It has been shown that their cysteine-rich furin-like (FU) domain and the thrombospondin (TSP) type I repeat domain are essential for initiating downstream signaling cascades and therefore for their biological functions. Although numerous studies have unveiled their pivotal role as critical developmental regulators, the most important finding is that Rspos synergize Wnt signaling. Recent studies have identified novel receptors for Rspos, the Lgr receptors, closely related orphans of the leucin-rich repeat containing G protein-coupled receptors, and proposed that Rspos potentiate canonical Wnt signaling via these receptors. Given that Wnt signaling is one of the most important developmental signaling pathways that controls cell fate decisions and tissue development, growth and homeostasis, Rspos may function as key players for these processes as well as potential therapeutic targets. Here, I recapitulate the Wnt signaling and then outline the biological role of Rspos in tissue development and homeostasis and explore the possibility that Rspos may be used as therapeutic targets.

Small molecules enhance neurogenic differentiation of dental-derived adult stem cells

OBJECTIVE

Dental-derived stem cells originate from the embryonic neural crest, and exhibit high neurogenic potential. This study aimed to investigate whether a cocktail of eight small molecules (Valproic acid, CHIR99021, Repsox, Forskolin, SP600125, GO6983, Y-27632 and Dorsomorphin) can enhance the in vitro neurogenic differentiation of dental pulp stem cells (DPSCs), stem cells from apical papilla (SCAPs) and gingival mesenchymal stem cells (GMSCs), as a preliminary step towards clinical applications.

MATERIALS AND METHODS

Neural induction was carried out with a small molecule cocktail based two-step culture protocol, over a total duration of 14 days. At the 8 and 14 day timepoints, the cells were analyzed for expression of neural markers with immunocytochemistry, qRT-PCR and Western Blot. The Fluo 4-AM calcium flux assay was also performed after a further 14 days of neural maturation.

RESULTS

More pronounced morphological changes characteristic of the neural lineage (i.e. neuritogenesis) were observed in all three cell types treated with small molecules, as compared to the untreated controls. This was corroborated by the immunocytochemistry, qRT-PCR and western blot data, which showed upregulated expression of several early and mature neural markers in all three cell types treated with small molecules, versus the corresponding untreated controls. Finally, the Fluo-4 AM calcium flux assay showed consistently higher calcium transient (F/F_o) peaks for the small molecule-treated versus untreated control groups.

CONCLUSIONS

Small molecules can enhance the neurogenic differentiation of DPSCs, SCAPs and GMSCs, which offer much potential for therapeutic applications.

Craniofacial, orofacial and dental disorders: the role of the RAS/ERK pathway

Deviations from the precisely coordinated programme of human head development can lead to craniofacial and orofacial malformations often including a variety of dental abnormalities too. Although the aetiology is still unknown in many cases, during the last decades different intracellular signalling pathways have been genetically linked to specific disorders. Among these pathways, the RAS/extracellular signal-regulated kinase (ERK) signalling cascade is the focus of this review since it encompasses a large group of genes that when mutated cause some of the most common and severe developmental anomalies in humans. We present the components of the RAS/ERK pathway implicated in craniofacial and orodental disorders through a series of human and animal studies. We attempt to unravel the specific molecular targets downstream of ERK that act on particular cell types and regulate key steps in the associated developmental processes. Finally we point to ambiguities in our current knowledge that need to be clarified before RAS/ERK-targeting therapeutic approaches can be implemented.

High-fluence low-power laser irradiation promotes odontogenesis and inflammation resolution in periodontitis by enhancing stem cell proliferation and differentiation

Periodontitis can exert a severe impact on the life of patients, and the use of stem cell therapy for this disease is promising. The inflammatory response consequent to periodontitis can promote stem cell proliferation. Activated inflammation triggers inhibitory cytokine secretion, thus reducing inflammation subsequent to stem cell activation. High-fluence low-power laser irradiation (HF-LPLI) has the ability to regulate stem cell function through its effect on inflammation. Thus, the aim of the present study was to examine whether HF-LPLI is able to activate stem cells to promote regeneration in periodontitis by promoting inflammation resolution, as well as to evaluate the underlying mechanism of action if an effect is observed. Stem cells were treated with HF-LPLI following inflammation activation. Reverse transcription-quantitative polymerase chain reaction and EdU assay were used to evaluate cell proliferation and differentiation. Flow cytometry and immunofluorescence were also used to detect the ability of HF-LPLI to regulate the surrounding inflammatory environment. Animal models of periodontal disease were treated with stem cells and HF-LPLI, and regeneration was detected by hematoxylin and eosin staining and in vivo imaging. It was observed that HF-LPLI promoted inflammation resolution by reducing the excessive inflammatory response, and finally stimulated stem cell proliferation and differentiation. Furthermore, in vivo results revealed that stem cells treated with HF-LPLI induced bone regeneration. HF-LPLI stimulated stem cell proliferation and differentiation by promoting inflammation resolution subsequent to stem cell activation, providing a new strategy for the clinical treatment of periodontitis.

