Odontoblasts in the dental pulp immune response.

Recent studies have demonstrated that human dental pulp cells sense pathogens and elicit innate and/or adaptive immunity. Particular attention has been paid to odontoblasts that are situated at the pulp-dentin interface and constitute the first line of defense to cariogenic bacteria entering dentin after enamel disruption. In this review, recent in vitro and in vivo data suggesting that odontoblasts initiate immune/inflammatory events within the dental pulp in response to cariogenic bacteria are discussed. These data include sensing of pathogens by Toll-like receptors (TLRs), production of chemokines upon cell stimulation with microbial by-products and induction of dendritic cell migration. Additional results presented here reveal that all TLR genes are expressed in the healthy human dental pulp that is thus well equipped to combat pathogens entering the tissue. Seventeen chemokine genes including CXCL12, CCL2, CXCL9, CX3CL1, CCL8, CXCL10, CCL16, CCL5, CXCL2, CCL4, CXCL11 and CCL3, and 9 chemokine receptor genes including CXCR4, CCR1, CCR5, CX3CR1, CCR10 and CXCR3, are also expressed in pulp. TLR2, CCL2 and CXCL1 are upregulated in odontoblasts both under caries lesions and upon stimulation with pathogen by-products. These molecules thus appear as preferential targets for the design of therapeutic agents able to reduce the immune/inflammatory response to cariogenic bacteria and favor pulp healing.

A clinical and histological study of dental defects in a 10-year-old girl with pseudoxanthoma elasticum and amelogenesis imperfecta.

BACKGROUND: The prominent dental feature of a 10-year-old girl was severely hypoplastic enamel in permanent teeth. CASE REPORT: Severe dental defects were detected in a 10-year-old female patient affected by pseudoxanthoma elasticum and amelogenesis imperfecta. An orthopantomographic examination revealed a reduction of enamel thickness on the crown of all erupted and unerupted teeth, agenesis of the maxillary right second premolar, delayed eruption of mandibular first premolars, and the presence of large calcifications in all tooth pulp chambers. A detailed histological analysis of permanent mandibular first molars showed that pulp calcifications presented a concentric laminate organization and merged to almost completely obliterate the pulp chamber. Osteodentine was visible all along the pulpal surface of the radicular dentine. Broad resorption areas were present in the outermost dentine at both coronal and radicular levels. Radicular resorption areas presented a typical rectangular form and were filled with acellular cementum. Cementum thickness was highly increased on the root surface. Apposition of cellular cementum-like tissue was also observed on the coronal dentine surface. CONCLUSION: Before treating patients affected by amelogenesis imperfecta and/or pseudoxanthoma elasticum, paediatric dentists should be aware of the presence of pulp calcifications that add to the complexity of endodontic procedures.

Expression of the TGF-beta/BMP inhibitor EVI1 in human dental pulp cells.

Members of the TGF-beta/BMP family of growth factors induce odontoblast differentiation and reparative dentin synthesis, and their use has been proposed to stimulate pulp healing during dental therapeutics in human. However, factors that modulate TGF-beta and/or BMP signalling during odontoblast differentiation and physiology remain largely unknown. To identify them, we compared expression profiles of TGF-beta/BMP-related genes in pulp fibroblast- and odontoblast-like cells cultured from human dental pulp explants using cDNA gene arrays. We evidenced that the gene encoding ecotropic viral integration site-1 (EVI1), a transcription factor that inhibits TGF-beta/BMP signalling, was under-expressed in odontoblast-like cells. This result was verified by real-time PCR and, at the protein level, by immunohistochemistry. In vivo, real-time PCR analysis revealed that EVI1 was expressed in the dental pulp, at a level similar to brain, but lower than in lung, kidney or trachea. The protein was localized in dental pulp samples in pulp core and subodontoblast cells. Staining intensity progressively decreased from the radicular to the coronal pulp where EVI1 staining was almost undetectable in odontoblasts. Our data suggest that fine regulation of the EVI1 level in the human dental pulp might be important in the TGF-beta/BMP-induced modulation of dental pulp cell kinetics and/or odontoblast differentiation.

Lipoteichoic acid increases TLR and functional chemokine expression while reducing dentin formation in in vitro differentiated human odontoblasts.

Gram-positive bacteria entering the dentinal tissue during the carious process are suspected to influence the immune response in human dental pulp. Odontoblasts situated at the pulp/dentin interface are the first cells encountered by these bacteria and therefore could play a crucial role in this response. In the present study, we found that in vitro-differentiated odontoblasts constitutively expressed the pattern recognition receptor TLR1-6 and 9 genes but not TLR7, 8, and 10. Furthermore, lipoteichoic acid (LTA), a wall component of Gram-positive bacteria, triggered the activation of the odontoblasts. LTA up-regulated the expression of its own receptor TLR2, as well as the production of several chemokines. In particular, an increased amount of CCL2 and CXCL10 was detected in supernatants from LTA-stimulated odontoblasts, and those supernatants augmented the migration of immature dendritic cells in vitro compared with controls. Clinical relevance of these observations came from immunohistochemical analysis showing that CCL2 was expressed in vivo by odontoblasts and blood vessels present under active carious lesions but not in healthy dental pulps. In contrast with this inflammatory response, gene expression of major dentin matrix components (type I collagen, dentin sialophosphoprotein) and TGF-beta1 was sharply down-regulated in odontoblasts by LTA. Taken together, these data suggest that odontoblasts activated through TLR2 by Gram-positive bacteria LTA are able to initiate an innate immune response by secreting chemokines that recruit immature dendritic cells while down-regulating their specialized functions of dentin matrix synthesis and mineralization.

