The difference on the osteogenic differentiation between periodontal ligament stem cells and bone marrow mesenchymal stem cells under inflammatory microenviroments

Developmental endothelial locus-1 promotes osteogenic differentiation and alveolar bone regeneration in experimental periodontitis with type 2 diabetes mellitus

OBJECTIVES

This study sought to explore the role of developmental endothelial locus-1 (DEL-1) in osteogenic differentiation of human periodontal ligament stem cells (hPDLSCs) and investigate the therapeutic effect of DEL-1 in ligature-induced experimental periodontitis with type 2 diabetes mellitus (T2DM).

BACKGROUND

T2DM is a significant risk factor for periodontitis. Treatment modalities for periodontitis with T2DM are being explored. DEL-1 is a versatile protein that can modulate the different stages of inflammatory diseases including periodontitis. The direct effect of DEL-1 on osteogenic differentiation of PDLSCs in periodontitis with T2DM is poorly understood.

METHODS

Primary hPDLSCs were isolated from periodontal ligament tissue and identified by flow cytometry. In osteogenesis experiments, alkaline phosphatase (ALP), Alizarin Red staining and western blot were used to assess the osteogenic effect of DEL-1 on hPDLSCs in high glucose and inflammation environments. The mouse model of ligature-induced experimental periodontitis was established. H&E and Masson's trichrome staining were used to assess the change of periodontal tissue after local periodontal injection of DEL-1. Immunohistochemical staining was used to evaluate osteogenic-related protein expression.

RESULTS

hPDLSCs expressed mesenchymal stem cell (MSC)-specific surface markers and were negative for hematopoietic cell surface markers. hPDLSCs had the potential for multidirectional differentiation. DEL-1 could enhance the osteogenic differentiation of hPDLSCs in high glucose and inflammation environments, although it did not return to the control level. Histological staining showed that DEL-1 contributed to alveolar bone regeneration and osteogenic-related protein expression, but the degree of improvement in T2DM mice was lower than in non-T2DM mice.

CONCLUSIONS

In summary, we demonstrated that DEL-1 could promote osteogenic differentiation of hPDLSCs in high glucose and inflammation environment and rescue alveolar bone loss in experimental periodontitis with T2DM, which could provide a novel therapeutic target for periodontitis with T2DM.

Low-energy LED red light inhibits the NF-κB pathway and promotes hPDLSCs proliferation and osteogenesis in a TNF-α environment in vitro

There are few studies on the effect of low-energy LED red light on periodontal tissue regeneration in an inflammatory environment. In this study, Cell Counting Kit-8 (CCK-8) assays were used to detect the effects of TNF-α at three different concentrations (0, 10 ng/ml, and 20 ng/ml) on the proliferation of human periodontal ligament stem cells (hPDLSCs), and 10 ng/ml was selected as the subsequent experimental stimulation concentration. CCK-8 assays were used to detect the effect of LED red light with energy density of 1 J/ cm2, 3 J/ cm2, and 5 J/cm2 on the proliferation of hPDLSCs. The promotion effect of energy density of 5 J/cm2 on the proliferation of hPDLSCS was the most obvious (p < 0.05). Set CON group, ODM group, ODM + 10 ng/ml TNF-α group, and ODM + 10 ng/ml TNF-α + 5 J/ cm2 LED red light group. Alkaline phosphatase staining and activity detection, alizarin red staining and calcium nodules quantitative detection of osteoblast differentiation products, real-time fluorescence quantitative PCR detection of osteoblast gene expression (Runx2, Col-I, OPN, OCN). The results showed that ODM showed the strongest osteoblast ability, followed by ODM + 10 ng/ml TNF-α + 5 J/ cm2 LED red light group. The osteoblast ability of ODM + 10 ng/ml TNF-α was decreased, but was not found in CON group. Western blot was used to detect the expression of NF-κB pathway protein and osteoblast-related proteins (Runx2, Col-I, OPN, OCN) after addition of PDTC inhibitor. The results showed that the expression of p-IκBα was increased and the expression of IκBα was decreased (p < 0.05). The expression of osteoblast protein increased after the addition of inhibitor (p < 0.05). Therefore, in an inflammatory environment constructed by 10 ng/ml TNF-α, 5 J/cm2 LED red light can upregulate the proliferation and osteogenesis of hPDLSCs by inhibiting NF-κB signaling pathway.

Graphene quantum dots enhance the osteogenic differentiation of PDLSCs in the inflammatory microenvironment

BACKGROUND AND OBJECTIVE

Graphene quantum dots (GQDs), a type of carbon-based nanomaterial, have remarkable biological, physical, and chemical properties. This study investigated the biological mechanisms of the proliferation and osteogenic differentiation of human periodontal ligament stem cells (PDLSCs) induced by GQDs in an inflammatory microenvironment.

MATERIALS AND METHODS

PDLSCs were cultured in osteogenic-induced medium with various concentrations of GQDs in standard medium or medium mimicking a proinflammatory environment. The effects of GQDs on the proliferation and osteogenic differentiation activity of PDLSCs were tested by CCK-8 assay, Alizarin Red S staining, and qRT‒PCR. In addition, Wnt/β-catenin signalling pathway-related gene expression was measured by qRT‒PCR.

RESULTS

Compared with the control group, the mRNA expression levels of ALP, RUNX2, and OCN and the number of mineralized nodules were all increased in PDLSCs after treatment with GQDs. Moreover, during the osteogenic differentiation of PDLSCs, the expression levels of LRP6 and β-catenin, which are Wnt/β-catenin signalling pathway-related genes, were upregulated.

CONCLUSION

In the inflammatory microenvironment, GQDs might promote the osteogenic differentiation ability of PDLSCs by activating the Wnt/β-catenin signalling pathway.

DNER and GNL2 are differentially m6A methylated in periodontitis in comparison with periodontal health revealed by m6A microarray of human gingival tissue and transcriptomic analysis

OBJECTIVE

This study aims to investigate the differences in the epigenomic patterns of N6-methyladenosine (m6A) methylation in gingival tissues between patients with periodontitis (PD) and healthy controls, identifying potential biomarkers.

BACKGROUND

As a multifactorial disease, PD involves multiple genetic and environmental effects. The m6A modification is the most prevalent internal mRNA modification and linked to various inflammatory diseases. However, the m6A modification pattern and m6A-related signatures in PD remain unclear.

MATERIALS AND METHODS

An m6A microarray of human gingival tissues was conducted in eight subjects: four diagnosed with PD and four healthy controls. Microarray analysis was performed to identify the differentially m6A methylated mRNAs (DMGs) and the differentially expressed mRNAs (DEGs). The differentially methylated and expressed mRNAs (DMEGs) were subjected to functional enrichment analysis by Metascape. The weighted gene co-expression network analysis (WGCNA) algorithm, the least absolute shrinkage and selection operator (LASSO) regression, and univariate logistic regression were performed to identify potential biomarkers. The cell type localization of the target genes was determined using single-cell RNA-seq (scRNA-seq) analysis. The m6A methylation level and gene expression of hub genes were subsequently verified by m6A methylated RNA immunoprecipitation (MeRIP) and quantitative real-time PCR (qRT-PCR).

