Mechanism of toxic action of fluoride in dental fluorosis: whether trimeric G proteins participate in the disturbance of intracellular transport of secretory ameloblast exposed to fluoride

In enamel fluorosis model rats treated with sodium fluoride, secretory ameloblasts of incisor tooth germs exhibited disruption of intracellular trafficking. We examined whether heterotrimeric G proteins participated in the disruption of vesicular trafficking of the secretory ameloblast exposed to fluoride, using immunoblotting and pertussis toxin (IAP)-induced adenosyl diphosphate (ADP)-ribosylation for membrane fractions of the cell. Immunoblotting of crude membranes, post supernatants of the ameloblast, with anti-G_i3/o and anti-G_s antibodies showed that G_i3 or G_o proteins existed in the secretory ameloblast, but G_s protein did not. Immunoblotting of the subcellular membrane fractions indicated that the G_i3 or G_o proteins were located in the Golgi membrane, but were not in the rough endoplasmic reticulum (rER) membrane. Autoradiograph of IAP-induced ADP-ribosylation, however, showed the existence of IAP-sensitive G proteins both in rER and Golgi membranes. Fluoride treatment decreased the G proteins bound to both membranes. These findings indicate that different G proteins, both of which are IAP-sensitive, are present in the rER and Golgi apparatus, and suggest that these G proteins participate in the disturbance of intracellular transport of the secretory ameloblast exposed to fluoride. Received: 24 June 1998 / Accepted: 8 September 1998     

High-fluoride acitivates the FasL signalling pathway and leads to damage of ameloblast ultrastructure

ObjectiveHigh fluoride can induce stress-mediated apoptosis and degradation of ameloblasts. Fas ligand (FasL) has been regarded as a key regulator in intracellular responses for stress-induced apoptosis in reproductive or cancerous cell lineages. The objective of this study is to explore the role of FasL in the regulation of ameloblast ultrastructure damage.DesignPrimary ameloblasts were isolated from the molar tooth germ of 4-day-old SD rats. The ameloblasts were incubated with 3.2 mM NaF or nothing. After incubation for different time arranging from 12 h to 72 h, ELISA was used to detected the secretion levels of FasL in the medium. Then at 48 h post treatment, the ameloblast ultrastructure was detected with Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM), and expression of apoptotic proteins and peroxidative enzymes/products were examined. Finally, a specific FasL inhibitor was applied to co-treat the ameloblasts with NaF, and the ameloblast ultrastructure was detected with TEM and SEM.ResultsThe secretion of FasL was notably increased by 3.2 mM NaF treatment, and the increase reached to the peak after incubation for 48 h. High fluoride incubation damaged the ameloblast untrastructure manifesting a series of intracelluar stress responsing cell organelle destruction, and a marked increase in expression of apoptotic genes and oxidative stress. The FasL inhibitor treatment partially mitigated the untrastructure damage caused by high dose NaF.ConlusionHigh-fluoride leads to damage of the ameloblast ultrastructure through paritially acitivating the FasL signalling pathway.     

Over- and Ectopic Expression of Wnt3 Causes Progressive Loss of Ameloblasts in Postnatal Mouse Incisor Teeth

Intercellular signaling is essential for the development of teeth during embryogenesis and in maintenance of the continuously growing incisor teeth in postnatal rodents. WNT intercellular signaling molecules have been implicated in the regulation of tooth development, and the Wnt3 gene shows specific expression in the enamel knot at the cap stage. We demonstrate here that Wnt3 also is expressed in specific epithelial cell layers in postnatal incisor teeth. To begin to delineate the functions of Wnt3 in developing and postnatal teeth, we determined the effects of over- and ectopic expression of Wnt3 in the tooth epithelium of mice carrying a keratin 14- Wnt3 transgene. Expression of the transgene caused a progressive loss of ameloblasts from postnatal lower incisor teeth. Loss of ameloblasts may be due to defective proliferation or differentiation of ameloblast precursors, progressive apoptosis of ameloblasts, or loss of ameloblast stem cells.     

Potential function of TGF-β isoforms in maturation-stage ameloblasts

Objectives

To investigate potential functions of transforming growth factor-beta (TGF-β) isoforms in maturation-stage ameloblasts during amelogenesis.

成釉细胞的培养及其在釉质形成中的作用

成釉细胞在牙齿形成过程中起主要作用,能够合成、分泌、重吸收和降解牙釉质基质。釉原蛋白和非成釉蛋白在牙釉质形成中起关键性作用。国内外已成功分离培养出成釉细胞,成釉细胞的培养、增殖及分化受培养液和基质的影响较大。现以国内外发表的文章做基础,就成釉细胞的培养及其分泌釉原蛋白、在牙齿形成中作用做一综述。     

T-2毒素中毒大鼠切牙成釉细胞的形态观察研究

目的观察不同剂量T-2毒素作用下大鼠切牙成釉细胞的形态变化,探讨其对牙釉质形成的影响。方法选择60只SD大鼠,随机分为3组:对照组,实验组1和实验组2,T-2毒素灌胃剂量分别为0ng/gBW/d,100ng/gBW/d和200ng/gBW/d。4周后处死动物,沿大鼠右下切牙长轴做连续切片,HE染色法观察T-2毒素对成釉细胞形态的影响。结果肉眼观察染毒组大鼠切牙色淡黄,透光度和光泽不好。光镜下可见染毒组成釉细胞Tome’s突消失,细胞扭曲变形且可见细空泡,高剂量T-2毒素影响更明显。结论 T-2毒素可使大鼠切牙的分泌期和转换器的成釉细胞形态发生改变,进而使肉眼观呈现釉质发育不全的临床改变。     

