A Novel Perspective on Tissue Engineering Potentials of Periodontal Ligament Stem Cells

All published articles of this journal are available on ScienceDirect.

REVIEW ARTICLE

A Novel Perspective on Tissue Engineering Potentials of Periodontal Ligament Stem Cells

Faraz Radmand1 , # Open Modal Milad Baseri1 , # Open Modal Maryam Farsadbakhsh1 Ayub Azimi1 Solmaz Maleki Dizaj2 , * Open Modal Simin Sharifi2
Authors Info & Affiliations
The Open Dentistry Journal • 21 Dec 2022 • REVIEW ARTICLE • DOI: 10.2174/18742106-v16-e221006-2021-216
Previous Article | Next Article

Abstract

It is challenging to completely and predictably regenerate the missing periodontal tissues caused by the trauma or disease. To regenerate the periodontium, there is a need to consider several aspects that co-occur with periodontal development. This study provides an overview of the most up-to-date investigations on the characteristics and immunomodulatory features of Periodontal Ligament Stem Cells (PDLSCs) and the recent interventions performed using these cells, focusing on cell survival, proliferation, and differentiation. Keeping in mind the relationship between age and potency of PDLSCs, this work also demonstrates the necessity of establishing dental-derived stem cell banks for tissue regeneration applications. The data were collected from Pubmed and Google Scholar databases with the keywords of periodontal ligament stem cells, tissue engineering, characteristics, and stem cell therapy. The results showed the presence of wide-ranging research reports supporting the usability of PDLSCs for periodontal reconstruction. However, a better understanding of self-restoration for adequate regulation of adult stem cell growth is needed for various applied purposes.

Keywords: Periodontal ligament stem cells, Tissue engineering, Guided Tissue Regeneration, Stem cell therapy, Disease, Tissues.

1. INTRODUCTION

The gingiva generally shows the first signs of inflammation through disease processes in the oral cavity. Therefore, knowledge about the structure of periodontium is necessary for understanding the effects of any disease process. Periodontium is a complicated structure in the oral cavity that contains soft (gingiva and periodontal ligament) and hard (cementum and bone) tissues [1]. Prominent functions of Periodontal Ligament (PDL) include supporting the tooth structure and protecting nerves and blood vessels within it from injury through mechanical loading [2]. It is acknowledged that PDL has significant roles in homeostasis, sensation, nutrition of teeth, protection against oral cavities' pathogens [3, 4], and renewal of periodontal tissue by providing the surrounding tissues with stem/progenitor cells [5].

Periodontal disease includes a variety of diseases that are caused by inflammation. Periodontal diseases have distinctive features, such as destroying the supporting tissues of the teeth and chronic inflammation commenced with the infection caused by bacteria [6]. If this inflammation is not treated and eliminated, it can cause attachment loss, bone resorption, and eventually tooth extraction [7]. A decline in individual living standards through significant aesthetic problems and dysfunctions is caused by tooth loss [8]. Scaling, root planning, and open-flap debridement are examples of conventional therapies that dentists achieved to decelerate periodontitis progression. Other periodontal regenerative therapies, including Guided Tissue Regeneration (GTR) and bone grafting, have commonly been used in clinics [9]. However, the results of these treatments have been limited since they have not reached a complete restoration of the periodontium [10]. Tissue Engineering (TE) is an alternative method that can ease the regeneration process of periodontal tissues [11]. TE is an advanced field of regenerative medicine that denotes the practice of combining scaffolds, cells, and biologically active molecules into functional tissues. The aim of TE is to gather functional constructs that restore, maintain, or recover damaged tissues or whole organs [12].

Stem cells and their derived products are great promises for novel medicinal management. Stem cell therapy, also recognized as regenerative medicine, endorses the repair response of diseased, dysfunctional or injured tissue using stem cells or their derivatives. Up to now, the various stem cells have extensive use in tissue engineering, including Mesenchymal Stem Cells (MSCs), Adipose tissue-derived Stem Cells (ADSCs), and other tissue-specific somatic stem cells [13]. MSCs, as multipotent cells, have the capability of differentiation into multiple lineages depending on the signals received from encircling the microenvironment [14].

Five disparate MSC sources have been detected in human postnatal dental tissue, including Periodontal Ligament Stem Cells (PDLSCs), Stem cells from Human Exfoliated Deciduous teeth (SHED), Dental Pulp Stem Cells (DPSCs), Dental Follicle Precursor Cells (DFPCs), and Stem Cells from the Apical Papilla (SCAP) [15, 16]. Fig. (1) shows the process for dental stem cell-based tissue engineering.

Although the number of PDLSCs that can be obtained by a single sample is limited [3], these stem cells can be easily isolated and expanded in vitro [17] Fig. (2). PDLSCs are mainly derived from the mid-third section of the root surface after permanent tooth extraction. Harvesting PDLSCs is not so difficult since they can be derived from both the surface of the root and the alveolar bone [18]. PDLSCs isolated from the remnants of PDL on the alveolar bone surface of extraction sockets have revealed a more promising osteogenic/adipogenic differentiation capability than those from the root surface [18, 19].

A prominent source of MSCs is provided by PDL to their approachability and obtainability for autologous transplantation [18]. This type of MSCs is capable of multipotent differentiation, including osteogenic, adipogenic, myogenic, and chondrogenic commitment. Besides, these mesenchymal lineages, through the ectomesenchymal origin of PDLSCs, can differentiate into neuronal phenotypes [20-22]. It has been substantiated that various paracrine factors with different functions, such as immunomodulation, anti-apoptosis, and anti-inflammation, are secreted by PDLSCs, and the secreted factors of surviving cells in the transplanted site show positive effects on periodontal wound healing [23, 24]. Some problems have been discovered associated with the use of PDLSCs, such as limitations in the number of stem cells obtained by a single sample [3], sensitive condition of stem cells according to donor quality [25], and tumorigenesis [5].

The current study investigated the PDLSCs from multiple viewpoints, including markers, immunomodulation, differentiation, aging, and tissue engineering.

2. MARKERS FOR PDLSCs

Markers that have been reported in numerous studies are Cluster of Differentiation (CD)105 [15, 16, 18, 22, 23, 26-38], CD90 [15, 16, 18, 22, 23, 26, 28, 29, 31-34, 36-40], CD73 [15, 22, 27-29, 31, 34, 39], Stromal Precursor Antigen-1 (STRO-1) [16, 30, 31, 35, 37, 38, 41, 42], CD146 [16, 30-33, 35, 37, 38, 41, 42], CD29 [16, 31, 33, 35, 38, 41, 42], CD13 [16, 31, 33, 36], CD44 [15, 16, 30, 31, 33, 34, 41], CD166 [16, 22, 31, 33] but lack expression of CD45 [15, 22, 28, 29, 32, 34, 36, 38, 40, 42], CD34 [15, 22, 28, 29, 32, 34, 37, 42], CD14 [22, 28, 29, 38], CD19 [28, 30, 34], CD31 [22, 37, 38, 40] (Fig. 3).

In some studies, PDLSCs are positive for CD9 [33], CD10 [31, 33], CD49d [33], STRO-4 [41], STRO-3 [31], CD106 [31], CD349 [31], CD26 [31], CD71 [31], and Mesenchymal Stromal Cell Antigen-1 (MSCA-1)/Tissue Nonspecific Alkaline Phosphatase (TNAP) [31] but negative for CD11b [28, 34], Human Leukocyte Antigen (HLA)-DR [22, 34], HLA Cl II [28], CD79a [22, 28], CD40 [16, 22], CD80 [16, 22], CD86 [16, 22], CD54 [22], and CD20 [29].

3. PDLSCs AND IMMUNOMODULATION

Immunomodulation is a favorable characteristic of PDLSCs. Studies have shown that the expression of immune co-stimulating factors is absent in PDLSCs. Furthermore, PDLSCs could inhibit immune cell proliferation [43, 44]. This valuable property might be beneficial for stem cell therapies in periodontal tissue regeneration since the inflammatory environment in periodontitis suppresses the physiological repair procedures, including stem and mature cells [45]. Besides cell regeneration, PDLSCs display immunomodulatory features, which are evaluable through immunomodulatory function expressing HLAE, HLAG and indoleamine-pyrrole 2,3-dioxygenase 1 (IDO1), IDO2 [46].

