Human odontoblasts contain S-100 protein-like immunoreactivity

The colocalizations of pulp neural stem cells markers with dentin matrix protein-1, dentin sialoprotein and dentin phosphoprotein in human denticle (pulp stone) lining cells

BACKGROUND

The primary dentin, secondary dentin, and reactive tertiary dentin are formed by terminal differentiated odontoblasts, whereas atubular reparative tertiary dentin is formed by odontoblast-like cells. Odontoblast-like cells differentiate from pulpal stem cells, which express the neural stem cell markers nestin, S100β, Sox10, and P0. The denticle (pulp stone) is an unique mineralized extracellular matrix that frequently occurs in association with the neurovascular structures in the dental pulp. However, to date, the cellular origin of denticles in human dental pulp is unclear. In addition, the non-collagenous extracellular dentin matrix proteins dentin matrix protein 1 (DMP1), dentin sialoprotein (DSP), and dentin phosphoprotein (DPP) have been well characterized in the dentin matrix, whereas their role in the formation and mineralization of the denticle matrix remains to be clarified.

METHODS

To characterize the formation of denticle, healthy human third molars (n = 59) were completely sectioned and evaluated by HE staining in different layers at 720 µm intervals. From these samples, molars with (n = 5) and without denticles (n = 8) were selected. Using consecutive cryo-sections from a layer containing denticles of different sizes, we examined DMP1, DSP, and DPP in denticle lining cells and tested their co-localizations with the glial stem cell markers nestin, S100β, Sox10, and P0 by quantitative and double staining methods.

RESULTS

DMP1, DSP and DPP were found in odontoblasts, whereas denticle lining cells were positive only for DMP1 and DSP but not for DPP. Nestin was detected in both odontoblasts and denticle lining cells. S100β, Sox10, and P0 were co-localized with DMP1 and DSP in different subpopulations of denticle lining cells.

CONCLUSIONS

The co-localization of S100β, Sox10, and P0 with DMP1 and DSP in denticle lining cells suggest that denticle lining cells are originated from glial and/or endoneurial mesenchymal stem cells which are involved in biomineralization of denticle matrix by secretion of DMP1 and DSP. Since denticles are atubular compared to primary, secondary, reactionary tertiary dentin and denticle formed by odontoblasts, our results suggest that DPP could be one of the proteins involved in the complex regulation of dentinal tubule formation.

Expression of HMGB1 during tooth development

High mobility group box 1 (HMGB1) is a nuclear and cytosolic protein that can act as a transcription factor, a growth factor, or a cytokine. To elucidate a possible role for HMGB1 in tooth development, we have studied the expression of HMGB1 and its receptor RAGE (receptor for advanced glycation end-products) during the late fetal and early postnatal period of rat by using light- and electron-microscopic immunohistochemistry. Low HMGB1 protein expression was observed during fetal and newborn stages of tooth development. However, from postnatal day 5 (P5) onward, a marked increase occurred in the levels of the protein in most dental cell types. Expression was particularly high in ameloblasts and odontoblasts at regions of ongoing mineralization. Although most HMGB1 immunoreactivity was confined to cell nuclei, it was also present in odontoblast cytoplasm. At P5, ameloblasts and odontoblasts also showed RAGE immunoreactivity, and reverse transcription-polymerase chain reaction demonstrated both HMGB1 and RAGE mRNA in human dental pulp cells in vitro. Immunoblots performed on extracts from bovine dentin demonstrated a principal band at approximately 27 kDa, indicating that HMGB1 participates in tooth mineralization. The expression of both ligand and receptor suggests an autocrine/paracrine HMGB1 signalling axis in odontoblasts.

Comparative evaluation of neural tissue antigens--neurofilament protein (NF), peripherin (PRP), S100B protein (S100B), neuron-specific enolase (NSE) and chromogranin-A (CgA)--in both normal and inflamed human mature dental pulp

The immunohistochemical detection of neurofilament protein (NF), peripherin (PRP), S100B protein (S100B), neuron-specific enolase (NSE) and chromogranin-A (CgA) has been studied in nerve fibres and bundles of human dental pulp. This was done in order to identify possible differences in the distribution pattern of the above markers between normal and inflamed pulp and, further, to evaluate their potential use as peripheral markers of dental innervation as well as objective markers for the determination of the extent of inflammation. Both normal and inflamed human dental pulp showed positive immunolabelling for NF, S100B and NSE and lack of labelling for PRP and CgA protein. An increased density of NF, S100B and NSE immunoreactive nerve fibres was observed in inflamed pulp samples compared to non-inflamed. The findings of this study suggest the possible application of NF, S100B and NSE as markers of dental innervation. Furthermore, they may be useful for the determination of the extent of pulpal inflammation, and might be utilized in alternative modalities of biological pulp therapy to reduce the inflammation process. The absence of CgA immunolabelling implies the presumptive absence of neuroendocrine antigens, while further research is required in order to clarify the involvement of PRP in dental pulp.