RESULTS

In total, 458 DMGs, 750 DEGs, and 279 DMEGs were identified based on our microarray. Pathway analyses conducted for the DMEGs revealed that biological functions were mainly involved in the regulation of stem cell differentiation, ossification, circadian rhythm, and insulin secretion pathways. Besides, the genes involved in crucial biological processes were mainly expressed in fibroblast and epithelial cells. Furthermore, the m6A methylation and expression levels of two hub biomarkers (DNER and GNL2) were validated.

CONCLUSION

The current study exhibited a distinct m6A epitranscriptome, identified and verified two PD-related biomarkers (DNER and GNL2), which may provide novel insights into revealing the new molecular mechanisms and latent targets of PD.

Gold nanoparticles targeting the autophagy-lysosome system to combat the inflammation-compromised osteogenic potential of periodontal ligament stem cells: From mechanism to therapy

Although substantial data indicate that the osteogenic potential of periodontal ligament stem cells (PDLSCs) is compromised under inflammatory conditions, the underlying mechanism remains largely unexplored. In this study, we found that both the autophagy levels and autophagic flux levels were decreased in PDLSCs incubated under inflammatory conditions (I-PDLSCs). Based on the increased expression of LC3 II (at an autophagy level) and decreased accumulation of LC3 II (at an autophagic flux level) in I-PDLSCs, we speculated that the disruption of I-PDLSC autophagy arose from dysfunction of the cellular autophagy-lysosome system. Subsequently, our hypothesis was demonstrated by inhibited autophagosome-lysosome fusion, damaged lysosomal function, and suppressed activation of transcription factor EB (TFEB, a master regulator of the autophagy-lysosome system) in I-PDLSCs and verified by TFEB overexpression in I-PDLSCs. We found that gold nanoparticle (Au NP) treatment rescued the osteogenic potential of I-PDLSCs by restoring the inflammation-compromised autophagy-lysosome system. In this context, Au NP ceased to be effective when TFEB was knocked down in PDLSCs. Our data demonstrate the crucial role of the autophagy-lysosome system in cellular osteogenesis under inflammatory conditions and suggest a new target for rescuing inflammation-induced cell dysfunction using nanomaterials to aid cell biology and tissue regeneration.

High-Intensity Red Light-Emitting Diode Irradiation Suppresses the Inflammatory Response of Human Periodontal Ligament Stem Cells by Promoting Intracellular ATP Synthesis

Periodontitis is an inflammatory lesion in the periodontal tissue. The behavior of human periodontal ligament stem cells (hPDLSCs), which play an important role in periodontal tissue regeneration, is restricted by the influence of inflammatory mediators. Photobiomodulation therapy exerts anti-inflammatory effects. The purpose of this study was to investigate the effects of light-emitting diode (LED) irradiation on the inflammatory responses of hPDLSCs. The light source was a red LED (peak wavelength: 650 nm), and the total absolute irradiance was 400 mW/cm². The inflammatory response in hPDLSCs is induced by tumor necrosis factor (TNF)-α. Adenosine triphosphate (ATP) levels and pro-inflammatory cytokine (interleukin [IL]-6 and IL-8) production were measured 24 h after LED irradiation, and the effects of potassium cyanide (KCN) were investigated. LED irradiation at 6 J/cm² significantly increased the ATP levels and reduced TNF-α-induced IL-6 and IL-8 production. Furthermore, the inhibitory effect of LED irradiation on the production of pro-inflammatory cytokines was inhibited by KCN treatment. The results of this study showed that high-intensity red LED irradiation suppressed the TNF-α-stimulated pro-inflammatory cytokine production in hPDLSCs by promoting ATP synthesis. These results suggest that high-intensity red LED is a useful tool for periodontal tissue regeneration in chronically inflamed tissues.

Regulation of osteogenic differentiation by the pro-inflammatory cytokines IL-1β and TNF-α: current conclusions and controversies

Treatment of complex bone fracture diseases is still a complicated problem that is urged to be solved in orthopedics. In bone tissue engineering, the use of mesenchymal stromal/stem cells (MSCs) for tissue repair brings hope to the medical field of bone diseases. MSCs can differentiate into osteoblasts and promote bone regeneration. An increasing number of studies show that the inflammatory microenvironment affects the osteogenic differentiation of MSCs. It is shown that TNF-α and IL-1β play different roles in the osteogenic differentiation of MSCs via different signal pathways. The main factors that affect the role of TNF-α and IL-1β in osteogenic differentiation of MSCs include concentration and the source of stem cells (different species and different tissues). This review in-depth analyzes the roles of pro-inflammatory cytokines in the osteogenic differentiation of MSCs and reveals some current controversies to provide a reference of comprehensively understanding.

High glucose inhibits the osteogenic differentiation of periodontal ligament stem cells in periodontitis by activating endoplasmic reticulum stress

Background

Periodontitis is a highly prevalent dental disease which is associated with diabetes and is challenging to cure in diabetic patients. However, the mechanism of comorbid diabetes and periodontitis is still unclear. This study aimed to uncover the role of endoplasmic reticulum (ER) stress in high glucose-associated periodontitis.

Methods

Periodontal tissues were obtained from diabetic patients with periodontitis, periodontitis patients without systemic disease, and healthy teeth. The expressions of ER stress-related factors GRP78, ATF6, PERK and XBP1 were detected by quantitative real-time polymerase chain reaction (qRT-PCR) and immumohistochemical staining. Periodontal ligament stem cells (PDLSCs) from three states of periodontal tissues were isolated and cultured as diabetic PDLSCs (dPDLSCs), inflamed PDLSCs (iPDLSCs) and healthy PDLSCs (hPDLSCs), and the cell stemness was assayed. Different concentrations (8, 11, and 25 mmol/L) of D-glucose were used on hPDLSCs to simulate high glucose microenvironment. The changes of osteogenic ability of PDLSCs were observed, and the expressions of ER stress-related factors in different time point (6, 12, 24, and 72 h) were detected. Finally, GRP78 shRNA lentivirus was used to block ER stress on PDLSCs in the 25 mmol/L D-glucose microenvironment, and the osteogenic ability of PDLSCs was observed.

Results

The results showed that the expressions of GRP78, ATF6, PERK, and XBP1 were highest in the diabetic periodontitis group and lowest in the healthy periodontal tissue group (P<0.05). The clone formation, osteogenic and lipogenic differentiation abilities were lowest in dPDLSCs and highest in hPDLSCs. With the increase of glucose concentration, the osteogensis ability of PDLSCs decreased. After 6 hours of stimulation with D-glucose 25 mmol/L, the ER stress pathways in PDLSCs were effectively activated, and the peak value was reached at 12 hours. The decrease in the osteogensis ability of PDLSCs in a high glucose microenvironment reversed when ER stress was blocked.

