Effects of Leukemia Inhibitory Factor on Proliferation and Odontoblastic Differentiation of Human Dental Pulp Cells

EDTA Promotes the Mineralization of Dental Pulp In Vitro and In Vivo

INTRODUCTION

Dentin regeneration is one of the main goals of vital pulp treatment in which the biological properties of dental pulp cells (DPCs) need to be considered. In our previous study, we showed that EDTA could enhance the stromal cell-derived factor 1 alpha-induced migration of DPCs. The purpose of this study was to explore the effects of EDTA on the mineralization of dental pulp in vitro and in vivo.

METHODS

DPCs were obtained from human premolars or third molars. Alkaline phosphatase assays and alizarin red S staining were used to examine the degree of differentiation and mineralized nodule formation of DPCs. Real-time polymerase chain reaction and Western blot analysis were performed to detect the messenger RNA and protein expressions of mineralization-related markers in DPCs. Extracellular-regulated protein kinase and Smad inhibitors were used to study the roles of these 2 signaling pathways in this process. In addition, pulp exposures were created on 18 premolars of 2 beagle dogs (>12 months) using a high-speed dental handpiece. The experimental group (n = 9) was treated with 12% EDTA for 5 minutes, and the control group (n = 9) was treated with sterile saline for the same duration. Mineral trioxide aggregate was used for direct pulp capping followed by glass ionomer cement sealing. Samples were collected 3 months later, and the regenerated dentin was assessed by micro-computed tomographic and histologic analyses.

RESULTS

Exposure to 12% EDTA promoted the activity of alkaline phosphatase, the formation of mineralized nodules, and the messenger RNA and protein expressions of mineralization-related markers in DPCs. Furthermore, the process of 12% EDTA enhancing the differentiation of DPCs was mediated by the extracellular-regulated protein kinase 1/2 signaling pathway and inhibited by the Smad2/3 signaling pathway. In vivo, compared with the control group, more regenerated dentin that had fewer tunnel defects was formed in the 12% EDTA-treated group.

CONCLUSIONS

Our results showed that 12% EDTA could promote the mineralization of dental pulp in vitro and in vivo.

Role and mechanism of the nod-like receptor family pyrin domain-containing 3 inflammasome in oral disease

OBJECTIVE

To summarize evidence and data from experimental studies regarding the role and mechanism of the Nod-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome in the pathogenesis of several representative oral diseases.

MATERIALS AND METHODS

A literature search of PubMed and EBSCO was performed. The literature was searched using a combination of keywords, e.g., NLRP3 inflammasome, inflammation, microorganisms, oral inflammatory diseases, and oral immunological diseases.

RESULTS

The initiation and activation of the NLRP3 inflammasome are associated with the pathogenesis and progression of several representative oral diseases, including periodontitis, oral lichen planus, dental pulp disease, and oral cavity squamous cell carcinoma.

CONCLUSIONS

The NLRP3 inflammasome plays a crucial role in the progression of inflammatory and adaptive immune responses. The possible role of the NLRP3 inflammasome in several oral diseases, including not only periodontitis and pulpitis but also mucosal diseases and oral cavity squamous cell carcinoma, may involve the aberrant regulation of inflammatory and immune responses. Understanding the cellular and molecular biology of the NLRP3 inflammasome is necessary because the NLRP3 inflammasome may be a potential therapeutic target for the treatment and prevention of oral inflammatory and immunological diseases.

Interferon-γ is a master checkpoint regulator of cytokine-induced differentiation

Cytokines are protein mediators that are known to be involved in many biological processes, including cell growth, survival, inflammation, and development. To study their regulation, we generated a library of 209 different cytokines. This was used in a combinatorial format to study the effects of cytokines on each other, with particular reference to the control of differentiation. This study showed that IFN-γ is a master checkpoint regulator for many cytokines. It operates via an autocrine mechanism to elevate STAT1 and induce internalization of gp130, a common component of many heterodimeric cytokine receptors. This targeting of a receptor subunit that is common to all members of an otherwise diverse family solves the problem of how a master regulator can control so many diverse receptors. When one adds an autocrine mechanism, fine control at the level of individual cells is achieved.

