Periodontal Ligament Stem Cells: Current Knowledge and Future Perspectives

Ethionamide Preconditioning Enhances the Proliferation and Migration of Human Wharton's Jelly-Derived Mesenchymal Stem Cells

Mesenchymal stem cells (MSCs) are a useful source for cell-based therapy of a variety of immune-mediated diseases, including neurodegenerative disorders. However, poor migration ability and survival rate of MSCs after brain transplantation hinder the therapeutic effects in the disease microenvironment. Therefore, we attempted to use a preconditioning strategy with pharmacological agents to improve the cell proliferation and migration of MSCs. In this study, we identified ethionamide via the screening of a drug library, which enhanced the proliferation of MSCs. Preconditioning with ethionamide promoted the proliferation of Wharton’s jelly-derived MSCs (WJ-MSCs) by activating phosphatidylinositol 3-kinase (PI3K)/Akt and mitogen-activated protein kinase/extracellular signal-regulated protein kinase kinase (MEK)/extracellular signal-regulated kinase (ERK)1/2 signaling. Preconditioning with ethionamide also enhanced the migration ability of MSCs by upregulating expression of genes associated with migration, such as C-X-C motif chemokine receptor 4 (CXCR4) and C-X-C motif chemokine ligand 12 (CXCL12). Furthermore, preconditioning with ethionamide stimulated the secretion of paracrine factors, including neurotrophic and growth factors in MSCs. Compared to naïve MSCs, ethionamide-preconditioned MSCs (ETH-MSCs) were found to survive longer in the brain after transplantation. These results suggested that enhancing the biological process of MSCs induced by ethionamide preconditioning presents itself as a promising strategy for enhancing the effectiveness of MSCs-based therapies.

Comparison of the Therapeutic Effect of Allogeneic and Xenogeneic Small Extracellular Vesicles in Soft Tissue Repair

Purpose

Small extracellular vesicles (sEV) are a heterogeneous group of vesicles that consist of proteins, lipids and miRNA molecules derived from the cell of origin. Although xenogeneic sEV have been applied for soft tissue regeneration successfully, the regeneration effect of allogeneic and xenogeneic sEV has not been compared systematically.

Methods

Our previous study has shown that sEV derived from rat adipose tissue successfully induced neoadipose regeneration. In this study, sEV were isolated from rat adipose tissue (r-sEV-AT) and porcine adipose tissue (p-sEV-AT), the morphology, size distribution and marker proteins expression of r-sEV-AT and p-sEV-AT were characterized. Besides, the sEV/AT ratio was evaluated and compared between r-sEV-AT and p-sEV-AT. Rat adipose-derived stromal/stem cells (rASCs) and rat aorta endothelial cells (rECs) were adopted to test the cellular response to allogeneic and xenogeneic sEV-AT. The effects of allogeneic and xenogeneic sEV-AT on host cells migration and neoadipose formation were evaluated in a subcutaneous custom-designed model. A full-thickness skin wound healing model was used to further compare the ability of allogeneic and xenogeneic sEV-AT in inducing complex soft tissue regeneration.

Results

p-sEV-AT showed similar morphology and size distribution to r-sEV-AT. Marker proteins of sEV were detected in both r-sEV-AT and p-sEV-AT. The sEV/AT ratio of porcine was slightly higher than that of rat. The effects of r-sEV-AT and p-sEV-AT on the differentiation of rASCs and rECs showed no significant difference. When allogeneic and xenogeneic sEV-AT were subcutaneously implanted into the back of SD rats, the host cells chemotactic infiltration was observed in 1 week and neoadipose tissue formation was induced in 8 weeks; no significant difference was observed between allogeneic and xenogeneic sEV-AT. For complex soft tissue regeneration, both allogeneic and xenogeneic sEV-AT significantly promoted wound re-epithelialization, granulation tissue formation and hair follicle regeneration and then accelerated skin wound healing.

