GSK3β is a checkpoint for TNF-α-mediated impaired osteogenic differentiation of mesenchymal stem cells in inflammatory microenvironments

Triptolide mitigates the inhibition of osteogenesis induced by TNF-α in human periodontal ligament stem cells via the p-IκBα/NF-κB signaling pathway: an in-vitro study

BACKGROUND

Triptolide is a widely utilized natural anti-inflammatory drug in clinical practice. Aim of this study was to evaluate effects of triptolide on hPDLSCs osteogenesis in an inflammatory setting and to investigate underlying mechanisms.

METHODS

Using the tissue block method to obtain hPDLSCs from extracted premolar or third molar. Flow cytometry, osteogenic and adipogenic induction were carried out in order to characterise the features of the cells acquired. hPDLSC proliferative activity was assessed by CCK-8 assay to determine the effect of TNF-α and/or triptolide. The impact of triptolide on the osteogenic differentiation of hPDLSCs was investigated by ALP staining and quantification. Osteogenesis-associated genes and proteins expression level were assessed through PCR and Western blotting assay. Finally, BAY-117,082 was used to study the NF-κB pathway.

RESULTS

In the group treated with TNF-α, there was an elevation in inflammation levels while osteogenic ability and the expression of both osteogenesis-associated genes and proteins decreased. In the group co-treated with TNF-α and triptolide, inflammation levels were reduced and osteogenic ability as well as the expression of both osteogenesis-associated genes and proteins were enhanced. At the end of the experiment, both triptolide and BAY-117,082 exerted similar inhibitory effects on the NF-κB pathway.

CONCLUSION

The osteogenic inhibition of hPDLSCs by TNF-α can be alleviated through triptolide, with the involvement of the p-IκBα/NF-κB pathway in this mechanism.

An injectable photopolymerizable chitosan hydrogel doped anti-inflammatory peptide for long-lasting periodontal pocket delivery and periodontitis therapy

Periodontitis is a common chronic inflammatory disease caused by plaque that leads to alveolar bone resorption and tooth loss. Inflammation control and achieving better tissue repair are the key to periodontitis treatment. In this study, human β-Defensin 1 short motif Pep-B with inflammation inhibition and differentiation regulation properties, is firstly used in the treatment of periodontitis, and an injectable photopolymerizable Pep-B/chitosan methacryloyl composite hydrogel (CMSA/Pep-B) is constructed. We confirm that Pep-B improves inflammation, and restores osteogenic behavior and function of injured stem cells. CMSA/Pep-B has good injectability, fluidity and photopolymerizability, and can sustainably release Pep-B to maintain drug concentration in periodontal pockets. Furthermore, animal experiments showed that CMSA/Pep-B significantly ameliorated the inflammation of the periodontium and reduced the alveolar bone loss by decreasing inflammatory infiltration, osteoclast formation and collagen destruction. In conclusion, CMSA/Pep-B is envisaged to be a novel bioactive material or therapeutic drug for treating periodontitis.

ELP2-NLRP3-GSDMD/GSDME-mediated pyroptosis is induced by TNF-α in MC3T3-E1 cells during osteogenic differentiation

Tumour necrosis factor-α (TNF-α) is a cytokine involved in systemic inflammation. TNF-α slows down osteogenic differentiation, which may contribute to poor bone development in the inflammatory microenvironment. TNF-α inhibits osteogenic differentiation by activating the JAK-STAT3 pathway, of which Signal transducer and activator of transcription 3 (STAT3)-interacting protein 1 (StIP1, also known as elongator complex protein 2, ELP2) is a key protein in the JAK-STAT3 pathway. We investigated whether and how ELP2 activation mediates the TNF-α-induced pyroptosis during osteoblastic differentiation. Using in vitro cell cultures of preosteoblastic MC3T3-E1 cells, we found that TNF-α exposure causes cell pyroptosis in an inflammatory microenvironment during osteoblastic differentiation. Bioinformatics, protein docking model and co-immunoprecipitation analysis revealed an association between ELP2, STAT3 and NLRP3. Forced ELP2 expression promoted MC3T3-E1 cells pyroptosis, with an increase in the expression of STAT3, NLRP3 inflammasome, GSDMD/GSDME, osteoblast marker genes, and the activity of alkaline phosphatase. In contrast, ELP2 silencing ameliorated MC3T3-E1 cells pyroptosis, and osteogenic differentiation, especially after TNF-α stimulation. The TNF-α-induced cells pyroptosis during osteoblastic differentiation was therefore mediated by ELP2. These results suggest that ELP2 is upregulated at the pyroptosis of MC3T3-E1 cells and inhibits osteogenic differentiation in response to TNF-α through NLRP3-GSDMD/GSDME activation.

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.

FoxO1 Agonists Promote Bone Regeneration in Periodontitis by Protecting the Osteogenesis of Periodontal Ligament Stem Cells

Protecting the function of periodontal ligament stem cells (PDLSCs) is crucial for bone regeneration in periodontitis. Forkhead box protein O1 (FoxO1) has been previously reported as a crucial mediator in bone homeostasis, providing a favorable environment for osteoblast proliferation and differentiation. In this study, we investigated the effect and mechanism of FoxO1 agonists on the osteogenesis of PDLSCs under inflammatory conditions. In this study, we screened FoxO1 agonists by detecting their effects on the osteogenic differentiation of PDLSCs. Then, the function of these agonists in bone regeneration was analyzed in the periodontitis model. We found that hyperoside or 2-furoyl-LIGRLO-amide trifluoroacetate salt (2-Fly) promoted osteogenic differentiation under inflammation by simultaneously inhibiting nuclear factor κB (NF-κB) activation, β-catenin expression, and reactive oxygen species (ROS) production. Moreover, local injection of hyperoside or 2-Fly rescued the expression of FoxO1 and runt-related transcription factor 2 (Runx2) in vivo, alleviating alveolar bone loss and periodontal ligament damage. These findings suggested that FoxO1 agonists exerted a protective effect on osteogenesis in PDLSCs, as a result, facilitating bone formation under inflammatory conditions. Taken together, FoxO1 might serve as a therapeutic target for bone regeneration in periodontitis by mediating multiple signaling pathways.

Inhibition of Wnt11 impairs the osteogenesis and aggravates the inflammatory response of human mesenchymal stem cells under LPS-induced inflammatory condition

In infectious bone defect, osteogenesis is very particularly important for treating. Currently, mesenchymal stem cells (MSCs) become a promising treatment protocol in clinical practice. In infectious environment, lipopolysaccharide (LPS) not only affects the osteogenic differentiation of MSCs, but also incurs inflammatory reaction from the host or cells and prompts the secretion of inflammatory cytokines. Wnt11 plays an important role of enhancing osteogenic ability of MSCs in treating bone infectious animal model in vivo. However, whether Wnt11 enhances the osteogenic capacity or influences the inflammatory reaction under inflammatory condition mediated by LPS in vitro remains unknown. In this study, we investigated the role of Wnt11 on the osteogenic differentiation of bone marrow mesenchymal stem cells (BM-MSCs) and the effect on the inflammatory reaction induced by LPS. Effects of Wnt11 on the osteogenic capacity of BM-MSCs and on the inhibition of inflammatory reaction induced by LPS were evaluated by Wnt11 RNAi assay, Alizarin staining, quantitative RT-PCR test, ALP activity test and ELISA assays. The results showed inhibiting Wnt11 expression exacerbated the expression of osteogenic differentiation related genes and decreased the mineral deposits formation. Moreover, inhibiting Wnt11 expression also exacerbated the inflammatory factors release, indicating Wnt11 might play an important role of enhancing the osteogenic differentiation of BM-MSCs and inhibiting the inflammatory reaction induced by LPS.

Low concentrations of tumor necrosis factor-alpha promote human periodontal ligament stem cells osteogenic differentiation by activation of autophagy via inhibition of AKT/mTOR pathway

BACKGROUND

Tumor necrosis factor-alpha (TNF-α) is one of the crucial inflammatory factors in alveolar bone metabolism during the process of periodontitis. Autophagy is indispensable for proper osteoblast function. However, the effects of autophagy on osteogenic differentiation of human periodontal ligament stem cells (hPDLSCs) in inflammatory microenvironment and the underlying mechanisms remain to be clarified. The aim of the present study was to investigate whether autophagy participates in hPDLSCs differentiation after treated with TNF-α and explore the underlying mechanisms.

METHODS AND RESULTS

Characterizations of hPDLSCs were evaluated by Alizarin-red S staining, Oil red staining and flow cytometry. hPDLSCs were treated with various concentrations of TNF-α. Rapamycin or 3MA was used to achieve or inhibit autophagy activation. AKT signaling was inhibited using ARQ092. Cell proliferation was evaluated using Cell Counting Kit-8 (CCK8) assay. Real-time reverse transcriptase-polymerase chain reaction assay (RT-PCR), western blot, alkaline phosphatase (ALP) staining and Alizarin Red S staining were applied to evaluate levels of osteogenic differentiation and autophagy. CCK8 showed that low concentrations of TNF-α had no influence on cell proliferation, while high concentrations of TNF-α inhibited proliferation. Low concentrations of TNF-α promoted osteogenic differentiation and autophagy, while high concentrations of TNF-α inhibited osteogenic differentiation and autophagy in hPDLSCs. The levels of osteogenic differentiation in hPDLSCs were partly effected after co-incubation with 0.1 ng/mL TNF-α with 3MA or Rapamycin. ARQ092 enhanced 0.1 ng/mL TNF-α-induced ALP expression and mineral nodule formation.