Fig. (1). Dental stem cell-based tissue engineering (with permission from [13]).
Reprinted from Tissue Engineering Part B: Reviews, 18, Kim BC, Bae H, Kwon IK, Osteoblastic/cementoblastic and neural differentiation of dental stem cells and their applications to tissue engineering and regenerative medicine, 235-544, 2012, with permission (Under the terms of the Creative Commons Attribution 4.0 International License (Creative Commons Public Domain Mark 1.0), which permits unrestricted use.)
Fig. (2). Light microscopy image represents periodontal ligament stem cells culture stained with toluidine blue (with permission from [20]).
Reprinted from European Cells and Materials, 32, Diomede F, Zini N, Gatta V, Human periodontal ligament stem cells cultured onto cortico-cancellous scaffold drive bone regenerative process, 181-201. 2016, with permission (under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use.)
Fig. (3). Markers, immunomodulatory properties, and harvesting of PDLSCs.

Besides their immunogenicity, an immunosuppressive possession with action on B and T cells should facilitate the use of allogeneic PDLSCs for periodontal regeneration [47]. Firstly, owing to co-stimulatory molecules of T cells (CD80 and CD86) and HLAII DR absence, the immunogenicity of PDLSCs is low. Secondly, due to the up-regulation of prostaglandin E2 (PGE2) and cyclooxygenase-2 (COX-2), PDLSCs restrain allogeneic T cell proliferation [48]. PDLSCs enhance the production of regulatory T cells (T-regs) in healthy tissue. In inflamed periodontium, PDLSCs have a low potential for induction of T-regs. Some studies also demonstrated reduced inhibitory effects on T cell proliferation [49]. Furthermore, PDLSCs blocked the activation of B cells by programmed death-1 [50].

Wang et al. proved that PDLSCs might decrease the apoptosis of neutrophils via interleukin-6 (IL-6) [51]. PDLSCs can be a valuable source for reducing the autoimmune disease destruction in Type 1 Diabetes (T1D) while they have an immunosuppressive impact on monocyte-derived dendritic cells (mDCs) in T1D patients [52]. Furthermore, PDLSCs may induce macrophage polarization to the M2 phenotype. This shift to M2 macrophages in the first stages of tissue regeneration is contributed to the promoted periodontal tissue regeneration [53, 54]. Collectively, signals from the PDLSCs could modify the immune-related niche to promote periodontal tissue regeneration. The reports proved the immunomodulatory impact of PDLSCs on both cellular and humoral immunity. It seems that this property is critical for periodontal tissue regeneration in inflamed environments and increases the success rate of cell transplantation.

Fig. (4). Identification of PDLSCs. (A) Single colony of periodontal ligament stem cells stained with methylene blue. (B) Osteogenic differentiation of PDLSCs. (C) Adipogenic differentiation of PDLSCs (adopted from [53] with permission).
Reprinted from Stem Cell Research & Therapy, 10, Liu J, Chen B, Bao J, Zhang Y, Lei L, Yan F, Macrophage polarization in periodontal ligament stem cells enhanced periodontal regeneration, 1-11, 2019, with permission (under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use.)

4. DIFFERENTIATION OF PDLSCs

Moreover, it has been reported that PDLSCs and DPSCs own the potential for osteogenic differentiation [22, 55]. PDLSCs favorably differentiate into osteoblasts and adipocytes [34, 56]. Fig. (4) shows the identification of PDLSCs. Within an osteogenic differentiation growth medium, osteoblasts formation occurs, and mineralization nodules are developed [15]. The capability of adipogenic differentiation is also demonstrated in several PDLSC differentiation studies [22, 34, 55, 57]. Moreover, it has been observed that due to exposure to a specific differentiation medium, PDLSCs would differentiate into chondrocytes [34, 55, 58].

PDL and dental follicles possess multipotent stem cells with differentiation capacity, especially neural cells [15]. The work from Bahrami et al. [15] revealed that the neurogenic differentiation potential of PDLSCs was more than DFPCs. The gene expression level and neural cell protein in PDLSCs were more than DFPCs of third molar [15]. Meanwhile, by plating on cytokine-free laminin-coated plates, impulsive differentiation into neuronal lineages was detected [59]. Also, another study showed that PDLSCs could augment Retinal Ganglion Cell (RGC) viability and axon regeneration [60]. Additionally, Li et al. confirmed odontogenic features of PDLSCs beyond their neuronal differentiation potential [61]. Furthermore, Pelaez et al. [62] illustrated that exposing PDLSCs to short-term mechanical strain induces them to differentiate into cardiac myocytes. PDLSCs can differentiate into endothelial cells that would provide capillary-like sprouts containing lumens in vitro [63]. Additionally, they possess the potential for differentiation into various PDL cells, such as fibroblasts, osteoblasts, endothelial cells, cementoblasts, and neural cells [64, 65].

PDLSCs have similarities with Bone Marrow-derived Mesenchymal Stem Cells (BMSCs) in some features, such as tri-linage differentiation potential and immunomodulatory and anti-apoptotic function [21, 23]. PDLSCs possess specific additional functions, such as cementum-PDL complex fabricating ability and a tooth-specific structure [22, 24]. Lee et al. [39] suggested that PDLSCs derived from the PDL of supernumerary teeth showed higher colony-forming efficiency than BMSCs and that they could differentiate in both adipocytes and osteoblasts. It has been found that PDLSCs have a remarkable potential to differentiate into PDL, alveolar bone, and cementum compared to BMSCs under regenerative conditions [21]. As reported, PDLSCs are multipotent stem cells. They have osteogenic, adipogenic, chondrogenic, neurogenic, and odontogenic differentiation potential. Additionally, PDLSCs could generate cardiac myocytes, endothelial cells, and cementoblasts. Hence, PDLSCs are appropriate cells in regenerative dentistry that can be used in periodontal disease. Furthermore, they could be used in other body parts for therapeutic goals.

5. EFFECT OF AGING ON PDLSCs

In clinical fields, the importance of PDL in auto-transplantation is known due to the potency of the donor’s PDL to cause the renewal of periodontium components, such as PDL, bone, and gingiva within the recipient site [8]. When the donor age increases, the functional and regeneration potential of stem cells will decrease [13, 66, 67] (Fig. 5). For example, Wu et al. [40] revealed that donor age has a negative impact on the osteogenic potential of PDLSCs. It was found that PDLSCs derived from aged donors had less regenerative potential than those from young donors [25]. Comparing biological characteristics of PDLSCs derived from donors at different ages and according to the results of various studies, proliferation [25, 68-70], migration ability [68], differentiation ability [25, 68, 70], and immunosuppression ability [70] of PDLSCs have a negative correlation with donor’s age.

Consequently, there is a need to design refined protocols for the successful proliferation and differentiation of PDLSCs derived from old individuals as a requirement for autologous cell-based strategies to treat periodontal diseases. Allogenic PDLSCs may be promising in the future by establishing cell banks. Cells from young donors may be beneficial for periodontal regeneration therapy because of their matrix protein production, osteogenic potential, and functional features following sheet fabrication.

Fig. (5). Dental stem cells with aging (Adopted from [13] with permission).
Reprinted from Tissue Engineering Part B: Reviews, 18, Kim BC, Bae H, Kwon IK, Osteoblastic/cementoblastic and neural differentiation of dental stem cells and their applications to tissue engineering and regenerative medicine, 235-544, 2012, with permission (Under the terms of the Creative Commons Attribution 4.0 International License (Creative Commons Public Domain Mark 1.0), which permits unrestricted use.)

6. TISSUE ENGINEERING WITH PDLSCs

Tissue engineering is an interdisciplinary field that includes the basics of engineering and biology to generate biological substitutes [71]. Tissue engineering in dentistry has two goals: first, to create therapeutic approaches to regenerate dental and craniofacial structures, and the second goal is to repair their natural functions [72]. Several types of cell-based regenerative therapies are currently being applied, including scaffold engineering and cell-sheet tissue engineering.

6.1. Scaffolds

The scaffold is an artificial extracellular matrix (ECM) and is a model for cell growth and tissue engineering. Scaffolds should have some vital characteristics, including biocompatibility, biodegradability, adequate mechanical and physical stability, and mimicking the niche to ease cell adhesion, proliferation, differentiation, and tissue regeneration [73-75].

Scaffolds are vital elements for periodontal tissue regeneration to hold cells and contain many bioactive materials [76]. Herein, we reviewed the different scaffolds and cell sheets applied for PDLSCs tissue engineering.

Chitosan is material extracted from invertebrates like crab, and lobster, which is also known as chitin. Chitosan has been used as bone graft material and has characteristics like high viscosity, water-binding properties, biocompatibility, biodegradability, and low cytotoxicity [77]. Ge et al. demonstrated that seeded PDLSCs on a nanohydroxyapatite-coated genipin-chitosan conjunction scaffold showed significantly superior viability and alkaline phosphatase (ALP) activity and up-regulated the bone-related markers to a more extent compared to PDLSCs seeded on the genipin-chitosan framework [78].