Role of leptin as a link between metabolism and the immune system

Leptin is an adipocyte-derived hormone not only with an important role in the central control of energy metabolism, but also with many pleiotropic effects in different physiological systems. One of these peripheral functions of leptin is a regulatory role in the interplay between energy metabolism and the immune system, being a cornerstone of the new field of immunometabolism. Leptin receptor is expressed throughout the immune system and the regulatory effects of leptin include cells from both the innate and adaptive immune system. Leptin is one of the adipokines responsible for the inflammatory state found in obesity that predisposes not only to type 2 diabetes, metabolic syndrome and cardiovascular disease, but also to autoimmune and allergic diseases. Leptin is an important mediator of the immunosuppressive state in undernutrition status. Placenta is the second source of leptin and it may play a role in the immunomodulation during pregnancy. Finally, recent work has pointed to the participation of leptin and leptin receptor in the pathophysiology of inflammation in oral biology. Therefore, leptin and leptin receptor should be considered for investigation as a marker of inflammation and immune activation in the frontier of innate-adaptive system, and as possible targets for intervention in the immunometabolic mediated pathophysiology.

Asperosaponin VI promotes bone marrow stromal cell osteogenic differentiation through the PI3K/AKT signaling pathway in an osteoporosis model

Asperosaponin VI (ASA VI), a natural compound isolated from the well-known traditional Chinese herb Radix Dipsaci, has an important role in promoting osteoblast formation. However, its effects on osteoblasts in the context of osteoporosis is unknown. This study aimed to investigate the effects and mechanism of ASA VI action on the proliferation and osteogenic differentiation of bone marrow stromal cells isolated from the ovariectomized rats (OVX rBMSCs). The toxicity of ASA VI and its effects on the proliferation of OVX rBMSCs were measured using a CCK-8 assay. Various osteogenic differentiation markers were also analyzed, such as ALP activity, calcified nodule formation, and the expression of osteogenic genes, i.e., ALP, OCN, COL 1 and RUNX2. The results indicated that ASA VI promoted the proliferation of OVX rBMSCs and enhanced ALP activity and calcified nodule formation. In addition, while ASA VI enhanced the expression of ALP, OCN, Col 1 and RUNX2, treatment with LY294002 reduced all of these osteogenic effects and reduced the p-AKT levels induced by ASA VI. These results suggest that ASA VI promotes the osteogenic differentiation of OVX rBMSCs by acting on the phosphatidylinositol—3 kinase/AKT signaling pathway.

Activation of the NLRP3/caspase-1 inflammasome in human dental pulp tissue and human dental pulp fibroblasts

The NLRP3/caspase-1 inflammasome pathway plays an important role in cellular immune defence against bacterial infection; however, its function in human dental pulp tissue and human dental pulp fibroblasts remains poorly understood. We demonstrate that NLRP3 protein expression occurs to a greater extent in pulp tissue with irreversible pulpitis than in normal pulp tissue and in tissue with reversible pulpitis. Caspase-1 is present in its active (cleaved) form only in pulp tissue with irreversible pulpitis. NLRP3 and caspase-1 are expressed in the odontoblast layers in normal human dental pulp tissue, whereas in inflamed pulp tissue, the odontoblast layers are disrupted and dental pulp cells are positive for NLRP3 and caspase-1. Additionally, we investigate the role of the NLRP3/caspase-1 inflammasome pathway in human dental pulp fibroblasts and show that ATP activates the P2X7 receptor on the cell membrane triggering K(+) efflux and inducing the gradual recruitment of the membrane pore pannexin-1. Extracellular lipopolysaccharide is able to penetrate the cytosol and activate NLRP3. Furthermore, the low intracellular K(+) concentration in the cytosol triggers reactive oxygen species generation, which also induces the NLRP3 inflammasome. Thus, the NLRP3/caspase-1 pathway has a biological role in the innate immune response mounted by human dental pulp fibroblasts.

