破骨细胞核因子κB受体活化因子配基和骨保护因子在种植体周围软组织及骨组织的表达

目的研究破骨细胞核因子κB受体活化因子配基（RANKL）及其伪受体骨保护因子（OPG）在非负荷期种植体周围软组织和骨组织中的表达变化及时间分布特点。方法选用6只1～2岁龄的雄性Beagle犬建立种植义齿动物模型,分别观测种植体植入后3、7、15、30、60、90 d种植体周围的骨改建情况。取种植体周围软组织进行实时荧光定量聚合酶链反应（PCR）;取犬下颌骨进行大体标本观察拍摄X线片;取种植体周围骨组织进行免疫组化染色,检测RANKL和OPG随时间的表达变化及分布特点。结果骨改建的最活跃期为种植体植入后的第7天,种植体周围软组织中的RANKL和OPG mRNA及骨组织中的RANKL和OPG均随种植体植入时间的增加而增加,第7天达高峰,而后均逐渐降低。RANKL和OPG在种植体周围软组织及骨组织中的表达变化规律一致。结论OPG和RANKL能在种植体周围软组织中表达,且变化规律与种植体周围骨组织改建过程一致。种植体周围组织可以通过OPG/RANKL系统参与破骨细胞的形成,调节骨质吸收,影响骨组织代谢微环境。     

Receptor activator NF kappaB ligand (RANKL) and osteoprotegerin (OPG) protein expression in periodontitis

OBJECTIVES AND BACKGROUND: This study investigated the expression of key mediators that regulate differentiation of osteoclasts, receptor activator of nuclear factor kappaB ligand (RANKL), and its natural inhibitor, osteoprotegerin (OPG), in periodontitis. We aimed to compare the levels of the RANKL and OPG in the granulomatous tissue adjacent to areas of alveolar bone loss from patients with periodontitis to that present in tissue from patients without periodontitis. In addition, we aimed to determine the types of cells expressing these factors in these tissues and to demonstrate the expression of the osteoclastic markers, RANK and tartrate-resistant acid phosphatase (TRAP), in periodontitis. MATERIALS AND METHODS: Frozen biopsy specimens were analysed using specific monoclonal antibodies and were evaluated by semiquantitative analysis and digital image analysis to compare levels of RANKL and OPG protein expression. Double labelling of frozen sections with antibodies to different cell lineage specific markers was used to determine the types of cells expressing these proteins. In situ hybridization was used to detect cells expressing RANK mRNA. RESULTS: Semiquantitative image analysis demonstrated that significantly higher levels of RANKL protein (P < 0.05) were expressed in the periodontitis tissue. Conversely, OPG protein was significantly lower (P < 0.05) in the periodontitis tissues. RANKL protein was associated with lymphocytes and macrophages. OPG protein was associated with endothelial cells in both tissues. Many leukocytes expressing RANK mRNA and TRAP were observed in periodontitis tissues. CONCLUSION: The change in the levels of these key regulators of osteoclast differentiation may play a major role in the bone loss seen in periodontitis.     

The influence of parathyroid hormone-related protein (PTHrP) on tooth-germ development and osteoclastogenesis in alveolar bone of PTHrP-knock out and wild-type mice in vitro

In a previous study, it was shown that tooth germs of neonatal homozygous parathyroid hormone-related protein (PTHrP)-knockout mice are penetrated or compressed by the surrounding alveolar bone, suggesting an important role for PTHrP in the formation and activation of osteoclasts around growing tooth germs. In order to elucidate the role of PTHrP during the development of the tooth germ and related structures, mandibular explants containing cap stage tooth germs of embryonic day 14, homozygous mice were here cultured with or without surrounding alveolar bone. There was no difference in the number of tartrate-resistant acid phosphatase-positive multinucleated osteoclastic cells around the first molars of homozygous and wild-type mice. After 10 days of culture, osteoclastic cells were rarely present in explants from homozygous mice and penetration of alveolar bone into the dental papilla was observed. The decline in osteoclast number was partly restored by the addition of PTHrP to the culture. Tooth germs of both wild-type and homozygous mice cultured without alveolar bone developed well, with no apparent structural abnormality; dentine formation was evident after 10 days. These data suggest that PTHrP is not required for the development of the tooth germ proper but is indispensable in promoting the osteoclast formation required to accommodate that development.     

Inhibition of osteoclastogenesis by the secretion of osteoprotegerin in vitro by rat dental follicle cells and its implications for tooth eruption

Tooth eruption requires the presence of the dental follicle, a loose connective tissue sac that surrounds each unerupted tooth. Early postnatally in the rat, the follicle secretes colony-stimulating factor-1 (CSF-1) and monocyte chemotactic protein-1 (MCP-1), chemotactic molecules that are probably responsible for the recruitment of mononuclear cells. These cells, in turn, fuse to form osteoclasts, which are required for alveolar bone resorption to form an eruption pathway. Recent studies have shown that the osteoprotegerin (OPG) gene is expressed in the dental follicle, but in the first mandibular molar of the rat, that expression is reduced at day 3, the time of maximal osteoclast numbers on the alveolar bone. Inhibition of OPG expression at this time would allow osteoclast formation/activation. To determine if the dental follicle cells do secrete OPG that inhibits osteoclastogenesis, spleen cell cultures were established and soluble osteoclast differentiation factor (ODF) and CSF-1 added to some of them to promote osteoclast formation. In other cultures, dental follicle cells were added in an insert, such that they did not touch the spleen cells. Using a quantitative, tartrate-resistant acid phosphatase (TRAP) assay, it was shown that ODF and CSF-1 promoted osteoclastogenesis in the spleen cell cultures, but the addition of the follicle cells inhibited this and returned the TRAP activities to those seen in cultures of spleen cells only. Adding anti-OPG to these cultures, however, negated the effect of the follicle cells, demonstrating that OPG was the inhibitory molecule secreted by those cells. The follicle cells also immunostained for OPG, confirming that they synthesize OPG. These findings, coupled with those of other studies which show that the periodontal ligament (a derivative of the dental follicle) also secretes OPG, indicate that, except for the period of time in tooth eruption, where osteoclast formation is needed to form an eruption pathway, secretion of OPG would be the norm, presumably to prevent resorption of alveolar bone and subsequent disruption of the periodontal ligament.