Cytokines during periodontal wound healing: potential application for new therapeutic approach.

Regeneration of periodontal tissues is one of the main goals of periodontal therapy. However, current treatment, including surgical approach, use of membrane to allow maturation of all periodontal tissues, or use of enamel matrix derivatives, presents limitations in their indications and outcomes leading to the development of new tissue engineering strategies. Several cytokines are considered as key molecules during periodontal destruction process. However, their role during each phase of periodontal wound healing remains unclear. Control and modulation of the inflammatory response and especially, release of cytokines or activation/inhibition in a time- and spatial-controlled manner may be a potential perspective for periodontal tissue engineering. The aim of this review was to summarize the specific role of several cytokines during periodontal wound healing and the potential therapeutic interest of inflammatory modulation for periodontal regeneration especially related to the expression sequence of cytokines.

Periodontal diseases and stress: a brief review.

Periodontal diseases are common chronic inflammatory diseases caused by pathogenic microorganisms colonising the subgingival area and inducing local and systemic elevations of pro-inflammatory cytokines resulting in tissue destruction. Apparition and evolution of periodontal diseases are influenced by many local or systemic risk factors. Psychological stress has been suggested as one of them and may negatively influence the outcome of periodontal treatment. However, mechanisms explaining the possible relationship between stress and increased susceptibility to periodontal disease remain poorly understood. Several stress markers are found in blood and saliva of patients with periodontal diseases and influence the development of periodontal diseases by several mechanisms including modifications of the inflammatory response and changes in the composition of the dental biofilm. The aim of this review is to provide an insight into the relationship between psychological stress and periodontal diseases.

La respuesta inmunológica innata y la destrucción del tejido óseo en la enfermedad periodontal: revisión de la literatura / The innate immune response and tissue destruction in periodontal disease bone. A literatura review

La periodontitis desencadena una respuesta inmunológica del huésped contra los microorganismos de la placa dentobacteriana y sus productos. La activación de los receptores Toll-like (TLR) y Nod-like (NLR) en presencia de antígenos bacterianos inducen la respuesta inflamatoria y celular, con la consecuente expresión de citocinas inflamatorias como interleucina 1 (IL-1), interleucina 6 (IL-6), interleucina-8 (IL-8), interleucina 11 (IL-11), interleucina 18 (IL-18) y el factor de necrosis tumoral alfa (TNF-?), así como moléculas antibacterianas como b-defensinas, catelicidina y calprotectina. La IL-1 se asocia con la activación severa de las metaloproteinasas de la matriz extracelular (MMPs) que promueve la perdida de los tejidos de sostén del diente. La IL-6 estimula la diferenciación de los osteoclastos y estimula la síntesis de IL-1. El TNF-? induce la diferenciación de osteoclastos, la resorción ósea y tiene actividad sinérgica con IL-1?. Los neutrófilos forman una barrera entre el epitelio de unión y la placa dentobacteriana cuya función sinérgica es la actividad secretora de especies de oxigeno reactivas y proteínas bactericidas con el mecanismo fagocítico cuya actividad afecta la integridad de los tejidos del periodonto. Los derivados lipídicos del ácido araquidónico como Prostanglandina E2 (PGE2), han sido estrechamente relacionados con la pérdida del hueso alveolar por estimulación de los osteoclastos. Todo esto sugiere que la persistencia de las bacterias, una excesiva respuesta inflamatoria y/o una inadecuada resolución de la inflamación pueden afectar la estructura del tejido óseo durante la enfermedad periodontal.

Periodontitis triggers a host immune response against plaque microorganisms and their products. Activation of Toll-like receptors (TLRs) and Nod-like (NLR) by bacterial antigens triggers an inflammatory response and cell, with the expression of inflammatory cytokines such as interleukin 1 (IL-1), interleukin 6 (IL-6) , interleukin-8 (IL-8), interleukin 11 (IL-11), interleukin 18 (IL-18) and tumor necrosis factor alpha (TNF-?) and antibacterial molecules as b-defensins, cathelicidin and calprotectin . Among the cytokines IL-1? is associated with severe activation of extracellular matrix metalloproteinases (MMPs) that promotes the loss of the tooth-supporting tissues. IL-6 stimulates osteoclast differentiation and stimulates the synthesis of IL-1. TNF-? induces the differentiation of osteoclasts, bone resorption and has synergistic activity with IL-1?. In the cellular response, the neutrophils form a barrier between the junctional epithelium and plaque and secrete reactive oxygen species and bactericidal proteins with the phagocytic mechanism whose activity affects the integrity of the periodontal tissues. Also an arachidonic acid lipid derivative as prostaglandin E2 (PGE2) has been closely related to the loss of alveolar bone by stimulating osteoclast. This suggests that the persistence of bacteria, excessive inflammatory response and / or an inadequate resolution of the inflammation can affect the structure of the bone tissue during periodontal disease.

