Abstract: BACKGROUND: First-trimester human decidual mesenchymal stem cells and tanshinone IIA have anti-adhesion effect, and both have a certain effect on intrauterine adhesion, but the specific mechanism needs to be further studied.  
OBJECTIVE: To explore the efficacy and mechanism of first-trimester human decidual mesenchymal stem cells combined with tanshinone IIA in the treatment of intrauterine adhesions.
METHODS:  First-trimester human decidual mesenchymal stem cells were isolated and cultured by collagenase I digestion. A total of 45 female SD rats aged 4-6 weeks were randomly divided into 5 groups with 9 rats in each group: control group, model group, tanshinone group, stem cell group and combined treatment group. Sham operation was performed in the control group, and no intervention was performed in the model group after modeling. In the stem cell group, 0.2 mL human decidual mesenchymal stem cell suspension (1×109 L-1) was injected parauterine 7 days after modeling, once every other 3 days, for a total of 3 times. In the tanshinone group, tanshinone IIA solution at 11 mg/(kg·d) was given via intragastulation for 1 week. The combined treatment group received the combination of the above two treatment methods. In the control group and model group, samples were obtained at 5, 10, and 15 days after operation and sham operation. In each treatment group, samples were taken at 5, 10, and 15 days after the last treatment. Hematoxylin-eosin staining and Masson staining were performed to observe the healing degree of the damaged uterus. Serum vascular endothelial growth factor and E2 levels were detected by ELISA. q-PCR was used to detect the expression of miR-29a mRNA in uterine tissue. The protein expression levels of transforming growth factor β1, Smad3 and matrix metalloproteinase 9 were detected by western blot assay.  
RESULTS AND CONCLUSION: (1) Compared with the control group, the endometrial fibrosis area ratio in the model group increased significantly (P < 0.05), while the endometrial thickness and the number of glands decreased significantly (P < 0.05). Compared with the model group, the degree of endometrial fibrosis in the combined treatment group was significantly lower (P < 0.05) and the thickness of the intima and the number of glands increased significantly (P < 0.05). The endometrial fibrosis area ratio of rats in the stem cell group and the tanshinone group also decreased significantly (P < 0.05). (2) Compared with the model group, the serum estrogen E2 level of the tanshinone, stem cell and the combined treatment groups was significantly increased (P < 0.05); vascular endothelial growth factor level was significantly decreased (P < 0.05); the expression of miR-29a mRNA was significantly increased (P < 0.05); the expression of transforming growth factor β1 and Smad3 protein in the combined treatment group was significantly decreased (P < 0.05), and the expression of matrix metalloproteinase 9 protein in the tanshinone group was significantly increased (P < 0.05). (3) Results suggest that the combined treatment of first-trimester human decidual mesenchymal stem cells and tanshinone IIA can effectively repair the endometrium in rats, and the mechanism may be through the regulation of miR-29a to reduce the levels of transforming growth factor β1 and Smad3 protein, and then improve the fibrosis.

Key words: intrauterine adhesion, first-trimester human decidual mesenchymal stem cells, tanshinone IIA, miR-29a, transforming growth factor-β1, Smad3