The mechanism of ameloblast movement: A hypothesis

A hypothesis is presented which defines, by means of five postulates, the forces which initiate and restrain ameloblast movement during the formation of the enamel of mammalian teeth. These postulates are: 1. Relative to tissue fluid pressure, a potentially high hydrostatic pressure is generated within the young enamel precursor material. It follows that this will result in a force pushing the ameloblasts radially outwards. 2. The ameloblasts produce a secretory force. It follows that to this force of secretion there will be a force of reaction pushing the ameloblasts outwards. 3. Crossing of ameloblasts is restrained. 4. Outwards movement of ameloblasts is restrained. 5. The proximal ends of ameloblasts are more firmly united than the distal ends, or alternatively, due to the fact that the forces causing ameloblast movement act on the distal ends of the cells, these latter ends are more readily induced to cross. On the basis of these postulates two analogues have been constructed to predict the distortion of the ameloblast layer that might be expected at the commencement of amelogenesis. The directions in which the forces indicated by the postulates will move ameloblasts (distorted in the manner predicted by the analogues) have been deduced. The actual directions in which ameloblasts have moved are represented in the fully developed tooth by the prisms of which enamel is composed. Prism directions in man, dog and the rat are close to the predictions of the hypothesis.

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Zusammenfassung Anhand von 5 Postulaten wird eine Hypothese vorgelegt, welche die Kräfte definiert, die die Ameloblastenbewegung während der Bildung des Schmelzes von Säugetierzähnen anregt und unterdrückt. Diese Postulate sind folgende: 1. durch den Druck der Gewebeflüssigkeit bedingt, wird ein potentiell hoher hydrostatischer Druck innerhalb des Vorstufenmaterials des jungen Schmelzes erzeugt. Es folgt daraus, daß eine Kraft entsteht, welche die Ameloblasten radial nach außen drängt. 2. Die Ameloblasten produzieren eine sekretorische Kraft; dieser steht eine Reaktionskraft entgegen, welche die Ameloblasten nach außen stößt. 3. Das Kreuzen der Ameloblasten wird verhindert. 4. Die Bewegung der Ameloblasten nach außen ist gehemmt. 5. Die proximalen Enden der Ameloblasten sind enger verbunden als die distalen oder wechselweise: da die Kräfte, welche die Bewegung der Ameloblasten verursachen, vor allem auf das distale Ende der Zellen einwirken, können die letztgenannten leichter zum Kreuzen angeregt werden. Gestützt auf diese Postulate wurden zwei Modelle konstruiert, um die Distortion der Ameloblastenschicht vorauszusagen, welche am Beginn der Amelogenesis erwartet werden kann. Die Richtungen, nach welchen die in den Postulaten besprochenen Kräfte die Ameloblasten (verzerrt in der durch die Modelle vorausgesagten Weise) bewegen, werden abgeleitet. Die tatsächlichen Richtungen, in welche sich die Ameloblasten bewegt haben, werden im vollentwickelten Zahn durch die Prismen gegeben, aus welchen der Schmelz aufgebaut ist. Die Richtungen dieser Prismen beim Menschen, beim Hund und bei der Ratte stimmen beinahe mit den Voraussagen der Hypothese überein.

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Résumé Une hypothèse, définissant, à l'aide de 5 postulats, les forces qui déclenchent et inhibent les mouvements de l'améloblaste pendant l'amélogenèse des dents de mammifères, est émise. Ces postulats sont: 1. en ce qui concerne la pression tissulaire liquidienne, une pression hydrostatique relativement élevée est produite dans les précurseurs de l'émail jeune. Il s'en suit une force repoussant les améloblastes vers la périphérie, en direction radiale. 2. Les améloblastes produisent une force génératrice. Il s'en suit une force de réaction poussant les améloblastes vers l'extérieur. 3. Le croisement des améloblastes est empêché. 4. Les mouvements vers la périphérie des améloblastes sont également empêchés. 5. Les extrémités proximales des améloblastes sont plus solidement unies que les extrémités distales, ou bien étant donnée que les forces induisant le mouvement des améloblastes agissent sur les pôles distaux des cellules, ces derniers peuvent se croiser plus facilement. En tenant compte de ces postulats, deux modèles ont été construits, afin de prédire les déformations de la couche des améloblastes susceptibles de se produire au début de l'amélogenèse. Les directions selon lesquelles les forces, déduites à partir des postulats, vont déplacer les améloblastes (déformés de la façon prédite par les modèles) ont pu être établies. Ces directions de déplacement des améloblastes sont indiquées, au niveau de la dent adulte, par les prismes qui constituent l'émail. Les directions des prismes chez l'homme, le chien et le rat sont très voisines des prédictions déduites de cette hypothèse.

     

Histoenzymological and ultrastructural study of a bifocal calcifying epithelial odontogenic tumor. characteristics of epithelial cells and histogenesis of amyloid-like material

Summary A calcifying epithelial odontogenic tumor, simultaneously located in the two jaws (maxilla and mandible) was examined by histochemical and electron microscopic methods. Squamous tumor cells without secretory polarity were different from those of common ameloblastoma. High activities of alkaline phosphatase and ATPases were demonstrated by light and electron microscopy on the cytoplasmic membrane, findings similar to those in the stratum intermedium cells of the normal dental germ from which these tumor cells seem to arise. The tumor cells, like preameloblasts of the dental germ, also produce a granulo-filamentous material in intracytoplasmic vesicles and discharge it into the stroma. This pseudo-amyloid substance represents an abnormal protein of the enamel matrix and calcification, mainly occurring in that substance, might be an attempt at mineralization.