Can Pulp Fibroblasts Kill Cariogenic Bacteria? Role of Complement Activation

Vital pulp therapy for permanent teeth with diagnosis of irreversible pulpitis: biological basis and outcome

Root canal treatment (RCT) has been considered the conventional standard for the management of teeth with carious pulp exposure, particularly in mature teeth presenting with symptoms. Following a better understanding of the histopathology of deep carious lesions, the histology of the cariously exposed pulp and the healing potential of the inflamed pulp, vital pulp therapy (VPT) is increasingly adopted around the world for the management of permanent teeth with clinical signs and symptoms indicative of irreversible pulpitis. Furthermore, VPT became a recognized treatment modality by the European Society of Endodontology (ESE) and the American Association of Endodontists (AAE) by virtue of its high success rates reported in outcome studies using contemporary hydraulic calcium silicate-based cements. However, proper case selection, strict asepsis, capping materials and good coronal seal are mandatory for success. The aim of this paper is to review the biological basis for VPT in symptomatic teeth with carious pulp exposure and to report on the outcome of pulpotomy in teeth with clinical diagnosis of irreversible pulpitis.

Engineered Lactococcus lactis secreting Flt3L and OX40 ligand for in situ vaccination-based cancer immunotherapy

In situ vaccination is a promising strategy to convert the immunosuppressive tumor microenvironment into an immunostimulatory one with limited systemic exposure and side effect. However, sustained clinical benefits require long-term and multidimensional immune activation including innate and adaptive immunity. Here, we develop a probiotic food-grade Lactococcus lactis-based in situ vaccination (FOLactis) expressing a fusion protein of Fms-like tyrosine kinase 3 ligand and co-stimulator OX40 ligand. Intratumoural delivery of FOLactis contributes to local retention and sustained release of therapeutics to thoroughly modulate key components of the antitumour immune response, such as activation of natural killer cells, cytotoxic T lymphocytes, and conventional-type-1-dendritic cells in the tumors and tumor-draining lymph nodes. In addition, intratumoural administration of FOLactis induces a more robust tumor antigen-specific immune response and superior systemic antitumour efficacy in multiple poorly immune cell-infiltrated and anti-PD1-resistant tumors. Specific depletion of different immune cells reveals that CD8⁺ T and natural killer cells are crucial to the in situ vaccine-elicited tumor regression. Our results confirm that FOLactis displays an enhanced antitumour immunity and successfully converts the 'cold' tumors to 'hot' tumors.

Minimally invasive endodontics: a new era for pulpotomy in mature permanent teeth

Emerging clinical and histologic evidence is challenging the long-established dogma that root canal treatment (RCTx) is the only therapeutic option for preservation of vital mature permanent teeth diagnosed with irreversible pulpitis or carious pulp exposure. Vital pulp therapy procedures like pulpotomy are not only technically simpler and more economical, but also afford patients a host of other benefits over conventional RCTx. This narrative review provides an update on the contemporary understanding of pulp pathophysiology and defence mechanisms, the proposed new diagnostic terminologies for pulpal inflammation, and how the biological characteristics of hydrophilic calcium silicate cements have enabled consistent successful outcomes for pulpotomy-treated mature teeth. The paper also details the evidence base from clinical trials and systematic reviews conducted over the past decade and outlines the practical treatment considerations for pulpotomy in mature permanent teeth.