CONCLUSION

Low concentrations of TNF-α promote hPDLSCs osteogenic differentiation by activation of autophagy via inhibition of AKT/mTOR signaling.

Periodontal ligament cells from patients with treated stable periodontitis: Characterization and osteogenic differentiation potential

BACKGROUND AND OBJECTIVE

Periodontal ligament progenitor cells (PDL cells) isolated from patients with inflammatory periodontitis have impaired regenerative capacity, but it is unknown whether this capacity can be recovered upon treatment and stabilization of the periodontal condition. The study aimed to investigate the expression of surface markers and the proliferation and osteogenic potential of PDL cells isolated from patients with treated stable periodontitis (S-PDL cells), periodontally healthy individuals (H-PDL cells), and patients with inflammatory periodontitis (I-PDL cells).

METHODS

H-PDL, I-PDL, and S-PDL cells were isolated from the extracted teeth of individuals who (1) were periodontally healthy, (2) had inflammatory periodontitis, and (3) had treated stable periodontitis, respectively. The expression levels of surface markers and the proliferative and osteogenic capacities of the PDL cells were assessed.

RESULTS

PDL cells derived from all three sources exhibited mesenchymal stem cell (MSC) characteristics. They were positive for MSC-related markers and negative for a hematopoiesis-related marker. However, S-PDL cells had higher proliferation rates, higher expression levels of osteogenic markers, higher alkaline phosphatase activity, and more calcium nodules than I-PDL cells. But all of these parameters remained lower in S-PDL cells than in H-PDL cells.

CONCLUSIONS

S-PDL cells proliferated faster and had greater osteogenic potential than I-PDL cells, although these values remained lower than those in H-PDL cells.

Wnt/β-catenin plays a dual function in calcium hydroxide induced proliferation, migration, osteogenic differentiation and mineralization in vitro human dental pulp stem cells

AIM

Calcium hydroxide is the gold standard material for pulp capping and has been widely used in clinical dentistry. Calcium hydroxide promotes proliferation, migration and osteogenic differentiation of dental pulp stem cells (DPSCs). However, the underlying mechanism is not clear. Our study investigated the role of Wnt/β-catenin pathway in calcium hydroxide-induced proliferation, migration, osteogenic differentiation and mineralization of human DPSCs.

METHODOLOGY

Protein and gene expression was detected by western blot (WB), immunofluorescence staining and quantitative real-time PCR (qPCR). Cell viability was analysed using the Cell Counting Kit-8 (CCK-8) assay. Wound-healing assay was used to analyse cell migration. The expression of alkaline phosphatase (ALP) was detected using ALP staining. Mineralization was analysed by alizarin red staining.

RESULTS

Calcium hydroxide increased the protein expression of phosphorylated-GSK3β/GSK3β, β-catenin and the gene expression of LEF-1. Inhibition of Wnt/β-catenin abolished calcium hydroxide-induced proliferation and migration of DPSCs in 24 h. However, incubation with calcium hydroxide for 7 days and 14 days reduced Wnt/β-catenin signalling. Inhibition of Wnt/β-catenin promoted calcium hydroxide-induced osteogenic differentiation and mineralization in DPSCs.

CONCLUSION

Wnt/β-catenin pathway plays a dual role in calcium hydroxide-regulated DPSC behaviour. Incubation with calcium hydroxide promoted rapid proliferation and migration of DPSCs, while prolonged incubation negatively regulated osteogenic differentiation and mineralization.

A Biomimetic Smart Nanoplatform as “Inflammation Scavenger” for Regenerative Therapy of Periodontal Tissue

Introduction

The functional reconstruction of periodontal tissue defects remains a clinical challenge due to excessive and prolonged host response to various endogenous and exogenous pro-inflammatory stimuli. Thus, a biomimetic nanoplatform with the capability of modulating inflammatory response in a microenvironment-responsive manner is attractive for regenerative therapy of periodontal tissue.

Methods

Herein, a facile and green design of engineered bone graft materials was developed by integrating a biomimetic apatite nanocomposite with a smart-release coating, which could realize inflammatory modulation by “on-demand” delivery of the anti-inflammatory agent through a pH-sensing mechanism.

Results

In vitro and in vivo experiments demonstrated that this biocompatible nanoplatform could facilitate the clearance of reactive oxygen species in human periodontal ligament stem cells under inflammatory conditions via inhibiting the production of endogenous proinflammatory mediators, in turn contributing to the enhanced healing efficacy of periodontal tissue. Moreover, this system exhibited effective antimicrobial activity against common pathogenic bacteria in the oral cavity, which is beneficial for the elimination of exogenous pro-inflammatory factors from bacterial infection during healing of periodontal tissue.

Conclusion

The proposed strategy provides a versatile apatite nanocomposite as a promising “inflammation scavenger” and propels the development of intelligent bone graft materials for periodontal and orthopedic applications.

Treatment of inflammatory bone loss in periodontitis by stem cell-derived exosomes

Periodontitis is the primary cause of tooth loss, but there is no effective treatment to repair inflammatory bone loss in periodontitis. Exosomes emerge as essential paracrine factors of mesenchymal stem cells (MSCs) that mediated tissue regeneration. Here, we investigated the potential of exosomes secreted by periodontal ligament stem cells (PDLSCs) as therapeutics for the bone defect in periodontitis. Exosomes secreted from PDLSCs derived from healthy periodontal ligaments (h-PDLSCs) and their function were evaluated on PDLSCs isolated from the inflammatory periodontal ligament of periodontitis patients (i-PDLSCs). Treatment of exosomes of h-PDLSCs led to an increase in the formation of mineralized nodules and the expressions of osteogenic genes and proteins in i-PDLSCs. Mechanistically, h-PDLSCs-exosomes suppressed the over-activation of canonical Wnt signaling to recover the osteogenic differentiation capacity of i-PDLSCs. To evaluate the therapeutic of exosomes on inflammatory bone loss, h-PDLSCs-exosomes loaded with Matrigel or β-TCP were employed to repair bone defects in rat models of periodontitis. Compared to the vehicle-treated control group, h-PDLSCs-exosomes-treated rats resulted in more bone formation in the defect of alveolar bone. In conclusion, these results demonstrated that exosomes derived from healthy PDLSCs could rescue the osteogenesis capacity of endogenous stem cells under an inflammatory environment and promote regeneration of alveolar bone. Our findings suggest that MSCs-derived exosome is an effective and practical cell-free MSC therapeutic for the treatment of periodontitis. STATEMENT OF SIGNIFICANCE: There is no effective treatment to repair inflammatory bone loss in periodontitis. As essential paracrine factors of PDLSCs, exosomes might mediate tissue regeneration during stem cell therapy. Here, we reported that exosomes secreted from healthy PDLSCs promoted the osteogenic differentiation of PDLSCs derived from periodontitis tissue. Healthy PDLSCs-exosomes treatment resulted in accelerated bone formation in the defect of alveolar bone in rat models of periodontitis. Mechanistically, h-PDLSCs-exosomes suppressed the over-activation of canonical Wnt signaling to recover the osteogenic differentiation capacity of inflammatory PDLSCs. These findings suggest that MSCs-derived exosome is an effective and practical cell-free MSC therapeutic for the treatment of periodontitis.

General Control Nonrepressed Protein 5 Modulates Odontogenic Differentiation Through NF-κB Pathway in Tumor Necrosis Factor-α-Mediated Impaired Human Dental Pulp Stem Cells

Dental pulp stem cells (DPSCs) from pulpitis patients showed defective osteogenic differentiation. However, as the most well-studied histone acetyltransferase, the impaired general control nonrepressed protein 5 (GCN5) plays essential roles in various developmental processes. The aim of this study was to investigate the effect of GCN5 on DPSCs odontogenic differentiation. The healthy dental pulp tissues were obtained from the extracted impacted third molar of patients with the informed consent. DPSCs were treated with a high concentration of tumor necrosis factor-alpha (TNF-α) (100 ng/mL) and odontogenic differentiation-related gene and GCN5 protein level by Western blot analysis. Proliferation of the DPSCs was evaluated using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Immunofluorescence staining detected GCN5 and NF-κB signaling for p-p65. The mechanism of GCN5 regulating odontogenic differentiation of DPSCs was determined by small interfering RNA analysis. Our data suggested that TNF-α can significantly reduce mineralization and the expression of dentin matrix acidic phosphoprotein 1 and dentin sialophosphoprotein at higher concentration (100 ng/mL). Meanwhile, it showed that the inflammation in microenvironment resulted in a downregulation of GCN5 expression and GCN5 knockdown caused decreased odontogenic differentiation of DPSCs was also found. In addition, the knockdown of GCN5 increased the expression of phosphorylation of p65, thus activating NF-κB pathway of DPSCs. Meanwhile, NF-κB pathway inhibitor pyrrolidinedithiocarbamic acid reversed the siGCN5 decreased odontogenic differentiation of DPSCs. Altogether, our findings indicated that in inflammatory microenvironments GCN5 plays a protective role in pulpitis impaired odontogenic differentiation of DPSCs by activating NF-κB pathway, which may provide a potential approach to dentin regeneration.