Conclusions

The osteogenic differentiation ability of PDLSCs cells is inhibited in a high glucose microenvironment, and this effect is realized by ER stress activation. Blocking ER stress can partially restore the reduced osteogenic ability of PDLSCs. These results suggest that high glucose inhibits the osteogenic differentiation ability of PDLSCs by activating ER stress, which ultimately exacerbates periodontitis.

The Effect of Diabetes Mellitus on IGF Axis and Stem Cell Mediated Regeneration of the Periodontium

Periodontitis and diabetes mellitus (DM) are two of the most common and challenging health problems worldwide and they affect each other mutually and adversely. Current periodontal therapies have unpredictable outcome in diabetic patients. Periodontal tissue engineering is a challenging but promising approach that aims at restoring periodontal tissues using one or all of the following: stem cells, signalling molecules and scaffolds. Mesenchymal stem cells (MSCs) and insulin-like growth factor (IGF) represent ideal examples of stem cells and signalling molecules. This review outlines the most recent updates in characterizing MSCs isolated from diabetics to fully understand why diabetics are more prone to periodontitis that theoretically reflect the impaired regenerative capabilities of their native stem cells. This characterisation is of utmost importance to enhance autologous stem cells based tissue regeneration in diabetic patients using both MSCs and members of IGF axis.

Although Anatomically Micrometers Apart: Human Periodontal Ligament Cells Are Slightly More Active in Bone Remodeling Than Alveolar Bone Derived Cells

The periodontal ligament (PDL) and the alveolar bone are part of the periodontium, a complex structure that supports the teeth. The alveolar bone is continuously remodeled and is greatly affected by several complex oral events, like tooth extraction, orthodontic movement, and periodontitis. Until now, the role of PDL cells in terms of osteogenesis and osteoclastogenesis has been widely studied, whereas surprisingly little is known about the bone remodeling capacity of alveolar bone. Therefore, the purpose of this study was to compare the biological character of human alveolar bone cells and PDL cells in terms of osteogenesis and osteoclastogenesis in vitro. Paired samples of PDL cells and alveolar bone cells from seven patients with compromised general and oral health were collected and cultured. Bone A (early outgrowth) and bone B (late outgrowth) were included. PDL, bone A, bone B cell cultures all had a fibroblast appearance with similar expression pattern of six mesenchymal markers. These cultures were subjected to osteogenesis and osteoclastogenesis assays. For osteoclastogenesis assays, the cells were co-cultured with peripheral blood mononuclear cells, a source for osteoclast precursor cells. The total duration of the experiments was 21 days. Osteogenesis was slightly favored for PDL compared to bone A and B as shown by stronger Alizarin red staining and higher expression of RUNX2 and Collagen I at day 7 and for ALP at day 21. PDL induced approximately two times more osteoclasts than alveolar bone cells. In line with these findings was the higher expression of cell fusion marker DC-STAMP in PDL-PBMC co-cultures compared to bone B at day 21. In conclusion, alveolar bone contains remodeling activity, but to a different extent compared to PDL cells. We showed that human alveolar bone cells can be used as an in vitro model to study bone remodeling.

Chronic inflammation-induced senescence impairs immunomodulatory properties of synovial fluid mesenchymal stem cells in rheumatoid arthritis

Background

Although the immunomodulatory properties of mesenchymal stem cells (MSCs) have been highlighted as a new therapy for autoimmune diseases, including rheumatoid arthritis (RA), the disease-specific characteristics of MSCs derived from elderly RA patients are not well understood.

Methods

We established MSCs derived from synovial fluid (SF) from age-matched early (average duration of the disease: 1.7 years) and long-standing (average duration of the disease: 13.8 years) RA patients (E-/L-SF-MSCs) and then analyzed the MSC characteristics such as stemness, proliferation, cellular senescence, in vitro differentiation, and in vivo immunomodulatory properties.

Results

The presence of MSC populations in the SF from RA patients was identified. We found that L-SF-MSCs exhibited impaired proliferation, intensified cellular senescence, reduced immunomodulatory properties, and attenuated anti-arthritic capacity in an RA animal model. In particular, E-SF-MSCs demonstrated cellular senescence progression and attenuated immunomodulatory properties similar to those of L-SF-MSC in an RA joint-mimetic milieu due to hypoxia and pro-inflammatory cytokine exposure. Due to a long-term exposure to the chronic inflammatory milieu, cellular senescence, attenuated immunomodulatory properties, and the loss of anti-arthritic potentials were more often identified in SF-MSCs in a long-term RA than early RA.

Conclusion

We conclude that a chronic RA inflammatory milieu affects the MSC potential. Therefore, this work addresses the importance of understanding MSC characteristics during disease states prior to their application in patients.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02453-z.

Cytotoxic Effects on Gingival Mesenchymal Stromal Cells and Root Surface Modifications Induced by Some Local Antimicrobial Products Used in Periodontitis Treatment

(1) Background: this study aims to test the cytotoxicity of three antimicrobial products used in periodontitis treatment on gingival mesenchymal stem cells (gMSCs) and their influence on root surfaces and gMSC adhesion. We tested the null hypothesis that the effects of the antimicrobials did not differ. (2) Methods: the commercial products based on sulphonic/sulphuric acids, sodium hypochlorite and silver nanoparticles, in five different concentrations, were added to culture medium for growing gMSCs. Cell proliferation capacity was tested using the Cell Counting Kit-8 (CCK8) and their viability was determined by succinate dehydrogenase activity (MTT) assay. Scanning electron microscopy evaluated the adhesion of gMSCs on root samples treated mechanically and with commercial products. (3) Results: the products induced a dose-dependent cytotoxicity in terms of reduced proliferation and viability of gMSCs, as well as cell shape modifications. Significant differences in CCK8 values between the different commercial products were observed. Based on proliferation tests, the null hypothesis was rejected. When MTT values of the three products were compared with each other, no significant differences were observed for any of the five concentrations (p = 0.065, p = 0.067, p = 0.172, p = 0.256, p = 0.060). (4) Conclusions: the three antimicrobials had a certain degree of cytotoxicity on gMSCs. gMSCs repopulated treated root surfaces.

