Odontoblast cell death induces NLRP3 inflammasome-dependent sterile inflammation and regulates dental pulp cell migration, proliferation and differentiation

AIM

To investigate the ability of dead odontoblasts to initiate NLRP3 inflammasome-dependent sterile inflammation and to explore the effect on dental pulp cell (DPCs) migration, proliferation and odontogenic differentiation.

METHODS

Odontoblast-like cells were subjected to freezing-thawing cycles to produce odontoblast necrotic cell lysate (ONCL). DPCs were treated with ONCL to assess proliferation and migration. THP-1 differentiated macrophages stimulated with ONCL and live cell imaging and western blotting were used to assess NLRP3 inflammasome activation. Cytokines were measured with multiplex arrays and ELISA. qPCR, alkaline phosphatase and Alizarin red assays were used to assess odontogenic differentiation of DPCs. Data were analysed using the t-test or anova followed by a Bonferroni post hoc test with the level of significance set at P ≤ 0.05.

RESULTS

ONCL induced migration and proliferation of DPCs. Treatment of THP-1 macrophages with ONCL resulted in the release of the inflammatory cytokines IL-1β, IL-6, IL-8, TNFα, IFN-γ, CCL2 and angiogenic growth factors, angiogenin and angiopoietin. This inflammatory response was associated with activation of NFκB, p38MAPK and NLRP3 inflammasome. To confirm that ONCL induced inflammatory response is NLRP3 inflammasome-dependent, treatment with a caspase-1 inhibitor and a specific NLRP3 inhibitor significantly reduced IL-1β release in THP-1 macrophages (P = 0.01 and 0.001). Inflammasome activation product, IL-1β, induced odontogenic differentiation of DPCS as evident by the increase in odontogenic genes expression DMP-1, RUNX-2, DSPP and SPP, alkaline phosphatase activity and mineralization.

CONCLUSION

Dead odontoblasts induced NLRP3 inflammasome-dependent sterile inflammation and activated the migration, proliferation and differentiation of DPCs.

An international survey on the use of calcium silicate-based sealers in non-surgical endodontic treatment

OBJECTIVES

To gain insight on the current clinical usage of bioceramic root canal sealers (BRCS) by general dental practitioners (GDPs) and endodontic practitioners (EPs) and to determine if BRCS clinical application is in accordance with the best available evidence.

MATERIAL AND METHODS

An online questionnaire of 18 questions addressing BRCS was proposed to 2335 dentists via a web-based educational forum. Participants were asked about socio-demographic data, clinical practice with BRCS, and their motivation for using BRCS. Statistical analysis (chi-squared test or Fisher's exact test) was applied, as appropriate, to assess the association between the variable categories (p value < 0.05).

RESULTS

The response rate was 28.91%. Among respondents, 94.8% knew BRCS (EPs more than GDPs, p < 0.05) and 51.70% were using BRCS. The primary reason for using BRCS was their belief of its improved properties (87.7%). Among BRCS users, single-cone technique (SCT) was the most employed obturation method (63.3%) which was more applied by GDPs (p < 0.05); EPs utilized more of the thermoplasticized obturation techniques (p < 0.05). A proportion of 38.4% of BRCS users indicated the usage of SCT with BRCS regardless of the root canal anatomy (GDPs more than EPs p < 0.05) and 55.6% considered that BRCS may influence their ability to re-establish apical patency during retreatment (GDPs more than EPs p < 0.05).

CONCLUSIONS

This study highlights wide variation in the clinical use of BRCS which is not in accordance with the current literature.

CLINICAL RELEVANCE

This inconsistency among EPs and GDPs on BRCS clinical application requires further clarifications to better standardize their use and improve their future evaluation.

