Determination of the optimal concentration and duration of C5aR antagonist application in an inflammatory model of human dental pulp cells

Deep tooth decay approaching the pulp may develop into pulpitis; to prevent this, pulp cells need to balance the rapid immune response to avoid rapid swelling of the pulp. Current treatment of deep decay that approaches the pulp involves the application of drugs that induce low-level inflammation in the dental pulp to promote its repair, but this treatment is sometimes insufficient. However, the unsuccessful treatment often resulted in pulpitis. The C5a-C5aR is the initial stage of the immune cascade response. Blocking the binding of C5a-C5aR can slow the immune response in the narrow pulp cavity, so that dental pulp cells have enough time to proliferate, migrate, and differentiate. In this study, we compared lipoteichoic acid (LTA) and lipopolysaccharides (LPS) at different concentrations and time points and used the C5aR antagonist W54011 to block the C5a-C5aR axis. The blocking effect was detected by analyzing the expression of C5a, C5aR, interleukin (IL)-6, and Toll-like receptors 2 and 4 (TLR-2, 4). Next, we determined the optimal concentration and duration of LTA and LPS treatment in combination with W54011. Based on our results, we selected 1.0 μg·mL-1 LPS treatment for 48 h to generate an inflammatory model of human dental pulp cells. We then regrouped the cells and conducted expression analyses to monitor the expression of C5a, C5aR, IL-6, and TLR-4 at the protein and mRNA levels. LPS stimulation for 48 h and treatment with W54011 for 48 h effectively inhibited inflammation and did not affect C5a expression. This study provides a basis for follow-up studies of W54011 in dental pulp cells.

C5a complement receptor modulates odontogenic dental pulp stem cell differentiation under hypoxia

AIM

Alterations in the microenvironment change the phenotypes of dental pulp stem cells (DPSCs). The role of complement component C5a in the differentiation of DPSCs is unknown, especially under oxygen-deprived conditions. The aim of this study was to determine the effect of C5a on the odontogenic differentiation of DPSCs under normoxia and hypoxia.

MATERIAL AND METHODS

Human DPSCs were subjected to odontogenic differentiation in osteogenic media and treated with the C5a receptor antagonist-W54011 under normal and hypoxic conditions (2% oxygen). Immunochemistry, western blot, and PCR analysis for the various odontogenic differentiation genes/proteins were performed.

RESULTS

Our results demonstrated that C5a plays a positive role in the odontogenic differentiation of DPSCs. C5a receptor inhibition resulted in a significant decrease in odontogenic differentiation genes, such as DMP1, ON, RUNX2, DSPP compared with the control. This observation was further supported by the Western blot data for DSPP and DMP1 and immunohistochemical analysis. The hypoxic condition reversed this effect.

CONCLUSIONS

Our results demonstrate that C5a regulates the odontogenic DPSC differentiation under normoxia. Under hypoxia, C5a exerts a reversed function for DPSC differentiation. Taken together, we identified that C5a and oxygen levels are key initial signals during pulp inflammation to control the odontogenic differentiation of DPSCs, thereby, providing a mechanism for potential therapeutic interventions for dentin repair and vital tooth preservation.

A role for the calcium-sensing receptor in the expression of inflammatory mediators in LPS-treated human dental pulp cells