PWAR6 interacts with miR‑106a‑5p to regulate the osteogenic differentiation of human periodontal ligament stem cells

Human periodontal ligament stem cells (hPDLSCs) associated with bone regeneration serve an important role in the treatment of periodontal disease. Long non-coding RNAs are involved in the osteogenesis of multiple stem cells and can act as a sponge of microRNAs (miRs). The present study aimed to investigate the interaction between Prader Willi/Angelman region RNA 6 (PWAR6) and miR-106a-5p, as well as their influences on the osteogenic differentiation of hPDLSCs. hPDLSCs were isolated and cultured in osteogenic medium (OM) or growth medium (GM) for 7 days prior to transfection with PWAR6 overexpression vector, short hairpin RNA PWAR6 or miR-106a-5p mimic. The expression levels of runt-related transcription factor 2, osteocalcin and bone morphogenetic protein 2 (BMP2) were detected by western blotting and reverse transcription-quantitative PCR (RT-qPCR), and the expression levels of PWAR6, miR-106a-5p and alkaline phosphatase (ALP) were determined by RT-qPCR. ALP activity assays and Alizarin red staining were performed to detect osteogenesis and mineralization, respectively. Luciferase activities of wild-type and mutant PWAR6 and BMP2 were assessed by conducting a dual-luciferase reporter assay. The results indicated that PWAR6 expression was upregulated in OM-incubated hPDLSCs compared with GM-incubated hPDLSCs, and PWAR6 overexpression increased the osteogenic differentiation and mineralization of hPDLSCs compared with the corresponding control group. By contrast, miR-106a-5p expression was downregulated in OM-incubated hPDLSCs compared with GM-incubated hPDLSCs. PWAR6 acted as a sponge of miR-106a-5p and PWAR6 overexpression promoted the osteogenesis of miR-106a-5p mimic-transfected hPDLSCs. BMP2 was predicted as a target gene of miR-106a-5p. Collectively, the results indicated that PWAR6 displayed a positive influence on the osteogenic differentiation of hPDLSCs. The results of the present study demonstrated that the PWAR6/miR-106a-5p interaction network may serve as a potential regulatory mechanism underlying hPDLSCs osteogenesis.

Calcium-siRNA Nanocomplexes Optimized by Bovine Serum Albumin Coating Can Achieve Convenient and Efficient siRNA Delivery for Periodontitis Therapy

Purpose

Reducing toxicity, immunogenicity, and costs of small interfering RNAs (siRNA) carrier materials are key goals for RNA interference (RNAi) technology transition from bench to bed. Recently, calcium ions (Ca²⁺) have garnered attention as a novel, alternative material for delivering siRNA to cells. However, the tolerance for Ca²⁺ concentration varies in different cell types, which has limited its applications in vivo. Bovine serum albumin (BSA) can bind to Ca²⁺ through chelation. Moreover, BSA is a favorable coating material for nanoparticles owing to its excellent biocompatibility. Therefore, we hypothesized that coating Ca²⁺-siRNA with BSA helps buffer Ca²⁺ toxicity in vivo.

Methods

BSA-Ca²⁺-siRNA nanoparticles were prepared, and the size, shape, encapsulation, and release efficiency were characterized using atomic force microscopy, scanning electronic microcopy, and gel electrophoresis. Binding nanoparticles were evaluated using attenuated total reflection-Fourier-transform infrared spectroscopy. The cellular uptake, intracellular release, cytotoxicity, and gene knockdown of nanoparticles were evaluated in periodontal ligament stem cells (PDLSCs) using laser-scanning confocal microscope, flow cytometry, and real-time quantitative polymerase chain reaction.

Results

BSA and Ca²⁺-siRNA could form a stable nano-scale complex (~140 nm in diameter). The nanocomplexes could maintain siRNA release for more than 1 week in neutral phosphate-buffered saline (PBS) and could induce accelerated degradation in acidic PBS (pH 5.0). The nanoparticles were taken up by the cells, primarily through macropinocytosis, and were then released intracellularly through the acidification of endosomes/lysosomes. Importantly, the BSA-Ca²⁺ carrier had high transfection efficiency and biocompatibility both in vitro and in vivo. To demonstrate the therapeutic potential of our BSA coating-optimized Ca²⁺-siRNA technology, we showed that BSA-Ca²⁺-siWWP1 complexes strongly enhanced the osteogenic differentiation of inflammatory PDLSCs.

Conclusion

BSA-Ca²⁺ could potentially be used for siRNA delivery, which is not only highly efficient and cost-effective but also biocompatible to host tissues owing to the BSA coating.

Mesenchymal Stem/Progenitor Cells: The Prospect of Human Clinical Translation

Mesenchymal stem/progenitor cells (MSCs) are key players in regenerative medicine, relying principally on their differentiation/regeneration potential, immunomodulatory properties, paracrine effects, and potent homing ability with minimal if any ethical concerns. Even though multiple preclinical and clinical studies have demonstrated remarkable properties for MSCs, the clinical applicability of MSC-based therapies is still questionable. Several challenges exist that critically hinder a successful clinical translation of MSC-based therapies, including but not limited to heterogeneity of their populations, variability in their quality and quantity, donor-related factors, discrepancies in protocols for isolation, in vitro expansion and premodification, and variability in methods of cell delivery, dosing, and cell homing. Alterations of MSC viability, proliferation, properties, and/or function are also affected by various drugs and chemicals. Moreover, significant safety concerns exist due to possible teratogenic/neoplastic potential and transmission of infectious diseases. Through the current review, we aim to highlight the major challenges facing MSCs' human clinical translation and shed light on the undergoing strategies to overcome them.

Long non-coding RNA FER1L4 promotes osteogenic differentiation of human periodontal ligament stromal cells via miR-874-3p and vascular endothelial growth factor A

Background

Periodontal ligament stromal cells (PDLSCs) are ideal cell sources for periodontal tissue repair and regeneration, but little is known about what determines their osteogenic capacity. Long non-coding RNAs (lncRNAs) are important regulatory molecules at both transcriptional and post-transcriptional levels. However, their roles in the osteogenic differentiation of PDLSCs are still largely unknown.

Methods

The expression of lncRNA Fer-1-like family member 4 (FER1L4) during the osteogenic differentiation of PDLSCs was detected by quantitative reverse transcription polymerase chain reaction. Overexpression or knockdown of FER1L4 was used to confirm its regulation of osteogenesis in PDLSCs. Alkaline phosphatase and Alizarin red S staining were used to detect mineral deposition. Dual luciferase reporter assays were used to analyze the binding of miR-874-3p to FER1L4 and vascular endothelial growth factor A (VEGFA). Bone regeneration in critical-sized calvarial defects was assessed in nude mice. New bone formation was analyzed by micro-CT, hematoxylin and eosin staining, Masson’s trichrome staining, and immunohistochemical analyses.

Results

FER1L4 levels increased gradually during consecutive osteogenic induction of PDLSCs. Overexpression of FER1L4 promoted the osteogenic differentiation of PDLSCs, as revealed by alkaline phosphatase activity, Alizarin red S staining, and the expression of osteogenic markers, whereas FER1L4 knockdown inhibited these processes. Subsequently, we identified a predicted binding site for miR-874-3p on FER1L4 and confirmed a direct interaction between them. Wild-type FER1L4 reporter activity was significantly inhibited by miR-874-3p, whereas mutant FER1L4 reporter was not affected. MiR-874-3p inhibited osteogenic differentiation and reversed the promotion of osteogenesis in PDLSCs by FER1L4. Moreover, miR-874-3p targeted VEGFA, a crucial gene in osteogenic differentiation, whereas FER1L4 upregulated the expression of VEGFA. In vivo, overexpression of FER1L4 led to more bone formation compared to the control group, as demonstrated by micro-CT and the histologic analyses.