Tissue Plasminogen Activator in Human Megakaryocytes and Platelets: Immunocytochemical Localization, Immunoblotting and Zymographic Analysis

Two approaches were used to identify and characterize the presence of tissue plasminogen activator (t-PA) in megakaryocytes and platelets. We investigated the fibrinolytic activity of human megakaryocytes (MK) and platelets. The presence of t-PA antigen in megakaryocytes and platelets was demonstrated using immunocytochemical techniques and polyclonal or monoclonal antibodies specific for t-PA. When cells were applied to fibrin plates, lysis zones developed around isolated human megakaryocytes, whereas no fibrinolytic activity appeared when either intact washed platelets or platelet lysate were deposited. After SDS-PAGE of platelet and MK extracts (Triton X-100) immunoblotting and peroxidase staining identified t-PA antigen in several bands. Zymographic analysis of SDS-PAGE carried out on fibrin film overlays identified one or two zones corresponding to free or complexed t-PA. These results indicate that t-PA is present in platelets as well as in the precursor cells, however, in platelets, t-PA may not be immediately available for plasminogen activation and fibrin degradation. From our findings and from previous work of others, it appears that platelets may either activate or inhibit the fibrinolytic system. Therefore the conditions of plasminogen activation by platelet t-PA and plasmin inhibition by platelet α2-antiplasmin or other inhibitors have to be precised before the role of platelets in clot dissolution is understood.

The physiological role of platelets in fibrinolysis and clot dissolution remains unclear. In 1953, the antifibrinolytic activity of blood platelets was demonstrated (1) and in the early 1960’s a fibrinolytic activity, increasing with platelet concentration in the experimental system, was shown (2, 3). In 1979, it was demonstrated that metabolically active platelets were necessary for platelets to play a role in the fibrinolytic system (4). More recently it was established by Plow and Collen (5) that the specific plasmin inhibitor, α2-antiplasmin is a constituent of platelet α-granules.

In the present study, we investigated the fibrinolytic components and activity of human megakaryocytes and platelets, using zymographic and immunochemical techniques. We report here our observations that human megakaryocytes and platelets contain tissue plasminogen (t-PA) which possesses fibrinolytic activity.

Pulp Vascularization during Tooth Development, Regeneration, and Therapy

The pulp is a highly vascularized tissue situated in an inextensible environment surrounded by rigid dentin walls, with the apical foramina being the only access. The pulp vascular system is not only responsible for nutrient supply and waste removal but also contributes actively to the pulp inflammatory response and subsequent regeneration. This review discusses the underlying mechanisms of pulp vascularization during tooth development, regeneration, and therapeutic procedures, such as tissue engineering and tooth transplantation. Whereas the pulp vascular system is established by vasculogenesis during embryonic development, sprouting angiogenesis is the predominant process during regeneration and therapeutic processes. Hypoxia can be considered a common driving force. Dental pulp cells under hypoxic stress release proangiogenic factors, with vascular endothelial growth factor being one of the most potent. The benefit of exogenous vascular endothelial growth factor application in tissue engineering has been well demonstrated. Interestingly, dental pulp stem cells have an important role in pulp revascularization. Indeed, recent studies show that dental pulp stem cell secretome possesses angiogenic potential that actively contributes to the angiogenic process by guiding endothelial cells and even by differentiating themselves into the endothelial lineage. Although considerable insight has been obtained in the processes underlying pulp vascularization, many questions remain relating to the signaling pathways, timing, and influence of various stress conditions.