The aim of this study is to investigate the role of calcium-sensing receptor (CaSR) in the expression of inflammatory mediators of lipopolysaccharide (LPS)-treated human dental pulp cells (hDPCs). The expression profile of CaSR in LPS-simulated hDPCs was detected using immunofluorescence, real time quantitative PCR (RT-qPCR), and Western blot analyses. Then, its regulatory effects on the expression of specific inflammatory mediators such as interleukin (IL)-1β, IL-6, cyclooxygenase 2 (COX2)-derived prostaglandin E2 (PGE₂), tumor necrosis factor (TNF)-α, and IL-10 were determined by RT-qPCR and enzyme-linked immunosorbent assay (ELISA). LPS significantly downregulated the gene expression of CaSR, but upregulated its protein expression level in hDPCs. Treatments by CaSR agonist R568 or its antagonist Calhex231, and their combinations with protein kinase B (AKT) inhibitor LY294002 showed obvious effects on the expression of selected inflammatory mediators in a time-dependent manner. Meanwhile, an opposite direction was found between the action of R568 and Calhex231, as well as the expression of the pro- (IL-1β, IL-6, COX2-derived PGE₂, and TNF-α) and anti-inflammatory (IL-10) mediators. The results provide the first evidence that CaSR-phosphatidylinositol-3 kinase (PI3K)-AKT-signaling pathway is involved in the release of inflammatory mediators in LPS-treated hDPCs, suggesting that the activation or blockade of CaSR may provide a novel therapeutic strategy for the treatment of pulp inflammatory diseases.

The role of complement C5a receptor in DPSC odontoblastic differentiation and in vivo reparative dentin formation

Therapeutic dentin regeneration remains difficult to achieve, and a majority of the attention has been given to anabolic strategies to promote dentinogenesis directly, whereas, the available literature is insufficient to understand the role of inflammation and inflammatory complement system on dentinogenesis. The aim of this study is to determine the role of complement C5a receptor (C5aR) in regulating dental pulp stem cells (DPSCs) differentiation and in vivo dentin regeneration. Human DPSCs were subjected to odontogenic differentiation in osteogenic media treated with the C5aR agonist and C5aR antagonist. In vivo dentin formation was evaluated using the dentin injury/pulp-capping model of the C5a-deficient and wild-type mice. In vitro results demonstrate that C5aR inhibition caused a substantial reduction in odontogenic DPSCs differentiation markers such as DMP-1 and DSPP, while the C5aR activation increased these key odontogenic genes compared to control. A reparative dentin formation using the C5a-deficient mice shows that dentin regeneration is significantly reduced in the C5a-deficient mice. These data suggest a positive role of C5aR in the odontogenic DPSCs differentiation and tertiary/reparative dentin formation. This study addresses a novel regulatory pathway and a therapeutic approach for improving the efficiency of dentin regeneration in affected teeth.

Role of Lipopolysaccharide, Derived from Various Bacterial Species, in Pulpitis—A Systematic Review

Lipopolysaccharide (LPS) is widely used for induction of inflammation in various human tissues, including dental pulp. The purpose of this study was to summarize current medical literature focusing on (1) cell types used by researchers to simulate dental pulp inflammation, (2) LPS variants utilized in experimental settings and how these choices affect the findings. Our study was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). We searched for studies reporting outcomes of lipopolysaccharide application on dental pulp cells in vitro using electronic databases: MEDLINE, Web of Science and Scopus. Having gathered data from 115 papers, we aimed to present all known effects LPS has on different cell types present in dental pulp. We focused on specific receptors and particles that are involved in molecular pathways. Our review provides an essential foundation for further research using in vitro models of pulpitis.

Different concentrations of C5a affect human dental pulp mesenchymal stem cells differentiation

Background

During the process of deep decay, when decay approaches the pulp, an immune response is triggered inside the pulp, which activates the complement cascade. The effect of complement component 5a (C5a) on the differentiation of dental pulp mesenchymal stem cells (DPSCs) is related to dentin reparation. The aim of the present study was to stimulate DPSCs with different concentrations of C5a and evaluate the differentiation of odontoblasts using dentin sialoprotein (DSP).

Methods

DPSCs were divided into the following six groups: (i) Control; (ii) DPSCs treated with 50 ng/ml C5a; (iii) DPSCs treated with 100 ng/ml C5a; (iv) DPSCs treated with 200 ng/ml C5a; (v) DPSCs treated with 300 ng/ml C5a; and (vi) DPSCs treated with 400 ng/ml C5a. Flow cytometry and multilineage differentiation potential were used to identify DPSCs. Mineralization induction, Real-time PCR and Western blot were conducted to evaluate the differentiation of odontoblast in the 6 groups.