Stem Cell Therapy in Chronic Periodontitis: Host Limitations and Strategies

The treatment of chronic periodontitis is undergoing a transition from simple plaque removal and replacement with substitute materials to regenerative therapy, in which stem cells play an important role. Although stem cell-based periodontal reconstruction has been widely explored, few clinical regeneration studies have been reported. The inflammatory lesions under the impact of host factors such as local microbial–host responses, may impede the regenerative properties of stem cells and destroy their living microenvironment. Furthermore, systemic diseases, in particular diabetes mellitus, synergistically shape the disordered host-bacterial responses and exacerbate the dysfunction of resident periodontal ligament stem cells (PDLSCs), which ultimately restrain the capacity of mesenchymal stromal cells (MSCs) to repair the damaged periodontal tissue. Accordingly, precise regulation of an instructive niche has become a promising approach to facilitate stem cell-based therapeutics for ameliorating periodontitis and for periodontal tissue regeneration. This review describes host limitations and coping strategies that influence resident or transplanted stem cell-mediated periodontal regeneration, such as the management of local microbial–host responses and rejuvenation of endogenous PDLSCs. More importantly, we recommend that active treatments for systemic diseases would also assist in recovering the limited stem cell function on the basis of amelioration of the inflammatory periodontal microenvironment.

Ascorbic Acid/Retinol and/or Inflammatory Stimuli's Effect on Proliferation/Differentiation Properties and Transcriptomics of Gingival Stem/Progenitor Cells

The present study explored the effects of ascorbic-acid (AA)/retinol and timed inflammation on the stemness, the regenerative potential, and the transcriptomics profile of gingival mesenchymal stem/progenitor cells' (G-MSCs). STRO-1 (mesenchymal stem cell marker) immuno-magnetically sorted G-MSCs were cultured in basic medium (control group), in basic medium with IL-1β (1 ng/mL), TNF-α (10 ng/mL) and IFN-γ (100 ng/mL, inflammatory-medium), in basic medium with AA (250 µmol/L) and retinol (20 µmol/L) (AA/retinol group) or in inflammatory medium with AA/retinol (inflammatory/AA/retinol group; n = 5/group). The intracellular levels of phosphorylated and total β-Catenin at 1 h, the expression of stemness genes over 7 days, the number of colony-forming units (CFUs) as well as the cellular proliferation aptitude over 14 days, and the G-MSCs' multilineage differentiation potential were assessed. Next-generation sequencing was undertaken to elaborate on up-/downregulated genes and altered intracellular pathways. G-MSCs demonstrated all mesenchymal stem/progenitor cells characteristics. Controlled inflammation with AA/retinol significantly elevated NANOG (p < 0.05). The AA/retinol-mediated reduction in intracellular phosphorylated β-Catenin was restored through the effect of controlled inflammation (p < 0.05). Cellular proliferation was highest in the AA/retinol group (p < 0.05). AA/retinol counteracted the inflammation-mediated reduction in G-MSCs' clonogenic ability and CFUs. Amplified chondrogenic differentiation was observed in the inflammatory/AA/retinol group. At 1 and 3 days, the differentially expressed genes were associated with development, proliferation, and migration (FOS, EGR1, SGK1, CXCL5, SIPA1L2, TFPI2, KRATP1-5), survival (EGR1, SGK1, TMEM132A), differentiation and mineral absorption (FOS, EGR1, MT1E, KRTAP1-5, ASNS, PSAT1), inflammation and MHC-II antigen processing (PER1, CTSS, CD74) and intracellular pathway activation (FKBP5, ZNF404). Less as well as more genes were activated the longer the G-MSCs remained in the inflammatory medium or AA/retinol, respectively. Combined, current results point at possibly interesting interactions between controlled inflammation or AA/retinol affecting stemness, proliferation, and differentiation attributes of G-MSCs.

Remodeling the periodontitis microenvironment for osteogenesis by using a reactive oxygen species-cleavable nanoplatform

Modestly removing the excessive reactive oxygen species (ROS) plays a crucial role in regulating the microenvironment of periodontitis and provides favorable conditions for osteogenesis. However, the current strategy for scavenging ROS is not controllable, substantially limiting the outcomes in periodontitis. Herein, we introduced a controllable ROS-scavenging nanoplatform by encasing N-acetylcysteine (NAC, (a well-known ROS scavenger) into tailor-made ROS-cleavable amphiphilic polymer nanoparticles (PEG-ss-PCL NPs) as an intracellular delivery carrier. The existing ROS in the inflammatory microenvironment facilitated polymer degradation via breakage of thioketal bonds, and then led to encapsulated NAC release. NAC eliminated all ROS induced by lipopolysaccharide (LPS), while PssL-NAC adjusted the ROS level slightly higher than that of the control group. The percentage of apoptotic cells cultured with NAC and PssL-NAC decreased observably compared with that of cells cultured with 10 µg/ml LPS. The microenvironment regulated by PssL-NAC was highly suitable for osteogenic differentiation based on PCR and Western blot results, which showed higher expression levels of BMP2, Runx2, and PKA. Analysis of ALP activity and Alizarin red S staining showed consistent results. Additionally, the injection of PssL-NAC into the periodontitis area could alleviate the tissue destruction induced by ligation of the maxillary second molar. PssL-NAC showed a better ability to decrease osteoclast activity and inflammation, consequently improving the restoration of destroyed tissue. Our study suggests that ROS-responsive polymer nanoparticles loaded with NAC (PssL-NAC) can be new promising materials for the treatment of periodontitis. STATEMENT OF SIGNIFICANCE: More and more studies indicate that periodontal tissue damage is closely related to the high reactive oxygen species (ROS) environment. Excessive ROS will aggravate periodontal tissue damage and is not conducive to tissue repair. However, as an essential signal molecule in human physiological activities, ROS absence is also useless for tissue repair. In this study, we proposed to improve ROS imbalance in the environment of periodontitis as a strategy to promote periodontal regeneration and successfully synthesized a smart drug-releasing nanoplatform that can respond to ROS. Besides, we validated its ability to regulate the ROS environment and promote osteogenesis through experimental data in vivo and in vitro.

Periodontal ligament stem cells in the periodontitis niche: inseparable interactions and mechanisms

Periodontitis is characterized by the periodontium's pathologic destruction due to the host's overwhelmed inflammation to the dental plaque. The bacterial infections and subsequent host immune responses have shaped a distinct microenvironment, which generally affects resident periodontal ligament stem cells (PDLSCs). Interestingly, recent studies have revealed that impaired PDLSCs may also contribute to the disturbance of periodontal homeostasis. The putative vicious circle underlying the interesting "positive feedback" of PDLSCs in the periodontitis niche remains a hot research topic, whereas the inseparable interactions between resident PDLSCs and the periodontitis niche are still not fully understood. This review provides a microscopic view on the periodontitis progression, especially the quick but delicate immune responses to oral dysbacterial infections. We also summarize the interesting crosstalk of the resident PDLSCs with their surrounding periodontitis niche and potential mechanisms. Particularly, the microenvironment reduces the osteogenic properties of resident PDLSCs, which are closely related to their reparative activity. Reciprocally, these impaired PDLSCs may disrupt the microenvironment by aggravating the host immune responses, promoting aberrant angiogenesis, and facilitating the osteoclastic activity. We further recommend that more in-depth studies are required to elucidate the interactions of PDLSCs with the periodontal microenvironment and provide novel interventions for periodontitis.

Near-infrared 940-nm diode laser photobiomodulation of inflamed periodontal ligament stem cells

Photobiomodulation (PBM) is an acceptable method of stimulating stem cells through its non-invasive absorption by the cell photoreceptors and the induction of cellular response. The current research was aimed at evaluating the effect of near-infrared PBM on proliferation and osteogenic differentiation in inflamed periodontal ligament stem cells (I-PDLSCs). I-PDLSCs were isolated and characterized. Third passage cells were irradiated with 940-nm laser at an output power of 100 mW in a continuous wave. A fluence of 4 J/cm² in three sessions at 48-h intervals was applied and compared with non-irradiated controls. Cell viability and proliferation were evaluated by MTT assay. Alkaline phosphatase activity, quantitative Alizarin red staining test, and q-RT-PCR were used to evaluate the osteogenic properties of the I-PDLSCs in four groups of (a) osteogenic differentiation medium + laser (ODM + L), (b) osteogenic differentiation medium without laser (ODM), (c) non-osteogenic differentiation medium + laser (L), and (d) non-osteogenic differentiation medium (control). There was a non-significant increase in the viability of cells at 48- and 72-h post last laser irradiation. Alizarin red staining revealed no significant stimulatory effect of PBM at 14 and 21 days. However, alkaline phosphatase activity was significantly higher in the L + ODM group. Expression of osteogenic-related genes had a statistically significant increase at 21-day post irradiation. The irradiation used in the present study showed no significant increase in the proliferation of I-PDLSCs by PBM. However, expression levels of osteogenic-related genes and alkaline phosphatase activity were significantly increased in irradiated groups.