Alginate scaffolds are excellent for TE in biological systems since they have natural biocompatibility and easily adjustable immunosuppression and degradation features [79]. Alginate can ease the spatial arrangement of the encapsulated MSCs within its three-dimensional (3-D) structure, causing the creation of a structural organization with similarity to the native in vivo microenvironment [80]. Moshaverinia et al. [81] suggested that chondrogenic differentiation and viability of PDLSCs encapsulated within Arg-Gly-Asp (RGD)-coupled alginate-hydrogel scaffold have been enhanced both in vitro and in vivo. In an injectable approach, encapsulated MSCs demonstrated high levels of proliferation, viability, and chondrogenic differentiation ability. Moreover, PDLSCs with transforming growth factor beta (TGF) b3-loaded RGD-modified alginate microspheres are favorable alternatives for tendon regeneration [17]. In another study, PDLSCs encapsulated in RGD-coupled alginate microspheres presented a moderate ability for osteodifferentiation [82].

HydroMatrix (HydM) is an advanced injectable peptide nanofiber hydrogel presented recently for cell culture. PDLSCs can adhere, survive, migrate, and proliferate on HydM, and this gel also enhances their osteogenic differentiation [83].

Collagen is one of the most broadly used natural scaffolds. It has been observed that the combination of collagen scaffolds with platelet growth factors and PDLSCs could not significantly improve osteogenic regeneration [84]. Due to their anti-inflammatory and regenerative qualities, natural ECM scaffolds are considered superior alternatives to type-I collagen (COLI) membranes [85, 86]. ECM scaffolds are derived from the dermis, small intestine, and pericardium. ECM molecular composition comprises various structural proteins, including COLI, proteoglycans, glycosaminoglycans, glycoproteins, cytokines, and growth factors that are expressed as guidance of cell behavior [87, 88]. An increase in viability, proliferation, and reduction in apoptosis compared to PDLSCs treated with COLI are caused by incubation with ECM. Additionally, co-culture with ECM membrane enhances PDLSC migration and bio-attachment. The ECM membrane could be used as an appropriate scaffold in the GTR application for periodontal disease treatment [36].

The amniotic membrane is a biological membrane that encircles the amniotic sac [89]. The amniotic membrane has several biological features appropriate for periodontal regeneration, including low immunogenicity, anti-fibrosis, anti-inflammation, and being rich in ECM constituents. Furthermore, this membrane can maintain close contact with the transplanted area due to its flexible nature [90, 91]. Amniotic membranes can be used as scaffolds and can serve as a substantial material in TE [92].

Calcium Phosphate Cement (CPC) can be used as an excellent scaffold material for dental and craniofacial treatments [93]. CPC has potent biocompatibility, osteoconductivity, osteoinductivity, and bioactivity [94, 95]. In a study, PDLSCs were cultured on a Biphasic Calcium Phosphate (BCP) scaffold, and the results exhibited that the PDLSC-seeded BCP enhanced periodontal tissue regeneration. Moreover, new bone formation and collagen fibers were also observed [96].

6.2. Cell Sheet Engineering

Cell sheet engineering is a modern method in TE; it can be used in various fields like corneal surface reconstruction and non-invasive endoscopic transplantation [97, 98]. Proteolytic enzymes are one of the privileges of cell sheets concerning the unfavorable shortage of degrading cell adhesion molecules and the deposited ECM [99]. Therefore, compared to scaffold-based tissue engineering, a cell sheet can bring healthy cells connected by intact cell-cell interactions and ECM proteins. It is also proved in some investigations that they have an important role in periodontal tissue regeneration [35, 100]. Iwata et al. confirmed that the autologous PDL-derived cell sheets are safe and efficient in severe periodontal defects. Besides, the stability of these sheets has been shown during long-term follow-up [101]. A nanopatterned substratum activated with thermos-responsive polymers eased the reproducible and robust production of patterned cell sheets utilizing PDLSCs. The PDLSCs showed accelerated impetuous monolayer creation, as well as enhanced gene expression patterns related to PDL regeneration compared to the control group [30].

Platelet-rich plasma (PRP) is a common autologous platelet concentration with different growth factors. It contains growth factors, such as platelet-derived growth factor (PDGF), TGF-β, vascular endothelial growth factor (VEGF), fibroblast growth factor-2 (FGF), and insulin-like growth factor I (IGF). These types of growth factors can increase the aggregation of cells in a periodontal defect [35]. PDLSCs treated with 1% PRP exhibited the highest osteogenic differentiation potential and superior periodontal tissue regeneration capability [35]. PRP may increase the proliferation and ECM release of PDLSCs in the process of cell sheet formation [35]. Platelet-rich fibrin (PRF) is known as the second generation of platelet concentrate. It has superior characteristics compared to conventional PRP, including simplicity of preparation and a lack of the biochemical handling of blood [102]. Notably, the 3D structure of this newly developed material is ideal for directing therapeutic stem cells to a particular site of destruction [103]. In a study, the authors claimed that the novel cell transplant approach using PDLSCs/PRF, containing cell sheet particles of PDLSCs and PRF granules, may stimulate periodontal defect healing and PDL regeneration [104].

Based on the reviewed literature in this section, the various existing scaffolds have shown great potential for periodontal regeneration. The above-reviewed scaffolds are mostly biodegradable biomaterials. They degrade in the body once the new tissue is formed. Besides, most of the polymers mentioned above display a sustained degradation process with some degree of controllability [105, 106]. The characteristics of biomaterial scaffolds have mainly been characterized in vitro, providing good fundamental information for future in vivo tests [106].

6.3. Chemical Interventions

The fabrication of functional organs with TE is very challenging. Such barricades consist of inadequate cell migration into and retaining within scaffolds, host inflammatory reactions, inadequate abilities in generating microscale vascularization for mass transfer, various rates of cell multiplication in comparison to scaffold destruction, and the incapability of generating functional tissues with the structural intricacy of native tissues due to scaffold-dependent techniques [107]. Some studies focus on improving the osteogenic potentiality of PDLSCs and modulating the expression profile of growth factor-linked genes [108-110].

Acetyl Salicylic Acid (ASA), known as aspirin, is a commonly used drug globally and is generally useful for the secondary prevention of cardiovascular disease [111]. The observations in the previous studies showed that ASA made a positive impact on reducing the loss of human alveolar bone and enhancing periodontal tissue health [112]. Aspirin can enhance the proliferation of PDLSCs and their osteogenic differentiation potential and can ameliorate periodontal health by stimulating growth factor-associated genes in PDLSCs and improving their osteogenic potential [29].

Vitamin C (Vc) is a water-soluble vitamin essential for immune system functions. It is critical in human health and is profoundly involved in numerous metabolic and signaling routes. It has an antioxidant role with the capability to less Reactive Oxygen Species (ROS). In Vc provided culture medium, Vc is a growth factor to enhance cell proliferation and DNA synthesis [113]. Moreover, in periodontal disease, Vc diminishes the development of the damage process, stimulates the differentiation of PDLSCs [114], and augments the viability of these cells [115]. Wei et al. suggested that Vc enhanced the proliferation ability and osteogenic differentiation of PDLSCs, engaging telomerase activity in PDLSCs, thus indicating the superior potential for regeneration and differentiation [116]. Another study recognized that Vc-treated PDLSCs in a long-term culture preserved a slender morphology, greater growth rate and migration ability, stemness, and osteogenic differentiation potential [117]. The development of a valid approach based on Vc treatment eased the construction of highly practical and functional PDLSC sheets and the subsequent regeneration of periodontal tissues [116].

Metformin (1,1-dimethylbiguanide hydrochloride) is a hypoglycemic medicine vastly consumed by type 2 diabetes mellitus patients [118]. Metformin can be applied for vast purposes, like antitumor, immunoregulatory, and anti-inflammatory functions [119]. It has been used as an additive material to scaling and root planning in the treatment of periodontal tissue in dentistry [120]. A review study concluded that metformin has anti-aging and anti-oxidative effects on PDLSCs [121]. Low amounts of metformin did not affect cell proliferation but hindered adipogenic differentiation and enhanced PDLSCs’ osteogenic differentiation. The results of this study showed that metformin both increases osteogenic differentiation of PDLSCs and protects PDLSCs against oxidative stress-produced harm, indicating that metformin can be greatly useful in increasing bone regeneration in the therapy of periodontitis by PDLSCs [34]. Yang et al. demonstrated that metformin could relieve oxidative stress-induced senescence by autophagy and could, to a degree, recover the osteogenic potential of PDLSCs [122]. The results of Zhang et al. [123] revealed that metformin generates a suitable niche for periodontal tissue regeneration via stimulating the proliferation and migration of PDLSCs.