Result

DPSCs can express mesenchymal stem cell markers, including CD105, CD90, CD73 and, a less common marker, mesenchymal stromal cell antigen-1. In addition, DPSCs can differentiate into adipocytes, neurocytes, chondrocytes and odontoblasts. All six groups formed mineralized nodules after 28 days of culture. Reverse transcription-quantitative PCR and western blotting indicated that the high concentration C5a groups expressed higher DSP levels and promoted DPSC differentiation, whereas the low concentration C5a groups displayed an inhibitory effect.

Conclusion

In this study, the increasing concentration of C5a, which accompanies the immune process in the dental pulp, has demonstrated an enhancing effect on odontoblast differentiation at higher C5a concentrations in vitro.

The molecular functions of Biodentine and mineral trioxide aggregate in lipopolysaccharide-induced inflamed dental pulp cells

AIM

To explore the proliferation, adhesion and differentiation response and the underlying mechanisms that occur in lipopolysaccharide (LPS)-induced inflamed dental pulp cells (DPCs) in contact with Biodentine and mineral trioxide aggregate (MTA).

METHODOLOGY

The DPCs were isolated from three healthy donors and named DPC-H1 to DPC-H3. The DPCs were pre-cultured with 2 or 5 μg mL^-1 LPS for 24 h to induce inflammation. The expression of inflammation marker miR-146a was detected by q-PCR. The normal and LPS-induced DPCs were further treated with 0.14 mg mL^-1 Biodentine or 0.13 mg mL^-1 MTA for 24 h. MTT assay and adhesion assay were used to analyse the changes of cell phenotypes. DSPP, AKT and ERK expressions were detected by Western blotting. The data were analysed by Mann-Whitney test or two-way anova. Differences were considered statistically significant when P < 0.05.

RESULTS

In LPS-induced DPCs, Biodentine and MTA treatment neither induced nor aggravated LPS-induced inflammation, but their presence did increase the expression of the odontogenic differentiation marker DSPP. Under 2 or 5 μg mL^-1 LPS-induced inflammation, Biodentine and MTA promoted the proliferation of DPC cells, and significantly in DPC-H2 (P < 0.0001 for both reagents). With the treatment of 2 μg mL^-1 LPS, the cell adhesion of DPCs on the fibronectin-coated culture plates was increased significantly by Biodentine (P = 0.0413) and MTA (P < 0.0001). Biodentine and MTA regulated cell adhesion on the fibronectin-coated culture plates (P < 0.0001 for both reagents) and proliferation (P < 0.0001 for both reagents) via the AKT pathway. However, the AKT pathway was not involved in the expression of DSPP induced by Biodentine and MTA.

CONCLUSION

Biodentine and MTA enhanced the proliferation, adhesion and differentiation of LPS-induced DPCs. The proliferation and adhesion process induced by Biodentine and MTA was via the AKT pathway. However, the cellular differentiation process might not use the same pathway, and this needs to be explored in future studies.

Investigation of PPARβ/δ within Human Dental Pulp Cells: A Preliminary In Vitro Study