Conclusion

Our results demonstrated that sEV derived from the same tissues of different species might be loaded with similar therapeutic substance benefitting tissue repair and regeneration, and paved the way for future research aimed at xenogeneic sEV application.

Stem Cells Secretome from Oral Tissue Could Represent a Promising Therapeutic Approach in COVID-19-Disease?

At present, severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection has quickly become a health emergency because no specifics vaccines or drugs, at this moment, are available. Recent studies have shown that the transplantation of mesenchymal stem cells (MSCs) into Coronavirus Disease 2019 (COVID-19) patients could represent a promising strategy for the development of new therapeutic methods. We speculate and suggest that the secretome of human Oral Tissue Stem Cells (hOTSCs), for their immunomodulatory and anti-inflammatory specific properties, could exert beneficial effects on the COVID-19 patients through an innovative aerosolisation technique. This non-invasive technique can offer multiple advantages in prophylaxis, as well as the prevention and treatment of severe epidemic respiratory syndrome with minimum risk and optimal therapeutic effects. This has the potential to create a novel pathway towards immunomodulatory therapy for the treatment of COVID-19 positive patients.

Dental Tissue-Derived Human Mesenchymal Stem Cells and Their Potential in Therapeutic Application

Human mesenchymal stem cells (hMSCs) are multipotent cells, which exhibit plastic adherence, express specific cell surface marker spectrum, and have multi-lineage differentiation potential. These cells can be obtained from multiple tissues. Dental tissue-derived hMSCs (dental MSCs) possess the ability to give rise to mesodermal lineage (osteocytes, adipocytes, and chondrocytes), ectodermal lineage (neurocytes), and endodermal lineages (hepatocytes). Dental MSCs were first isolated from dental pulp of the extracted third molar and till now they have been purified from various dental tissues, including pulp tissue of permanent teeth and exfoliated deciduous teeth, apical papilla, periodontal ligament, gingiva, dental follicle, tooth germ, and alveolar bone. Dental MSCs are not only easily accessible but are also expandable in vitro with relative genomic stability for a long period of time. Moreover, dental MSCs have exhibited immunomodulatory properties by secreting cytokines. Easy accessibility, multi-lineage differentiation potential, and immunomodulatory effects make dental MSCs distinct from the other hMSCs and an effective tool in stem cell-based therapy. Several preclinical studies and clinical trials have been performed using dental MSCs in the treatment of multiple ailments, ranging from dental diseases to nondental diseases. The present review has summarized dental MSC sources, multi-lineage differentiation capacities, immunomodulatory features, its potential in the treatment of diseases, and its application in both preclinical studies and clinical trials. The regenerative therapeutic strategies in dental medicine have also been discussed.

The effect of aging on the biological and immunological characteristics of periodontal ligament stem cells

Background

Periodontal ligament stem cells (PDLSCs) have many applications in the field of cytotherapy, tissue engineering, and regenerative medicine. However, the effect of age on the biological and immunological characteristics of PDLSCs remains unclear.

Methods

In this study, we compared PDLSCs isolated from young and adult individuals. PDLSC proliferation was analyzed by Cell Counting Kit-8 (CCK-8) and 5-ethynyl-2′-deoxyuridine (EdU) staining, and apoptosis level was detected by Annexin V-PE/7-ADD staining. PDLSC osteogenic/adipogenic/chondrogenic differentiation potentials were assessed by alkaline phosphatase (ALP), Alizarin Red, Oil Red O, Alcian Blue staining, and related quantitative analysis. PDLSC immunosuppressive capacity was determined by EdU and Annexin V-PE/7-ADD staining. To explore its underlying mechanism, microarray, quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR), and western blot analyses were performed to detect differentially expressed genes and proteins in PDLSCs.