Gold Nanoparticles Combined Human β-Defensin 3 Gene-Modified Human Periodontal Ligament Cells Alleviate Periodontal Destruction via the p38 MAPK Pathway

Periodontitis is a chronic inflammatory disease with plaques as the initiating factor, which will induce the destruction of periodontal tissues. Numerous studies focused on how to obtain periodontal tissue regeneration in inflammatory environments. Previous studies have reported adenovirus-mediated human β-defensin 3 (hBD3) gene transfer could potentially enhance the osteogenic differentiation of human periodontal ligament cells (hPDLCs) and bone repair in periodontitis. Gold nanoparticles (AuNPs), the ideal inorganic nanomaterials in biomedicine applications, were proved to have synergetic effects with gene transfection. To further observe the potential promoting effects, AuNPs were added to the transfected cells. The results showed the positive effects of osteogenic differentiation while applying AuNPs into hPDLCs transfected by adenovirus encoding hBD3 gene. In vivo, after rat periodontal ligament cell (rPDLC) transplantation into SD rats with periodontitis, AuNPs combined hBD3 gene modification could also promote periodontal regeneration. The p38 mitogen-activated protein kinase (MAPK) pathway was demonstrated to potentially regulate both the in vitro and in vivo processes. In conclusion, AuNPs can promote the osteogenic differentiation of hBD3 gene-modified hPDLCs and periodontal regeneration via the p38 MAPK pathway.

Matrix metalloproteinase (MMP)-degradable tissue engineered periosteum coordinates allograft healing via early stage recruitment and support of host neurovasculature

Despite serving as the clinical "gold standard" treatment for critical size bone defects, decellularized allografts suffer from long-term failure rates of ~60% due to the absence of the periosteum. Stem and osteoprogenitor cells within the periosteum orchestrate autograft healing through host cell recruitment, which initiates the regenerative process. To emulate periosteum-mediated healing, tissue engineering approaches have been utilized with mixed outcomes. While vascularization has been widely established as critical for bone regeneration, innervation was recently identified to be spatiotemporally regulated together with vascularization and similarly indispensable to bone healing. Notwithstanding, there are no known approaches that have focused on periosteal matrix cues to coordinate host vessel and/or axon recruitment. Here, we investigated the influence of hydrogel degradation mechanism, i.e. hydrolytic or enzymatic (cell-dictated), on tissue engineered periosteum (TEP)-modified allograft healing, especially host vessel/nerve recruitment and integration. Matrix metalloproteinase (MMP)-degradable hydrogels supported endothelial cell migration from encapsulated spheroids whereas no migration was observed in hydrolytically degradable hydrogels in vitro, which correlated with increased neurovascularization in vivo. Specifically, ~2.45 and 1.84-fold, and ~3.48 and 2.58-fold greater vessel and nerve densities with high levels of vessel and nerve co-localization was observed using MMP degradable TEP (MMP-TEP) -modified allografts versus unmodified and hydrolytically degradable TEP (Hydro-TEP)-modified allografts, respectively, at 3 weeks post-surgery. MMP-TEP-modified allografts exhibited greater longitudinal graft-localized vascularization and endochondral ossification, along with 4-fold and 2-fold greater maximum torques versus unmodified and Hydro-TEP-modified allografts after 9 weeks, respectively, which was comparable to that of autografts. In summary, our results demonstrated that the MMP-TEP coordinated allograft healing via early stage recruitment and support of host neurovasculature.

The protective effect of tetrahedral framework nucleic acids on periodontium under inflammatory conditions

Periodontitis is a common disease that causes periodontium defects and tooth loss. Controlling inflammation and tissue regeneration are two key strategies in the treatment of periodontitis. Tetrahedral framework nucleic acids can modulate multiple biological behaviors, and thus, their biological applications have been widely explored. In this study, we investigated the effect of tFNAs on periodontium under inflammatory conditions. Lipopolysaccharide and silk ligature were used to induce inflammation in vivo and in vitro. The results displayed that tFNAs decreased the release of pro-inflammatory cytokines and levels of cellular reactive oxygen species in periodontal ligament stem cells, which promoted osteogenic differentiation. Furthermore, animal experiments showed that tFNAs ameliorated the inflammation of the periodontium and protect periodontal tissue, especially reducing alveolar bone absorption by decreasing inflammatory infiltration and inhibiting osteoclast formation. These findings suggest that tFNAs can significantly improve the therapeutic effect of periodontitis and have the great potential significance in the field of periodontal tissue regeneration.

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tFNAs decreased the release of pro-inflammatory cytokines and promoted osteogenic differentiation.

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tFNAs ameliorated the inflammation of the periodontium and protect periodontal tissue.

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tFNAs can significantly improve the therapeutic effect of periodontitis.

Ascorbic Acid, Inflammatory Cytokines (IL-1β/TNF-α/IFN-γ), or Their Combination's Effect on Stemness, Proliferation, and Differentiation of Gingival Mesenchymal Stem/Progenitor Cells

Objective

Ascorbic acid (AA) and controlled inflammatory stimuli are postulated to possess the ability to independently exert positive effects on a variety of proliferative, pluripotency, and differentiation attributes of gingival mesenchymal stem/progenitor cells (G-MSCs). The current study's objective was to explore and compare for the first time the impact of the major inflammatory cytokines (IL-1β/TNF-α/IFN-γ), AA, or their combination on multipotency/pluripotency, proliferative, and differentiation characteristics of G-MSCs.

Design

Human G-MSCs (n = 5) were isolated and cultured in basic medium (control group), in basic medium with major inflammatory cytokines; 1 ng/ml IL-1β, 10 ng/ml TNF-α, and 100 ng/ml IFN-γ (inflammatory group), in basic medium with 250 μmol/l AA (AA group) and in inflammatory medium supplemented by AA (inflammatory/AA group). All media were renewed three times per week. In stimulated G-MSCs intracellular β-catenin at 1 hour, pluripotency gene expression at 1, 3, and 5 days, as well as colony-forming units (CFUs) ability and cellular proliferation over 14 days were examined. Following a five-days stimulation in the designated groups, multilineage differentiation was assessed via qualitative and quantitative histochemistry as well as mRNA expression.

Results

β-Catenin significantly decreased intracellularly in all experimental groups (p = 0.002, Friedman). AA group exhibited significantly higher cellular counts on days 3, 6, 7, and 13 (p < 0.05) and the highest CFUs at 14 days [median-CFUs (Q25/Q75); 40 (15/50), p = 0.043]. Significantly higher Nanog expression was noted in AA group [median gene-copies/PGK1 (Q25/Q75); 0.0006 (0.0002/0.0007), p < 0.01, Wilcoxon-signed-rank]. Significant multilineage differentiation abilities, especially into osteogenic and chondrogenic directions, were further evident in the AA group.

Conclusions

AA stimulation enhances G-MSCs' stemness, proliferation, and differentiation properties, effects which are associated with a Wnt/β-catenin signaling pathway activation. Apart from initially boosting cellular metabolism as well as Sox2 and Oct4A pluripotency marker expression, inflammation appeared to attenuate these AA-induced positive effects. Current results reveal that for AA to exert its beneficial effects on G-MSCs' cellular attributes, it requires to act in an inflammation-free microenvironment.

Short- and long-term treatment with TNF-α inhibits the induction of osteoblastic differentiation in cyclic tensile-stretched periodontal ligament fibroblasts

Background

Cyclic tensile stretching (CTS) induces osteoblastic differentiation of periodontal ligament fibroblasts (PDLF). On the other hand, increased concentrations of tumour necrosis factor-α (TNF-α) are found in inflammatory conditions, leading to periodontal disease and tooth loss. Accordingly, our aim was to investigate the short- and long-term effect of TNF-α on the response of human PDLF to CTS and its implication on osteoblastic differentiation.

Methods

PDLF were either pre-incubated for 4 hours or were repeatedly exposed to TNF-α for up to 50 days and then subjected to CTS. Gene expression was determined by quantitative real-time polymerase chain reaction. Activation of mitogen-activated protein kinase (MAPK) was monitored by western analysis and cell proliferation by bromodeoxyuridine incorporation. Intracellular reactive oxygen species were determined by the 2´, 7´-dichlorofluorescein-diacetate assay and osteoblastic differentiation by Alizarin Red-S staining after an osteo-inductive period of 21 days.

Results

CTS of PDLF induced an immediate upregulation of the c-fos transcription factor and, further downstream the overexpression of alkaline phosphatase and osteopontin, two major osteoblast marker genes. A 4-hour pre-incubation with TNF-α repressed these effects. Similarly, long-term propagation of PDLF along with TNF-α diminished their osteoblastic differentiation capacity and suppressed cells’ CTS-elicited responses. The observed phenomena were not linked with TNF-α-induced premature senescence or oxidative stress. While CTS induced the activation of MAPKs, involved in mechanotransduction, TNF-α treatment provoked a small delay in the phosphorylation of extracellular signal-regulated kinase and c-Jun N-terminal kinase.

Conclusion

Increased concentrations of TNF-α, such as those recorded in many inflammatory diseases, suppress PDLF’s immediate responses to mechanical forces compromising their osteoblastic differentiation potential, possibly leading to tissue’s impaired homeostasis.