Controlling the inflammatory response to restore tissue homeostasis is a crucial step to maintain tooth vitality after pathogen removal from caries-affected dental tissues. The nuclear peroxisome proliferator-activated receptor beta/delta (PPARβ/δ) is a ligand-activated transcription factor with emerging anti-inflammatory roles in many cells and tissues. However, its expression and functions are poorly understood in human dental pulp cells (hDPCs). Thus, this study evaluated PPARβ/δ expression and assessed the anti-inflammatory effects evoked by activation of PPARβ/δ in lipopolysaccharide- (LPS-) induced hDPCs. Our results showed that hDPCs constitutively expressed PPARβ/δ mRNA/protein, and treatment with LPS increased PPARβ/δ mRNA expression. The selective PPARβ/δ agonist GW0742 significantly decreased inflammation-related mRNA expression in hDPCs (IL6, IL1β, TNFα, MMP1, and MMP2) and RAW264.7 cells (Il6 and Tnfα). Further, PPARβ/δ agonist attenuated MMP2/9 gelatinolytic activity in hDPCs. Previously LPS-conditioned hDPCs increased the migration of RAW264.7 cells through the membrane of a Transwell coculture system. Conversely, pretreatment with GW0742 markedly decreased macrophage recruitment. These findings provide among the first evidence that hDPCs express PPARβ/δ. In addition, they suggest that activation of PPARβ/δ by GW0742 can attenuate some cellular and molecular in vitro aspects related to the inflammatory process, pointing out to investigate its potential target role in dental pulp inflammation.

Melatonin alleviates LPS-induced endoplasmic reticulum stress and inflammation in spermatogonial stem cells

Orchitis is one of the leading causes of male animal infertility and is associated with inflammatory reactions caused by the bacterium. It has been reported that there is a mutual coupling effect between endoplasmic reticulum stress (ERS) and inflammatory response. Our studies showed that lipopolysaccharide (LPS) could cause testicular damages, apoptosis, ERS, and inflammatory responses in spermatogonial stem cells (SSCs); ERS-related apoptosis proteins were activated and the expression of ERS genes was significantly upregulated; meanwhile, the expression of Toll-like receptor 4 and inflammation factors was apparently increased with LPS treatment. Moreover, melatonin (MEL) could rescue testicular damage, and significantly inhibited the expression of ERS-related apoptosis genes, ERS markers, and inflammatory factors in SSCs and MEL played repairing and anti-infection roles in LPS-induced testicular damage. Therefore, MEL may be used as a drug to prevent and control bacterial infections in male reproductive systems. However, the specific molecular mechanism of MEL to resist ERS and inflammatory response remains to be further studied.

Human amniotic mesenchymal stromal cells promote bone regeneration via activating endogenous regeneration

Rationale: The effectiveness of stem cell based-therapy for bone regeneration has been demonstrated; yet, clinical application of autologous stem cells is still limited by invasive acquisition, long culture processes, and high cost. Besides, it remains controversial whether autologous stem cells could directly participate in tissue repair after differentiation. Thus, increasing allogeneic stem cells have been developed into drugs to indirectly activate endogenous regeneration and induce tissue regeneration. Human amniotic mesenchymal stromal cells (HAMSCs) have been extensively studied, showing multiple regulatory functions, but mechanisms of HAMSCs in promoting bone regeneration are remain unclear. Methods: Proteome profile of HAMSCs and their functions on vascularized bone regeneration were investigated in vitro, while rabbit cranial defect model was used to further detect the effects of bone formation in vivo. Results: HAMSCs secrete many osteogenic, angiogenic, and immunomodulatory cytokines. In vitro, HAMSCs can promote human bone-marrow mesenchymal stromal cells (HBMSCs) migration and osteogenic differentiation; promote the capillary-tube formation of human umbilical vascular endothelial cells (HUVECs), induce HUVECs migration and pro-angiogenic genes expression, and promote M2 macrophage polarization. Further, in vivo studies suggested that transplanted HAMSCs could survive and induce M2 macrophages to secrete bone morphogenetic protein-2 (BMP-2) and vascular endothelial growth factor (VEGF) in rabbits' skull defects at an early stage, and, in turn, promote more new bone formation. Conclusion: HAMSCs have good biocompatibility and paracrine function to promote bone repair by stimulating endogenous regeneration.