Results

Our results demonstrated that with aging, the proliferation and osteogenic/adipogenic/chondrogenic differentiation potential of PDLSCs decreased, whereas apoptosis of PDLSCs increased. Moreover, the immunosuppressive ability of PDLSCs decreased with aging. Compared with PDLSCs from young subjects, analysis of mRNA expression revealed an upregulation of CCND3 and RC3H2, and a downregulation of Runx2, ALP, COL1A1, PPARγ2, CXCL12, FKBP1A, FKBP1B, NCSTN, P2RX7, PPP3CB, RIPK2, SLC11A1, and TP53 in those from adult individuals. Furthermore, protein expression levels of Runx2, ALP, COL1A1, and PPARγ2 in the adult group were decreased, whereas that of CCND3 increased.

Conclusions

Taken together, aging influences the biological and immunological characteristics of PDLSCs, and thus, it is more appropriate to utilize PDLSCs from young individuals for tissue regeneration, post-aging treatment, and allotransplantation.

Formation and Developmental Specification of the Odontogenic and Osteogenic Mesenchymes

Within the mandible, the odontogenic and osteogenic mesenchymes develop in a close proximity and form at about the same time. They both originate from the cranial neural crest. These two condensing ecto-mesenchymes are soon separated from each other by a very loose interstitial mesenchyme, whose cells do not express markers suggesting a neural crest origin. The two condensations give rise to mineralized tissues while the loose interstitial mesenchyme, remains as a soft tissue. This is crucial for proper anchorage of mammalian teeth. The situation in all three regions of the mesenchyme was compared with regard to cell heterogeneity. As the development progresses, the early phenotypic differences and the complexity in cell heterogeneity increases. The differences reported here and their evolution during development progressively specifies each of the three compartments. The aim of this review was to discuss the mechanisms underlying condensation in both the odontogenic and osteogenic compartments as well as the progressive differentiation of all three mesenchymes during development. Very early, they show physical and structural differences including cell density, shape and organization as well as the secretion of three distinct matrices, two of which will mineralize. Based on these data, this review highlights the consecutive differences in cell-cell and cell-matrix interactions, which support the cohesion as well as mechanosensing and mechanotransduction. These are involved in the conversion of mechanical energy into biochemical signals, cytoskeletal rearrangements cell differentiation, or collective cell behavior.

p75NTR optimizes the osteogenic potential of human periodontal ligament stem cells by up-regulating α1 integrin expression

Human periodontal ligament stem cells (hPDLSCs) are a promising source in regenerative medicine. Due to the complexity and heterogeneity of hPDLSCs, it is critical to isolate homogeneous hPDLSCs with high regenerative potential. In this study, p75 neurotrophin receptor (p75NTR) was used to isolate p75NTR⁺ and p75NTR⁻ hPDLSCs by fluorescence‐activated cell sorting. Differences in osteogenic differentiation among p75NTR⁺, p75NTR⁻ and unsorted hPDLSCs were observed. Differential gene expression profiles between p75NTR⁺ and p75NTR⁻ hPDLSCs were analysed by RNA sequencing. α1 Integrin (ITGA1) small interfering RNA and ITGA1‐overexpressing adenovirus were used to transfect p75NTR⁺ and p75NTR⁻ hPDLSCs. The results showed that p75NTR⁺ hPDLSCs demonstrated superior osteogenic capacity than p75NTR⁻ and unsorted hPDLSCs. Differentially expressed genes between p75NTR⁺ and p75NTR⁻ hPDLSCs were highly involved in the extracellular matrix‐receptor interaction signalling pathway, and p75NTR⁺ hPDLSCs expressed higher ITGA1 levels than p75NTR⁻ hPDLSCs. ITGA1 silencing inhibited the osteogenic differentiation of p75NTR⁺ hPDLSCs, while ITGA1 overexpression enhanced the osteogenic differentiation of p75NTR⁻ hPDLSCs. These findings indicate that p75NTR optimizes the osteogenic potential of hPDLSCs by up‐regulating ITGA1 expression, suggesting that p75NTR can be used as a novel cell surface marker to identify and purify hPDLSCs to promote their applications in regenerative medicine.

