The Immunolocalization And Significance Of Runx-2 Expression In Tertiary Dentinogenesis

The transcription effector runx-2 is essential for osteoblast differentiation and determines the lineage of osteoblasts from mesenchymal cell as well as also regulated many bone- and tooth- related genes. Many studies reveal that Runx-2 is involved in the initial development of calcified tooth tissue. Following external stimulation, the dental pulp could produce tertiary dentin when the local environment is in favour of healing. The purpose of this study was to investigate the critical role of Runx-2 in the process of dental pulp injury and repair.Methods An animal model of dental injury and renovation was established. One cavity was prepared on the occlusion of the first molars of SD rats. The animals were sacrificed in 1, 3, 5, 7, 14, and 21days. The mandible and teeth of each animal were fixed, decalcified, embedded in paraffin, and sectioned serially. The paraffin sections were⑴stained with H&E;⑵reacted with polyclonal antibodies against mouse ALP using sABC method;⑶reacted with polyclonal antibodies against mouse Runx-2. Result Immunolocalization demonstrated positive staining for ALP and Runx-2 in the different stages of reparative dentinogenesis. In normal dental pulp a slight ALP activity was present in the predentin zone, whereas all the other cells were negative. But in experiment groups, strong positive staining was detected in the site of the impaired pulp after 1 day; while only weak ALP staining was detectable 3 days after operation; 5 days later, followed by the reparative dentinogenesis, ALP expression vanished slowly, then totally disappeared at last.Runx-2 could be hardly detectable in normal dental pulp. The same as ALP staining, strong positive was detected beside the cavity after 1 day, and only weak Runx-2 staining was detectable 3 days after operation; 5 days later, a lot of stellate cells in the root tip expressed Runx-2; and after 7 days, Runx-2 staining became weaker and weaker.Conclusion The expression of Runx-2 in different stages in rat tertiary dentinogenesis had temporal and spatial specificity. The localization feature of Runx-2 suggested the Runx-2 may be an influential factor for the differentiation of the odontoblast-like cells and the mineralization of the tertiary dentin.