Non-immunogenic, low-toxicity and effective glioma targeting MTI-31 liposomes

Liposomes with peptide motifs have been successfully used in glioma-targeted delivery of various general chemotherapy agents. However, their use for the encapsulation of low-toxicity molecularly targeted anticancer agents has been limited. In the present study, we aimed to assess the efficacy and safety of a novel low-toxicity mTORC1/mTORC2 inhibitor (MTI-31) as a treatment for glioma when encapsulated in appropriate liposomes. Since some of the peptide-modified liposomes have been determined to be immunogenic and may have life-threatening consequences in mice, an immunogenicity-based investigation with candidate liposomal carriers was conducted. Following this study, ^DVAP (^DP^DA^DV^DR^DT^DN^DS) modified liposomes (^DVAP-liposomes) were identified as an immunologically safe carrier and therefore utilized for MTI-31 encapsulation. ^DVAP is a tumor homing peptide exhibiting high binding affinity to glucose regulated protein 78 (GRP78) overexpressed in glioma, glioma stem cells, vasculogenic mimicry and neovasculature. Modification of liposomes with ^DVAP imparts a glioma-directing property. In vitro, the developed ^DVAP-liposomes/MTI-31 were efficiently internalized by U87 cells and consequently showed a potent antiproliferation effect. In vivo, the safety and anti-glioma efficiency of ^DVAP-liposomes/MTI-31 were validated in intracranial glioma bearing BALB/c nude mice. While showing both systemic and immunological safety, ^DVAP-liposome/MTI-31 treatment resulted in a significant improvement in the median survival time (24.5 days for saline, 26 days for free MTI-31, 25 days for liposomes/MTI-31 and 36 days for ^DVAP-liposome/MTI-31). The results highlight MTI-31 as an effective anti-glioma agent when encapsulated in non-immunogenic glioma-targeted liposomes, which may contribute to the development of better anti-glioma treatment.

Time-dependent C5a and C5aR expression in dental pulp cells following stimulation with LTA and LPS

Clinically, deep decay can lead to inflammation in the dental pulp. Apart from the use of various materials to sooth the inflamed pulp, there is currently no adequate treatment, and the gold standard, calcium hydroxide, that is used to cover the dentin/pulp, has limited effect. Sometimes the pulp will remain infected and cause pulpitis, and ultimately, the pulp will need to be removed. The first principle of oral treatment is to protect the pulp. Therefore, it is necessary to study the immune response and regeneration of pulp cells in conditions of deep decay. Of the terminal complement system proteins, complement 5a (C5a) has the most potent effect compared to complement 3a (C3a) and complement 4a (C4a). C5a is 20- to 2,500-fold stronger than C3a and C4a. The purpose of this study was to elucidate the association between C5a, secreted by complement activation, and the duration of inflammation. Another key goal was to detect the expression of C5a and its receptor, complement 5a receptor (C5aR). To this end, the cells were divided into 4 groups as per stimulation with lipoteichoic acid (LTA) or lipopolysaccharide (LPS) as follows: i) The 1 µg/ml LTA group; ii) the 1 µg/ml LPS group; iii) the 1 µg/ml LTA and 1 µg/ml LPS group; and iv) the PBS-only group, which served as a control. There were 5 time points for all 4 groups: 1, 2, 3, 5 and 7 days. Reverse transcription-quantitative polymerase chain reaction was used to detect the gene expression levels of C5a, C5aR and interleukin (IL)-6 at different time points. Western blot analyses was carried out to detect the expression of C5aR. Transmission electron microscopy was also conducted to assess the ultra-structural features of dental pulp cells. The gene expression trends of C5a and C5aR mRNA were identical. C5a and C5aR mRNA was highly expressed on the second day of LTA or LPS stimulation. However, in the LTA and LPS co-stimulation group, C5a and C5aR mRNA were highly expressed on both the first and second day, with higher levels on the second day. IL-6 expression decreased as time progressed in the LTA only and in the LTA + LPS co-stimulation groups. However, a peak in its expression was observed on the second day in the LPS group. On the whole, this study demonstrates that a 1 µg/ml concentration of LTA and LPS stimulates human dental pulp cells to activate the expression of C5a.