Novel Antibacterial Properties of the Human Dental Pulp Multipotent Mesenchymal Stromal Cell Secretome

It is well recognized that clearance of bacterial infection within the dental pulp precedes pulpal regeneration. However, although the regenerative potential of the human dental pulp has been investigated extensively, its antimicrobial potential remains to be examined in detail. In the current study bactericidal assays were used to demonstrate that the secretome of dental pulp multipotent mesenchymal stromal cells (MSCs) has direct antibacterial activity against the archetypal Gram-positive and Gram-negative bacteria, Staphylococcus aureus and Escherichia coli, respectively, as well as the oral pathogens Streptococcus mutans, Lactobacillus acidophilus, and Fusobacterium nucleatum. Furthermore, a cytokine/growth factor array, enzyme-linked immunosorbent assays, and antibody blocking were used to show that cytokines and growth factors present in the dental pulp MSC secretome, including hepatocyte growth factor, angiopoietin-1, IL-6, and IL-8, contribute to this novel antibacterial activity. This study elucidated a novel and diverse antimicrobial secretome from human dental pulp MSCs, suggesting that these cells contribute to the antibacterial properties of the dental pulp. With this improved understanding of the secretome of dental pulp MSCs and its novel antibacterial activity, new evidence for the ability of the dental pulp to fight infection and restore functional competence is emerging, providing further support for the biological basis of pulpal repair and regeneration.

A critical analysis of research methods and experimental models to study pulpitis

Pulpitis is the inflammatory response of the dental pulp to a tooth insult, whether it is microbial, chemical, or physical in origin. It is traditionally referred to as reversible or irreversible, a classification for therapeutic purposes that determines the capability of the pulp to heal. Recently, new knowledge about dental pulp physiopathology led to orientate therapeutics towards more frequent preservation of pulp vitality. However, full adoption of these vital pulp therapies by dental practitioners will be achieved only following better understanding of cell and tissue mechanisms involved in pulpitis. The current narrative review aimed to discuss the contribution of the most significant experimental models developed to study pulpitis. Traditionally, in vitro two(2D)- or three(3D)-dimensional cell cultures or in vivo animal models were used to analyse the pulp response to pulpitis inducers at cell, tissue or organ level. In vitro 2D cell cultures were mainly used to decipher the specific roles of key actors of pulp inflammation such as bacterial by-products, pro-inflammatory cytokines, odontoblasts or pulp stem cells. However, these simple models did not reproduce the 3D organisation of the pulp tissue and, with rare exceptions, did not consider interactions between resident cell types. In vitro tissue/organ-based models were developed to better reflect the complexity of the pulp structure. Their major disadvantage is that they did not allow the analysis of blood supply and innervation participation. On the contrary, in vivo models have allowed researchers to identify key immune, vascular and nervous actors of pulpitis and to understand their function and interplay in the inflamed pulp. However, inflammation was mainly induced by iatrogenic dentine drilling associated with simple pulp exposure to the oral environment or stimulation by individual bacterial by-products for short periods. Clearly, these models did not reflect the long and progressive development of dental caries. Lastly, the substantial diversity of the existing models makes experimental data extrapolation to the clinical situation complicated. Therefore, improvement in the design and standardization of future models, for example by using novel molecular biomarkers, databased models and artificial intelligence, will be an essential step in building an incremental knowledge of pulpitis in the future.

Complementing the pulp proteome via sampling with a picosecond infrared laser (PIRL)

OBJECTIVES

The aim of this investigation was the detailed analysis of the human pulp proteome using the new picosecond infrared laser (PIRL)-based sampling technique, which is based on a completely different mechanism compared to mechanical sampling. Proteome analysis of healthy pulp can provide data to define changes in the proteome associated with dental disease.

MATERIAL AND METHODS

Immediately after extraction of the entire, undamaged tooth, 15 wisdom teeth were deep frozen in liquid nitrogen and preserved at -80°C. Teeth were crushed, and the excised frozen pulps were conditioned for further analysis. The pulps were sampled using PIRL, and the aspirates digested with trypsin and analyzed with mass spectrometry. Pulp proteins were categorized according to their gene ontology terminus. Proteins identified exclusively in this study were searched in the Human Protein Atlas (HPA) for gaining information about the main known localization and function.

RESULTS

A total of 1348 proteins were identified in this study. The comparison with prior studies showed a match of 72%. Twenty-eight percent of the proteins were identified exclusively in this study. Considering HPA, almost half of these proteins were assigned to tissues that could be pulp specific.

