Dentin-pulp regeneration: the primordial role of the microenvironment and its modification by traumatic injuries and bioactive materials

Advances in Regenerative Dentistry: A Systematic Review of Harnessing Wnt/β-Catenin in Dentin-Pulp Regeneration

Dentin pulp has a complex function as a major unit in maintaining the vitality of teeth. In this sense, the Wnt/β-Catenin pathway has a vital part in tooth development, maintenance, repair, and regeneration by controlling physiological activities such as growth, differentiation, and migration. This pathway consists of a network of proteins, such as Wnt signaling molecules, which interact with receptors of targeted cells and play a role in development and adult tissue homeostasis. The Wnt signals are specific spatiotemporally, suggesting its intricate mechanism in development, regulation, repair, and regeneration by the formation of tertiary dentin. This review provides an overview of the recent advances in the Wnt/β-Catenin signaling pathway in dentin and pulp regeneration, how different proteins, molecules, and ligands influence this pathway, either upregulating or silencing it, and how it may be used in the future for clinical dentistry, in vital pulp therapy as an effective treatment for dental caries, as an alternative approach for root canal therapy, and to provide a path for therapeutic and regenerative dentistry.

Influence of Lithium- and Zinc-Containing Bioactive Glasses on Pulpal Regeneration

OBJECTIVE

 To evaluate the potential of modified bioactive glasses containing lithium and zinc as pulp capping materials by investigating the odontogenic differentiation and mineralization response in the tooth culture model.

MATERIALS AND METHODS

 Lithium- and zinc-containing bioactive glasses (45S5.1Li, 45S5.5Li, 45S5.1Zn, 45S5.5Zn, 45S5.1Zn sol-gel, and 45S5.5Zn sol-gel), fibrinogen-thrombin, and biodentine were prepared to assess Axin2 gene expression at 0, 30 minutes, 1 hour, 12 hours, and 1 day and DSPP gene expression at 0, 3, 7, and 14 days in stem cells from human exfoliated deciduous teeth (SHEDs) using qRT-PCR. The experimental bioactive glasses incorporated with fibrinogen-thrombin and biodentine were placed on the pulpal tissue in the tooth culture model. Histology and immunohistochemistry were analyzed at 2 weeks and 4 weeks.

RESULTS

 Axin2 gene expression for all experimental groups was significantly higher than the control at 12 hours. The DSPP gene expression for all experimental groups was significantly higher than the control at 14 days. The presence of mineralization foci was significantly higher at 4 weeks for the modified bioactive glasses 45S5.5Zn, 45S5.1Zn sol-gel, and 45S5.5Zn sol-gel as well as Biodentine compared with the fibrinogen-thrombin control.

CONCLUSION

 Lithium- and zinc-containing bioactive glasses increased Axin2 and DSPP gene expression in SHEDs and can potentially enhance pulp mineralization and regeneration. Zinc-containing bioactive glasses are a promising candidate to be used as pulp capping materials.

Effect of Wnt10a/β-catenin signaling pathway on promoting the repair of different types of dentin-pulp injury

How to repair dentin-pulp injury effectively has always been a clinical problem, and the comparative study of repair process between different injuries is unknown. Dental pulp stem cells (DPSCs) often are selected as seed cells for the study of dentin-pulp injury repair due to excellent advantages in odontogenesis and pulp differentiation. Although many previous researches have indicated that the Wnt protein and Wnt/β-catenin signaling pathway were crucial for dental growth, development, and injury repair, the specific mechanism remained unknown. In this study, different dentine-pulp injury models of adult mice were established successfully by abrasion and cutting methods. The gross morphology and micro-CT were used to observe the repair of injured mice incisor in different groups. We found that the repair time of each group was different. The repair time of the cutting group was longer than the abrasion group and the qRT-PCR detection showed that the expression of DSPP in the cutting group was higher than that in the abrasion group, but there was no significant difference in proliferation among the groups. In vivo and cell experiments showed that activation of Wnt/β-catenin signaling pathway can promote the proliferation and odontoblast differentiation of DPSCs. In addition, by using RNAscope staining, we observed that Wnt10a was mainly expressed in the proliferative region and partially expressed in the odontoblast region. The Western blotting results showed that in the early stage of repair, the expression of Wnt10a increased with the extension of days after injury in both abrasion and cutting group and the increase of Wnt10a was tested obviously on the 5th day after injury. But on the 7th day after injury, the expression of Wnt10a was still obvious in the cutting group, while the expression of Wnt10a was significantly reduced in the abrasion group, which was close to the control group. It is suggested that Wnt10a acts as a repair-related protein and has an important role in tooth injury repair. Wnt10a was activated by R-spondin and LiCl, and Wnt10a-siRNA DPSCs were constructed to inhibit Wnt10a. The results showed that Wnt10a/β-catenin signaling pathway promoted the proliferation and odontoblast differentiation of DPSCs. It plays a crucial role in the repair process of different injuries. This study enriched the mechanisms of Wnt10a /β-catenin signaling pathways in different types of dentin-pulp injury repair, which could provide experimental evidences for the target gene screening and also give some new ideas for the subsequent research on the molecular mechanisms of tooth regeneration.