Undifferentiated pulp cells and odontoblast-like cells share genes involved in the process of odontogenesis

OBJECTIVE

Expression of a large number of genes during differentiation of undifferentiated pulp cells into odontoblastic cells is still unknown, hence the aim of this investigation was to compare undifferentiated pulp cells (OD-21) and odontoblast-like cells (MDPC-23) through the assessment of cell stimulation and gene expression profiling.

DESIGN

The cells were cultured and after the experimental periods, there were evaluated cell proliferation and viability as well as alkaline phosphatase activity (ALP) and mineralization nodules. To evaluate gene expression it was used fluorescence cDNA microarray technology in addition to bioinformatics programmes such as SAM (significance analysis of microarrays). Gene expression was validated by Real Time PCR (qPCR).

RESULTS

The results showed that viability was above 80% in both cells, cell proliferation and ALP activity was higher in MDPC-23 cells and mineralization nodules were present only in the cultures of odontoblast-like cells. There were observed genes associated to odontogenesis with similar behaviour in both cell types, such as Il10, Traf6, Lef1 and Hspa8. Regions of the heatmap showed differences in induction and repression of genes such as Jak2 and Fas.

CONCLUSION

OD-21 cells share many genes with similar behaviour to MDPC-23 cells, suggesting their potential to differentiate into odontoblasts.

Insulin-like growth factor 1 receptor and p38 mitogen-activated protein kinase signals inversely regulate signal transducer and activator of transcription 3 activity to control human dental pulp stem cell quiescence, propagation, and differentiation

Dental pulp stem cells (DPSCs) remain quiescent until activated in response to severe dental pulp damage. Once activated, they exit quiescence and enter regenerative odontogenesis, producing reparative dentin. The factors and signaling molecules that control the quiescence/activation and commitment to differentiation of human DPSCs are not known. In this study, we determined that the inhibition of insulin-like growth factor 1 receptor (IGF-1R) and p38 mitogen-activated protein kinase (p38 MAPK) signaling commonly activates DPSCs and promotes their exit from the G0 phase of the cell cycle as well as from the pyronin Y(low) stem cell compartment. The inhibition of these two pathways, however, inversely determines DPSC fate. In contrast to p38 MAPK inhibitors, IGF-1R inhibitors enhance dental pulp cell sphere-forming capacity and reduce the cells' colony-forming capacity without inducing cell death. The inverse cellular changes initiated by IGF-1R and p38 MAPK inhibitors were accompanied by inverse changes in the levels of active signal transducer and activator of transcription 3 (STAT3) factor, inactive glycogen synthase kinase 3, and matrix extracellular phosphoglycoprotein, a marker of early odontoblast differentiation. Our data suggest that there is cross talk between the IGF-1R and p38 MAPK signaling pathways in DPSCs and that the signals provided by these pathways converge at STAT3 and inversely regulate its activity to maintain quiescence or to promote self-renewal and differentiation of the cells. We propose a working model that explains the possible interactions between IGF-1R and p38 MAPK at the molecular level and describes the cellular consequences of these interactions. This model may inspire further fundamental study and stimulate research on the clinical applications of DPSC in cellular therapy and tissue regeneration.

KLF4 promoted odontoblastic differentiation of mouse dental papilla cells via regulation of DMP1