MicroRNAs (miRNAs) are a new type of posttranscriptional regulators. They are critical elements in regulating cell differentiation [124]. Inflammatory cytokines can control miRNAs and cause some inflammatory diseases [125]. Several types of miRNAs have been investigated in previous studies. MiR-21 may take part in the promotion of the osteogenic differentiation of PDLSCs [126]. Another study demonstrated that miR-21 is a mechano-sensitive gene that has an indispensable role in the osteogenic differentiation of PDLSCs [127]. Yan et al. proved that miR-22 enhanced PDLSC osteogenic differentiation by suppressing histone deacetylases (HDAC) expression [128]. HDAC regulates gene expression by removing negatively-charged acetyl groups from the positively-charged lysine on histone tails, tightening the interaction between histones and DNA and suppressing its access to transcription [129]. HDAC diminished the osteogenic differentiation potential of the PDLSCs under inflammatory conditions. In conclusion, HDAC inhibitors increased the osteogenesis of PDLSCs in vitro and in vivo [32]. On the other hand, some microRNAs showed adverse effects on periodontal tissue regeneration. For instance, miR‐146a exacerbates periodontitis by downregulating IL-17 and IL-35 expressions and proliferates PDLSCs [130]. Besides, miR-132 could hinder PDLSC osteogenesis [131].

PDLSCs constitutively express the chemokine stromal cell-derived factor-1 (SDF-1) that plays a crucial role in promoting cellular viability [132], migration [133] and homing of stem cells through signaling with its cognate receptor, C-X-C chemokine receptor type 4 (CXCR4) [134]. According to Feng et al. [135], SDF-1 plays a role in the protection of PDLSCs against apoptosis caused by oxidative stress by activating extracellular signal-regulated kinase (ERK) signaling. Based on the results of this study, it is suggested that SDF-1 therapy is a promising approach to promote PDLSC survival, which may assist in dental tissue regeneration [135]. In another study, the parathyroid hormone was used in combination with SDF-1. This co-therapy enhanced proliferation, migration and osteogenic differentiation of PDLSCs. Furthermore, it seems that co-therapy has the potential to promote periodontal tissue regeneration since it facilitates the chemotaxis of PDLSCs to the damaged site [136]. Additionally, SDF-1/Exendin 4 co-therapy was reported to have some other positive effects on PDLSC, including increasing ALP activity, mineral deposition and osteogenesis-related gene expression [137]. In conclusion, SDF-1 may promote periodontal tissue regeneration by the means of directing PDLSCs to injured periodontal tissue. SDF-1 enhances the activation and proliferation of PDLSCs and also induces the differentiation of these cells.

Semaphorin 3A (Sema 3A), one of the members of the semaphoring family secreted protein, has essential roles in developing different tissues, such as blood vessels, peripheral nerves, and skeletal tissues [138]. Additionally, Sema 3A functions as an osteoprotective factor by increasing bone production and preventing bone resorption [139]. It plays a vital role in maintaining the stem cell characteristics of PDLSCs. The expression level of Sema 3A was higher in multipotent human PDL cell lines compared to low-differentiation potential lines, and Sema 3A-overexpressing low-differentiation potential PDL clones promoted MSC-related marker expression and improved capacity to differentiate into osteoblasts and adipocytes [140].

Hypoxia has several effects on PDLSCs mineralization, osteogenic potency, and paracrine secretion. In hypoxic conditions, an increase in ALP activity and Runt-related protein 2 (RUNX2), Sp7, osteocalcin and osteopontin (OPN) expression was observed in PDLSCs [141, 142]. Moreover, hypoxia could regulate the expression of RUNX2 in PDLSCs via hypoxia-inducible factor-1α (HIF-1α) and play an effective role in the primary stage of osteogenesis of PDLSCs [143]. Zhang et al. observed an increased 2% O2 PDLSC cell count and osteogenic potential [144]. Hypoxia had a stimulatory effect on PDLSC proliferation, osteogenic differentiation, and migration [145].

Nitric oxide (NO) is a small, diffusible, diatomic, reactive element with various cellular functions in human cells [146]. NO plays a key role in the proliferation and differentiation of stem cells. It has been proved that NO is a negative modulator of stem cell proliferation in physiological concentrations and initiates cell differentiation [147]. Orciani et al. demonstrated that the upregulation in NO production was related to increased alkaline phosphatase activity. This study showed that NO had a key role in the osteogenesis of stem cells, especially PDLSCs [148].

Some researchers developed a new effective mineralization-inducing medium by adding KH2PO4 to the solution [149]. Cell Counting Kit-8 (CCK-8) assay suggested that 1.8 mmol/L KH2PO4 can increase the PDLSCs proliferation in the logarithmic phase of growth [150].

Some studies showed that tuning the settings of light-emitting diode (LED) irradiation, such as wavelength and dose, can significantly impact the proliferation rate and undifferentiated cells’ osteogenic differentiation. The advantages of irradiation could be used to regenerate PDL utilizing LED as a light source of antimicrobial photodynamic therapy (aPDT) [151, 152]. High-power, red LED irradiation increases the proliferation and eventually improves the osteogenic differentiation, mineralization, and ATP levels of PDLSCs [153]. A study by Chaweewannakorn et al. demonstrated that the PDLSCs responded to different LED wavelengths in various ways. 830-nm irradiation demonstrated better results in improving proliferation. Moreover, 630 and 680 nm wavelengths stimulated osteoblastic differentiation [154]. In another study, the results revealed that red LED enhanced osteogenic differentiation of the PDLSCs. The real-time polymerase chain reaction (RT-PCR) results showed upregulation of the expression of osteogenic genes, such as Bone sialoprotein (BSP), OPN, Osteonectin (OCN), and RUNX2, by the red LED. Moreover, red LED at 1, 3, and 5 J/cm2 stimulates proliferation and osteogenic differentiation of PDLSCs [155].

Improving the osteogenic potentiality of PDLSCs and modulating the expression outline of growth factor-linked genes are important stages in tissue engineering processes based on PDLSCs. For example, using continual cell sheets by preserving cellular junctions, endogenous ECM, and imitating cellular microenvironments with regard to different mechanical, chemical, and biological features may be advantageous for cell transplantation.

CONCLUSION AND FUTURE OUTLOOKS

Numerous factors need to be considered for the regeneration of periodontium. So far, there is no clinical evidence for the application of PDLSCs for immunomodulatory periodontology/medicine. Evidence indicates that the periodontal ligament is a replete resource of MSCs. Despite the apparent high regenerating potentiality of this tissue, harnessing and utilizing this capability are not easy for clinical applications. Up to now, oral and dental-tissue-derived stem/progenitor cells have been utilized to study tissue engineering in small and large animal models to evaluate their capability in preclinical utilization. This study provides an overview of the most up-to-date investigations on the characteristics and immunomodulatory features of PDLSCs and the recent interventions performed using these cells, focusing on cell survival, proliferation, and differentiation. Keeping in mind the relationship between age and potency of PDLSCs, this work also demonstrates the necessity of establishing dental-derived stem cell banks for tissue regeneration applications. For regeneration of periodontium, better understanding of the modes of self-restoration action is necessary for sufficient regulation of adult stem cell growth in vitro to produce cells necessary for various applied purposes and regulate stem cells for differentiating and maturating tissue-specific cell types, as well as wound remedy. In addition, the interplay between stem cells and the immune system is necessary, particularly in allogeneic cell populations.

AUTHORS’ CONTRIBUTION

All authors contributed to the drafting and scientific revision of the manuscript. All authors read and approved the final manuscript.

LIST OF ABBREVIATIONS

PDL = Periodontal Ligament
TE = Tissue Engineering
MSCs = Mesenchymal Stem Cells
ADSCs = Adipose Tissue-Derived Stem Cells
PDLSCs = Periodontal Ligament Stem Cells
SHED = Stem Cells from Human Exfoliated Deciduous Teeth
DPSCs = Dental Pulp Stem Cells
DFPCs = Dental Follicle Precursor Cells
ECM = Extracellular Matrix
FGF = Fibroblast growth factor-2
VEGF = Vascular Endothelial Growth Factor
IGF = Insulin-Like Growth Factor I
SCAP = Stem Cells from the Apical Papilla
T1D = Type 1 Diabetes
ASA = Acetyl Salicylic Acid
miRNAs = MicroRNAs
HDAC = Histone Deacetylases
CXCR4 = C-X-C Chemokine Receptor Type 4
NO = Nitric Oxide

CONSENT FOR PUBLICATION

Not applicable.