Can Pulp Fibroblasts Kill Cariogenic Bacteria? Role of Complement Activation

Complement system activation has been shown to be involved in inflammation and regeneration processes that can be observed within the dental pulp after moderate carious decay. Studies simulating carious injuries in vitro have shown that when human pulp fibroblasts are stimulated by lipoteichoic acid (LTA), they synthetize all complement components. Complement activation leads to the formation of the membrane attack complex (MAC), which is known for its bacterial lytic effect. This work was designed to find out whether human pulp fibroblasts can kill Streptococcus mutans and Streptococcus sanguinis via complement activation. First, histological staining of carious tooth sections showed that the presence of S. mutans correlated with an intense MAC staining. Next, to simulate bacterial infection in vitro, human pulp fibroblasts were incubated in serum-free medium with LTA. Quantification by an enzymatic assay showed a significant increase of MAC formation on bacteria grown in this LTA-conditioned medium. To determine whether the MAC produced by pulp fibroblasts was functional, bacteria sensitivity to LTA-conditioned medium was evaluated using agar well diffusion assay and succinyl dehydrogenase (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide [MTT]) assay. Both assays showed that S. mutans and S. sanguinis were sensitive to LTA-conditioned medium. Finally, to evaluate whether MAC formation on cariogenic bacteria, by pulp fibroblasts, can be directly induced by the presence of these bacteria, a specific coculture model of human pulp fibroblasts and bacteria was developed. Immunofluorescence revealed an intense MAC labeling on bacteria after direct contact with pulp fibroblasts. The observed MAC formation and its lethal effects were significantly reduced when CD59, an inhibitor of MAC formation, was added. Our findings demonstrate that the MAC produced by LTA-stimulated pulp fibroblasts is functional and can kill S. mutans and S. sanguinis. Taken together, these data clearly highlight the function of pulp fibroblasts in destroying cariogenic bacteria.

LPS Induces Pulp Progenitor Cell Recruitment via Complement Activation

Complement system, a major component of the natural immunity, has been recently identified as an important mediator of the dentin-pulp regeneration process through STRO-1 pulp cell recruitment by the C5a active fragment. Moreover, it has been shown recently that under stimulation with lipoteichoic acid, a complex component of the Gram-positive bacteria cell wall, human pulp fibroblasts are able to synthesize all proteins required for complement activation. However, Gram-negative bacteria, which are also involved in tooth decay, are known as powerful activators of complement system and inflammation. Here, we investigated the role of Gram-negative bacteria-induced complement activation on the pulp progenitor cell recruitment using lipopolysaccharide (LPS), a major component of all Gram-negative bacteria. Our results show that incubating pulp fibroblasts with LPS induced membrane attack complex formation and C5a release in serum-free fibroblast cultures. The produced C5a binds to the pulp progenitor cells’ membrane and induces their migration toward the LPS stimulation chamber, as revealed by the dynamic transwell migration assays. The inhibition of this migration by the C5aR-specific antagonist W54011 indicates that the pulp progenitor migration is mediated by the interaction between C5a and C5aR. Our findings demonstrate, for the first time, a direct interaction between the recruitment of progenitor pulp cells and the activation of complement system generated by pulp fibroblast stimulation with LPS.

Pulp progenitor cell recruitment is selectively guided by a C5a gradient

It recently became evident that activation of the complement system also contributes to tissue regeneration after infection/injury. The complement-derived fragment C5a induces vascular modifications and attracts cells expressing its receptor (C5aR/CD88) to the site of infection and tissue injury. Besides inflammatory cells, various tissue cells express this receptor. We hypothesized that pulp progenitor cells, being exposed to local complement activation in caries lesions, may respond to C5a via the C5aR. Our work aimed at evaluating the ability of C5a to induce pulp progenitor cell migration that may link complement activation to dentin regeneration. Immunofluorescence analysis of third molar pulp sections showed perivascular localization of the mesenchymal stem cell markers STRO-1 and C5aR. RT-PCR on STRO-1-sorted pulp progenitor cells, co-expressing both STRO-1 and C5aR, revealed high C5aR mRNA levels. Experiments with the C5aR antagonist W54011 revealed that C5a specifically bound to progenitor cells via C5aR, inducing their selective migration toward the C5a gradient. Since we could also demonstrate C5b-9 formation by immunohistochemistry in carious teeth, our findings suggest that, upon local complement activation, C5a induces pulp progenitor cell migration, which may be critical in initiating the regenerative process after dentin/pulp injury.