Human β-defensin 3 gene modification promotes the osteogenic differentiation of human periodontal ligament cells and bone repair in periodontitis

Efforts to control inflammation and achieve better tissue repair in the treatment of periodontitis have been ongoing for years. Human β-defensin 3, a broad-spectrum antimicrobial peptide has been proven to have a variety of biological functions in periodontitis; however, relatively few reports have addressed the effects of human periodontal ligament cells (hPDLCs) on osteogenic differentiation. In this study, we evaluated the osteogenic effects of hPDLCs with an adenoviral vector encoding human β-defensin 3 in an inflammatory microenvironment. Then human β-defensin 3 gene-modified rat periodontal ligament cells were transplanted into rats with experimental periodontitis to observe their effects on periodontal bone repair. We found that the human β-defensin 3 gene-modified hPDLCs presented with high levels of osteogenesis-related gene expression and calcium deposition. Furthermore, the p38 MAPK pathway was activated in this process. In vivo, human β-defensin 3 gene-transfected rat PDLCs promoted bone repair in SD rats with periodontitis, and the p38 mitogen-activated protein kinase (MAPK) pathway might also have been involved. These findings demonstrate that human β-defensin 3 accelerates osteogenesis and that human β-defensin 3 gene modification may offer a potential approach to promote bone repair in patients with periodontitis.

Hyperbaric Oxygen Therapy Improves the Osteogenic and Vasculogenic Properties of Mesenchymal Stem Cells in the Presence of Inflammation In Vitro

Hyperbaric oxygen (HBO) therapy has been reported to be beneficial for treating many conditions of inflammation-associated bone loss. The aim of this work was to in vitro investigate the effect of HBO in the course of osteogenesis of human Mesenchymal Stem Cells (MSCs) grown in a simulated pro-inflammatory environment. Cells were cultured with osteogenic differentiation factors in the presence or not of the pro-inflammatory cytokine Tumor Necrosis Factor-α (TNF-α), and simultaneously exposed daily for 60 min, and up to 21 days, at 2,4 atmosphere absolute (ATA) and 100% O₂. To elucidate osteogenic differentiation-dependent effects, cells were additionally pre-committed prior to treatments. Cell metabolic activity was evaluated by means of the MTT assay and DNA content quantification, whereas osteogenic and vasculogenic differentiation was assessed by quantification of extracellular calcium deposition and gene expression analysis. Metabolic activity and osteogenic properties of cells did not differ between HBO, high pressure (HB) alone, or high oxygen (HO) alone and control if cells were pre-differentiated to the osteogenic lineage. In contrast, when treatments started contextually to the osteogenic differentiation of the cells, a significant reduction in cell metabolic activity first, and in mineral deposition at later time points, were observed in the HBO-treated group. Interestingly, TNF-α supplementation determined a significant improvement in the osteogenic capacity of cells subjected to HBO, which was not observed in TNF-α-treated cells exposed to HB or HO alone. This study suggests that exposure of osteogenic-differentiating MSCs to HBO under in vitro simulated inflammatory conditions enhances differentiation towards the osteogenic phenotype, providing evidence of the potential application of HBO in all those processes requiring bone regeneration.

Synergistic Effect of Matrix Stiffness and Inflammatory Factors on Osteogenic Differentiation of MSC

Mesenchymal stem cells (MSCs) in vivo reside in a complex microenvironment. Changes of both biochemical and biophysical cues in the microenvironment caused by inflammation affect the differentiation behaviors of MSCs. Most studies, however, only focus on either biochemical or biophysical cues, although the synergistic effect of matrix stiffness and inflammatory factors on osteogenic differentiation of MSCs has not been explored yet. Here, we showed that there was a matrix stiffness-dependent modulation in the osteogenic differentiation of human MSCs (hMSCs) with higher matrix stiffness favoring osteogenesis bias. However, when interleukin-1 β (IL-1β) was added, the osteogenic differentiation of hMSCs was suppressed, which was independent of increasing matrix stiffness. Both experimental observations and mathematical modeling confirmed that matrix stiffness and IL-1β could activate the ERK1/2 signaling and contribute to osteogenic differentiation. The p38 signaling activated by IL-1β has a strong role in inhibiting osteoblastic differentiation, thus diminishing the vital effect of ERK1/2 signaling. In addition, sensitivity analysis of the model parameters revealed that activation/deactivation dynamics of sensitive factors (e.g., FAK, ERK, and p38) also played a key role in the synergistic effect of matrix stiffness and IL-1β on the osteogenic differentiation of hMSCs. The outcomes of this study provide new insights into the synergistic effect of biochemical and biophysical microenvironments on regulating MSC differentiation.

LncRNA-TWIST1 Promoted Osteogenic Differentiation Both in PPDLSCs and in HPDLSCs by Inhibiting TWIST1 Expression

HPDLSCs derived from periodontal ligament tissues contribute to tooth development and tissue regeneration. Exploring the effects of long noncoding RNAs (lncRNAs) in the process of osteogenic differentiation of periodontal ligament stem cells would provide novel therapeutic strategies for tissue regeneration. The expression levels of lncRNA, which significantly changed during osteogenic differentiation, were observed by real-time quantitative PCR (q-PCR). Then, we screened for osteogenic-related lncRNA, which was initially named lncRNA-TWIST1. Moreover, we detected the mRNA expression levels of TWIST1 and osteogenesis-related genes after upregulating and downregulating lncRNA-TWIST1 in PPDLSCs (periodontal mesenchymal stem cells from periodontitis patients) and HPDLSCs (periodontal mesenchymal stem cells from healthy microenvironment), respectively. The osteogenic degree was verified by detecting ALP activity and alizarin red staining. LncRNA-TWIST1 decreased the mRNA levels of TWIST1 and promoted osteogenic differentiation in PPDLSCs, which was confirmed by the increase in osteogenesis-related gene levels (Runx2, ALP, and OCN), the increase in ALP activity, and the formation of more osteogenic nodules. In contrast, downregulating lncRNA-TWIST1 decreased the expression of osteogenesis-related genes, ALP activity, and osteogenic nodules both in PPDLSCs and in HPDLSCs. LncRNA-TWIST1 promoted osteogenic differentiation both in PPDLSCs and in HPDLSCs by inhibiting the TWIST1 expression. LncRNA-TWIST1 may be a novel therapeutic strategy to regenerate dental tissues.

[Effects of tumor necrosis factor-α on osteogenic differentiation and Notch signaling pathway in human periodontal ligament stem cells]

OBJECTIVE

To evaluate the effects of tumor necrosis factor-α (TNF-α) on osteogenic differentiation and Notch signaling pathway of periodontal ligament stem cells (PDLSCs) and to investigate the regulatory role of Notch signaling pathway on the osteogenic differentiation of PDLSCs under the influence of TNF-α.

METHODS

PDLSCs were obtained through enzyme digestion and tissue block method. The expression levels of stem cell surface markers CD105, CD90, CD146, CD45, and CD31 were detected by fluorescence activated cell sorter (FACS). PDLSCs were divided into experimental (10 ng·mL⁻¹ TNF-α) and control groups (0 ng·mL⁻¹ TNF-α). The proliferation ability of PDLSCs was detected using cell counting kit-8 (CCK-8). The effect of TNF-α on the osteogenic ability of PDLSCs were tested by measuring alkaline phosphatase (ALP) activity and conducting alizarin red staining and quantitative real-time polymerase chain reaction (PCR). We tested Notch signal pathway receptors Notch1, Notch2, ligand JAG1, JGA2, and downstream gene Hes-1. Changes in DLL1 expression were detected by quantitative real-time PCR.

RESULTS

FACS profiling showed that PDLSCs were strongly positive for CD105, CD90, and CD146 but negative for CD45 and CD31. CCK-8 results showed that TNF-α could promote the proliferation of PDLSCs (P<0.05). ALP activity in the experimental group was lower than that in the control group (P<0.05). Alizarin red staining showed that the experimental group had decreased mineralized nodules as compared with the control group. Quantitative real-time PCR results showed that the mRNA expression of osteogenic marker genes cementum attachment protein (CAP), osteopontin (OPN), and Runt-related transcription factor 2 (Runx2) significantly decreased in the experimental group as compared with those in the control group (P<0.05). The expression levels of Notch1, Notch2, JAG1, JGA2 and Hes-1 were significantly decreased (P<0.05), whereas those of Notch3 and DLL1 were increased in Notch signaling pathway-related molecules (P<0.05).

CONCLUSIONS

TNF-α can promote PDLSCs proliferation and inhibit bone differentiation and Notch signaling pathway expression, indicating that the Notch signaling pathway regulates PDLSCs osteogenic differentiation.

Effect of tumor necrosis factor α on ability of SHED to promote osteoclastogenesis during physiological root resorption

Physiological root resorption of deciduous teeth is a normal phenomenon, however, the potential mechanisms underlying this process remain unclear. This study aimed to investigate ability of stem cells from human exfoliated deciduous teeth (SHED) on promoting the osteoclastic differentiation of osteoclast precursors and clarify mechanisms underlying this process in vitro. SHED and dental pulp stem cells (DPSCs) were obtained from deciduous teeth and healthy permanent teeth. An indirect co-culture system of SHED or DPSCs were used. The osteoclast precursor peripheral blood mononuclear cells (PBMCs) were established. Ability of SHED and DPSCs in promoting osteoclastogenesis was determined using triiodothyronine receptor auxiliary protein (TRAP) staining, real-time real-time PCR (RT-PCR) and western blotting. The effect of inflammation on the pro-osteoclastogenesis ability of SHED was determined using enzyme linked immunosorbent assay (ELISA), RT-PCR and western blotting. The function of the nuclear factor-κB (NF-κB) pathway in promoting the osteoclastogenesis ability of SHED was determined using RT-PCR and western blotting. SHED exhibited an increased ability to promote osteoclastic differentiation. Expression of tumor necrosis factor-α (TNF-α) was significantly higher in SHED than in DPSCs. Expression of cathepsin K (CTSK), TRAP, and receptor-activator of nuclear-factor-κ B ligand (RANKL), RANKL/osteoprotegerin (OPG) ratio, and expression of cytoplasmic phosphorylated inhibitor of NF-κB α (p-IκBα) and nuclear p65 were markedly up-regulated in SHED post the TNF-α treatment but decreased following NF-κB inhibition. In conclusion, inflammatory cytokine TNF-α appeared to activate NF-κB pathway to up-regulate expression of NF-κB, enhancing ability of SHED in promoting osteoclastogenesis via regulating RANKL/OPG expression.