Porphyromonas gingivalis and its lipopolysaccharide differentially regulate the expression of cathepsin B in endothelial cells.

Porphyromonas gingivalis infection and cathepsins protease upregulation are independently implicated in atherosclerosis worsening. In this study, we evaluated the effects of P. gingivalis infection and P. gingivalis -purified lipopolysaccharide (Pg-LPS) stimulation on the expression of cathepsin B (CATB) in endothelial cells (ECs). Analysis of the enzymatic activity and expression of CATB were investigated at the messenger RNA, protein and protein-phosphorylation levels. Effects of Toll-like receptors 2 and 4 blocking on CATB activity were also analysed. Our results showed that P. gingivalis and Pg-LPS significantly increased the activity of CATB but with different kinetics. The peak of CATB activity was observed 3 h after P. gingivalis infection but it appeared 48 h after Pg-LPS stimulation. The increase of CATB activity was related to its rapid tyrosine-dephosphorylation during P. gingivalis infection, whereas the levels of CATB messenger RNAs and proteins did not vary after P. gingivalis infection or Pg-LPS stimulation. Inhibition of Toll-like-receptors 2 and 4 differentially decreased P. gingivalis and Pg-LPS CATB activations. These results showed for the first time that P. gingivalis infection rapidly affects ECs and modulates CATB activity, whereas Pg-LPS effects appear to be delayed. This study suggests that direct infection of ECs by P. gingivalis may worsen atherosclerotic plaque formation via activation of the CATB pathway.

Relationship between periodontal diseases and preterm birth: recent epidemiological and biological data.

For ten years, the incidence of preterm birth does not decrease in developed countries despite the promotion of public health programs. Many risk factors have been identified including ethnicity, age, tobacco, and infection. However, almost 50% of preterm birth causes remain unknown. The periodontal diseases are highly prevalent inflammatory and infectious diseases of tooth supporting tissues leading to an oral disability. They influence negatively general health worsening cardiovascular diseases and diabetes. Periodontal diseases have been also suspected to increase the rate of preterm birth, but data remain contradictory. The objective of this review is to present the principal results of epidemiological, biological, and interventional studies on the link between periodontal diseases and preterm birth. The conclusions of this work underline the importance for the physician/obstetrician to identify women at risk for preterm birth and to address these patients to dentist for periodontal examination and treatment in order to limit adverse pregnancy outcomes.

Does Vitamin D play a role on Msx1 homeoprotein expression involving an endogenous antisense mRNA?

Msx1 homeobox gene, a member of Msx family, has been implicated in numerous organs. Its participation was established in different events, such as morphogenetic field determinism and epithelio-mesenchymal interactions. Most of Msx1 target organs are also known for their sensitivity to Vitamin D: such as bone, tooth germ, and hair follicle. Whereas, the expression of Msx2, another member of Msx family, has been shown to be controlled by Vitamin D, no information is available for Msx1. This study aims to analyze the potential relationships between Vitamin D and Msx1 through: (1) comparative analysis of Vitamin D receptor (VDR) and Msx1 protein expression, (2) investigation of Msx1 expression in VDR null mutant mice, and (3) study of Msx1 overexpression impact on osteocalcin VDR expression in immortalized MO6-G3 odontoblasts. Results show the existence of cross-talks between Vitamin D and Msx1 regulation pathways. In odontoblastic cells, Msx1 overexpression decrease VDR expression, whereas in rickets Msx1 sense transcript expression is decreased. These cross-talks may open a new window in the analysis of rickets mineralized tissues physiopathology. In Vitamin D null mutants, the study of the natural Msx1 antisense transcript which has been recently described should be informative.

Dental alveolar bone defects related to Vitamin D and calcium status.