[Selectins as adhesion molecules and potential therapeutic target]

Selectins belong to the family of adhesion molecules that recognize sugars as ligands through their Carbohydrate Recognition Domain (CRD). There are three types of selectin: the L-selectin (CD62L), which is constitutively expressed by most leukocyte populations, the P-selectin (CD62P) is found on activated platelets and endothelial cells, and the E-selectin (CD62E) expressed by activated endothelial cells. These three molecules exhibit high homology in their structures. Selectin-ligand interactions are among the most studied protein-glycan interactions in biology. The selectins and theirs ligands are involved in regulating inflammatory and immunological events that occur at the interface of the bloodstream and vessel walls. Their molecular partners are surface glycoconjugates harboring groups of the sialyl-Lewis antigens. This review presents an inventory of our current knowledge on the structures and functions of selectins and their ligands. We also provide an update on their involvement in pathophysiological processes, especially during inflammation and tumor development.

Changes in the profile of simple mucin-type O-glycans and polypeptide GalNAc-transferases in human testis and testicular neoplasms are associated with germ cell maturation and tumour differentiation

Testicular germ cell tumours (TGCT) exhibit remarkable ability to differentiate into virtually all somatic tissue types. In this study, we investigated changes in mucin-type O-glycosylation, which have been associated with somatic cell differentiation and cancer. Expression profile of simple mucin-type O-glycans (Tn, sialyl-Tn, T), histo-blood group H and A variants and six polypeptide GalNAc-transferases (T1-4, T6, T11) that control the site and density of O-glycosylation were analysed by immunohistochemistry during human testis development and in TGCT. Normal testis showed a restricted pattern; gonocytes expressed abundant sialyl-Tn and sialyl-T, and adult spermatogonia were devoid of any glycans, whereas spermatocytes and spermatids expressed exclusively glycans Tn and T and the GalNAc-T3 isoform. A subset of mature ejaculated spermatozoa expressed an additional glycan sialyl-T. The pattern found in testicular neoplasms recapitulated the developmental order: Pre-invasive carcinoma in situ (CIS) cells and seminoma expressed fetal type sialylated glycans in keeping with their gonocyte-like phenotype. Neither simple mucin-type O-glycans nor GalNAc-transferase isoforms were found in undifferentiated nonseminoma, i.e. embryonal carcinoma, whereas teratomas expressed them all to some extent but in a disorganized manner. We concluded that simple mucin-type O-glycans and their transferases are developmentally regulated in the human testis, with profound changes associated with neoplasia. The restricted O-glycosylation pattern in haploid germ cells suggests a role in their maturation or egg recognition/fertilization warranting further studies in male infertility, whereas the findings in TGCT provide new diagnostic tools and support our hypothesis that testicular cancer is a developmental disease of germ cell differentiation.

Structural and functional features of glycosyltransferases

Most of the glycosylation reactions that generate the great diversity of oligosaccharide structures of eukaryotic cells occur in the Golgi apparatus. This review deals with the most recent data that provide insight into the functional organization of Golgi-resident glycosyltransferases. We also focus on the recent successes in X-ray crystal structure determination of glycosyltransferases. These new structures begin to shed light on the molecular bases accounting for donor and acceptor substrate specificities as well as catalysis.

Tissue plasminogen activator in human megakaryocytes and platelets: immunocytochemical localization, immunoblotting and zymographic analysis

Two approaches were used to identify and characterize the presence of tissue plasminogen activator (t-PA) in megakaryocytes and platelets. We investigated the fibrinolytic activity of human megakaryocytes (MK) and platelets. The presence of t-PA antigen in megakaryocytes and platelets was demonstrated using immunocytochemical techniques and polyclonal or monoclonal antibodies specific for t-PA. When cells were applied to fibrin plates, lysis zones developed around isolated human megakaryocytes, whereas no fibrinolytic activity appeared when either intact washed platelets or platelet lysate were deposited. After SDS-PAGE of platelet and MK extracts (Triton X-100) immunoblotting and peroxidase staining identified t-PA antigen in several bands. Zymographic analysis of SDS-PAGE carried out on fibrin film overlays identified one or two zones corresponding to free or complexed t-PA. These results indicate that t-PA is present in platelets as well as in the precursor cells, however, in platelets, t-PA may not be immediately available for plasminogen activation and fibrin degradation. From our findings and from previous work of others, it appears that platelets may either activate or inhibit the fibrinolytic system. Therefore the conditions of plasminogen activation by platelet t-PA and plasmin inhibition by platelet alpha 2-antiplasmin or other inhibitors have to be precised before the role of platelets in clot dissolution is understood. The physiological role of platelets in fibrinolysis and clot dissolution remains unclear. In 1953, the antifibrinolytic activity of blood platelets was demonstrated and in the early 1960's a fibrinolytic activity, increasing with platelet concentration in the experimental system, was shown.(ABSTRACT TRUNCATED AT 250 WORDS)