Histological evaluation of a novel phosphorylated pullulan-based pulp capping material: An in vivo study on rat molars

AIM

To evaluate the dental pulp response to a novel mineral trioxide aggregate containing phosphorylated pullulan (MTAPPL) in rats after direct pulp capping.

METHODS

Ninety-six cavities were prepared in the maxillary first molars of 56 male Wistar rats. The dental pulps were intentionally exposed and randomly divided into four groups according to the application of pulp capping materials: MTAPPL; phosphorylated pullulan (PPL); a conventional MTA (Nex-Cem MTA, NCMTA; positive control); and Super-Bond (SB; negative control). All cavities were restored with SB and observed for pulpal responses at 1-, 3-, 7- and 28-day intervals using a histological scoring system. Statistical analysis was performed using Kruskal-Wallis and Mann-Whitney U-test with Bonferroni's correction, and the level of significance was set at 0.05. DMP1 and CD34 antigen were used to evaluate odontoblast differentiation and pulpal vascularization, respectively.

RESULTS

On day 1, mild inflammatory cells were present in MTAPPL and NCMTA groups; fewer inflammatory cells were present in the PPL, whereas SB was associated with a mild-to-moderate inflammatory response. A significant difference was observed between PPL and SB (p < .05). No mineralized tissue deposition was observed. On day 3, moderate-to-severe inflammatory cells were present in PPL and SB, whereas MTAPPL and NCMTA had a mild inflammatory response. Initial mineralized tissue deposition was observed in the NCMTA, MTAPPL and SB. A significant difference was observed between MTAPPL and PPL (p < .05). On day 7, a thin layer of mineralized tissue was observed in all tested groups with no or mild inflammatory response. On day 28, no inflammatory response was observed in MTAPPL, whereas NCMTA, PPL and SB had mild inflammatory responses. A significant difference was observed between MTAPPL and SB (p < .05). Complete mineralized tissue barrier formation was observed in MTAPPL, NCMTA and PPL with no significant difference (p > .05). SB exhibited incomplete mineralized tissue barriers, significantly different from NCMTA, MTAPPL and PPL (p < .05). The staining with CD34 was positive in all the groups on all observation days.

CONCLUSION

The favourable pulpal responses and induction of mineralized tissue formation associated with MTAPPL indicate its potential application as a direct pulp capping material.

Influence of 2-hydroxyethyl methacrylate (HEMA) exposure on angiogenic differentiation of dental pulp stem cells (DPSCs)

OBJECTIVE

The angiogenic differentiation of dental pulp stem cells (DPSCs) is important for tissue homeostasis and wound healing. In this study the influence of 2-hydroxyethyl methacrylate (HEMA) on angiogenic differentiation was investigated.

METHODS

To evaluate HEMA effects on angiogenic differentiation, DPSCs were cultivated in angiogenic differentiation medium (ADM) in the presence or absence of non-toxic HEMA concentrations (0.1 mM and 0.5 mM). Subsequently, angiogenic differentiation was analyzed on the molecular level by qRT-PCR and protein profiler analyzes of angiogenic markers and flow cytometry of PECAM1. The influence of HEMA on angiogenic phenotypes was analyzed by cell migration and sprouting assays.

RESULTS

Treatment with 0.5 mM HEMA during differentiation can lead to a slight reduction of angiogenic markers on mRNA level. HEMA also seems to slightly reduce the quantity of angiogenic cytokines (not significant). However, these HEMA concentrations have no detectable influence on cell migration, the abundance of PECAM1 and the formation of capillaries. Higher concentrations caused primary cytotoxic effects in angiogenic differentiation experiments conducted for longer periods than 72 h.