FUNDING

The vice chancellor for research at the Tabriz University of Medical Sciences provided financial support for this research that is greatly acknowledged.

CONFLICT OF INTEREST

Dr. Solmaz Maleki Dizajand and Dr. Simin Sharifi are editorial advisory board members of The Open Dentistry Journal.

ACKNOWLEDGEMENTS

Declared none.

REFERENCES

1
Xiong J, Menicanin D, Zilm PS, Marino V, Bartold PM, Gronthos S. Investigation of the cell surface proteome of human periodontal ligament stem cells. Stem Cells Int 2016; 2016(1): 1947157.
2
Tomokiyo A, Wada N, Maeda H. Periodontal ligament stem cells: Regenerative potency in periodontium. Stem Cells Dev 2019; 28(15): 974-85.
3
Di Vito A, Giudice A, Chiarella E, Malara N, Bennardo F, Fortunato L. In vitro long-term expansion and high osteogenic potential of periodontal ligament stem cells: More than a mirage. Cell Transplant 2019; 28(1): 129-39.
4
Tomokiyo A, Wada N, Hamano S, et al. Periodontal ligament stem cells in regenerative dentistry for periodontal tissues. J Stem Cell Res Ther 2016; 1(3): 17-9.
5
Nagata M, Iwasaki K, Akazawa K, et al. Conditioned medium from periodontal ligament stem cells enhances periodontal regeneration. Tissue Eng Part A 2017; 23(9-10): 367-77.
6
Yang S, Guo L, Su Y, et al. Nitric oxide balances osteoblast and adipocyte lineage differentiation via the JNK/MAPK signaling pathway in periodontal ligament stem cells. Stem Cell Res Ther 2018; 9(1): 118-25.
7
Abolfazli N, Jabali S, Saleh SF, Babaloo Z, Shirmohammadi A. Effect of non-surgical periodontal therapy on serum and salivary concentrations of visfatin in patients with chronic periodontitis. J Dent Res Dent Clin Dent Prospect 2015; 9(1): 11-7.
8
Onizuka S, Iwata T. Application of periodontal ligament-derived multipotent mesenchymal stromal cell sheets for periodontal regeneration. Int J Mol Sci 2019; 20(11): 2796-80.
9
Chen FM, Zhang J, Zhang M, An Y, Chen F, Wu ZF. A review on endogenous regenerative technology in periodontal regenerative medicine. Biomaterials 2010; 31(31): 7892-927.
10
Bosshardt DD, Sculean A. Does periodontal tissue regeneration really work? Periodontol 2000 2009; 51(1): 208-19.
11
Hynes K, Menicanin D, Gronthos S, Bartold PM. Clinical utility of stem cells for periodontal regeneration. Periodontol 2000 2012; 59(1): 203-27.
12
Langer RS, Vacanti JP. Tissue engineering: The challenges ahead. Sci Am 1999; 280(4): 86-9.
13
Kim BC, Bae H, Kwon IK, et al. Osteoblastic/cementoblastic and neural differentiation of dental stem cells and their applications to tissue engineering and regenerative medicine. Tissue Eng Part B Rev 2012; 18(3): 235-44.
14
Redman S, Oldfield S, Archer C. Current strategies for articular cartilage repair. Eur Cell Mater 2005; 9: 23-32.
15
Bahrami N, Manafi Z, Mohajeri F, Mohamadnia A. Neural differentiation potential of stem cells derived from dental follicle and periodontal ligament stem cells. J App Tissue Eng 2017; 4(1): 1-10.
16
Esmaeilzadeh A, Reyhani E, Bahmaie N. Immunobiology of dental tissue-derived stem cells; As a potentiated candidate for cell therapy. Gene Cell Ther 2016; 3(10): 28-9.
17
Moshaverinia A, Xu X, Chen C, et al. Application of stem cells derived from the periodontal ligament or gingival tissue sources for tendon tissue regeneration. Biomaterials 2014; 35(9): 2642-50.
18
Wang L, Shen H, Zheng W, et al. Characterization of stem cells from alveolar periodontal ligament. Tissue Eng Part A 2011; 17(7-8): 1015-26.
19
Singhatanadgit W, Donos N, Olsen I. Isolation and characterization of stem cell clones from adult human ligament. Tissue Eng Part A 2009; 15(9): 2625-36.
20
Diomede F, Zini N, Gatta V, et al. Human periodontal ligament stem cells cultured onto cortico-cancellous scaffold drive bone regenerative process. Eur Cell Mater 2016; 32: 181-201.
21
Gay IC, Chen S, MacDougall M. Isolation and characterization of multipotent human periodontal ligament stem cells. Rthod Craniofac Res 2007; 10(3): 149-60.
22
Seo BM, Miura M, Gronthos S, et al. Investigation of multipotent postnatal stem cells from human periodontal ligament. Lancet 2004; 364(9429): 149-55.
23
Wada N, Menicanin D, Shi S, Bartold PM, Gronthos S. Immunomodulatory properties of human periodontal ligament stem cells. J Cell Physiol 2009; 219(3): 667-76.
24
Menicanin D, Mrozik KM, Wada N, et al. Periodontal-ligament-derived stem cells exhibit the capacity for long-term survival, self-renewal, and regeneration of multiple tissue types in vivo. Stem Cells Dev 2014; 23(9): 1001-11.
25
Zheng W, Wang S, Ma D, Tang L, Duan Y, Jin Y. Loss of proliferation and differentiation capacity of aged human periodontal ligament stem cells and rejuvenation by exposure to the young extrinsic environment. Tissue Eng Part A 2009; 15(9): 2363-71.
26
Liu W, Konermann A, Guo T, Jäger A, Zhang L, Jin Y. Canonical Wnt signaling differently modulates osteogenic differentiation of mesenchymal stem cells derived from bone marrow and from periodontal ligament under inflammatory conditions. Biochim Biophys Acta 2014; 1840(3): 1125-34.
27
Feng F, Akiyama K, Liu Y, et al. Utility of PDL progenitors for in vivo tissue regeneration: A report of 3 cases. Oral Dis 2010; 16(1): 20-8.
28
Zhu W, Tan Y, Qiu Q, et al. Comparison of the properties of human CD146+ and CD146− periodontal ligament cells in response to stimulation with tumour necrosis factor α. Arch Oral Biol 2013; 58(12): 1791-803.
29
Abd Rahman F, Mohd Ali J, Abdullah M, Abu KNH, Musa S. Aspirin enhances osteogenic potential of Periodontal Ligament Stem Cells (PDLSCs) and modulates the expression profile of growth factor–associated genes in PDLSCs. J Periodontol 2016; 87(7): 837-47.
30
Kim JH, Ko SY, Lee JH, Kim DH, Yun JH. Evaluation of the periodontal regenerative properties of patterned human periodontal ligament stem cell sheets. J Periodontal Implant Sci 2017; 47(6): 402-15.
31
Tomokiyo A, Wada N, Maeda H. Contribution of stem cells to dental tissue regeneration: Isolation, function, and application. Front Stem Cell Reg Med Res 2016; 2: 3-38.
32
Li L, Liu W, Wang H, et al. Mutual inhibition between HDAC9 and miR-17 regulates osteogenesis of human periodontal ligament stem cells in inflammatory conditions. Cell Death Dis 2018; 9(5): 480.
33
Maeda H, Tomokiyo A, Fujii S, Wada N, Akamine A. Promise of periodontal ligament stem cells in regeneration of periodontium. Stem Cell Res Ther 2011; 2(4): 33-40.
34
Jia L, Xiong Y, Zhang W, Ma X, Xu X. Metformin promotes osteogenic differentiation and protects against oxidative stress-induced damage in periodontal ligament stem cells via activation of the Akt/Nrf2 signaling pathway. Exp Cell Res 2020; 386(2): 111717.
35
Xu Q, Li B, Yuan L, et al. Combination of platelet-rich plasma within periodontal ligament stem cell sheets enhances cell differentiation and matrix production. J Tissue Eng Regen Med 2017; 11(3): 627-36.
36
Wang Y, Papagerakis S, Faulk D, et al. Extracellular matrix membrane induces cementoblastic/osteogenic properties of human periodontal ligament stem cells. Front Physiol 2018; 9: 942-50.
37
Tang HN, Xia Y, Xu J, Tian BM, Zhang XY, Chen FM. Assessment of cellular materials generated by co-cultured ‘inflamed’ and healthy periodontal ligament stem cells from patient-matched groups. Exp Cell Res 2016; 346(1): 119-29.