Enhanced VEGF/VEGF-R and RUNX2 Expression in Human Periodontal Ligament Stem Cells Cultured on Sandblasted/Etched Titanium Disk

Bone formation, in skeletal development or in osseointegration processes, is the result of interaction between angiogenesis and osteogenesis. To establish osseointegration, cells must attach to the implant in a direct way without any deposition of soft tissue. Structural design and surface topography of dental implants enhance the cell attachment and can affect the biological response. The aim of the study was to evaluate the cytocompatibility, osteogenic and angiogenic markers involved in bone differentiation of human periodontal ligament stem cells (hPDLSCs) on different titanium disks surfaces. The hPDLSCs were cultured on pure titanium surfaces modified with two different procedures, sandblasted (Control—CTRL) and sandblasted/etched (Test—TEST) as experimental titanium surfaces. After 1 and 8 weeks of culture VEGF, VEGF-R, and RUNX2 expression was evaluated under confocal laser scanning microscopy. To confirm the obtained data, RT-PCR and WB analyses were performed in order to evaluate the best implant surface performance. TEST surfaces compared to CTRL titanium surfaces enhanced cell adhesion and increased VEGF and RUNX2 expression. Moreover, titanium TEST surfaces showed a different topographic morphology that promoted cell adhesion, proliferation, and osteogenic/angiogenic commitment. To conclude, TEST surfaces performed more efficiently than CTRL surfaces; furthermore, TEST surface results showed them to be more biocompatible, better tolerated, and appropriate for allowing hPDLSC growth and proliferation. This fact could also lead to more rapid bone–titanium integration.

Functional Relationship between Osteogenesis and Angiogenesis in Tissue Regeneration

Bone tissue renewal can be outlined as a complicated mechanism centered on the interaction between osteogenic and angiogenic events capable of leading to bone formation and tissue renovation. The achievement or debacle of bone regeneration is focused on the primary role of vascularization occurrence; in particular, the turning point is the opportunity to vascularize the bulk scaffolds, in order to deliver enough nutrients, growth factors, minerals and oxygen for tissue restoration. The optimal scaffolds should ensure the development of vascular networks to warrant a positive suitable microenvironment for tissue engineering and renewal. Vascular Endothelial Growth Factor (VEGF), a main player in angiogenesis, is capable of provoking the migration and proliferation of endothelial cells and indirectly stimulating osteogenesis, through the regulation of the osteogenic growth factors released and through paracrine signaling. For this reason, we concentrated our attention on two principal groups involved in the renewal of bone tissue defects: the cells and the scaffold that should guarantee an effective vascularization process. The application of Mesenchymal Stem Cells (MSCs), an excellent cell source for tissue restoration, evidences a crucial role in tissue engineering and bone development strategies. This review aims to provide an overview of the intimate connection between blood vessels and bone formation that appear during bone regeneration when MSCs, their secretome—Extracellular Vesicles (EVs) and microRNAs (miRNAs) —and bone substitutes are used in combination.

Adipose Stem Cells (ASCs) and Stromal Vascular Fraction (SVF) as a Potential Therapy in Combating (COVID-19)-Disease

A recent and interesting study reported improved respiratory activity after intravenous administration of mesenchymal stem cells (MSCs) into patients affected by coronavirus disease 2019 (COVID-19). These outcomes displayed that intravenous infiltration of MSCs is a safe and efficacy treatment for COVID-19 pneumonia, a severe acute respiratory illness caused by the coronavirus 2 (SARS-CoV-2). Only 7 patients were treated, but with extraordinary results, opening a new strategy in COVID-19 therapy. Currently, no specific therapies against SARS-CoV-2 are available. The MSCs therapy outcomes reported, are striking, as these cells inhibit the over-activation of the immune system, promoting endogenous repair, by improving the lung microenvironment after the SARS-CoV-2 infection. The MSCs could represent an effective, autologous and safe therapy, and therefore, sharing these published results, here is reported the potential use possibilities in COVID-19 of the most common MSCs represented by Adipose Stem Cells (ASCs).