In vitro study of a neodynium:yttrium aluminum perovskite laser on human nonexposed pulp after cavity preparation.

PURPOSE: The aim of this study was to investigate dental pulp reactions after a neodynium:yttrium aluminum perovskite laser pulse on the dentinal floor of occlusal cavities in an in vitro model. METHODS: A Lokki dt laser was used at 30 Hz, 5 W, and 160 mJ for 0.5 s. The pulp reactions were analyzed in a previously described human tooth slice cultured model. The following markers were identified by immunohistochemistry: collagens I, III, and IV and HLA-DR-positive cells. RESULTS: After 4 days of culture, under laser pulse, a concentration of type III collagen beneath the odontoblast layer, a higher level of vessels and an accumulation of HLA-DR-positive cells were routinely observed subjacent to the cavity. CONCLUSION: This laser treatment leads to the first step of rapid pulp repair under culture conditions.

Odontoblast primary cilia: facts and hypotheses.

Odontoblasts, the cells responsible for the dentine formation, are organized as a single layer of highly polarized and differentiated post-mitotic cells along the interface between the dental pulp and the mineralized tubules. They lay down the physiological secondary dentine throughout the life of the teeth. Odontoblasts play a central role in the transportation of calcium to the dentine and they possibly mediate early stages of sensory processing in teeth. A primary cilium, 9+0 configuration, have been regularly identified in a supra nuclear location. Calbindin D28k has been detected at the base of the cilium membrane. The cilium structure was positive with detyrosinated alpha tubulin antibodies in vivo and in cultured human odontoblasts. Transcripts of tektin, a protein involved in ciliogenesis, were expressed in vitro. The putative role of the primary cilium constituting a critical link between external teeth stimuli and odontoblast responses is extensively discussed.

Notch2 protein distribution in human teeth under normal and pathological conditions.

Notch signaling is essential for the appropriate differentiation of many cell types during development and, furthermore, is implicated in a variety of human diseases. Previous studies have shown that although the Notch1, -2, and -3 receptors are expressed in developing and injured rodent teeth, Notch2 expression was predominant after a lesion. To pursue the role of the Notch pathway in tooth development and disease, we have analyzed the expression of the Notch2 protein in embryonic and adult wounded human teeth. During the earlier stages of tooth development, the Notch2 protein was expressed in the epithelium, but was absent from proliferating cells of the inner enamel epithelium. At more advanced stages, Notch2 was expressed in the enamel-producing ameloblasts, while it was absent in mesenchyme-derived odontoblasts that synthesize the dentin matrix. Although Notch2 was not expressed in the pulp of adult intact teeth, it was reexpressed during dentin repair processes in odontoblasts and subodontoblastic cells. Transforming growth factor beta-1, which stimulates odontoblast differentiation and hard tissue formation after dental injury, downregulated Notch2 expression in cultured human dental slices, in vitro. These observations are consistent with the notion that Notch signaling is an important element in dental physiological and pathogenic conditions.

TGF beta 1 signaling and stimulation of osteoadherin in human odontoblasts in vitro.

Transforming growth factor beta 1 (TGF beta 1) is generally considered to be a potent inducer of dentin formation. In order to further assess this role, we studied the influence of this factor in human dental pulp cells on the expression of osteoadherin (OSAD), a newly described proteoglycan found in bone and dentin and suspected to play a role in mineralization events. We performed TGF beta 1 stimulation both in cultures of human tooth thick slices including mature odontoblasts and in pulp explant cultures giving rise to early secretory odontoblasts or pulpal fibroblasts. We first showed by immunohistochemistry that molecules involved in TGF beta 1 signal transduction, that is, membrane receptors T beta RI and T beta RII and intracellular proteins SMAD-2, SMAD-3, and SMAD-4, were present in human dental cells in vivo and were all maintained after culture of thick-sliced teeth in cells undergoing TGF beta 1 stimulation. In this culture system, OSAD synthesis was increased in mature odontoblasts close to the TGF beta 1 delivery system. In explant cultures, semiquantitative reverse-transcription polymerase chain reaction (RT-PCR) analysis indicated that the growth factor stimulated OSAD gene expression in early secretory odontoblasts and in pulpal fibroblasts. Taken together, these results indicate that OSAD expression is stimulated by TGF beta 1 in pulpal fibroblasts and in early secretory and mature odontoblasts. We suggest that TGF beta 1 in this way could control the organization and the mineralization of the extracellular matrix deposited by these cells during dentin formation.