SIGNIFICANCE

Non-cytotoxic HEMA concentrations seem to have a minor impact on the expression of angiogenic markers, essentially on the mRNA level, without affecting the angiogenic differentiation process itself on a detectable level.

Synthesis of di- and triacrylamides with tertiary amine cores and their evaluation as monomers in dental adhesive interfaces

PURPOSE/AIM

In an attempt to increase the service life of dental adhesive interfaces, more hydrolytically and enzymatically-stable methacrylate alternatives, such as methacrylamides, have been proposed. The aim of this study was to investigate polymerization behavior, as well as mechanical and biological properties of experimental adhesives containing multi-functional acrylamides.

MATERIALS AND METHODS

Multi-functional acrylamides (N,N-Bis[(3-methylaminoacryl)propyl]methylamine - BMAAPMA, Tris[(2-methylaminoacryl)ethyl]amine - TMAAEA, N,N'-bis(acrylamido) 1,4-diazepane - BAADA, N,N-Diethyl-1,3-bis(acrylamido)propane - DEBAAP) or HEMA (2-Hydroxyethyl methacrylate - control) were added at 40 wt% to UDMA. 0.2 wt% DMPA and 0.4 wt% DPI-PF6 were used as initiators. Polymerization kinetics was followed in real-time in near-IR during photoactivation (320-500 nm, at 630 mW/cm²). Water sorption/solubility and flexural strength/modulus were measured according to ISO 4049. ¹H NMR was used to assess monomer degradation kinetics. MTT assay was used to assess cytotoxicity against OD-21 and DPSC cells. Biofilm formation and adhesion were assessed by Luciferase Assay and Impingement technique, respectively. Solvated adhesives (40 vol% ethanol) were used to test interfacial adhesion strength. The results were analyzed by ANOVA/Tukey's test (α = 0.05).

RESULTS

In general, the pure methacrylate mixture had higher rate of polymerization (Rp_max), degree of conversion (DC) at Rp_max, and final DC than the acrylamides. Flexural properties after water storage decreased between 11 and 65%, more markedly for acrylamides. Interfacial bond strength was greater and more stable long-term for the newly synthesized acrylamide formulations (less than 4% reduction at 6 months) compared to the methacrylate experimental control (42% reduction at 6 months). HEMA degraded by almost 90%, while the acrylamides showed no degradation in acidic conditions. Cytotoxicity and biofilm formation, in general, were similar for all groups.

CONCLUSIONS

Despite demonstrating high water sorption, the acrylamide-containing materials had similar mechanical and biological properties and enhanced interfacial bond strength stability compared to the methacrylate control.

Bio-Inductive Materials in Direct and Indirect Pulp Capping-A Review Article

The article is aimed at analyzing the available research and comparing the properties of bio-inductive materials in direct and indirect pulp capping procedures. The properties and clinical performances of four calcium-silicate cements (ProRoot MTA, MTA Angelus, RetroMTA, Biodentine), a light-cured calcium silicate-based material (TheraCal LC) and an enhanced resin-modified glass-ionomer (ACTIVA BioACTIVE) are widely discussed. A correlation of in vitro and in vivo data revealed that, currently, the most validated material for pulp capping procedures is still MTA. Despite Biodentine’s superiority in relatively easier manipulation, competitive pricing and predictable clinical outcome, more long-term clinical studies on Biodentine as a pulp capping agent are needed. According to available research, there is also insufficient evidence to support the use of TheraCal LC or ACTIVA BioACTIVE BASE/LINER in vital pulp therapy.

Injectable phosphopullulan-functionalized calcium-silicate cement for pulp-tissue engineering: An in-vivo and ex-vivo study

OBJECTIVE

To evaluate, by means of an ex-vivo human tooth-culture model and in-vivo minipig animal study, the pulpal inflammatory reaction and reparative dentin-formation capacity of an injectable phosphopullulan-based calcium-silicate cement (GC, Tokyo, Japan) upon pulp capping, this in comparison with the commercial reference material Biodentine (Septodont).

METHODS

For the ex-vivo tooth model, 9 freshly-extracted teeth from 3 different patients were pulp-capped with the experimental biomaterial (n = 3), Biodentine (n = 3) or left uncapped (control; n = 3). The teeth were kept in fresh culture medium for 4 weeks and, upon fixation three-dimensional Micro-CT and histology were performed. For the in-vivo animal study, 40 teeth from 3 minipigs were exposed and pulp capped with the experimental biomaterial containing phosphopullulan (n = 24) or Biodentine (n = 16) for 7 or 70 days. The inflammatory reaction and the tissue-regenerative potential was qualitatively and semi-quantitatively characterized using three-dimensional micro-CT and histology.