Absence of functional activity of tissue plasminogen activator in patients with severe forms of von Willebrand's disease

Some patients with von Willebrand's disease do not respond to stimuli such as venous occlusion and infusion of a vasopressin analogue DDAVP. In these patients, fibrinolytic activity is not enhanced and von Willebrand's factor is not released into the blood. Skin biopsies and cryostat sections were used to study the fibrinolytic activity of skin vessels and localization of tissue plasminogen activator (t-PA) in three patients with severe form of von Willebrand's disease. On fibrin films, no fibrinolysis developed around the skin vessels of the patients; however, using specific polyclonal and monoclonal antibodies to t-PA, and peroxidase coupled specific IgG, presence of t-PA antigen was demonstrated in endothelial cells (EC) of all of them. In plasma no t-PA activity was detected either before or after venous occlusion although t-PA inhibitor activity was in a normal range. Small amounts of t-PA antigen was measured in blood by ELISA. From these results, it is concluded that in patients with severe forms of von Willebrand's disease, t-PA present in EC is not functional and can not transform plasminogen into plasmin.

An immunoradiometric assay for factor VIII related antigen (VIIIRAg) using two monoclonal antibodies-comparison with polyclonal rabbit antibodies for use in von Willebrand's disease diagnosis

Two monoclonal antibodies raised against FVIII/von Willebrand protein were used in an immunoradiometric assay (IRMA) to measure this antigen in normal plasma and plasma of patients with different forms of von Willebrand's disease. The first antibody, an IgG1, was used to coat polystyrene tubes, the second one, an IgG2a, iodinated and used in the second step. Both antibodies inhibit ristocetin induced platelet agglutination and react strongly with platelets, megakaryocytes and endothelial cells. The IRMA test using these antibodies showed greater sensitivity than that using rabbit polyclonal anti VIIIRAg antibodies. A good correlation between the two tests was nevertheless found when VIIIRAg was measured in the majority of patient's plasma. However 5 patients from 3 different families showed more antigenic material in the rabbit antibody IRMA than in the monoclonal antibody IRMA. It is suggested therefore that the monoclonal antibodies identify part of the VIIIR:Ag molecule showing structural abnormalities in these vWd patients, these structural changes remaining undetected by the polyclonal antibodies.

Use of monoclonal antibody and colloidal gold in E.M. localization of von Willebrand factor in megakaryocytes and platelets

The subcellular localization of Factor VIII/von Willebrand protein (VIII R:Ag) is studied with monoclonal antibody and gold immunocytochemical technique. Monoclonal antibody against purified VIII R:Ag is brightly fluorescent on megakaryocytes and platelets. In E.M., gold immunolabeling is performed on thin cell sections of human megakaryocytes and platelets. Different embedding materials are used to preserve the antigenicity : Epon embedded megakaryocytes show a high concentration of VIII R:Ag in alpha-granules using 4F9 monoclonal antibody. In comparison, lowicryl K4M embedded material does not improve the same specificity, only a few platelets granules were stained. This subcellular localization, in full agreement with biochemical results appears visualized for the first time in E.M.