CONCLUSION

PIRL is releasing proteins from the dental pulp which are not dissolved by conventional sampling techniques. Clinical Relevance The presented data extend current knowledge on dental pulp proteomics in healthy teeth and can serve as a reference for studies on pulp proteomics in dental disease.

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.

Ultrashort Peptide Hydrogels Display Antimicrobial Activity and Enhance Angiogenic Growth Factor Release by Dental Pulp Stem/Stromal Cells

Recent studies on peptide hydrogels have shown that ultrashort peptides (<8 amino acids) can self-assemble into hydrogels. Ultrashort peptides can be designed to incorporate antimicrobial motifs, such as positively charged lysine residues, so that the peptides have inherent antimicrobial characteristics. Antimicrobial hydrogels represent a step change in tissue engineering and merit further investigation, particularly in applications where microbial infection could compromise healing. Herein, we studied the biocompatibility of dental pulp stem/stromal cells (DPSCs) with an ultrashort peptide hydrogel, (naphthalene-2-ly)-acetyl-diphenylalanine-dilysine-OH (NapFFεKεK-OH), where the epsilon (ε) amino group forms part of the peptide bond rather than the standard amino grouping. We tested the antimicrobial properties of NapFFεKεK-OH in both solution and hydrogel form against Staphylococcus aureus, Enterococcus faecalis and Fusobacterium nucleatum and investigated the DPSC secretome in hydrogel culture. Our results showed NapFFεKεK-OH hydrogels were biocompatible with DPSCs. Peptides in solution form were efficacious against biofilms of S. aureus and E. faecalis, whereas hydrogels demonstrated antimicrobial activity against E. faecalis and F. nucleatum. Using an angiogenic array we showed that DPSCs encapsulated within NapFFεKεK-OH hydrogels produced an angiogenic secretome. These results suggest that NapFFεKεK-OH hydrogels have potential to serve as novel hydrogels in tissue engineering for cell-based pulp regeneration.

Inflammatory Response Mechanisms of the Dentine-Pulp Complex and the Periapical Tissues

The macroscopic and microscopic anatomy of the oral cavity is complex and unique in the human body. Soft-tissue structures are in close interaction with mineralized bone, but also dentine, cementum and enamel of our teeth. These are exposed to intense mechanical and chemical stress as well as to dense microbiologic colonization. Teeth are susceptible to damage, most commonly to caries, where microorganisms from the oral cavity degrade the mineralized tissues of enamel and dentine and invade the soft connective tissue at the core, the dental pulp. However, the pulp is well-equipped to sense and fend off bacteria and their products and mounts various and intricate defense mechanisms. The front rank is formed by a layer of odontoblasts, which line the pulp chamber towards the dentine. These highly specialized cells not only form mineralized tissue but exert important functions as barrier cells. They recognize pathogens early in the process, secrete antibacterial compounds and neutralize bacterial toxins, initiate the immune response and alert other key players of the host defense. As bacteria get closer to the pulp, additional cell types of the pulp, including fibroblasts, stem and immune cells, but also vascular and neuronal networks, contribute with a variety of distinct defense mechanisms, and inflammatory response mechanisms are critical for tissue homeostasis. Still, without therapeutic intervention, a deep carious lesion may lead to tissue necrosis, which allows bacteria to populate the root canal system and invade the periradicular bone via the apical foramen at the root tip. The periodontal tissues and alveolar bone react to the insult with an inflammatory response, most commonly by the formation of an apical granuloma. Healing can occur after pathogen removal, which is achieved by disinfection and obturation of the pulp space by root canal treatment. This review highlights the various mechanisms of pathogen recognition and defense of dental pulp cells and periradicular tissues, explains the different cell types involved in the immune response and discusses the mechanisms of healing and repair, pointing out the close links between inflammation and regeneration as well as between inflammation and potential malignant transformation.

