Lipoxin A₄ Suppresses Estrogen-Induced Epithelial-Mesenchymal Transition via ALXR-Dependent Manner in Endometriosis

Epithelial-mesenchymal transition (EMT) is essential for embryogenesis, fibrosis, and tumor metastasis. Aberrant EMT phenomenon has been reported in endometriotic tissues of patients with endometriosis (EM). In this study, we further investigated the molecular mechanism of which lipoxin A₄ (LXA₄) suppresses estrogen (E₂)-induced EMT in EM.

The EMT markers were analyzed by quantitative real-time polymerase chain reaction (qRT-PCR) and Western blot in eutopic endometrial epithelial cells (EECs) or investigated by immunohistochemistry and qRT-PCR in endometriotic lesion of EM mice. The invasion and migration under different treatments were assessed by transwell assays with or without Matrigel. The messenger RNA (mRNA) and activities of matrix metalloproteinase 2 (MMP-2) and MMP-9 were determined by qRT-PCR and gelatin zymography, respectively. Luciferase reporter assay was used to measure the activity of zinc finger E-box binding homeobox 1(ZEB1) promoter. The level of E₂ in endometriotic tissues was assessed by enzyme-linked immunosorbent assay.

In eutopic EECs, stimulatory effects of E₂ on EMT progress, migration, and invasion were all diminished by LXA₄. Lipoxin A₄ reduced E₂-induced ZEB1 promoter activity. Lipoxin A₄ also attenuated the phosphorylation of extracellular signal-regulated kinase and p38 mitogen-activated protein kinase induced by E₂. Co-incubation with Boc-2 rather than DMF antagonized the influence of LXA₄. Animal experiments showed that LXA₄ inhibited the EMT progress, MMP expression, and proteinase activities of endometriotic lesion in an LXA₄ receptor (ALXR) manner, which suppressed the progression of EM. ZEB1 mRNA expression was upregulated and well correlated with E₂ level in human endometrium.

Lipoxin A₄ suppresses E₂-induced EMT via ALXR-dependent manner in eutopic EECs, which reveals a novel biological effect of LXA₄ in EM.