Hypoxia increases the expression of enamel genes and cytokines in an ameloblast‐derived cell line

The aim of this study was to investigate the effect of hypoxic conditions on the expression of enamel genes and on the secretion of alkaline phosphatase (ALP), lactate dehydrogenase (LDH), cytokines, and interleukins by an ameloblast‐derived cell line. Murine ameloblast‐derived cells (LS‐8 cells) were exposed to 1% oxygen for 24 and 48 h and harvested after 1, 2, 3, and 7 d. The effect of culture in hypoxic conditions on the expression of structural enamel matrix genes and on the secretion of cytokines and interleukins, as well as ALP and LDH, into the cell‐culture medium was calculated relative to the expression and secretion of these factors by untreated cells (controls) at each time point. Hypoxia increased expression of the structural enamel matrix genes amelogenin (Amelx), ameloblastin (Ambn), and enamelin (Enam), and the enamel protease matrix metalloproteinase‐20 (Mmp20). Expression of hypoxia‐inducible factor 1‐alpha (Hif1α), and secretion of several vascularization factors and pro‐inflammatory factors, were increased after 24 and 48 h of hypoxia. The ALP activity was reduced after 24 and 48 h of hypoxia, whereas the LDH level in the cell‐culture medium was higher after 24 h of hypoxic conditions compared with 48 h. In conclusion, hypoxic exposure may disrupt the controlled fine‐tuned expression and processing of enamel genes, and promote the secretion of pro‐inflammatory factors.     

Enamel Mineralization and the Role of Ameloblasts in Calcium Transport

Amelogenesis is a dynamic and unique process of cell-matrix interactions in that matrix synthesis, degradation and resorption all proceed simultaneously, coupled with mineral depositions in a compartment between ameloblasts and dentin or dental papilla. Accumulation of data suggest the role of ameloblasts in tooth morphogenesis and matrix formation, but no fully acceptable explanation has been given concerning the role of ameloblasts in calcium transport. In this article, old and new points of issue raised regarding the role of ameloblasts in calcium acquisition are reviewed and possible mechanisms whereby the ameloblasts prevent the rise of cytosolic calcium while actively or less actively transporting calcium are elaborated upon based on recent findings.     

不同浓度氟化物对体外培养成釉细胞活性的影响

目的建立大鼠成釉细胞原代培养技术,观察不同浓度氟化钠对成釉细胞活性的影响,为研究氟斑牙的形成提供依据。方法取10¹5 d的Wistar大鼠磨牙牙胚组织进行原代培养,通过酶消化法,分离培养成釉细胞。加入不同浓度(0、0.4、0.8、1.6、3.2、6.4 mmol/L)的氟化钠作用于成釉细胞,分别培养24、48、72 h后,采用CCK-8法检测各组细胞的活性情况。结果①当氟化物浓度为0.4、0.8 mmol/L时,对成釉细胞的增殖有促进作用,且随着时间的增加而增强。②当氟化物浓度为1.6、3.2、6.4 mmol/L时,对成釉细胞的增殖有抑制作用,随着氟化钠浓度的增加,对细胞的抑制作用也逐渐增强,并且抑制作用随着时间的延长愈发明显。结论不同浓度的氟化物对体外培养成釉细胞的活性具有促进和抑制双向作用。     

饮水型氟中毒动物模型建立及硬组织形态学改变的研究

目的建立慢性饮水型氟中毒动物模型并观察其硬组织形态学改变。方法 48只Wistar大鼠随机分成4组,建立氟中毒动物模型。染氟组分别饮用含氟化钠浓度为50、100、150 mg/L的自来水,对照组饮用常规自来水。8周后取大鼠切牙及股骨,通过组织HE染色方法观察各组大鼠切牙成釉细胞和大鼠骨组织形态学改变,采用氟离子选择电极测定各组大鼠血氟、牙氟及骨氟浓度。结果实验组大鼠切牙出现不同的氟牙症表现。各染氟组大鼠血氟(F=11.234,P<0.05),牙氟(F=275.148,P<0.05),骨氟(F=217.337,P<0.05)含量显著高于对照组,且随浓度增加而增加,各组间均具有显著差异。HE染色发现实验组大鼠切牙成釉细胞排列不规则呈多层,高柱状细胞结构变矮或消失,少量细胞发生扭曲,且随氟浓度增加以上病理学改变加重。大鼠股骨HE染色发现实验组骨组织出现骨小梁增多,排列致密等骨硬化性表现,骨骺板增厚,增殖层软骨细胞排列紊乱,随浓度的增加以上病理学改变加重。结论长时间饮用高浓度含氟水可引起慢性氟中毒,硬组织出现氟斑牙和氟骨症的病理学改变。     

