Abstract: BACKGROUND: Erythropoietin has anti-inflammatory, anti-apoptotic, and pro-bone defect repair effects. To date, fewer studies have been conducted on its effects and molecular mechanism underlying restorative dentin formation after pulp injury.
OBJECTIVE: To explore the effect of erythropoietin on restorative dentin formation after pulp injury. 
METHODS: (1) Animal experiment: Thirty-two rats were randomly divided into control group (n=16) and experimental group (n=16). In the experimental group, collagen sponges containing erythropoietin were used to directly cap the pulp at the pulp injury, and in the control group, collagen sponges containing PBS were used to directly cap the pulp at the exposed pulp injury. The cavity was then closed with glass ionomer adhesive. After 2 and 4 weeks of treatment, the maxillary bones of the two groups were collected, and the expression of nestin in dentin was detected by immunohistochemistry, and the reparative dentin production was observed by hematoxylin-eosin staining. The maxillae of four Sprague-Dawley rats were taken for immunohistochemical detection of erythropoietin expression in molar and incisor teeth. (2) Cell experiment: Human dental pulp cells, human periodontal ligament cells and human gingival fibroblasts were obtained from human dental tissue, periodontal ligament, and gingival tissue. Real-time reverse transcription PCR (RT-PCR) was used to detect the mRNA expression of erythropoietin. Erythropoietin, dentin sialophosphoprotein, dentin matrix protein 1, and nestin mRNA levels in human pulp cells were detected by RT-PCR under induced or uninduced odontoblastic differentiation. After down-regulation of erythropoietin expression or exogenous administration of erythropoietin intervention under induced or uninduced differentiation odontoblastic differentiation, the relative mRNA expression of dentin sialophosphoprotein and dentin matrix protein 1 in human pulp cells was detected by RT-PCR, and the formation of mineralized nodules was detected by alizarin red S staining, and mRNA and protein expressions of bone morphogenetic protein 2 were detected by RT-PCR and western blot, respectively. 
RESULTS AND CONCLUSION: (1) Animal experiment: Compared with the control group, the restorative dentin production and nestin expression were higher in the experimental group after 2 and 4 weeks of treatment. The expression of erythropoietin was weakly positive in pulp, odontoblastic cell layer and periodontal membrane of the rat’s first maxillary molar, and strongly positive in odontoblasts. (2) Cell experiment: The mRNA expression of erythropoietin was higher in human dental pulp cells than in the other two types of cells. The mRNA expressions of dentin sialophosphorin, dentin matrix protein 1, nestin, erythropoietin and bone morphogenetic protein 2 in human pulp cells increased and the formation of mineralized nodules during odontoblastic differentiation under induction compared with non-induction conditions. The mRNA expression of dentin sialophosphoprotein, dentin matrix protein 1, nestin, bone morphogenetic protein 2 and the formation of mineralized nodules were decreased in human pulp cells after downregulation of erythropoietin under induced odontoblastic differentiation, and the protein expression of bone morphogenetic protein 2 was also decreased. After exogenous erythropoietin intervention, the expression of the above indexes in human dental pulp cells increased. To conclude, erythropoietin can promote the formation of dentin to some extent.

中国组织工程研究杂志出版内容重点：组织构建；骨细胞；软骨细胞；细胞培养；成纤维细胞；血管内皮细胞；骨质疏松；组织工程

Key words: erythropoietin, pulp injury, reparative dentin, direct pulp capping, odontoblast, human pulp cells