Vitamin D is important for skeletal development, growth, and homeostasis but has been sparsely studied in the oro-facial bone. Dental alveolar bone anchors teeth to mandible and maxilla bones via a periodontal ligament. Its formation and maintenance are strictly dependent on the presence of tooth organs and it is characterized by a high turnover rate. In order to study the role of Vitamin D and the calcium status on dental alveolar bone formation, microradiographic and histologic comparison of wild-type, Vitamin D receptor null mutant (VDR (-/-) hypo- and normo-calcemic mice and tissues were performed at 2 months. In hypo-calcemic VDR (-/-) mice, alveolar bone was hypomineralized and demonstrated a cellular and matrix organization, similar to the immature woven bone. In normo-calcemic VDR (-/-) mice, mineralization of dental alveolar bone appeared normal, but bone was morphologically abnormal in some specific anatomical locations. These data show that Vitamin D and calcium status may control the formation of dental alveolar bone. The differences of phenotype between hypo- and normo-calcemic VDR null mutant mice suggested a specific Vitamin D control of alveolar bone formation by the Vitamin D nuclear receptor pathway.

[Genetic and experimental approach to bony craniofacial growth: the role of the divergent homeobox gene Msx1]. / Pour une approche génétique et expérimentale de la croissance squelettique cranio-faciale: étude du rôle de l'homéogène divergent Msx1.

Tooth agenesis and clef palate are associated to the mutation of the Msx1 homeobox genes, highlighting the pivotal role of homeobox genes during the initial development of the craniofacial skeleton. Msx1 also controls the terminal differentiation of mineralised tissues forming cells. Recently, a Msx1 antisense RNA has been identified which inhibits Msx1 protein expression in odontoblastic cells. In order to investigate the role of Msx1 gene and its antisense RNAs during the late developmental stages of the craniofacial bone formation, the expression pattern of Msx1 protein, sense and antisense transcripts and the aspects of bone growth have been studied in post-natal normal and Msx1 knock-in mutant mice. Msx1 protein was strongly expressed in preosteoblasts of specific bone sites such as the basal mandible. At the same bone sites, bone growth was impaired or markedly decreased in knock-in mice. The comparison between the various expression patterns of Msx1 protein, sense and antisense RNAs suggests that the site-specific action of Msx1 protein on bone growth and craniofacial morphogenesis and that Msx1 protein level could be controlled by the local ratio of Msx1 sense and antisense RNAs. Regarding our experimental data and hypothesis, a clinical study of patients with MSX1 mutation will be performed in order to better characterize the abnormalities of the craniofacial skeleton growth.

Epithelial Dlx-2 homeogene expression and cementogenesis.

The Dlx-2 (distal-less gene) homeoprotein transcription factor controls early tooth development but has not been studied during the late stages of biomineralization. Transgenic mice containing a Dlx-2/LacZ reporter construct were used to map the Dlx-2 expression pattern in cementoblasts, the dental cells most closely related to bone cells and therefore suggested to be uniquely positioned osteoblasts. During initial root formation, marked expression of Dlx-2 was evident in molar and incisor root epithelium, whereas dental papilla and follicle were negative. Dlx-2 was expressed in this epithelium from the apical loop to the area of its disruption. During acellular cementum formation in both incisors and molars, Dlx-2 expression was observed in the majority of differentiated cementoblasts from the apical region to the erupting zones. During cellular cementum formation, the presence of which characterizes growth-limited molars, Dlx-2 expression was restricted to the innermost cementoblasts and entrapped cementocytes. These data further support the hypothesis of a complex origin and fate of cementum-forming cells, as previously suggested by the expression patterns of a set of mesenchymal and epithelial markers, notably ameloblastin as shown here. Dlx-2 expression might constitute a landmark of cementoblast subpopulations of epithelial origin. (J Histochem Cytochem 48:277-283, 2000)

Comparative study of MSX-2, DLX-5, and DLX-7 gene expression during early human tooth development.

Msx and Dlx family transcription factors are key elements of craniofacial development and act in specific combinations with growth factors to control the position and shape of various skeletal structures in mice. In humans, the mutations of MSX and DLX genes are associated with specific syndromes, such as tooth agenesis, craniosynostosis, and tricho-dento-osseous syndrome. To establish some relationships between those reported human syndromes, previous experimental data in mice, and the expression patterns of MSX and DLX homeogenes in the human dentition, we investigated MSX-2, DLX-5, and DLX-7 expression patterns and compared them in orofacial tissues of 7.5- to 9-wk-old human embryos by using in situ hybridization. Our data showed that MSX-2 was strongly expressed in the progenitor cells of human orofacial skeletal structures, including mandible and maxilla bones, Meckel's cartilage, and tooth germs, as shown for DLX-5. DLX-7 expression was restricted to the vestibular lamina and, later on, to the vestibular part of dental epithelium. The comparison of MSX-2, DLX-5, and DLX-7 expression patterns during the early stages of development of different human tooth types showed the existence of spatially ordered sequences of homeogene expression along the vestibular/lingual axis of dental epithelium. The expression of MSX-2 in enamel knot, as well as the coincident expression of MSX-2, DLX-5, and DLX-7 in a restricted vestibular area of dental epithelium, suggests the existence of various organizing centers involved in the control of human tooth morphogenesis.