RESULTS

Ex vivo, the treatment with the experimental phosphopullulan-based calcium-silicate cement and Biodentine stimulated the formation of fibrous tissue and mineralized foci. In vivo, early inflammatory reaction and regeneration of the pulp-tissue interface was promoted by both bioceramic materials after 7 and 70 days, respectively.

SIGNIFICANCE

Our findings bring new insights into calcium-silicate-mediated dental pulp repair and regeneration. The novel ready-to-use and self-adhering functionalized calcium-silicate cement revealed effective pulpal repair potential.

Survival of human dental pulp cells after 4-week culture in human tooth model

OBJECTIVES

This study aimed to validate the human tooth model by investigating the growth efficiency, expression of mesenchymal stem cell (MSC) markers and differentiation ability of human dental pulp cells (hDPCs) harvested from extracted immature third molars and cultured for different periods. Moreover, the effect of exposure and capping with a hydraulic calcium-silicate cement on pulp tissue after 4-week culture in the tooth model was investigated.

METHODS

Primary hDPCs were collected from 18 molars from six individuals (15-19 years). One tooth of each patient was immediately cultured (control), while the other teeth were exposed to culture medium for 1, 2 or 4 weeks. After different culture periods, cells were harvested using the explant method, upon which cells were evaluated for cell-doubling time, colony-forming efficiency and expression of cell surface markers. The osteogenic, adipogenic and chondrogenic differentiation efficacy was also determined. Two teeth from three different patients (n = 6) were used for the pulp-capping assay. Three teeth were capped with ProRoot MTA (Dentsply Sirona), while three other exposed teeth remained uncapped (control).

RESULTS

Cells were found to grow, express MSC markers and showed osteogenic, adipogenic and chondrogenic differentiation potential at all time periods. Histology of the teeth subjected to the pulp-capping assay showed the formation of mineralized tissue after 4-week exposure to ProRoot MTA (Dentsply Sirona) and normal histological features in the control teeth.

CONCLUSIONS

This study confirmed that hDPCs of teeth cultured for up to 4 weeks in a human tooth model are viable, express MSC markers and show differentiation ability.

CLINICAL SIGNIFICANCE

The human tooth model can be seen as an advanced cell-culture model that makes use of the original 3D pulp-chamber structure. It can serve as a screening tool to evaluate new pulp-capping formulations in a relatively cheap and fast manner.

C5L2 Regulates DMP1 Expression during Odontoblastic Differentiation

The presence of stem cells within the dental-pulp tissue as well as their differentiation into a new generation of functional odontoblast-like cells constitutes an important step of the dentin-pulp regeneration. Recent investigations demonstrated that the complement system activation participates in 2 critical steps of dentin-pulp regeneration: pulp progenitor's recruitment and pulp nerve sprouting. Surprisingly, its implication in odontoblastic differentiation has not been addressed yet. Since the complement receptor C5a receptor-like 2 (C5L2) is expressed by different stem cells, the aim of this study is to investigate if the dental pulp stem cells express C5L2 and if this receptor participates in odontoblastic differentiation. Immunohistochemistry performed on human third molar pulp sections showed a perivascular co-localization of the mesenchymal stem cell markers STRO1 and C5L2. In vitro immunofluorescent staining confirmed that hDPSCs express C5L2. Furthermore, we determined by real-time polymerase chain reaction that the expression of C5L2 is highly modulated in human dental pulp stem cells (hDPSCs) undergoing odontoblastic differentiation. Moreover, we showed that this odontogenesis-regulated expression of C5L2 is specifically potentiated by the proinflammatory cytokine TNFα. Using a C5L2-siRNA silencing strategy, we provide direct evidence that C5L2 constitutes a negative regulator of the dentinogenic marker DMP1 (dentin matrix protein 1) expression by hDPSCs. Our findings suggest a direct correlation between the odontoblastic differentiation and the level of C5L2 expression in hDPSCs and identify C5L2 as a negative regulator of DMP1 expression by hDPSCs during the odontoblastic differentiation and inflammation processes. This work is the first to demonstrate the involvement of C5L2 in the biological function of stem cells, provides an important knowledge in understanding odontoblastic differentiation of dental pulp stem cells, and may be useful in future dentin-pulp engineering strategies.