Immunocytochemical localization of factor VIII/von Willebrand factor antigen in human platelets

Specific antibodies against anti-human FVIII/vW protein were isolated by affinity chromatography on glutaraldehyde-activated gel (Ultrogel AcA22). They were coupled directly with peroxidase or visualized with anti-rabbit IgG (sheep)-peroxidase (Institut Pasteur). Fab fragments of the same specific antibodies were prepared to enhance the intracellular penetration and coupled to peroxidase. In washed human platelets, staining was observed on the plasma membrane and in the canalicular system, whereas in previous studies whole specific antibodies incubated with fixed platelets showed the labeling only on the plasma membrane. After thrombin activation, the release of granules containing FVIII/vW protein was better visualized in the surface canalicular system. This localization was discussed in regard to the exocytosis process: membrane fusion, granule labeling.

Localization of factor VIII/von Willebrand factor antigen by immunoelectron microscopy in human endothelial cells using Fab fragments coupled to peroxidase

Factor VIII/von Willebrand factor antigen (VIII R:Ag) has been localized in human endothelial cells by an immunoperoxidase method and electron microscopy. Specific antibodies against VIII R:Ag were isolated from monospecific rabbit antisera by an immunoadsorbant. Fab fragments were prepared and coupled to peroxidase. Native human endothelial cells from umbilical cord veins were incubated with the Fab conjugates. Peroxidase labeling was seen on the plasma membrane, in vesicles, and in the Golgi apparatus. In order to eliminate nonspecific antibody internalization, the same procedure was reproduced on fixed endothelial cells and similar localization was observed. Staining was only found when specific VIII R:Ag Fab conjugates were used. All the controls were devoid of labeling, thus the peroxidase reaction product localized in the Golgi cisternae is specific for VIII R:Ag and suggests VIII R:Ag synthesis in endothelial cells.

Monoclonal antibodies against human factor VIII molecular neutralize antihemophilic factor and ristocetin cofactor activities

A series of monoclonal antibodies have been raised against a preparation of the factor VIII/von Willebrand factor molecule. Of the seven hybridomas showing specific activity against the factor VIII molecule in a solid-phase radioimmunoassay, three (F4.55, F4.77, and F4.264) have been shown to partially inhibit ristocetin-induced platelet aggregation and two (F4.115 and F4.415) inhibit the antihemophilic activity of the factor VIII molecule. An additional monoclonal antibody was directed against a contaminant of the factor VIII preparation and is an antifibrinogen antibody.

[Monoclonal antibodies against the factor VIII/Willebrand factor molecule: inhibition of the cofactor action of ristocetin and the antihemophilic factor]

Seven hybridoma cell lines secreting antibodies active against the F.VIII/vWF protein, were established. Three of them inhibit ristocetin-induced platelet aggregation, two others are directed against the antihemophilic activity and two bind to the molecule without any effect on biological activities.

Platelet factor VIII-related antigen: studies in vivo after transfusion in patients with von Willebrand disease

Four unrelated patients with a severe form of von Willebrand disease showed no detectable factor VIII-related antigen (VIIIR:AG) in either their plasma or their platelets. They received cryoprecipitate infusions, three patients in a single injection each and one every day for 9 days before and after surgery. Platelet VIIIR:Ag was studied at different times during and after transfusion using electroimmunoassay of platelet extracts and electron microscopy of the platelets incubated with anti-VIIIR:Ag antibodies coupled to peroxidase. No VIIIR-Ag was detected in or around the patients' platelets, although this antigen was detected in the circulating blood. These results that there was no VIIIR:Ag uptake from the plasma by the platelets and that platelet VIIIR:Ag came from megakaryocytes.

[Platelet membrane glycoprotein defect, molecular basis for the abnormal adhesion of platelets to the subendothelium in thrombocytic hemorrhagic dystrophy]

A large reduction in the staining capacity of a glycoprotein of 155 000 M.W. was observed in the platelets of 2 macrogiant platelets syndrome patients, associated with a reduced platelet adhesion to rabbit aorta subendothelium and with the presence of von Willebrand protein on these platelets as revealed by an antihuman factor VIII-Von Willebrand protein rabbit antibody. These results led the authors to propose a strong hypothesis on the role of this glycoprotein rich in sialic acid - in platelet adhesion to subendothelium.