Fig. 1: Higher reactive oxyben species (ROS) levels in ectopic lesions than eutopic and normal endometriums, and hypoxia induction of DNA damage in endometrial cells in vitro.

a Immunohistochemistry photomicrographs of hypoxia-inducible factor 1α (HIF-1α) (the key regulator of hypoxia, which was stimulated by ROS) and 8-OHdG (an oxidative stress-induced DNA damage marker) in normal endometrium and paired eutopic and ectopic tissues. Scale bars = 100 µm for ×100 images. Scale bars = 50 µm for × 400 images. b Expression of HIF-1α in endometrial stromal cells (upper panel) and endometrial glandular cells (lower panel) by H-score (y-axis) was significantly higher in eutopic endometria and ectopic lesions than in normal endometria, with ectopic lesions showing the highest staining (n = 27 for normal endometria, n = 57 for paired eutopic and ectopic tissues). *P < 0.05 versus normal endometrial stromal cells; ^#P < 0.05 versus eutopic endometrial stromal cells. One-way ANOVA with LSD for multiple comparisons. c Expression of 8-OHdG in endometrial stromal cells (upper panel) and endometrial glandular cells (lower panel) by H-score (y-axis) was significantly higher in eutopic endometria and ectopic lesions than in normal endometria, with ectopic lesions showing the highest staining (n = 27 for normal endometria, n = 57 for paired eutopic and ectopic tissues). *P < 0.05 versus normal endometrial stromal cells; ^#P < 0.05 versus eutopic endometrial stromal cells. One-way ANOVA with LSD for multiple comparisons. d Representative fluorescence microscope images from alkaline comet assays of ESCs (left panel) and Ishikawa cells (right panel) after exposure to normoxia or hypoxia culture for 28 days. Scale bar = 200 μm for ×100 images. Scale bar = 100 μm for ×400 images. The tail lengths, tail DNA percentage and tail olive moments of comets were analysed using OpenComet. n = 5 for ESCs