Dental pulp stem cells in regenerative medicine

The mesenchymal stem cells (dental pulp stem cells; DPSC) found inside teeth represent a significant future source of stem cells for regenerative medicine procedures. This review describes the ontogeny of DPSC; the laboratory processing and collection of DPSC; the immuno-cytochemical characterisation of DPSC; the differentiation between adult DPSC and DPSC obtained from exfoliated deciduous teeth (SHED) and their potential use in regenerative medicine procedures in the future both in dental and general medical applications.

Freshly-mixed and setting calcium-silicate cements stimulate human dental pulp cells

OBJECTIVES

To evaluate the effect of the eluates from 3 freshly-mixed and setting hydraulic calcium-silicate cements (hCSCs) on human dental pulp cells (HDPCs) and to examine the effect of a newly developed hCSC containing phosphopullulan (PPL) on HDPCs.

METHODS

Human dental pulp cells, previously characterized as mesenchymal stem cells, were used. To collect the eluates, disks occupying the whole surface of a 12-well plate were prepared using an experimental hCSC containing phosphopullulan (GC), Nex-Cem MTA (GC), Biodentine (Septodont) or a zinc-oxide (ZnO) eugenol cement (material-related negative control). Immediately after preparing the disks (non-set), 3ml of Dulbecco's Modified Eagle Medium (DMEM) with 10% fetal bovine serum (FBS) were added. The medium was left in contact with the disks for 24h before being collected. Four different dilutions were prepared (100%, 50%, 25% and 10%) and cell-cytotoxicity, cell-proliferation, cell-migration and odontogenic differentiation were tested. The cell-cytotoxicity and cell-proliferation assays were performed by XTT-colorimetric assay at different time points. The cell-migration ability was tested with the wound-healing assay and the odontogenic differentiation capacity of hCSCs on HDPCs was tested with RT-PCR.

RESULTS

Considering all experimental data together, the eluates from 3 freshly-mixed and setting hCSCs appeared not cytotoxic toward HDPCs. Moreover, all three cements stimulated proliferation, migration and odontogenic differentiation of HDPCs.

SIGNIFICANCE

The use of freshly-mixed and setting hCSCs is an appropriate approach to test the effect of the materials on human dental pulp cells. The experimental material containing PPL is non-cytotoxic and positively stimulates HDPCs.

Sources of dentin-pulp regeneration signals and their modulation by the local microenvironment

Many aspects of dentin pulp tissue regeneration have been investigated, and it has been shown that dentin pulp has a high regeneration capacity. This seems to be because of the presence of progenitor cells and inductive regeneration signals from different origins. These signals can be liberated after the acidic dissolution of carious dentin as well as from pulp fibroblasts and endothelial cells in cases of traumatic injury. Thus, both carious lesions and pulp cells provide the required mediators for complete dentin-pulp regeneration including reparative dentin secretion, angiogenesis, and innervation. Additionally, all dentin pulp insults including carious "infection," traumatic injuries, application of restorative materials on the injured dentin pulp, and subsequent apoptosis are known activators of the complement system. This activation leads to the production of several biologically active fragments responsible for the vascular modifications and the attraction of immune cells to the inflammatory/injury site. Among these, C5a is involved in the recruitment of pulp progenitor cells, which express the C5a receptor. Thus, in addition to dentin and pulp cells, plasma should be considered as an additional source of regeneration signals.

Pulp Fibroblasts Control Nerve Regeneration through Complement Activation

Dentin-pulp regeneration is closely linked to the presence of nerve fibers in the pulp and to the healing mechanism by sprouting of the nerve fiber’s terminal branches beneath the carious injury site. However, little is known about the initial mechanisms regulating this process in carious teeth. It has been recently demonstrated that the complement system activation, which is one of the first immune responses, contributes to tissue regeneration through the local production of anaphylatoxins such as C5a. While few pulp fibroblasts in intact teeth and in untreated fibroblast cultures express the C5a receptor (C5aR), here we show that all dental pulp fibroblasts, localized beneath the carious injury site, do express this receptor. This observation is consistent with our in vitro results, which showed expression of C5aR in lipoteichoic acid–stimulated pulp fibroblasts. The interaction of C5a, produced after complement synthesis and activation from pulp fibroblasts, with the C5aR of these cells mediated the local brain-derived neurotropic factor (BDNF) secretion. Overall, this activation guided the neuronal growth toward the lipoteichoic acid–stimulated fibroblasts. Thus, our findings highlight a new mechanism in one of the initial steps of the dentin-pulp regeneration process, linking pulp fibroblasts to the nerve sprouting through the complement system activation. This may provide a useful future therapeutic tool in targeting the fibroblasts in the dentin-pulp regeneration process.

