AIM: To investigate the expression and role of Smad5 protein in mediating transforming growth factor-β superfamily(TGF-β) signaling transduction in human dental papillae cells (HDPC). METHODS: Smad5 was stained with immunohistochemical method in HDPC derived from primary culture by treatment with or without BMP-2 or TGF-β1. Difference of the amount of Smad5 was determined by Medical Image Analysis System. RESULTS: The protein of Smad5 was expressed in cytoplasm of HDPC in all the three groups, and also localized in the nucleus of BMP-2 group. Significantly high level of Smad5 was found in BMP-2 group(P<0.01), but low in the control and TGF-β1 group. No significant difference was found between the control group and TGF-β1 group(P>0.05).CONCLUSION: The expression and translocation of the protein Smad5 in HDPC were detected. It suggests that the Smad5 may participates in BMP-2 signaling pathway.%目的：观察Smad5蛋白在体外原代培养的人牙乳头细胞内的表达及其在转化生长因子-β超家族信号转导中的作用。方法：原代培养的人牙乳头细胞，分别以骨形成蛋白-2 (bone morphogenetic protein-2, BMP-2)和转化生长因子- β1(transforming growth factor-β1, TGF-β1)刺激，免疫组化检测Smad5的表达，图像分析仪半定量。结果：人牙乳头细胞（空白对照组）胞浆内可见Smad5阳性表达，胞核内未见阳性表达；BMP-2实验组胞核内Smad5强阳性表达，胞浆内为弱阳性表达； TGF-β1实验组细胞胞浆Smad5阳性，胞核未见表达。结论：人牙乳头细胞内存在Smad5的表达，Smad5能转导BMP-2信号至核内发挥作用，但不能转导TGF-β1信号，提示BMP-2在牙齿发育过程中信号传递可能是通过Smad5的信号转导途径实现的。
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