Expression of DLX5 during human embryonic craniofacial development.

Dlx (distal-less gene) homeogenes encode transcription factors that are involved in the patterning of orofacial skeleton derived from cephalic neural crest cells. In order to study the role of DLX genes during embryonic development in human, DLX5 expression pattern was investigated in 6- to 11-week-old human embryos. A DLX5 PCR fragment was amplified from a human dental cDNA library subcloned and used for in situ hybridization investigations. DLX5 gene expression was primarily detected in the mandible at 6 weeks and then, after in the maxilla. DLX5 gene expression became restricted to progenitor cells of developing tooth germs, bones and cartilages of mandible and maxilla. During odontogenesis from bud to late cap stages, DLX5 transcripts were present in both dental epithelium and mesenchyme tissues. DLX5 expression was restricted to few cells in the vestibular aspect of the dental epithelium, while DLX5 mRNA signal was more widely distributed in dental mesenchyme. The observed expression pattern of DLX5 homeogene extends the proposed site-specific combination of homeogene expression in neural crest derived cells to human specific dentition. Furthermore, during the bud and cap stages of tooth morphogenesis, the asymmetric expression of DLX5 in the dental epithelium and dental mesenchyme may contribute to the complex patterning of human tooth shape.

In situ investigation of vitamin D receptor, alkaline phosphatase, and osteocalcin gene expression in oro-facial mineralized tissues.

The aim of this study was to investigate the expression pattern of 1, 25-dihydroxyvitamin D3 receptor (VDR) and vitamin D-responsive gene expression during the steps of hard tissue formation in oro-facial development. In situ hybridization of VDR, alkaline phosphatase, and osteocalcin transcripts was performed in the mandibles of growing rats. Osteoblasts were used as the internal positive control for in situ detection of VDR messenger RNAs. Transcripts were present throughout the stages of differentiation and in differentiated osteoblasts and osteocytes, and showed some anatomical specificities in their developmental expression pattern. In dental tissues, VDR was strongly expressed in the inner dental epithelium at the beginning of the presecretion stage and, after a transient decrease at the end of the presecretion stage, in secretion stage ameloblasts. VDR was continuously expressed in epithelial supraameloblastic cells. During dentin formation, VDR was mainly present in subodontoblastic cells and was down-regulated during the terminal differentiation of odontoblasts. In these cells, VDR expression appeared to be induced by 1, 25-dihydroxyvitamin D3 injection. These data confirm that VDR is expressed in cells directly involved in mineralized tissue formation: ameloblasts, odontoblasts, and osteoblasts. Furthermore, they extend the idea of vitamin D sensitivity to cells that are not directly involved in this process: supraameloblastic, subodontoblastic, and osteoprogenitor cells. The differential expression pattern of VDR in odontoblasts and osteoblasts together with the similarity in the expression of potential vitamin D-responsive genes (osteocalcin in odontoblasts and osteoblasts, and alkaline phosphatase in osteoprogenitor and subodontoblastic cells) suggest the existence of a tissue specificity for the genomic action of 1, 25-dihydroxyvitamin D3, which may involve co-operation with additional nuclear factors.

Immunolocalization of vitamin D receptor and calbindin-D28k in human tooth germ.

The role of vitamin D in ameloblasts and odontoblasts has been studied experimentally in rodents. Dental dysplasias have also been reported in clinical studies of children with rickets. Vitamin D acts via a nuclear receptor which binds the major metabolite, 1,25-dihydroxyvitamin D3, and positively or negatively controls the expression of specific genes. The most extensively studied markers of 1,25-dihydroxyvitamin D3 action are calbindin-D9k, calbindin-D28k, and osteocalcin. Therefore, to study in more detail the potential role of 1,25-dihydroxyvitamin D3 in human dental development, 1,25-dihydroxyvitamin D3 receptor (VDR) was localized by immunofluorescence in forming teeth (8-26 wk of gestation). Calbindin-D28k was also mapped by immunoperoxidase in antenatal and postnatal forming and formed teeth. VDR were detected in both dental epithelium and mesenchyme of bud, cap, and bell stages of tooth germs. Nuclei of overtly differentiated ameloblasts and odontoblasts were also immunostained. Calbindin-D28k was present in differentiated ameloblasts and odontoblasts. The presence of VDR and calbindin-D28k in ameloblasts and odontoblasts suggests that 1,25-dihydroxyvitamin D3 may contribute to the regulation of enamel and dentin formation, as classically reported for bone formation. Finally, the early appearance of VDR supports the concept that 1,25-dihydroxyvitamin D3 may also control forward stages of tooth crown development in humans.

