Smad signaling coincides with epithelial-mesenchymal transition in a rat model of intrauterine adhesion.

Purpose: Intrauterine adhesion (IUA) is a fibrotic disease mainly caused by tissue injury, yet the mechanism is poorly understood. The aim of this study was to investigate the roles of TGF beta 1/BMP7/Smad signaling coincident with epithelial-mesenchymal transition (EMT) in IUA. Methods: Twenty-four female SD rats were divided into IUA and sham groups. For each animal, a mechanical injury or sham operation was performed on the left uterus (IUA-L, Sham-L), and the right uterus (IUA-R, Sham-R) was used as the control. Animals were sacrificed in batches on days 7 and 28. The endometrial morphology, number of endometrial glands, microvascular density (MVD), area of endometrial fibrosis and immunohistochemistry (IHC) analysis of biomarkers of EMT, as well as levels of TGF-beta 1, phosphorylated Smad3 (pSmad3), BMP7, phosphorylated Smad1/5 (pSmad1/5) and estrogen receptor (ER) were evaluated. Besides, the correlation between these IHC markers was also analyzed. RT-PCR and western blot were used to test relevant genes. Results: Compared with other groups, the IUA-L group showed a significant decrease in the number of glands and MVD. And it also showed a significant increase in the stromal fibrosis rate and a-SMA level. Moreover, in the IUA-L group, TGF-beta 1 and pSmad3 levels were consistently high, and levels of BMP7, pSmad1/5 and ER were low. EMT markers E-cadherin was decreased, while N-cadherin was increased. Sham and control groups showed no significant difference in these markers. In addition, E-cadherin with a-SMA, fibrosis rate with BMP7, TGF-beta 1 with pSmad3 and BMP7 with pSmad1/5 showed correlation in IUA-L group, which had statistical significance. The mRNA expression of TGF-beta 1, a-SMA and ccn2 in 7 d IUA-L was higher than 7 d IUA-R while BMP7 was lower, which had significant difference. The protein expression of BMP7 in 7 d IUA-L was lower than 7 d IUA-R, which had significant difference. Conclusions: These results suggest a potential role of Smad signaling together with EMT in endometrial fibrosis development.