Loss of smad7 promoted the stromal-myofibroblast transition of endometrium via autophagy

Abstract Background: Abnormal autophagy and TGFβ-SMAD3/7 signaling pathway plays an important role in intrauterine adhesions (IUA); however, the exact underlying mechanisms remain unclear. In this study, we aimed to detect whether SMAD7 effected IUA via regulating autophagy and TGFβ-SMAD3 signaling pathway. Methods: The expression of p-SMAD3 and SMAD7 were detected by Immunohistochemistry. Endometrial fibrosis was detected by masson staining. The expression of protein related autophagy and fibrosis was detected by western blot. The autophagic flux was monitored via Tandem mRFP-GFP-LC3 fluorescence system. Chip assay was used for SMAD3 binding site analysis. SMAD7 knockout mice were used for investigated the regulation of SMAD7 on intrauterine adhesions and autophagy. Results: we observed that patients with IUA exhibited a high expression of p-SMAD3 in the endometrium whereas SMAD7 expression decreased. In endometrial stromal cells, the silencing of SMAD7 inhibits autophagic flux, whereas overexpressed SMAD7 promotes autophagic flux. We also found that SMAD7-mediated autophagic flux regulated stromal-myofibroblast transition. These phenotypes are regulated by the transforming growth factor (TGF)β-SMAD3 signaling pathway. We found that SMAD3 directly binds to the 3ʹ-untranslated region of transcription factor EB (TFEB) and inhibits its transcription. SMAD7 promotes autophagic flux by inhibiting SMAD3, thereby suppressing the inhibition of TFEB. The endometria of SMAD7 knockout mice showed a fibrotic phenotype. Simultaneously, autophagic flux was inhibited. On administering the autophagy activator rapamycin, endometrial fibrosis of SMAD7 gene conditional knockout mice was partially restored. Conclusions: the loss of SMAD7 promotes endometrial fibrosis by inhibiting autophagic flux via the TGFβ-SMAD3 pathway. Therefore, this study reveals a potential therapeutic target for IUA.