Differential expression of the full-length and secreted truncated forms of EGF receptor during formation of dental tissues.

The developmental regulation of various receptor forms may be a key-element in the local fine tuning of growth factor effects. The present study focuses on the tissue- and stage-specificity of the alternative splicing of EGF receptor transcripts in the rat incisor. In situ hybridization, as well as light- and electron-microscopic immunolocalization were performed with a set of tools which enable us to discriminate the full-length and secreted truncated forms of EGF receptor. Our data show that, apart from a transient expression in differentiating odontoblasts, EGF receptor expression was predominantly observed in the dental epithelium. In the crown, the expression of the full-length EGF receptor was maximal during preameloblast proliferation and differentiation, decreased in differentiated ameloblasts, and remained low throughout enamel secretion. On the other hand, maturation stage ameloblasts, which regulate the final mineralization of enamel, express high levels of the full-length EGF receptor. In contrast with ameloblasts, epithelial supra-ameloblastic cells, which are not directly involved in the deposition of enamel matrix, showed an alternating predominance of the secreted truncated form during the secretion stage, and the full-length form during the maturation stage. The presence of the secreted truncated EGF receptor form was supported by the electron microscopic detection of extracellular aggregates of immunoreactive EGF receptor. Finally, Northern-blotting of enamel organ samples confirmed the presence of transcripts corresponding to mRNAs of both EGF receptor forms. During root formation, a decreasing gradient of full-length EGF receptor form expression was observed from the apical loop to the disrupting zone in root epithelium. The secreted truncated EGF receptor form was essentially detected in epithelial cells of the disrupting zone of root epithelium. During crown formation, the secreted truncated EGF receptor form, which appears to be synthesized by epithelial supra-ameloblastic cells and secreted toward ameloblasts, may competitively bind EGF receptor ligands and modify activation of the full-length EGF receptor.

Ameloblasts and odontoblasts, target-cells for 1,25-dihydroxyvitamin D3: a review.

The basic features on the vitamin D endocrine system, synthesis of the main metabolite 1,25-dihydroxyvitamin D3 (1,25) and its genomic action mediated via the vitamin D receptor (VDR), are reviewed. Calbindin-D9k, calbindin-D28k and osteocalcin are presented as the most-extensively investigated vitamin D-dependent calcium-binding proteins. The action of 1,25 on the basic process of proliferation and differentiation is introduced. Then, the basis of the systemic theory of vitamin D action on teeth (clinical and experimental data and the dissimilar distribution of VDR and of potential vitamin D-dependent proteins in dental cells) are exposed. Finally, the data obtained with calbindin-D9k, calbindin-D28k, osteocalcin and VDR, which supports the theory that ameloblasts and odontoblasts are target-cells for 1,25 is presented. As a perspective, a cross-survey of the 1,25 and tooth-related literature is proposed which may indicate potential target-genes for 1,25 in teeth as done previously for calbindins-D.

In situ hybridization of calbindin-D 28 k transcripts in undecalcified sections of the rat continuously erupting incisor.

Calbindin-D9k and calbindin-D-28k genes are useful systems to investigate the tissue- and stage-specificity as well as the hormonal control of gene expression. Since they regulate cellular calcium mobilization, their study may be of interest in mineralized tissues. However, thus far, immunocytochemical labelling has been mainly realized in these systems. In order to set up methods for mRNA investigation, in situ hybridization of calbindin-D28k mRNAs was performed in the continuously erupting incisor of Sprague-Dawley rats (15-, 30-, and 56-day-old). 35S UTP labelled antisense and sense riboprobes specific for brain calbindin-D 28k were used for in situ hybridization. Specific and non-specific signals could not be discerned when studying decalcified samples. In contrast, on sections not pretreated with EDTA, calbindin-D 28k transcripts (in tooth and kidney) appeared strongly labelled with antisense probes, while sense probes provided a negligible background. In ameloblasts, the signal (i.e., calbindin-D 28k mRNA levels) increased during the presecretory stage. Different mRNA gradients and subcellular distribution patterns characterized the secretory and maturation stages. A nuclear labelling was observed, associated with the highest levels of transcripts. These data suggest a developmental control of calbindin-D28k mRNA transcription. Calbindin-D28k gene expression appears to be up-regulated during the initiation of both secretory and maturation stages of enamel mineralization.