Salivary Small Extracellular Vesicles Associated miRNAs in Periodontal Status-A Pilot Study

This pilot study aims to investigate whether salivary small extracellular vesicle (sEV)-associated microRNAs could act as potential biomarkers for periodontal disease status. Twenty-nine participants (10 who were healthy, nine with gingivitis, 10 with stage III/IV periodontitis) were recruited and unstimulated whole saliva samples were collected. Salivary sEVs were isolated using the size-exclusion chromatography (SEC) method and characterised by morphology, EV-protein and size distribution using transmission electron microscopy (TEM), Western Blot and Nanoparticle Tracking Analysis (NTA), respectively. Ten mature microRNAs (miRNAs) in salivary sEVs and saliva were evaluated using RT-qPCR. The discriminatory power of miRNAs as biomarkers in gingivitis and periodontitis versus healthy controls was evaluated by Receiver Operating Characteristics (ROC) curves. Salivary sEVs were comparable to sEVs morphology, mode, size distribution and particle concentration in healthy, gingivitis and periodontitis patients. Compared to miRNAs in whole saliva, three significantly increased miRNAs (hsa-miR-140-5p, hsa-miR-146a-5p and hsa-miR-628-5p) were only detected in sEVs in periodontitis when compared to that of healthy controls, with a good discriminatory power (area under the curve (AUC) = 0.96) for periodontitis diagnosis. Our study demonstrated that salivary sEVs are a non-invasive source of miRNAs for periodontitis diagnosis. Three miRNAs that are selectively enriched in sEVs, but not whole saliva, could be potential biomarkers for periodontal disease status.

Dual-Functionalized Apatite Nanocomposites with Enhanced Cytocompatibility and Osteogenesis for Periodontal Bone Regeneration

The development of biomimetic bone graft materials for periodontal tissue engineering is a field of topical interest. In this study, we designed a dual-functionalized apatite nanocomposite, which could integrate multiple molecular cues for manipulating the fate of periodontal ligament stem cells (PDLSCs). Briefly, inspired by mussels, a biomimetic nanohydroxyapatite was fabricated using a polydopamine structure as a template (named as tHA) and then surface-modified with bone-forming peptide-1 (BFP-1) and vascular endothelial growth factor-mimicking peptide (QK) via a single step of catechol chemistry. Our study showed that the biofunctions of tethered peptides were not compromised on the surface of apatite nanoparticles. Because of the synergistic effect of BFP-1 and QK peptides, the dual-functionalized apatite nanocomposite showed improved cytocompatibility compared to controls. Moreover, it can boost the proliferation and osteogenic differentiation of PDLSCs, indicating excellent bioactivity of tHA-BFP/QK nanoparticles on cell fate decision. More importantly, animal experiments showed that dual-functionalized apatite nanocomposites could dramatically promote the regeneration of periodontal bone. It is concluded that our work provides an instructive insight into the design of biomimetic apatite nanocomposites, which holds a great potential for applications in periodontal bone repair.

Salvianolic acid B promotes the osteogenic differentiation of human periodontal ligament cells through Wnt/β-catenin signaling pathway

BACKGROUND

Osteogenic differentiation of human periodontal ligament cells (hPDLCs) is crucial for regenerate periodontal tissues. In this study, we investigated the function of salvianolic acid B (Sal B) in osteogenesis of hPDLCs.

METHODS

HPDLCs were isolated from healthy third molar roots. HPDLCs at passage 3 were identified by morphological observation and immunohistochemistry of vimentin. The viability of hPDLCs incubated with Sal B at concentrations of 0μM, 0.1μM, 0.5μM, 1μM and 5μM were measured by CCK-8 assay. To evaluate the effect of Sal B on osteogenic differentiation of hPDLCs, the alkaline phosphatase (ALP) activity, osteogenic differentiation markers, and mineralized nodules were determined by ALP kit, qRT-PCR and alizarin red S staining, respectively. To confirm the function of Sal B in hPDLCs involved in Wnt/β-catenin signaling pathway, hPDLCs were incubated with Sal B or co-incubated with Sal B and DKK-1 (a inhibitor of Wnt/β-catenin). The levels of Wnt/β-catenin signaling pathway and osteogenic differentiation-associated indicators were then determined.