Dentin-Pulp Tissue Regeneration Approaches in Dentistry: An Overview and Current Trends

Conventional treatment approaches in irreversible pulpitis and apical periodontitis include the disinfection of the pulp space followed by filling with various materials, which is commonly known as the root canal treatment. Disadvantages including the loss of tooth vitality and defense mechanism against carious lesions, susceptibility to fractures, discoloration and microleakage led to the development of regenerative therapies for the dentin pulp-complex. The goal of dentin-pulp tissue regeneration is to reestablish the physiological pulp function such as pulp sensibility, pulp repair capability by mineralization and pulp immunity. Recent dentin-pulp tissue regeneration approaches can be divided into cell homing and cell transplantation. Cell based approaches include a suitable scaffold for the delivery of potent stem cells with or without bioactive molecules into the root canal system while cell homing is based on the recruitment of host endogenous stem cells from the resident tissue including periapical region or dental pulp. This review discusses the recent treatment modalities in dentin-pulp tissue regeneration through tissue engineering and current challenges and trends in this field of research.

Complement activation links inflammation to dental tissue regeneration

OBJECTIVES

Complement is an efficient plasma immune surveillance system. It initiates inflammation by inducing vascular modifications and attracting immune cells expressing Complement receptors. Investigating Complement receptors in non-immune cells pointed out Complement implication in the regeneration of tissue such as liver, skin, or bone. This review will shed the light on Complement implication in the initial steps of dental tissue regeneration.

MATERIALS AND METHODS

Review of literature was conducted on Complement local expression and implication in oral tissue regeneration in vivo and in vitro.

RESULTS

Recent data reported expression of Complement receptors and soluble proteins in dental tissues. Cultured pulp fibroblasts secrete all Complement components. Complement C3b and MAC have been shown to control bacteria growth in the dental pulp while C3a and C5a are involved in the initial steps of pulp regeneration. Indeed, C3a induces pulp stem cell/fibroblast proliferation, and fibroblast recruitment, while C5a induces neurite growth, guides stem cell recruitment, and odontoblastic differentiation. Similarly, cultured periodontal ligament cells produce C5a which induces bone marrow mesenchymal stem cell recruitment.

CONCLUSIONS

Overall, this review highlights that local Complement synthesis in dental tissues plays a major role, not only in eliminating bacteria but also in the initial steps of dental tissue regeneration, thus providing a link between dental tissue inflammation and regeneration.

CLINICAL RELEVANCE

Complement provides an explanation for understanding why inflammation preceeds regeneration. This may also provide a biological rational for understanding the reported success conservative management of mature permanent teeth with carious pulp exposure.

Natural Antimicrobials in the Dental Pulp

INTRODUCTION

Like many tissues, the dental pulp is equipped with innate and adaptive immune responses, designed to defend against infection and limit its spread. The pulp's innate immune response includes the synthesis and release of antimicrobial peptides by several dental pulp cell types. These naturally-occurring antimicrobial peptides have broad spectrum activity against bacteria, fungi and viruses. There is a resurgence of interest in the bioactivities of naturally-occurring antimicrobial peptides, largely driven by the need to develop alternatives to antibiotics.

METHODS

This narrative review focused on the general properties of antimicrobial peptides, providing an overview of their sources and actions within the dental pulp.

RESULTS

We summarized the relevance of antimicrobial peptides in defending the dental pulp, highlighting the potential for many of these antimicrobials to be modified or mimicked for prospective therapeutic use.

CONCLUSION

Antimicrobial peptides and novel peptide-based therapeutics are particularly attractive as emerging treatments for polymicrobial infections, such as endodontic infections, because of their broad activity against a range of pathogens.