Odontoblasts, which derive from dental papilla, are a type of terminally differentiated matrix-secreting cells. Previous studies have identified various transcription factors involved in the differentiation process of odontoblasts. We have recently found that Krüppel-like factor 4 (Klf4) was expressed in the polarizing and elongating odontoblasts, but the function of Klf4 in the differentiation of odontoblasts is still unclear. We hypothesized Klf4 promoted the differentiation of odontoblasts by up-regulating some odontoblast-related genes. In this study, we found that the expression of Klf4 increased significantly during the odontoblastic differentiation of primary mouse dental papilla cells and the mouse dental papilla cell line-mDPC6T. Overexpression of Klf4 significantly up-regulated odontoblast-related genes, such as Dmp1, Dspp, and Alp, and promoted the accumulation of mineral nodules. Knock-down of Klf4 down-regulated expression of Dmp1, Dspp, and Alp, and inhibited mineral deposition. We applied in silico analysis and identified one target gene of Klf4-Dmp1. Based on further analysis of ChIP data, EMSA and dual luciferase activity assays, we confirmed that Klf4 was able to specifically bind to the Dmp1 promoter and transactivate its expression. Furthermore, forced expression of Dmp1 in the Klf4 knock-down mDPC6T cell line significantly recovered its odontoblastic differentiation ability. Our data confirmed our hypothesis that Klf4 promotes the differentiation of odontoblasts via the up-regulation of Dmp1.

Growth and differentiation factor-5 regulates the growth and differentiation of human dental pulp cells

INTRODUCTION

Growth and differentiation factor-5 (GDF-5) is a multifunctional protein that regulates the development and repair in many tissues. The purpose of this study was to investigate whether GDF-5 may influence the proliferation, differentiation, and collagen turnover of human dental pulp cells.

METHODS

Human dental pulp cells were treated with different concentrations of GDF-5 (0-500 ng/mL). Morphology of pulp cells was observed under a microscope. Cell proliferation was evaluated by 3-(4,5-dimethyl-thiazol-2-yl)-2,5-diphenyl-tetrazolium bromide assay. Immunofluorescent assay was used to observe the percentages of cell mitosis. Collagen content was measured by Sircol collagen assay. Tissue inhibitor of metalloproteinase-1 level in the culture medium was measured with enzyme-linked immunosorbent assay and Western blotting. Cell differentiation was evaluated by alkaline phosphatase (ALP) staining and ALP enzyme activity assay.

RESULTS

After exposure of dental pulp cells to various concentrations of GDF-5, cell number was up-regulated significantly in dose-dependent manner. GDF-5 also stimulated mitosis of dental pulp cells as indicated by an increased percentage of binucleated cells from 28% to 35%-45%. GDF-5 did not affect the collagen content and tissue inhibitor of metalloproteinase-1 level of pulp cells. GDF-5 decreased the ALP activity of pulp cells as analyzed by ALP staining and enzyme activity assay, with 14%-44% of inhibition.

CONCLUSIONS

GDF-5 revealed mitogenic and proliferative activity to dental pulp cells. GDF-5 showed inhibitory effect on ALP activity but little effect on the collagen turnover. These events are crucial in specific stages of dental pulp repair and regeneration. GDF-5 may be potentially used for tissue engineering of pulp-dentin complex.

A cell-permeable fusion protein for the mineralization of human dental pulp stem cells

Human dental pulp stem cells (hDPSCs) are the only mesenchymal stem cells in pulp tissue that can differentiate into osteoblasts, odontoblasts, and adipose cells. The transcriptional co-activator with PDZ-binding motif (TAZ) protein has been reported to modulate osteogenic differentiation in mouse MSCs. Therefore, we examined whether the TAZ protein plays the same role in human pulp stem cells. In this study, TAZ was applied to cells directly with low-molecular-weight protamine (LMWP) as a cell-penetrating peptide (CPP). The LMWP-TAZ fusion proteins were expressed in an E. coli system with a pET-21b vector and efficiently transferred into hDPSCs without producing toxicity in the cells. The efficient uptake of TAZ was shown by Western blot with an anti-TAZ antibody, fluorescence-activated cell sorting, and confocal microscopy in live cells. The delivered TAZ protein increased osteogenic differentiation, as confirmed by alkaline phosphatase (ALP) staining, RT-PCR, and Western blotting. In addition, TAZ also inhibited adipogenic differentiation, regulating peroxisome proliferator-activated receptor-γ (PPAR-γ), lipoprotein lipase (LPL), and adipocyte fatty acid-binding protein (aP2) mRNA levels. These in vitro studies suggest that cell-permeable TAZ may be used as a specific regulator of hard-tissue differentiation.