Vascular endothelial growth factor 165 inhibits pro-fibrotic differentiation of stromal cells via the DLL4/Notch4/smad7 pathway

Endometrial fibrosis is the main pathological feature of Asherman's syndrome (AS), which is the leading cause of uterine infertility. Much is known about the expression of VEGF165 in luminal/glandular epithelial cells and stromal cells of the endometrium in normal menstrual cycles; however, less is known about the role and mechanism of VEGF165 in endometrial fibrosis. Herein, we report that VEGF165 is a key regulator in endometrial stromal cells to inhibit α-SMA and collagen 1 expression. Compared to human control subjects, patients with AS exhibited decreased VEGF165 expression in the endometrium along with increased fibrotic marker expression and collagen production. A fibrotic phenotype was shown in both mice with conditional VEGF reduction and VEGF165-deleted endometrial stromal cells. Exogenous VEGF165 could suppress TGFβ1-induced α-SMA and collagen 1 expression in human primary endometrial stromal cells. However, this beneficial effect was hindered when the expression of smad7 or Notch4 was inhibited or when Notch signaling was blocked, suggesting that smad7 and Notch4 are essential downstream molecules for VEGFA functioning. Overall, our results uncover a clinical targeting strategy for VEGF165 to inhibit pro-fibrotic differentiation of stromal cells by inducing DLL4/Notch4/smad7, which paves the way for AS treatment.