Mesenchymal Stem Cells Derived from Dental Pulp: A Review

The mesenchymal stem cells of dental pulp (DPSCs) were isolated and characterized for the first time more than a decade ago as highly clonogenic cells that were able to generate densely calcified colonies. Now, DPSCs are considered to have potential as stem cell source for orthopedic and oral maxillofacial reconstruction, and it has been suggested that they may have applications beyond the scope of the stomatognathic system. To date, most studies have shown that, regardless of their origin in third molars, incisors, or exfoliated deciduous teeth, DPSCs can generate mineralized tissue, an extracellular matrix and structures type dentin, periodontal ligament, and dental pulp, as well as other structures. Different groups worldwide have designed and evaluated new efficient protocols for the isolation, expansion, and maintenance of clinically safe human DPSCs in sufficient numbers for various therapeutics protocols and have discussed the most appropriate route of administration, the possible contraindications to their clinical use, and the parameters to be considered for monitoring their clinical efficacy and proper biological source. At present, DPSC-based therapy is promising but because most of the available evidence was obtained using nonhuman xenotransplants, it is not a mature technology.

Angiogenic Potential and Secretome of Human Apical Papilla Mesenchymal Stem Cells in Various Stress Microenvironments

Stem cells from the apical papilla (SCAP) of human adult teeth are considered an accessible source of cells with angiogenic properties. The aims of this study were to investigate the endothelial transdifferentiation of SCAP, the secretion of pro- and antiangiogenic factors from SCAP, and the paracrine effects of SCAP when exposed to environmental stress to stimulate tissue damage. SCAP were exposed to serum deprivation (SD), glucose deprivation (GD), and oxygen deprivation/hypoxia (OD) conditions, individually or in combination. Endothelial transdifferentiation was evaluated by in vitro capillary-like formation assays, real-time polymerase chain reaction, western blot, and flow cytometric analyses of angiogenesis-related markers; secretome by antibody arrays and enzyme-linked immunosorbent assays (ELISA); and paracrine impact on human umbilical vein endothelial cells (HUVECs) by in vitro transwell migration and capillary-like formation assays. The short-term exposure of SCAP to glucose/oxygen deprivation (GOD) in the presence, but mainly in deprivation, of serum (SGOD) elicited a proangiogenesis effect indicated by expression of angiogenesis-related genes involved in vascular endothelial growth factor (VEGF)/VEGFR and angiopoietins/Tie pathways. This effect was unachievable under SD in normoxia, suggesting that the critical microenvironmental condition inducing rapid endothelial shift of SCAP is the combination of SGOD. Interestingly, SCAP showed high adaptability to these adverse conditions, retaining cell viability and acquiring a capillary-forming phenotype. SCAP secreted higher numbers and amounts of pro- (angiogenin, IGFBP-3, VEGF) and lower amounts of antiangiogenic factors (serpin-E1, TIMP-1, TSP-1) under SGOD compared with SOD or SD alone. Finally, secretome obtained under SGOD was most effective in inducing migration and capillary-like formation by HUVECs. These data provide new evidence on the microenvironmental factors favoring endothelial transdifferentiation of SCAP, uncovering the molecular mechanisms regulating their fate. They also validate the angiogenic properties of their secretome giving insights into preconditioning strategies enhancing their therapeutic potential.

Wnt/β-catenin signaling regulates Dental Pulp Stem Cells' responses to pulp injury by resinous monomers

OBJECTIVES

Aim of this study was to investigate whether Dental Pulp Stem Cells-DPSCs responses to pulp injury caused by resinous monomers is be mediated through activation of Wnt/β-catenin signaling.

METHODS

DPSCs cultures were established from third molars of healthy donors and characterized for stem cell markers with flow cytometry. Cells were exposed to TEGDMA (T: 0.5-2mM) with or without presence of the Wnt-1 ligand (W:25-100ng/ml) or the GSK3β inhibitor Lithium (L:1-10mM), used both as activators of Wnt/β-catenin signaling. Cell viability was evaluated by MTT assay, cell cycle profiles by flow cytometry and expression of key molecules of Wnt/β-catenin signaling by Real-time PCR and Western Blot.