EGF receptor expression in mineralized tissues: an in situ hybridization and immunocytochemical investigation in rat and human mandibles.

There is extensive evidence that growth factors play a central part in the autocrine/paracrine regulation of cell growth and differentiation in mineralized tissues. In order to investigate involvement of the EGFr receptor (EGFr) in forming mineralized tissues, its expression was studied by in situ hybridization and immunocytochemistry in mandibles of growing rats, as well as in human embryos. In Hertwig's epithelial root sheath of rat molar, EGFr mRNAs appeared strongly expressed, while dental pulp and dental follicle showed weak labeling. The lingual epithelium of rat incisor showed strong labeling, which decreased after epithelial dislocation. Cells of the adjoining lingual dental pulp and dental follicle, as compared to epithelium, contained a low level of EGFr mRNAs. In contrast, a significant signal with antisense RNA probe was observed in bone. Sense RNA probes provided a regular background or no labeling. Undifferentiated cells located in the periosteum and endosteal spaces were labeled. EGFr mRNAs were also present in osteoblasts and in lesser amounts in some osteocytes. In rat and in human bone, both osteoblasts and osteocytes were positive on immunostaining. Similarly in the Hertwig's root sheath, EGFr immunostaining and in situ hybridization labeling were closely related. These data show that different patterns of EGFr expression in forming mineralized tissues are tissue- and stage-specific. However, in all these cells, the present in situ investigation supports the assumption that EGFr is involved in the early stages of cellular proliferation and differentiation. This report also suggests that EGFr may play a role in differentiated and mature cells of mineralized tissues.

Developmental pattern and subcellular localization of parvalbumin in the rat tooth germ.

The EF-hand calcium-binding protein parvalbumin has been extensively studied in nerve and muscle cells. Its possible role in biomineralization during tooth development was here investigated by determining its subcellular localization by immunogold cytochemistry. The developmental sequences of amelogenesis and dentinogenesis were studied in rat molars, and in continuously growing rat incisors. The findings confirm that parvalbumin is a nuclear and a cytosolic protein, not associated with any particular intracellular organelle. Epithelial and mesenchymal undifferentiated cells contained no specific parvalbumin immunolabelling. In differentiated ameloblasts, secretory-pole (Tomes' process) formation was associated with a proximal-distal gradient of parvalbumin labelling. But after the Tomes' process had formed, parvalbumin was evenly distributed throughout the cell. The parvalbumin contents of ruffle-ended and smooth-ended ameloblasts appeared to be very different. Differentiated odontoblasts were less heavily labelled than ameloblasts, and the label was restricted to the cell body during the whole of dentinogenesis. These data suggest that parvalbumin could contribute to membrane plasticity during differentiation, as shown during dendritic growth in the nervous cells. Moreover, as may occur in excitable cells, parvalbumin could buffer calcium specifically in the cells producing mineralized enamel and dentine during the later stages of tooth development.

[Action of 1,25-dihydroxyvitamin D3 in the tooth germ. Modulations of receptor in the development]. / Action de la 1,25-dihydroxyvitamine D3 dans le germe dentaire. Modulations du récepteur au cours du développement.

The control of tooth development by 1,25-Dihydroxyvitamin D3 is analyzed by light- and electron-microscope immunocytochemistry and Northern-blotting in vitamin D-deficient rats. The receptor for 1,25-Dihydroxyvitamin D3, immunostained at the light microscope in all stem-cells, became immunodetectable only at the ultrastructural level in the ameloblasts which elaborate enamel and odontoblasts which synthetize dentin. Moreover, 1,25-Dihydroxyvitamin D3 induces an up-regulation specifically in these cells. In parallel, the calbindins-D9k, -D28k and osteocalcin, in contrast to the phosphoprotein, appear sensitive to vitamin D-deficiency. A single injection of 1,25-Dihydroxyvitamin D3 led to the increase of steady-state levels of the corresponding calbindin mRNAs. These data show that tooth constitutes a target-organ for 1,25-Dihydroxyvitamin D3, as other components of the phospho-calcic metabolism.