Pulp Fibroblast Contribution to the Local Control of Pulp Inflammation via Complement Activation

Upon traumatic injuries or carious lesions, the elimination of bacteria infiltrating the pulp is recognized as a prerequisite for initiating the regeneration process. Complement is a major system involved in initiating the inflammatory reaction and the subsequent bacteria elimination. This plasma system of above 35 proteins is synthesized by the liver and some immune cells. It is activated by 3 pathways: the classical, alternative, and lectin pathways that can be triggered by physical injuries, infection, and biomaterials. Recent data have shown that the pulp fibroblast represents a unique nonimmune cell type able to synthesize Complement proteins. Indeed, after physical injuries/bacteria stimulation, the pulp fibroblast has been shown to synthesize and to activate the complement system leading to the production of biologically active molecules such as C5a, C3b, and the membrane attack complex. This local secretion represents a rapid and efficient mechanism for eliminating bacteria invading the pulp, thus supporting complement activation from the plasma. Pulp fibroblast-secreted Complement proteins allow cariogenic bacteria direct lysis via membrane attack complex formation on their surface, phagocytic cell recruitment by producing C5a and cariogenic bacteria opsonization by C3b fixation on their surface, stimulating cariogenic bacteria phagocytosis. Overall, this review highlights that, in addition to initiating the inflammatory reaction, pulp fibroblasts also provide a powerful control of this inflammation via local Complement activation. The pathogen elimination capacity by fibroblast-produced complement demonstrates that this system is a strong local actor in arresting bacterial progression into the dental pulp.

Xenogeneic bone filling materials modulate mesenchymal stem cell recruitment: role of the Complement C5a

OBJECTIVES

When bone filling materials are applied onto the periodontal tissues in vivo, they interact with the injured periodontal ligament (PDL) tissue and modulate its activity. This may lead to mesenchymal stem cells (MSCs) recruitment from bone marrow and initiate bone regeneration. Our hypothesis is that the filling materials affect PDL cells and MSCs functional activities by modulating PDL C5a secretion and subsequent MSCs proliferation and recruitment.

MATERIALS AND METHODS

Materials' extracts were prepared from 3 bone-grafting materials: Gen-Os^® of equine and porcine origins and bovine Bio-Oss^®. Expression and secretion of C5a protein by injured PDL cells were investigated by RT-PCR and ELISA. MSCs proliferation was analyzed by MTT assay. C5a binding to MSCs C5aR and its phosphorylation was studied by ELISA. C5a implication in MSCs recruitment toward injured PDL cells was investigated using Boyden chambers.

RESULTS

MSCs proliferation significantly increased with Gen-Os^® materials but significantly decreased with Bio-Oss^®. C5a secretion slightly increased with Bio-Oss^® while its level doubled with Gen-Os^® materials. C5a fixation on MSCs C5aR and its phosphorylation significantly increased with Gen-Os^® materials but not with Bio-Oss^®. MSCs recruitment toward injured PDL cells increased with the three materials but was significantly higher with Gen-Os^® materials than with Bio-Oss^®. Adding C5a antagonist inhibited MSCs recruitment demonstrating a C5a-mediated migration.

CONCLUSIONS

Injured PDL cells secrete C5a leading MSCs proliferation and recruitment to the PDL injured cells. Gen-Os^® materials enhanced both C5a secretion by injured PDL cells and MSCs recruitment. Bio-Oss^® inhibited MSCs and was less efficient than Gen-Os^® materials in inducing MSCs recruitment.

CLINICAL RELEVANCE

Within the limits of this study in vitro, Gen-Os^® filling materials have a higher potential than Bio-Oss^® on MSCs proliferation and C5a-dependent recruitment to the PDL injury site and the subsequent bone regeneration.

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.

Human Pulp Fibroblast Implication in Phagocytosis via Complement Activation

INTRODUCTION

Previous works have shown that human pulp fibroblasts synthetize all complement components. Local complement activation in the dental pulp is known to be involved in inflammation and regeneration and also in pathogen destruction through membrane attack complex formation. Bacterial elimination by complement-mediated phagocytosis implies microorganism opsonization with the complement C3b protein, which is recognized by specific phagocytic cell CR1 receptors for subsequent intracellular destruction. This work was designed to find out whether pulp fibroblasts produce C3b and check its subsequent implication in bacteria phagocytosis.