The periodontal stem/progenitor cell inflammatory-regenerative cross talk: A new perspective

Adult multipotent stem/progenitor cells, with remarkable regenerative potential, have been isolated from various components of the human periodontium. These multipotent stem/progenitor cells include the periodontal ligament stem/progenitor cells (PDLSCs), stem cells from the apical papilla (SCAP), the gingival mesenchymal stem/progenitor cells (G-MSCs), and the alveolar bone proper stem/progenitor cells (AB-MSCs). Whereas inflammation is regarded as the reason for tissue damage, it also remains a fundamental step of any early healing process. In performing their periodontal tissue regenerative/reparative activity, periodontal stem/progenitor cells interact with their surrounding inflammatory micro-environmental, through their expressed receptors, which could influence their fate and the outcome of any periodontal stem/progenitor cell-mediated reparative/regenerative activity. The present review discusses the current understanding about the interaction of periodontal stem/progenitor cells with their surrounding inflammatory micro-environment, elaborates on the inflammatory factors influencing their stemness, proliferation, migration/homing, differentiation, and immunomodulatory attributes, the possible underlying intracellular mechanisms, as well as their proposed relationship to the canonical and noncanonical Wnt pathways.

ELP2 negatively regulates osteoblastic differentiation impaired by tumor necrosis factor α in MC3T3-E1 cells through STAT3 activation

Tumor necrosis factor‐α (TNF‐α) is a pluripotent signaling molecule. The biological effect of TNF‐α includes slowing down osteogenic differentiation, which can lead to bone dysplasia in long‐term inflammatory microenvironments. Signal transducer and activator of transcription 3 (STAT3)‐interacting protein 1 (StIP1, also known as elongator complex protein 2, ELP2) play a role in inhibiting TNF‐α‐induced osteoblast differentiation. In the present study, we investigated whether and how ELP2 activation mediates the effects of TNF‐α on osteoblastic differentiation. Using in vitro cell cultures of preosteoblastic MC3T3‐E1 cells, we found that TNF‐α inhibited osteoblastic differentiation accompanied by an increase in ELP2 expression and STAT3 activation. Forced ELP2 expression inhibited osteogenic differentiation of MC3T3‐E1 cells, with a decrease in the expression of osteoblast marker genes, alkaline phosphatase activity, and matrix mineralization capacity. In contrast, ELP2 silencing ameliorated osteogenic differentiation in MC3T3‐E1 cells, even after TNF‐α stimulation. The TNF‐α‐induced inhibitory effect on osteoblastic differentiation was therefore mediated by ELP2, which was associated with Janus kinase 2 (JAK2)/STAT3 activation. These results suggest that ELP2 is upregulated at the differentiation of MC3T3‐E1 cells into osteoblasts and inhibits osteogenic differentiation in response to TNF‐α through STAT3 activation.

Retinol/inflammation affect stemness and differentiation potential of gingival stem/progenitor cells via Wnt/β-catenin

BACKGROUND AND OBJECTIVE

Inflammatory cytokines impact the course of periodontal disease, repair, and regeneration. Vitamin A and its metabolites are inflammation-modulatory biomolecules, affecting cellular pluripotency. The aim of this study was to investigate the effect of retinol and periodontal inflammatory cytokines (IL-1β/TNF-α/IFN-γ) on pluripotency and proliferative properties of gingival mesenchymal stem/progenitor cells (G-MSCs), for the first time.

MATERIAL AND METHODS

Human G-MSCs (n = 5) were STRO-1 immuno-magnetically sorted, characterized and expanded in basic medium (control group), in basic medium with IL-1β (1 ng/mL), TNF-α (10 ng/mL), and IFN-γ (100 ng/mL) (inflammatory group), in basic medium with retinol (20 μmol/L) (retinol group) and with retinol added to the inflammatory group (inflammatory/retinol group). β-catenin levels at 1 hour, cellular proliferation over 14 days, and colony-forming units (CFUs) at 14 days were investigated. Pluripotency gene expressions were examined at 1, 3, and 5 days via reverse transcription-polymerase chain reaction (RT-PCR). Multilineage differentiation potential was evaluated, following 5 days priming, using qualitative and quantitative histochemistry and RT-PCR.

RESULTS

G-MSCs were CD14^- , CD34^- , CD45^- , CD73⁺ , CD90⁺ , CD105⁺ , and showed mesenchymal stem/progenitor cells' hallmarks, CFUs, and multilineage differentiation potential. Intracellular β-catenin significantly declined in the stimulated groups (P < 0.001, Friedman test). Cellular proliferation at 72 hours was most prominent in the control and inflammatory group [Median cell numbers (Q25/Q75); 6806 (4983/7312) and 5414 (4457/7230), respectively], followed by an upsurge in the retinol group. At 14 days, the retinol group exhibited the highest CFUs [Median CFUs (Q25/Q75); 35 (20/58), P = 0.043, Wilcoxon signed-rank]. Nanog was most expressed in the inflammatory and retinol group [Median gene expression/PGK1 (Q25/Q75); 0.0006 (0.0002/0.0014) and 0.0005 (0.0003/0.0008)]. Inflammation significantly upregulated Sox2 expression [0.0002 (0.0008/0.0005)], while its expression was diminished in the retinol and inflammatory/retinol group (P < 0.001, Friedman test). Inflammatory/retinol group exhibited the highest multilineage differentiation potential.

CONCLUSION

Controlled short-term inflammatory/retinol stimuli activate the Wnt/β-catenin pathway, affecting G-MSCs' pluripotency, proliferation, and differentiation. The present findings provide further insights into the inflammatory-regenerative interactions and their modulation potential for G-MSCs-mediated periodontal repair/regeneration.

MicroRNA-224 enhances the osteoblastic differentiation of hMSCs via Rac1

Osteogenesis is the differentiation of mesenchymal stem cells (MSCs) into osteoblasts. MicroRNAs (miRNAs) are short noncoding RNAs that target specific genes to mediate translational activities. In this study, we investigated how miR-224 regulates the osteoblastic differentiation of human MSCs (hMSCs) as well as the underlying mechanism. The results revealed the upregulation of miR-224 during hMSC differentiation. In vitro experiments showed that the downregulation of miR-224 suppressed the differentiation of hMSCs into osteoblasts. However, upregulation of miR-224 was concomitant with increased expression of relevant genes and augmented activity of alkaline phosphatase. Furthermore, the results indicated that Rac1 acted as the bona fide target of miR-224 and that Rac1 depletion promoted osteogenic differentiation in miR-224-silenced hMSCs. In addition, we found that both JAK/STAT3 and Wnt/β-catenin pathways were repressed by Rac1 depletion using quantitative reverse transcription polymerase chain reaction (qRT-PCR), western blotting, and immunofluorescence. Our data indicate a novel molecular mechanism in relation to hMSCs differentiation into osteoblasts, which may facilitate bone anabolism via miR-224. SIGNIFICANCE OF THE STUDY: In this study, we mainly explored the effects of miR-224 on hMSCs differentiation into osteoblasts. We find that induced miR-224 expression in hMSCs is considered closely associated with specific osteogenesis-related genes, alkaline phosphatase activity, and matrix mineralization, indicating that miR-224 may serve as a promising biomarker for osteogenic differentiation. Our data indicate a novel molecular mechanism in relation to hMSCs differentiation into osteoblasts, which may facilitate bone anabolism via miR-224.

miR-26b modulates OA induced BMSC osteogenesis through regulating GSK3β/β-catenin pathway

BACKGROUNDS

Osteoactivin (OA) is a key regulator promoting bone marrow stromal cells osteogenesis progress, while Dexamethasone (Dex) could inhibit OA induced osteogenesis and lead to osteoporosis. miR-26b increased during BMSC osteogenesis but whether it participates in this progress is enigma. Osteogenesis is under regulation of canonical Wnt signaling pathway which could serve as potential target for miR-26b. It bears therapeutic potential if miR-26b could regulate osteogenesis and antagonize Dex induced Osteoporosis (OP).

METHODS

BMSC were isolated from bone marrow of rats and induced for osteogenesis by OA administration. We detected miR-26b mRNA level together with osteogenesis related genes or Wnt signal pathway related genes by qRT-PCR. BMSC cells with miR-26b inhibitor or mimics revealed the effect of miR-26b on osteogenesis. The osteogenesis efficiency was detected by Alizarin Red staining and ALP activity. Protein level of canonical Wnt signal pathway and other proteins were detected by Western blot. The interaction between miR-26b and GSK3β was detected by dual luciferase reporter assay.

RESULTS

We found that miR-26b was increased during OA induced BMSC osteogenesis. Inhibiting miR-26b could lead to osteogenesis inhibition while miR-26b mimics could promote this progress. The key regulator of Wnt signal pathway GSK3β is down-regulated when miR-26b was overexpressed, resulting in β-catenin activation. Since Dex could promote GSK3β expression and inhibit Wnt signal, miR-26b could also alleviate Dex induced osteogenesis inhibition.