RESULTS

DPSC exposure to TEGDMA caused a concentration-dependent cytotoxicity, accompanied by G1 arrest at lower and G2/M arrest at higher concentrations or after prolonged exposure. Lithium caused a dual effect, by stimulating/inhibiting cell proliferation at lower/higher concentrations respectively and causing a G2/M arrest in a concentration-dependent manner. Wnt signaling could be activated in DPSCs after Lithium or Wnt-1 treatment, as shown by accumulation of β-catenin, its translocation into the nucleus and enhanced expression of key pathway players, like LEF1 and Cyclin D1. Importantly, exposure to TEGDMA caused a more pronounced activation of the pathway, whereas cumulative effects were observed after T/L or T/W co-treatment, indicating a very strong activation of Wnt signaling after treatment of already "activated" (by Lithium or Wnt-1) cells with TEGDMA.

SIGNIFICANCE

These findings highlight the important role of Wnt canonical signaling in pulp repair responses to common injuries.

Dental pulp stem cells' secretome enhances pulp repair processes and compensates TEGDMA-induced cytotoxicity

OBJECTIVES

Aim of this study was to investigate the effects of dental pulp stem cells' (DPSCs) secretome, expressed through their culture conditioned medium (CM), on biological endpoints related to pulp repair and on TEGDMA-induced cytotoxicity.

METHODS

DPSCs cultures were established and characterized for stem cell markers with flow cytometry. CM was collected from DPSCs under serum deprivation conditions (SDC) and normal serum conditions (NSC) at various time-points. CM effects on DPSCs viability, migration and mineralization potential were evaluated by MTT assay, transwell insert and in vitro scratch assay and Alizarin Red staining/quantification respectively. TEGDMA (0.25-2.0mM) cytotoxicity regarding the same biological endpoints was tested in the presence/absence of CM. TGF-β1 and FGF-2 secretion in CM was measured by ELISA.

RESULTS

CM collected under SDC (4d) was able to increase cell viability by 20-25% and to reduce TEGDMA cytotoxicity by 20% (p<0.05). CM positive effects were not obvious when collected under NSC. Transwell assay showed significant increase (26%, p<0.05) of DPSCs' migration after CM exposure, whereas both migration assays could not support a migration rate improvement in TEGDMA-treated cultures exposed to CM compared to TEGDMA alone. CM significantly (p<0.01) increased DPSCs mineralization potential and completely counteracted TEGDMA cytotoxicity on this process. ELISA analysis showed a time-dependent increase of TGF-β1 and a TEGDMA concentration-dependent increase of both TGF-β1 and FGF-2 in CM.

SIGNIFICANCE

These findings suggest that DPSCs secretome increases their viability, migration and mineralization potential and counteracts TEGDMA-induced cytotoxicy, revealing a novel mechanism of DPSCs autocrine signaling on pulp repair processes.

Pulp fibroblasts synthesize functional complement proteins involved in initiating dentin-pulp regeneration

The complement system is an efficient plasma immune surveillance system that controls tissue injury and infection. Although the liver constitutes the primary circulating complement protein synthesis site, extrahepatic synthesis is known to optimize local tissue inflammatory reaction. Because dentin-pulp regeneration is known to be regulated locally, we investigated activation of the local complement system within the dental pulp and its role in initiating the regeneration process. Membrane attack complex (C5b-9) formation and Gram's staining revealed that complement activation is correlated with the presence of Gram-positive bacteria in carious human teeth. RT-PCR analysis demonstrated that cultured human pulp fibroblasts stimulated with lipoteichoic acid produce all the proteins required for efficient complement activation. This was demonstrated in vitro by C5b-9 formation and C5a active fragment production in the absence of plasma proteins. Finally, the dynamic migration assays performed in μ-Slide chemotaxis chambers and use of a C5aR-specific antagonist (W54011) demonstrated that the activation of complement proteins synthesized by pulp fibroblasts and the subsequent release of C5a specifically induced pulp progenitor cell recruitment. Our study reveals human pulp fibroblasts as the first nonimmune cell type capable of synthesizing all complement proteins. These fibroblasts cells contribute significantly to tissue regeneration by recruiting pulp progenitors via complement activation, which suggests to a potential therapeutic strategy of targeting pulp fibroblasts in dentin-pulp regeneration.