METHODS

The expression of C3b was investigated in carious and healthy human pulp tissues. To simulate a bacterial infection in vitro, cultured human pulp fibroblasts were stimulated with lipoteichoic acid, and C3b secretion was quantified by an enzyme-linked immunosorbent assay. C3b fixation on bacteria (opsonization) and the inflammatory THP-1 cell complement receptor 1 was studied by immunofluorescence. A gentamycin protection assay was used to check the implication of C3b secretion by fibroblasts in bacteria phagocytosis.

RESULTS

Pulp cells constitutively express C3b in vivo, and cultured pulp fibroblasts produce C3b. We observed a fixation of this C3b protein on the bacterial surface (opsonization) and the THP-1 CR1 receptor. This recognition leads to a significant increase in bacteria phagocytosis.

CONCLUSIONS

These results showed that pulp fibroblasts mediate the process of phagocytosis by producing the complement C3b protein and opsonizing bacteria. This highlights a significant role of fibroblasts in the dental pulp local regulation of inflammation.

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.

Pulp capping materials modulate the balance between inflammation and regeneration

The interrelations between inflammation and regeneration are of particular significance within the dental pulp tissue inextensible environment. Recent data have demonstrated the pulp capacity to respond to insults by initiating an inflammatory reaction and dentin pulp regeneration. Different study models have been developed in vitro and in vivo to investigate the initial steps of pulp inflammation and regeneration. These include endothelial cell interaction with inflammatory cells, stem cell interaction with pulp fibroblasts, migration chambers to study cell recruitment and entire human tooth culture model. Using these models, the pulp has been shown to possess an inherent anti-inflammatory potential and a high regeneration capacity in all teeth and at all ages. The same models were used to investigate the effects of tricalcium silicate-based pulp capping materials, which were found to modulate the pulp anti-inflammatory potential and regeneration capacity. Among these, resin-containing materials such as TheraCal^® shift the pulp response towards the inflammatory reaction while altering the regeneration process. On the opposite, resin-free materials such as Biodentine™ have an anti-inflammatory potential and induce the pulp regeneration capacity. This knowledge contradicts the new tendency of developing resin-based calcium silicate hybrid materials for direct pulp capping. Additionally, it would allow investigating the modulatory effects of newly released pulp capping materials on the balance between tissue inflammation and regeneration. It would also set the basis for developing future capping materials targeting these processes.

Tricalcium Silicate Capping Materials Modulate Pulp Healing and Inflammatory Activity In Vitro

INTRODUCTION

On stimulation by lipoteichoic acid or by a physical injury, fibroblasts have been shown to play a major role in the initiation of the pulp inflammatory reaction and healing through secretion of complement proteins and growth factors. The application of direct pulp-capping materials on these cells may interfere with the inflammatory and the healing processes within the pulp's inextensible environment. This work was designed to study in vitro the effects of silicate-based materials on pulp fibroblast modulation of the initial steps of pulp inflammation and healing.

METHODS

The effects of Biodentine, TheraCal, and Xeno III eluates were studied on lipoteichoic acid-stimulated and physically injured fibroblasts. Cytokine secretion (interleukin 6, vascular endothelial growth factor, fibroblast growth factor-2, and transforming growth factor-β1) was quantified by enzyme-linked immunosorbent assay. Inflammatory THP-1 adhesion to endothelial cells and their migration and activation were studied in vitro. Human pulp fibroblast proliferation was investigated with the MTT test, and their migration to the injury site was studied with the scratch healing assay.