CONCLUSION

Our findings indicate that miR-26b promoted BMSC osteogenesis by directly targeting GSK3β and activating canonical Wnt signal pathway, suggesting miR-26b might be serve as potential therapeutic candidate of osteoporosis.

Role of the P2X7 receptor in inflammation-mediated changes in the osteogenesis of periodontal ligament stem cells

Accumulating evidence indicates that the pluripotency of periodontal ligament stem cells (PDLSCs) is compromised under inflammatory conditions; however, the underlying mechanisms remain largely unexplored. In this study, we hypothesize that the P2X7 receptor (P2X7R) is a key molecule linked to inflammation-associated impairment of PDLSCs. We first investigated P2X7R expression in PDLSCs under normal and inflammatory conditions and then determined the effect of a P2X7R agonist (BzATP) or antagonist (BBG) on PDLSC osteogenesis under various conditions. Gene-modified PDLSCs were used to further examine the role of P2X7R and the signaling pathway underlying P2X7R-enhanced osteogenesis. We found that inflammatory conditions decreased P2X7R expression in PDLSCs and reduced osteogenesis in these cells. In addition, activation of P2X7R by BzATP or overexpression of P2X7R via gene transduction reversed the inflammation-mediated decrease in PDLSC osteogenic differentiation. When selected osteogenesis-related signaling molecules were screened, the PI3K-AKT-mTOR pathway was identified as potentially involved in P2X7R-enhanced PDLSC osteogenesis. Our data reveal a crucial role for P2X7R in PDLSC osteogenesis under inflammatory conditions, suggesting a new therapeutic target to reverse or rescue inflammation-mediated changes in PDLSCs for future mainstream therapeutic uses.

Resveratrol enhances the functionality and improves the regeneration of mesenchymal stem cell aggregates

Mesenchymal stem cell (MSC)-based regeneration, specifically cell aggregate or cell sheet engineering, is a promising approach for tissue reconstruction. Considering the advantages of ease of harvest and lack of immune rejection, the application of autologous MSCs (i.e., patients' own MSCs) in regenerative medicine has developed considerable interest. However, the impaired cell viability and regenerative potential following MSCs impacted by disease remain a major challenge. Resveratrol (RSV) exhibits reliable and extensive rejuvenative activities that have received increasing clinical attention. Here, we uncovered that resveratrol enhances the functionality and improves the regeneration of mesenchymal stem cell aggregates. Periodontal ligament MSCs (PDLSCs) from normal control subjects (N-PDLSCs) and periodontitis patients (P-PDLSCs) were investigated. Compared to N-PDLSCs, P-PDLSCs were less capable of forming cell aggregates, and P-PDLSC aggregates showed impaired osteogenesis and regeneration. These functional declines could be mimicked in N-PDLSCs by tumor necrosis factor alpha (TNF-α) treatment. Notably, a TNF-α-induced functional decline in N-PDLSC aggregates was rescued by RSV application. More importantly, in both N-PDLSCs and P-PDLSCs, RSV promoted cell aggregate formation and improved their osteogenic potential. Furthermore, as proven ectopically in vivo, the tissue regenerative capability of P-PDLSC aggregates was also enhanced after RSV treatment during aggregate formation in vitro. Finally, in a rat in situ regeneration model, we successfully applied both N-PDLSC aggregates and P-PDLSC aggregates to repair periodontal defects upon long-term functional improvements by RSV preconditioning. Together, our data unravel a novel methodology for using pharmacology (i.e., RSV)-based cell aggregate engineering to improve the functionality and facilitate the regeneration of MSCs from both healthy and inflammatory microenvironments, shedding light on improving the application of autologous MSC-mediated regenerative medicine.

Concentration-dependent, dual roles of IL-10 in the osteogenesis of human BMSCs via P38/MAPK and NF-κB signaling pathways

Microenvironmental conditions can influence the differentiation and functional roles of mesenchymal stem cells (MSCs). Recent studies have suggested that an inflammatory microenvironment can significantly affect the osteogenic differentiation of MSCs. Here, we show, for the first time, that IL-10 has concentration-dependent, dual roles in the osteogenesis of human bone marrow mesenchymal stem cells (hBMSCs). Low physiologic concentrations of IL-10 (0.01-1.0 ng/ml) activate the p38/MAPK signaling pathway to promote the osteogenesis of hBMSCs, but higher pathologic doses of IL-10 (10-100 ng/ml) inhibit p38/MAPK signaling by activating NF-κB, inhibiting osteogenesis. These results demonstrate that p38/MAPK and NF-κB signaling mediates the double-edged sword effect of IL-10 on hBMSCs. The osteogenic impairment was reversed at higher doses of IL-10 when cells were supplemented with the NF-κB inhibitor BAY11-7082. These data provide important insights into the regulatory effects of IL-10 on the biologic behavior of hBMSCs.-Chen, E., Liu, G., Zhou, X., Zhang, W., Wang, C., Hu, D., Xue, D., Pan, Z. Concentration-dependent, dual roles of IL-10 in the osteogenesis of human BMSCs via P38/MAPK and NF-κB signaling pathways.

Exposure to reversine affects the chondrocyte morphology and phenotype in vitro

Articular chondrocytes derived from osteoarthritic tissues (OA HAC) show a severely reduced chondrogenic commitment. This impairment undermines their use for tissue-engineered cartilage repair, which relies on cell proliferation and growth to meet therapeutic needs, but also on efficient cell plasticity to recover the chondrogenic phenotype. Reversine (Rev), a 2,6-disubstituted purine inhibitor of spindle-assembly checkpoints, was described to convert differentiated mesenchymal cells to their undifferentiated precursors. We hypothesized that Rev exposure could divert OA HAC to more plastic cells, re-boosting their subsequent commitment. HAC were enzymatically released from OA cartilage specimens, expanded for 2 weeks and treated with 5 μm Rev in dimethylsulphoxide (DMSO) or with DMSO alone for 6 days. Cell growth was assessed using the AlamarBlue^TM assay. Cytoskeletal structure, endoproliferation and caspase-3-immunopositivity were assayed by epifluorescence microscopy. The OA HAC chondrogenic performance was evaluated by quantitative reverse transcription-polymerase chain reaction (RT-PCR) for glyceraldehyde-3-phosphate dehydrogenase, Sox9, Aggrecan (Agg), type II collagen (Col2), Ki67, cyclinD1, transforming growth factor-β1 (TGF-β1), -2 and -3, interleukin-1β (IL-1β) and -6 , SMAD3 and -7, and vascular endothelial growth factor. Rev-treated OA HAC recovered polygonal morphology and reduced Ki67 expression and proliferation. Cell-cycle impairment accounted for altered cytoskeletal organization, endoproliferation and apoptosis, whereas a compensatory mechanism sustained the increased cyclinD1 transcript levels. Sox9, Agg and TGFs were overexpressed, but not Col2. IL transcripts were massively downregulated. These events were dose-related and transient. Overall, in spite of a higher Rev-induced transcriptional activity for extracellular matrix components and in spite of a Rev-treated cell phenotype closer to that of the three-dimensional native articular chondrocyte, Rev effects seem unleashed from a full regained chondrogenic potential.

Tumor necrosis factor-alpha inhibits osteogenic differentiation of pre-osteoblasts by downregulation of EphB4 signaling via activated nuclear factor-kappaB signaling pathway

BACKGROUND AND OBJECTIVE

The majority of experiments show that tumor necrosis factor-alpha (TNF-α) inhibits osteogenic differentiation of mesenchymal stem cells and pre-osteoblasts by activated nuclear factor-kappaB (NF-κB) signaling. However, the underlying mechanisms by which NF-κB signaling inhibits osteogenic differentiation are not fully understood. The aim of the present study was to investigate whether EphB4 signaling inhibition mediates the effects of TNF-α-activated NF-κB signaling on osteogenic differentiation of pre-osteoblasts.

MATERIAL AND METHODS

Murine MC3T3-E1 pre-osteoblasts were treated with 10 ng/mL of TNF-α. NF-κB inhibitor, pyrrolidine dithiocarbamate, was used to achieve NF-κB signaling inhibition. EphB4 signaling was activated using ephrinB2-fc. The mRNA expressions of runt related transcription factor 2 (Runx2), bone sialoprotein (BSP) and EphB4 were determined using reverse transcription-polymerase chain reaction. The protein levels of Runx2, BSP, Col Ia1, osteopontin, EphB4, p-NF-κB p65 and NF-κB p65 were evaluated using western blot assays. Alkaline phosphatase (ALP) activity in MC3T3-E1 cells was evaluated by ALP activity kit, and mineral nodule formation was evaluated by Alizarin Red S staining.

RESULTS

TNF-α inhibited EphB4 expression, while it suppressed Runx2, BSP expression from gene and protein levels as well as ALP activity and mineral nodule formation in MC3T3-E1 cells. Activation of EphB4 signaling by ephrinB2-fc promoted osteogenic differentiation of MC3T3-E1 cells, whereas TNF-α impaired the osteogenic differentiation enhanced by ephrinB2-fc. Pyrrolidine dithiocarbamate blocked the activation of NF-κB signaling induced by TNF-α, while it prevented the downregulation of Runx2, BSP and EphB4, induced by TNF-α.