WITHDRAWN: Ameloblast-like characteristics of human Hertwig's epithelial rest of Malassez/epithelial rest of Malassez cells via interaction with stem cells from human exfoliated deciduous teeth

This article has been withdrawn at the request of the author(s) and/or editor. The Publisher apologizes for any inconvenience this may cause. The full Elsevier Policy on Article Withdrawal can be found at https://www.elsevier.com/about/our-business/policies/article-withdrawal.

Induction of Salivary Gland-Like Cells from Dental Follicle Epithelial Cells

The dental follicle (DF), most often associated with unerupted teeth, is a condensation of ectomesenchymal cells that surrounds the tooth germ in early stages of tooth development. In the present study, we aim to isolate epithelial stem-like cells from the human DF and explore their potential differentiation into salivary gland (SG) cells. We demonstrated the expression of stem cell-related genes in the epithelial components of human DF tissues, and these epithelial progenitor cells could be isolated and ex vivo expanded in a reproducible manner. The human DF-derived epithelial cells possessed clonogenic and sphere-forming capabilities, as well as expressed a panel of epithelial stem cell-related genes, thus conferring stem cell properties (hDF-EpiSCs). When cultured under in vitro 3-dimensional induction conditions, hDF-EpiSCs were capable to differentiate into SG acinar and duct cells. Furthermore, transplantation of hDF-EpiSC-loaded native de-cellularized rat parotid gland scaffolds into the renal capsule of nude mice led to the differentiation of transplanted hDF-EpiSCs into salivary gland-like cells. These findings suggest that hDF-EpiSCs might be a promising source of epithelial stem cells for the development of stem cell-based therapy or bioengineering SG tissues to repair/regenerate SG dysfunction.

Telomerase Expression in Medaka ( Oryzias melastigma) Pharyngeal Teeth

Nonmammalian vertebrates have the capacity of lifelong tooth replacement. In all vertebrates, tooth formation requires contact and interaction between the oral or pharyngeal epithelium and the underlying mesenchyme. To secure lifelong replacement, the presence of odontogenic stem cells has been postulated, particularly in the epithelial compartment. This study uses an advanced teleost fish species, the marine medaka Oryzias melastigma, a close relative to Oryzias latipes, to examine the expression and distribution of telomerase reverse transcriptase (Tert), the catalytic unit of telomerase, in developing pharyngeal teeth and to relate these data to the proliferative activity of the cells. The data are complemented by expression analysis of the pluripotency marker oct4 and bona fide stem cell marker lgr5. Tert distribution and tert expression in developing tooth germs show a dynamic spatiotemporal pattern. Tert is present first in the mesenchyme but is downregulated as the odontoblasts differentiate. In contrast, in the epithelial enamel organ, Tert is absent during early stages of tooth formation and upregulated first in ameloblasts. Later, Tert is expressed and immunolocalized throughout the entire inner enamel epithelium. The pattern of Tert distribution is largely mutually exclusive with that of proliferating cell nuclear antigen (PCNA) immunoreactivity: highly proliferative cells, as revealed by PCNA staining, are negative for Tert; conversely, PCNA-negative cells are Tert-positive. Only the early condensed mesenchyme is both Tert- and PCNA-positive. The absence of tert-positive cells in the epithelial compartment of early tooth germs is underscored by the absence of oct4- and lgr5-positive cells, suggesting ways other than stem cell involvement to secure continuous renewal.

Sox2/Oct4: A delicately balanced partnership in pluripotent stem cells and embryogenesis

Considerable progress has been made in understanding the roles of Sox2 and Oct4 in embryonic stem cells and mammalian embryogenesis. Specifically, significant progress has been made in answering three questions about the functions of Sox2 and Oct4, which are the focus of this review. 1) Are the first or second cell lineage decisions during embryogenesis controlled by Oct4 and/or Sox2? 2) Do the levels of Oct4 and Sox2 need to be maintained within narrow limits to promote normal development and to sustain the self-renewal of pluripotent stem cells? 3) Do Oct4 and Sox2 work closely together or is the primary role of Sox2 in pluripotent cells to ensure the expression of Oct4? Although significant progress has been made in answering these questions, additional studies are needed to resolve several important remaining issues. Nonetheless, the preponderance of the evidence suggests there is considerable crosstalk between Sox2 and Oct4, and further suggests Sox2 and Oct4 function as molecular rheostats and utilize negative feedback loops to carefully balance their expression and other critical genes during embryogenesis. This article is part of a Special Issue entitled: The Oct transcription factor family, edited by Dr. Dean Tantin.