38
Deng C, Sun Y, Liu H, Wang W, Wang J, Zhang F. Selective adipogenic differentiation of human periodontal ligament stem cells stimulated with high doses of glucose. PLoS One 2018; 13(7): e0199603.
39
Song JS, Kim SO, Kim SH, et al. In vitro and in vivo characteristics of stem cells derived from the periodontal ligament of human deciduous and permanent teeth. Tissue Eng Part A 2012; 18(19-20): 2040-51.
40
Wu RX, Bi CS, Yu Y, Zhang LL, Chen FM. Age-related decline in the matrix contents and functional properties of human periodontal ligament stem cell sheets. Acta Biomater 2015; 22: 70-82.
41
Mrozik K, Gronthos S, Shi S, Bartold PM. A method to isolate, purify, and characterize human periodontal ligament stem cells. Oral Biology 2017; 413-27.
42
Wang ZS, Feng ZH, Wu GF, et al. The use of platelet-rich fibrin combined with periodontal ligament and jaw bone mesenchymal stem cell sheets for periodontal tissue engineering. Sci Rep 2016; 6(1): 28126.
43
Duffy MM, Ritter T, Ceredig R, Griffin MD. Mesenchymal stem cell effects on T-cell effector pathways. Stem Cell Res Ther 2011; 2(4): 34.
44
Aggarwal S, Pittenger MF. Human mesenchymal stem cells modulate allogeneic immune cell responses. Blood 2005; 105(4): 1815-22.
45
Wada N, Tomokiyo A, Gronthos S, Bartold PM. Immunomodulatory properties of PDLSC and relevance to periodontal regeneration. Curr Oral Health Rep 2015; 2(4): 245-51.
46
Gao F, Chiu SM, Motan D A L, et al. Mesenchymal stem cells and immunomodulation: Current status and future prospects. Cell Death Dis 2016; 7(1): e2062-70.
47
Zhu J, Xiao Y, Li Z, et al. Efficacy of surgery combined with autologous bone marrow stromal cell transplantation for treatment of intracerebral hemorrhage. Stem Cells Int 2015; 2015: 318269.
48
Ding G, Liu Y, Wang W, et al. Allogeneic periodontal ligament stem cell therapy for periodontitis in swine. Stem Cells 2010; 28(10): 1829-38.
49
Liu D, Xu J, Liu O, et al. Mesenchymal stem cells derived from inflamed periodontal ligaments exhibit impaired immunomodulation. J Clin Periodontol 2012; 39(12): 1174-82.
50
Liu O, Xu J, Ding G, et al. Periodontal ligament stem cells regulate B lymphocyte function via programmed cell death protein 1. Stem Cells 2013; 31(7): 1371-82.
51
Wang Q, Ding G, Xu X. Periodontal ligament stem cells regulate apoptosis of neutrophils. Open Med 2017; 12(1): 19-23.
52
Ashour L, Al Habashneh RA, Al-Mrahelh MM, et al. The modulation of mature dendritic cells from patients with type 1 diabetes using human periodontal ligament stem cells. An in-vitro study. J Diabetes Metab Disord 2020; 19(2): 1037-44.
53
Liu J, Chen B, Bao J, Zhang Y, Lei L, Yan F. Macrophage polarization in periodontal ligament stem cells enhanced periodontal regeneration. Stem Cell Res Ther 2019; 10(1): 320.
54
Baseri M, Radmand F, Hamedi R, Yousefi M, Kafil HS. Immunological aspects of dental implant rejection. BioMed Res Int 2020; 2020: 7279509.
55
Iwata T, Yamato M, Zhang Z, et al. Validation of human periodontal ligament-derived cells as a reliable source for cytotherapeutic use. J Clin Periodontol 2010; 37(12): 1088-99.
56
Chadipiralla K, Yochim JM, Bahuleyan B, et al. Osteogenic differentiation of stem cells derived from human periodontal ligaments and pulp of human exfoliated deciduous teeth. Cell Tissue Res 2010; 340(2): 323-33.
57
Jo YY, Lee HJ, Kook SY, et al. Isolation and characterization of postnatal stem cells from human dental tissues. Tissue Eng 2007; 13(4): 767-73.
58
Choi S, Cho TJ, Kwon SK, Lee G, Cho J. Chondrogenesis of periodontal ligament stem cells by transforming growth factor-β3 and bone morphogenetic protein-6 in a normal healthy impacted third molar. Int J Oral Sci 2013; 5(1): 7-13.
59
Widera D, Grimm WD, Moebius JM, et al. Highly efficient neural differentiation of human somatic stem cells, isolated by minimally invasive periodontal surgery. Stem Cells Dev 2007; 16(3): 447-60.
60
Cen LP, Ng TK, Liang JJ, et al. Human periodontal ligament‐derived stem cells promote retinal ganglion cell survival and axon regeneration after optic nerve injury. Stem Cells 2018; 36(6): 844-55.
61
Li X, Liao D, Sun G, Chu H. Odontogenesis and neuronal differentiation characteristics of periodontal ligament stem cells from beagle dog. J Cell Mol Med 2020; 24(9): 5146-51.
62
Pelaez D, Acosta TZ, Ng TK, Choy KW, Pang CP, Cheung HS. Cardiomyogenesis of periodontal ligament-derived stem cells by dynamic tensile strain. Cell Tissue Res 2017; 367(2): 229-41.
63
Carnes DL, Maeder CL, Graves DT. Cells with osteoblastic phenotypes can be explanted from human gingiva and periodontal ligament. J Periodontol 1997; 68(7): 701-7.
64
Tomokiyo A, Maeda H, Fujii S, Wada N, Shima K, Akamine A. Development of a multipotent clonal human periodontal ligament cell line. Differentiation 2008; 76(4): 337-47.
65
Teramatsu Y, Maeda H, Sugii H, et al. Expression and effects of epidermal growth factor on human periodontal ligament cells. Cell Tissue Res 2014; 357(3): 633-43.
66
Encinas JM, Michurina TV, Peunova N, et al. Division-coupled astrocytic differentiation and age-related depletion of neural stem cells in the adult hippocampus. Cell Stem Cell 2011; 8(5): 566-79.
67
Dodson SA, Bernard GW, Kenney EB, Carranza FA. In vitro comparison of aged and young osteogenic and hemopoietic bone marrow stem cells and their derivative colonies. J Periodontol 1996; 67(3): 184-96.
68
Zhang J, An Y, Gao LN, Zhang YJ, Jin Y, Chen FM. The effect of aging on the pluripotential capacity and regenerative potential of human periodontal ligament stem cells. Biomaterials 2012; 33(29): 6974-86.
69
Du TT, Liu N, Zhang W, Shi HG, Zhang T. [Effect of aging on proliferative and differentiation capacity of human periodontal ligament stem cells]. Nan Fang Yi Ke Da Xue Xue Bao 2017; 37(3): 360-6.
70
Li X, Zhang B, Wang H, et al. The effect of aging on the biological and immunological characteristics of periodontal ligament stem cells. Stem Cell Res Ther 2020; 11(1): 326.
71
Langer R, Vacanti JP. Tissue engineering. Science 1993; 260(5110): 920-6.
72
Chang B, Ahuja N, Ma C, Liu X. Injectable scaffolds: Preparation and application in dental and craniofacial regeneration. Mater Sci Eng Rep 2017; 111: 1-26.
73
Nava MM, Fedele R, Raimondi MT. Computational prediction of strain-dependent diffusion of transcription factors through the cell nucleus. Biomech Model Mechanobiol 2016; 15(4): 983-93.
74
Donnaloja F, Jacchetti E, Soncini M, Raimondi MT. Natural and synthetic polymers for bone scaffolds optimization. Polymers (Basel) 2020; 12(4): 905-15.
75
Khezri K, Maleki Dizaj S, Rahbar Saadat Y, et al. Osteogenic differentiation of mesenchymal stem cells via curcumin-containing nanoscaffolds. Stem Cells Int 2021; 2021: 1-9.
76
Song IS, Han YS, Lee JH, Um S, Kim HY, Seo BM. Periodontal ligament stem cells for periodontal regeneration. Curr Oral Health Rep 2015; 2(4): 236-44.
77
Sebti I, Chollet E, Degraeve P, Noel C, Peyrol E. Water sensitivity, antimicrobial, and physicochemical analyses of edible films based on HPMC and/or chitosan. J Agric Food Chem 2007; 55(3): 693-9.
78
Ge S, Zhao N, Wang L, et al. Bone repair by periodontal ligament stem cell-seeded nanohydroxyapatite-chitosan scaffold. Int J Nanomed 2012; 7: 5405-14.