Conclusion

FER1L4 positively regulates the osteogenic differentiation of PDLSCs via miR-874-3p and VEGFA. Our study provides a promising target for enhancing the osteogenic potential of PDLSCs and periodontal regeneration.

A feed-forward regulatory network lncPCAT1/miR-106a-5p/E2F5 regulates the osteogenic differentiation of periodontal ligament stem cells

Periodontal ligament stem cells (PDLSCs) are characterized by multiple differentiation potential and potent self-renewal ability, yet much remains to be elucidated that what determines these properties. Long noncoding RNAs (lncRNAs) have been suggested to involve in multiple biological process under physiological and pathological conditions, including osteogenic differentiation. In the present study, we performed comprehensive lncRNA profiling by lncRNA microarray analysis and identified prostate cancer-associated ncRNA transcript-1 (lncPCAT1) was gradually increased in PDLSCs during consecutive osteogenic induction, and it could further positively regulate the osteogenic differentiation both in vitro and in vivo, whereas lncPCAT1 inhibition led to suppressed osteogenic differentiation. Thereafter, we inferred a predicted interaction between lncPCAT1 and miR-106a-5p and then confirmed the direct binding sites of miR-106a-5p on lncPCAT1. Although miR-106a-5p upregulation led to decreased osteogenic differentiation, lncPCAT1 overexpression could reverse its suppression, indicating that lncPCAT1 act as a competing endogenous RNA for miR-106a-5p. Moreover, lncPCAT1 could sponge miR-106a-5p to upregulate miR-106a-5p-targeted gene BMP2, which was a crucial gene involved in osteogenic differentiation. Interestingly, we found that E2F5, another target of miR-106a-5p, could bind to the promoter of lncPCAT1 and then form a feed-forward regulatory network targeting BMP2. In conclusion, our study provided a novel lncRNA-miRNA feed-forward regulatory network and a promising target to modulate the osteogenic differentiation of PDLSCs.

Immunomodulatory properties of dental tissue-derived mesenchymal stem cells: Implication in disease and tissue regeneration

Mesenchymal stem cells (MSCs) are considered as an attractive tool for tissue regeneration and possess a strong immunomodulatory ability. Dental tissue-derived MSCs can be isolated from different sources, such as the dental pulp, periodontal ligament, deciduous teeth, apical papilla, dental follicles and gingiva. According to numerous in vitro studies, the effect of dental MSCs on immune cells might depend on several factors, such as the experimental setting, MSC tissue source and type of immune cell preparation. Most studies have shown that the immunomodulatory activity of dental MSCs is strongly upregulated by activated immune cells. MSCs exert mostly immunosuppressive effects, leading to the dampening of immune cell activation. Thus, the reciprocal interaction between dental MSCs and immune cells represents an elegant mechanism that potentially contributes to tissue homeostasis and inflammatory disease progression. Although the immunomodulatory potential of dental MSCs has been extensively investigated in vitro, its role in vivo remains obscure. A few studies have reported that the MSCs isolated from inflamed dental tissues have a compromised immunomodulatory ability. Moreover, the expression of some immunomodulatory proteins is enhanced in periodontal disease and even shows some correlation with disease severity. MSC-based immunomodulation may play an essential role in the regeneration of different dental tissues. Therefore, immunomodulation-based strategies may be a very promising tool in regenerative dentistry.

Effect of the Histone Deacetylases Inhibitors on the Differentiation of Stem Cells in Bone Damage Repairing and Regeneration

Tissue damage repairing and regeneration is a research hot topic. Tissue engineering arises at the historic moment which is a defect repair compound composed of seed cells, tissue engineering scaffolds, and inducing factors. Stem cells have a limited growth period in vitro culture, and they have a pattern of replicating ageing, and these disadvantages are limiting the applications of stem cells in basic research and clinical treatment. The enhancement of stem cell differentiation ability is a difficult problem to overcome, and it is possible to enhance the differentiation ability of stem cells through histone modification so as to provide a more robust foundation for damage repairing and regeneration. Studies have shown that Histone Deacetylases (HDAC) inhibitors can improve mesenchymal stem cells in vitro induced in different directions, conversion efficiency, increasing the feasibility and safety of stem cell therapy and tissue engineering, to offer reference to promote the stem cell therapy in clinical application. Therefore, this paper mainly focusing on the usage and achievements of the deacetylase inhibitors in stem cell differentiation studies and their use and prospects in repair of bone tissue defects.

The Potential of Different Origin Stem Cells in Modulating Oral Bone Regeneration Processes

Tissue engineering has gained much momentum since the implementation of stem cell isolation and manipulation for regenerative purposes. Despite significant technical improvements, researchers still have to decide which strategy (which type of stem cell) is the most suitable for their specific purpose. Therefore, this short review discusses the advantages and disadvantages of the three main categories of stem cells: embryonic stem cells, mesenchymal stem cells and induced pluripotent stem cells in the context of bone regeneration for dentistry-associated conditions. Importantly, when deciding upon the right strategy, the selection needs to be made in concordance with the morbidity and the life-threatening level of the condition in discussion. Therefore, even when a specific type of stem cell holds several advantages over others, their availability, invasiveness of the collection method and ethical standards become deciding parameters.

Necrostatin-1 promotes ectopic periodontal tissue like structure regeneration in LPS-treated PDLSCs

Necroptosis is a programmed necrosis, regulated by receptor interacting protein kinase 1(RIP1) and receptor interacting protein kinase 3(RIP3), and could be inhibited by necrostatin-1(Nec-1) specifically. This study aims to evaluate the effect of Nec-1 on LPS-treated periodontal ligament stem cells (PDLSCs). In the research, three groups were established: normal cultured PDLSCs, Porphyromonas gingivalis (Pg)-LPS stimulated PDLSCs and Pg-LPS+Nec-1 treated PDLSCs. The expression of RIP1 and RIP3 and osteogenic differentiation of PDLSCs in three groups were analyzed. Then, we constructed cell aggregates (CA) using PDLSCs, then PDLSCs-CA were combined with Bio-Oss in three groups were transplanted subcutaneously in nude mice to assess their potentials of periodontal tissue regeneration. The results showed that RIP1 and RIP3 were fully expressed in Pg-LPS stimulated PDLSCs and the level increased significantly. Nec-1 inhibited RIP1-RIP3 interaction, and further inhibited necroptosis of PDLSCs in inflammatory state. Moreover, Nec-1 pretreatment ameliorates the osteogenic differentiation of LPS-treated PDLSCs and can effectively promote the cementum like structure ectopic regenerative ability of PDLSCs in nude mice. These findings show RIP1/RIP3-mediated necroptosis is an important mechanism of cell death in PDLSCs. Nec-1 has a protective effect in reducing cell death and promotes ectopic periodontal tissue like structure regeneration by inhibiting necroptosis. Nec-1 is a hopeful therapeutic agent which protects cells from necroptosis and ameliorates functional outcome.