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.

Interactive effects of LPS and dentine matrix proteins on human dental pulp stem cells

AIM

To investigate the combinatorial effects of lipopolysaccharide (LPS) and extracted dentine matrix proteins (eDMP) on regenerative and inflammatory responses in human dental pulp stem cells (DPSCs).

METHODOLOGY

Culture media were supplemented with several concentrations of LPS, eDMP and combinations of both. Cell viability was assessed over 1 week by MTT assay; cell survival was evaluated after 24 h and 7 days by flow cytometry. The expression of mineralization-associated marker genes was determined by real-time quantitative polymerase chain reaction (RT-qPCR). To analyse the inflammatory response, secretion of interleukin 6 (IL-6) was quantified in the initial and the late phase of cell culture by enzyme-linked immunosorbent assay (ELISA). Data were treated nonparametrically and Mann-Whitney U-tests were performed to compare all experimental groups (α = 0.05).

RESULTS

Whereas LPS had no impact on viability, eDMP led to a concentration-dependent decrease, which was significant after 7 days (P ≤ 0.024). A moderate decline of cell survival induced by LPS was detected after 48 h (P ≤ 0.026), whereas eDMP was able to reverse this effect. eDMP alone caused increased expression of tested marker genes, LPS had no regulatory effect. Combined eDMP and LPS induced an upregulation of collagen type I and osteocalcin, whereas expression levels of dentine matrix acidic phosphoprotein and dentine sialophosphoprotein were similar to the control. IL-6-secretion was increased by LPS over time. eDMP markedly elevated initial production of IL-6 (P ≤ 0.002), but suppressed LPS-induced cytokine production in the later phase.

CONCLUSIONS

Lipopolysaccharide did not affect cell viability but interfered with odontoblast-like cell differentiation of DPSCs. Proteins from the dentine matrix may have a protective effect, attenuate the detrimental impact of LPS and thus play an important role during pulp repair.

Complement Activation by Pulp Capping Materials Plays a Significant Role in Both Inflammatory and Pulp Stem Cells' Recruitment

INTRODUCTION

The role of complement, especially through the C5a fragment, is well-known for the initiation of inflammation. Its involvement in regeneration has been shown more recently by the recruitment of mesenchymal stem cells. C5a can be produced locally by the pulp fibroblasts in response to injury or infection. This work aims to investigate the effect of different pulp capping biomaterials on complement activation and its possible influence on inflammatory and pulp stem cell recruitment.

METHODS

Conditioned media were prepared from 3 pulp capping biomaterials: Biodentine (Septodont, Saint-Maur-des-Fosses, France), TheraCal (BISCO, Lançon De Provence, France), and Xeno III (Dentsply Sirona, Versaille, France). Injured pulp fibroblasts were cultured with these conditioned media to analyze C5a secretion using an enzyme-linked immunosorbent assay. Dental pulp stem cells (DPSCs) were isolated from human third molar explants by magnetic cell sorting with STRO-1 antibodies. The expression of C5a receptor on DPSCs and inflammatory (THP-1) cells was investigated by immunofluorescence. The migration of both DPSCs and THP-1 cells was studied in Boyden chambers.

RESULTS

Pulp fibroblast production of C5a significantly increased when the cells were incubated with TheraCal- and Xeno III-conditioned media. The recruitment of cells involved in inflammation (THP-1 cells) was significantly reduced by Biodentine- and TheraCal-conditioned media, whereas the migration of DPSCs was reduced with TheraCal- and Xeno III-conditioned media but not with that of Biodentine. The involvement of C5a in cell recruitment is demonstrated with a C5a receptor-specific antagonist (W54011).

CONCLUSIONS

After pulp injury, the pulp capping material affects complement activation and the balance between inflammation and regeneration through a differential recruitment of DPSCs or inflammatory cells.