79
Poncelet D, Lencki R, Beaulieu C, Halle JP, Neufeld RJ, Fournier A. Production of alginate beads by emulsification/internal gelation. I. Methodology. Appl Microbiol Biotechnol 1992; 38(1): 39-45.
80
Little C, Kulyk W, Chen X. The effect of chondroitin sulphate and hyaluronic acid on chondrocytes cultured within a fibrin-alginate hydrogel. J Funct Biomater 2014; 5(3): 197-210.
81
Moshaverinia A, Xu X, Chen C, Akiyama K, Snead ML, Shi S. Dental mesenchymal stem cells encapsulated in an alginate hydrogel co-delivery microencapsulation system for cartilage regeneration. Acta Biomater 2013; 9(12): 9343-50.
82
Moshaverinia A, Chen C, Xu X, et al. Bone regeneration potential of stem cells derived from periodontal ligament or gingival tissue sources encapsulated in RGD-modified alginate scaffold. Tissue Eng Part A 2014; 20(3-4): 611-21.
83
Nagy K, Láng O, Láng J, et al. A novel hydrogel scaffold for periodontal ligament stem cells. Interv Med Appl Sci 2018; 10(3): 162-70.
84
Kämmerer PW, Scholz M, Baudisch M, et al. Guided bone regeneration using collagen scaffolds, growth factors, and periodontal ligament stem cells for treatment of peri-implant bone defects in vivo. Stem Cells Int 2017; 2017: 3548435.
85
Currie LJ, Sharpe JR, Martin R. The use of fibrin glue in skin grafts and tissue-engineered skin replacements: A review. Plast Reconstr Surg 2001; 108(6): 1713-26.
86
Ghavimi MA, Bani SA, Jarolmasjed S, Memar MY, Maleki DS, Sharifi S. Nanofibrous asymmetric collagen/curcumin membrane containing aspirin-loaded PLGA nanoparticles for guided bone regeneration. Sci Rep 2020; 10(1): 18200.
87
Timpl R. Macromolecular organization of basement membranes. Curr Opin Cell Biol 1996; 8(5): 618-24.
88
Li F, Li W, Johnson SA, Ingram DA, Yoder MC, Badylak SF. Low-molecular-weight peptides derived from extracellular matrix as chemoattractants for primary endothelial cells. Endothelium 2004; 11(3-4): 199-206.
89
Díaz PS, Muiños LE, Hermida GT, et al. Human amniotic membrane as an alternative source of stem cells for regenerative medicine. Differentiation 2011; 81(3): 162-71.
90
Adachi K, Amemiya T, Nakamura T, et al. Human periodontal ligament cell sheets cultured on amniotic membrane substrate. Oral Dis 2014; 20(6): 582-90.
91
Iwasaki K, Komaki M, Yokoyama N, et al. Periodontal regeneration using periodontal ligament stem cell-transferred amnion. Tissue Eng Part A 2014; 20(3-4): 693-704.
92
Elahi A, Taib H, Berahim Z, et al. Amniotic membrane as a scaffold for periodontal tissue engineering. J Health Sci Med Res 2021; 39(2): 169-80.
93
Friedman CD, Costantino PD, Takagi S, Chow LC. BoneSource? hydroxyapatite cement: A novel biomaterial for craniofacial skeletal tissue engineering and reconstruction. J Biomed Mater Res 1998; 43(4): 428-32.
94
Xu HHK, Wang P, Wang L, et al. Calcium phosphate cements for bone engineering and their biological properties. Bone Res 2017; 5(1): 17056.
95
Diaz GL, Kontoyiannis PD, Melchiorri AJ, Mikos AG. Three-dimensional printing of tissue engineering scaffolds with horizontal pore and composition gradients. Tissue Eng Part C Methods 2019; 25(7): 411-20.
96
Shi H, Zong W, Xu X, Chen J. Improved biphasic calcium phosphate combined with periodontal ligament stem cells may serve as a promising method for periodontal regeneration. Am J Transl Res 2018; 10(12): 4030-41.
97
Ohki T, Yamato M, Ota M, et al. Prevention of esophageal stricture after endoscopic submucosal dissection using tissue-engineered cell sheets. Gastroenterology 2012; 143(3): 582-588.e2.
98
Nishida K, Yamato M, Hayashida Y, et al. Corneal reconstruction with tissue-engineered cell sheets composed of autologous oral mucosal epithelium. N Engl J Med 2004; 351(12): 1187-96.
99
Shimauchi H, Nemoto E, Ishihata H, Shimomura M. Possible functional scaffolds for periodontal regeneration. Jpn Dent Sci Rev 2013; 49(4): 118-30.
100
Carter SSD, Costa PF, Vaquette C, Ivanovski S, Hutmacher DW, Malda J. Additive biomanufacturing: An advanced approach for periodontal tissue regeneration. Ann Biomed Eng 2017; 45(1): 12-22.
101
Iwata T, Yamato M, Washio K, et al. Periodontal regeneration with autologous periodontal ligament-derived cell sheets – A safety and efficacy study in ten patients. Regen Ther 2018; 9: 38-44.
102
Anitua E, Sánchez M, Nurden AT, Nurden P, Orive G, Andía I. New insights into and novel applications for platelet-rich fibrin therapies. Trends Biotechnol 2006; 24(5): 227-34.
103
Ahmed TAE, Giulivi A, Griffith M, Hincke M. Fibrin glues in combination with mesenchymal stem cells to develop a tissue-engineered cartilage substitute. Tissue Eng Part A 2011; 17(3-4): 323-35.
104
Zhao YH, Zhang M, Liu NX, et al. The combined use of cell sheet fragments of periodontal ligament stem cells and platelet-rich fibrin granules for avulsed tooth reimplantation. Biomaterials 2013; 34(22): 5506-20.
105
Ahmadian E, Eftekhari A, Dizaj SM, et al. The effect of hyaluronic acid hydrogels on dental pulp stem cells behavior. Int J Biol Macromol 2019; 140: 245-54.
106
Woo HN, Cho YJ, Tarafder S, Lee CH. The recent advances in scaffolds for integrated periodontal regeneration. Bioact Mater 2021; 6(10): 3328-42.
107
Sharifi S, Zununi Vahed S, Ahmadian E, et al. Stem cell therapy: Curcumin does the trick. Phytother Res 2019; 33(11): 2927-37.
108
Negahdari R, Bohlouli S, Sharifi S, et al. Therapeutic benefits of rutin and its nanoformulations. Phytother Res 2021; 35(4): 1719-38.
109
Sharifi S, Moghaddam FA, Abedi A, et al. Phytochemicals impact on osteogenic differentiation of mesenchymal stem cells. Biofactors 2020; 46(6): 874-93.
110
Samiei M, Abedi A, Sharifi S, Maleki DS. Early osteogenic differentiation stimulation of dental pulp stem cells by calcitriol and curcumin. Stem Cells Int 2021; 2021: 9980137.
111
Raber I, McCarthy CP, Vaduganathan M, et al. The rise and fall of aspirin in the primary prevention of cardiovascular disease. Lancet 2019; 393(10186): 2155-67.
112
Wadia R, Chapple I. Periodontal care in general practice: 20 important FAQs - Part two. Br Dent J 2019; 227(10): 875-80.
113
Choi KM, Seo YK, Yoon HH, et al. Effect of ascorbic acid on bone marrow-derived mesenchymal stem cell proliferation and differentiation. J Biosci Bioeng 2008; 105(6): 586-94.
114
Yan Y, Zeng W, Song S, et al. Vitamin C induces periodontal ligament progenitor cell differentiation via activation of ERK pathway mediated by PELP1. Protein Cell 2013; 4(8): 620-7.
115
Marconi GD, Fonticoli L, Guarnieri S, et al. Ascorbic acid: A new player of epigenetic regulation in LPS-gingivalis treated human periodontal ligament stem cells. Oxid Med Cell Longev 2021; 2021: 6679708.
116
Wei F, Qu C, Song T, et al. Vitamin C treatment promotes mesenchymal stem cell sheet formation and tissue regeneration by elevating telomerase activity. J Cell Physiol 2012; 227(9): 3216-24.
117
Yang Y, Wang T, Zhang S, et al. Vitamin C alleviates the senescence of periodontal ligament stem cells through inhibition of Notch3 during long‐term culture. J Cell Physiol 2021; 236(2): 1237-51.
118
Foretz M, Guigas B, Bertrand L, Pollak M, Viollet B. Metformin: From mechanisms of action to therapies. Cell Metab 2014; 20(6): 953-66.
119