Strontium ion attenuates lipopolysaccharide-stimulated proinflammatory cytokine expression and lipopolysaccharide-inhibited early osteogenic differentiation of human periodontal ligament cells

BACKGROUND AND OBJECTIVE

Periodontitis is a chronic inflammatory disease characterized by the destruction of the periodontium. The strontium ion (Sr²⁺ ) can prevent the bone loss associated with periodontitis and promote the regeneration of the bone. The mechanisms by which the Sr²⁺ works remain poorly understood. We aim to investigate the effects of the Sr²⁺ ion on cell proliferation, inflammatory regulation and osteogenic differentiation of human periodontal ligament cells (hPDLCs) in pathological conditions.

MATERIAL AND METHODS

hPDLCs were obtained from premolars that came from the orthodontic extraction. The hPDLCs were treated with Sr²⁺ and/or lipopolysaccharide (LPS), which was applied as the pathological condition of periodontitis. The effect of the dose of Sr²⁺ on cell proliferation was analyzed using a Cell Counting Kit-8 assay. The gene and protein expression of proinflammatory cytokines were detected by the real-time polymerase chain reaction and enzyme-linked immunosorbent assay. The osteogenic differentiation and mineralization were assessed by the real-time polymerase chain reaction, alkaline phosphatase activity assay and alizarin red staining.

RESULTS

Results demonstrated that Sr²⁺ in a range of concentrations from 0.02 to 2.5 mmol/L significantly improved the proliferation of hPDLCs. Sr²⁺ reversed LPS-stimulated proinflammatory cytokine expressions such as tumor necrosis factor alpha, interleukin (IL)-1β, IL-6 and IL-8. Moreover, Sr²⁺ rescued the LPS-inhibited gene expression of osteogenic differentiation. Although it appeared to suppress the late mineralization, Sr²⁺ can reverse the LPS-inhibited early osteogenic differentiation of hPDLCs.

CONCLUSION

These results indicated that Sr²⁺ could attenuate the LPS-stimulated proinflammatory molecule expression and inhibit early osteogenic differentiation of hPDLCs.

Tenogenic Properties of Mesenchymal Progenitor Cells Are Compromised in an Inflammatory Environment

Transplantation of multipotent mesenchymal progenitor cells is a valuable option for treating tendon disease. Tenogenic differentiation leading to cell replacement and subsequent matrix modulation may contribute to the regenerative effects of these cells, but it is unclear whether this occurs in the inflammatory environment of acute tendon disease. Equine adipose-derived stromal cells (ASC) were cultured as monolayers or on decellularized tendon scaffolds in static or dynamic conditions, the latter represented by cyclic stretching. The impact of different inflammatory conditions, as represented by supplementation with interleukin-1β and/or tumor necrosis factor-α or by co-culture with allogeneic peripheral blood leukocytes, on ASC functional properties was investigated. High cytokine concentrations increased ASC proliferation and osteogenic differentiation, but decreased chondrogenic differentiation and ASC viability in scaffold culture, as well as tendon scaffold repopulation, and strongly influenced musculoskeletal gene expression. Effects regarding the latter differed between the monolayer and scaffold cultures. Leukocytes rather decreased ASC proliferation, but had similar effects on viability and musculoskeletal gene expression. This included decreased expression of the tenogenic transcription factor scleraxis by an inflammatory environment throughout culture conditions. The data demonstrate that ASC tenogenic properties are compromised in an inflammatory environment, with relevance to their possible mechanisms of action in acute tendon disease.

Receptor-Interacting Protein 3/Caspase-8 May Regulate Inflammatory Response and Promote Tissue Regeneration in the Periodontal Microenvironment

Background

Periodontal ligament stem cells (PDLSCs) possess characteristics of multi-potential differentiation and immuno-modulation, and PDLSCs-mediated periodontal tissue regeneration is regarded as a hopeful method for periodontitis treatment. Recent studies demonstrated that RIP3 and caspase8 regulate bacteria-induced innate immune response and programmed necrosis, which is also called necroptosis. This study aimed to determine the role of the RIP3/Caspase8 signal pathway on necroptosis of PDLSCs under the inflammatory microenvironment, both in vitro and in vivo.

Material/Methods

PDLSCs were cultured, and transmission electron microscopy and flow cytometry were used to detect necroptosis. PCR, ALP, and Alizarin Red S staining were used to assess the effect of necroptosis on osteogenesis differentiation of PDLSCs in vitro, while HE and Masson staining were taken after the nude mouse subcutaneous transplant experiment.

Results

Our research indicates that RIP3/caspase8 can regulate the immune response of PDLSCs, and blockade of RIP3/caspase8 can protect the biological characteristics of the PDLSCs, effectively promoting periodontal tissue regeneration in the inflammatory microenvironment.

Conclusions

Inhibiting RIP3/caspase8 can effectively promote periodontal tissue regeneration in the inflammatory microenvironment.

Time series clustering of mRNA and lncRNA expression during osteogenic differentiation of periodontal ligament stem cells

Background

Long noncoding RNAs (lncRNAs) are regulatory molecules that participate in biological processes such as stem cell differentiation. Periodontal ligament stem cells (PDLSCs) exhibit great potential for the regeneration of periodontal tissue and the formation of new bone. However, although several lncRNAs have been found to be involved in the osteogenic differentiation of PDLSCs, the temporal transcriptomic landscapes of mRNAs and lncRNAs need to be mapped to obtain a complete picture of osteoblast differentiation. In this study, we aimed to characterize the time-course expression patterns of lncRNAs during the osteogenic differentiation of PDLSCs and to identify the lncRNAs that are related to osteoblastic differentiation.

Methods

We cultured PDLSCs in an osteogenic medium for 3, 7, or 14 days. We then used RNA sequencing (RNA-seq) to analyze the expression of the coding and non-coding transcripts in the PDLSCs during osteogenic differentiation. We also utilized short time-series expression miner (STEM) to describe the temporal patterns of the mRNAs and lncRNAs. We then performed Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analyses to assess the biological relevance of genes in each profile, and used quantitative real-time PCR (qRT-PCR) to validate the differentially expressed mRNAs and lncRNAs that were associated with osteoblast differentiation. Lastly, we performed a knock down of two lncRNAs, MEG8, and MIR22HG, and evaluated the expression of osteogenic markers.

Results

When PDLSCs were differentiated to osteoblasts, mRNAs associated with bone remodeling, cell differentiation, and cell apoptosis were upregulated while genes associated with cell proliferation were downregulated. lncRNAs showed stage-specific expression, and more than 200 lncRNAs were differentially expressed between the undifferentiated and osteogenically differentiated PDLSCs. Using STEM, we identified 25 temporal gene expression profiles, among which 14 mRNA and eight lncRNA profiles were statistically significant. We found that genes in pattern 12 were associated with osteoblast differentiation. The expression patterns of osteogenic mRNAs (COL6A1, VCAN, RRBP1, and CREB3L1) and lncRNAs (MEG8 and MIR22HG) were consistent between the qRT-PCR and RNA-seq results. Moreover, the knockdown of MEG8 and MIR22HG significantly decreased the expression of osteogenic markers (runt-related transcription factor 2 and osteocalcin).