中间层在成釉细胞分化及分泌期的形态学观察

目的明确中间层细胞在釉质形成过程中的形态学变化,为进一步研究其在成釉细胞分化和釉质形成中的具体作用机制提供理论依据。方法建立出生后BALB／C小鼠牙胚中间层发育HE染色的实验模型;电镜观察其超微结构的变化。结果钟状晚期细胞处于分化期,中间层为2—3层的多细胞层结构,电镜下可见少量的粗面内质网、线粒体等细胞器成分,内釉上皮呈柱状或高柱状,可见中间层与成釉细胞间的桥粒连接;釉质分泌期,中间层呈明显的单细胞结构,细胞排列紧密,与周围组织的界限清楚,成釉细胞呈高柱状,可见大量釉质的分泌,线粒体、粗面内质网、高尔基复合体等细胞器成分明显增多,细胞间的桥粒连接明显;随着釉质的不断建立,釉质分泌基本完成,中间层结构已不易辨认,此时牙齿亦部分萌出,电镜下细胞间联系疏松,细胞器成分萎缩变减少。结论中间层对成釉细胞的分化及釉质形态的正常发育起到一定的调控作用,并在釉质形成中起到了一定的物质转运及营养支持功能。     

微小RNAs在牙釉质发育过程中的表达和作用

微小RNAs（microRNAs）是一类内源性的短链非编码RNA,在转录后水平调控基因的表达,在各项生物发生过程中发挥重要的调控作用。牙釉质发育过程中任何信号的干扰和突变都可能导致牙釉质形成障碍。本文对miRNAs在牙釉质发育过程中的表达和作用机制进行综述。     

Preparation of midsagittal semithin Epon sections of the entire secretory ameloblast population in the maxillary rat incisor

Abstract – To study cytological changes in the migrating cell layer of the ameloblasts in the rat incisor with semithin Epon sections the ideal section plane would consequently be along the midsagittal plane of the incisor. However, the small dimensions and the complex three-dimensional structure of the apical part of the odontogenic organ covered by alveolar bone make it difficult to orientate and position sections in the midsagittal plane. Serial sectioning of the apical half of the maxillary incisor in the horizontal and sagittal planes clarified the relation of the midsagittal plane of the odontogenic organ to the alveolar bone, and the changes of the sectional profile of the odontogenic organ as a function of its position on the transverse axis of the incisor. From this information a method was designed whereby the two axes of the midagittal plane were marked directly on the block surface before sectioning, and the position of sections in the midsagittal zone of the ameloblasts standardized.     

Transmission electron microscope observations on enamel following silver methenamine staining

Abstract – Transmission electron microscope observations on porcine enamel and secretory ameloblasts showed that silver methenamine material was located inside secretory vesicles in secretory ameloblasts and along the enamel crystals inside immature enamel. It is concluded that silver methenamine is able to stain enamel proteins selectively inside these tissues.     

Composition of mineralizing incisor enamel in cystic fibrosis transmembrane conductance regulator‐deficient mice

Formation of crystals in the enamel space releases protons that need to be buffered to sustain mineral accretion. We hypothesized that apical cystic fibrosis transmembrane conductance regulator (CFTR) in maturation ameloblasts transduces chloride into forming enamel as a critical step to secrete bicarbonates. We tested this by determining the calcium, chloride, and fluoride levels in developing enamel of Cftr‐null mice by quantitative electron probe microanalysis. Maturation‐stage enamel from Cftr‐null mice contained less chloride and calcium than did wild‐type enamel, was more acidic when stained with pH dyes ex vivo, and formed no fluorescent modulation bands after in vivo injection of the mice with calcein. To acidify the enamel further we exposed Cftr‐null mice to fluoride in drinking water to stimulate proton release during formation of hypermineralized lines. In Cftr‐deficient mice, fluoride further lowered enamel calcium without further reducing chloride levels. The data support the view that apical CFTR in maturation ameloblasts tranduces chloride into developing enamel as part of the machinery to buffer protons released during mineral accretion.