Nerve Growth Factor Secretion From Pulp Fibroblasts is Modulated by Complement C5a Receptor and Implied in Neurite Outgrowth

Given the importance of sensory innervation in tooth vitality, the identification of signals that control nerve regeneration and the cellular events they induce is essential. Previous studies demonstrated that the complement system, a major component of innate immunity and inflammation, is activated at the injured site of human carious teeth and plays an important role in dental-pulp regeneration via interaction of the active Complement C5a fragment with pulp progenitor cells. In this study, we further determined the role of the active fragment complement C5a receptor (C5aR) in dental nerve regeneration in regards to local secretion of nerve growth factor (NGF) upon carious injury. Using ELISA and AXIS co-culture systems, we demonstrate that C5aR is critically implicated in the modulation of NGF secretion by LTA-stimulated pulp fibroblasts. The NGF secretion by LTA-stimulated pulp fibroblasts, which is negatively regulated by C5aR activation, has a role in the control of the neurite outgrowth length in our axon regeneration analysis. Our data provide a scientific step forward that can guide development of future therapeutic tools for innovative and incipient interventions targeting the dentin-pulp regeneration process by linking the neurite outgrowth to human pulp fibroblast through complement system activation.

Complement C3a Mobilizes Dental Pulp Stem Cells and Specifically Guides Pulp Fibroblast Recruitment

INTRODUCTION

Complement activation is considered a major mechanism in innate immunity. Although it is mainly involved in initiating inflammation, recent data reported its involvement in other processes such as tissue regeneration. In the dental pulp, complement C5a fragment has been shown to be involved in the recruitment of dental pulp stem cells (DPSCs). This study sought to investigate the possible role of C3a, another complement fragment, in the early steps of dentin-pulp regeneration.

METHODS

Expression of C3a receptor (C3aR) was investigated by immunofluorescence and reverse transcriptase polymerase chain reaction on cultured pulp fibroblasts, STRO-1-sorted DPSCs, as well as on human tooth sections in vivo. The effect of C3a on proliferation of both DPSCs and pulp fibroblasts was investigated by MTT assay. Cell migration under a C3a gradient was investigated by using microfluidic chemotaxis chambers.

RESULTS

C3aR was expressed in vivo as well as in cultured pulp fibroblasts co-expressing fibroblast surface protein and in DPSCs co-expressing STRO-1. Addition of recombinant C3a induced a significant proliferation of both cell types. When subjected to a C3a gradient, DPSCs were mobilized but not specifically recruited, whereas pulp fibroblasts were specifically recruited following a C3a gradient.

CONCLUSIONS

These results provide the first demonstration of C3aR expression in the dental pulp and demonstrate that C3a is involved in increasing DPSCs and fibroblast proliferation, in mobilizing DPSCs, and in specifically guiding fibroblast recruitment. This provides an additional link to the tight correlation between inflammation and tissue regeneration.

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.

Dental Pulp Stem Cell Recruitment Signals within Injured Dental Pulp Tissue

The recruitment of dental pulp stem cells (DPSC) is a prerequisite for the regeneration of dentin damaged by severe caries and/or mechanical injury. Understanding the complex process of DPSC recruitment will benefit future in situ tissue engineering applications based on the stimulation of endogenous DPSC for dentin pulp regeneration. The current known mobilization signals and subsequent migration of DPSC towards the lesion site, which is influenced by the pulp inflammatory state and the application of pulp capping materials, are reviewed. The research outcome of migration studies may be affected by the applied methodology, which should thus be chosen with care. Both the advantages and disadvantages of commonly used assays for investigating DPSC migration are discussed. This review highlights the fact that DPSC recruitment is dependent not only on the soluble chemotactic signals, but also on their interaction with neighboring cells and the extracellular matrix, which can be modified under pathological conditions. These are discussed to explain how these modifications lead to the stimulation of DPSC recruitment.