Neurotensin-like immunoreactivity in odontoblasts and their processes in rat maxillary molar teeth and the effect of pulpotomy

A strong neurotensin-like immunoreactivity (NT-like IR) was detected in the odontoblast cells of the rat teeth. 4 h after a partial pulpotomy performed in two maxillary molar teeth a decreased NT-like IR was observed in the odontoblast layer located at the vicinity of the lesion together with edema and nuclear pyknosis. NT-like IR became further decreased after 24 h. After 7 days NT-like IR had almost fully disappeared with signs of necrosis of the dental pulp and infiltration of polymorphonuclear lymphocytes. It seems possible that NT like peptides in the odontoblast cell layer may play a role, e.g., in dentinogenesis and/or nociception.

S100 protein in oral biology and pathology

The demonstration of S100 protein is used extensively for both research and diagnostic purposes in oral biology and pathology. This article reviews the structure and putative function of S100, technicalities of S100 immunohistochemistry, the cells of the oral and perioral tissues which express S100 and the possible significance of S100 expression in disease.

Neural form of voltage-dependent sodium current in human cultured dental pulp cells

Intradental, i.e. pulpal, cells may play an important part in sensory transduction in teeth, although the cellular mechanisms and the identity of the specific cell types involved are still unclear. Because the majority of cells in dental pulp are derived from neural crest, it seemed likely that these might have the membrane properties of other neural-derived cells found in the peripheral or central nervous system. The patch-clamp recording technique was used to show that cells in explant cultures from human dental pulp contain a voltage-gated, tetrodotoxin-sensitive inward current. Mean activation potential of the current was -42 +/- 2.5 mV and the voltage at half-inactivation was -79.4 +/- 5.3 mV, suggesting a neural-like sodium conductance. In addition, these cells were immunoreactive to glial acidic fibrillary protein, growth-associated protein (GAP-43), and vimentin, further suggesting that dental pulp contains a population of cells with membrane properties similar to neuronal satellite cells. These cells may contribute, either directly or indirectly, to somatosensation in teeth.

An immunocytochemical study of the innervation of developing human fetal teeth using protein gene product 9.5 (PGP 9.5)

Developing teeth of 32 human fetuses (crown-rump length 11-205 mm) were examined immunohistochemically by antisera to protein gene product 9.5 (PGP 9.5) in an attempt to shed light upon the possible role of innervation in odontogenesis. As a control for the specificity of PGP 9.5 as a neuronal marker, the results were verified by immunocytochemical co-localization in peripheral nerves of neurone-specific enolase, neurofilaments and S-100 protein. The dental follicle received the first nerve fibres in the early cap stage. At this stage, fibroblasts differentiated in the presence of nerve fibres and formed the dental follicle surrounding the developing tooth. In the dental papilla, however, no fibres were demonstrated until the dentine and enamel matrices had formed, about half of the present height of the tooth germ. Most nerve fibres were localized in the basal part of the papilla until the last stage examined and usually followed the blood vessels of the papilla. Thus the effect of innervation on tooth development may be associated with the development of the dental follicle. A novel finding was that functional odontoblasts were not only positive for S-100 but also for PGP 9.5, indicating their neural crest origin.

Expression of intermediate filaments and actins in human dental pulp and embryonic dental papilla

The localization of different cytoskeletal proteins (keratin, vimentin, desmin, actin, and alpha-smooth muscle actin) was examined by immunohistochemistry in normal human adult dental pulp and compared with dental papilla of tooth germs. Keratin and actin were localized in enamel organ. Vimentin and actin were observed in the dental papilla and in the adult dental pulp. Desmin and alpha-smooth muscle actin were present only in the vessel walls. These data are discussed paying particular attention to the origin and the peculiar functional characters of the dental papilla and pulp.