Discussion

During the osteogenic differentiation of PDLSCs, both mRNAs and lncRNAs showed stage-specific expression. lncRNAs MEG8 and MIR22HG showed a high correlation with osteoblastogenesis. Our results can be used to gain a more comprehensive understanding of the molecular events regulating osteoblast differentiation and the identification of functional lncRNAs in PDLSCs.

Mesenchymal endometrial stem/stromal cells for hard tissue engineering: a review of in vitro and in vivo evidence

Hard tissues including teeth, bone and cartilage have inability or poor capacity to self-renew, especially in large defects. Therefore, repair of damages in these tissues represents a huge challenge in the medical field today. Hard tissue engineering commonly utilizes different stem cell sources as a promising strategy for treating bone, cartilages and tooth defects or disorders. Decades ago, researchers successfully isolated and identified endometrial mesenchymal stem/stromal cells (EnSCs) and discovered their multidifferentiation potential. Current studies suggest that EnSCs have significant advantages compared with stem cells derived from other tissues. In this review article, we summarize the current in vitro and in vivo studies that utilize EnSCs or menstrual blood-derived stem cells for differentiation to osteoblasts, odontoblasts or chondroblasts in an effort to realize the potential of these cells in hard tissues regeneration.

IL-1/TNF-α Inflammatory and Anti-Inflammatory Synchronization Affects Gingival Stem/Progenitor Cells' Regenerative Attributes

Cytokines play major roles in tissue destruction/repair. The present study investigates proliferative and osteogenic differentiation potentials of gingival mesenchymal stem/progenitor cells (G-MSCs), influenced by IL-1/TNF-α inflammatory/anti-inflammatory conditions. Human G-MSCs were isolated, characterized, and cultured in basic medium (control group, M1), in basic medium with IL-1β, TNF-α, and IFN-γ (inflammatory group, M2) and with IL-1ra/TNF-αi added to M2 (anti-inflammatory group, M3). MTT tests at days 1, 3, and 7 and CFU assay at day 12 were conducted. Osteogenic differentiation was analyzed by bone-specific transcription factors (RUNX2), alkaline phosphatase (ALP), type I collagen (Col-I), osteopontin (OPN), and osteonectin (ON) expression at days 1, 3, 7, and 14 and Alizarin red staining at day 14. At day 3, the control group showed the highest cell numbers. At day 7, cell numbers in inflammatory and anti-inflammatory group outnumbered the control group. At day 12, CFUs decreased in the inflammatory and anti-inflammatory groups, with altered cellular morphology. The anti-inflammatory group demonstrated elevated bone-specific transcription factors at 14 days. After 14 days of osteogenic induction, calcified nodules in the anti-inflammatory group were higher compared to control and inflammatory groups. For regeneration, initial inflammatory stimuli appear essential for G-MSCs' proliferation. With inflammatory persistence, this positive effect perishes and is followed by a short-term stimulatory one on osteogenesis. At this stage, selective anti-inflammatory intervention could boost G-MSCs' differentiation.

Inhibiting PHD2 in bone marrow mesenchymal stem cells via lentiviral vector-mediated RNA interference facilitates the repair of periodontal tissue defects in SD rats

Hypoxia-inducible factors (HIFs) play an important role in angiogenesis, and they can activate the expression of several downstream angiogenic factors. HIF-1 is a major transcriptor of HIFs, composed of α and β subunits. Prolyl hydroxylase domain-containing protein 2 (PHD2) is the main catabolic enzyme for HIF-1α, and it can accelerate its degradation under normoxic conditions. PHD2 expression in bone marrow mesenchymal stem cells (BMMSCs) of SD rats was down-regulated under normoxic conditions in this study by utilizing lentiviral vector-mediated RNA interference to promote HIF-1α accumulation, thus enhancing the expression of angiogenic factors. A tissue-engineered compound was constructed using the composite collagen membrane of BMMSCs after PHD2 gene silencing to repair periodontal fenestration defects in SD rats. The results of this study indicated that, after PHD2 gene silencing, the osteogenic differentiation of BMMSCs was enhanced in vitro, the resistance of cells to oxidative stress was also validated in vitro, thereby illustrating the promotion of the repair of artificially constructed periodontal tissue defects in rats. The results of this study provide a reference and guidance for future applications of RNA interference in periodontal tissue engineering and serve as a basis for improving the survival of seed cells in recipient tissues.

Foreskin as a source of immunotherapeutic mesenchymal stromal cells

Mesenchymal stromal cells (MSCs) have well-characterized properties and thus represent an attractive cell population for use in several therapeutic applications. Due to the limitations and inconveniences associated with classical sources of MSCs, the identification and characterization of alternative sources are required for safe and efficient cell therapy. The skin tissue is currently referred to as a reservoir of cells with therapeutically relevant functions. Historically considered biological waste, foreskin (FSK) is increasingly used to provide immunotherapeutic MSCs for medicinal products. This review discusses for the first time the nature and profile of MSCs within the foreskin tissue and, in particular, their immunobiology. A better immunological characterization and understanding of foreskin-derived cells will be critical for improving MSC-based cellular strategies for immunotherapeutic applications.

[Tumor necrosis factor-α regulates the osteogenic differentiation of bone marrow mesenchymal stem cells in chronic periodontitis]

Bone marrow mesenchymal stem cells (BMSCs) and ideal adult stem cells for alveolar bone regeneration considerably help restore the structure and function of the periodontium and promote the healing of periodontal disease. Thus, BMSC features, especially the mechanism of osteogenic differentiation, has recently become a research hotspot. Tumor necrosis factor-α (TNF-α), which is the main factor in the periodontal inflammatory microenvironment, is directly related to the osteogenic differentiation of BMSCs. Exploring the TNF-α-regulated differentiation mechanism of BMSCs aids in the search for new treatment targets. Such investigation also promotes the development of stem cell therapy for periodontal diseases. This article aims to describe the potential of TNF-α in regulating the osteogenic differentiation of stem cells.

Stem cells applications in bone and tooth repair and regeneration: New insights, tools, and hopes

The exploration of stem and progenitor cells holds promise for advancing our understanding of the biology of tissue repair and regeneration mechanisms after injury. This will also help in the future use of stem cell therapy for the development of regenerative medicine approaches for the treatment of different tissue-species defects or disorders such as bone, cartilages, and tooth defects or disorders. Bone is a specialized connective tissue, with mineralized extracellular components that provide bones with both strength and rigidity, and thus enable bones to function in body mechanical supports and necessary locomotion process. New insights have been added to the use of different types of stem cells in bone and tooth defects over the last few years. In this concise review, we briefly describe bone structure as well as summarize recent research progress and accumulated information regarding the osteogenic differentiation of stem cells, as well as stem cell contributions to bone repair/regeneration, bone defects or disorders, and both restoration and regeneration of bones and cartilages. We also discuss advances in the osteogenic differentiation and bone regeneration of dental and periodontal stem cells as well as in stem cell contributions to dentine regeneration and tooth engineering.