RESULTS

Interleukin 6 and vascular endothelial growth factor secretion increased with all materials but to a lesser extent with Biodentine. Fibroblast growth factor-2 and transforming growth factor-β1 secretion was significantly higher with Biodentine than with all other materials. THP-1 cell adhesion to endothelial cells and their activation were reduced by Biodentine and TheraCal. However, their migration decreased only with Biodentine. Fibroblast proliferation significantly increased with Biodentine but significantly decreased with Xeno III after day 6. Finally, only Biodentine induced fibroblast migration to the injury site in the scratch assay.

CONCLUSIONS

These results confirm that pulp-capping materials affect the early steps of pulp inflammation and healing. They show that Biodentine had the highest pulp healing and anti-inflammatory potential when compared with the resin-containing materials. This highlights the interest of the material choice for direct pulp-capping.

Novel Two-Component System of Streptococcus sanguinis Affecting Functions Associated with Viability in Saliva and Biofilm Formation

Streptococcus sanguinis is a pioneer species of teeth and a common opportunistic pathogen of infective endocarditis. In this study, we identified a two-component system, S. sanguinis SptRS (SptRS _Ss ), affecting S. sanguinis survival in saliva and biofilm formation. Isogenic mutants of sptR_Ss (SKsptR) and sptS_Ss (SKsptS) showed reduced cell counts in ex vivo assays of viability in saliva compared to those of parent strain SK36 and complemented mutants. Reduced counts of the mutants in saliva were associated with reduced growth rates in nutrient-poor medium (RPMI) and increased susceptibility to the deposition of C3b and the membrane attach complex (MAC) of the complement system, a defense component of saliva and serum. Conversely, sptR_Ss and sptS_Ss mutants showed increased biofilm formation associated with higher levels of production of H₂O₂ and extracellular DNA. Reverse transcription-quantitative PCR (RT-qPCR) comparisons of strains indicated a global role of SptRS _Ss in repressing genes for H₂O₂ production (2.5- to 15-fold upregulation of spxB, spxR, vicR, tpk, and ackA in sptR_Ss and sptS_Ss mutants), biofilm formation, and/or evasion of host immunity (2.1- to 11.4-fold upregulation of srtA, pcsB, cwdP, iga, and nt5e). Compatible with the homology of SptR _Ss with AraC-type regulators, duplicate to multiple conserved repeats were identified in 1,000-bp regulatory regions of downstream genes, suggesting that SptR _Ss regulates transcription by DNA looping. Significant transcriptional changes in the regulatory genes vicR, spxR, comE, comX, and mecA in the sptR_Ss and sptS_Ss mutants further indicated that SptRS _Ss is part of a regulatory network that coordinates cell wall homeostasis, H₂O₂ production, and competence. This study reveals that SptRS _Ss is involved in the regulation of crucial functions for S. sanguinis persistence in the oral cavity.

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.

Stem Cells of Dental Origin: Current Research Trends and Key Milestones towards Clinical Application

Dental Mesenchymal Stem Cells (MSCs), including Dental Pulp Stem Cells (DPSCs), Stem Cells from Human Exfoliated Deciduous teeth (SHED), and Stem Cells From Apical Papilla (SCAP), have been extensively studied using highly sophisticated in vitro and in vivo systems, yielding substantially improved understanding of their intriguing biological properties. Their capacity to reconstitute various dental and nondental tissues and the inherent angiogenic, neurogenic, and immunomodulatory properties of their secretome have been a subject of meticulous and costly research by various groups over the past decade. Key milestone achievements have exemplified their clinical utility in Regenerative Dentistry, as surrogate therapeutic modules for conventional biomaterial-based approaches, offering regeneration of damaged oral tissues instead of simply “filling the gaps.” Thus, the essential next step to validate these immense advances is the implementation of well-designed clinical trials paving the way for exploiting these fascinating research achievements for patient well-being: the ultimate aim of this ground breaking technology. This review paper presents a concise overview of the major biological properties of the human dental MSCs, critical for the translational pathway “from bench to clinic.”

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.