Koh SJ, Kim JM, Kim IK, Ko SH, Kim JS. Anti-inflammatory mechanism of metformin and its effects in intestinal inflammation and colitis-associated colon cancer. J Gastroenterol Hepatol 2014; 29(3): 502-10.
120
Lim WH, Liu B, Cheng D, Williams BO, Mah SJ, Helms JA. Wnt signaling regulates homeostasis of the periodontal ligament. J Periodontal Res 2014; 49(6): 751-9.
121
Jiang LL, Liu L. Effect of metformin on stem cells: Molecular mechanism and clinical prospect. World J Stem Cells 2020; 12(12): 1455-73.
122
Yang Z, Gao X, Zhou M, et al. Effect of metformin on human periodontal ligament stem cells cultured with polydopamine‐templated hydroxyapatite. Eur J Oral Sci 2019; 127(3): 210-21.
123
Zhang R, Liang Q, Kang W, Ge S. Metformin facilitates the proliferation, migration, and osteogenic differentiation of periodontal ligament stem cells in vitro. Cell Biol Int 2020; 44(1): 70-9.
124
Wang Y, Baskerville S, Shenoy A, Babiarz JE, Baehner L, Blelloch R. Embryonic stem cell–specific microRNAs regulate the G1-S transition and promote rapid proliferation. Nat Genet 2008; 40(12): 1478-83.
125
Kurowska SM, Alivernini S, Ballantine LE, et al. MicroRNA-155 as a proinflammatory regulator in clinical and experimental arthritis. Proc Natl Acad Sci USA 2011; 108(27): 11193-8.
126
Wei F, Yang S, Guo Q, et al. MicroRNA-21 regulates osteogenic differentiation of periodontal ligament stem cells by targeting Smad5. Sci Rep 2017; 7(1): 16608.
127
Wei F, Liu D, Feng C, et al. microRNA-21 mediates stretch-induced osteogenic differentiation in human periodontal ligament stem cells. Stem Cells Dev 2015; 24(3): 312-9.
128
Yan GQ, Wang X, Yang F, et al. MicroRNA‐22 promoted osteogenic differentiation of human periodontal ligament stem cells by targeting HDAC6. J Cell Biochem 2017; 118(7): 1653-8.
129
Haldar S, Dru C, Mishra R, et al. Histone deacetylase inhibitors mediate DNA damage repair in ameliorating hemorrhagic cystitis. Sci Rep 2016; 6(1): 39257.
130
Zhao S, Cheng Y, Kim JG. microRNA‐146a downregulates IL‐17 and IL‐35 and inhibits proliferation of human periodontal ligament stem cells. J Cell Biochem 2019; 120(8): 13861-6.
131
Xu Y, Ren C, Zhao X, Wang W, Zhang N. microRNA-132 inhibits osteogenic differentiation of periodontal ligament stem cells via GDF5 and the NF-κB signaling pathway. Pathol Res Pract 2019; 215(12): 152722.
132
Du L, Yang P, Ge S. Stromal cell-derived factor-1 significantly induces proliferation, migration, and collagen type I expression in a human periodontal ligament stem cell subpopulation. J Periodontol 2012; 83(3): 379-88.
133
Wang Y, Li J, Qiu Y, et al. Low‑intensity pulsed ultrasound promotes periodontal ligament stem cell migration through TWIST1‑mediated SDF‑1 expression. Int J Mol Med 2018; 42(1): 322-30.
134
Peled A, Petit I, Kollet O, et al. Dependence of human stem cell engraftment and repopulation of NOD/SCID mice on CXCR4. Science 1999; 283(5403): 845-8.
135
Feng Y, Fu X, Lou X, Fu B. Stromal cell-derived factor 1 protects human periodontal ligament stem cells against hydrogen peroxide-induced apoptosis. Mol Med Rep 2017; 16(4): 5001-6.
136
Du L, Feng R, Ge S. PTH/SDF-1α cotherapy promotes proliferation, migration and osteogenic differentiation of human periodontal ligament stem cells. Cell Prolif 2016; 49(5): 599-608.
137
Liang Q, Du L, Zhang R, Kang W, Ge S. Stromal cell‐derived factor‐1/Exendin‐4 cotherapy facilitates the proliferation, migration and osteogenic differentiation of human periodontal ligament stem cells in vitro and promotes periodontal bone regeneration in vivo. Cell Proliferation 2021; 54(3): e12997-3001.
138
Roskies AL. Dissecting semaphorin signaling. Neuron 1998; 21(5): 935-6.
139
Fukuda T, Takeda S, Xu R, et al. Sema3A regulates bone-mass accrual through sensory innervations. Nature 2013; 497(7450): 490-3.
140
Wada N, Maeda H, Hasegawa D, et al. Semaphorin 3A induces mesenchymal-stem-like properties in human periodontal ligament cells. Stem Cells Dev 2014; 23(18): 2225-36.
141
Wu Y, Cao H, Yang Y, et al. Effects of vascular endothelial cells on osteogenic differentiation of noncontact co-cultured periodontal ligament stem cells under hypoxia. J Periodontal Res 2013; 48(1): 52-65.
142
Wu Y, Yang Y, Yang P, et al. The osteogenic differentiation of PDLSCs is mediated through MEK/ERK and p38 MAPK signalling under hypoxia. Arch Oral Biol 2013; 58(10): 1357-68.
143
Xu Q, Liu Z, Guo L, et al. Hypoxia mediates runt-related transcription factor 2 expression via induction of vascular endothelial growth factor in periodontal ligament stem cells. Mol Cells 2019; 42(11): 763-72.
144
Zhang QB, Zhang ZQ, Fang SL, Liu YR, Jiang G, Li KF. Effects of hypoxia on proliferation and osteogenic differentiation of periodontal ligament stem cells: An in vitro and in vivo study. Genet Mol Res 2014; 13(4): 10204-14.
145
Zhao L, Wu Y, Tan L, et al. Coculture with endothelial cells enhances osteogenic differentiation of periodontal ligament stem cells via cyclooxygenase-2/prostaglandin E2/vascular endothelial growth factor signaling under hypoxia. J Periodontol 2013; 84(12): 1847-57.
146
MacMicking J, Xie Q, Nathan C. Nitric oxide and macrophage function. Annu Rev Immunol 1997; 15(1): 323-50.
147
Lee SK, Choi HI, Yang YS, et al. Nitric oxide modulates osteoblastic differentiation with heme oxygenase-1 via the mitogen activated protein kinase and nuclear factor-kappaB pathways in human periodontal ligament cells. Biol Pharm Bull 2009; 32(8): 1328-34.
148
Orciani M, Trubiani O, Vignini A, Mattioli BM, Di Primio R, Salvolini E. Nitric oxide production during the osteogenic differentiation of human periodontal ligament mesenchymal stem cells. Acta Histochem 2009; 111(1): 15-24.
149
Bakopoulou A, Leyhausen G, Volk J, et al. Comparative analysis of in vitro osteo/odontogenic differentiation potential of human Dental Pulp Stem Cells (DPSCs) and Stem Cells From The Apical Papilla (SCAP). Arch Oral Biol 2011; 56(7): 709-21.
150
Xu Y, Wang Y, Pang X, et al. Potassium dihydrogen phosphate promotes the proliferation and differentiation of human periodontal ligament stem cells via nuclear factor kappa B pathway. Exp Cell Res 2019; 384(1): 111593.
151
Holder MJ, Milward MR, Palin WM, Hadis MA, Cooper PR. Effects of red light-emitting diode irradiation on dental pulp cells. J Dent Res 2012; 91(10): 961-6.
152
Turrioni APS, Basso FG, Montoro LA, Almeida LFD, Costa CAS, Hebling J. Phototherapy up-regulates dentin matrix proteins expression and synthesis by stem cells from human-exfoliated deciduous teeth. J Dent 2014; 42(10): 1292-9.
153
Yamauchi N, Taguchi Y, Kato H, Umeda M. High-power, red-light-emitting diode irradiation enhances proliferation, osteogenic differentiation, and mineralization of human periodontal ligament stem cells via ERK signaling pathway. J Periodontol 2018; 89(3): 351-60.
154
Chaweewannakorn C, Santiwong P, Surarit R, Sritanaudomchai H, Chintavalakorn R. The effect of LED photobiomodulation on the proliferation and osteoblastic differentiation of periodontal ligament stem cells: In vitro. J World Fed Orthod 2021; 10(2): 79-85.
155
Wu Y, Zhu T, Yang Y, et al. Irradiation with red light-emitting diode enhances proliferation and osteogenic differentiation of periodontal ligament stem cells. Lasers Med Sci 2021; 36(7): 1535-43.