Innate Immune Response of Human Embryonic Stem Cell-Derived Fibroblasts and Mesenchymal Stem Cells to Periodontopathogens

Periodontitis involves complex interplay of bacteria and host immune response resulting in destruction of supporting tissues of the tooth. Toll-like receptors (TLRs) play a role in recognizing microbial pathogens and eliciting an innate immune response. Recently, the potential application of multipotent stem cells and pluripotent stem cells including human embryonic stem cells (hESCs) in periodontal regenerative therapy has been proposed. However, little is known about the impact of periodontopathogens on hESC-derived progenies. This study investigates the effects of heat-killed periodontopathogens, namely, Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans, on TLR and cytokine expression profile of hESC-derived progenies, namely, fibroblasts (hESC-Fib) and mesenchymal stem cells (hESC-MSCs). Additionally, the serotype-dependent effect of A. actinomycetemcomitans on hESC-derived progenies was explored. Both hESC-Fib and hESC-MSCs constitutively expressed TLR-2 and TLR-4. hESC-Fib upon exposure to periodontopathogens displayed upregulation of TLRs and release of cytokines (IL-1β, IL-6, and IL-8). In contrast, hESC-MSCs were largely nonresponsive to bacterial challenge, especially in terms of cytokine production. Further, exposure of hESC-Fib to A. actinomycetemcomitans serotype c was associated with higher IL-8 production than serotype b. In contrast, the hESC-MSCs displayed no serotype-dependent response. Differential response of the two hESC progenies implies a phenotype-dependent response to periodontopathogens and supports the concept of immunomodulatory properties of MSCs.

Controlled release of recombinant human cementum protein 1 from electrospun multiphasic scaffold for cementum regeneration

Periodontitis is a major cause for tooth loss, which affects about 15% of the adult population. Cementum regeneration has been the crux of constructing the periodontal complex. Cementum protein 1 (CEMP1) is a cementum-specific protein that can induce cementogenic differentiation. In this study, poly(ethylene glycol) (PEG)-stabilized amorphous calcium phosphate (ACP) nanoparticles were prepared by wet-chemical method and then loaded with recombinant human CEMP1 (rhCEMP1) for controlled release. An electrospun multiphasic scaffold constituted of poly(ε-caprolactone) (PCL), type I collagen (COL), and rhCEMP1/ACP was fabricated. The effects of rhCEMP1/ACP/PCL/COL scaffold on the attachment proliferation, osteogenic, and cementogenic differentiations of human periodontal ligament cells, (PDLCs) were systematically investigated. A critical size defect rat model was introduced to evaluate the effect of tissue regeneration of the scaffolds in vivo. The results showed that PEG-stabilized ACP nanoparticles formed a core-shell structure with sustained release of rhCEMP1 for up to 4 weeks. rhCEMP1/ACP/PCL/COL scaffold could suppress PDLCs proliferation behavior and upregulate the expression of cementoblastic markers including CEMP1 and cementum attachment protein while downregulating osteoblastic markers including osteocalcin and osteopontin when it was cocultured with PDLCs in vitro for 7 days. Histology analysis of cementum after being implanted with the scaffold in rats for 8 weeks showed that there was cementum-like tissue formation but little bone formation. These results indicated the potential of using electrospun multiphasic scaffolds for controlled release of rhCEMP1 for promoting cementum regeneration in reconstruction of the periodontal complex.

The use of platelet-rich fibrin combined with periodontal ligament and jaw bone mesenchymal stem cell sheets for periodontal tissue engineering

Periodontal regeneration involves the restoration of at least three unique tissues: cementum, periodontal ligament tissue (PDL) and alveolar bone tissue. Here, we first isolated human PDL stem cells (PDLSCs) and jaw bone mesenchymal stem cells (JBMSCs). These cells were then induced to form cell sheets using an ascorbic acid-rich approach, and the cell sheet properties, including morphology, thickness and gene expression profile, were compared. Platelet-rich fibrin (PRF) derived from human venous blood was then fabricated into bioabsorbable fibrin scaffolds containing various growth factors. Finally, the in vivo potential of a cell-material construct based on PDLSC sheets, PRF scaffolds and JBMSC sheets to form periodontal tissue was assessed in a nude mouse model. In this model, PDLSC sheet/PRF/JBMSC sheet composites were placed in a simulated periodontal space comprising human treated dentin matrix (TDM) and hydroxyapatite (HA)/tricalcium phosphate (TCP) frameworks. Eight weeks after implantation, the PDLSC sheets tended to develop into PDL-like tissues, while the JBMSC sheets tended to produce predominantly bone-like tissues. In addition, the PDLSC sheet/PRF/JBMSC sheet composites generated periodontal tissue-like structures containing PDL- and bone-like tissues. Further improvements in this cell transplantation design may have the potential to provide an effective approach for future periodontal tissue regeneration.

Tumor Necrosis Factor-α Attenuates the Osteogenic Differentiation Capacity of Periodontal Ligament Stem Cells by Activating PERK Signaling

BACKGROUND

Human periodontal ligament stem cells (PDLSCs) display efficient osteogenic differentiation capacity but fail to rescue bone breakdown associated with periodontitis. Endoplasmic reticulum (ER) stress and the unfolded protein response have recently been linked to inflammation and osteogenic differentiation. Therefore, the role of the double-stranded RNA-activated protein kinase (PKR)-like ER kinase (PERK) pathway in the impaired osteogenic differentiation ability of PDLSCs treated with tumor necrosis factor (TNF)-α was investigated.

METHODS

PDLSCs were isolated and stimulated with osteogenic media containing 1, 10, or 20 ng/mL TNF-α. Assessment included: 1) expression of runt-related transcription factor 2 and osteocalcin; 2) mRNA expression and activity of alkaline phosphatase; and 3) formation of mineralization nodules. Furthermore, expression of PERK pathway-related factors: 1) glucose-regulated protein (GRP) 78; 2) PERK; 3) activating transcription factor (ATF) 4; and 4) CCAAT-enhancer-binding proteins (C/EBP) homologous protein were also measured. Osteogenic differentiation and inhibition of the PERK pathway were also examined in cells pretreated with an inhibitor of ER stress, 4-phenylbutyric acid (PBA), followed by TNF-α stimulation. Finally, PERK small interfering RNA was used to examine osteogenic differentiation attenuated by TNF-α.

RESULTS

Higher concentrations of TNF-α (10 and 20 ng/mL) impaired osteogenic differentiation of PDLSCs but activated the PERK pathway. Pretreatment of PDLSCs with lower concentrations of 4-PBA prevented the TNF-α-induced upregulation of GRP78, PERK, and ATF4 and recovered differentiation ability. Finally, PERK knockdown also restored osteogenic differentiation.

CONCLUSION

TNF-α attenuates osteogenic differentiation ability of PDLSCs through activation of the PERK pathway.