RESULTS

HPDLCs showed a typical fibroblast-like and spindle-shaped, with vimentin-positive. The viability of hPDLCs had no obvious change with stimulation of Sal B at various doses. Sal B promoted the increase of ALP activity, osteogenic differentiation markers levels, mineralized nodules and activation of Wnt/β-catenin signaling pathway, and DKK-1 could block those effects of Sal B on hPDLCs.

CONCLUSION

Sal B promoted osteogenesis of hPDLCs through Wnt/β-catenin signaling pathway, which providing a potential drug for periodontitis treatment.

Recombinant Klotho Protects Human Periodontal Ligament Stem Cells by Regulating Mitochondrial Function and the Antioxidant System during H2O2-Induced Oxidative Stress

Human periodontal ligament stem cells (hPDLSCs) are a favourable source for tissue engineering, but oxidative stress conditions during cell culture and transplantation could affect stem cell viability and stemness, leading to failed regeneration. The aim of this study was to evaluate the antioxidant and protective effects of Klotho, an antiageing protein, against cell damage and the loss of osteogenesis in hPDLSCs in H₂O₂-induced oxidative environments. H₂O₂ was used as an exogenous reactive oxygen species (ROS) to induce oxidative stress. Recombinant human Klotho protein was administered before H₂O₂ treatment. Multitechniques were used to assess antioxidant activity, cell damage, and osteogenic ability of hPDLSCs in oxidative stress and the effects of Klotho on hPDLSCs. Mitochondrial function was analyzed by an electron microscopy scan of cellular structure, mitochondrial DNA copy number, and cellular oxygen consumption rate (OCR). Furthermore, we explored the pathway by which Klotho may function to regulate the antioxidant system. We found that pretreatment with recombinant human Klotho protein could enhance SOD activity and reduce intracellular oxidative stress levels. Klotho reduced H₂O₂-induced cellular damage and eventually maintained the osteogenic differentiation potential of hPDLSCs. Notably, Klotho promoted mitochondrial function and activated antioxidants by negatively regulating the PI3K/AKT/FoxO1 pathway. The findings suggest that Klotho protein enhanced the antioxidative ability of hPDLSCs and protected stem cell viability and stemness from H₂O₂-induced oxidative stress by restoring mitochondrial functions and the antioxidant system.

Ferritin expression in the periodontal tissues of primates

Ferritin, an iron-binding protein, is composed of two subunits, ferritin heavy chain and ferritin light chain. It regulates many biological functions, such as proliferation, angiogenesis, and immunosuppression. The objective of this study was to determine the expression and distribution of ferritin in the periodontal tissues of primates. First, we assessed the expression of ferritin in primary cultured cells isolated from human periodontal tissues using the polymerase chain reaction and immunofluorescent staining in vitro. Second, we investigated the expression and distribution of ferritin in the periodontal tissues of Macaca fascicularis, human gingival tissues, and human gingival carcinoma tissues using immunohistochemistry in vivo. Both protein and mRNA of ferritin were constitutively present in human primary cultured cells, including those from the dental apical papilla, periodontal ligament, dental pulp, and gingival epithelium, as well as gingival fibroblasts. In M. fascicularis tissues, the immunohistochemical staining was particularly strong in blood vessel and mineralizing areas of the dental pulp and periodontal ligament. Ferritin heavy chain exhibited specific immunopositivity in the stratum basal of the epithelium in human gingival tissue, and strong immunostaining was found in peripheral regions of gingival carcinoma sites. Ferritin is constitutively present and widely distributed in the periodontal tissues of primates. Ferritin may play roles in epithelial proliferation, vascular angiogenesis, and mineralization in these tissues.