CONCLUSION

TNF-α inhibits osteogenic differentiation of pre-osteoblasts by downregulation of EphB4 signaling via activated NF-κB signaling pathway.

[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.

Periodontal Ligament Stem Cells in the Periodontitis Microenvironment Are Sensitive to Static Mechanical Strain

During orthodontic treatment, periodontium remodeling of periodontitis patients under mechanical force was abnormal. We have previously confirmed the function impairment of periodontal ligament stem cells (PDLSCs) in the periodontitis microenvironment which might be involved in this pathological process. However, the response of PDLSCs in periodontitis microenvironment to mechanical force remains unclear. Therefore, in the present study, we introduced a Flexcell tension apparatus and investigated the response of PDLSCs obtained from periodontal tissues of periodontitis patients (PPDLSCs) and of those obtained from healthy periodontal tissues (HPDLSCs) to different magnitudes of static mechanical strain (SMS). PPDLSCs showed increased proliferation, decreased osteogenic activity, activated osteoclastogenesis, and greater secretion of inflammatory cytokines. Different magnitudes of SMS exerted distinct effects on HPDLSCs and PPDLSCs. An SMS of 12% induced optimal effects in HPDLSCs, including the highest proliferation, the best osteogenic ability, the lowest osteoclastogenesis, and the lowest secretion of inflammatory cytokines, while the optimal SMS for PPDLSCs was 8%. Excessive SMS damaged PPDLSCs function, including decreased proliferation, an imbalance between osteogenesis and osteoclastogenesis, and an activated inflammatory response. Our data suggest that PPDLSCs are more sensitive and less tolerant to SMS, and this may explain why mechanical force results in undesirable effects in periodontitis patients.

Human albumin attenuates excessive innate immunity via inhibition of microglial Mincle/Syk signaling in subarachnoid hemorrhage

Subarachnoid hemorrhage (SAH) is a devastating subtype of stroke. Microglial macrophage-inducible C-type lectin (Mincle) receptor launches microglial innate immunity after SAH, and thereby achieves a key step of early cerebral injury in SAH. We previously revealed albumin could improve long-term neurological outcomes after SAH. In this study, we examined the role of microglia-mediated innate immunity in the salutary effects of albumin. SAH was induced by endovascular perforation in rats. We found that albumin can significantly mitigate early neurovascular dysfunction of SAH rats. Albumin administration resulted in reduced Iba-1 and CD68 staining in cortex. Markers of microglia M1 polarization (iNOS, IL-1β, CD16, and CD32) were remarkably suppressed. Neutrophil invasion was inhibited as chemokines (MCP-1, CINC-1, and CXCL-2) mRNA levels, myeloperoxidase (MPO) and intracellular adhesion molecule-1 (ICAM-1) expressions were decreased. Mechanistically, albumin bound with microglial Mincle receptor, and retarded Mincle/Syk/IL-1β signaling in ipsilateral hemisphere subjected to SAH. In the cultured BV-2 microglial cells, we found Mincle and its ligand SAP130 mediate the cross-talk between neuronal necroptosis and microglial immunity response following SAH-related injury. Albumin could attenuate SAP130-induced Mincle upregulation and subsequent microglial inflammatory responses. The anti-inflammation effect of albumin was similar to the effect of genetic knockdown of Mincle. This effect may be attributed to a direct association between albumin and Mincle. The interaction also yielded a depression in the initiation of Mincle/Syk/IL-1β pathway. In conclusion, our results indicate that albumin can ameliorate innate immune responses after SAH. This anti-inflammatory action may be through direct restraining microglial Mincle receptor.

Hypoxia and low-dose inflammatory stimulus synergistically enhance bone marrow mesenchymal stem cell migration

OBJECTIVES

Cell migration is necessary for numerous physiological cell processes. Although either inflammatory or hypoxic stimuli of certain dose and duration have positive influence on cell migration, their combination has not been shown to result in a synergistic effect.

MATERIALS AND METHODS

In this study, we investigated combined effects of hypoxia and low-dose inflammatory stimulus (one-tenth of that of a previously used concentration) on migration of human bone marrow-derived mesenchymal stem cells (BMMSCs).

RESULTS

Our results from real-time PCR, Western blot analysis and an immunofluorescence assay, showed that dual stimulation up-regulated CXCR4 expression. Based on tablet scratch experimentation and transwell assay, the dual stimuli exhibited greater positive effects on cell migration than a single inflammatory or hypoxic stimulus. When effects of various pre-treatments on cell proliferation, differentiation and immunosuppression were screened, cells subjected to the hypoxic stimulus or dual stimuli had increased cell proliferation, while short-term inflammatory stimulus and/or hypoxic stimulus had no negative effect on cell differentiation and immunosuppression.

CONCLUSIONS

These findings suggest that the combination of hypoxia and low-dose inflammatory stimuli enhances the potential of BMMSCs to migrate, thus identifying cell pre-treatment conditions that could enhance future stem cell-based therapeutics.

Long noncoding RNA related to periodontitis interacts with miR-182 to upregulate osteogenic differentiation in periodontal mesenchymal stem cells of periodontitis patients

Periodontitis impairs the osteogenic differentiation of human periodontal mesenchymal stem cells (hPDLSCs), but the underlying molecular mechanisms are still poorly understood. Long noncoding RNAs (lncRNAs) have been demonstrated to have significant roles under both physiologic and pathological conditions. In this study, we performed comprehensive lncRNA profiling by lncRNA microarray analysis and identified a novel lncRNA, osteogenesis impairment-related lncRNA of PDLSCs from periodontitis patients (lncRNA-POIR), the expression of which was significantly decreased in PDLSCs from periodontitis patients (pPDLSCs) and was upregulated by osteogenic induction. To study the functions of lncRNA-POIR, we prepared cells with overexpression and knockdown of lncRNA-POIR and found that lncRNA-POIR positively regulated osteogenic differentiation of hPDLSCs and pPDLSCs both in vitro and in vivo. Using quantitative real-time PCRs (qPCRs) and luciferase reporter assays, we demonstrated that lncRNA-POIR may act as a competing endogenous RNA (ceRNA) for miR-182, leading to derepression of its target gene, FoxO1. In this process, lncRNA-POIR and miR-182 suppress each other and form a network to regulate FoxO1. FoxO1 increased bone formation of pPDLSCs by competing with TCF-4 for β-catenin and inhibiting the canonical Wnt pathway. Finally, inflammation increases miR-182 expression through the nuclear factor-κB pathway, and the miR-182 overexpression in the inflammatory microenvironment resulted in an imbalance in the lncRNA-POIR-miR-182 regulatory network. In conclusion, our results provide novel evidence that this lncRNA-miRNA (microRNA) regulatory network has a significant role in osteogenic differentiation of pPDLSCs and that it has potential as a therapeutic target in mesenchymal stem cells during inflammation.

Decreased MORF leads to prolonged endoplasmic reticulum stress in periodontitis-associated chronic inflammation

The association between inflammation and endoplasmic reticulum (ER) stress has been described in many diseases. However, if and how chronic inflammation governs the unfolded protein response (UPR) and promotes ER homeostasis of chronic inflammatory disease remains elusive. In this study, chronic inflammation resulted in ER stress in mesenchymal stem cells in the setting of periodontitis. Long-term proinflammatory cytokines induced prolonged ER stress and decreased the osteogenic differentiation of periodontal ligament stem cells (PDLSCs). Interestingly, we showed that chronic inflammation decreases the expression of lysine acetyltransferase 6B (KAT6B, also called MORF), a histone acetyltransferase, and causes the upregulation of a key UPR sensor, PERK, which lead to the persistent activation of the UPR in PDLSCs. Furthermore, we found that the activation of UPR mediated by MORF in chronic inflammation contributes to the PERK-related deterioration of the osteogenic differentiation of PDLSCs both in vivo and in vitro. Taken together, our results suggest that chronic inflammation compromises UPR function through MORF-mediated-PERK transcription, which is a previously unrecognized mechanism that contributes to impaired ER function, prolonged ER stress and defective osteogenic differentiation of PDLSCs in periodontitis.

Microenvironmental Views on Mesenchymal Stem Cell Differentiation in Aging

Aging is characterized by common environmental changes, such as hormonal, immunologic, and metabolic disorders. These pathologic factors impair the capability of mesenchymal stem cells (MSCs) to generate and maintain functionalized tissue components, contributing to age-related tissue degeneration (e.g., osteoporosis). However, in organismal aging, whether the microenvironmental signals induce common or differential MSC compromise and how they interact at the molecular level in mediating the functional decline of MSCs are not fully understood. In this review, we discuss the respective contribution of microenvironmental pathologic factors to age-related MSC dysfunction-particularly, the shifted differentiation from osteoblasts to adipocytes of bone marrow-derived MSCs. The authors summarize recent works regarding mechanisms underlying MSC-biased differentiation under altered microenvironments, which involve the activation of key signaling pathways, intracellular oxidative stress, and posttranscriptional regulations. In addition, we compare the differential influences of systemic and local microenvironments on MSC differentiation based on our findings. The authors also propose strategies to rescue differentiation disorders of MSCs in aging via modulating microenvironments, by using signaling modulators, anti-inflammatory agents, antioxidants, and metabolic regulators and by promoting mobilization of systemic MSCs to local injury sites. The authors hope that these insights contribute to MSC-based organismal aging research and treatments.